Selective removal of chloride and potassium in kraft pulp mills

Chloride (Cl) and potassium (K) are nonprocess elements (NPEs) that can accumulate to high levels in highly closed pulp mills and cause serious problems, particularly in the recovery boiler operation. Based on data from two pulp mills, we collected the following information for Cl and K: the chemical composition of precipitator ash where these two NPEs are accumulated, input and output mass flow streams entering and leaving the process, and the corresponding enrichment factors. To identify the best process to minimize this accumulation, we evaluated direct purge, leaching, evaporation/crystallization, and ion-exchange techniques. Using one of the pulp mills as a reference, we performed computer simulations to study how the sticky temperature of the ashes varies with the amount treated. A preliminary economic analysis led to the conclusion that the leaching and the ion-exchange techniques were the more attractive alternatives for treating ash collected from the electrostatic precipitator.