Release behaviors of sulfur-containing pollutants during combustion and gasification of coals by TG-MS

Abstract

Sulfur-containing pollutants are released during coal thermal conversion processes and must be controlled to satisfy the requirements of industrial production and protect the environments. This study investigated the release behaviors of sulfur species in Zhundong (ZD) coal during combustion and gasification. H2O-washed ZD coal and Shenmu (SM) coal were also investigated as reference samples to compare with ZD coal and to obtain general release properties. The experiments were carried out using online thermogravimetric analysis coupled with mass spectrometry. Theoretical calculation of the released gas was obtained by a novel method and equivalent characteristic spectrum analysis. The mass flow rate, the release proportion and the release temperature range of individual sulfur-containing pollutant were evaluated. The results show that water washing process did not change the combustion reactivity and the sulfur release temperature ranges of ZD coal, but the maximum gasification rate and the SO2 release rate were decreased. H2S, COS and SO2 were observed in gasification of the coals, while COS and SO2 were observed in combustion. SO2 was always the main sulfur-containing gaseous product in both combustion and gasification. Some sulfur starts to release as SO2 at high temperature (at about 1000 °C for ZD coal and H2O-washed ZD coal, and at about 1100 °C for SM coal) due to the decomposition of sulfate, at which temperature carbon had already burned out in combustion, and the coal conversion in gasification reached about 90%. With combustion temperature lower than 1000 °C, the release of SO2 from ZD coal, H2O-washed ZD coal and SM coal can be decreased by 46.14%, 38.95% and 4.36%, respectively. With gasification temperature lower than 1000 °C, few SO2 from ZD coal and H2O-washed ZD coal and SM coal can be released. It was observed that the releases of sulfur species were related to their occurrence, reaction evolution, temperature and atmosphere. Controlling the temperature is helpful in reducing the release of SO2 in both combustion and gasification. This work also shows that it is possible to achieve high carbon conversion of ZD coal gasification at a moderate temperature and simultaneously reduce the release of sulfur.