Improving the removal of particles and trace elements from coal-fired power plants by combining a wet phase transition agglomerator with wet electrostatic precipitator

Abstract

A novel technology for flue gas pre-treatment in the phase transition process is proposed in this paper to better remove the fine particles and trace elements from coal-fired power plants. Wet removal, Brownian diffusion, diffusiophoresis, thermophoresis and disturbed pipe flow occurring in the phase transition process were taken into consideration during the development of the technology. An item of equipment called a wet phase transition agglomerator (WPTA) was developed based on the aforementioned technology. The WPTA and the wet electrostatic precipitator (WESP) constituted a wet dust removal system (WDRS), which was used at a 660 MW ultra-supercritical unit in China as a demonstration project. The particles at the inlet and outlet of the WDRS, as well as the wastewater from the system, were sampled to investigate the performance of the WDRS. The results indicate that the WDRS helps to bring about ultra-low emissions of particles from the coal-fired power plant, keeping the level of particle emission below 5 mg/m3 under all measurement conditions. It was found that the collection efficiency of the WESP increased significantly with an increasing applied voltage. The performance of the WDRS can be further improved by the WPTA, for the removal efficiency of total suspended particulates at boiler operating loads of 90% and 75% rose 4.01 and 3.17 percentage points, respectively. Moreover, the removal efficiency of PM1 increased from 68.67% to 83.61% with the WPTA running at a load of 90%. The TEs removal was also found to be enhanced by the WPTA. The masses of Hg, As and Mn carried by the wastewater per hour with the WPTA running increased 4.2, 2.8 and 1.5 times, respectively, over values when the WPTA was turned off.