Effects of Neutralization of Recovery Boiler Ash in Ash Leaching

摘要

Over the last five years, many Kraft mills have been equipped with systems for chloride (Cl) and potassium (K) removal from recovery boiler ash. The positive effects of removing these elements are reduced boiler corrosion, less boiler plugging and reduced dead load in the liquor cycle. Metso Power's solution for ash treatment is a leaching process. Today the company has eight Ash Leaching plants in operation. Plants that operate with ash of high carbonate (CO_3) content have shown lower efficiency in comparison with those that operate with lower CO_3 content. This finding has prompted development work with a view to removing the negative effects of high CO_3 content. The focus of this paper is the pH-control of the ash, where the results from one full-scale application of pH-control are presented. Said results show that properly exercised pH-control can eliminate the negative effects of high carbonate concentrations on solid/liquid separation.