Energy and environmental research emphasizing low-rank coal -- Task 5.1, Stability issues

摘要

Low-sulfur subbituminous and lignite coals have high moisture content and, consequently, low heating value, leading to boiler derating in US midwestern and eastern utilities as well as switching and/or blending coals to achieve SO(sub 2) compliance. In the drive to develop cost-effective coal-drying processes, coal developers have focused on heat content of the products and generally neglected the critical stability issues of friability and dusting, moisture reabsorption, and spontaneous heating. The Energy and Environmental Research Center (EERC), in an effort to establish new standards for dried products, has used established methods and has developed new ones to evaluate the propensity of lump western coals, raw and dried, to produce dust and absorb water. Three drying methods--air, hydrothermal, and saturated steam--were used to generate low-moisture upgraded products. New indices for dust generation and friability were determined to assess the effects of moisture removal and upgrading methodology on coal stability. Analysis of the dried coals using various strength tests indicated that the reduction in moisture made the lump coal unstable, yielding substantially higher dust and friability indices relative to those of the raw coals.