Process of producing light weight aggregate
We've documented many times from many sources the great potential value of Coal Ash, to the Cement and Concrete manufacturing and construction industries.
In the most straightforward way, as explained for one instance in:
West Virginia Coal Association | US EPA Headquarters Housed in Coal Ash | Research & Development; wherein we're told, in part, that: "fly ash has been used in concrete since the 1930’s. Most notably, it has been used in several construction projects and prominent buildings, including the Ronald Reagan Government Office building, home to the Environmental Protection Agency (EPA) in Washington, D.C.";
Coal Ash can simply be added to a Cement mix as a partial or full replacement for sand or other fine aggregate, where it's properties as a reactive "pozzolan" actually contribute to a higher ultimate strength and, as explained for one example in:
West Virginia Coal Association | Coal Ash Concrete More Durable, Resists Chemical Attack | Research & Development; concerning: "United States Patent 5,772,752 - Sulfate and Acid Resistant Concrete and Mortar; 1998; Assignee: New Jersey Institute of Technology; Abstract: The present invention relates to concrete, mortar and other hardenable mixtures comprising cement and fly ash for use in construction and other applications, which hardenable mixtures demonstrate significant levels of acid and sulfate resistance";
an enhanced resistance to chemical corrosion of the cured Concrete.
Further, Coal Ash can be treated and processed in such a way so as to form larger particles, comparable to slag, which can be utilized as the coarse aggregate, as a replacement for gravel or crushed stone, in Concrete mixes; as established, for one example, in our report of:
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, Pittsburgh; Abstract: A process for making high-strength aggregates including hydrating calcium oxide containing coal combustion ash for a sufficient period of time to convert a high percentage of the calcium oxide to calcium hydroxide prior to forming the aggregates and curing the aggregates in high humidity. The moisture of the hydrated material is monitored to vary the hydration moisture to the desired set point. Further, the process involves producing high-strength aggregates from calcium hydroxide containing FGD ashes such as generated from duct sorbent injection and spray dryer processes. Method of producing high-strength aggregates from ... coal combustion ash (and) flue gas desulfurization (FGD) ashes".
Even further, Coal Ash can be treated and processed in such a way so as to form specialty, lightweight aggregate for Concrete mixes, as seen, for one example, in:
West Virginia Coal Association | Coal Ash and Sewer Sludge to Lightweight Concrete Aggregate | Research & Development; concerning: "United States Patent 5,342,442 - Lightweight Aggregate from Flyash and Sewage Sludge; 1994; Assignee: Wisconsin Electric Power Company; 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 (and) 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".
And, as far as why we might want a lower-weight aggregate, and, thus, a lower-weight Concrete, some explanatory background is available via:
http://www.ide.titech.ac.jp/~otsukilab/lecture/advanced%20concrete%20technology/14Lightweight%20Aggregate%20Concrete.pdf; and:
http://www.structuremag.org/Archives/2008-6/D-InSights-Ries-June08.pdf; "'Structural Lightweight Aggregate and Concrete; How a 90-Year-Old Industry Finds Itself on the Leading Edge of the Sustainability Movement'; by John Ries, P.E.".
In any case, the production of such specialty, lightweight aggregates from Coal Ash was actually established in one of the hearts of US Coal Country a little more than half a century ago.
We remind you that we have many times made report of the Coal technology innovations established over the decades by Pittsburgh, PA's Koppers Company.
A few, perhaps interesting, examples would include:
West Virginia Coal Association | Pittsburgh & Germany 1940 Coal & Steam to Hydrocarbons | Research & Development; concerning: "United States Patent 2,220,357 - Synthetical Production of Liquid Hydrocarbons; 1940; Assignee: Koppers Company, Pittsburgh, PA; Abstract: This invention relates to the synthetical production of liquid hydrocarbons by reacting gases containing hydrogen and carbon monoxide, in the presence of catalytic substances ... . (In the invention) hydrocarbons are converted with steam into carbon monoxide and hydrogen. (And) carbon dioxide ... also reacts with the steam. A process for making liquid hydrocarbons by catalytically reacting (Hydrogen and Carbon Monoxide in specified proportions, which are made by) alternate blows of air and ... steam through ... carbonaceous fuel. (And) in which the steam and hydrocarbon vapors for the runs of ... water-gas comprise steam and coke oven gas"; and:
West Virginia Coal Association | Pittsburgh 1941 CO2 + Methane = Hydrocarbon Syngas | Research & Development; concerning: "United States Patent 2,266,989 - Manufacture of a Gas from CO2 and Methane; 1941; Assignee: Koppers Company, Pittsburgh, PA; Abstract: The present invention relates to the manufacture of gases suitable for the synthesis of higher hydrocarbons or the like, said gases containing definite volumes of carbon monoxide and hydrogen in a certain proportion, by reacting on methane ... with carbon dioxide or a mixture of carbon dioxide and steam, so that the methane ... is decomposed into hydrogen and carbon monoxide. The reactions between methane and carbon dioxide ... as adopted for the process according to the present invention are already known, but heretofore these reactions have not yet been used on an industrial scale, mainly due to the fact that up to now no suitable source for the carbon dioxide ... was available".
And, herein, we learn that Koppers applied themselves as well to the issue of Coal Ash.
They developed a method whereby Coal Ash could, in a way related to that disclosed in the above-cited "United States Patent 5,342,442 - Lightweight Aggregate from Flyash and Sewage Sludge", be processed and converted into a replacement for conventional light weight aggregates suitable for use in the forming of lighter-weight, specialty concretes.
As seen in excerpts, with comment inserted and appended, from the initial link in this dispatch to:
"United States Patent 2,946,112 - Process of Producing Light Weight Aggregate
Date: July, 1960
Inventors: L.G. Tucker and Andrew Kantor, Pittsburgh, PA
Assignee: Koppers Company, Inc.
Abstract: This invention relates to a process for producing light weight aggregate and more particularly to a process for producing light weight aggregate for various construction purposes by utilizing fly ash derived from coal combustion in boiler plants and the like.
With the increasing industrial expansion of today and the ever increasing demand for power, there has been a resulting increase in the by-products obtained in furnishing such power, one of these by-products being the fly ash which comes off of the exhaust stacks of coal burning boilers and the like, this fly ash being precipitated from the air by electrical and mechanical precipitators.
So large has this quantity of fly ash become, that it has been estimated by experts in the field that industry will produce approximately 17 million tons of such material per year in the very near future.
Accordingly, with such tremendous quantities of this material now being made available and with the industrial horizon promising even larger quantities, there has been a growing urgency to find ways of utilizing the material in the most efficient manner possible.
(Note the refreshing emphasis on "utilizing" a "material ... being made available", rather than on "disposing" of a "waste". Isn't that an attitude we should strive to cultivate in just about everything we do, including, for instance, as it might pertain to Carbon Dioxide?)
It has long been known in the art to utilize such fly ash as an additive in a road base, as an additive in cement mix, as a material in forming briquette blocks, and as a replacement for cement, concrete and cinder blocks.
(Regarding the above statements, see, for example:
West Virginia Coal Association | More Coal Fly Ash Facts for Highway Engineers | Research & Development; concerning: "Fly Ash Facts for Highway Engineers; American Coal Ash Association; DTFH61-02-X-00044; (for the) Federal Highway Administration; 2003", which tells us, in part, that: "Currently, over 20 million metric tons (22 million tons) of fly ash are used annually in a variety of engineering applications. Typical highway engineering applications include: portland cement concrete (PCC), soil and road base stabilization, flowable fills, grouts, structural fill and asphalt filler. Fly Ash in Stabilized Base Course: Fly ash and lime can be combined with aggregate to produce a quality stabilized base course. These road bases are referred to as pozzolanic-stabilized mixtures (PSMs). Typical fly ash contents may vary from 12 to 14 percent with corresponding lime contents of three to five percent"; and:
West Virginia Coal Association | US Government Coal Ash Cement Stronger than Portland Cement | Research & Development; concerning: "United States Patent 4,256,504 - Fly Ash-based Cement; 1981; Assignee: The United States of America (as represented by the Secretary of the Interior)"; and:
West Virginia Coal Association | Coal Fly Ash Bricks are Greener and Stronger | Research & Development; concerning: "United States Patent 7,998,268 - Method to Produce Durable Non-vitrified Fly Ash Bricks and Blocks; 2011; Assignee: Ecological Tech Company, Inc., Columbia, MO; Abstract: A method of making durable, non-vitrified masonry units comprising fly ash".)
And, more recently, new and promising markets have opened up in utilizing the fly ash as a means to form a light weight aggregate for numerous construction purposes. In this connection, however, the fly ash has not proven entirely successful since there has been little, if any, control of the size and quality of particles formed from the ash when making up the aggregate.
The present invention provides a process for utilizing fly ash to form a light weight aggregate ... which is continuous, efficient, and economical ... .
(The) present invention provides a process of forming a light weight aggregate comprising treating fly ash derived from coal combustion with a binder material, pelletizing the binder-treated fly ash to form pellet particles which provide porosity in subsequent treatment, and sintering the pellet particles to form a hardened light weight aggregate which is suitable for various construction purposes. Further, the present invention provides a process which utilizes with this fly ash in producing the light weight aggregate, a boiler grate bottom ash of coarser nature than the fly ash.
(In other words, all of the solid residues resulting from Coal combustion can be utilized.)
(The) first step in the process is to collect and introduce the fly ash into a mixing apparatus (as illustrated).
Once the fly ash or combination of fly ash and bottom ash have been introduced into the mixing apparatus a binding material is then added ... . It has been found that one of the most advantageous materials to serve as a binder is bentonite, an extremely alkaline plastic material which serves to stabilize the fly ash when it is formed into pellets, as is described hereinafter. In this connection, whenever fly ash with a comparatively high carbon content (approximately 10% or higher) is used, a binder of sodium silicate, also of an alkaline nature, can be substituted for the bentonite.
(The specified "bentonite" is a rather broad label applied to clay deposits typically originating from volcanic ash; and, there is a lot of it around, though most originates in the western US. It is a commercially-available and widely-used commodity mineral, as the following references should help to attest:
Bentonite - Wikipedia, the free encyclopedia; "Bentonite is ... essentially impure clay consisting mostly of montmorillonite. ... Bentonite usually forms from weathering of volcanic ash ... "; and:
Bentonite; "Industrial Minerals Association - North America"; and:
Bentonite Performance Minerals LLC - Halliburton; "Bentonite Performance Minerals LLC (BPM) is a world leader in the production of Wyoming bentonite ... . Mission Statement: to develop, manufacture, market, and support the finest bentonite products in the world".
The alternative "sodium silicate", too, is a readily-available and inexpensive industrial commodity:
Sodium silicate - Wikipedia, the free encyclopedia; "Sodium silicate is the common name for a compound sodium metasilicate, Na2SiO3, also known as water glass ... . It is available in aqueous solution and in solid form and is used in cements, passive fire protection, refractories, textile and lumber processing, and automobiles."
Performance Chemicals > North America > Products > Sodium Silicate Liquids; "PQ Corporation is the world’s leading producer of sodium silicate. Sodium silicate, also known as waterglass, is a versatile inorganic chemical made by combining sand and soda ash (sodium carbonate) at high temperature. Adjusting the ratio of sand to soda ash yields a variety of products with unique functionality used in many industrial and consumer product applications. We offer the largest variety of high quality products shipped from the most extensive sodium silicate manufacturing network in the world.")
The binders, of either bentonite or sodium silicate, can be added to the mixing apparatus either in powder or slurry form so that they constitute approximately one-half percent to approximately two percent by weight of the entire dry mix.
(And, you don't, as above, need a lot of the added materials, with their added expense, in any case.)
Once the binder has been properly mixed with the fly ash material, the material is conveyed by an endless conveyor to a pelletizer. The pelletizer can be one of several well known commercial types commonly referred to as disc type or saucer type pelletizers.
(The specified "pelletizers", too, are almost commodity industrial items, even though you might never have heard of such a thing, See:
Pelletizing - Wikipedia, the free encyclopedia; "Pelletizing is the process of compressing or molding a material into the shape of a pellet. A wide range of different materials are pelletized including chemicals, iron ore, animal compound feed, and more"; and:
Pelletizer-Pelletizer Manufacturers, Suppliers and Exporters on Alibaba.com.)
Once the material has been properly pelletized into ball-like particles of a uniform dimension (as fully specified) and of sufficient firmness to maintain identity in the steps that follow, the material is then conveyed from the pelletizer by endless conveyor to a receiving hopper which feeds raw pellets into a sintering machine. The sintering machine can be any one of several well known types of sintering machines which can perform continuous sintering with either an induced or forced draft.
(Again, well-known and long-established industrial technologies are specified. See:
Sintering - Wikipedia, the free encyclopedia; "Sintering is a method used to create objects from powders. It is based on atomic diffusion. Diffusion occurs in any material above absolute zero, but it occurs much faster at higher temperatures. In most sintering processes, the powdered material is held in a mold and then heated to a temperature below the melting point. The atoms in the powder particles diffuse across the boundaries of the particles, fusing the particles together and creating one solid piece"; and:
Sintering Machine-Sintering Machine Manufacturers, Suppliers and Exporters on Alibaba.com.)
The pelletized material is sintered at the rate of approximately .75 inch per minute to approximately .95 inch per minute with a sinter bed depth of about 7 inches and with temperatures ranging from approximately 250 degrees F. to approximately 500 F.
It is to be noted that in instances where a high carbon fly ash is utilized, the pellets are fused together and the solidly caked material is then broken into light weight aggregate by a conventional type mechanism such as a jaw crusher or a roller, reducing the cake to a desired size depending upon its use. In this connection, it is also to be noted that the low carbon material does not fuse into cake form but retains a pellet-like status ... .
(If it is preferable to start with a low-carbon Ash, then, as we have seen in previous reports, such as:
West Virginia Coal Association | Virginia Converts Coal Ash to Cash | Research & Development; concerning: "Dominion Recycling Center Turns Ash to Cash; 2006; It looks like a really big igloo, or maybe an indoor skating rink. But Dominion Virginia Power says the new, domed structure next to its Chesapeake power station will make money, create jobs and help the environment. The waterfront facility, on the Elizabeth River just south of the Gilmerton Bridge, is an ash recycling center - the first of its kind in Virginia, and just the fourth in the nation. The facility acts like a big oven. It bakes black, carbon-laden fly ash into a kinder, gentler and paler byproduct that can be sold and made into concrete, roof tiling and construction blocks, among other alternative uses"; and:
West Virginia Coal Association | US EPA Approves Coal Fly Ash Carbon Burn Out | Research & Development;
with additional reports concerning the technicalities to follow, there exist established techniques for getting rid off the residual Carbon in "high carbon fly ash".)
Claims: A process for forming a light weight aggregate from fly ash derived from the combustion of coal."
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As we noted in our introductory comments, there are applications where a lighter-weight Concrete is desirable; and, as herein, Coal Ash can be processed to serve as a light weight coarse aggregate that contributes, perhaps when blended into a Cement made via a process like that disclosed in:
West Virginia Coal Association | Fly Ash and Desulfurization Waste Make "Premium" Cement | Research & Development; concerning: "United States Patent Application 20060201395 - Blended Fly Ash Pozzolans; 2006; Inventors: Gregory Barger and Charles Widenhoft, Overland Park, Kansas (Ashgrove Cement Company); Novel premium blended pozzolans for use with hydraulic cement are created by intergrinding an ASTM Class F or Class C coal fly ash and a source of calcium sulfate, such as gypsum ... . Alternately, a novel concrete composition can be formed using the blended pozzolan with a hydraulic cement, aggregate and water so as to produce a concrete having improved strength, ASR mitigation, improved sulfate resistance and lowered permeability. The novel pozzolans not only reduce production costs by decreasing fuel and raw material consumption per ton of cement, but they also use by-product waste materials from another industry to create a premium product for the construction industry";
to the making of such lighter-weight Concrete.
Since, as herein, a coarse, but light weight, aggregate can be made from Coal Ash that can be added to Cement made from Coal Ash, perhaps in combination with a fine aggregate that consists primarily of Coal Ash, you might be led to conjecture that Concrete can be manufactured that consists in it's entirety, 100%, of Coal Ash, or Coal Ash-derived products.
And, as we will document in some reports to follow, you would be correct.
And, you would also be correct in thinking that, rather than being some sort of noxious, valueless waste we must somehow, at great unproductive expense, find some way to satisfactorily dispose of, Coal Ash is, instead, a valuable raw material resource.
We can consume and utilize Coal Ash in the manufacture of a full range of Cement and Concrete construction materials; with such employment offering the benefits of lower cost and higher performance, while at the same time preventing the disruption of natural environments; disruption that might otherwise be caused by the mining, quarrying and dredging of the traditional and conventional Cement and Concrete raw materials.
