Burning Rates of Lignite Particles at Low Furnace Temperatures
Titel:
Burning Rates of Lignite Particles at Low Furnace Temperatures
Auteur:
Macek, Andrej Charagundla, S. Rao
Verschenen in:
Combustion science and technology
Paginering:
Jaargang 49 (1986) nr. 3-4 pagina's 205-212
Jaar:
1986-10-01
Inhoud:
Experimental burning times of particles were obtained for a sample of a Type A lignite, screened between 88 and 105 im, in a laboratory furnace with essentially cold walls at a constant gas temperature of U50±20 K. The mass fraction of oxygen in the furnace, X,, ranged from about 0.20, below which no combustion was observed, to 0.46. Over most of this range, the combustion of particles was essentially complete. The measured burning times were short (30 to 50 msec) and are shown to be inversely proportional to the gas phase mass transfer rates, suggesting diffusion-controlled kinetics. There is only a narrow range, 0.20 < Xg < 0.23, in which the burning times were clearly higher, indicating an intermediate regime. It was also observed that, in this narrow range, the particles tended to extinguish before complete combustion. Thus, it appears that, as X, was progressively decreased, there was unusually rapid transition from the diffusion-controlled regime to extinction at relatively high values of X". It is reasonable to ascribe this behavior to unusually high heat losses in these low-temperature experiments. Burning times calculated on the assumption of diffusion control are shown to agree roughly with the experiment at very high X" values. In addition, a set of equations is formulated, including both Stefan flow and chemical kinetics. The equations allow semi-quantitative heat balance estimates which, at the low gas temperature of the present experiments, confirm the occurrence of extinction at substantial values of Xg.
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