Catalytic cracking commercial regenerators

Commercial Development of Fixed-Bed Process. From the above process considerations it became obvious that the capacity of a commercial unit, and its economic value, were closely related to its ability to burn coke. Indeed, most of the design problems associated with catalytic cracking have been centered around the question of catalyst regeneration. To obtain the most favorable economic return from a 10,000-barrel-per-day unit, it was designed to burn approximately 6000 pounds per hour of coke. This coke yield represents approximately 5% by weight of the charge. 

In catalytic cracking, a large amount of heat needs to be supplied at the reactor inlet to vapourize the feed and provide the heat of reaction. In commercial units, this heat is provided by the hot catalyst recirculated from the regenerator. High heat transfer rates are achieved when the fluidized catalyst is mixed with the feed. In some experimental units, feed and catalyst are injected at reactor temperature. The heat of reaction must then be supplied by an external heating element, at much slower rates of heat transfer. The product selectivity from such laboratory units cannot be expected to simulate that of commercial units... 

A significant application of FF on a commercial scale is the FF regenerator in fluid catalytic cracking processes. In Chapter 9, J. Chen, H. Cao, and T. Liu of Luoyang Petrochemical Engineering Corporation (LPEC) describe the development and design of four types of FF regenerators and the results of their commercial operation. More than 30 such units are in operation in China. 

Several attempts were made to prepare pillared smectites with sufficient hydrothermal stability for use as active components in catalysts for catalytic cracking of heavy oil fractions. Although improvements were made, none of the attempts resulted in pillared materials stable enough to withstand the hydrothermal conditions found in the regenerator of a commercial FCC. One type of materials studied, i.e. alumina-montmorillonites, may be attractive alternatives to the active matrices, often alumina, currently used in FCC-catalysts designed for cracking of heavy oils. The alumina-montmorillonites can, perhaps, not be considered to be bona fide pillared smectites as they have considerably larger pores and a wider pore-size distribution than what is characteristic for pillared smectites. 

Evidence for the two-phase model came from measurements of the gas concentration profile in a commercial catalytic cracking regenerator 40 ft in diameter with a 15-ft bed [8]. The exit gas had 1% O2, but samples drawn from different bed depths had only 0.1-0.4% O2. The bed samples also showed 12-14% CO2, compared to 10% CO2 in the exit gas. Although most of the gas flow was in the bubbles, the probe saw mainly dense-phase gas, where the conversion was higher than in the bubbles. Samples taken very rapidly showed wide fluctuations in oxygen content, since the probe was sometimes in a bubble and sometimes in the dense bed. 

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