A consequence of processing at higher-than-design crude rates is the generation of additional feed requiring significant upgrading to finished products. Two streams that are particularly challenging are the extra heavy gas oil (XHGO) and light vacuum gas oil (LVGO) fractions. In recent years, refiners have explored cost-effective ways of capturing maximum value from these feeds without affecting refinery economics. One approach that is generating a lot of interest – and substantial additional margin – is to revamp a distillate hydrotreater (DHT) into a distillate mild hydrocracker (DMHC).
There are several options for managing XHGO and LVGO streams. Blending directly into the fuel oil pool without upgrading clearly fails to capture maximum value. Routing to the hydrocracker potentially constrains the capacity of this critical unit for costly yield losses of both the normal and incremental feedstock. Lastly, processing in the DHT does not enable sufficient shift in the distillation tail to meet ultra-low-sulphur diesel specifications.