Merox Operating Manual

MEROX OPERATING MANUAL INDEX S. No. 1 2

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DESCRIPTION Page No. INTRODUCTION MEROX PROCESS DESCRIPTION • MEROX PROCESS EQUIPMENT • PRETREATMENT • EXTRACTION SECTION • SWEETENING • POST TREATMENT • MEROX CATALYSTS U-21 ATF /SK MEROX • UNIT CAPACITY • FEED SPECIFICATIONS • PRODUCT SPECIFICATIONS • TYPE OF CATALYST USED • PROCESS DESCRIPTION • DETAILED DESCRIPTION OF P&ID • PRE-COMMISSIONING OPERATION • STARTUP PROCEDURE • REACTOR BED WATER WASHING AND REIMPREGNATION • SHUTDOWN PROCEDURE • EMERGENCIES • OPERATING VARIABLES • CHEMICALS AND CATALYSTS • MODIFICATIONS U-22 STRAIGHT RUN LPG MEROX • UNIT CAPACITY • FEED SPECIFICATIONS • PRODUCT SPECIFICATIONS • PROCESS DESCRIPTION • DETAILED DESCRIPTION OF P&ID • PRE-COMMISSIONING OPERATION • STARTUP PROCEDURE • SHUTDOWN PROCEDURE • EMERGENCIES • OPERATING VARIABLES • CHEMICALS AND CATALYSTS • MODIFICATIONS

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S. No. 5

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DESCRIPTION Page No. U-23 VBN MEROX • UNIT CAPACITY • FEED SPECIFICATIONS • PRODUCT SPECIFICATIONS • TYPE OF CATALYST USED • PROCESS DESCRIPTION • DETAILED DESCRIPTION OF P&ID • PRE-COMMISSIONING OPERATION • STARTUP PROCEDURE • REACTOR BED WATER WASHING AND REIMPREGNATION • SHUTDOWN PROCEDURE • EMERGENCIES • OPERATING VARIABLES • CHEMICALS AND CATALYSTS U-24 CRACKED LPG MEROX • UNIT CAPACITY • FEED SPECIFICATIONS • PRODUCT SPECIFICATIONS • TYPE OF CATALYST USED • PROCESS DESCRIPTION • DETAILED DESCRIPTION OF P&ID • PRE-COMMISSIONING OPERATION • STARTUP PROCEDURE • SHUTDOWN PROCEDURE • EMERGENCIES • OPERATING VARIABLES • TROUBLE SHOOTING U-25 CRACKED FCCG MEROX • UNIT CAPACITY • FEED SPECIFICATIONS • PRODUCT SPECIFICATIONS • PROCESS DESCRIPTION • DETAILED DESCRIPTION OF P&ID • PRE-COMMISSIONING OPERATION • STARTUP PROCEDURE • SHUTDOWN PROCEDURE • EMERGENCIES • OPERATING VARIABLES • MODIFICATIONS SAFETY & FIRE FIGHTING FACILITIES -3-

1. INTRODUCTION: Straight-run LPG, gasoline and kerosene fractions obtained from atmospheric distillation may contain hydrogen sulphide and mercaptans. the extent of which mainly depends upon the type of crude processed. Similar products from secondary processes such as FCC also contain hydrogen sulphide and mercaptans to a greater degree compared to straight-run products. Hydrogen sulphide is corrosive and should be remove in order to meet specifications on corrosion rate. The specification for LPG, gasolene, Kerosene and ATF include copper strip corrosion test which is a measure of rate of corrosion on copper containing materials.Mercaptans are substances with obnoxious odour and, therefore, in order to handle and store them, mercaptan level will have to be brought down to a acceptable odour level. The specifications of above products include 'Doctor Test' which must be negative and is generally related to the extent of mercaptan present. Hydrogen-sulphide can be easily removed by washing with dilute caustic solution. However, for reducing the mercaptans level many processes are available like: Strong alkali-wash Copper sweetening Doctor sweetening Merox process Hydrodesulphurisation Alkali-wash is effective only if low molecular weight mercaptans are involved. Hydrodesulphurisation is normally employed only if reduction of total sulphur level is also required. Both investment and operating costs are higher in case of hydrodesulphurisation. Out of other proceses available, Merox process is considered a superior and proven process.

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2. MEROX PROCESS DESCRIPTION The Merox process licensed by M/S Universal Oil Products Co., (UOP), USA, is for the chemical treatment of LPG, gasolene and distillates to remove mercaptans into disulphides. The removal of mercaptans may be either partial or full. The chemical treatment is based on the ability of Merox catalysts to promote the oxidation of mercaptan to disulphide using air as the source of oxygen. The overall reaction is as follows: 2RSH + 1/2O2 -> RSSR + H2O The oxidation is carried out in the presence of an aqueous alkaline solution such as either sodium hydroxide or potassium hydroxide. The reaction proceeds at an economical rate at normal rundown temperature of refinery streams. Low molecular weight mercaptans are soluble in caustic solution and therefore when treating LPG and light gasoline fractions, the process can be used to extract mercaptan to the extent, they are soluble in caustic. Extraction of mercaptan reduces the sulphur content of the treated product. Alternatively mercaptans can be converted to disulphides without removing any sulphur from the treated stock in which case the operation is referred to as sweetening. In the treatment of heavier boiling fractions such as heavy naphtha and kerosene only sweetening is possible. •

MEROX PROCESS EQUIPMENT:

In order to understand the function of various Merox process equipment. the equipment can be broadly divided into following sections : Pretreatment for removal of hydrogen sulphide and naphthenic acids, if present. The method varies with properties and conditions of feedstock and in some cases may not be required. Extraction section where required, for removal of caustic soluble mercaptans and thus reduce sulphur in the treated product. Sweetening for conversion of mercaptans to disulphides. For a given capacity plant, the Merox reactor size can vary depending on the case of sweetening due to the type of mercaptans present and also on product requirement. Post-treatment to remove caustic haze and to control properties not affected by Merox process. Hence post-treatment needed depends on products, utilisation and type of contaminants present in the feedstock. Taking each section in turn, function of each equipment can be described. •

PRETREATMENT

Petroleum fractions may contain hydrogen sulphide and stocks boiling higher than 180°C may also contain naphthenic acids. Hydrogen sulphide is not a catalyst poison as such, but will dilute the caustic containing Merox catalyst by reacting -5-

with caustic. Further it blocks some of the catalyst activity sites slowing down the normal reaction and also consumes part of the oxygen available. Hence, it is recommended that hydrogen sulphide is removed by washing with dilute alkali solution before the distillate is sent to reactor for treatment. Naphthenic acids also interfere with treating operations and must be removed prior to treatment. The reactor contains caustic and if naphthenic acids are not remove they form sodium naphthenates which coat the catalyst and block the pores. For removal of napthenic acids, the procedure used is to wash with dilute caustic. Dilute caustic is used so as to avoid formation of emulsions. There could, however, be some carry-over of haze depending on the acidity of stock treated. The haze can easily be removed by coalescing through a sand filter. Feedstocks, where carry-over of water from distillation units can be expected must be passed through a coalescer for removal of suspended water prior to caustic wash, which would otherwise dilute the caustic used for pretreatment. •

EXTRACTION SECTION

As previously stated, low molecular weight marcaptans are caustic soluble and can easily be removed by washing with caustic in a counter current tower. Improved extraction is favored by: Low temperature. High concentration of caustic. Lower molecular wt. of mercaptans Type of mercaptans, viz. normal mercaptans are easily extractable, tertiary mercaptans least extractable and secondary being in between. The mercaptan enters the caustic solution and reacts as follows: RSH + NaOH NaSR + H2O This is being a reversible reaction the degree of completion of reaction is governed by normal equilibrium laws. The sodium mercaptide is readily oxidised to disulphide in the presence of Merox catalyst as shown : 2NaSR + l/2O2 + H2O -> 2NaOH + RSSR This is not a reversible reaction and the reaction rate is speeded up by: Raising the temperature. Use of excess air. Increasing the intimacy of contact. -6-

Increasing the catalyst concentration. The oxidation of mercaptides is carried out in oxidiser in the presence of merox catalyst. The disulfides oil, which is formed, separates out from caustic as it is insoluble in caustic. Caustic can be reused for extraction. The presence of Merox catalyst in extraction caustic does not however, affect the amount of mercaptans extracted. and extraction is dependent only on parameters explained earlier . •

SWEETENING

Sweetening can be defined as conversion of mercaptan sulphur present in a hydrocarbon stream to disulphide sulphur without actually reducing sulphur content of treated stock. The sweetening process is based on the ability of Merox catalyst to promote the oxidation of mercaptans to disulphides using air as the source of oxygen. The reaction is as follows: RSH + NaOH NaSR + H2O 2NaSR + l/2O2 + H2O -> 2NaOH + RSSR As can be seen from reactions, the oxidation is carried out only in the presence of alkali solution. The Sweetening can be accomplished either in solid bed sweetening, where the hydrocarbons and caustic are simultaneously controlled over a solid support impregnated with Merox catalyst. Liquid-liquid sweetening where hydrocarbon, air and caustic containing Merox catalyst, air simultaneously controlled in a mixer. Solid bed sweetening consists of a reactor, which contains a bed of activated charcoal impregnated with Merox catalyst and kept wet with caustic solution. Impregnation of catalyst on bed is achieved by dissolving the catalyst with ammonia solution and pumping ammonia solution over charcoal. Air is injected ahead of reactor and in the presence of merox catalyst the mercaptans are oxidised to disulphides. The reactor is followed by a settler which serves as reservoir of caustic. Caustic is intermittently circulated from the settler over the catalyst bed to wet the charcoal. For liquid-liquid sweetening, the most common type of mixer used is the orifice plate mixer, which is a vessel, fitted with a series of plates with orifices. The vessel provides adequate residence time and the orifice plates create enough turbulence to bring about the intimate contact between hydrocarbon, caustic, catalyst and air. The problem of accomplishing liquid-liquid sweetening is one of getting the difficulty soluble mercaptans into the caustic phase for sufficient time to permit their oxidation. The higher the molecular weight or the more highly branched the mercaptan is, the more difficult it is to accomplish necessary mixing. Hence heavy gasoline and Kerosene may have to be treated using fixed bed reactor.

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POST TREATMENT

The product from the merox reactor will at times contain caustic haze. Post treatment is required if the product is to go to storage, clear and bright. In most cases provision of caustic settler and sand filter is adequate to remove caustic haze. However, for treatment of ATF, which has to meet stringent specification caustic must be removed by water wash after caustic settling. Water wash removes entrained caustic as well as water soluble surfactants, Water wash is followed by a salt filter to remove entrained water and part of the dissolved water. This may be followed by clay filter to remove copper and water insoluble surfactants, if present in feed. •

MEROX CATALYSTS:

There are two types of Merox catalyst, each one being used for specific service. Catalyst FB is to be used on units equipped with solid bed sweetening reactors. Catalyst WS is used for liquid-liquid sweetening in mixers. This is a caustic dispersible catalyst. This is also used for oxidation of extraction caustic in oxidisers.

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3. U-21 ATF /SK MEROX : •

UNIT CAPACITY:

The Merox Unit for treating kerosene & ATF streams from the Atmospheric Distillation unit has been designed to feed 1.5 million metric tons per year of kerosene while processing a 50: 50 mixture of Light Arabian: North Rumalia crudes. The Unit shall operate for 345 stream days in a year. •

FEED SPECIFICATIONS:

The kerosene to be treated in the Merox Unit shall have substantially the following properties: (i)

Boiling Range IBP/FBP oC

(ii)

Specific gravity at 15.6°C

0.795 to 0.82

(iii)

Total acidity, Mg KoH/Gm

0.02

(iv)

Mercaptan Sulphur wt ppm

150

(v)

Total Sulphur wt.%.

0.22

(vi)

H2S wt ppm

10 max

(vii)

Colour, Saybolt

+ 30

•

140-270 Max.

PRODUCT SPECIFICATIONS:

The Product kerosene/ATF after Merox treatment shall meet the following specifications: (i)

Appearance

Visually, clear, bright and free from solid matter and undissolved water at normal ambient temperature.

(ii)

Corrosion copper strip

No 1 Maximum

(iii)

Corrosion silver strip

No 0 Maximum

(iv)

Mercaptan sulphur wt ppm

10-20 ppm (max.)

(v)

Doctor test

Negative

(vi)

Colour loss, saybolt

5 Maximum when feed stock is 25 min., provided that the feed stock comes directly from the fractionation facility. -9-

(vii)

Thermal stability: (a) Filter pressure drop in mm Hg. (b) Tube Rating visual

25.0 maximum Less than code 3

(viii)

Water separameter index

90 minimum

(ix)

Acidity, mg. KOH/Gm (a) Water Separometer index (modified) (b) WATER REACTION Interface Rating Volume Change

0.012 maximum 90 minimum

Conductivity (ATF)

50-450 psm

(x)

1.0 maximum 1.0 maximum

"H2S free fresh stock charge" shall mean fresh stock charge containing no H 2S or if the fresh stock charge contains H 2S, it shall be scrubbed out with caustic soda solution or sodium carbonate solution in the laboratory without exposure to oxygen. •

TYPE OF CATALYST USED:

Catalyst used for sweetening kerosene/ATF Stream in this treating unit is merox catalyst FB which is supplied by the Universal Oil-Products Company. This catalyst is used in the two sweetening Reactors 021 R1 A and B. The catalyst is impregnated on activated charcoal beds in the reactors. Quantity of catalyst required for one impregnation in the reactors is 250 Kg. of active ingredient. The catalyst is supplied in liquid from each US gallon containing 1 kg. of active ingredient. •

PROCESS DESCRIPTION

Pretreatment for kero/ATF consists of a coalescer and caustic prewash vessel, for removal of suspended water and hydrogen sulphide, Naphthenic acid etc. Sweetening is achieved in supported catalyst bed reactor. Two reactors in parallel have been provided. Air requirement of all Merox units is supplied from a common compressor. Also, storage tanks for receipt, dilution and storage of caustic and storage for methanol have been provided. Post treatment for kero/ATF consists of caustic settling. water wash to wash of any carry-over caustic salt drier for drying and clay filters for improving colour stability of treated product. Clay adsorbs coloured nitrogen compounds. •

DETAILED DESCRIPTION OF P&I DIAGRAM

Kerosene/ATF as obtained from distillation unit stripper under flow control is charged to the unit charge pumps 021 P4A/B. Pretreatment for kero/ATF consists of coalescer for removal of water and caustic prewash for removal of hydrogen - 10 -

sulphide, etc. The feed goes to coalescer 021-V-9 where feed passes through pass blanket as coalescing media to coalesce tiny water droplets into sufficiently big droplets which settle down in the water boot provided in the coalescer. Float type trap is provided in the water boot to drain water. Water from boot will have to be periodically drained to oily water sewer. Provision also exists for bypassing this vessel and directly feeding to caustic prewash vessel. Kero/ATF from coalescer is sent to caustic prewash vessel 021-V1 (4750 mm OD x 9150 mm) where the feed bubbles through caustic and rises to the top of vessel due to gravity differential between feed and caustic. The feed is charged into the vessel through a distributor pipe mounted inside the vessel and holes drilled to a specified pattern on the distributor pipes. There are three inlet nozzles provided on the vessel. Normally the feed should be maintained thro' the B" nozzle. Maintain caustic level and charge caustic when the caustic is spent as indicated by its strength. The vessel is also provided with a wiremesh in its top portion to remove any caustic entrainment. The feed is then mixed with air as necessary for reaction, on flow control 021 FRC 16 in the air-mixer 021 Y2 where intimate mixing of air and feed is achieved. The feed then passes on to two reactors operating in parallel (021 RI A&B) (4000 mm OD x 7200 m). The reactor consists of a bed of charcoal impregnated with Merox catalyst. Impregnation being carried out as per laid out procedures using ammonia as an agent for impregnation. The reactor bed also may need water washing and reimpregnation to restore activity whenever catalyst activity drops. the period depending on the type of feed proceesed in the unit. The feed ex reactors is passed on to the caustic settler 021 V2 (3600 mm OD x 12200 mm). In the caustic settler. required settling time is provided for separation of any carry-over caustic. Since the unit is also designed to treat ATF, which has to meet stringent specifications, water wash and salt drier also have been provided. Hydrocarbon from caustic settler passes into water wash vessel 021 V3 (4750 mm OD x 9150 mm). The water wash vessel is continuously charged with demineralised water taken from the refinery source through a water tank 021 V7 provided with a level controller 021 LC 27 which regulates water entry into water tank. From the water tank, water is charged into water wash vessel by pump 021 P3 A & B. Flow control is by 021 FIC 24. Water hydrocarbon interface level is maintained by 021 LC 24. The vessel is also provided with a wire mesh in its top section to reduce water carry-over by hydrocarbons. After water wash, hydrocarbon stream enters the salt drier 021 V4 (5000 mm OD x 8000 mm) for removal of any last traces of water. The salt drier is filled with rock salt and the feed is distributed at the bottom of the vessel and leaves from the top. The final step of treatment is filtering through clay towers to remove water insoluble contaminants. For this purpose two clay filters 021-V5 A&B (4750 mm OD x 7500) have been provided which are operated in parallel. The hydrocarbon is distributed on top of clay filter and collected from the bottom using collector pipe assembly wrapped with wiremesh screens. The outlet of each clay filter is combined into a common product run down line where flow is recorded by 021FRQI-55. The necessary back pressure to the unit is maintained by 021-PIC-32 - 11 -

which ensures constant pressure in the reactor and other vessels. The treated product is run-down to storage. Feed stocks which do not call for complete treatment but which meet product specifications after caustic pre-wash, can be diverted to storage after caustic prewash, vessel 021-V1 using the bypass line between 021-V1 outlet and upstream of 021-PIC-32. For meeting the requirement of caustic for all Merox units, two caustic storage tanks 021- T1 & 021- T2 have been provided in this unit. 021- T1 is meant for preparing and storing 3 deg. Be caustic required for caustic , prewash vessel 021V1. 021- T2 is meant for 10 deg. Be caustic required for reactors and other Merox units. This unit receives 48.8 deg Be caustic from which 3 deg. Be and 10 deg. Be caustic solution will be I prepared. DM water is used for diluting caustic. The air reqirement of all Merox units is met by air compressors 021-C1-A & B. Compressed air from 021-C1-A&B is supplied to other Merox units. • I.

PRE-COMMISSIONING OPERATIONS: CHECKING OF COMPLETION OF CONSTRUCTION INSPECTION AND BOXING UP OF EQUIPMENT

WORK,

All unit equipment and pipelines must be checked to see that they conform Strictly to the specification of design and as per drawings. Location of vents, drains, gauge glasses, pressure gauges, sample points etc. on equipment must be checked to ensure that they are installed in accessible locations. Also, the internal fittings in columns and vessels like trays, packing supports screws, distributors etc. must be checked in position and in order. When the equipments have been satisfactorily cleared as to their internal installations and cleanliness of construction debris, the manholes can be boxed up. II.

PRESSURE TESTING OF EQUIPMENT AND PIPELINES :

After inspection and box-up of equipment as mentioned above the entire unit has to be pressure tested with water to maximum allowable pressure to ensure that the plant equipment and lines can safely with-stand operating pressures. According to convenience, equipment are tested individually or divided into sections depending on locations and test pressure of various equipment and pipelines. proper isolation by blinds of equipment or section under test must be done so as not to over pressurise connected lines and vessels of lower pressure rating. Before the hydrostatic test is undertaken, relief valves and orifice plates must be removed from the system and blinded off. After carrying out hydrostatic tests on unit equipment and pipelines water must be drained out completely. In order to prevent vacuum pulling in vessels, their top vents must be opened up before attempting to drain water. III.

WATER FLUSHING OF THE UNIT : - 12 -

On completion of pressure test of the unit, water flushing of the different systems in the unit is carried out with all the pumps running on line to flush out all muck, scale and other construction debris contained in the lines. Suction screens must be installed on each pump to protect them from damage. In the initial stages of commissioning of the unit, it is better to install a finer (60") mesh on the normal filter of each pump. This finer filter can be removed only 2 to 3 months of actual run of the unit when frequency of cleaning comes down to normal. The pumps are to be run at least for 24 hours to ensure that they are running freely and smoothly. The discharge valves of the pumps have to be suitably throttled so as not to overload the motors during the water flushing operations. Periodically, the pumps have to be stopped and the debris accumulated in the suction screens to be cleared. This operation has to continue till the suction screens remain clear continuously at least for eight hours. When the water flushing operation has been successfully completed, all water from the systems has to be drained out completely, especially from the low points. Air blow the system thoroughly to remove the traces of water from equipment and lines. All orifice plates should be checked for proper specifications before their installation in place. All instruments must be checked and calibrated before the unit start-up. IV.

SCREENING AND LOADING OF ACTIVATED CHARCOAL SALT & CLAY

Activated charcoal has to be screened properly before it is loaded in the reactors. Screening is done with 10 to 30 mesh sieve screens. To reject fines etc. which are formed during transportation and handling coarser than 10 mesh and fines after 30 mesh are rejected from the charcoal supply. The reactors are isolated from other equipment and their top and side man ways are opened up. The inlet distributor pipe assembly at top has to be suitably covered to prevent any charcoal entry into the distributor while loading. Loading is done through a hopper and adjustable loading sock which extends to the bottom of the reactors. As the loading progresses, the length of the sock is adjusted so that no cone formation occurs on the charcoal surface. Improper leveling will cause maldistribution of hydrocarbon flow through the bed. Loading personnel must wear dust masks covering the nose and the mouth to prevent inhalation of charcoal dust. While loading, it must be ensured that the bottom Johnson screen collector pipe assembly is fully submerged in charcoal by physical checking from the bottom man way. The person going inside for checking must wear a fresh air masks. The bottom man way is then boxed up and loading continued with the sock till the inlet distributor pipe is 230 mm from the charcoal bed. The Top surface of the bed is leveled after the dust has settled. Here again, the person entering the reactor for leveling the bed must wear a fresh air mask. A record of loading in the reactors has to be kept for reference and accounting, When loading to the required height is over, the loading hopper and sock are removed the inlet distributor covering is taken off and the top man way boxed up properly. V.

ROCK SALT LOADING : - 13 -

After inspection of salt drier internals for cleanliness and fittings, it is loaded with rock salt up to a height of 600 mm below the top tangential line. Then the top man way is boxed up. The surface must be leveled similar to the procedure followed for charcoal loading. VI.

LOADING OF CLAY IN CLAY FILTERS:

The clay filters are checked for internal fittings and are cleaned up dry, prior to loading clay. The inlet distributor pipe has to be covered suitably to prevent clay entering into it while loading. The recommended grade of clay of the correct mesh, 30-60, is loaded from the top of the vessels. periodically leveling the surface so that no cone formation takes place. The loading personnel going inside the vessels for leveling must wear dust mask. The height of loading in each reactor will be up to 920 mm from the top tangential line. After leveling of the top surface of clay in the filters, their distributors are uncovered and the top man ways can be boxed up. VII.

IMPREGNATION OF CHARCOAL BED REACTORS WITH UOP REAGENT FB.

IN

KERO/ATF

MEROX

The two reactors will be impregnated as a rule one after the other, as noted below: Start filling 21 R 1 A with DM Water. Block off Reactor outlet lines. Start circulation pump 21P-2 after DM water level is 1 metre below top distributor pipe. Continue to fill DM water. When water level rises to 1 metre above the distributor pipe, stop addition of DM water ( Be careful, not to float charcoal out of reactor ) Continue water circulation for 2 to 3 hours Start Ammonia gas injection after the cylinder is connected in to the circulating water. Regulate the outlet pressure at 3.0 kg/cm2, inject approximately 150 kg of Ammonia in about 5 to 6 hours time. (Each cylinder lasts for 2 1/2 hrs). Measure the rate by keeping the cylinder on a weigh bridge. Keep a steam hose playing at the gas injection pipe to prevent freezing on the line. Circulate the Ammonia solution for about 2 to 3 hrs. keeping the pump capacity to maximum i. e. 58 M3/hr . Sample the solution and send to lab for analysis. Ammonia concentration should be 0.2 + or - 0.02 wt. %. Add or dilute the solution as necessary. Meanwhile get the catalyst dissolving drum system ready with the hoses connected. Ordinary drum of 200 liters will solve the purpose. After achieving the required Ammonia concentration in the circulating water. route a slip stream from 21 P2 discharge to the catalyst drum. Fill it up to 50 to 60%. Start gentle air blowing in the Air Sprayer.

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Add 7 bottles of Merox FB after shaking. Stir the mixture to help dispersing the catalyst if required. Make up the volume to 180 litres. Start educting the catalyst solution by routing the slip stream through the eductor 21 G-2 from 21 P-2 discharge to suction. Regulate the catalyst eduction rate to 3 to 4 litres/minute. After establishing the above rate, fill the drum from Pump discharge with a rate equal to eduction rate. Add 1 bottle of Merox FB every 10 minutes. After about 11/2 hrs. start checking the color of the circulating Ammonia at the pump suction before educting point. This color should be clear or faint blue. If the color is dark blue, it means that there is channeling in the charcoal bed In such a case the impregnation is to be stopped and Reactor bed should be flushed with air to rectify the bed channeling. Add 45 bottles of Merox FB. After the last batch of solution is educted, flush the catalyst drum several times with Ammonia solution and educt to the Reactor . Continue circulation for about 4 hrs. Start transferring Ammonia solution to the second reactor R1 B by opening the inlet block valve to top distributor when the solution level in R1 A falls below top distributor, shut off the inlet and continue to transfer all the circulating Ammonia solution into R1B. When the pump loses suction shut off the pump. Block in R1A. Open hydrocarbon outlet from R1 B and start circulation back to the inlet. Start taking DM water to fill R1 B until the level is 1 metre above the distributor pipe. Stop DM water flow to the Reactor, but continue the circulation. Sample the solution and analyze for Ammonia concentration. Inject Ammonia gas again into the circulating solution to get 0.2 + or - 0.02 wt %. Impregnate R1 B charcoal bed similar to R1 A. (Add 45 bottles of Merox FB). After completing the impregnation of both charcoal beds, the circulating solution can be discarded to sewer. Drain out all the remnant Ammonia solution from both reactors to sewer. Flush and drain each reactor with DM water to remove residual Ammonia (keeping checking the effluent pH). Close the top man ways of both reactors. Start alkalising each reactor bed with 10% caustic soda solution and then circulate the same for 2 hrs. About 8M3 of NaOH for each reactor will be sufficient. - 15 -

Now the reactors are ready for commissioning with Kero/ATF. Requirement of Catalysts/Chemicals: (a)

Merox FB catalyst

-90 Bottles.

(b)

Ammonia

-5 Cylinders of 60 Kg net wt.

(c)

DM water

-250 M3

VIII.

CHARGING OF CHEMICALS:

The caustic storage tanks 021- T1 and T2 are meant to prepare and store 3°Be and 10°Be caustic solutions respectively in them. These two tanks take care of the caustic requirements of all the five Merox units. 26.5°Be' caustic is received in the unit tanks prior to unit start-up. The caustic is then diluted and the solution of required strength prepared in each tank. 3°Be' caustic is used for pre-wash in vessel 021-V1 while 10°Be. Caustic is used in the reactors R1A and B as well as in other Merox Units. Solutions of required strength are prepared in the unit by diluting with demineralised water. •

START UP PROCEDURE

As soon as Kerosene/ATF becomes available from the Atmospheric Vacuum Distillation Unit, slowly fill up the unit vessels viz., the coalescer V9, caustic prewash vessel V1, Merox Reactors R1A and R1 B. caustic settler V2, water wash vessel V3, Salt Drier V4 and the clay filters V5A and V5B one by one. Ensure all air from the resepctive vessels is removed by opening the top vents. before filling them with the product kerosene/ATF. Proceed further, as follows: Fill up 3°Be' caustic solution in the pre-wash column V-1 to the specified operating level so that the kerosene/ATF stream bubbles through caustic solution which will absorb all the hydrogen sulphide and naphthenic acid contaminants from the feed stock. In a freshly charged Merox reactor no circulation of caustic is needed in the beginning. Hence commissioning the feed charge pumps 021-P4 A/B Kerosene is charged through the coalescer. pre-wash column, reactors and caustic settler and the pressure are raised in the vessels to their normal operating levels. Setting the back pressure controller 021-PC-32 on the product rundown line, for giving the desired pressures in the vessels, air injection to the mixer 021-Y-2 is started at the specifed rate through flow controller FRC-16. The rate of air is approximately 30 lbs/lb of mercaptan sulphur in the feed. The back pressure controller PC-32 is set such that all air used for the process is kept in the hydrocarbon solution. Initially, the product after treatment is to be routed to the slop tank. When doctor test is consecutively negative for 2 hours the kerosene stream may be routed to its normal storage tanks. - 16 -

Water washing the product to remove the entrained caustic has to be done. Hence, start water-washing the product, pumping DM water into the water wash vessel 021-V3 on flow control F1C-34 through the distributor in the vessel. A steady level has to be maintained by operating the controller LC-24 which controls the spent water effluent from V-3 bottom. The water washed product stream is passed through the drier which removes traces of water carried over. Finally, route the product through the clay filters 021V5A and B to remove water insoluble contaminants and give clarity to the product. After passing the quality control tests which are very stringent in the case of ATF, the product is routed to the normal storage tanks. Off-spec material when treating ATF stream is diverted to Kerosene tanks. If the feed Kerosene contains very little mercaptans i. e. less then 10 ppm, then the entire Merox treatment may not be required at all. It can be directly routed to run-down by-passing the treating section. In cases where feed contains traces of H2S. but very less mercaptans, the feed can be routed through caustic pre-wash and then direct to product run-down by passing reactors etc. When the plant has been fully in operation, set the feed rate to the desired level. Check the air injection rate for mixing before reactors is adequate and ensure proper levels are maintained in all vessels. Pressure, as already mentioned has to be set by the pressure controller PC-32 on the product rundown line. • I.

REACTOR BED WATER WASHING & REIMPREGNATION WATER WASHING

Over a period of time, the catalyst impregnated on charcoal in the reactors loses its activity. Wetting the catalyst with fresh caustic circulation also may not help in bringing the product to specifications. At this stage, the charcoal bed has to be hot water washed to remove the organic and soap deposits from its pores and bring back the active surface of the catalyst, for reaction. This deposition of cold organic material on charcoal takes place gradually and hence the water washing step can be conveniently planned to suit the product requirements. The water used for this washing must be free of dirt, suspended matter, hardness salts and active chlorine. Hence, steam condensate or DM water is used for washing. Proceed as follows: Stop air injection and hydrocarbon charge to the reactors. Pump out all the kerosene/ATF from the bottom of the reactors under steam pressure. Steam out the reactors for about an hour giving steam through the beds at a rate equal to 10 lbs per cu feet of bed, i. e. about 14 MT/hr for each reactor. Commission the water heater 021-J1 and start giving hot water at a temp. of about 85-95°C to the reactors through the distributor pipes at a rate of 8 gallons/minute for 100 cu. feet of charcoal i.e. about 55 M 3/hr. fill up the reactors and then drain them to the sewer at the same rate as filling water into them. - 17 -

It was experienced that while using water heater (21 J1) lot of hammering was taking place resulting severe vibration of the lines and therefore it was difficult to maintain the water temp, Later on BFW line connection was given d/s of DM Water B/V. This does not require water heater services. BFW temp. can be controlled by controlling the steam to deareator. Initially, the draining effluent will be dark brown and foamy which will change colour and eventually becomes colourless. When the water from the drain is clear and clean, the water washing can be stopped. Stop the water flow and blowout as much water as possible from the reactor beds with steam given to reactor top. Keep the steam flow through the beds for another 30 minutes to remove as much residual heavy oil as possible from the charcoal bed. Stop steam injection and block off water heater. Introduce air into the reactors and blow the reactors well for an hour or so that there is no water drip noticed from the bottom drain. Next alkalize the beds with fresh 10 deg. Be caustic solution and then return the unit to normal working condition as discussed under "Start-up Procedure". II.

CATALYST REIMPREGNATION

This step is necessary only when hot water washing, higher feed temperatures, stronger caustic saturation, reduced feed rates etc., do not help in mercaptan oxidation and the product remains doctor positive. The reimpregnation interval may vary from three months to one year depending on proper prewashing feed mercaptan content, crude source etc. III.

REIMPREGNATION OF KEROSENE/ATF REACTORS

Hot water washing. Acidising the reactor bed. Impregnation IV.

HOT WATER WASHING

Isolate Reactor (21 R-1 A) from the rest of the unit. Start pumping out the kerosene, keep reactor under positive pressure by steam. After kerosene is pumped out, start steam flow from the water heater (21J-1) to the Reactor (Keep the bed temp. 190 deg C. Drain out the condensate from Reactor bottom. This is to remove the residual kerosene and heavy hydrocarbon in the bed. Start introducing DM Water through the water heater into Reactor. Keep the water temp. (21 T1-15) around 90-95 deg C by introducing steam into the water heater. - 18 -

When the Reactor is full, open reactor bottom to drain. Keep the drain rate close to the hot water fill rate i.e. about 50 M3/hr. NOTE:

Instead of using water heater, BFW can directly be taken.

Check the drain water color. When the colour is clear, check the reactor effluent pH. Continue hot water washing till reactor effluent pH is down to 8,9. Follow step 1.1 to 1.5 for another reactor (21R-1B) and 23R-1. V.

ACIDISING OF REACTOR BED:

Stop the water and steam flow. Flush out the caustic circulation system by opening up the suction lines from the reactor bottom to the circulation pump 21 P-2 and pump discharge to spent caustic tank. Open the top manway of the Reactor. Refill reactor (21 R-1A) with DM water after the reactor has been pumped out till water level is 1 M below the distribution pipe, Block in Reactor outlet line. Start circulation from bottom to top of the reactor. Both the kerosene outlet and the bottom pump out of the reactor are open to the pump suction. Continue to fill DM Water till water level is 1 M above the distributor pipe. Inject steam occasionally to keep the circulating water temp. at 50-65°C. Take about 0.1 M3 glacial acetic acid to the Acetic acid addition pot 21V-8. Route a slip stream from the circulating pump discharge to the eductor 21J-2. Start educting acetic acid to the circulating system & it should be added to the system over a 5-10 minutes period. After circulating acidified water for about one hour check the reactor effluent pH. If pH is higher than 6.5, add another batch of about 0.1 M 3, This acetic acid addition is necessary to neutralise the trace alkalinity on the bed and to provide a slight acidic medium. Transfer the acidified water to reactor 21 R-1B and continue the circulation in 21 R-1A, Stop circulation when the level is 1 M below the distributor pipe. Follow step 2.6 to 2.8 for acidising the bed of 21R-1B. Transfer the acidic solution to 23R-1 from 21 R-1B with circulation on. Stop circulation when level is 1 M below the distributor pipe. Keep a moderate steam flow through each reactor for 30-60 minutes. Air purge each reactor for about 60-90 minutes. - 19 -

VI.

IMPREGNATION

Start filling reactor 21 R-1A with DM water. Block in reactor outlet lines. Start circulation pump 21 P-2 after reactor level is 1 M below the distributor pipe, Continue to fill DM water. When water level rises to 1 M above the distributor. Stop water addition (Be careful not to flood the charcoal out of the reactor). Continue circulation for about 2-3 hours. Start Ammonia injection after the cylinder is connected. Regulate the outlet pressure at about 3 kg/cm 2. Inject approx. 150 kg of ammonia i.e about 5-6 hours (one cylinder in 2-21/2 hrs.) Measure the rate by weighing scale. Put steam hose to prevent freezing of pipe due to gas expansion. Circulate ammonia for about 2-3 hours keeping the rate at pump maximum i. e. 58 M3/hr. Sample the solution and send to lab analysis. Ammonia concentration should be 0.2 + or - 0 02 wt.%. Add or dilute solution if necessary. After confirmation of solution concentration, route a slip stream from 21 P-2 discharge to the catalyst drum (200 litre drum). Fill it up to 50-60%. Start gentle air blowing in the air sprayer. Add 7 bottles of Merox FB after shaking. Stir the mixture to help dispersing the catalyst, if required. Make up the volume to 180 litres. Start educting the catalyst by routing the slip stream through the eductor 21J-2 from 21 P-2 discharge to suction. Regulate the catalyst solution rate at about 3-4 litre/min. After establishing the eduction rate, fill the drum from pump discharge with a rate equal to the educting rate. Add 1 bottle of Merox FB every 10 minutes. Approx. after 11/2 hour start checking the colour at pump suction before the educting point. The colour of the solution should be clear as a very light tint blue. If the blue colour is observed, impregnation must be stopped & reactor bed be 'fluffed' with air to correct bed channeling. Add 45 bottles of Merox FB. After the last batch of solution is educted, flush the catalyst drum several times with ammonia solution and educt it into the reactor. Continue circulation for about 4 hours.

- 20 -

Start transfer ammonical solution to reactor 21 R-1 B by opening the inlet distributor block valve. When the level in reactor 21R-1A falls below the distributor pipe, shut off the inlet. Continue/transfer to ammonical solution into reactor 21 R-1 B. When the pump loses suction, shut off the pump. Block in reactor 21 R-1A. Open HC outlet from reactor 21R-1B and start circulation to its inlet. Start taking DM water to fill the reactor until the level is 1 M above distributor pipe. Stop DM water flow to the reactor but continue circulation. Sample the solution and analyse for ammonia. Inject ammonia to get 0.2 + or - 0.02 wt. % of ammonia in the solution. Impregnate R1 B charcoal bed in the same as way as that of R1 A (add 45 bottles of Merox FB). After impregnation, ammonia solution is to be transferred to VB Naphtha reactor (To be impregnated). Drain out all remaining ammonia solution in both reactors. Flush and drain each reactor with DM water to remove residual ammonia, 2 hours is adequate. Sample the charcoal in plastic bag for each reactor at three/four points. Close the top manways. Start alkalizing each reactor with 15°Be' caustic, use 8.5 M 3 of caustic for each reactor. Circulate the solution for 2 hours. The reactors are ready for kero/ATF introduction. REQUIREMENT OF CATALYST/CHEMICALS -

Merox FB catalyst

-

90 bottles

-

Ammonia cylinder

-

5 cylinders of 60 kg each

-

Glacial acetic acid -

200 litres (approx.)

-

DM Water

-

•

250 M3

SHUT DOWN PROCEDURE:

For planned shut down for inpsection of equipment and maintenance work in the unit, follow the steps given below: Shutdown air injection to the mixer and shut off feed charge pumps P4A/4B to the coalescer 021-V9. Shut off water wash pumps P3A/3B. Empty out the salt-drier and clay filters into the kerosene storage tanks. - 21 -

If the caustic is spent in settler 021- V2, it can be pumped out to spent caustic system for disposal. Empty out the reactors also of the spent caustic. Kerosene remaining in the coalescer has to be drained out. When all the vessels have been emptied out of their contents, they are to be isolated by blinds. Blind list of the unit has to be kept upto date. Steam and water wash individual equipment and systems to make them free of hydrocarbons, caustic etc. and safe for entry. Detailed instruction for this step will be given at the time of actual shutdown. Entry to the vessels should be given only after making sure that they have been isolated properly, ventilated enough, gas tested free and safe to enter. Recommended safety equipments must be worn by workman entering the vessels which contained caustic etc. Dust masks and fresh air equipment must be used when charcoal loading/unloading and levelling are done inside the reactors.

•

EMERGENCIES:

Emergencies can result from equipment failure and from interruption of feed and utilities. Operators should be thoroughly familiar with the emergency procedures and understand the reason for each move. Nature and degree of emergency varies from time to time and hence good judgement and discretion should be exercised to tackle such situations. I.

ELECTRIC POWER FAILURE:

If it is a general power failure, feed to the unit will be interrupted with the failure of the pumps. Hence a shutdown of the unit is inevitable. Shut off air injection to the mixer immediately and block off feed to the unit. Shut off discharge valve of unit pumps and close pressure controller at unit limits and hold system pressure. Start up the unit as per procedure when power supply is resumed. II.

STEAM FAILURE:

Local steam failure will not affect the unit running immediately, but if AVU running is affected by the emergency, feed to the unit might be interrupted. In such a case, the unit will have to be shutdown and kept in a standby condition pending resumption of feed supply from AVU. III.

INSTRUMENT AIR FAILURE:

Instrument air failure will result in all unit control valves operating in the fail-safe position, i. e., they will all close. Close off feed to the caustic pre-wash vessel V-1. Shutdown caustic circulation pump P1, circulation pump P2 and water injection - 22 -

pump P3 and block level controllers with isolation valves. Monitor all levels. Hold system pressure by blocking off pressure controller at unit limits. Revert back to normal operations, starting the unit following standard procedure, once air supply to the instruments has been resumed. IV.

COOLING WATER FAILURE :

A total failure will effect feed supply to the unit and pumps. Hence, unit will have to be shutdown immediately. Isolate all the pumps after stopping them. Close the pressure controller and hold system pressure. Maintain levels in the vessels. Startup the unit in the normal way, when cooling water supply becomes available and feed from AVU is restored to the unit. V.

AIR COMPRESSOR FAILURE:

If the duration of the failure is only short, the product may not go off specification. But the mercaptan conversion efficiency drops off rapidly and the product will have to be slopped as soon as it goes off quality. Air injection block valve has to be immediately shut-off to the reactors R1A and B, on air compressor failure. On resumption of air supply, check the product quality and when it is on specification, route it to storage tank. If both the compressors are not available for a longer duration due to break-downs and maintenance, the Unit will have to be shut-down. •

OPERATING VARIABLES:

The caustic solution used for Merox treatment viz. In pre-wash column and in reactors become spent eventually. Weak acids like CO2 picked up from air, naphthenic acids and other aliphatic acids present in the feed stock make the alkalinity of the caustic lesser and its ability to extract mercaptans will suffer. Hence, it becomes necessary to remove part of the spent caustic and replace from time, to time to restore its alkalinity. The feed stock should be freed of all hydrogen sulphide by passing it through the pre-wash column. Otherwise the oxidation reaction will be suppressed in the reactors. It will give rise to increased caustic consumption. Lowering hydrocarbon feed rate and caustic temperature will improve mercaptan extraction Naphthenic acid in feed stock may give rise to emulsion problems and hence must be removed by prewash with 3°Be caustic solution. Oxidation rate is increased by increasing the temperature and catalyst concentration. About 30 cubic feet of free air is required for each pound of mercaptan sulphur to be oxidised. The amount of Merox Catalyst needed will be approximately one pound for 1000 gallons of 25°Be caustic solution.

- 23 -

Sufficient back pressure must be maintained at each extraction stage to prevent vaporisation and caustic entrainment. Presence of acid oils upto a limit of 8% will increase solubility of mercaptans in the caustic.

- 24 -

• Sr

CHEMICALS & CATALYST Vessel No.

Initial fill,M3

Approx. level of initial fill 30-50% of upper LG

Caustic strength %wt 2.1

Caustic2 1V1

9.3

Caustic2 1R1A/B

51.5

Refer 10oBe caustic tank calibrati on chart -

6.9

-

About 250 litres reimpregnation

-

-

-

-

-

-

-

-

-

-

After every 3 months run of the unit. Check the salt level and make up accordingly -

90 bottles of 7.5 litres each. (active ingredient per litre is 0.325 kg)

-

90 bottles required during each impregnation

About once in 4 months at design throughput

Acitic acid 21R1A/B Activated 171 charcoal 21R1A/B Rock salt 161 (200MT) 21V4 Filter clay 21V5A/B UOP Catalyst FB 21R1A/B

256

- 25 -

Make up / change out when Quantity required

Expected duration with design crude

When caustic strength to 1.0%

About 70% of Every 9 days initial fill (drain up to bottom LG & make up) Circulate reactor caustic once a 51.5 M3 Once in 5 days days. After about 5 circ. Charge caustic. Caustic strength would be around 6.2% for

each -

About once months.

in

4

-

• I.

MODIFICATIONS : ANTISTATIC DOSING FACILITY

This facility is given to maintain ATF conductivity between 50 to 450 psm (PICO simen per meter) to meet the specification. Antistatic Agent is stored in a small vessel (0.088 M3). Two dosing pumps, 21P6A/B have been provided to dose ASA to D/S of 21PIC-32 as per specification. II.

ATF REPROCESSING FACILITY

With AVU revamp, ATF production has gone high. During ATF crude processing part of untreated ATF is sent to separate tank 404 directly from AVU B/L. this untreated ATF stored in tank can be reprocessed in kero/ATF unit at the time when AVU is on BH crude processing. A line is layed from tank 404 to unit 21. A pump 21P7 is given which takes suction from tank 404. Pump discharge line joins to 21P4A/B suction line with a C/V and flow transmitter namely (21FRC40). This facility can also be used for blending BH ATF with imported ATF.

- 26 -

4. U-22 STRAIGHT RUN LPG MEROX

•

UNIT CAPACITY:

The Merox Extraction Unit for straight run LPG has been designed to process 70,000 MT/year of an essentially C3/C4 mixture obtained from the stabilizer column of the Atmospheric distillation unit. The unit shall operate for 345 stream days in a year. •

FEED SPECIFICATIONS:

The straight-run LPG feed to the Merox unit shall have substantially the following properties: Vapour pressure at 65°C

: 17 kg/cm2 max.

C 5's mol.%

: 1.0 max.

Specific gravity at 15.6°C

: 0.56

Mercaptan sulphur wt. ppm.

: 900 max.

Hydrogen sulphide wt. ppm

: 200 max.

•

PRODUCT SPECIFICATIONS :

The straight run LPG after Merox treatment shall meet the following specifications excepting its vapour pressure shall not exceed 17.0 kg/cm 2 at 65°C. Total Sulphur wppm: 15 max RSH wppm : 5 max H2S wppm : Nil Cu Corrosion : No worse than H2S Free feed •

PROCESS DESCRIPTION:

Amine absorber for removal of H2S and caustic prewash vessel are provided for pretreatment. Treatment for SR LPG consists of only an extractor with caustic, as all mercaptans present in feed are in the extractable range. Extraction caustic is oxidised in a common oxidiser section. Caustic settler has been provided for settling and separation of carry-over caustic from extractor. - 27 -

•

DETAILED DESCRIPTION OF P&ID

LPG obtained from crude unit stabiliser overhead is charged to unit by unit charge pumps 022P-1A/B. The feed is sent to the bottom of amine absorber 022C1 (1000 mm x 19500 mm). The column is provided with 4 sieve type trays. Regenerated DEA from amine regenerator is received in a surge drum pumps provided in cracked LPG merox unit. DEA from surge drum is pumped to the column top on flow control 022 FRC5. Rich DEA from column bottom is sent to amine regenerator located in Bitumen/Sulphur unit area via level control 022 LC 4, under column pressure. The H2S free LPG leaves from top of 022 C1 to caustic prewash vessel 022V1 ( 1100 OD x 6100 mm ) on flow control 022 FRCQI-1. Provision for bypassing 22C-1 in running condition is made by giving a jump over from inlet to outlet bypassing the Amine absorber. In order to keep up the extraction efficiency constant at lower throughputs, a recirculation stream back to crude unit stabiliser is provided. This recirculation flow can be maintained by flow controller 022 ERC 13. In LPG caustic prewash vessel, LPG is introduced at the bottom of the vessel through a distributor pipe. For this purpose, three nozzles at different levels have been provided. The vessel is provided with a wire mesh at top to remove caustic mist. Caustic in the vessel has to be replaced when it becomes spent. LPG is then sent to the extractor 022-C-2 (1000 OD mm x 16400 mm) where mercaptans are extracted by caustic from caustic regenerator section. The extractor is provided with 11 sieve type trays. Caustic is charged on flow control 022 FRC-9. Rich caustic from extractor is sent to caustic regenerator section on level control 022 LIC-8. LPG after extractor goes to Caustic settler 022 V2 (1000 mm OD x 4000 mm). After caustic settling LPG is run down to storage through a back pressure controller 022PC-12 to ensure constant back pressure in the Unit. To run-down LPG, mercaptan is added from odorant pot 022V03 by odorant pumps 022P02 to maintain odour specification. Caustic from settler can be drained into extractor caustic line going for regeneration. NOTE: Mercaptan dosing pumps have been removed for some other services and dosing lines have been blinded as dosing is not required.

- 28 -

• I.

PRE-COMMISSIONING OPERATIONS: CHECKING COMPLETION OF CONSTRUCTION WORKS, INSPECTION AND BOXING UP OF EQUIPMENTS

The following preliminary operations have to be carried out to ensure a successful start-up of the unit: Check that all mechanical works of construction have been completed, equipments inspected, boxed up and signed off on unit check lists made for this purpose. Scaffolding, debris, tools and other construction materials removed from the unit area. Make a final list of blinds which should be in position or taken out before starting purging operations. Make sure all blinds have been installed at the proper sides of valves and signed off in the list. Check and ensure Fire-fighting and safety equipment is in place and in good working condition. Ensure all utility systems and flare release headers are in service and ready for use. Isolate the unit from other plants and tankages at the unit limits with block valves. Keep the fuel gas and flare header isolated from the unit pending purging operations. Isolate or remove orifice blocks of all flow meters for flushing purposes. II.

WATER FLUSHING OF THE UNIT :

For water flushing of a new unit, use ordinary water. Water flushing of the entire unit has to be done with all pumps running on line so that all muck, scale and construction debris are washed out of all equipment and unit pipelines. The unit can be conveniently taken in sections or individual equipment wise and the flushing operation is carried out with temporary connections from the Fire water header. Suction screens have to be installed on the pumps during the flushing period to protect them from damage. They have to be run at least for 24 hours continuously to ensure their free and smooth service. During the flushing period, care should be taken to throttle the pump discharge valves suitably so as not to overload the motors. The screens on the pump suction lines have to be cleared off all debris collected periodically after stopping the pumps. till they remain clear continuously at least for eight hours. Disconnect all instruments lead lines and flush the leads thoroughly. Make sure that all process lines, control valve loops are thoroughly flushed, to atmosphere to remove muck, construction debris, etc. Better to drop each C/V and flush the assembly and bypass also thoroughly. Then the C/V can be refixed in position. Make sure all low - 29 -

points bleeders are clear and all columns and vessels vents and drains should be clear. When water flushing operation is completed, we have to pressure test the entire unit with water as detailed below: III.

PRESSURE TEST OF EQUIPMENT & LINES :

In order to check for leaks on equipment and lines after water flushing, they are all subjected to water pressure of about 16-20 kg/cm2 .For this purpose LPG inlet to amine scrubber and its outlet after the pressure controller are isolated by block valves. Rich amine and rich caustic outlets from scrubber 22C1, pre-wash vessel 22V1, extractor 22C2 must also be blocked off. Initial filling of the entire unit can be done with Fire water for removal of air. For pressurising we have to use Boiler feed water. Keep running the pump out of 19 P14 A/B/C group and through the permanent supply line take BFW to this unit and slowly pressurise the entire system to normal operating pressure for a period of 15 to 30 minutes. If necessary one or two drains may be kept open to have a small discharge from the pump. During pressure test safety valve down-stream flanges may be kept wedge open or to check tight shut-off of safety valves before their set pressure. Tighten all leaky flanges, valves glands etc. where required. Gaskets may have to be replaced after pressure test. Keep a record of such flange joints for subsequent testing before cutting in of feed LPG. After the system pressure test is successfully completed depressurise the unit, but keep the system filled with water. Now the system is ready for taking in Fuel gas. This is the best way of keeping air out of the unit. LPG can be taken in to the unit from Atmospheric Unit in small quantities. LPG can be lined up slowly to pressurise the unit to a slight positive pressure with gas. This has to be done slowly and carefully to avoid chilling. If. however, fuel gas is available, gas can be taken directly. LPG vapourises slowly giving positive pressure. Now drains off the water from the entire system under gas pressure. IV.

CHARGING OF CHEMICALS:

After pressurising the unit with fuel gas, inlet valve to the scrubber 22C1 is blocked off. Ensure that DEA inlet and outlet from 22C1 are also blocked off. Similarly, ensure that caustic charge line to 22 V1 and its exit as well as Merox coustic inlet to extractor 22 C2 are all shut off. The Merox regeneration system is also pressured up with fuel gas upto the disulphide separator in cracked LPG Merox unit and the extractor 22C2 bottom valve is blocked off. Make sure air inlet valve to the oxidiser 024-V3 remains blocked off. Alternatively regeneration section can be filled with caustic and vented at suitable points to remove air . In preparation for charging chemicals into the unit, vent gas from the caustic regeneration system till the system pressure drops to 0.5 kg/cm 2. prepare 20° Be - 30 -

caustic solution in the storage tank provided and transfer to disulphide separator 024-V4,with a good level in 24V4, start circulation pump 024-P1A/B and establish a level in LPG extractor 22C2. Then line up the pump 24P1 A/B for circulating caustic to extractor 22C2, through bottom LIC to the caustic heater 024-E1, oxidiser 024-V3 and back to disulphide separator 024-V4. Adjust the circulation on FRC control at the stipulated rate. From the 10° Be caustic solution tank in Kerosene Merox unit, transfer enough material into prewash vessel 22V1 to hold sufficient level. Line up lean DEA from sulphur Recovery Unit and establish working level in amine scrubber 22C1. Establish DEA circulation putting into commission the level controller at bottom of the column to control the rich amine solution returning for regeneration in the sulphur recovery unit.

•

START-UP PROCEDURE:

After the precommissioning activities have been completed and all equipment and piping etc. are purged to remove air proceed as follows: Establish Merox caustic circulation to top of extractor column 22C2 after establishing a working level in disulphide separator 24V4 in cracked LPG Merox Unit. when normal level of caustic is obtained in 22C2, commission the bottom level controller to regulate rich caustic flow back to disulphide separator 24V4. Charge lean amine on flow control to the amine scrubber 22C1. Maintain level at the bottom of 22C1 by commissioning the level controller regulating the rich amine flow to regenerator section in ARU. Lining up the product flow upto the rundown valve at battery limits, charge straight run LPG to the amine scrubber by means of pumps P1A and B. Control the flow rate from the scrubber to the caustic prewash vessel 22V1 with the FRC on line. Route LPG to rundown passing through the extractor 22C2 and caustic settler 22V2 displacing all the fuel gas to a horton-sphere lined up at LPG receiving station. When operating conditions become steady, with the level controllers of 22C1 and 22C2 maintaining adequate level, adjust the flow rate of LPG to the prewash vessel 22V1 to normal rate. Commission the recycling line of LPG back to the stabilizer column of AVU. Use the recycle line if 22C1 operates at low throughputs. Operate the rundown line pressure controller to maintain the desired back pressure in the system. Check the product after caustic settler for quality. When it is doctor negative. it can be routed to the regular storage spheres, kept ready for the purpose.

- 31 -

Commission odorant injection to the rundown LPG after caustic settler at the specified rate. Check the odorant injection facility is ready in all respects beforehand. Then start the injection pump 22P2 and set dosage. as instructed. NOTE:

Odorant injection is no more in use nowadays.

Check frequently LPG for H.S after the prewash vesel1 22V1 and replace caustic as necessary. 22V1 caustic is be replaced when caustic becomes 50% spent. Check the regenerated caustic being charged to the extractor 22C2. For extractable sulphur in it. This will give an idea of the efficient operation of disulphide separator.

•

SHUTDOWN PROCEDURE:

Inform all concerned of intention to shutdown the unit and proceed as follows: Shut off DEA charge pump to the scrubber 22Cl. Shut off LPG charge pump to 22C1 immediately after this. Stop odorant injection pump 22P-02. Stop caustic circulation through the extractor 22C2 from the disulphide separator 24V4. Stop caustic supply to pre-wash vessel 22V1. Empty out caustic levels from 22V1, 22C2 and 22V2 to spent caustic disposal or to the disulphide separator 24V4 in the cracked LPG Merox unit, as instructed. Empty out DEA level in 22C1 to its regeneration section in Bitumen/Sulphur area. Depressure the vessels and columns slowly to the flare system, after isolation at unit limits. Isolate the vessels and columns by blinds and make them gas and chemicals free by water washing repeatedly, as per special instruction that will be issued at the time of shutdown. Keep an upto date record of the blind list. Entry to the vessels has to be given only after ensuring that they are absolutely free from all gases and chemicals used in the plant. Gas test must be done before entry permit is given. Proper ventilation inside the vessels must be ensured. Personnel entering the vessels must wear proper protective equipment as mentioned in the clearance permits.

- 32 -

• I.

EMERGENCY PROCEDURE POWER FAILURE:

In case of general power failure LPG supply to the unit will stop and the unit pumps running will be interrupted. DEA solution circulation also will stop. Block off pressure controller at unit rundown line and hold pressure in the system. Monitor all levels. When power supply and LPG feed are restored, put the unit back into normal operation, following standard procedure. II.

STEAM FAILURE:

In case of general steam failure, LPG to the unit will be affected and hence unit will have to be shut down and kept under pressure till feed supply is resumed from AVU. If the steam failure is confined to the Merox unit only then LPG Merox section can run without any interruption. III.

COOLING WATER FAILURE:

Failure of cooling water will affect the feed supply to the unit as well as the unit pumps. Unit will have to be shutdown and kept standby till water supply is restored. IV.

INSTRUMENT AIR FAILURE:

On instrument air failure, all the control valves in the unit will close. If AVU is also affected by air failure, feed to the unit will be interrupted. Close off the pressure controller on LPG rundown line and maintain pressure in the system. Monitor all levels till air supply is resumed to normal. Revert to normal operation. • I.

OPERATING VARIABLES : LPG PREWASH:

LPG is passed through amine scrubber 22C1 and caustic prewash vessel 22V1 to remove all traces of hydrogen sulphide. The DEA solution should be kept at the specified value of 25% by wt. The amine circulation rate also should be at the design rate of about 800 kg/hr. Caustic concentration for prewash should be 1020° Be, when it becomes spent, caustic must be replaced with fresh stock. II.

LPG EXTRACTOR:

Mercaptan extractor 22C2 removes these undesirable components from LPG stream by intimate mixing with a caustic solution containing Merox catalyst. The caustic concentration for the circulation should be 20° Be. The catalyst - 33 -

concentration in the caustic should be 100 ppm. Merox solution circulation rate should be 0.17 M3/hr. Operating pressure which is maintained by the pressure controller on the rundown line should be about 18.0 kg/cm2 at the extractor 22C2. Reducing any of these variables excepting the pressure will affect mercaptan extraction efficiency. Too Iow an operating pressure favours amine and caustic entrainment in LPG stream. III.

TYPICAL OPERATING DATA AS OBSERVED IN THE NORMAL RUN OF THE UNIT

LPG flow Amine flow Caustic flow Back pressure

M3/hr M3/hr M3/hr Kg/cm2

ACTUAL-1 11.76 0.34 0.17 12

- 34 -

ACTUAL-2 24 0.8 Nil 12.5

•

CHEMICALS & CATALYSTS:

Vessel no

Initial fill M3

Approx. Caustic level of strength initial fill % wt.

Caustic 022V1

3

30-50% 6.9 of upper LPG

Ethyl tan

-

-

•

mercap-

Make up/ Quantity charge out when reqd.

Exp.to run when design crude Caustic About 70% of Every strength down initial fill month to 1.5% (drain upto bottom LG and make up) As required to maintain rundown LPG Not in use now odour at level 2(min)

MODIFICATIONS:

I.

Facility to route SR LPG to CR LPG unit and vice-versa.

II.

Facility to route CR LPG to SR LPG Xerox (unit 22) partially.

III.

After AVU revamp, SRLPG make has gone up and now SRLPG is being treated in 24 Unit which was earlier treating CRLPG. Now SR LPG is treated In Unit 22. Following changes in operation have been done to achieve LPG specifications. Caustic circulation in extractor has been stopped due to caustic, carryover 8 M3 caustic is taken in this column which is acting as another prewash. Due to high LPG production. caustic carry over continued resulting LPG falling in Cu corrosion test. Now BFW is being taken in this column to wash the caustic haze carried from 22V1.

IV. Name of the Scheme

Scheme for conversion of 22C2 to amine absorber

- 35 -

Scheme No Scheme implemented on

MR/PS/300/2001/12 Apr’02

Description of Scheme

Conversion of water wash column 22C2 into Amine absorber in cracked LPG Merox

Reason for modification

Due to higher LPG generation of around 36-38 m3/hr, load on 22C1 had increased leading to very often amine carryover from 22C1.Water wash column if converted into amine absorber would take part of the LPG load and would lead result in better extraction of H2S from LPG 1. 22C2 will now be operated as amine wash column. LPG from FCCU would get distributed in 22C1 and 22C2.10 M3/hr of LPG flow would go to 22C2 controlled through 22FRC13. 2. 22FRC13 would be given a set-point of 10 m3/hr. 3. Amine flow through 22C2 would be maintained through 22FRC9. This would be given a set point of 0.7 M3/hr. 4. Amine level in 22C2 would be maintained by 22LIC 8. This would always remain on auto. 5. Amine and LPG level interface is maintained in the lower half of the column.

Operating Instructions

- 36 -

5. U-23 VISBREAKER NAPHTHA MEROX •

UNIT CAPACITY

The Merox treating unit for sweetening the naphtha stream obtained from the visbreaker unit has been designed to feed 65,000 MT/year of naphtha. The unit shall operate for 330 stream days in a year. •

FEED SPECIFICATIONS

DESIGN

ACTUAL

H2S wppm

10 max

70-110

Mercaptan wppm

3000 max

3000-4000

Density at 15°C

0.74

0.71-0.72

Distn.

IBP

50

52

FBP

116

•

150

PRODUCT SPOECIFICATIONS

Merox treated naphtha shall meet the following specifications (i) Copper strip corrosion ( 3 hours at 50°C )

1 max. ASTM D-130-65

(ii) Mercaptan sulphur wt ppm 163-62 (iii) Oxidation stability minutes.(after injection of UOP No.5 copper deactivator)

•

5 max. UOP 390 min ASTM D-525-55

TYPE OF CATALYST USED

Merox catalyst ws which is dispersed in caustic solution is used in the extractor column 023-C2 of this treating unit. Merox Catalyst FB is used in the sweetening Reactor 023-R1 of the unit. This is impregnated on activated charcoal bed in the reactor both the catalysts are supplied by UOP. Initial charge of catalyst WS is 4.0 gal. and it is added whenever spent caustic is dumped and fresh caustic solution is made up in the extractor column for one impregnation on the reactor bed. 7.3 gal. of catalyst FB is used.

- 37 -

•

PROCESS DESCRIPTION

Caustic prewash vessel is provided for removal of hydrogen sulphide etc. For visbreaker naphtha, both extraction and sweetening sections are provided. After caustic prewash naphtha goes to extraction tower where partial extraction of mercaptans, to the extent possible are extracted. Extraction is followed by sweetening in reactor with supported merox catalyst bed. Air requirement is met from the common compressor . Post treatment consists of a caustic settler, and a sand filter for removing caustic haze. The treated product requires anti-oxidant injection, since visbreaker naphtha is a cracked product. •

DETAILED DESCRIPTION OF P&ID

Visbreaker naphtha as obtained from Visbreaker stabiliser bottom is fed to the unit by feed pumps 023-P1 A&B.Flow control 023-FRC-3 on discharge of pump is cascaded with visbreaker stabiliser bottom level control. Visbreaker naphtha can be diverted to slops, when necessary,downstream of 023-FRC-3. Caustic prewash vessel 023-V-1 ( 1000 MM x 6100 MM ) is provided for removal of hydrogen sulphide etc. The vessel is also provided with a stainless steel wiremesh blanket at the top to remove any caustic entrainment. There are three inlet nozzles like in other prewash vessels. Caustic in the vessel is to be changed out as indicated by its strength. The feed then goes to extractor column 023C-1 ( 1000 MM x 13300 MM ) and is introduced at the bottom of column where counter-current contact is made with caustic under circulation. Regenerated caustic from caustic regenerator section is introduced at column top on flow, control 023-FRC-8. Through the extractor trays caustic flows downwards due to its higher gravity. Caustic after extraction is sent to caustic regeneration section by maintaining the 023-CI bottom caustic level by 023-LIC-7. In the extractor, mercaptans are partially extracted to the extent these are soluble in caustic. About 40-60% mercaptans are normally extracted. This will vary with the type of feed to visbreaker and operating conditions of visbreaker . The extracted naphtha then goes to Merox Reactor 023-R1 ( 1400 MM x 4500 MM ) for sweetening of unextracted mercaptans. The reactor consists of a solid bed of activated charcoal impregnated with merox catalyst No.1. Oxidation air is added to visbreaker naphtha on flow control 023-FRC-15 and mixed thorougly with feed in the air-mixer 023 M x 1 before it goes to reactor. Uniform distribution of feed over reactor bed is ensured by the distributor pipe assembly placed inside the reactor. The collector assembly at the bottom is wrapped with Johnson screen to ensure filtering of reactor bed material from the hydrocarbon stream. From the outlet of reactor, caustic removal from visbreaker naphtha is achieved in the caustic settler 023V2( 1100 x 4700 ). The feed to the settler is distributed by a slotted vertical pipe. - 38 -

The treated product from settler is sent to storage via a sand filter 023-V3 ( 1400 x 3800 ) for removal of caustic haze. The inlet distributor consists of slotted pipes assembly. Sand is filled from half way up the vessel and supported on the packing support provided at that level. Below the sand packing segmented baffle is provided in front of outlet nozzle' to ensure clear hydrocarbon withdrawal from sand filter. The treated product is sent to storage after the pressure control 023PC-19 which ensures constant back pressure to the unit. The sand filter is also provided with a bypass, for use when necessary. Visbreaker naphtha being a cracked product requires to be dozed with oxidation inhibitors. UOP No.5 inhibitor from drums can be transferred to inhibitor melting pot 023-V6. Three inhibitor metering pumps 023P-3A, B&C are provided. 023P-3A is for injecting inhibitor into visbreaker naphtha, 023P-3C is for injecting to FCC gasoline and 023P-3B is a common spare. Inhibitor is added upstream of 023PC19 control valve which ensures constant pressure. For circulation of reactor caustic as well as for water wash and methanol circulation, pumps 023-P2 A&B are provided. For impregnation of catalyst, catalyst addition pot 023-V4 and flow indicators 023FI-10 & 023FI-11 are to be used when impregnation is carried out in line with standard impregnation procedure. For acidifying charcoal bed during reimpregnation acetic acid addition pot 023-V5 and eductor 023-J2 are provided. The treated and inhibited visbreaker naphtha which is doctor sweet shall normally be used as a motor gasoline-blending component. • I.

PRECOMMISSIONING OPERATIONS CHECKING OF CONSTRUCTION WORK COMPLETION, INSPECTION AND BOXING UP OF EQUIPMENT.

The following preliminary operations are to be carried out in order to ensure a trouble free and smooth startup of the unit. Check that all mechanical works of construction have been completed. All equipments and lines in the unit must be hydraulically tested at pressure depending upon design conditions so that we can be certain that they will stand operating pressures. After the hydraulic test, equipment are finally inspected for proper internal fittings and fixtures as well as cleanliness. Clearance are given to box up equipment after final inspection as above. Checklists are signed off as complete in all respects for individual equipment and pipelines. Make a final blind list indicating which blinds are to remain in position and which are to be taken out before starting gas-purging operations. Ensure that all blinds have been installed at the proper sides of valves and entered in the list. Check and ensure that fire fighting and safety equipment are readily available in the unit in good working condition. Ensure that all utility systems and flare release header are in service and ready for use. - 39 -

Ensure free movement in the unit area. Get scaffoldings, construction debris tools and tackles etc. removed from the unit area. Isolate the unit from other plants and storage tanks at the unit limits with block valves/blinds for carrying out flushing and purging operations. Isolate or remove instrument orifice blocks for flushing purposes. II.

WATER FLUSHING OF THE UNIT

In preparation for start-up of the unit, water flushing of the entire unit has to be carried out to remove and wash out all muck, scales construction debris etc. from equipment and lines for the purpose of water flushing, the unit can be taken up in convenient sections as well as individual equipment-wise also. Hooking up temporary fire water hose connections on equipment or lines, thorough flushing of all equipment and lines are carried out. All the unit pumps are tried out during water flushing with suitable wire mesh screens ( preferably 100 each )fitted on to their suction spools to prevent them from damages. The pumps have to be run at least for 24 hours continuously to ensure their free and smooth functioning. Care has to be taken while running the pumps not to overload their motors, during the water flushing operations Their discharge valve have to be suitably throttled to take care of the loads on motor. During the pumps running-in period, the suction screen will get choked up with debris washed out into them and they will start losing suction. Immediately the pumps are to be stopped. screens opened up, cleaned and then pumps restarted. This cleaning operation will have to be continued till the suction screens remain clear of all debris and muck at least for 8 hours. On satisfactory completion of water flushing of the unit. All the water from equipment and lines are to be drained out, opening drains and flanges at low points. Care should be taken not to pull any vacuum in the equipment while draining water. Then, thoroughly air blow the entire unit to remove all traces of water remaining after water washing. III.

PRESSURE TESTING OF EQUIPMENT & PIPELINES

Subsequent to water flushing of equipment and lines in the unit, a pressure test is carried out with water to about 10 kg/cm2 to detect leaks, if any, in the system and repair them in the time before the actual start-up of the unit and to tighten most of the flanges. During the test safety valve downstream flanges are opened up to check holding of safety valves. Any safety valve which requires resetting is removed and sent to workshop for repair. Pressure test with water can be conveniently carried out by running the feed pump or caustic pump and pressure up the unit by restricting the flow at the plant outlet till the desired pressure is reached. Care has to be taken during pressure test to isolate equipment and piping which are designed for lower pressure, like e.g. methanol system. These can be tested separately at lower pressure. - 40 -

After pressure test is satisfactorily completed, drain water from system at all low point and air blow it thoroughly to remove all moisture. IV.

SCREENING AND LOADING OF CHEMICALS

ACTIVATED CHARCOAL Activated charcoal which merox catalyst impregnation will be screened properly before it is loaded in the reactor 23R1. Standard ASTM Sieve Nos. 10 and 30 screens have to be used and charcoal coarser then No.10 and fines after No.30 screen are separated out. The charcoal thus screened is loaded in 23R1 after isolating it from other equipment. Its top and side manways are kept open. Its inlet distributor pipe assembly has to be kept 'Covered during loading to prevent charcoal entry into the pipe. Charcoal loading is done through a hopper and adjustable canvass chute, which extends to the bottom of the reactor. As loading progresses, the length of the chute is adjusted. No cone formation is to be allowed on the charcoal surface in the reactor. Improper leveling will cause nonuniform distribution of hydrocarbon flow through the charcoal bed. Personnel must wear dust masks covering their noses and mouths to prevent inhalation of charcoal dust, while loading for leveling inside the reactor, the person entering must wear a fresh air mask. While loading, it has to be ensured that the 'bottom Johnson screen collector Is fully submerged in the charcoal by physical checking, from the bottom manway. The charcoal loading is continued till the inlet distributor pipe is about 900 mm from the charcoal bed. Final leveling is done entering the reactor top with protective equipment. Record of quantity of charcoal loaded in the reactor is kept for reference. The loading hopper and canvas chute are removed after loading, the cover on distributor pipe is taken out and the top maway of the reactor is boxed up tight. SAND Check the internals of sand filter 23-V3 for proper fittings and support for sand 'bed, Check also it is wiped clean from inside sand screened to the specification of 8-16 ASTM Nos. is then loaded to a height of 1.4 meters in the filter. The surface is levelled properly and then the vessel is boxed up finally. V.

PRESSURE TEST FOR TIGHTENESS

When all chemicals have been loaded as required and all manways, flanges, etc boxed up the unit is ready for impregnation of catalyst on charcoal bed. Before impregnation of catalyst, it is preferable to test the unit for tightness of flanges, manways. etc. under air pressure. Compressed air ex 21 CI A, B can be used for pressuring up the unit to about 10 kg/cm 2' pressure. After the unit is pressured up. check all flanges manways, etc for tightness with soap solution. Tighten as required. When pressure test is over release the pressure gradually in order not to disturb the bed of charcoal. VI.

IMPREGNATION OF CATALYST ON REACTOR 23-R1 - 41 -

After the reactor is filled with charcoal to the required level and boxed up proceed to impregnate charcoal with Merox catalyst FB as detailed in the following steps. Fill the reactor with DM water being careful not to add so much water as to float charcoal out of reactor.To ensure this. reactor top manway can be kept open. Once level is ensured manway can be kept in closed position without bolting to enable inspection of bed after impregnation. Stop D M water supply and line up reactor bottom to reach circulation pump 23-P2 A. B and establish from bottom of bed to top of bed. Estimate the amount of water in the system i. e. reactor, lines etc. If water is charged from a tank, this can be estimated conveniently from tank dips. Estimate should take into account piping, dead spaces etc. The total quantity will be about 6-7 M3. Calculate the amount of ammonia required to raise the concentration of water to a 0.2% wt solution of ammonia. The quantity of ammonia required will be about 12-14 kgs. With water in circulation, inject the desired amount of ammonia into the water upstream of suction line to pump 23-P2 A. B. Ammonia is injeted from a cylinder mounted on a suitable weighscale so that the quantity of ammonia injection can be controlled. Adjust ammonia injection rate in such a way that the amount needed will be introduced during the time it takes to pump the entire water inventory through this system twice; with pump this would takes 3 to 4 hrs and hence adjust ammonia injection to last this period. When ammonia concentration is uniform in the system. fill the catalyst mix drum with ammonia water. Add the content of 3 bottles of 2.5 gallons each of merox FB catalyst. This contains 7.5 kg of active ingredient. Mix ammonia water and catalyst solution thoroughly using an air sparger. In the catalyst mix drum do not exceed 80% level. With water still circulating from the bottom of the reactor to top, educt the catalystammonia water into the system at a rate of approximately 4 liters per minute. After emptying the mix-drum, flush it several times with Ammonia water and educt the water into the reactor to get all of the residual catalyst into the reactor. Continue circulation of ammonia water for one more hour after all catalyst has been educted. Finally drain all water from the system. The catalyst is now ready for alkalizing with a 10°Be solution of caustic. Transfer caustic of this strength to the settler 23V2 to about 30% of its volume. Start caustic circulation with pump 23-P2 A/B through the reactor 23-R1. Initially keeping the drain valve open, remove all the free water till caustic appears at the drain. Close off the drain and continue circulation at the maximum discharge rate for about two hours. If necessary. take additional caustic from storage tank into settler 23-V2. Stop circulation after two hours and the reactor is now ready after impregnation to receive hydrocarbon feed for sweetening. - 42 -

VII.

CHARGING OF CHEMICALS

Caustic requirements of the unit is met from the storage facility available in the kerosene merox section. Fresh caustic of 26.5 %Be strength is received in storage tanks 21 TI & T2 and diluted with demineralised water to the desired strength. 10oBe caustic is charged into the prewash vessel 23-V1 till a working level is established in 23-V1. 20°Be caustic from the disulphide separator 24-V4 of the cracked LPG Merox Unit is charged to the extractor column 23-C1 top through a 11/2" line by the transfer pump at cracked LPG Merox Unit. This caustic drop after extraction of mercaptans is sent back to the regeneration section on level control from the bottom of extractor column. To begin with 20°Be caustic is transferred to the disulphide separator from kero merox unit to establish sufficient level for subsequent transfer to other merox sections. •

START-UP PROCEDURE

It is assumed that the merox system is fully lined up for startup. Proceed to start-up the unit as follows :When visbreaker naphtha becomes available commission the charge pumps 23P1 A/B and slowly introduce naphtha into the prewash vessel 23-V1 and fill it up. Let it pass through the extractor and then the reactor and caustic settler. Finally, pass naphtha through the sand filter 23-V3 to the rundown line to storage. Vent out all air before filling the vessels. Commission the pressure controller 23-PC-19 to have the required back pressure in the system. Maintain proper levels of interface in 23-V1 and 23-C1.Commission the bottom 23LC7 of 23-C1. Start air injection thro' mixer 23 MY1. Take the flow on control 23-FRC15 and set the flow rate to the requirement (30 kgs/hr.) of mercaptan sulphur in the feed. 23 PC-19 should be set such that all air injected is in hydrocarbon solution. In a freshly charged merox Reactor, no caustic circulation will be needed on the initial start-up period. Hence it is enough to pass the feed through the reactor, with air mixing as already mentioned above. When catalyst activity declines over a period of time, resaturation with caustic circulation is resorted to. Caustic carried over alongwith naphtha is settled in 23-V2 and drained back to the circulating pump suction. Any traces of caustic haze still remaining is removed in the sand filter 23-V3 and the treated naphtha is routed to storage from the sand filter. Commissioning the inhibitor injection facility, the metering pump 23-P3A/B is started to inject the measured quantity of inhibitor into the naphtha stream going out to storage. The present injection rate is 80 to 90 ppm so as to get a minimum induction period of 360 minimum. - 43 -

Initially, the product stream is routed to the slop tank till satisfactory results are obtained consistently for about 2 hours. Then naphtha can be routed to the regular storage tanks. Set the feed rate to normal consistent with other control systems parameters. •

REACTOR BED WATER WASHING & CATALYST REIMPREGNATION

Over a period of time, catalyst in the reactor bed loses its activity and even wetting with fresh caustic circulation does not help in restoring the activity and the product continued to go off specifications. Then the charcoal bed has to be hot water washed to remove the organic deposits on its pores. Washing will bring back the activity of the catalyst for reaction again. As the loss of activity by deposits on charcoal surface occurs gradually the water washing operation can be planned conveniently The water used should be dust free and free from suspended matter. hardness, salts and active chlorine. DM Water is therefore, used in our plant for this purpose. Water washing procedure is as follows : Stop air injection and hydrocarbon charge to the reactor 23 R1. Pump out all naphtha from 23 R1 under steam pressure. Steam out the reactor for about an hour. Commission water heater 23 JI and start introducing hot water into reactor at a temperature of 85 - 95°C at a rate of 8 gallons/minute for 100 cubic feet of charcoal bed i. e. about 3.5 M3/hr. Fill up the reactor and drain water to sewer at the same rate as filling. The effluent from reactor bottom will be dark brown and foaming in the beginning. This will change and become colourless gradually when water washing progresses. When the drain water is clean and clear. The washing of the reactor bed can be stopped. Then blow out as much water as possible from the reactor with steam given to it from the top. Continue steam blowing for another half an hour to remove from the charcoal voids as much residual heavy oil as possible. Stop steam to reactor and block of water heater. Blanket the reactor with nitrogen and blow it with N2 gas for an hour or so till there is no water dripping from the bottom drain. Next alkalize the reactor bed with 10 oBe caustic solution and then return the unit back to normal operations, as detailed under "Start-up procedure." I.

CATALYST REIMPREGNATION

Catalyst reimpregnation step is necessary only when hot water washing, higher feed temperature, stronger caustic reduced feed rates etc. do not help in mercaptan oxidation and the product remains off-spec. Gap between one reimpregnation and another will depend on proper prewashing, feed mercaptan content, crude etc. Period may vary from three months to one year depending on feed quality. Detailed steps for reimpregnation are as given below:

- 44 -

Follow the steps 5.1.1 to 5.1.4 given under "Reactor Bed Water washing", excepting the steaming of reactor. Fill up the reactor with hot water. Then stop water and steam flow to the water heater by blocking off the valves. Line up reactor bottom drain line to caustic circulation pump 23 P2 A/B and flush out the lines free of caustic into the spent caustic disposal system. Close the reactor outlet valve and fill it up with hot water again. Start hot water circulation from reactor top to bottom, regulating water temperature with steam around 50-70°C. Keep both the drain line and reactor outlet lined up to the circulating pump. Take about 20 liters of glacial acetic acid in the addition pot 23-V5 and close the lid of 23- V5. Educt the acid from 23-V5 into the circulating water with the help of the 3/4" globe valve on pump 23-P2 A/B discharge. Eductor 23-J2 takes suction from the acetic acid addition pot 23-V5. Educt the acid to the circulating water to reactor over a period of 5-10 minutes. Circulate the acidified water for an hour and check its PH at the pump 23-P2 A/B suction. If PH is more than 6.5 another 20 litres of acetic acid will have to be educted till the circulating water PH is 6.5 or less. Stop water circulation; introduce steam into the reactor and remove all water from the bottom drain. Keep steam blowing for another half an hour and displace all traces of residual oils from charcoal voids. Stop steam to reactor and blow it with air till water drips from its drain stop. Then follow the steps given under "Impregnation of catalyst" under 3.6. Unit can be returned to its normal duty as soon as reimpregnation of catalyst is over. •

SHUTDOWN -PROCEDURE

For planned shutdown for inspection of equipment and maintenance work in the unit, follow the sequence of operations given below: Inform all concerned of intention to shutdown the unit. Shut off air injection block valve to the mixer MX1. Shut off naphtha charge pump 23P1A/B to the prewash vessel 23 V1. Close off the pressure controller 23PC-19 at the battery limit. Shut off anti-oxidant injection pump 23P3A/B to the naphtha stream before 23 PC-19. Stop caustic circulation through the extractor 23C1 and reactor 23 R1. Pump out caustic from 23 C1, 23 R1, 23 V2 and 23 V3 to spent caustic disposal system. Pump out all caustic from 23 V1 bottom into the spent caustic drainage system. Pump out hydrocarbons remaining in the vessels to the slop tank with circulation pump 23 P2 A/B. - 45 -

Flush out reactor 23 R1 with hot water thoroughly and drain off all water. Isolate all individual equipment by blinds as required for maintenance. Steam and water wash them thoroughly till they are hydrocarbons and chemicals free. Maintain an upto date blind list of unit equipment. Follow detailed instructions that will be given at the time of shutdown for preparing equipment and lines gas free and for maintenance. Entry to the vessels should be given only after ensuring complete isolation by blinds, making gas free and free of chemicals. Also, it must be ensured that the vessels are well ventilated and are safe to enter. Gas test must be taken before issuing clearance for entry into a vessel Safety equipments recommended must be worn by personnel entering vessels which previously contained caustic and other chemicals. •

EMERGENCIES

Emergencies result out of equipment failures and from interruption of utilities. Operating personnel must be thoroughly familiar with the emergency procedures so that quick actions can be taken in such situations. Nature and degree of an emergency varies from time to time. Hence, good judgement and discretion should be exercised to tackle any emergency. I.

ELECTRIC POWER FAILURE

If it is a general failure, naphtha feed to the unit will be lost and all unit pumps will stop. Unit will have to be immediately shutdown. blocking off air injection to mixer MX1. Close off the pressure controller at battery limit and hold the system pressure. Shut off the discharge valve of pumps. Hold the levels in the vessels. Start up the unit again following standard procedure. when power supply is restored. II.

STEAM FAILURE

Local steam failure will not effect the unit immediately If the naphtha feed supply from visbreaker is affected then unit will have to be shutdown and kept standby till the feed naphtha is available again. III.

INSTRUMENT AIR FAILURE

All control valves will operate to fail safe position i.e. they will close. Shut off the air to the reactor by the block valve to the mixer MX1. Hold the pressure in the system and monitor all levels till air supply is restored to the instruments. Start-up the unit as per normal procedure and bring it back on stream. IV.

COOLING WATER FAILURE

A total water failure will affect feed supply to the unit as well as unit pumps. Hence. unit will have to be shut down immediately. Stop the pumps. Block off pressure - 46 -

Controllers and hold system pressure. Maintain all levels in unit vessels. When cooling water becomes available, start up the unit, as per normal procedure. For a short duration, process air failure will not affect the treated naphtha quality. But the mercaptan conversion efficiency drops off rapidly with no air for oxidation. Hence the product will have to be stopped as soon as it becomes doctor positive. Shut off air injection block valve to mixer MX1 immediately on air failure. •

OPERATING VARIABLES

Caustic solutions used in prewash vessel 23 V1 and reactor 23 R1 become spent eventually and mercaptan extraction will suffer. Hence, periodically, part of the caustic will have to be replaced with fresh stock. Caustic concentration in the solution for extracting lighter mercaptans in 23 C1 must be 20°Be. Catalyst concentration in caustic should be 100 ppm. Operating pressure should be about 8 kg/cm2 to keep the air injected dissolved in hydrocarbon. Lower pressure results in vaporisation and caustic entrainment. Too little air will result in incomplete oxidation of mercaptans to disulphides. About 30 cu. feet of free air is required for each lb of mercaptans sulphur to be oxidised. Catalyst activity in the reactor bed is increased by resaturation with 10°Be caustic circulation freshly taken and circulated through the bed. Hot water washing and reimpregnation with catalyst are further steps to restore the activity of the catalyst. Acid oils upto 8-12% in caustic solution will increase solubility of mercaptans in caustic. H2S and naphthenic acid from feed naphtha must be fully removed in the prewash vessel 23 V1. Otherwise oxidation reaction will be suppressed in the reactor. Naphthenic acid may give rise to emulsion problems. I.

Typical Operating Data :

DESIGN

ACTUAL

Feed flow

M3/hr 10.5

Air rate

NM3/hr

2.4 to 4.0 7.1

3.0 to 6.0

Caustic Circulation rate M3/hr

25

2 to 2.5

Feed temperature: °C

40

30-35

- 47 -

• Sr

CHEMICALS & CATALYSTS Vessel No. 23V1

Initial fill,M3 2.4

Approx. level of Caustic initial fill strength %wt 30-50% of 6.9 upper LG

23R1

1.5

Ammonia 23R1

12-14 kg

Refer caustic 6.9 tank calibration chart -

Acetic acid 23R1

-

-

-

UOP No.5 oxidation inhibitor UOP copper deactivato r Charcoal 23R1 Sand 23V3 Catalyst Merox reagent FB 23R1

About 10 drums About 3 drums

-

-

Rate of injection 760 cc/hr

-

-

3 drums good for six months

6.0

-

-

Rate of injection 1000 CC/hr of mixture of UOP No 5 & deactivator in the ratio of 1:0.32 -

2.2

-

-

-

-

7.5 gal for initial impreg nation

-

7.5 gal for impregnation

- 49 -

Make up / change out Quantity when required When caustic strength to About 70% of initial fill 1.5% (drain up to bottom LG & make up) Circulate caustic once in 15 M3 9 days. Caustic good for about 5 circulations Some quantity required during each reimpregnation About 20 litres for each reimpregnation

each -

Expected duration with design crude Every month Once in 45 days About once in 4 months at design throughput About once in 4 months at design throughput 10 drums good for 6 months

-

About once in 4 months at design throughput

6. U-24 CRACKED LPG MEROX •

UNIT CAPACITY

Cracked LPG Merox unit is designed to process 1,45,000 MT/Year of LPG from Catalystic Cracking Unit with an on stream days 345 per year. •

FEED SPECIFICATIONS

C5 + material H2S RSH-S •

- < 1% (Mol) - < 2100 WPPM - 300 WPPM (Max)

PRODUCT SPECIFICATIONS

LPG PRODUCT: Total sulphur - < 15 WPPM RSH-S - < 5 WPPM Copper Corrosion - Not worse than H2S free feed.

•

TYPE OF CATALYST USED

The Merox Catalyst used in the extraction section of this unit is UOP Merox WS. It is a replacement for the original conventional powdered Merox Reagent No.2. Merox WS is an aqueous solution of the reagent having equivalent catalytic activity and stability as merox Reagent No.2. Although it is not truly soluble in water, it has got considerable dispersibility in caustic solution. It is packed in polythene bottles with 1 kg. of active ingredient in each bottle of 3.8 litters capacity. Catalyst is added to the circulating caustic going to regeneration section. The initial inventory in a process unit is recommended at 100 PPM (by wt.) or approximately 1 bottle per 4 M3 of caustic soda and up to 5 times this concentration in units treating high severity FCC gasoline. One distinguished characteristic of this Merox Catalyst leads to a simple control of unit operation. If mercaptans or excessive amounts of acid contaminants such as sulfides are absent. A medium containing approximately 100 WPPM Merox catalyst imparts a deep blue color. However should mercaptan be added, the solution will become deep green. In this complex state, the catalyst exhibits a considerably greater ability to remain suspended. If the mercaptans in this green merox catalyst medium were oxidized, the blue color would reappear This phenomenon can, be observed in the shake test which is an extremely useful parameter in evaluating the process.

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•

PROCESS DESCRIPTION

THEORY OF MEROX TREATMENT OF CRACKED LPG: The extraction mode of Merox Process is for the treatment of light hydrocarbons in LPG and light naphtha streams. It is designed to reduce the total sulfur content by extracting the mercaptan compounds in these streams. The extracted mercaptan compounds can be effectively removed after being oxidized to disulfide oils. The Hydrocarbon stream is contacted with caustic solution in an extractor. Extracted mercaptans are then oxidized and separated from the caustic. Thus the Merox process is easily described in two parts: MERCAPTAN EXTRCTION Mercaptans present in the LPG are readily dissolved in the caustic solution when extracted by means of a high efficiency, counter flow extractor. As the hydrocarbon and caustic are intimately contacted, the mercaptans combine chemically with the sodium hydroxide molecules. RSH + NaOH NaSR + H2O Since the reaction is reversible, the sodium mercaptide must be removed from the caustic solution from time to time. The UOP designed counter amount extractor provides the effective extraction of mercaptans in to the caustic solution and its removal from cracked LPG. MEROX CAUSTIC REGENERATION Caustic regeneration is for the removal of sufficient mercaptides from the rich caustic solution to allow the reuse of this caustic solution to continuously affect the desired mercaptan removal from the hydrocarbon stream. Sodium mercaptides in the rich caustic are readily oxidized to disulfide in the presence of oxygen and enough Merox catalyst. Sodium hydroxide reliberated. This is represented as: Merox NaSR + 1/4 02 + 1/2 H2O -------> 1/2 RSSR + NaOH Catalyst This is an irreversible reaction. The disulfide oil produced is essentially in soluble in the caustic solution and thus allow it to be gravity separated from the regenerated caustic before the lean caustic is allowed to return to the extractor. The composite reaction is RSH + 1/2 02 ->

1

/2 RSSR + H2O

The composite reaction does not consume caustic, if only the mercaptans are extracted. However the other extractable compounds such as H 2S, C02, COs do not allow full recovery of caustic. Pretreatment of hydrocarbon stream becomes - 51 -

necessary to remove maximum amount of H 2S. This is accomplished by Amine absorption followed by washing with dilute caustic of 7% by wt. Post treatment is normally for the removal of entrained caustic solution due to its corrosive nature to protect down stream process equipment and to meet product specification. •

DETAILED DESCRIPTION OF P & I D

The cracked LPG from FCC gas concentration stabilizer overhead is received in amine scrubber 24C1 (14000 mm x 19500) having 11 absorption trays Lean amine from Amine Regeneration unit located in Sulphur plant area after regeneration is received in surge drums 024 V7 (900 mm x 3100 mm). The entry of amine into surge drum is controlled by 024 LC 28 to maintain level in the vessel. The drum is maintained under pressure by blanketing with sweet fuel gas as available from fuel gas amine absorption unit The pressure controller 024 PIC 31 is a split range controller with two control valves one on the fuel gas line and one on the flare line. Amine from surge drum is pumped to 024 C1 by pumps 024 P2 A & B on flow control 024 FRC-5. The pump also delivers amine to amine absorber of unit 022 for SR LPG. There is also a minimum from bypass line from discharge to suction of the amine pumps for use when pumped out quantity is less. In 024 C1 amine enters the top of the column and LPG is introduced at the bottom. Counter-current absorption takes place as LPG rises up through the perforated trays provided in the column. Rich amine from column bottom is sent to Amine Regeneration unit under column pressure. The flow of rich amine is controlled to maintain column bottom level by 024 LlC 4. LPG from top of 024 C1 goes to caustic prewash vessel 024 V1 on flow control 024 FRC-1, which is cascaded to FCC gas conc. stabilizer overhead vessel level control. In order to keep good extraction efficiency at low throughputs or to have good control on flow in case flow of LPG is unsteady, part of LPG from extractor can be circulated back to FCC stabilizer overhead vessel, using 024 FRC 27 for overall LPG flow control. LPG to caustic prewash vessel (1600 x 6100) can be distributed into the vessel using one of the three distributors provided. Normally the one at the bottom is used. Caustic in the vessel is changed out whenever caustic strength comes down below specified level. The vessel is provided with an SS wire mesh blanket to minimize caustic mist carryover. LPG after removal of hydrogen sulfide in absorber and prewash vessel goes to extraction column 024 C2 (1400 x 13300) for extraction of mercaptans. The extractor is fitted with 7 trays of perforated tray type. Regenerated caustic from caustic regeneration section enters the top of column on flow control 024 FRC-9. Extraction of mercaptans takes place in the column and extracted LPG from top of column is sent to caustic settler 024 V2 (1400 x 5600). Rich caustic from bottom of extractor goes to caustic regeneration section. The flow of rich caustic is controlled to maintain bottom level by 024 LlC 8. LPG is introduced into the caustic settler through a slotted vertical pipe distributor. The caustic settling down in settler can also be diverted to caustic regeneration - 52 -

section. LPG from top of settler is sent to storage. Back pressure controller 024 PC 11 on run-down line maintains sufficient and constant back pressure in the unit. Injection of ethyl mercaptan to maintain odor level is also done on the run-down line. Mercaptan storage and pumping facility is common for straight run LPG and cracked LPG. The extractor caustic from straight run LPG, visbreaker naphtha and cracked LPG are combined together for caustic regeneration. The combined caustic goes to caustic heater 024 E1 where caustic temperature can be increased by about 10°C or so to favor caustic regeneration reactions. The heating is with steam and to avoid caustic embrittlement it may be necessary to operate with a minimum back pressure on steam-side to ensure lower condensation temperature. Air required for oxidation is introduced into caustic at the outlet of heater. 024 FRC-13, 024 FRC-14, & 025 FRC-15 have been provided on the airline to regulate air flows to suit caustic flows from three merox units. A special spring loaded check valve mounted in the airline ensures proper mixing of air and caustic going to oxidize. Merox catalyst as necessary is injected into caustic going to oxidizer at a point upstream of heater. For preparation of catalyst slurry & injection, catalyst addition pot 024 V6 (450 x 900) and necessary hose connections are provided. Caustic-air mixture enters oxidizer 024 V3 (700 x 7000) at the bottom through a slotted horizontal pipe distributor. The vessel is filled with 1 1/2" carbon rasching rings upto the top cover. The bed of carbon rasching rings packing provides sufficient contact surface necessary for oxidation of mercaptides in caustic. The caustic containing mercaptides, which are oxidized to disulfides, leaves at the top of vessel and goes to disulfide separator. The disulfides in caustic after oxidizer are insoluble in caustic and hence separate out when caustic is given enough settling time. The disulfide separator vessel 024 V4 (1600 x 6500 & 450 x 1800) is provided in line to separate out disulfide oil and to safely vent out unreacted air which will separate in the vessel. This is a horizontal vessel provided with anthracite packing as coalescing medium to separate out disulfide oil. A small cylindrical vessel known as 'skim pot' packed with steel rasching rings in its top portion is mounted on one side of the vessel. The separated air will contain traces of disulfide vapor mercaptans, and traces of hydrocarbon. Because of its composition, a possibility exists for destructive internal combustion. The steel rasching ring packing ensures relatively short residence time for the vapors and also prevents propagation of flame should it ever occur. Besides the steel rings reduce the possibility of ignition occurring due to static discharge. The regenerated caustic enters the skim pot of separator at a point just below the ring packing, through a horizontal slotted pipe distributor. Caustic level is maintained in the skim pot by 024 LIC 25 by controlling the flow rate of incoming caustic to regeneration section which is achieved by controlling either one of extractor caustic streams; coming from SR LPG, Cracked LPG or VB naphtha meroxes. Caustic flows across the vessel through the anthracite packing to effect separation of disulfide from caustic. The anthracite packing in the form of fine powder is held - 53 -

between two support rings which hold wiremesh screens supported on grating bars. For searing of the supporting grids, nylon ropes are used. Disulfide oil which separates out while passing through the anthracite packing floats on top of caustic From time to time as indicated by level disulfide oil shall be pumped out to slop tanks. From the disulfide outlet nozzle there is a line connecting to skim pot vent off any air, which does not separate in the skim pot. While pumping out disulfide oil from vessel. It is advisable to check the level of caustic in skim pot and ensure that the level is sufficiently below the vent line joining from disulfide outlet line. Otherwise there is a chance of draining out caustic alongwith disulfide oil. The Caustic from the bottom of the separator is circulated back to extractor column by caustic circulating pumps 024 P1 A&B. The caustic streams to extractor columns are all under flow control in the respective merox units. As regulating one of the rich caustic streams from extractors controls the caustic level in separator, that particular extractor will be without any bottom level control. Hence the extractor level should be watched carefully and if necessary maintain a slightly higher level to take care of surges in hydrocarbon level which would upset the column bottom level. If the caustic flow to oxidizer tends to fluctuate due to hydrocarbon surges. It is advisable to commission the hydrocarbon recycle stream at the outlet of extractors in order to hold steady flow to extractor and variable flow on to recycle streams. The recycling stream facility is provided in SR LPG and cracked LPG merox extractors. If necessary fresh caustic can be added into the system. The air, etc. from the top of separator is safely disposed off either by venting it at a high point or by diverting into a nearby firebox. The back pressure controller 024 PC 24 on the vent line ensures necessary & constant back pressure in the caustic regeneration section. There is an oxygen analyzer 024 AR 22 placed on the line to monitor continuously the composition of gas and should it fall in the combustible range, This will activate the solenoid valve trip system placed on the air-line to oxidizer. Thus cutting-off air supply to oxidizer. The vent gas can be diluted with fuel gas to reduce oxygen concentration. 024 FI 26 on fuel gas line indicates locally the flow rate of gas which can be adjusted depending on the vent gas composition. This will support combustion in the firebox. The vent gas is lined up to 019 F1 fire box. Two flame arrestors are provided upstream of fire box entry. One of them shall be lined up. If a firebox is not available, the gas can be vented to atmosphere via vent tank 024 V5 (450 x 1800) exhausting the material at a high point. Fuel gas addition is to be stopped in this case. The vent tank is filled with steel rasching rings in its top portion on a suitable support. Any condensate collection in the vessel is drained to sewer automatially by gooseneck drain piping. LIST OF PACKINGS (1) Oxidizer -11/2" carbon Rasching rings (7000 mm height) (2) 24-V-4 Dome

-1" steel Rasching rings - 54 -

24-V-4 Horizontal portion

-4 to 8 mesh anthracite coal

(3) Vent tank NOTE :books. •

-1" steel Rasching rings The packing details should be checked with U.O.P original project

PRECOMMISSIONING OPERATION

Checking completion of construction works, inspection and boxing of equipment. The following preliminary checks should be carried out to ensure a successful startup of the unit. Check that all the mechanical works of construction have been completed as per project book. Check the entire erection of the unit, equipment and lines and compare with the Process and Instrumentation diagrams and any discrepancies should be pointed out and corrected. Scaffolding, debris, tools and other unnecessary construction material should be removed from unit areas. Make a final list of blinds which should be in position or taken out before starting purging operations. Make sure all blinds have been installed at the proper sides of valves and signed off in the list. Check and ensure Fire-fighting and safety equipment is in place and in good working condition. Ensure all utility systems and flare release header is in service and ready for use. Isolate the unit from other plants and tanks at the unit limits with block valves. Keep the fuel gas and flare header isolated from the unit pending purging operations. Isolate or remove orifice blocks of all flow meters for flushing purposes. WATER FLUSHING OF THE UNIT : Water flushing of the unit is meant for thorough cleaning of equipment internals, and entire piping; so that all muck, scale and construction debris are removed completely. Water supply can be taken by temporary hoses from the fire hydrant systems. The unit can be conveniently divided into small sections and the flushing operations are to be carried out. All pumps suction screens should be fitted with fine mesh wires during the flushing operations to protect the pumps' internals. The following precautions are very important during flushing out period.

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Isolate all instruments, disconnect the lead lines and flush thoroughly each lead line. Drop control valves and flush through the inlet, outlet and bypass lines thoroughly. Disconnect pumps' suction flanges; keep tin sheet to prevent water getting in to the pumps; open suction strainer flanges, pull out the strainer and flush each suction line to outside thoroughly. Then only we can make up the pumps suction flanges and run the pumps for further effective flushing. While running the pumps; the fine strainer gets choked quite often; and needs frequent cleaning. These fine strainers can be totally removed only after cleaning frequency comes down to once in 8 to 10 hours. While flushing the entire system, make sure that all low point bleeders are proved clean. PRESSURE TEST OF EQUIPMENT AND LINES The cracked LPG unit contains two sections. The LPG treatment section operates at 15 to 16 kg/cm2 pressure, whereas the Regeneration section operates at 5 kg/cm2. The pressure testing of these two sections should be done independently to check for leak and for rectifying the same. NOTE :-Caustic regeneration being common to SR LPG and VB Naphtha Merox Units in addition to CR LPG Merox Unit, it depends upon which Merox Unit is being commissioned first. Naturally the first unit to be commissioned will be SR LPG; so also all the precommissioning and commissioning activities of caustic. Regeneration Section will have to be done at this time. The procedural details are noted below: PRESSURE TEST OF MEROX TREATMENT SECTION The high-pressure section consists of Amine Absorber, caustic prewash, Merox extractor, caustic settler and the various connected high-pressure lines and pumps. This system will be pressure tested after complete isolation from Regeneration Section with water supply from 19-P-14A/B/C. For this purpose LPG inlet to Amine absorber and its outlet after pressure controller are isolated by block valves. Rich amine and rich caustic outlets from 24-C-1, prewash vessel V1 and 24C-2 must also be blocked off. Initial filling of the Merox treatment section can be done from fire hydrant water with a temporary hose connection. Fill up the entire system and equipment with water and displace air completely. Pressurizing the system can then be done by taking Boiler feed water supply from 19-P-14A/B/C. Slowly raise the system pressure up to 18 to 20 kg/cm2. Check for leaks in the entire high-pressure section and rectify the same. One or two bleeders can be kept slightly open so that Boiler - 56 -

feed water pump will have some positive discharge. The amine surge drum test pressure will be around 1 to 1.5 kg/cm2 only. So this needs pressure testing separately from high-pressure section and can be done independently by initially filling the vessel with water and then pressuring with hydraulic pumping. After pressure test fuel gas backing in to this vessel should be done by separate hose connection. After successful completion of pressure testing, depressurize the section to around 0.2 kg/cm2 water pressure. Now pullout all blinds in the unit as preparatory step for unit startup and keep system isolated by block valves only. Cut in fuel gas or take small quantity of LPG into the system and let it evaporate. Slowly the system water should be totally drained out under fuel gas pressure. PRESSURE TEST OF REGENERATION SECTION This section can be pressure tested with service air up to 5 kg/cm2. The caustic heater, oxidizer, disulfide separator and connecting lines and equipment are subjected to this pressure. With soap solution check for leaks and rectify the same. Then depressurize the regeneration section to atmosphere. In this section there is no need to displace air because later on air will be injected in to this system as per process needs. CHARGING OF CHEMICALS After pressuring up the unit with fuel gas, and total draining of water inlet valve to the scrubber C1 is blocked off. Ensure that DEA inlet and outlet from C1 are also blocked off. Similarly, ensure that caustic charge line to V1 and its exit as well as Merox caustic inlet to extractor C2 are all shut off. Prepare 20°Be caustic solution in the storage tank provided and transfer to disulfide separator 024-V4. With a good level in V4, start circulation pump 024-P1A/B and establish a level in LPG extractor 24-C-2. Then line up the pump P1A/B for circulating caustic to extractor C2, through bottom LIC to the caustic heater 024-E1. Oxidizer 024-V3 and back to disulfide separator 024-V4. Adjust the circulation on FRC control at the stipulated rate. From the 10oBe caustic solution tank in kerosene Merox unit. transfer enough material into prewash vessel V1 to hold sufficient level. Line up lean DEA from sulfur Recovery Unit to Amine surge drum 24-V7. Entry of Amine in to V7 is controlled by 24-LC-28 to maintain a level in the vessel. The drum is maintained under pressure by blanketing with sweet fuel gas available from fuel gas amine absorption unit. The pressure controller 24-PIC-31 is a split range controller with 2 control valves one on fuel gas line and one on the flare line. Establish working level in amine scrubber c1, using 24-P-2A/B and 24-FRC-5. Establish DEA circulation putting into commission the level controller at bottom of the column to control the rich amine solution returning for regeneration in the sulfur recovery unit. ADDITION OF MEROX CATALYST: W. S. - 57 -

While commissioning a fresh unit. there is no need to add catalyst in the beginning. We can add catalyst only when the circulating caustic becomes partly spent after absorption of Mercaptans from the LPG. But we will describe the steps for adding the catalyst here. Calculate the approximate quantity amount of caustic circulating from regeneration to extractor 24-C-2 and back. This will be equal to 16 to 18 KL. The rate of addition of catalyst is approximately a bottle for every 4 M 3 of circulating caustic. Prepare slurry of catalyst in caustic taken in a bucket. Then transfer the slurry to the make-up pot. Mix the slurry thoroughly in the pot by using Air sparger provided. Transfer the solution under air pressure in to the circulating caustic. It is desirable to add the total catalyst in small lots of 1 to 2 bottles at a time to ensure uniform distribution over the entire circulating caustic. Same principle for catalyst addition will be followed whenever part of the caustic is replaced with Fresh caustic to ensure minimum catalyst presence and activity in the caustic. •

START-UP PROCEDURE

After the pre-commissioning activities have been completed the unit will be commissioned as per standard procedure noted below: Charge circulating caustic solution to top of extractor column C2 after establishing a working level in disulphide separator V4 in cracked LPG Merox Unit. When normal level of caustic is obtained in C2. commission the bottom level controller to regulate rich caustic flow back to disulphide separator V4. Charge lean amine in flow control to the amine scrubber C1. Maintain level at the bottom of C1 by commissioning the level controller regulating the rich amine flow to regenerator section in SRU. NORMAL START-UP PROCEDURE At this stage all the chemicals are charged to the unit and the unit ready for taking in hydrocarbon. Line up cracked LPG flow from battery limit to Amine scrubber -> Caustic prewash (bottom two distributors) -> Extractor-> Caustic settler -> Back pressure controller. Commission the controller and set it at 15 kg/cm 2. Open battery limit valve and direct LPG flow to Amine scrubber. Be prepared to draw more DEA from Amine regeneration unit as the Amine scrubber trays are being washed with Amine. Set the Amine flow FRC. - 58 -

Fill the scrubber, prewash and extractor vessels with LPG, As extractor is being filled, caustic solution level in the regeneration section may be made to fill up the circulating caustic inventory. Make sure there is always some caustic level in the extractor. LPG should never be allowed to enter regeneration section. Once the unit is filled with LPG and is at the operating pressure (of to 22 kg/cm2 at the inlet of the unit), check LPG flow rate and verify all the gauge glasses. Commission steam to caustic heater to maintain the inlet temperature to oxidiser at 45° C. Start air injection. Commission back pressure controller 24-PC- 24 and set it at 3.5 kg/cm2. Send waste air to vent tank 24V-5. Commission oxygen analyser. Once oxygen concentration in the vent air is below 12% (by vol), start fuel gas. Set FRQI-26 at a flow rate such that oxygen content after dilution should fall below 5% ( by vol ). Send air/fuel gas mixture to the highest disposal point in to the atmosphere. As disulphide/caustic inter phase appears in the horizontal body of the disulphide separator, open disulphide oil disposal line to 24-P-3. The formation of disulphide oil will be very little and will be discharged to slop oil tank. The pumping is expected to be intermittent. Make sure that some disulphide oil is seen in the sight glass of disulphide separator. Do not pump out caustic also. Check the product after caustic settler for quality. When it is doctor negative, it can be routed to the regular storage bullets, kept ready for the purpose. Commission odorant injection to the rundown LPG after caustic settler at the specified rate. Check the odorant injection facility is ready in all respects beforehand. Then start the Injection pump P-O2 and set the dosage as instructed. Check frequently LPG for H2S after the prewash vessel V1 and replace cautic as necessary. Check the acid oil content of the caustic solution once in a week. If it is more then 8-12% then some caustic from V-1 will have to be replaced. Check the regenerated caustic being charged to the extractor C2. This will give an idea of the efficient operation of disulphide separator . •

SHUTDOWN PROCEDURE :

Inform all concerned of intention to shutdown the unit and proceed as follows : Shut off DEA charge pump to the scrubber C1. Shut off LPG charge pump to C1 immediately after this. Stop odorant injection pump PO 2. Stop caustic circulation through the extractor C2 from the disulphide separator V4. Stop caustic supply to pre-wash vessel V1. - 59 -

Empty out caustic levels from V1 C2 and V2 to spent caustic disposal or to the disulphide separator V4 as instructed. Empty out DEA level in C1 to its regeneration section in SRU. Depressure the vessels and columns slowly to the flare system, after isolation at unit limits. Isolate the vessel and column by blinds and make them gas and chemicals free by steaming and water washing repeatedly, as per special instructions that will be issued at the time of shutdown. Keep an upto date record of the blind list. Entry to the vessels has to be given only after ensuring that they are absolutely free from all gases and chemicals used in the plant. Gas test must be done before entry permit is given. Proper ventilation inside the vessels must be ensured. Personnel entering the vessels must wear proper protective equipment as mentioned in the clearance permits. • I.

EMERGENCIES: POWER FAILURE

In case of general power failure LPG supply to the unit will stop and the unit pumps running will be interrupted. DEA solution circulation also will stop. Block of pressure controller at unit rundown line and hold pressure in the system. Monitor all levels. When power supply and LPG feed are restored, put the unit back into normal operation, following standard procedure. II.

STEAM FAILURE

In case of general steam failure, LPG supply to the unit will be affected and hence unit will have to be shut down and kept under pressure till feed supply is resumed from FCC. III.

COOLING WATER FAILURE

Failure of cooling water will affect the feed supply to the unit as well as the unit pumps. Unit will have to be shutdown and kept standby till water supply is restored. IV.

INSTRUMENT AIR FAILURE

On instrument air failure, all the control valves in the unit will close. If FCC is also affected by air failure. feed to the unit will be interrupted. Close off the pressure - 60 -

controller on LPG rundown line and maintain pressure in the system. Monitor all levels till air supply is resumed to normal. Revert back to normal operation. •

OPERATING VARIABLES

1.

Amine concentration

-25% by wt. in water.

2.

Lean DEA temperature

-As low as possible.

3.

DEA circulation rate

-10 M3/Hr.

4.

LPG feed temperature

-35 to 40°C.

5.

Inlet pressure

-22 kg/cm2.

6.

Caustic prewash

-10°Be (Caustic conc.)

Change out the caustic at 50% spent or H2S break through. 7.

Merox causitic concentration

-18 to 20°Be.

8.

Caustic circulation rate

-4 M3/Hr.

9.

Extractor inlet pressure

-20 kg/cm2.

10.

Oxidizer inlet temperature -45 to 48°C.

Air injection to maintain 1.78 NM3/kg of Mercaptan Sulphur (initially) 45 to 60 seconds, shake test. 8 to 12 vol % of oxygen vent gas. Lean Merox Caustic Caustic concentration -18 to 20° Be. 50 to 100 wt ppm of NaSR If this figure is exceeding dump out around 6 M 3 of 24-V-4 caustic to ETP , take fresh caustic into the system and add Merox Reagent No.2 as required. LPG PREWASH LPG is passed through amine scrubber C1 and caustic prewash vessel V1 to remove all traces of hydrogen sulphide. The DEA solution should be kept at the specified value of 20%wt. The amine circulation rate also should be at the design rate of 10 m3/hr. Caustic concentration for prewsh should be 10°Be when it becomes spent. caustic must be replaced with fresh stock. LPG EXTRACTOR - 61 -

Mercaptan extractor C2 removes these undesirable components from LPG stream by intimate mixing with a caustic solution containing Merox catalyst. The caustic concentration for the circulation should be 20°Be. The catalyst concentration in the caustic should be 100 ppm. Merox solution circulation rate should be 4 to 5 M 3/hr. Operating pressure which is maintained by the pressure controller on the rundown line should be about 18.0 kg/cm2 at the extractor C2. Reducing any of these variables excepting the pressure will affect mercaptan extraction efficiency. Too low an operating pressure favours amine and caustic entrainment in LPG stream. • I.

TROUBLE SHOOTING MERCAPTAN EXTRACTION

Mercaptan Extraction can be adversely affected by one or a combination of the followings : Poor Mercaptan oxidation (This would be identified by a high Mercaptide Concentration in the regenerated Merox Caustic. That is 'shake test" time too long). This is the most frequent cause of poor mercaptan extraction. A dramatic increase in Hydrocarbon Feed and/or regenerated Merox Caustic temperature, for example, 55-60°C versus 45°C. Increase Mercaptan content of the Hydrocarbon Feed, for example, higher mercaptan loading or higher molecular weight mercaptan in the hydrocarbon feed. Accumulation of non-regenerable acidic compounds or salts in the Merox Caustic. The most obvious effect is the consumption of caustic free alkalinity. This problem can be identified by analysing the Merox Caustic solution for % NaOH as a strong base (U P method 209). This value should always be maintained above 10 WT.%. Some of the undesirable compounds are H 2S ( as sodium sulfide). carbon dioxide (as sodium carbonate), and sodium thiosulfate which is oxidised sodium sulfide. Proper feed prewashing is essential in preventing the rapid contamination of Merox Caustic with such compounds.Contamination are purged by replacing a portion of the caustic inventory in the system with fresh caustic. (The concentration should be chosen so as to keep the concentration in the Merox Caustic between 18 and 25° Be).Only plant Operating experience can determine what is the maximum allowable concentration of each contaminant. Upsets in extractor column hydraulics which are reflected as a marked reduction in extractor tray efficiency, This can be caused by partial vaporization of hydrocarbon in the extractor, improperly stalled trays, excessive hydrocarbon or caustic flows to the extractor, etc. Partial hydrocarbon vaporization is the result of increased feed temperature or the inclusion of lighter compounds in the charge stock and/or lowering of extractor operating pressure. An upset in column hydraulics is evidenced by excessive caustic carryover with the extracted hydrocarbon into the caustic settler. II.

MEROX CAUSTIC REGENERATION - 62 -

Improper Merox Caustic Regeneration is caused by one or a combination of the following : Air Injection is insufficient. Insufficient air injection is quickly ascertained by noting the oxygen content of the Vent Gas from the Disulfide Separator. A value of less than 8 Vol. % Oxygen would confirm that insufficient air is being injected. However, this should be confirmed by a "Shake Test" of the lean Merox Caustic or by Laboratory Analysis of the lean caustic for Mercaptide (and Sulfide). Immediately check the Air Injection System to verify that air is flowing to the Regeneration Section at the rate previously established. If there is reduced or no air flow, re-establish proper air flow. However. if air injection is found to be at the previously prescribed rate, then lack of sufficient regeneration air is probably due to : III.

SULFIDE CONTAMINATION

A lead acetate paper check on the prewash hydrocarbon stream will determine if sulfide contamination is happening and determine its relative severity. If the presence of H2S in the extractor feed is confirmed, necessary steps must immediately be taken to re-establish proper hydrocarbon/DEA and prewash operation. Increase air injection in 10% increments. If there has been a sudden decrease in the Vent Gas Oxygen concentration (for example: 8 Vol. % to 4 Vol. %). the cause is likely to be massive sulfide contamination. It may be impossible to inject sufficient air to oxidize all the sulfide on its initial pass through the regeneration system. In this case air injection should be increased to its maximum value. It may be necessary for the sake of expediency to permit the oxygen content to go higher than normal. Maximum air is limited to maximum flow meter and control valve capacity. The disulfide separator pressure control valve should be monitored in this case. Maximum temperature at the oxidizer outlet should be 60°C. The inlet temperature should be 50-60°C or as high as required without allowing the outlet temperature to exceed 60°C. Samples of the rich and lean Merox Caustic should be sent to the Laboratory for Mercaptide and Sulfide Analysis. Since the oxidation of sulfide is an exothermic reaction substantial sulfide contamination is evident if temperature rise greater than 3°C is noted across the oxidizer. It may be necessary to note only increase in oxidizer temperature and pressure, but also begin purging the contaminated Merox Caustic from the system when this is done, be sure to make up with fresh caustic of the correct concentration. Proper amount of catalyst should also be added. Continue taking these appropriate measures until the prewashed Hydrocarbon is free of H2S and the rich Merox Caustic contains less than 3000 WPPM Sodium Thiosulfate Periodic Analysis of rich and lean caustic as well as check on the Vent Gas Oxygen content will indicate when the sulfide has been completely oxidized to thiosulfate and proper Mercaptan Oxidation is re-established. At this time reestablish normal oxidizer temperature and air injection conditions. Slowly add extra merox catalyst to the system over a four hour period. - 63 -

On the other hand, should sulfide contamination be verified but the source quickly eliminated and the rich merox caustic analysis confirm low sulfide contamination. e. g. less than 3000 PPM Na 2S2O3 immediately add some merox catalyst. say 1 litre of WS to the system. The air injection rate may be increased at 10% intervals (to maintain ( 8 -12 Vol. % oxygen in the Vent Gas) and Oxidizer inlet temperature increased so that the regeneration system will recover in five to twenty hours. IV.

INCREASED SYSTEM MERCAPTAN LOAD

If various checks outlined previously indicate the absence of sulfide contamination, insufficient regeneration air is due solely to increased hydrocarbon flow and/or increased system mercaptan concentration resulting in increased feed mercaptan loading. In any event, with increased air injection and temperature, the regeneration system will recover rapidly. Additional catalyst make up may be considered at this time. Merox Caustic flow to the extractor and increased air injection should have been increased proportionately with any increase in Mercaptan loading from increased hydrocarbon feed rate. V.

MEROX Catalyst CONCENTRATION IS INSUFFICIENT

Insufficient Merox Catalyst in the oxidizer and caustic solution is confirmed by the lean Merox Caustic Mercaptan concentration greater then 200 WPPM (or the "Shake Test" time of longer than 90 sec), when the Vent Gas Oxygen content is greater than 19%. This may be further confirmed by noting the physical appearance of the lean caustic. Lack of catalyst will leave the caustic solution pale green or even relatively colorless. If this situation exists, add 1 bottle of Merox WS over an eight hour period. Frequently the problem is not too little catalyst or increased catalyst consumption, but improper addition of merox catalyst. To prevent any loss of catalyst (usually at the disulfide/caustic interface in the disulfide separator). A special effort should be made to always add make up catalyst slowly and to mix it well to obtain a more uniform catalyst distribution. Also never over-oxidize the Merox Caustic (evidenced by blue rather than green lean Merox Caustic). For this decrease the disperisibility of the Merox Catalyst causing catalyst loss. VI.

OXIDIZER TEMPERATURE IS TOO LOW

The normal recommendation for the LPG Merox Unit is to maintain the Oxidizer Inlet temperature at the minimum required in the range of 38-45°C. Above 45°C, over oxidation reactions can actually lead to acid generation causing further caustic neutralization. However this temperature may be increased to 50-60 oC in instances requiring sulfide oxidation. VII.

EMULSIFICATION AND CAUSTIC ENTRTAINMENT

Merox Catalyst Caustic Solution does not increase the tendency of caustic solution to emulsify with Hydrocarbon. It does increase the detergent or foaming properties of caustic. Consequently, dirt and scale in equipment will be dislodged by Merox Caustic. Part of this dirt or scale may consist of iron sulfide. Therefore, equipment - 64 -

which is new or long out of service should be thoroughly flushed and cleaned before being commissioned or it may be necessary to discard the first batch of caustic if it becomes subsequently loaded with iron sulfide scale from improperly conditioned equipment. Also, certain corrosion inhibitors or the acid treatment of the inhibitor, promote emulsion problems The inhibitor is picked up by the Merox Caustic from the LPG being treated. The presence of inhibitor or excessive concentrations of inhibitor can normally be traced to improper inhibitor injection and thus with proper additive control, the problem can be eliminated. VIII.

INADEQUATE DISULFIDE SEPARATION

Poor disulfide separation from the lean Merox caustic in the disulfide separator can be caused by surfactant materials, which keep the disulfide suspended in the caustic. Disulfides in the Merox Caustic can be analyzed by UOP Method 393. The presence of surfactants in the lean Merox Caustic can be determined by a surface tension test comparison between plant and fresh Merox Caustic. Plant and Fresh Merox Caustic are each shaken with equal volume of isooctane. The time required for the hydrocarbon-caustic phase to separate completely is noted in each case. Significant difference in surface tension and settling time is indicative of the presence of surfactant in the caustic. The settling time for the plant Merox Caustic will be significantly longer if surfacants are present. If the Merox Caustic is not sufficiently regenerated when leaving the oxidizer, some further mercaptan to disulfide may occur in the settling compartment of the disulfide separator down stream of the coalescing section. Any disulfide formed there will not have been coalesced into sufficiently large droplets to gravity separate from the caustic and will remain suspended. Comparison of the Mercaptan content of the Caustic sampled at the oxidizer outlet and disulfide separator caustic outlet will indicate the Mercaptan are oxidizing to disulfides in the disulfide separator settling compartment. This is usually caused by insufficient merox catalyst. or mixing. Slowly add extra Merox Catalyst and take steps to keep the Merox Catalyst suspended will eliminate this problem. If insufficient separation is suspected, a Laboratory Coalescing Test can be conducted to check if dislfide separation could be improved. Insufficient separation is likely to be caused : Improper installation of coalescing partition so that anthracite coal has migrated. Improper installation of anthracite coal, or No anthracite coal at all. At the earliest opportunity the vessel should be opened and the situation verified and corrected. Proper disulfide removal from the lean Merox Caustic is imperative - 65 -

if full benefit is to be received from the extraction operation. All of the disulfide cannot be gravity separated from the regenerated caustic. A low re-entry sulfur concentration (less than 10 PPM in the Hydrocarbon) is considered adequate. IX.

INADEQUATE PREWASHING

Aside from the obvious cause associated with the break-through of acidic compounds due to excessive quantities of H 2S or CO2 in the feed or Spent Caustic, the only remaining cause for a problem is inadequate contacting or mixing in the prewash. This is caused by insufficient hydrocarbon flow. Hydrocarbon distribution into the batch caustic is insufficient to assure proper mixing and contact. This situation can only be corrected by plugging some distributor holes. The number of holes to be plugged should be propertionate to the decrease in feed rate.

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7. U-25 CRACKED FCCG MEROX •

UNIT CAPACITY

Cracked Naphtha Merox Unit is designed to Process 300,000 T/Yr.of cracked gasolene and Straight Run gasolene; the LSR component being 60,000 T/Yr. The Unit Shall operate for 345 on stream days in a year. • (i) (ii) (iii) (iv) (v) (vi) •

FEED SPECIFICATIONS Boiling range TBP oc Sp. Gravity at 15.6°C Total Sulphur wt. ppm. Mercaptan Sulphur wt. ppm H2S wt. ppm RVP : Kg/Cm2

C5 -90 0.67 100 max. 850 " 10 " 0.7 "

PRODUCT SPECIFICATIONS

The Merox treated gasolene shall meet the following specifications : (a) Copper strip corrosion (3Hrs.at 50°C) (b) Mercaptan'S' wt. ppm

1 Max ASTM D-130-65 5 Max UOP -163 -62

(c) Oxidation stability minutes

•

390 min. ASTM D -525 -55

TYPE OF CATALYST USED

Caustic dispersible Merox(catalyst WS supplied by Universal Oil Products Company, Illinois USA, is used in the sweetening Reactor 25V2 of this unit. Initial charge of catalyst about 3kg of active ingredient of catalyst. Whenever caustic solution is replaced, catalyst make up is necessary. Normally we use 12M 3 of NaOH of 8% concentration. The catalyst make up is 1 kg. of active ingredient for every 4 KL of caustic. When the circulating caustic becomes more than 50% spent, the entire caustic should be discarded to Effluent Treatment Plant and fresh catalyst should be taken in as detailed above, followed by addition of fresh catalyst to the caustic. •

DETAILED DESCRIPTION OF P&ID

Merox treatment of SRN and FCC gasolene consist of Caustic prewash - 67 -

Liquid-liquid sweetening Caustic settling Passing through sand filter Caustic prewash is provided on for straight Run naphtha, as FCC Gasolene after stripper and Debutaniser contains little or no Hydrogen Sulphide. For sweetening proper a mixer type of Reactor has been provided. Post treatment consists of a caustic settler and sand filter. Anti-oxidant injection facility is also provided. Straight-run naptha stabilisation from distillation unit stabiliser is "charged to the unit by feed pumps 025 P2 A&B. The flow-rate is controlled by 025 FRC-1. and is taken into caustic prewash vessel 025 V1 {100 x 600). There are three inlet nozzles and a stainless steel wire mesh at the top as in other prewash vessels. Caustic is to be changed out as indicated by its strength. FCC gasolene from gas concentration section stabiliser bottom joins straight run naptha at the outlet of caustic prewash vessel and the mixture goes to the merox Reactor. The flow of FCC gasolene into merox is recorded by 025 FR 14. The combined flow of naphtha and gasolene is recorded by 025 FR 4. Caustic with suspended merox Catalyst No.2 is added to combined hydrocarbon under 025 FRC 10 flow control. Air required for oxidation is added to the combined stream plus caustic through a special check valve 025 y 1 which ensures thorough mixing of air and hydrocarbon. Air flow rate is controlled by 025 FRC 5. The reactor 025 V2 (1600 x 6100) is a liquid-Iiquid sweetener effected in a mixer vessel having perforated trays to achieve intimate mixing of hydrocarbon and caustic containing suspended merox catalyst in order to accomplish desired sweetening reactions. Each tray has a total of 62 perforations distributed evenly at four different radial distances. The tray joints are all fixed with neoprene gasket to avoid any leakage at joints which would affect mixing efficiency. The mixture of hydrocarbon, air and caustic containing catalyst rises up the mixer through the perforated plates and exits at the top of vessel and goes to caustic settler vessel 025 V3 (2400 x 9000). The mixture enters the settler through a vertical slotted pipe distributor. The hydrocarbon leaves from the top of settler to sand filter 025 V4 (2200 x 4800). The caustic containing merox catalyst settling down at the bottom of settler is withdrawn through a perforated riser pipe having 50 Nos. 7/8" holes placed circumferentially in a spiral fashion. The riser pipe ensures withdrawal of clear caustic from the settler for circulating back to feed. The settler caustic is pumped by pump 025 P1 A&B and circulated under flow control 025 FRC 10. For addition of catalyst into circulating caustic stream, when necessary catalyst addition may be done through the pot 025V5 (450x900) by pushing the catalyst solution by air pressure. The hydrocarbon enters the top of sand filter through a distributor pipe assembly with holes drilled to a specified pattern. The sand packing is provided in the top half portion of vessel and supported at the level. Hydrocarbon filtering out of the sand bed is picked up from a high enough level to ensure clear hydrocarbon withdrawal. The treated product is sent to storage after maintaining the necessary - 68 -

back pressure in the unit by 025 PIC 12. Injection of UOP No.5 antioxidant with or without copper deactivator is done by dozing pumps (23P-3A/B/C/D) located in unit 023. A slip-stream of run-down product acts as a carrier for inhibitor discharging from the dozing pump. Sand filter is provided with a bypass. Excess unreacted air accumulating on top of sand filter can be vented from the floor level itself by the extended vent line. Facility also exists for back washing the sand-bed, if required. The treated product from the unit is a component of motor gasolene pool. NOTE: LSR gasolene is now not processed in 25 unit. 25V1 is being used as knock out pot for sponge gas from 20-C-2 to 20-C-6. 25-P-2A/B have been removed to other services and gasolene inlet and outlet lines have been blinded. • I.

PRE-COMMISSIONING OPERATIONS CHECKING COMPLETION OF CONSTRUCTION WORK, INSPECTION AND BOXING UP OF EQUIPMENTS.

The following preliminary operations will have to be carried out to ensure a successful start-up of the unit : Check that all mechanical work of construction have been completed. All equipments and pipelines must be inspected and tested hydraulically at stipulated pressure depending on design conditions. They are to be boxed up only after internal inspection for proper fittings and cleanliness. Finally, all unit equipments and lines are to be signed off as complete in all respects in the Production Deptt. check lists made for the purpose. Make a final blind list indicating which should be in position and taken out before starting gas purging operations. Ensure that all blinds have been installed at the proper sides of valves and signed off in the list. Check and ensure the availability of Fire-fighting and safety equipment in the unit area in good working condition. Ensure all utility systems and flare release header is in service and ready for use. Check that free movements inside the unit area are not obstructed by scaffoldings, construction debris, tools etc. Get them cleared away from the unit area. Isolate the unit from other plants and storage tanks at the unit limits with block valves, for carrying out flushing and purging operation. Isolate to remove instrument orifice blocks for flushing purposes. II.

WATER FLUSHING OF THE UNIT

Water flushing of the entire unit has to be done with all pumps running on line so that all muck, scale and construction debris are washed out of all equipments and - 69 -

lines. For this purpose, the unit can be conveniently divided into sections and individual equipment wise water flushing can be done, Temporary fire water hose connections are made on unit equipment or lines at suitable points and thorough flushing is done. Suitably wire mesh strainers are to be installed on pump suction spools during the water flushing operation to protect the pumps from damages. The pumps are to be run at least for 24 hours continuously to ensure their free and smooth functioning. During the water flushing operations, care should be taken to see that pump discharge valves are sufficiently throttled so as not to overload their motors. The suction screens installed will have to be opened up and cleared of all debris collected periodically after stopping the pumps, This type of cleaning the screens will have to be continued till they remain free of any muck continuously at least for 8 hours. On completion of water flushing the unit equipments and lines satisfactorily, we have to pressure test entire system with steam. III.

PRESSURE TEST & PURGE EQUIPMENT AND LINES

In order to check for leaks on equipment and lines after water flushing they are all tested with steam pressure of about 5 kg/cm 2 proceed as follows : Block off caustic circulation pumps Pl A & B with their suction, discharge valves. Open wide all vents and drains in vessels Vl, V2, V3. Isolate sand filter V4 closing off its inlet and outlet valves. The sand fi1ter is to be purged with gas and tested under gas pressure to avoid caking of the sand bed. Hook up steam hoses to the steam out connections of the vessels Vl, V2 and V3 and back up steam into the vessels and lines upto the unit limit block valve. After sufficient steam purging for about 15 minutes from all possible vents and drains. Close these points and pressure up the system to about 5 kg/cm2 with steam. Check up the entire unit for leaks and get them attended. After successful completion of pressure test. continue with steam purging of the unit system till all air from equipment and lines have been removed. The system is ready for taking in hydrocarbon when all air from the system has been displaced by steam. Maintain a positive pressure of steam till fuel gas is taken into the unit and it is pressured up with gas. Fuel gas is slowly taken into the pre-wash vessel V1 and then to mixer V2 and caustic settler V3. The sand filter is also purged with gas first to displace all air and then pressured up to fuel gas system pressure. Catalyst addition pot V5 must be isolated from the gas purging lines. Drain all steam condensate from low points and drains. When gas smell comes out of the vents of the vessels. steam can be completely shut off and system allowed to remain at 0.5 kg/cm2 pressure of fuel gas.

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IV.

CHARGING OF CHEMICALS AND CATALYST

Before actual start-up of the unit, the treatment systems should be made ready to receive LSR gasoline from AVU. Prepare system as below: Pump in 10°Be caustic solution from storage tank in Kero Merox section and establish working level in the prewash vessel V1. Charge 10oBe caustic solution into caustic settler V3 from Kero Merox section till sufficient level is obtained in the settler for circulating caustic through mixer V2. Prepare Merox catalyst slurry in catalyst addition pot V5. taking desired quantity of catalyst in it with caustic and water to make the solution. Keeping the vent of V5 open. Add air through the air connection to the pot for proper mixing of the slurry. Then close the vent and increase the pressure in the pot, to blow the catalyst slurry into the system along with the caustic solution circulated through the mixer V2. Care should be taken not to blow air into the system to avoid explosion. The catalyst is blown into the system alongwith caustic circulating after introducing gasoline feed in the unit. Catalyst addition to the system has to be done in batches depending on the doctor test conducted on the treated gasoline. Make ready the anti-oxidant injection facility in visbreaker Naphtha Merox section for dosage into the treated gasoline stream from the unit, before it is routed out to storage tanks. •

START-UP PROCEDURE

When pre-commissioning operations in the unit have been successfully completed and the entire system is under Fuel gas pressure then Hydrocarbon can be taken directly into the unit. Confirm straight run gasoline from AVU is ready to be supplied for Merox treatment proceed further as follows: Fill up with straight run gasoline the unit vessel, viz., prewash vessel V1, mixer V2, caustic settler V3 and Sand filter V4, one by one which have been kept under fuel gas presssure. Pressure up each vessel to about respective operating pressure. Prepare Merox catalyst slurry in catalyst addition pot V4 and keep it ready for blowing into the circulating caustic solution to the mixer V2. Inform Kerosene Merox section and charge 10 oBe caustic solution from there to the prewash vessel V1 and bring up normal operating caustic level. Transfer caustic solution with the help of circulation pumps P1 A/B to the mixer V2. Commission flow controller to regulate the flow to mixer. Commission injection air system from kero Merox unit and start air injection to the mixer at specified rate on FRC control.

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Commission gasoline charge pumps and commence flow with FRC-on line through the mixer V2 after prewashing stage in V1 Route gasoline to storage passing through settler V3 and sand filter V4, with the pressure in service. Start injecting the required quality of merox catalyst into the caustic stream going to the mixer V2, taking care not to blow air into the system. Bring operating conditions to normal. When cracked gasoline becomes available from GCU, charge it to the mixer V2. Start anti-oxidant injection into the treated gasoline stream at the stipulated rate. The above procedure was applicable when 25V1 was used as prewash vessel. Now 25V1 is being used as the additional Knock Out Pot for the sponge gases from 20C2 to 20C6. LSR naphtha from AVU is not processed in 25 Unit. When the precommisioning operations in the unit have been completed and the unit is under fuel gas pressure, confirm CR gasoline from FCC is ready to be supplied for merox treatment proceed as follows : prepare merox catalyst slurry in the catalyst addition pot 25V5 and keep it ready for blowing into the circulating caustic solution to the mixer 25V2. Charge 10oBe caustic solution into 25V3. When cracked gasoline becomes available from GCU charge to the mixer V2. Transfer caustic solution with the help of 25P1A/B to the mixer 25V2 . commision controller 25FRC10 to regulate flow. Commision air injection system and start air injection to the mixer at specified rate on 25FRC5 control. Start anti-oxidant injection into the treated gasolene stream. •

SHUT DOWN PROCEDURE

Before commencement of the shutdown, stop antioxidant injection to the gasoline stream. Then inform all concerned of intention to shutdown the plant and proceed as follows : Shut off air injection to mixer V2 and block off the valves. Stop cracked gasoline to mixer V2. Close of pressure controller (25PIC-12) on the gasoline rundown line an hold system pressure. . Pump out caustic from settler V3 and mixer V2 to the disulphide separator or to spent caustic disposal system. - 72 -

Displace all gasoline from the vessels to the storage or slop tank with fire water. Finally drain all the water and hydrocarbons from the vessel taking care not to pull any vacuum in them. Isolate vessels with blinds and steam them out thoroughly using the steam out connections provided. Drain all condensate from low points. Maintain upto date record of blind list. Water wash the caustic vessels and sand filter and mixer with fire water repeatedly till they are free of chemicals and clear water flow out from the drains freely. Make sure that individual equipment has been properly isolated by blinds and made gas and chemicals free, as per laid down procedure. Conduct a gas test before allowing entry inside a vessel. Insist on protective equipment being worn by personnel entering in vessels in caustic and other chemicals service. • I.

EMERGENCIES POWER FAILURE

If it is a general power failure, all the pumps in the unit will stop. Feed to the unit will also be interrupted. In this case the plant has to be shutdown. Follow the steps given below: Shut off air injection to mixer V2. Close off the discharge valves of all pumps which have stopped. Shut off pressure controller at unit limits and hold pressure in the system, till power supply is resumed. Start-up the unit, as per standard procedure as soon as power supply is restored. II.

STEAM FAILURE

If feed supply to the unit is interrupted due to general steam failure; unit will have to shutdown and wait for resumption of feed supply from AVU/GCU. If it is a local failure gasoline Merox treating section can continue to run, as long as possible. III.

COOLING WATER FAILURE

The unit will have to be shutdown as pumps cooling water supply will be affected. as well as feed supply from AVU/GCU. IV.

INSTRUMENT AIR FAILURE

Air failure will result in all the unit control valves operating in their fail safe positions. i. e., they will all close. If feed supply is interrupted unit will have to shutdown. Otherwise unit can be operated with the control valves blocked off and - 73 -

maintaining pressure and flows on bypass. Levels in vessels will have to be monitored till air supply is restored. V.

UTILITY AIR FAILURE

If the failure is only for a short duration unit operation can be continued normarly. In the absence of oxidising air injection, the mercaptan conversion efficiency drops off quite rapidly. Hence, the product will have to be slopped as soon as it is doctor positive. Normal operations can be reverted to when air injection is restarted and the product is on grade. •

OPERATING VARIABLES

In the mixer V2, all heavier mercaptans are converted to disulphides. Here, the operating variables are air injection rate, Merox catalyst concentration in caustic solution and circulating caustic strength. Air injection rate should be @ 1.75 NM3/kg of sulphur converted. Too much air will give rise to continuous venting from the sand filter V3 and increases the fire hazard. Merox catalyst concentration should be 100 ppm in the caustic solution Caustic circulated should be 10-20 deg. Be. Operating pressure of the Mixer is about 8.4 Kg/cm2, Hence, the pressure controller will have to be set accordingly to give the desired back pressure in the mixer. •

MODIFICATIONS

1. SR Naphtha from AVU is not treated in 25 unit as 25 unit capacity is being utilised with CR gasoline. To remove light mercaptans which can be removed in prewash, modification was done to route part of CR gasoline to 25V1. 2. Facility to use 25V1 as additional knockout pot for sponge gas from 20C2 to 20C6 gasoline inlet and outlet kept blinded. 3. Name of the Scheme

Scheme for butane blend in MS

Scheme No

MR/PS/300/2002/4

Scheme implemented on

Apr’03

Description of Scheme

Provision of routing of butane rich streams from Depropaniser bottom in PRU to FCCG line at the downstream of backpressure control valve in Merox. Butane stream addition is a very good media to increase octane. This can be added to MS subject to meeting the RVP/VLI limit. Thus octane boost obtained after butane addition would be used to upgrade naphtha to MS.

Reason for modification

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Operating instructions

1. Butane rich stream from 18C1 bottom is blended into U-25 R/D to boost the Octane of MS. This also helps in upgradation of additional Naphtha into MS. The blending is done through a new control valve 25-FIC1109, provided at the downstream of U-25 BPC. 2. Butane blend into MS also poses some hazards like addition of more butane into MS can lead to MS quality failure in RVP & VLI and can also lead to potentially dangerous situation in MS tank. 3. Interlocks provided in butane blend facility are :  25-FIC-1109 would close at 18C1 bottom temp less than 92 Deg C. 

25-FIC-1109 would close when 25-FR-4 ( FCCG flow to Merox ) falls below 10 m3/hr.

4. 25-FIC-1109 would normally remain on ratio control. Ratio would be set between 0.04 -0.07. This means butane flow would be 0.04-0.07 times sum of Reformate and FCCG flow. But this facility is yet to be created. 5. At present , 25-FIC-1109 would remain on Auto and set point has been locked at 6 M3/hr (max). This means at all times when the control valve is on auto, the butane blending can be set at a flow equal to or less than 6 M3/hr. 6.

Please stop butane blend in the event of following :  



No Reformate rundown from CRU No FCCU gasoline rundown (Interlock has been provided on this and blending control valve should automatically shutdown) Upset conditions in PRU

7. Butane in Total MS pool (Reformate+FCCU gasoline+OHCU Naphtha+VBN) should be limited to 3.5-4.0%w

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8. SAFETY & FIRE FIGHTING FACILITIES All the general safety rules and practices applicable to Petroleum Refinery operations are to be followed in Merox Treating Plants also. Additionally some of the safety precautions to be taken in each case are presented below: I.

CHEMICAL HANDLING

Chemicals, Amine & Caustic are used in this unit. Rubber gloves, aprons and face shields are supplied for any job in the chemical area of this unit and they should be used for any job here. Any spillage of chemicals on the body can be washed off with copious amounts of water. A safety shower is provided in Merox Units for any chemical spillage-emergency on the body of any person. All safety equipment should be cleaned with water so that they can be safely re-used later on. CAUSTIC SODA: Caustic solution, commonly called lye, used in Merox units is to be handled carefully with due precautions. Gloves, Goggles and face shields must always be used in the treating area for any job. Painful injury and possible blindness can result out of caustic splash into the eyes. A safty shower is provided in the treating area for washing the body immediately if an accident occur. In case of caustic splash into the eyes, both the eyes must be thoroughly washed with plenty of water and the person should be sent for firstaid. All eye injuries must be referred to proper medical attention after the first aid. Workmen should be made aware of the fact that caustic does not give immediate warning of its presence on the skin by burning or irrit3tion. But its presence on the skin can be recognised by its slippery, soapy feeling. A doctor must be consulted immediately in case of a severe skin burn. In view of the hazards mentioned above, workmen must wear rubber gloves and apron besides goggles and face shields when working in an area exposed to caustic. Caustic is destructive to leather and it is advisable to wear rubber footwear also while handling caustic. when caustic comes into contact with the skin, the area must immediately be washed with plenty of water. Depending upon the severity of exposure, washing with a 2% solution of acetic acid can be followed. Fecilities for immediate washing with water like safety shower must be readily available in the caustic handling area. Pumps, valves and process equipment scheduled for maintenance must be flushed thoroughly with water prior to opening. Maintenance workmen must wear all protective equipment while doing jobs on equipment in caustic service. CATALYST : Merox catalyst has no harmful effect on the skin. However, workman should be advised not to contaminate any part of their bodies with catalyst. Should any contact takes place, the catalyst must be carefully washed off the skin with copious - 76 -

amount of soap and water until the blue colour is no longer seen. Catalyst should not be taken internally nor breathing of its dust permitted. DISULPHIDE Disulphides are high boiling oily organic liquids having sp. gravity from 0.95 to 1.06. They have an obnoxious odour of onions. They may cause skin irritation and hence contact with skin should be avoided. No data is available about their dangerous properties. They should not be consumed. They are insoluble in water, but can be washed of the skin with warm water and a good detergent. Clothes contaminated with disulphides must be removed from the body. Breathing of their vapors is also not allowed. AMMONIA Ammonia gas leaks will be pungent and are easily detected by smell. The cylinder should be immediately shut off. Ammonia gas is highly soluble in water and at low concentration of 0.2 wt %, it does not present any critical safety problems. If there is a spillage of Ammonia solution on the body, it should be washed, off with plenty of fresh water. For storage and handling methanol all the safety precautions as applicable to gasoline should be followed. II.

FIRE FIGHTING FACILIITIES :

Portable Dry powder extinguishers and Foam extinguishers are kept at various locations in the Units and can be used for all small fires.All the Merox Units are provided with two parallel fire water mains one on east and another on west side. The normal pressure in these mains remains at 2kg/cm 2 and in case of fire, this pressure can be boosted upto 10 kg/cm 2. Fire water monitors which are provided on the mains can divert the water jet to any angle we require and can be used for fire fightingDry powder extinguishers, and foam extinguishers of portable type are provided in the unit at different locations for fighting small fires.For fighting bigger fires, fire water is available in the unit which is surrounded by fire water mains. The normal pressure in the mains is about 3 to 4 kg/cm2.

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