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ExxonMobil Proprietary PRODUCT LOADING SYSTEMS

SPECIAL PRODUCT LOADING SYSTEMS DESIGN PRACTICES

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CONTENTS Section

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SCOPE ............................................................................................................................................................2 REFERENCES.................................................................................................................................................2 ASPHALT ........................................................................................................................................................3 TYPES OF ASPHALT .............................................................................................................................3 GENERAL ...............................................................................................................................................4 MODES OF PRODUCT LOADING..........................................................................................................4 CONTAMINATION AND PRODUCT SEGREGATION ............................................................................4 STORAGE AND LOADING TEMPERATURE .........................................................................................4 TEMPERATURE MAINTENANCE AND CONTROL ...............................................................................5 PUMPS....................................................................................................................................................5 PRODUCT MEASUREMENT ..................................................................................................................5 LIQUEFIED PETROLEUM GAS (LPG) ...........................................................................................................6 MODES OF PRODUCT LOADING..........................................................................................................6 SYSTEM DESIGN CONSIDERATIONS AND ALTERNATIVES..............................................................6 PRODUCT MEASUREMENT ..................................................................................................................7 ODORIZING ............................................................................................................................................7 RAIL CAR LOADING AND UNLOADING ................................................................................................8 TRUCK LOADING AND UNLOADING ....................................................................................................8 MARINE LOADING AND UNLOADING...................................................................................................8 MOLTEN SULFUR ..........................................................................................................................................9 BACKGROUND.......................................................................................................................................9 MODES OF PRODUCT LOADING........................................................................................................10 TEMPERATURE MAINTENANCE ........................................................................................................10 PRODUCT MEASUREMENT ................................................................................................................10 LOADING ARMS AND PUMPS.............................................................................................................11 SAFETY CONSIDERATIONS ...............................................................................................................11 SOLID SULFUR ....................................................................................................................................11 TABLE Table 1

Sulfur Solidification Processes ..........................................................................................12

FIGURES Figure 1 Figure 2 Figure 3 Figure 4

Flow Plan for the Manufacture of Various Asphalt Products..............................................13 LPG Marine Loading System.............................................................................................14 Typical LPG Rail Unloading Systems ................................................................................14 Pressure Drop in Liquid Sulfur Lines .................................................................................15 Revision Memo 12/01

Highlights of this revision are as follows: (1) References have been updated / added. (2) Additional advice and resources provided for LPG loading system. (3) Minor additions / corrections to write-up for Asphalt.

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PRODUCT LOADING SYSTEMS

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SCOPE This section covers tank truck, rail car, and marine loading of asphalt, pressurized and refrigerated LPG, and sulfur. This section is intended to supplement Section XXIII-A, presenting additional design considerations which are specific to the products mentioned above. References given in Section XXIII-A are not repeated herein but generally apply to this section as well.

REFERENCES DESIGN PRACTICES Section II Section X Section XI Section XII Section XVI

Design Temperature, Design Pressure, and Flange Ratings Pumps Compressors Instrumentation Thermal Insulation

GLOBAL PRACTICES GP 3-3-2 GP 3-5-1 GP 3-9-2 GP 3-10-1

Suction & Discharge Piping for Centrifugal Pumps Fill & Discharge Lines, and Auxiliary Piping for Storage Tanks & Vessels External Steam Tracing Piping Selection Criteria

API STANDARDS API 2510, Design & Construction of Liquefied Petroleum Gas (LPG) Installations API 2510A, Fire Protection Considerations for the Design and Operation of Liquefied Petroleum Gas (LPG) Storage Facilities API 2023, Guide for Safe Storage and Handling of Heated Petroleum Derived Asphalt Products and Crude Oil Residua

OTHER LITERATURE 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

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The Asphalt Handbook, Asphalt Institute. Safe Storage and Handling of Asphalt, ER&E Report No. EE.85E.83. Hot Oil and Slop Tankage, Safety Guidelines, EEEL Report, January 1987. Asphalt and Fuel Oil Plant Design Guide, Report MERP.4M.73. Safe Asphalt Operations Study, ER&E Letter No. 91 ECS 3016. Rail and Truck Loading Guide for Pressurized/Refrigerated Products, Report No. CE IE 82. Evaluation of Rail Car Petroleum and Hazardous Chemical Loading/Unloading Facilities,ER&E Report No. EE.98E.86. Impact of API 2510/2510A Revisions on ExxonMobil LPG Standards, ER&E Report No. EE.94E.90. Standard for the Storage and Handling of Liquefied Petroleum Gases, NFPA No. 58. Sulfur Plant Safety Guidelines, ER&E Report EE.69E.86. Handling Liquid Sulfur, Data Sheet 592, National Safety Council. H2S Hazards with Liquid Sulfur, ER&E Letter 84 ECS3-16 Containing SOC Communication 84-4. Safe Handling of Liquid Sulfur, Exxon Chemicals Report, August 1979. Pipe Heating Guide, ER&E Report EE.111E.76. Solid Sulfur Handling and Storage, ER&E Report No. EE.1EL.81. Handling and Storage of Molten Sulfur, Texas Gulf Sulfur Report. Marine Facilities, Design, Specification and Evaluation, Marketing Engineering Standard EE.3M.86. LHG Marine Cargo Transfer Fire/Explosion Risk Assessment Procedure, ER&E Memorandum (93 CMS 010). Marine Dock Hose Technology and Practice Training Video with its companion Application Guide, ER&E Report No. EE.40E.94. 20. Purchase Specification and Inspection Guidelines for Marine Cargo Transfer Hose, ER&E Report No. EE.76E.92. 21. Safety in LPG Design, EMRE Manual No. TMEE-111. 22. LPG Safe Operations Guidelines, EMRE Manual No. TMEE-113. ExxonMobil Research and Engineering Company – Fairfax, VA

ExxonMobil Proprietary PRODUCT LOADING SYSTEMS

SPECIAL PRODUCT LOADING SYSTEMS DESIGN PRACTICES

Section XXIII-B

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ASPHALT TYPES OF ASPHALT Petroleum asphalts fall in the general classification of materials called “bitumens." Figure 1 illustrates a typical flow plan for the manufacture of various asphalt products. As shown, the four major types of asphalt produced are straight reduced (referred to as asphalt cement), cutback asphalts, air blown (referred to as oxidized), and emulsified. Although solid or semi-solid at ambient temperatures, asphalt cement may be readily liquefied by heating, by blending it with petroleum solvents of varying volatility (referred to as cutter stock or diluent), or by emulsifying it. Asphalt liquefied by these latter methods is known as cutback asphalt and emulsified asphalt. For cutback asphalts, after completion of construction, the cutter stock will evaporate leaving behind the asphalt cement to perform its function. In the case of emulsified asphalt, the water will evaporate leaving behind the asphalt cement. Environmental regulations may restrict or prohibit the use of cutbacks in many areas. Petroleum asphalt for use in pavements is usually called paving asphalt or asphalt cement to distinguish it from asphalt made for non-paving uses such as roofing and industrial purposes. Asphalt cement at ambient temperatures is a black, sticky, solid or semi-solid, highly viscous material. Because asphalt cement is sticky, it adheres to stone aggregate and is used to cement or bind them into asphalt concrete. Asphalt cement is classified according to standard ranges of consistency grades (viscosity). For many years these ranges were based on lab measurements of penetration (distance that a standard needle penetrates the surface of asphalt cement within 5 seconds at 140°F (60°C). These five standard grades are 40 - 50, 60 - 70, 85 - 100, 120 - 150, and 200 - 300 which correspond to the allowable range of penetration for each grade. Grading of asphalts based on penetration has largely but not completely been replaced by viscosity. There are two series of viscosity grades by which asphalt cement is available. One consists of grades AC-2.5, AC-5, AC-10, AC-20, AC-30, and AC-40. The numerical values correspond to viscosity in hundreds of poises at 140°F (60°C). The other series consists of grades AR-1000, AR-2000, AR-4000, AR-8000, and AR-16000 with the numerical values indicating the viscosity in poises but with the viscosity being measured after the asphalt has been subjected to conditions occurring in hot mix asphalt concrete plants. The AR stands for aged residue. The various grades of asphalt cement are often obtained by refinery production of both high and low viscosity straight reduced asphalt and then blending the two base grades as required. Cutback asphalts are classified into three types based on the relative speed of evaporation of the cutter stock. Rapid curing (RC) cutback asphalt is a blend of asphalt cement and a cutter stock in the naphtha boiling range. Medium curing (MC) cutback asphalt utilizes kerosene or similar boiling point material. Slow curing (SC) utilizes higher boiling point cutter stock or can also be produced directly in the refinery. Figure 1 illustrates the various grades of cutback asphalt. The types (RC, MC, SC) indicate the relative speed of evaporation and the grades (70, 250, 800, and 3000) indicate the minimum allowable kinematic viscosity in centistokes at 140°F (60°C). One additional grade, MC-30, serves as a special priming grade in some sections of the United States. The maximum allowable viscosity for each grade is twice the minimum allowable value. The most viscous grades of RC-3000, MC-3000, and SC-3000 are only moderately less viscous than the lowest viscosity graded asphalt cement AC-2.5. The least viscous grades (RC-70, MC-30, MC-70, and SC-70) may be readily poured at room temperature and have the consistency of heavy dairy cream. Emulsified asphalts are produced by mechanical milling of warm asphalt cement in a device called a colloid mill and mixing the very small asphalt particles in water containing an emulsifying agent. Emulsified asphalts have advantage over hot asphalt in that they can be used with cold as well as heated aggregate and with aggregate that is dry or damp. This type of asphalt is outside the scope of normal refining/terminalling operations and is, therefore, not discussed further herein. Air blowing of asphalt cement at high temperature produces an asphalt of higher than normal softening point. Blown asphalts are used for industrial and specialty purposes rather than for paving. Because the higher softening point is the most desirable property of blown asphalts, they are usually classified in terms of softening point test rather than viscosity or penetration. Nevertheless, their overall specification includes both softening point, and penetration at three temperatures for overall quality control. The higher softening point grades of blown asphalt have very high melting points, are very viscous, and are difficult to handle except at high temperature. For this reason, oxidized asphalt is more difficult and costly to store or ship in bulk liquid form than most other commercial grades of asphalt. This provides incentive to locate asphalt oxidizer facilities at the terminal or close to its point of final destination, rather than in the refinery. Although outside the scope of this Design Practice, it should be mentioned that asphalt oxidizers should be carefully designed and operated to avoid potentially serious safety incidents. Oxidizer Safety is covered in EE.85E.83 and 91ECS 3016. The specific gravity of asphalt at 60°F (15.6°C) ranges from about 0.93 to 1.05.

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ASPHALT (Cont) GENERAL The most common asphalts handled at ExxonMobil plants are asphalt cement and cutback asphalt. Emulsified asphalt is generally not handled. Air blown (oxidized) asphalt is handled at a limited number of locations. Loading systems are provided for tank truck, rail tank car, and marine transport of liquid asphalt. In addition, asphalt is also handled in solid form after drums are filled. Drum filling and loading are not covered by the Design Practices. Asphalt is also used as fuel within the refinery where advantageous or necessary to do so. Fuel Systems are covered in Section XXV. The information contained in Section XXIII-A, Basic Loading Systems, should be referred as it is not repeated herein. Similarly, Section XXII-B of the Design Practices, Atmospheric Storage, and Section XV-B, Minimizing the Risks of Fire, Explosion, or Accident, contain information pertinent to asphalt storage. Safety issues related to asphalt handling are covered in Design Practice Sections XV-B and J.

MODES OF PRODUCT LOADING Asphalt is top loaded into trucks and rail cars through open hatches without emissions control. The loading arm must be restricted (e.g., by rods or chains) to prevent movement due to reaction forces. Asphalt trucks are uncompartmented and range up to approximately 5,000 gal (20 m3) per tank. Some are equipped with heaters. When they are not equipped for heating, in-line loading heaters may be required to compensate for heat losses on long hauls. Rail cars are also uncompartmented and range up to about 10,000 gal (40 m3). These are usually provided with steam heating coils which can be placed in service at the final destination prior to unloading. Rail cars have traditionally been equipped with internal steam coils that heat the contents of the car directly. Some cars have external steam coils that heat the tank shell or are equipped with thermostatically controlled electric immersion heaters. Asphalt trucks and rail cars are top loaded through open hatches. The loading arm or hose should be equipped with a locking device to insure the arm cannot pull out of the hatch. Heated barges and tankers are also used for asphalt transport. Barges are generally single cargo shipments in the 10 to 20,000 barrel (1,600 to 3,200 cu m) range. Tanker shipments of asphalt are often combined with fuel oil movements although dedicated tankers ranging in size from 5,000 to 30,000 DWT are in service. Parcel size is dependent on logistics considerations. Prior to loading, the receiving container/vessel should be inspected to confirm that it is free of water, light hydrocarbon liquids or any other material that will vaporize when filled with hot asphalt. Low initial loading rates should be used to detect frothing which usually occurs due to residual water or light hydrocarbons in the tank. Loading temperatures should be limited to avoid excessive vapor evolution. These vapors may contain toxic concentrations of H2S. Splash loading of asphalts in tank cars and trucks is permissible since asphalts are not static accumulators. In contrast to large storage tanks, the space within tank car and truck compartments is small enough so that formation of a charged mist is not a concern. Grounding of tank cars and trucks is not necessary. However, from a general safety standpoint, loading operations should minimize misting. The considerations given in Section XXIII-A regarding loading rates apply to asphalt as well.

CONTAMINATION AND PRODUCT SEGREGATION Contamination is the most common reason for asphalts failing to meet specification. Conditions such as low flash point, low viscosity, and high penetration are typical of solvent type contamination. For example, experiments indicate that 0.1% diesel oil in asphalt cement can lower the flash point by up to 50°F (28°C). Flash point of asphalt is an important safety related specification. Positive separation of piping systems for penetration grades and cutbacks/blending solvents is required by eliminating or not introducing interconnections. If this is not practical, blinds are required to prevent contamination that could lead to product degradation and safety problems involving volatile components and hot asphalt.

STORAGE AND LOADING TEMPERATURE Even in hot climates, asphalts are stored and loaded at temperatures above ambient to facilitate handling. Table 2 of DP, Section XV-B, provides guideline temperatures for the storage and handling of asphalts. The source of this information is API Publication 2023, Guide for Safe Storage and Handling of Heated Petroleum Derived Asphalt Products and Crude Oil Residua, the Asphalt Handbook issued by the Asphalt Institute, and ER&E Letter No. 91 ECS 3016, Safe Asphalt Operations Study. Oxidized asphalt is produced at a temperature of about 425°F (218°C). The storage and loading temperature should be limited to 425°F (218°C) maximum for oxidized asphalt. All other asphalts are handled at lower temperatures as shown in Table 2. All metal loading arms are recommended for hot asphalt service.

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SPECIAL PRODUCT LOADING SYSTEMS DESIGN PRACTICES

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ASPHALT (Cont) TEMPERATURE MAINTENANCE AND CONTROL ➧

Asphalt systems are predominantly heated by steam, circulating hot oil, or a combination thereof. Electric heating is rarely used on a plant wide scale, but may be considered in remote locations where fuel gas or steam may not be available. Fired heaters utilizing combustion heating are also used occasionally. These heaters can be located at the storage tank, in the suction line to the loading pump, or in the pump discharge line enroute to the loading rack. Because these heaters fire fuel, and are generally located in dispersed and relatively remote areas rather than one centralized location, they may be a safety concern. Where used, this type of heater must be provided with a safety shutdown system. The choice of heating media (steam, hot oil, or fired heater) is determined on the basis of the heat requirements for the overall storage, blending, and loading system. As winter tank heating loads are generally much greater than loading system requirements, overall system considerations most often determine the type of heating used for loading line tracing. Overall system considerations include temperature requirements of asphalt, heat duties, availability and characteristics of steam, safety, and economics. Hot oil heating of asphalt storage is inherently safer than steam heating because of the hazards associated with steam/condensate vaporization in the event of heater leakage within the tank. If natural circulation within the tank is not adequate, consider use of forced circulation to provide relatively uniform temperature & prevent stratification. Hot oil systems are composed of a furnace(s) with associated fuel system firing controls and safeguards, and a hot oil circulation system with associated pumps. Separate pumps are usually required for storage tank and line tracing circulation. The hot oil is circulated to and from heating coils within each tank as well as the line tracing system. Hot oil flow to each tank is set by the temperature controller. A hot oil system is of higher investment than a comparable steam heating system where steam is readily available. The hot oil facilities also introduce another set of operating and maintenance complexities. Nevertheless, site specifics may require that hot oil be used rather than steam. Line tracing is of the external type. Internal steam tracing is not permitted for safety and maintenance reasons per GP 3-5-1. Steam jacketing is seldom justified. Heat tracing media should be limited to 500°F (260°C) maximum. Long loading lines are difficult to heat effectively particularly when the steam source is from one end only. Localized use of electric tracing is sometimes used at the end of a long run in order to eliminate local cold spots. In order to minimize the risk of asphalt setup, long lines are often air blown into tankage to clear the line. This may be necessary during periods of extreme cold or in areas where the seasonal nature of the asphalt business will idle the system for extended periods. Lines may also be blown in systems which include a common line for multiple products. Compressed air of nominal 100 psig pressure is expanded into the loading line at the tank truck or marine berth location in order to blow the line contents into the appropriate storage tank. Precautions to be followed in connection with asphalt line blowing are covered in Section XXII of the DPs, Storage Facilities, Section XV-B, Minimizing the Risks of Fire, Explosion, or Accident, and GP 3-5-1.

PUMPS Both centrifugal and positive displacement pumps have been successfully used in asphalt service. Pump selection should be based on the criteria given in Section X of the DPs, Pumps. Viscosity, solids content and temperature are key asphalt characteristics for assessing pump applicability and performance. The need for pump warm-up facilities per GP 3-3-2, steam jacketing, and facilities for purging the pump of asphalt with a lighter material immediately prior to idle periods should also be evaluated. Per GP 3-5-1, pumps and piping manifolds must be located outside of diked areas, however, pumps may be located within the diked area to limit the suction line pressure drop of heavy viscous stock. In such cases, remote shutoff facilities must be provided outside the diked area.

PRODUCT MEASUREMENT Both weigh scales and positive displacement meters (PDM) are each acceptable for product measurement and billing purposes. Local requirements or practices such as road and rail transport regulations often set the preferred alternative. Because of the relatively high viscosity of asphalt, the maximum capacity of the PDM must be derated and a greater pressure drop should be considered as a result. Air eliminators in high viscosity service must be physically very large to be effective and are, therefore, usually not installed for this reason.

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LIQUEFIED PETROLEUM GAS (LPG) MODES OF PRODUCT LOADING LPG is handled in two types of closed systems, pressurized and refrigerated. Refrigerated storage and associated loading systems are used where economic study shows them to be more attractive than pressure storage. Refrigerated systems are generally used in large volume operations or where local regulations do not permit pressure storage. Pressurized LPG barges and coasters carry cargoes ranging up to 5,000 DWT; refrigerated coasters and tankers range from about 3,000 to 80,000 DWT. Pressurized tank trucks and rail cars range in capacity up to 11,600 gal (45 cu m) and 33,500 gal (125 cu m), respectively. LPG is loaded using liquid filling or spray filling methods. Splash filling defined in Section XXIII-A is not done for LPG. Liquid filling requires two connections on the transport vehicle, one for the liquid line and one for the vapor balance line. For liquid filling, a standpipe extends to near the bottom of the carrier so that liquid enters below the liquid surface or as in the case of a tank truck, the liquid connection enters the truck at or near the bottom. Spray filling is done by loading through the carrier's spray fill line and normally a vapor balance line is not used. Loading areas are often remote and require long vapor return lines back to the storage area which may not be justified because of cost. Systems without a vapor return line usually require a higher head loading pump to overcome pressure drop across the spray nozzle and back pressure in the receiving carrier's vapor space. Depending on ambient temperature, product vapor pressure, and receiving carrier's pressure rating, it may be necessary to reduce loading rate to avoid lifting the pressure relief valve on the transport vehicle. The various tank truck and rail car connections are described in OTHER LITERATURE, References 6 and 7. The loading connections, both liquid and vapor, for tank trucks are generally at a level within easy reach from grade. For rail cars, all connections are generally in the dome at the top of the rail car. Loading rate considerations are given in Section XXIII-A. NPSH considerations will have major impact on storage vessel elevation and on loading pump location, elevation, and type.

SYSTEM DESIGN CONSIDERATIONS AND ALTERNATIVES

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The loading system designer starts with knowledge of the type of storage facilities being provided, pressurized or refrigerated, and the related type of vessel being used for LPG transport. Rail cars are pressurized type transport whereas marine vessels and tank trucks may be pressurized or refrigerated. In cases where LPG production rate is high or transport parcels are large, studies show that refrigerated storage is more economic than pressurized storage. A typical marine loading system is shown in Figure 2. For both pressure and refrigerated systems, a vapor return or balance line is required. For refrigerated systems, a separate circulation pump and line are sometimes provided to cool down the system in advance of main loading pump use. Vapors displaced during loading are returned to onshore storage. For refrigerated vessels, the ship may be equipped with sufficient on-board refrigeration to liquefy vapor generated when enroute or when being loaded. Vapor line sizing requires consideration of the cargo tank safety valve setting in order to avoid releases at the desired loading rate. Some vessels are also provided with vapor blowers to assist in transferring vapor to onshore storage during loading. Alternatively, a shoreside blower may be required or is economical for systems involving large and/or long vapor return lines. In cases where several grades of LPG are handled, the use of a common vapor return line may be adequate as an alternative to providing separate vapor return lines. Due to the specialized nature of LPG carriers, fleet composition should be established as the basis for design, particularly for refrigerated carriers. The more common refrigerated LPG systems are for butane, and propane. Storage conditions for these products are about 30°F (-1°C), and -45°F (-43°C), respectively, at near atmospheric pressure. Consideration should be given to designing new systems for propane vapor pressure. The difference in cost, compared with butane conditions, is not significant. However, if at a later date a butane system would be changed to propane service, this could only be done at high cost. Hoses should be used where no other method of product transfer is practical, such as on hose reels on small bulk delivery trucks. Hoses should comply with applicable standards (BS 4089 Hose Standards), be designed and certified specifically for LPG (in liquid and vapor phase) and the materials used in fabrication should also be certified resistant to the action of LPG and should be corrosion resistant. Pressurized road and rail cars are equipped for either liquid space or vapor space (spray) loading. A vapor balance connection back to the storage vessel is usually employed for loading into the liquid space. Loading into the vapor space is sometimes done without a balance line as the spray and agitated liquid surface contacts and condenses the vapor as the level rises. Spray loading does not completely eliminate vapor space back pressure so this must be considered in the design. The large majority of LPG transport vehicles are equipped with safety valves but in certain cases this overpressure protection is not permitted. In either case, the loading system should be designed to eliminate overpressure conditions in the transport vehicle. Minimizing overpressure of the system requires careful design of the pump and downstream piping and fittings to minimize the shut-in head. In addition to reviewing the loading system hydraulic loss, the designer should carefully review the required pressure at the tank or railcar nozzle. If this is not available at the time of intial design, the required pressure at full loading rate can be estimated by combining pressure loss in the piping system, the vapor pressure, plus an allowance of 15-25 psi for vapor space or spray loading. Note that the required loading pressure needs to be confirmed during detailed design stage when ExxonMobil Research and Engineering Company – Fairfax, VA

ExxonMobil Proprietary PRODUCT LOADING SYSTEMS

SPECIAL PRODUCT LOADING SYSTEMS DESIGN PRACTICES

Section XXIII-B

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LIQUEFIED PETROLEUM GAS (LPG) (Cont)

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appropriate data is available. Depending on loading pump and vehicle characteristics, an independent PHCO on the loading arm should be considered as a means of closing the MOV in the loading line at the vehicle. Where pumps are used for LPG loading care must be taken to ensure that the system is adequately vented. Pumping operations are typically intermittent and heat input from ambient conditions can lead to vapor build up at high points in both the pump suction piping and pump casing. Preference is to install suction and pump casing vents which are permanently vented back to the suction vessel(s). If a low flow recycle is provided to protect the pumps during low or no flow situations this should be routed back to the suction vessel, preventing excessive heat build up and vaporization in the pump suction. In addition, if custody metering is used to control loading, consideration should be given to locating recycle connection immediately upstream of the meter. This minimizes the possibility of vapor being routed to the custody meter. Safety issues related to marine, tank truck and rail car loading of LPG are covered in Section XV-J, Safety in Plant Design Docks, Loading Racks and LPG Storage Facilities. Topics include loading arms, emergency shutdown, overfill protection, and control of ignition sources.

PRODUCT MEASUREMENT Marine parcels of LPG, both refrigerated and pressurized can be measured either by metering or gauging. Rail car and tank truck parcels can be measured by metering, receiving vessel gauging, or weight. The choice of metering or weighing depends on the basis for custody transfer (mass or volume). Metering of LPG may require that a back pressure controller be located downstream of the meter in order to prevent the liquid from flashing across the meter. Also, when using a vapor balance line and meter for custody transfer, consideration should be given to the need for locating an orifice meter in the vapor return line. This meter may be necessary to obtain the net quantity of material transferred. Vapor quantity is often estimated rather than measured depending on vapor quantity relative to parcel size and cost considerations. Turbine meters are preferred over positive displacement meters for liquid measurement based on improved performance with more recent installations. Gauging of pressurized rail cars most often involves the use of a slip tube gauge. The slip tube gauge consists of a small steel tube with valve that runs inside the tank and ends at a level set by the loading operator. The operator determines the level when liquid begins to flow from the tube. Some locations use only the slip tube gauge for all transfer operations. Tank trucks are generally equipped with 2 types of level gauges. The first type consists of 4 fixed tube gauges which operate similar to rail car gauges. Each of the tubes ends at a calibrated level such as 80, 86, 90 and 92% of the truck's capacity. The second type is an adjustable gauge which is either an adjustable tube gauge or a float gauge. Weighing of tank trucks for custody transfer is a common practice within the U.S. and Europe. In Europe, rail car loading by weight is also normally done. Rail car scales are not utilized in U.S. ExxonMobil terminals. These sites load rail cars by gauging the product height using the slip tube gauge.

ODORIZING Local regulations generally require odorizing of LPG before it reaches the consumer. Among exceptions are some industrial sales where odorant would be detrimental to subsequent processing operations. Odorizing is commonly done during the loading operation. Ethyl Mercaptan is recommended as the odorant. Careful control over the quantity of odorant added is necessary to ensure that the smell of LPG is indeed detectable yet is not a nuisance due to overdosing. Ethyl mercaptan addition of 1 - 2 lb per 10,000 gal of LPG (20 - 40 wppm) is generally adequate for this purpose. The quantity of odorant, established based on parcel size, can be premeasured into a calibrated pot and bled into the line during loading. Agitation during loading, transit and unloading is sufficient to ensure thorough mixing. Skid-mounted odorant injection units are also available from specialty vendors. The skid includes the odorant receipt drum, calibration pot and sight glass, controlled volume pump for odorant injection, and associated instrumentation. The odorant pump rate is set in proportion to a signal from the LPG loading meter. Materials used in these systems are stainless steel or internally coated carbon steel lines and drums. The odorant storage drum requires nitrogen blanketing due to flash point safety considerations and the desire to minimize system corrosion. An alternative to use of a pump for odorant injection is to use nitrogen pressure at the drum as the motive force for injection. Odorant systems should be designed to minimize leakage or spillage and to provide a means of containing and neutralizing such leaks. Household bleach is often used as the neutralizing agent.

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SPECIAL PRODUCT LOADING SYSTEMS DESIGN PRACTICES

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LIQUEFIED PETROLEUM GAS (LPG) (Cont) RAIL CAR LOADING AND UNLOADING Refinery LPG handling may include unloading as well as loading. Unloading methods involve the use of a pressuring medium such as product gas or the use of a liquid pump. Generally, all unloading connections are located within the dome on the top of the car. When a pump is used, the liquid must flow from the bottom of the tank up through a dip tube to the dome and then back down to grade to the pump. The use of a pressurizing gas is simpler than a pump. The gas can be provided by compressing LPG vapor from the receiving tank which is then sent to the rail car to provide the pressure differential required for unloading. Alternatively, a separate vaporizer which is fed by a higher pressure liquid could be used. Figure 3 illustrates these two configurations. Nitrogen is another pressurizing gas alternative. However, since nitrogen is non-condensible, an undesirable safety valve lifting situation may occur during subsequent spray loading operations without a vapor return line. A device called an unloading pot has been used to detect when the rail car is empty and to prevent vapors from entering the storage tank. This pot is included in Figure 3. It is especially important to prevent non-condensable pressurizing vapor to enter the sphere. As long as the liquid level in the pot remains above the cut-out level, the control valve is open. Once the car is empty and vapors enter the pot, the level drops and the instrumentation closes the valve. It may be necessary to depressure the pot to the flare at the start of unloading if it is full of vapor. New or renovated loading racks should be equipped with swivel hard arms for liquid and vapor connections. Hard arm material should be Schedule 80 Seamless Steel - ASTM Specification A-106, Grade B. The rail car tank can be considered adequately grounded through the connection of carriage, and wheels. The two rails of the siding should be permanently bonded to the metal loading rack. The unloading rail spur should be insulated from the main track to guard against stray currents which might cause a spark.

TRUCK LOADING AND UNLOADING New truck loading and unloading points should be equipped with swivel hard arms and break-away connections for liquid and vapor return lines. In special cases where a variety of customer trucks are loaded, the additional use of hoses may be necessary to accommodate the diversity of connection points. Hose connections for bulk transfer should be designed such that they can be emptied of liquid after loading. They may be left under vapor phase. Hard arms may be left under liquid, however, they need thermal expansion protection. The piping system should be designed to accommodate maximum forces originating from a truck drive-away rupturing the break-away connections. Also, the loading rack area should be protected against accidental crash by trucks. An electrostatic grounding (earthing) point should be provided at each loading and unloading location. A permissive grounding (earthing) system is preferred for road vehicles at each loading rack. This should ensure that the loading pump should only work as long as the grounding contact is intact.

MARINE LOADING AND UNLOADING The design of marine loading and unloading facilities is specific to both the individual pier and the marine transportation unit(s) selected to serve it. A number of design issues, both general for marine berths and specific to LPG berths should be considered, such as site selection, berth layout/spacing, and berth pier and pipeline design to reduce the risk of vessel collision with loading platforms, transfer lines and berthing structures. Information on such issues is available in the Marketing Engineering Standard EE.3M.86, Marine Facilities, Design, Specification and Evaluation, and DP Section XV-J, Safety in Plant Design Docks, Loading Racks and LPG Storage Facilities. Pumps are generally used for loading vessels. Vessel unloading is usually by compressor for small vessels and by ship pumps for large vessels. Marine Cargo Dock Hose should not be used for refrigerated or partially refrigerated LPG Cargo Transfer. For pressurized LPG, the use of all steel Marine Loading Arms is recommended, however, under certain circumstances, (i.e., when the throughput rate and the volumes are small and cargo transfer is infrequent) use of Marine Cargo Dock Hose may be acceptable for existing facilities. A formal LPG Cargo Transfer Risk Assessment can be of help in determining whether use of Marine Cargo Transfer Dock Hose may be used. ER&E's Memorandum on LHG Marine Cargo Transfer Fire/Explosion Risk Assessment Procedure (93 CMS2 010) can serve as a starting point for such an assessment. GP 3-11-1 should be used for the purchase specification of Marine Cargo Dock Hose. The ER&E Report EE.76E.92 provides details on the purchase specification, inspection and retirement criteria. The ER&E Report EE.40E.94, Marine Dock Hose Technology and Practice Training Video with its Companion Application Guide, is also a source of useful information regarding hose purchase specification, inspection and testing, hose handling and retirement criteria.

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LIQUEFIED PETROLEUM GAS (LPG) (Cont) Steel Marine Loading Arms should be used to conduct cargo transfer at new and renovated facilities. Hard arm material should be Schedule 80 Seamless Steel - ASTM Specification A-106, Grade B. GP 3-11-2 covers the requirements for the design of Marine Loading Arms and associated equipment [such as Quick Connect / Disconnect couplers, Accessories, Range Monitor Systems and Emergency Release System (ERS)]. Emergency Release Systems (ERS) are recommended for LPG arms. An ERS consists of dual isolation valves at the ship/loading arm connection. The ERS allows for rapid, automated disconnect in the event of an emergency with little loss of product. As general guidance, circumstances where LPG transfer without an ERS may be used are as follows: 1. Facility is a loading terminal, and 2. Arm is equipped with a range monitoring system which shuts down loading pumps and closes remote operated block valve at base of loading arm in event vessel begins to approach limits of loading arm operating envelope, and 3. Total arm contents that might be spilled in the event the arm is damaged by ship motion is less than 500 liters of LPG, and 4. Surge analysis has been conducted to ensure there is minimal risk of pipe rupture in event of emergency shutdown described in Item 2 above, and 5. Probability of excessive ship motions is minimal based on historical records and average wind and current conditions at the site. 6. Relatively infrequent marine transfer. The decision whether to equip LPG Loading Arms with ERS can be made after an LPG Cargo Transfer Risk Assessment. The considerations described above are assessed in detail in ER&E's Memorandum on LHG Marine Cargo Transfer Fire/Explosion Risk Assessment Procedure (93 CMS2 010). Marine Pier Installations The berthing operations should be reviewed to establish the number of tugs and other berthing aids (bow thrusters, berthing monitoring systems). Issues related to rapid and fail safe communications, including providing the ship with a control box to shut down shore pumps and close EBVs in the event of an emergency, should be considered. Quick release mooring hooks should be considered, so that the vessel can be removed from the berth area quickly in the event of an emergency. An anemometer should be provided to monitor wind conditions, so that cargo transfer can be shut down at pre-determined wind limits. Flammable gas detectors should be installed in the berth loading/discharge manifold area to detect product leaks and sound the alarm in the berth area as well as the control center. It is recommended that the designer seek assistance from ExxonMobil Research and Engineering for guidance in LPG marine facilities matters. Electrical insulating flanges are required for stray current protection on marine loading and unloading lines for both vapor and liquid. Installation should be such that the pier piping is insulated from both the on-board piping and the shore piping (the latter to maintain the separation of the pier cathodic protection system). Normally, LPG Cargo Transfer Equipment is empty when not in use. Appropriate piping for depressurizing and venting should be included at the pier manifold. Also, depending on the operations and vessels involved, vapor return lines may be required.

MOLTEN SULFUR BACKGROUND Liquid sulfur produced in refineries is a by-product associated with fuels product quality specifications and environmental regulations. Several factors determine the quantity of sulfur produced at a location. These include crude throughput, quality of crude (% sulfur), governmental regulations concerning distillate fuel standards, and local environmental regulations regarding stack emissions. The upper range of refinery produced sulfur at one location is currently 500 - 1000 tons per day (TPD) with 100 TPD of sulfur production being common. Refinery produced sulfur accounts for about 15% of worldwide sulfur production. The key sulfur product quality specifications are purity, ash, and carbon. Liquid sulfur produced in the Sulfur Recovery Unit (SRU) is normally rundown at about 290°F (143°C) to a below grade concrete storage pit located within the battery limits of the SRU. The pit generally accommodates from 1 to 3 stream days of sulfur production. The pit includes steam coils for heating the sulfur, injection line for degassing catalyst, snuffing steam supply connections, utility air or nitrogen supply, and pit sweep gas outlet to the SRU incinerator. There is usually one pit per SRU. From the storage pit(s), liquid sulfur is typically pumped to an offsite storage tank of greater capacity. A loading rack near the storage tank is used for product shipment. In situations involving small sulfur production rates, loading may be performed directly from the sulfur pit in the SRU. While this arrangement minimizes capital cost, the impact of truck traffic in the onsite area requires evaluation.

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MOLTEN SULFUR (Cont) MODES OF PRODUCT LOADING Liquid or molten sulfur is shipped by tank truck, rail car, barge and tanker. Sulfur is loaded into tank trucks and rail cars through open hatches without emissions control. Dedicated liquid sulfur carriers are used since the presence of trace amounts of water, hydrocarbon, or other chemicals in the carrier could be very hazardous. Tank trucks are often in the 10 to 20 ton size range with occasional use of 40 ton sizes. Rail cars are often in the 65 to 85 ton size range with occasional use of smaller cars. Both truck and rail cars are usually single compartment type. River barges are often in the 1,000 to 2,500 ton size range but barge tows will be substantially larger. Ocean-going barges and tankers are in the 8,000 to 25,000 ton size range. Liquid sulfur loading rates vary from about 40 tons per hour for trucks to about 1,000 tons per hour for marine shipments. One or two loading spots are generally adequate for truck or rail car shipments. The considerations given in Section XXIII-A for determining loading rate apply to liquid sulfur as well.

TEMPERATURE MAINTENANCE The loading system should be designed to maintain the liquid sulfur within the range of 270°F (132°C) and 290°F (143°C). Molten sulfur will solidify at temperatures below about 240°F (116°C). Above 318°F (159°C), sulfur viscosity increases sharply and pumping becomes difficult. Figure 4 provides pressure drop information. Key sulfur properties are as follows: Specific Gravity @ 270°F (132°C)

1.8

Viscosity @ 250°F (121°C)

11.5 cP

270°F (132°C)

9.0 cP

290°F (143°C)

7.5 cP

Melting Point 230 - 240°F (110 - 115°C) Bulk Density (solid form) 65 - 80 lb per cu ft Steam jacketing and electric heating have been used successfully for heating molten sulfur lines. The choice depends on steam availability in the area, local plant preference, and economics. For long lines, electric heating capital cost will be considerably lower than comparable steam jacketing costs. External steam tracing is not as effective as jacketing and is not recommended. Proper installation is particularly critical to successful use of electric heating systems. Of the various types of electric heating systems, impedance heating has been applied most often to sulfur. In these cases, steam jacketing is used for heating pumps, valves, and loading arms since impedance heating of large mass equipment is not practical. Impedance heating is the only pipe-line heating system that does not require removal and replacement of pipe insulation if failure of the system occurs. Saturated steam at the 50 to 60 psig (345 to 415 kPa gauge) level should be used to maintain the molten sulfur within the required temperature range noted above. Steam jacketing or tracing of the loading system should be thorough including lines, valves, flanges, loading arms and pumps. Steam jacketed or traced lines should be supported and insulated so that there are no uninsulated sections. The piping layout should not have dead legs and should permit lines to be drained back to the sulfur pit wherever possible. Lines should be sloped about 1 - 2% to permit gravity draining. Where unavoidable, low points should be provided with steam jacketed drains. Within onsite & offsite areas, rod out connections are usually provided at every elbow. Offsite loading lines are often long, making it impractical to install rod out connections at frequent intervals. Therefore, reliable heating systems are particularly important.

PRODUCT MEASUREMENT Mass is the usual basis for the sale of sulfur. However, local regulations or preferences may dictate the billing method. Tank truck and rail car parcels can be measured by weighing, positive displacement metering, or direct mass flow metering. Because of the low rates normally encountered, metering is the lower investment alternative unless the weigh scale can be shared with other products such as asphalt. A coriolis meter, which provides a direct measurement of mass flow without the need for compensation, is suitable for sulfur metering. Coriolis meters measure the twisting force generated by a fluid as it flows through a sensor tube that vibrates perpendicular to the direction of flow. The magnitude of the twist is directly proportional to the mass flow rate through the sensor.

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MOLTEN SULFUR (Cont) LOADING ARMS AND PUMPS Steam jacketed all metal loading arms are recommended for loading sulfur into tank trucks, rail cars, and marine vessels. Marine loading arms are usually provided with a nitrogen purge connection to assist in draining the arm. Loading pumps, such as those made by Lewis Pumps, are typically steam jacketed as well. Block valves should be either ball or plug type.

SAFETY CONSIDERATIONS Claus Plant produced sulfur entering the pit may contain 200 - 400 wppm of H2S. H2S levels can be reduced to 10-15 wppm by using the ExxonMobil System for Degassing Liquid Sulfur, purging, and agitating the sulfur pit. Nevertheless, safety precautions and practices are still necessary when handling degassed sulfur. H2S is a toxic gas that could build up to lethal concentrations in vapor spaces over a period of time and has a low explosive limit in air. In terms of safety facilities associated with loading system design, the following should be provided: •

H2S alarms should be located at strategic places in the loading area.

•

Liquid sulfur is a static accumulator. The loading arm should be capable of extending to near the bottom of the truck or car during loading to avoid splash loading. For marine vessels, internal loading pipes extend to near the bottom of the vessel to prevent excessive agitation or splashing of liquid sulfur during loading.

•

Liquid velocity in the loading arm should be limited to about 3.3 ft (1.0 m) per second until the outlet is submerged. A ramp up and ramp down flow controller is generally provided to ensure this velocity criteria is maintained.

•

The remote start/stop of the loading system should be located upwind of and a safe distance away from the truck/car hatches (at least 5 ft). Although opening and closing of tank hatches are potentially hazardous operations, proper operating precautions and practices are sufficient to preclude the need for hatch exhaust facilities that are vented to a safe location.

SOLID SULFUR Market conditions and refinery location may require solidification of the liquid sulfur prior to shipment. In this situation, ocean going bulk carriers of about 10,000 to 20,000 ton capacity are generally used for transport of the sulfur. At other locations, rail car transport of solid sulfur from the plant to an industry terminal having water access is common. Within the refinery, facilities are, therefore, required for solidification, storage, and reclaim/loading onto ships or rail cars. These solids handling facilities have considerably higher capital cost than the comparable liquid handling system. Table 1 summarizes the available solidification processes. Liquid sulfur can be solidified using a wet process, where there is direct contact between the sulfur and water, or a dry process. The dry process can be the direct cooling type, where air cools the sulfur by convection, or the indirect type, where the sulfur is cooled by conduction after being deposited on a steel pan conveyor. In the latter case, molten sulfur droplets are fed onto the top side of a moving steel belt which is cooled from the underside by water sprays. There is no water contact with the sulfur. If solid sulfur is to be transported by ship, it must have a very low moisture content due to corrosion concern. Wet formed product is usually not acceptable for ocean shipment unless it is dried thoroughly, which is very expensive. Dry processes for solidifying sulfur are, therefore, highly preferred. Sulfur dust is another major consideration in solidification process selection because of safety and environmental concerns. Sulfur dust can be inherently produced in the solidification process and indirectly as a consequence of the friability of the product. Solidification methods referred to as flaking or slating produce a product that is friable and, therefore, dusty during handling. The maximum sulfur forming capacity of the steel belt dry type system is about 120 tons per day per unit. Product consists of non-dusty, free-flowing pellets having a diameter of 1/8 to 3/16 in. (3 to 4 mm) and a height of 1/8 in. (3 mm). The maximum capacity of the air cooled dry type system is about 1,000 tons per day per unit. Selection of the solidification process is a function of sulfur production rate, plot space, dusting characteristics of the product and economics. The amount of required inplant storage is primarily dependent on parcel size. The storage system will be of the silo or in-building type since open storage of sulfur will probably be environmentally unacceptable. The reclaim and shiploading system is normally sized to load the maximum parcel in 24 hours but this guideline requires evaluation based on site specifics. A solids handling pier, separate from the liquid handling piers, is also required.

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TABLE 1 SULFUR SOLIDIFICATION PROCESSES

NOTES

WET (W) OR DRY (D)

CAPACITY PER UNIT

Flaking

(1)

D

Low

Slating

(2)

W

Medium

Pellet Forming

(3)

D

Low

Prilling

(4)

(4)

Very high

Granulating Drum

(5)

D

High

PROCESS

PRODUCT SHAPE AND SIZE Irregular, very thin, dusty Irregular, 1/4 in. (6 mm) thick, dusty Regular & consistent, non-dusty, strong Spherical, size varies, can be dusty Spherical, size varies, good strength quality

Notes: (1)

The flaking process utilizes a rotating internally water cooled drum that is partially submerged in a molten sulfur bath. A thin film [~.012 in. (0.3 mm)] of sulfur is solidified as the rotating drum surface rises above the bath level. A doctor blade then scrapes the film of sulfur off the drum. Flakes break easily and can be wind blown if stored outdoors.

(2)

In the slating process, liquid sulfur is fed onto a flat rubber or steel conveyor belt by means of a weir feeder. The sulfur is cooled and solidified into a continuous 1/4 to 3/8 in. (6 to 9.5 mm) thick layer after being submerged in and withdrawn from a cooling water bath. As the continuous strip of solid sulfur is discharged from the end of the conveyor belt, it breaks into very irregular pieces whose long dimension is 1 to 3 in. (25 to 75 mm). There are many variations to the cooling portion of the slating process. Water is sometimes applied beneath the belt as well as directly on the sulfur. Air cooling is also used.

(3)

In the pellet-forming process, individual pellets (droplets) of liquid sulfur are deposited on a stainless steel belt conveyor. Heat is removed from the sulfur using water sprays that impinge on the underside of the belt and do not contact the sulfur. The sulfur pellets are easily removed from the belt using a doctor blade (scraper).

(4)

In the prilling process, liquid sulfur is sprayed downward at the top of a tower. Upward flowing forced air cools the sulfur as it falls down the tower. For sulfur, this process poses severe safety risk and should not be considered for refinery application. Instead of using air as the cooling source, liquid sulfur can also be sprayed into a liquid quench tank containing water. The product has an irregular “popcorn" shape and is porous and fragile. Additives are sometimes used in the quench tank for the purpose of waterproofing and improving the strength of the product.

(5)

The granulating drum is a seed process in which molten sulfur is sprayed into a horizontal drum that also receives solid sulfur fines. The molten sulfur coats the solid sulfur fines increasing the overall pellet size. Cooling is by means of concurrent forced air flow through the drum. The air passes through a cyclone which removes fines carryover from exhaust air prior to being discharged into atmosphere or to another cleanup step. Solid sulfur pellets of various sizes are discharged from the drum and then screened to remove fines and oversize material. Product is dry, free-flowing and has good strength. Cooling air is sometimes humidified to maximize cooling. As a result, this process is sometimes referred to as wet.

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FIGURE 1 FLOW PLAN FOR THE MANUFACTURE OF VARIOUS ASPHALT PRODUCTS Naphtha

Atmospheric Pipestill

Kerosene Gasoline

Crude Oil

Vacuum Pipestill

Residual Fuels

Road Oils SC-70 SC-250 SC-800 SC-3000

Vacuum Gas Oil

Paving Grades Furnace

Kerosene Asphalt Cements Penetration Grades 40 - 50 60 - 70 85 - 100 120 - 150 200 - 300

Straight Reduced Asphalts

Viscosity Grades AC-2.5 AC-5 AC-10 AC-20 AC-40

Emulsion Flux 180 - 200

Naphtha

Medium Curing Cutback Asphalts MC-30 MC-70 MC-250 MC-800 MC-3000 Rapid Curing Cutback Asphalts RC-70 RC-250 RC-800 RC-3000

Anionic Emulsion Plant

Anionic Emulsified Asphalts RS-1 RS-2 MS-1 MS-2, 2h SS-1, 1h

Water

Cationic Emulsion Plant

Water Asphalt Oxidizer

Cationic Emulsified Asphalts CRS-1 CRS-2 CMS-2, 2h CSS-1, 1h

Air Blowing Flux Air Blown Asphalts Air

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FIGURE 2 LPG MARINE LOADING SYSTEM Boiloff Vapor

Small Liquid Circulation Line (1)

Vapor Return Compressor

Vapor Return Liquid

Liquid Loading Line N2

Refrigeration/ Liquefaction System (1) (2)

Loading Arms

Loading Pump(s)

Refrigerated LPG Storage Tank or Pressure Vessel

Circulation Pump (1)

Notes: (1) (2)

LPG Carrier

Not required for pressure storage alternative. Described in DP Section XXII-D.

DP23Bf02

FIGURE 3 TYPICAL LPG RAIL UNLOADING SYSTEMS

Note 1

MOV Vapor NC

Pressurized Sphere To Flare Compressor LL (CO)

MOV

MOV

MOV Vaporizer

Pressurized RR Car Top Connections Note 3

Notes: (1) (2) (3)

Liquid

Note 2

Unloading Pot

Another option for providing pressurizing product vapors. Alternative source of high pressure liquid may be available. Liquid loading / unloading connection extends to bottom of car.

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FIGURE 4 PRESSURE DROP IN LIQUID SULFUR LINES

1000 800 600

100 80 60

ipe 2" ,1 Pip .61 2-1 0" e, 2 I.D /2" .06 . Pip 7" e, I.D 3" 2 . Pip .46 9" e, 3 I.D . 4" 06 . Pip 8" I e, . D 4.0 . 5" 26 Pip " I e, .D. 6" 5.0 Pip 47 e, " I. 6.0 D. 8" 65 P ip " I.D e, . 8.0 10 "P 71 i " p I.D e, 12 "P 10 . .19 ipe 2" ,1 I.D 2.0 . 90 " I. D.

200

40

1-1 /2" P

ion nsit Tra

low Flow nt F ous bule Visc Tur nt to bule Tur

Pounds Per Square Inch Pressure Drop Per 1,000 Feet Straight Pipe

400

20

10 8 6 4 2 1 1

2

3 4 5 6 8 10

20

40

100

200

400

1000

4000

Gallons of Sulfur Per Minute(1)(2)

Notes: (1) (2)

For pounds per minute, multiply by 15. For cubic meters per hour, multiply by 0.23.

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DP23Bf04

10000