Thermally stable cocurrent gasification system and associated methods

Abstract

A method and apparatus, in one example, relates to a system and method for the generation of very low-tar, high-energy synthesis gas from a large variety of carbonaceous feedstock, including those with higher moisture levels than conventional gasifiers. The system comprises a gasification reactor wherein a portion of the energy of the output syngas of the reactor is used to heat the gasification zone of the reactor via an annular space surrounding the gasification zone of the gasifier, to maintain a temperature condition above 800° C. The maintenance of a long, quasi-uniform high-temperature gasification zone reduces the amount of input air or oxygen, reduces bridging within the gasifier, cracks pyrolysis oils, increases the conversion of char, minimizes heat losses from the bed, and converts moisture within the packed bed into a gasification medium. This results in a very low tar synthesis gas with less nitrogen dilution and higher energy content than conventional gasifiers. The reduction in bridging reduces operating costs.

1 . An apparatus for gasifying carbonaceous feedstock to produce a low-tar, high-energy synthesis gas, the apparatus comprising:
 a gasification reactor having a gasification zone; and   a space at least partially surrounding the gasification zone, wherein the gasification zone is maintained at a temperature above 800° C. by providing heat to the space.   
     
     
         2 . The apparatus of  claim 1 , wherein the space is an annular-shaped space. 
     
     
         3 . The apparatus of  claim 1 , wherein the heat provided to the space to maintain the temperature of the gasification zone is obtained from the chemical energy of the synthesis gas produced by the gasification reactor. 
     
     
         4 . The apparatus of  claim 1 , further comprising a combustor for converting chemical energy from the produced synthesis gas to thermal energy to heat the gasification zone of the gasification reactor. 
     
     
         5 . The apparatus of  claim 1 , further comprising a combustor for converting chemical energy from exhaust of a secondary energy converter to thermal energy to heat the gasification zone of the gasification reactor. 
     
     
         6 . The apparatus of  claim 1 , further comprising a high-temperature fuel cell disposed at least partially within the space surrounding the gasification zone of the gasification reactor, such that the endothermic heat of reaction of the gasification zone is at least partially balanced by the exothermic heat of reaction of the fuel cell. 
     
     
         7 . The apparatus of  claim 6 , wherein the fuel cell further comprises one or more fuel cell tubes at least partially disposed in the space surrounding the gasification zone. 
     
     
         8 . A method of gasifying carbonaceous feedstock to produce a low-tar, high-energy synthesis gas using a gasification reactor having a gasification zone, the method comprising:
 forming a space around the gasification zone; and   providing heat to the space to maintain a desired temperature in the gasification zone.   
     
     
         9 . The method of  claim 8 , wherein the space formed around the gasification zone is an annular-shaped space. 
     
     
         10 . The method of  claim 8 , wherein heat is provided to the space to maintain a temperature in the gasification zone above 800° C. 
     
     
         11 . The method of  claim 8 , further comprising using a combustor to convert chemical energy from synthesis gas to thermal energy to provide heat to the gasification reactor. 
     
     
         12 . The method of  claim 8 , further comprising using at least some of the synthesis gas to power a secondary energy converter. 
     
     
         13 . The method of  claim 12 , further comprising using a combustor to convert chemical energy from exhaust of the secondary energy converter to thermal energy to provide heat to the gasification reactor. 
     
     
         14 . The method of  claim 8 , further comprising using chemical energy from exhaust of a secondary energy converter to heat the gasification zone above 800° C. 
     
     
         15 . The method of  claim 8 , further comprising:
 integrating a high-temperature fuel cell with the gasification reactor;   using the synthesis gas to fuel the high-temperature fuel cell; and   using heat generated by the fuel cell to provide heat to the gasification zone.   
     
     
         16 . The method of  claim 15 , wherein the fuel cell includes one or more fuel cell tubes at least partially disposed in the space formed around the gasification zone. 
     
     
         17 . A method of reducing solid waste that is capable of generating toxic emissions in synthetic gas produced by a gasification reactor having a gasification zone, the method comprising:
 gasifying the solid waste in the gasification zone of the gasification reactor;   oxidizing synthetic gas produced by the gasification reactor using a combustor to decompose toxic emissions in the synthetic gas; and   using the combustor to convert chemical energy from synthesis gas to thermal energy to provide heat to the gasification reactor.   
     
     
         18 . The method of  claim 17 , wherein heat from exhaust of the gasification reactor is used by a secondary energy converter. 
     
     
         19 . The method of  claim 18 , wherein heat from exhaust of the gasification reactor is used to generate electricity.