In the OSTI Collections: Clean Coal

Article Acknowledgement: Dr. William N. Watson, Physicist DOE Office of Scientific and Technical Information

Separating Combustible, Toxic, and Other Constituents 

Carbon Sequestraion

Alternative Fuels and Other Products Made from Coal

Other Improvements

References

Research Organizations

Reports available through OSTI's SciTech Connect

Additional References

Practical limits to any process that produces a desirable result are often due to undesirable results of the same process.  With some processes, the undesirable results directly limit the desired ones:  for instance, if you run an incandescent light bulb at a higher temperature to get more light from a given amount of electric power, the bulb burns out sooner.  With other processes, the undesirable results don’t interfere with the desired ones directly, but may be otherwise detrimental:  run a noisy motor at higher speed to make it work faster, and the noise may become too loud to make the time savings worthwhile.  Finding ways to reduce or eliminate the detrimental effects of useful processes often leads to the surpassing of the processes’ previous limits and thus to technical progress. 

Some significant examples of such progress relate to the process of coal burning.  Coal, when burned, produces heat that can be used to warm our surroundings, induce useful chemical reactions, or drive electric generators or other machines.  Burning coal also releases greenhouse gases, air pollutants, and other toxins.  So considerable thought and effort have been devoted to figuring out ways to reduce or eliminate the detrimental by-products of coal burning to make it a better fuel.  Details of a sample of such recent projects, including the kinds of problems they have addressed and overcome, are described in the following reports available through OSTI’s SciTech Connect. 

Separating Combustible, Toxic, and Other Constituents

Seventeen projects conducted in a four-year period by a five-university consortium, the Center for Advanced Separation Technology, are briefly described in a late 2013 report.^{[SciTech Connect]}  The investigations, by researchers at the University of Kentucky, West Virginia University, the University of Utah, Virginia Polytechnic Institute and State University, and Montana Tech of the University of Montana, involve separating portions of coal that can be burned to release energy from portions that don’t burn and from portions that would produce harmful effects if released into our environment. 

Coal is less useful if it has high moisture content in its pores, so such coal is dewatered before being burned.  The efficiency of filters^[Wikipedia] in partially separating water from fine coal particles is influenced by the flow rate, the structure of the particles’ pore network, and the coal’s wettability as expressed by the contact angle^[Wikipedia] that the water makes with the coal surface.  Filtration of fine coal was studied in one project by mathematical simulations and physical experiments to identify conditions that will lead to improved water removal and coal moisture content.  Another project compared a conventional drying technique, in which fine coal particles are dried while suspended in an upward flow of fast-moving air or other gas, to a new technique that involved forming the coal fines into pellets and drying them in an air stream that didn’t suspend them.  The suspended-particle technique is known as a “fluidized-bed” method because the suspended particles behave as a fluid; the technique in which the particles aren’t suspended is a “fixed-bed” method.  Experiments showed that, in the new fixed-bed method, the heat input required to achieve a specific amount of moisture reduction was minimized with high drying temperatures and low air velocities.  Pellets briquetted with six different biomass types were also tested for compressive strength and resistance to attrition; such briquettes appeared adequate for immediate handling and transport. 

Several of the other projects also relate to coal fines.  One involved particles from the Powder River Basin^[Wikipedia] of Montana and Wyoming.  While most Powder River Basin coal, being found in thick seams with few partings, is typically shipped without any upgrading, up to 5% of the basin’s reserve is found outside such seams and rejected in the mine pit.  But experiments with a dry density-based separator indicated that particles from the reject material with diameters between 1 and 6 millimeters could be upgraded to meet typical user specifications, for example by significantly reducing their feed ash content.  In a different project, air-current separation of 1- to 6-millimeter particles by density was analyzed with a numerical computer model, which showed that vortices forming around steps, or riffles, in the separator result in 43% displacement of the middlings and 29% displacement of the high-density particles, and that the separator’s effectiveness is reduced by an increase in the feed rate and high local variance of airspeed and pressure near the feed end.  

Still another project examined the recoverability of fine coal particles from waste slurries that also contained silica, clays, pyrite, and calcite, but found no cost-effective way to separate the coal particles from the clays.  This project’s experiments examined selective heating with microwaves and centrifugation to dewater the slurries as well as electrochemical generation of hydrogen from the slurries without separation of the coal particles.  Another experiment, testing whether clay and coal particles would separate in a fluidized bed by differences in the particles’ size or density, showed that even at the optimal gas velocity, the difference in ash content of the separated run-of-mine materials was only about 6%, with the cleaner material still being about 20% ash.  The technique didn’t work much better when additional clay was mixed with the run-of-mine coal, or when an electromagnetic field was introduced, but results of introducing an electrostatic field were more promising, with the cleaner material’s ash content decreasing by 10% on average. 

A different technique for separating coal from other matter, flotation^[Wikipedia], depends on the other matter’s greater attraction for water (“hydrophilia”^[Wikipedia]) so that small particles of it adhere to water molecules while “hydrophobic”^[Wikipedia] coal particles adhere much less and float to the top of the water.  In a standard version of the technique, the material to be separated is ground up and put into water mixed with other chemicals.  These chemicals decrease the coal surfaces’ already-low attraction to water molecules and enhance the stability of the froth that forms at the water’s upper surface when the water is aerated.  Recently, the use of these chemicals has been reduced because of cost and environmental concerns, but this has resulted in a less effective separation process.  One project addressed this problem by the generation of micrometer-sized bubbles on the particle surfaces and the feed material; the bubbles help the coal particles aggregate and increase their flotation rate.  Tests of a pre-aerator in a flotation system revealed the potential to improve coal recovery by 10% using only bubbles formed by cavitation^[Wikipedia], and by 15% when 50 cubic feet of air was added to the cavitation feed per minute.  Coal separation using the pre-aeration technique but 67% less surfactant chemical was as effective as the usual method with 100% of the chemical and no pre-aeration. 

Flotation was mathematically modeled in another project by equations for bubble generation, bubble-particle collision, attachment, and detachment, and froth-phase recovery that included chemistry parameters as well as physical and hydrodynamic parameters.  The model was validated with flotation experiments conducted on single-size glass beads as well as on mixtures of silica and magnetite particles; the latter experiments allowed further magnetic separation of the flotation products to determine the flotation’s own effectiveness in separating the hydrophilic magnetite from the hydrophobic silica.  A related project involved measuring forces on silica surfaces with an atomic force microscope^[Wikipedia].  The project’s results support the idea that when hydrogen bonds^[Wikipedia] can’t form between water molecules and the hydrophobic materials’ surfaces, the hydrogen bonds among the water molecules rearrange in a way that causes the water’s nonadherence to the hydrophobic materials. 

Coal and coal wastes contain substances that can be harmful to living things if released into their environment.  This has led to much interest in new methods of processing coal before it’s burned and of disposing of coal-processing wastes.  On the preprocessing side, one project tested a modification of a standard flotation process to remove toxic trace elements from coal fines.  Partial leaching of coal pyrite with sodium sulfite was found to lower the coal’s pyritic sulfur content by about 25% compared to flotation without leaching, and increased the rejection of trace selenium as well, but was less effective than the non-leaching process at rejecting arsenic and mercury.  Because of problems on the waste-disposal side, the permitting of new waste slurry storage areas has become, according to the report, “a nearly improbable venture”.  While codisposing of coal fines with coarse reject has become a common alternative to slurry storage, this combined waste may be hard to handle and sometimes doesn’t meet regulatory requirements.  One potential solution, adding Portland cement^[Wikipedia] to the reject to stabilize it, results in a refuse that meets compaction requirements and eliminates mine acid formation and leaching of trace elements.  A lab investigation and a mining operation using the cement technique provide conceptual proof of its validity. 

Leaching toxins out of coal before burning it can be beneficial, but toxins may also get into our environment from coal wastes stored under water.  Experiments with wastes from a coal-preparation plant and a power plant compared leaching from waste that was stored under water and stored with exposure to air and humidity variations.  Keeping the wastes completely under water for 5 months or more was much more effective in minimizing the mobility of trace elements than keeping them under the variable conditions.  The experiments also showed that the neutralization of liquids associated with coal wastes, fly ash, or codisposal of coal waste streams to a pH^[Wikipedia] around 7 (i.e., having little or no acidity or alkalinity) can powerfully minimize trace-element mobility, and that to use such methods most effectively, it’s important to model the neutralization correctly, particularly with regard to exposing mixed wastes to air. 

Methods specifically focused on removing mercury from different waste streams were addressed in two projects.  In one, a metallic nanoparticle filter with a polymer coating was tested for mercury-removal efficiency and regeneration potential and found viable.  In the other, bacteria were studied that carry genes for proteins that allow the bacteria to bind mercury in their environment, transport it into  themselves, and reduce it to a less toxic volatile form that diffuses out.  The project’s main goals were to isolate and identify such bacteria native to coal-impoundment sites in West Virginia, characterize the genes involved, produce partially purified mercury-resistance proteins, understand the proteins’ structure and mercury-bonding action, and devise a process in which the proteins could be used numerous times. 

The other two projects described in the Center for Advanced Separation Technology report involve separating carbon dioxide from other flue gases^[Wikipedia] produced when coal is burned.  One project developed a new solid sorbent made of the nanoclay^[Wikipedia] montmorillonite^[Wikipedia], which is commonly used in producing polymer nanocomposites, grafted with commercially available amines.  The sorbent’s carbon-dioxide capture capacity is comparable to that of other emerging technologies, but the material has low cost and is easily available.  The new sorbent can also be regenerated for reuse over multiple cycles by three different methods:  with pure nitrogen at 100°C, with water-saturated carbon dioxide at 155°C, and in vacuum at 85°C.  The other project produced a new class of organic-inorganic porous hybrid photocatalysts that adsorb carbon dioxide and absorb light; photoelectrochemical cells made of material of this class have been optimized to get the highest carbon-dioxide reduction efficiency. 

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Carbon Sequestration

Several reports describe different projects that dealt with various aspects of carbon-dioxide sequestration^[OSTI]. 

Effects that limit the removal of carbon dioxide from power-plant flue gas are addressed in a report^{[SciTech Connect]} from Alstom Power, Inc.  The report notes that coal burned in air, which is about 78% nitrogen and 21% oxygen near the earth’s surface, produces a flue gas that is mostly nitrogen, about 15% carbon dioxide, and about 3% oxygen.  Removing the carbon dioxide from this gas mixture consumes a lot of energy.  On the other hand, if the coal is burned in nearly pure oxygen, less than a fourth as much flue gas would be produced, and being mostly carbon dioxide and moisture, the gas would be easier to extract carbon dioxide from.  However, extracting pure oxygen from the air requires running an air separator, which itself takes energy.  In practice, burning coal in pure oxygen produces flames with too high a temperature for practical boiler materials and can also results in severe slagging and fouling from coal ash, so most “oxy-combustion” is actually done by mixing oxygen with some recycled flue gas.  This dilutes the oxygen with carbon dioxide to control the furnace temperature. 

Since flue gas goes through different stages of processing that alter its composition after it’s generated, the exact points from which flue gas is recycled to mix with oxygen affect how much the oxygen is diluted, which affects how easy it is to remove the carbon dioxide that ultimately leaves the combustion process.  Alstom Power conducted extensive combustion tests at their Boiler Simulation Facility (Figure 1) with different types of coal, combustion processes, and test conditions, resulting in “a wealth of detailed information” that “has proven extremely useful for the refinement and validation of engineering design tools” and has “also provided the basis for the development of procedures and guidelines for oxy-boiler design” by Alstom and other researchers and organizations.  They found no technical barriers from a boiler standpoint to continued development and commercialization of oxy-combustion obtained from an air separation unit.  In view of the results of this test and other large-scale test programs around the world, they consider the technology viable and ready to proceed to the final development step of commercial-scale demonstration. 

Projects like Alstom Power’s aim to design combustion methods that result in flue gas that’s easier to extract carbon dioxide from, while other investigations focus on the means of extraction.  Ion Engineering, Inc. evaluated a new class of concentrated-organic solvents and compared them to a commercial benchmark using simulations based on theory and empirical data.  The goal was to see if the company’s leading solvent could achieve the Energy Department’s target of 90% carbon-dioxide capture from a pulverized coal plant generating 550 megawatts of electric power without increasing the electricity cost by more than 35%.  A test of the solvent at a 0.2-megawatt pilot plant at the University of North Dakota’s Energy & Environmental Research Center showed that the solvent captured 90% of the carbon dioxide in the plant’s flue gas, as described in their report “Novel Solvent System for Post Combustion CO₂ Capture”^{[SciTech Connect]}.  The solvent, designed to overcome the inherent thermodynamic inefficiencies of processes using aqueous monoethanolamine^[Wikipedia], also took 65% less energy to regenerate. 

There are in fact many possible materials that might absorb CO₂, and testing all of them to see which ones could not only do the job but do it cost-effectively (unlike currently used energy-intensive materials) would require a great deal of effort.  However, much relevant data about many materials is already available from experiments, some of which were conducted for quite different purposes.  “Efficient Theoretical Screening of Solid Sorbents for CO₂ Capture Applications”^{[SciTech Connect]}, a report published in the International Journal of Clean Coal and Energy by researchers with the National Energy Technology Laboratory, describes their procedure to efficiently evaluate different materials’ potential from existing published data.  According to the report’s abstract, the data sought for each material are chemical potentials (i.e., how much the work a thermodynamic system can do changes per unit change in the amount of the material that the system contains) and heats of reaction (how much heat is emitted or absorbed when reactions involving the material occur).  If those data are unavailable, they are calculated from published information about the crystal structure of the material’s atoms.  From the chemical-potential and reaction-heat data, the energy costs of using the material to capture carbon dioxide by reacting with it under desired conditions are calculated; if the figures found are low enough, the material is to be considered further for experimental tests.  Sorbents that contain alkali and alkali-earth metals are widely considered candidates for carbon-dioxide capture, so the researchers’ methods were tested on those materials.  Their preliminary results indicate that increasing the lithium-oxide/silicon-oxide ratio in lithium silicates increases the temperatures at which carbon-dioxide capture reactions and their inverses are at equilibrium. 

The United States Carbon Sequestration Council, in a 2012 report financially supported by the International Energy Agency’s Clean Coal Centre, noted that while current technology for capturing and sequestering carbon was not being deployed, largely because of its high cost, methods to make use of captured carbon for enhanced oil recovery could reduce that cost.  The report describes the current injection of carbon dioxide from natural-gas reservoirs and processing plants into oil wells and discusses the potential expansion of this technique by using carbon dioxide from power plants, which is currently expensive to capture.  The report, “An early deployment strategy for carbon capture, utilisation, and storage”^{[SciTech Connect]}, uses a case study of conditions in the United States to explore subsidizing the technology’s early deployment to provide a range of societal benefits immediately (such as reducing reliance on foreign oil, improving the nation’s international trade balance, increasing domestic economic activity, and of course enhancing domestic oil production and permanently removing carbon dioxide from the atmosphere), and to increase the technology’s chances of becoming widespread and less costly in the long run.  The report concludes that a temporary subsidy program, combined with current research and development of carbon-dioxide capture technologies, could lead to cost reductions that would make the capture and use of unsubsidized power-plant carbon dioxide economically viable for projects begun after 2025. 

Actually demonstrating the technical and economic feasibility of enhancing oil recovery using carbon dioxide from an existing coal-fired boiler is the goal of a project conducted by NRG Energy, Inc. and described in their report “W.A. Parish Post-Combustion CO₂ Capture and Sequestration Project Phase 1 Definition”^{[SciTech Connect]}.  The project’s first phase, project definition and front-end engineering design, resulted in a preliminary design of a system that would capture and compress carbon dioxide from Unit 7 of NRG’s W.A. Parish Generating Station near Thompsons, Texas, and pipe it to an oilfield, with the equipment to do this (not including oilfield preparation) having an estimated total installed cost between $600 million and $900 million.  The considerations involved in arriving at the design and cost estimate are described in the report’s “Interpretation and Conclusions” section: 

The report noted additional work to be finished before proceeding to detailed engineering, procurement, and construction, and then mentioned remaining risks to commercial-scale deployment of carbon-capture technologies: 

The report concludes that NRG is committed to make investment decisions aimed at sharing and minimizing these risks to the furthest extent possible before entering the project’s next phase and incurring significant additional project cost. 

China’s Ordos Basin contains abundant oil, natural gas, and coal resources, and has become a significant site for both energy-based industry and carbon-dioxide emissions.  Capturing carbon dioxide from sources in the Ordos and Qinshui basins, storing it in unmineable coal beds, and using it to enhance oil and gas recovery were explored in the “U.S. China Carbon Capture and Storage Development Project at West Virginia University”^{[SciTech Connect]} by collecting data about the sites’ physical properties and having computers simulate the results of injecting carbon dioxide there.  Figure 3 shows oil and gas fields in the Ordos Basin, as well as the location of a significant source of carbon dioxide from coal processing:  a coal-liquefaction plant in the basin’s northeastern region.  Figure 4 shows one stage of a computer simulated scenario in which carbon dioxide from several plants is injected into different storage sites.  The project was originally to have concluded with the initial design of a demonstration site to store and use carbon dioxide in this way, but interruption and reduction of funding resulted in this last stage being omitted. 

Another way to do useful work with carbon dioxide is based on the fact that when CO₂ reacts with calcium compounds in concrete, it produces solid calcium carbonates in the concrete’s binding matrix.  The feasibility of storing carbon in concrete was investigated by researchers at McGill University and 3H Company of Lexington, Kentucky and reported in “Beneficial Use of Carbon Dioxide in Precast Concrete Production”^{[SciTech Connect]}.  Precast concrete blocks and fiber-cement^[Wikipedia] panels are currently mass-produced and cured by steam.  The investigators found that carbon dioxide can replace steam in the curing process to accelerate early strength, improve long-term durability, and reduce energy use and carbon-dioxide emissions.  The authors suggest that an initial demonstration project be done with concrete-block carbonation because of the size of that market, and that the demonstration be done at a block plant that uses autoclave-based curing, replacing steam with commercially available CO₂, so that no capital investment would be needed. 

Making a superior concrete in this way uses carbon dioxide generated by burning coal.  Coal can also be put through chemical reactions to make other materials, such as synthesis gas (“syngas”)^[Wikipedia], as a first step in making other useful products (Figure 5).  As it happens, though, syngas often contains carbon dioxide.  A project conducted by URS Corporation and the Illinois State Geological Survey of the University of Illinois at Urbana-Champaign, described in a report entitled “Evaluation of Dry Sorbent Injection Technology for Pre-Combustion CO₂ Capture”^{[SciTech Connect]}, involved the development of a new technology to separate carbon dioxide from the other syngas components, doing so under conditions that minimize energy penalties and provide continuous gas flow to advanced syngas combustion and processing systems.  Computational modeling was used to determine optimal thermodynamic properties for sorbents, by which seven candidate materials were identified.  Sorbents’ cycle of absorbing carbon dioxide and being regenerated by condensable vapors were simulated, as were the effects of impurities like hydrogen sulfide^[Wikipedia], which are common in gasified coal^[Wikipedia], on the absorption, as well as the effects of mechanically stabilizing dopants on the sorbents.  Methods for synthesizing sorbents were also developed.  Candidate sorbents were tested under conditions mimicking those of actual use, and the sorbent-enhanced gasification process was assessed for technical and economic feasibility.  The investigators also found that if a way were developed to transport sorbent material from a dedicated absorber to a dedicated regenerator, and if a stream of syngas were burned with pure oxygen in the regenerator to supply regeneration energy directly to the sorbent, energy could be produced by the carbon capture process instead of being lost to it. 

Interest in keeping pre- and post-combustion carbon dioxide from trapping heat in the atmosphere has led to the construction of the National Carbon Capture Center, at which developers can test their carbon-dioxide capture technologies with coal-derived syngas and flue gas under commercially representative conditions.  The Center, housed at the Power Systems Development Facility in Wilsonville, Alabama, was in 2012 the site of tests of a new water-gas shift^[Wikipedia] catalyst that promotes the formation of carbon dioxide and hydrogen from carbon monoxide and water vapor, pre- and post-combustion carbon-dioxide solvents, pre- and post-combustion gas-separation membranes, two enzyme technologies for post-combustion carbon capture, an advanced sensor for coal gasification, and the cofeeding of biomass with coal.  Several gasification support technologies were also refined.  These accomplishments are further described in the Center’s report for 2012.^{[SciTech Connect]} 

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Alternative Fuels and Other Products Made from Coal

One of the useful components of syngas is hydrogen, which can be used in fuel cells and hydrogen-burning engines.  Projects to efficiently extract hydrogen from syngas using separation membranes are described in a National Energy Technology Laboratory - Regional University Alliance slide presentation and a report from the University of North Dakota’s Energy & Environmental Research Center. 

The NETL-RUA’s presentation “Metallic Membrane Materials Development for Hydrogen Production from Coal Derived Syngas”^{[SciTech Connect]}, prepared for the American Ceramic Society’s 2012 conference on Materials Challenges in Alternative & Renewable Energy, gives an overview of their development of metallic membrane materials.  The hydrogen-from-coal program described in the presentation has two specific goals.  One is to prove the feasibility of a 40%-efficient plant with almost zero emissions that produces syngas and removes impurities from it before combustion, using membrane separation and other advanced technologies to reduce electricity costs by at least 35%.  The other goal is to develop technologies to produce and process hydrogen that will contribute about 3% in improved efficiency and 12% reduction in the cost of electricity.  The key problem addressed in the presentation is that membranes used to filter hydrogen out of the syngas can be degraded by absorbing or being corroded by syngas impurities.  To counter this, computer models of different metals and their interactions with common syngas impurity atoms were made to identify those metals that could be made into membranes that would filter hydrogen from high-temperature syngas and be chemically stable against the syngas impurities hydrogen sulfide, arsenic, antimony, and mercury. 

The experiments reported in the University of North Dakota report, “Long-Term Demonstration of Hydrogen Production from Coal at Elevated Temperatures”^{[SciTech Connect]}, showed that a new technology from Western Research Institute for upgrading and gasifying subbituminous and lignite coals produced a syngas with significantly lower carbon dioxide and significantly higher carbon monoxide contents than syngas made from the raw fuels themselves.  Warm-gas cleanup and hydrogen separation were tested with two different membranes; sulfur in the syngas was reduced to one part per million, and each membrane was able to produce at least two pounds of hydrogen from the syngas per day.  This report not only provides details about the test results, but also considerable background detail, explaining different coal gasification reactions, gasifier types, impurities and purification technologies, what happens in gas cleanup, and how hydrogen separation membranes work. 

Interest in using torrefaction^[Wikipedia], a process to remove moisture and volatile substances from biomass by decomposing it at high temperatures, to produce a fuel that could be combined with coal led to a Small Business Technology Transfer project reported in “STTR Phase 1 Final Technical Report for Project Entitled ‘Developing a Mobile Torrefaction Machine’”^{[SciTech Connect]}.  The project, a joint effort by North Carolina State University and Agri-Tech Producers, LLC,  investigated whether a torrefaction technology developed by NCSU could be deployed in a mobile unit that could be taken directly to forests and used there.  While miniature torrefaction units with acceptable mobility could be manufactured at a reasonable price, and their operation could be linked to a mobile briquetting or pelletizing function, the mobile units’ output would be very small (about 200 pounds/hour), the costs per ton of fuel produced would make their use economically infeasible, and fire hazards in a forest setting would be very high, with lots of support being required to prevent or extinguish any fires started.  Also, the torrefied fuel would have to be cooled before densifying it into pellets or briquettes, which would require bulky cooling equipment that used very expensive mobile power.  While these findings meant that the small mobile torrefaction units would not be practical for making fuels that could be used alone or in combination with coal, the company’s design/manufacturing partner (Kusters Zima Corporation) was able to design mobility enhancements into their more practical larger units.  These would allow a pilot torrefaction plant to be moved around to provide test-burn fuels to different region’s utilities—a capability of interest to the Electric Power Research Institute.  Such mobile units might also profitably convert large numbers of trees damaged or downed by disease, hurricanes, or other disasters into fuel. 

Coal can also be turned into a liquid fuel.  Different aspects of coal liquefaction were investigated in two different recent projects, conducted by Western Research Institute and West Virginia University. 

Western Research Institute’s report, “Conversion of Low-Rank Wyoming Coals into Gasoline by Direct Liquefaction”^{[SciTech Connect]}, notes that liquefying coal directly instead of liquefying gasified coal is considered among the most environmentally friendly, resource-conserving, and technically efficient ways to make liquid fuel from coal.  Direct liquefaction breaks the large coal molecules into small hydrocarbons that preserve the coal’s carbon ring structures, which are valuable components of oils and fuels.  Direct liquefaction also retains more of the coal’s heating value than processes that liquefy gasified coal typically do.  Western Research systematically studied the effects of various additives, solvents, and catalysts on direct liquefaction, and found that while most additives have little effect, or adverse ones, some additives have important positive effects, pointing to specific features of the liquefaction mechanism that “are currently underutilized yet could be exploited to intensify the process or to simplify it.”  One interesting effect is that, while hexane^[Wikipedia] and ethyl phenyl ether^[Wikipedia] both diminish product yield fractions when added separately, they noticeably increase the oil yield when added in the same amounts together.  Also, in certain conditions the regenerable catalyst Raney nickel^[Wikipedia] increased the conversion of directly liquefied coal by as much as 20%, and increased the oil yield fraction by as much as 35%.  The investigators conclude that “[o]verall, a judicious choice of catalysts, solvents, and additives might enable practical and economically efficient direct conversion of Wyoming coals into liquid fuels.” 

The second project, described in “Long Term Environment and Economic Impacts of Coal Liquefaction in China”^{[SciTech Connect]}, relates to West Virginia University’s previously mentioned cooperative project, in which one of the activities producing carbon dioxide was coal liquefaction.  Air and water weren’t monitored as completely as planned, so the data at the time of the report weren’t sufficient to assess the liquefaction’s environmental effects.  The report also noted similar difficulty in obtaining enough economic data for detailed, comprehensive analysis: 

With those caveats, though, the report’s authors conclude that the 10 billion yuan^[Wikipedia] (about 1.6 billion 2012 dollars) invested in the direct coal liquefaction project in Ordos, Inner Mongolia increased Inner Mongolia’s total income by 10.7 billion yuan and total regional output by 23.6 billion yuan.  The authors also point out that policy makers in China are more interested in mastering the technology of direct coal liquefaction than in stimulating the local economy, stating further that “such a mega-development of a new technology, naturally will bring forth various other technologies and inventions, which then benefit the coal industry and other sectors in Inner Mongolia and the national economy.” 

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Other Improvements

Additional improvements in technology related to making coal use cleaner are described in four more reports. 

To understand water-rock interaction, carbon cycling, and carbonate equilibrium in our environment, it’s important to determine how much inorganic carbon in the environment is dissolved in water.  A poster^{[SciTech Connect]} by researchers with West Virginia University and the National Energy Technology Laboratory describes their adaptation of a carbonation meter used in the beverage industry to accurately determine this data rapidly in the field instead of by later laboratory analysis of environmental samples.  The poster provides details of how amounts of dissolved inorganic carbon are calculated from carbon-dioxide measurements, how the method was tested, and the method’s known advantages and disadvantages. 

A way to measure smokestack emissions of trace metals and acid gases by trapping them with a sorbent material is described in another report from the University of North Dakota’s Energy & Environmental Research Center (“Subtask 4.27 - Evaluation of the Multielement Sorbent Trap (MEST) Method at an Illinois Coal-Fired Plant”^{[SciTech Connect]}).  The report notes that sorbent traps are simpler to use than existing sampling methods and don’t require expensive, fragile glassware or the handling and shipping of hazardous reagents.  Sorbent trap methods were tested at two power plants fueled by Illinois Basin bituminous coal.  The sorbent trap method for measuring hydrochloric-acid emissions appeared to be a good candidate alternative to the Environmental Protection Agency’s standard test method^[Wikipedia] 26A since it could register small amounts of hydrogen chloride that the EPA method couldn’t.  The metal sorbent trap tested could also detect smaller emission amounts for several metals than EPA Method 29 could, but didn’t do as well for measuring cadmium, nickel, lead, and chromium near the hazardous-emission limits for existing coal-fired power plants, so further improvement of the sorbent-trap technique for metals would be needed before it could serve as an alternative to EPA Method 29 for all trace metals. 

The same research center reported, in “Subtask 5.10 - Testing of an Advanced Dry Cooling Technology for Power Plants”^{[SciTech Connect]}, on a new dry cooling technology for power plants in arid environments that is intended to address current methods’ high capital costs and degraded cooling performance during daytime temperature peaks.  The new technology’s key feature is the use of a liquid desiccant to transfer heat between a power plant’s steam condenser and the atmosphere, which avoids the consumptive use of cooling water.  The project’s overall goal was to accurately define the new method’s performance and cost characteristics to see whether further development was warranted; analysis found that it could cost less than the use of air-cooled condensers and could even compete with conventional wet recirculating cooling under some circumstances.  Among the technical problems that remained to be addressed were the following: 

Finally, the report of Excelsior Energy Inc. entitled “The Mesaba Energy Project - Clean Coal Power Initiative, Round 2”^{[SciTech Connect]} describes the first budget period of a project to demonstrate, at utility scale (600 megawatts’ capacity) with high reliability (90% availability), a project to demonstrate a technology that produces syngas from coal, removes impurities from the syngas, and burns the remainder to produce power.  The integrated gasification combined-cycle^[Wikipedia] demonstration plant is designed to emit mercury and other pollutants at rates far below the lowest ones found in current utility-scale coal-based power generation, and according to preliminary engineering and cost studies should, with Federal assistance under the Energy Policy Act of 2005^[Wikipedia], have costs similar to those of a new greenfield coal plant using conventional supercritical pulverized coal boiler technology.  The report also discusses a carbon capture and sequestration plan with the preferred approach being enhanced oil recovery, which, though not required of the project for Energy Department cost sharing, was confirmed to be prudent by later studies and developments.  A project site was chosen that has access to competitive rail providers, is near abundant water resources, minimal reinforcement costs for transmission interconnection, and strong local community backing.  The report points out, however, that in the five years required to develop the project’s final environmental impact statement, “sweeping and unforeseeable changes in the macroeconomy, law and regulation have created significant barriers for a coal-based project to succeed”, though the critical macroeconomic trends “are historically cyclical” some cycles “already returning to more favorable conditions” at the time of the report.  The report’s Conclusion section ends by noting: 

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References

Wikipedia

• Filtration
• Contact angle
• Froth flotation
• Hydrophile
• Hydrophobe
• Cavitation
• Atomic force microscopy
• Hydrogen bond
• Portland cement
• pH
• Flue gas
• Nanomaterials
• Montmorillonite
• Ethanolamine: Applications
• Quantitative structure-activity relationship
• Computational fluid dynamics
• Fiber cement siding
• Syngas
• Hydrogen sulfide
• Gasification
• Water-gas shift reaction
• Torrefaction
• Hexane
• Ethyl phenyl ether
• Raney nickel
• Chinese yuan
• EPA Methods
• Integrated gasification combined cycle
• Energy Policy Act of 2005

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Research Organizations

• Center for Advanced Separation Technology
• University of Kentucky
• West Virginia University
• University of Utah
• Virginia Polytechnic Institute and State University
• Montana Tech of the University of Montana
• Alstom Power, Inc.
• Ion Engineering, Inc.
• University of North Dakota: Energy & Environmental Research Center
• United States Carbon Sequestration Council
• International Energy Agency: Clean Coal Centre
• NRG Energy, Inc.
• McGill University
• 3H Company
• URS Corporation
• University of Illinois at Urbana-Champaign: Illinois State Geological Survey
• Power Systems Development Facility: National Carbon Capture Center
• National Energy Technology Laboratory - Regional University Alliance
• Western Research Institute
• North Carolina State University
• Agri-Tech Producers, LLC
• Kusters Zima Corporation
• Electric Power Research Institute
• National Energy Technology Laboratory
• Excelsior Energy Inc.

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Reports available from OSTI’s SciTech Connect

• “Center for Advanced Separation Technology” [Metadata and full text available from OSTI’s SciTech Connect]
• “Recovery Act: Oxy-Combustion Technology Development for Industrial-Scale Boiler Applications – Task 4: Testing in Alstom’s 15 MW_th Boiler Simulation Facility” [Metadata and full text available from OSTI’s SciTech Connect]
• “Novel Solvent System for Post Combustion CO₂ Capture” [Metadata and full text available from OSTI’s SciTech Connect]
• “Efficient Theoretical Screening of Solid Sorbents for CO₂ Capture Applications” [Metadata and full text available from OSTI’s SciTech Connect]
• “An early deployment strategy for carbon capture, utilisation, and storage” [Metadata and full text available from OSTI’s SciTech Connect]
• “W.A. Parish Post-Combustion CO₂ Capture and Sequestration Project Phase 1 Definition”  [Metadata and full text available from OSTI’s SciTech Connect]
• “U.S. China Carbon Capture and Storage Development Project at West Virginia University” [Metadata and full text available from OSTI’s SciTech Connect]
• “Beneficial Use of Carbon Dioxide in Precast Concrete Production” [Metadata and full text available from OSTI’s SciTech Connect]
• “Evaluation of Dry Sorbent Injection Technology for Pre-Combustion CO₂ Capture” [Metadata and full text available from OSTI’s SciTech Connect]
• “The National Carbon Capture Center at the Power Systems Development Facility: Topical Report, Budget Period Four, January 1, 2012 – December 31, 2012” [Metadata and full text of this report, and of a shorter version, available from OSTI’s SciTech Connect]
• “Metallic Membrane Materials Development for Hydrogen Production from Coal Derived Syngas” [Metadata and full text available from OSTI’s SciTech Connect]
• “Long-Term Demonstration of Hydrogen Production from Coal at Elevated Temperatures: Year 6 - Activity 1.12 - Development of a National Center for Hydrogen Technology” [Metadata and full text available from OSTI’s SciTech Connect]
• “STTR Phase 1 Final Technical Report for Project Entitled ‘Developing a Mobile Torrefaction Machine’” [Metadata and full text available from OSTI’s SciTech Connect]
• “Conversion of Low-Rank Wyoming Coals into Gasoline by Direct Liquefaction” [Metadata and full text available from OSTI’s SciTech Connect]
• “Long Term Environment and Economic Impacts of Coal Liquefaction in China” [Metadata and full text available from OSTI’s SciTech Connect]
• “Rapid Field Measurement of Dissolved Inorganic Carbon Based on CO₂ Analysis” [Metadata and full text available from OSTI’s SciTech Connect]
• “Subtask 4.27 - Evaluation of the Multielement Sorbent Trap (MEST) Method at an Illinois Coal-Fired Plant” [Metadata and full text available from OSTI’s SciTech Connect]
• “Subtask 5.10 - Testing of an Advanced Dry Cooling Technology for Power Plants” [Metadata and full text available from OSTI’s SciTech Connect]
• “The Mesaba Energy Project - Clean Coal Power Initiative, Round 2” [Metadata and full text available from OSTI’s SciTech Connect] [June 1, 2006-August 31, 2012]  Excelsior Energy Inc. on behalf of MEP-I LLC (Fluor, ConocoPhillips)  August 31, 2012 http://www.osti.gov/scitech/biblio/1093542

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Additional References

• "DoE Science Showcase - Carbon Sequestration"
• International Journal of Clean Coal and Energy
• American Ceramic Society: 2012 conference on Materials Challenges in Alternative & Renewable Energy
• Small Business Technology Transfer (DoE Office of Science)
• Clean Coal Power Initiative

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