Application of coal gasification technology as a flue gas pre-conditioning step for the catalytic reduction of acid gases

Abstract

Typical flue gas contains an excess amount of oxygen, which can deactivate the reduction catalyst for NO X and SO 2, such as the lanthanum oxysulfide-based catalyst. The reductant available in a flue gas stream rich in oxygen is usually scarce and not sufficient for the reduction. Coal gasification was applied to pre-condition the flue gas to remove the excessive oxygen and co-generate carbon monoxide for the reduction of NO X and SO 2 in this study. Coal was carbonized to porous semi-coke to prevent clogging caused by the condensation of volatiles before being gasified. The reactivity of the semi-coke with simulated flue gas was found to be the same as activated carbon. The semi-coke samples prepared from various coal sources proved to be effective in removing O 2 (over 90%) from the flue gas and a sufficient amount of CO was co-generated for the conversion of NO and SO 2 over a supported lanthanum oxysulfide catalyst in a subsequent reduction reactor. NO and SO 2 in the flue gas were also reduced in the gasification process, contributing to the overall denitrification and desulfurization efficiency. An overall NO and SO 2 removal efficiency of over 96% was achieved for a sequential coal gasification and catalytic reduction process, and the selectivity to elemental sulfur was as high as 98%.