Contents 7 Continuous catalyst regeneration

The process consists of a reactor section, continuous catalyst regeneration unit (CCR), and product recovery section. Stacked radial-flow reactors are used to minimize pressure drop and to facilitate catalyst recirculation to and from the CCR. The reactor feed consists solely of LPG plus the recycle of unconverted feed components no hydrogen is recycled. The liquid product contains about 92 wt% benzene, toluene, and xylenes (BTX) (Figure 6-7), with a balance of Cg aromatics and a low nonaromatic content. Therefore, the product could be used directly for the recovery of benzene by fractional distillation (without the extraction step needed in catalytic reforming). 

The calculations are iterative, starting from assumed values for (Cc)i G and for Trg, the catalyst temperature and coke content in the regenerator and also at the inlet of the reactor. First, the fluidized bed reactor is calculated by means of the continuity equations, (13.8.2.1-1) and (13.8.2.1-2), and the (Cc)i and Tr from the balances, (13.8.5-1) and (13.8.5-3), which requires iteration in itself. Then, with (Cc)i and Tr obtained in this way, the regenerator values are calculated. This leads to new values for (Cc)i G and Trg- A new cycle is then started, until convergence is reached. In a typical case, four iterations were required for convergence with an initial Trg 13 K off and an initial (Cc)ffc 0.15 wt-% off. 

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