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Show tern incorporating a fabric filter is expected to minimize the emissions of m a n y air toxic species, especially the trace elements (metals) and condensible (semi-volatile) organics. Containing the condensibles within the power plant system first depends on condensing the species - many of which are volatilized in the furnace - onto the particulate matter, thereby removing them from the gas phase. Condensation is enhanced by low-temperature operation in the back-end equipment (air heater, scrubber, baghouse. etc.). Since it also appears that these substances are concentrated on particles at the fine end of the particle size distribution, their ultimate containment within the boiler system depends on the small particle capture efficiency of the particulate collector. Many believe that a fabric filter represents the best available technology for control of fine particulate. Overall. then, the LIDS approach, consisUng of a fabric filter operating at low temperature (<150'F). is entirely consistent with the desire to minimize the emissions of trace metals. Sorbent Injection. The limestone injection process. an integral part of the LIDS concept, m a y enhance the capture of trace elements and condensible organic species by providing additional particulate matter surface upon which condensation may take place. Alternatively, the form of the sorbent. or its composition m a y be altered to maximize capture of particular u;>'Jcs species such as mercury. *•/€• FGD and Air Toxics Enhanced Capture of Volatile Species. Wet scrubbers have been shown to effectively capture mercury and other volatile air toxic species. While the details of the capture mechanism are not well understood, it seems likely that wet scrubbing provides good potential for the capture of these species. Condensing Heat Exchanger. Wet scrubbers in combination with upstream particulate removal facilitate the use of a condensing heat exchanger Just ahead of the scrubber. While the primary driving force for the use of such a device is heat recovery, it may also have benefits for the removal of air toxics species. Advanced Staged Combustion and Air Toxics Organics Formation. There is the remote possibility that the combustion of coal under advanced staged combustion conditions may favor the formation of certain organic compounds. Work during the LEBS project will focus on design and operation of the power plant subsystems to preclude the emission of organic toxics. Unburned Carbon. The unburned carbon particulate matter created in the combustion process may act as a good adsorbent for certain toxic species such as mercury and organics in downstream, low-temperature portion of the power plant system. SOLID BY-PRODUCT IMPACTS Babcock & Wilcox is also aggressively pursuing ways to reduce or utilize the solid by-product produced by its L E B S plant through a variety of in-house and externally-funded development programs. Work is being done in the areas of sorbent regeneration, by-product utilization, and improved disposal techniques. Similar work is currently being conducted by several other organizations. B & W intends its LEBS development work to result in an environmentally sound solid by-product disposal approach. Work throughout the program will address ways in which the amount of by-product can be reduced through its subsequent utilization. LIDS Solid By-product Dry By-product Handling. B & W is confident that an environmentally sound LIDS waste disposal technique can be demonstrated, and continues to work to identify ways in which waste can be utilized. Overall. the chemical composition of LIDS by-product is similar to that of fly ash/lime and lime/Portland cement mixtures. As such, pozzuolanic reactions have been postulated for the expected LIDS solid waste product. Preliminary laboratory studies have verified this hypothesis. This self-binding reaction, coupled with the inherent alkalinity of the residue, is expected to result (with proper conditioning) in the formation of a solidified mass suitable for landfilling which will yield low landfill permeability and thus lower teachability of soluble species. The same properties which are expected to make the residue acceptable for landfilling m a y also make the material suitable for mine backfilling or road base construction. These options will be specifically evaluated. Other ways to uUlize the waste, such as for the treatment of sewage sludge, will also be evaluated during the LEBS project. Wet FGD Solid By-product Impacts Gypsum By-product. Limestone forced-oxidation wet scrubber systems yield a gypsum product that is environmentally benign for disposal purposes, and. where a local market exists, can be utilized for the production of gypsum wallboard. Advanced Staged Combustion Air Solid By-product Unburned Carbon. The unburned carbon particulate matter created in the combustion process may have deleterious effects on the disposal and/or utili-zaUon characteristics of the LEBS plant solid byproducts). CONCLUSION For the B & W LEBS project to be successful, all 8 Paper No. 11-13 |