Desulfurization of high sulfur fine coal using a novel combined beneficiation process

Abstract The throughput of high-ash and high-sulfur fine-grain coal (0–6 mm) increases year by year. The serious problem of direct combustion is the formation of acid rain and smog. Therefore, the pre-combustion desulfurization and ash reduction can reduce environmental pollution. A combined process of dry separation and microwave desulfurization for the cleaning of the 0–6 mm fine coal was applied. The effects of gas velocity, vibration amplitude and frequency on the removal of inorganic sulfur were analyzed systematically. At the same time, the effects of additives, microwave power, irradiation time and temperature on the removal of organic sulfur in the microwave desulfurization reactor were investigated. The results show that the compound dry separator can sorts the 0–6 mm fine coal under the optimal operating parameters (A = 3 mm, f = 22.5 Hz, v = 0.68 m3/s). After the separation, the yield, ash and sulfur contents of the pre-separated clean coal is 63.6%, 12.4% and 4.12%, respectively. The compound dry separator can effectively remove mineral impurities such as inorganic sulfur. The ash is reduced apparently. However, the organic sulphide cannot be removed by the separator. As the pre-separated clean coal has high sulfur content that is mainly organic sulfide, the microwave desulfurization reactor is used to remove this part of organic sulfur. The results show that the NaOH solution additive is more beneficial to improve the microwave desulfurization. The desulfurization rate increase with the increasing of temperature and radiation time and the irradiation time has a more obvious effect. After the microwave desulfurization the yield, sulfur and ash contents of the clean coal are 60.8%, 0.98% and 9.74%, respectively. As a result, the microwave desulfurization process can effectively remove the organic sulfur compounds.