(28g) Debottlenecking a FCC Gas Plant with Ultra System Limit Consep Trays

In the middle of 2006 a new Hydrocracker plant was put on stream at Preemraff Lysekil Refinery, Sweden. This affected the feed quality to the FCC Unit and its products yields as well. In particular, the flow rate and composition of the stream going to the debutanizer did change significantly. The intention of Preemraff was to maximize the production of propylene; therefore the catalytic cracking conversion was reset accordingly resulting in a higher feed rate to the debutanizer. This column had been already retrofitted few years back with first generation of High Performance Trays which increased the capacity by 15% over the conventional trays. The column was running at its hydraulic limitation, therefore it could not handle the additional vapor and liquid loadings coming from the latest unit modifications. A new generation of High Performance Trays was required at the stripping section, while multiple downcomer trays could fit in the rectifying section. It was of great importance to minimize the amount of C5 in the top since they damage the catalyst of the down stream Polymerization Unit. It was also important to minimize the C4 in the light cracked naphtha due to the vapor pressure specification. To achieve such challenging targets ConSep trays were selected at the stripping section and HiFi at the rectifying section.

The scope of the paper is to describe the design approach of such difficult revamp projects and report the achieved results.