Morphological changes and ash fusibility of coal, rice straw and their mixture during CO2 gasification

The gasification behavior of single particle of coal, rice straw, and coal-rice straw mixture were investigated by in-situ heating stage microscope, X-ray diffraction, and scanning electron microscopy. The gasification process of coal particle can be divided into three stages consisting of swelling stage, shrinkage stage, and ash fusion stage, while the swelling stage is not observed for the gasification of rice straw particle. The presence of rice straw particle facilitates the shrinkage of coal particle during the co-gasification process due to the migration and catalytic effect of alkaline components which are abundant in biomass. Further, it was found that the average melting temperature of particles is close to the deformation temperature (DT) of ash sample, implying that the DT may reflect the melting properties of particles in a real gasifier. Finally, the ash fusion mechanisms were explored. It was identified that the formation of high-melting points mullite, quartz and anorthite are responsible for the high ash fusion temperatures of coal (with flow temperature over 1500 ?C). The addition of 20 wt% rice straw (with flow temperature of 1133 ?C) to coal improves the formation of lower-melting points minerals containing alkaline and alkaline-earth elements, and sulphur in the mixture that facilitates the ash fusion process and induces the slag formation. Thus, the flow temperature of the mixture decreases to 1369 ?C. The ash fusion behavior of coal follows the ?softening-melting? mechanism, while this behavior of rice straw shows a typical ?melting-dissolution? mechanism. The ash fusion behavior of coal-rice straw mixture reveals both mechanisms; however, the ?melting-dissolution? mechanism seems to be more characteristic for this mixture.

Automated summary

The gasification behavior of coal and rice straw differs when gasified separately, but during co-gasification, the presence of rice straw particles promotes the shrinkage of coal particles due to their abundant alkaline components. The ash fusion mechanism of coal is characterized by a "softening-melting" process, while rice straw follows a typical "melting-dissolution" mechanism.