Method for high efficiency for producing fuel gas for power generation

Abstract

A method is provided for operating a coal gasifier, preferably an oxygen-blown two zone-coal gasifier, without the need for the addition of water and producing a high LHV-content coal product fuel gas from coal. A first supply of coal, preferably dry coal, first supply of carbon dioxide, and a supply of oxygen are passed into a high pressure combustion vessel wherein the coal reacts with the oxygen and carbon dioxide to form an exothermic zone producing a combustion temperature in excess of the melting point of the ash in the coal. This in turn produces a melted ash and a combustion product gas comprising carbon monoxide. The melted ash is drained or otherwise removed for disposal and the combustion product gas subsequently is passed into an entrained flow reaction vessel. A second supply of dry coal and a second supply of carbon dioxide are injected into the entrained flow reaction vessel wherein the coal thermally reacts with the combustion product gas and the carbon dioxide and produces a product fuel gas. The resultant product fuel gas comprises more moles of carbon monoxide than moles of carbon in the first and second supplies of coal. The product fuel gas may exhibit a gas exit temperature at a value below the melting point of the coal ash but no lower than about 1400° Kelvin, and it may be passed to a turbine having closed loop internal cooling thereby recovering energy and lowering the product gas pressure and temperature prior to potential heat exchange with incoming gasifier feed gases.

1 . A method of operating a coal gasifier comprising:
 a) injecting a first supply of dry coal and a first supply of carbon dioxide into a high pressure combustion vessel;   b) passing to the vessel a supply of oxygen;   c) reacting the first supply of dry coal with the oxygen and the first supply of carbon dioxide to form an exothermic zone producing a combustion temperature in excess of the melting point of ash in the coal;   d) producing melted ash and a combustion product gas comprising carbon monoxide;   e) removing melted ash for disposal;   f) passing the combustion product gas into an entrained flow reaction vessel;   g) injecting a second supply of dry coal and a second supply of carbon dioxide into the entrained flow reaction vessel;   h) thermally reacting the second supply of dry coal with the combustion product gas and the second supply of carbon dioxide; and   i) producing a product fuel gas comprising more moles of carbon monoxide than moles of carbon in the first and second supplies of coal.   
     
     
         2 . The method of  claim 1  wherein the steps of thermally reacting the second supply of coal with the combustion product gas and the second supply of carbon dioxide and producing product fuel gas further comprises:
 a) producing coal ash and other particulates;   b) separating the product fuel gas from the coal ash and other particulates; and   c) passing the separated coal ash and other particulates to the combustion vessel.   
     
     
         3 . The method of  claim 2  wherein the separated product fuel gas is expanded in a turbine. 
     
     
         4 . The method of  claim 3  wherein the turbine delivers an exhaust gas at a pressure greater than about twenty atmospheres. 
     
     
         5 . The method of  claim 3  wherein the turbine delivers an exhaust gas and the exhaust is further cooled by heat exchange with the supply of oxygen, the first supply of carbon dioxide, and/or the second supply of carbon dioxide. 
     
     
         6 . The method of  claim 1  wherein the product fuel gas is fed to a fuel cell. 
     
     
         7 . The method of  claim 1  wherein the product fuel gas is fed to a gas turbine. 
     
     
         8 . The method of  claim 7  wherein an exhaust produced by the gas turbine is fed to a heat recovery boiler. 
     
     
         9 . A method of operating a gasifier comprising:
 a) injecting a first supply of coal and first supply of carbon dioxide into a pressure vessel at a pressure of at least forty atmospheres;   b) passing a supply of oxygen to the vessel for combustion of the coal;   c) reacting the first supply of coal with the oxygen and the first supply of carbon dioxide to form an exothermic zone producing a combustion temperature in excess of the melting point of ash in the coal;   d) producing melted ash and a combustion product gas comprising carbon monoxide;   e) removing melted ash for disposal;   f) passing the combustion product gas into an entrained flow reactor;   g) injecting a second supply of coal and a second supply of carbon dioxide into the entrained flow reactor;   h) thermally reacting the second supply of coal with the combustion product gas and the second supply of carbon dioxide;   i) producing a product fuel gas comprising more moles of carbon monoxide than moles of carbon in the first and second supplies of coal, and having a gas exit temperature at a value below the melting point of the coal ash but no lower than about 1400 Kelvin; and   j) passing the product fuel gas to a turbine having closed loop internal cooling thereby recovering energy and lowering the product fuel gas pressure and temperature prior to heat exchange with incoming gasifier feed gases.   
     
     
         10 . The method of  claim 9  wherein the pressure is at least 100 atm. 
     
     
         11 . The method of operating a coal gasifier comprising:
 a) passing a supply of coal to a gasifier operating at a pressure in excess if forty atmospheres;   b) reacting the coal with an oxidant gas to produce a product fuel gas comprising carbon monoxide at temperature of at least about 1400° Kelvin but below the melting temperature of the coal ash;   c) separating particulate solids from the product fuel gas; and   d) passing the fuel gas to a turbine having closed loop internal cooling thereby recovering energy and lowering the product fuel gas pressure and temperature prior to heat exchange with coolant fluids.