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Selective removal of chloride and potassium in kraft pulp mills.

Application: Mills can use the information from this research to help address boiler plugging problems caused by high levels of chloride and potassium.


Chloride (Cl) and potassium (K) are two 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 chloride and potassium: the chemical composition of precipitator ash where these two NPEs accumulate, input and output mass flow streams entering and leaving the process, and the corresponding enrichment factors (EF). Wood chips are the major input sources for Cl and K (80%-85 % of the total input). The enrichment factor values we found are: EF = 2.3 for Cl and EF = 1.6 for K.

To investigate the best process for minimizing this accumulation, we evaluated direct purge, leaching, evaporation/crystallization, and ion-exchange techniques. Using one of the pulp mills as a reference, we performed model computer simulations to study how the sticky temperature of the ashes varies with the amount treated. We also prepared a preliminary economic analysis, which indicated that leaching and ion-exchange were the more attractive alternatives for treating ash collected from the electrostatic precipitator. S!

Ferreira, Soares, Egas, and Castro are with the Department of Chemical Engineering, University of Coimbra, Polo II, Pinhal de Marrocos, 3030-290 Coimbra, Portugal; email Ferreira at
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Title Annotation:Nonprocess Elements
Author:Castro, Jose Almiro A.M.
Publication:Solutions - for People, Processes and Paper
Date:Apr 1, 2003
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