Release of alkali metal, sulphur, and chlorine species from high temperature gasification of high- and low-rank coals

The limitation of fossil fuel resources and the necessity of reducing CO2 emission require an increase of the efficiency of coal based power plants. The Integrated Gasification Combined Cycle (IGCC) is a potential concept to realise these objectives. In the IGCC a broad range of different coals can be used to produce a fuel gas for gas turbines or synthesis gas for chemical applications. The direct use of hot flue gas for driving a gas turbine requires a hot gas cleanup to achieve corrosion prevention of the turbine blades and prevention of catalysts from poisoning. Main problems are related to alkali metal, sulphur, and chlorine compounds released during the coal gasification process. High and low-rank coals differ in the amount, mode of occurrence and release mechanism of alkali metal, sulphur, and chlorine. Therefore, release experiments have been done with 8 different coals at 1400 °C, 1 atm and a gas stream with 7.5% O2 and 2.5% water steam. Differences of the release mechanisms of high and low-rank coals were identified. The modes of occurrence of several inorganic coal constituents were shown to have a remarkable effect on the release, e.g., the results could distinguish between organic and inorganic bound sulphur.

► Release mechanisms of Na-, K-, S-, and Cl-species were determined. ► Effect of the mode of occurrence of coal constituents on the release► Competitive reactions of S and Cl can influence the formation of NaCl. ► Ash-rich coals have a higher potential for the capture of Na. ► The use of coal blends with high ratio of Ca(carboxylic bound)/S is recommended.