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- Page 3 Environmental Tidbits
- Page 4 Announcements
Air Quality Update: Mercury Emissions
The U.S. Environmental Protection Agency (EPA) is in the process of regulating mercury emissions from power plants. EPA is scheduled to propose regulations on December 15, 2003 and to issue final regulations by December 15, 2004. Coal-fired electric utilities are listed as the largest source of mercury air emissions in the EPA's Mercury Study Report to Congress. Utilities are followed by municipal waste combustors, medical waste incinerators, and hazardous waste combustors (see chart).
The EPA has already taken steps to regulate mercury emissions from the following sources:
- Municipal waste combustors (MWCs) – final regulations issued on October 31, 1995. Target: mercury emissions reduced by 90%.
- Medical waste incinerators (MWIs) – emission standards issued on August 15, 1997. Target: mercury emissions reduced by 94%.
- Hazardous waste combustors (HWCs) – emission standards issued in February 1999. Target: mercury emissions reduced by 50%.
According, to the EPA, power plants can reduce mercury emissions by switching to cleaner fuels and by using fuels more efficiently. EPA is issuing regulations to control SO2 and NOx and these are also expected to result in modest reductions in mercury emissions. Measures designed to reduce emissions of greenhouse gases could also substantially reduce mercury emissions from utilities and from other industrial boilers.
Research is proceeding on several approaches to reduce the mercury emissions from coal-fired power plants. Activated carbon injection (ACI), TOXECON (an injection of carbon between the electrostatic precipitator (ESP) and a compact baghouse added behind the ESP) and an injection of chemical additives to promote oxidation of mercury are under review. When using Activated Carbon Injection (ACI), if the carbon achieves good contact with the gaseous mercury for a sufficient amount of time, mercury will be adsorbed. Combined use of alkali (calcium hydroxide) and ACI has been shown to reduce ACI demand considerably. Based on tests, TOXECON appears to be an economic choice.
An injection of a chemical additive can include some form of chlorine, such as common salt (NaCl) or calcium chloride. However, most plants are reluctant to add these corrosive materials to their boilers. Another concern is that adding chlorine would increase halogen emissions resulting in a toxic chemical release inventory (TRI) reportable species.
In addition, during the past decade, U.S. industrial demand for mercury has dropped 75 percent. The decrease in demand is due to federal bans on mercury additives, voluntary reductions by industry, and increasing regulation of mercury emissions and mercury in products.
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