Mineral Additive Blend Compositions and Methods for Operating Waste to Energy Combustors for Improving their Operational Performance and Availability, Protecting Combustor Materials and Equipment, Improving Ash Quality and Avoiding Combustion Problems

Abstract

Mineral additives and a method for operating a waste-to-energy furnace are provided in order to improve its operational performance and availability, increase the lifetime of the combustor building materials (refractory walls and heat-exchanger metallic tubes) and flue gas treatment equipment, improve ash quality, reduce emissions and avoid combustion problems such as agglomeration, slagging, deposition, and corrosion. A method for operating a waste-to-energy furnace, such as a fluidized bed reactor, pulverized-fuel combustor, grate combustor includes introducing mineral additive into the furnace. The method further includes heating at least a portion of the mineral additive either intimately in contact with the fuel, such that the ability of mineral additive to induce crystallization of the surface of forming ashes is enhanced, or minimizing the contact of the mineral additive with the fuel and the forming ashes, such that the solid-gas reactions between the mineral additive and the volatile compounds in the flue gas are favored and the mineral additive power to capture at least a portion of the inorganic volatile compounds present in the furnace is enhanced.

Claims

1-21. (canceled)

22. A method for combusting waste material, the method comprising: providing a fuel comprising a waste material, said fuel having an ash content ranging from 1.5% to 75%; adding 1% to 100% by weight on a fuel ash content basis of an aluminosilicate-containing mineral additive to said fuel to produce a mixture of fuel and mineral additive; and combusting the mixture of fuel and mineral additive to produce ash, wherein the mineral additive comes into contact with the forming ash during combustion to induce crystallization of the ash surfaces and thereby reduce ash coalescence.

Description

DESCRIPTION OF EMBODIMENTS

[0037] Reference will now be made in detail to a number of exemplary embodiments. Fuel may be combusted in a furnace to produce heat, and the heat produced may, in turn, be used to generate electric power, via, for example, a steam generator. Heating the fuel and/or materials (e.g., calcium carbonate) associated with a combustion process may result in release of inorganic components in the furnace, such as alkalis, alkaline earths, sulfur, chlorine, fluorine, oxides and metals (iron, zinc, antimony, vanadium, arsenic, cadmium, barium, lead, mercury, nickel, chromium, cobalt, copper, tin, manganese).

[0038] According to some embodiments, a mineral additive may be added to the furnace, and the heat may at least partially calcine the mineral additive, such that the at least partially calcined mineral additive captures at least a portion of the alkali and/or inorganic volatile compounds within the furnace. Additionally, the mineral additive may come into contact with the forming ashes and act as nucleation sites on the ash surfaces, increasing its crystallization ability, its crystalline fraction and its viscosity, resulting in more refractory ashes. Consequently, the mineral additive renders ashes less sticky, less deformable and less prone to undergo deposition and densification on the exposed surfaces of the combustor components.

[0039] The combustion can occur in a grate furnace, a stoker combustor, a fluidized bed combustor, a pulverized fuel combustor, a rotary furnace, or any other furnace configured to burn waste.

[0040] The fuel used in the combustion can be a mixed heterogeneous waste, such as for example a municipal solid waste, a biomass waste, an animal waste, or an industrial waste. Municipal solid waste can include, for example, domestic household waste, sewage sludge, medical or hospital waste, furniture, tires, textiles, plastics, rubber, cartons and the like. Animal waste can include, for example, meat scraps, bone fragments, bone meal, litter, manure, and other substances generated by or from animal production and processing. Biomass can include, for example, agricultural waste, forest residues, waste wood, demolition wood, chipboard, fiberboard, plywood, wood pallets and boxes, and other plant-based substances generated by forestry or farming. In another aspect, the fuel can include a contaminated biomass waste such as demolition wood, furniture wood, currency shredded, refuse-derived fuel. Industrial waste can include, for example, industrial sludge, paper pulp sludge, waste paper, waste paperboard, furniture, textiles, plastics, rubber, cartons and tannery waste.

[0041] Fuel based wastes differ from the more homogeneous fuels commonly used in fossil fuel based power plants in several aspects. Waste fuels tend to have a much wider variety of shapes, sizes, and in some instances plasticity and flowability, especially in cases where plastic or rubber are present.

[0042] The composition of waste fuels can also vary greatly, depending on source. Ash content can range from as low as 0.4% by weight (for plywood waste) to as high as 75% by weight (for aged cattle manure). This can lead to the production of a greater amount of bottom ash than fly ash.

[0043] In one aspect, the fuel used in the combustion can have an ash content of at least 10%, such as for example at least 20% by weight, at least 30% by weight, at least 40% by weight or greater than about 50% by weight.

[0044] The relatively high ash content of waste fuels can lead to several undesirable effects. For example, slag formation and/or bottom ash agglomeration can occur on the grate or furnace bed, blocking fuel feeding and ash removal. It is necessary to maintain controlled ash removal flux from the grate or the fluidity of the fluidized bed in order to maintain a regular fuel feeding, guarantee a steady and efficient combustion and suitable boiler operation and availability. Furthermore, ash, slag and deposits can be chemically reactive and can damage refractory wall linings and other furnace components, as large amounts of volatiles can be released from waste fuel into the flue gas, including for example sodium, potassium, sulphur, chlorine, fluorine, phosphorous, and metals (e.g., Hg, Pb, Cd, Cr, As, Sb, Fe, Zn, V, Ba, Ni, Co, Cu, Mn, Sn) and subsequently condensate on the combustor surfaces. Flue gas containing fluorine compounds (e.g., HF) produced by combustion of plastics and other synthetic materials can be especially corrosive.

[0045] In some cases, incineration of large waste volumes can be more important than high energy production. Legislation imposes constraints on ash disposal, flame temperature for burning dioxins and furans and emissions of toxic metal compounds and fine particulate matter. Ashes containing high amount of soluble sulfates, chlorides and toxic metal compounds usually have to be landfilled (with the exception of biomass ashes).

[0046] In one aspect, it can be beneficial in some cases to introduce the mineral additive in such a manner to maximize its contact with and subsequent interaction with the forming ashes, for example, fly ash, bottom ash, and slag. Such application can provide a number of benefits such as: reduction of slagging, increased slag friability, minimization of falling of large pieces of slag from the upper parts of the combustor that can cause bed defluidization, improved fuel feeding flux into the combustion chamber, improved combustion efficiency, easier or more efficient slag and ash removal from the combustion chamber (from walls, grate, and/or bed), stabilization of heat release rate, improved ash chemical resistance in wet environments and reduction of leaching of toxic metals in aqueous solutions. Such application can also improve the characteristics of the bottom ash and fly ash, as well as increase the ratio bottom ash to fly ash generated, increasing its quality and suitability for use in applications such as road base materials, construction filler materials, and create the possibility to explore new end-uses. In addition to the effect on the ash and combustion properties, the mineral additive added at low dosages in intimate contact with the fuel can still beneficially capture part of the volatile alkalis released during combustion before coming into contact with the forming ashes, also contributing to reduce the partial pressure of alkali chlorides and sulphates (NaCl, KCl, Na.sub.2SO.sub.4, K.sub.2SO.sub.4) in the flue gas and thereby the condensation of alkali salts on the heat-exchanger tubes, i.e. fouling. By the reduction of fouling, corrosion is also reduced and heat transfer in the heat exchangers is improved. This benefit can be obtained as long as the dosage of the mineral additive is at least 10% of the stoichiometric ratio of the alkali in the fuel available for the reactions between the mineral additives and the alkali volatiles (1) to (8) described previously.

[0047] Adding the mineral additive to the furnace in a manner such that contact with the ash surfaces is maximized can induce surface crystallization of the ash. Ash agglomeration and slagging generally involves a mechanism of coalescence of individual ash particles followed by sintering. Coalescence and sintering of ash particles are strongly dependent on the mass transport mechanisms taking place on the ash surface. Viscous flow of molten ash particles can be the primary mass transport mechanism leading to coalescence and sintering of ash particles during ash agglomeration and slagging. Mineral additives can act as nucleation sites for crystals on the molten ash surfaces. Crystallization of the ash surfaces prevents the viscous flow and consequently the coalescence of ash particles, thereby hindering sintering. Slags and ash agglomerates eventually formed have higher porosity and increased friability. Gas permeability through the forming ashes is also increased, which allows an even flow of air and combustion gases through the fuel and forming ash particles, avoiding punctual increase of gas velocity and therefore avoiding fine ash particles to be entrained into the flue gas. As a result a reduction of the amount of fly ashes is promoted. In this way the ratio bottom ash to fly ash generated is increased.

[0048] Relatively low amounts of well-dispersed fine mineral additive particles can be sufficient to induce surface crystallization of ash, such as from about 0.2% to about 15% by weight in comparison to the weight of the fuel. For example, crystallization can be induced by the mineral additive particles on the ash surface by the introduction of a large number of nucleation sites and by the local increase of the concentration of the elements Al.sub.2O.sub.3 and/or MgO and/or CaO on the ash surface. Surface crystallization induction performance can be favoured by the use of clays having single silicate sheet structure (1:1 clays). Surface crystallization of ashes decreases ash agglomeration and densification, hindering slag formation. The resultant slags have increased porosity and friability leading to the easy reduction of the slag into small pieces. Large slag pieces falling from the combustor upper parts on the fluidized bed can be avoided. Slags and bottom ashes are also more easily evacuated from grate and fluidized bed boilers, so that fuel feeding and ash removal from the grate and fluidized bed is maintained constant. Combustion of the fuel is improved by two factors, a better and regular fuel feeding into the combustor and the higher porosity and permeability of the forming ashes during combustion which allow a better access of oxygen to the combustion reaction of the fuel material.

[0049] In another aspect, alkali and toxic metals localized on the ash surface (either originating from adsorption or condensation on the ash surface) can be immobilized by crystallization and fixed into crystalline 3D structures, reducing their availability for the formation of soluble chlorides and sulfates. In this way, the resulting bottom ash also has improved chemical resistance in wet environments and leaching of toxic metals by aqueous solutions is considerably reduced. The characteristics and quality of the resulting bottom ash improves its suitability for use in applications such as road base materials, construction filler materials, and create the possibility to explore new applications otherwise not allowed.

[0050] For example, the mineral additive can be added to the waste fuel prior to its introduction into the boiler. In some cases it can be beneficial to co-process the waste fuel and mineral additive by subjecting them to mechanical processes such as pressing, compacting, grinding, shredding, shearing, cutting and the like or by subjecting them to thermal processes or pre-heating. In another example, the mineral additive can be introduced by spraying it as a slurry onto the waste fuel prior to its introduction into the boiler. In another example, the mineral additive can be injected directly onto the waste fuel during its introduction into the boiler. In yet another aspect, in a fluidized-bed combustor, the mineral additive can be introduced through the bed material feeding or re-feeding system or be injected directly onto the fluidized-bed. In yet another example, the mineral additive can be introduced into the boiler as a powder, agglomerate, or slurry with the primary air.

[0051] In cases where the mineral additive is added in a manner to maximize contact with the waste fuel and ashes, the dosage of mineral additive can be adapted to ensure that sufficient mineral additive is provided to interact with the anticipated ash content produced by the fuel. For example, it can be beneficial to provide the mineral additive in an amount ranging from about 1% to about 100% by weight in comparison to the non-volatile ash content of the fuel. This can range from about 0.2% by weight in comparison to the fuel in cases where the waste fuel is a wood waste, to 15% in cases where the waste fuel includes sewage sludge or aged cattle manure. In some aspects, the mineral additive can include kaolin, ball clay, bauxitic clay, smectite, bentonite, clayey marl, marl, calcareous marl, other clays, and/or refractory aluminosilicate minerals such as halloysite, calcined clay, andalusite, kyanite, sillimanite, perlite, mica, chlorite, attapulgite or palygorskite and pyrophyllite.

[0052] In some aspects the mineral additive can include one or more of the above, and a second mineral such as a calcium based mineral or a magnesium based mineral, such as calcium carbonate, limestone, marble, chalk, dolomite, aragonitic sand, sea shells, coral, cement kiln dust, talc, brucite and magnesium carbonate.

[0053] In another aspect, the mineral additive can be added to the combustion zone or furnace in a manner intended to maximize the reaction of the mineral additive with flue gas constituents, while minimizing direct contact with the fuel and ash. Such introduction mode favors reactions between mineral additive particles and volatile compounds released in the flue gas during combustion of wastes.

[0054] According to this aspect, mineral additive is introduced in a manner to avoid contact with solid or liquid ash and the fuel. For example, in grate boilers the mineral additive particles can be injected in the flue gas flux after the fuel introduction zone, thereby avoiding contact with the fuel and the bottom ash in the grate. In bubbling fluidized bed boilers, the mineral particles can be injected in the flue gas flux after the fluidized bed. These injection modes are intended to direct the mineral additive particles parallel to the direction of flue gas flow in order to avoid projection of the mineral particles onto slags and deposits at the bottom of the combustion zone.

[0055] When the mineral additive is added directly to the flue gas, benefits can include: reduction or elimination of salt deposits formation on the heat-exchanger tubes, reduction of corrosion of the combustor building materials due to the reduced amount of deposits and modification of the composition (lower in alkalis, chlorides and sulphates) and structure of deposits eventually formed (being more porous and easily removed by the flue gas turbulence), reduction of toxic metals or other metal compounds such as Hg, Pb, Cd, Cr, As, Sb, Fe, Zn, V, Ba, Ni, Co, Cu, Mn, Sn emissions into the environment, reduction of fine particulate matter emissions (aerosols <1 μm), reduction of water soluble chlorine and sulphates in the fly ash, increased fly ash chemical resistance and consequently reduction of the leaching of toxic metals in aqueous environments, improvement of fly ash quality for safer and less expensive landfilling, improvement of fly ash quality for use as construction material filler (i.e. improve pozzolanic properties for application in cements), reduction of corrosion of metallic parts and refractories caused by alkali salts and HF vapour, and an increased lifetime of flue gas treatment equipment (cyclones, SCR, ESP, etc.). Additionally, in the case that the mineral additive particles eventually come into contact with the fly ashes, all the benefits of increasing the crystallization ability of the ashes and its crystalline fraction is obtained. The resulting fly ashes is then more refractory, less sticky, less deformable and less prone to undergo deposition and densification on the exposed surfaces of the combustor components.

[0056] According to this aspect, mineral additive particles can be in a powder or slurry form to facilitate dispersion into individual mineral particles during injection into the combustion chamber in order to maximize reaction rate with the flue gas compounds. The dispersion of the mineral additive into individual particles coupled with the maximization of the exposition time of the individual particles in the flue gas results in increased total reaction yield between the mineral additive and the volatile compounds in the flue gas.

[0057] Dispersion of the mineral additive into individual particles can be effective to increase the exposure of the oxygen-rich mineral surfaces. These oxygen-rich mineral surfaces then can act to increase the oxidation of volatile toxic metal elements released during waste combustion such as Pb, Hg, As, Cd, Cr, Sb, Co, Cu, Ba, Mn, Ni, V, Sn, Zn leading to the formation of the corresponding metal oxides on the mineral surface and effectively immobilizing the metals. Furthermore, at the high operating temperatures in the heat radiant or convective zone (between 600° C. and 1200° C.), the oxidized metals ions formed on the mineral particles surface are also capable of diffusing into the mineral particle and becoming fixed in the mineral three-dimensional aluminosilicate structure. Diffusivity of metal elements into the mineral particles, and consequently metal fixation in the aluminosilicate structure, increases with temperature, therefore, in one aspect, mineral additive can be injected in a high temperature zone (between 600° C. and 1200° C.) of the boiler.

[0058] Mineral additives having a silicated surface are also able to react with HF contaminants in the flue gas, which can arise during the combustion of some plastics and synthetic polymers (fluoropolymers). HF can react with the silicate network structure of silicate minerals through the reaction: HF+-Si—O—Si—.fwdarw.—Si—OH+—Si—F incorporating fluorine in its structure. Clays having a double silicate sheet structure (2:1 structure) can provide a relatively high reaction rate with toxic metal elements and fluorine. Diatomite also has a highly porous silicate structure and high surface area and can be added to the mineral additive blend to increase the effectiveness of reaction with toxic metal and fluorine volatile compounds in the flue gas. In one aspect, calcium- and magnesium-containing minerals can also be blended with aluminosilicate mineral additives in order to enhance the reaction of the mineral additive with fluorine and chlorine, forming CaF2, CaCl2), MgF2, MgCl2, and capture volatile phosphorus compounds. Accordingly, by introduction of mineral additive to the flue gas, the HF content can be reduced upstream of the flue gas treatment system, and corrosion can also be reduced.

[0059] According to this aspect, the mineral additive can be added to a dosage ranging from 10% to 150% or higher of the stoichiometric ratio of the alkali in the fuel available for the reactions K2O+Al2O3.2SiO2.fwdarw.2KAlSiO4 and Na2O+Al2O3.2SiO2.fwdarw.2NaAlSiO4, or any of the former reactions from (1) to (8) between aluminosilicates and alkali compounds such as NaCl, KCl, NaOH, KOH, Na2SO4, K2SO4 presented before. The excess of aluminosilicate being added sometimes with the aim to increase its availability to capture toxic metal volatiles and fluorine in the flue gas; CaCO3 or any calcium- and magnesium-base compound content ranging from 10% to 150% of the stoichiometric ratio of the fluorine and chlorine in the fuel available to form CaCl2 or CaF2 or MgCl2 or MgF2. Typically, according this aspect, the dosage can range from about 0.1% by weight on a fuel basis for wood waste, to as high as 12% or greater by weight on a fuel basis for sewage sludge, paper pulp sludge or animal waste.

[0060] According to this aspect, it can be preferable to inject the mineral additive with the secondary or tertiary air into the boiler in a powder or slurry form. Secondary and tertiary air is injected to ensure complete combustion of the gas phase organic components volatilized from the waste fuel during combustion with primary air. Alternately, the mineral additive can be injected into the flue gas above the flame or fluidized bed in the radiant heat zone of the boiler in powder or slurry form. The mineral additive can also be injected into the heat convective zone of the boiler in powder or slurry form. Alternately, the mineral additive can be injected into the flue gas via a SNCR De-NOx system with or without ammonia- or urea-containing compounds.

[0061] In accordance with this aspect, the mineral additive can include one or more of ball clay, kaolin, or other aluminosilicate minerals or clays. In another aspect, the mineral additive can include a blend of an aluminosilicate mineral with a calcium- or magnesium-based mineral. In another aspect, the mineral additive can include a blend of an aluminosilicate mineral with a silica mineral, e.g., diatomite.

[0062] According to some embodiments, a method of operating a furnace may include at least the steps of introducing an inorganic compound-containing fuel material into a furnace, introducing a mineral additive having a moisture content of at least about 5% (e.g., a moisture content ranging from about 5% by weight to about 15% by weight) into the furnace, and removing at least a portion of the mineral additive from the furnace or its exhaust gas stream.

[0063] According to some embodiments, the mineral additive may include lump clay, for example, hydrous clay that may be partially dried to a moisture content ranging from at least about 1% by weight to at least about 50% by weight. According to some embodiments, the lump clay may be partially dried to a moisture content ranging from about 4% by weight to about 16% by weight, for example, from about 8% by weight to about 12% by weight (e.g., about 10% by weight), from about 5% by weight to about 10% by weight, or from about 10% by weight to about 15% by weight.

[0064] According to some exemplary embodiments, the clay may include one or more of lump clay, clay that has been shredded and/or crushed, non-beneficiated clay, kaolin, ball clay (e.g., clay that includes about 20-80% kaolin, 10%-35% mica, and/or 6%-65% quartz), and clay derived from overburden or process waste from a kaolin or any aluminosilicate mining operation (e.g., clay derived from material located over kaolin deposits being mined). According to some embodiments, the clay may have a BET surface area of at least about 9 m.sup.2/g, for example, at least about 10 m.sup.2/g or at least about 15 m.sup.2/g.

[0065] In some embodiments, the mineral additive may be at least partially converted to a calcined mineral additive in a furnace. In some embodiments, the at least partially calcined mineral additive may serve to capture at least a portion of alkali present in the furnace. In some embodiments, the mineral additive may come into contact with ash in order to act as nucleation sites for crystallization of the ashes surface, thereby, increasing its crystallization ability, crystalline fraction and its viscosity, eliminating viscous flow and the coalescence of the ashes. Sintering of the ash particles is avoided or hindered as a result of more refractory ashes.

[0066] Before the mineral additive is introduced to the furnace, the size of at least one of the mineral additive may, in some embodiments, be subjected to at least one physical modification process. For example, physical modification process(es) may serve to reduce the size of the mineral additive to, for example, about 1 inch or less. In some embodiments, an exemplary physical modification process may reduce the size of the mineral additive to about ¾ inch or less, for example, to about ½ inch or less. In some embodiments, the exemplary physical modification process may reduce the size of the mineral additive to about ¼ inch or less (e.g., to about ⅛ inch or less). In other embodiments, the mineral additive may comprise clay agglomerates having a maximum lump size of not more than about 3 inches, such as not more than about 2 inches or not more than about 1 inch. Exemplary physical modification processes may include at least one of milling, hammering, roll crushing, drying, grinding, screening, extruding, triboelectric separating, liquid classifying, and air classifying.

[0067] According to some embodiments, inert material may be introduced into the furnace as a fluidization media. Exemplary inert materials may include, for example and without limitation, sand, residues of fuel, and/or gypsum. In some embodiments, a fine inert material may be selected to improve separation efficiency in one or more cyclones that may be associated with the furnace system.

[0068] The mineral additive used in the exemplary methods disclosed herein may take various forms and/or may have undergone various processes. For example, the mineral additive may include shredded and/or crushed clay. In some embodiments, clay may be non-beneficiated clay. As used herein, non-beneficiated clay may include clay that has not been subjected to at least one process chosen from dispersion, blunging, selective flocculation, ozone bleaching, classification, magnetic separation, chemical leaching, froth flotation, and dewatering of the clay. In some embodiments, at least a portion of the clay may be kaolin, for example, a hydrous aluminosilicate having a formula, Al.sub.2Si.sub.2O.sub.5(OH).sub.4. In some embodiments, the clay may include ball clay. In some embodiments, the clay may include clay derived from overburden or process waste from a kaolin or any aluminosilicate mineral mining operation. In some embodiments, the clay may be clay derived from crude clay having a moisture content of at least about 15%. For example, the clay may include montmorillonitic kaolin.

[0069] The mineral additive used in the exemplary methods disclosed herein may be a combination of hydrous clays. For example, at least one hydrous clay may be selected to provide bonding strength to the combination of hydrous clays. In some embodiments, at least one hydrous clay may be selected to increase the coarseness of the hydrous clay combination.

[0070] According to some embodiments, the mineral additive used in the exemplary methods disclosed herein may have a measurable BET surface area. For example, the BET surface area may be at least about 5 m.sup.2/g, for example, the BET surface area may be at least about 10 m.sup.2/g or at least about 15 m.sup.2/g, or at least about 25 m.sup.2/g.

[0071] The mineral additive used in the exemplary methods disclosed herein may have a measurable particle size. Particle sizes and other particle size properties referred to herein, such as particle size distribution (“psd”), may be measured using a SEDIGRAPH 5100 instrument as supplied by Micromeritics Corporation. For example, the size of a given particle may be expressed in terms of the diameter of a sphere of equivalent diameter that sediments through the suspension, that is, an equivalent spherical diameter or “esd.”

[0072] The measurable particle size may indicate the relative coarseness of the mineral additive. In some embodiments, about 20% to about 90% of the mineral additive has a particle size less than about 1 μm. In some embodiments, about 20% to about 70% of the mineral additive has a particle size less than about 1 μm. In some embodiments, about 35% to about 45% of the mineral additive has a particle size less than about 1 μm. In some embodiments, about 30% to about 40% of the mineral additive has a particle size less than about 1 μm. In some embodiments, about 40% to about 60% of the mineral additive has a particle size less than about 1 μm.

[0073] In some embodiments, about 20% to about 95% of the mineral additive has a particle size less than about 2 μm. In some embodiments, about 30% to about 80% of the mineral additive has a particle size less than about 2 μm. In some embodiments, about 65% to about 75% of the mineral additive has a particle size less than about 2 μm. In some embodiments, about 60% to about 70% of the mineral additive has a particle size less than about 2 μm. In some embodiments, about 70% to about 80% of the mineral additive has a particle size less than about 2 μm.

[0074] The mineral additive used in the exemplary methods disclosed herein may have a measurable washed screen residue, for example, a measurable +325 washed screen retention. For example, the +325 mesh wash screen retention may be from about 0.2% to about 9%. In some embodiments, the +325 mesh wash screen retention may be from about 0.5% to about 8%. In some embodiments, the +325 mesh wash screen retention may be from about 0.5% to about 8%. In some embodiments, the +325 mesh wash screen retention may be from about 0.5% to about 5%. In some embodiments, the +325 mesh wash screen retention may be from about 0.5% to about 1.5%. In some embodiments, the +325 mesh wash screen retention may be from about 4% to about 5%. In some embodiments, the +325 mesh wash screen retention may be from about 1% to about 4.5%. In some embodiments, the +325 mesh wash screen retention may be from about 4.5% to about 9%.

[0075] According to some embodiments, inorganic compounds-containing fuel materials may include calcium carbonate. In some embodiments, the calcium carbonate may be provided as particulate limestone, marble, chalk, dolomite, aragonitic sand, sea shells, coral, and/or mixtures thereof. In one embodiment, the inorganic compounds-containing material may include a calcium carbonate originating from a marine originating deposit, for example, wherein the inorganic compound may include residual salt from seawater.

[0076] According to some embodiments, combustion may occur in a furnace that is part of a fluidized-bed reactor system for generating electric power via, for example, a steam generator. For example, the furnace may be part of a bubbling fluidized-bed reactor system. The furnace may be part of other systems for combusting inorganic compounds-containing materials known to those skilled in the art.

[0077] The exemplary methods disclosed herein may be used in association with a variety of fuel(s) and/or inorganic compounds-containing materials. In some embodiments, the fuel may contain an alkali material.

[0078] According to some embodiments, the fuel associated with exemplary methods disclosed herein may include waste biofuel derived from, for example, biomass. Exemplary biomass sources may include, without limitation, wood, wood pellets, straw pellets, peat, lignocellulose, waste biomass, such as bagasse, wheat stalks, corn stalks, oat stalks, and/or energy biomass, such as, for example, grasses of the Miscanthus genus.

[0079] In some embodiments, inorganic compounds-containing materials may include materials selected to reduce at least one of SOx and NOx. For example, the inorganic compounds-containing material(s) selected to reduce at least one of SOx and NOx may include calcium carbonate. For example, calcium carbonate may be derived from the sea. According to some embodiments, the material(s) may include at least one of a SOx- and NOx-getter.

[0080] In addition to mineral additive, in some embodiments, the solid material particles may include at least one of a SOx- and NOx-getter and/or an inert material. An exemplary SOx-getter may include be, for example and without limitation, calcium carbonate. Exemplary inert materials may include, for example, sand, gypsum, and/or residues of fuel.

[0081] For the avoidance of doubt, the present invention includes the subject-matter as defined in the following numbered paragraphs.

EXAMPLES

[0082] Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the exemplary embodiments disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.

Example 1: Combustion of Municipal Solid Waste in a Stoker Furnace

[0083] This test was performed using a kaolinite containing clay in a 20 MWe Stoker furnace burning Municipal Solid Waste. The objective of the test was to demonstrate increased plant availability and thus the energy production, as well as decreased requirement for cleaning of ash deposits (using explosive+jack hammer).

[0084] The fuel used was a municipal solid waste having a fuel ash content of 28% by weight. Mineral additive was added to a dosage of 2% by weight of the municipal solid waste. The mineral additive was introduced in slurry form by spraying onto the waste fuel at the entrance to the furnace, just prior to introduction of the fuel to the conveyor to the grate.

[0085] Addition of the mineral additive had no observable adverse effect on the steam outlet temperature (maintained at 860° F.) after a 3 week trial. This result would previously have required reducing the fuel feeding rate by a factor of two. Use of the mineral additive was also observed to reduce slagging at the entrance to the grate. Ash deposits appeared to be more friable and easy to clean. Bottom ash contained less unburned carbon indicating a better and more complete combustion of the fuel.

Example 2: Combustion of Animal Waste in a Fluidized-Bed Reactor

[0086] This test was performed using a kaolinite containing clay in a 16 MWth Bubbling Fluidized-Bed reactor burning animal waste. The fuel used was a mixed animal waste including: solid waste such as meat and bone meal, dried egg, wood waste, and liquid wastes such as blood, detergent and chemical washing effluents. The fuel ash content of the solid components was 22.5% by weight and of the liquid components was 0.5% by weight. The ash content of the mixture was 7.4%.

[0087] Kaolin based mineral additive was added at a dosage of 6.3% by weight of the solid fuel, or 2.5% of the total fuel mixture. The mineral additive was mixed with the fuel prior to introduction into the combustion chamber.

[0088] Use of the mineral additive was observed to increase the operation time of the furnace from 14 days to 37-71 days. This allowed a much longer run time than was previously possible for waste containing egg shells. At the end of the run, fouling was easy to remove and the ash deposits were friable and easy to clean.

[0089] Use of the mineral additive allowed for increase of the percentage of liquid waste used. This also resulted in a slight reduction of the reactor bed temperature (from 750° C. to 700° C.).