Improved electrostatic precipitator performance by use of fly-ash conditioning agents

Abstract

Pilot-scale (75 kg/hr) combustion trials using a pulverised western Canadian bituminous coal of low sulphur content have shown that the fly-ash resistivity can be significantly modified by adding SO 3 , H2 SO4 , NH2 S020H and NH 3 to flue-gases as fly-ash conditioning agents. The measured fly-ash resistivity(11) when using these conditioning agents was found to decrease exponentially, from its original lçvel (R0 ) to a limiting value (RSat) as the concentration of the conditioning _agents was increased: Log (R) - Log (Rsat) = e -k(c) Log (Ro)- Log (Rsat) For each conditioning agent k is a constant and (c) is the gas-phase concentration of the conditioning agent. The dissociation products (SO 3 and NH 3 ) of NH2SO2OH act independently and cumulatively in their effect on the resistivity of the fly-ash from Luscar coal. The resistivity reductions produced by SO 3' H 2 SO 4 and NH2 SO2OH were accompanied by increases in precipitator efficiency from the base level of 85%. Maximum efficiencies were recorded at additive concentrations in the range 10-15 ppm S0 3 : Emax( SO3) = 99% at 13 ppm SO 3 Emax(H2 SO4 ) = 98% at 10 ppm SO3 Emax( NH2S020H)= 95% at 10 ppm SO 3 Ammonia was not found to be an effective conditioning agent with this coal: Emax(NH3) = 90% at 45 ppm NH3