Effects of multiple agglomeration technology on the removal of particulate matters and particulate heavy metals: A pilot study

The emmision of particulate matters and heavy metals such as As, Se and Pb from coal combustion into the atmosphere would cause a serious environmental and human health hazard. Therefore, a multiple agglomeration based on the principle of turbulent coalescence and wall surface adsorption was developed to investigate the agglomeration effects on the removal of particulate matter and particulate heavy metals. Firstly, a numerical simulation method was adopted to comprehensively study the pressure loss, the velocity uniformity and the particle agglomeration effect, and a folded blade was selected for the multiple agglomeration device. Subsequently, a pilot study at a coal-fired plant on the particle agglomeration at different flue gas velocities was carried out. It is found that the agglomeration rate of PM₁ in the multiple agglomeration device is up to 32.84%. As the gas velocity is increased from 11.1 to 17.6 m/s, the agglomeration rate of PM_2.5 shows a certain decline, indicating that an increase in gas velocity would lead to a shorter residence time of particles and thus a decrease in agglomeration rate of particles. By comparing the concentration changes of As, Se and Pb in the particles before and after agglomeration, it is found that the agglomeration process can enhance the adsorption to gaseous heavy metals and also aggregate the nano-particles rich in heavy metals, thus resulting in an increase in the concentration of heavy metals in PM₁. The decrease of the absolute concentrations of As, Se and Pb in PM₁ after coalescence shows a cooperative removal effect in the multiple agglomeration device on the particulate matter and particulate heavy metals.