The Study Of Simultaneous Water And Energy Minimization For Multiple-Contaminant System

Along with the rapid development of the global economy and the progress of the society, human have paid great price of material resources and environmental destruction. Due to the increasingly sharp contradiction between environment and development, governments around the world have put on the agenda the problem of energy crisis and environmental pollution. In the twelfth five-year-plan outline, the China government has proposed a project to build a resource-saving and environment-friendly society. Synthesis of mass exchange network (MEN) and heat exchange network (HEN) are two branches of process system engineering, which can distribute the use of resource and energy reasonably. Since 1990s, due to the waste and pollution of water resources, much more attention has been paid on water utilization network, which is a kind of special MEN. At present the design of water utilization network is comparatively mature and tends to the multiple-contaminant system water utilization network. But there is less study of simultaneously energy integration in water utilization network, which have complicated problem description and cumbersome solving process. Based on the research background, this thesis has, respectively, studied the stepwise design method and simultaneous design method of energy integration in the multiple-contaminant system water utilization network, and also considers the energy integration in water utilization network within extra heat-exchange system. The main research improvements are as follow:(1) The stepwise design method is used to deal with the energy integrated multiple-contaminant system in water utilization network. The nonlinear programming (NLP) mathematical models of water utilization network and HEN are established according to the mathematical programming approach. Firstly, the optimal water utilization network is obtained by minimizing the freshwater flow rate; secondly, the optimal HEN is obtained by its minimum total annual cost (TAC) and the way of heating is stage-wise, split-flow and non-isothermally mixed; and finally the lowest TAC of heat integrated water-using network is got through synthesizing these two optimal sub-networks. Two illustrations demonstrate the feasibility of this method.(2) Since the stepwise design method cannot realize reach the simultaneous minimi-zation of water and energy, further research is conducted on that problem. Mathematical programming method can simultaneously optimize and manage multiple objectives together. This thesis establishes the NLP mathematical models of the whole system whose objective function is the minimum total annual cost. Adaptive simulated annealing genetic algorithm is used to solve problems to receive global optimum. Comparing the simultaneous design method with the stepwise one, it is showed that the former is more accurate and effective.(3) The study of energy integrated multiple-contaminant system in water utilization network is not only in the internal system but also considering the external heat exchange system. According to the idea of simultaneous design method, the super structure including more heat exchange system is put forward and the NLP mathematical model of the whole system is established. By solving two instances, it is proved that the simultaneous design method can be used to resolve more complex problems.