Patent GB-499839-A (GB)
Title: Improved process of cracking hydrocarbon oils
IPC: C10G9/00
Filed: 1937-07-30
Abstract: <PICT:0499839/III/1> <PICT:0499839/III/2> <PICT:0499839/III/3> In a process of the kind in which oils are cracked in admixture with normally gaseous hydrocarbon containing 3 to 4 carbon atoms in the molecule, the oils containing at least 15 per cent of such gaseous hydrocarbons on a liquid-volume basis are cracked at temperatures from 20-300 DEG  F. higher than the oil could be subjected to without the presence of the gaseous hydrocarbons, which are preferably present in such quantity that the critical temperature of the mixture is below the temperature to which oil is subjected in the conversion zone.  The gaseous hydrocarbons are preferably obtained from the gases produced in the cracking reaction by scrubbing these gases with the oil to be cracked.  In a single-stage straight-through process applied to cracking and reforming naphtha, the naphtha is fed through line 8 into an absorption tower 5 to which the gases produced in the process are fed through line 37 and cooler 38.  The gases containing 3 to 4 carbon atoms are absorbed by the naphtha while hydrogen, methane, ethane, and ethylene are rejected through line 10.  The enriched naphtha is collected in a tank 13 to which part of the charge may be fed direct, and is cracked in the system comprising cracking furnace 1, evaporator 2, fractionator 3 and condenser-stabilizer 4, the stabilized naphtha being recovered through line 36.  With a recycle ratio (ratio of total charging stock to liquid charging stock) of between 2/1 and 3/1 , the reforming temperature for different ranges of naphtha may be raised from 950-1150 DEG  F. to 975-1450 DEG  F., temperatures of 1030-1050 DEG F. being preferably used.  In a plant for treating a heavier gas-oil stock, Fig. 2, the latter is fed as absorption medium to the tower 55 and thus enriched with gaseous hydrocarbons is cracked in coils 70 of furnace 50 while a recycle stock, collected at the bottom of the fractionating tower 53, is mixed with the required proportion of gaseous hydrocarbons collected in a receiver 83 and the mixture is recracked in the coils 92 of a furnace 51.  The products of both stages, after quenching with cool oil supplied through lines 72, 73, 93, are passed into the evaporator 52.  In a further modification for treating a still heavirr stock, the recycle stock collected in the tower 53 is used as absorption medium for the gaseous hydrocarbons, and the enriched oil is cracked in the second cracking coil 92 while the crude oil, together with a clean condensate, is collected on a tray in the evaporator 52 and, after admixture with gaseous hydrocarbons, is cracked in the first cracking coil 70.  In treating a crude petroleum oil, Fig. 4, the latter preheated to 700 DEG  F. is fractionated in a tower 200 into gasoline, naphtha, gas oil, and reduced crude fractions, recovered through lines 215, 214, 213 212 respectively.  The naphtha fraction is used as absorption medium in tower 210 for the gaseous hydrocarbons, while the gas oil, reduced crude, and part of a recycle stock collected at the bottom of tower 207, are mixed with gaseous hydrocarbons removed from a cooler 209 and fed through line 276.  The four fractions containing gaseous hydrocarbons thus obtained are cracked in separate coils 202-205 in furnace 201 and passed into the evaporator 206 where they are quenched with the remainder of the condensate from tower 207.