FCC reactor-regenerator

The evolution and improvement of the above-mentioned topics set the background for providing FCC design parameters. The following sections present the latest commercially-proven process and mechanical design recommendations for FCC reactor-regenerator components. 

Improving mechanical reliability of the FCC reactor-regenerator components. 

Components with similar reaction kinetics are grouped into 21 lumps. These kinetic liunps are listed in Table 6. In practice, the 21 components provide sufficient granularity to model all of the important steady-state cause-and-effect relationships in the FCC reactor-regenerator complex. Kinetic parameters for the riser and reactor models are segregated from the hydraulics and heat balance relationships. This permits different FCC kinetic schemes to be implemented within the same rigorous riser/reactor models. The off-line version of the model includes a simplified fractionator model and a product-property model. 

Figure 8. UOP High Efficiency - FCC Reactor-Regenerator Assembly Hemler (1989)...

The reactor-regenerator is the heart of the FCC process. In a modem cat cracker, virtually all the reactions occur in 1.5 to 3.0 seconds before the catalyst and the products are separated in the reactor. 

Hydroprocessing reduces the Conradson carbon residue of heavy oils. Conradson carbon residue becomes coke in the FCC reactor. This excess coke must be burned in the regenerator, increasing regenerator air requirements. 

Many aspects of FCC development have been the result of trial and error. The development of present design standards is as much art as it is science. Consequently, it is appropriate to review some of the key developments that have influenced the current design philosophy behind the FCC reactor and regenerator ... 

The FCC reactor is really two reactors with sohd catalyst pellets cycled between them. The vaporized gas oil is fed along with fresh catalyst to the first, called the reactor, and the spent catalyst is separated from the products in a cyclone and sent to the regenerator, where air (now sometimes O2) is added to oxidize the carbon. The flows of reactants, products, air, and catalyst are indicated in Figure 2-13. The reactor cracks the hydrocarbon and forms coke on the catalyst Then in the regenerator the coke is burned off and the catalyst is sent back into the reactor. 

Typical operating conditions of these components of the FCC reactor are indicated in Table 2-5. The residence time in the regenerator is longer than in the reactor, and it is therefore considerably larger. 

A variant on the fluidized bed is the riser reactor. In this reactor the flow velocity is so high that the solids are entrained in the flowing fluid and move with nearly the same velocity as the fluid. The solids are then separated trom the effluent gases at the top of the reactor by a cyclone, and the solids are returned to the reactor as shown in Figure 7-4. The FCC reactor is an example where the catalyst is carried into the regenerator, where carbon is burned off and the catalyst is heated before returning to the reactor. 

Energy coupling between the reactor and regenerator are crucial in designing the FCC reactor, because the heat liberated from burning off the coke from the catalyst suppHes the heat to maintain the temperature in the reactor where reactions are endothermic. Therefore, the energy balance equations and the description of flow of fluid and solid phases must be considered carefully in this reactor. 

Not listed in Table 6.4 of possible unit modifications are improved unit controls. These can be applied in many ways to both the reactor/regenerator and gas plant. Operating closer to limits increases revenue by forcing the operation to several limits rather than one or two. A good FCC model is needed if all the benefits are to be realized. 

SO, additive chemistry has been described previously in literature [3]. SO, reduction additives remove SO, from the regenerator flue gas and release the sulfur as H2S in the FCC reactor. In a full bum regenerator, the amount of SO2 removed is directly proportional to the amount of additive used. Normal additive levels in the catalyst inventory range from 1-10%, with up to 20% being used in some units. Typical SO, removal rates have historically been in the 20-60% range. With the introduction of new super additives, rates in excess of 95% are commonly being achieved [4]. 

Fig. 7.9. Schematic of Fluid Catalytic Cracking (FCC) reactor with catalyst regenerator.

Description DCC is a fluidized process to selectively crack a wide variety of feedstocks into light olefins. Propylene yields over 24 wt% are achievable with paraffinic feeds. A traditional reactor/regenerator unit design uses a catalyst with physical properties similar to traditional FCC catalyst. The DCC unit may be operated in two operational modes maximum propylene (Type I) or maximum iso-olefins (Type II). Each operational mode utilizes unique catalyst as well as reaction conditions. DCC maximum propylene uses both riser and bed cracking at severe reactor conditions, while Type II utilizes only riser cracking like a modern FCC unit at milder conditions. 

The fluidized reactor system is similar to that of a refineiy FCC unit and consists of riser reactor, regenerator vessel, air compression, catalyst handling, flue-gas handling and feed and effluent heat recovery. Using this reactor system with continuous catalyst regeneration allows higher operating temperatures than with fixed-bed reactors so that paraffins, as well as olefins, are converted. The conversion of paraffins allows substantial quantities of paraffins in the feedstream and recycle of unconverted feed without need to separate olefins and paraffins. 

Description The DCC process selectively cracks a wide variety of feedstocks into light olefins, with a reactor/regenerator configuration similar to traditional fluid catalytic cracking (FCC) units (see figure). Innovations in catalyst development and process variable selection lead to synergistic benefits and enable the DCC process to produce significantly more olefins than an FCC that is operated for maximum olefins production. 

Fluid catalytic cracker (FCC) units are characterized by reaction in the transport lines between the reactor and the regenerator, in addition to that in the main reactor. Thns, the design of these reactors is very complicated, involving more than one regime of flnidization. Innumerable studies have been reported on the modeling of FCC reactors and they shonld be consnlted for detail (e.g., de Croocq, 1984 Chuang et al., 1992). Some salient features are desaibed here. 

FCC is by far the most important petrochemical process that involves the broadest scope of particulate technology. Although the chemistry of the FCC process is rather complex, many of the operational problems are in fact associated with handling fluid-particle systems and related mechanical issues, such as erosion. In particular, the reactor/regenerator section of the FCC unit includes many aspects of fluid-particle systems that are critical to FCC design and operation. 

The results presented separately for the FCC reactor and the regenerator in Sections 13.8.2 and 13.8.4, respectively, were, in fact, obtained from their simultaneous simulation along the lines given here. 

Figure 2. Model Components for Aspen FCC (Riser/Reactor/Regenerator)...

Fluid catalytic cracking (FCC) produces more that half the world s gasoline. A typical FCC unit comprises three major sections - riser/reactor, regenerator, and fractionation. Table 12 provides important details on FCC. 

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