Satyendra Balot - MRPL
MRPL PFCC Feed comprises of Straight Run VGO, Hydrocracker bottoms and Hydrotreated HCGO. The unit is designed to process low value Vacuum gas Oil and to produce High value Polymer grade Propylene, olefinic Naphtha, LPG etc. As per design case, there is 8 wt% coke yield with the feed. However, to maintain coke yield at 8 wt% apart from Fresh Feed, slurry recycle from MF bottom was also injected in the Upper riser section. An option is also provided to inject Slurry recycle in the Reactor stripper section in case of low coke make from the Feed.
From commissioning of the PFCC unit, design coke yield was not achieved due to less coke precursors in PFCC Feed. However, to maintain required heat balance across Rx-Reg, Torch oil is being continuously injected in the Regenerator. Apart from torch oil, slurry recycle is also being injected into the Reactor stripper section for additional coke make. Slurry recycle is being injected at 10%w of Fresh Feed, however, due to insufficient yield of slurry for recycling into Rx-Riser/Stripper section, part of Fresh feed is being routed to Main Fractionator bottom.
Later, it was observed during the unit run that Hydrotreated HCGO and Straight Run VGO are major contribution towards coke make and as percentage of these streams in Feed increases, torch oil injection also comes down.
This paper discusses about the challenges faced during the unit run due to continuous torch oil injection and available feedstock and silver lining indicating reduction in torch oil when using higher percentage of Hydrotreated HCGO and Straight Run VGO, which is limited by Unit Feed Total Sulfur content.