Air supply systems for combustion of granular biomass fuels

Abstract

An air supply system for a pellet stove has an air supply system providing primary and secondary combustion air, the secondary combustion air being introduced into a burn pot above, and orthogonal to, the primary air. The system and methods for the use thereof improve the emissions performance of stoves burning solid fuel in granular form, including solid biomass fuel. Stoves incorporating such air supply systems have reduced emissions, including reduced emissions of one or more of carbon monoxide, particulate matter (PM2.5), and black carbon.

What is claimed is: 
     
         1 . A stove configured to burn granular solid fuel, comprising:
 a burn pot, the burn pot generally cylindrical in shape and having an outer wall, a top open end and a closed bottom end configured to support a fuel bed thereon, wherein the closed bottom end has a plurality of apertures formed therein;   a fuel bed plenum disposed generally below the closed bottom end and configured to cause air within the fuel bed plenum to flow through the plurality of apertures formed in the closed bottom end;   a primary air source in fluid communication with the fuel bed plenum, the primary air source configured to direct pressurized air to the fuel bed plenum;   a secondary air plenum positioned within the burn pot above the closed bottom end, the secondary air plenum configured to direct secondary air radially outwardly from a center of the burn pot toward the outer wall; and   a secondary air source in fluid communication with the secondary air plenum, the secondary air source configured to direct pressurized air to the secondary air plenum; and   wherein the primary air source and the secondary air source are individually controllable to vary a ratio of secondary air to primary air delivered to the burn pot.   
     
     
         2 . The stove as in  claim 1 , wherein the fuel bed plenum is coupled to the primary air source by a primary air conduit and further comprising an igniter disposed along the primary air conduit. 
     
     
         3 . The stove as in  claim 1 , wherein the secondary air plenum comprises a cylindrical pipe that extends generally orthogonally through the closed bottom end and into the burn pot. 
     
     
         4 . The stove as in  claim 3 , wherein the secondary air plenum comprises a plurality of secondary air delivery nozzles arranged circumferentially about the secondary air plenum. 
     
     
         5 . The stove as in  claim 4 , wherein the plurality of secondary air delivery nozzles are arranged in one or more rings about the secondary air plenum. 
     
     
         6 . The stove as in  claim 4 , wherein the plurality of apertures formed in the closed bottom end are arranged in an array about the closed bottom end. 
     
     
         7 . The stove as in  any one of the preceding claims , wherein the primary air source is a first fan arranged to blow air into the fuel bed plenum. 
     
     
         8 . The stove as in  any one of preceding claims 1-6 , wherein the secondary air source is a second fan arranged to blow air through the secondary air plenum. 
     
     
         9 . The stove as in any one of  claims 1-6 , wherein the secondary air plenum is configured to inject secondary air into the burn pot in a direction generally orthogonal to the direction of primary air injected into the burn pot. 
     
     
         10 . A method of operating the stove of in  claim 1 , comprising:
 adding pelletized fuel to the burn pot;   activating the primary air source;   activating the secondary air source;   activating an igniter to provide ignition heat to the pelletized fuel in the burn pot; and   controlling the secondary air source and the primary air source such that a ratio of secondary air to primary air is greater than 3:1.   
     
     
         11 . The method of operating the stove as in  claim 10 , wherein the ratio of secondary air to primary air is 4:1. 
     
     
         12 . The method of operating the stove as in  claim 10 , further comprising, adjusting, in response to a parameter associated with the stove, the ratio of secondary air to primary air. 
     
     
         13 . The method of operating the stove as in  claim 12 , wherein the parameter is a power setting of the stove. 
     
     
         14 . The method of operating the stove as in  claim 10 , further comprising adjusting the primary air source to inject primary air with a Reynolds number between 20 and 2,500. 
     
     
         15 . The method of operating the stove as in  claim 10 , further comprising adjusting the secondary air source to inject secondary air into the burn pot with a Reynolds number of between 200 and 3,000.