EFFECTIVE DIFFUSIVITIES IN CHAR PARTICLES (DIFFUSION, FAST FOURIER TRANSFORM, PYROLYSIS, COAL, FLUIDIZED BED)
MOUDGALYA, KANNAN MANI
Doctor of Philosophy thesis
Illinois #6, Illinois #5, Pittsburgh #8 coal and Texas Lignite particles of size range 150-16 mesh were pyrolyzed at a heating rate of 3.8 K/min up to 900(DEGREES)C. A stainless steel annular fluidized bed reactor yielded unagglomerated char particles. On-line analysis of the low molecular weight gaseous effluents was performed using a Series-Bypass column arrangement. The effluent profiles were in agreement with previous results. The char particles were gasified with oxygen in the annular fluidized bed reactor and with CO(,2) in a U tube spouted bed reactor. In both cases, the on-line analysis of the effluent gases helped determine the conversion of char. The transient pulse chromatography method was chosen to measure the macro pore effective diffusivities in Illinois #6 and Texas Lignite char particles reacted with oxygen. For a known pulse of helium into a Single Pellet String Reactor packed with char particles, the output chromatogram was measured as discrete data. Using the Kubin-Kucera model, the output profile was predicted also in discrete form in the Fourier domain. The residuals, the (,2) norms of the differences between the model predictions and the experimental observations, were minimized to extract the model parameters. The COMPLEX optimization procedure and an intelligent search scheme were used for this purpose. This is the first time the Discrete and Fast Fourier Transform techniques have been used to extract the model parameters. The intelligent search scheme is another novelty of this work. The diffusivities increased linearly with porosity for the reacted Illinois #6 and Texas lignite char. The tortuosity factor was found to be about 75 for the reacted Illinois #6 char and about 175 for Texas Lignite char. It was not possible to determine the diffusivity values for the unreacted Illinois char.