|Coal Ash and Sewer Sludge to Lightweight Concrete Aggregate|
|Friday - December 09, 2011|
We've been sporadically documenting the fact that Coal power plant Fly Ash can actually be treated as a resource of great utility in the concrete and construction industries.
It can be utilized both as a raw material, replacing some of the limestone traditionally used, in the making of Portland-type cement itself; it can, after treating, be blended into Portland cement after the cement is made as an additional cementitious component; and, it can also be treated in various other ways for use simply as "aggregate", replacing some of the traditional sand and gravel which is added to the cement in order to make concrete.
The aggregate used in concrete, in fact, is one of the primary contributors to the concrete's final properties, which properties, aside from the obvious one of, simply, "strength", can include some important ones like resistance to water intrusion and chemical corrosion.
All of that, of course, would be in addition to the reduction in cost, and attendant environmental benefits, of using what would otherwise be seen and treated as waste in the productive and profitable making and use of concrete.
Intriguingly, the utilization of waste Coal Fly Ash in certain aspects of concrete manufacturing can also enable the productive consumption and use of other, more unsavory, waste materials.
First, we remind you of Coal Ash utilization technologies that have been developed in Wisconsin, and about which we have previously reported in:
Wisconsin Cleans Ammonia from Coal Ash | Research & Development; concerning, among other things: "United States Patent 6,755,901 - Ammonia Removal from Fly Ash; Assignee: Wisconsin Electric Power Company, Milwaukee; Abstract: A method and apparatus for the application of beat to remove ammonia compounds from fly ash, thereby making the fly ash a marketable product is disclosed"; and: "United States Patent 6,945, 179 - Ammonia Removal from Fly Ash; 2005; Assignee: Wisconsin Electric Power Company, Milwaukee; Abstract: An apparatus for the application of heat to remove ammonia compounds from fly ash".
Both of the above technologies are directed towards the beneficiation of Coal ash that has been contaminated by mandated "pollution control" measures, so that the Ash would then be more acceptable for use in commercial cement and concrete applications.
Herein, we see that the corporate sponsor and owner of those environmentally beneficial Fly Ash improvement and utilization technologies has taken their concepts even a step further, and has demonstrated how the use of Coal Ash in concrete can enable the consumption and use of a genuinely obnoxious waste resulting from human activities.
Comment, with additional links, follows and is inserted within excerpts from the initial link in this dispatch to:
"United States Patent 5,342,442 - Lightweight Aggregate from Flyash and Sewage Sludge
Date: August, 1994
Inventors: Timothy Nechvatal and Glenn Heian, WI
Assignee: Wisconsin Electric Power Company, Milwaukee
Abstract: A method is shown for producing a lightweight aggregate by treating flyash and sewage sludge. The flyash and sewage sludge are mixed together and then agglomerated into pellets, with or without the use of a binder. The pellets may be coated and then are dried. The dried pellets are introduced into a rotary kiln in a direction that is co-current with the flow of fuel and air through the kiln. The pellets in the kiln will be indurated and will experience complete calcination as well as varying degrees of pyrolizing and sintering. The product of the kiln is a nodular material having a low density but with a hard and porous structure. The product of the kiln is feed to a cooler. The flyash sewage sludge mixture has a significant fuel value that is usable in the kiln. Furthermore, the fuel value available in the kiln off-gases may be used for drying the materials.
(First of all, note that the residual Carbon in the "sewage sludge" serves as additional fuel in the "calcination" of the Fly Ash-Sludge mixture, thus contributing some economy to the process.)
Claims: A lightweight aggregate consisting of a porous nodular heat-hardened agglomerate of 35-80% by dry weight of flyash and 20-65% by dry weight of uncombusted sewage sludge having an organic content.
(We'll interrupt here to explain why we might want such a thing as "lightweight aggregate" for concrete, since most of us would tend to think that we want our concrete structures, such as dams and bank buildings, to be as heavy and strong as possible.
Some explanation can be had from the concrete industry itself, as seen in the following link to the National Ready Mix Concrete Association's web site:
"Concrete in Practice: Structural Lightweight Concrete: which tells that "Structural Lightweight Concrete" is made "with a lightweight coarse aggregate" and has specific, value-added applications in "bridge decks" and certain "elements in steel and concrete frame buildings", and other structures where strength is needed, but where "dead load" is an important consideration.)
Description and Background: This invention relates to a treatment of flyash and sewage sludge, and particularly to the production of a lightweight aggregate from a mixture of flyash and sewage sludge.
As with flyash, sewage sludge presents a considerable problem of disposal in an economical and environmentally sound manner.
Summary: Our invention involves the mixture of sewage sludge with flyash, agglomerating the mixture such as by pellitizing, and indurating the agglomerated mixture in a rotary kiln. The resultant nodular product, after cooling, can be used as a lightweight aggregate for concretes, masonry, or insulation purposes ... .
Depending on the amount of sewage sludge added to the mixture, the combustion of the organic portion of the sewage sludge will provide a significant percentage of the total heat energy required in the kiln and in other stages of the process.
The sewage sludge also results in a significant weight loss from the agglomerated mixture through the formation of voids in the aggregate after volatilization or combustion of the organic portion of the sewage sludge in the kiln. Additional reduction in the aggregate product density is obtained from bloating of the pellets because of the entrapment of gases within the aggregate from the combustion of volatile organics and fixed carbon in the pellets and from calcination reactions.
The resulting products from the pilot plant operations proved sufficient to satisfy the standard ASTM specifications for lightweight aggregates for structural concrete (designation C 330), lightweight aggregates for concrete masonry units (designation C 331), and lightweight aggregates for insulating concrete (designation C 332).
A principal object of this invention is to provide a method of utilizing flyash and sewage sludge by combining them and treating the combination to form a useful product.
And, thus, by blending and "cooking" Fly Ash and Sewage Sludge, in a process wherein one of the raw materials provides much of the fuel needed for that "cooking", we can make a lightweight aggregate for concrete that meets all the applicable, official American Society for Testing and Materials specifications for such standard, lightweight concrete aggregate.
Please understand that such use is, indeed, a value-added application.
Lightweight aggregate is currently employed in many situatations, and, that aggregate is often what is known as "vermiculite", which is most often composed of specific clay minerals that must themselves be mined, "pelletized", and then heated to achieve their lightweight cellular structure.
And, there is an expense to all of that which would offset the expense of processing Coal Ash and Sewer Sludge to serve the same purpose, with the attendant economic benefit of avoiding waste disposal costs for both the Ash and the Sludge.
More about the many and varied uses for lightweight concrete can be learned via the link:
Note, as well, that Wisconsin Electric Power also suggests, in the full Disclosure of their "United States Patent 5,342,442", the further use of such expanded Coal Ash-Sewer Sludge pellets as insulating backfill in the void spaces of buildings, i.e., hollow walls, etc., much as loose vermiculite is also currently used, with consequent, indirect savings in energy.
Finally, keep in mind that the use of Coal Fly Ash and Sewer Sludge in the making of lightweight concrete aggregate would be separate from, and in addition to, the market for Coal Fly Ash in the making of solid and high-strength structural aggregate for concrete, i.e., a replacement for sand and gravel, as exemplified in our earlier report of:
Consol Converts Coal Ash to Concrete Aggregate | Research & Development; concerning: "United States Patent 5,364,572 - Process for Making High-Strength Synthetic Aggregates; 1994; Assignee: Consolidation Coal Company; Abstract: A process for making high-strength aggregates (from) coal combustion ash".
It all goes to support our contention, that, as with Carbon Dioxide and it's many potentials, as seen for just one example in:
August 2011, CO2-to-Gasoline US Patent Awarded | Research & Development; concerning: "United States Patent 7,989,507 - Production of Fuel Materials Utilizing Waste Carbon Dioxide; 2011: Assignee: Siemens Aktiengesellschaft; (A) method for utilizing CO2 waste (for) producing a hydrocarbon material";
we need to start viewing, and treating, the by-products arising from our varied and productive used of Coal not as wastes, but, as valuable raw materials which can be utilized in the manufacture and synthesis of many other needed things; which utilization not only serves to productively and profitable deal with what might otherwise be treated as wastes, but, which utilization also helps to conserve both energy and other raw material resources.