This Small Business Innovation Research Phase I project addresses the question of mitigating the undesirable side-effects associated with ammonia, urea, or cyanuric acid injection for NOx control in coal combustion. (Urea and cyanuric acid act as convenient ammonia precursors.) The above method is known as selective noncatalytic reduction (SNCR) or selective catalytic reduction (SCR), depending on whether or not a solid catalyst is used. Both techniques have a common shortcoming known as ammonia slip, which is simply the release of unreacted ammonia into the stack. The effectiveness of ammonia/urea injection depends on current process conditions, especially the temperature and NOx levels, and thus sophisticated process control is required, but not always provided. As a consequence, combustors often operate under high-NOx or high-ammonia conditions. SNCR has also been reported to give rise to incomplete NOx reduction and the formation of appreciable amounts of nitrous oxide (N2O). A strong need thus exists for a simple and cost-effective method for the removal of residual NOx, excess ammonia and N2O from the combustion flue gas. As the main innovation of this program, Advanced Fuel Research proposes the use of microwave discharge in the stream of flue gas in order to generate free radicals (microwave plasma) instrumental in the destruction of NOx, NH3 and N2O. The objective of the Phase I program is to demonstrate the technical and economic feasibility of a novel gas-cleanup method based on microwave-induced radical generation. If proved successful, the proposed approach may result in a powerful method of mitigating undesirable side-effects of ammonia/urea injection, and in significantly reducing N2O emissions which plague fluidized-bed systems. The proposed method can be conveniently combined with virtually any other pollution-control measure. Due to the `end-of-pipe` approach, only minor, if any, modifications in combustor design and operation will be required to accommodate the new technique. These advantages will be partly offset by the cost of microwave-power generation but the overall economics are expected to be favorable.
