GB830968A - Process for the production of coke and gaseous unsaturated hydrocarbons - Google Patents

Abstract

Coke and gaseous unsaturated hydrocarbons, particularly ethylene or acetylene, are produced from a heavy hydrocarbon charge by (1) heating to a temperature of 700-800 DEG F. but below the cracking temperature and introducing into a flash zone from which a bottoms fraction boiling in the heavy fuel oil range is withdrawn; (2) heating such bottoms to 900-950 DEG F. and introducing the heated bottoms, partly in the vapour phase, into a coking zone to crack the liquid mildly and form coke and additional vapours; (3) withdrawing vapours from the coking zone and introducing them into the flash zone of step (1) below the pre <PICT:0830968/IV (b)/1> heated charge whereby heavy constituents are condensed out; (4) withdrawing vapours, including gas, gasoline, gas oil and light ends from the charge, from the flash zone, mixing them with superheated steam and cracking them by contact with a thermally regenerated refractory mass at 1500-2200 DEG F. for a period of time of a fraction of a second to several seconds to produce an effluent containing a high percentage of gaseous unsaturated hydrocarbons; and (5) quenching the effluent and separating unsaturated hydrocarbons as product and withdrawing coke from the coking zone as product. Charge is heated in heater 11 and passed to flash tower 13 operated at 15-30 p.s.i.g. The bottoms are further heated and introduced into one or other of coking zones 17 and 17a operated at 20-35 p.s.i.g. Coke is removed by lines 19 and 19a. Vapours pass by line 21 to the flash tower from which overhead vapours pass to the furnace 23, usually one of a pair operating alternately and being alternately heated and used for cracking. There the vapours are cracked at 1500-1800 DEG F. and 1-2 atmospheres diluted with 0.5-2 times their weight of steam for 0.05-0.15 second to produce ethylene or 1800-2200 DEG F. and 1 atmosphere with 3-6 times their weight of steam or 0.5 atmosphere and 2.5-5 times their weight of steam for 0.02-0.08 second to form acetylene. The product vapours are partially quenched in the furnace and further in tower 31 then temporarily held in holder 35. After compression the vapours are contacted in absorber 38 with a side stream from flash tower 13 to remove C5+ hydrocarbons and aromatics, the bottoms from the absorber being returned to the flash tower as a reflux. The overhead is passed to acidic removal section 62, if desired acetylene is selectively hydrogenated at 64, and the vapours finally fractionated at 68.