Refinery Glossary

on 15 November 2024. Posted in Refinery Engineering

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Acid Gas Removal Unit (AGR) (Amine Gas Treating) - Involve removal of inert gasses such as carbon dioxide, hydrogen sulfide, and nitrogen from unprocessed natural gas. These must be removed prior to use or sale of the natural gas to meet standards of less than 4% inert gases. Acid gases such as carbon dioxide (\(CO_2\)) and hydrogen sulfide (\(H_2 S\)) are corrosive when water molecules are present and represent the major source of maintenance problems in pipelines. Acid gas removal plants are essential to natural gas processing and transportation and are one of the major parts of natural gas processing equipment manufactured.
Additives - Any materials incorporated in finished petroleum products for improving their performance in existing applications or for broadening the areas of their utility.
Acid Treating - Process in which unfinished petroleum products, such as gasoline, naphthas, kerosine, diesel fuel, and lubricating-oil stocks, are contacted with sulfuric acid to improced their color, odor, and other properties.
Alkylation Unit - This is a secondary refinery unit operation that because it adds high octane hydrocarbons to motor and aviation gasoline. High octane hydrocarbons are needed to help prevent autoignition of gasoline (knocking) in an engine and to meet recommended engine octane ratings. The process combines an unsaturated light hydrocarbon with isobutane to produce alkylate. Either sulfuric or hydrofluoric acid is used as the catalyst for the alkylation reaction. Alkylate is high in octane but has low volatility and can be added to motor gasoline and aviation gasoline to increase octane while meeting stringent volatility specifications.
Allowable Gas Velocity Through a Gas Separator - The maximum speed at which gas can pass through the separator without causing inefficient separation or operational issues, such as liquid carryover. Exceeding the allowable velocity leads to poor separation performance, causing entrainment or carryover of liquids.
Allowable Velocity in a Downcomer of a Tray-type Distillation Tower - The maximum liquid velocity that can be achieved in the downcomer without causing operational issues, such as excessive liquid backup, flooding, or entrainment of vapor. Proper downcomer design is necessary to ensuring that the liquid can move from one tray to another effectively without hindrance.
Aromatic Hydrocarbons - Hydrocarbon characterized by unsaturated ring structures of the carbon atoms. Commercial petroleum aromatics are benzene, toluene, and xylenes.
Ash - The amount of ash or nonvolatile, incombustible content left from heating petroleum oils to the point of complete burning of the oil. Ash content is expressed in weight per cent of the original sample.
Asphalt - A dark brown to black cementatious material - solid, semisolid, or liquid in consistency in which the predominating constituents are bitumens. Petroleum asphalt, as distinguished from asphalt occurring as such in nature, is refined from crude petroleum into commercial grades of widely varying consistency. Asphalt is a natural constituent of asphaltic-base crude oils, some of which are refined primarily for its recovery.
Atmospheric Distillation Unit - This distillation unit begins with desalting of the crude and then continues through significant heat exchange train and fired heater prior to entering the main atmospheric column. The main column itself is designed with several sections with side product draws to produce the various product streams such as light ends, naphtha, kerosene, diesel, gas oil, and the bottoms reduced crude stream.
Auxiliary Facilities - A wide assortment of processes and equipment not directly involved in the refining of crude oil is used in functions vital to the operation of the refinery. Examples are listed below. Products from auxiliary facilities (clean water, steam, and process heat) are required by most process units throughout the refinery.

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Bleeding - The tendency of a liquid component to separate from liquid-solid or semi-solid mixture, as oil from lubricating grease in storage.
Blending - The major refinery products produced by the product blending process are gasoline, jet fuels, heating oils, and diesel fuels. The objective of product blending is to allocate the available blending components in such a way as to ensure all product
demands and specifications are met at the least cost and to produce products which maximize overall profit.
Bloom - The fluorescent color of a lubricating oil as shown by reflected light when this color differs from that shown by transmitted light.
Blowdown System - The blowdown system provides for the safe disposal of hydrocarbons (vapor and liquid) discharged from pressure relief devices.
Boilers - Boilers are used in many different processes in the oil and gas industry, including drilling and refining. Boilers are used to generate hot water and steam for drilling operations, such as to power the drilling rig, heat the drilling mud, and melt the drilling bit. Boilers are also used in the refining process to heat the crude oil and separate it into its various components. Boilers can also be used to power pumps, compressors, and other machinery used in the refining process.
Burning Oil - Kerosine, mineral seal, or other petroleum light oils of such gravity and other properties that they can be used for illuminating and similar purposes.
Burning Point - The lowest temperature at which a volatile oil in an open vessel will continue to burn when ignited by a flame held close to its surface. It determines the degree of safety with which kerosine and other illuminating oils can be used.
Byproduct - A secondary or additional petroleum product, not of primary importance in the conventional refinery operating schedule. Examples: residual fuel oil, coke, asphalt, and road oil.

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Carbon Black - A solid or finely divided carbon recovered by burning natrual gas or oil in a deficient supply of air or by thermal decomposition. Used in compounding rubber and making inks, paints, etc.
Catalyst - A substance used to accelerate or retard a chemical reaction without itself undergoing significant chemical change or change in volume during the process.
Catalytic Reforming - A catalytic process to improve the antiknock quality of low grade naphthas and virgin gasolines by the conversion of naphthenes and paraffins into higher octane aromatics such as benzene, toluene and xylenes.
Cat Cracker - Trade term for the refinery operating unit where a catalytic cracking process is being carried out.
Cetane Index - A measure used to estimate the ignition quality of diesel fuel. It correlates with the cetane number, which is the primary indicator of diesel fuel’s combustibility, but the cetane index is calculated rather than directly measured. The cetane index is widely used to gauge fuel quality, often in cases where additives are not present, as they can affect combustion properties but may not influence the cetane index directly.
Chemical Sweetening Unit - This is the process for removal of mainly acid gases (H2S and CO2) and, in addition, the simultaneous removal of sulphur organic species (RSH, COS, CS2) from process gas. It is an essential step of sour gas processing for natural gas treatment, NGL recovery, LNGs, refineries and petrochemicals in order to meet transport and market specifications, to comply with environmental regulations for emissions and to control corrosion.
Coke - It’s created as a byproduct during the refining of crude oil, specifically in the process of thermal cracking or coking, which breaks down large hydrocarbon molecules into smaller ones to produce lighter products like gasoline and diesel. The heavy residual oil left after refining undergoes further treatment, resulting in petcoke.
Coking Unit - Coking is a thermal cracking process used to convert low value residual fuel oil to highervalue gas oil and petroleum coke. Vacuum residuals and thermal tars are cracked in the coking process at high temperature and low pressure. Products are petroleum coke, gas oils, and lighter petroleum stocks. Delayed coking is the most widely used process today, but fluid coking is expected to become an important process in the future.
Cold Settling - Process for removing petroleum wax from cylinder stock and high viscosity distillate by chilling a naphtha solution of the oi and allowing the wax to crystallize out of the solution and settle to the bottom of the pans.
Compressor Engines - For various processes, refineries use a compressor type unique to the functions and needs of the oil and gas industry, the gas compressor. Whereas an air compressor pressurizes air by reducing its volume, gas compressors do the same with gases. Inside a gas compressor, incoming gas supplies get pressurized in a compression chamber and released for various uses. Gas compressors are common for hydrocracking, hydrotreating, diesel and gas desulfurization, catalytic reforming and other processes.
Cooling Towers - Cooling towers are used extensively in refinery cooling water systems to transfer waste heat from the cooling water to the atmosphere. The only refineries not employing cooling towers are those with once-through cooling. The increasing scarcity of a large water supply required for once-through cooling is contributing to the disappearance of that form of refinery cooling. In the cooling tower, warm cooling water returning from refinery processes is contacted with air by cascading through packing.
Compressed Natural Gas - Primarily natural gas composed of methane that has been compressed to less than 1% of its volume at standard atmospheric pressure. CNG is used as a cleaner alternative to gasoline, diesel, and propane for fueling vehicles, as well as for industrial and household energy needs.
Cracking Unit - Catalytic cracking, using heat, pressure, and catalysts, converts heavy oils into lighter products with product distributions favoring the more valuable gasoline and distillate blending components. Feedstocks are usually gas oils from atmospheric distillation, vacuum distillation, coking, and deasphalting processes.
Crude Oil - A naturally occurring, unrefined petroleum product found deep underground, formed from the remains of ancient marine organisms such as plants, algae, and bacteria.
Cutting Oil - Oil used to lubricate and cool metal-cutting tools; usually mineral oil blended with other substances to make them water-soluble or water-insoluble, as required.
Cycle Stock - Unfinished product taken from a stage of a refinery process and recharged to the process at an earlier period in the operation.
Cycling - A series of operations in petroleum refining or natural-gas processing so conducted that the steps are periodically repeated in the same sequence.

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Debutanizer - The fractionating column in a natural gasoline plant in which the butane and lighter components are removed overhead. The gas stream remaining is referred to as debutanized.
Deethanizer - The fractionating column in a natural gasoline plant in which ethane and lighter components are removed overhead. The gas stream remaining is deethanized.
Delayed Coking - A process by which heavier crude oil fractions can be thermally decomposed under conditions of elevated temperatures and pressure to produce a mixture of lighter oils and petroleum coke. The light oils can be processed further in other refinery units to meet product specifications. The coke can be used either as a fuel or in other applications such as the manufacturing of steel or aluminum.
Depropanizer - The fractionating column in a natural gasoline plant in which propane and lighter components are removed overhead. The gas stream remaining is depropanized.
Desalting - Removing calcium chloride, magnesium chloride, and sodium chloride from crude petroleum.
Dewaxed Oils - Lubricating oils from which a portion of the wax has been removed.
Diesel Fuel - A type of liquid fuel primarily used to power diesel engines, which are commonly found in vehicles like trucks, buses, and some cars, as well as in machinery, generators, and heavy equipment. Diesel fuel is derived from crude oil and refined through a distillation process that separates it from other hydrocarbons like gasoline.
Distillation - The general process of vaporizing liquids, crude oil, or one of its fractions in a closed vessel, collecting and condensing the vapors into liquids. Commercial forms of distillation in petroleum refining are crude, atmospheric, vacuum, rerun, steam, extractive, etc.
Dry Gas - Natural gas, mainly from gas fields rather than oil fields, which does not contain appreciable quantities of the heavier hydrocarbons, such as propane and butane, which condense easily. Methane and ethane are principal components of dry gases.
Dry Point - In the standard distillation test, the temperature when the last drop of liquid evaporates from the bottom of the flask. For solvents and some other products considered to be more indicative of final boiling point than end point, which is the maximum temperature observed on the distillation thermometer when no more vapor can be driven from the flask by heating.

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Emulsified Asphalt - An emulsion of asphalt cement and water, containing a small amount of an emulsifying agent.
Emulsification - The phenomenon of fine dispersion of one liquid held in suspension in a second liquid in which it is partly or completely immiscible.
Engine Sludge - The insoluble degradation product of lubricating oils and/or fuels formed during their use in internal combustion engines and deposited from the oils outside the combustion space. Water may or may not be present.
Epoxy Resins - Plastics materials, petrochemically derived, used as surface coatings, laminating adhesives, in paints, etc.
Extractive Distillation - In the distillation process, the separation of different components of mixtures which have similar vapor pressures by flowing a solvent which is selective for some of the components in the feed down the distillation column as the operation proceeds. By this means, the less soluble component passes overhead while the soluble component is scrubbed from the vapors. The solvent with the dissolved component is deposited in the bottom of the column and withdrawn for separation.

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Feed Preparation Unit - A fractionation unit in a refinery, the primary purposes of which is to prepare one or more close-boiling point cuts to be used as feed for subsequent processing.
Film Strength - The property of a lubricant which enables it to maintain an unbroken film over lubricated surfaces under operating conditions, thus avoiding scuffing or scoring of bearing surfaces.
Filter Press - In petroleum refining, the equipment used to separate wax and oil in paraffin-wax distillates. It consists of a series of canvas-covered plates separated by narrow iron rings. The distillate is run into a narrow bore extending the length of the press and is forced into the spaces between the plates formed by the rings. The oil penetrates the canvas covering the plates and drips into a trough beneath the press, the wax remaining in the plates.
Flash Point - The lowest temperature at which vapors from an oil will ignite momentarily on application of a flame under standard test conditions. In the range of 90 - 150ºF, flash point is significant in determining safety conditions for the storage, handling, and use of petroleum products.
Fuel Oils - Any liquid or liquefiable petroleum product burned for the generation of heat in a furnace or firebox or for the generation of power in an engine, exclusive of oils with a flash point below 100ºF and oils burned in cotton- or wool-wick burners.

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Gasoline Blending - The process of mixing different hydrocarbon components, additives, and sometimes biofuels to create gasoline with specific properties that meet regulatory and market requirements. The blending process is crucial because crude oil, when refined, produces a variety of hydrocarbon streams, each with unique characteristics.
Gas Oils - A fraction derived in refining petroleum with a boiling range between kerosine and lubricating oil. Derives its name from having originally been used in the manufacture of illuminating gas. Now supplies distillate type fuel oils and diesel fuel, also cracked to produce gasoline.
Gas Sweetening - The process of removing acidic components primarily hydrogen sulfide and carbon dioxide from natural gas. These components are considered "acidic" because they form acidic compounds when they dissolve in water, and their presence can make the gas corrosive, reduce its heating value, and make it hazardous for transportation and usage.
Gasoline - A refined petroleum naphtha which by its composition is suitable for fuel in a reciprocating-type internal combustion engine. ASTM D 439 specifies three grades for various types of motor vehicle operations. Straight-run gasoline is the product of distillation; cracked gasoline that of a cracking process.
Gasoline Blending - The process of mixing different hydrocarbon components, additives, and sometimes biofuels to create gasoline with specific properties that meet regulatory and market requirements.
Girbitol Process - A process for removing hydrogen sulfide, carbon dioxide, and/or organic gases from petroleum gases and liquids.

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Heart Cut - In refining, a narrow boiling range fraction, usually taken near the middle portion of the stock being processed.
Heavy Ends - The highest boiling portion of a gasoline or other petroleum oil. The end point as determined by the distillation test reflects the amount and character of the heavy ends present in a gasoline.
Hydrodesulfurizing - A process for combining hydrogen with the sulfur in refinery petroleum streams to make hydrogen sulfide, which is removed from the oil as a gas.
Hydrodesulfurization Unit (HDS) - A catalytic process to remove sulfur from natural gas and refined products, including gasoline, jet fuel, diesel fuel, fuel oil, and naphtha. Sulfur removal is critical in order to reduce the sulfur dioxide emissions from the combustion of those fuels in automobiles, aircraft, locomotives, ships, power plants, residential or industrial furnaces, etc. Sulphur removal from naphtha is also important in a refinery as it can poison, or render ineffective, the noble metal catalysts, such as platinum and rhenium, used in the catalytic reforming units necessary to upgrade the naphtha octane ratings, even in very minute concentrations.
Hydrofining - A process for treating petroleum fractions and unfinished oils in the presence of catalysts and substantial quantities of hydrogen to upgrade their quality.
Hydrogen Production Plant - To produce hydrogen, it must be separated from the other elements in the molecules where it occurs. Hydrogen can be produced from many different sources in different ways to use as a fuel. The two most common methods for producing hydrogen are steam-methane reforming and electrolysis (splitting water with electricity).
Hydrogen Sulfide - An objectionable impurity present in some natural gas and crude oils and formed during the refining of sulfur-containing oils. It is removed from products by various treating methods at the refinery.
Hydrotreating Unit (HDT) - A process performed to produce high-quality fuels and feedstocks. It involves reducing sulfur or nitrogen content, saturating olefins for stability improvement, or reducing aromatic content. During hydrotreating, refineries use filters to filter the hydrotreater feed to prevent plugging and fouling of the catalyst fixed bed. These filters are also vital for filtering hydrotreater product to capture catalyst fines that may escape from the fixed bed. This filter processes hydrotreater product, recycles any catalyst that escapes from the ebullated bed, and ensures the integrity and efficiency of the hydrotreating process.

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Induction Period - A period under given conditions in which a petroleum product does not absorb oxygen at a substantial rate to form gum.
Isomerization - A refining process which alters the fundamental arrangement of atoms in the molecule. Used to convert normal butane into isobutane, an alkylation process feedstock, and normal pentane and hexane into isopentane and isohexane, high-octane gasoline components.
Isomerization Unit - Converts linear molecules such as normal pentane into higher-octane branched molecules for blending into the end-product gasoline. Also used to convert linear normal butane into isobutane for use in the alkylation unit.

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Light Ends - The lower boiling components of a mixture of hydrocarbons.
Light End Recovery (Gas Processing) Unit - The light ends recovery unit uses absorption and distillation steps to remove propane and heavier components from refinery gas streams prior to their use as fuel gas. The recovered components are then separated and used in various product streams.
Lime Treatment - The process of introducing lime into the still during the distillation of petroleum to reduce the acidity of the distillate. Other forms of distillate treatment are often preferred.
Liquefaction of Gas - The process of converting gases into a liquid form, primarily by cooling and/or applying high pressure. This is often done to store or transport gases more efficiently, as liquids occupy much less volume than gases.
Liquefied Natural Gas - Natural gas (primarily methane) that has been cooled to a very low temperature, around -162°C (-260°F), to transform it into a liquid form. This process reduces its volume by about 600 times, making it much more efficient for storage and transportation over long distances where pipelines are impractical, such as overseas shipping.
Liquefied Petroleum Gas - A type of fuel made up of hydrocarbon gases, primarily propane and butane, which are compressed and stored in liquid form.
Loading and Unloading - Pipeline infrastructure includes numerous miles of small diameter pipeline gathering systems that move crude oil and natural gas from the wellhead to storage, processing facilities and connections to larger pipeline systems. It also includes pipelines that transport and distribute consumer-grade natural gas to refineries, petrochemical plants and power generation facilities that support refinery and petrochemical manufacturing operations.
Lube Stocks - Refinery term for fractions of crude petroleum of suitable boiling range and viscosity to yield lubricating oils when further processed and treated.

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Mercaptans - Compounds of sulfur having a strong, repulsive garlic-like odor. A contaminant of sour crude oil and products.
Motor Oils - Lubricating oils designed for used in the oil circulating systems of automotive, aircraft, and diesel engines.

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Naphtha - Liquid hydrocarbon fractions, generally boiling within the gasoline range, recovered by the distillation of crude petroleum. Used as solvents, dry-cleaning agents, and charge stocks to reforming units to make high-octane gasoline.
Naphthenic Crudes - A type of crude petroleum containing a relatively large proportion of naphthenic-type hydrocarbon.
Neutralization Number - An indication of the acidity of a petroleum product or lubricant. ASTM D 664 and D 974 are standard procedures for establishing neutralization values.

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Octane Number - A measure of a fuel’s ability to resist "knocking" or "pinging" during combustion.
Oil Emulsion - A mixture of oil and water in which the oil is permanently suspended in the water in the form of very small droplets or vice versa.
Olefins - A class of unsaturated paraffinic hydrocarbons recovered from petroleum, of which butene, ethylene, and propylene are examples.
Oxidation Inhibitor - A chemical additive used to slow down or prevent oxidation, a chemical reaction where substances lose electrons, often in the presence of oxygen. Oxidation can lead to deterioration, especially in materials and fluids exposed to heat, air, or light, such as oils, lubricants, fuels, and polymers.

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Paraffin - A white, tasteless, odorless, chemically inert, waxy substance obtained from some petroleum oils.
Paraffin-base Crude - A type of crude oil containing predominantly paraffin hydrocarbons as distinguished from asphaltic and naphthenic-base crudes. It is a source of high quality lubricating oils.
Petroleum Conversion (Cracking) - To meet the demands for high-octane gasoline, jet fuel, and diesel fuel, components such as residual oils, fuel oils, and light ends are converted to gasolines and other light fractions. Cracking, coking, and visbreaking processes are used to break large petroleum molecules into smaller ones. Polymerization and alkylation processes are used to combine small petroleum molecules into larger ones. Isomerization and reforming processes are applied to rearrange the structure of petroleum molecules to produce higher-value molecules of a similar molecular size.
Petrolatum - A semi-solid product, ranging from white to yellow in color, composed of heavy residual oils and paraffin wax produced by filtration of cylinder stocks. Has varied pharmaceutical and industrial uses.
Petroleum Separation - The first phase in petroleum refining operations is the separation of crude oil into its major constituents using 3 petroleum separation. Crude oil consists of a mixture of hydrocarbon compounds including paraffinic, naphthenic, and aromatic hydrocarbons with small amounts of impurities including sulfur, nitrogen, oxygen, and metals.
Petroleum Treatment Process - Petroleum treating processes stabilize and upgrade petroleum products by separating them from less desirable products and by removing objectionable elements. Undesirable elements such as sulfur, nitrogen, and oxygen are removed by hydrodesulfurization, hydrotreating, chemical sweetening, and acid gas removal. Treating processes, employed primarily for the separation of petroleum products, include such processes as deasphalting. Desalting is used to remove salt, minerals, grit, and water from crude oil feedstocks before refining. Asphalt blowing is used for polymerizing and stabilizing asphalt to improve its weathering characteristics.
Plant Steam - The steam generated in an industrial or commercial facility for various applications within the plant. Unlike clean steam, which is produced from purified water and intended for specific high purity applications, plant steam is typically generated from ordinary water sources and used for general purposes within the facility.
Polomerization Unit - The process of converting light olefin gases including ethylene, propylene, and butylene into hydrocarbons of higher molecular weight and higher octane number that can be used as gasoline blending stocks. Polymerization combines two or more identical olefin molecules to form a single molecule with the same elements in the same proportions as the original molecules. Polymerization may be accomplished thermally or in the presence of a catalyst at lower temperatures.
Precipitate - A substance separating in solid form from a liquid as the result of some physical or chemical change, differing from a substance held only mechanically in suspension, which is known as sediment.
Precipitation Number - The basis for classifying steam cylinder stocks and other classes of residual oils as to relative content of asphaltic constituents by a standard test method (ASTM D 91).
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.

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Quenching Oil - An oil introduced into high-temperature process streams during refining to cool them.

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Raffinate - In solvent refining, that portion of the oil which remains undissolved and is not removed by the selective solvent. Also called "good" oil.
Reboiler - An auxiliary unit of a fractionating tower designed to supply additional heat to the lower portion of the tower.
Refinery Capacity Utilization - Ratio of the total amount of crude oil, unfinished oils, and natural gas plant liquids run through crude oil distillation units to the operable capacity of these units.
Refinery utilization rate - Represents the use of the atmospheric crude oil distillation units. The rate is calculated by dividing the gross input to these units by the operable refining capacity of the units.
Refluxing - In fractional distillation, the return of part of the condensed vapor to the fractionating column to assist in making a more complete separation of the desired fractions. The material returned is reflux.
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.
Reid Vapor Pressure - A measure of a liquid's volatility, particularly for gasoline and other volatile fuels. It indicates how easily a fuel evaporates at a given temperature and is measured in pounds per square inch (psi) at 100°F (37.8°C).
Reforming Unit - Catalytic reforming is a process to reform hydrotreated naphtha feed into high octane gasoline to meet today’s requirement for high efficiency, high compression engines. Reforming is the result of several simultaneous reactions. The most important products are aromatics which can be used as high-octane blending components or petrochemicals.
Retention Time in a Liquid-liquid Vessel - The amount of time that a liquid phase spends inside the vessel. In the context of liquid-liquid separators, this is the time it takes for the dispersed phase (often droplets of one liquid) to coalesce and separate from the continuous phase.

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Scrubbing - Purification of a gas or liquid by washing it in a tower.
Selective Solvent - A solvent which, at certain temperatures and ratios, will selectively dissolve more of one component of a mixture than of another and thereby provide partial separation.
Shale Oil - The liquid obtained from the destructive distillation of oil shale. Further processing is required to convert it into products similar to petroleum oils.
Slop Oil - A term designating the small amounts of oil lost in various refining operations which are collected and used as charge stocks.
Sludge - The residue left after treatment in the refinery of petroleum oils to remove impurities. Also an insoluble degradation product of crankcase oils.
Solvent Deasphalting - A refining process used to separate heavier components (asphaltenes) from crude oil, vacuum residue, or other heavy oil fractions. The purpose of SDA is to produce deasphalted oil (DAO), a lighter fraction that can be further processed or used to produce lubricants, while also isolating asphaltenes that can either be used as fuel or disposed of.
Solvent Deasphalting Unit (SDA) - A separation process in which residues are selectively separated by molecular type by mixing with paraffinic solvents and precipitating out of solution asphaltenes and other residue heavy components. SDA produces a low-contaminant, relatively high hydrogen deasphalted (DOA) oil product and a pitch product that contains the majority of the residue’s contaminants (CCR) (metals, asphaltenes).
Solvent Dewaxing - A process used in oil refineries to remove wax from lubricating oil stocks to improve their flow properties, especially at low temperatures. In this process, waxy feedstocks, such as vacuum distillates, are mixed with solvents to separate out waxy components, which can hinder the oil's performance.
Solvent Extraction - A separation process used to isolate specific compounds from a mixture. It involves transferring a solute from one liquid phase to another based on the relative solubility of the solute in two immiscible liquids, typically an organic solvent and water.
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.
Storage - An oil terminal, also called tank farm, oil installation or oil depot, is an industrial facility for the storage of oil, petroleum and petrochemical products, and from which these products are transported to end users or other storage facilities. An oil terminal typically has a variety of above or below ground tankage and pipeline connections.
Straight-run - Fractions derived from the straight distillation of crude oil and containing no cracked material. Also called virgin stock.
Straight-run Distillation - Continuous distillation of petroleum oils which separates the products in the order of their boiling points without cracking.
Sulfonates - A group of petroleum hydrocarbons resulting from treating oils with sulfuric acid.
Sulfur Recovery Plant - Sulfur recovery plants are used in petroleum refineries to convert the hydrogen sulfide (H2S) separated from refinery gas streams into the more disposable byproduct, elemental sulfur. Emissions from sulfur recovery plants and their control are discussed in Section 8.13, "Sulfur Recovery".
Sweet Wax - A white, moisture-free wax with the oil removed by a sweating process in which the unrefined wax is heated in shallow pans. In a semi-refined state it is known as sweated-scale wax. It can be filtered or re-run to yield a completely refined commercial roduct.
Sweetening - The process of improving petroleum products in color and odor by converting the undesirable sulfur compounds into less objectionable disulfides with sodium plumbite or by removing them by contacting the petroleum stream with alkalies or other sweetening agents.
Synthetic Crudes - The total liquid, multicomponent mixture of hydrocarbons resulting from a process involving molecular rearrangement of charge stock. Commonly applied to such products from cracking, reforming, visbreaking, etc.
Sweet Crude - Crude petroleum containing little sulfur, with no offensive odor.
Sweet Gas - A gas containing no corrosive components such as hydrogen sulfide and mercaptans.
Sweet Wax - A white, moisture-free wax with the oil removed by a sweating process in which the unrefined wax is heated in shallow pans. In a semi-refined state it is known as sweated-scale wax. It can be filtered or re-run to yield a completely refined commercial roduct.
Switch Loading - The loading of a high static-charge retaining hydrocarbon (diesel fuel) into a tank truck, tank car, or other vessels that has previously contained a low flash hydrocarbon (gasoline) and may contain a flammable mixture of vapor and air.

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Tailings - Remains, residues, or final byproducts from refining crude petroleum or its fractions.
Tank Farm - Land on which a number of large-capacity storage tanks are located, generally for crude oil.
Thermal Cracking - The breaking up of heavy oil molecules into lighter fractions by the use of high temperature without the aid of catalysts.
Topped Crude - A residual product remaining after the removal, by distillation or other artificial means, of an appreciable quantity of the more volatile components of crude petroleum.
Tower - A refinery apparatus used in connection with a still to increase the degree of separation of fractions obtained during the distillation of oil in the still. Also called a column.
Tray-type Tower - A type of column used in chemical processes, particularly for distillation, absorption, or stripping operations. In these towers, trays or plates are installed at different levels to promote contact between vapor and liquid phases, enhancing mass transfer.
Turnaround - With a refinery unit, the procedure of shutting the unit down after a normal run, doing the necessary maintenance and repair work and putting the unit back on stream.

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Unsaturates - Hydrocarbon compounds of such molecular structure that they readily pick up additional hydrogen atoms. Olefins and diolefins, which occur in cracking, are of this type.
Unsulfonated Residue - That portion of an oil which is not acted upon when the oil is agitated with a definite amount of sulfuric acid under specified conditions.

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Vacuum Distillation Unit - Topped crude withdrawn from the bottom of the atmospheric distillation column is composed of high boiling-point hydrocarbons. When distilled at atmospheric pressures, the crude oil decomposes and polymerizes and will foul equipment. To separate topped crude into components, it must be distilled in a vacuum column at a very low pressure and in a steam atmosphere.
Vapor Mass Velocity of Trat Type Tower - A tray-type tower is the mass of vapor that flows through a specific area cross-section of the tower per unit of time.
Virgin Stock - Oil processed from crude oil which contains no cracked material. Also called Straight Run Stock.
Visbreaking Unit - Topped crude or vacuum residuals are heated and thermally cracked in the visbreaker furnace to reduce the viscosity, or pour point, of the charge. The cracked products are quenched with gas oil and flashed into a fractionator. The vapor overhead from the fractionator is separated into light distillate products. A heavy distillate recovered from the fractionator liquid can be used as either a fuel oil blending component or catalytic cracking feed.

W

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Water Loading in an Adsorption Unit - The amount or percentage of water vapor that is adsorbed onto the adsorbent material. Adsorption units are typically used to remove moisture from gases or liquids in processes like gas dehydration, water treatment, or air purification.
Wash - In petroleum refining, to cleanse or purify oils by agitation with water or chemicals.
Waste Water Treatment Plant - Typical refinery wastewater treatment includes primary treatment such as oil/water separation, and a clarifier to remove solids and secondary treatment to remove organics, metals, and other contaminants; and tertiary treatment for polishing before discharge into the environment.
Weathered Crude - Crude petroleum which, owing to evaporation and other natural causes during storage and handling, has lost an appreciable quantity of its more volatile components.
Wet Gas - Mainly natural gas produced along with crude petroleum in oil fields. In addition to methane, ethane, propane and butane, wet gas contains some higher hydrocarbons such as pentane and hexane which, with propane and butane, are easily recoverable as liquids.
Work Done by Expansion Tube Refrigerator - The work associated with the thermodynamic process used in certain refrigeration systems, specifically in relation to gas expansion in an expansion tube or valve. This process is commonly seen in vapor compression refrigeration cycles, where the refrigerant undergoes phase changes and pressure variations to achieve cooling.

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