Study Of Efficient Complex Flux And Melting Mechanism In Shell Coal Gasification Process

The Shell coal gasification process employs the ash fusion temperature (AFT) of feedstocks should be lower 1400℃. Recent work has demonstrated that the traditional methods used to lower the AFT by adding limestone are becoming increasingly outdated. Hence, improving the fusibility of high ash fusion temperature coals, which ash fusion temperature is over 1400℃, has become an urgent affair.In this paper, two representative coals selected from North Anhui (AQ007 and BS) were used in the study. Some agents were mixed with the coals in different propositions respectively and then studied an efficient complex flux by doing lots of experiments. Effect of flux addition on AFT and slag viscosity was studied. The mechanisms of fluxing were determined. Some primary results are obtained as follows:1) The complex flux was more efficiently than limestone. It could reduce the ash fusion temperature to 1350℃and improving the viscosity-temperature characteristic of the slag with only 4% addition.2) The minerals have great effect on the ash melting characteristic. In weak reducing atmosphere, as the temperature increased, thermal decomposition, transformation and reaction occurred between the components and some compounds melted to become glassy phase matter. With the addition of complex flux, mineral component could be changed to improve the ash fusion character. The main mineral matters of ash were quartz, with the temperature increased, it reacted with Al2O3 to formed mullite,which was the major crystalline phase observed at high temperature. Thus the AFT of coal is above 1400℃. The content of mullite in the mixed slag is decreased with the addition of complex flux. One hand the MgO reacted with SiO₂ & Al₂O₃ to form forsterite and spinel, which restrained the appearance of it. On the other hand, it reacted with CaO to form anorthite and reacted with MgO to form cordierite. From the scanning electron micrographs of melting slag, a lot of glasses were observed at 1300℃. These minerals coexisting will produce a low-melting eutectic mixture which decreases the ash fusion temperature.3)The ash fusion temperatures of mixed ash first increasing then decreasing with the addiction of complex flux coupling with the CaO/ MgO changed.