Transition temperature and thermal conduction behavior of slag in gasification process

The thermal conduction behavior of slags affects the stable operation of entrained-flow gasifier. The thermal conduction behavior of five-element synthetic slag system with four series variable composition was systematically studied. The turning point of thermal conductivity changing with temperature is observed in each sample, where thermal conductivity is at peak value. The temperature of this point is defined as the transition temperature Tct, which is determined by the intersection point of two fitting lines based on two mechanisms. When T > Tct, the thermal conductivity is exponentially related to the reciprocal of temperature. With decrease of temperature, two different downward trends of thermal conductivity are observed, which is probably caused by the difference of crystal precipitating rate, and the effects of glassy and crystal state also cannot be neglected. When T < Tct, the thermal conductivity is positively linear with temperature. It was found that Tct is between the initial crystallization temperature and the ash melting point, where thermal conductivity of slag begins to be affected by the crystal thermal conduction. A prediction model of the transition temperature is established based on the liquid phase temperature without the requirement of experimental tests and verified by five actual coal ashes.