Heat-integrated process improvement of petroleum refinery FCC light-ends separation

Abstract

This research presents a methodology for investigating and proposing operational changes that can improve product recovery, heat recovery, and economics of a gas concentration unit of a FCC plant. The methodology starts by collecting relevant information from an existing plant, followed by development of a simulation model of a gas concentration unit in Aspen HYSYS. Next, the developed model is used to conduct optimisation studies to identify process changes (solvent temperature, operating pressure, solvent flow rate, solvent composition and inter-stage cooling) that improves product recovery, heat recovery, and economics. Key findings from this research includes the following trade-offs: increasing operating pressure from 1300 kPa to 1700 kPa increases gasoline and LPG recovery by 1% and 0.4% respectively whilst heat recovery and cooling water demand increases by 0.5% and 0.1%, leading to total benefit increase of 1%; increase in recycled gasoline flow rate by 9628 kmol/h (20% of initial flow rate) improves recovery of gasoline and LPG by 0.1% and 0.3% and heat recovery and cooling water demand by 18% and 77%, but steam generation decreases by 35%, which results to decrease in benefit of 1%; increasing C6 content of solvent (unstabilized naphtha) by 50 kmol/h increase in gasoline recovery 7.5% and heat recovery and cooling water demand increases by 0.1% and 1%, and benefit increases by 5%; for ambient cooling medium, varying solvent temperature and pumparound return temperature (inter-stage cooling) does not improve product recovery and heat recovery. Analysis of results indicate that high C6 composition in solvent has the highest impact on product recovery, heat recovery, and process economics compared with other degrees of freedom.