Existing PCC power plant ash ponds are a resource of recoverable carbon that potentially can be marketed as valuable carbon products. Reclamation of ash ponds is becoming an increasingly critical issue as sites suitable for landfill continue to diminish, existing ponds generate environmental concern and energy demand continues to rise. The introduction of next generation coal fired power plants and IGCC gasifiers, necessitates the assessment of their waste streams as potential value-added carbon products. These materials represent a new class of resource from coal.
A program of work has been initiated to explore applications for recovered carbon from IGCC and PCC power generation plants. A carbon rich IGCC gasifier char and high carbon spiral product (SP) (recovered from a PCC ash pond) will be upgraded and processed to fabricate activated carbons as possible sorbents for NOx and Hg removal from effluent process streams. The upgraded char and SP carbon materials will also be assessed as fillers in conductive plastics.
A technology has been developed at CAER to recover SP carbon from utility ash ponds and landfills. The process consists of initially classifying a slurry of ash into appropriate size fractions. Coarse carbon particles (> 150 µm) are then concentrated by gravity separation and then dewatered while fine carbon particles (> 150 µm) are concentrated by froth flotation and then dewatered. Pilot-scale testing of the process has recovered a coarse fraction with a carbon content as high as 70%, while the fine fraction recovered by froth flotation had a carbon content as high as 60%. A 50ton per hour demonstration facility funded by U.S. DoE, Western Kentucky Energy Corp (WKE) and CAER is in the design phase and will be installed at Coleman Station, Hawesville, KY.
Similar technology used to recover SP carbon has also been implemented at an operating IGCC plant. This power plant produces a high carbon content slag/char mixture by-product that is stored on site. A by-product processing facility designed by CAER has been constructed and is operated by Charah Environmental Inc. The plant produces three distinct products; a coarse slag (> 850 µm), a carbon rich char (< 850 µm > 75 µm) and fines (< 75 µm) at a total design throughput of 100tons per day. At present, the slag and char products are marketed while the fines are rejected as a waste fraction. The slag and char are recovered by classification and then dewatered, the slag containing typically < 1%C while the carbon content of the char is typically 60 to 70%. At present, char production is in the range 400 to 600tons/day.
One of the fastest growing markets for carbon products is in environmental applications, where enormous interest has been generated by ecological awareness and regulation, and the need to find relatively low cost solutions for environmental protection and remediation. Activated carbons can be produced with a wide range of properties and physical forms to meet these needs. Preliminary investigations have shown that both materials produced in these studies maybe suitable for generating activated carbons for many industrial and remediation needs, and with fine tuning of the plant cut, maybe useable for some applications without the need for further activation.
Contact: Rodney Andrews
The program is directed toward the development of technologies for producing coal-derived feedstocks for the production of a range of high value carbon materials and specialty chemicals. The program has successfully demonstrated that a broad range of value-added carbon materials such as carbon fibers, activated carbon fibers, binder pitches, and carbon/carbon composites can be produced from coal utilizing mild, non-hydrogenative solvent extraction.
Coal tar pitch, a liquid by-product from coke oven operations, is a feedstock for manufacturing a wide range of carbon materials such as anode binders, coke, graphite and different types of carbon fiber. However, the amount of pitch and other coal liquids available from this source is essentially determined by the demand for metallurgical coke, which has decreased due to a decline in the demand for steel and technological improvements in steel making. Furthermore, coke oven operations continue to close due to their failure to meet increasingly stringent environmental regulations and the need for capital investment to rebuild and maintain existing coke ovens. CAER seeks to address these issues by altering the "Liquefaction Concepts" developed in an earlier program, towards economically attractive processes for producing high value chemicals and carbon materials from coal. These processes include low-severity, non-hydrogenative solvent extraction of coal and mild thermal co-processing of coal and solid municipal waste.
The low severity non-hydrogenative solvent extraction process produces a coal-derived pitch. This pitch has been successfully used to produce general-purpose carbon fibers, activated carbon fibers and binders. In all cases, the materials produced were comparable in performance with those commercially available. Mild thermal co-processing of coal with solid municipal waste produces high value oxygenates which can be used as feedstocks for specialty chemical applications. In conjunction with other projects in the Carbon Materials Group, the Coal-Derived Pitch project provides feedstocks to be assessed for use in producing other carbon materials and composites. Recently, coal derived pitch has been used to produce pitch / multiwall carbon nanotube (MWNT) fiber composites. The addition of low concentrations of MWNTs (1-4%) to coal derived pitch fibers dramatically increased the tensile strength and elastic modulus of the pitch based carbon fibers. The production pitch/MWNT composites, continues to be developed by the group.
In continuing the development of the low severity, non-hydrogenative extraction process, a new process concept has been developed: an integrated extraction process. This integrated process, designed to minimize processing and solvent costs will produce high value chemicals, carbon products and fuel. Extraction processes currently under development suffer from solvent depletion due to adduction, thermal cracking or chemical reaction with the feed coal. As a result, these processes require a significant amount of expensive solvent makeup and/or solvent treatment. The integrated extraction process solves this problem by generating its own indigenous, coal-derived solvent while simultaneously producing high value chemicals, such as phenols and cresols.
Conceptually, the integrated extraction process could be part of a larger co-production power plant where the solid and gas by-products of the process would be utilized as fuel for the power generation plant.
The growth in high-tech applications of fiber-reinforced composite materials has fueled the demand for engineering fibers of continuingly improved mechanical properties. The aerospace industry and others continue to push the limits of available engineering materials while simultaneously balancing the need for high strength and stiffness with minimum weight penalty. Traditional carbon fibers, either pitch or polymer based, have become commonplace in fiber reinforced composites. Yet the very best carbon fibers have strengths only approximately 60% greater than steel wire. Super high modulus fibers, those that deform very little under an applied load, have been produced that deform by a fraction of that shown by steel wire under the same load. However, they suffer a consequential reduction in strength.
Multiwall carbon nanotubes (MWNTs) correspond to the ultimate carbon fiber. These tiny tubes, composed of concentric shells of carbon atoms, offer unique mechanical properties unattainable with existing materials: tensile strength ˜2340% greater than steel wire, Young's modulus ˜380% greater than steel wire, and strains to failure of approximately 20 times greater than typical carbon fiber. The objective of this project is to develop a process to harness these remarkable mechanical properties, yielding a new engineering material capitalizing on the high strength and modulus of the MWNT.
It is proposed to create an engineering fiber consisting primarily of interlocked MWNTs (> 50%) bonded together with polymer-derived carbon welds. To ensure these welds are strong, modification of the surfaces of the MWNTs will be used to produce chemical bonding with the polymer binder. Furthermore, avoidance, or removal, of surface defects of these fibers including the occurrence of small cracks, will maximize the structural integrity of the fiber. In a method similar to wet spinning as used in the manufacture of acrylic fiber, MWNTs dispersed in a polyacrylonitrile (PAN) or epoxy binder solution will be extruded and drawn into a fiber and collected. The shear stresses generated in the die and the stretching process cause the MWNTs to align with the axis of the fiber maximizing tensile reinforcement. Heating these fibers to temperatures greater than 1400°C converts the polymer binder into carbon welds. The resulting composite fiber, of very high strength and modulus, will effectively exploit the unique mechanical properties of the MWNTs in a usable engineering material.
Contact: Matt Weisenberger
Existing PCC power plant ash ponds are a resource of recoverable carbon that potentially can be marketed as valuable carbon products. Reclamation of ash ponds is becoming an increasingly critical issue as sites suitable for landfill continue to diminish and energy demand continues to rise. The introduction of next-generation coal fired power plants and IGCC gasifiers necessitates the assessment of their waste streams as potential value-added carbon products. These materials represent a new class of resource from coal.
A technology has been developed at CAER to recover carbon from utility ash ponds and landfills. Pilot-scale testing of the process has recovered a coarse fraction with carbon content as high as 70%, while the fine fraction recovered by flotation had a carbon content as high as 60%. Similar technology implemented at the Polk Station IGCC power plant located in Mulberry, FL produces a high carbon slag/char mixture. Charah Environmental Inc. operates a by-product processing facility designed by CAER at Polk Station with a gasification char product production of 400 to 600 tons per day.
The suitability of recovered carbon from PCC and IGCC power plants will be assessed as potential marketable value-added carbon materials. Utilizing technologies developed by CAER and collaborators, carbon fractions from operating PCC and IGCC power plants will be produced for the study. An assessment of the steam and chemical activation of recovered carbons will be performed. A range of activation methods will be pursued to develop activated carbons with sufficient porosity for environmental and industrial separations. Activation methods will be tailored to produce an activated carbon suitable for Hg and NOx adsorption. Hg and NOx adsorption isotherms will be measured and adsorption capacities determined. Simultaneous Hg and NOx adsorption will also be investigated.
Recovered PCC and IGCC carbons will also be assessed as potential fillers in plastics for electrostatic discharge control applications.
Contact: Rodney Andrews