The potential for low NOx front a precessing jet burner of coal

The effectiveness of the Precessing Jet nozzle at yielding low NOx levels f rom burning coal was examined at the pilot scale. Thus, a coal burner of no minal thermal load of 138 kW was sampled two dimensionally, and subsequentl y modeled. The one-dimensional, steady-state, semiempirical mathematical mo del considered the release and combustion of volatiles, and subsequent oxid ation of char 'A comprehensive reaction scheme was formulated to account fo r the oxidation of the resulting CO, the formation of NO from various sourc es (volatile, char, preheated air) and the oxidation of H2S to SO2 The agre ement between the experimental and predicted profiles of coal burnout, [O-2 ], [NO] and gas temperature was not good near the burner; however, the agre ement improved in the postflame region. The model was also used to simulate the center line characteristics of the same flame, but with the secondary air preheated to 500 degreesC. This flame was then scaled for constant velo city and constant residence time to 20 MW. It was deduced that constant res idence-time scaling predicts ignition and combustion of the coal at the sam e axial location as the baseline flame. However, constant velocity scaling shifts combustion closer to the burner. Constant-velocity scaling was found to be more suitable for the theoretical scaling of pulverized coal flames. It was not possible to comment on the potential of the burner for low NOx in cement kilns, because the measured and computed gas temperatures were lo w. However, the model predicted low concentrations of fuel NOx. (C) 2001 by The Combustion Institute.