An innovative technology that could potentially help some coal-based power generation facilities comply with anticipated new mercury emissions standards was successfully demonstrated in a recently concluded milestone project at a Michigan power plant. Under a co-operative agreement with the US Department of Energy’s (DOE) National Energy Technology Laboratory (NETL), WE Energies demonstrated the TOXECON process in a $52.9 million project at the Presque Isle power plant in Marquette. TOXECON is a relatively cost-effective option for achieving significant reductions in mercury emissions and increasing the collection efficiency of particulate matter while maximising the use of coal combustion byproducts.
The technology, which resulted from NETL research and was patented by the Electric Power Research Institute (EPRI), involves the injection of sorbents between an existing particulate control device, such as an electrostatic precipitator, and a pulsed-jet baghouse, capturing pollutants before they are emitted into the atmosphere.
The sorbents collect in the baghouse along with the small amount of fly ash that escapes the primary particulate control. The baghouse provides excellent contact between gas and sorbent which results in high mercury-removal efficiency since the flue gas must pass through the dust cake of ash and sorbent on the bags in the baghouse. This configuration segregates the ash collected in the primary particulate control device (the precipitator) from the baghouse ash/sorbent mixture, enabling the ash collected in the primary particulate control device to continue to be sold for use in making concrete. Aside from the environmental benefits of recycling, fly ash is a vital ingredient in improving the performance of a wide range of concrete products; more than 12 Mt of coal fly ash are used annually in concrete products in the US.
During the three-year demonstration period, the TOXECON technology removed more than 90% of the mercury contained in the flue gas from three 90-MW units firing sub-bituminous Powder River Basin coal. Annually, the process is expected to capture 97 lb of mercury and 250 t of particulate matter at the Presque Isle plant.
The US Environmental Protection Agency has indicated its intent to regulate mercury emissions from the America’s coal-based power plants. TOXECON technology will provide an approach for segments of the power-generating industry, especially those using western subbituminous coal, to achieve timely compliance with future mercury regulations. NETL says the process has application to an estimated 167 GW of existing coal-fired capacity.
The technology is particularly important to the state of Michigan, which recently promulgated rules to reduce mercury emissions to protect its environment and, specifically, its inland lakes. The new rules require the state’s power plants to reduce mercury emissions by 90% by 2015.
The successful demonstration of the process, which received an R&D 100 Award as one of the 100 most significant new technologies of 2003, puts it in the position of being a leading mercury-control choice for western coals, especially in units that use a ‘hot-side’ electrostatic precipitator located upstream of the power plant’s air preheater.
The project was part of DOE’s Clean Coal Power Initiative, a cost-shared collaboration between the Federal Government and private industry to increase investment in low-emission coal technology by demonstrating advanced coal-based power generation technologies prior to commercial deployment.
The project was administered by DOE’s Office of Fossil Energy and NETL. WE Energies managed the project. Among We Energies’ team members, ADA-ES conducted the test program, Cummins & Barnard provided architectural and engineering services, Wheelabrator Air Pollution Control Inc. provided baghouse design and installation support, and EPRI served as technical advisor.
