GB764203A - Improved coking processes - Google Patents

Abstract

In a process of cracking heavy hydrocarbon oils wherein the oil is contacted with hot particles of inert solid maintained in a fluidized state and wherein particles having a carbonaceous deposit are continuously withdrawn from the reactor for reheating; some of these withdrawn particles are conveyed by oxygen-containing gas through a transfer line burner wherein the particles are heated by combustion, the stream of hot particles and combustion gases is mixed at the end of the transfer line with the remainder of the particles withdrawn from the reactor, or alternatively, the stream discharged from the transfer line is subjected to gas/solids separation <PICT:0764203/III/1> <PICT:0764203/III/2> and the separated combustion gases are then mixed with the remainder of the particles withdrawn from the reactor. In either case the hot particles separated from the combustion gases are in part returned to the reactor and in part introduced into the inlet of the transfer line. In this way the working temperature of the burner is increased, but without additional heat losses. The invention is particularly applicable to a process wherein residual petroleum oils are converted into lighter oils, such as gas oil, and coke by contacting the residual oil with a fluidized bed of hot particles of coke. A mixture of a fresh vacuum residuum and a recycle bottoms fraction from the product fractionator is injected by nozzle 5 (Fig. 1) into vessel 3 which contains a bed of coke particles at 900 DEG -1000 DEG F. maintained in a fluidized state by steam introduced through line 16. The cracked vapours are withdrawn, via an adsorptive coke-bed and cyclone 6, to the product fractionator. Product coke is removed from vessel 3 though line 9. A portion of the fluidized bed is continuously withdrawn though line 11 and transferred, by steam introduced through lines 18, into the discharge end of transfer line burner 20. The mixture of spent particles combusted particles and flue gases flows into cyclone 24. The coke particles withdrawn from cyclone 24 are at a temperature of about 1300 DEG F.; and portion of these hot particles are introduced into vessel 3 through line 12, and the remaining particles are transferred through line 15 to the inlet end of transfer line burner 20. Combustion air is supplied to this burner through line 21. The average temperature attained in the burner is 1330 DEG F. In Fig. 3 the combustion zone 71a of the burner is separated from a recycle passageway 70a by baffle 69a. The particles to be subjected to combustion are carried along the combustion zone by air introduced through line 66a. A preliminary separation of hot particles from combustion gases takes place in vessel 78; and those particles to be returned to the coker (not shown) are taken off through line 72a. The particles to be recycled to the combustion zone pass along passageway 70a, aerating gas being admitted through lines 80. The hot flue gases, containing a minor amount of entrained particles, pass overhead through line 68a into which the relatively cool particles from the coker are introduced via line 57a. The quench mixture is separated in cyclone 73a, from which the particles flow down through line 75a to the burner. A burner is also described which incorporates helical baffles for achieving gas/solids separation. As an aid to temperature-control, a minor proportion of the relatively cool particles, withdrawn from the reactor, may be introduced at one or more points along the combustion zone.