Operational cost minimization in cooling water systems

In this work, an optimization model that considers thermal and hydraulic in teractions is developed for a cooling water system. It is a closed loop con sisting of a cooling tower unit, circulation pump, blower and heat exchange r-pipe network. Aside from process disturbances, climatic fluctuations are considered. Model constraints include relations concerning tower performanc e, air flowrate requirement, make-up flowrate, circulating pump performance , heat load in each cooler, pressure drop constraints and climatic conditio ns. The objective function is operating cost minimization. Optimization var iables are air flowrate, forced water withdrawal upstream the tower, and va lve adjustment in each branch. It is found that the most significant operat ing cost is related to electricity. However, for cooled water temperatures lower than a specific target, there must be a forced withdrawal of circulat ing water and further makeup to enhance the cooling tower capacity. Additio nally, the system is optimized along the months. The results corroborate th e fact that the most important variable on cooling tower performance is not the air temperature itself but its humidity.