petroleum definitions

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14.0-1

14.0 - Definitions

14.0 - DEFINITIONS

This section defines most of the units, abbreviations, technical terms, and slang used in this manual.

14.1 Units

The following units and unit abbreviations are commonly used with regard to the Isocracker and its operation.

°API Degree API. Used to describe the density of liquid hydrocarbon streams at 15.6C (60°F). Denser streams like residuum have a low API gravity number while lighter streams like gasoline have a high API gravity. API gravity is related to specific gravity by the following equation:

API 141.5Specific Gravity

131.5

BPOD Barrels Per Operating Day. Used to describe the flow rate of oil streams. One barrel contains 42 U.S. gallons or 5.614 cubic feet. An "operating" day refers to a day on which the plant is operating. These barrels are corrected to standard conditions of 15.6C (60°F). If the oil is a different gravity or flowing at a different temperature than the orifice meter design, the meter reading must be corrected. Sometimes feed rates are expressed per "calendar" day (BPCD), which averages the rate over the whole year, including downtime.

BPSD Barrels Per Stream Day. The same as BPOD (Barrels Per Operating Day).

°Bé Degree Baumé. Used to describe the gravity of some aqueous streams, especially caustic. A 25°Bé caustic solution contains about 19.2 wt % caustic and has a specific gravity of 1.208.

cP Centipoise. A unit of viscosity. Water has a viscosity of 1.00 cP at 20°C.

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14.1 - Units

cSt CentiStoke. A unit of kinematic viscosity. Centistoke viscosity of a fluid is the centipoise viscosity divided by the density of the fluid. Water has a kinematic viscosity of 1.00 cSt at 20°C.

kcal Kilocalorie. Used to describe a quantity of heat. It takes 1 kcal to heat 1 kg of water 1°C and about 556 kcal to vaporize 1 kg of water into 1 kg of steam.

kg/cm2 (a) Kilograms per Square Centimeter Absolute. Used to express pressures relative to total vacuum [0 kg/cm2 (a)] used in calculating meter correction factors and compression ratios. Atmospheric pressure at sea level is 1.033 kg/cm2 (a).

kg/cm2 (g) Kilograms per Square Centimeter Gauge. Used to express gauge pressures (pressure above atmospheric pressure). This is the pressure shown on the face of a pressure gauge. To determine absolute pressure, add 1.033 to the reading on a pressure gauge.

kg/hr Kilograms per Hour. Used to describe the mass flow rate of a stream.

kg-mole Kilogram-Mole. Used to describe a quantity of compounds or mixture of compounds equal in weight to its average molecular weight. For example, 1 kg-mole of oxygen (O2, molecular weight = 32.0) weighs 32.0 kg, while 1 kg-mole of butane (C4H10, molecular weight = 58.1) weighs 58.1 kg.

kW Kilowatt. Used to describe the power (rate of energy usage) of an electric motor or other electrical device.

L/Min. Liters per Minute. Used to describe the flow rate of liquid streams at process conditions such as pump suction. Unlike BPOD or BPSD, these units are not corrected to standard conditions.

m3/hr Cubic Meters per Hour. Used to describe the flow rate of liquid streams at either standard or process conditions. In this project, m3/hr refers to flow at process conditions; m3/hr @ 15.6C refers to flow at standard conditions.

mm Hg Millimeters of Mercury. (The chemical symbol for mercury is Hg.) Used to express absolute pressures, especially for vacuum systems. Atmospheric pressure at sea level is 760 mm Hg. A total vacuum is 0 mm Hg absolute or 760 mm Hg vacuum

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14.1 - Units

MM kcal/hr Million Kilocalories per Hour. Used to describe the rate of heat transfer in an exchanger or fired heater.

Nm3 Normal Cubic Meter. Used to describe a quantity of gas which would occupy 1 cubic meter at 0°C and 760 mm Hg. 22.4 Nm3 of a gas is equivalent to 1 kg-mole. Thus, 22.4 Nm3 of oxygen (O2) weighs 32.0 kg. One normal cubic meter is equivalent to about 37.3 SCF.

Nm3/m3 Normal Cubic Meter per Cubic Meter of Oil. Used to describe a relative gas-to-oil ratio, especially hydrogen consumption or recycle gas ratio. One normal cubic meter of gas per cubic meter of oil is equivalent to about 5.92 SCFB.

ppb Parts Per Billion. 1000 ppb is equal to 1 ppm.

ppm Parts Per Million. Used to express a small weight concentration of liquids (ppmw) or volume concentration of gases (ppmv). It takes 10,000 ppm to make 1%.

SCF Standard Cubic Feet. Used to express gas volume at standard conditions of 15.6C (60°F) and atmospheric pressure at sea level.

SCFB Standard Cubic Feet Per Barrel of Oil. Used to describe a relative gas-to-oil ratio, especially hydrogen consumption or recycle gas ratio.

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14.2 - Abbreviations

14.2 Abbreviations

The following abbreviations are from refinery processing in general and hydrocracking in particular.

ATF Aviation Turbine Fuel. A cut which generally boils between 121°C (250F) and 285°C (545F).

BAT Bed Average Temperature. The arithmetic average of the inlet and outlet level average temperatures (LATs) of a given catalyst bed.

BFW Boiler Feedwater. Specially treated and deaerated water which is low in dissolved solids and oxygen and used to make steam in a boiler.

CAT Catalyst Average Temperature. The weighted average of the BATs. Each individual BAT is weighted by the fraction of the total active catalyst in that bed.

CHPS Cold High Pressure Separator.

CLPS Cold Low Pressure Separator.

COP Catalyst Oriented Packing. A technique for dense loading of catalyst pellets which gives 5-10% more catalyst in a given volume than sock loading.

DMDS Dimethyl Disulfide. A molecule (CH3SSCH3) used to sulfide fresh catalyst.

D 86 An ASTM test method used to determine the boiling point distribution of a cut with an end point lower than about 370°C (700F).

D 1160 An ASTM test method used to determine the boiling point distribution of a cut with an end point higher than about 370°C (700F).

EOR End-of-Run. The point in time when the catalyst has fouled so much that catalyst replacement or regeneration is required.

F.V. Full Vacuum.

HHPS Hot High Pressure Separator.

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HLPS Hot Low Pressure Separator.

ID Inside Diameter.

ICR Isocracker or Isocracking.

LAT Level Average Temperature. Average temperature at a level in a catalyst bed.

LHSV Liquid Hourly Space Velocity. The ratio of reactor feed rate (bbl/hr or m3 at standard conditions) to catalyst volume (bbl or m3). Unit of measure is inverse hours (l/hr).

LPG Liquefied Petroleum Gas. Primarily propane and butanes with lesser amounts of ethane and pentane.

MOR Middle-of-Run. A point in time midway between SOR and EOR.

MOV Motor Operated Valve. A valve with a motor operator._

pH2 or pH2 Partial Pressure of Hydrogen or average partial pressure (denoted with a line over the p). For Chevron’s kinetic estimates, the hydrogen partial pressure in the reactor is calculated by assuming all oil molecules are vaporized. The average partial pressure in the reactor generally refers to the linear average of the inlet and outlet. (See Section 13.0 for example.)

PPC Per Pass Conversion. Per pass conversion is the percentage of combined first-stage unconverted product and second-stage recycle oil which is converted to products in the second-stage reactor during each pass through the reactor. (See Section 13.0 for example.)

RCP Recycle Cut Point. The TBP cut point between the heaviest product cut and recycle feed. (See Section 13.0 for example.)

RVP Reid Vapor Pressure. A measure of the vapor pressure of a light hydro-carbon stock, used especially with gasolines and gasoline blending stocks.

SOR Start-of-Run. The point in time when the catalyst is fresh or newly regenerated.

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SWS Sour Water Stripping. The sour water treating facilities.

TBP True Boiling Point. The boiling point of a pure liquid at atmospheric pressure.

TEOR Catalyst Average Temperature when the catalyst is at End-of-Run.

TSOR Catalyst Average Temperature when the catalyst is at Start-of-Run or fresh conditions.

T* "T-Star." A temperature used to characterize feeds. It is intended to approximate the initial cut point of the feed. It is the intersection of a line drawn through the TBP 30% and 50% points and the 0 LV % axis. (See Section 13.0 for illustration.)

T-T Tangent to Tangent Length. Length of cylindrical sections of columns, vessels, and reactors.

VGO Vacuum Gas Oil. An oil which is taken as a sidecut from a crude vacuum column.

X(RCP) Conversion Below Recycle Cut Point. The amount of product boiling below RCP, minus the expansion. (See Section 13.0 for illustration.)

X(T*) Conversion Below T*. The amount of product boiling below T*, minus the expansion. (See Section 13.0 for illustration.)

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14.3 - Technical Terms

14.3 Technical Terms

The following technical terms are useful in understanding the operations of the Isocracker; most are used in this manual:

Ammonia A molecule (NH3) which is formed by reaction of hydrogen with organic nitrogen molecules in the feed. Ammonia forms a basic solution in water and helps to absorb hydrogen sulfide.

Ammonium A compound (NH4Sx) which is injected into the effluent cooler toPolysulfide eliminate cyanide-induced corrosion and to harden iron sulfide scale to

limit erosion.

Aromatics A class of molecules which contain one or more benzene rings. In the hydrotreating process, some of the feed aromatics are saturated to naphthenes by hydrogenation.

Asphaltenes A class of molecules which contain a very high number of unsaturated rings and high levels of metals, sulfur, and nitrogen. Quantitatively measured as material insoluble in hot heptane.

Assay A set of boiling point data used to describe a mixture of molecules.

ASTM D 86 A test method used to obtain an assay of a mixture whose heaviest mole-cule boils at about 370°C (700F).

ASTM D 1160 A test method used to obtain an assay of a mixture whose heaviest mole-cule boils higher than 370C (700°F).

Aviation Turbine A cut which generally boils between about 121°C (250F) and 285°CFuel (545F).

Base Metal A nonnoble metal. Typical base metals are Ni, Fe, Mo, etc.

Bed Channeling Maldistribution of liquid and vapor flow in a catalyst bed such that sections of the bed are bypassed by liquid.

Bleed Gas A high pressure stream drawn from or "bled off" from the reactor loop recycle gas stream to control loop pressure or recycle gas purity.

Blind A flat plate inserted between flanges in a pipe to prevent flow.

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14.0-8


Block Valve A synonym for gate valve.

Boiling Point The temperature at which the vapor pressure of a liquid equals the system pressure. The boiling point refers to atmospheric pressure if no pressure is stated. For example, the boiling point of water is 100°C at atmospheric pressure. But it is also 208°C at the 17.6 kg/cm2 (g) pressure in a steam drum.

Boiling Range The range of temperatures over which a mixture boils, usually at atmo-spheric pressure.

Bottoms The liquid stream which leaves the bottom of a distillation column.

Bubble Point The temperature at which the vapor pressure of a mixture just equals the system pressure (same as boiling point). So called because this is the temperature at which the first "bubble" of vapor forms as the mixture is heated.

Catalyst A substance which accelerates the rate of a reaction but which remains basically unchanged after the reaction is complete.

Catalyst Activity The desulfurization, denitrification, demetalization, saturation, or hydrocracking (depending on the type of catalyst) ability of a catalyst at a particular temperature. The greater its degree of conversion for a given temperature, the more "active" a catalyst is.

Catalyst Life The total time a single catalyst charge is in service from startup until EOR is reached.

Catalyst Poison A substance which partially destroys the ability of a catalyst to speed up a reaction.

Catalyst Scalping Removal and replacement of the top layer of catalyst in the first reactor(Skimming) bed. This is performed when deposits severely plug the upper catalyst

layer, imposing a pressure drop across the first bed.

Caustic A basic molecule usually used in a water solution to neutralize an acid, such as sodium hydroxide (NaOH).

Cetane Number The percentage of pure cetane in a blend of cetane and alpha-methyl-naphthalene which matches the ignition quality of a diesel fuel sample.

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This quality, specified for middle distillate fuels, is analogous to the octane number for gasolines.

Check Valve A valve which permits flow in the forward direction but not in the reverse direction. [Also called a nonreturn valve (NRV).]

Circulating Reflux A stream which is drawn from the side of a distillation column, cooled below its bubble point then returned to a tray further up the column to partially condense some of the upflowing vapor. Also known as a pumparound.

Cladding A thin, protective layer of corrosion-resistant metal bonded to the surface of a thicker layer of a base metal with less corrosion resistance.

Coalescer Pad A fine steel mesh pad used to promote the separation of water from oil.

Coke Deposits of carbon-rich material which slowly accumulate on the catalyst from undesirable side reactions and reduce its activity.

Coking The process by which coke is deposited on catalyst or process equip-ment and piping.

Column A tall vertical vessel containing trays or packing used for distillation or absorption.

Convection Section The part of a fired heater immediately above the firebox in which most of the heat is transferred by convection rather than radiation.

Conversion The amount of feed material which becomes light products in the reactor. (See Section 13.0 for illustration.)

Corrosion An undesirable reaction between the metal of a vessel wall or pipe and certain chemicals which gradually "eats" away enough metal to require replacement.

Cut One of the products from a distillation column. A light cut contains low boiling components and comes from the upper section of the column. A heavy cut contains high boiling components and comes from the lower section of the column.

Cut Point The boiling point corresponding to the intersection of the cumulative composite assay curve drawn between two adjacent cuts and a vertical

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line connecting the start and end points of the two cuts. (See Section 13.0 for example.)

Demetalation The process by which metal-bearing molecules react with hydrogen to form metal sulfides which deposit on the catalyst surface.

Demister Pad A fine steel mesh pad placed at the top of a vessel just below the vapor outlet to coalesce and remove tiny liquid droplets or mist entrained in the rising vapor.

Denitrification The process by which nitrogen is removed from hydrocarbon com-pounds by reaction with hydrogen to form ammonia.

Desulfurization The process by which sulfur is removed from hydrocarbon compounds by reaction with hydrogen to form hydrogen sulfide.

Dew Point The temperature at which a mixture of vapor molecules first forms a drop of liquid when it is cooled.

Diesel A cut which generally boils between about 150°C (302F) and 370°C (700F), used to power automobile, truck, or marine engines.

Dimethyl Disulfide A molecule (CH3SSCH3) used to sulfide fresh catalyst.

Discharge The exit or high pressure end of a pump or compressor.

Distillation The process of separating a mixture of molecules into two or more boiling ranges by contacting upflowing vapor with downflowing liquid.

Double Blocks Two consecutive block valves, separated by a short length of pipe with a

and Bleeder third block valve off a tee. Used to give positive isolation between two systems. The third valve is usually kept open to detect if there is a

leak through either of the two main valves.

Draft A measure of furnace firebox gauge pressure usually measured in inches of water. A typical draft is 13 mm of water at the burners of a fired heater, which means that the pressure inside the firebox near the burners is 13 mm of water less than atmospheric. Higher draft means lower pressure (higher gauge reading).

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Dropout Spool A short length of pipe with flanges at both ends to permit easy removal. Used for positive isolation of two systems. Also known as a removable spool (RS).

Effluent The stream leaving the bottom of the reactor.

Embrittlement The aging process of reactor metal, particularly weld metal, in which prolonged exposure to high temperatures causes the metal to deteriorate slightly and become brittle.

Endothermic A chemical reaction which absorbs heat.Reaction

End Point The last and highest temperature reported in an assay which indicates the boiling point of the molecules boiling when the assay was stopped.

Entrainment The physical phenomenon of a mist or fog of liquid droplets being transported in a vapor stream.

Equilibrium In a chemical system, the state of affairs in which a chemical reaction and its reverse reaction are taking place at equal velocities, so the concentrations of reacting substances remains constant.

Excess Air Air which enters a furnace over and above the amount theoretically required for complete, stoichiometric combustion of the furnace fuel.

Exothermic A chemical reaction which gives off heat.Reaction

Firebox The section of a fired heater where the burners are located and where heat is transferred to the tubes by radiation. The radiant section.

Flash Point The lowest temperature at which an oil gives off enough vapor to make a small flash when a flame is passed over it. The lowest temperature at which the vapor of an oil can ignite.

Flash Zone The section of a distillation column where the feed enters and flashes into separate vapor and liquid streams.

Flooding A condition in a distillation column where the liquid and vapor rates are so high that either massive amounts of liquid are carried upward with

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the vapor (vapor rate is too high) or liquid backs up in the downcomers and spills out on the trays above.

Flue Gas The gas stream containing fired heater combustion products which flows through the convection section and up the stack.

Fouling Rate The rate at which catalyst temperature must be increased with time to hold the target product level constant. Catalyst temperature is increased to offset loss of activity due to coking and metals deposition on the catalyst.

Fractionator A name used for a distillation column which makes three or more cuts.

Freeze Point The temperature at which the first wax crystals become visible when a light oil (usually jet or naphtha) is chilled.

Fresh Catalyst Catalyst which has not yet been deactivated by coke or catalyst poisons.

Fresh Feed Feed which has not yet passed through the reactor.

Gate Valve A valve designed to be either fully open or fully closed. In the open position, the valve will cause essentially no pressure drop. Significant valve trim erosion can occur if a gate valve is used to regulate flow.

Globe Valve A valve designed to regulate the flow rate of a stream. It causes a substantial pressure drop, even in the open position.

Heavy Ends The highest boiling molecules in a mixture.

Heavy Naphtha The high boiling molecules of the naphtha cut. The hydrocracker heavy naphtha cut generally boils between 110°C (230F) and 121°C (250F). Maximum naphtha recovery increases the boiling end point to 165°C (330F). It is normally used to make gasoline, often after being pro-cessed in a catalytic reformer.

Hot Spots Areas of a catalyst bed in which large amounts of heat are released due to maldistribution of liquid and vapor feed across the bed. In areas of low flow, the oil is reacted under more severe conditions and overcracking and coking can result. Catalyst in hot spot areas is deacti-vated much more rapidly than under design operating conditions.

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Hydrocarbon A class of molecules which contain only carbon and hydrogen atoms. In practice, molecules which contain only trace levels of sulfur, nitro-gen, or metals are also called hydrocarbons. Crude oil and its refined products are hydrocarbons.

Hydrocrackate The product from a hydrocracker.

Hydrocracking A process in which large molecules are cracked into smaller ones accompanied by a large consumption of hydrogen such that the products are richer in hydrogen than the feed.

Hydrogenation The process of adding hydrogen to a compound either to saturate it or to separate it into two or more compounds.

Hydrogen Partial Defined by Chevron Research and Technology Company as the partial Pressure pressure of hydrogen in the reactor assuming all the components of the

oil feed are vaporized. Usually expressed as the arithmetic mean of inlet and outlet hydrogen partial pressures.

Hydrogen Sulfide A molecule (H2S) which is formed by reaction of hydrogen with organic sulfur molecules in the feed. A highly toxic gas.

Hydrotreating A process in which oil feed is desulfurized, denitrified, demetalized, saturated, and mildly cracked in the presence of excess hydrogen and a catalyst.

Injection Water Water injected into the effluent vapor air cooler to dissolve ammonium salts from the effluent.

Interface Level The top of the water layer and the bottom of the oil layer in a separator.

Isocracking The trade name of the hydrocracking process licensed by Chevron Research and Technology Company.

Iso/Normal Ratio The ratio of isoparaffins (branched chain) to normal paraffins (straight chain).

Jet Often used interchangeably with kerosene. Within this manual, it is synonymous with ATF.

Kerosene Within this manual it is synonymous with ATF.

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Kinematic Viscosity The viscosity of a fluid divided by its density. The viscosity in cP divided by the density in g/cc equals the kinematic viscosity in centis-tokes (cSt).

Leaks High pressure gas (mostly hydrogen) lost from the high pressure section through loose connections or through the recycle gas compressor seals.

Light Ends The lowest boiling molecules in a hydrocarbon mixture. Typically butane and lighter molecules.

Light Naphtha The lightest boiling molecules of the naphtha cut. The hydrocracker light naphtha cut generally boils between 30°C (90F) and 110°C (230F) (C5-110°C cut).

Live Catalyst Any sulfided catalyst which has been in hydrocarbon service.

Manufactured High purity hydrogen (95-100%) produced by reacting hydrocarbonsHydrogen with steam in a hydrogen plant. The reaction products are hydrogen and

carbon oxides.

Mercaptans Mercaptans is a common name for Thiols. Thiols are a class of hydrocarbon molecules containing sulfur. The chemical structure of a mercaptan contains a sulfur atom bonded to one carbon atom and one hydrogen atom. These compounds typically have a noxious odor. Skunk scent is butyl mercaptan.

Metal Carbonyls Highly poisonous compounds which are produced by reaction between catalyst metals and carbon monoxide in the recycle gas. Carbonyls form at temperatures less than 205°C (400F). If a reactor is to be opened following a shutdown, CO must be purged to below 30 ppm in the recycle gas before cooling the reactor below 205°C (400F).

Millimeters of A unit of pressure used to define absolute pressures below 1 atmosphere,

Mercury 760 mm of mercury represents a pressure equal to 1 atmosphere.

Naphtha A cut which generally boils between 30°C (90F) and about 170°C (338F) and is used to make gasoline.

Naphthenes A class of molecules which contain one or more saturated rings but no unsaturated rings.

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Nickel Carbonyl A metal carbonyl [Ni(CO)4] which is one of the most toxic substances known to man. (See Section 9.0.)

Noble Metal A precious metal. Usually a rare metal, sometimes used in catalysts. Typical noble metals are platinum (Pt), palladium (Pd), and gold (Au).

Octane Number A term numerically indicating the relative antiknock value of a gasoline.

Olefins Straight- or branched-chain hydrocarbon compounds which contain one or more unsaturated bonds.

On Control A situation in which a controller is modulating a control valve stem position to match a process variable with the desired set point. The situation is “off control” when the control valve goes fully open or fully closed.

Orbit Valve A special valve which gives exceptionally tight shutoff.

Overflash A measure of the extent of overvaporization of the fractionator feed as it enters the flash zone.

Overflash Liquid The liquid passing through the flash zone from the tray above.

Overhead The vapor stream leaving the top of a column.

Overlap (a) (Distillation) - The spread between two assay temperatures of two adjacent cuts. The most common spread is the difference between the ASTM D 86 95% point of the lighter cut and the ASTM D 86 5% point of the heavier cut. (b) (Feed) - The volume percent of feed that boils less than T*.

Oxidation The phase during catalyst regeneration in which coke and sulfur are oxidized (burned off) by reaction with oxygen.

pH A scale for describing how acidic or basic a solution is. Neutral water has a pH of 7.0. Solutions with pH below seven are ten times more acidic for each lower pH number. Solutions with pH above seven are ten times more basic for each higher pH number. Example: A solution with a pH of 9.0 is 100 times more basic than a solution with a pH of 7.0.

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Packing (a) A specially formed metal ring (Pall ring) or other shaped objects used to promote effective contact between liquid and vapor in a column. (b) A device used to seal the shafts of valves and pumps.

Paraffins Straight- or branched-chain hydrocarbon compounds with no unsatu-rated bonds or rings.

Partial Pressure The proportionate share of the total vapor pressure attributed to a given molecular compound in a mixture of compounds. (See Section 13.0.)

Polysulfide See ammonium or sodium polysulfide.

Pour Point The lowest temperature at which an oil will flow.

Precious Metals See Noble Metal.

Pumparound Within this manual, it is synonymous with circulating reflux.

Purge Steam Steam that is injected into a firebox to prevent the possibility of an uncontrolled fire.

Pyrophoric A word used to describe a solid material (for example, iron sulfide) capable of spontaneous ignition when exposed to the air.

Quench Gas The portion of recycle gas which is injected between catalyst beds to control the temperature of the reactants.

Quench Solution A solution used during regeneration to cool the acid gases through their dew point and neutralize them before any severe corrosion occurs.

Radiant Section The section of a fired heater contained in the firebox in which most of the heat is transferred by direct radiation from the flames rather than by convection.

Reboiler A fired heater or heat exchanger which partially vaporizes some of the column bottoms to generate vapor for stripping.

Recycle Feed A portion of fractionator bottoms containing second-stage fresh feed and recycle feed returned to the second-stage reactor as feed. Products are used as recycle feed during startup and sometimes during emergency situations.

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Recycle Gas The portion of the recycle compressor discharge which is not used as quench gas.

Reduction A phase during catalyst regeneration in which metal sulfates formed during the oxidation phase are partially reduced by controlled reaction with hydrogen to prevent temperature runaway during subsequent catalyst sulfiding.

Reflux The portion of the condensed overhead vapor which is returned to the top tray of the column.

Regeneration The process of restoring the activity of the catalyst. See oxidation and reduction.

Run Plot A graph showing the CAT as a function of days onstream.

Saturated A hydrocarbon compound in which all carbon atoms are connected by single bonds.

Sidecut A liquid product drawn from the side of a distillation column.

Skin Temperature The temperature of the outside of a fired heater tube wall or reactor wall.

Smoke Point A test used to indicate the tendency of a jet fuel to smoke upon combustion.

Sodium Polysulfide A compound (Na2Sx) which is injected into the effluent vapor air cooler to eliminate cyanide-induced corrosion and to harden iron sulfide scale to limit erosion.

Sour A term used to characterize any stream containing H2S or sulfur or any equipment processing such a stream.

Specific Gravity The specific gravity of a liquid or solid is the ratio of its density to the density of water at a specified reference temperature. The specific gravity of a gas is the ratio of its density to the density of air at the same temperature and pressure as those of the gas.

Spent Catalyst Catalyst which has lost its activity and which will be discarded or regenerated.

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Spillback A stream which "spills back" from compressor (or pump) discharge to suction to ensure that the compressor (or pump) operates above a minimum flow rate.

Stabilization The process which strips light hydrocarbons from a product stream to meet storage requirements.

Steady State A system is in steady state when there is no accumulation or depletion of heat or mass (i.e., the total mass flowing into a system is equal to the total moss flowing out of the system, and the temperature of the system is constant).

Stop-Check Valve A valve which functions as a check valve when the handwheel is unscrewed and as a closed block valve when the handwheel is screwed down.

Straight-Run (Oil) An oil stream which has not undergone any cracking or other chemical modification. A product from crude distillation.

Stripper A small distillation column which is used to remove the light ends from a cut by reboiling or steam stripping.

Suction The entrance or low pressure end of a pump or compressor.

Sulfiding A process in which the highly active metals deposited on a base metal catalyst are converted from oxides to metal sulfides, which promotes smoother, more stable hydrotreating reactions.

Sulfur An element contained in some of the feed molecules which gets con-verted to hydrogen sulfide in the reactor.

Surge (a) A condition of highly unstable operation of a centrifugal compressor due to low flow. (b) A volume in the bottom of a vessel used to hold liquid.

Sweet A stream containing no hydrogen sulfide or sulfur.

Tail The difference between the end point of a cut and the nominal final cut point or the difference between the start point of a cut and the nominal initial cut point.

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Temperature A condition in which a high temperature leads to a high reaction rateExcursion which, in turn, leads to a higher temperature and so on. This can only

happen if the reaction is exothermic.

Temperature A rapidly accelerating temperature excursion.Runaway

Thermal Shock Structural damage produced in metal equipment (such as reactors) by heating or cooling the equipment too quickly.

Thermosiphon A reboiler in which the process fluid moves due to the density difference

Reboiler of the inlet and outlet fluid caused by partial vaporization.

Titration A procedure during startup of a reactor in which ammonia or other basic compounds are adsorbed onto the catalyst surface to improve performance.

True Boiling A characteristic distillation curve for an oil which relates the volumePoint Curve fraction in which a component vaporizes to its atmospheric boiling (TBP Curve) point. The curve is usually represented by a series of temperatures, tn,

where t is the atmospheric distillation temperature at n LV % distilled.

Turnaround A period of downtime used for general maintenance or catalyst handling operations.

Unstabilized Naphtha Naphtha which has a high content of butane and other light gases (hydrocarbons and H2S) such that its RVP is too high to permit safe storage.

Valve Tray A type of tray used in a distillation column which has many small caps which slide up and down in holes through the tray. This gives a higher turndown ratio than the more common sieve tray.

Vapor Pressure The pressure exerted by a liquid in a closed system. The vapor pressure increases with increasing temperature. When the temperature gets high enough that the vapor pressure equals the system pressure, that temperature is called the bubble point and the liquid begins to boil.

Viscosity The resistance of a fluid to flow. The unit of viscosity is the Poise. A more convenient unit is 1/100th of a Poise, the centipoise (cP). Water has a viscosity of 1 cP at 20°C.

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Wash Water Water injected into the effluent air cooler to "wash out" ammonia and hydrogen sulfide. Within this manual, it is synonymous with injection water.

Weeping A condition in a distillation column where the tray pressure drop is so low (from low vapor rate) that some of the liquid flows through the holes in the tray instead of flowing over the outlet weir into the downcomer.

Yield The percentage of a given product formed in the reactor relative to the fresh feed.

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14.4 - Chemical Symbols

14.4 Chemical Symbols

The following standard chemical symbols are used in this manual:

Ca Calcium

CH3SSCH3 Dimethyl Disulfide (DMDS)

Co Cobalt

CO Carbon Monoxide

CO2 Carbon Dioxide

Cr Chromium

Fe Iron

Hg Mercury

H2 Hydrogen

H2O Water

H2S Hydrogen Sulfide

Mg Magnesium

Mo Molybdenum

Na Sodium

Na2Sx Sodium Polysulfide

NH3 Ammonia

NH4Cl Ammonium Chloride

NH4HS Ammonium Bisulfide

NH4OH Ammonium HydroxideNH4Sx Ammonium Polysulfide

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14.4 - Chemical Symbols

Ni Nickel

Ni(CO)4 Nickel Carbonyl

N2 Nitrogen

O2 Oxygen

TBA Tri-n-butylamine

V Vanadium

W Tungsten

Revision 029 Sep 95

petroleum definitions

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