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Question 27.2: A 32.5 percent solution of MgSO4 at 120°F (48.9°C) is cooled......

A 32.5 percent solution of MgSO_4 at 120°F (48.9°C) is cooled, without appreciable evaporation, to 70°F (21.1°C) in a batch water-cooled crystallizer. How much heat must be removed from the solution per ton of crystals?

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The initial solution is represented by the point on Fig. 27.4 at a concentration of 0.325 in the undersaturated-solution field on a 120°F isotherm. The enthalpy coordinate of this point is -33.0 Btu/lb. The point for the final magma lies on the 70°F isotherm in area cihb at concentration 0.325. The enthalpy coordinate of this point is – 78.4. Per hundred pounds of original solution the change in enthalpy of the solution is

100(33.0- 78.4) = -4540 Btu

This is a heat evolution of 4540 Btu/100 lb (1.06 × 10^5 J/kg).

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