Release of K-, Cl- und S-Species during Co-Combustion of Coal and Straw

Straw as a renewable energy source can either be used alone or be used in existing coal-fired power plants (co-combustion). The objective of the present work was to investigate the influence of fuel composition and interactions between various types of straw and coal on the release of K, Cl, and S species during co-combustion of coal and straw at temperatures between 800 and 1100 degrees C. The amount of HCl released during co-combustion was higher than expected on the basis of the combustion results of the pure fuels because of the reaction of the straw KCl with the coal silica. However, the amount of potassium released in gaseous form is only slightly lower than expected. The relative amount of sulfur released during co-combustion in comparison to the expected amount depends upon the temperature and the biomass share of the blends. At higher temperatures or lower straw share, the release is increased because of the reaction of the straw K2SO4 with the coal clay minerals. At lower temperatures and high straw share, available straw potassium and calcium capture some coal sulfur