Time-resolved weight loss kinetics for the rapid devolatilization of a bituminous coal

Abstract

The weight loss kinetics for the rapid devolatilization of a bituminous coal were measured over broad ranges of temperature (to 1000 C) and heating rate (10 2 to 10 4 K/s) in vacuum. The reaction period was resolved in 0.1 s time increments with rapid quenching. In addition, the effects of pressure (13.3 Pa–10 MPa) and particle size (50, 85, and 125 μm) were studied. We found that the rate of generation of volatiles increases slowly with temperature andis relatively insensitive to pressure changes. However, the heating rate does affect the devolatilization rate and the total yield. Below 600 C, two stages of product evolution were observed, one with and the other without coliberation of tarry liquids. At higher temperatures these two stages coalesced. Although the concept of simultaneous, parallel reactions can account for the low apparentactivation energy of the first stage of the devolatilization process, a multiple reaction model with a Gaussian activation energy distribution does not adequately describe the total time-temperature history. In addition, extant models with competitive rate processes to describe the redeposition of volatiles and their escape from the particle seem incompatible with the effects of particle size and heating rate observed in vacuum.