Utilization of a High-Alkali Lignite Coal Ash for SO2 Capture in Power Generation

Abstract

This work explored the use of ashes of a low-sulfur, high-alkali lignite coal for partially capturing the sulfur dioxide emissions from combustion of a high-sulfur bituminous coal. The bituminous coal was mixed with the lignite ashes and then burned in a laboratory drop-tube furnace (DTF) externally heated to 1,400 K. The gas-phase emissions in the combustion effluents of the neat bituminous coal were monitored and compared with those of the bituminous coal mixed either with the lignite ashes or with other additive compounds, such as a specially prepared sorbent from the ash of the lignite coal or with calcium oxide (CaO). All experiments were executed at a molar Ca:S=0.3 in air, under fuel-lean conditions. Coal particles were in the size range of 75–90 μm. Results showed that the addition of lignite ashes caused substantial reductions, by up to 21% in the SO2 emissions of the bituminous coal. Such reduction was akin to that caused by burning the coal mixed with the CaO sorbent. Significant reduction in NOx emission was also attained. This observation, in conjunction with ash analysis, showed that the alkali-rich ashes of the lignite coal acted as sulfur sorbents for the abundant SO2 emissions of the bituminous coal.