Producing Low Tar Gases in a Multi-Stage Gasifier

Abstract

A system for gasifying solid matter uses multiple stages to produce low-tar combustible gas includes a first reactor having a fluidized bed to produce hydrogen containing gas, pyrolysis vapors, tars, and char particles at temperature less than the exit of the second reactor and a higher temperature partial oxidation combustor zones. A second reactor includes a higher temperature partial oxidation zone to activate hydrogen and cause cracking of aromatic ring compounds, a co-flow moving granular bed with a char gasification stage to catalyze tar reduction, and control char residence time, and a media screen comprising a parallel wire screen substantially vertically oriented supporting granular media.

1 . A multi-stage reaction system for producing low-tar combustible gas, the system comprising:
 a fluidized bed reactor that includes a partial oxidation zone, in which a gas and a plurality of char particles are created in said partial oxidation zone; and   an entrained flow partial oxidation reactor positioned downstream from the fluidized bed reactor.   
     
     
         2 . The system disclosed in  claim 1  wherein said entrained flow partial oxidation reactor includes a moving granular bed. 
     
     
         3 . The system of  claim 1 , wherein the fluidized bed reactor further comprises a freeboard, said freeboard operated at a velocity controlled to create a generally consistent char particle size feed. 
     
     
         4 . The system of  claim 2  wherein said plurality of char particles is of generally consistent char particle size and at least a portion of said plurality of char particles is provided to the entrained flow partial oxidation reactor. 
     
     
         5 . The system of  claim 3  wherein provision of said generally consistent char particle size comprises modulating a pressure of the fluidized bed reactor. 
     
     
         6 . The system of  claim 1 , further comprising a sand recovery cyclone. 
     
     
         7 . The system of  claim 1 , wherein the entrained-flow partial oxidation reactor further includes a partial oxidation zone and means for injecting a stream of combined gas and char into said partial oxidation zone. 
     
     
         8 . The system of  claim 7 , further comprising a cyclone for concentrating the plurality of char particles out of a fed gas stream prior to injection into said partial oxidation zone. 
     
     
         9 . The system of  claim 8 , wherein said cyclone concentrates the plurality of char particles out of the fed gas stream prior to injection into said partial oxidation zone. 
     
     
         10 . The system of  claim 2 , wherein the entrained-flow partial oxidation reactor includes a plurality of blast inlet ports configured around a periphery of a vessel enclosing the reactor. 
     
     
         11 . The system of  claim 10 , wherein said plurality of blast inlet ports is arranged in an alternating pattern such that each of the plurality of blast inlet ports targets a tangent curve of a tangent circle. 
     
     
         12 . The system of  claim 10 , wherein said plurality of blast inlet ports is arranged in an alternating pattern such that a first one of the plurality of blast inlet ports targets a first tangent curve of a first tangent circle and a second one of the plurality of blast inlet ports targets a second tangent curve of a second tangent circle, wherein the first and second tangent circles are located at the same elevation. 
     
     
         13 . The system of  claim 10 , wherein said plurality of blast inlet ports is arranged in an alternating pattern such that a first one of the plurality of blast inlet ports targets a first tangent curve of a first tangent circle and a second one of the plurality of blast inlet ports targets a second tangent curve of a second tangent circle, wherein the first and second tangent circles are located at different elevations. 
     
     
         14 . The system of  claim 7 , wherein the moving granular bed operates in co-flow with respect to the stream of combined gas and char to create a gas-char contacting zone. 
     
     
         15 . The system of  claim 14 , wherein a gas-media disengagement screen is oriented at an angle that is steeper than an angle of repose of the combined media and char mixture. 
     
     
         16 . The system of  claim 15 , wherein the gas-media disengagement screen is oriented substantially vertically. 
     
     
         17 . The system of  claim 15 , wherein the gas-media disengagement screen includes a plurality of parallel wires extending between an upper frame edge and a lower frame edge. 
     
     
         18 . The system of  claim 17 , wherein each of the plurality of wires includes a cross section partially defined by a first side that converges with a second side at a vertex in the direction of the disengaging gas flow. 
     
     
         19 . The system of  claim 18 , wherein the cross section is wedge shaped. 
     
     
         20 . The system of  claim 2  wherein the entrained-flow partial oxidation reactor further includes a partial oxidation zone, means for injecting a stream of combined gas and char into said partial oxidation zone, and a plurality of blast inlet ports configured around a periphery of a vessel enclosing the reactor. 
     
     
         21 . The system of  claim 20  wherein the moving granular bed operates in co-flow with respect to the stream of combined gas and char to create a gas-char contacting zone. 
     
     
         22 . The system of  claim 2  wherein the entrained-flow partial oxidation reactor further includes a partial oxidation zone and means for injecting a stream of combined gas and char into said partial oxidation zone and said moving granular bed includes a gas-media disengagement screen oriented at an angle steeper than the angle of repose of the combined media and plurality of char particles. 
     
     
         23 . A method for controlling an operating pressure of a two-stage gasification system, the method comprising:
 performing a partial oxidation of a portion of biomass in a fluidized bed reactor, wherein the partial oxidation creates a gas and a plurality of char particles;   elutriating at least a portion of said plurality of char particles and gas from the fluidized bed reactor, wherein said elutriating includes removing a mixture of gas and char particles from the fluidized bed reactor;   receiving the mixture into an entrained flow reactor, wherein the entrained flow reactor includes a moving granular bed of filtering media;   allowing the mixture to flow through the moving granular bed; and   capturing a portion of the plurality of char particles in the filtering media.   
     
     
         24 . The method of  claim 23  further comprising screening a portion of the filtering media to remove captured char particles; and returning the screened filtering media to the entrained flow reactor. 
     
     
         25 . A multi-stage reaction system for producing low-tar combustible gas, the system comprising:
 a fluidized bed reactor that includes a partial oxidation zone in which a portion of the feedstock is partially oxidized, wherein said partial oxidation creates a gas and a plurality of char particles;   an entrained flow partial oxidation reactor situated downstream from the fluidized bed reactor, the entrained flow partial oxidation reactor including a moving granular bed;   a media screening device that screens media from the moving granular bed; and   a media recycle system that returns the screened media to the entrained flow partial oxidation reactor.