Optimal water-using network with the simplest structure

Up to now, the researches on water-using network synthesis have been focused mainly on minimizing the freshwater consumption, ignoring the fact that there are many kinds of networks structures with the same minimum freshwater consumption for a given water system. In order to reduce the total cost of the network, the network with the simplest structure should be chosen from those networks with the same minimum freshwater consumption. In this paper, the conception of connection number is used to express the complex degree of a network. The connection number counts in the total number of connections between processes, between freshwater and processes, and between processes and wastewater discharged, so it is related to the capital cost of the network. Base on the established superstructure of water allocation network, the optimization model for water-using network is established. The model consists of two steps. Firstly, the freshwater consumption is used as the objective function of the optimization, and secondly, the minimum freshwater consumption obtained in the first step is used as a constraint, and the connection number is used as the objective function of the optimization. The model proposed can be used for the water utilization systems with multiple contaminants. The network determined by using the model proposed has the features of minimum freshwater consumption and simplest network structure, and so the network determined would have good economic characteristics. Finally, the advantage and effectiveness of the optimizing method proposed were fully expressed via two practical examples.