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PRODUCT LOADING SYSTEMS BASIC LOADING SYSTEMS DESIGN PRACTICES

Section XXIII-A

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CONTENTS Section

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SCOPE ............................................................................................................................................................ 3 REFERENCES ................................................................................................................................................ 3 BACKGROUND .............................................................................................................................................. 4 DEFINATIONS ................................................................................................................................................ 4 MODES OF PRODUCT LOADING ................................................................................................................. 7 MARINE .................................................................................................................................................. 7 TANK TRUCK ......................................................................................................................................... 7 RAIL CARS ............................................................................................................................................. 7 DESIGN CONSIDERATIONS.......................................................................................................................... 8 LOADING CONTROL SYSTEMS ........................................................................................................... 8 PRODUCT MEASUREMENT.................................................................................................................. 9 LOADING ARMS................................................................................................................................... 11 MANIFOLDING AND LOADING ARMS ................................................................................................ 13 MULTI–PRODUCT LOADING LINES ................................................................................................... 13 LAYOUT OF THE LOADING AREA...................................................................................................... 14 LOADING RACKS................................................................................................................................. 15 BUNKERING......................................................................................................................................... 16 TERMINAL AUTOMATION ................................................................................................................... 16 VAPOR CONTROL ............................................................................................................................... 16 Marine Loading .................................................................................................................................. 17 Vapor Collection/Transport................................................................................................................. 17 Vapor Recovery ................................................................................................................................. 18 Vapor Destruction .............................................................................................................................. 20 Vapor Balancing................................................................................................................................. 21 Truck Loading .................................................................................................................................... 21 Rail Car Loading ................................................................................................................................ 22 System Selection ............................................................................................................................... 22 DESIGN PROCEDURES............................................................................................................................... 23 MARINE LOADING SYSTEMS ............................................................................................................. 23 TRUCK LOADING SYSTEMS............................................................................................................... 24 RAIL CAR LOADING SYSTEMS .......................................................................................................... 26 GUIDANCE AND CONSULTING .................................................................................................................. 28

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TABLES Table 1 Rack Occupancy Time For Tank Truck Loading Facilities............................................................... 28 Table 2 Rack Occupancy Time For Rail Car Loading Facilities.................................................................... 29 Table 3 Vapor Processing System Selection................................................................................................ 29 FIGURES Figure 1 Typical Top–Loading Truck Rack .................................................................................................... 30 Figure 2 Marine Loading Control System ...................................................................................................... 31 Figure 3 Tank Truck (Or Rail Car) Loading Control System .......................................................................... 32 Figure 4 Spring Balanced Pantograph Top Loading Arm .............................................................................. 33 Figure 5 Counterweighted Hose Loader........................................................................................................ 34 Figure 6 “A" Frame Bottom Loading Arm ...................................................................................................... 35 Figure 7 Common Manifolding With Stripping Facility For Marine Loading System ...................................... 36 Figure 8 Layout Of Truck Loading Area ........................................................................................................ 37 Figure 9 Layout Of Rail Car Loading Area .................................................................................................... 38 Figure 10 Marine Loading Vapor Emissions Collection ................................................................................. 38 Figure 11 Carbon Adsorption Vapor Recovery Facilities (Vacuum Regeneration) ........................................ 39 Figure 12 Carbon Adsorption Vapor Recovery Facilities (Steam Regeneration)........................................... 40 Figure 13 Lean Oil Absorption Vapor Recovery Facilities ............................................................................. 41 Figure 14 Refrigeration (Condensation) Vapor Recovery Facilities............................................................... 41 Figure 15 Simplified Membrane System........................................................................................................ 42 Figure 16 Facilities For Emission Control By Thermal Oxidation.................................................................. 43 Figure 17 Average Delay Vs. Berth Occupancy For Calibration With Historical Data ................................... 44

Revision Memo 5/04 Highlights of this revision are as follows: 1. References have been updated. 2. Definitions have been expanded. 3. Fig. 15 updated

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Section XXIII-A

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SCOPE This design practice subsection covers the offsites systems aspects of marine, tank truck, and rail car product loading systems for refineries and chemical plants. System planning and design procedures are presented, supplemented by component design considerations. Specialized product handling systems such as pressurized LPG loading are covered in Subsection B. Pipeline movements of products are outside the scope of this section. REFERENCES ç DESIGN PRACTICES DP XIV, Fluid Flow DP XV, Safety in Plant Design DP XXII, Storage Facilities BASIC PRACTICES GP 03–11–01, GP 03–11–02, GP 04–04–01, GP 09–07–01, GP 15–04–01, GP 16–01–01,

Marine Cargo Transfer Hose Marine Loading Arms Marine Piers and Mooring Facilities Accessories for Atmospheric Storage Tanks Flow Instruments Area Classification and Related Electrical Design

API STANDARDS API Manuals of Petroleum Measurement Standards. API 1003, “Precautions Against Electrostatic Ignition During Loading of Tank Truck Motor Vehicles." API RP 1004, “Bottom Loading and Vapor Recovery for MC–306 Tank Motor Vehicles." OTHER LITERATURE 1. "Guidelines for Prevention of Electrostatic Ignitions", Safety Technology Manual Section II-O, TMEE073, November, 2002. 2. “Electrostatic Precautions with Metal Filters," ERE Report No. EE.86E.83, December 1983. 3. “Interfacial Mixing in Products Pipeline," Pipeline Research Report No. PLR–F–60–63, April 1963. 4. “Pipeline Pigging Guide," Exxon Chemicals Report No. 78CE1510, Rev 1, January 1979. 5. “Implementation Guidelines for Custody Transfer of Hydrocarbons," ERE Report Nos. EE.13E.86 and EE.81E.86, January/July 1986. 6. “Comparative Evaluation of Turbine versus Displacement Flowmeters in Tank Truck Loading Application," ERE Report No. EE.5M.86, December 1986. 7. “Truck Loading Rack Design Guide for Clean Products," ERE Report No. EE.1M.85, June 1985.

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8. “Rail and Truck Loading Guide for Pressurized/Refrigerated Products, Exxon Chemical Co.," Report No. CE.1E.82, January 1982. 9. “Evaluation of Gasoline and Hazardous Chemical Truck Loading/Unloading Facilities," ERE Report No. EE.32E.85, July 1985. 10. “Evaluation of Railcar Petroleum and Hazardous Chemical Loading/Unloading Facilities," ERE Report No. EE.98E.86, December 1986. 11. “Automatic Crude Oil Sampling Handbook," ERE Report No. EE.40E.84, May 1984. 12. “Guidelines for Selecting Vapor Recovery/Destruction Technology", ERE Report No. EE. 19E.90, March 1990. 13. Vapor Recovery Design Consideration Memos, 90PD 5 and 90PD 50, dated January 19, 1990 and June 29, 1990, respectively. 14. Improved Analysis Method for Use in Pipe Pressure Surge Evaluations, ERE Report No. EE.62E.86, June 1986. 15. Truck Loading Rack Design Guidelines, Esso Europe–Africa Services Inc., Letter No. 88 EEEL 0098, June 28, 1988. 16. ExxonMobil Corporate Measurement Guidelines for Custody Transfer. 17. ExxonMobil Marketing Design Practices. 18. International Chamber of Shipping, International Safety guide for Oil Tankers and Terminals, Witherby and Co. Ltd., London, England. 19. ExxonMobil Recommended Terminal Operating Practices - Marine. 20. Department of Transportation, Coast Guard, Marine Vapor Control Systems: Final Rule, June 21, 1991. 33 CFR Part 154, 46 CFR Part 30, Federal Register. 21. Seelye, Elwyn E, Data Book for Civil Engineers, Volume 1, Design, John Wiley and Sons Inc. 22. Radian Corporation, A FGuide to Vapor Control Options for the Petroleum Industry, prepared for the American Petroleum Institute, 5 June 1992. 23. Marine Vapor Recovery Study; Bayway Refinery, April 18, 1988. Document Number: 88 ECSI 99. 24. Dock Emissions Control Study; Baton Rouge Refinery, March 11, 1988. Document Number: 88 ECSI 65. 25. Singapore Aromatics Project--Preliminary Report--SAC Marine Vapor Control Facility, May 2, 1994. Document Number: GER-046. 26. Port Jerome Benzene Vapor Control Study, June 5, 1990. Document Number: 90 EEEL 0518. 27. Screening Study for Hydrocarbon Emission Reduction during Loading Operations at the Esso Refinery; Rotterdam Refinery, June 1992. By H. C. M. Van Benthem. (No document number available). 28. Truck and Rail Terminal Vapor Recovery Unit Technical Specification, 1994. Document Number: 94 PD 10. BACKGROUND Product loading systems consist mainly of equipment to transport liquid products from storage tanks to loading areas, to load the products into product carriers, and to measure the amount of product loaded for billing purposes. Loading systems deliver product to marine, truck, and rail product carriers. Vapor collection systems collect displaced vapor and process it to comply with environmental regulations. The basic modes of product loading are described and system design considerations and procedures are presented.

DEFINITIONS ç

(See also DP XXII–A) ARRIVAL PATTERNS The distribution of vessel arrivals over a given period for a particular type of product carrier. BOTTOM LOADING The method for loading liquid into the bottom of a tank truck or railcar from ground level with a dry disconnect type fitting. BUNKER FUEL Fuel used to power a marine vessel. ExxonMobil Research and Engineering Company – Fairfax, VA

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BUNKERING The transfer of bunker fuel to a vessel's storage tanks. Commercial bunkering is the sale and transfer of bunker fuel to a ship calling exclusively for that service. CUSTODY TRANSFER A loading operation in which ownership of the product changes hands. DARK PRODUCTS Products composed primarily of residual stocks and generally classified as fuel oils. DEAD MAN VALVE A valve which closes unless manually held in the open position. DEMURRAGE The excess of actual vessel turnaround time over the allowed port time. Demurrage charge; a cost penalty associated with demurrage. DWT (DEAD WEIGHT TONS) A figure representing vessel displacement loaded, less displacement empty, expressed in 2240 lb. “long" tons. DWT indicates the weight that the vessel can carry including cargo, stores, and gear. Cargo weight is typically 85% of total DWT. Total ship displacement includes the weight of the ship and is greater than DWT. FAST–TABLET II A computer simulation program that is often used to evaluate alternative marine product loading configurations. LIGHT PRODUCTS Products composed primarily of distillate stocks and ranging from gasolines and naphthas to diesel oils. LOADING ISLAND The area on which is mounted the loading equipment (meters, control valves, loading arms, control equipment, etc.) necessary to load a tank truck. Islands can have single or multiproduct loading positions (spots) on one or both sides depending on the design. LOADING RACK The complete loading facility structure consisting of one or more truck or rail loading islands. MECHANICAL DISPLACEMENT METER PROVER A device for calibrating meters consisting of a cylindrical container (pipe) of known volume, a mechanical sealing element and two signaling detectors. The metered stream is diverted through the prover, displacing the sealing element past the signal detectors. Simultaneously the corresponding metered volume is indicated. OCCUPANCY The amount of time a loading location (such as a marine berth) is occupied, often expressed as a percentage of either total or available time. Berth occupancy includes not only pumping time but also includes the time required for maneuvering the vessel into and out of the berth, and the time required for product sampling and analysis prior to vessel departure from the berth.

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OPERATING ENVELOPE The volume in space that contains all of the expected vessel manifold positions during the cargo transfer. For marine loading, this volume must include ship manifold location variations due to differences in ship sizes, ship load on board, water level (tides), and allowances for surge and sway. The surge and sway allowances typically used are 10 ft(3m) each for the forward direction, backward direction, and drift away from the face of the berth. For truck loading it must include bottom manifold or top dome location variations due to differences in trucks as well as an allowance for truck position variations. POSITIVE DISPLACEMENT METER (PDM) An in–line device used for measuring the volume of product transferred. PDM's mechanically isolate the flowing liquid into segments of known volume. PRE–SET (SET–STOP) VOLUME OR WEIGHT CONTROL Automatic feature which stops a loading operation when a programmed volume or weight has been loaded. PRODUCT DEMAND PATTERN A tabulation distributing calendar day product yields over the various modes of product shipping. This tabulation should reflect variations over time, if any. RESIDENCE TIME (RELAXATION TIME) The time it takes liquid leaving a filter to reach the receiving vessel at the maximum flow rate of the system. During this time a reduction in electrostatic charge, or relaxation takes place. SORTING HUMP Elevated section of track that permits rail car sorting without the yard engine entering the marshalling yard. SPLASH FILLING The method of top loading product into a tank truck where the fill pipe extends only partially into the product compartment, leaving a vapor space between the end of the fill pipe and the liquid level. This results in much splashing, considerable vapor emissions, and generation of static charge in products with low electrical conductivity (static accumulators). SPURS A section or sections of track not on the main railroad line. STRIPPING The removal of the heel from a ship's compartment at the conclusion of an unloading operation. Stripping may also include the removal and transfer to the ship of product remaining in a loading line. Although not common, stripping is usually done with special pumps. SURGE PRESSURE Transient pressures in long lines resulting from rapid changes in flow. TOP LOADING The method for loading liquid into a tank truck or rail car via hatches on the top of the carrier. Open top loading is the insertion of the fill pipe loosely through an open hatch. Closed Top loading involves a vapor–tight fit between the fill pipe and the hatch and is used when vapor recovery is used. TURBINE METER An in–line device used for measuring the volume of product transferred. Turbine meters consist of a rotor that senses the linear velocity of a flowing stream. The moving fluid imparts a rotational velocity to the rotor that is proportional to flow rate. ExxonMobil Research and Engineering Company – Fairfax, VA

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TURNAROUND TIME The start to finish elapsed time for loading product onto a ship, rail car or truck. This time includes not only pumping time but time spent at the loading dock/rack for other reasons such as hose connect/disconnect and document clearance. Note:

Definitions of other terms used in this section but not covered here are covered in DP XXII–A. MODES OF PRODUCT LOADING

MARINE Marine product loading is most commonly conducted over a conventional pier or jetty with the product vessel moored to the fixed structure. Other less common installations include breasting islands, multiple buoy berths and single point moorings. Choice of the type of facility depends on local conditions, sizes of vessels, and cargos to be handled. Vessels arriving for product can be company–owned, leased or independent, and can range in size from small barges (less than 1000 DWT) to large tankers (100,000 DWT and greater). The local affiliate is relied upon to establish fleet characteristics for planning and design of new or expanded marine loading facilities. The number of berths and loading rates are based on economics. Vessel waiting charges (demurrage charges) supply the incentive for increasing marine facilities investment and reducing ship turnaround times. Pumping rates vary widely depending upon target vessel turnaround times. These in turn depend upon ship size, tidal constraints, and other local conditions. TANK TRUCK Tank trucks are loaded at island–type racks. In general, a rack is equipped with several islands, each of that has loading positions (spots) on one or both sides. Each loading spot is generally equipped with several product loading arms, a vapor recovery connection, and metering and electrical grounding equipment. In the past, most terminals were designed for top loading - generally through a top opening dome using a metal loading arm (Figure 1). However, due to emission regulations bottom loading is used extensively in the U.S. and Canada and is becoming more common in Europe. Bottom loading offers numerous advantages over top loading. It increases safety by eliminating the need for personnel on top of the truck, and reduces fire risk due to splashing and vapor emissions. It also decreases turnaround time, spillage, vapor emissions, and loading rack investment. A dry–break type disconnect coupling is used between the truck and the loading arm which allows quick and safe connection and disconnection without the loss of product. The truck fleet can consist of company–owned vehicles, hired trucks and/or independent haulers. Total truck capacities vary from 1,500 to 15,000 gallons (6 to 57 m3), the average within ExxonMobil ranging from 4,000 to 13,000 gallons (15 to 49 m3). The vehicles are generally divided into 2 to 6 separate compartments, but can be equipped with more. The number of loading spots and loading rates provided for a particular location are based primarily on minimizing vehicle waiting times to within acceptable limits during periods of daily peak operation, and on maintaining rack occupancies within recommended ranges during longer duration peaks and average operations. Pumping rates are often in the 500 to 800 gpm (30 to 50 dm3/s) range and turnaround times are usually about 15–20 minutes. RAIL CARS Rail cars are loaded at single or double-sided racks with one or more spots per side. Top loading is the standard loading position in the U.S. and Canada with metal loading arms or telescoping arms inserted through top–opening domes. However, pressurized rail cars are loaded through other positions in other regions. In Europe, some rail cars are loaded through a position that is midway between the bottom and the side centerline. Bottom loading also exists in other regions. Most rail cars are leased from rail car companies, however, some rail cars are company–owned. The cars usually have a single compartment with average sizes ranging from 7,500 to 30,000 gallons (25 to 113 m3). In Europe, LPG rail car size has been increased to the 20,000 gallon (75 m3) range. Loading rack configuration and rates are selected to handle the anticipated daily peak load of cars. Efficient car handling is also required since railroad charges for switching/moving rail cars is a major cost factor. Turnaround times are often set by the Railroad based on contractual requirements.

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DESIGN CONSIDERATIONS A typical loading system consists of a pumping installation, a loading control system, a method for product measurement, a loading arm for tie–in to the product carrier and vapor emission control facilities if required. In addition, a physical structure, e.g., a pier or loading rack, is required to accommodate the product vessel or vehicle and downstream equipment associated with the loading operation. Tankage is a major component of the overall product movement system. Tankage sizing criteria are given in other sections of these Design Practices (DP XXII). Product shipping facilities are also sometimes used for blending, mixing or inter–tank transfer operations requiring tie–ins between blending and shipping. The design considerations that follow deal with various aspects of these components. For existing refineries and chemical plants, the emphasis of planning and design work is to identify the means of accommodating throughput or product slate changes without having to add an additional pier or berth. The relatively high cost of marine structures requires that alternatives such as loading rate increases, loading system reconfigurations ( additional lines, increased line size, simultaneous product loading, etc.), and larger shipping parcel sizes be investigated prior to considering additional piers/berths. LOADING CONTROL SYSTEMS Figures 2 and 3 show several possible control systems. Normally the loading pumps are started manually, either locally at the pump pad and/or remotely at the loading location. Automatic pump cut in on low pressure can be provided when two or more pumps per product are specified. Rail and truck loading facilities may also provide more than one pump per product in which case the control system described above would be provided. Low flow protection is usually provided for loading pumps to maintain flow above the minimum continuous requirement of the pump. The protection can be provided in several ways: ·

Low flow cut–out (with time delay if loading can involve intermittent flow).

·

Recirculation line with flow controller or restriction orifice sized to maintain minimum pump rate.

A means of limiting the initial filling and final topping off velocities in the vessel and shore side loading systems to 3 ft/s (0.9 m/s) is necessary to avoid electrostatic charge accumulation when during initial loading, and hydraulic surge at shutdown. It will also minimize vapor generation and the chance of overfilling the product carrier. The methods of control for marine and tank truck/rail car loading are discussed below: Marine loading at reduced rates can be accomplished in one of the following ways: 1. Gravity flow, which requires a bypass around the loading pump. Topography, i.e., relative elevations of storage tank and berth, must be suitable. 2. Loading control valve, the FCV in Figure 2 and automatic pump recirculation. This device is mounted upstream of the loading arm and is operable from a remote location such as from the deck of the ship. Manpower savings and faster turnarounds may justify this approach over alternative 1. Tank truck and rail car loading facilities are generally provided with a multi–purpose valve (FCV in Figure 3) which automatically performs flow rate control functions using signals from the meter and the preset. A two–stage valve is required in order to limit fill pipe velocity to 3 ft/sec (0.9 m/s) at the start and the end of the loading operation. This slower rate is necessary to avoid electrostatic ignition when initiating loading operations for a static accumulator and to avoid hydraulic surge problems prior to shutdown. The slow rate also minimizes vapor generation and the likelihood of overfilling the product carrier. The valve generally also performs the following functions: 1. Pre–set volume/weight control in conjunction with the meter/ weigh scale (refer to “Terminal Automation"). 2. Permissive loading control to insure that the vehicle is properly grounded and a ticket is inserted in the printer. Local and/or remote push–bottoms are provided to initiate the loading cycle and stop the operation in the event of an emergency. After initial filling, the loading velocity may be increased. In order to avoid excessive turbulence, inlet (fill pipe) velocities are generally limited to a value of 64/d (English Units) or 500/d (Metric Units) where velocity is in ft/s (m/s) and pipe diameter (d) is in inches (mm).

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The pumps in all loading system designs should be evaluated for possible problems resulting from the low initial and final topping–off rates. High horsepower, high vapor pressure applications are the most prone to operating difficulties during these modes of operation. When excessively low flows can be imposed, an additional, smaller pump or automatic recycle back to the suction system should be provided. The occurrence of hydraulic pressure surge is a function of line length and rate of change of flow. It is more common in long lines equipped with motor operated valves. It is controlled by increasing or staging valve closing time or adding gas pressurized surge vessels in the line. Additional information is contained in EMRE Report No. EE. 62E.86.

PRODUCT MEASUREMENT Techniques of measuring parcel size fall into three categories - gauging, metering and weighing. For custody transfer operations, designs must comply with local regulations and the Corporate Measurement Guidelines for Custody Transfer. Gauging Manual ship or tank gauging is typically used for custody transfer in many locations. See Design Practice DP 22B for details of tank gauging. Metering Metering is the primary method used to measure tank truck and rail car product shipments. Although not a firm requirement, truck and rail loading systems often include small day tanks that isolate these systems from the overall product storage and marine loading system. For marine shipments, metering is required if more than one product vessel is loaded simultaneously from the same product tank. In some locations, deduction of truck loading rack meter readings from tank level readings is acceptable in lieu of metering every stream leaving the tank. Positive displacement (PDM) and turbine (TM) are the two types of flowmeters acceptable as primary measurement instruments for custody transfer of liquid petroleum products. They both typically provide volumetric accuracy at line conditions of " 0.2%. The rangeability of a TM is typically 10:1 whereas PDM rangeability can be 30:1 and more. TMs use a bladed rotor contained in a flow tube that is axially suspended in the direction of flow. As fluid passes through the tube, the rotor spins at a rate proportional to the fluid velocity. Blade rotation is generally detected by a sensor whose output is used to infer a volumetric flowrate. A PDM divides the flowstream into discrete volumetric segments. A known volume of fluid is mechanically isolated in the meter and passed from inlet to outlet by the alternate filling and emptying of compartments. This process is usually translated into a rotary motion that operates a counter. Most PDMs are direct reading and do not require an external power source. Each segment of fluid volume passing through the meter is counted to yield a measure of total volume. Terms used to describe the type of PDM include rotating disk, oscillating piston, sliding vane, bi–rotor and oval gear designs. TMs infer a volumetric flowrate from a velocity measurement whereas PDMs do not measure flowrate but measure totalized volume directly. Both PDMs and TMs can be used for products with viscosities lower than about 10cSt (mm2/s). PDMs are normally selected for products with viscosities higher than about 10cSt (mm2/s). PDMs with special clearances are the choice for metering very viscous products such as asphalt. Both types of meters are available for design temperatures up to about 500°F (260°C). For the same capacity, TMs have lower capital cost than PDMs. TMs can be used for lower flow rates than PDMs but this characteristic is not important for product loading systems. TMs are available for capacities up to 40,000 gpm (2515 dm3/s) and PDMs are available up to 9,000 gpm (565 dm3/s). The need for parallel meters is limited to pipeline or marine loading applications. Both PDMs and TMs are available in standard sizes. Good practice is to select a meter such that the normal operating flow is about 70% of the specified maximum flowrate. TMs are relatively small in size and lightweight whereas PDMs are relatively large and heavy. For revamp projects, plot space and foundation requirements require consideration, particularly for large meter capacities.

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TMs can register incorrectly and become damaged by over-speeding as a result of loss of backpressure. One vendor recommends 25 psig be used as a minimum TM backpressure. PDM backpressure is not as critical as that of TMs but they can cavitate. In both cases, the designer should check backpressure conditions with meter vendors or an instrumentation specialist. The pressure drop across the meter should also be obtained from meter vendors. For planning purposes, a pressure drop of 10–15 psi (69–104 kPa) can be assumed. Both types of meters contain moving parts that are subject to mechanical wear especially for products contaminated with abrasive particulates. Strainers and possibly filters are therefore required upstream of both types of meters. If the loading system is susceptible to air entrainment, an air eliminator is required upstream of the meter. PDMs require little or no upstream and downstream piping runs. TMs require upstream and downstream straight piping runs of 5 to 10 diameters. In addition, straightening vanes are often included within the upstream piping run for TMs. Temperature measurement is part of the metering system as this is required to convert meter readout at the operating temperature to a standard reference temperature. Generally, TMs are equipped with electronic pickups and pulse counting systems. PDMs have traditionally been supplied with mechanical readout systems. However, PDMs equipped with all–electronic accessories and readouts minimize meter maintenance and improve meter performance. Electronic readout systems are also compatible with microprocessor equipment that can perform a wide variety of control and data reporting functions. Most meter vendors offer microprocessor-based packages as part of their meter supply. TMs, if allowed to operate at very low flowrates, will stop registering whereas this is not the case for PDMs. For this reason, TMs should be applied in conjunction with reliable electronic register/preset systems that offer protection against “meter milking" (unauthorized removal of product from the loading system). Meter design specifications should include the following information: ·

Properties of the liquid to be metered - viscosity, density, vapor pressure, contaminants, corrosiveness, and lubricity.

·

Operating flow rates - normal, minimum, and maximum.

·

Operating temperature - normal, minimum and maximum.

·

Type of meter and accuracy requirements over the intended flow range.

Periodic proving is required when meters are used for custody transfer. Four types of provers are available. These are: ·

Pipe provers - both unidirectional and bi-directional.

·

Compact or Low Volume provers

·

Master meter provers - both positive displacement and turbine meters may be used for this service.

·

Volumetric tank provers.

In selecting a prover, the most important consideration is the capability to prove the meter over its full range of operating conditions (viscosity, temperature, etc.). Other factors to take into account are: ·

Number of meters, location, and accessibility.

·

Time, manpower, and personnel skills required for proving operations.

·

Applicability of portable versus stationary provers.

·

Government regulations and contractual requirements.

·

Environmental and industrial regulations.

All provers should be located as close as possible to the meters. Manifolding can be provided to allow calibration of a number of meters with a single prover or a single high capacity meter with two or more provers. In these cases, the provers must be flushed and alternative routes or pump back facilities must be provided for the downgraded products. An instrumentation technology specialist should be consulted for additional details and requirements for meter provers.

Weighing, rather than volume measurement by metering, is sometimes used to measure product shipments in rail cars. In addition, weigh scales are often used to measure tank truck shipments of some special products such as sulfur, asphalt, and bulk solids such as petroleum coke. The purpose of a weigh scale is not only to measure the weight of product for billing purposes but to insure that the road and rail systems are not being overloaded by the product carrier.

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Both static and in–motion weigh scales are available. In–motion weighing of coupled rail cars is commonly practiced in the coal industry for shipments involving 100 car or more unit trains. For the large majority of refinery and chemical plant weigh scale applications, uncoupled static rail car weighing is acceptable. The design parameters associated with static weigh scale specifications are as follows: ·

Dual use (truck and rail) or single use - the high cost of weigh scales indicates dual use wherever possible.

·

Tank truck and rail car fully loaded weights - sets scale capacity.

·

Physical dimensions of trucks and rail cars and wheel loads - sets vendor's design of weigh bridge and layout of scale approach and departure ramps.

·

Desired accuracy (generally expressed as % of full load capacity) and precision (generally expressed in absolute units - pounds, tons, etc.).

·

Pitless (low profile) or pit type of scale - Pitless type is less expensive, generally is of lower accuracy than pit type, eliminates safety concerns of large pits, and is acceptable for most refinery applications. If a pit–type of scale is required to insure a highly accurate system, the pit should be provided with a fan to prevent the accumulation of hazardous vapors. In addition, the pit will probably require a sump pump.

·

Extent of desired scale automation - weight documentation only, pre–set control of product to be loaded, etc. Availability of electronic load cells for weighing in combination with microprocessor technology have created a very wide range of automation options. The justification for automating the weigh scale system should be decided on a case–by–case basis based on Owner review.

Weigh scales, where used for custody transfer, are under the jurisdiction of local Weights and Measures authorities. These authorities have very specific requirements which must be adhered to both during the weigh scale system design and during operations (such as scale calibration requirements, maintenance, and frequency thereof). LOADING ARMS Marine loading operations are conducted with all–metal loading arms or flexible hoses. Although loading arms are higher cost than hoses, higher loading rates, safer operation and increased life are the primary factors responsible for a trend away from flexible hoses to hard piping. When comparing the costs of hoses and loading arms, facilities for handling and storing hoses must be considered since these represent a substantial portion of a hose system cost. For guidelines on the mechanical specifications of hoses or metal arms for marine service, consult an EMRE marine specialist. Refer to DP XV– J for guidance on safety features for loading arms and hoses used in marine loading operations. Loading arms generally include several segments of pipe (riser, inboard and outboard segments) with swivel assemblies at the joints and at the ends. The arm acts as a mechanical linkage with many degrees of freedom which enable it to reach the manifolds of the different vessels expected and to accommodate vessel movement. The arms are frequently counterweighted and provided with other devices, such as cables, pulleys, or hydraulics, to assist movement. Selection of number and size of arms for a given berth depends upon the number of products which can be loaded simultaneously, the number of products which can be handled in a common arm, and loading rates. Normally a sufficient number of arms are provided to enable a vessel to simultaneously load the maximum number of products, limited by vessel manifolding and manifold spacing. Most tankers have three or four independent piping systems. Product barges can generally load up to three products simultaneously. When both light and dark products are handled at a berth, it is necessary to install separate arms for each product class or to use common light/dark arms (see “Manifolding and Loading Arms"). The velocity through a loading arm should preferably be limited to 30 ft/s (9 m/s) and this criterion should be applied for sizing. Higher velocities can cause excessive vibration and stresses. Actual test data on the specific type of arm to be employed should be used to establish pressure drop. When this is unavailable or the type of arm is unknown, pressure losses can be approximated by expressing the entire loading arm in terms of equivalent length of steel pipe. Typical arm pressure drop at full flow is approximately 10 psi (70 kPa). A typical ship rail pressure should be 15 to 20 psi (105 to 140 kPa) Loading arms can be engineered for sizes up to 24 inches (600 mm) diameter. Manual operation is generally possible with arms up to 8 inches (150 mm) diameter depending on the arm length. Winches or hydraulic assistance are needed for larger sizes.

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The counterweighted arms are generally balanced in the empty condition. Following a transfer operation, the outboard leg is drained to the tanker and the inboard leg to a sump at the pier. A vacuum vent at the apex of the arm is employed to insure complete drainage. Provision must be made to pump the contents of the sump to slop or crude tankage for reprocessing. Purge systems employing an inert gas under pressure are sometimes used to drain the loading arms following the transfer operation. Advantages over simple gravity draining include a faster and more thorough operation, a reduction in the risk of spills and positive flushing even if the apex is lower than the loading arm heel. The loading arms should be purged to the vessel, if purging is done to the shore tank gas pockets can accumulate under the tank's floating roof and potentially sink the floating roof. Range controllers are also often included. These consist of devices to monitor ship movement and detect excursions outside the loading arm design envelope. The system can be instrumented to alarm and even shut down the loading operation when safe limits are exceeded. Tank truck and rail car loading can either be from the top or bottom. Most rail car, and many truck loading operations are done through a top opening dome or hatch. All metal arms are recommended for top loading applications. The spring–balanced, pantograph–type metal arm (Figure 4) is generally preferred over the bulky and less maneuverable counterweighted type. The loading valve is located at the base of the inboard arm so that most or all product is drained to the truck, or rail car thus allowing the arm to be stored empty. For top loading installations, it is common to provide individual loading assemblies dedicated to one side of the island. Although this requires two sets of assemblies for each product, the additional investment is offset by the increased operational efficiency, particularly where high truck or rail car volume is anticipated. In some situations though, it may be desirable to provide a common assembly serving both sides. If this is the case, the arm selected must be capable of 360° rotation and the layout of the platform and loading equipment must enable such rotation without interfering with the arm movement. Also, for invoicing purposes, a side select switch connected to the automation system may be required at the base swivel joint to indicate on which side of the island the product is being loaded. Hose loaders and “A" frame loaders (Figures 5 and 6) are the two basic arm choices available for bottom loading operations. A hose loader configuration is recommended where three or more products will be loaded simultaneously and multiple crossover of the arms is required. Both of these bottom loaders are the wet–line type, meaning that they are stored filled with product and must be balanced accordingly. Truck loading arms are normally 3 or 4 inches (80 or 100 mm) diameter with 6 inch (150 mm) diameter arms available for specific applications. Hose arrangements are often required for vapor recovery when emissions during loading operations must be collected. Truck loading arms are generally restricted to a single service because of the high utilization factor and the small parcel sizes involved. Consideration should be given to providing common rail car loading arms for compatible products, to maximize the flexibility of a single spot. Fill pipes on arms in static accumulator services should extend as close as possible to, and preferably contact, the bottom of the tank truck or rail car compartment being top loaded. The fill pipe should end in a 45° slice as an additional precaution against splashing and misting. In addition, for both top and bottom loading, provision should be made to ground trucks prior to loading and to provide time (typically a minimum of 30 seconds) between static generators such as some filters and the discharge tip of the fill pipe. Refer to the Safety Technology Manual TMEE073 for further discussion of the hazards associated with static accumulators. Other accessories which should be considered are vacuum breakers to insure complete drainage, and lockup and lockdown latches, the latter item restraining the “jet" reaction to sudden pressure surges caused by pump cut–ins and cut– outs. When preset volume or weight control is not employed, a loading valve with a “dead man" feature should be provided to protect against overfilling. The valve should be of the shockless closing type to avoid hydraulic hammer.

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MANIFOLDING AND LOADING ARMS Manifolding of light or dark products maximizes marine cargo transfer flexibility by permitting multiple products to be handled through a given loading arm. It may be necessary to drain common piping. The use of single, soft seat, double– face type block valves with integral body bleed generally provides adequate product segregation. Although flexibility has advantages, it also has the potential for increased incidents as a result of improper equipment lineups. This potential must be minimized through careful design and clear operating procedures. When frequent and/or extensive draining is required, consideration should be given to a stripping system to pump the contents of arms and manifolds to the ships' compartments. The economic justification for stripping versus recycling through the ballast and/or crude systems depends on the cost of re–running product. A system with common manifolding is shown in Figure 7. When light and dark products are handled at the same berth, provision of a single arm for both services rather than multiple arms may offer investment savings although this is not a normal practice. Washing of the arm with a solvent such as naphtha may be required when switching from dark to light stocks. In addition, vessel turnaround time will be greater than for simultaneous loading with two or more loading arms. MULTI–PRODUCT LOADING LINES The cost of marine loading lines can often represent a substantial portion of the investment in loading facilities, particularly where long piping runs, pipe trestles or submarine lines are involved. In these instances reducing the number of lines and placing others in multiple product service may be justified by the significant savings obtained. When line service is changed, line contents can be pumped to the tanker, back to tankage or slopped. The two basic methods of displacing the line are discussed below: Direct interfacial contact, where one product is pumped behind the other. The amount of detectable interface contamination will depend upon how far the interface has traveled in the line (line length) and property differences between the two products. A rough estimate of the detectable interface contamination length in a line is as follows: 0.5

Lc

=

k(L)

where: Lc L k

= = =

Length of line with detectable contamination: ft(m) Line total length over which interface travels: Miles (km) constant as follows: API Gravity Difference

50

25

10

2

1

0.5

k (FT/mile units)

300

260

240

170

130

90

k (m/km units)

72

62

58

41

31

22

The contaminated volume is equal to the volume of liquid contained in the contaminated line length. Additional information may be found on interface contamination in ER&E and Pipeline Research reports such as PLR–F–60–63. Pigging, which employs an element at the interface, physically separating the two products. An intermediate propulsion fluid (inert gas, water or a third more compatible product) has also been used to reduce contamination. Although a pigged system can reduce the number of lines, it is more complex to operate and raises the risk of incidents. Historically, pigged systems have been used in cases involving very long lines and many products. In addition, these systems have been used where product specifications are tight and therefore have minimal tolerance for direct interfacial contact contamination volumes. The following factors should be considered against the investment credit when evaluating the justification for common loading lines: Interproduct Contamination - Direct interfacial contact will result in an operating cost debit for either product giveaway or reprocessing. Pigging may also require some interface flushing as a result of residuals remaining in the line. Impact on Shipping - Use of common lines will impose restrictions on the loading of multiple products. Operating costs may be incurred as a result of increased vessel waiting time. Investment debits for additional equipment required for the line clearing operation. ExxonMobil Research and Engineering Company – Fairfax, VA

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LAYOUT OF THE LOADING AREA Layout of the marine loading platform cannot be finalized until detailed engineering on piping, manifolding and other equipment has been completed. However, the final layout should consider the following requirements: 1. Piping, including blending, metering and pigging equipment. 2. Product loading arms, hoses and hose supports. 3. Vapor collection arms and hoses and associated equipment in the loading area: compressors, flame or detonation arresters, knockout/seal drums, etc. 4. Pumps and sumps associated with stripping, draining and washing the loading lines and arms. 5. Access platforms for valves, meters, etc. 6. Loading control house or operator's shelter. 7. Electrical equipment and shelters. 8. Fire fighting equipment. 9. Stores handling equipment. 10. Landing platform. 11. Ship gangway. 12. Bollards and quick release hooks. 13. Vehicular and personnel access. Bulk loading and shipment of containerized products, e.g., asphalt drums, lube oil drums, LPG cylinders, etc, over a common pier should be avoided. The storage space and special equipment required for handling of containers restrict accessibility and interfere with the safety and operability of the bulk loading operation. A separate berth or pier in dedicated containerized shipping service is recommended. LPG is also frequently handled over a separate berth. Layout of the truck loading area requires careful consideration of traffic flow. A smooth pattern of flow as the trucks progress through the area will promote safe and efficient handling of the trucks and minimize turnaround time. Figure 8 presents an idealized plot plan for a truck loading facility. The dispatching method may require trucks to stop at the office on entrance, exit, or both. Space should be allocated for a queue wherever stopping is required. Traffic patterns should not require crossing traffic as part of the normal flow. The parking area should allow for easy movement of the trucks out of and into the normal flow of traffic. The path can be directed past a service facility to encourage use during the waiting period. The size of the parking area is generally based on the average anticipated waiting time during peak periods and terminal throughput. The morning queue at the start of daily operations should also be considered when establishing parking requirements. A queue space at the entrance to the rack provides for sorting prior to entry. Ample approach space should be provided ahead of all rack positions so that the largest trucks can enter without backing up. The loading racks consist of islands which usually provide loading on both sides for top–loaded operations and on one side for bottom–loaded operations (See “Loading Racks"). A separate truck park for loaded trucks is shown on the outgoing path. It is located there for safety and operational reasons. LPG loading racks should be located a minimum of 150 feet (45 m) from main paths of traffic flow. Truck movements should not be permitted within this radius during an LPG loading operation, since this zone has a Division 1 area classification (see GP 16–01–01 for definitions of area classifications). Additional particulars on LPG loading are covered in Subsection B. For other spacing criteria, refer to DP XV–G. A rail car loading layout can generally be broken down into the following functional plot areas: 1. 2. 3. 4. 5.

Shipping and receiving spurs. Sorting spur. Marshalling yard. Transfer and approach spurs. Loading spurs and racks.

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See Figure 9 for a typical layout. Some or all of these facilities may be required at a specific location. Data on railroad requirements such as minimum curve radii, switching space, and clearances may be found in the Data Book for Civil Engineers, Volume 1 - Design, by Elwyn E. Seelye. Trains are delivered to and shipped from the receiving and shipping spurs. Spur capacity is based on the length occupied by empty and full cars entering and leaving the area. Sorting and marshalling spurs should satisfy any requirements for sorting by destination and/or product. Average car residence time is also a consideration in establishing marshalling yard capacity. A sorting hump can be provided to reduce marshalling time. Cars transferred from the marshalling spurs to the loading spurs by the yard engines can be positioned at the rack individually or in groups by use of remotely–operated, bi–directional car pullers (see “Loading Racks"). Loading spurs can be dead–ended as shown in the example, or straight through, depending on the restrictions of the particular layout. The responsibility for car cleaning when changing service may rest with the loading terminal, and space should be allocated accordingly. Cleaning is generally accomplished by steaming, requiring the appropriate utility connections and drainage facilities. LOADING RACKS Truck Loading - The “starting gate" type of loading rack is recommended over the older “tandem" type for a safer and more efficient operation. With the “starting gate" arrangement, the rack consists of multiple islands lined up in a row with a single truck loading position at one side (bottom loading) or both sides (top loading) of each island. The “tandem" arrangement consists of one or two islands with several truck loading positions per side such that the trucks are lined up one behind the other. A typical “starting gate" type rack is shown in Figure 1. It is common to have one rack with anywhere from two up to ten or more islands. However, layout and plot space considerations may necessitate two parallel “starting gate" racks. A common roof is normally provided over the entire loading rack for weather protection and to minimize waste water treating facilities. It is desirable to segregate the loading islands according to product types. For instance, all motor gasoline and diesel fuel loading islands would be grouped at one end of the rack and all jet fuel and heating oil islands grouped at the other end. Similarly, top and bottom loading islands should be segregated as much as possible. Several grades of products are usually loaded at each island. For example, regular and premium motor gasoline might be loaded at five adjacent islands, while diesel fuel might need to be loaded at only two of the five islands. Bottom loading islands will have loading on one side only, since standard bottom loading connections are on the curb side of the truck and two–way traffic flow is not allowed at the rack. However, top loading islands enable loading on each side. Thus, it is possible to have trucks side by side at the rack. Sufficient spacing should be provided between the loading islands for easy truck maneuverability. The actual distance will depend on whether one or two trucks will be positioned between two islands. Where two trucks will be adjacent, allow for a distance of about 6 to 8 feet (1.8 to 2.4 meters) between the widest trucks expected. The total width and length of the island will be based on the layout of the loading facilities, structural requirements and the size of the anticipated trucks. The two basic types of rack operation are: 1. Single compartment loading, where multiple compartments per truck are loaded in sequence. 2. Simultaneous, multi–compartment loading. The second type should be considered when spout withdrawal, transfer and insertion is a substantial component of rack occupancy time, i.e., where large volume multi–compartment trucks are common. Preset control is a necessity with this type of operation. In some areas local regulations may prohibit simultaneous fillings. Rail car loading racks can generally be classified into one of the following types: 1. Single Spot per Side Racks - These are characterized by manual insertion and withdrawal of articulated, spring– balanced, metal loading arms. They are generally limited to 2 to 3 arms per spot. The ability to accommodate a range of car sizes becomes more restrictive as the number of product grades increases.

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2. Multiple Spots per Side Racks - These are similar to the above, but with 2, 3 or more loading locations on each side. Groups of cars are spotted together. Fillings can be simultaneous at all or some spots, depending on car sizes. This configuration has a higher capacity and more flexibility to handle multiple products and a range of car sizes than the single spot per side type. 3. “High–Speed" Single Spot per Side Racks - These are characterized by a number of remotely–operated telescoping loading lances. This type of rack should be considered for high throughput terminals over approximately 20,000 B/D (3,200 m3/D), Types 1 and 2 are generally limited to 6 inch (150 mm) loading arms and loading rates up to about 1,500 gpm (95 dm3/s). The “high–speed" racks have been provided with 8 inch (200 mm) and 10 inch (250 mm) lances and loading rates up to 2,000 gpm (130 dm3/s) and higher. BUNKERING Provisions for bunkering the product fleet are likely to be required at a marine loading installation. Separate bunkering facilities that enable this operation to be conducted simultaneously with the transfer of product can usually be justified. All– metal arms can generally satisfy manifold and envelope requirements when dealing exclusively with the product fleet; however, this should be confirmed with the affiliate and/or a logistics specialist. Consideration should be given to providing two bunker arms per berth, one on each side of the product arms. In–line blending of bunker fuels directly to the ship often can be economically justified by savings in additional tankage and product quality giveaway when a wide range of fuel and/or diesel oils is to be supplied. Commercial bunkering imposes unique requirements on a marine facility, since wide variations in fleet composition, manifold characteristics and bunker fuel grades are common and difficult to assess. The incidence of nonstandard manifolds and limited manifold accessibility is frequent with commercial bunkering. Generally, all–metal arms are insufficient to permit bunkering of all vessels and consideration should be given to metal arms with hoses, a half metal/half hose system or an all flexible hose system. TERMINAL AUTOMATION Generally, the most automated loading operations involve trucks. However, marine loading operations at several ExxonMobil plants have also been automated to the extent of lining up of tanks, valves, and pumps prior to loading, operation of valves (ROV's) and pumps, monitoring of the loading operation, and compilation of data for document preparation. Automation philosophy for marine and rail loading is established at the beginning of the project in conjunction with the owner. The specific automation applications are developed by the offsite engineer and the instrumentation and control technology specialist. Automatic loading systems are recommended for all new and modernized truck loading racks. They are based on preset meter control. This means that the driver selects the required amount of product to be loaded via a preset feature on the meter. Once this product volume has passed through the meter, the loading system is automatically shut down. This system is also tied into the Terminal Automation System (TAS). TAS guidelines have been established for most regions and should be followed regarding the degree and details of terminal automation to provide. Computer–Based Terminal Automation Systems (TAS) have been or are being implemented at most truck marketing terminals. TAS provides security and control for various terminal functions one of which is the loading rack operation. A fully–automated rack operation results in increased security since access to product through the system is gained only through a access card issued to each driver or truck and there is control over load authorization. TAS also provides improved measurement accuracy for accounting and billing purposes, increased efficiency with associated cost savings, and prompt and detailed invoicing. Incentives for computerization of loading activities have included reduction in manpower and turnaround time and improved security, and reduced risk of spill or safety incidents. VAPOR CONTROL Emission of vapors occurs during most loading operations resulting in product loss, releases to the atmosphere, and, in the case of toxic products such as benzene, worker exposure concerns. Regulations on hydrocarbon vapor emissions occurring during loading operations are becoming common and increasingly more stringent. Initially, these regulations applied primarily to truck loading operations. However, vapor control on marine and rail loading operations for volatile ExxonMobil Research and Engineering Company – Fairfax, VA

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hydrocarbons and toxic materials is now being mandated in many locations. Because of its high vapor pressure, gasoline loading is a primary target for such regulations. In addition, toxic chemicals such as benzene are under close scrutiny in many locations because of the concern over operator exposure. Vapor control systems consist of vapor collection/transport facilities and vapor processing units. technologies fall into one of the following categories. 1.

Vapor Recovery

2.

Vapor Destruction

Vapor processing

3. Vapor Balancing Vapor balancing is seldom used due to various operational and safety concerns. Vapor recovery has been economically justified in some special cases by the products recovered. However, vapor destruction is the most frequently used system. These are discussed below under Marine Loading. They may also be applied to tank truck or rail car loading. Marine Loading Regulations have been developed by the U.S. Coast Guard defining the facilities required to minimize the risks associated with fire, detonations, explosions, cargo tank overfilling, and cargo tank over or under pressuring. These regulations are detailed in US Code of Federal Regulations 33 CFR Part 154 for shoreside facilities and 46 CFR Part 30 for vesselside facilities. Although these regulations may only be mandated in the United States, they provide a good basis for the safety of design and are often used in addition to any applicable local regulations for defining marine vapor control systems. Installation of a marine vapor control system will introduce equipment and controls that are, in all likelihood, unfamiliar to the terminal and/or vessel operators. Accordingly, a significant training effort is required for the operators. Minimum training requirements are contained in 33 CFR Part 154 for the shoreside operators and 46 CFR Part 39 for vessel operators. The API has also put together a recommended practice for training guidelines for marine vapor control systems (API RP 1127). The new equipment and controls also will increase maintenance requirements as well as instrument checking and calibration requirements. This will, to some degree, reduce the use of the marine terminal since there is more equipment to connect/start-up. With proper maintenance and attention, the impact on occupancy and/or demurrage can be kept to a minimum. However, without adequate maintenance, the occupancy of the marine terminal and/or demurrage charges can be significantly impacted. The following sections are intended to provide an overview of Vapor Control System components and technology. Vapor Collection/Transport (See Fig. 10) Regardless of which vapor processing technology is used, vapor collection manifolding is needed from each of the vessel's product compartments to deliver vapor to the onshore vapor collection/ transport system. The following discussion pertains only to the onshore vapor collection system. When loading non-inerted vessels, the vapors displaced during some portion of the loading operation will likely be within a flammable range. During the early phase of loading the vapors may be lean or within the flammable range. During the latter stages of loading, the vapors will likely be rich and well above the upper flammable limit (UFL). To minimize the potential for detonations/explosions in the shoreside vapor control system, the preferred approach is to ensure the collected vapors are outside the flammable range throughout the loading cycle. This can be achieved by enriching with a hydrocarbon gas (typically natural gas or vaporized LPG) or by inerting with nitrogen or carbon dioxide as soon as possible in the shoreside system. Safety margins for enriching relative to the UFL limit or inerting are required. For enriching, EMRE recommends a minimum hydrocarbon concentration of 150% of UFL. For inerting, EMRE recommends a maximum oxygen concentration of 10%. Local regulations may require more conservative margins. Analyzers are required to monitor the enriched/inerted vapors and alarm and/or shutdown the vapor control system when the hydrocarbon/oxygen concentration is outside allowable limits. Detonation flame arresters (i.e., devices which prevent the transmission of detonations and deflagrations) are required within the shoreside system as a means of preventing the propagation of an ignition. One detonation flame arrester must be provided within a minimum distance of each vessel/shore interface and at any other point within the vapor control system which represents a potential source of ignition. Detonation flame arresters must be specified as either Type I or Type II. For additional information concerning detonation flame arresters, their testing requirements and differences between Type I and Type II, refer to Appendix A of 33 CFR Part 154 titled “Guidelines for Detonation Flame Arresters."

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Since the vapor collection facilities must operate at low pressures due to the pressure limitations of the vessels being loaded (typically in the range of 1 to 1.5 psig [6.9-10.4 kPa]), friction losses are critical and a compressor is frequently required to boost the pressure and avoid large diameter piping. If used, a compressor must be specified so as to minimize the potential of being an ignition source. Liquid ring compressors, special construction materials, or large blade tip clearances are sometimes used. Also, where compressors are used, vacuum protection is required for the system and vessel. In general, the ship-to-shore vapor collection facilities are consistent with those used for liquid loading; e.g., if hoses are used for the product loaded, hoses are used to collect the vapors and if loading arms are used for the product loaded, loading arms are used for the vapor. In some cases, vapor arms/hoses have been piggybacked on the liquid loading arm to minimize dock space taken up. If hoses are used, special light weight hose is available which has been developed specifically for vapors and approved by the US Coast Guard. The hose is sufficiently rigid to avoid damage in the typical marine environment yet is approximately one seventh the weight of conventional hoses used for liquid loading. The ship– to–shore vapor connection must be designed to prevent the possibility of inadvertently cross connecting liquid and vapor systems. Another important design concern is the control philosophy to be used. Whether the unit is manually controlled or automated and where the system is monitored have significant impact on cost. Also whether programmable logic controllers (PLC) or hard wired relay logic is used will influence the system cost. The Owner must clearly define how the system is to be controlled and from where. This philosophy is highly dependent on the affiliate. Vapor Recovery There are four major types of vapor recovery processes in commercial use today; carbon adsorption, lean oil absorption, condensation (refrigeration), and membrane seperation. Carbon adsorption is by far the most common; it is widely used and is well developed. Lean oil absorption, has also been accepted widely. Condensation, although widely used in the past when target recovery efficiencies were in the range of 80 to 85 percent, has been used less frequently in recent years due to the higher recovery efficiencies required (typically 95 percent and above). Membrane separation is a relatively new technology that has advantages for certain vapor recovery conditions. The various vapor recovery units differ mainly by the process used to separate the hydrocarbon vapor from the air or inert vapors. In all cases, the recovered hydrocarbon is ultimately blended into a recirculated lean hydrocarbon stream, typically the primary product being loaded. The recovered hydrocarbon, which consists mainly of light ends, is allowed to mix into a much larger volume of the product. In general, all four vapor recovery processes will not capture low molecular weight compounds such as methane, ethane, and/or propane. They are therefore best suited to recovery of vapor which has been enriched by saturation with mogas (vs. natural gas or LPG) or which has been inerted. Carbon bed adsorption -- There are two types of carbon adsorption systems: one incorporating vacuum regeneration of adsorbed vapors (Figure 11) and one which utilizes steam regeneration (Figure 12). A typical system incorporating vacuum regeneration (Figure 11) consists of two parallel carbon beds and vacuum regeneration facilities including a vacuum pump, an absorber, a separator, and associated valving. Hydrocarbon vapors pass through one of the two activated carbon beds where the hydrocarbons are removed from the vapor stream by adsorption on the carbon surface. Simultaneously the other carbon bed is vacuum regenerated to desorb the recovered hydrocarbons. The desorbed hydrocarbons are transferred via a vacuum pump to an absorber/separator where the vapors are partially condensed and recovered in a slip stream of mogas. Vapors from this absorber are recycled back to the carbon bed in the adsorption mode. In the steam regeneration adsorption system (Figure 12), the hydrocarbon vapor stream passes through one of the two beds of activated carbon where adsorption occurs. Concurrently, the other carbon bed is regenerated with low pressure steam which strips the adsorbed hydrocarbons from the activated carbon in the bed. The stripped vapors are condensed and the hydrocarbon components separated from the water in a coalescer/separator. The exit vapors from the separator are recycled to the on–stream carbon bed operating in the adsorption mode. Carbon adsorption has demonstrated vapor recovery efficiencies of up to 98% in certain applications. In addition, this process is commercially demonstrated, reliable, and used widely. The units are available as "packaged" systems. Disadvantages include the inability to capture light hydrocarbons (C3 and lighter), difficulty desorbing heavier molecules (C6 and heavier during carbon regeneration) and an inability to handle hydrocarbon vapors containing hydrogen sulfide (such as from crude) which will foul the activated carbon. In addition, certain compounds (i.e. aldehydes, ketones and other reactive compounds) may result in temperature runaways or “hot spots" in the carbon beds. This is due to the exothermic reaction on the carbon surface that causes heat to build up inside the carbon bed. Unchecked, these “hot

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spots" can approach the autoignition temperature of the hydrocarbons collected. Therefore, carbon adsorption is used most often in pure hydrocarbon product service (i.e. gasoline, benzene or other products with constant qualities or specifications). Where vapor from multiple products (gasoline, solvents, etc) are to be processed in a common bed, the vendor should be consulted to avoid possible problems associated with contamination, temperature excursions, and regeneration. In addition, testing has shown that the correct selection and initial conditioning of carbon adsorbent type can aid in minimizing bed temperature excursions. A coal base carbon tends to inhibit reactions between the carbon and vapor being absorbed, and is therefore recommended over other types. Carbon adsorption processes are also more complex (and costly) than thermal destruction (see following section). Finally, the carbon must be replaced periodically (every 7-10 years) as it degenerates.

Lean Oil Absorption -- Figure 13 shows a simplified lean oil absorption system. Hydrocarbon vapors enter the bottom of a counter–current absorber utilizing either a packed bed, trays, or sprays for contacting the vapor with an absorbing liquid. Hydrocarbon is removed from the vapor based on its solubility in the absorbing liquid, which may be simply a lean hydrocarbon stream such as mogas from the available refinery products as shown or a solvent which is regenerated. In the latter case, absorbent regeneration facilities are required. These usually include absorbent heaters, vapor strippers, and either vapor condensers or absorbers to recover the hydrocarbon vapors separated from the rich solvent. The regenerated solvent is recycled back to the absorber. The primary advantage of absorption is its ability to handle most hydrocarbon vapors. It can also accommodate variations in vapor flow rate and hydrocarbon concentrations better than carbon adsorbtion systems. It is available in sizes to handle high flow rates. Recovery efficiencies range up to 95% depending on the solvent used, absorbing column size and internals, and solvent temperature and flow. Typical efficiencies of 75 to 85% can be expected when absorbing gasoline vapors. These do not match the performance of carbon adsorption units. Refrigeration (condensation) -- (Figure 14) In a refrigeration system, hydrocarbon vapors enter a precooler, where most of the water vapor is removed, and then enter the condensing column where the remaining moisture, hydrates, and + heavier hydrocarbons (C4 ) are condensed and separated from the gas stream. Periodically the condensing columns must be defrosted with the circulation of deicing agents such as a warm brine solution or methylene chloride. Advantages of the refrigeration process shown in Figure 14 include recovery of hydrocarbons without contamination by carbon or oil absorbent. Disadvantages include relatively low hydrocarbon removal efficiencies typically in the 90% range. Typical units can cool the vapor to approximately -100 °F (-70 °C) at best. This will not allow collection of lighter hydrocarbons. In addition, this process has high maintenance and operating costs. ç

Membrane systems -- Figure 15 shows a simplified membrane system. The vapor stream enters a liquid ring compressor and is compressed to approximately 3.5 bara and then introduced into the lower portion of the scrubber tower. The absorbent stream is introduced into the upper portion of the tower cascading downward absorbing a portion of the vapor in the process. The remaining vapor portion exits the top of the tower and flows onto the membrane modules. A vacuum pump on the permeate side of the membrane module creates a pressure differential across the membrane. This causes the hydrocarbon vapors to preferentially pass or permeate through the membrane. Separating the mixture into two streams: a retentate stream at a reduced hydrocarbon level and permeate stream rich in hydrocarbons. The retentate stream is below the emission limit and is released to the atmosphere. The permeate stream is returned via the vacuum pump to the suction side of the liquid ring compressor and is mixed with the inlet stream.

Advantages of the membrane system are its relatively compact size, potential HC recovery, and inherent safety (no thermal process).

Disadvantages include the need for a suitable absorbent stream and higher potential cost for new greenfield installations.

Hybrid systems -- Hybrid recovery systems may incorporate combinations of vapor recovery systems to improve efficiencies or reduce costs. For example in cases with high hydrocarbon concentration in the vapor, a lean oil absorption system may be placed upstream of an adsorption system to reduce maximum hydrocarbon loading on the carbon beds.

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Vapor Destruction Vapor destruction processes destroy the hydrocarbons in collected vapor by thermally oxidizing (burning) them. Several types of equipment can accomplish this including the following: • Flares • Thermal Oxidizers • Catalytic Oxidizers While controlling hydrocarbon emissions, the thermal oxidation processes will also produce other compounds such as nitrous oxides (NOx), sulfur oxides (SOx) and carbon dioxide (CO2), which may also be limited by local regulations. Therefore, when proposing a vapor destruction process, it is important to consider permitting requirements relative to all emission products. Also, with inerted vapors, the addition of supplementary gas may be required to ensure combustibility. In general, any process using thermal oxidation must be isolated from the vapor collection system since it represents a continuous source of ignition. A detonation flame arrester and/or a water seal drum located upstream of the thermal oxidizer provide the necessary protection from the flame propagating upstream into the vapor collection/transfer system. Flares -- Flaring is a process which burns the collected vapors in an open flame located at the top of a stack using specially designed burners and pilots. The flare must be located in a remote location because it is an ignition source and emits heat. Flares are the least expensive vapor destruction process to purchase and operate. They offer significant reduction of hydrocarbon emissions (destruction efficiency of open flares is generally accepted as better than 98%) and can handle fluctuations in vapor composition and flow rate. The primary disadvantages of flares are the open flame and its associated luminosity, possible noise and smoke, and that the emission control efficiency cannot be monitored for compliance with regulations. Thermal oxidizers -- Thermal oxidizers are essentially enclosed flares. They consist of a burner and pilot assembly located at the base of a vertical stack. The stack is sized to completely contain the flame at maximum firing rate. The stack reduces heat radiation, luminosity, and noise. It also provides wind protection for the burners, and offers some residence time for more complete combustion than occurs in flares. Thermal oxidizers can be specified with or without temperature control. Without temperature control, the unit relies on natural draft through the open bottom of the stack to provide sufficient air for combustion. The resultant stack temperature will vary with vapor throughput and composition. At low rates and/or low hydrocarbon concentration of the vapors, the exit stack temperature can easily be down in the 300 to 500 °F (149-260 °C) range. Accordingly, any vapor not combusted right at the burner will likely not be combusted. Therefore the mixing of the vapors with combustion air is critical to ensure good destruction efficiency (greater than 98 %). With temperature control, as shown in Figure 15, the stack bottom is shrouded and the combustion air is regulated by louvers and / or forced draft blowers. With temperature controlled units, auxiliary fuel may also be required to maintain a minimum temperature to promote complete combustion when the vapors treated do not have sufficient hydrocarbon present. Typically, temperature controlled units operate with a stack exit temperature in the range of 1500 to 1800 °F (815-980 °C). The stack typically provides a 0.5 second residence time. Under these conditions, destruction efficiencies in excess of 99.9% have been demonstrated. Thermal oxidizers represent a higher purchase cost than open flares. However, they are capable of higher vapor destruction efficiencies, can be monitored for compliance, and can handle fluctuations in vapor composition and flow rate. The primary disadvantages with thermal oxidizers are the generation of NOx and SOx and possible incomplete combustion resulting in emissions of carbon monoxide (CO). Catalytic Oxidizers -- Catalytic oxidizers are similar to flares and thermal oxidizers except the combustion (oxidation) occurs at a much lower temperature. Catalytic oxidizers typically consist of a hot gas heat exchanger, thermal preheat zone with a standard burner and a catalyst bed. The incoming vapor stream is heated to the desired reaction temperature (about 600 °F [315 °C]) and run through the catalyst bed. The catalyst initiates and assists in the oxidation reaction. The catalysts are sensitive to contaminants in the vapor stream; lead, zinc, mercury and other heavy metals as well as halogenated compounds and hydrogen sulfide. As the catalyst becomes less active, the efficiency of the unit cannot be restored by increasing the combustion temperature and the catalyst must be replaced. Because they run at relatively low temperatures, catalytic units are most effective at treating low concentration vapor streams. Vapor concentrations experienced for gasoline or similar product loading operations are too highly concentrated and require dilution with excessive quantities of air and/or an inert gas prior to combustion to maintain catalyst bed temperatures within an ExxonMobil Research and Engineering Company – Fairfax, VA

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acceptable range. Accordingly catalytic oxidizers are generally not suitable for most loading operations but should be considered only for special applications with a low hydrocarbon concentration (i.e., about 1%) in the incoming vapor. Vapor Balancing In vapor balancing, vapors from the loading operation are collected and routed back to the tank from which loading is occurring. This simple system is low both in investment and operating costs. It is used mainly for LPG loading, which is covered in Subsection B. It cannot be applied to floating roof tanks which have no vapor space. Floating roof tanks are used to store most light products including crude, mogas, naphtha, and distillates. In addition, if gas is added to the vapor collection system for inerting or enrichment, vapor will be vented at the tank, which is unacceptable. Not adding gas to assure that the collected vapor is outside of its flammable range raises safety concerns associated with explosive gas mixtures in the vapor collection system and the tank. In general, vapor balancing is not used in marine vapor control. Truck Loading Vapor collection facilities at truck loading racks are somewhat simpler than for marine loading. The vapor is collected from all racks and routed to a common vapor processing system. The vapor processing technologies described for marine loading operations also apply to truck loading. The vapor collection systems are smaller than those required for marine loading due to the lower loading rates and the shorter distances that usually exist between the loading and vapor processing areas. The vapor is frequently displaced into the collection system by the product filling the truck without the use of a blower. Inerting or enriching have not been provided in existing installations since the vapors from trucks are generally well above their UFL. A detonation flame arrester is recommended immediately upstream of the vapor processing unit to isolate it (as a source of ignition) from the trucks. The displacement operation results in a small positive pressure both in the tank truck and in the vapor collection system. This pressure ranges from about 10" (254 mm) water column to a maximum regulated by law in some locations of 15–18" (380–460 mm) water column at the truck connection to the loading rack. Some regulatory authorities in the USA have recognized that not all systems are leak free (tight) and have been requiring the use of “vacuum assisted loading" to prevent vapors leaking into the atmosphere. A blower or fan designed to produce a small negative pressure (approximately -5" (-130mm) water column at the truck connection) is placed in the collection system piping to produce the vacuum assist. The vapor collection/processing system is designed to handle a vapor rate equal to the truck volumetric loading rate. Vapor composition is obtained from data provided by the owner or from samples. If no data are available a typical gasoline vapor composition, from U.S. EPA publication EPA–450/2–77.026. is as follows: Component Air Propane Iso–butane Butane N–Butane Iso–Pentane Pentane N–Pentane Hexane Total

Vol % 58.1 0.6 2.9 3.2 17.4 7.7 5.1 2.0 3.0 100.0

A knockout drum is frequently provided ahead of the vapor processing unit to protect this unit from truck overfills resulting in slugs of liquid in the collection system. The truck loading rack design must provide for the vapor collection arms or hoses. Vapor collection is possible from both top and bottom loading trucks. However, the facilities are more cumbersome, inefficient, and costly for top loading trucks. Therefore, bottom loading is preferred where vapor recovery is required.

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For bottom loading, much of the vapor collection equipment is on the truck. This minimizes the rack collection facilities required. The vapors are collected in a manifold on the truck and routed to a connection, which is usually located at the right hand (curb) side of the truck near the loading connections. The loading rack is provided with a hose that is attached to the truck connector during loading. The hose may be connected to an arm or directly to a vapor return line at grade. In the latter case, a hose lift/retraction mechanism is usually provided to store the hose off the ground when not in use. For top loading, a more complex system is required typically consisting of a tapered conical plug assembly attached to the fill pipe and a vapor return line which parallels the loading arm. Because of its taper, the plug fits various size truck hatches and provides a vapor–tight fit around the hatch. The fill pipe extends down through the plug for compartment loading and the vapors generated are forced out through a separate opening in the plug to the vapor return line. An emergency high level cutout must be provided for overfill protection. Rail Car Loading Where light products are loaded into railcars, vapor collection and processing may be required. The vapor collection system must conform to the railcar configuration. The vapor collection and processing technologies and considerations described for truck loading also apply to rail car loading. If vapor venting is permitted, an elevated vent should be provided to minimize personnel exposure to vapors. If regulations prohibit venting, a vapor recovery or destruction system will be required. System Selection Table 3 shows a summary of the vapor processing systems for marine, truck, and rail loading. This table is intended to give an overview of which systems to consider for various applications. The following comments elaborate on Table 3. General ·

Venting (not shown in Table 3) is increasingly not permitted.

·

Vapor balancing (not shown in Table 3) is generally not used because of operational and safety problems as discussed previously.

·

Flaring on a regular basis is not permitted in many locations.

·

Refrigeration vapor recovery systems do not meet current emission regulations in many locations.

Marine Loading ·

Venting (not shown in Table 3) is increasingly not permitted.

·

Vapor balancing (not shown in Table 3) is generally not used because of operational and safety problems as discussed previously.

·

Flaring on a regular basis is not permitted in many locations.

·

Refrigeration vapor recovery systems do not meet current emission regulations in many locations.

·

Vapor recovery not often economically justified by the products recovered over vapor destruction for new installations. Therefore, vapor destruction can most likely be the economic choice unless prohibited by regulations. However on replacement systems where the infrastructure exists (i.e. replacement of existing refrigeration) unit vapor recover may be justified in some cases. A rigorous cost and economic analysis is needed to make the determination.

·

Enriched/inerted vapor systems have been commonly used to date along with vapor destruction processes.

Truck or Rail Loading ·

Carbon adsorption systems have been widely used and their use is increasing.

·

Lean oil absorption is also used.

·

Refrigeration systems have been used in the past but their use is decreasing because they cannot meet regulations in many locations.

·

Vapor destruction units have been used either alone or as backup to a vapor recovery system where required in certain locations.

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DESIGN PROCEDURES The following outlines are intended to serve as guides and checklists during the planning and design of a new or expanded loading installation. MARINE LOADING SYSTEMS Step 1 - Establish the shipping schedule and fleet characteristics: 1. 2. 3. 4. 5.

Product slate for design year. Parcel and vessel sizes. Multi–product cargos. Vessel arrival pattern. (Vessel arrivals for each vessel size) Deballasting and bunkering requirements.

Step 2 - Define local factors affecting design and operation: 1. 2. 3. 4. 5.

Desired degree of automation and control philosophy. Vapor recovery regulations - enacted or anticipated. Custody transfer measurement. Laboratory analysis time, cargo documentation and clearance procedures. Existing berth characteristics (ship sizes handled, operating schedule, and products handled).

Step 3 - Develop a preliminary design: 1. Define major equipment sizes: a. Loading pumps. (Number and rates) b. Loading lines. c. Number of berths. 2. Use the following criteria: a. Classify berths by ship size, rather than by product. b. Provide berth occupancy rates of 35 to 45% for single berth installations. For multi–berth installations, acceptable berth occupancies are in the 60–70% range. c. Set loading rates equal to the maximum (see Step 4). If this information is unavailable the loading rate for each product can be set to result in a net pumping time of approximately 12 hours to load the maximum parcel for each product. This loading time is generally considered reasonable in the tanker trade. For a single product vessel, this corresponds to a loading rate (barrels/hr) @ vessel DWT/2 (dm3/s @ vessel DWT/45). The relation of loading rate to vessel DWT assumes a product specific gravity of 0.85 and a ship net cargo weight of approximately 85% of vessel DWT. d. Assume non-simultaneous loading of multi–product cargos or use basis from step 4. Step 4 - Define the vessel characteristics and local and environmental factors affecting design and operation: 1. Simultaneous or singular loading of multi–product cargos. 2. Maximum vessel loading rates for each product. This will depend on vessel size, target vessel turnaround times, tide cycle lengths, etc. 3. Berthing and departure restrictions due to weather, tides, port regulations, etc. 4. Port operational details such as traffic control, availability of pilots tug assistance, etc. 5. Historical arrival patterns.

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Step 5 - Select the optimum number of berths and loading rates: 1. Estimate the investment in loading pumps, lines and piers for the most viable cases. 2. Estimate total vessel waiting (delay) times for each case. A computer simulation program such as FAST–TABLET II should be used for design and for definitive planning. Curves (Figure 17) are also available which estimate waiting times as a function of berth occupancy. The curves are used for existing installations by plotting known data on delay time vs. berth occupancy. A new curve can then be developed similar in shape to the curves shown. This new curve can then be used to predict delay time at new occupancies. In the absence of historical data, the curves may also be used to estimate vessel delay times for screening studies. Additional detail and curves are available in Memo 83 CMS 2–215 dated July 1983 to all Members of MES from T. B. Sittema. However, because a number of simplifying assumptions are built into the curves, their use should be restricted to screening. The curves assume that all berths service all classes of ships. The likely situation is that certain ship sizes will be restricted to individual or groups of berths. In this case, the delay times should be calculated for each berth or group of berths and added. 3. Estimate vessel delay costs for each case, using waiting times estimated in Step 2 and demurrage costs obtained from a logistics specialist. 4. Select the most economic case, using return on investment criteria. Step 6 - Consider the following items: 1. Common loading lines, manifolding and/or arms. 2. The most economic method of product measurement. 3. Tank recirculation using loading pumps versus mechanical agitators. 4. In–line bunker blending. 5. Locating pumps on a common pad to facilitate future changes in service. 6. Automatic loading control. 7. Couplings on the end of the loading arm to facilitate connection to the ship manifold. 8. Maximum loading arm velocities. 9. Future requirements when defining pipe trestles; e.g., pile loadings, pipe band widths. 10. Space for future metering facilities. Step 7 - Check that the following items have been evaluated and/or specified: 1. 2. 3. 4. 5. 6.

Loading arms and hoses: operating envelope, materials, etc. Low initial loading rates are not below the minimum continuous flow requirements of pumps. Loading pumps are preferentially the same size (for interchangeable service and common spare parts). Thirty second relaxation time between filters and marine vessels for static accumulators. Onshore, local and remotely operated emergency isolation valves, one for each loading line (refer to DP XV–F). The possibility of hydraulic hammer in long lines and/or lines with substantial changes in elevation. The contractor should demonstrate adequacy of pipeline and valve design to withstand and minimize pressure surges. 7. Vapor collection equipment, if required. TRUCK LOADING SYSTEMS The owner/ affiliate marketing organization are the primary sources of information for steps 1 through 3. Refer to “Truck Loading Rack Design Guide for Clean Products", EE.1M.85. Step 1 - Establish the design year product shipping slate. 1. Volume per year of each product. 2. Peak volumes and time duration. a. Peak arrival frequency (trucks/hour). b. Volume per peak period.

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Step 2 - Establish fleet characteristics and local factors affecting operation: 1. Vehicle characteristics. a. Vehicle capacities. b. Number of compartments per truck. c. Number of products per truck. d. Top or bottom loading. e. Exterior dimensions. f. Minimum turning radius. 2. Local factors, preferences, and regulations regarding type of rack operation. a. Rack operation hours per day and days per year. b. Desired degree of terminal automation. c. Vapor recovery regulations, enacted or anticipated. d. Sequential or simultaneous truck compartment filling. e. Metering and custody transfer operations. 3. Average/maximum allowable waiting time per truck during peak periods. 4. Owner/local preferences or regulations regarding rack operation. Step 3 - Predict arrival patterns based on local experience with customer demands within the delivery area: 1. Peak arrival periods: Trucks per hour, period duration (hours). (Morning queues at start of operation can represent greatest arrival frequency over a relatively short time.) 2. Seasonal variations: can be significant with some products; e.g., mogas, heating oils, fuel oils, asphalts. Step 4 - Establish base case configuration: 1. Classify (group) trucks by products loaded. 2. Calculate average loading time per truck for each class of truck: a. Assume one stop loading. b. Assume sequential compartment filling unless advised otherwise. c. Calculate filling time. (1) Allow for low initial and topping–off rates (see Table 1). (2) Base normal filling rates on local practice or use: 500 gpm (30 dm3/s) for trucks < 4,000 gal. (15 m3) 800 gpm (50 dm3/s) for trucks ³ 4,000 gal. (15 m3) (3) Calculate filling time per compartment = Total Volume Loaded - volume loaded in slow start/stop period Loading Rate (Assume start/stop filling rate is 10% of normal filling rate) (4) Total filling time = (Filling Time per Compartment) (Number of Compartments) d. Include additional time for preparation and hookup (See Table 1). e. The reciprocal of the occupancy time in hours represents the number of trucks per hour that can be loaded at each spot. 3. For daily peak arrival periods, calculate the number of spots required for each product class with 100% rack utilization. No. of spots = (Peak Arrival Frequency, trucks/h) (Arrival Period, h) (Loading Time/Truck , h) (Arrival Period + Maximum Allowable Waiting Time, h) 4. For peak arrival periods in excess of 1–2 weeks, calculate the number of spots required for each product class based on a rack utilization of approximately 50%. No. of spots =

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(Volume/Pe ak Period) (Loading Time/Truck , h) (Peak Days) (Volume/Tr uck) (Rack open hrs/Day) (Rack open Days/year) (0.50) 365 5. For overall yearly average loading rates, calculate the number of spots required for each product class based on a rack utilization of approximately 35%. No. of spots = (Volume/Year) (Loading Time/Truck , h) (Volume/Tr uck) (Rack open hrs/Day) (Rack open Days/year) (0.35) 6. Select the highest number of spots resulting from the controlling case above rounded off to a whole number. 7. Attempt to minimize the total number of spots where possible by considering: a. Re–examining requirements (peak volumes, periods, etc) which result in a high number of spots. b. Combining low volume and/or fractional spots. c. Two–stop loading for low volume product classes. d. Dual service loading spots based on seasonal variations of different product classes. Step 5 - Examine the impact on rack occupancy and waiting times of the following: 1. Simultaneous filling with preset control: a. Multiple products per spot. b. Multiple arms per product per spot. 2. Increased and reduced filling rates. Step 6 - Consider the following items: 1. 2. 3. 4. 5. 6.

Provision for future expansion. The need for pump–off facilities. Provisions for washing or inerting trucks. Loading arms, including envelops or arm dimensions. Local and remotely operated emergency isolation valves, one for each loading line (refer to DP XV–F). Grounding equipment for all loading spots.

RAIL CAR LOADING SYSTEMS Step 1 - Establish the design year product shipping slate. 1. Volume per year of each product. 2. Peak volumes and time duration. a. Peak arrival frequency (cars/day). b. Volume per peak period.

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Step 2 - Establish fleet characteristics and local factors affecting design and operation. A survey of available rail transport is likely to be required. 1. Rail car characteristics. a. Capacities. b. Dimensions. c. Top or bottom loading. 2. Train characteristics. a. Maximum train length. b. Railway sorting requirements. 3. Local or national railway service restrictions on terminal entry, number of deliveries/pickups per day, operating hours, car switching and movement by refinery or railroad, etc. 4. Local or national railway regulations affecting layout, such as minimum curve radii, track spacing etc. 5. Plot space designated for rail facilities. 6. Local factors, preferences and regulations regarding type of rack operation. a. Hours per day and days per year of terminal operation. b. Desired degree of automation. c. Vapor recovery regulations. d. Product measurement basis (volume or weight) 7. Make a preliminary selection of basic type of rack operation. Step 3 - Lay out the area: 1. 2. 3. 4.

Shipping and receiving spurs. Sorting spur. Marshalling yard. Approach and loading spurs.

Step 4 - Establish the base case configuration for rack operation and layout: 1. Classify (group) rail cars by product. 2. Calculate average loading time per railcar for each product class: a. Calculate Filling time per car. (1) Allow for low initial and topping off–rates (See Table 2). (2) For normal filling rates use 1,000 gpm (60 dm3/s) per car. Use 1,500 gpm (90 dm3/sec) per car if a high speed, single spot per side (Type 3) rack is to be used. b. Include additional time for spotting and preparation (See Table 2). 3. Calculate the net available loading hours per day by deducting times required for the following from the total hours per day of terminal operation. a. Delivery and removal of cars to and from rack. b. End–of–day accounting. c. Customs and/or excise requirements, e.g., bonding. 4. For the peak number of cars to be loaded per day calculate the number of spots required for each product class with 100% rack utilization. No. of spots = (Peak number of Cars/Day) (Loading Time/car, h) (Net Available Loading Time/Day, h)

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5.

For peak arrival periods in excess of 1–2 weeks, calculate the number of spots required for each product class based on a rack utilization of approximately 50% of net available loading time/Day. No. of spots = (Volume/Pe ak Period) (Loading Time/Car, h) (Peak Days) (Volume/Ca r) (Net Loading Time/Day) (Rack Open Days/Year) (0.50) 365 6. For overall yearly average loading rates, calculate the number of spots required for each product class based on a rack utilization of approximately 35% of net available loading time/Day. No. of spots = (Volume/Year) (Loading Time/Car, h) (Volume/Ca r) (Net Loading Time/Day) (Rack Open Days/Year) (0.35) 7. Select the highest number of spots resulting from the controlling case above rounded off to a whole number. Step 5 - Optimize the type of rack operation and layout. 1. Re–examine the peak volumes and periods. 2. Consider presorting by product and selective rack loading. 3. Consider multiple spots per side before evaluating multiple racks.

GUIDANCE AND CONSULTING For guidance on product loading systems planning, design and troubleshooting, the Offsites Section of ExxonMobil Engineering's Project Development Division should be contacted. Table 1 Rack Occupancy Time For Tank Truck Loading Facilities (1)

See note below Preparation, Minutes(2)

Number of Compartments A

B

C

1

6

5

4

2

7

5

3

8

6

4

9

5

10

Total Hookup Time, Minutes

Slow Start and Stop Time, Minutes(3) D

E

1/2

3

2

4

1

4

3

4

1

5

4

6

5

1

6

4

7

5

2

7

5

6 11 8 6 2 7 5 Notes: (1) In the absence of local data, Table 1 may be used to calculate rack occupancy. Occupancy time per truck is the sum of preparation, spout switch time, slow start and stop penalty and filling time. Table assumes that multiple compartments are loaded in sequence. (2) Period when no loading occurs, including spotting, grounding, spout insertion and withdrawal and document preparation. Types of operation are: A = Manual document preparation. B = (3)

Local ticket printer.

C = Remote document preparation Based on a typical truck capacity of approximately 5,000 U.S. gallons (20 m3). Types of operation are: D =

Manual control.

E =

Automatic, preset control.

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Table 2 Rack Occupancy Time For Rail Car Loading Facilities (1)

See note below

Type of Operation(2) Element, Minutes

A

B

C

D

E

F

G

Spotting

2

1 1/2

–

–

–

–

–

Preparation(3)

3

1 1/2

–

–

–

–

–

Slow Start & Stop Time

–

–

(4)

(4)

–

–

–

Document – – – – 2 1 0 Preparation Notes: (1) In the absence of local data, Table 2 may be used to calculate rack occupancy. Occupancy time per rail car is the sum of the four elements plus filling time. Table assumes a single spot per side. (2) Types of operation are: A =

(3) (4)

Single spot per side.

B =

“High–speed" operation, single spot per side.

C =

Manual control of quantity loaded.

D =

Automatic, preset control.

E =

Manual document preparation.

F =

Local ticket printer.

G = Remote document preparation. Includes opening hatch, inserting, withdrawing and draining arm and closing hatch. Time allowed depends on rail car capacity and loading arm size. For C, assume 25 percent of volume loaded at low rate; for D, 12 percent. Take low rates as follows: 100 gpm for 4–inch arm (6.3 dm3/s for 100 mm arm). 250 gpm for 6–inch arm (16 dm3/s for 150 mm arm). 450 gpm for 8–inch arm (28 dm3/s for 200 mm arm). 700 gpm for 10–inch arm (44 dm3/s for 250 mm arm).

Table 3 Vapor Processing System Selection (1)

See note below

Marine Loading

Truck or

Enriched Vapor

Inerted Vapor

Rail Loading

Carbon Adsorption

NR(2)

3

3 (commonly used)

Lean Oil Absorption

NR(2)

3

3 (commonly used)

Refrigeration

NR(2)

3 (3)

3 (3)

3 (4)

3 (4)

3 (4)

3

3

3

Vapor Recovery

Vapor Destruction Flares Thermal Oxidizers

Catalytic Oxidizers 3 3 3 Notes: (1) Items indicated by a check should be evaluated. Notes indicate known disadvantages. NR indicates not recommended.

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(2) (3) (4)

Not recommended where vapor is enriched with natural gas, C2, or C3 all of that will not be captured. Enriching vapor by saturation with mogas will result in high recovery loads. May not meet current emission regulations. Not permitted in many locations due to regulatory requirements.

Figure 1 Typical Top–Loading Truck Rack

Loading Arm Counter and Ticket Printer

Positive Displacement Meter

Strainer

SIDE VIEW

Handrails

Counterbalanced Ramp. (Folds back unless locked down.)

DP23AF01

END VIEW

ExxonMobil Research and Engineering Company – Fairfax, VA

ExxonMobil Proprietary

PRODUCT LOADING SYSTEMS

Section

Page

XXIII-A

BASIC LOADING SYSTEMS DESIGN PRACTICES

31 of 44

May, 2004

Figure 2 Marine Loading Control System Selector Switch

Note 2

FL (CO)

PL (CI)

RBV

Product Recirculation

RBV

FIQ

TM

0 0 Stop Minimum Flow Bypass

Product Loading Pumps

FC

Shoreline

Flow Controller

Flow Straightener

Strainer

FL (CO)

Start

DP23AF02

Air Eliminator

To/From Product Storage

FL (CO)

Meter and Counter

Berth 1

FCV

Berth 2

Typical for Each Arm

Notes: (1) Refer to Section XV for requirements associated with emergency shutdown and isolation. (2) Optional for multiple pump installations.

ExxonMobil Research and Engineering Company – Fairfax, VA

ExxonMobil Proprietary Section XXIII-A

PRODUCT LOADING SYSTEMS

Page 32 of 44

BASIC LOADING SYSTEMS DESIGN PRACTICES

May, 2004

Figure 3 Tank Truck (Or Rail Car) Loading Control System

Product/Water Level Gauges, Temperature Ind.

Product

Pump Mov

Water

I/O

Mo v Temperature Probe

I/O Alarm

I/O High Level Cutoff I/O

Filter

Micro Processor

Ground

Meter with Pulser and Preset

DP23AF03

(PDM or TM)

FC V

Printer Card Reader and Keypad Display

ExxonMobil Research and Engineering Company – Fairfax, VA

To Admin Computer

ExxonMobil Proprietary

PRODUCT LOADING SYSTEMS

Section XXIII-A

BASIC LOADING SYSTEMS DESIGN PRACTICES

Page 33 of 44

May, 2004

Figure 4 Spring Balanced Pantograph Top Loading Arm

2

6 9

10

4 6

7 2

5 3

1

8

Item No.

DP23AF04

Description

1

Counter Balance Swing Joint

2

Spring Balance

3

Loading Valve

4

Vacuum Breaker

5

Primary Arm

6

Drop Pipe Swing Joint

7

Drop Pipe

8

150 psi Flange

9

Intermediate Swing Joint

10

Secondary Arm

ExxonMobil Research and Engineering Company – Fairfax, VA

ExxonMobil Proprietary Section XXIII-A

PRODUCT LOADING SYSTEMS

Page 34 of 44

BASIC LOADING SYSTEMS DESIGN PRACTICES

May, 2004

Figure 5 Counterweighted Hose Loader

Swivel Joint

Product From Loading Assembly

Truck Fill Coupling

C Swivel Elbow

DP23AF05

Dry-Break Coupling and Spacer

ExxonMobil Research and Engineering Company – Fairfax, VA

ExxonMobil Proprietary

PRODUCT LOADING SYSTEMS

Section XXIII-A

BASIC LOADING SYSTEMS DESIGN PRACTICES

35 of 44

May, 2004

Figure 6 “A" Frame Bottom Loading Arm

3

9

2

4

7

6 8 1 5

Item No.

DP23AF06

Page

Description

1

Counter Balance Swing Joint

2

Primary Arm

3

Apex Swing Joint

4

Secondary Arm

5

Outboard Swing Joint

6

Coupling

7

Spring Balance

8

Handle

9

Compound Link

ExxonMobil Research and Engineering Company – Fairfax, VA

ExxonMobil Proprietary Section XXIII-A

PRODUCT LOADING SYSTEMS

Page 36 of 44

BASIC LOADING SYSTEMS DESIGN PRACTICES

May, 2004

Figure 7 Common Manifolding With Stripping Facility For Marine Loading System

To/ Fro mO the rB erth s Va cuu mB rea ker

(1) (1)

p Slo

ter Wa t s lla ct D Ba du Pro ct C du o B r P uct rod ct A To P du /Fr o r om P Ta nka ge

(1)

(1)

(1) (1)

Loa din gA rm

Slo pe

Min .

Slo pe

(1) Me ter s

(1)

Min .

(1) (1)

Note: (1) Soft-seat, double-face valve with integral body bleed.

Stripping Pump Slop Oil Sump

DP23AF07

ExxonMobil Research and Engineering Company – Fairfax, VA

ExxonMobil Proprietary

PRODUCT LOADING SYSTEMS

Section XXIII-A

BASIC LOADING SYSTEMS DESIGN PRACTICES

Queue Loading Racks

Truck Park

Dispatch Office

Queue

Loaded Truck Park

Storehouse x

x

x

x

Car Park

x

x

x

x Queue

x

37 of 44

May, 2004

Figure 8 Layout Of Truck Loading Area

x

Page

x

x

x

x

x

Fuel, Oil & Air x x x x

Truck Wash x

x

x

Fence

DP23AF08

ExxonMobil Research and Engineering Company – Fairfax, VA

x

x

x

x

ExxonMobil Proprietary Section XXIII-A

PRODUCT LOADING SYSTEMS

Page 38 of 44

BASIC LOADING SYSTEMS DESIGN PRACTICES

May, 2004

Figure 9 Layout Of Rail Car Loading Area Fence Sorting Spur

Marshalling Spur

x

x

Transfer Spur

Sp

x

ac h

ur s

Receiving and Shipping Spurs

x

pr o

x

Ap

x

x

x

x x

x

Sorting Hump

x

x

x

Loading Racks

Loading Spurs Car Pullers

DP23AF09

Figure 10 Marine Loading Vapor Emissions Collection

Enriching or Inerting Gas Detonation Flame Arrester SV Detonation Flame Arrester Liquid Ring Vacuum Compressor Seal Water Separation Drum

Cooler Condensate K/O Drum

Vessel Berth

Seal Water Pump

Detonation Flame Arrester

Loading Pump DP23AF10

ExxonMobil Research and Engineering Company – Fairfax, VA

Vapor Control Facilities

ExxonMobil Proprietary

PRODUCT LOADING SYSTEMS

Section XXIII-A

BASIC LOADING SYSTEMS DESIGN PRACTICES

39 of 44

May, 2004

Figure 11 Carbon Adsorption Vapor Recovery Facilities (Vacuum Regeneration) Exhaust Vapors

Flame Arrester Purge Air

Purge Air

Carbon Adsorption Beds

Recycle Line Lean Absorbent Absorber Product To/From Storage

Vacuum Pump Separator Inlet HC Vapors from Loading Operations

Page

Rich Absorbant Detonation Flame Arrester

ExxonMobil Research and Engineering Company – Fairfax, VA

DP23AF11

ExxonMobil Proprietary Section XXIII-A

PRODUCT LOADING SYSTEMS

Page 40 of 44

BASIC LOADING SYSTEMS DESIGN PRACTICES

May, 2004

Figure 12 Carbon Adsorption Vapor Recovery Facilities (Steam Regeneration) Exhaust

Vapors Flame Arrester Low Pressure Steam

Carbon Adsorption Beds

Condensor

Inlet HC Vapors from Loading Operations

Cooling Water Detonation Flame Arrester

Recovered Hydrocarbon Condensate DP23AF12

Water Separator

ExxonMobil Research and Engineering Company – Fairfax, VA

ExxonMobil Proprietary

PRODUCT LOADING SYSTEMS

Section XXIII-A

BASIC LOADING SYSTEMS DESIGN PRACTICES

41 of 44

May, 2004

Figure 13 Lean Oil Absorption Vapor Recovery Facilities Exhaust Vapors

Flame Arrester

Lean Oil from Storage

Cooler/ Chiller

Inlet HC Vapors from Loading Operations

Cooler

Rich Oil to Storage

Absorber Tower

DP23AF13

Figure 14 Refrigeration (Condensation) Vapor Recovery Facilities Exhaust Vapors Flame Arrester Inlet HC Vapors from Loading Operations

Precooler Refrigeration Unit

Page

Precooler Coil

Low Temperature Refrigeration Unit

Defrost Fluid

Water DP23AF14

ExxonMobil Research and Engineering Company – Fairfax, VA

Hydrocarbon Condensate

ExxonMobil Proprietary Section XXIII-A

PRODUCT LOADING SYSTEMS

Page 42 of 44

BASIC LOADING SYSTEMS DESIGN PRACTICES

May, 2004

Figure 15 Simplified Membrane System ç

Scrubber Tower

Vapor Inlet

Vent stack

Liquid Ring Compressor

Membrane Module Retentate

Permeate

Vacuum pump

Absorbent inlet

Absorbent + recovered

ExxonMobil Research and Engineering Company – Fairfax, VA

ExxonMobil Proprietary

PRODUCT LOADING SYSTEMS

Section XXIII-A

BASIC LOADING SYSTEMS DESIGN PRACTICES

Atmosphere

Temperature Controller

Insulation (Jacketing or Internal Refractory)

TRC

Combustor

Fuel Gas Supply

Pilot/Fuel Gas Knockout Drum

Pilot Valve

Burner Detonation/Flame Arrester

Seal Drum DP23AF15

43 of 44

May, 2004

Figure 16 Facilities For Emission Control By Thermal Oxidation

Inlet HC Vapors from Loading Operations

Page

Makeup Water

ExxonMobil Research and Engineering Company – Fairfax, VA

Combustion Air Blower

ExxonMobil Proprietary Section XXIII-A

PRODUCT LOADING SYSTEMS

Page 44 of 44

BASIC LOADING SYSTEMS DESIGN PRACTICES

May, 2004

Figure 17 Average Delay Vs. Berth Occupancy For Calibration With Historical Data

10.0

5.0 4.0 3.0 2.0

1.0

Average Delay in Multiples of Average Service Time

.50 .40 .30

S=

1

.20

=2

.03

3

S

=

4 S

.02

=

5 S

=

6 =

7 S

S

S

8

=

S

=

.01

10

S

.04

=

.05

9

S

=

.10

.005 .004 .003 .002

.001

.2

.3

.4

.5

.6

.7

.8

Berth Occupancy

DP23AF16

Notes: (1) S is the Number of Berths (2) Curves are based on a Poisson distribution for arrivals and a constant service time (3) Curves taken from memo 83CMS2-215 to all members of MES from T. B. Sittema

ExxonMobil Research and Engineering Company – Fairfax, VA

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