Boiler Modifications Cut Emissions 70 Percent

Mercury enters the atmosphere as a gas and can remain airborne several years before it precipitates with rain and falls into bodies of water, where it is ingested by fish. Because mercury is a neurotoxin, people who consume large quantities of fish can develop brain and nervous ailments. Forty-four states have mercury advisories.

Coal-fired power plants are the largest single-known source of mercury emissions in the U.S. Estimates of total mercury emissions from coal-fired plants range from 40 to 52 tons. The U.S. Environmental Protection Agency last March issued its first-ever regulations restricting the emission of mercury from coal-fired power plants. The order mandates reductions of 23 percent by 2010 and 69 percent by 2018.

In response to that, in full-scale tests at three power plants, says Carlos E. Romero from the Energy Research Center, the Lehigh system reduced flue-gas emissions of mercury by as much as 70 percent or more with modest impact on plant performance and fuel cost.

The reductions were achieved by modifying the physical conditions of power-plant boilers, including flue gas temperature, the size of the coal particles that are burned, the size and unburned carbon level of the fly ash, and the fly ash residence time. These modifications promote the in-flight capture of mercury, Romero said.

The changes in boiler operating conditions prevent mercury from being emitted at the stack and promote its oxidation in the flue gas and adsorption into the fly ash instead. Oxidized mercury is easily captured by scrubbers, filters and other boiler pollution-control equipment.; Source: Lehigh University