Effect of modified fly ash injection on As, Se, and Pb emissions in coal-fired power plant

Abstract Modified fly ash injection was installed at the outlet of selective catalytic reduction (SCR) systems in a 1000 MW coal-fired power plant, reaching 94% mercury capture rate. Due to chemical and mechanical treatment of raw fly ash, the modified fly ash has a higher oxidation capability, finer particle size, and more active sites. The co-benefit of the reduction of trace elements (TEs), such as arsenic (As), selenium (Se), and lead (Pb), when using on-line modified fly ash was investigated in this study. The results between with and without modified fly ash indicated that it is between 30% and 74% of reduction on the three TEs’ emission in both electrostatic precipitator (ESP) and wet flue gas desulfurization (WFGD) systems with the additional fly ash injection. The finer particle property is the dominant factor to reduce the emission of Se and Pb at such lower temperature (Temp) range. The Se itself also has the higher volatility to make capture more difficult than that of Pb. The strong chemical reaction between As and calcium with the smaller particle size reduced the As in the gas phase. The materials balance including solid, liquid, and gas phase also establish to confirm the sampling and measurement are validated of each value in this study. Above 97% of As and Pb are in the fly ash. Around 67% of the Se was captured in the WFGD unit. The Se had the higher emission in the stack.