Removal of K and Cl by leaching of straw char

A pretreatment process to remove potassium from straw fuel may be based on pyrolysis followed by char wash. The straw is pyrolysed at moderate tempera tures at which the potassium is retained in the char. Potassium and residua l chlorine are extracted from the residual char by water. Char and pyrolysi s gases may then be used in a conventional boiler without problems due to t he high straw potassium content. To evaluate this pretreatment process know ledge about the char wash process is needed. In this study wheat straw char s were experimentally investigated in the laboratory to determine the extra ction time of potassium and chlorine during char wash with water. The influ ence of particle size, water temperature, straw type, potassium content in water and pyrolysis conditions were investigated. Based on the experimental data a mathematical model describing the extraction, was developed. The la boratory experiments showed that three fractions of potassium in the straw reacted differently: 35-58% of the char potassium was dissolved very fast, followed by a secondary slow potassium release that was strongly influenced by particle sizes, water temperature, char type and water KCl content. The residual 5-10% of the char potassium remains in the char and could not be removed with pure water. (C) 2001 Elsevier Science Ltd. All rights reserved .