Prediction of the Solubility of Recovery Boiler Precipitator Ash, 2007 Engineering, Pulping & Environmental Conference

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The solubility of recovery boiler precipitator ash in water is an important parameter in the design and operation of ash treatment systems used to control chloride (Cl) and potassium (K) accumulation in the kraft recovery cycle. A study was conducted to determine the solubilities of mixtures of alkali salts that constitute precipitator ash and several precipitator ash samples, through laboratory experiments and through theoretical simulation using a thermodynamic program, OLI. The results show that the solubility of precipitator ash in water at 85oC varies widely, from 400 to 550 g/L H2O, depending on ash composition. The composition of the liquid portion of an ash-water slurry changes significantly with an increase in ash concentration in the slurry: the Cl concentration increases, the sulphate (SO4) concentration decreases, while the K and carbonate (CO3) concentration remain the same. Between 30 and 100ºC, temperature has little effect on the solubility of precipitator ash and on the composition of the liquid portion of the slurry.