Prediction of SO2 and NOx emissions for low-grade Turkish lignites in CFB combustors

The CFB technology is widely used for combustion of coal because of its unique ability to handle low quality, high ash, high sulphur and low heating value coals. This paper presents a modeling study of pollutant emissions such as sulphur dioxide (SO2) and nitric oxide (NOx) resulting from coal combustion in a CFBC. Using this model, overall SO2 and NOx emissions are predicted for the combustion of three different kinds of low-grade Turkish lignites. The contents of these lignites are as follows: ash from 23.70% to 45.31%, sulphur from 1.81% to 8.40% and calorific values (LHV) from 10,283 to 15,215 kJ/kg. The data is obtained from two pilot scale CFBCs (50 and 80 kW) and an industrial scale CFBC (160 MW). The present study proves that CFB combustion demonstrated by both experimental data and model predictions produces low and acceptable level of SO2 and NOx emissions resulting from the combustion of low-grade lignites. Developed model can also investigate the effects of different operational parameters on overall SO2 and NOx emissions. As a result of this investigation, it is observed that increase of excess air decreases SO2 and NOx emissions. However, NOx emission increases with the operational bed velocity while SO2 emission decreases. A bigger inlet bed pressure value results in lower emissions of SO2 and NOx if other parameters are kept unchanged.