Numerical Modeling and Experimental Investigation on the Use of Brown Coal and Its Beneficiated Semicoke for Coal Blending Combustion in a 600 MWe Utility Furnace

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• 作者：Jian Zhang ; Qunying Wang ; Yajuan Wei ; Lian Zhang
• 刊名：Energy & Fuels
• 出版年：2015
• 出版时间：February 19, 2015
• 年：2015
• 卷：29
• 期：2
• 页码：1196-1209
• 全文大小：938K
• ISSN：1520-5029

文摘

In this paper, coal blending combustion performance in a 600 MW_e supercritical boiler has been investigated through a series of on-site measurements and computational fluid dynamic modellings. A bituminous coal was used as reference, which was blended with brown coal or brown coal semicoke in an indirect way, i.e., different coals being fed separately into the boiler without prior mixing in the mill. The coal blending combustion behavior was assessed upon varying brown coal injection location, brown coal blending ratio, air staging ratio, and the use of brown coal pyrolysis-derived semicoke. ANSYS FLUENT 15.0 was employed for numerical simulations. Upon a successful validation, the model was further used to predict the influence of individual variables. The main conclusions achieved include (1) the bituminous coal-designed mill can be used safely for brown coal, at the expense of an increased mass ratio of primary air to coal, a decreased temperature for the outlet of the mill, and an incomplete drying of brown coal. (2) The allocation of brown coal in the middle burner zone is the best option that ensures a relatively long residence time of bituminous coal particles in the boiler, as well as provides sufficient heat to bituminous coal particles for a quicker ignition and burnout. (3) The 50 wt % blending ratio for brown coal is optimum, striking a good balance between the feeding amounts of combustible hydrocarbons and inherent moisture into the burner. (4) The separate over fire air of 30% ratio is beneficial in reducing total NO_x emission through increasing the unburnt char quantity in the NO_x reduction zone. (5) The high heating value of beneficiated Victorian brown coal and its semicokes ensures a lower feeding rate for each of them to be used as a substitute fuel. The high volatile-O₂ and char-O₂ oxidation reactivity of these samples also ensured a strong heat provision from their flame to the bituminous coal allocated in both the bottom and top of the burner zones. (6) The use of brown coal and semicoke is in favor of the reduction in NO_x, particularly fuel-NO_x, due to the generally low nitrogen content within these samples, relative to bituminous coal.