We've documented many times that Coal-fired power plant fly ash can be utilized, in a number of forms and in a number of ways, in the manufacture of Portland-type cement and of concrete, with the consequent benefits of utilizing what is typically thought of only as a noxious solid waste that must, at some great expense saddled onto the backs of consumers of Coal-based electrical power, be gotten rid of in some fashion satisfactory to groups notorious for not being satisfied with much of anything; and, the conservation of resources that would otherwise be consumed in the mining and processing of the traditional raw materials that go into the making of Portland-type cement and of concrete formed from that cement.
And, all of that is aside from the fact that the use of Coal Ash in the making of cement also helps to reduce emissions of Carbon Dioxide from the cement-making process, especially to the extent that Coal Ash is used to displace any limestone which might otherwise be used as raw material for, and processes in, a cement kiln, where it's "calcined", as explained in:
Calcination - Wikipedia, the free encyclopedia; "The process of calcination derives its name from the Latin 'calcinare' (to burn lime) due to its most common application, the decomposition of calcium carbonate (limestone) to calcium oxide (lime) and carbon dioxide, in order to produce cement";
in order to produce the reactive components of Portland-type cement.
Actually, the product of a cement kiln is called "clinker", as described in:
Portland cement clinker; "Portland cement clinker is a dark grey nodular material made by heating ground limestone and clay at a temperature of about 1400C-1500C. The nodules are ground up to a fine powder to produce cement ... ";
and we wanted to get that term defined, since it will appear often in reports we have in process that further explain how the use of Coal Ash in the making of Portland cement clinker offers multiple advantages, relative to the conventional raw materials, in terms of CO2 reduction, energy conservation, and, improved cement and concrete product qualities; all through the utilization of a resource that some would prefer to have us believe is nothing but valueless, or even hazardous, waste.
Herein, we submit yet more, and very credible, documentation of the fact, that, the solid residua resulting from our combustion of Coal for the generation of economically essential electric power can not only be utilized as the raw material for manufacturing Portland-type cement, and Portland cement products, but, that, the technologies for utilizing Coal Ash in such applications are actually well-established and have been developed to a high degree.
First, we remind you of one earlier report concerning this topic, as accessible via:
West Virginia Coal Association | Virginia Converts Coal Ash to Cash | Research & Development; which contained additional information concerning:
"South Carolina Electric and Gas Successful Application of Carbon Burn-Out (CBO) at the Wateree Station; 1999 International Ash Utilization Symposium; Center for Applied Energy Research, University of Kentucky; South Carolina Electric and Gas Company; Progress Materials, Inc.; and, Southeastern Ash Co., Inc.; CBO combusts residual carbon in fly-ash, producing a very consistent, low-carbon, high-quality pozzolan";
wherein it was explained, that, in order to utilize Coal Ash as a "pozzolan" additive for cement, a fine aggregate with inherent cementitious properties of it's own, which, as seen in:
Coal Ash Can Reduce Construction Costs | Research & Development; concerning:
"United States Patent 5,624,491 - Compressive Strength of Concrete and Mortar Containing Fly Ash; 1997; 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 ... which can achieve greater compressive strength than hardenable mixtures containing only concrete";
can improve the physical strength and other properties of concrete made by blending cement with such Coal Ash pozzolan, any residual Carbon in the Coal Ash needs to be removed, typically through a procedure referred to as "Carbon Burn-Out".
Herein, we see that one of the largest manufacturers of cement products in the world, a multinational construction products company, has devised a way to utilize Coal Ash in the manufacture of cement that not only removes the residual Carbon as an integral and economical step in the cement manufacturing process, but does so in a way that neutralizes other potential contaminants, as well.
Comment follows, and is inserted within, excerpts from the initial link in this dispatch to:
"United States Patent 5,837,052 - Process for Producing Cement Clinker Containing Coal Ash
Date: November, 1998
Inventors: David Oates, et. al., Canada and Kansas
Assignee: Lafarge Canada, Inc.,
(Note: "Lafarge" is possibly a name unfamiliar to many of our readers, though some in the US construction trades will recognize it.
As can be learned via:
Lafarge - Wikipedia, the free encyclopedia; "Lafarge is a French industrial company specialising in four major products: cement, construction aggregates, concrete and gypsum wallboard. In 2010 the company was the world's second-largest cement manufacturer by mass shipped"; and:
Home : Lafarge - Cement, concrete, aggregates and gypsum; and:
About Lafarge North America < About Us: Lafarge;
LaFarge is a very major international manufacturer of construction materials, especially cement, which, though based in France, moved into the North American market some decades ago, via British Columbia, in Canada, and, after a move or two east, is now headquartered, as "Lafarge North America", near Washington, DC; and, is billed as " the largest diversified supplier of construction materials in the United States and Canada".)
Abstract: Contaminated coal ash, for example flyash contaminated with carbon is introduced to hot clinker in a cooler downstream of a cement kiln; the carbon is combusted in the cooler to provide a cement clinker having an effective content of flyash free of carbon; this permits use of flyash contaminated with carbon without the need for separate special steps for carbon removal; volatile contaminants or contaminants having a volatile component, for example adsorbed ammonia are similarly removed in the cooler by volatilization.
(Note: Concerning the above-implied need to remove "ammonia", resulting from the application of certain flue gas scrubbing technologies to Coal-fired power plant exhaust streams, see our earlier report of:
Wisconsin Cleans Ammonia from Coal Ash | Research & Development; concerning: "United States Patent 6,755,901 - Ammonia Removal from Fly Ash; 2004; Assignee: Wisconsin Electric Power Company; Abstract: A method and apparatus for the application of heat to remove ammonia compounds from fly ash, thereby making the fly ash a marketable product is disclosed."
In the process of our subject, the above "application of heat" is effected by blending the Ash with hot cement clinker as it exits the kiln, as an integral function of actually making the finished ash-cement product.)
Claims: A process for producing a cement clinker having a content of pozzolanic coal ash comprising:
a) producing hot cement clinker from cement clinker raw ingredients in a cement kiln;
b) feeding hot cement clinker from step a) into a cooler;
c) feeding a pozzolanic coal ash, having a content of a contaminant, into contact with said hot cement clinker in said cooler and liberating said contaminant from said coal ash with heat evolved from said hot cement clinker as said hot cement clinker cools in said cooler; and
d) recovering a cooled cement clinker containing said coal ash free of said contaminant.
A process ... wherein said contaminant is adsorbed ammonia or an ammonium salt.
A process ... wherein said coal ash is bottom ash.
A process ... wherein said coal ash is flyash.
A process for producing a cement clinker having a content of flyash comprising:
a) producing hot cement clinker from cement clinker raw ingredients in a cement kiln;
b) feeding hot cement clinker from step a) into a cooler,
c) feeding a flyash, having a content of carbon, into contact with said hot cement clinker in said cooler and oxidizing said carbon in the presence of the hot cement clinker in said cooler, said flyash being selected from type F flyash or Type C flyash of ASTM C618 and
d) recovering a cooled cement clinker containing said flyash free of carbon.
A process ... wherein said flyash has a content of carbon of 1 to 30% by weight.
A process ... wherein said flyash is fed ... in an amount to provide up to 40%, by weight, of flyash based on the weight of clinker and flyash.
(Nearly half the finished cement clinker can be composed of Coal Ash, in other words.)
A process ... wherein said hot cement clinker ... has a temperature of at least 500C.
A process for producing a cement clinker having a content of pozzolanic flyash comprising:
i) producing hot cement clinker from cement clinker raw ingredients in a cement kiln,
ii) feeding hot cement clinker from step a) into a cooler at an upstream end of said cooler,
iii) feeding said hot cement clinker along a path from said upstream end to a downstream end of said cooler, and exposing said clinker to cooling air in said path such that said clinker is progressively cooled from about 1300C to 120C as it travels from said upstream end to said downstream end,
iv) feeding a pozzolanic flyash, contaminated with 1 to 30% by weight of carbon into contact with said clinker in said path such that said flyash contacts said clinker at a temperature of at least 500C, and maintaining said flyash in contact with said clinker, in said cooler, for a residence time sufficient for combustion of the carbon contamination while maintaining the integrity of the flyash, said pozzolanic flyash being selected from Type F flyash or Type C flyash of ASTM C618 and
v) recovering a cooled cement clinker containing pozzolanic flyash free of carbon.
(Note: The "cement clinker cooler" mentioned several times above is an integral component of nearly all cement kilns, wherein the hot clinker is cooled by air flow to a more desired temperature. In some cases, the hot air exiting the cooler is used to preheat raw materials being fed to the kiln, thereby helping to economize on the costs of operating the overall system. Herein, adding Coal Ash to the hot clinker should also serve to help minimize, or even eliminate, any need for, and the costs of operating, such a clinker cooler.)
A process ... wherein said flyash is Type F flyash of ASTM C618.
(Note: The Federal Highways Administration informs, via:
Fly Ash; that: "Class F is fly ash normally produced from burning anthracite or bituminous coal".)
Background and Field: This invention relates to a process for producing a cement clinker having an effective content of pozzolanic coal ash; more especially the invention is concerned with a process in which a contaminated pozzolanic flyash having a contaminant deleterious to cement is the source of the pozzolanic coal ash content of the cement clinker.
In a cement plant, cement clinker is created at elevated temperatures in a cement kiln from cement clinker raw ingredients which travel through the kiln from a feed end to a discharge end, while passing through different processing zones at elevated temperature.
The resulting hot cement clinker which typically has a temperature of about 1300C. at the discharge end of the kiln, is fed into a cooler and travels as a bed of clinker from the cooler entry port to the cooler exit port on a cooler grate. Air is blown through the bed from jets disposed below the grate to cool the hot clinker. The clinker at the cooler entry port has a temperature of about 1300C and the clinker at the cooler exit port has a temperature of about 120C.
The cooled cement clinker is ground to a desired fineness and may be employed as such in cement or may be admixed with fine particulate pozzolanic flyash to produce a Type IP-Portland pozzolan cement or a Type I (PM) pozzolan-modified Portland cement according to ASTM C595-94a (Standard Specification for Blended Hydraulic Cements); or a blended hydraulic cement according to ASTM C 1157M-95 (Standard Performance Specification for Blended Hydraulic Cement).
Pozzolanic flyash is a finely divided residue from the combustion of ground or powdered coal in coal burning power plants, as Class F or Class C defined in ASTM C618-94a (Standard Specification for Coal Fly Ash . . . for use as a Mineral Admixture in Portland Cement Concrete).
Since about 1986, the emphasis on controlling emission gases from power plants has resulted in the installation of low NOx burners as a means of reducing oxides of nitrogen in emission gases. The impact of these controls has been an increase in carbon content of Type F and to a lesser extent Type C pozzolanic flyash.
Carbon is a detrimental contaminant in cement, having the effect of absorbing chemicals with resulting deterioration of concrete performance.
Prior attempts to remove the carbon from the flyash involve electrostatic separation; mixing the flyash with a fluid such as kerosene and separating the carbon out by foaming; and mixing the flyash with limestone in a fluid bed combustion chamber for combustion of the carbon.
(The above refers to the separate and preliminary "Carbon Burn-Out", as described in our above-cited earlier report by the University of Kentucky and South Carolina Electric and Gas Company. The Lafarge technique disclosed herein accomplishes the same end, but perhaps more efficiently, since it serves to make unnecessary that separate and preliminary step.)
Flyash may also be contaminated with ammonia which coats the flyash particles during flyash recovery by precipitators. The ammonia is strongly adsorbed on the flyash particles and may chemically react to form ammonium salts. Ammonia is deleterious to cement performance, and thus it is also desirable to remove adsorbed ammonia from flyash particles.
The flyash is recovered from the exhaust gases of the coal burning plants, as described hereinbefore, and bottom ash is recovered from the bottom of the boiler as a granular coal ash.
It has recently been determined that ground bottom ash also has pozzolanic activity (and) it is also appropriate to remove contaminants such as carbon from such ground bottom ash, to render it more suitable for use as partial replacement for cement.
Summary: It is an object of this invention to prepare a contaminated pozzolanic coal ash, for use in cement manufacture, without the need to employ a separate pretreatment to remove the contaminant before addition to the cement clinker.
It is a particular object of this invention to prepare a pozzolanic flyash contaminated with carbon, for use in cement manufacture, without the need to employ a separate pretreatment to remove the carbon before addition to the cement clinker.
It is a further object of this invention to provide a process for producing a cement clinker having an effective content of pozzolanic coal ash, especially flyash.
In accordance with the invention there is provided a process for producing a cement clinker having an effective content of pozzolanic coal ash comprising (a) producing cement clinker, at an elevated temperature, from cement clinker raw ingredients in a cement kiln, (b) feeding hot cement clinker from step (a) into a cooler, (c) feeding a pozzolanic coal ash having a content of a contaminant into contact with said hot cement clinker at an elevated temperature in said cooler and liberating said coal ash of said contaminant at said elevated temperature in the presence of the hot cement clinker in said cooler, and (d) recovering a cooled cement clinker containing said flyash free of said contaminant."
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Our take on this is that it is simply a more efficient way to consume some significant amount of Coal Ash, as a pozzolanic additive and fine aggregate, in the making of Portland-type cement; one which enables the use of Coal Ash without the need for a more significant capital investment in preliminary processing equipment.
Further, there is some energy conservation and efficiency, relative to a separate Carbon Burn-Out and Ammonia decomposition, since residual heat from the calcination is relied upon to drive those processes, which at the same time helps to cool the cement clinker.
The trade-off seems to be that you can't use as much of the Ash, only, as specified herein by Lafarge, "up to 40%, by weight, of flyash", as might otherwise be the case, if the Ash were pre-processed for removal of the Ammonia and residual Carbon.
As we will document in at least one report to follow in coming days, it is conceivable to manufacture such Portland-type cement that is made entirely of Coal Utilization Byproducts, but, with what would be the investment of some additional energy.
And, since, as we have documented in reports such as:
West Virginia Coal Association | Consol Converts Coal Ash to Concrete Aggregate | Research & Development; concerning:
"United States Patent 5,364,572 - Process for Making High-Strength Synthetic Aggregates; 1994; Consolidation Coal Company; Abstract: A process for making high-strength aggregates (from) coal combustion ash";
it is also possible to make the coarse aggregate, which would be added to the Fly Ash cement to make structural concrete, as well, out of Coal Ash, the potential volumes of Coal Ash which could be consumed in such applications, and the natural raw materials which would be thereby conserved, become somewhat staggering, immense.
We'll have more to offer on the specifics of the energy and material economies which can be achieved through such employment of our solid Coal Utilization Byproducts in coming reports; but, herein, we see that a very significant multi-national manufacturer of cement and cement products has defined a way in which Coal Ash can be employed, and productively consumed, so that both energy and natural raw materials can be conserved, in the making of an essential commodity product, i.e., Portland Cement, with very little, if any, additional capital expense levied onto, or built into, the cement-making process.
Our only question here, given that Coal Ash sometimes entails mandated costs for it's simple disposal, is:
Why it isn't a matter of law that Coal Ash be commercially, and profitably, utilized in such a way?
That is, why isn't there a minimum recycled components content established for Portland-type cement which could be fulfilled by such use of Coal Ash?
In US Coal Country, there oughta be.