Effect of preheating on coking coal and metallurgical coke properties: A review

This study provides a review on research for improving the properties and qualities of coking coal and metallurgical coke using preheating. Factors such as coal type, preheating temperature, and heating rate significantly impact its structural evolution during carbonization after preheating. The influence of heat treatment conditions on the physical and chemical structures of coal, such as microcrystalline carbon (aromatic nuclei), graphite-like carbon, functional groups, and chemical bonds, is an important research area, especially quantitative analysis of the aromatic structure parameters. During heat treatment, the aromatic structure of coal continuously develops, and graphitization increases. The aromatic structure changes associated with thermoplastic temperature range (~350–550 °C) critically influences the thermoplasticity of coking coal. Through experimental studies on the influence of coal type, gas, preheating temperature, heating rate, and other factors about coking coal caking property (CP), the mechanism of rapid preheating (~100–104 °C/min) is explored. According to molecular depolymerization theory, rapid preheating relaxes the macromolecular structure of coal, thereby enhancing its fluidity during thermoplastic stage. After preheating coking coal, the cold and hot strengths of coke are commonly improved. In this review, the shortcomings and future research scope of the rapid preheating are also summarized. •Size growth and structure perfection of coal microcrystals with temperature lead to aromatization and graphitization•Parent substances of coal determines the extent of liquid crystal development and thermoplasticity during heating•A suitable heating rate and an adequate preheating temperature range are necessary for improving caking property of coal•Rapid preheating relaxes macromolecular structure of coal, increases mobile components, thereby enhancing its fluidity•Blending ratio of low-caking coal can be raised to 50% in rapid preheating process