To establish the nature of oxygen tranport into chars burned under Regime II conditions; measurements of gas diffusion coefficient into partially burned chars were conducted using a non-isobaric gas chromatographic technique. The chars used included two low volatile bituminous chars, Norwich Park and Collinsville and one brown coal chars. The chars were prepared by conducting the combustion in an entrained flow reactor between 900- 1300 K and comparisons were made with chars burned under Regime I in a fixed bed between 500-800K. The experimental results were compared with coefficient predicted from Wheeler's equation based on the assumption of Knudsen diffusion. The results suggest gas transport occur mainly by activated diffusion. This mode of transport appearing more as Knudsen diffusion at the elevated temperatures. Analysis of the surface area suggest the development of fine pores under Regime II condition, which may suggest that the activated diffusion is accompanied or is due to surface migration of oxidant at the elevated temperatures.
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