The critical condition and kinetics of interaction between residual char and slag in the coal slagging gasifier

Due to low gasification reactivity of carbon feedstock and improper discharge operation, residual char is often found in bath of moving bed slagging gasifier, which affects the carbon conversion and slag discharge significantly. Moreover, the critical condition of interaction between char and slag determines whether char can be wrapped and consumed by slag in bath, while kinetics of interaction affects consumption rate of residual char wrapped by slag. In this work, the critical condition and kinetics of interaction between residual char and slag were investigated in terms of wetting behavior and carbothermal reaction. Results show that the increase of temperature not only lowers the contact angle between the slag and char, but also be beneficial to carbothermal reaction, thus, high temperature can improve wetting behavior at the slag/char interface. According to different factors that affect wettability during heating, the curve of contact angle between char and ash can be divided into three stages. Besides, it was found that the coal char with low graphitization degree is easy to be wrapped by ash with high SiO2/Al2O3 ratio, and quantitative relation between wrapped temperature and property of slag and char was established to predict critical condition of interaction. In addition, a limit of carbothermal reaction in thermodynamics was observed, and non-isothermal kinetic equations of carbothermal reaction were established, which can provide guidance for slag discharge operation of moving-bed slagging gasifier.