This unit employs a suspended or "ebuliated catalyst-bed" technology which allows onstream addition and withdrawal of catalyst and eliminates the need for shutdown for catalyst changeout and maintains uniform catalyst activity. The catalyst is maintained in a fluidized state by the upward velocity of the feed. This turbulence provides uniform heat distribution and efficient contact on the catalyst between the residuum and hydrogen.
Used with permission (© SAIT Polytechnic, MacPhail School of Energy, 2009)
Atmospheric residuum from the Crude Unit is preheated in a fired heater and mixed with a hydrogen rich gas stream. This preheated mixture enters the expanded bed of catalyst where cracking of the residuum occurs. The hydrogen reacts with the cracked compounds, forming a partially desulphurized, demetallized, denitrified and hydrogen-saturated product. Hydrocracking yields full range boiling products, converting approximately 60 percent volume of the initial vacuum residuum to lighter fractions.
The reaction products and excess hydrogen pass through a series of flashing and cooling stages to separate the vapour from the liquid. The flashing vapours are stripped of hydrogen sulphide in an amine absorber and the hydrogen rich stream is recycled to the reactors. A purge gas stream maintains recycle gas purity and is routed to a Pressure Swing Adsorption (PSA) Unit for hydrogen recovery.
The separated liquid is routed to the Hydrocracker Fractionation Unit for splitting into naphtha, jet kerosene, gas oil and heavy residuum.