Investigation of brown coal char-CO₂ gasification in a laboratory scale drop tube furnace

This paper provides detailed investigation of Victorian brown coal char gasification in laboratory scale drop tube furnace (DTF) under CO ₂/N₂ mixtures. The DTF is a 2.0 m long quartz reactor consisting of two concentric tubes (diameters 50 mm and 80 mm). Morwell coal char with diameter of <106μm (mean value = 50μm) is used for this investigation. This char sample was prepared in a tubular furnace under pure N₂ at 823K. The char is gasified under CO₂/N₂ atmosphere at temperatures of 1173 and 1273K. The gas compositions from char gasification in the DTF are measured on-line using micro gas chromatography (GC). The results show that char conversion and CO concentration increases with increasing the inlet gas temperature. At 1273K, CO concentration increases due to increased rate of the char-CO₂ reaction. A 3D comprehensive numerical modeling is employed to investigate the char-CO₂ gasification process under various operating conditions. The calculated results are compared with experiments at two different temperatures of 1173 and 1273K using at 20 vol. % CO₂ /N₂ mixtures. The comparisons show a good agreement confirming the validity of the current model. We predict carbon conversion from char-CO₂ gasification for various char particle sizes at elevated gas temperature (>1273K). The temperature distribution in the furnace is found to be uniform under current operating conditions. It is also found that the char conversion significantly depend on the inlet gas temperature and particle size.