Chang's new technique to clean up fossil fuel emissions
A team of researchers at the Lawrence Berkeley National Laboratory (Berkeley Lab) Environmental Energy Technologies Division (EETD) has developed a technology that removes mercury from coal-fired power plant emissions.
The EETD team, which includes Shih-Ger (Ted) Chang and visiting professors Nai-Qiang Yan from Shanghai Jiao Tong University, Shou-Heng Liu from Taiwan Cheng-Kung University, and Zhao-Rong Liu from Beijing University, say the primary advantages of their new technology are its simplicity and affordability. On March 15, 2005, the U.S. Environmental Protection Agency (EPA) issued the first Clean Air Mercury Rule (CAMR) to control emissions from coal-fired power plants. The CAMR requires an overall average emissions reduction of about 70 percent by 2018.
Coal-fired power plant emissions can affect human health and the environment. To reduce these effects, air quality regulations significantly restrict emissions of nitrogen oxides (NOx), sulfur dioxide (SO2), particulate matter, and mercury (Hg) from coal plants. The overall project goal was to develop low-cost approaches for controlling Hg, SO2, and NOx emissions from power plants using air pollution control devices (APCDs).
Elemental mercury can be transported over long distances in the atmosphere because of its insolubility, and oxidized mercury is deposited near the point of emission because of dissolution in fog, cloud, or rain. Once mercury is deposited on land or in water, it can transform into methyl mercury, an organic form, and enter the food chain. Humans are most likely to be exposed to methyl mercury by consuming fish. Mercury in power plant flue gases is present in varying percentages in three basic forms: elemental mercury in gas form, or oxidized mercury in either particle-bound or gas form. Existing APCDs, including particulate collectors and SO2 scrubbers, can readily remove oxidized mercury. However, elemental mercury is difficult to remove because it is volatile and insoluble in water. Several technologies have been developed that can control mercury. Currently, the leading one involves injection of powder-activated carbon to adsorb mercury at a cost of about $60,000/lb of mercury removed.
Chang's approach is to inject gas oxidants such as bromine to oxidize the elemental mercury in flue-gas ducts ahead of the existing APCDs. To keep the reagent cost to a minimum, the key was to find a gas oxidant that can selectively oxidize elemental mercury without oxidizing other flue-gas components, such as SO2, NO, and CO. Also, the oxidation rate had to be very rapid because flue gas remains for less than 10 seconds between the port of injection and the APCD. Berkeley Lab has applied for a patent on this technology, and Mobotec USA, Inc., located in Walnut Creek CA, has recently negotiated a license with Berkeley Lab's Technology Transfer Department to use the gas-oxidant injection technology to remove mercury from power plant emissions. This technology will help reduce the approximately 48 tons of mercury that U.S. coal-fired power plants emit each year.
For more information, contact:
- Shih-Ger (Ted) Chang
- (510) 486-5125; Fax (510) 486-5401