http://www.flyash.info/2011/157-Zhang-2011.pdf
We have been researching the issue of Mercury control regulations that are pending imposition by the US EPA on our economically vital Coal-based power generation industries.
There are, actually, a number of good options for Mercury control that would enable us to continue using Coal profitably for the generation of abundant, affordable electric power; and, our research is far from complete.
This dispatch will serve only as further introduction to the topic.
What prompted us to write at this point is a current article indirectly related to the subject:
EPA to reduce power plant toxics discharged to waterways - Business, Government Legal News from throughout WV; "EPA to reduce power plant toxics discharged to waterways; April 19, 2013; By Pam Kasey; The April 19 proposal, part of a legal settlement, seeks comment on options for controlling discharges into waterways from coal ash and other power plant wastes. Final rule is due in May 2014."
One reason that substances might, but only might, as will be seen following, can get into environmental water supplies from Coal-fired power plants is because some of the Coal Ash is just left sort of piled up and lying around, prior to final disposal or disposition; and, any chemical substances adhering to the Ash which can be mobilized by water might have the opportunity to be washed out of the Ash by rain or snow, and thereby get into the groundwater.
That, when, as we've demonstrated in numerous reports, such as, for a few examples:
West Virginia Coal Association | Coal Ash in Concrete Saves $100 Billion | Research & Development; "The Economic Impacts of Prohibiting Coal Fly Ash Use in Transportation Infrastructure Construction; 2011; Prepared by the American Road & Transportation Builders Association Transportation Development Foundation. Executive Summary: Fly Ash: A High-Return “Green” Building Material; Coal fly ash ... is nearly identical in composition to volcanic ash. When mixed with calcium hydroxide, it has many of the same properties as cement. Replacing a portion of the cement with fly ash creates a cementitious material that, when used as an input with aggregates, water and other compounds, produces a concrete mix that is well-suited to road, airport runway and bridge construction"; and:
West Virginia Coal Association | Pittsburgh Converts Coal Ash and Flue Gas into Cement | Research & Development; concerning: "United States Patent 5,766,339 - Producing Cement from a Flue Gas Desulfurization Waste; 1998; Assignee: Dravo Lime Company, Pittsburgh; Abstract: Cement is produced (from) a flue gas desulfurization process waste product containing 80-95 percent by weight calcium sulfite hemihydrate and 5-20 percent by weight calcium sulfate hemihydrate, aluminum, iron, silica and carbon, (and) wherein said source of aluminum and iron comprises fly ash";
Coal Ash can be consumed and utilized both as a raw material for the making of Portland-type Cement and as a reactive, "pozzolanic" aggregate which can be added to Cement, as a substitute for sand and fine gravel, and even as a replacement for some of the Cement itself, to make Concrete; a Concrete that is actually superior in nearly all levels of performance to conventional Portland Cement Concrete. And, if Coal Ash were to be used in such applications, it wouldn't be left exposed to the environment at Coal-fired power plants, where it can cause concerns about water contamination.
One looming barrier now to increased use of Coal Ash in the making of Cement and Concrete, a set of applications whose volume requirements are such that they could conceivably consume all, and more, of the Coal Ash we produce each year, is the imposition of Mercury controls on Coal-fired power plants.
There are multiple methods being proposed, and implemented, for the control of Coal plant Mercury emissions. We'll address others in reports to follow, but, herein, we demonstrate that one of those strategies being developed involves the injection of a chemical Mercury absorbent, usually powdered activated carbon, "PAC", perhaps enhanced with additives, into raw exhaust streams. The carbon particles, after absorbing Mercury, are then filtered out with the Fly Ash, thus resulting in a Fly Ash product burdened both with Mercury and with unburned Carbon; Fly Ash that Concrete producers are afraid will disqualify their Concrete for use, due in part to Mercury leaching concerns in the end-use Concrete application.
First of all, as can be learned via:
http://c.ymcdn.com/sites/www.icac.com/resource/resmgr/MercuryControl_PDF's/Clearwater03_ADA_Hg.pdf;
"'Characterization of Fly Ash From Full-Scale Demonstration of Sorbent Injection for Mercury Control on Coal Fired Power Plants'; Constance Senior; et. al., Reaction Engineering International (and) ADA Environmental Solutions, LLC; With impending regulation of mercury from coal-fired power plants, control efforts have focused on the most mature retrofit technologies. Powdered activated carbon (PAC) injection (is) the most mature technology, but has until recently only been demonstrated in bench- and pilot-scale experiments. Under a DOE NETL cooperative agreement, large-scale, continuous injection of PAC was accomplished for periods of several weeks at four utility power plants. Leaching analyses were performed using two widely accepted methods in order to assess the stability of the ash byproduct in landfill situations. Results (show that in several different applications, little) or no detectable Hg leached (from) any of the ash samples. The amounts of mercury leached from these samples were about 100 times lower than the primary drinking water standard. At one plant, where ash was tested for mercury leaching with and without injection of PAC, PAC injection did not seem to have increased the amount of mercury leached from the ash"; .
even unconsolidated, un-encapsulated Ash that has been used to absorb Mercury doesn't seem to release that Mercury under, as the full report specifies, standard and approved leaching test procedures.
Simple logic suggests that it would be even less likely to do so when encapsulated in Concrete.
Second, we note that Mercury in Coal Ash could well be re-volatilized and released during the calcination process in a Cement kiln, where Fly Ash was being used, as in the above-cited "United States Patent 5,766,339 - Producing Cement from a Flue Gas Desulfurization Waste", as a raw material for Cement.
And, that leads to an entirely different line of discussion relating to Mercury emission requirements that are being mandated for Cement kilns which we must postpone, so that we can focus on our primary topic of using Mercury-laden Coal Ash as a component of Concrete.
As indicated to some extent by our above citation of "Characterization of Fly Ash From Full-Scale Demonstration of Sorbent Injection for Mercury Control on Coal Fired Power Plants", there is little likelihood that Mercury-laden Coal Ash used as a component of Concrete mixes would lead to Mercury being leached into the environment from the cured Concrete. And, that is really the central point of this dispatch.
A few companies accomplished in the field have developed chemical technology to enable the capture of Mercury with Coal Ash, while at the same time retaining the properties of Coal Ash which enable it to serve so well as a component of Concrete.
Recall that we have previously reported to you on a Coal Ash beneficiation process known generically as "Carbon Burn-Out", wherein residual Carbon in Coal Ash, Carbon which would interfere with air-entrainment agents added to Concrete mixes to improve certain aspects of the Concrete's performance, is simply burned out of the Ash. An example would include:
West Virginia Coal Association | Virginia Converts Coal Ash to Cash | Research & Development; concerning, in part: "'South Carolina Electric and Gas Successful Application of Carbon Burn-Out (CBO) at the Wateree Station'; CBO combusts residual carbon in fly-ash, producing a very consistent, low-carbon, high-quality pozzolan. Extensive concrete testing has been and continues to be undertaken in order to demonstrate the superior characteristics of very low-carbon Class F fly ash from Carbon Burn-Out".
Unfortunately, such Fly Ash beneficiation strategies could not, in all likelihood, be applied on a practical basis to Fly Ash which has been contaminated through use in a flue gas Mercury removal process.
However, as we've seen in a few dispatches, such as:
West Virginia Coal Association | EPA-Sponsored Fly Ash Concrete Sequesters Flue Gas Mercury | Research & Development; concerning, in part: "United States Patent Application 20030206843 - Methods and Compositions to Sequester Combustion-Gas Mercury in Fly Ash and Concrete; 2003; The United States Government may own certain rights to present invention pursuant to U.S. Environmental Protection Agency Contract No. 68-D-01-075 and National Science Foundation Award No. DMI-0232735, to Sorbent Technologies Corporation. Abstract: A method for removing mercury from a combustion gas in an exhaust gas system (through use of a specified absorbent). Concrete compositions with fly ash containing the mercury sorbents will have reduced interference with air-entraining-admixtures";
Mercury control technologies have been developed which not only absorb Mercury onto Fly Ash, but, render that Fly Ash amenable for use in Concrete without the need for Carbon Burn-Out beneficiation.
As we noted in that dispatch, Sorbent Technologies Corporation was subsequently acquired by the much larger Albemarle Corporation, of Louisiana, a diversified manufacturer of catalysts and specialty chemicals:
Albemarle Corporation - Wikipedia, the free encyclopedia; "Albemarle Corporation is a ... specialty chemical manufacturing enterprise. The company employs approximately 4,000 people and serves customers in approximately 100 countries".
And, herein we see that Albemarle has continued their development of Mercury control technologies that, while economically removing Mercury from Coal plant exhaust streams, also leave the Coal Ash as a product which can be used in the formulation of Concrete mixtures.
As seen, first, in very brief excerpts from the initial link in this dispatch to:
"New Applications of the Concrete-Friendly Mercury Sorbent C-PAC (TM)
2011 World of Coal Ash Conference
Yinzhi Zhang, Ron Landreth and Daryl Lipscomb, Albemarle Corporation
(The) Concrete Friendly (TM) mercury sorbent, C-PAC (TM) can preserve the salability of fly ash in the concrete market after being used for mercury emission control at coal-fired power plants.
C-PAC is in commercial production at Albemarle's Twinsburg (OH) facility. It is one of Albemarle's powdered activated carbon (PAC) mercury sorbent products. Recently, it has been demonstrated that C-PAC is also able to control the emissions from cement kilns while preserving the cement kiln dust properties."
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The full paper is accessible via the initial link in this dispatch, and we recommend it's study; but, we have limited our excerpts due to rather stringent copyright infringement warnings. An Albemarle Corporation product information sheet concerning C-PAC (TM) should be accessible via:
http://www.albemarle.com/Products-and-Markets/SOR-0001-C-PAC-332C18.html.
We had, in initial drafts of this dispatch, included some information and links relative to the above "cement kiln dust", usually abbreviated as "CKD"; a by-product of Cement-making that the US EPA has been beating on in a way similar to Coal Ash. The absorption of Mercury, as we read the literature, onto CKD would, in fact, negatively affect at least some of it's potentials for it's reuse. Due to it's composition, unlike Coal Ash, it can be added to Concrete mixes only up to a level of about 15 percent. Further, much of it in the past was simply returned to a Cement kiln for further processing, which wouldn't, it would seem, be desirable for CKD already loaded with Mercury.
But, CKD and Fly Ash are so similar in some respects that they can be utilized together in concrete mixes; and, in Mercury absorption processes, as should be clear from the following US Patent Application, disclosing Albemarle's additional technology, developed subsequent to their acquisition of Ohio's Sorbent Technologies, as cited above, and their earlier, precedent process of "United States Patent Application 20030206843 - Methods and Compositions to Sequester Combustion-Gas Mercury in Fly Ash and Concrete":
United States Patent Application: 0110197791 - Compositions and Methods to Sequester Flue Gas Mercury in Concrete
COMPOSITIONS AND METHODS TO SEQUESTER FLUE GAS MERCURY IN CONCRETE - Albemarle Corporation
Date: August, 2011
Inventors: Ronald Landreth, et. al., OH and LA
Assignee: Albemarle Corporation, Baton Rouge, LA
Abstract: Mercury adsorbed from combustion gas by activated carbon can be sequestered in concrete containing air-entraining admixtures. The activated carbon may be made by providing a carbon char made from coconut shell, wood, or lignite that was activated by a method selected from the group consisting of activating with steam, activating with CO2, activating in an environment containing free oxygen, and combinations thereof to provide an activated carbon ... . The activated carbon may be injected into a combustion gas stream containing fly ash and mercury and may then be removed with fly ash from the gas stream.
The resulting composition may be used as a partial substitute for cement in air-entrained concretes.
A method comprising: providing a carbonaceous mercury sorbent precursor consisting of wood, lignite, coconut shell, and combinations thereof; activating or reactivating the mercury sorbent precursor by a method selected from the group consisting of activating with steam, activating with CO2, activating in an environment containing free oxygen, and combinations thereof, to provide an activated carbonaceous mercury sorbent (as further specified, and) injecting the activated carbonaceous mercury sorbent into a gas stream containing mercury, mercury-containing compounds, or a combination thereof, and fly ash, cement kiln dust, or a combination of fly ash and cement kiln dust, and allowing the activated carbonaceous mercury sorbent to contact the mercury or mercury-containing compounds to create mercury sorbent with adsorbed mercury; and removing the mercury sorbent with adsorbed mercury along with fly ash, cement kiln dust, or both, from the gas stream in a particulate control device, such that the mercury sorbent with adsorbed mercury along with fly ash, cement kiln dust, or both, is suitable for combining with an air-entraining admixture to provide a cementitious or pozzolanic composition.
The method ... additionally comprising: adding the mercury sorbent with adsorbed mercury along with fly ash, cement kiln dust, or both, to water, cement, and an air-entraining admixture to provide a cementitious or pozzolanic composition.
The method ... additionally comprising adding sand and coarse aggregate.
Background: Fly ash created from the combustion of coal is frequently used as a partial replacement for cement in concretes and mortars. Effluent gas from the combustion of coal contains mercury. This contaminant may be adsorbed by powdered activated carbon ("PAC") injected into the flue gas stream and collected with the fly ash in a particulate removal device.
However, when known PAC sorbents used for mercury emission control become mixed in with the fly ash from coal-fired power plants, the ash can no longer be sold for its highest-value use, namely, as a partial replacement for cement in concretes. This is because the highly-adsorptive PAC used for capturing the mercury also adsorbs the air-entraining agent chemicals (AEAs) later added to the concrete slurry to generate the air bubbles required for concrete workability and freeze-thaw capabilities.
Reuse of fly ash to partially substitute cement in concrete represents a major success of waste recycling in the US and has significant economic, environmental, and technical benefits.
The economic benefits of using fly ash to replace a fraction of the cement in concrete include increased revenue from the sale of the ash, reduced costs for fly ash disposal, and savings from using the ash in place of the more costly cement.
Concrete performance benefits include greater resistance to chemical attack, increased strength, and improved workability.
(For confirmation of the above statements, see, for one example, our report of:
West Virginia Coal Association | Coal Ash Concrete More Durable, Resists Chemical Attack | Research & Development; concerning both: "US Patent 5,772,752 - Sulfate and Acid Resistant Concrete and Mortar; 1998; Assignee: New Jersey Institute of Technology; 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 ... . (Mortar) containing 50% fly ash and 50% cement in cementitious materials demonstrated superior properties of corrosion resistance. Government Interests: The research leading to the present invention was conducted with Government support under Contract No. DE-FG22-90PC90299 awarded by the Department of Energy. The Government has certain rights in this invention"; and: "US Patent 6,802,898 - Preparing Fly Ash for High Compressive Strength Concrete; 2004; Assignee: New Jersey Institute of Technology; The present invention relates to concrete, mortar and other hardenable mixtures comprising cement and fly ash for use in construction. The invention relates to hardenable mixtures comprising cement and fly ash which can achieve greater compressive strength than hardenable mixtures containing only concrete".)
Environmental benefits include reduced greenhouse gas emissions, reduced land disposal, and reduced virgin resource use.
(We've explained and documented many times that conventional Cement kilns emit prodigious amounts of Carbon Dioxide, i.e., "greenhouse gas emissions", both through the calcination of limestone, via the chemical equation: CaCO3 + Heat = CaO + CO2; and, through the combustion of fuel to generate the needed heat. To the extent "CaO" is replaced by Fly Ash, at least an equivalent molecular amount of CO2 emission would be avoided.)
All of these benefits are lost if fly ash compositions contain prior-art mercury sorbents beyond de minimis levels. This is doubly negative, because not only must the fly ash be disposed of rather than beneficially used, but the opportunity is missed to physically and chemically sequester the mercury from release and interactions with the environment by encasing it (in) the concrete.
For the majority of coal-fired power plants, those without sulfur-dioxide wet scrubbers, the lowest-cost, leading-candidate technology to comply with current reduced mercury emission requirements is the injection of PAC into the flue gas in front of the plants' existing particulate controls. In this process, however, the PAC gets mixed in with the plant's collected fly ash. Because of the high surface area of typical PACs and their high adsorption capacity, if even the smallest amount gets mixed in with fly ash, the fly ash can no longer be used in concrete. The PAC adsorbs the Air Entrainment Agents later added to the concrete slurry. These surfactants enable incorporation of the precise amount of air bubbles needed to create the air voids required for concrete workability and freeze-thaw capabilities. For plants that could otherwise sell their ash for concrete, but now must dispose of it, this would be a big economic loss. U.S. Department of Energy National Energy Technology Laboratory analyses indicate that this deleterious by-product effect would effectively quadruple the cost of mercury reductions at some plants.
Mercury emissions from cement kilns are also increasingly recognized as a problem.
PACs could similarly be injected into these exhaust gases and be collected in the particulate removal devices that separate the cement kiln dust from the exhaust gases. However, because the collected cement kiln dust would then contain AEA-adsorbent PACs, it could no longer be sold as cement for air-entrained concretes.
This invention (comprises): providing a carbonaceous mercury sorbent precursor consisting of wood, lignite, coconut shell, and combinations thereof; activating or reactivating the mercury sorbent precursor by a method selected from the group consisting of activating with steam, activating with CO2, activating in an environment containing free oxygen, and combinations thereof, to provide an activated carbonaceous mercury sorbent, wherein the activation temperature and time period is limited such that the Acid Blue 80 Index of the activated carbonaceous mercury sorbent does not exceed 30 mg per gram of sorbent; grinding the activated carbonaceous mercury sorbent after activation or reactivation to an average particle size less than about 325 mesh; injecting the activated carbonaceous mercury sorbent into a gas stream containing mercury, mercury-containing compounds, or a combination thereof, and fly ash, cement kiln dust, or a combination of fly ash and cement kiln dust, and allowing the activated carbonaceous mercury sorbent to contact the mercury or mercury-containing compounds to create mercury sorbent with adsorbed mercury; and removing the mercury sorbent with adsorbed mercury along with fly ash, cement kiln dust, or both, from the gas stream in a particulate control device, all such that the mercury sorbent with adsorbed mercury along with fly ash, cement kiln dust, or both, is suitable for combining with an Air Entrainment Agent to provide a cementitious or pozzolanic composition."
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We haven't, obviously, reproduced many of the technical details; the full Disclosure is very thorough in it's exposition of them.
The point is that, the technology exists to effect the mandated removal of Coal power plant, and Cement Kiln, flue gas Mercury in a way that doesn't require reconfiguring or reconstructing the basic physical plant.
It is a process that can be "added on", as in a retrofit, but still enables Fly Ash to be produced that is acceptable for use as a property-enhancing additive to, or replacement for some of, the Portland-type Cement in Portland Cement Concrete mixes; thereby consuming Coal Ash in a profitable way, so that it isn't left lying about on or in the ground and attracting the malevolent interest of the ill-informed.
There are some potential, though perhaps minor, negatives associated with the process, relative to the aesthetic qualities of the Fly Ash produced, which we will address in a future report concerning alternatives to Albemarle's process herein; processes better suited to be designed into new Coal-fired power plants prior to their construction, as opposed to being installed via retrofit at existing power plants as this process seems intended.
In sum: Mercury capture and control processes and technologies exist which can be retrofitted, at some admittedly significant cost, to Coal-fired power generation facilities; but, which processes would still allow the recovery and reuse, as an additive to and/or partial substitute for Cement, of Coal Fly Ash in the making of Portland-type Cement Concrete; a Concrete wherein any Mercury that might have been adhered to the Coal Ash would be permanently, safely, forever entombed.