Commercial development is underway for a technology that uses ultraviolet light to oxidize and remove mercury from coal-fired power plants. The process, developed by the U.S. Department of Energy’s National Energy Technology Laboratory (NETL), has been licensed by New Durham, N.H.-based Powerspan Corp. The Environmental Protection Agency has proposed a rule to permanently cap and reduce mercury emissions from power plants and will finalize the rule by the end of this year.
Mercury exists in the elemental and oxidized forms in power plant flue gas streams with the elemental form being the more difficult to capture. The Photochemical Oxidation (PCO) process uses ultraviolet light to produce an “excited state” mercury species in coal combustion flue gas, leading to the oxidation of elemental mercury. Once in the oxidized form, mercury can be collected in existing air pollution control devices such as wet scrubbers and particulate collectors. With the ability to work with conventional pollution control systems, PCO has the potential to serve as a low-cost technology for reducing mercury emissions from power plants.
“Owners of coal-fired generating plants, particularly those that burn lower rank coals, are searching for a technology to provide substantial reductions in mercury emissions while minimizing the impact on plant operations and power costs,” says Powerspan chairman and CEO Frank Alix. “The PCO technology has the potential to meet these needs.”
Preliminary tests conducted by Powerspan have shown that the process is capable of oxidizing and removing 90% of incoming elemental mercury when UV lights are used upstream of an electrostatic precipitator, bag house or scrubber. The UV lights used are similar to those used in municipal water treatment systems to kill bacteria and other harmful organisms.
“We have received considerable interest from utilities for pilot testing the PCO process,” says Stephanie Procopis, director of marketing for Powerspan. “Although we have not yet selected a test site, we plan to pilot test PCO at one or more power plants in the next year, with our focus on oxidation and removal of elemental mercury from the flue gas of low rank coals such as sub-bituminous and lignite.”
She adds that the company expects commercial PCO systems would be available in two to three years. “Initial cost estimates indicate that PCO would cost less than other mercury control technologies,” she says. “Our initial estimate of power consumption for 90% oxidation of elemental mercury is less than 0.5% of plant power.”