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

Pilot-scale (75 kg/h) combustion trials using a pulverized western Canadian coal of low sulphur content have shown that fly-ash resistivity can be significantly modified by use of SO3, H2SO4, NH2S02H, NH3, (NH4) 2 SO4, (C2H5) 3N and Na2SO4 as fly-ash conditioning agents. These conditioning agents were added as solutions to the combustion products and also, in some instances, as solids in the coal feed to the pulverizer. The measured fly-ash resistivity was found to decrease exponentially from its base level of 5 x 10 11 ohm-cm to a limiting value as the concentration of the conditioning agent increased. Optimum electrostatic precipitator efficiency always occurred at a resistivity of 5 x 10 9 ohm-cm. Reduced resistivity, however, was not always synonymous with improved precipitator performance.