Reactivity of Coal and Char in CO sub 2 Atmosphere.

摘要

Reactivities of a few raw coals and chars of these coals obtained from gasifiers operating under different conditions were measured in CO sub 2 at the temperatures 1550 to 2000 exp 0 F. The reactivities were measured in a thermogravimetric analyzer up to complete conversions of the samples in most cases. Properties like surface area pore size distribution, porosity and density have been determined for each sample. Actual pore structures of a few samples have been observed at different conversion levels by a scanning electron microscope. In order to compare the reactivities of different samples, the char-gasification process was divided into two distinct stages: the first stage due to pyrolysis and the second stage due to char-CO sub 2 reaction. Reactivities due to the first stage can be roughly related to volatile matter contents of the solids and the rate of heating. Through an Arrhenius type equation, an activation energy of about 2.5 Kcal/mole is obtained for the first stage. The reactivity of a char in the second stage is found to depend more on its coal seam than on the gasification scheme used in its production. Activation energy for the second stage reaction has been found to be about 59 Kcal/mole. A rate equation has been proposed for the second stage that incorporates the effect of relative available pore surface area changing during reaction. The rate conversion curves calculated from this equation fit well with the experimental data.