Catalytic reduction of SO2 during combustion of typical Chinese coals

The catalytic effects of doping agents on SO2 emission as well as the coal combustion behavior were investigated by thermogravimetry. All experiments were carried out in a flowing air atmosphere at a heating rate of 20 or 30 degreesC/min up to 1000 degreesC. The doping agents employed were NaCl, CaCl2, FeCl3, FeCl2 and Fe2O3. The experimental results show that the agents added in coal reduce SO2 emission of coal, with CaCl2 being the most effective. The doping agents work with different mechanisms. The catalysis of NaCl, CaCl2, and Fe2O3 promotes the reactions between SO2 and the minerals in coal, and enhances the sulfur retention capacity of coal ash, thus decreasing SO2 concentration in flue gas. They have weak effects on the combustion behavior of the coal. FeCl3 and FeCl2 have strong effects on coal combustion behaviour. They accelerate the combustion and improve the ignition of the char subsequently formed, increasing SO2 concentration in flue gas in the region from 300 to 520 degreesC. However, they reduce the total amount of SO2 emission during combustion. The reduction of SO2 yield by FeCl3 and FeCl2 mainly results from the Fe2O3 created from them at high temperatures. (C) 2002 Elsevier Science B.V. All rights reserved.