A Comparison of Particle Size Distribution, Composition, and Combustion Efficiency as a Function of Coal Composition

Wednesday, November 10, 2010: 2:36 PM
Grand Ballroom J (Marriott Downtown)
William J. Morris, Dunxi Yu and Jost O. L. Wendt, Department of Chemical Engineering, University of Utah, Salt Lake City, UT

The need to understand the effects of fuel on utility boiler efficiency and emissions is critical to optimize efficiency and reduce emissions in the current conventional air fired utility boilers. Stringent sulfur emissions regulations have resulted in the widespread use of Powder River Basin coal, which is low in cost and sulfur while being abundant in supply. Powder River Basin (PRB) coal is now the most widely used coal in the United States and is increasingly fired in existing power plants to reduced targeted emission products such as SO2. However, PRB's unique properties also can create problems with emissions equipment, boiler tube slagging, and temperature profiles in furnaces that have fired other coals in the past. This paper examines two coals, PRB and a high sulfur Illinois bituminous coal, in a down fired furnace to determine the effects of coal composition on ignition loss, particle size distribution, soot formation, and particle chemical composition. Both coals were fired at a rate of 36.6 kW while the particle size distribution was measured in the ultrafine region of 15-660nm by SMPS simultaneously with an APS covering 0.518-20Ám. At the same time, photoacoustic measurements were made to determine the mass of soot or black carbon aerosols that were produced. Black carbon particles have been shown to be important for radiative heat transfer in the furnace and atmosphere as well as having significant health effects. In addition, loss on ignition measurements were performed to determine combustion efficiency. Samples were collected at four stoichiometric ratios ranging from 1 to 1.17 in order to determine the optimum operating parameters. Finally, size segregated sub micron samples were collected using a low pressure impactor with 3% O2 in the flue gas to be analyzed by ICP-MS.

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