Investigation and analysis of a grid-type electrostatic precipitator

Abstract

The grid-type electrostatic precipitator consists of a number of flat perforated metallic plates (or grids) placed parallel to one another and perpendicular to the flow of air laden with electrically charged dust particles. Alternate grids are connected together at ground potential and the intervening grids at high voltage, so that as the dust particles pass through the device they experience a succession of electric fields whose directions are alternately opposed to or aligned with the gas flow. When the electric force on the particles opposes the gas flow, collection is by vortex-enhanced electrostatic precipitation, where the particles are precipitated after being trapped in the vortices formed in the wakes of the solid portions of the upstream grid. When the electrical force is aligned with the gas flow, collection is by electrostatic interception on the downstream grid. Optical measurements on the performance of a bench-scale, 12-stage (25 grids in all) device placed on the outlet of a conventional precipitator, using fly-ash as the test dust, demonstrated that collection efficiencies in excess of 90 per cent can be obtained at a gas velocity of 183 cm s −1. Theoretical calculations of efficiency based on a model involving the two basic mechanisms were in reasonable qualitative but limited quantitative agreement with the experimental data. Initially the grid precipitator is intended to be employed as an add-on unit for the upgrading of existing precipitator installations with minimal increase in overall system dimensions.