Process improvement of petroleum refinery fcc light-ends separation

To satisfy global demand for valuable petroleum refined products such as gasoline and liquefied petroleum gas (LPG) by achieving high recovery in gas concentration unit of a FCC plant, an insightful understanding of which degrees of freedom has significant impact on product (gasoline and LPG) recovery is required. This research proposes a methodology for investigating degrees of freedom that significantly impacts product recovery in gas concentration unit, in addition to proposing operational changes that improves overall process performance. First, a model of gas concentration unit builds in Aspen HYSYS, followed by setting up case study based on investigated degrees of freedom (solvent temperature, operating pressure, solvent flow rate, solvent composition and inter-stage cooling) from literature, and lastly evaluating each case on the developed model and analysing results. Key findings from this research includes the following trade-offs: increasing operating pressure in primary absorber by 30% (400 kPa), increases gasoline and LPG recovery by 1% and 0.4%; recovery of gasoline and LPG are improved by 0.1% and 0.3% due to increase in recycled gasoline flow rate by 20% (9628 kmol/h); increasing C6 content of solvent (unstabilized naphtha) by 50 kmol/h (from 15.1 kmol/h), increases gasoline recovery by 7.5%; for ambient cooling medium, varying solvent temperature and pumparound return temperature (inter-stage cooling) does not improve product recovery. Results show that high C6 composition in solvent has the highest impact on product recovery compared with other degrees of freedom. Proposed methodology and research outcomes can be used by plant operators to optimise performance of FCC light-end separation unit, thereby improving product recovery.