Effect of gas recycle rate on the hydrocracking of vacuum bottoms in a pilot plant

Abstract

Hydrocracking runs were carried out in a 1 bbl/d pilot plant using vacuum tower bottoms (VTB) from a blend of Western Canadian heavy crudes. The effect of the superficial gas velocity on the reactor dynamics and on the conversion of VTB to distillate was examined for several sets of superficial gas velocities and various temperatures. A gamma-ray interrogation method was applied to examine the hydrodynamics of multi-phase flows in the bubble column reactor. Because hydrocracking reactions occur in the liquid phase, the pitch (524 ° C+) conversion is strongly affected by the liquid holdup which is a function of the superficial gas velocity. In these runs, the effect of gas velocity on pitch conversion was strong enough to offset the normal increase in pitch conversion with temperature so that similar pitch conversion could be obtained for different combinations of temperature and gas velocity. Product distributions were uniquely correlated with the pitch conversion and a first order lumped parameter kinetic model was applicable. Sulphur conversion was also correlated with pitch conversion.