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This post was last posted by LQ198619 on 2017-5-23 08:15 Edit Chapter 2 Basic knowledge of catalytic cracking unit 1. Overview of the unit The catalytic cracking process refers to the process in which raw oil (normal pressure residual oil, vacuum or hydrogenated wax oil) undergoes a catalytic cracking reaction under the action of a high-temperature catalyst to generate cracked oil and gas, and the cracked oil and gas are separated into dry gas, liquefied gas, stabilized gasoline, diesel, recycled oil, and oil slurry through distillation, absorption, desorption and other means. The main reactions of catalytic cracking include decomposition, isomerization, hydrogen transfer, aromatization, condensation, coke generation, etc. Compared with thermal cracking, it has a high yield of light oil, high gasoline octane number, good diesel stability, and by-products liquefied gas rich in olefins. 2. Device Types There are many types of fluidized bed catalytic cracking devices, which can be divided into two categories according to the relative positions of the reactor (or settler) and the regenerator.: ①Side-by-side reactor and regenerator arranged separately ； ②The reactor and regenerator are stacked coaxially. The parallel type is divided into two types: the same-height parallel type and the high-low parallel type due to the different heights of the reactor (or settler) and the regenerator. l The main features of the same-height parallel type are: ① The catalyst is transported in dense phase by the U-shaped tube; ② The catalyst circulation between the reactor and the regenerator is mainly adjusted by changing the catalyst density at both ends of the U-shaped tube ； ③The catalyst transported from the reactor to the regenerator does not pass through the distribution plate of the regenerator, but is directly sent to the fluidized bed on the distribution plate through the dense phase riser, which can reduce the abrasion of the distribution plate. l The characteristic of high-low parallel type is short reaction time, which reduces secondary reactions. ； The catalyst circulation is controlled by a slide valve, which is more flexible. l The characteristics of the coaxial device are:: ①The catalyst transportation between the reactor and the regenerator is controlled by a plug valve; ② A vertical riser pipe and a 90° abrasion-resistant elbow are used; ③ The raw materials are sprayed into the riser pipe with multiple nozzles. 3. Catalytic unit process (the high-low parallel riser catalytic cracking unit in the figure below is an example) l Reaction - The regenerated part of the fresh feed oil is mixed with the recycled oil slurry after heat exchange, and is heated to 180-320°C by the heating furnace and then reaches the nozzle at the lower part of the catalytic cracking riser reactor. The feed oil is atomized by steam and sprayed into the riser, where it contacts the high-temperature catalyst (600-750°C) from the regenerator, and then vaporizes and reacts. The residence time of oil and gas in the riser is very short, usually only a few seconds. The reaction product passes through the cyclone separator to separate the entrained catalyst and then leaves the settler to go to the fractionation tower. The catalyst with accumulated coke (called spent catalyst) falls from the settler into the stripping section below. The stripping section is equipped with multi-layered herringbone baffles and superheated steam is introduced at the bottom. The oil vapor adsorbed on the waiting catalyst and the oil vapor in the space between the particles are replaced by the water vapor and returned to the upper part. The stripped catalyst enters the regenerator through the inclined tube. The main function of the regenerator is to burn off the carbon deposits generated by the reaction on the catalyst to restore the activity of the catalyst. The air for regeneration is supplied by the main fan, and the air enters the fluidized bed through the auxiliary combustion chamber and distribution pipe below the regenerator. For thermal balance devices, the auxiliary combustion chamber is only used when starting to heat up, and does not burn fuel oil during normal operation. The regenerated catalyst (called regenerated catalyst) falls into the flood flow pipe and is sent back to the reactor through the regeneration inclined pipe for recycling. After the regeneration flue gas separates the entrained catalyst through the cyclone separator, it is discharged into the atmosphere through the double-action slide valve. When processing raw materials with a high coke production rate, such as raw materials containing residual oil, due to the high coke yield, the regenerator has excess heat, and a heat extraction facility must be installed in the regenerator to remove the excess heat. The temperature of the regenerated flue gas is very high. Many catalytic cracking units are equipped with flue gas energy recovery systems, which use the heat energy and pressure energy of the flue gas (when an energy recovery system is installed, the operating pressure of the regenerator should be higher) to do work, drive the main fan to save electric energy, and even output residual power to the outside. For some incomplete regeneration devices, the regeneration flue gas contains 5%-10% (volume fraction) CO, and a CO boiler can be set up to completely burn the CO to recover energy. During the production process, the catalyst will be lost and deactivated. In order to maintain the storage capacity and activity of the catalyst in the system, it is necessary to replenish or replace fresh catalyst into the system regularly or frequently. For this purpose, at least two catalyst storage tanks should be installed in the device. The dilute phase transportation method is used when loading and unloading the catalyst, and the transportation medium is compressed air. In the automatic control system of the fluidized catalytic cracking unit, in addition to the automatic control systems of temperature, pressure, flow rate, etc. similar to other refining units, there is also a complete set of automatic control systems to maintain the normal circulation of the catalyst and an automatic protection system when fluidization abnormality occurs. This system generally includes multiple self-protection systems, such as the reactor feed low-flow self-protection system, the main fan outlet low-flow self-protection system, the two-reactor differential pressure self-protection system, etc. Taking the reactor feed low-flow self-protection system as an example, when the feed amount is lower than a certain lower limit, the density cannot be low enough in the riser, the normal pressure balance between the two reactors is destroyed, the catalyst cannot circulate according to the prescribed route, and the catalyst backflow will occur and a large amount of oil and gas will be taken into the regenerator, causing accidents. At this time, the feed low flow self-protection system automatically performs the following actions: cutting off the reactor feed and returning the feed to the raw oil tank (or intermediate tank), and introducing accident steam into the riser to maintain fluidization and circulation of the catalyst. l Fractionation system A typical catalytic cracking fractionation system is shown in the figure above. The reaction product (oil and gas) from the reactor enters the fractionation tower from the bottom. After passing through the desuperheating section at the bottom, it is divided into several intermediate products in the fractionation section: rich gas and gasoline at the top of the tower, and light diesel oil, heavy diesel oil and recycled oil in the side line. The bottom product is oil slurry. After the light diesel oil and heavy diesel oil are stripped respectively, they are heat exchanged and cooled before leaving the device. The fractionation tower of the catalytic cracking unit has several characteristics: ① The feed is superheated oil and gas with catalyst dust. Therefore, the bottom of the fractionation tower is equipped with a desuperheating section. The cooled oil slurry is used to cool the oil and gas to a saturated state and wash off the entrained dust to facilitate fractionation and avoid clogging the tray. ②The residual heat of the whole tower is large and the product separation accuracy requirements are relatively easy to meet. Therefore, there are generally multiple circulation refluxes: tower top circulation reflux, 1-2 mid-section circulation reflux and oil slurry circulation. ③The main reason for using circulating reflux instead of cold reflux at the top of the tower is that the oil and gas entering the fractionating tower contain a considerable amount of inert gas and non-condensable gas, which will affect the effect of the condensing cooler at the top of the tower. Using circulating reflux instead of cold reflux can reduce the pressure drop from the top of the fractionating tower to the entry of the air compressor, thereby increasing the inlet pressure of the air compressor and reducing the power consumption of the air compressor. l Stabilization system absorption-stabilization system mainly consists of absorption tower, re-absorption tower, desorption tower and stabilization tower. The rich gas coming out of the oil and gas separator at the top of the fractionation tower contains gasoline components, while the crude gasoline contains dissolved C3 and C4 components. The function of the absorption stabilization system is to use absorption and distillation methods to separate rich gas and crude gasoline into dry gas (≤C2) liquefied gas (C3, C4) and stable gasoline with qualified vapor pressure. The liquefied gas is reused for rectification to separate propylene and butylene through a gas fractionation device for chemical utilization. The fractionation system and absorption-determination system of the catalytic cracking unit generally do not differ greatly in each catalytic cracking unit. 1- Absorption tower ； 2-Resolving Tower ； 3-Reabsorption tower ； 4-Stabilization tower ； 5-Balance tank ； 6-Condenser or cooler ； 7-Heat exchanger ； 8-Reboiler ； 9-reflux tank ； l Product refining and desulfurization system. Since catalytic gasoline and catalytic diesel are now refined in a hydrogenation unit and are no longer directly desulfurized by alkali washing, the desulfurization of gasoline and diesel is not introduced here. The focus is on the desulfurization of dry gas and liquefied gas. Dry gas and liquefied petroleum gas desulfurization part: The liquefied petroleum gas and dry gas produced by the catalytic cracking unit contain harmful impurities such as hydrogen sulfide and sulfur dioxide, which affect the use of the products. Therefore, they must be desulfurized before use. The commonly used method for desulfurizing hydrogen is to use the alkyl alcohol amine absorption method, which uses a weak organic base (amine liquid) as the absorbent to conduct countercurrent contact in the liquefied petroleum gas desulfurization tower and the dry gas desulfurization tower. The hydrogen sulfide in the liquefied petroleum gas and dry gas is absorbed by the amine liquid, and the gas is purified. The absorption of hydrogen sulfide by amine liquid is a reversible process. The rich amine liquid that has absorbed hydrogen sulfide decomposes when heated under low pressure, and releases hydrogen sulfide. Using this reversible chemical reaction, the rich amine liquid is regenerated through the solvent regeneration tower and becomes a lean liquid, and at the same time, acidic gas containing hydrogen sulfide is generated. The lean amine liquid is recycled as an absorbent, and the acid gas is sent to downstream equipment for treatment. Liquefied petroleum gas sweetening part: Liquefied petroleum gas demercaptanization uses a catalyst alkali solution to extract the mercaptans in the liquefied petroleum gas, and after oxidation and regeneration, the disulfides are separated and discharged from the device, and the catalyst alkali solution is recycled. 1. MDEA desulfurizes hydrogen: The main desulfurization methods for dry gas and liquefied gas include: Dry desulfurization: Refinery gas is passed through a bed of fixed adsorbent to remove hydrogen sulfide. The solid adsorbents used include metal oxides such as zinc, iron, manganese, and activated carbon. Dry desulfurization is basically an intermittent operation, with heavy equipment and high investment. Wet desulfurization is: The refinery gas is washed with a liquid absorbent to remove hydrogen sulfide in the refinery gas. The wet desulfurization method uses monoethanolamine (MEA), diethanolamine (DEA), diisopropanolamine (DIPA), methyldiethanolamine (MDEA), etc. as desulfurizers. Wet desulfurization is a continuous operation with large processing capacity. Principle of MDEA dehydrogenation sulfide H2S is weakly acidic and MDEA is weakly alkaline. The reaction generates water-soluble salts. Since the reaction is reversible, MDEA can be regenerated and recycled. The alkalinity of N-methyldiethanolamine decreases as the temperature increases. At low temperatures, the weakly alkaline N-methyldiethanolamine can combine with H2S to form an amine salt. At high temperatures, the amine salt can decompose into H2S and methyldiethanolamine. Hydrogen sulfide is absorbed (absorbed) at lower temperatures (20°C to 40°C), and desorbed at higher temperatures (>105°C). Its chemical reaction equation is: 2R2NH+H2S→(R2NH2)2S Ammonium sulfide salt (R2NH2)2S +H2S→2R2NH2HS Acid amine sulfide salt 2R2NH+CO2+H2O→(R2NH2)2CO3 Ammonium carbonate salt (R2NH2)2CO3+CO2+H2O→2R2NH2HCO3 If there are multiple sets of desulfurization units in an acid ammonium carbonate refinery, a centralized regeneration scheme can be adopted. Each unit sends the rich amine liquid to the regeneration unit for centralized regeneration, and then the acid gas is sent to the nearby sulfur production unit. The sulfur recovery unit will be explained in detail later. 2. Basic principle of pre-alkali washing to remove hydrogen sulfide. The liquid hydrocarbons after dehydrogenation with MDEA solution still contain part of hydrogen sulfide. Use 4~20% NaOH solution for neutralization to further remove hydrogen sulfide. The chemical reaction formula is:: 2NaOH+H2S ─→Na2S+H2O This reaction is an acid-base neutralization reaction between a strong base and a weak acid. The soluble salt and water generated are irreversible reactions. 3. Principle of Desulfanization: The sulfur contained in the liquid hydrocarbons after two-stage dehydrogenation mainly remains in the form of mercaptans. The mercaptans in the liquid hydrocarbons are extracted with an alkali solution containing a catalyst (polytitanocyanine cobalt or sulfonated titanium cobalt). The chemical equation is:: The extracted alkali solution contains sodium mercaptan salt and enters the oxidation tower for oxidation regeneration. Oxygen molecules form an unstable activation complex with the catalyst (polycobalt phthalocyanine or sulfonated cobalt titanium cyanine), and the activation complex hydrolyzes with sodium mercaptide to form a stable disulfide. The lye can thus be regenerated and recycled. The chemical equation of its transformation is:: 5. Main positions of the catalytic unit: l Reaction-Regeneration Post: The cracking of raw oil and catalyst regeneration are completed in this part, and the product yield has been determined at reaction station nine. l Fractionation station: The task is to change the mixed oil and gas from the settler from a superheated state to a saturated state, wash the catalyst carried by the reaction oil and gas, and divide it into rich gas, naphtha, light diesel, heavy diesel, recycled oil, and slurry according to the boiling point range. l Absorb stable positions: The task is to further separate crude gasoline and compressed rich gas into dry gas, liquefied gas and stabilized gasoline, ensure the pressure balance of the fuel gas system, keep the high and low pressure gas flare system open, and the flare can burn normally. l Refined desulfurization station: The task is to carry out alkali washing and desulfurization of gasoline, diesel and liquefied gas products to ensure that the product quality is qualified. With the development of the technology, catalytic gasoline and diesel are no longer directly alkali washed, but enter the hydrogenation unit for desulfurization. l Crew post: The main fan's task is to provide air for the catalyst burnt regeneration of the reaction system. The gas compressor compresses the rich gas at the top of the fractionation tower and sends it to the stable system. The supercharger supercharges a part of the main air to provide power air for fluidization of the external heat exchanger and the regeneration sleeve. 6. Main equipment of each system of the catalytic device: reaction regeneration system l pre-lift section: The catalyst can form a "plunger flow" in the middle and lower part of the riser, with good speed and density, so as to facilitate full contact with the raw materials. l Feeding nozzle: At a suitable preheating temperature of the raw material oil, the raw material oil is atomized into small droplets through the action of the raw material atomizing steam, so as to fully contact the catalyst. l Riser reactor: It is a place where raw oil comes into contact with high-temperature catalyst for catalytic cracking. The structural characteristics of the riser reactor enable it to better control the reaction time, avoid backmixing and reduce secondary reactions. The technology of rapid separation of coarse rotation and rapid oil and gas export is an oil and gas-catalyst separation device at the outlet of the riser, which is used to reduce the contact time of oil, gas and catalyst, avoid secondary reactions, and reduce excessive cracking and thermal cracking. l Stripping section: The catalyst separated by rough rotation falls to the stripping section and contacts the stripping steam in reverse direction, displacing the oil and gas carried between the catalyst particles and the catalyst itself, thereby achieving the purpose of increasing the yield of light oil and reducing the yield of dry gas and coke. l Regenerator: The main function is to burn off the carbon deposits on the surface of the waiting catalyst, restore the activity of the catalyst, and provide the heat required for the cracking reaction of the raw materials. l Auxiliary combustion chamber: Using gas (diesel) as fuel, the main air enters into primary and secondary air. The primary air enters the combustion chamber to provide the oxygen required for combustion, and the secondary air passes through the jacket to cool the furnace. After the primary and secondary air are mixed, the furnace outlet temperature is controlled. The auxiliary combustion chamber is only used for the regenerator to heat up when it is started, and is only used as a channel for the main air during normal production. l Main air distribution duct: The main purpose is to enable the main wind to be evenly distributed along the entire bed cross-section, thereby creating a good fluidization and scorching condition. l Cyclone separator: When the catalyst enters the dilute phase from the second dense phase, it carries part of the catalyst. The flue gas containing the catalyst enters the cyclone separator in a tangential direction and forms a rotating external vortex between the riser and the shell. From top to bottom to the bottom of the cone, the catalyst is suspended in the flue gas flow. Under the action of centrifugal force, one side of the catalyst is thrown toward the wall of the device, while the other side rotates downward with the flue gas flow. Finally, it falls into the ash hopper and returns to the dense phase of the regenerator through the material leg. After purification, the flue gas forms an ascending internal vortex and is discharged through the riser pipe. l External heater: The catalyst is led from the second dense phase bed, enters the top of the external heat collector through the inclined tube, passes through the external heat extraction shell under the action of fluidized wind, exchanges heat with the deoxygenated water in the tube side, and then returns to the bottom of the coking tank to achieve the purpose of removing excess heat from the regeneration system. It is the main means to adjust the temperature of the first dense phase and the second dense phase. l Waiting for valve: Its function is to control the storage capacity of the stripping section. l Double-acting slide valve: Its function is to control the regenerator pressure. l Regeneration slide valve: Its function is to control the circulation amount of the regenerated catalyst to adjust the reaction temperature. l Waste heat boiler: The flue gas outlet of the regenerator (around 680°C) enters the shell side of the waste heat boiler, exchanges heat with the medium in the superheat section, evaporation section, and economizer preheating section. After being cooled to below 180°C, it enters the chimney for venting. The use of waste heat boilers can make full use of flue gas heat energy, thereby reducing device energy consumption. Fractionation system l Fractionation tower: Using the principle of distillation, under the condition of providing reflux, the two phases of vapor and liquid inside the fractionation tower are in reverse contact on the tray multiple times to perform mass and heat transfer between phases. Through the process of multiple partial vaporization and multiple partial condensation, the light components gather at the top of the tower and the heavy components gather at the bottom of the tower. Each component in the mixture can be effectively separated. l Diesel stripper: In the stripping tower, the stripping steam enters from the lower part and contacts the diesel in reverse direction, stripping out the light components in the diesel to control the flash point of the diesel. l Oil slurry filter: After the oil slurry passes through the filter element in the oil slurry filter to remove the carried catalyst, it is cooled by the oil slurry cooling water tank and sent to the tank area as combustion oil. Rinse the filter element with recycled oil, and send the backwash oil to the reaction feed nozzle and accident bypass line. Set up two filter tanks for intermittent operation. Stabilization system l stabilization tower: It uses absorption, desorption, and distillation methods to separate compressed rich gas and crude gasoline into dry gas, liquid hydrocarbons, and stable gasoline of qualified quality. Unit system l Main fan: The bottom of the regenerator of the reaction regeneration system must be supplied with air, and the fan that compresses and delivers the air is the main fan. The main fan is very important in the catalytic device. It is the heart equipment of the catalytic device and must run continuously. If the main fan stops running, the catalytic device will stop production. From a process perspective, the main function of the main fan is: A: Provide the oxygen needed for charring. B: Ensure that the catalyst in the regenerator and coking tank is in a fluidized state. l Air compressor: The pneumatic compressor unit is mainly used to compress the rich gas (pressure 0.06MPa, temperature 40°C) from the oil and gas separator at the top of the fractionation tower. After being compressed by the pneumatic compressor (pressure 0.4MPa, temperature 100°C), it enters the intermediate cooler for cooling and then enters the intermediate liquid separation tank for separation. The gas phase enters the second stage, and after continuing to increase the pressure (pressure 1.25Mpa, temperature 107°C), it is sent to stability through the outlet of the second stage. This unit is responsible for controlling the reaction pressure while compressing the gas. Normally, the reaction pressure is used to adjust the unit speed to control the reaction pressure. In addition, there are two flare valves, one large and one small, at the compressor inlet to assist in adjusting the reaction pressure. There is an anti-fly valve at the compressor outlet to prevent the compressor from flying. l Supercharger: After pressurizing part of the main air, it provides lifting and fluidizing air for the external heat collector and fluidizing air for the sleeve to be regenerated. 7. Main adjustment methods and influencing factors of catalytic device 1. Control of reaction temperature and influencing factors: The reaction temperature is an important process parameter for the reaction station. A suitable reaction temperature can ensure that the device maximizes the yield or the target product. During normal production, the reaction temperature is controlled by controlling the catalyst circulation amount by controlling the opening of the regeneration slide valve. When the inlet of the lifting medium remains constant, the higher the reaction temperature, the greater the reaction depth. The yields of gasoline, liquefied gas, dry gas, and coke increase while the yield of diesel oil decreases. There are many factors that influence the reaction temperature, such as: l Changes in the opening of the single-acting slide valve l Changes in the total feed amount of the reaction l Changes in the feed preheating temperature l Changes in the regeneration bed temperature l Water in the raw material l The amount of pre-lift steam and feed atomization steam is too large or contains water l Enable small-scale feeding l Choking or coking in the riser l Terminator with water or dry gas with liquid l Termination dosage and temperature changes l Changes in the pre-lift dry gas volume l Large fluctuations in differential pressure between the two devices l Failure of instrument and single-acting slide valve 2. Control of pressure of two devices and influencing factors. The pressure between the two devices refers to the settler pressure and the regenerator pressure. During normal production, the regenerator pressure is 40KPa higher than the settler pressure. The differential pressure between the two devices is an important driving force for the catalyst cycle. If the differential pressure between the two devices is reversed, the catalyst will flow backward, and the reaction oil and gas will escape into the regenerator, resulting in equipment overheating or even a vicious accident. During normal production, the settler pressure is controlled by the speed of the air compressor and the opening of the anti-surge valve. The main influencing factors are:: Changes in the medium entering the lift tube, changes in liquid level or cold reflux in the fractionating tower, fluctuations in the speed of the air compressor, water in the raw oil, etc. The regenerator pressure is controlled by the opening of the double-action slide valve. The influencing factors include changes in the medium entering the regenerator, oil on the catalyst, external heat exchanger failure, etc. 3. Stripping section storage volume control and influencing factors. The storage capacity in the stripping section refers to the amount of catalyst present in the equipment in the stripping section. Controlling the storage capacity in the stripping section is to better replace the oil and gas in the to-be-generated catalyst and prevent the main wind from escaping into the settler. The storage capacity index of the stripping section is controlled by the opening of the waiting plug valve. The storage capacity of the stripping section is compressed, which will cause the main air to escape into the settler, leading to a serious accident. 4. Respond to workplace accident handling principles. l Under no circumstances should the catalyst reservoirs in the reaction-regeneration system be emptied of each other. l The reaction-regeneration system must be fed with fluidized medium to prevent collapse or dead bed. l Once the main air is interrupted, the feed must be cut off immediately and the injection of combustion oil must be stopped. l When feeding, the outlet temperature of the riser cannot be lower than 480°C. If it cannot be lifted for a while, the feeding should be cut off. l When the main fan is stopped and the feed is cut off, the temperature of the two devices cannot be lower than 400°C. If it is lower than this temperature, the catalyst should be unloaded. l When the reaction-regeneration system has catalyst circulation, the oil slurry circulation must be maintained. If the oil slurry circulation is interrupted for a long time, the regenerator should be changed to single-unit fluidization or the catalyst should be discharged according to the situation. l In the event of a serious overtemperature reaction regeneration system fire accident in the regenerator, the feed should be cut off. l Even if the feed is cut off and the main fan is stopped in the reverse-recycle system, if there is still catalyst in the system, the reverse blowing air and loose air (steam) must be kept uninterrupted. a) Fractionation tower bottom liquid level control and impact. The liquid level at the bottom of the fractionation tower reflects changes in the material balance of the entire tower, and the material balance depends on pressure, temperature and flow. At the same time, the liquid level at the bottom of the tower is a specific manifestation of the reaction depth. Too low a liquid level can easily cause the oil slurry pump to be evacuated, interrupt the oil slurry circulation and return, and cause tower flushing, overtemperature and overpressure accidents. ； The high liquid level will cause the oil slurry to stay at the bottom of the tower for a long time, causing coking at the bottom of the tower. At the same time, it may flood the overheated oil and gas feed port of the reaction, causing pressure in the reaction system and causing serious consequences. Its influencing factors include: l Responds to changes in depth, as the depth increases and the liquid level decreases. l Changes in processing capacity, the liquid level rises as the processing capacity increases. l Changes in the properties of raw materials, the raw materials become lighter and the liquid level drops. l The temperature of the oil slurry returning to the tower changes, the temperature decreases and the liquid level increases. l Changes in the oil slurry refining amount and external rejection amount, the refining amount and external rejection amount increase, and the liquid level decreases. l Changes in the pressure of the fractionating tower, the pressure increases, and the liquid level increases. l Changes in the temperature at the bottom of the fractionation tower, the temperature increases and the liquid level decreases. l The pump is faulty and the instrument is malfunctioning. l The amount of oil slurry returning to the tower changes up and down. l Circulation volume and heat intake changes in each section of the fractionation tower, or pump evacuation. 6. Control and influencing factors of solid content of oil slurry. During normal production, the solid content of the oil slurry should be controlled to ≯ 8.0 g/l. If the solid content in the oil slurry is high, it will wear out the equipment or block the pipeline and cause production accidents. Therefore, the solid content in the oil slurry should be controlled during normal production. The solid content in the oil slurry mainly depends on the separation effect of the cyclone separator of the reaction settler. Its influencing factors include: l The pressure of the settler fluctuates greatly, causing the oil and gas to carry too much catalyst. l The efficiency of the internal rotary separator in the settler becomes poor or malfunctions. l The catalyst strength is not high or there is a lot of dust. l The oil slurry has not been thrown out for a long time or the refining amount is too small. l The liquid level at the bottom of the tower is high and the residence time is too long. l The temperature at the bottom of the tower is high and coking is serious. 7. Control of crude gasoline dry point. During normal production, the dry point of crude gasoline is mainly controlled by the temperature at the top of the fractionation tower. The higher the top temperature, the higher the dry point of crude gasoline. The main influencing factors are:: Changes in temperature and pressure at the top of the fractionating tower, changes in the reflux volume in the middle section and the distillation temperature of light diesel oil, changes in the top circulation volume and return tower temperature, changes in reaction depth and processing capacity, etc. 8. Diesel dry point control and influencing factors. The dry point of diesel is mainly controlled by the temperature in the middle section of the fractionating tower and the opening of the lower distillation outlet valve of diesel. The main influencing factors are:: Changes in reaction depth, changes in feed oil properties, changes in mid-stage reflux volume and return tower temperature, changes in fractionation tower pressure, etc. 9. Control of the content of components above C3 in dry gas. l The amount of rich gas is large, the absorbed dose is small, and the absorption effect is not good. l E2301 and E2302 have poor cooling effect, rich gas enters the tower, crude gasoline enters the tower or stable gasoline enters the tower at a high temperature. l The amount of the middle section is small or the cooling effect of E2303 and E2304 is poor, and the temperature in the tower is high. l The pressure of the absorption tower is low or fluctuates greatly. l The high temperature of the desorption tower causes a large amount of C3 and C4 to be desorbed, increasing the absorption load. l The temperature of the reabsorption tower is high or the absorption dose is small. l T2303 pressure is low or fluctuates greatly. l Crush the absorption tower. l The liquid level at the bottom of the reabsorption tower is too high. 10. Control of the content of components above C5 in liquefied gas. l The stable tower top reflux volume is small and the tower top temperature is high. l The pressure of the stabilizing tower is low. l The reboiler at the bottom of the stable tower returns to a high temperature. l The gas thermal bypass adjustment range is large. The feed temperature of the stabilizing tower is high and the feed port is upward.