BASIC ENGINEERING ( Incl Design Calculations)

Document No: D/D&P/PRO/G/06 rev 1 w.e.f. 16/9/98

GUIDELINES FOR BASIC ENGINEERING (Incl. Design Calculations) Basic engineering includes the following activities: a) b) c) d) e) f) g) h) i)

Study the DOB Prepare the scheme Batch time cycle finalization / Material balance Prepare the PFD Prepare the Conceptual layout Prepare the equipment specifications Prepare the P&ID Prepare the IPDS (Incl. ON-OFF valves), RD/SRV data sheet Prepare the other documents ( Linelist, service list, Drive list, Effluent data, RM / Utility calculation etc) j) Prepare the Operation manual and Logic k) Commissioning of the plant 1.

STUDY THE DOB. Study the DOB. Witness the experiments carried out in the Lab and/or and discuss with R&D / Customer to confirm the understanding. Check for any mismatch between the data in the entire DOB and get it corrected by R&D. Check for any missing information as required for engineering and get it from R&D While preparing appraisal, for costing of Plant / individual equipment / item, LAN data is used.

2.

PREPARE THE SCHEME List out the key equipment. List out the major operations / steps and sub-steps. Allocate these operations to the key equipment.

3.

BATCH TIME CYCLE FINALIZATION / MATERIAL BALANCE -

-

-

Assume batch time cycle for each key equipment. Find batch size considering Plant capacity and Yield ( Overall and per pass) and Batch time cycle. Batch size change from one key eqpt to next should be studied carefully. (Check whether such # size change will be practical, e.g. slurry intermediate splitting from 3 batches to 4 batches.) If necesssary correct / increase the batch size accordingly. Calculate the equipment size for the batch size from the DOB data and select appropriate size from the standard equipment sizes available (Refer equipment specification section for standard sizes). Select the required size in case standard is not available /suitable. Calculate the actual time required for Batch taking into account 10 % margin. ( for human factor, batch to batch performance variation etc.)

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4.

Check whether the assumed and calculated time cycle is matching. If not, repeat the above steps till these match. In case the equipment size is too high, more equipment in parallel can be considered. These calculations should preferably be done in EXCEL to facilitate check of any other alternative. CONTINUOUS PROCESS. In case of a continuous plant a detailed flowsheet with stream nos added is to be used and material balance (Component wise) is to be prepared.

PREPARE THE PFD Prepare the PFD as per the guideline and following information: After the key equipment and their sizes are decided, prepare the PFD. Show all equipment around these key equipment taking into account the following: -

Raw material supply packaging Product physical specs Collection, storage , handling and recycle/ disposal of all streams ( Try to use gravity than pumping/ pressure or vacuum transfer) Solid handling ( Keep slurry / solid handling to the minimum by reslurrying, dissolving in situ after isolation, extraction etc) Vent scrubbers, condensers, high level venting / dilution Required catch pots / seals to avoid mixing / contact with eqpt with different MOC. Intermediate cuts Storages for countercurrent washes Traps for the effluent Weighing / accounting requirements Dump reactor / tanks

5.

CONCEPTUAL LAYOUT Prepare the conceptual layout as per the guideline.

6.

PREPARE THE EQUIPMENT SPECIFICATIONS Process Data Sheets of various equipment to be prepared taking following into account : Flexibility as required for any probable change in the DOB Uniformity in various equipment e.g. Pump model, GCL std reactors /tanks to facilitate common inventory for easy replacement at a later date. System balancing for maximum possible batch size in key equipment Corrosion data as available from the DOB and following literature : Corrosion Resistance Tables, Third Edition, Part A and B, Philip A. Schweitzer. Corrosion guide by Erich Rabald Physical properties data as given in DOB and following literature : a) Lange’s Handbook of Chemistry, Eleventh Edition, John A. Dean. b) Perry’s Chemical Engineers’ Handbook, Perry & Green. c)

Vapor Liquid Equilibrium Data at Normal Pressures, First Edition, E. Hala, I. Wichturle, J. Polak & T. Boublin.

d) Azeotropic Databook , Lee Horsely. e)

The Properties of Gases & Liquids , Fourth Edition, Robert C. Reid, John M. Prausnitz, Bruce E. Poling.

f)

Computer Aided Databook of Vapor Liquid Equilibrium , Hirata Mitsuho, Ohe Shuzo & Naga Hama.

In case data is not available then study/ use the experimental data from Lab. Design of various equipment should be done as per the reference / guideline mentioned below : TYPE OF EQPT

REFERENCE / GUIDELINE

Reactors Columns Centrifuges Filter Vacuum pump / Ejector Exchangers and Other Heat transfer calculations Pumps Tanks Other eqpt

Annexure I Annexure II Annexure III Annexure IV Annexure V Process Heat transfer by D Q KERN Annexure VI Use 80-90% filling max As per literature data

FORMAT No D/D&P/PRO/F/05 D/D&P/PRO/F/04 D/D&P/PRO/F/06 D/D&P/PRO/F/07 D/D&P/PRO/F/08 D/D&P/PRO/F/04

Refer explanatory notes for the format also. 7.

P&ID PREPARATION P&ID should be prepared as per the guideline and after taking into account the following : -

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Legends document should be prepared for each project showing the symbols used in the P&IDs. A legend drawing prepared for BP0095 to be generally followed. MOC of piping etc should be judiciously decided to keep the cost to the minimum and taking into account the corrosion data as available from the DOB and Corrosion Resistance Tables, Third Edition, Part A and B, Philip A. Schweitzer Corrosion guide by Erich Rabald One system should preferably be provided with single MOC, however vapor / vent equalisation lines can have a different spec. Take into account effect of moisture ingress by any means on MOC selected. Piping specs should be selected from the available std specs and used. In case of non-availability of suitable spec, FLUID service list should be issued to PIP for their recommendation on suitable spec to be used. Refer MSDS and properties data to decide the Conductivity strip ( for Static electricity problem) and Flange guard ( For hazardous / hot fluids) requirement. Provide various safety gadgets like Flame arrestor, RD, SRV, TRV, Gas detectors etc (Smoke and heat detectors, Fire alarm system are to be provided but not to be mentioned in the P&ID) Provide adequate piping connections to take care of any probable abnormal operation and recycle / reprocessing of the off spec materials.

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Provide adequate local / panel instruments, sight glasses, and proper type of manual valves at proper location so as to facilitate smooth operations from field / panel. Local instruments should be provided to crosscheck the Panel instruments and to control of operations from the field in exceptional cases. Pressure gauge to be provided on steam in jacket, pressure and return temp of cooling/heating media to assess the performance of heating / cooling operation Adequate isolation valves to be provided for each equipment or a group of equipment to isolate them in case of emergency. Slurry piping should be considered critically for routing specified, valves and instrument or any other items specified in the piping. Provisions for cleaning should also be considered. Adequate drains and vents should be provided to facilitate proper cleaning / draining of the system. Jacketting / tracing requirements should be carefully studied / provided. Action plan in case of jacketting / tracing is not used ( by mistake) should also be thought of and incorporated. U seals (Incl. inverted) should be specified wherever required to avoid mix-ups / backflow. Slopes and non-hold up lines requirement should be critically studied and specified. Check valves / catch pots to be provided to avoid reverse flow. Strainer requirement to be studied to avoid foreign material ingress from MS eqpt to SS / MSGL assemblies OR to trap solids. Venting locations should be properly specified for safety. Blinds should be provided on various nozzles / valves to avoid any leakage to atmosphere of Toxic material. Nitrogen blanketing / Vacuum connections to be provided as required. Line sizing in a batch plant is not so critical due to cushion available in the time cycle from other activities. However, it should be done as per ANNEXURE VIII and the comments given below : All lines (except steam) should preferably be 25 NB size minimum. Transfer lines to be sized as per the timing available in time cycle and 2-3 M/sec (liquid) velocity. Gravity transfer and slurry transfer to be at ~0.6 M/sec velocity. Transfer time should generally be kept below 1 hr. Steam lines to be sized at 10-15 M/sec velocity. Vent equalisation / vent lines can be of 25/ 40 NB size. Steam lines to limpets for temp maintenance to be of 15 NB / 25 NB. Sizing of all other vapor /vacuum lines should be recorded.

8

PREPARE IPDS / RD/SRV DATA SHEET RD/SRV data sheet to be prepared as per the procedure given in. Annexure VII IPDS to be filled in the prescribed formats as per the explanatory notes.

9 .

PREPARE THE OTHER DOCUMENTS ( Linelist, service list, Drive list, . Effluent data, Energy balance, RM / Utility calculation etc) Prepare these documents in prescribed formats as applicable as per explanatory notes. RM calculations should have reference to DOB data. (Preferably to be done in EXCEL to check . the variations in DOB easily) . Following norms to be used for solvent losses calculations :

.

TYPICALSOLVENT > Operation involved General handling Vac distillation Atm distillation Filteration Extraction

Methanol 1 5 5 5 2

Toluene / Xylene 1 5 3 3 2

10

PREPARE OPERATION MANUAL AND LOGIC : To be prepared as per the guideline. Logic requirement should be in line with the Operation manual.

11

COMMISSIONING OF THE PLANT : To be done as per the guideline

12

LIST OF ADDITIONAL IMPORTANT REFERENCES ( Available in Library) a)

Applied Process Design for Chemical & Petrochemical Plants Vol. 1/2/3, Second Edition, Ernest E. Ludwig.

b) Mass Transfer Operations, Second Edition, Robert Treybal. c)

Coulson & Richardson’s Chemical Engineering Vol. 6 ( Design ) , Second Edition, R. K. Sinnott.

d) Encyclopedia of Chemical Technology, Fourth Edition, Kirk Othmer. e)

Ullmann’s Encyclopedia of Industrial Chemistry, Fifth Edition. ****************

ANNEXURE I (Prepared by KSS)

REACTOR MS & SS reactors MS/GL reactors MS/LB, MS/LB/TL, MS/FRVE/TL, MS/CTL reactors MS & SS reactors a) Capacity

For calculation click

Capacity chart

Based on the batch size & reaction mass volume the capacity of the reactor is decided. The R.M volume is available from R & D in the DOB. The # size is decided based on the capacity of the plant. For a given # size the volume of R.M, lit. = Max R.M volume (lit/km) x # size (km). From this volume of the reaction mass the suitable reactor is selected from the GCL standard. Standard reactor in GCL 4400 lit. 5750 lit. 9400 lit. 15700 lit. 19000 lit. 25000 lit.

Nominal capacity

After selecting a particular reactor the % filling is checked. % Filling =

Vol. R.M *100 --------------------Nominal cap. of reactor

The % filling chosen is 80 % to start with but it can be as high as 90 % based on the GCL standard reactor. For reaction involving gas sparging the % filling should be more 75-80 % for gas space. For washing / extraction it can be as high as 95 % even in some cases. b) MOC selection MOC is selected based on the information given in the DOB. If the information is ambiguous the actual corrosion study should be done by corrosion lab (Activities to be co-ordinated by R & D ) & actual corrosion data to be furnished. The reaction mixture contains so many components in it that the reference can not be taken from books also in most of the cases. So corrosion study is must. If the process is to be fitted in the existing plant which is having some equipment then the corrosion study should be done for the MOC of the said equipment to certify its suitability.

c) Agitator design The design of the agitation system involves: Selection of type of agitator Deciding sweep Deciding RPM Calculation of fluid power Calculation of motor HP / Motor selection Sizing / Selection of gear box Selection of pulleys & belt

Selection of type of agitator The type of agitator is decided based on the type of application. Various types of agitator & their combinations are used. Paddle: 2 bladed paddles are used mainly for blending operations. The sweep is normally 60-80 %. Paddle may be used with or without baffles. If baffles are provided it will give good intense agitation & vortex formation will be minimized. Either 2 or 4 baffles are used. Paddles may be straight or pitched (45° pitched). Pitched paddles are used for solid suspension. Gate anchor: It may be single or double gate anchor. When the height of the vessel is less single gate anchor is used. If height is more staggered double gate anchor is used. Gate anchors are used mainly for crystallization / Distillation operation. Sweep of these agitators is 80-90 %. These agitators provide very good scraping action on the wall thereby preventing the deposition of solid on the wall (Preventing caking). This results in good heat transfer which is the main criteria for crystallization / Distillation. Baffles are not used because baffle will help in solid deposition on the wall of the vessel. This type of agitator operate at low RPM of the order of 20-40 depending upon the size of the vessel. 3 bladed curved paddle: These are used in chemical reaction, distillation etc. This type of agitator is available on glasslined vessels operating at very high speed of the order of 96 RPM. It provides very intense agitation. The sweep is 55-60 %. Turbine: There are 2 types of turbine agitator: Open turbine and Disc turbine. In open turbines 6 / 4 bladed the blades are connected to the hub directly. In disc turbine the blades are connected to disc which in turn is connected to the hub. As per the mounting of the blades the turbines can be flat blade or pitched blade. In pitched turbine the blades are at an angle of 45°. Due to this angle the flow pattern becomes axial in pitched turbine whereas it is radial in flat blade turbines. The sweep is 33-43 %. These operate at very high speed. Agitation is very vigorous. Normally baffles are used with turbines ( 2 or 4 baffles). Pitched turbines are used for solid suspension. Disc turbines are used for 2-phase reaction, gas-liquid reaction.

Multiple agitator: In this various kind of agitation is possible depending upon the method of installation. In the reactors used in GCL following combination can be achieved by proper fixing of impellers.  60 % & 70 % paddle, no baffle.  60 % & 70 % paddle, 2 baffles or 4 baffles.  80 % staggered double gate anchor, no baffles.  40 % disc turbine, 4 baffles.  70 % paddle + single gate anchor, 2 baffles. Examples of Some of the Typical Agitators used are:  

  



6 bladed flat blade disc turbine is used in GCL for IP condensation. The DMA gas is sparged in p-cumidine. 4 baffles are used. 6 bladed flat blade disc turbine is used for Cypermethrin condensation, Temephos condensation, Napropamide condensation reaction in GCL. These reactions are between aqueous & organic phase with the help of phase transfer catalyst. Very intense agitation is required which disc turbine is quite capable of providing. 80 % staggered double gate anchor is used for 2 CB crystallization in CMAC process, IP crystallization etc. Paddles are used for distillation operation. Combination of flat blade disc & pitched turbine is used in hydrogenation of vegetable oil. This reaction is done using raney nickel catalyst. Hydrogen gas is sparged into the vegetable oil. The flat blade disc turbine is used for effective dispersion of hydrogen in oil. The pitched turbine is used for suspending the raney nickel catalyst solid. The bottom pitched turbine is upward flow type & top one is of downward flow type. The reaction is 3 phase reaction involving gas-liquid-solid. In some of the applications the particular use is playing significant role in the very selection of the agitator. For example in 2 CB preparation in CMAC process previously multiple agitator was sued where disc turbine was extended with blades to make paddle. These blades were connected with verticals to make gate anchor. In the reaction some tarry material was generated. Before starting next batch the vessel needs to be washed very thoroughly. The tar used to stick on the disc turbine & washing became real problem. For this reason the idea of multipurpose agitator was dropped for this particular application. Standard double gate anchor was made & installed. So in this case the very process is playing very significant role in governing the agitator type.

Terminology’s used in agitation Sweep: It is the ratio of outside diameter of impeller to the inside diameter of the vessel expressed as the percentage. If the vessel dia is 1500 mm and impeller dia is 600 mm the sweep is 40 %. RPM: It is the revolution per minute the shaft makes. Power per unit volume: It is the power input to the liquid per unit volume of the liquid.

Power number: It is a constant & characteristic of a given type of impeller. The power number chart is given in the calculation program. P X gc X 75  = --------------------------------------, where  X 1000 X (N/60)3 X D5 F = Power number P = Input fluid power, HP gc = Acceleration due to gravity, 9.8 m/sec²  = Density of liquid, gm/cc N = RPM D = Sweep of the impeller, m Having known the power number for particular agitator the power required can be calculated. L/D ratio: It is the ratio of the liquid height to the dia of the vessel. Deciding sweep The sweep is decided by the agitator type. Deciding RPM It is decided using various scale up scale down criteria, type of application. Some of the scale up criteria are: 

Constancy of power per unit volume. This is the criteria very useful & used in more than 90 % of the cases. If we know the type of agitator in one vessel & its RPM the RPM of other geometrically similar vessel can be determined. P --V 1

=

P --V 2

From power number formula P X gc X 75  = ------------------------------------- X 1000 X (N/60)3 X D5 .

. . P  N3 D5 . . . N13D15 --------V1 

N23 D25 = ---------V2 1/3 N13 D15 V1 N2 = --------------V1D25



Constancy of tip speed. This is used mainly for reaction. To start with some value of tip speed is taken such as 800900 ft/min. for reaction involving gas sparging in liquid. Based on this the RPM is calculated. From this RPM scale down is done to lab scale. Experiments are conducted in lab varying some parameters. The best results obtained in lab are again scaled up to plant scale. V

=

V r 

= = =

 . . . V

rwhere

Tip speed in ft/min. Sweep/2 Angular speed 2 = ---- = 2 T =

2rN = DN,

D = Sweep N = RPM

V1 = V2 . . . D1N1 = D2N2 D1  N2 = ---- X N1 D2 

Constancy of Reynolds number This criteria is used mainly for heat transfer purpose such as in applications like crystallization, distillation etc. The overall heat transfer coefficient consists of inside & outside h.t.c. The outside h.t.c is constant depending on the flow rate of utility fluid in the jacket / limpet of the vessel. The inside h.t.c is directly proportional to some power of Reynolds number. D2 N  Re = --------- , where  Re = Reynolds number D = Sweep, cm N = RPS ( revolutions per second )  = Density, gm/cc  = Viscosity, poise. Re1 = Re2 . . . D12 N1  D22 N2  ------------ = ----------- D12 N11 2 . . N2 = -------------D22 2  .

RPM

Calculation of Fluid Power

For calculation click---- Agitator calculation

Having calculated the required RPM based on the appropriate scale up criteria power can be calculated. Pgc X 75  = ---------------------------- X 1000 X ( N/60)3 D5 . . . P = P = = = N = D =

f X r X 1000 X (N/160)3 X D5 --------------------------------------- HP , where 75 X 9.81

Fluid power, HP Power number Density, gm/cc RPM Sweep of impeller, m

Calculation of motor HP / motor selection To the fluid power calculated various losses added such as frictional loss in bottom guide, shaft transmission losses, gear box loss, belt friction loss etc. The calculation is shown in the calculation program. After calculating the motor HP suitable motor is selected for the required duty. The HPs of the standard motor’s are: 0.5, 1.0, 1.5, 2, 3, 5, 7.5, 10, 12.5, 15, 20, 25, 30, 40,50, 60 etc. The nearest higher size motor should be selected. For example if the motor HP comes to 13.5 by calculation select 15 HP motor. The RPM of the motors used for agitators is normally 1440. If 2900 RPM motor is used lot of reduction will be required to attain the required RPM. Some times where there is a chance of agitator jamming deliberately higher size motor is selected than calculated to overcome the initial torque. Sizing / selection of gear box Having selected the motor, gear box is selected by referring to the gear catalogue. Two criteria should be satisfied by the gear selected. 1. 2.

The actual output torque is lesser than the allowable input torque to gear. The actual input HP is lesser than the allowable input HP to gear.

HP X 63000 Torque = ---------------- or (lb-inch) RPM

KW X 9550 Torque = --------------(Nm) RPM

For turbine agitators power is more but RPM is also more so the output torque may not be that high. For anchor agitators where RPM is very low, the output torque becomes very high. The gear in such cases may be suitable from HP point of view but may not be o.k from torque carrying capacity point of view. So such gears should not be selected. The reduction ratio of gear should be selected such that the ratio of pulleys sizes required is 1.7 lot of slippage will occur. Depending upon the HP of motor, its shaft dia is fixed & for that shaft dia some minimum size of pulley will fix and not less than that. So this should be borne in mind while selecting the pulleys. The calculation program shows power calculation, motor, gear, pulleys design / selection.

MS/GL reactors

For calculation & chart click----

Glass lined vessels

For corrosive applications glass lined reactors are used. The design is totally by supplier. For various capacities the details of GMM glass lined reactors are shown in the chart. The reaction mass volume for the given # size is calculated as per the procedure mentioned for MS-SS reactors. In conventional GMM glass lined vessels three bladed curved paddle is typical impeller used but now various other types of agitators are also available such as turbine, anchor etc. Some of the typical uses of MS/GL reactors in GCL are: Chlorination, Bromination, Acidification to low pH of the order of 27 use  =27  = Liquid viscosity in CP Values of ‘A’ and ‘B’ depends on size of packing and are as under Values of A’ and ‘B’ are in mm . Packing size #15 #25 #40

A 272 351 412

B 296 383 452

Norton’s standard designs use operating HETP = 13 % above system base HETP Rule of thumbs : For ceramic intalox saddles HETP =24*Diameter of packing

Appendix 2

Calculation of capacity & pressure drop in column . Column

C 3401

Function Cut

Toluene

Toluene

Packing

IMTP 15

IMTP 15

Vapour rate: V

Kg/hr

Reflux ratio: R Liquid rate L= (R/R+1)*V

Kg/hr M3/M2/HR

Liquid density: l Molecular weight: M Surface tension S

Kg/M3 Dynes/cm

1400.000

750.000

0.500

0.500

466.667

250.000

5.401

2.893

870.000

870.000

92.000

92.000

21.00

21

Pressure: P

MM Hg

760.000

200.000

Temperature:T

Deg C

50.000

50.000

Vapour density: g= (M*P*273)/ (760*(t+273)*22.4) Liquid. viscosity:  Column Diameter :D

Kg/M3

3.471

0.914

Cp

0.450

0.450

14.000

14.000

Area: A

Inch M2

0.099

0.099

Superficial velocity: U

M/Sec

1.128

2.296

Capacity factor Cs

M/Sec

0.071

0.074

0.021

0.011

CS

0.517

0.517

M/Sec

0.115

0.120

M/Sec

0.105

0.110

%

67.875

67.829

Y

2.620

2.849

MM H2O/M

55.000

55.000

Inch H2O/ft

0.660

0.660

MM Hg/ft

1.233

1.233

Parameter X Kinematic viscosity:  =/l Capacity Co: From graph given in Noton catalouge Efficient. capacity Csc=Co*(S/20)^0.16*(/0.2)^-0.11 Capacity Rating: (Cs*100)/Csc Ordinate value (from graph ) Pressure drop:from graph given in Norton catalouge

APPENDIX 3 LIQUID DISTRIBUTORS: The design is based on article by F MOORE & F RUKOVENA presented in 36 th Canadian conferance of chemical engineers . This article describes design of liquid & gas distributors based on concept of distribution quality `DQ'. DQ is a measure of uniformity of liquid flow at the top of the bed. Each distribution point is representated by a point circle, whose centre is located where liquid strikes the top of bed. Sum of area of point circles is equal to Cross Sectional area of column. DQ = 0.4 (100-A) + 0.6B - [0.33 * (C-7.5)] where

A = Cross sectional tower area not covered by point circles in %. B = Least point circle area in 1/12th of tower area x 100 tower area / 12 OR

tower area / 12 most point circle area in 1/12th tower area

x 100

whichever is less C = area of overlap of point circles x 100 tower area An optimum distributor evaluated by this method will have all tower area on top covered by point circles. It is geometric fact this is not possible & there will be overlap between point circles and/or point circle overlap outside the tower area. It is also geometric fact, with this method of evaluation, tower area not covered by point circle (A) is equal to point circle area which overlaps tower wall plus overlapping area of adjacent point circles. Both ‘A’ and ‘C’ values are a measure of uniformity of liquid distributed over the cross sectional tower area at the top of bed .Factor `B' is a measure of deviation of liquid flow from average flow in any relative small area of tower. A 1/12 tower area seems to be an appropriately small area to determine maximum deviation whether flow in that area is high or low. This is most difficult value to determine and requires examination at several locations in tower cross section.Points to be kept in mind while selecting 1/12 th of area are a) 1/12 th of area should be a continous section. b) Section can be rectangular or formed from arc of circle at any location across cross-section of distributor. It is generally found that if liquid hydraulic design will ensure that random flow variation across tower cross section does not exceed 10 % ,each point circle can be assumed to be equal area to simplify distribution quality evaluation procedure. Norton defines three categories of liquid distributors : High performance distributors : DQ > 90%. Intermediate performance distributors : DQ = 75 -90 % Standard : DQ = 30 -65 %

Procedure 1)

Assume no. of orifices such that there are minimum 65 points per m 2 of column Xn Each orifice corresponds to a point circle. Area of each point circle = Cross sectional area of column no. of points

2)

Assume pitch and fix liquid orifices on a triangular pitch. It has been seen that DQ for orifices on circular pitch is always less than DQ for orifices on triangular pitch .As a first trial ,pitch can taken = diameter of point circle . Draw point circles with orifice as center . Ensure that distance orifice from column wall = min 25 mm for column of diameter > 16 “ .

3)

Draw point circles starting with either distribution point at centre of column distribution point.

4)

Calculate A,B & C . Calculate ‘B’ at several locations across Xn of tower. Calculate DQ.

5)

Repeat with various values of pitch and location of distribution point and find out alternative which gives highest value of DQ. Locate gas risers such that a) X nal area of gas riser is not less than 15 % of tower X nal area . b) Gas riser area inside 5 0 % of tower cross sectional area is 40 to 60 % of tower area c) Distance between gas riser & orifice is minimum 20 mm.

6)

or non central

Table I gives value of DQ of some of GCL columns. Other points to be noted are : a)

Distributor or redistributor must be close to the bed. If there is considerable spacing between distributor & top of bed, the flow stream position on top of packed bed becomes uncontrolled and reduces distribution quality.

b)

Bed limiter must not alter flow pattern from distributor.

Distribution quality VS tower performance Sensitivity of tower performance to liquid distribution quality depends only on number of stages each bed of packing could achieve at its system base HETP . Beds of packing designed for many stages will be more sensitive to distribution quality .This is indicated infig 1 . It has been found that in 1 meter diameter debutanizer number of stages increased from 8 to 15 when distributor with DQ of 36 % was changed to distributor with DQ of 93 %. In 380mm dia. iso octane/toluene system no. of stages increased from 7 to 8.5 when distributor with DQ of 55% was changed to distributor with DQ of 85%. Conclusion : The importance of liq. distributor increases as number of stages per section of column increases . Liquid & gas flow , packing size and type does not affect the performance of distributor.

TABLE - I DETAILS OF LIQUID DISTRIBUTORS

Diam eter

No. of orifice

14” 18” 22” 28”

3+3+6=12 3+3+6=12 1+6+12=17 1+6+12+12 = 31

DQ Pitch Dia. % (MM) of

No. of Ratio of PCD of gas riser Risers X’nal

No. of Dist. Point per M²

76 72 87 79

6 6 1+6 1+6+6

125.0 73.5 80.0 78.0

Riser (NB)

100 130 126 140

65.0 80.0 90.0 90.0

area of riser to column 20.0 18.6 18.0 20.0

(MM)

242 303 0;396 0;380;576

Riser area in side : Outside of 50% Col. area. 68 : 32 62 : 38 61 : 39 55 : 45

ANNEXURE III (Prepared by KSS)

CENTRIFUGE A centrifuge is an equipment utilizing centrifugal force for separation of liquid from solids. It is essentially a development of Gravity Filter wherein the force acting on the liquid, instead of being restricted to gravity, is enormously increased by utilizing centrifugal force. Due to good performance and high cost, centrifuges are often referred to as the Rolls – Royces of solid – liquid separation. G- level :- Centrifugal acceleration (G) is measured in multiples of earth gravity: G ------ = g

rb ------g

Where, G n) rb g n

:  : : :

Centrifugal acceleration , m/s2 Angular velocity Basket radius, m Acceleration due to gravity, 9.81 m/s2 Revolutions per second, s-1

G- force vs. Throughput :- As stated above Centrifugal acceleration is, G = rb The throughput capacity (Q) of a machine, depending on the process need , is roughly proportional to the nth power of basket radius: Q = C1 (rb)n Where n is normally between 2 to 3 , depending on the characteristics of slurry to be centrifuged and specifications of centrifuged cake, viz., purity, LOD, absorbent value. It follows that large centrifuges can deliver high flow rates but separation is @ lower G- force; vice versa, smaller centrifuges can deliver lower flow rate but separation is @ higher G – force. Centrifuges are classified according to the mechanism used for solids separation: Sedimentation Centrifuges and Filtration Centrifuges 1. Sedimentation Centrifuges :- In these centrifuges the separation is dependent on a difference in density between the solid and liquid phases (solid heavier). Decanter centrifuge (S-1002; Model No.: S-3400, Make: Pennwalt India Ltd.) used at GCL, Panoli is a type of Sedimentation centrifuge. S-1002 is the only Decanter Centrifuge in GCL. Decanter Centrifuge:- They are generally applicable to particle size range 1 – 5,000 m. A decanter centrifuge is basically a settling tank of circular form mounted on an axis (horizontal) and spun at high speed to produce separation of solids in decanter bowl. A screw type conveyor carried internally and rotated relative to the bowl provides continuous discharge. The speed with which the cake transports is controlled by differential speed (between bowl and conveyor). High differential speed facilitates high solid throughput where the cake thickness is kept minimum so as not to impair filtrate quality due to entrainment of solids. Also cake de - watering is improved due to reduction in drainage path with smaller

cake height; however, this is offset by fact that the higher differential speed also reduces cake residence time. Therefore, an optimum differential speed is required to balance filtrate clarity and cake dryness.

2.

Filtration Centrifuges :- They separate the phases (solid – liquid) by filtration. Such filters essentially consist of a rotating perforated basket equipped with a filter medium. Similar to other filters, filtration centrifuges do not require a density difference between the solids and the suspending liquid. If such density difference exists sedimentation takes place in the liquid head above the cake. This may lead to particle size stratification in the cake, with coarser particles being closure to the filter medium and acting as precoat for the fines to follow. The capacity of filtration centrifuges is very much dependent on the solids concentration in the feed. As a general rule, sedimentation centrifuges are used when it is required to produce a clarified filtrate whereas filtration centrifuges are used to produce a pure dry solid. It is convenient to classify the filtration centrifuges into two broad classes, depending on how solids are removed : fixed bed and moving bed In the fixed - bed type, the cake of solids remains on the walls of the perforated basket equipped with filter medium until removed manually, or automatically by means of a knife arrangement. They are essentially cyclic in operation. Top Discharge & Bottom Discharge Basket Centrifuges and Peeler Centrifuges are fixed – bed centrifuges. In the moving – bed type, the mass of solids is moved along the basket by a ram. Washing and drying zones can be incorporated in the moving - bed type. It is essentially continuous in operation. Pusher Centrifuge is moving – bed centrifuge. Basket Centrifuges ( Top & Bottom Discharge):They are applicable to particle size range 10 – 8,000 m. The basket housing is supported by a three – point suspension called the three – column centrifuge. Suspension of machine on three columns provides extensive compensation of any imbalances of the system, thus dispensing with concrete or damper foundations. The simplest of the fixed – bed centrifuges is the perforated basket centrifuge which has a vertical axis. They are equipped to handle feeding, washing and discharge requirements in a discontinuous filtration process with minimum attrition of the solids. The suspension to be separated enters the machine via a stationary feed pipe. When the basket is filled, the feed valve is closed by automatic control. The subsequent treatment consists of drainage of mother liquor, washing of solids, drainage of the wash liquid, and discharge of the cake. In the case of bottom discharge, a knife removes the cake towards the open centre, leaving a thin residual layer of cake in the basket. In the top discharge machine, the solids are removed manually ( can be removed pneumatically, mechanically, or by withdrawal of the entire filter bag). After removal of the cake, the centrifuge is ready for another charge. Programming the sequence of events can be accomplished by a fully automatic control unit.

These types of centrifuges are in use in GCL. Peeler Centrifuges :- They are applicable to particle size range 10 – 8,000 m. The vertical axis of the basket centrifuge may cause some non-uniformity due to the effects of gravity, with the accompanying problems when cake washing is used. This can be eliminated by making the axis horizontal. This is known as Peeler Centrifuge. A peeler centrifuge is designed to deal with a wide range of suspensions discontinuously in lots. Each lot is subdivided into the necessary operations – Feeding, Spinning-I to drain off mother liquor, Washing, Spinning-II to drain off wash liquid, Scraping the cake. This adjustable lot cycle is mostly controlled automatically. The various operations within a lot can be performed at constant or varying speed of the centrifuge drum. The principal application is for high output duties with non-fragile crystalline materials giving reasonable drainage rates which requires good washing and de-watering. The suspension to be separated is fed to the centrifuge through a feed pipe. In the filtration process the liquid filters through a filter cloth under the effect of centrifugal force. Filtrate is drained through the perforated basket into the filtrate tank. The solid material is retained in the basket by filter cloth and forms a uniform layer. The wash liquid is sprayed on the solid layer through a wash pipe to wash it. The resulting wash liquor leaves the centrifuge in the same manner as the main filtrate and is stored in wash liquor tank. The solids are centrifuged until the desired residual moisture / organic liquid content is reached, and scraped out by a hydraulically operated scraper knife down to a residual layer – which remains on filter cloth. The solid material is discharged by means of a chute or screw. The scraper knife can not be allowed to contact filter medium, a residual layer of solids / products remains in the basket after each unloading. This serves as a precoat to prevent loss of fines to the filtrate through the filter medium during next cycle. The disadvantage is that it also adds resistance to filtration similar to filter medium. The residual layer may become glazed and impervious from the rubbing action of the knife and a rinse may be frequently required to restore the permeability. Disadvantages & Advantages :- (Based on experience in Polymer project @ GCL, Panoli). Centrifuge used: 1250 MM dia (Make: ANUP) Filtering area: 2.46 M² 1. 2. 3. 4. 5.

6.

Peeler centrifuge has parts rotating at high speeds and require high engineering standards of manufacture, high maintenance cost, and special foundations or suspensions to absorb vibrations. It is a very sophisticated and critical equipment. Overflow of basket due to malfunctioning of feed-controller can cause loss of solids to the filtrate as well problems associated with processing of filtrate. It can be operated even @ 200°C of process temperature using suitable lubricating oil. (It is already established in case of salt filtration from PES Polymer solution @ 200 °C) Cake gets washed thoroughly even with 0.5 Cake Volume wash liquid). Here the cake mentioned is final product (DCDPS plant). Throughput obtained is 5-7 TPD wet cake with 5-7 % w/w LOD (with 45 – 30 minutes lot cycle & approx. 150 kg lot and 24 hrs operation basis)[DCDPS plant ]. Whereas throughput in case of centrifugation of PES slurry in water containing 4-5 % Sulfolane is 11 TPD wet cake with 45 % LOD (with 20 minutes lot cycle & approx.150 Kg lot and 24 hrs operation basis) [PES plant ]. In other words, throughputs obtainable per unit filtering area for equivalent products are always greater in centrifuges than in conventional filters. Filter cloth fixing / replacement is easier as well as less time consuming. Filter cloth can be replaced in two hours.

Following are the details of the Make : Model : MOC : NO. OFF : Basket I.D. Basket Height Basket rpm (max.) G – level (max.) Filtering Area Nominal volume Direction of rotation Motor Cost

: : : : : : : : :

Peeler Centrifuges being used in GCL: ANUP ENGG. LTD., AHMEDABAD HZ – 125 SS – 304 8 NOS. [5 NOS. at Panoli , 2NOS. at Lote & 1 NO. at Dombivli] 1250 MM 625 MM 1200 1000 g 2.46 M² 320 litres Clockwise (looking from front side) 100 H.P. (1440 rpm; flameproof) Rs. 40.0 lacs (including motor & inverter) (12/02/96)

Pusher Centrifuges :- They are applicable to particle size range 100 – 10,000 m. Pusher centrifuges utilize continuous filtration for separation of suspended, fast – draining crystalline and granular solids from liquids. A pusher ring plate intermittently moves the cake over the screen or filter area in axial direction up to the edge, over which it is discharged. No cloth can withstand the abrasion due to the cake forced on the cloth and pushed over its surface. So the particle size range they are applicable to is generally coarser (larger than 100m). The material is handled more gently. The pusher plate is usually powered hydraulically. The pusher frequencies are around 60 – 100 per minute. Pusher centrifuges require high feed concentrations to enable formation of a sufficiently rigid cake to transmit the thrust of piston. The capacities of biggest centrifuges are 60 - 80 TPH. They are used mainly in the Potash and salt industries and for other fertilizers.

ANNEXURE IV (Prepared by KSS)

FILTER Types of filters Filer cloth & filter aid Calculation of filtration time Types of filters Open nutche Agitated closed nutche (Rosenmund) Spiral Candle Sparkler Plate & frame Cartridge (For polishing filtration) Rotary vacuum drum Pressure leaf Bag Horizontal belt

Used in GCL

Open nutche In this filter the filtration is by vacuum. The slurry is dumped in the nutche. Vacuum is applied & filtration done. Cake is washed by putting the wash liquid above the cake. For effective washing of the cake the wash liquid is distributed over the entire surface of the cake. For removal of the cake person has to go inside the filter & remove the cake by showel. The design is very simple. This type of filter comes in MS, SS, PP etc. Moc. The washing of cake is problematic as well as discharge of the cake. Also being open this filter can not be used for foul smelling chemicals. Agitated closed nutche As the name suggests this is also nutche filter but agitation is possible. This filter has got lot many other advantages over conventional nutche filters. Because of its closed design it can be used for nasty smelling chemicals. The contamination with foreign particles is avoided. Pressure can be applied in addition vacuum & hence higher pressure differential is possible for filtration. Because of agitation the cake can be reslurried in wash liquid & hence the washing is very effective compared to conventional open nutche. The discharge of the filtered cake is possible by rotating the agitator in reverse direction. In one direction the agitator is pressing the cake & in another direction it is discharging the cake. The final cake can be fed directly to dryer for drying or it can be reslurried & transferred to another vessel for further processing. The very popular MOC is SS. Spiral This is pressure filter. There is a shaft around which the rod is wound in the form of spiral. Over this spiral filter cloth is wound. The slurry is fed from the side entry of the filter. The filtrate comes out from the bottom outlet & cake is deposited inside the filter around the spiral. After the pressure drop across filter increases the filter is to be opened, the cake discharged & fitted back

again for next filtration. Spiral filters are used where cake volume is small. It comes in MS, SS, Hast C MOC. Candle Candle filter is small in nature. This is used after spiral filter & before cartridge filter. The slurry is fed by pressure. Major filtration is done by spiral filter & only small load comes to this filter. As the pressure drop across it increases it indicates that the filter cloth has clogged, filter is opened & cake discharged. Popular MOCs are MS, SS, Hast C etc. Sparkler In this filter there are filter plates mounted one above another. The slurry is fed under pressure by pump. The filtrate comes out from bottom hollow shaft & cake is deposited on various filter plates. As the pressure drop across filter increases it indicates that the plate has been loaded with cake. Filter is opened & cake discharged. The combination of sparkler, spiral,candle & cartridge is used for fine filtration such as charcoal filtration where the carbon particles are not allowed in the filtrate. In the conventional nutche filter these fine charcoal is very difficult to trap. The method of operation is that the slurry is circulated through the spiral by pump & filtrate pumped back to the reactor. As the clear filtrate starts coming out the filtrate is paseed through spiral. When the clear filtrate comes out from the spiral it is passed through candle. When the clear filtrate comes out from the candle the filtrate is passed finally through cartridge filter for final polishing filtration. The MOCs are SS, Nickel, Hast C etc. Plate & frame As the name suggests this filter consists of plate & frame mounted over a horizontal shaft. The slurry is fed by pump & clear filtrate is collected. Being open in nature it can not be used for foul smelling chemicals. The cake deposits on individual plate. After filtration is over the plates are dismantled & cake removed. The plates & frames can be washed individually & refitted for next filtration. The MOCs available are SS, PP,Hast C etc. In GCL this type of filter has been used only for one or two applications. Advantages:  Because of its basic simplicity it is versatile & may be used for wide range of materials under varying operating condition of cake thickness & pressure.  Maintenance cost is low.  It provides a large filtering area on a small floor space and few additional associated units are needed.  Most of the joints are external & leakage is easily detected.  High pressure operation is usually possible.  It is equally suitable whether the cake or the filtrate is the main product. Disadvantage:  It is intermittent in operation & continual dismantling is apt to cause high wear on the cloths.  Despite the improvements mentioned above it is fairly heavy on labour. Cartridge Cartridge filters are for very fine filtration at micron level. The cartridge is disposable after it has clogged. For fine charcoal filtration cartridge filter is used at the last stage to trap any carbon

which has passed the candle. The MOCs available are SS, Nickel, Hast C, PP etc. In pharmaceutical industries this type of filters are very common. In GCL the cartridge filters are used for Oxyclosanide (Veterinary drug) purification with fine charcoal. CPF (Insecticide) purification with fine charcoal. Rotary vacuum drum The arrangement consists of a trough in which slurry is fed. There is rotating drum on which filter cloth is fixed. Vacuum is applied within the drum. The drum rotates at very very slow speed. By vacuum the slurry is sucked to the top of drum, it is filtered & cake is deposited on the filter cloth. The deposited cake is cut by knife blade & discharged. This filter is very useful for pasty sticky cake. The disadvantage being that it is not very much air tight so there is smell if some foul smelling chemical is handled. For CPF filtration this filter is used where other types of filters failed to give satisfactory performance. Other types of filter Some other types of filters are pressure leaf filter, bag filter, horizontal belt filter etc. For details refer books. Filter cloth & filter aid The filter cloths used in GCL are PP, Cotton, Terylene etc. These cloths are available in various mesh sizes. For fine filtration higher size mesh cloth is used. In addition to cloth porous filtration tiles (Grindwell Norton) have also been used. These tiles act as filter cloth. These are very fine in nature. For fine filtration, say filtration of fine powered charcoal from slurry Hyflo is used. The procedure is to prepare bed of hyflo over filter cloth by circulating slurry of hyflo prepared separately. Once the filter cloth is embedded with hyflo the slurry is fed to the filter. The hyflo bed is easy to prepare. In spiral filter almost always hyflo bed is prepared first & then filtration done. Calculation of filtration time By the very nature of the cake two types of cakes are there. Compressible & Non compressible. In filtration two resistances are encountered: Cake resistance (  ) Filter medium resistance ( Rm ) The pressure drop across filter consists of: P across cake P across filter medium Total pressure drop is the addition of these two pressure drops. If the cake resistance is independent of the pressure drop it is called non-compressible cake. If the cake resistance is dependent on pressure drop it is called compressible cake. The method is different for compressible & non-compressible cake. By nature almost all the cakes are compressible to some extent or other. It is their degree of compressibility that decides whether the cake is compressible or non-compressible. Non compressible cake

For calculation click--- Filtration time

From lab study time (t) vs filtrate volume (v) data is given. Two methods are available for analyzing these datas. Method-1 The t/v on y-axis is plotted against v on x-axis. From the slope & intercept the cake resistance & filter medium resistance are calculated respectively. The values are fed along with some other values in the INPUT DATA in program & OUTPUT RESULT is obtained. Method-2 This is quicker method but it does work for non-compressible cake to the satisfactory level. Here v on y-axis is plotted against t on x-axis. In the lab data the cake thickness is mentioned at the end of filtration. For half of the filtration cake thickness will be half of the total thickness. Time for half filtration is found from the plot. Respective values are put in the INPUT DATA & OUTPUT RESULT is obtained. The filtration factor ‘n’ is calculated which is very close to 2 for most of the non-compressible cakes. Hence filtration is said to follow the square law. Compressible cake The filtration data time vs filtrate volume should be collected at various differential pressures in lab. For individual P the plots of t/v vs v are made. From these plots the cake resistance  and filter medium resistance Rm are calculated. Table is made of , Rm P. From these datas two graphs are drawn:  Log () vs Log (P)  Rm vs P The slope of first graph is ‘s’. The equation showing the relationship between cake resistance,  & pressure drop P is: = 0 (P)S When ‘s’ = ‘0’ the cake is non-compressible. As the value of ‘s’ goes away & away from ‘0’ the cake tends to become compressible. The slope of first plot is ‘s’. From the graph by putting the value of & P into above equation 0 can be calculated. From Rm vs P graph the value of Rm is taken in the equation for nearest value of P. The cake resistance  & P can be plotted on Log-Log scale also instead of taking Log & then plotting.

ANNEXURE V ( Prepared by KSS )

VACUUM EQUIPMENTS Introduction In chemical process industries vacuum is very oftenly used for various purposes e.g.  Vacuum distillation of high boiling organic compounds. At atmospheric distillation, the products may deteriorate due to higher temperature, but in vacuum distillation temperature is lower.  For transferring a material from on place to another, pressure differential can be created by applying vacuum.  In chemical reactions where gases are generated negative pressure that is vacuum is applied for scrubbing gases so that leakage to atmosphere is minimised.  In filtration and drying operations also vacuum is used very frequently. For creating vacuum common devices used are: Ejectors Venturi scrubbers Vacuum pumps Ejectors These are the most common equipments used for creating vacuum because of their simple design, No moving parts. Basic principle Type of ejectors Points to be considered while purchasing steam jet ejector Performance factors Steam flow through ejector nozzle Information required for ejector selection Cost factors Basic principles of steam jet ejector Steam ejectors are pumps without moving parts. Construction and operation are extremely simple in as much as only three main processes are involved. The main parts are head, the driving nozzle and the diffuser. The main processes are expansion of driving steam in the driving nozzle, mixing of the steam jet thus produced with the medium to be drawn off ( air, gasses or vapors) and the conversion of velocity of this mixture into pressure in the diffusers. Steam jet ejectors operate at very high velocities. The velocity of the driving steam jet is nearly always many times that of the speed of sound. The large volumes under vacuum can therefore be easily handled. This is the reason why stem ejectors are eminently suitable as vacuum pumps. These are simple is construction, constructed from wide range of material of construction, simple in operation, robust in design, long working life, extremely safe operation. Type of ejector 

Single stage To compress from about 80 torr to atmospheric pressure. It is used generally for compression ration < 10. It is suitable as pre-evacuator.

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Two-stage Without intercondensation, to compress from about 30 torr to atmospheric pressure. It is used for small suction quantities and as two-stage pre-evacuator. Three- stage With intercondensation to compress from about 10 torr to atmospheric pressure. It is mainly used to evacuate large condensers. These ejectors have a smaller steam and water consumption than the two stage steam jet ejectors with intercondensation, if the working conditions are same for both the units. Four-stage With surface condenser for vacuum from about 3 torr to about 30 torr when the drawn off medium must not come into contact with the cooling water or if the condensate is to be recovered. These ejectors are used extensively in the mineral oil industries. Five stage With mixing condensers for vacuum from about 0.1 torr to about 3 torr. For suction quantities from about 0.5 kg/hr upto about 1000 kg/hr condensable and in condensable vapor and gases. These ejectors are used for freeze drying where large quantities of water vapor are drawn off from a vacuum of about 1 torr. Also used in steel de-gassing where large quantities of incondensable gases must be drawn off. Six-stage With intercondenser and an after condenser, for vacuum from about 0.05 torr to about torr. These are used in the manufacture of synthetic fibres where vacuum between about 0.1 torr and 0.3 torr is required. An after condenser is always used, if the exhaust from the final stage can not flow direct into the atmosphere. 2 Steam stage + water ring vacuum pump For vacuum from about 0.5 to 5 torr. This combined pump is particularly suitable if barometric erection is not possible. 1 Stem stage + water jet This combination is used for vacuum upto 10 torr. 2 Steam stage + 1 water jet This combination is very famous in the chemical process industries. This gives vacuum in the range of 2 to 5 torr.

Points to be considered while purchasing steam jet ejector: Suction capacity Vacuum Pre-evacuator MOC Type of condenser Method of installation Suction capacity The steam consumption of a stem jet vacuum pump does not depend upon whether the whole or only part of the suction is ejected. No steam is saved when a large capacity pump is operating below full load. Hence it is important to make the plant to be held under vacuum as air tight as possible, to determine the suction capacity as accurately as possible and to design the pump for this capacity. However the capacity should always be chosen with a safety margin so as not to endanger safe working. The suction capacity is best calculated by weight that is Kg/hr. The suction capacity be weight is made up of:  Air leakage For calculating the air leakage rate click here Air leakage rate

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This leakage is that which enters through gaps in sealing. ( A hole of 1 mm² lets in approximately 1.8 lbs/hr ). Gases, vapor & air released from the material handled in the plant The condensable part must be distinguished from the noncondensables ( Inert gas ). The molecular weight & temperature must be taken into consideration. For discontinuous operation, it is important to know at what vacuum the gas or vapor quantities are released. Gases & air from the cooling water The air tightness of the vacuum plants can vary greatly depending upon whether the plant is mainly welded or whether it has many flange connections, valves, cocks, inspection glasses, stuffing boxes etc. The type of sealing material, the condition of the sealing surfaces and the degree of the use of the fillings are important. However it is possible to give a rough guide for a practical evaluation of the suction capacity ( Not including of course vapors or gases released in the chemical process ).

Vacuum The vacuum should not be chosen higher than the absolutely necessary. Too high a vacuum leads to unnecessarily large suction pipelines, unnecessarily large steam jet ejectors, excessive steam consumption and excessive cooling water consumption. Pre-evacuator If a vacuum plant is in constant operation, evacuating time on start-up is generally not an important factor and it is not necessary to provide special pre-evacuator ( Start-up ejector ). If however the vacuum plant has to be started up frequently, a short evacuating time is desirable. To achieve this a pre-evacuator is used. A pre-evacuator is normally a single stage steam jet ejector with a large suction capacity, which is put to operation simultaneously with the steam jet ejector. Together with the ejector it evacuates the plant very quickly to an intermediate vacuum, say upto 150 torr. At 150 torr almost 80 % of the original volume of air in the plant has already been pumped out. The pre-evacuator is then shutoff and the steam jet ejector alone evacuates in the remaining time to the required working vacuum. The pre-evacuator has a high steam consumption. However this is not of great importance since it operates only for 10-15 minutes during the start-up of the plant. The steam consumption of preevacuator decreases considerably with increasing stem pressure. The steam consumption at 10 atm is only 40 & of that at 3 atm. MOC A steam jet vacuum pump should be constructed of a material at least resistant to corrosion as the plant to which it will be attached. The various MOCs available are: MS, SS-304, SS-316, Graphite, MS/FRVE lines, PP etc. The jet comes in various MOCs such as: SS-304, S-316, Titanium, PTFE etc. Type of condenser Mixing condensers are simple, reliable and inexpensive. Mixing condensers like steam jet ejectors can be manufactured from many different materials and also make the best use of cooling water. With surface condenser, the cooling water does not enter the vacuum. The cooling water is separate from the condensate. Surface condensers must be used when  The cooling water must not be contaminated by the condensate of the vapors drawn off.  The condensate is to serve as cooling water for units such as steam turbine condenser.  The condensate is to be reclaimed.

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Ammonia vapors are contained in the drawn off vapors because insoluble condensate are quickly formed in mixing the condensates which would cause breakdowns, that is, blocking of the water outlet etc. Even small amount of ammonia are dangerous.

Method of installation 

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Barometric erection If possible steam jet ejectors should be erected barometrically because then the water flows from the condensers without pumping. A column of 760 mm Hg ( 29.92” ) high balances the pressure of the atmosphere. Since water is 13½ times lighter than mercury, the corresponding height of water is 10.33 m. This height of 10.33 m is called the barometric height. According to the pressure in difference condensers at reduced height may be sufficient to ensure a free outlet of the cooling water. At a barometric height of 760 mm Hg and a condenser pressure of 300 torr. A height of 6.3 m ( 20.7” ) is necessary. Since the water may be mixed with same air and hence will no longer have a sp.gravity of 1, it is safer to assume a full barometric height of 11 meters. Non barometric erection In many cases it is not possible to install a steam jet ejector 11 m ( 36 ft ) above the water drain. There are various alternatives depending on the height available.

Performance factors: Driving steam Suction pressure Discharge pressure Cooling water Dry and saturated air Gas and vapor densities Driving steam Steam jet ejectors can be designed for driving steam from about 15 psia to 600 psig. A steam jet ejector operates at the driving steam pressure for which it is designed. It is necessary to ensure that the designed pressure is maintained otherwise a breakdown is possible. On the other hand operating above the design pressure results in steam wastage. In this case it is necessary to install a pressure regulator. It is essential to check what working steam pressure is available at the site of steam jet ejector. The ejector should be designed for that pressure. ( This pressure is often much lower than the boiler pressure ). Steam jet ejectors operate most efficiently with dry saturated steam or superheated steam. Low superheat can be disregarded. Wet steam is not desirable at all. The motive steam design pressure must be selected as the lowest expected pressure at the ejector steam nozzle. The unit will not operate stably on steam pressures below the design pressure. Recommended steam design pressure = Minimum expected design pressure at the ejector nozzle – 10 psi. This design basis allows for stable operation under minor pressure fluctuations. An increase in steam pressure over design pressure will not increase vapor holding capacity for the usual “ Fixed capacity ejector “. The increased pressure usually decreases capacity due to the extra steam in the diffuser. The best ejector steam economy is attained when the steam nozzle and diffuser are proportionated for a specified performance. For a given ejector an increase in steam pressure over the design value will increase the steam flow through the nozzle in direct proportion to the increase in the absolute steam pressure. The higher the actual design pressure of an ejector the lower the lower the steam consumption. This is more pronounced on one or two stage ejectors. When this pressure is above 350 psig, the decrease in steam requirement will be negligible. As the absolute suction pressure decreases

advantage of high pressure steam becomes less pronounced. In very small units the physical size of steam nozzle may place a lower ceiling on the pressure. For the ejectors discharging to the atmosphere, steam pressure below 60 psig at the ejector are generally uneconomical. If discharge pressure is lower in multistage units, the steam pressure at inlet can be lower. Single stage ejectors designed for pressure below 200 mm Hg (abs) cannot operate efficiently on steam pressures below 25 psig. The first stage for two of a multistage system can be designed although perhaps not economically to use stem pressure below one psig. To ensure stable operations the steam pressure must be above a minimum value. This minimum is called motive steam pick-up pressure, when the pressure is being increased from unstable region.

Effect of wet steam Wet steam erodes the ejector nozzle and interferes with performance by clogging the nozzle with water droplets. The effect on performance is significant and is usually reflected in fluctuating vacuum. Effect of superheated steam A few degree of superheat (5-15°C) is recommended, but if superheated steam is to be used its effect must be considered in the ejector design. A high degree of superheat is of no advantage because the increase in available energy is offset by the decrease in the steam density. Suction pressure The suction pressure of an ejector is expressed in absolute units. The suction pressure follows the ejector capacity curve, varying with the non-condensable and vapor load to the unit. Discharge pressure All types of ejectors are sensitive to discharge pressure just as they are to the steam supply pressure. Normally designed ejectors are suitable for operating against a pressure only slightly in excess of atmospheric. In most cases ejectors can be designed to discharge at a pressure of 5 psi, provided a considerable increase in steam consumption can be permitted. It must be appreciated, however, that the discharge of an ejector is contaminated with incondensable gases and is therefore in many cases unsuitable for further use. The pressure drop through discharge piping and aftercooler must be taken into consideration. Discharge piping should not have pockets for condensation. Cooling water The cooling water temperature is of great importance. Well water : 10 to 15°C River water : 5 to 25°C Re-circulated water : 10 to 28°C Seawater : 15 to 30°C Steam jet ejectors must be designed for the maximum cooling water temperature available. Steam and water consumption are greatly dependent on the design temperature as can be seen from the following example. A unit to eject at 5 torr using steam at 45 psig. The steam consumption at a cooling water temperature of 25°C is double that of 15°C. If the cooling water temperature varies to a large extent throughout the year, it is advisable to adjust the steam consumption in relation to the water temperature by suing different nozzles, or by altering

the steam pressure ( The lower in only possible at high pressure ). The pressure of the cooling water should not oscillate as this may affect the vacuum. With missing condensers it is not necessary to have any particular water pressure. With water jet condensers a minimum pressure of 30 psig is required. With surface condensers the pressure loss in the tubes must be overcome. In general the cooling water outlet temperature must not exceed 45°C to 50 °C, otherwise chalk deposits will cause breakdown. Amount of gases released from cooling water, W W T1 G

= = = =

G/t 1, where Air liberated lbs/hr Inlet temperature °C Cooling water, gal/min

Ws X L GPM of cooling water required = ------------, where tw X 500 Ws = Lbs of steam to condense L = Latent heat of vaporisation, usually taken as 1000 BTU/lb for process application and 950 BTU/lb for turbine exhaust steam. tw = Cooling water temperature rise °F Dry and saturated air When an ejector is maintaining a condenser vacuum, the air extracted by the ejector is saturated with water vapor. The amount of water vapor entrained by the dry air which leaks into the condenser depends upon the temperature of the mixture and the vacuum at the ejector suction. Gas and vapor densities When an ejector or thermo-compressor is required to handle chemical gases or vapors, it is necessary that the gas density ( For failing this the temperature & molecular weight ) be known. The compression of a given weight of heavy gas requires less operating steam than the same weight of light gas. As a simple example on pound of air is more easily handled by an ejector than one pound of water vapor. The correct proportioning of the ejector & thermo-compressor therefore necessitates detailed knowledge of the properties of the gas or vapor to be compressed. Steam flow through ejector nozzle The quantity of steam passing through any ejector nozzle varies directly as the steam pressure, but decreases with an increase of steam temperature. It is therefore essential that the maximum steam temperatures be stated to enable the ejector to be correctly designed. The weight of steam flowing through an ejector nozzle may be obtained from the following simple formula. S = KPD2, where S P D K

= = = =

Steam flow in lbs/hr Steam pressure at the upstream of nozzle in psi (abs) Diameter of nozzle bore in inches. A constant which depends on the steam pressure and temperature.

Information required for ejector selection

To enable the manufacturer to design most suitable type of vacuum system, it is essential that correct data be available upon which to base proposals & designs. Whenever possible the following information should be supplied with any enquiry.  Brief description of purpose for which equipment is required.  Weight of air or vapor to be handled in lbs/hr. If a mixture of air, vapor and /or other noncondensable gases. Their approximate proportions should be stated Lbs/hr of condensable vaporous & lbs/hr of non-condensable gases, either dissolved, injected or carried in process formed by reaction, air leakage etc.  The absolute pressure required at the ejector suction in inches mercury, or millimeters mercury.  If ejector is required to discharge at other than atmospheric pressure, the maximum discharge pressure must be stated.  If normal steam pressure and also the minimum steam pressure at which the plant is required to operate. If steam is superheated give maximum temperature.  Maximum temperature of cooling water. Cost factors Of all the classes of Chemical Engineering Equipments, ejectors are unique in that the actual operating cost is usually much greater than the installed equipment cost. Ejectors have low first cost because they are simple in design, have no moving parts and occupy a small space. In general operating cost increases as the ejector steam pressure increases. If an ejector is supplied with steam above the design pressure, steam consumption will be increased in direct proportion to the ratio of actual operating pressure to the design pressure. It is good practice to install a stem pressure regulating valve to maintain a uniform steam pressure at the ejector. The other things which affect the performance of on ejector are.  Discharge pressure  Wet and superheated steam  Load variation  Back pressure  Capacity and suction pressure  Number of stages  Condenser requirements  Material of construction Water jet ejectors As the name suggests it water jet ejector the motive fluid is water instead of steam. Ejectors using water as the motive fluid are designed for reasonable non-condensable load together with large condensable flows. Water pressures as low as 10-20 psig are usable, while pressures of 40 psig and higher will maintain a vacuum of 1-4 inches of Hg (abs) in a single stage unit. Combination of water & steam ejectors are used to effectively handle a wide variety of vacuum situations. The water ejector serves to condense steam from the steam ejector. Water ejectors and water jet eductors are also used for mixing liquids, lifting liquids and pumping + mixing suspended solids & slurries ranging from ½” to 24. The ejectors are usually in pumping air or gases while the eductors are used in pumping liquids. Unlike steam jet ejector there is pump in water jet ejector which is the moving part. Venturi scrubbers These are used for scrubbing gases coming out from chemical reactions. For example gases evolved such as S02, HCl are scrubbed in caustic soda solution. For venturi scrubbers slight vacuum is required to ensure that the gases do not leak to atmosphere. The venturi scrubbers used at GCL are of model: 25D, 40D, 60D of H. K. Industries make.

Vacuum pumps Vacuum pumps are mainly used for handling large quantities of air leakage at relatively low vacuum in operations such as filtration, drying etc. The vacuum pump may be liquid ring type or dry pump. Amongst liquid ring more common are water ring and oil ring vacuum pumps. Water ring vacuum pump Water ring machines are used principally as vacuum pumps, but can also serve as compressors for special applications. Their main advantage lies in their simple and trouble free operations. They may be used for handling moist air as well as aggressive gases and vapors, provided that the material of construction is properly selected. Dust-laden gases can also be handled without difficulty. Water ring machines are absolutely oil-free and do not contaminate the medium passing through. Compression takes place with a small temperature rise since most of the heat is absorbed by the ring fluid which also acts as a seal. For special applications, an alternative sealing fluid instead of water may be used. Principle of operation The casing of the machine is cylindrical with control discs on either side. Within this is an eccentrically located impeller with curved blading. The liquid introduced, preferably water is set into rotary motion by the blading, thus forming a water ring concentric with the casing. Cells are formed between the ring and the blades of the impeller, which vary in volume from a maximum to a minimum with each revolution. The conveying medium enters the working chamber through the openings in the lateral control discs and is compressed by the decrease in volume of the cells. It then flows together with the cooling water through discharge openings the control disc to the delivery port. The impeller runs in bearings arranged in brackets outside the casing covers. At the bottom of the casing an automatic drain valve is provided, through which the ring fluid can flow off when the pump is at a standstill. The pump should be brought into operation without the ring fluid whereby easy starting is ensured. Drive The pump is usually driven by a direct coupled electric motor. Pump with an automatic water drain valve can be driven by squirrel-cage motors with star/delta starting. Smaller units may depending on the regulations of the local electricity suppliers, be switched on by means of direct on line starters. Installation as a vacuum pump With normal installation using water as a ring and cooling fluid, the water as well as the exhaust air are delivered together into the drains. A silencer cum water separator can be provided as an optional accessory if required. This would have to be fitted in the exhaust piping. A non-return valve is normally supplied for fitting in the suction piping so that in case of operational failure, the water does not flow back into the vacuum line. A vacuum relief valve can also be supplied if it is desired to limit the vacuum. At a pre-set maximum value the valve opens automatically allowing atmospheric air into the piping. The ultimate vacuum attinable by this type of machine will depend upon the temperature and evaporation properties of the ring fluid. Installation as a compressor When ring compressors are equipped on the pressure side with a water separator in which the ring water is separated from the compressed air. This is fitted with a float valve, which allows the water to escape. It is possible to re-circulate this water with a closed system, similar to that for a

vacuum pump. The non-return valve for a water ring compressor is to be fitted to the pressure piping. The working pressure is limited by fitting a safety valve in the delivery piping. Material of construction The standard material of construction is cast iron. However, for special application these can be supplied in various materials such as bronze, Gunmetal, SS-304, SS-316, Rubber-lined etc. Details of normal water ring vacuum pumps Speed, RPM

Max. Suction M3’hr

Recommended Motor, HP

Water consumption Lit/min.

2850 2850 2850 1450 1450 1450 1450 980 980 980 725 725 580

49 81 123 160 220 330 440 725 850 1080 1500 2030 3650

4 5 7.5 7.5 10 15 20 30 35 40 65 90 200

7 9 14 16 20 30 40 60 80 100 150 200 350

Oil ring vacuum pumps Oil ring vacuum pump is similar to water ring vacuum pump in operation except that the sealing fluid used is oil instead of water. The advantage of oil ring vacuum pump is that high vacuum can be obtained due to much lower vapor pressure of oil as compared to water. The disadvantage is that after some usage oil gets contaminated with chemicals and vacuum starts dropping. The recovery of oil is very expensive. Because of this reason the oil ring vacuum pumps are not very common. Dry pump By using water ring/oil ring vacuum pump the chemicals/solvents get contaminated with water/oil. The recovery of these solvents become very costly affair. In such cases dry pump scan be used though the initial costs are high. The principle of dry pumps is different from ring pump. In dry pump drip oil lubrication is used, whereas in ring pump, there is continuous seal of liquid. In dry pump oil used is once through pass. Heat exchanger can be installed on the discharge side of dry pumps to condense the gases. The condensed solvent may be contaminated with little bit of oil, which is used for drip lubrication of dry pump. The condensed solvent can be distilled out to separate it from oil. To boost the capacity of dry pump mechanical boosters can be used. Combination of one roots pump and two dry pumps will give capacity of 800 M 3/hr at 1 torr absolute pressure. The roots pump is volumetric flow device. At high vacuum mass flow will be lower. The oil consumption for both the dry pumps is 250 CC/8 hr. For 800 M3/hr flow at 1 torr air = 1.22 kgs/hr. The combination of two dry pumps and one roots pump can be used in place of 4-stage steam jet ejector. Advantages over steam jet ejector  No steam consumption

 

Low HP required Pollution free operation

There are dry pumps which are totally dry, no drip lubrication required. In steam jet ejectors the last stage discharges to atmosphere, thereby contaminating the atmosphere with chemical/solvent vapors, whereas in case of dry pumps chilled condenser can be installed to recover any solvent loss to atmosphere, thereby improving environment as a whole.

ANNEXURE VI (Prepared by KSS)

TRANSFER PUMPS For transferring liquid from one place to another three methods are used. Pressure, Vacuum, Pump. Pumping is very common & popular in chemical process industries. The various types of pumps are as shown below: Types of pump Centrifugal pump Coupled Pump Air operated Double diaphragm

Positive displacement pump

Mono block Magnetically Reciprocating Pump coupled pump Pump Plunger Diaphragm Gear Shuttle block pump type metering pump pump pump

Single diaphragm pump

Rotary pump Lube Screw pump pump

Double diaphragm pump

Centrifugal pump The centrifugal pump develops its pressure by centrifugal force on the liquid passing through the pump and generally applicable to high capacity, low to medium head installations. For high discharge head centrifugal pumps can be multistage instead of single stage. e.g multistage centrifugal pump is used for boiler feed water.     

Basic parts of a centrifugal pump Arrangement of pump Hydraulic characteristics Pump affinity laws Selection of pump

Basic parts of a centrifugal pump

Impeller The three common types of impellers used are:  Fully closed: Used for high head & high pressure applications.  Semiopen: Used for general purpose applications. It has got open vane tips at the Entrance to break up suspended particles & prevent clogging.  Open: Used for low heads, suspended solid s applications, very small flows. These impellers are available in any nearly any material of construction as well as rubber, rubber lined, teflon lined, glasslined. The lined impellers are of open type. Casing The casing may be constructed of a wide variety of metal, lined material, plastic materials etc. Shaft Care should be taken in selecting the shaft material. It must be resistant to the corrosive action of the process fluid yet posses good strength characteristic for design. Generally sleeves are used over shaft to prevent direct corrosion / mechanical danger to shaft. These sleeves may be metal, ceramic, rubber etc. Bearings The bearings must be adequate to handle the shaft load without excessive wear provided lubrication is maintained. In all cases bearings should be of the outboard type, that is not in the process fluid unless special conditions prevail to make this situation acceptable. Packing & seals on rotating shaft Conventional soft or metallic packing in a stuffing box is satisfactory for many low pressure, noncorrosive fluid systems. Special packings such as mechanical seals are commonly used for corrosive fluids when the pressure becomes high above (about 50 psig) or the fluid is corrosive, additional means of sealing the shaft must be provided. Particular care must be taken in handling and using the mechanical seals. Arrangement of pump 

Pumps in series Sometimes it is advantageous or economical to use two or more pumps in series to reach the desired discharge pressure. In this situation the capacity is limited by the smaller capacity of any one of the pumps at its speed of operation. The total discharge pressure of the last pump is the sum of individual discharge pressure of the individual pumps. The pump casing of each stage (particularly the last) must be of sufficient pressure to withstand developed pressure.



Pumps in parallel Pumps are operated in parallel to divide the total load in two or more smaller pumps. The individual pump operates on its own characteristic curve. The capacity gets added up.

Hydraulic characteristics :  Capacity  Total head  Suction head or suction lift  Discharge head  NPSH & pump suction 1. Capacity

It is the rate of liquid or slurry flow through a pump. For proper selection and corresponding operation a pump capacity must be identified with the actual pumping temperatures of the liquid in order to determine the proper power requirements as well as the effects of viscosity. Pumps are normally selected to operate in the region of high efficiency and particular attention should be given to avoiding the extreme rights side of the characteristic curve where capacity & head may change abruptly. 2. Total head The pressure available at the discharge of a pump as a result of change of mechanical input energy into kinetic & potential energy. This represents the total energy given to the liquid by the pump. Head is expressed as feet of liquid being pumped. The head is independent of the fluid being pumped & is therefore the same for any fluid thorough the pump at a given speed of rotation & capacity. 3. Suction head or suction lift The total suction head is the difference in elevation between the liquid on the pump suction side and the centerline of the pump + the velocity head. When the liquid level is below the pump centerline the difference in elevation is known as suction lift. Total suction head (TSH) = Static head – friction head loss. Total suction lift (TSL) = Static lift + friction head loss. 4. Discharge head The discharge head of a pump is the head measured at the discharge nozzle 7 is composed of static head, friction losses through pipes, fittings, contractions, expansions, entrances & exit, thermal system pressure. 5. Velocity head As a component of both suction and discharge heads, velocity head is determined at the pump suction & discharge flanges respectively and added to the gage reading. The actual pressure head at any point is the sum of the gage reading + the velocity head. The values of velocity heads are usually small and negligible often. 6. NPSH and pump suction The net positive suction head (NPSH) is very important criteria for centrifugal pumps. There are two types of NPSH. NPSHa and NPSHr. NPSHa = Net positive suction head available = Pressure on suction side – friction loss – vapour pressure of liquid being pumped at pumping temp. NPSHr = Net positive suction head required. It is specified by the pump manufacturers. The NPSHr is very important consideration in selecting a pump, which might handle liquids at or near boiling points or liquids of high vapour pressures. If this consideration of NPSH r is ignored, the pump may well be inoperative in the system or it may be on the borderline and become troublesome and expensive. The significance of NHSH R is to ensure sufficient head of liquid at the entrance of the pump impeller to overcome the initial flow losses of the pump. This allows the pump impeller to operate with a full bite of liquid essentially free of flashing bubbles of vapour due to boiling action of the fluid poor suction condition to cavitation in

pump impellers and this is a contributor at which pump can not operate for a very long without physical erosion, damage to the impeller. Cavitation in a centrifugal pump or any pump develops when there is insufficient head for the liquid to flow into the inlet of the pump allowing flashing or bubble formation in the suction system and entrance to the pump. Each pump design or “family” of dimensional features related to the inlet and impeller entrance pattern requires a specific minimum value of NPSH to operate satisfactorily without flashing, cavitating and loss of suction flow. Under cavitating conditions a pump will perform below its head performance curve at any particular flow rate. Although the pump may operate under cavitating conditions, it will often be noisy because of collapsing vapour bubbles and severe pitting and erosion of the impeller often results. This damage can become so severe as to completely destroy the impeller and create excessive clearance in the casing. To avoid these problems, the following are few situations to watch.  Have NPSH available at least 2 feet of liquid greater than the pump manufacturer  Requires under worst possible operating conditions.  Internal clearance wears inside pump.  Entrained gas (non condensables)  Deviations or fluctuations in suction side pressure, temperature increases, low liquid level.  Piping layout on suction, low particularly tee intersections, globe valves, baffles etc.  Liquid vortexing in suction vessel, thus creating gas entrainment into suction piping.  Nozzle size on liquid containing vessel may create severe problems if inadequate. Liquid suction velocities in general are held at 3-6.5 ft/sec. Usually as a guide the suction line is at least one pipe size larger than the pump suction nozzle. The NPSH required by the pump is a function of the physical dimensions of casing, speed and type of impeller and must be satisfied for proper pump performance. The required NPSH of a pump increases as the pump speed increases. RPM  NPSHr0.75 For this reason many critical suction condition installations use relatively slow speed pumps.

Pump affinity laws 

For change in speed with fixed impeller design, diameter & efficiency the following conditions and characteristics change simultaneously. Q2 = Q1 X (N2/N1)

Q2 = Flow rate at N2 RPM

H2 = H1 X (N2/N1)2

Q1 = Flow rate at N1 RPM

BHP2 = BHP1 (N2/N1)3

H = Head of pump BHP = Break horse power

The relations do not hold good exactly if the ratio of speed change is greater than 1.2 to 2 nor do they hold good if the suction conditions become limiting such as NPSH. 

For change in impeller diameter at a fixed speed and efficiency. Q2 = Q1 X (D2/D1) D1 = Impeller diameter H2 = H1 X (D2/D1)2

An impeller can be cut from one size down to another on a lathe and provided the change in diameter is not greater than 20 percent, the conditions of new operation can be described by the type of calculation shown in above formulae. Selection of pump :  Capacity  Head  Effect of viscosity  Effect of temp. rise and minimum safe flow  MOC  Operating condition of fluid / nature  System condition  Motor details

Capacity Capacity is decided by the batch time. Batch time is fixed by the capacity of the plant. For example if 10000 litres of liquid is to be transferred from one vessel to another in 1 hr the capacity becomes 10 M3/hr. For most of the normal operations the capacity of the pumps used is of the order of 10,000 lit/hr.

Head After deciding the capacity the head is to be calculated. For this the total pressure drop in the suction & discharge piping is calculated. The elevation of discharge point & suction point is taken into account. The pressure conditions at suction & discharge are also considered. For discharge piping use velocity in pipeline as 6-8 ft/sec ( Source : Ludwig vol.1 ). For suction piping use velocity limpet/jacket ,SRV is to be sized for maximum flow rate possible which is calculated based on line size ,length & number of fittings.

Types of R D : 1. a. b. c. d.

2. a. b. c.

Conventional Prebulged tension loaded solid metal disks . Max. operating of vessel /tank = 70 % of rated pressure of disk for non pulsating service. For pulsating service max.. operating of vessel /tank = 50 % of rated pressure of disk .Disk is installed with dome facing away from process side . Disk can be used for liquid service also. Least expensive of all disks. Drawbacks : i)Disk fragments on bursting & hence cannot be installed below SRV ii) Vacuum support is required if vacuum exceeds 600 mm Hg. Because of vacuum support if disk is installed upside down it will burst at pressure higher than rated pressure.

d.

Prescored tension loaded disks : his disk is a solid metal disk prescored in a specific pattern to weaken the disk. Max.. operating of vessel /tank = 80 to 85 % of rated pressure of disk They avoid disadvantage of conventional tension loaded disk viz.fragmentation & need for vacuuum support. Since there is no vacuum support ,disk with PTFE on process side is available. However they are costlier than conventional solid metal disks. Disk installed incorrectly will burst at rated pressure or lower.

3.

Composite disk :

a.

b. c.

This is prebulged disk & has a slotted top metal section wherein burst pressure is controlled by size & location of slots & perforations.The disk is isolated from process by PTFE membrane . Since burst pressure is not controlled by thickness , disk is available at lower burst pressure than conventional disks . Max.. operating of vessel /tank = 80 % of rated pressure of disk. Drawbacks : Similar to conventional metal disks viz.need for vacuum support ; fragmentation & bursts at higher pressure if installed upside down.

4. Reverse buckling disks Installed with dome facing towards process side & hence disk is in compression. The bursting action of disks is due to either knife blades on downstream or prescoring on disks. Advantage over tension loaded disks : b. Disk does not fragment & hence can be installed below SRV . a. Vacuum support is not required .Disk is available with PTFE seal facing process & hence can be used for corrosive applications. b. Disk can be used up to 90 % of operating pressure. c. Manufacturing range is zero. d. Disadvantage :Cost is higher than conventional tension loaded disks.Except RLS other types are not suitable for liquid service . 5. Non metallic disks: Rupture disks in graphite are available which are useful in highly corrosive services .The drawbacks of graphite disks are : a. Cannot be installed below SRV because of fragmentation ; b. lower shelf life due to resin bonding . Effect of temperature : The burst pressure of disk is function of temperature .The temp. :pressure relation for RD is different than that for parent metal .In order to minimise effect of temp. it is recommended to install R D at least one metre away from vessel nozzle so that disk faces much lower temp. than the vessel. In this case operating temp. of disk can be specified as 50 ° C. Sizing of R D : For vapour or gas service area of R D is calculated from formula : W = C*K*A*P*(M/T)^0.5 Ref: Loss prevention in process industries by F Lees Page 12/67 Where W is venting rate in Kg/hr A is area of disk in sq. mm P is absolute pressure in bars M is molecular weight of gas or vapour T is temperature in ° K K is Coeff. of discharge = 0.6 C is constant = 2.7 From A , diameter of disk is calculated .

Types of SRV: a. Conventional relief valve : Conventional relief valves operate satisfactorily when builtup back pressure is less than 10 % of set pressure .Changes in back pressure affects both set pressure & capacity. b. Balanced relief valve: Balanced relief valves have bellows & they operate satisfactorily under varying back pressure .In addition bellows protect SRV from corrosion from discharge side . Definition of terms : Accumulation : Pressure increase over MAWP during discharge expressed as %.Accumulation = 10 % of set pressure or 3 psi whichever is higher . Blowdown:Blowdown is differance between set pressure & reseating pressure .This is adjustable from 7 % to 12 % of set pressure.

Sizing of SRV : For gases & vapours at constant backpressure orifice area is calculated as under : A = W*(Z*T/M)^0.5 --------------------C*K*P*Kb Ref: LUDWIG Page 254 Where W is flow rate in lb/hr A is area of orifice in sq. inch P is inlet pressure in psia M is molecular weight of gas or vapour T is temperature in ° R Kb = 1 for backpressure below 55 % of absolute relieving pressure K is orifice Coeff. = 0.97 for nozzle type SRV C is constant depending on ratio of specific heats. SRV are available in with specific orifice area which are designated by by code D to H ; J to N ; P to Q . **********

ANNEXURE VIII PIPELINE SIZING (Prepared by KKV) Pipe Sizing: Pipe size is generally chosen as the minimum size able to carry the desired maximum flow rate required at a pressure loss equal to the pressure available. In addition to friction and velocity-head losses in the piping and fittings, the pressure loss owing to flow meters and valves in the line, must be included as a part of the pressure loss in the piping system. Appropriate Safety margin must be considered for off-design operating conditions that may involve changes in the available pressure differential between the terminals of the piping system and changes in the required flow rate to ensure that the line size is adequate for all anticipated operating conditions. Secondly piping economics shall be considered as, increase in the pipe size reduces the pressure loss, but increase piping cost. The important equations for calculation of pressure drop are determination of the Reynolds number (Re) and the head loss ( hf) Re = d * v *  /  and hf = 4( f * L / d ) ( v2 / 2gc) Where d = pipe inside diameter in meter, v = fluid velocity in m/s,  = fluid density in kg/m 3,  = fluid dynamic viscosity in Pa.s, f = Fanning friction factor (non-dimensional), L = length of line in meter, gc = acceleration of gravity in m/s2. For laminar flow (Re < 2000), generally found only in circuits handling heavy oils or other viscous fluids, f = 16 Re. For turbulent flow, the friction factor is dependent on the relative roughness for the pipe and on the Reynold number. In such case it is preferable to use charts of friction factor versus Reynolds number and proper equation must be used with the proper friction factor. An approximation of the Fanning friction factor for turbulent flow in smooth pipes, reasonably good up to Re = 150000, is given by f = (0.079) / (4 * Re1/2). The flow resistance of pipe fittings (elbows, tees, etc) and valves is expressed in terms of either an equivalent length of straight pipe or velocity head loss (head loss = K v2 / 2gc). Most handbooks and manufacturers’ publications dealing with fluid flow incorporate either tables of equivalent length for fittings and valves or K values for velocity head loss. Suggested Fluid Velocities in Pipe and Tubing for liquids, gases and vapors at low/moderate pressure to 50 psig and 50°C to 100°C are given in table on next page :

Fluid

Pipe Material

Fluid

Acetylene Air 0 – 30 psig Ammonia (Gas) Ammonia (Liquid) Benzene Bromine (Liquid) Bromine (Gas) Calcium Chloride CCl4

Velocity fpm 4000 4000 6000 360 360 240 2000 240 360

Steel Steel Steel Steel Steel Glass Glass Steel Steel

Chlorine (Liquid)

300

Steel,sch.80

Chlorine (Gas) Chloroform (Liq) Chloroform (Gas) Ethylene Gas Ethylene Dibromide Ethylene Dichloride Ethylene Glycol Hydrogen HCl (Liquid) HCl (Gas)

3500 360 2000 6000 240 360 360 4000 300 4000

Oxygen (ambient temp)

1800

Oxygen (Low temp)

4000

Steel Cu & Steel Cu & Steel Steel Glass Steel Steel Steel Rubberlined RL, Saran, Haveg Steel 300 psig max. SS304l

NaOH upto 30% NaOH 30 – 50% NaOH 50 - 73% NaCl Solution NaCl slurry Perchlorethylene Steam 0-30 psi saturated 30-150 psi satu. Or superheated Above 150 psi superheated Steam(Short Line) H2SO4 88-93% H2SO4 93-100% SO2 Styrene Trichloroethylene

Velocity fpm 360 300 240 300 430 360

Pipe Material

5000 8000

Steel Steel Steel Steel Steel Steel Steel Steel Steel

12500

Steel

15000 240 240 4000 360 360

Steel Lead,SS316 Steel,sch80 Steel Steel Steel Steel Steel Steel Steel

Steel