Using microwave pretreatment to improve the high-gradient magnetic-separation desulfurization of pulverized coal before combustion

Abstract

Coal preparation before combustion is an efficient and low-cost method for the clean utilization of coal. In this study, a dry high-gradient magnetic separator was used to conduct magnetic-separation desulfurization of pulverized coal. The effects of feed size, microwave pretreatment time and background field intensity of the high-gradient magnetic separation on the desulfurization rate, Srej, and specific susceptibility, X0, of the coal were investigated, and the degree of influence of the operating parameters on Srej was explored via an orthogonal test method. The experimental results indicated that microwave pretreatment effectively increased both Srej and X0. Particularly, X0 exhibited a maximum value with increasing pretreatment time and was 1.8 times higher than that for un-pretreated coal. Further, Srej increased monotonically with increasing field intensity and decreasing feed size, which indicated that classification can effectively improve the desulfurization performance of pulverized coal. The optimum desulfurization conditions, which resulted in a maximum Srej value of 52%, were achieved at a microwave pretreatment time of 4 min, a background field strength of 5000 Gs, and a raw coal particle size of −0.074 mm.