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 . Apparatus for gasifying organic material, the apparatus comprising:
 a gasifier chamber having a floor and an exit port for syngas produced by gasification of the organic material;   a feed device for carrying the organic material upwardly into the gasifier through an opening in the floor to form a heap of organic material on the floor;   wherein the gasifier chamber comprises an ash dump device provided in the floor of the gasification chamber, the ash dump device comprising:   a first grate ring in a floor of the gasification chamber, the first grate ring having a plurality of openings therethrough;   a second grate ring having a plurality of openings therethrough positioned above the first grate ring and being moveable relative to the first grate ring; and   a plurality of wedge members projecting from an upper surface of the second grate ring, the wedge members having first and second faces, the first faces adjacent to the openings of the second grate rings and being steeper than the second faces;   wherein the second grate ring is movable between a first configuration wherein the openings of the first and second grate rings are aligned and a second configuration wherein the openings of the first and second grate rings are misaligned, and wherein the wedge members are oriented to push the material toward the openings of the first grate ring when the second grate ring is moved from the second configuration toward the first configuration.   
     
     
         2 . Apparatus according to  claim 1 , wherein the openings of the first and second grate rings are square or rectangular in shape. 
     
     
         3 . Apparatus according to  claim 1  wherein the first and second grate rings encircle the opening in the floor of the gasifier chamber. 
     
     
         4 . A method for generating syngas from organic material, the method comprising:
 introducing organic material upwardly into a gasifier chamber having a floor and an exit port for syngas produced by gasification of the organic material through an opening in the floor to form a heap of organic material on the floor;   heating and oxidizing the organic material in the presence of an oxidant gas to generate syngas;   allowing a layer of ash to form under the heap; and   removing ash of the layer of ash from the gasifier chamber while performing partial oxidation of the organic materials.   
     
     
         5 . A method according to  claim 4  wherein removing the ash comprises opening a grate under the heap and collecting ash that passes through the grate. 
     
     
         6 . A method according to  claim 4  comprising measuring a temperature difference between two different elevations within the heap of organic material and regulating a rate at which ash is removed from the gasifier chamber based on the temperature difference. 
     
     
         7 . A method according to  claim 4  comprising measuring the temperature differences between different elevations within the heap at a plurality of locations within the gasifier chamber and regulating a rate at which ash is removed from the gasifier chamber based on an average of the temperature differences. 
     
     
         8 . A method according to  claim 4  comprising measuring a temperature difference between two different elevations within the heap of organic material; wherein removing the ash from the gasifier chamber is performed in response to the temperature difference between the two different elevations having a first predetermined value. 
     
     
         9 . A method according to  claim 8  comprising continuing to remove ash from the gasifier chamber until the temperature difference reaches a second predetermined value. 
     
     
         10 . A method according to  claim 4 , wherein removing ash of the layer of ash from the gasifier chamber comprises removing ash of the layer of ash from the gasifier chamber via an ash dump device,
 wherein the ash dump device comprises:   a first grate ring in a floor of the gasification chamber, the first grate ring having a plurality of openings therethrough;   a second grate ring having a plurality of openings therethrough positioned above the first grate ring and being moveable relative to the first grate ring; and   a plurality of wedge members projecting from an upper surface of the second grate ring, the wedge members having first and second faces, the first faces adjacent to the openings of the second grate rings and being steeper than the second faces;   wherein the second grate ring is movable between a first configuration wherein the openings of the first and second grate rings are aligned and a second configuration wherein the openings of the first and second grate rings are misaligned, and wherein the wedge members are oriented to push the material toward the openings of the first grate ring when the second grate ring is moved from the second configuration toward the first configuration.   
     
     
         11 . A method according to  claim 10 , wherein the openings of the first and second grate rings are square or rectangular in shape. 
     
     
         12 . A method according to  claim 10  wherein the first and second grate rings encircle the opening in the floor of the gasifier chamber. 
     
     
         13 . Apparatus for gasifying organic material, the apparatus comprising:
 a gasifier chamber having a floor and an exit port for syngas produced by gasification of the organic material;   a feed device for carrying the organic material upwardly into the gasifier through an opening in the floor to form a heap of organic material on the floor;   an oxidizer;   a conduit connected between the exit port and the oxidizer;   a syngas burner at an upstream end of the conduit; and   an oxidant source connected to supply an oxidant to the syngas burner.   
     
     
         14 . Apparatus according to  claim 13  wherein the oxidant source comprises a combustion air blower. 
     
     
         15 . Apparatus according to  claim 14  comprising an intake system connected to supply an oxygen starved atmosphere to the gasifier chamber, the intake system comprising an air inlet, a flue gas inlet and a conduit configured to deliver a mixture of air and flue gas to the gasification chamber. 
     
     
         16 . A method for generating syngas from organic material, the method comprising:
 introducing organic material upwardly into a gasifier chamber having a floor and an exit port for syngas produced by gasification of the organic material through an opening in the floor to form a heap of organic material on the floor;   heating and oxidizing the organic material in the presence of an oxidant gas to generate syngas;   flowing the syngas from the exit port of the gasifier chamber to an oxidizer by way of a conduit; and, in the conduit, at least partially oxidizing the syngas.   
     
     
         17 . A method according to  claim 16  comprising mixing an oxidant with the syngas at an upstream end portion of the conduit. 
     
     
         18 . A method according to  claim 17  wherein at least partially oxidizing the syngas comprises igniting the syngas at a syngas burner at the upstream end portion of the conduit. 
     
     
         19 . A method according to  claim 16  comprising removing the syngas from the gasifier chamber at a first temperature less than about 600° F. 
     
     
         20 . A method according to  claim 19  wherein the first temperature is in the range of about 500° F. to about 600° F. 
     
     
         21 . A method according to  claim 16  comprising partially oxidizing the syngas in the conduit to provide a temperature rise of 600° F. or more. 
     
     
         22 . A method according to  claim 16  comprising partially oxidizing the syngas in the conduit to provide a temperature of 1200° F. or more. 
     
     
         23 . A method according to  claim 16  comprising delivering the syngas to the oxidizer at a temperature in the range of about 1200° F. to 1400° F.