Coal combustion: Effect of process conditions on char reactivity. Sixth quarterly technical report, December 1, 1992--March 1, 1993

摘要

During the past quarter, we developed the image analysis procedure for obtaining the transient swelling patterns of pyrolyzing coal particles. Pyrolysis experiments were videotaped and a sequence of digital images was acquired from each experiment tape at rates of 1.5 to 6 images per second. These digital images were then processed to measure the size and shape of pyrolyzing particles as a function of pyrolysis temperature. A systematic analysis of the transient swelling patterns showed significant differences among runs carried out at different heating rates. At low heating rates (1(degree)C/s), the particles swelled rapidly to their maximum size. This initial swelling was followed by a ''bubbling'' phase during which the particles underwent a rapid sequence of expansions and contractions as bubbles of volatiles grew in the particle interior and broke through their surface. The particle size then decreased to show a small final swelling. At higher heating rates, the particle size decreased significantly during the ''bubbling'' phase and the final swelling was higher. A systematic comparison of particle swelling and devolatilization rates is also presented.