MEMBRANE WESP-A Lower Cost Technology to Reduce PM2.5, SO_3 Hg~(+2) Emissions

摘要

Multi-pollutant control technologies will become more important in the future. This newmembrane wet electrostatic precipitator (WESP) system is ideally suited to, and very costeffective 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 existingWFGD scrubbers, especially after installing a Selective Catalytic Reduction (SCR) for NOxControl. Achieving co-benefits of Hg removal by installing SCR's and WFGD systems is alreadybecoming 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 andvirtually no re-entrainment. The WESP can also enhance collection of Hg (Hg ash & Hg~(+2)). Themain historical limitation associated with wet precipitators has been the higher cost of specialalloys and stainless steel material used in their manufacture. This new technology WESP, basedon 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 betweenthe fibers, providing even water distribution, & continuous flushing, which removes collectedmaterial without spraying, so the entire precipitator remains on line.Operation of several pilot units using the membrane technology has demonstrated excellent PMremoval efficiency. The first commercial size unit, collecting fine particulate and sulfuric acidmist after two boilers firing No. 6 oil with 4% sulfur, shows high SO_3 removal as well. Theoperation and performance of this two-module, upflow, membrane, single-field unit, along withsome 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 arepresented. Recommendations are made to show how the membrane technology can be used after