INVESTIGATION OF THE CHARACTERISTICS OF A COAL BURNING RIJKE TYPE PULSATING COMBUSTOR

This study is concerned with the evaluation of the performance characteristics of a coal burning Rijke type pulsating combustor. The combustor consists of an open ended vertical tube with a coal burning bed located in the middle of its lower half. The liberation of heat by the combustion process at this location results in spontaneous excitation of the fundamental, longitudinal, acoustic mode of the tube and the acoustic oscillations lead to significant intensification of the combustion process. An 108 inch long 5.5 inch internal diameter combustor was constructed and instrumented for this investigation. The measurements performed during a series of experiments conducted at various air/fuel ratios and coal feed rates include: dB level of pulsations at the mid section of the combustor, frequency of oscillations, temperatures at different locations inside the combustor, mass emission rates of generated particulates, and CO, CO(,2), NO(,x), and SP(,2) concentrations in the exhaust products of the combustor. The study demonstrated that the developed pulsating combustor can burn coal stably and continuously under a variety of air/fuel ratios and that maximum amplitudes of acoustic pressure occur when operation is conducted near stoichiometric conditions. It was also verified that the presence of pulsations resulted in a very efficient and intense combustion process. The measured CO and CO(,2) concentrations were used to determine the combustion efficiencies of the combustor which were higher than 95% for operations conducted with 13% excess of air at feed rates located in the range 42 - 60 lb/ft('2) hr (52.5 - 75 gr/min). Maximum heat release rates of approximately 0.87 MBtu/ft('2) hr were obtained with the developed combustor, a value that compares very favorably with the characteristic heat release rates of state-of-the-art combustors.