http://www.osti.gov/scitech/servlets/purl/1084480

We've previously reported on the fact that the Ash arising from our economically essential use of Coal in the generation of abundant, reliable, and truly-affordable electric power can be seen and treated as a valuable raw material mineral resource, a raw material which can be used and consumed in such a way that it contributes to the economically and environmentally desirable concept and goal of "sustainability". 

 

An example would include:

California "Builds It Green" with Coal Ash Concrete | Research & Development | News; which presents a number of articles pertaining to the use of Coal Ash as a material for "sustainable construction", including: 

"Coal Fly Ash: The Most Powerful Tool for Sustainability of the Concrete Industry; P.K. Mehta; University of California, Berkeley, CA; Ash at Work; 2008; In the last 15 years the global cement industry has almost doubled its annual rate of direct emissions of carbon dioxide. These can be cut back by reducing global concrete consumption, reducing the volume of cement paste in mixtures and reducing the proportion of portland clinker in cement. It has recently been proved that use of high volumes of coal fly ash can produce low cost, durable, sustainable cement and concrete mixtures that would reduce the carbon footprint of both the cement and the power generation industries".

The concept of "sustainability" still might seem a little fuzzy to all of us nuts and bolts Coal miners, and similar hands-on working folks, but, as told by the US EPA in:

http://www.epa.gov/sustainability/basicinfo.htm; "Sustainability is based on a simple principle: Everything that we need for our survival and well-being depends, either directly or indirectly, on our natural environment. Sustainability creates and maintains the conditions under which humans and nature can exist in productive harmony, that permit fulfilling the social, economic and other requirements of present and future generations. Sustainability is important to making sure that we have, and will continue to have, the water, materials, and resources to protect human health and our environment".

One of the entities seemingly committed to developing technologies for such use of Coal Ash as a raw material for  sustainable industry and sustainable construction is the University of Kentucky, as represented by at least two of it's faculty members, as in, for one example, our report of:

University of Kentucky Prepares Coal Ash for Market | Research & Development | News; concerning: 

"United States Patent 6,533,848 - High Quality Polymer Filler and Super-Pozzolan from Fly Ash; 2003; Inventors: Thomas Robl and John Groppo; Assignee: The University of Kentucky; Abstract: A novel method for producing fly ash material with a range of particle sizes (as specified) is provided utilizing superplasticizers. The method produces fly ash material suitable for use as filler material in the plastics industry and super pozzolan for the concrete industry".

As it happens, the University of Kentucky, again as represented by the above Robl and Groppo, and other of their UK colleagues, has been at work further studying and developing the technologies for recovering Coal Ash and preparing it for use in industry, in projects sponsored by the US Government. One example is accessible via the link:

Pilot Demonstration of Technology for the Production of High Value Materials from the Ultra-Fine (PM2.5) Fraction of Coal Combustion Ash; "T. L. Robl; J. G. Groppo; R. Rathbone; B. Marrs; R. Jewell; 2008; The overall objective of this research was to determine the feasibility of recovering a very fine fraction of fly ash, that is 5 microns in diameter or less and examining the characteristics of these materials in new or at least less traditional applications. These applications included as a polymer filler or as a 'super' pozzolanic concrete additive. As part of the effort the ash from 6 power plants was investigated and characterized".

We might return to some of the University of Kentucky's specific Coal Ash research and development projects and activities, and treat them more fully, in future reports. Herein, though, we wanted to present you with a more recent culmination of their development efforts relative to Coal Ash, in which the University of Kentucky describes the work performed in their pilot facility, or "Center", for the preparation of Coal Ash for, and it's use in, various "Sustainable Construction" applications.

Comment follows excerpts from the initial link in this dispatch to:  

"Center for Coal-Derived Low Energy Materials for Sustainable Construction

SciTech Connect: Center for Coal-Derived Low Energy Materials for Sustainable Construction

Final Scientific/Technical Report; Project Period: October 1 2009 to March 30 2012

Principal Authors: Robert Jewell, Tom Robl, Robert Rathbone

(One note, in passing: This work tends to focus on the solid byproducts of "fluidized bed combustion (FBC) boilers", a newer technology gaining some market share, as opposed the solid byproducts of "pulverized coal combustion". The distinction isn't a minor one, but discussion of it is beyond our scope herein. Although we might treat it in future reports, many of the facts concerning Coal Combustion Byproducts presented by our subject do generally apply. Further, though, the focus is also more on "low-energy" "calcium sulfoaluminate (CSA) cements", as opposed to more standard Portland-type cement. And, again, there are some important differences, but generalities still apply.)

July 2012

Work performed under Agreement DE-FE0000660; Submitted by: University of Kentucky Research Foundation; On Behalf of The University of Kentucky Center for Applied Energy Research

Principal Investigator: Thomas L. Robl

Submitted to: U. S. Department of Energy; National Energy Technology Laboratory

Abstract: The overarching goal of this project was to create a sustained center to support the continued development of new products and industries that manufacture construction materials from coal combustion by-products or CCB’s (e.g., cements, grouts, wallboard, masonry block, fillers, roofing materials, etc). Specific objectives includes the development of a research kiln and associated system and the formulation and production of high performance low-energy, low-CO2 emitting calcium sulfoaluminate (CAS) cement that utilize coal combustion byproducts as raw materials.

(We've previously documented all of the above-specified uses for Coal Ash, "coal combustion by-products", in previous reports. We won't include links to those past reports here, but will be treating each of those uses for "CCB's" again, separately, in future reports.)

Executive Summary: The goal of this project was to create a center to support the development of new products and industries that manufacture construction materials from coal combustion by-products or CCB’s. The center served three functions:

1. facilitated the development of technology to produce new forms of non-Portland cement, pozzolanic concrete additives, and masonry from coal products;

2. provided informational transfer and technical liaison between coal combustion producers and the construction industry;

3. supported relevant education and training via participation of graduate and co-operative students.

This center conducted research into the development of low energy, low CO2 emitting construction materials from CCB’s, including calcium sulfoaluminate and plaster based cements, high performance pozzolanic cement additives and geopolymers.

(Based on our ongoing research, the concept of "geopolymers" seems especially important to us, since, although not well-explained, "geo-polymerization" reactions lie behind the efficacy of Coal Ash as an additive that enhances the properties of Portland-type Cement and Portland-type Cement Concrete. See, for some further explanation, our report of:

Coal Ash Polymer Reduces CO2, Gives Concrete Longer Life | Research & Development | News; concerning work at Louisiana Tech University conducted by and in the laboratories of Professor Erez Allouche:

"'Geopolymer Concrete Protects against Corrosion'; 2012; A new form of concrete made with geopolymer binders rather than portland cement exhibits high strength, low permeability, and high resistance to corrosion and heat. A novel form of concrete made from geopolymer binder technology developed by researchers at Louisiana Tech University is stronger and more resistant to corrosion and high temperatures than portland cement, potentially offering an ideal product for replacing the traditional construction material in harsh environments. For example, the geopolymer concrete recently performed well serving as a refractory surface at a facility used to test rocket engines. Because its main ingredient is an industrial by-product, the geopolymer binder technology requires much less energy to produce and results in significantly less carbon dioxide emissions relative to portland cement, making it a more environmentally sustainable option as well. Geopolymers represent a class of cementitious materials that harden and gain strength without the use of portland cement. Although a variety of materials may be used to create geopolymers, the basic components are a fine-powdered material rich in aluminum and silica - - including fly ash ... - - and sodium hydroxide, potassium hydroxide, or another alkali to cause the aluminum and silica to leach out of the powdered material. “We can use a variety of waste products or natural sources to get the powder that we are looking for,” says Erez Allouche, Ph.D., P.E., M.ASCE, the director of Louisiana Tech University’s Trenchless Technology Center. Fly ash has turned out to be the main ingredient of choice for Allouche and his colleagues";

and, which contains links to supplemental documents, including one published by the Federal Highways Administration:

"'Geopolymer Concrete'; Geopolymer materials represent an innovative technology that is generating considerable interest in the construction industry, particularly in light of the ongoing emphasis on sustainability. In contrast to portland cement, most geopolymer systems rely on minimally processed natural materials or industrial byproducts to provide the binding agents. Since portland cement is responsible for upward of 85 percent of the energy and 90 percent of the carbon dioxide attributed to a typical ready-mixed concrete ..., the potential energy and carbon dioxide savings through the use of geopolymers can be considerable. Consequently, there is growing interest in geopolymer applications in transportation infrastructure".)

The specific objectives of this project included the design, procurement, installation and finally testing of a processing system built around a research kiln. This system was installed in a new 6,400 ft2 facility constructed with funds from the State of Kentucky. The project has four broad task components: project management and planning, design of equipment, purchasing, construction and testing of equipment, and production and performance testing of low energy cements. Important milestones and deliverables include the formation of a technical advisory board; the final design of the system; system procurement and testing; final shakedown operation and finally the production and testing of a calcium sulfoaluminate clinker.

The production of Portland cement requires prodigious amounts of energy, mainly because of the high temperatures required to partially melt and fuse the raw materials into clinker. Portland cement clinker, which is comprised mainly of calcium silicates, is also very hard and requires considerable energy to grind to the final product.

Furthermore, limestone is the predominant raw material used to produce Portland cement and releases large amounts of CO2 during the thermal processing.

In order to realize substantial reductions in energy consumption and CO2 emissions, significantly lowering the clinkering temperature and the proportion of limestone in the feed is necessary. This is unfortunately not possible with Portland cement. However, energy-conserving or "low-energy" cements can be produced at lower temperatures and using much less limestone than Portland cement. They can also be much softer and easier to grind. An additional environmental benefit is that CSA cements can be prepared using substantial amounts of coal combustion wastes as the raw materials. These include Flue Gas Desulfurizaton gypsum, pulverized coal combustion (PCC) fly ash, and fluidized bed combustion (FBC) ash.

There are several types or classes of low-energy, low-CO2 cements. This study focused on two types: calcium sulfoaluminate (CSA) cements, and FBC ash-based “clinkerless” cement. Both of these cements gain strength primarily from the formation of a calcium aluminum sulfate hydrate called ettringite. Because of the rapid rate of formation of ettringite, CSA cements gain strength very quickly. However, there remain questions around the durability of CSA cement concrete. The research described herein involved the formulation, production and evaluation of two classes of FBC byproduct-based products:

1) a medium strength material produced directly from the hydration of the FBC byproducts, and:

2) CSAB cement produced by heating the FBC spent bed in the presence of limestone, bauxite, and PCC fly ash.

The formulation, production, and performance testing of these two classes of materials are described in this report. The free lime and calcium sulfate present in the ... spent bed material and fly ash imparted cementitious properties to these materials when they were mixed with water.

Another problem with using FBC-based clinkerless cements instead of Portland cement was the slow strength gain of the former. To overcome this, addition of alkali (e.g. sodium hydroxide) to the paste could increase the dissolution rate of Class F fly ash, which would cause an increase in the rate of ettringite and calcium silicate hydrate formation, with a concomitant increase in strength. A second strategy could be to blend the clinkerless cement with rapid hardening cement (RHC) such as plaster. The RHC would provide early strength, whilst the pozzolanic reactions in the clinkerless component would provide additional longer-term strengths. The Gilbert fluidized bed combustion material has potential for use in the production of calcium sulfoaluminate belite (CSAB) cements. Production of clinker from FBC spent bed material, limestone, and bauxite produced a large quantity of Klein’s compound and belite. The Gilbert FBC ash provided mainly calcium sulfate and calcium oxide, with the latter being an effective substitute for limestone that is normally required for CSAB cement clinker. The synthesized CSAB clinkers were soft and readily milled to cement fineness. Milling the clinker with FGD gypsum was effective in provide the additional calcium and sulfate required to “activate” the clinker to form ettringite. The compressive strength of the commercial and laboratory CSAB cements produced high-early strengths that exceeded those of ordinary Portland cement. Additional long-term strength was possibly provided by hydration of dicalcium silicate (C2S) within the clinker. The tests in which the CSAB cements performed well were compressive strength, drying shrinkage and expansion.

A major issue regarding the production of CSAB cement is one of cost. Because CSAB clinker production requires substantial quantities of bauxite, the cost of these cements is high. In order to minimize or eliminate bauxite, alternatives to this raw material need to be pursued. The replacement of some bauxite with high-iron raw materials, as presented in this report as a CSA with calcium aluminoferrite, CSFAB. This could have the net effect of replacing some of the aluminum with iron, which is considerably less expensive. Thus, the use of high-iron materials, such as certain Class F fly ashes ... can be utilized as partial replacements for bauxite.

(The above several paragraphs of discussion concerning "CSAB" and "CSA" cements are, again, treating a cement chemistry somewhat different from standard Portland-type cement, and PC clinkers, which, as seen for one example in our report of:

Pittsburgh Converts Coal Ash and Flue Gas into Cement | Research & Development | News; concerning:

"United States Patent 5,766,339 - Producing Cement from a Flue Gas Desulfurization Waste; 1998;  Assignee: Dravo Lime Company, Pittsburgh, PA; Abstract: Cement is produced by forming a moist mixture of a flue gas desulfurization process waste product (and) aluminum, iron, silica and carbon, agglomerating the moist mixture while drying the same to form a feedstock, and calcining the dry agglomerated feedstock in a rotary kiln. Sulfur dioxide released from the calcium sulfite hemihydrate and calcium sulfate hemihydrate during calcination may be used to produce sulfuric acid, while heat recovered in the process is used to dry the agglomerating feedstock (and) calcining said dry agglomerated kiln feedstock in a rotary kiln to produce a cement clinker; and pulverizing said cement clinker to produce cement. The process for producing cement from a flue gas desulfurization process waste product ... wherein said source of aluminum and iron comprises fly ash";

can be manufactured almost entirely from "coal combustion by-products", that is, by using Coal Ash as a total replacement for any aluminum-bearing raw materials/minerals, such as shale rock or clay, which might be used in the making of standard Portland-type cement..)

 Introduction: Center for Coal-Derived Low Energy Materials for Sustainable Construction.

The Center, also known as the Center for Coal Combustion Derived Materials or CCDM*, has three missions:

First to facilitate the development of technology to produce new forms of non-Portland cement, advanced pozzolanic concrete additives and high performance masonry materials from coal products through research. This was the focus of this project.

The second was to provide informational transfer and technical liaison between coal combustion producing utilities and the construction industry and its trade groups. This was addressed through a technical advisory board consisting of industrial and trade group representatives including the Kentucky Department of Highways, Cemex, Inc., IMI, Inc., the Kentucky Ready Mix Association, E.ON USA LLC, TVA, and the East Kentucky Power Cooperative (EKPC).

Thirdly this project supported education via participation of graduate and co-operative students. It operated in close collaboration with the UK Department of Civil Engineering. Professor Mahboub will be a faculty associate and coordinator of this activity. Additionally the UK Department of Design has dedicated a course to the study and innovative use of CCBs in the design of innovative products from decorative art to functional furniture and housing.

The project was focused on moving existing research on energy efficient cement production beyond the workbench to the next level, that is, the manufacture of low energy cements of various types and formulations in a continuous pilot kiln in sufficient quantity to conduct realistic demonstrations of the cements and investigate their properties. The effort to accomplish this had four broad task components: project management and planning, design of equipment, purchasing, construction and testing of equipment, and production of low energy cements for use in concrete. The Center itself is housed in a new 6,400 ft2 laboratory that has been constructed on the property of the Center for Applied Energy Research Campus.

Currently in the U.S., there are approximately 60 fluidized bed combustion (FBC) boilers used to generate electricity. There are two units in Kentucky that use this technology: the Shawnee Plant, operated by TVA, and the Gilbert Unit, operated by East Kentucky Power Cooperative (EKPC). Although FBC boilers can substantially reduce SOx and NOx emissions relative to a pulverized coal combustion (PCC) boiler, they generate a much larger quantity of solid byproducts. FBC burns coal in a fluidized bed of sorbent, usually limestone ... .

Currently in the U.S., there are approximately 60 fluidized bed combustion (FBC) boilers used to generate electricity. There are two units in Kentucky that use this technology: the Shawnee Plant, operated by TVA, and the Gilbert Unit, operated by East Kentucky Power Cooperative (EKPC). Although FBC boilers can substantially reduce SOx and NOx emissions relative to a pulverized coal combustion (PCC) boiler, they generate a much larger quantity of solid byproducts. FBC burns coal in a fluidized bed of sorbent, usually limestone, which removes most of the SOx emissions. The resultant byproducts are thus mainly composed of calcium sulfate, and also contain lesser amounts of unreacted sorbent i.e. lime or CaO. There are two types of byproducts produced in an FBC boiler: spent bed material, which is a coarse sandy material, and “fly ash”, which is a much finer material that is captured from the flue gas. The spent bed material generally contains a higher proportion of lime and calcium sulfate than the fly ash, whereas the latter contains more alumina and silica because of the presence of ash from the combusted coal.

The lime, alumina, and calcium sulfate within FBC byproducts imparts a cementitious nature when they are mixed with water. The cementitious properties are largely the result of the formation of two hydrated phases: gypsum and ettringite. Gypsum is formed from the hydration of the anhydrous calcium sulfate (anhydrite). This reaction can be slow because of the “hard burned” nature of the FBC anhydrite, which results from the high temperatures within the boiler.

(The making of useful "gypsum", as seen in our report of:

Pittsburgh Makes Coal Flue Gas Gypsum for Fly Ash Cement | Research & Development | News; concerning: "United States Patent 5,312,609 - Sulfur Dioxide Removal from Gaseous Streams with Gypsum Product Formation; 1994; Assignee: Dravo Lime Company, Pittsburgh";

from "pulverized coal combustion" desulfurization waste has long been known, and practiced.) 

Ettringite is a calcium aluminum sulfate hydrate that forms in a high pH environment (i.e. that occurring from the dissolution of lime in the FBC ash) ... .

The formation of these cementitious compounds in hydrated FBC byproducts has prompted a considerable research effort over the past 25 years or so to utilize the byproducts. The material is currently used in applications such as soil stabilization, structural fills, road subbase, and various fills

No-cement concrete and synthetic aggregates, prepared with spent bed material, have also been investigated ... but are not produced commercially.

Another pathway to the utilization of FBC byproducts is to produce a calcium sulfoaluminate-belite (CSAB) cement via a high temperature clinkering process, similar to the production of Portland cement.

An issue regarding the widespread use of CSA cements involves cost. ... (Production) of CSA cement requires a high alumina feedstock, which is traditionally bauxite. There are ostensibly no reserves of bauxite remaining in the U.S., which means that it must be imported from other countries such as Jamaica (USGS, 2006). This can make the cost of manufacturing CSA cement for widespread general use prohibitively expensive.

Because of their cost, as well as the durability questions, CSA cements in the U.S. ... have historically been used as minor additives to Portland cement concrete to compensate for shrinkage, and for self leveling screeds and rapid repair materials. In summary, CSA cements can potentially present considerable environmental advantages compared to Portland cement because of the lower energy use, lower CO2 emissions, and use of coal combustion wastes as raw materials. In order to support widespread introduction of the cements in the marketplace there are several issues that must be addressed, namely, high cost, durability issues, and appropriate applications. As was discussed above, although only a limited amount of research has been conducted on the durability of CSA cements, there is sufficient information indicating that the cements can be quite durable in certain environments. The research described herein has focused on the production of two classes of FBC byproduct-based products: 1) a low, medium and high strength material produced directly from the hydration of the FBC byproducts, and 2) two formulations of CSAB cement produced by heating the FBC spent bed in the presence of limestone, bauxite, and with/without red mud. The formulation, production, and performance testing of these two classes of materials are described.

Research Mission and Strategy: The primary research focus of this Center is the creation of new construction products and materials from coal by-products that require lower energy to produce and emit less carbon dioxide. These include: cold bonded geopolymers, plaster-based cement, and calcium sulfoaluminate (CSA) cement. CSA cement in particular has the potential to be a direct replacement for Portland cement and can be fabricated using substantial amounts of CCBs. The production of low energy cements and other green construction materials from coal combustion products is the primary near-term focus of this center and this agreement."

----------------------------- 

In essence, the above represents new and growing efforts to use, primarily, the Coal Ash arising from the newer fluidized bed combustion, FBC, technology, which technology is intended to capture some forms of pollutants in the spent bed material, before those pollutants, such as sulfur, would be discharged into the flue gas, where they would have to be captured by exhaust gas scrubbers, etc., before entering the atmosphere.

There are downsides to the use of FBC boilers, which downsides include the co-production of a relatively larger amount of solid "CCB's", as compared to pulverized coal combustion, PCC, boilers.

However, the report is also concerned with the making of a special type of cement, among other products, for construction applications from such FBC boiler CCB's.

The full report also contains photographs of the University of Kentucky's pilot plant for proving out their Coal Ash utilization technologies, and other illustrations of the processes described. It's worth a look, and we'll be forwarding a copy of the document to the West Virginia Coal Association, should they wish to make it available.

But, the point of it all is, that, the solid residua arising from our economically essential use of Coal in the generation of reliable and affordable electric power, regardless of what Coal combustion technology might be utilized, comprise a reservoir of valuable mineral raw materials, which, if utilized for their fullest value, could reduce the extraction of natural raw materials for use in the construction industry; reduce the emission of CO2 related to the manufacture of certain construction materials; and, reduce the consumption of energy during the manufacture of those construction materials, thus generally contributing to "sustainability".

All while creating a bundle of new Coal Country jobs.


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