Study On Multiple-property Integration Of Water-using Network Based On Superstructure Approach

As an inevitable resource for all the lives on our planet, water plays such an essential role that water shortage will seriously threaten our human being's sustainable development. Water shortage does not only connect to resource shortage itself, but human activities aggravated water pollution seriously. With an increasingly strict law about preventing water pollution in China, the industrial water regulation, especially on the after-treatment has been constantly improved. Thus, process industries should pay special attention to water saving and after-treatment either considering water resource crisis or national water regulation. Conventionally, the industrial water utilization networks only regard impurity concentration as the restricting factor for controlling material reuse while overlook the effect of stream's characteristic or effect on the stream's reuse. The actual industrial requirement is unable to be evaluated. Therefore, it is of great significance to work on water integration with multiple properties. This paper presents some new methods for the water network integration with multiple properties considering those un-existed methods, such as wastewater discharged directly after regeneration and the large number of interceptors contributed to a complex water network. The main contents are listed as follows:(1) Based on the environmental multiple-property water utilization models, a new method is proposed about the superstructure model in the treated water stream of the sink units. The minimum annual cost taken as the target function, this method builds a mixed integer non-linear programming (MINLP) mathematical model considering the after-treatment stream environmentally. This model has been solved by GAMS software and evaluated by two examples. The result reveals that this method effectively reduces the annual total cost, the use of fresh water as well as the amount of waste water discharge, which validates the efficacy and superiority of the proposed method.(2) In order to avoid the mixing of streams, the publications strictly prevents the existence of bilinear products in the property balances around the mixing points. However, such method will cause a large number of interceptors and a more complexity of water networks. Such problems can be solved by some rules of interceptors combination and procedures presented in this paper. These rules search/combine interceptors to optimize the initial water network and reduce the complexity of water networks through reducing the number of interceptors. The validity of this method has been proved by three examples.(3) We construct a new superstructure of water network concerning the possible mixed streams in the treated process. We also consider the constraints of environment and sink units in our MINLP mathematical programming. The objective function includes minimize the annual cost of fresh water and the cost of interceptors. The number of interceptors has been initially considered and the same interceptor has been strictly restrained to use only once. Such method can efficiently reduce the number of interceptors and simplify the structure of the water network. Three calculated examples directly show the validity of this method.