The U.S. EPA recently determined that mercury (Hg) emissions from coal-fired power plants pose significant hazards to public health and must be reduced. Oxides of nitrogen (NO_x) are other harmful pollutants emitted from coal-fired boilers. GE EER is addressing the problems of multiple pollutant control from coal-fired plants and utilization of high-carbon ash by developing a new Hg/NO_x/LOI technology that reduces the cost of Hg removal by combining it with control of NO_x emissions and simultaneous reduction of carbon in fly ash. The Hg/NO_x/LOI approach is based on commercial combustion modification technologies for NO_x control, such as low-NO_x burners, staged combustion, and coal reburning. These technologies control NO_x, but generate fly ash with relatively high carbon content. It has been demonstrated that under certain conditions the carbon in fly ash can efficiently absorb Hg from flue gas at temperatures below 400 deg F. Pilot-scale experiments in a 1x10~6 Btu/hr combustion facility have been conducted to optimize the technology with respect to process conditions and obtain the experimental data required for a full-scale demonstration. Two approaches to increase carbon-in-ash were used: coal reburning and limiting air in the combustion zone. Measurements of elemental and oxidized Hg were conducted using CEM mercury analyzer in a slip stream after flue gas passed through a fabric filter. Tests demonstrated that an increase in carbon-in-ash resulted in Hg removal up to 90%. Parameters that affect efficiency of Hg removal by fly ash include carbon-in-ash content and temperature of the fabric filter.
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