Crystallization-controlled fusion mechanism of the amorphous fly ash from the Shell coal gasifier by particle sieving

The mineral in coal is transformed to the fly ash of different particle sizes during the entrained flow coal gasi-fication, causing the ash deposition problem on the radiant syngas cooler. In this study, the fusion behavior of fly ash collected from a Shell coal gasifier was analyzed by particle sieving. Results indicated that the fusibility of amorphous fly ash was influenced by the anorthite crystallization at high temperature. The fusion process of fly ash particle was divided into the sintering stage, plateau stage, and melting stage, which were caused by the flow of the amorphous fly ash, anorthite crystallization, and anorthite melting, respectively. The high theoretical anorthite content and the low fly ash viscosity improved the anorthite crystallization reaction in the fly ash particles <45 mu m, resulting in a wide plateau stage, narrow melting stage, and high ash fusion temperatures (AFTs). Therefore, the fusion behavior of fly ash particles <45 mu m followed "melting-dissolution" mechanism. In contrast, the fusion of fly ash particles >45 mu m belonged to the "softening-melting" mechanism for the weak anorthite crystallization behavior. The fly ash particles <45 mu m may cause the serious ash deposition problems for its low viscosity.