(128a) Investigation of Brown Coal Char-CO2 Gasification in a Laboratory Scale Drop Tube Furnace

In the viewpoint of nowadays environmental issue for CO₂ reduction relating to global warming, efficient carbon conversion by utilizing CO₂ becomes attracting interest worldwide. Char-CO₂ reaction is considered to be a dominant reaction in oxygen-blown entrained flow gasification. This paper provides detailed investigation of Victorian brown coal char gasification in laboratory scale drop tube furnace (DTF) under different CO₂/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 of two size fractions (150-355 µm and 355-500 µm) are used for this investigation. These char samples were prepared in a tubular furnace under pure N₂ at 550°C.  The sized char samples are gasified under a CO₂/N₂ atmosphere at temperatures of 1073K and 1273K. The gas compositions from char gasification in the DTF are measured on-line using a micro GC. The results show that char conversion and CO to H₂ molar ratio increases with increasing the furnace temperature. For the 150-355 µm sample, carbon conversion becomes doubled from 14% to 28% while an increase of almost four times, from 4% to 15%, is observed for the 355-500 µm sample. At 1273K, CO to H₂ molar ratio increases due to increased reaction rate of the char-CO₂ reaction. The experimental results are compared with numerical results. A 3D species transport modeling is employed to investigate the char-CO₂ gasification process under various operating conditions mentioned above. The char gasification model considered in this calculation is composed of particle inert heating, particle devolatilization, gas phase reactions and solid-gas phase reactions. The calculated outlet gas species concentrations are compared with those of experimental results at two different gasification temperatures of 1073K and 1273K using 20% CO₂ in CO₂/N₂ mixtures. The comparisons show a good agreement confirming the validity of the current model. We predict the gasification characteristics in terms of gas temperature distribution, char particle temperature and its residence time inside the furnace under varying CO₂ concentrations at elevated furnace temperature (>1273K). We also predict the yield of gas produced from char-CO₂ gasification at different operating conditions.