Operation of the fractionation tower in a catalytic cracking unit

Salt formation in the fluidized catalytic cracking fractionation tower is mainly caused by nitrogen compounds and inorganic chlorides present in the feed; these substances generate NH_3 and HCl in the catalytic cracking environment, and after dissolving in water, they form NH_4Cl which deposits on the tray surfaces. Salt formation is accompanied by issues such as inflexible control of the top temperature of the tower, vacuum conditions in the top circulation pump, as well as problems with the flash point of light diesel and difficulties in its extraction. To prevent salt formation, it is necessary to improve the feed and operating conditions. Washing with water is an effective method for dealing with salt accumulation. Mathematical simulation methods were used to qualitatively analyze the characteristics of the equilibrium operating points in heavy oil catalytic cracking units; the results showed that due to the high coke production rate and significant heat release associated with heavy oil, it is necessary to remove excess heat from the regenerator in order to keep the unit’s equilibrium regeneration temperature within industrial operational limits. Within the operating range of the industrial unit, there are two equilibrium points; the one at a lower temperature is an unstable point, while the one at a higher temperature is a stable point. Therefore, the regeneration temperature should be chosen carefully to prevent the device from operating at an unstable equilibrium point. When the amount of heat absorbed reaches a certain level, the two equilibrium points converge into one unstable equilibrium point. At this point, it becomes difficult to operate the fluidized catalytic cracking unit smoothly. Furthermore, the main air volume has a significant impact on the position of the equilibrium point. Therefore, the proper selection of the main air volume and heat uptake is a key factor in determining the position of the equilibrium point and its characteristics. Generally, the bottom temperature in a fractional distillation tower for processing heavy oil should not exceed 370 degrees, and for processing wax oil, it should not exceed 360 degrees

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