Sheehan, M.E., and Donaldson, M. (2011) Validation and optimization of an equilibrium model of a hot-lime-softening treatment system. Journal of Environmental Engineering, 137 (3). pp. 205-212.

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Abstract

This paper describes the development and validation of an equilibrium model of an industrial hot-lime-softening boiler-water-treatment unit for a large-scale nickel processing facility in which approximately 6.6 ML per hour of water is processed. In the industrial process, multiple water sources of varying quality are combined before the softening treatment, which makes control and optimization of the softening unit complicated and has brought about the necessity of a robust numerical model of water treatment. In this paper, the numerical thermodynamic and adsorption relations describing the softening treatment process are presented. Lime, magnesia, and soda ash additions are modeled. Emphasis has been placed on calcium, magnesium, and silica treatments as these are of most relevance to the industry. Jar tests described in this paper are used to determine adsorption relations, estimate statistical uncertainties, validate the model performance, and optimize the model parameters. Parameter estimations for equilibrium constants are undertaken and provide insights into the range of model validity and interactions between additions and softened water quality. Further jar testing is utilized to evaluate the effectiveness of using the model to numerically derive optimal chemical additions.

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