Grate and method of burning a granular fuel material

Abstract

The grate is used for burning a granular fuel material, for instance a biomass material, to be fed onto a loading area of the grate while a primary air feed is coming from below the grate. The grate includes a perforated bed floor having a downwardly-sloping upper surface converging towards a discharge opening where char is concentrated as the granular fuel material is burned during operation. The grate also includes an elongated and bottom-perforated char-receiving conduit positioned immediately under the bed floor. The char-receiving conduit has an inlet end positioned under the discharge opening, and an outlet end that is opposite the inlet end. The char-receiving conduit downwardly slopes between the inlet end and the outlet end. A method of burning a granular fuel material is also disclosed. The proposed concept can increase the overall thermal efficiency of a heat generator and reduce gas and particle emissions in the atmosphere.

What is claimed is: 
     
         1 . A substantially horizontally-disposed grate for burning a granular fuel material to be fed onto a loading area of the grate while an air feed is coming from below the grate, the grate including:
 a perforated bed floor having a downwardly-sloping upper surface converging towards a discharge opening where char is concentrated as the granular fuel material is burned during operation; and   an elongated and bottom-perforated char-receiving conduit positioned immediately under the bed floor, the char-receiving conduit having an inlet end positioned under the discharge opening, and an outlet end that is opposite the inlet end, the char-receiving conduit downwardly sloping between the inlet end and the outlet end.   
     
     
         2 . The grate as defined in  claim 1 , wherein the bed floor has at least two regions with distinct perforation patterns, a first region among the at least two regions being adjacent to the periphery of the upper surface and including the loading area, and a second region among the at least two regions being generally located between the first region and the discharge opening 
     
     
         3 . The grate as defined in  claim 2 , wherein the perforation pattern of one of the at least two regions creates a larger overall primary air feed passageway than the perforation pattern of another of the at least two regions. 
     
     
         4 . The grate as defined in  claim 1 , wherein the discharge opening is located within the periphery of the upper surface. 
     
     
         5 . The grate as defined in  claim 4 , wherein the discharge opening is offset with reference to a geometric center of the upper surface. 
     
     
         6 . The grate as defined in  claim 1 , wherein the upper surface of the bed floor is generally conical in shape. 
     
     
         7 . The grate as defined in  claim 1 , wherein the periphery of the upper surface is generally circular in shape. 
     
     
         8 . The grate as defined in  claim 1 , wherein the periphery of the upper surface is generally rectangular in shape. 
     
     
         9 . The grate as defined in  claim 1 , wherein the char-receiving conduit is substantially tubular in shape. 
     
     
         10 . The grate as defined in  claim 1 , wherein the char-receiving conduit is substantially rectangular in shape. 
     
     
         11 . The grate as defined in  claim 1 , wherein the bed floor has a vertical plane of symmetry and the char-receiving conduit generally has a longitudinal axis that extends substantially parallel to the plane of symmetry. 
     
     
         12 . The grate as defined in  claim 1 , wherein the char-receiving conduit is supported under the bed floor using at least one bracket. 
     
     
         13 . The grate as defined in  claim 1 , further including at least one additional discharge opening and at least one additional char-receiving conduit, one for each additional discharge opening, the discharge openings being spaced apart from one another and the char-receiving conduits extending substantially parallel to one another. 
     
     
         14 . The grate as defined in  claim 1 , wherein the conduit has a cross-sectional area that is about 2 to 4% of an area of the upper surface of the bed floor. 
     
     
         15 . The grate as defined in  claim 1 , wherein the upper surface has an average slope between  5  and  25  degrees with reference to the horizontal. 
     
     
         16 . The grate as defined in  claim 1 , wherein the char-receiving conduit has an average slope between 5 and 20 degrees with reference to the horizontal. 
     
     
         17 . A method of burning a granular fuel material, the method including the concurrent steps of:
 loading the granular fuel material in a loading area of a substantially horizontally-disposed bed floor;   vibrating the bed floor to move the granular fuel material from the loading area towards a discharge opening located away from and vertically below the loading area;   feeding primary air across the bed floor, the primary air coming from a bottom side and passing through a multitude of spaced-apart perforations made in the bed floor;   drying, mostly by radiation heat, the granular fuel material immediately after the granular fuel material is loaded onto the bed floor;   transforming, by pyrolysis, the dried granular fuel material into volatile compounds and char, and generating heat above the bed floor;   collecting and concentrating the char passing through the discharge opening into an elongated chamber extending substantially horizontally underneath the bed floor; and   generating heat by burning the char inside the chamber as the char is moved from the discharge opening towards an outlet end of the chamber by the vibrations of the bed floor.   
     
     
         18 . The method as defined in  claim 17 , wherein during continuous operation, the perforations of the bed floor are constantly covered by some of the granular fuel material. 
     
     
         19 . The method as defined in  claim 17 , wherein feeding the primary air across the bed floor includes passing the primary air through at least two different sets of perforations in the bed floor, a first set among the at least two sets providing less air across the bed floor than a second among the at least two sets. 
     
     
         20 . The method as defined in  claim 17 , wherein feeding the primary air across the bed floor includes passing some of the primary air through the discharge opening while the discharge opening is filled with some of the char. 
     
     
         21 . The method as defined in  claim 17 , further including:
 feeding secondary air above the bed floor to complete the combustion of the volatile compounds.