Kinetics of CO2/Char gasification at elevated temperatures: Part I: Experimental results

The gasification kinetics of char has so far been mainly studied based on data measured at low temperatures and low heating rates with a thermo-gravimetric analyzer. The results cannot be directly applied to high temperature gasifiers such as entrained flow gasifiers. In this work, gasification of seven types of chars in CO2 at elevated temperatures and high heating rates was investigated with a uniquely made fluidized bed. It was found that the reaction rates for various chars were very different in low and high temperature ranges, and two orders of magnitude more pronounced in the lower temperature range. From 1273 K to 1673 K, all chars demonstrated a strong tendency to increase reaction rate with temperature. However, at a high temperature range (1773 to 1873 K), different chars demonstrated different temperature dependences. The seven types of chars studied can be roughly separated into three groups based on ash fusion temperature. Each group demonstrated a different temperature dependence at a high temperature range. For chars with low ash fusion temperatures, the reaction rate leveled off, or even decreased a little as temperature increased, which was presumed to be because of the ash fusion at elevated temperatures. These results suggest that a high temperature does not necessarily raise the gasification rate.