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Chapter 7: Explanations of Common Chemical Engineering Terms and Abbreviation Guide. This section provides definitions for common terms, offering explanations for most of the units, abbreviations, technical terms, and jargon used in HC/RDS systems. Section 1: Units: 1. During the operation of HC/RDS units, the following units and abbreviations are commonly used. 2. BPOD: Number of barrels per operating day (Barrels Per Operating Day). It is used to indicate the flow rate of material; one barrel equals 42 U.S. gallons or 5.614 cubic feet. An “operating day” refers to a day when the facility operates normally; the flow rate is expressed in days, and it represents the average flow rate throughout the year. The number of barrels per operating day (BPOD) refers to conditions at 60°F. If the specific gravity of the oil is different, or if the temperature during flow differs from the design temperature of the orifice flow meter, it is necessary to correct the readings from the gauge. 3. Kcal: Kilocalorie is used to denote heat energy. The amount of heat required to raise the temperature of 1 kilogram of water by 1°C is defined as 1 Kcal ； It takes about 556 Kcal of heat to turn 1 kilogram of water into 1 kilogram of steam. 4. Kg/cm2(a): Kilograms per square centimeter (absolute) (Kilograms per Square Centimeter Absolute), used to represent absolute pressure. The atmospheric pressure is 1.033 kg/cm2(a). 5. Kg/cm²(g): Kilograms per square centimeter (gauge). This unit is used to indicate gauge pressure. This is the reading on the pressure gauge; to obtain the absolute pressure, add 1.033 kg/cm2(a) to the gauge reading. 6. Kg/hr: Kilograms per hour; it is used to indicate the mass flow rate of materials in logistics. 7. Kg·mole: kilogram-mole. It is used to denote the amount of a chemical molecular compound, or a mixture whose weight is equal to its average molecular weight. For example, 1 kilogram-mole of oxygen (molecular weight of O2 = 32.0) weighs 32.0 kilograms, while 1 kilogram-mole of butane (C4H10, molecular weight = 58.1) weighs 58.1 kilograms. 8. KW: Kilowatts. It is used to indicate the power of an electric motor or other electrical equipment. 9. L/Minute: Liters per minute. They are used to indicate the flow rate of liquid streams under process conditions (such as the displacement of a pump), and unlike BPOD, these units do not need to be corrected to standard conditions. 10. m3/hr: Cubic Meters per Hours, used to represent the flow rate of the liquid stream under BPOD conditions (see the definition of BPOD). 11. mmHg: Millimeters of mercury. (The chemical symbol for mercury is Hg). It is used to represent absolute pressure, especially in pressure reduction systems, with atmospheric pressure being 760 mmHg. 12. MM Kcal/hr: Million Kilocalories per Hour. It is used to indicate the heat transfer rate of a heat exchanger or a combustion heater. 13. Nm3: Normal Cubic Meters. It is used to indicate the volume of gas (1 cubic meter of gas at 0°C and 760 mmHg). 22.4 Nm3 of gas is equivalent to 1 kilomole. For example, 22.4 Nm3 of oxygen (02) weighs 32.0 kilograms. 14. Nm3/KL: Normal Cubic Meter per Kilo Liter of oil, used to indicate the relative air-oil ratio, especially hydrogen consumption or cycle air ratio. 15. PPb: Parts Per Billion, i.e., the number of parts per one billion. 1000 PPb is equal to 1 PPm. 16. PPM: Parts per million. It is used to indicate the weight concentration (PPmv) of liquids or the volume concentration (ppmw) of gases when there is very little of them. 10,000 PPM is equal to 1%. 17. SCF: Standard Cubic Foot, used to denote the volume of a gas under standard conditions of 60°F and atmospheric pressure. 18. SCF/Bbl: Standard Cubic Feet per Barrel of crude oil, used to indicate the relative oil-to-gas ratio, especially in terms of hydrogen consumption or recycle gas ratio. Section 2: Abbreviation Guide The following abbreviations are generally used for HC/RDS devices. 1. BAT: Bed Average Temperature. It refers to the arithmetic mean of the horizontal average temperatures within the catalyst bed. 2. BFW: Boiler Feed Water – specially treated deoxygenated water with very low levels of dissolved solids and oxygen, used to generate steam in boilers. 3. CAT: Catalyst Average Temperature – the volume-weighted average of BATs, with each BAT value being weighted by the volume fraction of active catalysts in that reactor series. 4. COP: Catalyst Oriented Packing, a technology for densely packing catalyst particles. Within a given volume, it allows for 10–15% more catalyst to be loaded compared to conventional catalyst loading methods. 5. EFO Barrel: A Barrel of Equivalent Fuel Oil is defined as 3,300,000 Btu (HHV) or 6,000,000 Btu (LHV). 6. EOR: End Of Run is defined as a situation where the catalyst is severely fouled, and increasing the reaction temperature is no longer sufficient to meet the requirements for product quality. At this point, the catalyst must be replaced. 7. fH2: The molar fraction of hydrogen in the feed gas. 8. HHV: The heat value of a fuel, which is the heat generated when the fuel is completely oxidized at 60°F into carbon dioxide and liquid water at the same temperature. 9. LAT: Level Average Temperature – the average temperature on a horizontal plane within the catalyst bed. 10. LHSV: Liquid Hourly Space Velocity – the ratio of the reactor feed rate (bbL/hr) to the catalyst volume (bbL). 11. LHV: Low calorific value of fuel (net heat released upon combustion). The heat generated when material at 60°F is completely oxidized into carbon dioxide and water vapor at 60°F. 12. LPG: Liquefied Petroleum Gas mainly consists of propane and butane, with small amounts of ethane and pentane. 13. MCR: Residual carbon. It is a measurement value that represents the precursor to coke in petroleum products, namely the ASTM (ASTM D189) Conradson carbon equivalent. 14. MOR: Middle Of Rum (midpoint of the distillation process). It falls right at the midpoint between SOR and EOR, which is also a period with a relatively low scaling rate. 15. MOV: (Motor Operated Valve) An electrically controlled valve, a shut-off valve equipped with an electric controller. 16. O/H: (Over Head) Top product of the tower. 17. PCD: Process Control Diagram. 18. PFD: Process Flow Diagram. 19. PH2 or PPH2, or the partial pressure of hydrogen – the average hydrogen pressure in the reactor assuming that all oil molecules have vaporized. 20. PID: Process and Instrument Diagram. 21. RVP: Reid Vapor Pressure. 22, S/D: Shut Down. 23、 SOR: Start Of Run. The fresh stage of the catalyst generally refers to the first 30 days after it is introduced into the feed. 24. SPGR: Specific Gravity. 25. TBP: True Boiling Point – the boiling point of a pure liquid at standard pressure. 26、 TEOR: Average temperature of the catalyst at the end of operation. 27. TSOR: Average temperature of the catalyst at the beginning of operation. 28. T–T: Tangent length. Cylindrical cross-sectional length of towers, tanks, and reactors. 29. VR: Vacuum residue. 30. VRDS: Vacuum Residual Desulfurization. 31. AR: Atmospheric residue. 32. ARDS: Desulfurization of atmospheric residue oil. 33. RDS: Heavy oil hydrodesulfurization. 34. X: Conversion rate, the volume fraction of feedstock converted into product. Section 3: Technical Terms 1. Technical terms are very useful for understanding the operation of HC/RDS devices; some of the more commonly used terms are: 2. Absorption tower: A tower in which rising gas comes into contact with falling liquid, allowing part of the gas to be absorbed by the liquid. 3. Amines: Any compound that can be considered a derivative of ammonia (NH3), that is, in which one or more hydrogen atoms of ammonia are replaced by hydrocarbon groups (for example, aniline, C4H5NH2). 4. Ammonia: A compound formed by the reaction of organic nitrogen molecules in the feed with hydrogen (NH3); its aqueous solution is alkaline and helps to absorb H2S. 5. API specific gravity: A scale of arbitrary specific gravity that indicates the specific gravity or density of liquid petroleum streams; an increase in API specific gravity corresponds to a decrease in density, with the measurement scale being adjusted according to the API value. 6. Aromatic hydrocarbons: Compounds that contain one or more unsaturated rings, which are converted into naphthenic hydrocarbons through hydrogenation in hydrogenation processes. 7. Asphaltenes: A class of compounds containing a large number of unsaturated rings and high contents of metal, sulfur, and nitrogen. Quantitative measurement indicates a substance insoluble in hot heptane. 8. Experiment: A set of data used to illustrate the boiling point distribution of different molecular mixtures. 9. ASTM D 86: A testing method used to obtain boiling point data for mixtures, in which the heaviest component of the mixture boils at around 370°C or lower temperatures. 10. ASTM D1160: A testing method used to obtain boiling point data for mixtures in which the majority of components boil at temperatures above 370°C. 11. Baffle: A type of partial restriction, usually a plate placed in the device where it is installed, used to change the direction of a fluid, guide its flow, or promote mixing. 12. Boundary Area (BL): The boundary that encloses any process equipment, including special process equipment, but excluding auxiliary facilities and storage tanks. 13. Bed cross-flow: The distribution of liquid and gas within the catalyst bed is poor, causing the liquid to take shortcuts across the bed cross-section. 14. Covering gas: The gas above the liquid in the tank; this gas protects the liquid from being affected by air. If the covering gas is inert, it can reduce the risk of liquid explosion under positive pressure. 15. Release: Generally, the valve is slightly opened to discharge a small amount of material from the pipeline or tank. 16. Exhaust gas flow: Under normal operation, in order to maintain the hydrogen partial pressure in the reactor, high-pressure gas streams (light hydrocarbons) are released from the reactor system. 17. Blind plate: A flat plate inserted between pipeline flanges to prevent flow. 18. Shut-off valve: A synonym for gate valve. 19. Venting: The action of reducing the pressure in a container. This term is also used to refer to substances that must be removed from a process in order to control impurity levels (for example: cooling tower vents and boiler vents). 20. Boiling point: The temperature at which the vapor pressure of a liquid equals the system pressure. If no pressure is specified, then the pressure refers to atmospheric pressure. For example, at atmospheric pressure, the boiling point of water is 100°C, while in a steam boiler at a pressure of 18.2 kg/cm2, its boiling point is 208°C. 21. Boiling range: Generally, the temperature range over which a mixture boils at atmospheric pressure. 22. Bottom product of the distillation tower: The liquid stream that flows out from the bottom of the distillation tower. 23. Bubble point: The temperature at which the vapor pressure of the mixture is equal to the system pressure; in other words, it is the temperature at which the first bubbles form when the mixture is heated. 24. By-products: Secondary or additional products that are of little importance, products other than the main product. 25. Carbon disulfide or dimethyldisulfide: Compounds used to vulcanize fresh catalysts. 26. Catalyst: A substance that can accelerate the rate of a reaction, but remains essentially unchanged after the reaction is complete. For HC/RDS operations, the catalyst is an aluminum-based solid containing precious metals such as nickel and cobalt. 27. Catalyst activity: At a specific temperature, it refers to the catalyst’s ability to remove sulfur, nitrogen, metals, and residual carbon through nickelation, as well as to saturate or hydrogenate substances. At that given temperature, the higher the conversion rate, the greater the catalyst activity. 28. Catalyst bed: A layer of catalyst in the reactor. 29. Catalyst life: The total time during which a catalyst is used from startup to EOR, for a single loading. 30. Catalyst poisons: Substances that partially destroy a catalyst’s ability to accelerate reaction rates. 31. Catalyst skimming or catalyst head removal: Removing or replacing the top layer of catalyst. This task needs to be carried out when the sediment severely clogs the upper catalyst bed, causing the pressure drop across the first bed to increase. 32. Catalytic cracking: A process in which large molecules are broken down into smaller molecules by using heat, pressure, and catalysts. 33. Check valve: A valve that allows flow in only one direction, preventing flow in the opposite direction (also known as a one-way valve or NRV). 34. Chemical reaction: A chemical change in which one or more molecules are transformed into other types of molecules. 35. Metal lining: A thin layer of corrosion-resistant metal that serves a protective purpose, and is attached to a thick base material with poor corrosion resistance. 36. Condenser mesh: A fine steel mesh structure used to facilitate the separation of water from oil. 37. Coke: Carbon-rich deposits that gradually accumulate on the catalyst through unwanted side reactions, reducing the catalyst’s activity. 38. Coke-forming precursor: Molecules in oil that will yield coke in downstream processing equipment (such as coking units and FCC units). 39. Coking: The process in which coke deposits on catalysts or process equipment and pipelines. 40. Tower: A tall, upright container filled with trays or packing, used for distillation or absorption. 41. Compression ratio: For a given compressor stage, it is the ratio of the absolute pressure at the compressor outlet to that at the compressor inlet. 42. Compressor: A machine that draws in gas, compresses it (such as by reducing its volume), and releases it at a higher pressure. 43. Condensation: (1) The liquid is condensed from the vapor leaving the top of the distillation tower ； (2) Condensed steam ； (3) Increase the pressure and use cooling to separate petroleum liquids from rich natural gas. 44. Convection zone: The part where combustion occurs above the furnace chamber; heat is transferred through convection rather than radiation. 45. Conversion rate: The amount of feed that is converted into lighter products within the reactor. 46. Corrosion: A reaction that occurs between metal in containers or pipelines and certain chemicals; it gradually weakens the properties of the metal, eventually forcing its replacement. This is a reaction that people do not want to occur. 47. Cracking: A refining process that breaks down larger, heavier, and more complex hydrocarbon molecules into smaller, lighter molecules. Cracking requires heating and pressure, and catalysts are generally used as well; it effectively increases the production of gasoline. 48. Fraction: A product of a distillation tower. The light fractions, which contain components with low boiling points, flow out from the upper part of the tower. The heavy distillate contains high-boiling-point components and flows out from the lower part of the tower. 49. Cut point: Determines the boiling points at which two adjacent products in a distillation column are separated. 50. Demetallization: A process in which molecules containing metal react with hydrogen to produce metal sulfides, which deposit on the surface of the catalyst. 51. Denitration: A process method in which hydrocarbons and hydrogen are reacted to produce ammonia, thereby removing nitrogen. 52. Desalination tank: A processing device used to remove salt from crude oil. 53. Desulfurization: A process method in which hydrocarbons react with hydrogen to produce hydrogen sulfide, thereby removing sulfur. 54. Foam breaker: A mesh pad placed at the top of the tank, below the steam outlet, used to remove any liquid \"fog\" entrained in the gas. 55. Diesel: Generally refers to fractions with a boiling point between 150°C and 370°C, used in automotive, truck, or marine engines. 56. Diethanolamine (DEA): An amine compound used in absorption towers to remove H2S from gas streams. 57. Outlet: The outlet or high-pressure side of a pump or compressor. 58. Distillation: A process in which rising steam is brought into contact with descending liquid, in order to separate a mixture of various liquids into two or more products with different boiling points. 59. Double isolation valve: A pair of sequential isolation valves, typically used on tees where a short pipeline with a third switching valve is present to reliably separate two systems; the third valve is usually left open to detect leaks in the two main valves. 60. Ventilation: A method of measuring the gauge pressure in the furnace chamber of a heating furnace, usually expressed in terms of water column height. At the burner location in a combustion heating furnace, the ventilation value is typically 13 mm of water column, which indicates that the pressure near the burner inside the furnace is 13 mm lower than atmospheric pressure. The higher the ventilation value, the lower the pressure. 61. Disconnecting short pipe: A short pipeline with flanges at both ends that can be easily removed, used to reliably separate two systems; it can also be considered a detachable short pipe. 62. Effluent: The stream that exits the reactor. 63. Embrittlement: The aging process of reactor metals, especially the welded metal, occurs as a result of prolonged exposure to high temperatures, which causes the metal to degrade slightly and become more brittle. 64. Endothermic reaction: A chemical reaction that absorbs heat. 65. Final boiling point: The last temperature recorded in the experiment, which indicates the boiling point of the vaporized molecules at the time the experiment was stopped. 66. Entrainment: A physical phenomenon in which liquid droplets are transported within a steam stream. 67. Exothermic reaction: A chemical reaction that releases heat, causing the temperature of the reacting substances to rise. 68. Feed gas: a mixture of make-up gas and reaction feed gas, which is mixed with the feed oil, passes through a heat exchanger and a feed heater before entering the reactor. 69. Feed: The substance that is introduced into a process unit or a single processing device. 70. Filtration: Passing a liquid through a porous material to remove suspended solids. 71. Furnace chamber: A part of the combustion heating furnace, where the burners are located; heat is transferred to the furnace tubes through radiation. 72. Fixed-bed operation: A mode of operation in which the catalyst remains in a fixed state within the reactor; the catalyst can be regenerated periodically at appropriate times, as opposed to fluidized-bed operation. 73. Flare: A flare is a method for safely disposing of waste gases through combustion, involving burning at the top of a pipe or chimney (equipped with a burner and igniter) using a raised flare. Similar to burns carried out on or near the ground, ground torches are also installed. 74. Flashing (or flash vaporization): A process in which oil is heated to a high temperature (usually kept in liquid state), then released into a low-pressure environment where it undergoes extensive vaporization (flash vaporization). 75. Flash point: The lowest temperature at which sufficient vapor is released from the oil to be ignited by a spark, producing a small flash. 76. Flux: A quantity per unit time and cross-sectional area; for example, heat flux in Btu/hr·ft2 is an indicator used to determine the acceptable rate of heat transfer in a reboiler. 77. Foaming: The formation of foam or bubbles on the surface of a liquid, as a result of gas being introduced into it or dissolved in it. 78. Scale: The deposition of solids or contaminants on process equipment (such as heat exchangers or reactor beds) reduces the efficiency of the equipment. 79. Fouling rate: To maintain the conversion rate, it is necessary to increase the catalyst temperature over time; the increase in catalyst temperature compensates for the loss of activity due to coking and metal deposition on the catalyst. 80. Fractionation tower: A tower used to separate various petroleum components through a single distillation process; it can have multiple extraction trays placed at different heights along its structure, based on the boiling points of the components. 81. Separation: Sequential separation, with each separation removing a certain proportion of one substance from the mixture. The operations can include precipitation, crystallization, distillation, etc. 82. Fresh catalyst: Any sulfurizing catalyst used in hydrocarbons. There are still catalysts that have not been deactivated by coke or catalyst poisons. 83. Gas oil: Its viscosity and boiling range lie between kerosene and lubricating oils, and it is a liquid petroleum fraction; heavy gas oil boils within the range of lubricating oils, with the distillation endpoint sometimes reaching 593°C (1100°F). 84. Fuel oil: a general term used to refer to fuel used for power generation and heating. 85. Heating furnace: A term used to refer to furnaces that use fuel or gas for heating. 86. Gate valve: A valve designed to be either fully open or fully closed; in the open position, it essentially does not cause any pressure drop. 87. Ball valve: A type of valve designed to regulate the flow rate of fluid, which generates a large pressure drop even when in the open position. 88. Head: A term used to denote pressure; it is the height of a liquid column that exerts an equal pressure on a surface. 89. Manifold: (1) A common pipeline to which two or more pipelines are connected. (2) The “U”-shaped fitting between two nozzles in the furnace coil. 90. Heat exchanger: A device that transfers heat from one fluid stream to another; specifically, it is a device equipped with tubular channels through which heat is transferred from the hotter substance to the relatively colder one. 91. Heavy tail (residual oil) fraction: the molecules with the highest boiling point in the mixture. 92. Overheating: In certain areas of the catalyst bed, poor distribution of the liquid and gaseous feed streams through the bed results in the generation of large amounts of heat. In regions with low flow rates, the oil reacts under more severe conditions, leading to excessive cracking and coking. The catalyst in these overheated areas loses its activity more rapidly than under the designed operating conditions. 93. Hydrocarbons: A class of compounds that contain only carbon and hydrogen atoms; in fact, molecules that contain trace amounts of sulfur, nitrogen, or metals are also considered hydrocarbons. Crude oil and its refined products are both hydrocarbons. 94. Hydrocracking: A process that cracks large molecules into smaller ones, with significant hydrogen consumption, resulting in products that contain more hydrogen than the feedstock. 95. Hydrodenitrogenation (HDN): A process in which oil is heated together with hydrogen to remove nitrogen, thereby reducing the nitrogen content in the oil. 96. Hydrodesulfurization (HDS): A process in which oil is heated together with hydrogen to remove sulfur from crude oil. 97. Hydrogenation: Hydrogenation saturates a compound or splits it into two or more molecules. 98. Hydrogen partial pressure: Defined by CHEVRON Research and Technology Company as the hydrogen partial pressure in the reactor, assuming that all components of the feed oil or product are vaporized. It is generally expressed as the arithmetic mean of the outlet and inlet hydrogen partial pressures. In the operation manual, we denote it as the inlet hydrogen partial pressure. 99. Hydrogen sulfide: A compound formed by the reaction of sulfur and hydrogen in the feed, and it is a highly toxic gas. 100. Hydrogenation process: Hydrogen is added during the process to refine the product. 101. Hydrofining: A process licensed by Chevron Research and Technology Company, in which the feed oil is desulfurized, denitrified, demetalized, saturated, and deeply cracked under harsh temperature and pressure conditions in the presence of a catalyst and excess hydrogen. 102. Inhibitors: Substances that, when added in small quantities to petroleum products or to the equipment used to process them, can prevent or slow down the occurrence of unwanted chemical reactions. In general, the main function of inhibitors is to prevent or slow down oxidation or corrosion. 103. Wash water: Water is injected into the air cooler of the reaction products to wash away the salts present in them. 104. Interface level: In the separator, it refers to the bottom of the oil layer and the top of the water layer. 105. Baffle-type gas-liquid separation tank or vessel: Equipped with baffles; as the gas-liquid mixture passes through, the gases and liquids are separated from each other. When the mixture comes into contact with the baffles, the impact force causes the gases to be released and pass through the top, while the heavier liquids fall to the bottom of the tank. 106. Leakage: High-pressure gas (mostly hydrogen) that is lost from the high-pressure section due to loose connections or poor sealing of the recycle gas compressor. 107. Light hydrocarbons: In a mixture, these are the molecules with the lowest boiling points, usually CH4 to C4H10. 108. Light naphtha: The lightest distilled molecules in the naphtha fraction. 109. Light products: Products that are lubricant distillates with a boiling point lower than the lowest boiling point. 110. Low-sulfur fuel oil (LSFO): A desulfurized fuel oil product produced at the bottom of the product distiller. 111. Hydrogen production: In hydrogen production plants, hydrocarbons are steam-reformed to produce high-purity hydrogen (95–100%). 112. Metal carbonyls: Compounds with high toxicity, formed as a result of the reaction between catalyst metals and carbon monoxide in the recycle gas. Carbonyls are generated at temperatures below 205°C; therefore, after shutting down the operation, it is necessary to reduce the concentration of carbon monoxide in the recycle gas to below 30 PPm before lowering the temperature of the reactor to below 205°C. 113. Residue carbon: An ASTM procedure used to determine the amount of carbonaceous residue remaining after the vaporization and pyrolysis of an oil sample, thereby indicating the relative amount of coke-forming components in the feedstock. 114. Millimeters of mercury: A unit of pressure used to define pressures that are lower than 1 atmosphere; 760 millimeters of mercury indicates a pressure equal to 1 atmosphere. 115. Naphtha: a fraction that boils between 30–170°C and is used to produce gasoline. 116. Cycloalkanes: a class of molecules that contain one or more saturated rings, but no unsaturated bonds. 117. Nickel carbonyl: a metal carbonyl, it is one of the most toxic substances known to affect humans. 118. Non-process equipment: Equipment and support systems that complement the refinery’s processes and are not located within the plant boundary; this generally includes oil tanks, loading/unloading facilities, flares, etc. 119. Alkenes: Compounds with straight-chain or branched structures that contain one or more unsaturated bonds. 120. One-pass: A figurative description of: (1) conditions or operations involving no recycling of any portion of the product, and (2) products resulting from such operations. 121. Controlled: A state in which the controller adjusts the position of the control valve stem to bring the process variable in line with the desired setpoint; the state is uncontrolled when the control valve is fully open or closed. 122. Excessive vaporization: The liquid passes above the tray through the heavy feed vaporization zone. 123. Top product: The product in the distillation process with the lowest boiling point. These products come out at the top of the tower in the form of steam. 124. Overlap: The amount of substance in a fraction whose boiling point exceeds the nominal cut point. 125. Oxidation: A reaction in which a substance combines chemically with oxygen. 126. Paraffin: A straight-chain or branched hydrocarbon with no unsaturated bonds. 127. Partial pressure: Specifies the proportional share of the total vapor pressure of a compound. 128. pH: A scale used to indicate the acidity or alkalinity of a solution. The pH value of natural water is 7.0. For solutions with a pH value less than 7, each decrease in pH value indicates that the acidity becomes twice as strong. For solutions with a pH value greater than 7, for each increase in pH value, the basicity and plasticity increase. For example, a solution with a pH of 9.0 is 100 times more alkaline than one with a pH of 7.0. 129. Phase: In complex systems, solids, liquids, or gases exist as distinctly separate entities with identical properties. 130. Polymerization: Two or more molecules combine to form a single, larger molecule. This new molecule is more complex and has different physical properties. 131. Tilt point: The lowest temperature at which, under certain conditions and without interference, oil can tilt or flow when cooled. 132. Precipitation: (By heating or using chemical reagents) converting a soluble substance into an insoluble one, thereby separating it from the solution. 133. Preheater: A device that preheats materials before feeding them into the main processing equipment. 134. Pressure drop: The decrease in pressure caused by friction. When a liquid or gas flows through pipes, tanks, or other equipment, friction is generated. 135. Circulating reflux: A stream that is drawn from the side of the distillation column, cooled below its bubble point, and then returned to the upper trays. This helps to partially condense the vapor flowing upward, thereby removing heat from the tower. 136. Purging steam: Steam injected into the furnace to prevent the possibility of uncontrolled combustion. 137. Spontaneous combustibles: A substance (e.g., iron sulfide) that ignites immediately when exposed to air. 138. Quenching: To halt or suppress a reaction, hot materials are suddenly cooled. This method is frequently used in thermal cracking operations; typically, cold oil is injected into the discharge line. 139. Quench gas: A portion of the recycle gas injected between reactors to control the temperature of the reactants. 140. Radiation zone: Fuel oil is burned inside the furnace, and here, most of the heat is transferred through direct radiation rather than convection. 141. Lan residue: An ASTM procedure for determining the amount of carbonaceous residue remaining after the vaporization and pyrolysis of an oil sample, used to indicate the relative amount of coke-forming components in the feedstock. 142. Reactor feed gas: a mixture of make-up gas and recycle gas, which is mixed with the feed oil, passes through the feed heat exchanger and the feed heater, and then is sent to the first reactor. 143. Recycle feed: A portion of the fractionator product that is returned to the reactor; during startup, and sometimes in emergency situations, this product is used as recycle feed. 144. Circulating gas: The exhaust gas from the circulation compressor, which provides part of the reactor feed gas and all of the quench gas. 145. Atmospheric residue: Crude oil whose API gravity decreases after the lighter, low-boiling-point components have been distilled off. 146. Reflux: The condensed portion of the vapor at the top of the tower is sent back to the upper tray of the tower. 147. Regeneration: (1) A process of restoring a substance to its original capacity or properties; (2) In catalytic processes, burning off carbon deposits under carefully controlled conditions of temperature and oxygen content in the regeneration gas to restore the catalyst’s activity. 148. Reid Vapor Pressure (RVP): The vapor pressure at 100°F, with the volume of air being 4 times that of the liquid, indicating the tendency of automotive gasoline to form vapor clouds, as well as the risks of explosion and vaporization, per ASTM D323. It is usually expressed in pounds per square inch 2 (gauge pressure) (Psig). 149. Venting system: A system composed of valves, tanks, and flares, used to prevent overpressure in refineries. 150. Relief valve: The valve opens when the pressure in the pipeline or equipment exceeds the maximum safe value. Therefore, the valve releases the high-pressure condition (to the flare system). 151. Residence time (or retention time): Used to characterize the properties of reactors and vessels, representing the amount of time that the average flow element spends within the reactor. 152. Residue: Heavy oil or bottom product, which is the residue left after gasoline and other components with relatively low boiling points have been distilled, or it is the remaining part of crude oil after all lighter components have been distilled off, leaving only the heaviest components. 153. Operation chart: A graph representing CAT as a coefficient for the number of working days. 154. Saturated: Refers to hydrocarbons that contain no double or triple bonds, and have the maximum possible amount of hydrogen; thus, the molecule is \"saturated\" with hydrogen. 155. Side-stream fraction: The liquid product extracted from the side of the distillation tower. 156. Separator: A pressure vessel used to divide a fluid stream into gas and liquid components. 157. Severity level: The intensity of the operating conditions of a process unit. 158. Surface temperature: The temperature outside the wall of a combustion heating furnace or a reactor. 159, Sodium polysulfide: a compound (Na2Sx). It is injected into the product cooler to eliminate cyanide-induced corrosion and harden iron sulfide scaling, thereby limiting corrosion. 160. Dissolution loss: Hydrogen that flows out from the high-pressure area as gas dissolves into the liquid downstream flow. 161. Sulfur-containing: Specifically used to denote streams containing H2S or sulfur, or equipment for handling such streams. 162. Spent catalyst: A catalyst that has lost its activity and needs to be removed from the reactor. 163. Backflow: The flow of fluid that \"backs up\" from the compressor outlet to the compressor inlet, ensuring that the compressor operates at a flow rate above the minimum level. 164. Stability: A process that removes light hydrocarbons from the product to meet storage requirements. 165. Straight-run oil: A product obtained from crude oil without undergoing any cracking or other chemical treatments. 166. Distillation column: A small distillation tower used to remove light fractions from a distillate by reboiling or stripping. 167. Inlet: the inlet or low-pressure side of a pump or compressor. 168. Sulfidation: A process in which highly active metals deposited on a catalyst are converted from oxides to metal sulfides, thereby facilitating a smoother and more stable hydrogenation reaction. 169、 Sulfur: An element present in some oil molecules; most of the sulfur in the HC/RDS feed is converted to H2S in the reactor. 170. Surge: An extremely unstable operating condition of a centrifugal compressor due to low flow rate. 171. Buffer tank: A container or buffer tank used to pump liquids through pipelines, thereby stabilizing fluctuations in the fluid flow. 172. Tailing: The difference between the final boiling point of a fraction and its nominal final boiling point, or the difference between its initial boiling point and its nominal initial boiling point. 173. Tank: A cylindrical or spherical container used for storing, measuring, or transporting liquids. 174. Temperature offset: High temperatures lead to high reaction rates, and conversely, high reaction rates result in high reaction temperatures, and so on. This situation occurs only if the reaction is exothermic; rapid cooling is a method used to control the reaction and prevent temperature deviations. 175. Thermal shock: Structural damage in metal equipment such as reactors, caused by heating or cooling the equipment system too rapidly. 176. Temperature out of control: A rapid increase in temperature deviation. 177. Processing volume: The amount of feed added to the process equipment within a specified time period. 178. True Boiling Point Curve (TBP curve): It is a characteristic distillation curve of oils, which relates the volume fraction of vaporized components to their boiling point at atmospheric pressure. The curve is generally represented by a series of temperatures (tn), where tn refers to the distillation temperature at atmospheric pressure when nLV% has been distilled away. 179. Normal shutdown for maintenance: The necessary time to clean and repair refining equipment after normal operation. 180. Unsaturated compounds: Hydrocarbons that contain one or more multiple carbon-carbon bonds. 181. Unstable naphtha: Naphtha with a high content of butane and other light gases; it can be stored safely only after the light fractions are removed to stabilize it. 182. Vapor pressure: The pressure exerted by a liquid in a closed system. Vapor pressure increases as the temperature rises; when the temperature rises to a certain level such that the vapor pressure equals the pressure of the system, this temperature is known as the boiling point, at which the liquid begins to boil. 183. Vaporization: The transformation of a liquid into vapor, such as turning water into steam. 184. Yield: The percentage of the specified product produced in the reactor relative to the fresh feed.