GB594982A - Improvements relating to the high temperature cracking of hydrocarbons - Google Patents

Abstract

Thermal decomposition of normally gaseous hydrocarbons such as methane to give hydrogen and/or highly unsaturated hydrocarbons such as acetylene or ethylene is effected at above 1800 DEG F. in a reaction zone containing a finely-divided refractory solid, a stream of which is continuously withdrawn, passed to a zone where it is heated materially above the reaction zone temperature and recycled to the reaction zone, the rate of flow of the solid through the system being such as to maintain the temperature in the reaction zone substantially constant. The refractory solid may be inert, e.g., carborundum, brick dust, sand, silica, metal and alloy powders, or may comprise a dehydrogenation catalyst, e.g., metals of Group 8. The heating is effected by combustion of the carbon carried out of the reaction zone or other combustible material injected into the heating zone. Methane, preheated to 500-1000 DEG F., is fed by line 10 to conduit 11 into which heated powder is fed from conduit 121 through valve 13. The amount and temperature of the powder is sufficient to give a reaction temperature of, for example, 1800-2600 DEG F. The suspension passes to reactor 12 and, for reactions not requiring a short contact time, the gas velocity is sufficiently low to give a dense layer of powder above the grid 131, the depth of said layer being controlled to give the required contact time. Products pass through a separator 14 and washer 19 to remove entrained powder which is returned by conduits 15, 20. Powder is withdrawn from reactor 12 by conduit 23, into which steam, hydrogen, methane or other gas may be introduced by lines 25, 26 to strip volatile hydrocarbons, and is fed in a stream of air through line 29 to a carbon burner 31 constructed similar to reactor 12 wherein a dense layer of powder forms above grid 32. The hot powder discharges into conduit 121 into which the feed or other gas may be introduced, as at 34, to maintain fluidity. Combustion products are treated to <PICT:0594982/III/1> remove powder and leave by line 37. Where excess heat is produced, part of the powder may be taken by a conduit 42 to line 44 through which a stream of air passes and carries the powder through a suitable heat exchanger 45 before return to the burner 31. For production of acetylene, short contact times followed by rapid quenching are required. The conduit 11 may form the reaction zone, and reactor 12 a quenching zone. A dense layer of powder at 1000 DEG F. or below on the grid 131 is continuously withdrawn through conduit 51, and carried by an air stream through cooler 54 before return. Aerating lines 56-58 are provided. In a modification, Fig. 2 (not shown), the enlarged reaction or quenching zone 12 is omitted and reaction is effected in a vertical conduit discharging into a separator for rapid removal of the powder. This is discharged into a standpipe with aerating means for forming a suspension and conveyance to the burner. Products leaving the separator are treated by injecting a quenching material. The carbon burner has internal cooling tubes for removing excess heat from the powder. Specifications 568,913 and 582,624 are referred to.ALSO:Thermal decomposition of normally gaseous hydrocarbons such as methane to give hydrogen and/or highly unsaturated hydrocarbons such as acetylene or ethylene is effected at above 1800 DEG F. in a reaction zone containing a finely-divided refractory solid, a stream of which is continuously withdrawn, passed to a zone where it is heated materially above the reaction zone temperature, and recycled to the reaction <PICT:0594982/IV/1> zone, the rate of flow of the solid through the system being such as to maintain the temperature in the reaction zone substantially constant. The refractory solid may be inert, e.g. carborundum, brick dust, sand, silica, metal and alloy powders, or may comprise a dehydrogenation catalyst, e.g. metals of Group 8. The heating is effected by combustion of the carbon carried out of the reaction zone or other combustible material injected into the heating zone. Methane, preheated to 500-1000 DEG F., is fed by line 10 to conduit 11 into which heated powder is fed from conduit 121 through valve 13. The amount and temperature of the powder is sufficient to give a reaction temperature of, for example, 1800-2600 DEG F. The suspension passes to reactor 12 and, for reactions not requiring a short contact time, the gas velocity is sufficiently low to give a dense layer of powder above the grid 131, the depth of said layer being controlled to give the required contact time. Products pass through a separator 14 and washer 19 to remove entrained powder which is returned by conduits 15, 20. Powder is withdrawn from reactor 12 by conduit 23, into which steam, hydrogen, methane or other gas may be introduced by lines 25, 26 to strip volatile hydrocarbons and is fed in a stream of air through line 29 to a carbon burner 31, constructed similar to reactor 12, wherein a dense layer of powder forms above grid 32. The hot powder discharges into conduit 121 into which the feed or other gas may be introduced, as at 34, to maintain fluidity. Combustion products are treated to remove powder and leave by line 37. Where excess heat is produced, part of the powder may be taken by a conduit 42 to line 44 through which a stream of air passes and carries the powder through a suitable heat-exchanger 45 before return to the burner 31. For production of acetylene, short contact times followed by rapid quenching are required. The conduit 11 may form the reaction zone, and reactor 12 a quenching zone. A dense layer of powder at 1000 DEG F. or below on the grid 131 is continuously withdrawn through conduit 51, and carried by an air stream through cooler 54 before return. Aerating lines 56-58 are provided. In a modification, Fig. 2 (not shown), the enlarged reaction or quenching zone 12 is omitted and reaction is effected in a vertical conduit discharging into a separator for rapid removal of the powder. This is discharged into a stand-pipe with aerating means for forming a suspension and conveyance to the burner. Products leaving the separator are treated by injecting a quenching material. The carbon burner has internal cooling tubes for removing excess heat from the powder. Specifications 568,913 and 582,624, [Group III], are referred to.