Influence of experimental protocol on activation energy in char gasification: the effect of thermal annealing

We report on the influence of experimental protocol on activation energy for the gasification of coal chars under kinetically controlled conditions. In experiments performed according to protocol 1, each char prepared at a given pyrolysis temperature is subjected to gasification at temperatures lower than during pyrolysis. In experiments following protocol 2, chars are pyrolyzed at different temperatures and the resulting chars are gasified at the same temperatures as during pyrolysis. We show that a lower activation energy for gasification can be expected when employing protocol 2, due to the influence of annealing effects that tend to reduce the sensitivity of char reactivity to temperature changes during the reaction with the gasifying agent. The analysis shows that the influence of annealing must be taken into account when interpreting the activation energies of gasification reactions undertaken at temperatures comparable to those of the previous pyrolysis stage or under conditions where the char may anneal still further during gasification.