Catalytic purification of tarry fuel gas with carbonate rocks and ferrous materials

This study compared the capability of various low-cost materials to catalyse the decomposition of tarry constituents in fuel gas. Carbonate rocks (dolomite, limestone) and ferrous materials (iron sinter, pellet) were tested in a tube reactor. Sample gas flow from a peat-fired gasifier was used as feed. An increase in the treatment temperature and extension of the residence time decreased the tar content. With carbonate rocks almost complete tar decomposition was accomplished at 900 °C. The ferrous materials were not as effective, but the content of the most problematic tar fraction decreased significantly. The thermal value of dry gas increased, due to the increase of H₂ and CO contents by catalytic water-gas and water-gas shift reactions. The activity of the carbonate rocks increased with a greater CaMg ratio and smaller grain size of the original rock. Activity was also increased by the presence of iron in the carbonate rocks and by the mineral matter in the ferrous materials.