Meeting emission standards with high-sulfur coals

The economics of strategies for meeting sulfur oxides (SOx) emission standards from furnaces fueled with high-sulfur coals has been assessed based on published data. The strategy of SOx control depends on how the coal is utilized. For large power plants, flue-gas desulfurization (FGD) is preferable to conversion of coal to clean fuel. In comparison with coal conversion, the total capital and operating costs for FGD are almost an order of magnitude lower, thermal efficiencies are higher, and utility requirements are lower. Even with possible breakthroughs in coal-conversion technologies, it appears that FGD will remain the economically preferred route to desulfurization. FGD has been in commercial operation since 1968, and the reliability of the process has reached an acceptable level. For industrial furnaces, direct combustion is preferred to gasification because gasification is inherently expensive. Fluidized-bed combustion is the only viable option for clean direct combustion of coal in small industrial furnaces. Fluidized-bed combustion has reached commercial status and is economically competitive in many parts of the world. For furnaces requiring gaseous or liquid fuels, gasification to medium-Btu gas is preferred. For domestic and commercial uses, coal can be gasified to clean, low-Btu gas. This is an old process and might be amenable to cost reduction through application of new technologies. The only other economically viable approach involves the production of clean solid fuel by compounding coal with additives such as limestone and manganese nodules.