CFB combustion of low-grade lignites: Operating stability and emissions

This work presents the results of a comprehensive experimental investigation on the combustion of the low grade Turkish lignites in a 30 kWth circulating fluidized bed combustor. This is the first study of this kind has ever been undertaken on these coals. Eighteen lignite samples procured from various lignite sites of Turkey have been burned under similar combustion conditions in order to access to their combustion stability and to determine the emissions of the major pollutants such as CO, NOX and SO2 in the flue gas from combustor. The qualities of lignites were evaluated based on van Krevelen graph which was highly scattered and diverse in respect to the degree of ageing. A steady and stable combustion was observed in the temperature range of 725–950 °C with an average operating temperature of around 850 ± 50 °C for all lignites. Under the operating condition applied in the study, CO, NOX and SO2 emissions varied mostly in the ranges of 120–600 mg/Nm3, 90–420 mg/Nm3 and 1100 mg/Nm3 - 18000 mg/Nm3, respectively. From the experimental results it seems that the most challenging problem may be faced during the CFB combustion of most of these lignites will be SO2 emissions.