GB724213A - Improvements in or relating to the cracking of heavy hydrocarbon oils - Google Patents

Abstract

In a process for the thermal cracking of a heavy residual petroleum oil or a heavy reduced crude petroleum oil in the presence of a hot fluidized bed of inert solid particles, the heavy oil is distributed onto the particles without causing <PICT:0724213/III/1> particle-agglomeration by mixing the heavy oil, before it is fed to the fluidized bed, with a low boiling liquid, such as water or a light hydrocarbon fraction, which evaporates suddenly on entering the hot conversion zone and thereby atomizes the heavy oil evenly over particles of the bed. The mixture of oil and low boiling liquid is preferably preheated under pressure before being introduced into the conversion zone. Finely divided solids suitable for use are coke, pumice, Kieselguhr, clay, sand, alumina, carborundum, spent clay catalysts, and previously used silica/alumina synthetic catalysts. In a preferred embodiment, a water-in-oil type emulsion is sprayed into the bed of hot particles. Emulsions suitable for the purpose may be produced by high-velocity or jet mixing, particularly in the presence of emulsifiers such as alkyl, alkaline earth or aluminium derivatives of fatty acids, rosin acids, naphthenic acids and sulphite liquors, or of even those acid constituents present in the residuum feed itself or after air blowing, to form water-in-oil emulsions containing about 5 to 35 per cent of water. Organic sulphonates, lecithin, and sodium lauryl sulphate are also referred to as emulsifying agents. Preheat temperatures between 500 DEG and 700 DEG F. at pressures of 700-3500 p.s.i.g. are suitable; the emulsion is then sprayed through nozzles into the bed of particles which is maintained at 800 DEG -1400 DEG F. and about atmospheric pressure. Suitable hydrocarbon fractions are light naphtha, heavy naphtha and relatively low boiling fractions separated from the cracked products. The proportion of the hydrocarbon fractions to be added to the heavy oil is about 2 to 6 per cent, but a smaller proportion (0.2 to 2 per cent) is required when water is also present. Residual oil having an initial boiling point of 1100 DEG F. is pumped into the plant through line 10, and is mixed therein with 5 per cent of naphtha (B.R. 250 DEG -400 DEG F.) which is pumped in through line 14. The mixture is heated to 750 DEG F. under a pressure of 250 p.s.i.g. in preheater 28; and is then sprayed through nozzle 30 into a dense fluidized bed 22 of coke particles (100-400 mesh) in reactor 18. The particles are maintained in the fluidized state by steam introduced through line 34 and grid 32; the temperature of the particles is 950 DEG F. and the pressure is atmospheric. A feed rate of 3 pounds of residual oil per hour per pound of solids within reactor 18 may be obtained without agglomeration of the particles. Vaporous cracked products are withdrawn from the reactor via cyclone separator 36 and line 42, and are submitted to fractionation. The bottoms from the fractionation step may be recycled to the reactor via line 10. Coke particles are continually withdrawn from reactor 18 through well 44, wherein they are stripped of volatile hydrocarbons by gas introduced through line 46. The stripped particles pass down standpipe 48, and are then transported by air, introduced through line 56, into heater 31 via line 54. The particles are maintained as a dense fluidized bed in the heater. Some of the coke is burned off the particles in the heater, and they are thereby raised to a temperature 50 DEG to 200 DEG F. higher than that maintained in reactor 18. The heated particles are withdrawn from heater 31 through well 76; and are returned to the heater 18 via standpipe 78 and line 34. Coke required as product is withdrawn from the reactor through line 92. Instead of using preheater 28, the feed may be preheated by passing it through a coil disposed in the dense bed of either reactor 18 or heater 31.