Method and Apparatus for Improved Firing of Biomass and Other Solid Fuels for Steam Production and Gasification

Abstract

A ground supported single drum power boiler is described combining a refractory lined and insulated stepped floor; refractory lined and insulated combustion chamber; integrated fuel chutes configured to pre-dry wet solid fuel; internal chamber walls; configurable combustion air systems; a back pass with after-burner ports and cross flow superheaters; and a rear wall that acts as the downcomers feeding the other walls. A second embodiment is adaptable as a gasifier.

We claim as follows: 
     
         1 . A solid fuel fired boiler comprising one or more walls internal to the furnace section of the boiler, with said walls comprised of closely spaced steel tubes in mutually parallel relationship and aligned such that the axes of the tubes are vertical for the majority of their length, with said tubes comprising one or more water and/or steam circulation circuits within the boiler, with said wall or walls dropping through the roof of the boiler until one or more tubes but not all tubes comprising the internal wall or walls exits through a first wall of the boiler and the remaining tube or tubes exit through the opposite wall of the boiler. 
     
     
         2 . The boiler of  claim 1  in which said internal walls are parallel to the side walls of the boiler, and said tubes drop vertically for most of their length then bend to become more or less horizontal then exit the furnace through the front and rear walls of the boiler. 
     
     
         3 . The boiler of  claim 1  in which said internal walls are parallel to the front wall of the boiler, and said tubes drop vertically for most of their length then bend to become more or less horizontal then exit the furnace through the side walls of the boiler. 
     
     
         4 . The boiler of  claim 1  in which the width of said internal wall or walls is not more than 80% of the interior dimension of the boiler, measured horizontally and in the plane of said wall or walls. 
     
     
         5 . The boiler of  claim 4  in which combustion gasses circulate horizontally around said internal wall or walls as said gasses rise vertically along the height of said wall or walls. 
     
     
         6 . The boiler of  claim 5  in which combustion air, oxygen, or recirculated flue gas is injected into the boiler in a manner to induce said circulation around said internal wall or walls. 
     
     
         7 . The boiler of  claim 3  in which one half or more of said tubes comprising said internal wall or walls are bent out of the plane of said wall or walls to allow passage of gasses through said wall or walls, with said bent portion comprising less than one half the total internal height of said wall or walls. 
     
     
         8 . The boiler of  claim 1  in which circulation develops through said internal wall or walls in which the lower end of said tubes comprising said internal wall or walls are fed water from the steam drum of said boiler via downcomers and said water is heated as it rises through said internal wall or walls and some of said water may boil therein, and said water or saturated steam or a mixture thereof is relieved at the top of said tubes and flows back to said steam drum. 
     
     
         9 . The boiler of  claim 8  in which the water in said internal wall or walls is heated by combustion gases and the flow through said wall or walls is created by a natural circulation in which the colder and denser water in said downcomers forces the hotter and less dense water and/or water and saturated steam mixture to flow upward through said internal wall or walls. 
     
     
         10 . The boiler of  claim 1  used in conjunction with a refractory lined and insulated stepped floor delivering combustion air and or recirculated flue gas through slots in the face of the steps with oscillating step cleaners residing inside the steps to periodically clean the steps with jets of steam blown out through said slots. 
     
     
         11 . The boiler of  claim 1  used in conjunction with a refractory lined and insulated stepped floor with slots in the face of the steps with oscillating nozzles inside the steps to blow combustion air or oxygen out through the slots to agitate and burn fuel residing on the steps. 
     
     
         12 . The boiler of  claim 1  used in conjunction with a combustion air system arranged with one or more levels of port openings situated to blow combustion air and/or recirculated flue gas across the steps of a stepped floor, with the lowest level, if more than one, zero to two feet above the tops of the steps. 
     
     
         13 . Any combination of  claim 1  used in conjunction with a combustion air system arranged with one or more levels of air port openings situated to blow combustion air and/or re-circulated flue gas across the steps of a stepped floor, with the air ports arranged to produce horizontal circulation of the combustion gasses in a zone up to ten feet above the steps. 
     
     
         14 . The boiler of  claim 1  used in conjunction with a combustion air system arranged with one or more levels of air port openings at any elevation in the boiler and situated to blow combustion air and/or re-circulated flue gas into the boiler to produce horizontal circulation of the combustion gasses, with automated dampers that periodically reverse the circulation pattern. 
     
     
         15 . The boiler of  claim 1  used in conjunction with refractory lined and insulated lower furnace walls for the purpose of retaining heat in a combustion chamber and returning that heat to the interior of the combustion chamber if the temperature of combustion falls. 
     
     
         16 . The boiler of  claim 1  used in conjunction with refractory lined and insulated lower furnace walls with an air plenum between the insulation and surrounding supporting structure. 
     
     
         17 . The boiler of  claim 1  used in conjunction with a ground supported boiler in which a concrete foundation surrounds a refractory lined and insulated combustion chamber with or without an air plenum in between. 
     
     
         18 . The boiler of  claim 1  used in conjunction with a ground supported boiler in which the lower ends of tube walls surrounds a refractory lined and insulated combustion chamber. 
     
     
         19 . The boiler of  claim 1  used in conjunction with one or more fuel chutes integral with one or more exterior walls of the boiler in which fuel flowing through the chute or chutes is exposed to hot boiler gas and/or radiation to effect partial drying of the fuel. 
     
     
         20 . The boiler of  claim 1  used in conjunction with combustion air ports located in a back pass and used to complete the combustion of volatile gasses and control the temperature of the steam exiting a superheater. 
     
     
         21 . The boiler of  claim 1  used in conjunction with a horizontal tube, cross flow superheater with in-line or staggered tube arrangement. 
     
     
         22 . The boiler of  claim 1  used in conjunction with a horizontal tube, cross flow superheater in which the tubes bends are external to the flue gas flow. 
     
     
         23 . The boiler of  claim 1  used in conjunction with a gasifier in which oxygen is used to combust part of the fuel therein and the heat released by that combustion gasifies the remaining fuel and may also generate steam. 
     
     
         24 . The boiler of  claim 1  used in conjunction with a gasifier in which the pyrolysis gases are rapidly cooled by one or more tube walls internal to the furnace chamber. 
     
     
         25 . The boiler of  claim 1  used in conjunction with oil or gas fired burners located upstream of superheaters in a back pass and used to control outlet steam temperature. 
     
     
         26 . The boiler of  claim 1  used in conjunction with at least the rear tube wall of the back pass acting as the downcomers to deliver water from the steam drum to the remaining boiler walls. 
     
     
         27 . The boiler of  claim 1  in which with said wall or walls drop through the roof of the boiler until the lowest extremity of said internal wall or walls is no more than thirty feet above the lowest level of the interior floor of the boiler.