CRITICAL ISSUES IN SMELT DISSOLVING TANK OPERATION, 2010 TAPPI/PAPTAC International Chemical Recovery Conference

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Effective smelt dissolution is critical for control and optimization of subsequent processes in the kraft recovery cycle. Smelt dissolution can be violent and constitutes a potential safety hazard. This paper focuses on dissolving tank performance during periods of heavy smelt runoff when safety issues are paramount, and outlines the key pieces of information required for a scientific attack on the problem. There is a fundamental need for good solubility data on green liquor components including the role played by calcium in smelt and weak wash in pirssonite precipitation and scaling. It is necessary to characterize the magnitude of potential smelt flow variations out of spouts as a function of smelt depth in the trough and spout geometry, as well as smelt viscosity. The interaction between the shatter jets and the smelt stream needs to be characterized as a function of jet characteristics, smelt flow and properties, and the interaction geometry. Unsteady state dissolving tank material and energy balances tying together smelt flow variations with density (TTA) variations, make-up water (weak wash) flow requirements and green liquor level provide perspective on how green liquor density varies during unstable smelt flow or high runoff conditions. Information is also needed on the rate of dissolution of smelt droplets into green liquor as a function of droplet size, green liquor concentration and degree of agitation