Patent GB-752400-A (GB)
Title: Improvements in or relating to fluid coking of heavy hydrocarbons and apparatus therefor
IPC: C10G9/32
Filed: 1954-05-20
Abstract: <PICT:0752400/III/1> Hydrocarbons such as coal tars, shale oils, pitches, asphalts, whole petroleum crudes and distillate and residual fractions therefrom are coked in contact with hot fluidized solids by injecting a number of preferably preheated streams 5 into a retort 3, circulating the solids through a heater 48 and back to maintain a temperature of 900 DEG -1200 DEG F., passing steam and gases up the retort at a velocity to maintain a dense turbulent fluidized bed, the residence time of the oil, &c., being sufficient to convert it into vapours and coke, separating and returning at least part to the retort high boiling constituents from the vapours and withdrawing excess coke. The feed is distributed quickly over the bed by dispersion as by steam through nozzles 6 at a multiplicity of circumferentially and vertically spaced points, the retort walls flaring upwardly so that the gas velocity may be kept uniform despite the increase in volume.  The average particle size ranges between 150 and 300 microns.  Pressures above or below atmospheric may be employed.  Steam or light hydrocarbon gases may be introduced at high velocity through a bottom line 11 to strip the coke of oil and cause attrition of the larger particles.  Above the bed surface 12 the retort is narrowed to increase vapour velocity and entrain coke; additional hotter coke may also be introduced to increase the scouring action and raise the vapour temperature above dew point. The amount of solids separated by cyclones 14 may be controlled by varying the inlet of gas introduced into their dip legs 15.  Vapours pass into a scrubbing and fractionating tower 18, heavy condensates at the base passing in part through a cooler 26 before return to the tower above baffles 27 and in part to the bottom of the retort. Temperature at the base of tower 18 is controlled by the cooled condensate so that the heaviest portions of the vapours which contain iron, nickel and vanadium compounds are collected.  Fresh feed may be introduced instead of recycled condensate.  From the upper fractionating section some condensate may be returned to the scrubbing section and another portion cooled and used as reflux; the remainder withdrawn constitutes a gas oil which may be cracked to form gasoline.  From the vapours passing through a condenser 37 to a separating drum 38 a naphtha fraction and water are removed from the gas remaining.  Solids are continuously withdrawn from the bottom of the retort through a standpipe 43 leading through an inclined pipe 45 to which fluidizing gas is introduced at points 49 to a riser 47 opening into the burner vessel 48.  Combustion air is supplied through an inlet 52 and fuel for starting up through a line 54. Subsequently some of the coke is burnt or extraneous fuels continue to be supplied, a dense turbulent bed 56 is maintained and the coke heated to 1000 DEG -1500 DEG F. overflows into a return standpipe 57, returning to the retort through pipes 63, 64, desirably as shown both below and above the level of the bed.  Circulation between retort and burner vessel is effected by maintaining the density in pipes 47, 64 less than that in pipes 43, 57.  Excess coke is withdrawn by steam, &., to storage through a pipe 70 connected with the bottom of the standpipes, and larger pieces are periodically extracted from the retort through a conduit 50.  To keep the solids down to the optimum particle size by a continuous replacement of coarser by finer particles solids withdrawn from the retort may be classified and a coarser fraction passed to the burner or ground and returned.  For this purpose an elutriator vessel containing, e.g. perforated baffles or coarse packing may be located below the retort to receive part or all of the coke for contact with a rising stream of gas which carries the fines back to the retort. Coarser solids may be divided into three streams, one being passed to storage, one recirculated through the burner vessel or other heater and one preferably after cooling passed through a grinder for return to the elutriator.