Effect of drying conditions on moisture re-adsorption and particulate matter emissions during the classification drying of coking coal

Abstract

A simple classification drying method, in which moisture re-adsorption performance is crucial, is proposed to solve the problem of particulate matter emissions during coking coal drying. Coal particles were classified as fine and coarse particles. To maintain the high moisture level of fine particles, lab-scale experiments were used to investigate the influences of the initial moisture of coarse particles before mixing, the mixing time, the mixing temperature, and the drying temperature of the coarse particles. The re-adsorption performance and particle properties were studied using the desiccator method, the FTIR technique and the nitrogen adsorption technique. We concluded that the moisture of fine particles after mixing decreases with the decreasing initial moisture of the coarse particles or with increasing mixing time and that an optimal value would appear at a mixing temperature for coarse particles dried at 205 °C. Additionally, we found that the re-adsorption performance is not only dramatically affected by the water pressure gradient and the properties of the particles but also by the temperature gradient. These factors limit the universality of this technology. Particulate matter emissions decrease because the weight of fine particles increases, and fine particles aggregate slightly at high moisture levels.