Pilot plant thermal hydrocracking of GCOS (Great Canadian Oil Sands) bitumen: 1. the effect of heavy oil recycle on the plant operation

Abstract

The objective of the present investigation was to determine the operability of the thermal hydrocracking plant using a recycle-oil stream to increase liquid velocity in the reactor, in an attempt to reduce sludge or coke formation. Life runs of about three weeks were conducted with heavy oil recycle fed to the bottom of the reactor. The two long experimental runs in this series, R-2-1-2 and R-2-2-4, are described in detail. All shorter runs in which recycling of heavy oil was attempted are also described. Of main concern in this report are those factors which influenced the steady operation of the pilot plant, such as coke formation and deposition of metal sulphide which caused fouling and line plugging. The heavy-oil recycling, at a recycle to feed weight ratio of 2:1 or greater, reduced coke formation in the reactor compared with once-through operations at the same temperature, pressure and pitch conversion. Total recycle of the heavy ends before reaching the required temperature gave a smooth start-up. Adjusting the recycle-oil withdrawal rate was better than adjusting the feed flow as a means of maintaining the hot-catch-pot level. The increase in the ash content of the reactor fluid, coupled with a short "first-pass" residence time are perhaps the reasons for the suppression of coke formation when heavy oil is recycled.