Study On Optimal Design Of Single-impurity Water Network With Energy Integration

Effective utilization of water and energy is the key factor of sustainable development in process industries. Because the lack of water and the environment pollution become worse year after year, the study on water network brings the most persons. But few studies contain the energy integration. The paper carries out the study on water network with the mathematical programming method expecting to afford some theoretic direction of economizing on water and energy. In this paper, the researches have been done as follows:(1) The necessary optimality conditions of water utilization network in process plants with single contaminant are brought out, with the analysis of the water utilization network in process plants with single contaminant. These necessary conditions are used to simplify the NLP model featuring minimum fresh water targeting to LP model, which not only makes the problem easy to be solved but also saves the computing cost. The strict mathematical proofs for these conditions are carried out in this paper.(2) As to the multiple-objective optimization of water and energy in process industry, this article firstly uses the stepwise design method which departs the optimal problem into two stages. In stage one, the water pinch method or mathematical programming method is used to minimize the freshwater flowrate. In stage two, the energy integration is carried out under the minimum freshwater flowrate. The integration of energy can make the use of energy more rational.(3) Stepwise design method of minimum water and energy does not reach the simultaneous minimization of water and energy in reality. Mathematical programming method is a powerful tool to perform simultaneous design because it has the advantage of simultaneous optimization and dealing with multiple objectives together. As the research hot spot and difficult point, simultaneous design of optimization of water and energy is studied with mathematical programming method.(4) In the end, an example has been applied to the two methods discussed in this paper. What's more, the compare between the two results is carried out. The contrast of case study with stepwise design method indicates the simultaneous design method is efficient.