Clean coal

US. Department of Uner Clean Coal Technology Program Update 1991, publication DOE/FE-0247P, U.S. Dept, of Energy, Washington, D.C. 

In the United States the Clean Coal Technology program was created to develop and demonstrate the technology needed to use coal in a more environmentally acceptable manner. Activities range from basic research and estabUshing integrated operation of new processes in pilot plants through demonstration with commercial-scale equipment. 

Flotation. The appfication of flotation (qv) to coal cleaning is a relatively new development iu the United States. In 1960, only 0.6% of the clean coal produced came from flotation. However, by 1983 flotation accounted for about 5% of the clean coal production (Table 2). Utilization of the flotation process is expected to grow rapidly because more fine size coal is produced as a result of beneficiation schemes that require significant size reduction of the taw coal prior to cleaning to enhance the fiberation of pyrite and ash minerals. 

The flotation process usually iuvolves three steps (/) the conditioning of the coal surface iu a slurry with reagents, (2) adhesion of hydrophobic coal particles to gas bubbles, and (J) the separation of the coal-laden bubbles from the slurry. In the conventional flotation process, when the coal particles become attached to air bubbles, the particles ate allowed to rise to the top of the flotation cell and form a stable froth layer (9). A mechanical scraper is used to remove the froth layer and separate the clean coal product from the refuse-laden slurry. 

The use of a water-immiscible Hquid to separate coal from impurities is based on the principle that the coal surface is hydrophobic and preferentially wetted by the nonaqueous medium whereas the minerals, being hydrophilic, remain suspended in water. Hence, separation of two phases produces a clean coal containing a small amount of a nonaqueous Hquid, eg, oil, and an aqueous suspension of the refuse. This process is generally referred to as selective agglomeration. 

Dry Coal Cleaning. Developments in the areas of magnetic and electrostatic separation as a means of cleaning coals in the dry state include high gradient magnetic separation (HGMS), triboelectrostatic separation (TESS), and dry coal purifier (D-CoP). 

When the Clean Air Act of 1990 was signed into law, electric utiUties were requited to estabUsh plans and initiate projects to comply with that Act s Tide IV. Each utihty had to evaluate how the various commercial and emerging clean coal systems fit into the utiUty s technical and business environment resulting in strategies to utilize fuel switching and wet throwaway FGD processes almost exclusively (38,85,86). 

R. N. Franklin, R. P. Jensen, and R. T. Perry, "SCGP— Efficient Clean Coal Power for Today and Tomorrow," EPRJ Conference on Technologiesfor ProducingElectricity in the Twenty-Eirst Century, San Francisco, Calif., Oct. 30—Nov. 2,1989. 

A successful variation of oil agglomeration was used for removal and dewatering of soot from a 1—3% soflds suspension consisting of <5 — fim particles in refinery process waters (Fig. 8). Heavy oil was added to the dilute slurry and intensely agitated in a multistage mixer. The soot agglomerated with the oil to form 3—5 mm pellets that were easily screened from the water (95). The pellets contained only 5—10% water. The process was modified to recover very fine clean coal, and it produced highly uniform, hard, spherical pellets 1—2 mm in diameter. 

Eastman Chemical Company has operated a coal-to-methanol plant in Kingsport, Tennessee, since 1983. Two Texaco gasifiers (one is a backup) process 34 Mg/h (37 US ton/h) of coal to synthesis gas. The synthesis gas is converted to methanol by use of ICl methanol technology. Methanol is an intermediate for producing methyl acetate and acetic acid. The plant produces about 225 Gg/a (250,000 US ton/a) of acetic anhydride. As part of the DOE Clean Coal Technology Program, Air Products and Cnemicals, Inc., and Eastman Chemic Company are constructing a 9.8-Mg/h (260-US ton/d) slurry-phase reactor for the conversion of synthesis gas to methanol and dimethyl... 

Nationwide, plants that emit SO2 at a rate below 1.2 Ibs/mm Btu will be able to increase emissions by 20% between a baseline year and 2000. Bonus allowances will be distributed to accommodate growth by units in states with a statewide average below 0.8 Ibs/mm Btu. Plants experiencing increases in their utilization in the last five years also receive bonus allowances, 50,000 bonus allowances per year are allocated to plants in 10 mid western states that make reductions in Phase I. Plants that repower with a qualifying clean coal technology may receive a 4 year extension of the compliance date for Phase II emission limitations. 

A Planner s Guide for Selecting Clean Coal Technologies for Power Plants, Technical Paper No. 387. Washington The World Bank, 1997. 

Clean Coal Technology Conipendiuin. (1999). Los Alamos, NM Los Alamos National Laboratoiy. . 

Clean Coal Technology Program. (2000). Washington, DC U.S. Department of Energy, Office of Fossil Energy. . 

Monitoring Effort Initiated Under PM,5 Program. (1998). Clean Coal Today (30) 8-10. 

Should clean coal plants meeting more stringent new source review standards be differentiated from older plants grandfathered to lesser requirements in an energy-environmental matrix Restated, should operational distinctions used for other renewable sources and natural gas also be made for coal plants for the purpose of environmentally based price differentiation ... 

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