Biomass gasification in atmospheres modified by flue gas

Abstract

Systems and methods are provided for generating energy from biomass. A gasifier is provided for generating syngas from the biomass. The gasifier comprises a housing for providing a first, oxygen starved environment in which the biomass is sub-stoichiometrically combusted to generate syngas—an effluent comprising gaseous combustibles. An oxidizer is connected to receive the syngas from the gasifier and configured to oxidize the syngas in a second environment distinct from the first, oxygen starved environment and to thereby generate heat energy. An oxidative agent supply mechanism introduces an oxidative agent to the first, oxygen starved environment in the gasifier housing, the oxidative agent comprising a mixture of flue gas and air.

1 . A system for generating energy from biomass, the system comprising:
 a gasifier comprising a housing for providing a first, oxygen starved, environment in which the biomass is sub-stoichiometrically combusted to generate syngas;   an oxidizer connected to receive syngas from the gasifier and configured to oxidize the syngas in a second environment distinct from the first, oxygen starved environment and to thereby generate heat energy;   an oxidative agent supply mechanism for introducing an oxidative agent to the first, oxygen starved, environment in the gasifier housing, the oxidative agent comprising flue gas.   
     
     
         2 . A system according to  claim 1  wherein the oxidative agent comprises a mixture of flue gas and air. 
     
     
         3 . A system according to  claim 2  wherein the flue gas comprises recirculated flue gas generated by the oxidation of syngas in the oxidizer. 
     
     
         4 . A system according to  claim 3  wherein the oxidative agent consists essentially of a mixture of flue gas and air. 
     
     
         5 . A system according to  claim 3  wherein the oxidative agent supply mechanism comprises an eductor connected to educe the flue gas from a conduit at a location downstream from the oxidizer and connected to a source of air, the eductor operative to mix the flue gas and the air to provide the oxidative agent. 
     
     
         6 . A system according to  claim 3  comprising an air supply mechanism connected to introduce air to the second environment of the oxidizer, the introduced air making the second environment an air-enriched environment. 
     
     
         7 . A system according to  claim 3  further comprising at least one heat exchanger located downstream of the oxidizer, through which the recirculated flue gas is directed prior to being introduced to the first, oxygen starved environment in the gasifier housing. 
     
     
         8 . A system according to  claim 3  further comprising at least one NO x  oxidizer located downstream of the oxidizer, and through which the recirculated flue gas is directed prior to being introduced to the first, oxygen starved environment in the gasifier housing. 
     
     
         9 . A system according to  claim 3  wherein the oxidative agent supply mechanism comprises a plurality of conduits arranged to deliver the oxidative agent into the biomass within the gasifier. 
     
     
         10 . A system according to  claim 9  wherein the housing of the gasifier comprises a side wall and the oxidative agent supply mechanism comprises a plurality of conduits for delivering the oxidative agent through the side walls of the gasifier. 
     
     
         11 . A system according to  claim 9  wherein the gasifier comprises a feed cone, the feed cone penetrated by a generally vertically oriented feed bore through which biomass may be introduced to the housing of the gasifier and wherein the oxidative agent supply mechanism comprises a plurality of conduits for delivering the oxidative agent through the feed cone and into the biomass within the housing of the gasifier. 
     
     
         12 . A system according to  claim 11  wherein the feed cone comprises an upwardly facing concave surface surrounding the feed bore and a frustro-conical exterior surface surrounding the upwardly facing concave surface and wherein the plurality of conduits for delivering the oxidative agent through the feed cone comprises a first plurality of conduits located to introduce oxidative agent through the upwardly facing concave surface and a second plurality of conduits located to introduce-oxidative agent through the frustro-conical exterior surface. 
     
     
         13 . A system according to  claim 12  wherein an interior of the housing of the gasifier is generally rectangularly shaped and the frustro-conical exterior surface comprises a rectangular frustro-conical surface. 
     
     
         14 . A system according to  claim 12  wherein an interior of the housing of the gasifier is generally circularly shaped and the frustro-conical exterior surface comprises a circular frustro-conical surface. 
     
     
         15 . A method for generating energy from biomass, the method comprising:
 providing a first, oxygen starved environment;   sub-stoichiometrically combusting the biomass in the first, oxygen starved environment to generate syngas;   oxidizing the syngas in a second environment distinct from the first environment to thereby generate heat energy;   wherein sub-stoichiometrically combusting the biomass in the first, oxygen starved environment comprises introducing an oxidative agent to the first, oxygen starved environment, the oxidative agent comprising flue gas.   
     
     
         16 . A method according to  claim 14  wherein the oxidative agent comprises a mixture of flue gas and air. 
     
     
         17 . A method according to  claim 15  wherein the oxidative agent consists essentially of a mixture of flue gas and air. 
     
     
         18 . A method according to  claim 15  wherein introducing the oxidative agent to the first, oxygen starved environment comprises recirculating flue gas generated by the oxidation of the syngas in the second environment and mixing the recirculated flue gas with air to provide the oxidative agent. 
     
     
         19 . A method according to  claim 17  comprising recovering heat from the recirculated flue gas prior to introducing the recirculated flue gas into the first, oxygen starved environment. 
     
     
         20 . A method according to  claim 18  comprising introducing air into the second environment to make the second environment an air enriched environment. 
     
     
         21 . A method according to  claim 15  wherein introducing the oxidative agent to the first, oxygen starved environment comprises introducing the oxidative agent to the first environment from locations beneath the biomass and from locations beside the biomass. 
     
     
         22 . A method according to  claim 18  wherein a temperature of the syngas generated by sub-stoichiometrically combusting the biomass in the first, oxygen starved environment is less than about 600° F. and a temperature of an oxidation product resulting from oxidizing the syngas in the second environment is greater than about 1200° F. 
     
     
         23 . A method according to  claim 18  wherein the temperature of the oxidation product resulting from oxidizing the syngas in the second environment is about 2000° F. 
     
     
         24 . A method according to  claim 15  wherein a temperature of the syngas generated by sub-stoichiometrically combusting the biomass in the first, oxygen starved environment is less than about 600° F. and a temperature of an oxidation product resulting from oxidizing the syngas in the second environment is greater than about 1200° F.