Novel Wet Electrostatic Precipitator for Sub - Micron Particles

The waste incineration plants, power generation utility, chemical industry, etc. require the efficient removal of submicrometer particles from raw gases. Wet electrostatic precipitators (WESP) are the most effective control device for fine aerosol from the humid raw gases. They use less energy than mechanical collection devices, have no moving parts to wear, their maintenance costs are lower, production downtime is minimized and WESP compact design allows the integration with wet scrubbers. But WESPs suffer with clogging problems due to build up of fine particles on the high voltage and collection electrodes leading to spark-over and loss of efficiency. Electrostatic precipitators also suffer with decreasing of collection efficiency when dealing with corona discharge suppression. These problems are overcome in a novel wet electrostatic precipitator developed in the Forschungszentrum Karlsruhe. The unit consists of a DC corona discharge ionizing stage and of an electric field-free grounded collector. The use of high gas velocities (over 20 m/s) in the nozzles of the ionizing stage minimizes the clogging of the high voltage electrodes with fine particles and diminishes the corona suppression in the zone of particle charging. By redesign of the plenum chamber between the high gas velocity ionizing stage and low gas velocity collector (less than 3 m/s) it was possible to increase the efficiency of particle collection under the influence of the space charge. The results of the laboratory and pilot tests of a oneand two-field wet electrostatic precipitator are presented in the paper. The WESP was used for collection of submicrometer particles of H2SO4, HCl, (NH4)2SO4 and (NH4)Cl from humid raw gases. The high velocities of the gas flow in the nozzles increase the stability of WESP operation and decrease the corona suppression at high particle concentrations. The modification of the plenum chamber increased the mass collection efficiency without increasing of power consumption for particle charging. The mass collection efficiency of a one-field wet electrostatic precipitator was 8095% and of the two-field precipitator increased up to 98-99%. The use of high velocity gas ionizing stage and electric field-free collector with improved stability of operation and diminished corona suppression phenomenon allows to develop a cost-effective flue gas cleaning technology for fine particles.