Synergetic removal characteristics of mercury for ultra-low emission coal-fired power plant

Abstract

The synergetic mercury removal by flue gas treatment process in coal-fired power plants is widely accepted, but there is a lack of a corresponding model to describe mercury transformations. In this work, a model for mercury transformations is established in a flue gas treatment process model using Aspen Plus. The concentrations, mass flow rates, and normalized emission factors of mercury, NOX, particulate matters (PM), and SO2 are investigated in a 660 MW coal-fired power plant. The mercury oxidation efficiency of the selective catalytic reduction (SCR) unit is 56.9 %. The mercury removal efficiency of the electrostatic precipitator (ESP) and wet flue gas desulphurization (WFGD) units are 53.5 % and 34.4 %, respectively. The ultra-low emission system achieves 63.3 % removal of mercury. Approximately 53.5 % of mercury is retained in the fly ash. The emission factor of mercury is 0.0131 mg/kWh and increases to 0.0265 mg/kWh when the load decreases from 100 % to 50 %. The emission factors of PM, SO2 and NOX are 7.1, 97.1, and 142.9 mg/kWh at full load, and 10.9, 97.4, 150.0 mg/kWh at 50 % load, respectively. The proposed flue gas treatment process model is considered a feasible approach for quantitative evaluation of multi-pollutants emissions at plant level.