Improvement measures for catalytic cracking operations

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Improvement measures for catalytic cracking operations: 1. Synchronize the shutdown of the steam turbine with the interruption of reaction feed to reduce the time required for flaring. During the shutdown of the catalytic unit, when the processing volume decreases, the compressor is stopped when its rotation speed is controlled mechanically. At this point, the rich gas begins to be vented from the compressor inlet, up to the point when the catalyst has been transferred from the reactor to the regenerator. It takes at least 3 to 4 hours to light the torch. By synchronizing the shutdown of the compressor with the cessation of reaction feed, the flare time is reduced to only 30 minutes. During the reduction in processing volume, as the amount of rich gas fed into the compressor decreases, the reaction pressure is controlled using the amount of rich gas that is reflected back at the outlet. When the catalyst is unloaded from the regenerator, in order to maintain pressure balance between the two units, the oil vapor separator at the top of the fractionator is promptly fed with fuel gas to ensure a minimum amount of rich gas at the compressor inlet. When the reaction feed is stopped, the compressor also shuts down; the fuel gas used for pressurization is vented through the compressor inlet. The time required for this venting is equal to the time needed to transfer the catalyst from the reactor to the regenerator, which is usually around 30 minutes. Another advantage of this approach is that it directly cuts off the reactor feed, allowing the gasoline quality in the system to remain stable and meet all specifications; thus, it ensures that all products produced during the shutdown process are of satisfactory quality. 2 The gaseous hydrocarbons from the stabilizing system are returned to the absorption tower to recover the liquefied gas components. In accordance with the pressure control scheme for the top of the stabilizing tower, the gaseous hydrocarbons in the reflux tank at the top of this tower are directly discharged into the plant’s high-pressure fuel gas network. Since the gas phase differs from the dry gas emitted from the top of the secondary absorption tower, the components with molecular weights above C3 account for over 95% of its mass fraction, which is equivalent to about 0.4% of the liquefied gas yield. Therefore, when gaseous hydrocarbons are directly discharged into the combustion pipeline network, while the pressure at the top of the control stabilizer is maintained, 0.4% of the liquefied gas is lost. To recover this portion of the liquefied gas component, a bypass line was added between the gas hydrocarbons leaving the stabilizer top reflux tank and those entering the absorption tower via the compressed rich gas condensate tank, thereby enabling the reabsorption of the gas hydrocarbons. The 3 CO combustion aids are mixed with the fresh catalyst and loaded into the fresh catalyst storage tank. During normal operation of the plant, it is necessary to continuously add CO combustion aids to the regenerator in order to recover the heat released from the combustion of CO. The manual method of addition not only increases the workload for workers but also poses a health risk due to the dust generated by these combustion aids. When filling the fresh catalyst storage tank with catalyst, we mixed the CO oxidant evenly into the fresh catalyst at a mass ratio of 60:1 between catalyst and oxidant, and then loaded them together into the fresh catalyst storage tank. In this way, when a small feeder is used to add catalyst to the regenerator, the CO combustion aid enters the regenerator as well, overcoming the aforementioned drawbacks. A certain level of platinum content is maintained in the system; when tail burning occurs occasionally during operation, an oxidizer is manually added as a supplementary measure. It has been proven that adopting this measure is very effective in ensuring the combustion of CO in a dense-phase bed, reducing the workload on workers and minimizing pollution.