Gunaratnam, M., Alva-Argáez, A., Kokossis, A., Kim, J.-K., Smith, H.
Industrial and Engineering Chemistry Research, vol.44, no.3, p.588-599
An automated method for the design of total water systems is developed in this paper. This approach considers simultaneously the optimal distribution of water to satisfy process demands and optimal treatment of effluent streams. Treatment can be for discharge to the environment or for regeneration of wastewater. The cases of regeneration reuse and regeneration recycle can be distinguished in the approach. It combines engineering insights with mathematical programming tools based on a superstructure model that results in a mixed-integer nonlinear programming problem. The approach features a fast and robust solution strategy. Complex tradeoffs involving operating, as well as capital, costs and other practical constraints have been included. In particular, piping and sewer costs, which are a major element in the capital cost of such systems, can be included. Network complexity is controlled by specifying the minimum permissible flow rates in the network, the maximum number of streams allowed at mixing junctions, and the inclusion of piping costs in the problem formulation. In addition to being able to solve the problem of total water system design, the approach is capable of designing water-using systems and effluent treatment systems when considered individually. Case studies are used to demonstrate the method.