Hydrothermal Treatment of Lignite for CO₂ Gasification

Abstract

Hydrothermal treatments of lignite, Loy Yang Coal, having high water content of about 60 % were conducted at temperatures ranging from 200 ℃ to 380 ℃. The solid products were examined from various angles like fuel characterization, equilibrium moisture content, solid state VACP (Variable Amplitude Cross Polarization)/ MAS ¹³C-NMR spectroscopic study and thermogravimetry. As a result, the treatment produced upgraded solid fuel; the rising treatment temperature yielded increasing carbon content, fixed carbon, fuel ratio and carbon aromaticity. The advantages of the solid products obtained at harsh condition, 300 ℃ or higher, were low moisture content, high calorie and their slight variation regardless of wide variety in humidity. On the other hand, mild hydrothermal treatments at 250 ℃ or lower demonstrated advantages in terms of energy recovery and solid yield. Addition of a small amount of alkali at hydrothermal treatment improved the gasification reactivity of the solid phase in the successive gasification stage more than twofold, rather decreasing the ash content. Further alkali dose may influence the coal structure that leads to a decrease in the slope of the Arrhenius plot.