Revamp considerations

A model for the riser reactor of commercial fluid catalytic cracking units (FCCU) and pilot plants is developed This model is for real reactors and feedstocks and for commercial FCC catalysts. It is based on hydrodynamic considerations and on the kinetics of cracking and deactivation. The microkinetic model used has five lumps with eight kinetic constants for cracking and two for the catalyst deactivation. These 10 kinetic constants have to be previously determined in laboratory tests for the feedstock-catalyst considered. The model predicts quite well the product distribution at the riser exit. It allows the study of the effect of several operational parameters and of riser revampings. 

The aforementioned example showed that good yield improvements can be obtained by an LSCC design because of better cracking parameters which means lower MCP. This example also shows that utility costs can be decreased considerably with LSCC revamping. 

This integrated technology is suitable for revamps of ethylene plants, as well as grassroots applications. The figure shows a maximum integration scenario for an HO FCC and steam cracking. The level of integration is a function of contaminant levels, HO FCC effluent gas composition and other capital reduction considerations. 

In packed columns, response to liquid changes appears faster, and the speed of response of the schemes 16.46 and d is less troublesome. In one case (388), considerable improvement in the speed of response of a butene splitter was experienced after trays were replaced by packings. A feed-forward loop, used for speeding the response of trays, was found unneeded and undesirable following the revamp. 

A considerable interest has been expressed in using the SBCR to carry out FTS particularly for the conversion of stranded natural gas into liquids. Currently, the Center for Applied Energy Research (CAER) is utilizing a Prototype Integrated Process Unit (PIPU) system for scale-up research of the FTS. The purpose of this study was to compare the performance and activity decline of a precipitated Fe/K Fischer Tropsch Synthesis (FTS) catalyst in a revamped slurry bubble colurtm reactor (SBCR) to that of previous CSTR and SBCR rans using the same catalyst and operating conditions. The activity decline measured in the revamped SBCR system was shown to be similar to that of the CSTR experiments. The apparent activity decline in a previous SBCR run was due a transient startup effect from the slurry filtration system. 

Project plot siting is very important for revamp projects. A careful review of the surrounding facilities is also necessary. Some of the important considerations are ... 

Another option is to debottleneck an existing hydrogen plant by revamping or upgrading portions of it. However, these cases should be evaluated on a case-by-case basis as different sites have different utility and/or plot considerations. Some of the upgrades are discussed in Section 8 ... 

If the only consideration is to reduce sulfur, the preferred solution would probably be to add reactor volume as in Case 3, but this assumes that the existing gas recycle system can manage the increased pressure drop and that the diesel yield loss due to cracking is acceptable. It may be necessary to revamp the recycle gas system and the overhead fiactionator. In many cases, the performance of the existing reactor can also be improved by installing state-of-the-art liquid distribution trays and quench mixers. " ... 

In connection with revamps , i.e. modification of existing plants for increased capacity and/or increased energy efficiency (see Sect. 6.4.3.4), where the pressure shell of existing converters is reused, it has, however, again become a major consideration to maximize the production capacity of the volume available inside the pressure shell. 

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