Investigation on the mercury nucleation mechanism based on the release characteristics of inhalable particles during coupled combustion of sewage sludge-coal washery tailing

Abstract

Establishing an integrated treatment technology system for sewage sludge and coal washery tailing by mixed combustion can effectively overcome the disadvantages of the low calorific value and utilization efficiency, realizing the efficient resource. The single-component and coupled fuel were analyzed. Aiming at the generated inhalable particulate matter during the combustion process, using multiple characterization means and the fluidized bed experimental system, the micro-characteristics and elemental distribution of coupled fuel and combustion products were obtained, and the theory based on nucleation control was analyzed to reveal particle size distribution and particulate matter emission characteristics under multiparameter coupling conditions. The nucleation mechanism of Hg on the surface of the particulate matter under mixed combustion conditions was clarified. The results show that the weight loss process of sewage sludge in the combustion process mainly includes four stages. An obvious boundary between the volatilization and combustion processes of fixed carbon does not exist; furthermore, there is some overlap between the two processes. Volatiles and minerals interact in the mixed combustion process. The constituent elements of PM1 and PM1∼10 in the generated particulate matter are mainly easily vaporizable and refractory elements, respectively. The particle size of the particles produced presents the characteristics of bimodal distribution. There is a critical value (800 °C) for the influence of combustion temperature on the emission characteristics of particulate matter. It mainly affects the emission characteristics of coarse and fine particles through dominating the occurrence forms of tar, easily gasified and refractory elements, and the collision and aggregation process between particles. Homogeneous nucleation and heterogeneous condensation are the basic pathways for the transition of Hg from the gas phase to particle nucleation, and there are different nucleation control mechanisms. The heterogeneous condensation process includes diffusion control and surface reaction control. In addition, after the coupled fuel is demineralized by acid washing, the nucleation control mechanism changes significantly from diffusion control to chemical reaction control for the particles in the continuum region.