Study of pyrite transformation during coal samples heated in CO2 atmosphere

Abstract

Pyrite transformation in two coals heated in CO2 was investigated. It was found that the pyrite experienced two visibility DTG peaks at temperature above 840 °C in CO2. It may be due to the pyrite decomposed products further reacting with CO2 to form iron oxides, sulfur oxide and CO as temperature increased. There are two main parts during the coal-pyrite blends heated to 1300 °C in CO2, which are the main pyrolysis part and the main gasification part, respectively. It shown that the coal decomposition processes did influence the pyrite transformation behaviors. During the main pyrolysis part, two DTG peaks were significantly observed related to the devolatilization of acid-washed coal and the pyrite pyrolysis desulfurization, respectively. The pyrite in coal-pyrite blends decomposed at lower temperature than the pure pyrite. The decomposition temperature of pyrite in coal-pyrite blends are decreased as the pyrite content in blends decreased in the main pyrolysis part. The flue gas analysis shows that, H2S is the main sulfur-containing gaseous product in the main pyrolysis part, SO2 and CO are the major gas products in the main gasification part of the coal-pyrite blends. During the main gasification process, the SO2 and CO release peaks move to high temperature zone as the pyrite content decreased. The ashes from the fix-bed reactor were also analyzed. It was shown that the iron oxide (magnetite) may be formed at temperature as low as 600 °C in the coal-pyrite blends. At higher temperature (main gasification part), it suggested the pyrite in coal-pyrite blends may be transformed together with char gasification and the co-transformation temperature is different with the coal type.