FCC systems

The eomplex FCC system involves not only turbomaehinery, but also related proeess eomponents. All of these must be properly designed and sized to operate within system parameters from startup to steady state design point, and through shutdown. System response to emergeney eonditions is also mandatory. Computer simulation is, therefore, an integral part of the design proeess. A eomputer program eapable of this simulation is deseribed below. 

Elliott s digital simulation program (EDSCAN) was developed to assist eustomers in designing reliable and eeonomie FCC systems. The program is used for analyzing any type of Elliott equipment, assoeiated... 

In die simulation model, die FCC system was subdivided into discrete elements and suitable subsystems. This model provided all die process parameters such as pressures, flowrates, and temperatures. Figure 6-44 shows die corresponding block diagram. (The model for die expander, piping systems, and vessels is based on a gas turbine model described by GHH Borsig in a paper by W. Blotenberg.)... 

In heterogeneous systems AP must be critically reviewed, especially if the reaction involves a two-phase mixture of liquid and gas, or if the gas flows through a deep bed of catalyst particles as in the FCC systems. AP should be checked early in the design process to assess its influence on the overall plant integrity. 

Deactivation of zeolite catalysts occurs due to coke formation and to poisoning by heavy metals. In general, there are two types of catalyst deactivation that occur in a FCC system, reversible and irreversible. Reversible deactivation occurs due to coke deposition. This is reversed by burning coke in the regenerator. Irreversible deactivation results as a combination of four separate but interrelated mechanisms zeolite dealu-mination, zeolite decomposition, matrix surface collapse, and contamination by metals such as vanadium and sodium. 

We relax some of our previous FCC system assumptions now and restate our model assumptions first. Namely ... 

For units operating at the middle unstable steady state, the steady-state response of the system is generally very sensitive to variations in the operating conditions. Therefore, a detailed parametric investigation of such a system is highly advised. We now do so for the present model to give our readers a deeper insight into the behavior of these rather complex FCC systems. 

When selecting a bellows valve, it is important to pay some special attention that the material selection is in accordance with the process conditions. Some SRV manufacturers use as standard bellow material INCONEL alloy 625LCF-UNS N06625 (ASME SB0443). This material is not perfect either but, compared to simple stainless steel, has an enhanced resistance to mechanical fatigue and sour gases it is commonly used in refinery FCC systems for expansion joints. 

Figure 13 The apparent flow regime diagram calculated with EMMS-based multiscale CFD and the intrinsic flow regime diagram for the air-FCC system (fluid catalytic cracking particle, dp = 54 m, pp = 930 kg/m3) calculated by using the EMMS model without CFD. The intrinsic flow regime diagram is independent of the riser height (Wang et al., 2008).

The SUPERFLEX process is a proprietary technology patented by ARCO Chemical Technology, Inc. (now Lyondell Chemical Co.), and is exclusively offered for license by Kellogg Brown Root. It uses an FCC system with a proprietary catalyst to convert low-value feedstock with high olefin content to petrochemical products such as propylene and ethylene. 

The SUPERFLEX FCC system is similar to that of a conventional FCC unit and consists of riser reactor, regenerator vessel and units for air compression, catalyst handling, flue gas handling and feed and effluent heat recovery. The SUPERFLEX system should be integrated into an ethylene plant in order to minimize capital investment, with the feedstock obtained directly from the steam cracker and shared common product recovery. The cooled reactor effluent can be processed in a nearby existing ethylene plant recovery unit. Alternatively, the effluent can be processed in a partial recovery unit to recover recycle streams and olefin-rich streams concentrated for further processing in a nearby ethylene plant. 

The FCC system is mostly hypothetical and light hydrocarbons. Consequently, the Peng-Robinson equation of state is sufficient. We discuss the implications of the process thermodynamics in Chapter 1. In the case of the FCC model, equation of state or hydrocarbon correlation methods (Grayson-Streed, etc.) can sufficiently model the processs. 

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