Experimental Study on Microwave-Assisted Non-Thermal Plasma Technology for Industrial-Scale SO2 and Fly Ash Control in Coal-Fired Flue Gas

Growing efforts to reduce air pollution have accelerated the development of advanced flue gas treatment technologies for coal-fired power plants. This study presents the design, development, and industrial-scale implementation of a microwave-assisted non-thermal plasma reactor, powered by a 75 kW, 915 MHz magnetron, for simultaneous sulfur dioxide (SO2) removal and fly ash agglomeration. The reactor was installed on the outlet line of the selective catalytic reduction (SCR) system of a 22 MWe pulverized-coal-fired boiler and evaluated under real flue gas conditions. The flue gas stream, extracted by an induced-draft fan, was supplied to the reactor through two configurations—radial and axial injection—to investigate the influence of gas flow rate and microwave power on SO2 abatement performance. Under radial injection, the system achieved a maximum SO2 removal efficiency of 99.0% at 5194 Nm3/h and 75 kW, corresponding to a specific energy consumption of 14.4 Wh/Nm3. Axial injection resulted in a removal efficiency of 97.5% at 4100 Nm3/h. Beyond SO2 mitigation, exposure of flue gas to the microwave-assisted plasma environment significantly enhanced particle agglomeration, as confirmed by means of SEM imaging and particle size distribution analyses. Notably, the proportion of fine particles smaller than 2.5 µm (PM2.5) decreased from 70.25% to 18.63% after plasma treatment, indicating improved capture potential in the downstream electrostatic precipitator (ESP). Overall, microwave-assisted plasma provides efficient SO2 removal and enhanced particulate capture, offering a compact and potentially waste-free alternative to conventional systems.