GB710144A - Improvements in or relating to the coking and catalytic cracking of hydrocarbons - Google Patents

Abstract

<PICT:0710144/III/1> A hydrocarbon feed stock is fed to a coking zone in which a dense fluid bed of inert particles is maintained, vapours from the coking zone are passed either direct or after fractionation to a fluidized catalyst cracking zone from which catalyst is continuously withdrawn to a regenerator, and regenerated catalyst and coking zone inert particles are brought into indirect heat exchange association so that the heat required for the coking zone is supplied by the regenerated catalyst. In the apparatus of Fig. 1, coke particles in reactor 3 are maintained as a dense fluidized bed by steam injected at 6 and hydrocarbon feed stock is supplied to the bed at 1. Coke is continuously withdrawn at 171 and vapours pass via cyclones 29 to a fluidized catalyst bed 20 above the coking zone and contained in a reactor 19 of larger diameter. Catalyst is continuously withdrawn from the bed at 15 and fed by an air lift 16 to regenerator 30. From the regenerator catalyst returns to the cracking reactor 19. A catalyst circulation is also maintained by lines 37, 14 and 16 between the regenerator and a shell and tube heat exchanger 8 in the coking reactor 3. The catalyst is maintained in a fluidized state in the shell of the heat exchanger by steam introduced at 10 while the fluid coking bed extends through the tubes 11 of the heat exchanger. Excess heat in the regenerator may be removed by coil 36. The heat-exchanger may alternatively be arranged in the catalyst regenerator. In another arrangement the cracking reactor is separate from the coking reactor so that vapours from the coking zone may be fractionated and a gas oil fraction only passed to the cracking reactor; Fig. 2, (not shown). When the cracking and coking reactors are separate with the heat exchanger in the coking bed, cooled regenerated catalyst from the heat exchanger may be mixed with the gas oil fraction and passed to the cracking reactor, any excess catalyst from the heat exchanger being returned to the regenerator. The feed may be preheated and may be cut back with naphtha and diluted in the reaction zones with steam, recycle gas or other inert gas to increase gas velocity. Coking and cracking temperatures range from 800 to 1200 DEG F. and regeneration temperatures from 1000 to 1500 DEG F. The heat exchangers may be only part submerged in the coking of regenerator bed. The feed may be injected into either the dense or disperse phase of the coking reactor.