Other Refinery Operations

1. Heat Exchangers, Coolers, and Process Heaters
2. Heating Operations. Process heaters and heat exchangers preheat feedstock in distillation towers and in refinery processes to reaction temperatures. Heat exchangers use either steam or hot hydrocarbon transferred from some other section of the process for heat input. The heaters are usually designed for specific process operations, and most are of cylindrical vertical or box-type designs. The major portion of heat provided to process units comes from fired heaters fueled by refinery or natural gas, distillate, and residual oils. Fired heaters are found on crude and reformer preheaters, coker heaters, and large-column reboilers.
3. Cooling Operations. Heat also may be removed from some processes by air and water exchangers, fin fans, gas and liquid coolers, and overhead condensers, or by transferring heat to other systems. The basic mechanical vapor-compression refrigeration system, which may serve one or more process units, includes an evaporator, compressor, condenser, controls, and piping. Common coolants are water, alcohol/water mixtures, or various glycol solutions.

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3. Health and Safety Considerations
4. Fire Protection and Prevention. A means of providing adequate draft or steam purging is required to reduce the chance of explosions when lighting fires in heater furnaces. Specific start-up and emergency procedures are required for each type of unit. If fire impinges on fin fans, failure could occur due to overheating. If flammable product escapes from a heat exchanger or cooler due to a leak, fire could occur.
5. Safety. Care must be taken to ensure that all pressure is removed from heater tubes before removing header or fitting plugs. Consideration should be given to providing for pressure relief in heat-exchanger piping systems in the event they are blocked off while full of liquid. If controls fail, variations of temperature and pressure could occur on either side of the heat exchanger. If heat exchanger tubes fail and process pressure is greater than heater pressure, product could enter the heater with downstream consequences. If the process pressure is less than heater pressure, the heater stream could enter into the process fluid. If loss of circulation occurs in liquid or gas coolers, increased product temperature could affect downstream operations and require pressure relief.
6. Health. Because these are closed systems, exposures under normal operating conditions are expected to be minimal. Depending on the fuel, process operation, and unit design, there is a potential for exposure to hydrogen sulfide, carbon monoxide, hydrocarbons, steam boiler feed-water sludge, and water-treatment chemicals. Skin contact should be avoided with boiler blowdown, which may contain phenolic compounds. Safe work practices and/or appropriate personal protective equipment against hazards may be needed during process maintenance, inspection, and turnaround activities and for protection from radiant heat, superheated steam, hot hydrocarbon, and noise exposures.
7. Steam Generation
8. Heater and Boiler Operations. Steam is generated in main generation plants, and/or at various process units using heat from flue gas or other sources. Heaters (furnaces) include burners and a combustion air system, the boiler enclosure in which heat transfer takes place, a draft or pressure system to remove flue gas from the furnace, soot blowers, and compressed-air systems that seal openings to prevent the escape of flue gas. Boilers consist of a number of tubes that carry the water-steam mixture through the furnace for maximum heat transfer. These tubes run between steam-distribution drums at the top of the boiler and water-collecting drums at the bottom of the boiler. Steam flows from the steam drum to the superheater before entering the steam distribution system.
9. Heater Fuel
10. Heaters may use any one or combination of fuels including refinery gas, natural gas, fuel oil, and powdered coal. Refinery off-gas is collected from process units and combined with natural gas and LPG in a fuel-gas balance drum. The balance drum provides constant system pressure, fairly stable Btu-content fuel, and automatic separation of suspended liquids in gas vapors, and it prevents carryover of large slugs of condensate into the distribution system. Fuel oil is typically a mix of refinery crude oil with straight-run and cracked residues and other products. The fuel-oil system delivers fuel to process-unit heaters and steam generators at required temperatures and pressures. The fuel oil is heated to pumping temperature, sucked through a coarse suction strainer, pumped to a temperature-control heater, and then pumped through a fine-mesh strainer before being burned.
11. In one example of process-unit heat generation, carbon monoxide boilers recover heat in catalytic cracking units as carbon monoxide in flue gas is burned to complete combustion. In other processes, waste-heat recovery units use heat from the flue gas to make steam.
12. Steam Distribution. The distribution system consists of valves, fittings, piping, and connections suitable for the pressure of the steam transported. Steam leaves the boilers at the highest pressure required by the process units or electrical generation. The steam pressure is then reduced in turbines that drive process pumps and compressors. Most steam used in the refinery is condensed to water in various types of heat exchangers. The condensate is reused as boiler feedwater or discharged to wastewater treatment. When refinery steam is also used to drive steam turbine generators to produce electricity, the steam must be produced at much higher pressure than required for process steam. Steam typically is generated by heaters (furnaces) and boilers combined in one unit.
13. Feedwater
14. Feedwater supply is an important part of steam generation. There must always be as many pounds of water entering the system as there are pounds of steam leaving it. Water used in steam generation must be free of contaminants including minerals and dissolved impurities that can damage the system or affect its operation. Suspended materials such as silt, sewage, and oil, which form scale and sludge, must be coagulated or filtered out of the water. Dissolved gases, particularly carbon dioxide and oxygen, cause boiler corrosion and are removed by deaeration and treatment. Dissolved minerals including metallic salts, calcium, carbonates, etc., that cause scale, corrosion, and turbine blade deposits are treated with lime or soda ash to precipitate them from the water. Recirculated cooling water must also be treated for hydrocarbons and other contaminants.
15. Depending on the characteristics of raw boiler feedwater, some or all of the following six stages of treatment will be applicable:

• Clarification;
• Sedimentation;
• Filtration;
• Ion exchange;
• Deaeration; and
• Internal treatment.

5. Health and Safety Considerations
6. Fire Protection and Prevention. The most potentially hazardous operation in steam generation is heater startup. A flammable mixture of gas and air can build up as a result of loss of flame at one or more burners during light-off. Each type of unit requires specific startup and emergency procedures including purging before lightoff and in the event of misfire or loss of burner flame.
7. Safety. If feedwater runs low and boilers are dry, the tubes will overheat and fail. Conversely, excess water will be carried over into the steam distribution system and damage the turbines. Feedwater must be free of contaminants that could affect operations. Boilers should have continuous or intermittent blowdown systems to remove water from steam drums and limit buildup of scale on turbine blades and superheater tubes. Care must be taken not to overheat the superheater during startup and shut-down. Alternate fuel sources should be provided in the event of loss of gas due to refinery unit shutdown or emergency. Knockout pots provided at process units remove liquids from fuel gas before burning.
8. Health. Safe work practices and/or appropriate personal protective equipment may be needed for potential exposures to feedwater chemicals, steam, hot water, radiant heat, and noise, and during process sampling, inspection, maintenance, and turnaround activities.
9. Pressure-Relief and Flare Systems
10. Pressure-Relief Systems. Pressure-relief systems control vapors and liquids that are released by pressure-relieving devices and blow-downs. Pressure relief is an automatic, planned release when operating pressure reaches a predetermined level. Blowdown normally refers to the intentional release of material, such as blowdowns from process unit startups, furnace blowdowns, shutdowns, and emergencies. Vapor depressuring is the rapid removal of vapors from pressure vessels in case of fire. This may be accomplished by the use of a rupture disc, usually set at a higher pressure than the relief valve.
11. Safety Relief Valve Operations. Safety relief valves, used for air, steam, and gas as well as for vapor and liquid, allow the valve to open in proportion to the increase in pressure over the normal operating pressure. Safety valves designed primarily to release high volumes of steam usually pop open to full capacity. The overpressure needed to open liquid-relief valves where large-volume discharge is not required increases as the valve lifts due to increased spring resistance. Pilot-operated safety relief valves, with up to six times the capacity of normal relief valves, are used where tighter sealing and larger volume discharges are required. Nonvolatile liquids are usually pumped to oil-water separation and recovery systems, and volatile liquids are sent to units operating at a lower pressure.
12. Flare Systems. A typical closed pressure release and flare system includes relief valves and lines from process units for collection of discharges, knockout drums to separate vapors and liquids, seals, and/or purge gas for flashback protection, and a flare and igniter system which combusts vapors when discharging directly to the atmosphere is not permitted. Steam may be injected into the flare tip to reduce visible smoke.
13. Pressure Relief Health and Safety Considerations
14. Fire Protection and Prevention. Vapors and gases must not discharge where sources of ignition could be present.
15. Safety. Liquids should not be discharged directly to a vapor disposal system. Flare knockout drums and flares need to be large enough to handle emergency blowdowns. Drums should be provided with relief in the event of overpressure.

Pressure relief valves must be provided where the potential exists for overpressure in refinery processes due to the following causes:

• Loss of cooling water, which may greatly reduce pressure in condensers and increase the pressure in the process unit.
• Loss of reflux volume, which may cause a pressure drop in condensers and a pressure rise in distillation towers because the quantity of reflux affects the volume of vapors leaving the distillation tower.
• Rapid vaporization and pressure increase from injection of a lower boiling-point liquid including water into a process vessel operating at higher temperatures.
• Expansion of vapor and resultant over-pressure due to overheated process steam, malfunctioning heaters, or fire.
• Failure of automatic controls, closed outlets, heat exchanger failure, etc.
• Internal explosion, chemical reaction, thermal expansion, or accumulated gases.

Maintenance is important because valves are required to function properly. The most common operating problems are listed below.

• Failure to open at set pressure, because of plugging of the valve inlet or outlet, or because corrosion prevents proper operation of the disc holder and guides.
• Failure to reseat after popping open due to fouling, corrosion, or deposits on the seat or moving parts, or because solids in the gas stream have cut the valve disc.
• Chattering and premature opening, because operating pressure is too close to the set point.

1. Health. Safe work practices and/or appropriate personal protective equipment may be needed to protect against hazards during inspection, maintenance, and turnaround activities.
2. Wastewater Treatment
3. Description. Wastewater treatment is used for process, runoff, and sewerage water prior to discharge or recycling. Wastewater typically contains hydrocarbons, dissolved materials, suspended solids, phenols, ammonia, sulfides, and other compounds. Wastewater includes condensed steam, stripping water, spent caustic solutions, cooling tower and boiler blowdown, wash water, alkaline and acid waste neutralization water, and other process-associated water.
4. Pretreatment Operations. Pretreatment is the separation of hydrocarbons and solids from wastewater. API separators, interceptor plates, and settling ponds remove suspended hydrocarbons, oily sludge, and solids by gravity separation, skimming, and filtration. Some oil-in-water emulsions must be heated to assist in separating the oil and water. Gravity separation depends on the specific gravity differences between water and immiscible oil globules and allows free oil to be skimmed off the surface of the wastewater. Acidic wastewater is neutralized using ammonia, lime, or soda ash. Alkaline wastewater is treated with sulfuric acid, hydrochloric acid, carbon dioxide-rich flue gas, or sulfur.
5. Secondary Treatment Operations. After pretreatment, suspended solids are removed by sedimentation or air flotation. Wastewater with low levels of solids may be screened or filtered. Flocculation agents are sometimes added to help separation. Secondary treatment processes biologically degrade and oxidize soluble organic matter by the use of activated sludge, unaerated or aerated lagoons, trickling filter methods, or anaerobic treatments. Materials with high adsorption characteristics are used in fixed-bed filters or added to the wastewater to form a slurry which is removed by sedimentation or filtration. Additional treatment methods are used to remove oils and chemicals from wastewater. Stripping is used on wastewater containing sulfides and/or ammonia, and solvent extraction is used to remove phenols.
6. Tertiary Treatment Operations. Tertiary treatments remove specific pollutants to meet regulatory discharge requirements. These treatments include chlorination, ozonation, ion exchange, reverse osmosis, activated carbon adsorption, etc. Compressed oxygen is diffused into wastewater streams to oxidize certain chemicals or to satisfy regulatory oxygen-content requirements. Wastewater that is to be recycled may require cooling to remove heat and/or oxidation by spraying or air stripping to remove any remaining phenols, nitrates, and ammonia.
7. Health and Safety Considerations
8. Fire Protection and Prevention. The potential for fire exists if vapors from wastewater containing hydrocarbons reach a source of ignition during treatment.
9. Health. Safe work practices and/or appropriate personal protective equipment may be needed for exposures to chemicals and waste products during process sampling, inspection, maintenance, and turnaround activities as well as to noise, gases, and heat.
10. Cooling Towers
11. Description. Cooling towers remove heat from process water by evaporation and latent heat transfer between hot water and air. The two types of towers are crossflow and counterflow. Crossflow towers introduce the airflow at right angles to the water flow throughout the structure. In counterflow cooling towers, hot process water is pumped to the uppermost plenum and allowed to fall through the tower. Numerous slats or spray nozzles located throughout the length of the tower disperse the water and help in cooling. Air enters at the tower bottom and flows upward against the water. When the fans or blowers are at the air inlet, the air is considered to be forced draft. Induced draft is when the fans are at the air outlet.
12. Cooling Water. Recirculated cooling water must be treated to remove impurities and dissolved hydrocarbons. Because the water is saturated with oxygen from being cooled with air, the chances for corrosion are increased. One means of corrosion prevention is the addition of a material to the cooling water that forms a protective film on pipes and other metal surfaces.
13. Health and Safety Considerations
14. Fire Prevention and Protection. When cooling water is contaminated by hydrocarbons, flammable vapors can be evaporated into the discharge air. If a source of ignition is present, or if lightning occurs, a fire may start. A potential fire hazard also exists where there are relatively dry areas in induced-draft cooling towers of combustible construction.
15. Safety. Loss of power to cooling tower fans or water pumps could have serious consequences in the operation of the refinery. Impurities in cooling water can corrode and foul pipes and heat exchangers, scale from dissolved salts can deposit on pipes, and wooden cooling towers can be damaged by microorganisms.
16. Health. Cooling-tower water can be contaminated by process materials and by-products including sulfur dioxide, hydrogen sulfide, and carbon dioxide, with resultant exposures. Safe work practices and/or appropriate personal protective equipment may be needed during process sampling, inspection, maintenance, and turnaround activities; and for exposure to hazards such as those related to noise, water-treatment chemicals, and hydrogen sulfide when wastewater is treated in conjunction with cooling towers.
17. Electric Power
18. Description. Refineries may receive electricity from outside sources or produce their own power with generators driven by steam turbines or gas engines. Electrical substations receive power from the utility or power plant for distribution throughout the facility. They are usually located in nonclassified areas, away from sources of vapor or cooling-tower water spray. Transformers, circuit breakers, and feed-circuit switches are usually located in substations. Substations feed power to distribution stations within the process unit areas. Distribution stations can be located in classified areas, providing that classification requirements are met. Distribution stations usually have a liquid-filled transformer and an oil-filled or air-break disconnect device.
19. Health and Safety Considerations
20. Fire Protection and Prevention. Generators that are not properly classified and are located too close to process units may be a source of ignition should a spill or release occur.
21. Safety. Normal electrical safety precautions including dry footing, high-voltage warning signs, and guarding must be taken to protect against electrocution. Lockout/tagout and other appropriate safe work practices must be established to prevent energization while work is being performed on high-voltage electrical equipment.
22. Health. Safe work practices and/or the use of appropriate personal protective equipment may be needed for exposures to noise, for exposure to hazards during inspection and maintenance activities, and when working around transformers and switches that may contain a dielectric fluid which requires special handling precautions.
23. Gas and Air Compressors
24. Description. Both reciprocating and centrifugal compressors are used throughout the refinery for gas and compressed air. Air compressor systems include compressors, coolers, air receivers, air dryers, controls, and distribution piping. Blowers are used to provide air to certain processes. Plant air is provided for the operation of air-powered tools, catalyst regeneration, process heaters, steam-air decoking, sour-water oxidation, gasoline sweetening, asphalt blowing, and other uses. Instrument air is provided for use in pneumatic instruments and controls, air motors and purge connections.
25. Health and Safety Considerations
26. Fire Protection and Prevention. Air compressors should be located so that the suction does not take in flammable vapors or corrosive gases. There is a potential for fire should a leak occur in gas compressors.
27. Safety. Knockout drums are needed to prevent liquid surges from entering gas compressors. If gases are contaminated with solid materials, strainers are needed. Failure of automatic compressor controls will affect processes. If maximum pressure could potentially be greater than compressor or process-equipment design pressure, pressure relief should be provided. Guarding is needed for exposed moving parts on compressors. Compressor buildings should be properly electrically classified, and provisions should be made for proper ventilation.

Where plant air is used to back up instrument air, interconnections must be upstream of the instrument air drying system to prevent contamination of instruments with moisture. Alternate sources of instrument air supply, such as use of nitrogen, may be needed in the event of power outages or compressor failure.

1. Health. Safe work practices and/or appropriate personal protective equipment may be needed for exposure to hazards such as noise and during inspection and maintenance activities. The use of appropriate safeguards must be considered so that plant and instrument air is not used for breathing or pressuring potable water systems.
2. Marine, Tank Car, and Tank Truck Loading and Unloading
3. Description. Facilities for loading liquid hydrocarbons into tank cars, tank trucks, and marine vessels and barges are usually part of the refinery operations. Product characteristics, distribution needs, shipping requirements, and operating criteria are important when designing loading facilities. Tank trucks and rail tank cars are either top- or bottom-loaded, and vapor-recovery systems may be provided where required. Loading and unloading liquefied petroleum gas (LPG) require special considerations in addition to those for liquid hydrocarbons.
4. Health and Safety Considerations
5. Fire Protection and Prevention. The potential for fire exists where flammable vapors from spills or releases can reach a source of ignition. Where switch-loading is permitted, safe practices need to be established and followed. Bonding is used to equalize the electrical charge between the loading rack and the tank truck or tank car. Grounding is used at truck and rail loading facilities to prevent flow of stray currents. Insulating flanges are used on marine dock piping connections to prevent static electricity buildup and discharge. Flame arrestors should be installed in loading rack and marine vapor-recovery lines to prevent flashback.
6. Safety. Automatic or manual shutoff systems at supply headers are needed for top and bottom loading in the event of leaks or overfills. Fall protection such as railings are needed for top-loading racks where employees are exposed to falls. Drainage and recovery systems may be provided for storm drainage and to handle spills and leaks. Precautions must be taken at LPG loading facilities not to overload or overpressurize tank cars and trucks.
7. Health. The nature of the health hazards at loading and unloading facilities depends upon the products being loaded and the products previously transported in the tank cars, tank trucks, or marine vessels. Safe work practices and/or appropriate personal protective equipment may be needed to protect against hazardous exposures when loading or unloading, cleaning up spills or leaks, or when gauging, inspecting, sampling, or performing maintenance activities on loading facilities or vapor-recovery systems.
8. Turbines
9. Description. Turbines are usually gas- or steam-powered and are typically used to drive pumps, compressors, blowers, and other refinery process equipment. Steam enters turbines at high temperatures and pressures, expands across and drives rotating blades while directed by fixed blades.
10. Health and Safety Considerations
11. Safety. Steam turbines used for exhaust operating under vacuum should have safety relief valves on the discharge side, both for protection and to maintain steam in the event of vacuum failure. Where maximum operating pressure could be greater than design pressure, steam turbines should be provided with relief devices. Consideration should be given to providing governors and overspeed control devices on turbines.
12. Health. Safe work practices and/or appropriate personal protective equipment may be needed for noise, steam and heat exposures, and during inspection and maintenance activities.
13. Pumps, Piping and Valves
14. Description
15. Centrifugal and positive-displacement (i.e., reciprocating) pumps are used to move hydrocarbons, process water, fire water, and wastewater through piping within the refinery. Pumps are driven by electric motors, steam turbines, or internal combustion engines. The pump type, capacity, and construction materials depend on the service for which it is used.
16. Process and utility piping distribute hydrocarbons, steam, water, and other products throughout the facility. Their size and construction depend on the type of service, pressure, temperature, and nature of the products. Vent, drain, and sample connections are provided on piping, as well as provisions for blanking.
17. Different types of valves are used depending on their operating purpose. These include gate valves, bypass valves, globe and ball valves, plug valves, block and bleed valves, and check valves. Valves can be manually or automatically operated.
18. Health and Safety Considerations
19. Fire Protection and Prevention. The potential for fire exists should hydrocarbon pumps, valves, or lines develop leaks that could allow vapors to reach sources of ignition. Remote sensors, control valves, fire valves, and isolation valves should be used to limit the release of hydrocarbons at pump suction lines in the event of leakage and/or fire.
20. Safety. Depending on the product and service, backflow prevention from the discharge line may be needed. The failure of automatic pump controls could cause a deviation in process pressure and temperature. Pumps operated with reduced or no flow can overheat and rupture. Pressure relief in the discharge piping should be provided where pumps can be overpressured. Provisions may be made for pipeline expansion, movement, and temperature changes to avoid rupture. Valves and instruments that require servicing or other work should be accessible at grade level or from an operating platform. Operating vent and drain connections should be provided with double-block valves, a block valve and plug, or blind flange for protection against releases.
21. Health. Safe work practices and/or appropriate personal protective equipment may be needed for exposure to hazards such as those related to liquids and vapors when opening or draining pumps, valves, and/or lines, and during product sampling, inspection, and maintenance activities.
22. Tank Storage
23. Description. Atmospheric storage tanks and pressure storage tanks are used throughout the refinery for storage of crudes, intermediate hydrocarbons (during the process), and finished products. Tanks are also provided for fire water, process and treatment water, acids, additives, and other chemicals. The type, construction, capacity and location of tanks depends on their use and materials stored.
24. Health and Safety Considerations
25. Fire Prevention and Protection. The potential for fire exists should hydrocarbon storage tanks be overfilled or develop leaks that allow vapors to escape and reach sources of ignition. Remote sensors, control valves, isolation valves, and fire valves may be provided at tanks for pump-out or closure in the event of a fire in the tank, or in the tank dike or storage area.
26. Safety. Tanks may be provided with automatic overflow control and alarm systems, or manual gauging and checking procedures may be established to control overfills.
27. Health. Safe work practices and/or appropriate personal protective equipment may be needed for exposure to hazards related to product sampling, manual gauging, inspection, and maintenance activities including confined space entry where applicable.

VI. Bibliography

American Petroleum Institute. 1971. Chemistry and Petroleum for Classroom Use in Chemistry Courses. Washington, D.C.: American Petroleum Institute.

__________. 1973. Industrial Hygiene Monitoring Manual for Petroleum Refineries and Selected Petrochemical Operations. Manual 2700-1/79-1M. Washington, D.C.: American Petroleum Institute.

__________. 1980. Facts About Oil. Manual 4200-10/80-25M. Washington, D.C.: American Petroleum Institute.

__________. 1990. Management of Process Hazards. RP 750. Washington, D.C.: American Petroleum Institute.

__________. 1990. Inspection of Piping, Tubing, Valves and Fittings. RP 574. Washington, D.C.: American Petroleum Institute.

__________. 1991. Inspection of Fired Boilers and Heaters. RP 573. Washington, D.C.: American Petroleum Institute.

__________. 1992. Inspection of Pressure Vessels. RP 572. Washington, D.C.: American Petroleum Institute.

__________. 1992. Inspection of Pressure Relieving Devices. RP 576. Washington, D.C.: American Petroleum Institute.

__________. 1994. Fire Protection in Refineries. Sixth Edition. RP 2001. Washington, D.C.: American Petroleum Institute.

Armistead, George, Jr. 1950. Safety in Petroleum Refining and Related Industries. New York: John G. Simmons & Co., Inc.

Exxon Company, USA. 1987. Encyclopedia for the User of Petroleum Products. Lubetext D400. Houston: Exxon Company, USA.

Hydrocarbon Processing. 1988. Refining Handbook. Houston: Gulf Publishing Co.

__________. 1992. Refining Handbook. Houston: Gulf Publishing Co.

IARC. [No date given.] Occupational Exposures in Petroleum Refining. IARC Monographs, Volume 45.

Kutler, A. A. 1969. "Crude distillation." Petro/Chem Engineering. New York: John G. Simmonds & Co., Inc.

Mobil Oil Corporation. 1972. "Light Products Refining, Fuels Manufacture." Mobil Technical Bulletin, 1972. Fairfax, Virginia: Mobil Oil Corporation.

Parmeggiani, Luigi, Technical Editor. 1983. Encyclopaedia of Occupational Health and Safety. Third Edition. Geneva: International Labour Organization.

Shell International Petroleum Company Limited. 1983. The Petroleum Handbook. Sixth Edition. Amsterdam: Elsevier Science Publishers B.V.

Speight, James G. 1980. The Chemistry and Terminology of Petroleum. New York: Marcel Dekker, Inc.

Vervalin, Charles H., Editor. 1985. Fire Protection Manual for Hydrocarbon Processing Plants. Volume 1, Third edition. Houston: Gulf Publishing Co.

Appendix IV: 2-1. Glossary

Absorption

The disappearance of one substance into another so that the absorbed substance loses its identifying characteristics, while the absorbing substance retains most of its original physical aspects. Used in refining to selectively remove specific components from process streams.

Acid Treatment

A process in which unfinished petroleum products such as gasoline, kerosene, and lubricating oil stocks are treated with sulfuric acid to improve color, odor, and other properties.

Additive

Chemicals added to petroleum products in small amounts to improve quality or add special characteristics.

Adsobption

Adhesion of the molecules of gases or liquids to the surface of solid materials.

Air Fin Coolers

A radiator-like device used to cool or condense hot hydrocarbons; also called fin fans.

Alicyclic Hydrocarbons

Cyclic (ringed) hydrocarbons in which the rings are made up only of carbon atoms.

Aliphatic Hydrocarbons

Hydrocarbons characterized by open-chain structures: ethane, butane, butene, acetylene, etc.

Alkylation

A process using sulfuric or hydrofluoric acid as a catalyst to combine olefins (usually butylene) and isobutane to produce a high-octane product known as alkylate.

API Gravity

An arbitrary scale expressing the density of petroleum products.

Aromatic

Organic compounds with one or more benzene rings.

Asphaltenes

The asphalt compounds soluble in carbon disulfide but insoluble in paraffin naphthas.

Atmospheric Tower

A distillation unit operated at atmospheric pressure.

Benzene

An unsaturated, six-carbon ring, basic aromatic compound.

leeder Valve

A small-flow valve connected to a fluid process vessel or line for the purpose of bleeding off small quantities of contained fluid. It is installed with a block valve to determine if the block valve is closed tightly.

Blending

The process of mixing two or more petroleum products with different properties to produce a finished product with desired characteristics.

Block Valve

A valve used to isolate equipment.

Blowdown

The removal of hydrocarbons from a process unit, vessel, or line on a scheduled or emergency basis by the use of pressure through special piping and drums provided for this purpose.

Blower

Equipment for moving large volumes of gas against low-pressure heads.

Boiling Range

The range of temperature (usually at atmospheric pressure) at which the boiling (or distillation) of a hydrocarbon liquid commences, proceeds, and finishes.

Bottoms

Tower bottoms are residue remaining in a distillation unit after the highest boiling-point material to be distilled has been removed. Tank bottoms are the heavy materials that accumulate in the bottom of storage tanks, usually comprised of oil, water, and foreign matter.

Bubble Tower

A fractionating (distillation) tower in which the rising vapors pass through layers of condensate, bubbling under caps on a series of plates.

Catalyst

A material that aids or promotes a chemical reaction between other substances but does not react itself. Catalysts increase reaction speeds and can provide control by increasing desirable reactions and decreasing undesirable reactions.

Catalytic Cracking

The process of breaking up heavier hydrocarbon molecules into lighter hydrocarbon fractions by use of heat and catalysts.

Caustic Wash

A process in which distillate is treated with sodium hydroxide to remove acidic contaminants that contribute to poor odor and stability.

CHD Unit

Coke

A high carbon-content residue remaining from the destructive distillation of petroleum residue.

Coking

A process for thermally converting and upgrading heavy residual into lighter products and by-product petroleum coke. Coking also is the removal of all lighter distillable hydrocarbons that leaves a residue of carbon in the bottom of units or as buildup or deposits on equipment and catalysts.

Condensate

The liquid hydrocarbon resulting from cooling vapors.

Condenser

A heat-transfer device that cools and condenses vapor by removing heat via a cooler medium such as water or lower-temperature hydrocarbon streams.

Condenser Reflux

Condensate that is returned to the original unit to assist in giving increased conversion or recovery.

Cooler

A heat exchanger in which hot liquid hydrocarbon is passed through pipes immersed in cool water to lower its temperature.

Cracking

The breaking up of heavy molecular weight hydrocarbons into lighter hydrocarbon molecules by the application of heat and pressure, with or without the use of catalysts.

Crude Assay

A procedure for determining the general distillation and quality characteristics of crude oil.

Crude Oil

A naturally occurring mixture of hydrocarbons that usually includes small quantities of sulfur, nitrogen, and oxygen derivatives of hydrocarbons as well as trace metals.

Cycle Gas Oil

Cracked gas oil returned to a cracking unit.

Deasphalting

Process of removing asphaltic materials from reduced crude using liquid propane to dissolve nonasphaltic compounds.

Debutanizer

A fractionating column used to remove butane and lighter components from liquid streams.

De-ethanizer

A fractionating column designed to remove ethane and gases from heavier hydrocarbons.

Dehydrogenation

A reaction in which hydrogen atoms are eliminated from a molecule. Dehydrogenation is used to convert ethane, propane, and butane into olefins (ethylene, propylene, and butenes).

Depentanizer

A fractionating column used to remove pentane and lighter fractions from hydrocarbon streams.

Depropanizer

A fractionating column for removing propane and lighter components from liquid streams.

Desalting

Removal of mineral salts (most chlorides, e.g., magnesium chloride and sodium chloride) from crude oil.

Desulfurization

A chemical treatment to remove sulfur or sulfur compounds from hydrocarbons.

Dewaxing

The removal of wax from petroleum products (usually lubricating oils and distillate fuels) by solvent absorption, chilling, and filtering.

Diethanolamine

A chemical (C₄H₁₁O₂N) used to remove H₂S from gas streams.

Distillate

The products of distillation formed by condensing vapors.

Downflow

Process in which the hydrocarbon stream flows from top to bottom.

Dry Gas

Natural gas with so little natural gas liquids that it is nearly all methane with some ethane.

Feedstock

Stock from which material is taken to be fed (charged) into a processing unit.

Flashing

The process in which a heated oil under pressure is suddenly vaporized in a tower by reducing pressure.

Flash Point

Lowest temperature at which a petroleum product will give off sufficient vapor so that the vapor-air mixture above the surface of the liquid will propagate a flame away from the source of ignition.

Flux

Lighter petroleum used to fluidize heavier residual so that it can be pumped.

Fouling

Accumulation of deposits in condensers, exchangers, etc.

Fraction

One of the portions of fractional distillation having a restricted boiling range.

Fractionating Column

Process unit that separates various fractions of petroleum by simple distillation, with the column tapped at various levels to separate and remove fractions according to their boiling ranges.

Fuel Gas

Refinery gas used for heating.

Gas Oil

Middle-distillate petroleum fraction with a boiling range of about 350°-750° F, usually includes diesel fuel, kerosene, heating oil, and light fuel oil.

Gasoline

A blend of naphthas and other refinery products with sufficiently high octane and other desirable characteristics to be suitable for use as fuel in internal combustion engines.

Header

A manifold that distributes fluid from a series of smaller pipes or conduits.

Heat

As used in the Health Considerations paragraphs of this document, heat refers to thermal burns for contact with hot surfaces, hot liquids and vapors, steam, etc.

Heat Exchanger

Equipment to transfer heat between two flowing streams of different temperatures. Heat is transferred between liquids or liquids and gases through a tubular wall.

High-line or High-pressure Gas

High-pressure (100 psi) gas from cracking unit distillate drums that is compressed and combined with low-line gas as gas absorption feedstock.

Hydrocracking

A process used to convert heavier feedstock into lower-boiling, higher-value products. The process employs high pressure, high temperature, a catalyst, and hydrogen.

Hydrodesulfurization

A catalytic process in which the principal purpose is to remove sulfur from petroleum fractions in the presence of hydrogen.

Hydrofinishing

A catalytic treating process carried out in the presence of hydrogen to improve the properties of low viscosity-index naphthenic and medium viscosity-index naphthenic oils. It is also applied to paraffin waxes and microcrystalline waxes for the removal of undesirable components. This process consumes hydrogen and is used in lieu of acid treating.

Hydroforming

Catalytic reforming of naphtha at elevated temperatures and moderate pressures in the presence of hydrogen to form high-octane BTX aromatics for motor fuel or chemical manufacture. This process results in a net production of hydrogen and has rendered thermal reforming somewhat obsolete. It represents the total effect of numerous simultaneous reactions such as cracking, polymerization, dehydrogenation, and isomerization.

Hydrogeneration

The chemical addition of hydrogen to a material in the presence of a catalyst.

Inhibitor

Additive used to prevent or retard undesirable changes in the quality of the product, or in the condition of the equipment in which the product is used.

Isomerization

A reaction that catalytically converts straight-chain hydrocarbon molecules into branched-chain molecules of substantially higher octane number. The reaction rearranges the carbon skeleton of a molecule without adding or removing anything from the original material.

Iso-octane

A hydrocarbon molecule (2,2,4-trimethylpentane) with exccellent antiknock characteristics on which the octane number of 100 is based.

Lean Oil

Absorbent oil fed to absorption towers in which gas is to be stripped. After absorbing the heavy ends from the gas, it becomes fat oil. When the heavy ends are subsequently stripped, the solvent again becomes lean oil.

Low-Line/Low-Pressure Gas

Low-pressure (5 psi) gas from atmospheric and vacuum distillation recovery systems that is collected in the gas plant for compression to higher pressures.

Naphtha

A general term used for low boiling hydrocarbon fractions that are a major component of gasoline. Aliphatic naphtha refers to those naphthas containing less than 0.1% benzene and with carbon numbers from C₃ through C₁₆. Aromatic naphthas have carbon numbers from C₆ through C₁₆ and contain significant quantities of aromatic hydrocarbons such as benzene (>0.1%), toluene, and xylene.

Naphthenes

Hydrocarbons (cycloalkanes) with the general formula C_nH_2n, in which the carbon atoms are arranged to form a ring.

Octane Number

A number indicating the relative antiknock characteristics of gasoline.

Olefins

A family of unsaturated hydrocarbons with one carbon-carbon double bond and the general formula C_nH_2n.

Paraffins

A family of saturated aliphatic hydrocarbons (alkanes) with the general formula C_nH_2n+2.

Polyforming

The thermal conversion of naphtha and gas oils into high-quality gasoline at high temperatures and pressure in the presence of recirculated hydrocarbon gases.

Polymerization

The process of combining two or more unsaturated organic molecules to form a single (heavier) molecule with the same elements in the same proportions as in the original molecule.

Preheater

Exchanger used to heat hydrocarbons before they are fed to a unit.

Pressure-regulating Valve

A valve that releases or holds process-system pressure (that is, opens or closes) either by preset spring tension or by actuation by a valve controller to assume any desired position between fully open and fully closed.

Pyrolysis Gasoline

A by-product from the manufacture of ethylene by steam cracking of hydrocarbon fractions such as naphtha or gas oil.

Pyrophoric Iron Sulfide

A substance typically formed inside tanks and processing units by the corrosive interaction of sulfur compounds in the hydrocarbons and the iron and steel in the equipment. On exposure to air (oxygen) it ignites spontaneously.

Quench Oil

Oil injected into a product leaving a cracking or reforming heater to lower the temperature and stop the cracking process.

Raffinate

The product resulting from a solvent extraction process and consisting mainly of those components that are least soluble in the solvents. The product recovered from an extraction process is relatively free of aromatics, naphthenes, and other constituents that adversely affect physical parameters.

Reactor

The vessel in which chemical reactions take place during a chemical conversion type of process.

Reboiler

An auxiliary unit of a fractionating tower designed to supply additional heat to the lower portion of the tower.

Recycle Gas

High hydrogen-content gas returned to a unit for reprocessing.

Reduced Crude

A residual product remaining after the removal by distillation of an appreciable quantity of the more volatile components of crude oil.

Reflux

The portion of the distillate returned to the fractionating column to assist in attaining better separation into desired fractions.

Reformate

An upgraded naphtha resulting from catalytic or thermal reforming.

Reforming

The thermal or catalytic conversion of petroleum naphtha into more volatile products of higher octane number. It represents the total effect of numerous simultaneous reactions such as cracking, polymerization, dehydrogenation, and isomerization.

Regeneration

In a catalytic process the reactivation of the catalyst, sometimes done by burning off the coke deposits under carefully controlled conditions of temperature and oxygen content of the regeneration gas stream.Scrubbing

Purification of a gas or liquid by washing it in a tower.

Solvent Extraction

The separation of materials of different chemical types and solubilities by selective solvent action.

Sour Gas

Natural gas that contains corrosive, sulfur-bearing compounds such as hydrogen sulfide and mercaptans.

Stabilization

A process for separating the gaseous and more volatile liquid hydrocarbons from crude petroleum or gasoline and leaving a stable (less-volatile) liquid so that it can be handled or stored with less change in composition.

Straight-Run Gasoline

Gasoline produced by the primary distillation of crude oil. It contains no cracked, polymerized, alkylated, reformed, or visbroken stock.

Stripping

The removal (by steam-induced vaporization or flash evaporation) of the more volatile components from a cut or fraction.

Sulfuric Acid Treating

A refining process in which unfinished petroleum products such as gasoline, kerosene, and lubricating oil stocks are treated with sulfuric acid to improve their color, odor, and other characteristics.

Sulfurization

Combining sulfur compounds with petroleum lubricants.

Sweetening

Processes that either remove obnoxious sulfur compounds (primarily hydrogen sulfide, mercaptans, and thiophens) from petroleum fractions or streams, or convert them, as in the case of mercaptans, to odorless disulfides to improve odor, color, and oxidation stability.

Switch Loading

The loading of a high static-charge retaining hydrocarbon (i.e., diesel fuel) into a tank truck, tank car, or other vessel that has previously contained a low-flash hydrocarbon (gasoline) and may contain a flammable mixture of vapor and air.

Tail Gas

The lightest hydrocarbon gas released from a refining process.

Thermal Cracking

The breaking up of heavy oil molecules into lighter fractions by the use of high temperature without the aid of catalysts.

Turnaround

A planned complete shutdown of an entire process or section of a refinery, or of an entire refinery to perform major maintenance, overhaul, and repair operations and to inspect, test, and replace process materials and equipment.

acuum Distillation

The distillation of petroleum under vacuum which reduces the boiling temperature sufficiently to prevent cracking or decomposition of the feedstock.

Vapor

The gaseous phase of a substance that is a liquid at normal temperature and pressure.

Visbreaking

Viscosity breaking is a low-temperature cracking process used to reduce the viscosity or pour point of straight-run residuum.

Wet Gas

A gas containing a relatively high proportion of hydrocarbons that are recoverable as liquids.

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