COMBUSTION CHARACTERISTICS OF PULVERIZED COAL AND AIR/GAS PREMIXED FLAME IN A DOUBLE SWIRL COMBUSTOR

摘要

An experimental work was performed to investigate the co-firing of pulverized coal and premixed gaslair streams in a double swirl combustor. The results showed that the NOx emissions are affected by the relative rates of thermal NOx formation and destruction via the pyrolysis of the fuel-N species in high temperature fuel-rich zones. Various burner designs were tested in order to vary the temperature history and the residence time across both coal and gas flames inside the furnace. It was found that by injecting the coal with a gaslair mixture as a combined central jet surrounded by a swirled air stream, a double flame envelope develops with high temperature fuel-rich conditions in between the two reaction zones such that the pyrolysis reactions to N_2 are accelerated. A further reduction in the minimum NO_x emissions, as well as in the minimum CO concentrations, was reported for the case where the coal particles are fed with the gaslair mixture in the region between the two swirled air streams. On the other hand, allocating the gaslair mixture around the swirled air-coal combustion zone provides an earlier contact with air and retards the NO_x reduction mechanism in such a way that the elevated temperatures around the coal particles allow higher overall NO_x emissions. The downstream impingement of opposing air jets was found more efficient than the impinging of particle non-laden premixed flames for effective NO_x reduction. In both cases, there is an upstream flow from the stagnation region to the coal primary combustion region, but with the case of air impingement, the hot fuel-rich zone develops earlier. The optimum configuration was found by impinging all jets of air and coal-gaslair mixtures that pronounced minimum NOx and CO concentrations of 310 and 480ppm, respectively.