Effects of Hydrotreating on FCC Performance

Many refiners are including die hydrotreating of FCC feed in their plans to make clean fuels. To demonstrate the feasibility of running a rigorous model for an FCC-plus-pretreater complex, we connected AHYC to AFCC. To link 

Initially, the combined model was huge, containing more than 1.2 million non-zero terms in its matrix of variables. To allow the model to run in a reasonable amount of time on a Pentium III computer, we made some simplifications. In the reduced model, the four catalyst bed models are still fully rigorous. However, the hydrogen furnaces are represented with a heat-exchanger model, quench valves are modeled with mixers, a component splitter model is used for the wash-water system, and a group of component splitters is used for the fractionation section. These changes reduce the number of equations and non-zeros to 130,000 and 680,000 respectively. Despite these simplifications, the slimmed-down model remains, in our collective opinion, a useful tool for offline what-if studies and for economic comparisons of different process options. 

We first looked at the effect of varying the amount of hydrotreated material in an FCC feed blend from 0.0 to 96.7 vol%. Table 10 presents selected process conditions for the feed hydrotreater, which achieved 90% desulfurization and roughly 23 wt% conversion of vacuum gas oil to middle distillate and naphtha. 

In another approach to modeling the effects of FCC feed pretreating, the FCC model receives a blend of hydrotreated feed from AHYC with straight-run feed from a tank model. The latter case is discussed here. 

Variable Units Case 1 Case 2 Case 3 Case 4 

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