The gasification of wood-char spheres in CO2---N2 mixtures: analysis and experiments

Dasappa, S and Paul, PJ and Mukunda, HS and Shrinivasa, U (1994) The gasification of wood-char spheres in CO2---N2 mixtures: analysis and experiments. In: Chemical Engineering Science, 49 (2). pp. 223-232.

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Abstract

The gasification of charcoal spheres in an atmosphere of carbon-dioxide-nitrogen mixture involving diffusion and reactions in the pores is modelled and the results are compared with experiments of Standish and Tanjung and those performed in the laboratory on wood-char spheres to determine the effects of diameter, density, gas composition and flow. The results indicate that the conversion time, t(c) approximately d1.03 for large particles (> 5 mm), departing substantially from the t(c) approximately d2 law valid for diffusion limited conditions. The computational studies indicate that the kinetic limit for the particle is below 100 mum. The conversion time varies inversely as the initial char density as expected in the model. Predictions from the model show that there is no significant change in conversion time up to 60% N2 consistent with the CO2-N2 experiments. The variation of diameter and density with time are predicted. The peculiar dependence of conversion time on flow velocity in the experiments is sought to be explained by opposing free and forced convection heat transfer and the attempt is only partly successful. The studies also indicate that the dependence on the CO concentration with low CO2 is significant, indicating the need for multistep reaction mechanism against the generally accepted single-step reaction.

Item Type:	Journal Article
Publication:	Chemical Engineering Science
Publisher:	Elsevier science
Additional Information:	Copyright of this article belongs to Elsevier science.
Department/Centre:	Division of Mechanical Sciences > Aerospace Engineering(Formerly Aeronautical Engineering) Division of Mechanical Sciences > Mechanical Engineering Division of Physical & Mathematical Sciences > Astronomy and Astrophysics Programme
Date Deposited:	15 Apr 2011 07:38
Last Modified:	15 Apr 2011 07:38
URI:	http://eprints.iisc.ac.in/id/eprint/36877

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