Effect of recycle on fluidized-bed combustion and emission characteristics of high-sulfur lignite

The effect of recycle on gaseous pollutant emissions from fluidized-bed combustion of high-quality coals has extensively been investigated and is well documented. However, the effect of recycle on gaseous emissions from combustion of Turkish lignites with high ash, volatile matter, and sulfur contents has not been investigated to date. Recent trends in the utilization of indigenous lignites in fluidized-bed boilers necessitated investigation of pollutant emissions and adaptation of fluidized-bed combustion technology to these lignites. In this study, experimental results of various runs pertaining to gaseous emissions from the Middle East Technical University 0.3 MWt atmospheric bubbling fluidized-bed combustor test rig burning a typical indigenous lignite, Beypazari, at various recycle ratios, with and without limestone addition, are presented. Measurements show that the effect of recycle on already high combustion efficiency in once-through operation is not pronounced. As for the gaseous emissions, introduction of recycle reduces NOx and SO2 emissions but enhances CO emission.