Patent Application: US-62987200-A

Abstract:
a method of treating a fossil fuel for combustion , which includes heating the fossil fuel and an additive in a combustion zone . the additive contains a lime flux that lowers the melting point of lime sufficiently so that lime in the combustion zone melts wholly or partially . the additive reacts with the fossil fuel char and its sulphur plus ash components , in the combustion zone to achieve the following results alone or in combination : accelerated combustion , desulphurization , nitrogen oxides emission reduction , pozzolanic or cementitious product production or combustor anti - fouling .

Description:
a preferred embodiment fires single or multiple synthetic or naturally occurring materials able to melt lime , i . e . “ lime fluxes ”, in whole or part , at temperatures typical of furnace injectors such as coal furnace injectors and / or combustion zones in a furnace such as a coal furnace , preferably in powdered or , possibly , liquid form , and , preferably , while in contact with powdered coal . examples of such materials , known as “ lime fluxes ”, are well known in the non - fossil fuel combustion industry and include minerals shown in table 1 below ( note w , x , y , z values indicate that differing ratios of ingredients are possible to achieve approximately similar melting points . numbers under the “ reference ” column are page numbers in the cited reference ): thermodynamic calculations ( e . g . janaf free energy of reaction calculations based on free energy of formation data at elevated temperatures as described in reference 2 ) indicate that the chemical reactions described below are all feasible . some of these reactions have been described in the references cited previously . the wholly or partially melted lime desulphurizes coal during combustion in a variety of ways , which operate sequentially , symbiotically or in parallel . in such a process molten lime adsorbs sulphur dioxide to form calcium sulphite , calcium sulphide and calcium sulphate according to the following : molten lime reacts with sulphur species such as pyrite or elemental sulphur in the absence or presence of oxygen and in the absence or presence of carbon to form ferrous oxide , calcium sulphide , calcium sulphite , calcium sulphate and carbon monoxide . note that the proper choice of lime - flux combinations ( e . g . low viscosity and low melting points ) allows flooding of coal or char particles especially during their devolatilization stage to effect numerous desulphurization reactions which do not require exclusively the so 2 adsorption requirements of prior art technologies . feo released from coal via fes 2 pyrite decomposition or feco 3 siderite decomposition reduces “ lime melt viscosity ” due to lowering of the lime species melting point ( see table 1 ) resulting in more rapid adsorption of hydrogen sulphide , sulphur dioxide , elemental sulphur , ferrous sulphide or pyrite adsorption by the melt . note also that the substitution of liquid phase cao chemistry instead of the prior art solid state cao chemistry eliminates sintering issues and speed of reaction issues . it should be understood however that desulphurization reactions via so 2 adsorption are possible upon freezing ( solidification ) of the lime - flux - ash - desulphurization product mixtures . desulphurization efficiency will be a function of cao / s ratios , coal volatiles content ( i . e . char porosity ), cao melt chemistry including viscosity , plus combustor residence time and cao / ash ratios which will control the levels of “ free cao ” on freezing of the “ product ” melts . the reactions between molten lime and coal containing sulphur species described in example 1 above are rapid and exothermic , since molten chemical species are in their ionized states , resulting in improved coal combustion even in the absence of oxygen or at lower than normal oxygen levels . the unique ability of molten lime containing mixtures to catalytically oxidize carbon in coal or char via calcium carbide cac 2 formation guarantees enhanced coal combustion resulting in lower levels of unburned carbon under all combustion conditions including low nox combustor operation . the unique ability of molten cao to provide the desirable co required by nox destruction reactions via its catalytic effect on catalytic coal or char carbon oxidation guarantees reduction in nox levels . the ability of molten cao to flood carbon - containing surfaces in chars guarantees maximization of cao catalytic effects on nox destruction . the output of examples 1 and 2 above are clearly suited for pozzolanic and cementitious material production . the zaitsev reference mentioned previously illustrates that it is possible to predict the crystal structure of frozen cao - flux - ash mixtures . the production of caso 4 product from desulphurization reactions is compatible with pozzolanic / cementitious product end uses since this material is a common component in concrete and / or cement production . it is certain that the present method is highly flexible in the production of a wide variety of pozzolanic or cementitious materials via unique combinations of lime / flux chemistry , lime - flux - ash chemistry , lime - flux - ash - sulphur chemistry , lime / flux ratios , lime - flux / sulphur ratios , lime - flux / ash ratios and lime - flux / coal ratios . for instance , the molten alkaline lime - flux containing mixture can react with air to form a calcium sulphate containing byproduct or with coal ash to form mixtures of calcium aluminates , calcium silicates , calcium ferrates , calcium sulphate , calcium fluoroborates , calcium fluoroaluminates , calcium fluorosilicates , calcium fluorophosphates or their mixtures . these calcium salts become evident on cooling of the calcium - enriched reaction products of the fluxed lime and coal sulphur and ash species below their melting points ( e . g . a molten cao . sio 2 species could freeze as casio 3 for example ). the alkalinity of the calcium enriched coal ash containing sulphur species such as calcium sulphate can be controlled unlike the prior art , merely by adjusting the lime to coal ash or lime to coal sulphur dosing ratio . in a sense this allows one to essentially titrate acidic coal species such as aluminum oxide , silicon dioxide , ferric oxide , sulphur dioxide etc . to form salts such as aluminates , silicates , ferrates , sulphoaluminates etc . with desirable properties for the production of concrete or cement . “ free lime ” residual levels i . e . lime untitrated by acidic coal sulphur and ash species can be set to virtually any desirable level . a unique feature of the current method is to use low - grade ash ( e . g . land filled ash ) as a component of the flux or as a fuel in combination with the fossil fuel e . g . coal or char . the advantage of this approach is that the pozzolanic or cementitious material of the combustor is no longer restricted to the ash content of the fossil fuel . this allows for a unique economical technique for the recovery and recycling of heretofore disposed metal containing ash waste . it is clear from the above examples and the background discussion that the current invention allows a degree of control with respect to prevention of combustor fouling due to “ sticky ” deposits at a level of control unavailable on a commercial scale by any known techniques . for instance a wide variety of lime - flux combinations can be chosen to modify the viscosity “ stickiness ” profile of particularly troublesome fossil fuels such as coals rich in iron species such as pyrite fes 2 and / or feco 3 siderite . molten cao - flux mixtures have a unique ability to depolymerize the “ silicate ” chains in sticky deposits such as xfeo — ysio 2 — zal 2 o 3 implicated in combustor fouling . this feature is especially relevant to combustors attempting to run under low - nox conditions and burning high sulphur fuels containing pyrite or siderite . a non - exclusive list of materials able to melt lime , in whole or part , over a wide range of temperatures is given in the above table . their choice could be made on either their ability to cause sulphur control , nitrogen oxides control , accelerated coal combustion , antifouling or enrich the calcium content of coal ash or both . these materials can be used alone or in an almost infinite number of desirable combinations . they can be derived alone or in combinations from both synthetic and natural sources . the calcium enriched ash products of this invention could be considered as lime fluxing agents in their own right . finally , even if the “ fluxed lime ” does not come in contact with the fossil fuel combustion ash ( e . g . non - turbulent fossil fuel combustor ), desulphurization is improved over the prior art . it is clear , however , that the maximum benefit of the current invention may be obtained under conditions where the lime plus lime fluxing additive come into intimate contact with the fossil fuel , e . g . coal or char , either by mixing them in their solid form prior to injection into the fossil fuel combustor , and / or by injecting them into a combustor with sufficient turbulence to cause collisions between the “ fluxed lime ” and the fossil fuel combustion ash . accordingly , while this invention has been described with reference to illustrative embodiments , this description is not intended to be construed in a limiting sense . various modifications of the illustrative embodiments , as well as other embodiments of the invention , will be apparent to persons skilled in the art upon reference to this description . it is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention . 1 . aarna , i . and e . m . suuberg . 1999 . the role of carbon monoxide in the no - 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