Study on electric agglomeration of bipolar-charged coal-fired fly ash particles and its effect on filtration performance of fibrous filter

Abstract

Efficient removal of fly ash from flue gases produced by power plants is a major technological challenge in environmental protection, and these particles suspended in the air can cause serious harm to humans as well. One effective method to enhance fly ash capture and removal is through bipolar-charged particle agglomeration. In this study, a hybrid electrostatic filter was designed, which is combined with an electrostatic particle pre-charger, preceding the fibrous filter. The effects of positive/negative matching voltage, flow velocity, and dust type on the agglomeration behavior of bipolar-charged fly ash particles were studied using the new hybrid electrostatic filter. The agglomeration phenomena were also characterized by scanning electron microscopy. The optimal agglomeration condition (+ 18 kV, -16 kV, 0.5 m/s) was identified for coal-fired fly ash particle. Subsequently, the collection efficiency and the pressure drop characteristics of the fibrous filter for uncharged, unipolarly and bipolarly charged fly ash particles were compared and studied. The results indicated that the bipolar-charged particle agglomeration can significantly increase the collection efficiency of the fibrous filter, especially for the most permeable particle with a size of 0.3 mu m, whose increment is up to 12%. Moreover, the growth rate of pressure drop across the fibrous filter for bipolar-charged particles is 67% smaller than that for uncharged particles. The electric agglomeration between particles of a similar size is the main model, and the smaller particles usually attach around the agglomerated large particles. These findings were rarely investigated in previous research, but they are very important for the removal of micron and submicron fly ash particles.