GB418547A - Improvements relating to the cracking of hydrocarbon oils - Google Patents

Abstract

<PICT:0418547/III/1> Oils are cracked by subjecting them to high cracking temperatures e.g. from 850 DEG F. upwards under pressures of 500--2000 lbs. in a coil 2 and reaction chamber 6 so that 35 per cent of the oil is cracked in a single pass and the resulting cracked products are separated in an evaporator 8 into a liquid heavytar and vapours which are fractionated in a tower 10 into a light final distillate and an intermediate condensate which is then cracked in the vapour phase with a relatively low degree of cracking per pass. This condensate is led through a pipe 20, and if desired through a cooler 20<a>, to the upper end of a chamber 21 where it is vaporized by hot vapours from a cracking coil 41. Alternatively the condensate may be led directly through a pipe 96 to mix with the cracked vapours in a pipe 47 and the mixed vapours are fractionated in an evaporator 28 from which vapours are led overhead through a pipe 24 to a final fractionator 25, vapours from which are condensed in a cooler 36 separated from gases in a chamber 37 and finally mixed with the final distillate from the tower 10 collected in a separator 19. The condensate collecting in the tower 25 is led through a pipe 39 to a vapour phase cracking coil 41 and the cracked vapours are passed into the reaction chamber 21 or directly through the pipe 47 into the evaporator 28. Residues collecting in the towers 8, 28 are passed with reduction of pressure into flash drums 12, 26 the distillates obtained being recirculated to the line 20 and the evaporator 28 or reaction drum 21 respectively. In a modification, a single tower is employed for fractionating the vapours from both the primary and secondary cracking operations, the coils for which are arranged in a single furnace, while the tar residues from the evaporating zones are combined and flashed in a single evaporator. Specification 409,875 is referred to.