Heating – With heating gas conveying – agitating – scattering or...
Reexamination Certificate
2001-10-03
2002-11-26
Wilson, Gregory (Department: 3749)
Heating
With heating gas conveying, agitating, scattering or...
C110S212000, C110S203000, C048S1970FM
Reexamination Certificate
active
06485296
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to heating systems with fuel treatment means for liberating combustible gas from solid fuel and in particular to a controlled system and method for clean-emission variable biomass gasification and combustion using a thick fuel bed on stationary fixed grates with controlled evenly distributed primary air to produce gasification and a burner above the fuel with secondary air directed into the burner for burning gasses with high turbulence to enable the creation of a system using biomass containing either low or high moisture content and either low or high ash content for an efficient heating system with low emissions, and with system feedback controls to enable constantly managed combustion kept at an even rate and burning cleanly so that the system needs no down time for cleaning.
2. Description of the Prior Art
Biomass waste provides an abundant source of fuel from what might otherwise be considered waste. In addition, the plant matter from which the biomass waste comes is a renewable resource. As long as trees and other plants are harvested ecologically they keep replacing themselves with new growth by the natural growth cycle in many forests or by replanting. In addition, using plant growth as fuel maintains the natural carbon cycle in a 100% balanced state, because the clean gasification and combustion of biomass fuel puts back into the environment the same amount of carbon that occurs in the natural decay of plants. The carbon is then taken in by the living plants. However, burning coal, oil and natural gas creates a carbon overload in the environment from the centuries of stored carbon suddenly released into the environment.
Sources for biomass waste in the form of wood chips include whole tree chips from forestry maintenance including tree tops and waste in forests, brush and tree cuttings from parks and roadways, lumber mill waste, woodworking waste, crushed pallets, and any other sources of discarded wood or wood byproducts. Many other sources of biomass waste exist in other forms from landfill sites, municipal waste collection, waste from companies using plant matter in any form, paper waste, and many other sources. The community itself can become the source of fuel for the community's own plants burning biomass fuel.
The major problem with biomass fuel is the substantial creosote and smoke discharge normally associated with wood burning and biomass burning stoves and furnaces which burn at relatively low temperatures and low turbulence at low thermal efficiency rates. As well as a pollution problem, this is a great waste of resources, because the “pollutants” given off by such stoves and furnaces are hydrocarbon gases, tar and fuel particulates.
Most stoves, furnaces, and power plants using wood and biomass fuel are set up to burn somewhat efficiently, but only with specific qualities of fuels, typically limited in an allowable range of moisture content and other criteria such as phosphate content, which creates ash. Finding sources of biomass waste that meet specific requirements of moisture content and other criteria consistently is a major problem that further limits the efficiency of other systems, thereby wasting fuel and creating considerable pollution.
In other systems, such as large power plants, burning at relatively high temperatures in very large chambers “gasification” and burning of some of the hydrocarbon gases occurs spontaneously because of the high temperatures created from a huge fire source, the blown-in fuel and the fact that gases remain in some locations within the huge chambers to eventually burn up. Because these systems are relatively static and uncontrolled they are designed for a very limited range of fuel types and qualities and therefore burn less efficiently than they were designed for much of the time because of variations in fuel quality.
Smaller scale systems such as furnaces for buildings and stoves for homes are generally less efficient than the large power plants because they don't develop the same level of gasification spontaneously, because in smaller chambers the gases generally don't remain in the system as long, the same high temperature conditions are usually not attained, and fuel sources are even less uniform than municipal systems with rigid fuel requirements.
Although some systems have some controls built in to vary air input through flues or with some provision for creating gasification and combustion of the combustible gases, most systems are relatively static with no feedback means to monitor the efficiency of the system; so they fail to control the gasification and gas combustion for variations in fuel quality and climatic conditions. Most biomass and wood burning systems require considerable time and labor in monitoring and manual adjustments to maintain some level of efficiency, especially systems requiring manual loading of fuel and unloading of ash.
Most prior art systems have a problem when burning wood with bark or branches with dirt on them, because of clinkering, or the build-up of ashes and dirt on the grates and other interior furnace surfaces, requiring regular shut downs and cleaning of the systems. The shut downs may cost considerable income if the heat is producing power or other income producing energy sources. It often takes a considerable amount of time to reload the systems and get them running at an efficient level of output.
Heating systems employing thin fuel beds, especially in gasification systems with high temperatures, run the risk of damaging the grates underneath the fuel creating frequent grate problems requiring maintenance or replacement.
Most prior art heating systems with feedback controls produce quite a variance in heat output from the time the sensors detect a drop in temperature and signal the controls to the time it takes to add fuel or vary the air mixture to increase heat output. This produces ups and downs in the output with fuel inefficiencies and less than optimum burning conditions, which may produce more air pollution than desired.
While prior art patents describe technologies employing gasification, none are optimized for maximum constant thermal efficiency with no shut downs. In prior art patents, burn downs or shut downs can cause damage to the system.
U.S. Pat. No. 5,823,122, issued Oct. 20, 1998 to Chronowski et al, provides horizontal blast tubes for biomass gasifiers in
FIGS. 1-3
and a vertical blast tube for a biomass gasifier in FIG.
4
. They introduce swirling air, which may be preheated, into the ignition point of the fuel gas produced by the gasification of the biomass.
U.S. Pat. No. 5,634,412, issued Jun. 3, 1997 to Martin et al, indicates a method for regulating a refuse incinerator furnace using an infrared pyrometer to measure temperature of the waste gases to regulate the supply of fuel and the speed of the combustion grate and a regulating quantity derived from the mass flow of steam serves to influence the supply of primary air.
U.S. Pat. No. 5,581,998, issued Dec. 10, 1996 to Craig, puts forth a gas turbine combustor in conjunction with a biomass fueled pressurized gasifier having the fuel gas and primary air injected into a primary combustion chamber at independently controlled rates for a rich burn of the fuel gas. A nozzle leads into a secondary combustion chamber having air injected into the secondary combustion chamber at an independently controlled rate to provide a lean burn.
U.S. Pat. No. 5,505,145 issued Apr. 9, 1996 to Gross et al, concerns a process and apparatus for waste incineration in an upright shaft furnace having oxygen-containing gas fed into the lower part of the furnace into a thick fuel bed.
U.S. Pat. Nos. 5,806,440 and 5,720,231 and 5,524,556, issued Sep. 15, 1998 and Feb. 24, 1998 and Jun. 11, 1996 to Rowlette et al, show a method for controlling a draft fan at a desired rate and a draft monitoring method and the use of a microprocessor.
U.S. Pat. No. 5,694,868, issued Dec. 9, 1997 to Mitthof, claims a biomass furnace with a slopi
Asplund Frank
Bender Robert J.
Tomassi John P.
Meeker Donald W.
Wilson Gregory
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