Behavior of fluorine in the combustion of Chinese coal in small furnaces

Research into fluoride emissions from coal-combustion systems is becoming increasingly important as the issue of fluoride pollution in China becomes more serious. In some rural areas in China, indoor fluoride pollution has particularly been caused by the use of high fluorine content coal in stoves. As a result, many residents suffer from dental fluorosis and bone fluorosis. In this study, X-ray diffraction (XRD) analysis was carried out to confirm the mode by which inorganic fluorides exist in such coals. Analytical results showed that inorganic fluorides in Chinese coals exist mainly as muscovite and apatite. The fluorine concentration in gases emitted from a boat in a quartz tube furnace was measured during combustion of volatile matter and char. The times for volatile matter and char combustions were determined through continuous monitoring of SO2. Experimental results under different combustion conditions showed that fluoride in the emitted gas increased with an increase in oxygen concentration and temperature, while fluoride in the residue decreased with the increase in oxygen concentration and temperature.