Study on bromine release from bituminous coal during combustion

Modes of occurrence of Br in bituminous coal from China were extracted using sequential chemical extraction; coal combustion was simulated with a tube furnace, and the effects and mechanisms of combustion temperature, combustion time, O2 flow rate and water vapor access on the Br release from bituminous coal were investigated. The results showed that the Br release rate increased with the increase of temperature, and 500-900 °C was the main stage of Br release. The Br occurred as water-soluble, ion exchangeable and organic fraction may be completely emitted before 700 °C, bound to carbonate and Fe-Mn oxide may be mainly emitted in 700-900 °C, and occurred in residual fraction which cannot be extracted using sequential chemical extraction can be largely emitted during combustion. Moreover, the Br release rate in bituminous coal increased with the increase of combustion time and O2 flow rate, and more than 97% Br may be emitted at the given experimental condition of combustion temperature of 1000 °C, water vapor access, O2 flow rate of 90 mL min−1 and combustion time of 20 min. During combustion, the Br in bituminous coal was transformed into HBr and easily taken out of the furnace with the help of water vapor, which indicated water vapor can obviously promote the Br release. The additive of SiO2 can capture the Br effectively in the process of the coal combustion.