Straw quality for its combustion in a straw-fired power plant

ENERGÍA HIDROELÉCTRICA DE NAVARRA, S.A. (Navarra, Spain) is erecting a 25 MW power generation plant using straw for electricity generation. Cereal straws have proved to be difficult to burn in most existing combustion systems. During the last two years, a study has been carried out in Navarra to investigate the possibilities of improving the fuel quality of straw by a reduction in its K+ and Cl− contents. The simple leaching of K+ and Cl− with water by exposure to natural rainfall in the field resulted in considerable reductions of these two elements. A reduction in the K+ content of the cereal plants caused by exposure to natural rainfall has been observed during plant ripening (before crop harvesting). Some varieties of straw show lower initial K+ contents, making them more suitable for this purpose. There seems to be no clear correlation between the relative decrease in K+ content and the amount of accumulated rainfall. Our results have also shown a very close correlation between K+ content and electrical conductivity. The simplicity of this latter measurement makes this parameter a very interesting option to test the straw quality directly in the field. Structural components of the straw were not decomposed during the time when we left the straw in the field. Finally, the Cl− content in straw was increased when the Cl− dose from the fertilizer was increased. On the other hand, the content of K+ was not influenced by the applied amount of K+ fertilizer.