Optimization of mechanical draft counter flow wet-cooling towers using a rigorous model

In this paper, an optimal design algorithm for mechanical draft counter flow wet-cooling towers based on the rigorous Poppe model and mixed-integer nonlinear programming (MINLP) is presented. Unlike the widely used Merkel method, the Poppe model takes into consideration the effects of the water loss by evaporation and the nonunity of the Lewis factor. As a result, the Poppe model is able to predict the performance of wet-cooling towers very accurately compared to the Merkel method. The optimization problem is formulated as an MINLP model by considering all the mass and energy balances, equations for physical properties, and empirical correlations for the loss and overall mass transfer coefficients in the packing region of the tower, in addition to feasibility constraints. The objective function to be minimized is the total annual cost, which includes capital and operating costs. The mathematical programming problem is solved with the GAMS software. Six case studies are used to show the application of the proposed algorithm. The case studies demonstrate that there can be large differences between the optimal designs based on the Poppe method and the Merkel method.