Heat exchanger fouling parameters have been estimated with data from a CaCl2 concentration plant. The data consisted merely of periodic measurements of the product and steam flow rates during a production cycle of a couple of weeks. The first principle model incorporates a thermodynamic description of the vapour/liquid/solid equilibria and important heat transfer losses relevant for an industrial evaporator system. Although an excellent fit is obtained, the results are not satisfactory as the estimated scale growth rates have large confidence regions. Using simulations we identified the pressure in the first and second effect as optimal additional measurements to decrease the parameter uncertainty, With these measurements it is possible to gain insight into the extent to which each heat exchanger is fouled, and also to discriminate between different fouling models.