Next Generation Wet Electrostatic Precipitators

摘要

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, SO_3 and Hg~(+2) after limestone wet flue gas desulphurization (WFGD) scrubbers in the utility industry. Several coal-fired utilities have been experiencing increased SO_3 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. 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~(+2)). 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. Cleaning of the corrosion resistant fabric membranes, is facilitated by capillary action between the fibers, providing even water distribution, & continuous flushing, which removes collected material without spraying, so the entire precipitator remains on line. 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 after two boilers firing No. 6 oil with 4% sulfur, shows high SO_3 removal as well. The operation and performance of this two-module, upflow, membrane, single-field unit, along with some of the problems encountered and overcome in the start-up, will be described. Cost estimates comparing the membrane design to conventional metal plate WESP's are presented. Recommendations are made to show how the membrane technology can be used after utility-size, limestone WFGD scrubbers. Capital cost comparison of both vertical up-flow and horizontal flow WESP's will be made.