Fluidized combustor

Abstract

A system and method to permit fluidized combustion without requiring a separate fluidizing medium, such as sand. The system may include a combustion chamber, a fuel feed system coupled to the combustion chamber, an ignition system coupled to the combustion chamber, a fluidizing system coupled to the combustion chamber, where the fluidizing system includes a fuel and fluidizing medium formed from the same material, and a heat recovery system. The method may include delivering a pelletized fuel into a combustion chamber by a fuel feed system and onto a fluidizing plate, igniting the pelletized fuel with an igniter system coupled to the fluidizing plate, fluidizing the pelletized fuel after combustion is started in the absence of a fluidizing medium beyond the pelletized fuel, and heating a medium in a heat exchanger with combustion gases.

1 . A combustion system for use with a pelletized fuel in the absence of a separate fluidizing medium, comprising:
 a combustion chamber;   a fuel feed system coupled to the combustion chamber;   an ignition system coupled to the combustion chamber;   a fluidizing system coupled to the combustion chamber, wherein the fluidizing system includes a fuel and fluidizing medium formed from a same material; and   a heat recovery system.   
     
     
         2 . The combustion system according to  claim 1 , wherein the fluidizing system further comprises a fluidizing plate at a bottom of the combustion chamber with a plurality of holes to distribute air over the combustion chamber from a primary air system coupled to the combustion chamber through the fluidizing plate. 
     
     
         3 . The combustion system according to  claim 2 , wherein the fluidizing system further comprises a secondary air system to introduce air into the combustion chamber over the fluidizing plate, wherein the secondary air system introduces air into the combustion chamber off a radial axis of the combustion chamber to promote swirling of combustion gases. 
     
     
         4 . The combustion system according to  claim 3 , wherein the fuel feed system enters the combustion chamber at a common port as the secondary air system, and the secondary air system introduces air into the combustion chamber at a speed greater than a flame propagation speed to prevent combustion of incoming fuel. 
     
     
         5 . The combustion system according to  claim 2 , wherein the ignition system comprises an igniter on a first side of the fluidizing plate and a fin on a second side of the fluidizing plate coupled to the igniter through the fluidizing plate, wherein the first side of the fluidizing plate faces away from the combustion chamber. 
     
     
         6 . The combustion system according to  claim 6 , wherein the fluidizing plate comprises a heat insulating material, the fin comprises a heat transfer material, and the igniter further comprises a pulse cartridge to provide heat to the fin in pulses. 
     
     
         7 . The combustion system according to  claim 1 , wherein the fuel feed system includes a fuel bin and fuel transport, wherein the pelletized fuel is introduced into the combustion chamber along the fuel transport at a non-zero angle from horizontal. 
     
     
         8 . The combustion system according to  claim 1 , wherein the combustion chamber is coupled to the combustion system by a hinge to permit access to an interior of the combustion chamber and ignition system. 
     
     
         9 . The combustion system according to  claim 1 , wherein the heat recovery system comprises a heating device positioned over the combustion chamber to share a common interior space, the heating device including at least three surfaces positioned so that combustion gases contact a first surface of the heating device at a first pass, contact a second surface of the heating device during a second pass, and contact a third surface of the heating device during a third pass; wherein the first surface is an interior surface of the heating device facing the common interior space, and the second and third surfaces are substantially vertical so that the second pass and third pass occur in substantially opposite directions. 
     
     
         10 . The combustion system according to  claim 1 , wherein the fluidizing medium and fuel are wood pellets. 
     
     
         11 . A method of combusting a pelletized fuel, comprising:
 Delivering a pelletized fuel into a combustion chamber by a fuel feed system and onto a fluidizing plate;   igniting the pelletized fuel with an igniter system coupled to the fluidizing plate;   fluidizing the pelletized fuel after combustion is started in the absence of a fluidizing medium beyond the pelletized fuel; and   heating a medium in a heat exchanger with combustion gases.   
     
     
         12 . The method according to  claim 11 , wherein delivering the pelletized fuel further comprises introducing the pelletized fuel into the combustion chamber at a non-zero angle from horizontal through a port in the combustion chamber positioned over the igniter system and below the heat exchanger. 
     
     
         13 . The method according to  claim 11 , wherein igniting the pelletized fuel comprises utilizing an igniter system including an igniter on a first side of the fluidizing plate and a fin on a second side of the fluidizing plate coupled to the igniter through the fluidizing plate, wherein the first side of the fluidizing plate faces away from the combustion chamber. 
     
     
         14 . The method according to  claim 13 , wherein fluidizing the pelletized fuel comprises supplying air to the pelletized fuel from a primary air source from under the fluidizing plate, and supplying air to the pelletized fuel from a secondary air source over the fluidizing plate entering the combustion chamber at a non-zero angle from a radial axis of the combustion chamber. 
     
     
         15 . The method according to  claim 14 , wherein air from the primary air source is passed through the fluidizing plate and contacts the igniter to cool the igniter during combustion, the method further comprising shutting off the igniter after fluidizing the pelletized fuel once combustion is started. 
     
     
         16 . The method according to  claim 11 , wherein heating the medium in the heat exchanger comprises contacting the combustion gases along three separate surfaces of the heat exchanger during separate passes of the combustion gases, wherein a second surface and third surface are substantially vertical such that combustion gases passing the second surface are traveling substantially downward, and combustion gases passing the third surface are traveling substantially upward. 
     
     
         17 . The method according to  claim 11 , wherein igniting the pelletized fuel comprises supplying heat in pulses and supplying air to the combustion chamber by an air system at a velocity not sufficient to fluidize the fuel, and wherein fluidizing the pelletized fuel comprises supplying air to the combustion chamber by the air system at a second velocity sufficient to fluidize the fuel. 
     
     
         18 . The method according to  claim 11 , further comprising extinguishing combustion by stopping the fuel feed system and supplying air to the combustion chamber to cool the pelletized fuel below a combustion temperature. 
     
     
         19 . The method according to  claim 11 , further comprising rotating a portion of the combustion chamber relative to a remainder of the combustion system to provide access to an interior of the combustion chamber and igniter system. 
     
     
         20 . A method of combusting a wood pellets, comprising:
 introducing wood pellets into an interior of a combustion chamber at a non-zero angle from horizontal;   igniting the wood pellets by heat supplied by an igniter displaced from the wood pellets;   fluidizing the ignited wood pellets in the absence of a separate fluidizing medium with a primary air source separated from the ignited wood pellets by a fluidizing plate and a secondary air source entering the interior of the combustion chamber substantially tangential to an edge of the combustion chamber to provide circumferential air flow;   passing combustion gases from the ignited wood pellets through a heat exchanger in at least three passes, wherein a second pass and third pass are substantially vertical and the combustion gases are transitioned 180 degrees between the second pass and third pass; and   removing particulate from the combustion gases utilizing gravity, a temperature variation between the second pass and the third pass, and the transition of the combustion gases between the second pass and the third pass.