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.
ADSORPTION 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.
BLEEDER 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.
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.
HYDROGENATION 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 excellent antiknock characteristics on which the octane number of 100 is based.
KNOCKOUT DRUM A vessel wherein suspended liquid is separated from gas or vapor.
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 or 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 CnH2n, 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 CnH2n.
PARAFFINS A family of saturated aliphatic hydrocarbons (alkanes) with the general formula CnH2n+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.
VACUUM 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