A Study of the Behavior of Chlorine and Sulfur from Coal During Combustion in an AFBC System

With the advent of increased usage of coal as an energy source, environmental considerations must be examined. The purpose of this study is to understand the emission behavior of chlorine and sulfur during combustion in an atmospheric fluidized bed combustion (AFBC) system. A two-phase investigation was carried out in order to evaluate combustion performance, the extent of hydrochloric acid formation during combustion, and the effect of combustion conditions (limestone addition) on chlorine and sulfur emission. Two 1,000-hour burns were conducted with the 12-inch (0.3 m) laboratory AFBC system at Western Kentucky University. Operating conditions similar to those used at the 160-MWe AFBC system at the Shawnee Steam Plant near Paducah, Kentucky were used. The first 1000-hour burn was done with a low-chlorine (0.012% CI and 3.0% S) Western Kentucky University # 9 coal. The second 1000-hour burn was done with a high-chlorine (0.28% CI and 2.4% S) Illinois # 6 coal. The behavior of chlorine and sulfur was studied by collection of samples of chloride and sulfate emissions from the combustion flue gases in a buffer solution and analyzed by ion chromatography (IC). The results indicated that the greater the increase in bed temperature, the higher the concentration of hydrogen chloride and sulfur dioxide emitted from the AFBC system. The higher contents of chlorine and sulfur in the coals also contribute to higher emissions. The limestone is effective in capturing the hydrogen chloride and sulfur dioxide emissions, especially at lower temperatures (optimal temperature at 1120 K). Sulfur dioxide emissions are more easily retained by limestone than by hydrogen chloride in our experimental conditions. There is no significant change in the emission of HC1 when the Ca/S ratio is varied. When the sulfur or chlorine content in coal reaches a certain point, the Ca/S ratio in the combustion mixture will be an important factor in the absorption of S02 and HC1