Char swelling and shrinking behavior at early stage of coal gasification

Abstract

The char morphology after devolatilization and its evolution during gasification plays an important role in determining the coal quality impact on the performance of gasifier. The particle size distribution of devolatilized char affects particle trajectories in gasifier and char entrainment to heat exchanger. The purpose of this study is to propose prediction method of char swelling and shrinking ratio in the early stage of gasification. Swelling and shrinking behavior of single particle was observed using pressurelized laser heater. In order to quantitatively measure the change of particle size, char samples were also produced by drop tube reactor for several types of coal by changing reaction temperature and initial particle size. Moreover, XRD and NMR analyses were carried out to investigate the change of carbon structure during devolatilization. Swelling and shrinking ratio after devolatilization could be described by coal properties, such as volatile matter, ash, carbon, hydrogen, oxygen and macerai content. In particular, vitrinite had large effect on the swelling behavior. The result of XRD and NMR analyses indicated that the development of carbon lamination layer was recognized in plastic range and the hexagonal network extended at solidification stage during devolatiolization.