Herek Clack

Mercury Emission Control

Research Associate Professor Herek Clack and his students are researching the control of toxic air pollutants, specifically toxic metals like mercury, that are emitted from combustion-related processes such as coal-fired power plants.

The U.S. Environmental Protection Agency (U.S. EPA) issued the world’s first regulation limiting the emission of toxic metals, including mercury, from U.S.-based electric utilities and industrial boilers. Clack says there is momentum for other countries to follow suit, such as the recent passage by the United Nations Environment Programme (UNEP) of the “Minamata” Convention, so named for the Japanese city where thousands were inadvertently poisoned by industrial discharges of methyl mercury in the mid-20th century.

For nearly two decades, and in anticipation of the EPA regulation, researchers primarily in the U.S. have been testing and developing various methods for capturing the ultra-trace concentrations of mercury that are present in combustion flue gases.  One of the leading approaches is the injection of dry powdered sorbents, such as powdered activated carbon, into flue gas to absorb the gas-phase mercury, followed by the collection of the contaminated powder with the residual ash and other particulate matter. Clack and his group are investigating the simultaneous adsorption of mercury and collection of particles within electrostatic precipitators, or ESPs.  At issue is the complex fluid and gas-fluid phenomena resulting from the superposition of fluid dynamics and charged particle transport within ESPs.   And because every man-made device operates at less than 100% efficiency, some of these injected powders  escape into the environment, posing both toxic risks from the adsorbed mercury on their surfaces and potential implications for climate as a result of their light-absorbing properties, similar to those of black carbon or soot. Clack aims to find out what the trade-offs are for operating ESPs such that they can optimally minimize the emissions of both mercury these fine particles into the atmosphere.

If you're interested in learning more about engineered devices for controlling air quality, be on the lookout for Clack’s upcoming air quality engineering focused course in winter 2014.

Dr. Clack

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