EVOLUTION AND YIELD OF PRODUCTS FROM COALS UNDER RAPID PYROLYSIS CONDITIONS

This study was designed to determine the effects of temperature and particle size on coal pyrolysis. Seven coals were studied. Coal samples with a geometric mean particle size of 40(mu)m were pyrolyzed at 673 K, 873 K and 1073 K. Three coals had additional samples prepared with geometric mean particle sizes of 193(mu)m and 545(mu)m. These coals were pyrolyzed at 873 K. The rank of the coals covered the range of subbituminous B to semi-anthracite.; An apparatus was designed to provide rapid heating of small aliquots of the prepared samples. Heating rates of particle's surface were calculated to be greater than 1000 K/sec. Sample weight changes were determined using an ash tracer technique. The evolution of methane, ethane and carbon dioxide was monitored with a mass spectrometer. The mass spectrometer was computerized to provide rapid data acquisition.; The evolution in time and yield of the products were recorded. The weight loss of samples under rapid heating conditions is greater than that determined by the standard ASTM tests. The yield of methane increases as temperature increases. The rate of methane evolution increases as temperature increases. The yield of ethane decreases in temperature. The rate of evolution of ethane does not increase with temperature for any conditions or coals. The yield of carbon dioxide remains constant as temperature increases, its rate of evolution behaves much like ethane. Weight loss decreases as final particle size increases.; Coal pyrolysis may be chemically or physically controlled. The controlling pyrolysis mechanism is a function of final temperature, particle size and the chemical and structural nature of the particular coal. Changing particle size may change the controlling mechanism during pyrolysis. Particle heating, molecular desorption, thermal decomposition, phase change, swelling, diffusion, and cracking occur during coal pyrolysis.; The rate of evolution of methane, ethane and carbon dioxide can often be described by a single first order reaction at a given temperature. The rates of evolution do not always increase with temperature. The yields of methane and ethane are not independent of temperature. Therefore, the evolution of methane, ethane and carbon dioxide in the temperature range of 673 to 1073 K cannot be described by single first order reactions with Arrhenius rate constants.