Improve FCC margins by processing more vacuum residue in feed

摘要

With the greater processing of heavy crude oils in refineries, the importance of fluid catalytic cracking units (FCCUs) has increased. Metals content in heavy feeds is one of the limiting factors in FCCUs, as increased levels of metals lead to high coke and dry gas yields. Heavy feeds also have high sulfur contents, causing increased SO_x emissions from the FCCU. However, processing heavy oil streams in FCCUs also leads to increased distillate yields and improved margins. One of Hindustan Petroleum Corp. Ltd.'s (HPCL's) refineries has a resid FCCU with a catalytic cooler designed to process feed with a vacuum residue (VR) content of 18 wt%, with feed Conradson carbon residue (CCR) up to 4.2 wt% and metals content (nickel and vanadium) of 4.1 ppmw. The actual feed processed in the unit contained 11% VR and had a metals content of 7 ppmw. A higher amount of VR leads to poor product yields and is limited by the main air blower and the wet gas compressor. One approach to increase VR concentration in the feed blend is to hydrotreat the vacuum gasoil (VGO) component of the feed and reduce the sulfur and metals content. This study is an attempt to process higher concentrations of VR in a resid FCCU with partial hydrotreatment of feed. Based on the laboratory studies performed, VR concentration in the FCC feed stream can be increased by an additional 10 wt% with improved conversion.