http://congress.cimne.upc.es/
As we've reported a couple of times, as, for one example, in:
West Virginia Coal Association | 1936 Ceramics "New Market" for Coal Ash | Research & Development; concerning: "United States Patent 2,055,706 - Method of Making Ceramic Products; 1936; Chicago District Electric Generating Corporation; Description: This invention relates to an improved method of making fired ceramic bodies by the addition thereto in the unfired state of fly ash resulting from the combustion of pulverized fuel, and the improved product resulting from the use of such method";
it's been known for quite a while that Coal Ash can substitute very effectively for some, or even most, of the traditional raw materials in the making of fired-clay, that is, ceramic, bricks. And, as seen in our report of:
West Virginia Coal Association | Coal Ash Makes Better Bricks | Research & Development; concerning: "United States Patent Application 20120031306 - Bricks and Method of Forming Bricks with High Coal Ash Content; 2012; Inventor: Robert Thomas Belden, et. al.; (Presumed eventual Assignee: The Belden Brick Company, OH); Abstract: There is provided an apparatus and process for manufacturing a brick or paver with a high content of coal ash (ranging from 60% to 100% coal ash or fly ash) so that a waste product (coal ash, and more particularly Class F coal ash) from a coal-fired power plant is incorporated into a building product (high content fly ash brick or paver). Also provided is a variable firing tray to support the dried, high content coal ash bricks/pavers as the dried products are sent through a tunnel kiln, to improve circulation around the individual bricks/pavers and thereby result in reduced firing time in the kiln";
the knowledge base for so using Coal Ash continues, in certain circles, to advance and improve.
The market for fired bricks, and other, related industrial and commercial ceramics isn't nearly as large, of course, as that for Portland-type cement and concrete; but, it is still significant and offers the potential of an incremental increase in the amount of Coal Ash that could be constructively consumed and utilized, while at the same time sparing the natural raw materials traditionally used for making bricks, and related ceramics, and forestalling some of the environmental disruption that might be caused by their extraction.
Moreover, the substitution of Coal Ash in brick making is rather direct, requiring little change in operating practices; and, Coal Ash is cheap, resulting in obvious potentials for cost savings.
We submit recognition and confirmation of those facts herein, from a European nation where they no longer mine any Coal, and, import only several million tons of it each year for power generation.
Comment follows excerpts from the initial link in this dispatch to:
"Recycling Of Coal Fly Ash By Ceramic Processing
Regina C. C. Monteiro, Cláudia S. Mota and Maria M. A. R. Lima
Department of Materials Science, New University of Lisbon, Portugal
Abstract: Coal fly ash was used as raw material for the preparation of ceramic materials by a conventional powder technology route. Powder compacts were made from as-received fly ash, from calcined fly ash and from powder mixtures having 90% of calcined fly ash plus a low-cost mineral as additive (dolomite).
(Note: The above "dolomite" is simply limestone with a relatively high content of Magnesium Carbonate. It is quite common; and, most limestones consist of blends of Calcium Carbonate and Magnesium Carbonate in varying relative amounts, in any case.)
The compacts were sintered in air at temperatures between 900 and 1300 degrees C for 2 hours.
The effects of the processing parameters on the densification, microstructural development and properties of the ceramic bodies were investigated. The unburned carbon present in the as-received fly ash inhibited densification due to gas formation during firing, resulting in an increased porosity.
(As seen, for one example, in our report of:
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. 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";
there have been techniques developed for the removal of such unburned Carbon from Coal Ash, so that the Ash might be made more suitable for use in a variety of applications. Some of those techniques, as above, facilitate the recovery of the energy content of any unburned Carbon through secondary combustion processes. Other expositions of making bricks with Coal Ash we've seen prescribe instead a "staged" firing process to oxidize Carbon and vitrify the bricks more gradually, allowing escape of CO2 from the molded bodies without the formation of voids and cracks.
Such gradual staged firing might or might not be effective in very dense, highly compressed "compacts", that is, the compacted green body of the brick prior to firing.)
The density, thermal expansion coefficient and the modulus of rupture of the densest fly ash-based ceramic materials are identical to those exhibited by some traditional ceramics used in civil construction.
(In other words, Coal Ash bricks are at least as good as those made in the usual way from the standard and traditional raw materials.)
The present results indicate a convenient way to treat coal fly ash, transforming it into useful ceramic products via a simple and cost effective powder technology and sintering route.
The valorisation and recycling of by-products and waste materials coming from industrial or municipal sources has become more and more pressing due to the need of reducing the environmental and economical impacts associated with the landfill disposal of such residues.
For the recycling and exploitation of coal fly ash produced by power plants, several approaches have been developed, mainly in the cement industry and also in the production of glass-ceramic materials.
Typically, the glass-ceramics are obtained by a combined vitrification/devitrification technique, i.e., the melting of the fly ash followed by a one or two stage heat treatment for crystallization, nucleation and crystal growth. Other alternative approaches involving a sintering process have also been developed, and the use of coal fly ash to synthesize different materials, such as mullite ceramics, cordierite and glass matrix composites has been reported.
(The above "mullite", aka "porcelainite", and "cordierite", are naturally-occurring alumino-silicate minerals; but, herein they represent synthetic transitional materials as the clay fuses and re-crystallizes in the formation of ceramic materials.)
The aim of the work reported in this paper was to investigate the treatment of coal fly ash via a simple and cost effective powder technology and sintering route in order to transform this waste material into a useful ceramic product.
The fly ash used in this study was produced in Tapada do Outeiro, an extinguished coal power plant in the north of Portugal.
(They used waste Coal Ash from an old, shuttered power plant, in other words; implying, of course, that discarded or disposed-of Ash could be reclaimed for use in a process like the one described herein.)
The as-received fly ash ... was calcined during 3 hours at 800 C, after which it exhibited a loss on ignition (LOI) of (about)15 weight percent, attributed mainly to the unburned carbon and to some organic residues.
(They subjected the Ash to a Carbon Burn-Out process, in other words, related to that disclosed in our above-cited report concerning: "United States Patent 8,234,986 - Method and Apparatus for Turbulent Combustion of Fly Ash".)
After calcination, the fly ash exhibited some agglomeration and therefore, it was wet ball-milled, dried overnight, and then passed trough a sieve in order to get a non-agglomerated fine powder.
The mineralogical composition of the fly ash, investigated by X-ray diffraction analysis (XRD), showed that it contained some crystalline phases such as quartz (SiO2), mullite (3Al2O3SiO2) and a small amount of hematite (Fe2O3) and that a vitreous phase was also present.
The main objective of this work was to develop a cost effective powder technology and sintering route in order to obtain a useful ceramic material made near exclusively from fly ash. This included the preparation of powder compacts, which were made from 100 percent as-received fly ash, made from 100 percent calcined fly ash and made from powder mixtures containing a low cost additive to promote densification at a lower sintering temperatures.
Powder mixtures of calcined fly ash and 10 weight percent dolomite, used as source of CaO and MgO that would act as fluxes during the firing process, were prepared.
The compacts were subsequently sintered in air, at temperatures varying between 900 and 1300 C (usual temperature range for firing traditional ceramics).
Characterization of sintered samples: The characterization of sintered samples was performed using standard methods of current use for testing ceramic materials.
It is observed that samples made from as-received fly ash showed a lower final density, even when sintered at the highest temperatures. It is suggested that the presence of unburned carbon in the as-received fly ash can negatively influence the densification as the gas formation during firing will contribute to increase the porosity in the material.
Compacts with 100 percent calcined fly ash attained the maximum density at a sintering temperature of 1100 C, while compacts having 10 weight percent dolomite addition achieved the maximum density at a lower temperature (1050 C). Achievement of high density is important because the final properties of the products, especially the mechanical properties, which increase with increasing density. From the densification results, sintered samples made from calcined fly ash and from the mixture of calcined fly ash with 10 weight percent dolomite exhibiting high final densities were selected for further characterization.
The linear thermal expansion coefficient of the sintered samples in the temperature range between 20 and 400 C was ... within the range of the values indicated in literature for several types of ceramic tiles.
The bending strentgh (modulus of rupture) of the 100 percent calcined fly ash samples sintered at 1100 C has a value of 106 MPa and, as expected, a lower value (78 MPa) for the more porous materials made from 10 weight percent added dolomite.
(The "calcined fly ash", having been treated in a Carbon Burn Out-type process prior to being formed into compacts, resulted, in other words, in much stronger bricks.)
Considering the bending strength values quoted in the literature for several types of wall and floor tiles, including for porcelain tiles, it is observed that the present waste-based ceramic materials exhibit a higher mechanical strength.
(The Coal Ash tiles, in other words, seemed to perform somewhat better than standard tiles.)
Conclusions:
Sintering of as-received fly ash resulted in poor densification due to the presence of non-burned carbon , which caused a high porosity in the final products.
(A Carbon Burn-Out pretreatment would be beneficial, in other words.)
The density, thermal expansion coefficient and the modulus of rupture of the densest fly ash-based ceramic materials are identical to those exhibited by some commercially available traditional ceramic products used in civil construction.
The results indicate a convenient way for treating coal fly ash, transforming it into useful ceramic products via a simple and cost effective powder technology and sintering route."
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In sum, it's a fairly simple and straightforward proposition to substitute, with an energy-recovering Carbon Burn-Out pretreatment, Coal Ash for nearly 100 percent of the traditional raw materials used in making fired bricks and construction-grade tiles.
The resulting Coal Ash-based ceramic bodies perform at least as well in all standard measures as those ceramic bodies made from the conventional mined clays and other minerals.
And, they do so at a much lower economic and environmental cost.