RELATED SOLID FUEL

Field of the Invention

This invention relates to systems for firing fuel for the purpose of supplying heat to power generation and industrial processes, and in particular to systems for using biomass or peat in conjunction with hydrocarbon fuels as the firing fuel. More particularly, the invention relates to a conversion burner and a method of conversion of biomass or peat, by combustion, gasification or partial gasification, such that products from the conversion burner can be delivered directly to a combustor for firing, or co-firing with another fuel.

Background of the Invention

Various attempts have been made to use biomass as a fuel for power generation and industrial processes, to reduce the environmental impact of using traditional fuels such as coal, and to take advantage of biomass as a fuel source where available. These attempts have included various methods of using the biomass, including mixing the biomass with the fuel, separate injection of the biomass into the furnace, separate gasification and injection of syngas. However, each of these attempts has suffered from its own disadvantages, including difficulties in practice, which arise primarily from the two opposing factors, namely the problems inherent in using wet biomass, and conversely the problems arising from pre-drying the biomass.

The deposit of ash within a furnace creates general problems requiring the provision of means for removal of such deposits. Biomass ash in particular contains large quantities of potassium and sodium, which reduce the melting temperature of the ash, thereby further increasing the tendency for fouling and slagging in co-firing applications.

The use of pre-drying systems can address some of the problems of firing wet biomass; but pre-drying systems have their own disadvantages, including the high costs of providing additional plant and equipment, the costs and practical disadvantages of remote storage of dried biomass product prior to delivery to the furnace, and the necessary transfer equipment for such delivery. Further, there is an inherent and serious risk of fire or explosion in such storage, and during delivery from a remote location to the furnace, due to factors inherent in such dried products, including, but not limited to, the high levels of dust content, temperatures, oxygen concentration, surface area, fineness of the material, and the type of material.

Where biomass is mixed with a solid fuel such as coal prior to a pulverization stage, e.g. in a power generation process, the disadvantages include the risks of explosions and fires; poor pulverization performance of some types of biomass, particularly wood; clogging during pulverization resulting from the tendency of biomass to deform plastically, in contrast to the normal breaking of coal particles in a pulverizer; and slagging and fouling in the furnace. Where biomass is injected separately into the furnace, the disadvantages include similar risks of explosions and fires in processes in which the biomass is pre-dried and reduced in size prior to injection; and similar risks of slagging and fouling in the furnace.

However, although these risks are reduced or avoided in injection processes not requiring pre-drying, such processes have the disadvantages of requiring separate handling of the biomass, and large economic costs, arising primarily from the large capital investment required for such systems, and the large operational costs in general; and the practical difficulties and costs of providing the structure for delivery of hot flue gases from the gasifier to the furnace. Further disadvantages include the difficulty and sometimes impossibility of providing such systems as retrofits, and problems arising from tar accumulation in the distribution system.

It would therefore be highly desirable to provide a means of directly using wet biomass, or similar solid fuels such as peat, without the pre-drying requirement and its

disadvantages, and doing so at the furnace, or in close proximity thereto, by gasification of the biomass and delivery of the gas product, and not the biomass itself, to the furnace, thereby avoiding the delivery of ash to the furnace, and the associated risks of slagging and fouling, and other disadvantages of introducing wet biomass directly into the furnace.

Currently, as a fuel, peat is not considered as being a "biomass" product, although sharing some of the properties of other products within this general class, including the problems associated with wetness and residue. In general, and for the purposes of the present invention, "biomass" includes, but is not limited to, wood, generally white wood, and in the form of e.g. chips, bark, hog or sawdust; plant products, e.g. switchgrass, willow, miscanthus, yard waste; construction waste, sludges, e.g. pulp and paper sludge, municipal sewage wastes, other by-products of pulp and paper; and agricultural waste, e.g. bagasse, wheat shorts, straw, husks, shells, renderings and manure. However, it should be understood in the discussion below of the features of the invention that the apparatus, system and method of the invention are applicable to a wide range of solid fuels comprising biomass and peat, and any other solid fuel having similar properties, and references to "biomass" should be understood as including such similar solid fuels.

Summary of the Invention

It has now been found that an apparatus, system and method can be provided which substantially reduces or completely overcomes the disadvantages of known approaches, including those discussed above, by providing for conversion of wet biomass or peat at, or in close proximity to, a combustor, by providing conversion burners integrally and operatively connected to the combustor. It has further been found that it is particularly advantageous to provide for a plurality of small conversion burners each connected to the combustor, each of which can be controlled and operated independently of the others, allowing for more accurate regulation and control of the gasification process than if a single larger burner is used.

The apparatus, system and method of the invention provide important advantages, including but not limited to the following: The risks of explosions and fires are substantially reduced, as the biomass or peat can be fed into the conversion burner in larger sizes and without any pre-drying requirement. As it is not directly mixed with the fuel, the combustibility issues arising from such mixing are avoided.

The operating costs associated with comminuting and drying are minimized or avoided entirely, as the biomass or peat can be handled as large particles and fed moist.

For example, in the case of co-firing and co-feeding with coal in a pulverizer, the problems of introducing biomass or peat, with the tendency to deform plastically, with coal particles, leading to fouling or plugging in the pulverizer, are avoided. Further, the tendency of biomass or peat, which contain larger amounts of volatile matter and oxygen than coal, to ignite near a hot air inlet or within the pulverizer, in co-fed processes, is avoided.

The gasification or conversion of the biomass allows for at least partial removal of ash from the conversion burner in a low temperature environment, which reduces the alkali loading to the furnace and the exposure of ash to the high temperatures of the furnace, thus minimizing the potential problems of fouling and slagging inherent in existing processes. The apparatus, system and method of the invention can provide advantages of lower costs of installation and operation than external gasifier systems, and the apparatus and system can readily be provided as retrofits to existing combustion systems.

In a first broad embodiment, the invention therefore seeks to provide a conversion burner for a solid fuel selected from at least one of biomass and peat, constructed and arranged to be affixed to a combustor having a combustion region, the burner comprising

(i) a housing defining a burner chamber;

(ii) a grate within the burner chamber defining an upper chamber region and a lower chamber region;

(iii) at least a first solid fuel inlet; (iv) at least a first air inlet operatively connected to the upper chamber region and constructed and arranged to be connected to a first air source;

(v) a product gas outlet constructed and arranged to be operatively connected to the combustion region of the combustor; and

(vi) at least one waste outlet.

Preferably, the conversion burner is constructed and arranged to be affixed in a plurality to the combustor. Preferably, the first solid fuel inlet comprises a biomass feed control means.

Preferably, the conversion burner further comprises at least a second air inlet operatively connected to the lower chamber region and constructed and arranged to be connected to a second air source. In such embodiment, preferably at least one of the first air inlet and the second air inlet comprises an air feed control means, which preferably also comprises at least one air distribution plate constructed and arranged to direct and distribute air from the respective one of the first air inlet and the second air inlet in selected directions within the burner chamber. Optionally, the grate is affixed within the burner chamber, or is secured so as to be at least one of adjustable and movable within the burner chamber. Where the grate is movable within the burner chamber, preferably the movement is selected from at least one of vibration, oscillation, travelling and reciprocation. Optionally, the conversion burner further comprises a startup burner within the upper chamber region and proximate the grate.

Preferably, the at least one waste outlet comprises an ash hopper. In a second broad embodiment, the invention therefore seeks to provide a system for conversion of a solid fuel material selected from at least one of biomass and peat for delivery to a combustion region of a combustor, the system comprising at least one conversion burner each constructed in accordance with the invention, and each operatively connected by a product gas delivery means to the combustor at the combustion region.

Preferably, the conversion is selected from at least one of combustion, gasification and partial gasification.

In a third broad embodiment, the invention therefore seeks to provide a method of conversion of a solid fuel material selected from at least one of biomass and peat and delivering a supply of converted product to a combustion region of a combustor, the method comprising the steps of

(i) providing at least one conversion burner, each comprising a housing defining a burner chamber, a grate within the burner chamber defining an upper chamber region and a lower chamber region;

(ii) connecting each conversion burner to the combustor at the combustion region to provide a flow path from the upper chamber region to the combustion region;

(iii) delivering a supply of the solid fuel material to the upper chamber region of selected ones of the conversion burners;

(iv) for each selected conversion burner, converting the supply of the solid fuel material on the grate, and concurrently selectively delivering a first supply of air to the upper chamber to produce a flow of the converted product;

(v) delivering the flows of the converted product from the respective conversion burners to the combustion region; and

(vi) collecting waste materials in the respective lower chambers for selective removal. Preferably, step (iv) further comprises delivering a second supply of air to the lower chamber.

Preferably, step (iii) comprises delivering the solid fuel material at a rate selected from continuous input and periodic batch input.

Preferably, step (i) further comprises providing an air feed control means to at least one of the upper chamber region and the lower chamber region, and preferably this comprises providing to at least one of the first air inlet and the second air inlet an associated air distribution plate constructed and arranged to direct and distribute air from the respective one of the first air source and the second air source in selected directions and selected amounts within the burner chamber.

Preferably, step (i) further comprises affixing the grate within the burner chamber, or securing the grate so as to be at least one of adjustable and movable within the burner chamber. Where the grate is secured so as to be movable, preferably the movement is selected from at least one of vibration, oscillation, travelling and reciprocation.

Optionally, step (i) further comprises providing a startup burner within the upper chamber region and proximate the grate.

Preferably, step (i) further comprises providing air in a combined amount by volume to meet at least a portion of the stoichiometric requirement between 30% and 150%. Preferably, at least a portion of the solid fuel material delivered in step (iii) is a wet solid fuel material comprising up to 60% water by weight %.

Preferably, step (v) further comprises selectively delivering additional air into the combustor together with the converted product. Preferably, step (vi) comprises collecting waste materials in an ash hopper.

Preferably, the conversion is selected from at least one of combustion, gasification and partial gasification.

Brief Description of the Drawings

The invention will now be discussed in relation to the drawings, in which

Figure 1 is a schematic representation of a biomass gasification burner in an embodiment of the invention;

Figure 2 is a schematic representation of a combustion system including a biomass gasification burner in an embodiment of the invention; and

Figure 3 is a schematic cross-sectional representation of an induration furnace including biomass gasification burners in an embodiment of the invention. Detailed Description of the Drawings

Referring first to Figure 1, a biomass gasification burner 10 in an embodiment of the invention is shown schematically. The burner comprises a housing 12, defining a burner chamber 14. Within burner chamber 14, a grate 20 defines an upper chamber region 16 and a lower chamber region 18. In this embodiment, two air inlets are shown, an upper first air inlet 22 operatively connected to the upper chamber region 16, and a lower second air inlet 24 operatively connected to the lower chamber region 18. The first air inlet receives air selectively from a first air source 36, and the second air inlet receives air selectively from the second air source 38. At or proximate the connection of the first air inlet 22 to the burner 10, an upper air distribution plate 26 can be provided, to allow for selective direction of the air flow through the first air inlet 22 to the upper chamber region 16, to regulate the flow path as desired. Similarly, a lower air distribution plate 28 can be provided at or proximate the connection of the second air inlet 24 to the burner 10, for direction and regulation of the flow of air into the lower chamber region 18. At a suitable location at an upper region of the housing 12, at least one biomass inlet 30 is provided, preferably including a biomass supply chute 32, regulated by feed control means 34, for delivery of biomass from a source 31 into the upper chamber region 16. Optionally, upper chamber region 16 can also include a start-up burner 46. From the upper chamber region 16, at least one product gas outlet 48 is provided, for delivery of the product gas to the combustor 50, for combustion with or without other fuel in the manner described below in relation to Figure 2.

From the lower chamber region 18, a waste outlet means is provided for removal of any waste resulting from the gasification within the burner chamber 14. Preferably, the waste outlet means comprises an ash hopper 40, to deliver the waste product into a collection container 42, for removal at waste outlet 44.

Referring now to Figure 2, a combustion system including a biomass gasification burner in an embodiment of the invention is shown schematically. A combustor 250 comprises a combustion region having an upper combustion zone 254 and a lower combustion zone 256. At least one biomass gasification burner 210, provided with a biomass supply at biomass inlet 230, and an air supply at air inlet 224, is affixed and operatively connected to the combustor 250, such that the product gas flow 248 from the biomass gasification burner 210 can be delivered to the upper combustion zone 254. In schematic Figure 2, for simplicity of representation, air inlet 224 is shown at the lower region of the biomass gasification burner 210; however air inlet 224 will generally be structured to deliver the air supply selectively to either or both of an upper air supply path and a lower air supply path (not shown), in a similar manner to that shown in Figure 1 in relation to first air inlet 22 and second air inlet 24. For co-firing applications, at a region of the combustor below the one or more inlets for receiving the gas product flow 248, at least one fuel inlet 258 is provided for delivering the selected appropriate fuel into the lower combustion region 256. Referring now to Figure 3, an iron ore induration furnace 350 is shown in cross-section. Furnace 350 is provided with a plurality of biomass gasification burners 310, located along the travelled length of the furnace 350, in an embodiment of the invention. Each burner 310 receives a biomass supply at biomass inlet 330, and an air supply at air inlet 324. In schematic Figure 3, for simplicity of representation, air inlet 324 is shown at the lower region of burner 310; however air inlet 324 will generally be structured to deliver the air supply selectively to either or both of an upper air supply path and a lower air supply path (not shown), in a similar manner to that shown in Figure 1 in relation to first air inlet 22 and second air inlet 24.The product gas flow 348 from burner 310 joins the downflow gas stream A from the upper region 362, and the combined flow B is delivered to the combustion zone 360 of the furnace, where the combined flow B releases heat in suspension above the iron ore 366 which is carried by the grating bed 364.