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Principles for dealing with accidents in the reaction system and general procedures for handling accidents. Principles for accident handling: To prevent serious accidents, this facility is equipped with an automatic protection system; during normal operation, it is required that this protection system remain in good standby condition at all times. Operators must have a thorough understanding of the self-protection system, master it skillfully, and use it accurately. In the event of a major accident, the following principles must be observed: 1. The catalyst must not flow backward, and the catalyst inventories in both reactors must not be depleted, to prevent the mixing of air and oil vapor, which could lead to an explosion. When the pressure difference between the two reactors exceeds 35 kPa (or falls below 15 kPa), the slide valve pressure drop safeguard and feed cut-off safeguard should be activated to isolate both reactors from the feed. 2. When feeding into the reactor, the reaction temperature should be maintained above 485°C. If the reaction temperature is low and cannot be kept up even by measures such as reducing the feed rate, the feed supply should be automatically cut off. 3. When shutting off feed for self-protection, it is necessary to promptly close all feed manual valves on the manifold, open wider the bypass line of the preheat line orifice plate; when feed needs to be cut off for an extended period, the residue oil removal system must also be activated. When cutting off the feed, a fluidizing medium must be introduced to prevent a dead bed from forming. If the emergency steam supplied to the safety valve is not sufficient to maintain fluidization, the bypass line can be opened appropriately. 4. In the event of a main air supply interruption, the main air self-protection system and the feed self-protection system must be activated promptly to cut off the feed. When dealing with a main air supply interruption, action must be taken decisively to prevent the hot catalyst from flowing back into the main air pipeline system. When there is no main wind, combustion oil must not be injected into the regenerator. 5. Sufficient fluidizing medium must be available in the lift tube reactor, settler, regenerator, external heat exchanger, etc. In the event of an accident, self-protection measures should be activated promptly as appropriate, and accident steam should be introduced to maintain fluidization and prevent dead bed formation. After cutting off the feed, both reactors should be maintained at a temperature of no less than 400°C. If the main air flow is still being supplied, the regeneration temperature should be kept above 650°C to facilitate resumption of feeding. When the regeneration temperature drops below 380°C, the catalyst in the reaction system must be promptly removed. 6. When a catalyst is present in the reactor, it is necessary to maintain the circulation of slurry at the bottom of the fractionator; if the circulation cannot be maintained for an extended period, the operation must be halted and the material unloaded. 7. As long as there is catalyst present in the system and the temperature remains at or above 250°C, it is strictly prohibited to shut down the fluidization media and all purge points, so as to prevent blockage of the reverse purge points. When the temperature falls below 250°C, air should be used for fluidization or purging at all fluidization/purge points; for those points where this cannot be done, steam purging must be discontinued to prevent the catalyst from “clumping together”. 8. The flare butterfly valves must remain flexible and functional; the flare pipeline network must be kept unobstructed. 9. After an accident occurs, the team leader and operators must remain calm, conduct a thorough analysis, make correct judgments, take timely measures, and act decisively. They must avoid panicking at all costs. Afterwards, the team leader should organize a discussion among all team members to summarize the experiences and lessons learned. Principles for shutting off feed: 1. Severe carbon buildup. 2. Main air flow interruption. 3. Severe conditions of overheating and overpressure. 4. The catalyst circulation in both reactors is interrupted, and the catalyst ceases to flow. 5. Stripping steam interruption. 6. The pressure drop across the regenerated single-acting slide valve and the unregenerated plug valve is out of limit. 7. Excessive catalyst loss makes it impossible to maintain production. 8. Severe power outages, water supply disruptions, air supply interruptions, or steam supply disruptions that cannot be resolved promptly. 9. In the event of a failure in critical equipment that prevents production from continuing, or in the face of irresistible accidents such as fires or explosions. 10. Other reasons resulting in the inability to produce. Minor accident: Secondary combustion. Cause: The CO generated during the regenerative charring reaction continues to oxidize to form CO2 under conditions of excess oxygen and high regeneration temperature, releasing heat in the process and resulting in excessively high local temperatures. Phenomenon: Secondary combustion occurs in the dilute phase, cyclone, or flue sections; excess oxygen levels drop sharply, temperatures rise rapidly, which can damage equipment, cause catalyst loss, and disrupt operations. Treatment method: During normal operation, the main approach is to ensure complete combustion of carbon monoxide in the dense-phase bed of the regenerator by using carbon monoxide as an oxidizing agent. It is necessary to regularly monitor the carbon monoxide content in the flue gas, add the oxidizing agent on schedule, and increase its dosage when needed to prevent secondary combustion. In cases where this has already occurred, thin-phase spray cooling steam or flue gas spray steam can be used, along with an appropriate amount of oxidizer to bring the situation under control. As a last resort, emergency measures such as reducing the opening degree of the raw material stop valve and lowering the processing capacity until feed is stopped can be taken to prevent equipment damage. Carbon accumulation: Cause: Carbon accumulation occurs when the coking capacity of the device exceeds its burning capacity, resulting in poor burning effects. The carbon content in the catalyst increases rapidly, leading to a severe decline in the activity of the regenerated catalyst and a significant deterioration in its selectivity, ultimately causing the catalyst to become completely inactive. The main reasons are as follows: 1. The total feed volume is too high (due to intentional increase or instrument failure), resulting in an excessive amount of coke formation, which was not adjusted in a timely manner. The raw material composition is too heavy, the residual carbon value is too high, or it contains a large amount of polycyclic aromatic hydrocarbons, all of which increase the amount of coke formed, without being detected in time. 2. The circulation rate decreases, and the feed rate is increased too rapidly, resulting in an excessively low reaction temperature; this causes the green catalyst to contain oil, and adjustments are not made in a timely manner. 3. The amount of stripping steam is too low, resulting in the catalyst slurry containing oil. 4. The burning oil is sprayed too forcefully and in excessive amounts. 5. The failure of the feedstock stop valve to close properly results in an excessive circulation rate of feedstock, leading to poor stripping efficiency. 6. An excessive feeding rate and high catalyst activity lead to increased reaction depth, thereby increasing the amount of coke formed. 7. The oxygen content meter malfunctioned or gave false readings, and this was not detected in time. 8. Oil-laden steam enters the regeneration system. 9. After the feed is stopped, the catalyst remains highly active; if the feed rate is increased too quickly, the amount of coke formed increases sharply. Phenomenon: 1. The oxygen content indicator gradually decreases and eventually returns to zero, while the CO level in the flue gas increases. 2. The carbon content increases due to the regenerant, and visual inspection of the sample shows blackening. 3. The richness of the gas decreases, and its composition becomes lighter (with an increase in the ratio of hydrogen to methane and a decrease in the content of C3 and C4). Sometimes, this leads to an increase in the compressor speed, a decrease in the outlet flow rate, and unstable operation of the unit. 4. The levels of gasoline and light diesel have decreased significantly, while the level of reprocessed oil has risen markedly. 5. Due to the increased carbon content in the catalyst, its specific gravity rises, which results in increases in the density of the fluids in both reactors, as well as in the pressure drops across the slide valves, lift pipes, cyclones, distribution pipes, and the thrust exerted by the inclined tubes. 6. Observation of the flue gas reveals an increase in its color intensity. 7. At higher oxygen levels, the regeneration temperature rises; when the oxygen level is very low, the regeneration temperature drops suddenly. Treatment method: After carbon accumulation occurs, the reaction process can no longer be maintained; in mild cases, the feed rate is reduced, while in severe cases, the feed is stopped and fluidized coking is carried out. During this process, it can easily lead to over-temperature and over-pressure accidents that may damage the equipment, as well as impair the activity and selectivity of the catalyst. Therefore, carbon buildup is an accident with relatively serious consequences, and special attention must be paid to it. Once such an incident occurs, the temperature changes in the regeneration system must be closely monitored during the burning process. When dealing with carbon buildup, it is first necessary to take samples and visually assess the degree of blackening of the catalyst, in order to determine the extent of the carbon buildup and estimate the time since it began to accumulate. This information helps decide whether to reduce the feed rate or to stop the feed flow for coking. Generally, the steps for dealing with carbon buildup are as follows: 1. Reduce the amount of oil slurry fed back into the process; decrease the feed rate accordingly based on the level of carbon buildup. Slightly open the emergency steam valve for feeding or increase the amount of pre-heating steam to reduce the formation of coke. It is important to control the reaction temperature during any significant reduction in the feed rate. Do not exceed the temperature limit. 2. Reduce the flow rate by closing the regeneration slide valve and the dead zone plug valve, thereby slightly lowering the system pressure to reduce coke formation. 3. The main air flow should be adjusted according to the temperatures of the two devices; it is not advisable to increase the main air flow significantly in order to enhance the coking effect. Instead, the main air flow can be reduced slightly to prevent overheating caused by excessive coking. 4. When there is an excess of heat in the system, (activate the external heat exchanger) to increase the heat absorbed by the heat exchanger; keep the regeneration temperature at or below 700°C, and try to avoid using dilute-phase cooling steam, or if it is used, do so gradually. 5. If carbon accumulation is severe and the reduction in flow rate is significant to the point that feeding to the fluidized coking unit is interrupted, the manual valve on the feed nozzle manifold can be reduced gradually until it is closed. The emergency bypass line should then be opened to some extent to allow circulation within the feeding system. When the liquid level in the reprocessing tank overflows, the slurry discharge system should be activated. 6. Based on the degree of charring, take samples frequently for observation; once the catalyst’s color returns to normal, feeding should be resumed promptly. However, do not rush this process in order to avoid secondary combustion, as the catalyst remains highly active after charring, and rapid feeding can lead to another accumulation of carbon. 7. During the fluidized coking process, emergency steam must be injected into the reaction riser, and the coking rate as well as the temperature difference between the dense and dilute phases must be strictly controlled to prevent overheating and secondary combustion; if necessary, cooling gasoline should be used in the riser. The green body is oily: Reasons: 1. The reaction temperature is too low. 2. The amount of stripping steam is too low. 3. Large fluctuations in differential pressure. 4. The total feed amount has increased too much. Phenomenon: 1. The regeneration temperature rises, and the regeneration pressure increases. 2. The oxygen content drops back to zero rapidly. 3. In severe cases, yellow smoke emerges from the chimney. Treatment method: 1. When oil contamination is severe, it is necessary to immediately activate the plug valve for pressure drop protection, as well as the main air protection and feed protection systems. After using accident steam to blow away the large amount of oil and gas in the regenerator, treat it as a case of severe carbon accumulation. 2. Under normal circumstances, it is treated as carbon accumulation. 3. In the event of significant fluctuations in reaction pressure due to a compressor failure, the flare valve can be used to regulate and stabilize the reaction pressure; in the case of a failure of the double-acting slide valve, manual or crank-controlled operation should be used instead. 4. The feed rate should be adjusted slowly, in small increments. Procedure for handling main fan failures: If the operating unit fails, coordinate with the main fan crew to switch to the backup unit. If two units fail, or if the operating units stop suddenly, the following actions should be taken. 1. Immediately activate the main air self-protection and feed self-protection functions; close the feed nozzles and increase the preheating temperature. When the differential pressure fluctuates significantly, activate the slide valve pressure drop self-protection function. 2. Once the differential pressure returns to normal, the slide valve pressure drop self-protectively resets, maintaining fluidization in both vessels. 3. The fractionation unit shall be operated by shutting off the feed. 4. If the main wind cannot be restored for an extended period and the regeneration temperature is below 380°C, proceed with normal shutdown procedures. 5. If the compressor cannot circulate, it shall be stopped; the reaction pressure is controlled by the flare valve or the split-top butterfly valve. 6. Be sure to prevent the catalyst from entering the main fan housing; if it does enter, it must be cleaned thoroughly before the fan can be started. 7. Once the main wind is restored, all components shall be gradually brought back online. Main fan flying: Causes: 1. Failure of the regenerator pressure control or of the double-acting slide valve, resulting in a sudden increase in system pressure. 2. The too-small opening of the inlet butterfly valve causes the main fan to spin out of control (stop the purification air supply or activate the main fan’s self-protection mechanism). Phenomenon: Significant changes in the main air flow lead to substantial variations in regeneration pressure, the density and volume of the two reactors, as well as the circulation rate. This disrupts normal operations, and it also makes it very easy for the catalyst to flow back into the equipment, resulting in serious damage to the main fan and other accidents. Handling method: 1. When the system pressure is too high, the pressure should be reduced as soon as possible; if the double-acting slide valve fails to function, switch to manual operation or cranking immediately. If it does not work within a short time, main air self-protection or slide valve pressure drop self-protection should be activated; at the same time, the personnel in charge of the main fan should quickly open the outlet vent to help the unit return to normal as soon as possible. 2. In case of a malfunction in the control of the butterfly valve, immediately turn it open manually using the handwheel. When the regeneration pressure is low, the emergency steam bypass line may be slightly opened. 3. When the main air unidirectional damping valve fails and closes, the main air emergency protection system must be activated immediately. At the same time, the outlet of the main air blower should be vented to prevent the unit from overspeeding. Contact the instrumentation personnel for handling promptly. During the recovery process, proceed slowly to prevent overheating and accidents. 4. When the main fan starts to run uncontrollably, the operator of the main fan should promptly determine the cause. The air flow rate should not be set too high in order to stop the uncontrolled operation of the fan. It is necessary to ensure that the pressure at the fan’s outlet is higher than the pressure in the regeneration system, in order to prevent catalyst backflow. Catalyst circulation interrupted: Cause: 1. The regenerating single-acting slide valve or the unregenerated plug valve failed to close completely. 2. The pressure of the loosening medium in the inclined pipe is too low; water presence or interruptions can lead to bridge formation and blockage. 3. The amount of stripping steam is too high. Phenomenon: 1. The reaction temperature drops rapidly, while the regeneration temperature first rises and then drops quickly. 2. The reaction pressure decreases, while the oxygen content in the flue gas increases. 3. Sudden change in spool valve pressure drop. 4. Significant fluctuations in system pressure cause coke particles at the top of the settler to fall off, blocking the catalyst channels. Solution: 1. When catalyst circulation is interrupted due to the complete closure caused by a faulty slide valve, it is necessary to immediately switch to manual or crank operation to maintain fluidization. 2. When bridging occurs due to changes in medium pressure causing the inclined tubes to become loose, the pressure should be adjusted, and any blockages at the loose areas must be dealt with promptly. 3. In the event of a failure in the control of the stripping steam, switch to manual control or use an auxiliary line to regulate the flow; if the steam contains water, drain all the condensate. 4. When the system pressure changes significantly, the catalyst circulation rate should be adjusted by changing the opening degree of the slide valve, while striving to restore normal conditions as quickly as possible. 5. If the catalyst circulation cannot be restored, treat it as a shutdown. For more information, please follow the WeChat official account 【Catalyst People】