Next Generation Wet Electrostatic Precipitators

Multi-pollutant control technologies will become more important in the future. This new membrane wet electrostatic precipitator (WESP) system is ideally suited to, and very cost effective for, removing PM2.5, SO3 and Hg after limestone wet flue gas desulphurization (WFGD) scrubbers in the utility industry. Several coal-fired utilities have been experiencing increased SO3 emissions from their existing WFGD scrubbers, especially after installing a Selective Catalytic Reduction (SCR) for NOx Control. Achieving co-benefits of Hg removal by installing SCR's and WFGD systems is already becoming a key strategy for reducing mercury levels after coal fired power plants. In the future CO2 removal from flue gas may be necessary. For a CO2 absorption to operate effectively very low loadings of PM, SO2 & SO3 are required (deep cleaning). A WESP offers the most cost effective technology to achieve deep cleaning. A WESP can readily collect acid aerosol and fine particulate due to greater corona power and virtually no re-entrainment. The WESP can also enhance collection of Hg (Hg ash & Hg). The main historical limitation associated with wet precipitators has been the higher cost of special alloys and stainless steel material used in their manufacture. This new technology WESP, based on fabric membrane for the collecting electrodes, dramatically reduces weight and cost, compared to conventional, metallic WESPs. Operation of several pilot units using the membrane technology has demonstrated excellent PM removal efficiency. The first commercial-size unit, collecting fine particulate and sulfuric acid mist emitted from two boilers firing No. 6 oil with 4% sulfur, shows high SO3 removal as well. The operation and performance of this 5 year old unit, will be described. The Benefits of being able to operate the unit as a condensing WESP will also be described. INTRODUCTION Fine particulate, PM 2.5 and pseudo particulate (H2SO4 mist) is of concern to coal-fired utilities because it effectively scatters light, leading to increased stack opacity. Soot, or condensed hydrocarbons and acid aerosols, are capable of causing significant opacity problems at concentrations as low as 10 ppmv. Acid aerosols form when an acid (notably sulfuric acid) condenses, providing excellent condensation nuclei for water accumulation, eventually creating aerosol particles 1-2 μm in diameter. Sulfuric acid condensation nuclei are prevalent when SO3