Patent GB-789228-A (GB)
Title: Improvements in or relating to thermal cracking processes and plant therefor
IPC: C10G9/32
Filed: 1954-11-29
Abstract: Gaseous or liquid alkenes are obtained from paraffin-containing mixtures of higher hydrocarbons (containing not more than 25 per cent by weight of aromatic hydrocarbons) by contacting the mixture with hot, finely-divided, inert solid (e.g. sand, alumina or ground pumice-stone) in a tubular reactor, while the hot solid particles are carried up the reactor in the form of a dilute suspension in a gaseous fluidizing agent, such as steam; the suspension is discharged into a gas/solids separation zone, and the rate of flow through the reactor is regulated by the injection of the fluidizing agent into the lower part thereof so that the contact time between the hydrocarbon mixture and the hot particles does not exceed 2 seconds. The cracking temperature should be between 750 DEG  and 850 DEG  C. with a contact time between 0.1 and 1.0 second when ethylene is to be produced.  When mainly liquid alkenes are required, the cracking temperature is between 550 DEG  and 650 DEG  C., and the contact time is between 0.5 and 1.5 seconds.  The hot reaction products, separated from the solid particles, are preferably quenched, e.g. by injection of cold water, to 350-450 DEG  C., in order to prevent undesirable coke formation.  Examples of suitable starting materials are mineral oil distillates and residues, paraffin wax obtained by dewaxing lubricating oils, and raffinates obtained by solvent-extraction of heavy cycle oil obtained in the catalytic cracking of hydrocarbon oils.  In an example, a paraffinous oil residue boiling above 500 DEG C. was thermally cracked using sand at 800 DEG  C. The feed rates of the oil residue, which was preheated to about 100 DEG  C., and of the hot sand to the lower part of the vertical tubular reactor (see Group III) were so adjusted that the temperature of the mixture of sand and vapour issuing from the top of the reactor into the separator was approximately 700 DEG  C., and the contact time was approximately 0.4 seconds.  The product separated from the sand contained 70 per cent of components boiling below 30 DEG  C.  An ethene-ethane fraction containing about 90 per cent ethene was separated from the product by fractional distillation.  Propene and butene fractions were also obtained.ALSO:<PICT:0789228/III/1> A mixture of higher hydrocarbons containing not more than 25 per cent by weight of aromatics is cracked by contact with hot, finely-divided, inert solid (e.g. sand, alumina or ground pumice-stone) in a tubular reactor, while the hot solid particles are carried up the reaction zone in the form of a dilute suspension in a gaseous fluidizing agent, such as steam; the suspension is discharged into gas/solids separation zone, and the rate of flow through the reaction zone is regulated by the injection of the fluidizing agent into the lower part thereof so that the contact time between the hydrocarbon mixture and the hot particles does not exceed 2 seconds.  The cracking temperature should be between 750 DEG  and 850 DEG  C. with a contact time between 0.1 and 1.0 second when mainly ethylene is to be produced.  When mainly liquid alkenes are required, the cracking temperature is between 550 DEG  and 650 DEG  C. and the contact time is between 0.5 and 1.5 seconds.  Gasoline and higher boiling fractions suitable as motor fuels can also be produced.  The hot reaction products, separated from the solid particles, are preferably quenched, e.g. by injection of cold water, to 350-450 DEG  C. in order to prevent undesirable coke formation.  Examples of suitable starting materials are mineral oil distillates and residues, paraffin wax obtained by dewaxing lubricating oils, and raffinates obtained by solvent-extraction of heavy cycle oil obtained in the catalytic cracking of hydrocarbon oils.  The plant shown comprises a reactor 1 provided with a riser 2, and a heater 7 provided with a riser 8 at the bottom of which is a burner 9.  An auxiliary chamber 19 surrounds the lower part of riser 2 and is in communication therewith through openings 20.  The lower part of riser 8 is surrounded by an auxiliary chamber 16 and is in communication therewith through openings 17.  Fuel fed through line 21 is burned in burner 9 with air fed under pressure through line 22. Sand, or other finely-divided heat-transfer agent, is fed at such a rate from chamber 16 via openings 17 into the hot combustion gases flowing upward through riser 8 that it becomes heated to the required temperature.  Most of the solid particles are separated from the hot combustion gases by means of baffle plate 23 disposed above riser 8; and these solid particles fall into the fluidized bed maintained at the bottom of heater 7 by means of steam admitted through annular distributer 24.  The combustion gases discharged from the top of the heater pass through separator 11 to chimney 13.  Any solid particles separated from the gases in separator 11 are led back through line 12 to the fluidized bed maintained at the bottom of heater 7.  The hot particles flow from the fluidized bed in heater 7 through line 18 to chamber 19, and then pass through openings 20 into riser 2.  Steam is injected into chambers 16 and 19 through distributers 30 and 31 in order to keep the solid particles therein in a fluidized state.  The hot particles are carried up riser 2 by steam admitted through line 25.  The hydrocarbon material to be cracked is fed, in a preheated state, through line 26 into riser 2 in which it immediately evaporates on contacting the ascending hot particles, and is ver rapidly raised to the cracking temperature.  Most of the solid particles are separated from the suspension, leaving the top of riser 2, by means of baffle 27, and the separated particles fall back into a fluidized bed thereof which is maintained in the lower part of reactor 1 by means of steam introduced through distributer 28.  The gaseous reaction products rising in reactor 1 are rapidly cooled by water injected through nozzles 29.  The cooled gases then flow through cyclone 4, and are discharged through line 5 to a product recovery plant (not shown). The solid particles are recycled continuously from the bottom of the fluidized bed at the bottom of the reactor, via line 15, to chamber 16.  The steam introduced through distributers 24 and 28 not only maintains the particles in the heater and the reactor in a fluidized state, but prevents combustion gases from entering riser 2 from the heater, and also prevents the reaction products from entering riser 8 from the reactor.  By regulating the supply of steam through distributers 30 and 31, the rate at which the solid particles enter the risers 8 and 2 can be effectively regulated.  The risers and cyclone 4 are made of a steel alloy which is able to withstand high temperatures and erosion.