Impact of the mercury removal system using modified fly ash on particulate matter emission

This study examines the impact of adding a mercury removal system which uses modified fly ash on particulate matter (PM) emissions from a coal-fired power plant. The modified fly ash injection technology has been demonstrated and was installed in a commercial power plant and reached 91.9% mercury removal efficiency. An important consideration was that the emission limitation for PM -5 mg/Nm3, should not be exceeded due to the addition of 0.2% (by mass) of modified fly ash to untreated fly ash fed to a coal boiler unit. Thus, the effect of modified fly ash injection on the PM emissions was studied at different locations in the power plant: before and after the Electrostatic Precipitator (ESP), after the Flue Gas Desulphurization (FGD) unit. Measurements were also made at the stack. The results showed that after the modified fly ash was injected into the flue gas stream from the boiler, the mass concentration of particulate matter leaving the particulate emission control device (PECD) was slightly increased. However, the distribution of PM10, PM2.5, PM1 and PM0.2 was not significantly changed due to the addition of 0.2% (by mass) of modified fly ash. The results indicated that the total PM removal efficiency of the PECD was still around 99.1 - 99.9% for the case of mass concentration and 98.6 99.7% for number concentration. The mass emission concentration of PM10 with modified fly ash injection were 2.46 and 1.96 mg/m3 at 100% and 50% load, respectively.