Production of high strength metallurgical coke by modification of Xinjiang low quality coking coal

The formation of Xinjiang coking coals is characterized by unique geological conditions and relative late geological age, so that the medium volatile Xinjiang coking coals contain a relatively low degree of coalification and high oxygen content, resulting in the coke prepared from these coals with high reactivity of coke (CRI) and low strength after reaction (CSR). In order to improve the coke quality, adding a high proportion of inland medium volatile coking coals to Xinjiang coking coals is an effective method to manufacture metallurgical coke, but the coking costs will increase significantly. Therefore, four low quality coking coals from Xinjiang have been carbonized singly, in coal blends with two high quality coking coals from inland or self-developed modifier in a 10 kg iron pot, which was buried in an industrial coke oven.To investigate the influence of modifier on coke structure, modified coke and raw coke were investigated by using Micro-photometer, SEM, and XRD techniques. The modification mechanisms were also analyzed by the pyrolysis experiment of medium volatile Xinjiang coking coal and modifier using TG analyzer. The results showed that the CRI value of modified coke decreased by about 14% while the CSR value increased by about 15% when coal blends obtained from four Xinjiang coking coals were carbonized with 0.3% modifier.Besides, the comprehensive performance indexes of modified coke could match that of common coke that was prepared from the high proportion of inland coking coals and Xinjiang coking coals. The modifier could combine the active oxygen-containing fragments so that the reactions of transferable hydrogen and active oxygen-containing fragments were going to be decreased, which were responsible for the lower consumption of transferable hydrogen in the fast pyrolysis stage of coal. Therefore, more amount of stable mesophase could be observed in modified coal, which contributed not only to reduce the spacing of microcrystalline layers and the porosity but also to increase the size and stacking height of the microcrystalline layers, volume of microcrystalline, the degree of anisotropy, and the consistency of surface in subsequent coke. © 2021, Editorial Office of Journal of China Coal Society. All right reserved.