Coal Ash - the solid residua produced by our economically essential use of Coal in the generation of abundant and affordable electric power - can be seen and treated as a valuable mineral resource.
It can, for one example, be used and consumed through various means and methods as a raw material, in place of the virgin mineral raw materials conventionally used, in the making of Portland-type cement and Portland-type cement concrete. And, as seen for a few examples in our reports of:
Ohio State Says Coal Ash Extends Service Life of Concrete | Research & Development | News; concerning:
"'Prevention of Corrosion in Concrete Using Fly Ash Concrete Mixes'; Keith Bargaheiser (and) Tarunjit S. Butalia; ISG Resources, Inc., Toledo, Ohio (and) The Ohio State University, Columbus, Ohio; This paper reviews the benefits of using high-volume fly ash in resisting corrosion damage in concrete structures"; and:
Coal Ash Concrete More Durable, Resists Chemical Attack | Research & Development | News; concerning:
"United States Patent 5,772,752 - Sulfate and Acid Resistant Concrete and Mortar; 1998; Inventors: John Liskowitz, et. al., New Jersey and Thailand; Assignee: New Jersey Institute of Technology, Newark; Abstract: The present invention relates to concrete, mortar and other hardenable mixtures comprising cement and fly ash for use in construction and other applications, which hardenable mixtures demonstrate significant levels of acid and sulfate resistance ... . ... The cementitous materials may comprise fly ash as well as cement. The fine aggregate may comprise fly ash as well as sand. The total amount of fly ash in the hardenable mixture ranges from about 60% to about 120% of the total amount of cement, by weight, whether the fly ash is included as a cementious material, fine aggregate, or an additive, or any combination of the foregoing. In specific examples, mortar containing 50% fly ash and 50% cement in cementitious materials demonstrated superior properties of corrosion resistance. Government Interests: The research leading to the present invention was conducted with Government support under Contract No. DE-FG22-90PC90299 awarded by the Department of Energy. The Government has certain rights in this invention"; and:
"United States Patent 6,802,898 - Preparing Fly Ash for High Compressive Strength Concrete; 2004; Inventors: John Liskowitz, et. al., New Jersey and Ohio; Assignee: New Jersey Institute of Technology, Newark; Abstract: The present invention relates to concrete, mortar and other hardenable mixtures comprising cement and fly ash for use in construction. The invention relates to hardenable mixtures comprising cement and fly ash which can achieve greater compressive strength than hardenable mixtures containing only concrete";
the concrete made with Coal Ash can be both stronger and more resistant to chemical attack than standard Portland-type cement concrete.
As explained, however, in discussion and via additional reference links included in our report of:
South Carolina Prepares Coal Ash for use in Concrete | Research & Development | News; which centers on:
"United States Patent 8,234,986 - Method and Apparatus for Turbulent Combustion of Fly Ash; 2012; Inventors: Jimmy Knowles and Richard Storm, SC and NC; Assignee: The Sefa Group, Inc., Lexington, SC;
Claims: A method for reducing the carbon content of small particulate combustion products said small particulate combustion products consisting essentially of fly ash or fly ash with chemical residue and/or contaminants, said small particulate combustion products being a product of a previous combustion and containing unburned carbon and incombustible matter";
Coal Ash, given especially the effects of some environmental controls imposed on the combustion of Coal in electric power generation furnaces, does require some post-combustion treatment before the full benefits of using it as a component of Portland-type cement can be realized. Residual carbon in Coal Ash, for one example, needs to be removed since it, among other effects, interferes with air entrainment chemicals used in concrete to improve it's freeze-thaw performance.
The removal, or deactivation, of such unburned carbon from Coal Ash is just one of the benefits of the two recently-developed technologies we bring you report of herein; technologies intended to improve the already-exemplary performance of Coal Ash used as a component of concrete mixtures.
Another benefit is that the process of making Coal Ash more suitable for use in Concrete mixes can, in fact, be conducted in the Coal combustion furnace itself, via a process that also enable the permanent disposal, through productive utilization, of a number of other industrial wastes.
As seen in excerpts from the initial and one following link in this dispatch to the recent:
"US Patent 8,961,684 - Production of Coal Combustion Products for Use in Cementitious Materials
Date: February 24, 2015
Inventor: Wayne Fried, NY
Assignee: Ash Improvement Technology Incorporated, NY
(Ash Improvement Technology Inc. (AIT) | a technology-driven mineral resources company; "Ash Improvement Technology Inc. (AIT) is a technology-driven mineral resources company. We have developed a proprietary process to convert more than 100 million annual tons in the US, and 1 billion tons worldwide, of landfilled coal combustion residues into a valuable building product with proven environmental benefits.
AIT’s ... technology, named CleanCem, is applied directly at power plants and eliminates the production of waste ash, instead converting it into a chemically modified product that mimics the behavior of cement. Through application of the CleanCem process directly at the power plant, ash is never created. Instead, the material collected is a cogenerated cementitious product. CleanCem overcomes the traditional barriers that have until now impeded higher utilization of ash in concrete, making the product obtained a cost effective and abundant substitute for ordinary cement.
When used in concrete, any non-reactive trace elements resulting from coal combustion are encapsulated (or chemically bound) in the concrete structure. With much debate about the environmental impact of storing ash in landfills, mostly due to the presence of metals such as lead, mercury, arsenic, and other toxic elements, the CleanCem, technology enables use of coal combustion byproducts in the only way proven not to compromise the environment. Because of the encapsulation, potential leaching of any trace elements is reduced to levels that are far below EPA’s safe drinking water limits.
AIT’s CleanCem process transforms ash into a high value cementitious material. By applying the CleanCem process, we not only eliminate mountains of waste ash, close to a billion tons every year, but every ton of CleanCem material used also avoids 0.85 tons of CO2 emissions".) - - -
Abstract: A method and system for producing modified coal combustion products are disclosed. The additives reduce the particle sizes of the coal combustion product and may reduce the amount of un-burned carbon in the coal combustion product, making the modified product useful as an addition to cementitious materials.
Claims: A method of producing a modified coal combustion product comprising combusting coal in the presence of a particle size-reducing additive, wherein the modified coal combustion product has an average particle size less than an average particle size of a coal combustion product combusted from the coal without the additive.
The method ... wherein the modified coal combustion product has an average particle size of from 5 to 20 microns (and) wherein the modified coal combustion product has a carbon content less than a carbon content of a coal combustion product combusted from the coal without the additive (and) wherein the carbon content of the modified coal combustion product is from 0.5 to 2 weight percent.
The method ... wherein the particle size-reducing additive has an average particle size of greater than 50 microns (and) wherein the particle size-reducing additive comprises at least one material selected from the group consisting of limestone, concrete, Portland cement concrete, recycled ground granulated blast furnace slag, recycled crushed glass, kaolin, recycled crushed aggregate fines, silica fume, cement kiln dust, lime kiln dust, weathered clinker, clinker, aluminum slag, copper slag, granite kiln dust, rice hulls, rice hull ash, zeolites, limestone quarry dust, red mud, ground mine tailings, oil shale fines, bottom ash, dry stored fly ash, landfilled fly ash, ponded fly ash, sopodumene lithium aluminum silicate materials, lithium-containing ores and combinations thereof.
(Note, in the above, the potentials for productively utilizing, disposing of, other waste materials; potentials made possible by the use of Coal Ash.)
The method ... wherein the particle size-reducing additive comprises limestone, blast furnace slag, concrete, glass, kaolin and combinations thereof (and) wherein the particle size-reducing additive comprises at least 8 weight percent of the total combined weight of the coal and the additive.
(Granted, blending the "additive" into the Coal prior to combustion would reduce the effective Btu content of the blend, and, some of the heating value of the Coal would be made unavailable for the generation of thermal energy and, thus, electricity. The payback is that a byproduct of commercial value is being produced and disposal costs for the Ash are being avoided.)
Background and Field: The present invention relates to coal combustion products, and more particularly relates to the production of coal combustion products having improved properties for use in cementitious materials.
Concrete and other hydraulic mixtures used for construction rely primarily on the manufacture of Portland cement clinker as the main binder controlling the rate of development of mechanical properties.
The manufacture of Portland cement clinker is energy intensive and releases large amounts of carbon dioxide into the atmosphere. To reduce the environmental impact of cement and concrete manufacture, supplementary materials with lower carbon dioxide footprint may be used to partially replace Portland cement clinker as the binder in hydraulic mixtures.
Large amounts of coal ash and other coal combustion products are generated worldwide from the burning of coal as fuel for electricity generation and other energy intensive applications. (The) use of coal ash and other coal combustion products in concrete (can result) in a product with low air entrainment and low early strength development. (However) initially the fly ash significantly retards the development of mechanical properties of the concrete. Tests (show) that the compressive strengths of fly ash concrete at early ages are lower than those for the control concrete ... .
(The above is an issue with Coal Ash concrete which we have previously treated in our reports. Although the use of Coal Ash in concrete mixtures can result in a cured concrete that is ultimately much stronger and more durable than conventional Portland-type Cement Concrete, "PCC", such Coal Ash concrete mixtures take a significantly longer time to "cure", or harden, than conventional PCC, which is a significant factor to consider in major construction projects that must proceed in stages, or which are time-constrained because of other factors, such as changing seasons and weather. The technology being disclosed herein serves to address some of those considerations.)
(Coal) fly ashes can (also) contain high levels of free carbon ... . The presence of excessive carbon levels inhibits the action of chemical additives used as air entrainment agents in concrete. Air entrainment in concrete is essential to ensure the durability of concrete under repeated freeze-thaw cycles. Hence, the use of combustion products in concrete is limited by the presence of free carbon.
In practice, these drawbacks prevent the economical use of coal ash at higher substitution levels than 25 to 30 percent in most construction concrete. As a result, a large amount of coal combustion byproducts are disposed of in landfills, at a high economical and environmental cost. Existing methods to beneficiate coal ash so as to make it suitable for other uses, such as in construction, generally do not enable 100 percent usage of coal ashes in beneficial applications. Furthermore, existing treatment methods commonly either use cost ineffective application of chemicals, or require treatment at a separate facility from where the coal combustion takes place, therefore incurring additional transportation costs and capital investments. Currently, most changes made to beneficiate coal combustion products are strictly related to the cleaning or sequestration of harmful chemicals within the coal combustion product. Some methods involve the use of external grinding facilities to reduce the particle size of combustion product particles. Other existing methods include carbon burn-out methods, utilizing the application of heat to the combustion product to reduce the levels of free carbon. Yet other methods utilize electrolytic methods to sequester carbon atoms. All of the aforementioned methods require high capital and ongoing costs in building and operating separate facilities.
Summary: The present invention provides a method and system for producing modified coal combustion products for addition to concrete, mortar and other hydraulic mixtures comprising Portland cement clinker and coal combustion products for use in construction and other industries. The invention provides a method for decreasing the particle size and increasing the total surface area of the resulting combustion product, thus increasing the rate of development of mechanical properties in hydraulic mixtures containing such combustion products. The invention further relates to the improvement of combustion efficiency resulting from the smaller particle size and resulting increased surface area of coal particles, and the dilution effect of the original combustion product after addition of the aforementioned materials, both leading to lower levels of total free carbon in the resulting combustion product.
An embodiment of the invention provides for the selection and addition of raw materials to be added in a coal combustion process to increase the reactivity of the resulting coal combustion products ... . Currently, limestone is added to the combustion chamber of coal burning boilers to reduce sulfur emissions from flue gases to achieve sulfur removal rates range from 75 to 95 percent, however with very limited, if any, improvement of the development of mechanical properties when used with Portland cement clinker in a hydraulic mixture.
An aspect of the present invention is to provide a method of producing a modified coal combustion product comprising combusting coal and a particle size-reducing additive, wherein the modified coal combustion product has an average particle size less than an average particle size of a coal combustion product combusted from the coal without the additive.
Another aspect of the present invention is to provide a system for producing a modified coal combustion product comprising a combustion chamber for co-combusting coal and a particle size-reducing additive, a source of the coal, a source of the particle size-reducing additive, and at least one injector configured to deliver the coal and the particle size-reducing additive to the combustion chamber.
In accordance with an embodiment of the invention, a coal fired boiler can be used as a co-generator to produce both heat for electrical power generation as well as excess heat, combustion synthesis, and thermal blending to produce a highly reactive pozzolanic powder in the form of the modified coal combustion product having reduced particle sizes. A comparison of the starting material particle size and the resulting product particle size demonstrates that a combination of combustion and comminution within the boiler takes place, rapidly reducing large oxide materials into fine powders. Moreover, the combustible additives may blend with the fume from the coal combustion to permit the formation of a chemically enhanced coal ash.
The raw materials for use as the additives may be derived either from industrial waste streams or not, and may include recycled concrete dust, ground blast steel slag, fine ground soda lime glass, fine ground E glass, fine ground geopolymer cements, blends and mixes of fly ash and high alkali chemicals in the presence of heat, or any other materials which increase levels of silica or alumina in the resulting fly ash.
The raw materials may also be used to decrease the levels of total free carbon in the resulting combustion ash. Such carbon-reducing materials can be derived either from industrial waste streams or not, and may include recycled concrete dust, ground blast steel slag, fine ground soda lime glass, fine ground E glass, fine ground geopolymer cements, blends and mixes of fly ash and high alkali chemicals in the presence of heat, or any other materials which increase levels of silica or alumina in the resulting fly ash. In certain embodiments, the modified coal combustion product has a carbon content less than a carbon content of a coal combustion product combusted from similar coal without the additive. For example, the carbon content of the modified coal combustion product may be at least 10 weight percent less than the untreated coal, typically, at least 50 weight percent less. The carbon content of the modified coal combustion product may be less than 5 weight percent, for example, from 0.5 to 2 weight percent.
In accordance with the present invention, selected types and amounts of metal oxide strength enhancing additives are used as raw materials that undergo co-combustion with coal to produce a useful cement additive material having controlled amounts of calcium oxide, silicon dioxide and aluminum oxide".
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And, to emphasize, the "cement additive material" is created by the "co-combustion" of the "additives" with Coal in a power plant furnace.
Among the additives specified in the disclosure, as excerpted above, are industrial wastes, such as: "recycled ground granulated blast furnace slag, recycled crushed glass, kaolin, recycled crushed aggregate fines, silica fume, cement kiln dust, lime kiln dust, weathered clinker, clinker, aluminum slag, copper slag, granite kiln dust, rice hulls, rice hull ash, zeolites, limestone quarry dust, red mud, ground mine tailings, oil shale fines, bottom ash, dry stored fly ash, landfilled fly ash, ponded fly ash".
So, the costs of the additives needed herein to make Coal Ash a high-performance component of concrete aren't great, and, since certain industrial wastes can be used, the costs might even be negative; that is, there could be a direct economic payoff for "disposing" of those wastes through a productive utilization.
And, Ash Improvement Technology's above "US Patent 8,961,684 - Production of Coal Combustion Products for Use in Cementitious Materials" was actually preceded, last year, by:
"United States Patent: 8741054 - Production of Cement Additives from Combustion Products of Hydrocarbon Fuels and Strength Enhancing Metal Oxides
Date: June 3, 2014
Inventor: Wayne Fried, NY
Assignee: Ash Improvement Technology, Inc., NY
Abstract: The present invention provides combustion products of hydrocarbon fuels and controlled amounts of metal oxide strength enhancing materials. The combustion products are useful as additives to cementitious materials. A hydrocarbon fuel such as coal is introduced into a combustion chamber and selected amounts of materials comprising CaO, SiO2 and Al2O3 are also introduced into and/or downstream from the chamber. The hydrocarbon fuel undergoes combustion while the metal oxide strength enhancing materials react with each other and/or the ash or other reaction products of the hydrocarbon fuel. The combustion products have been found to significantly increase compressive strengths of cements such as Portland cement. A reduction in SO2 emission levels also results from the introduction of the metal oxide strength enhancing materials into the combustion process.
Claims: A cementitious material comprising: cement; and a pozzolanic cement additive comprising coal combusted in the presence of at least 8 weight percent of a strength enhancing material comprising combinations of limestone, clay, kaolin, waste concrete, recycled ground granulated blast furnace slag, recycled crushed glass, recycled crushed aggregate fines, silica fume, cement kiln dust, lime kiln dust, weathered clinker, clinker, aluminum slag, copper slag, granite kiln dust, zeolites, limestone quarry dust, red mud, mine tailings, oil shale fines, bottom ash, dry stored fly ash, landfilled fly ash, ponded flyash (and) wherein the cement additive comprises weight ratios of from about 20 to about 80 weight percent CaO, from about 5 to about 60 weight percent SiO2, and from 7.5 to about 40 weight percent Al2O3 based on the combined total weight of the CaO, SiO2 and Al2O3.
(Note that materials like "clay, kaolin, ... aluminum slag" are added to the Coal prior to combustion to increase the amounts of the Aluminum Oxide, "Al2O3", in the product "pozzolanic cement additive". Fly ash will have high amounts of Aluminum Silicate to begin with, and conventional cement chemistry does rely on the presence of significant percentages of Aluminum compounds, usually supplied by the clays, such as "kaolin", or shales, that are components, along with limestone, of standard cement kiln feedstock. The chemistry is very complex, and beyond our meager abilities to adequately explain. But, the Aluminum Silicates will slowly react in cement to form what are becoming called "geopolymers", while Aluminum Oxides are beneficial, as well. The Calcium Oxide, "CaO" is a, perhaps the, major component in any case of Portland-type cement, and results from the calcining of limestone, CaCO3, in the kilns, which process results in the co-production of CO2. The combustion of low-grade lignite Coal, as opposed to our high-Btu eastern US bituminous Coal, typically, because of it's mineral content, results in the presence of a lot of CaO in the ash, in any case. Further, note as well that, as in: "landfilled fly ash, ponded flyash", just as in our prior report of:
Landfilled Fly Ash Recovered for Use in Concrete | Research & Development | News; concerning: "United States Patent 7,670,424 - Methods for Reclaiming and Beneficiating Fly Ash Particles and Systems Thereof; 2010; Inventor: Joseph Cochran, FL; Assignee: PMI Ash Technologies, NC; and: "United States Patent 5,160,539 - Method and Product of Fly Ash Beneficiation by Carbon Burnout in a Dry Bubbling Fluid Bed; 1992; Inventor: Joseph Cochran, FL; Assignee: Progress Materials, Inc., FL; Abstract: This invention relates to an apparatus, method and product wherein fine particles of fly ash containing carbon are oxidized in a dry, bubbling fluid bed of previously introduced fine particles of the same fly ash so that the subsequently removed particles have reduced carbon content and are useful as pozzolan, suitable for use, without further processing, to replace a portion of the cement in concrete. ... Claims: A method for reclaiming and beneficiating fly ash particles, the method comprising: recovering at least a portion of landfill fly ash particles from reclaimed feed previously disposed in at least one landfill site";
older deposits of Coal Ash previously disposed of in landfills can be mined and then used and consumed in this process, thus providing, through productive utilization, both environmental restoration and a permanent, chemical disposal of the old Coal Ash.)
The cementitious material ... wherein the strength enhancing material is combusted with the coal in an amount of at least 10 weight percent of the total combined weight of the strength enhancing material and the coal.
The cementitious material ... wherein the strength enhancing material comprises at least two materials selected from the group consisting of limestone, blast furnace slag, concrete, glass and kaolin.
The cementitious material ... wherein the strength enhancing material comprises from about 7 to about 20 weight percent limestone based on the total combined weight of the strength enhancing material and the coal.
(The above inclusion of "limestone" with Coal in the combustion process, although it does reduce the effective Btu content and leads to the emission of more Carbon Dioxide, is one of the means proposed for, as seen for example in:
Patent US4111755 - Method of producing pelletized fixed sulfur fuel - Google Patents;
capturing Sulfur, and reducing the amount of Sulfur compounds released to the environment in the stack gases. The resulting Sulfur compounds would then be permanently bound in the product "cementitious material".)
A cement mix comprising: cement; and a pozzolanic cement additive comprising coal combusted in the presence of at least 10 weight percent of a strength enhancing material comprising combinations of limestone, clay, kaolin, waste concrete, recycled ground granulated blast furnace slag, recycled crushed glass, recycled crushed aggregate fines, silica fume, cement kiln dust, lime kiln dust, weathered clinker, clinker, aluminum slag, copper slag, granite kiln dust, zeolites, limestone quarry dust, red mud, mine tailings, oil shale fines, bottom ash, dry stored fly ash, landfilled fly ash, ponded flyash (and) wherein the cement additive comprises weight ratios of from about 20 to about 80 weight percent CaO, from about 5 to about 60 weight percent SiO2, and from 7.5 to about 40 weight percent Al2O3 based on the combined total weight of the CaO, SiO2 and Al2O3.
(And) wherein the cement additive comprises from about 30 to about 95 weight percent of the cement mix.
(And) wherein the cement comprises Portland cement.
In accordance with an embodiment of the invention, a coal fired boiler can be used as a co-generator to produce both heat for electrical power generation as well as excess heat, combustion synthesis, and thermal blending to produce a highly reactive pozzolanic powder. A comparison of the starting materials particle size and the resulting product particle size demonstrates that a combination of combustion and comminution within the boiler takes place, rapidly reducing large oxide materials into fine powders. Moreover, the combustible additives may blend with the fume from the coal combustion to permit the formation of a chemically enhanced coal ash.
The present process does not clean waste products post-generation for industrial use, but rather avoids the production of waste materials altogether. The generated product can be made at a production cost below that of the industrial materials it is replacing. For example, every ton of product used in lieu of cement may also reduce CO2 emissions by close to 0.85 tons, the equivalent emissions produced by the manufacturing of the cement that is being replaced".
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Thus, certain types of industrial wastes, or very inexpensive mineral additives, can be blended with Coal prior to combustion in a Coal-fired electric power plant.
And, the resulting "chemically enhanced coal ash" can then serve as an additive, or blending component, for Portland-type cement and, thus, Portland-type cement concrete.
Moreover, it is feasible to co-produce such a "cement additive" during the generation of Coal-fired electric power which could then serve to comprise up to "95 weight percent" of a "cement mix".
Given the vast amount of "cement mix" used in the United States of America each year, it seems likely that technologies such as the ones disclosed herein, if ever implemented, would co-produce a lot of new Coal Country jobs, as well.