Patent GB-810808-A (GB)
Title: Combined coking and thermal cracking process
IPC: C10G9/28
Filed: 1955-09-08
Abstract: <PICT:0810808/III/1> In a process for the thermal cracking of hydrocarbons, hot catalytically-inert solid particles, preferably coke, are circulated through two reaction zones and a heating zone; a heavy hydrocarbon oil is cracked in one of the reaction zones at a temperature between 850 DEG  and 1200 DEG  F. whereby motor fuels and coke are formed, and another hydrocarbon feed such as light hydrocarbons or gas oil or heavy ends separated from the products of the first reaction zone is cracked in the second reaction zone at a temperature between 1200 DEG  and 1800 DEG  F. whereby unsaturated hydrocarbons such as ethylene and propylene are produced.  The products from the reactor at higher temperature may be introduced into the reactor at lower temperature whereby the high-temperature products are quickly quenched to prevent further degradation; alternatively relatively cool solids withdrawn from the reactor at lower temperature may be used to quench the high-temperature products.  The apparatus shown comprises a coking reactor 20, a transfer line 10 for the high-temperature thermal cracking, and a transfer line burner 91.  A bed of petroleum coke particles (average particle size 250 microns), at a temperature of 950 DEG  F., is maintained in a fluidized state in reactor 20 by steam introduced through line 16.  A vacuum residuum, boiling above 850 DEG  F., is preheated and then introduced into the fluidized bed via line 17. The product vapours are discharged via cyclone, and scrubbed in tower 30 to remove heavy ends.  These heavy ends are introduced via line 11 into the inlet of transfer line 10 where admixture takes place with freshly heated coke particles at 1400 DEG  F. supplied through line 8; the suspension rises rapidly up the transfer line (the average vapour residence time being 0.5 seconds), and is discharged via line 13a into coker 20.  Coke is removed from the base of the coker via standpipe 22, and is transferred through line 21 to transfer line burner 91 where it is heated to 1400 DEG  F. by partial combustion in air, supplied through line 93.  The reheated coke particles are separated from the flue gases in cyclone 94, and recycled to the two reactors via lines 96 and 8.  Excess coke is withdrawn from the system via line 97, the amount being about 20 per cent by weight of the feed.  The vapours and gases leaving scrubber 30 are subjected to fractionation to obtain ethylene, propylene, naphtha, heating oil and gas oil.  The material boiling in the range of about 650-900 DEG  F. may be used as catalytic feedstock, in which case the cycle oil from the cat. cracker makes suitable feedstock for transfer line 10.  In an alternative mode of operation, the effluent from transfer line 10 is passed to cyclone 14 while being quenched with relatively cool coke particles withdrawn from the coker via line 7.  The unsaturated hydrocarbons are then withdrawn from the top of cyclone 14.  The coke withdrawn from the base of the cyclone is passed to the transfer line burner 91, but a portion may be recycled to the coker.  In another alternative, the effluent from the transfer line reactor is introduced into the dilute phase above the fluid bed in the coker so that the coker effluent will be heated; this prevents fouling of the vapour-phase equipment due to polymerization and condensation reactions.  The heat in the flue gases discharged from the transfer line burner may be recovered by direct contact with a portion of the coke particles separated from the effluent from the transfer line reactor.  Heavy fractions separated from the products may be recycled to the coker or to an auxiliary coker at a higher temperature; in the latter case the vapours from the auxiliary coker may be introduced into the primary coker.ALSO:<PICT:0810808/IV (b)/1> In a process for the thermal cracking of hydrocarbons, hot catalytically-inert solid particles, preferably coke, are circulated through two reaction zones and a heating zone; a heavy hydrocarbon oil is cracked in one of the reaction zones at a temperature between 850 and 1200 DEG  F. whereby motor fuels and coke are formed, and another hydrocarbon feed such as light hydrocarbons or gas oil or heavy ends separated from the products of the first reaction zone is cracked in the second reaction zone at a temperature between 1200 DEG  and 1800 DEG  F. whereby unsaturated hydrocarbons such as ethylene and propylene are produced. The products from the reactor at higher temperature may be introduced into the reactor at lower temperature whereby the high-temperature products are quickly quenched to prevent further degradation; alternatively relatively cool solids withdrawn from the reactor at lower temperature may be used to quench the hightemperature products. The apparatus shown comprises a coking reactor 20, a transfer line 10 for the high-temperature thermal cracking, and a transfer line burner 91.  A bed of petroleum coke particles (average particle size 250 microns), at a temperature of 950 DEG  F., is maintained in a fluidized state in reactor 20 by steam introduced through line 16.  A vacuum residuum, boiling above 850 DEG  F., is preheated and then introduced into the fluidized bed via line 17.  The product vapours are discharged via cyclone, and scrubbed in tower 30 to remove heavy ends.  These heavy ends are introduced via line 11 into the inlet of transfer line 10 where admixture takes place with freshly-heated coke particles at 1400 DEG  F. supplied through line 8; the suspension rises rapidly up the transfer line (the average vapour residence time being 0.5 seconds), and is discharged via line 13a into coker 20. Coke is removed from the base of the coker via standpipe 22, and is transferred through line 21 to transfer line burner 91 where it is heated to 1400 DEG  F. by partial combustion in air, supplied through line 93.  The reheated coke particles are separated from the flue gases in cyclone 94, and recycled to the two reactors via lines 96 and 8.  Excess coke is withdrawn from the system via line 97, the amount being about 20 per cent by weight of the feed.  The vapours and gases leaving scrubber 30 are subjected to fractionation to obtain ethylene, propylene, naphtha, heating oil and gas oil.  The material boiling in the range of about 650-900 DEG  F. may be used as catalytic feedstock, in which case the cycle oil from the cat. cracker makes suitable feedstock for transfer line 10.  In an alternative mode of operation, the effluent from transfer line 10 is passed to cyclone 14 while being quenched with relatively cool coke particles withdrawn from the coker via line 7.  The unsaturated hydrocarbons are then withdrawn from the top of cyclone 14.  The coke withdrawn from the base of the cyclone is passed to the transfer line burner 91, but a portion may be recycled to the coker.  In another alternative, the effluent from the transfer line reactor is introduced into the dilute phase above the fluid bed in the coker so that the coker effluent will be heated; this prevents fouling of the vapour-phase equipment due to polymerization and condensation reactions.  The heat in the flue gases discharged from the transfer line burner may be recovered by direct contact with a portion of the coke particles separated from the effluent from the transfer line reactor.  Heavy fractions separated from the products may be recycled to the coker or to an auxiliary coker at a higher temperature; in the latter case the vapours from the auxiliary coke may be introduced into the primary coker.