Method and apparatus for drying solid fuels

Abstract

A method for drying solid fuels prior to injection and burning in solid fuel boilers is described. High moisture content solid fuels such as bark, sludge, wet coal, etc. must be dried before they can burn. Embodiments of the present invention incorporates a fuel delivery chute integrated with the boiler wall using a flow of combustion gasses and radiant heating to partially dry the solid fuel before it reaches the combustion zone of the boiler. The combustion gasses are drawn through the delivery chute by means of the flowing fuel and air jet inductors that then blows the combustion gasses back into the boiler. A refractory wall separates the fuel chute from the boiler proper, is heated by the combustion in the boiler, and radiates heat to the fuel falling through the fuel chute.

We claim as follows: 
     
         1 . An apparatus for drying fuel entering a solid fuel boiler having a combustion chamber within tube walls carrying fluid to be heated by combustion in the combustion chamber, the apparatus comprising:
 a fuel chute for transferring solid fuel to the combustion chamber, the chute having an interior region through which fuels falls, the interior region being separated from the interior of the combustion chamber by a refractory material that transfers heat from the combustion chamber to the solid fuel as it drops in the chute to reduce the moisture content of the solid fuel before it reaches the combustion chamber;   an entrance for inserting solid fuel into the fuel chute; and   an exit in the fuel chute for dispensing solid fuel into the combustion chamber;   the chute wall transferring heat to the solid fuel as it drops in the chute to reduce the moisture content of the solid fuel before it reaches the combustion chamber.   
     
     
         2 . The apparatus of  claim 1  in which the refractory material is heated by the combustion chamber and heats the fuel by radiation. 
     
     
         3 . The apparatus of  claim 1  in which the refractory material comprises of tiles, board, or other prefabricated components. 
     
     
         4 . The apparatus of  claim 1  in which the refractory material is a cast in place material. 
     
     
         5 . The apparatus of  claim 1  in which the refractory material reaches an equilibrium temperature of at least 2000° F. 
     
     
         6 . The apparatus of  claim 1  in which solid fuel includes bark, coal, sludge, wood, waste, refuse, tires, or fossil fuels having a residual moisture content of 50% or greater prior to entering the chute. 
     
     
         7 . The apparatus of  claim 1  in which the chute is positioned between a tube wall and the combustion chamber. 
     
     
         8 . The apparatus of  claim 1  in which the interior of the chute is lined on four sides with refractory material. 
     
     
         9 . The apparatus of  claim 1 , further comprising a fuel distributor that dispenses fuel to the combustion chamber from the fuel chute. 
     
     
         10 . The apparatus of  claim 1  in which the fuel chute includes an opening for gas from the combustion chamber to enter the fuel chute, the gas being drawn into the chute by the flow of fuel down the chute and mixing with the fuel as it descends the chute. 
     
     
         11 . The apparatus of  claim 1 , further comprising a gas nozzle for injecting gas into the portion top of the chute. 
     
     
         12 . A solid fuel boiler including:
 tube walls for carrying fluid to be heated;   a combustion chamber for combusting fuel to heat the fluid in the rube walls; and   an apparatus for drying fuel in accordance with  claim 1 .   
     
     
         13 . A method for providing solid fuel to a combustion chamber of a solid fuel boiler, comprising:
 inserting the fuel into a gravity fed chute through an entrance in the gravity fed chute;   reducing the moisture content of the solid fuel while the fuel is passing through the gravity fed chute by heating the fuel in the chute by radiation from at least one wall of the gravity fed chute that is heated by thermal contact with the combustion chamber; and   delivering the fuel with the reduced moisture content into the combustion chamber.   
     
     
         14 . The method of  claim 13  further comprising drawing gas from the combustion chamber into the chute near the top of the chute, the gas flowing down the chute with the fuel. 
     
     
         15 . The method of  claim 13  further comprising injecting gas into the chute near the top to circulate gas at the top of the chute. 
     
     
         16 . The method of  claim 13  in which reducing the moisture content of the solid fuel while the fuel is passing through the gravity fed chute by heating the fuel in the chute by radiation from at least one wall comprises passing the fuel through a chute that is separated from the interior of the combustion chamber by a refractory material and not by a tube wall. 
     
     
         17 . The method of  claim 13  in which delivering the fuel includes the fuel dropping onto a sloping floor of the gravity fed chute, the sloping floor lined with abrasion resistant refractory material. 
     
     
         18 . The method of  claim 13  in which delivering the fuel includes injecting gas into the gravity fed chute to help deliver the solid fuel to the combustion chamber. 
     
     
         19 . An apparatus for drying fuel entering a solid fuel boiler having a combustion chamber within tube walls carrying fluid to be heated by combustion in the combustion chamber, the apparatus comprising:
 a fuel chute for transferring solid fuel to the combustion chamber, the chute having at least one chute wall in thermal contact with the combustion chamber, the chute wall not being separated from the interior of the combustion chamber by a tube wall;   an entrance for inserting solid fuel into the fuel chute; and   an exit in the fuel chute for dispensing solid fuel into the combustion chamber,   the at least one chute wall transferring heat to the solid fuel as it drops in the chute to reduce the moisture content of the solid fuel before it reaches the combustion chamber.   
     
     
         20 . The apparatus of  claim 19  in which the at least one chute wall in thermal contact with the combustion chamber comprises a refractory material.