Gasification of sulfur-containing carbonaceous fuels

Abstract

A process for converting sulfur-containing carbonaceous fuel into a combustible product gas is described. The fuel, in the form of fine particles, is mixed with a first aqueous solution containing dissolved alkali metal carbonate at approximately atmospheric pressure to form concentrated slurry. The slurry is pressurized and fed into a gasifier operating at an elevated pressure. An oxygen-containing gas is also fed into the gasifier where it reacts with the fuel to produce hydrogen and carbon monoxide-containing gases and heat the reacting mixture to about 900-1400° C. Oxygen combined with steam may also be used as the oxidizer to produce hydrogen-rich product gas. Alkali metal salts in the slurry are melted and absorb sulfur from the reacting fuel to form a liquid smelt containing alkali metal sulfide. The smelt is dissolved in water to form a second aqueous solution which is regenerated by converting dissolved alkali metal sulfide into dissolved alkali metal carbonate and hydrogen sulfide gas which is released from the solution. The regenerated solution is recycled as the principal ingredient of the first aqueous solution. The hydrogen and carbon monoxide-containing gases are cooled, separated and purified to produce combustible product gases.

What is claimed is: 
     
         1 . A process for converting a sulfur-containing carbonaceous fuel into a combustible product gas having a higher heating value of at least 100 Btu/scf, dry basis, by reaction with oxygen in the presence of a molten alkali metal salt comprising steps of:
 (a) Mixing particles of said fuel with a first solution containing about 5% to 35% by weight alkali metal carbonate, at approximately atmospheric pressure to form slurry containing about 25% to 75% by weight un-dissolved fuel particles;   (b) Pressurizing and feeding said slurry into a gasifier operating at an elevated pressure in the range of 4 to 50 atmospheres, said gasifier containing a drying zone and a gasification zone;   (c) Feeding pressurized oxygen-containing gas into said gasifier;   (d) Drying said slurry in said drying zone and gasifying the resulting dried mixture of fuel and salts by reaction with said oxygen at a temperature in the range of about 900 to 1400° C. in said gasification zone to produce a gasifier off-gas, containing carbon monoxide and water vapor, and a hot liquid smelt containing molten alkali metal sulfide;   (e) Draining said smelt into a quench tank operating at essentially the same pressure as the gasifier, and dissolving it in an aqueous medium to form a second solution containing 5% to 35% by weight, alkali metal salts including alkali metal sulfide;   (f) Recovering said gasifier off-gas as said combustible product gas;   (g) Reducing the pressure on said second solution and regenerating it by converting said alkali metal sulfide to alkali metal carbonate in said solution and hydrogen sulfide gas which is released from solution; and   (h) Utilizing the depressurized and regenerated second solution as the principal ingredient of said first solution.   
     
     
         2 . The process of  claim 1  wherein said alkali metal is sodium. 
     
     
         3 . The process of  claim 1  wherein said alkali metal is potassium. 
     
     
         4 . The process of  claim 1  wherein said oxygen-containing gas is air. 
     
     
         5 . The process of  claim 1  wherein said oxygen-containing gas is a mixture of oxygen and steam. 
     
     
         6 . The process of  claim 1  wherein said sulfur-containing carbonaceous fuel is petroleum coke. 
     
     
         7 . The process of  claim 1  wherein the amount of oxygen fed into the gasification zone is less than about 60% of the amount needed for complete combustion of the fuel. 
     
     
         8 . The process of  claim 1  wherein step (g) includes the removal of ash components from said second solution. 
     
     
         9 . The process of  claim 1  wherein step (g) includes contacting said second solution with a carbon dioxide-containing gas to form alkali metal bi-sulfide and bicarbonate in solution, depressurizing the solution, and stripping hydrogen sulfide gas from it to produce a stream of hydrogen sulfide-rich gas and a stream of depressurized and regenerated second solution. 
     
     
         10 . The process of  claim 1  wherein steps (f) and (g) include treating said gasifier off-gas by contacting it with said second solution at an elevated pressure, thereby purifying said combustible product gas and absorbing carbon dioxide into said second solution; depressurizing the carbonated second solution and-stripping hydrogen sulfide gas from it at a reduced pressure in the range of 0.1 to 2.0 atmospheres to produce a stream of hydrogen sulfide-rich gas and a stream of depressurized and regenerated second solution. 
     
     
         11 . The process of  claim 1  wherein step (g) includes contacting said second solution with a carbon dioxide-containing gas and absorbing sufficient carbon dioxide to convert alkali metal sulfide and bi-sulfide into alkali metal bicarbonate thereby displacing hydrogen sulfide gas from solution; and heating the resulting bicarbonate solution to produce a stream of carbon dioxide gas and a stream of depressurized and regenerated second solution. 
     
     
         12 . The process of  claim 1  wherein step (b) includes feeding said slurry into the drying zone of said gasifier in the form of a spray. 
     
     
         13 . The process of  claim 1  wherein step (c) includes feeding pressurized oxygen-containing gas into the gasification zone of said gasifier. 
     
     
         14 . The process of  claim 1  wherein step (d) includes discharging said gasifier off-gas from the drying zone of said gasifier.