As should now be incontrovertible, Coal Ash can serve as a property-enhancing additive - - as a substitute for other fine aggregates which would otherwise, at great expenditure of energy, have to be mined, quarried or dredged, with attendant environmental disruption - - for Portland Cement Concrete.
However, as we've elsewhere earlier discussed, some mandated Coal-fired power plant exhaust treatment processes have resulted in the Ash from such facilities being contaminated with an even higher amount of residual, unburned Carbon than previously; which Carbon interferes with air entrainment additives put into the Concrete mix to improve the cured Concrete's resistance to freeze-thaw cycles.
Thus, a number of processes have been developed to remove such residual Carbon, most centering on a secondary combustion process, that, in some cases, does enable the recovery of additional energy while improving the quality of the Coal Ash product.
Discussions of the above can be found, for two examples, in our reports of:
West Virginia Coal Association | Fly Ash Product Improvement Captures Flue Gas Sulfur | Research & Development; concerning: "United States Patent 5,160,539 - Fly Ash Beneficiation by Carbon Burnout; 1992;
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"; and:
West Virginia Coal Association | South Carolina Prepares Coal Ash for use in Concrete | Research & Development; concerning: "United States Patent 8,234,986 - Method and Apparatus for Turbulent Combustion of Fly Ash; 2012; Assignee: The Sefa (Southeastern Fly Ash) Group, Inc., Lexington, SC;
Abstract: An apparatus for processing fly ash comprising a heated refractory-lined vessel having a series of spaced angled rows of swirl-inducing nozzles which cause cyclonic and/or turbulent air flow of the fly ash when introduced in the vessel, thus increasing the residence time of airborne particles. Also disclosed is a method of fly ash beneficiation using the apparatus".
However, such processes require a significant capital investment for the secondary combustion and heat transfer facilities, and, consequently, alternative processes have been developed for treating such residual Carbon in Coal Ash, without actually combusting it or otherwise removing it, so that the Ash can still be used effectively as a fine, reactive aggregate in Portland Cement Concrete.
Some rather extensive development work on such technology has been undertaken, perhaps somewhat surprisingly, by the State of Rhode Island's Brown University.
As seen in excerpts from the initial link in this dispatch to:
"United States Patent 6,136,089 - Apparatus and Method for Deactivating Carbon in Fly Ash
Patent US6136089 - Apparatus and method for deactivating carbon in fly ash - Google Patents
Apparatus and method for deactivating carbon in fly ash - Brown University Research Foundation
Date: October 24, 2000
Inventors: Robert Hurt, et. al., RI
Assignee: Brown University Research Foundation, Providence
Abstract: An apparatus and method for improving the properties of carbon-containing fly ash through ozonation is described. The apparatus includes a chamber for containing the fly ash and an ozonator that generates an ozone-containing gas. The ozonator supplies the ozone-containing gas such that it enters the chamber with the fly ash and deactivates carbon within the fly ash. Afterwards, the fly ash will have decreased surfactant absorptivity so that it can be effectively mixed with cement ... .
Claims: A method of deactivating carbon in coal fly ash, said method comprising the steps of: delivering coal fly ash to a reaction zone; and exposing said coal fly ash to ozone-containing gas to deactivate carbon in said coal fly ash; wherein said exposing step passivates carbon within said coal fly ash and operates to reduce surfactant uptake of said coal fly ash.
The method ... wherein said delivering and exposing steps are performed at substantially ambient temperature (and) wherein said delivering and exposing steps are performed at a common fly ash handling and storage temperature.
(Note the economies: The Ash doesn't have to be heated and the process can be performed in what we would presume to be an Ash storage and dispensing bunker, or silo.)
The method ... wherein said exposing step includes the step of exposing said fly ash to an ozone-containing gas comprising oxygen and 3 percent ozone (and) wherein said exposing step includes the step of exposing said fly ash to an ozone-containing gas comprising approximately 500 ppm ozone in air.
(Note that it seems plain air can be used as the carrier gas, and, you don't need to add a lot of Ozone, not much at all, to it. If you're unfamiliar with Ozone, more can be learned via:
Ozone - Wikipedia, the free encyclopedia; "Ozone (O3), or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. ... Ozone is formed from dioxygen by the action of ultraviolet light and also atmospheric electrical discharges, and is present in low concentrations throughout the Earth's atmosphere."
If the air has ever smelled particularly fresh, or "brisk", to you after a thunderstorm, that was likely due to Ozone formed during the lightning strikes. It can be pretty easily made by controlled electric discharges and ultraviolet light; and, if the link doesn't time out, you can see, via:
Patent Database Search Results: ttl/(ozone and generator) in US Patent Collection;
that a lot, really a lot, of efficient means, methods and devices have been developed for making Ozone, on both large and small scales.)
The method ... wherein said exposing step includes the step of exposing said fly ash to said ozone-containing gas by delivering said ozone-containing gas to the bottom of said reaction zone such that said ozone-containing gas passes through said fly ash.
Description and Background: This invention relates generally to the processing of fly ash. More particularly, this invention relates to treating fly ash with ozone in order to deactivate carbon in the fly ash and thereby allow the fly ash to be used as an additive in various applications.
Fly ash is the by-product of the combustion of coal. Disposal of fly ash is expensive. Thus, there are ongoing efforts to identify uses for fly ash. Fly ash is presently used as a concrete admixture, as a soil stabilizer,
and as a filler for asphalt and structural materials, such as bricks.
(See, for example, our report of:
West Virginia Coal Association | USDOE and WVU Sponsor Illinois Coal Ash Brickmaking | Research & Development; concerning: "Combustion Byproducts Recycling Consortium Project Number: 02-CBRC-M12; Manufacturing Fired Bricks With Class F Fly Ash from Illinois Basin Coals; 2006; Illinois State Geological Survey (and) University of Illinois; Support for this project provided in part by the US Department of Energy, National Energy Technology Laboratory, through its Cooperative Agreement (No. DE-FC26-998FT40028) with the West Virginia University Research Corporation, Combustion Byproducts Recycling Consortium (CBRC). A technical feasibility assessment was conducted for this process, which uses fly ash as a substitute for part of the clay and shale used in making conventional bricks. Commercial-scale production demonstrations, which included extrusion and firing evaluations, have produced a total of about 4,000 commercial-size paving bricks and 8,000 commercial-size three-hole building bricks for evaluation. The paving bricks contained 20% by volume of fly ash, and the building bricks contained 20%, 30%, or 40% by volume (about 37% by weight) of fly ash. These final products have met or exceeded ASTM standard specifications for pedestrian and lightweight traffic paving bricks and for building bricks of a severe weather grade. An economic evaluation indicated that it would be economically feasible for the brick plant to use the fly ash as a raw material in commercial brick production".)
The concrete industry serves as one of the most important commercial outlets for fly ash, since fly ash is used in concrete as a partial replacement for Portland cement. However, high levels of unburned carbon can make fly ash samples unusable as a concrete filler. Carbon in the fly ash interferes with the action of air entraining admixtures, or specialty surfactants, which are used to stabilize air bubbles in concrete mixtures. Measurements made on a variety of model additives suggest that admixtures are adsorbed by carbon surfaces from the aqueous phase. The adsorption process is believed to occur preferentially on nonpolar carbonaceous surface area.
Exposing fly ash to air at high temperatures, called thermal air oxidation, reveals a change in surface chemistry that occurs just prior to combustion of carbon in fly ash. The surface oxidation has the effect of changing a carbon property so that fly ash can be effectively utilized in cement-containing mixtures. Unfortunately, thermal air oxidation is an impractical industrial process because temperatures on the order of 400 C are required to effectively passivate carbon.
Additionally, processes utilizing other oxidizing agents such as hydrogen peroxide (H2O2) and nitric acid (HNO3) are available. The problem with these other processes is that the oxidizing agents are liquid. Wet treatments make fly ash difficult to handle, transport, and use.
In view of the foregoing, it would be highly desirable to provide an inexpensive and practical technique that allows deactivation of carbon within fly ash samples. The technique should reduce the surfactant adsorptivity of carbon without detrimentally changing other properties of the fly ash. Furthermore, the technique should be a dry process that functions at low temperature.
Summary: The invention includes an apparatus and method for deactivating carbon in fly ash. The apparatus includes an ozonator and a chamber enclosing the fly ash. The ozonator generates an ozone-containing gas that is fed to the chamber so that the ozone-containing gas deactivates carbon in the fly ash. The method of the invention includes the steps of delivering fly ash to a reaction zone and exposing the fly ash to ozone-containing gas to deactivate carbon in the fly ash.
The invention is used to deactivate carbon within fly ash by changing a property of the carbon so that the fly ash can be used as an additive, for example, in cement to form concrete. The invention allows profitable sale of fly ash for which disposal is otherwise expensive."
--------------------------
We'll leave it at that, for now; especially since this somewhat preliminary work led almost immediately to additional development, by Brown University, of the technology for "passivating" the residual Carbon in Coal Ash with Ozone, thus making the Coal Ash more suitable for such use "as an additive, for ... cement to form concrete", and thus enabling the "profitable sale of fly ash" - - additional development that was sponsored by the United States Department of Energy.
The points are, that, we can treat raw Coal Ash with small amounts of Ozone, which can be generated rather economically and which we don't need a lot of in the first place, and thereby convert Coal Ash into a property-enhancing additive for Portland Cement Concrete, which we make and use quite a lot of.
And, we don't really need a large capital investment to do it. Our read of the full Disclosure of our subject herein, "United States Patent 6,136,089 - Apparatus and Method for Deactivating Carbon in Fly Ash", and of the following technical developments made by Brown University for the USDOE, indicates to us that the process can be performed in, basically, Coal Ash storage and load-out silos. Temperature, or other process environment, controls don't seem to be required; the needed reaction is accomplished simply by "delivering said ozone-containing gas to the bottom of said reaction zone such that said ozone-containing gas passes through said fly ash"; and, the "reaction zone" is just the Ash silo.
Again, the trade-off is, that, unlike the Carbon Burn-Out technology of, for one example, the above-cited process of "United States Patent 5,160,539 - Fly Ash Beneficiation by Carbon Burnout", we don't have the option of reclaiming and utilizing the heat energy of the residual Carbon, but, conversely, we don't have to make the capital investment in a "heated refractory-lined vessel" as defined by "United States Patent 8,234,986 - Method and Apparatus for Turbulent Combustion of Fly Ash" to accomplish the Carbon removal.
We'll have more to offer on both the Carbon Burn-Out and Ozone treatment technologies in future reports; and, it seems likely to us that one or the other would be suitable for Ash beneficiation in specific facilities where varying situations of size, current operation and future plans could lead to one option being more suitable than the other.
The real point seems to us to be that we do have options available to us that would, one way or another, enable us to improve the quality of our Coal Ash, and, thus, enable us to more effectively and profitably present and convey our Coal Ash to the Cement and Concrete industries, and to the public at large, as what it truly is:
A valuable mineral resource that can be consumed and utilized in the manufacture of Portland Cement Concrete; Concrete that, as we have thoroughly documented, and as we will document further, can not only be stronger than conventional Portland Cement Concrete, but, can better resist chemical attack and physical deterioration, as well.