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 °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 K 2 SO 4 with the coal clay minerals. At lower temperatures and high straw share, available straw potassium and calcium capture some coal sulfur.

Straw and other biomasses can cause severe problems when used as fuel in combustion systems. Some of the major problems include high emission of alkalis, HCl, and especially SO 2 to the gas phase. The development of low-cost primary measures for achieving a SO 2 emission below the European Union (EU) emission limit of 200 mg/Nm 3 without the need for the installation of a flue gas desulfurization unit requires an increased understanding of the chemistry of biomass combustion. For this reason, laboratory combustion experiments with two different high alkaline (HIAL) biomasses doped with additives have been conducted in the temperature range of 800-1100°C. The use of a high-pressure mass spectrometry (HPMS) sampling technique allows the on-line specification of combustion byproducts such as K, Na, S, and Cl species in the combustion flue gases. The results of the measurements show that the SO 2 emission may be related to the K/S and K/Si ratios in the initial samples. The release of potassium is mostly dependent on the chlorine content of the samples. Calcium-and potassium-based additives are able to reduce the release of SO 2 into the gas phase.