Nano-Enhanced Composite Electrodes for Electrostatic Precipitators

With the increasing volatility of petroleum and natural gas resources, small coal-fired boilers have become increasingly more attractive for steam and power generation in several industries. This switch to small-scale, coal-fired plants is expected to continue, and increases the need for clean coal utilization technology. The U.S. Energy Policy Act includes support for a clean coal technology initiative focusing on the environmental challenges of using coal. While initial efforts focused on addressing acid rain, more recent efforts focus on addressing the potential health risks of particulate matter (PM). A key technology for removing PM from flue gases generated by coal-fired power plants is the electrostatic precipitator (ESP). ESPs operate with an efficiency of 90 to 99 percent for the removal of mercury and fly ash from the flue gas stream. ESPs work by applying an electric voltage to an electrode, which in turn applies a charge to the PM entrained in the gas flow; the charged PM then is collected on a large plate with the opposite voltage. The collection surface and electrodes are made from metal, are extremely heavy with a high installed cost, are easily corroded, and have a limited service life unless very expensive alloys are used. To address these issues associated with using metallic ESP components, Applied Sciences, Inc., working closely with Ohio University, investigated the use of inexpensive carbon nanofibers (CNF) to enhance the capture efficiencies of ESPs. The joint effort focused on producing polymeric, composite electrodes enhanced with the addition of CNF. This combination of low-cost materials and processing techniques has led to the production of composite electrodes that generate up to 20 percent more corona current than metal electrodes at the same voltage. The superior performance of the composite electrode increases the capture efficiency and lowers the power requirements of both dry and wet ESPs. These enhancements are attributed to the presence of the CNF, which provides a conductive path to the surface where the corona current is generated. Additionally, each CNF exposed to the surface of the composite acts as a source of charge emission. Polymeric-based nanocomposite electrodes are less expensive to produce, easier and cheaper to install, and corrosion resistant. Based on the generous support, technical guidance, and level of interest expressed by Southern Environmental Inc., and feedback from other ESP providers, this technology will advance the state of ESP performance for both large and small units.