Experimental estimate of CO2 concentration distribution in the stagnant gas layer inside the thermogravimetric analysis (TGA) crucible

The measurement of char gasification reactivity and kinetic parameters by TGA is generally complicated with mass transfer limitations. There is a reactant gas concentration gradient in the stagnant gas region between the mouth of the TGA crucible and the surface of the char bed because of gas consumption by the sample. The counter-diffusions between the reactant and product gases occur in this stagnant region. The Maxwell-Stefan equation has been used to estimate the distribution of gas concentration in the stagnant gas region. However, there is some uncertainty associated with semi-empirical gas diffusion coefficients used in the equation. In this study, we propose a new method to estimate the distribution of CO2 concentration in the stagnant gas region during CO2 gasification of coal char in TGA. The external effectiveness factors obtained in this way were in a reasonably good agreement with the value obtained by the traditional method widely used in literature.