Water Is The Source Of Life

Water is the most essential source for the life of human beings, animals, and plants, also it is a major stream in utility system and probably the most widely used raw material in process industries. Being an efficient technology for saving freshwater and reducing wastewater. In 1980, Takama and coworkers (1980) addressed an approach for optimal water allocation in a petroleum refinery based on a superstructure of all possible re-use and regeneration opportunities. Then in 1989, El-Halwagi and Manousiouthakis (1989) defined the composite curve to denote mass exchange operation, which was adapted from the methodology developed for heat exchanger networks by Linnhoff and Hindmarsh.

Remarkable work was done by Wang and Smith (1994a) by introducing the important concepts of water pinch and limiting water profile, which is further improved later.

The graphical method can give the minimum fresh water requirement of the entire process in a direct way, but when multiple contaminants are present, graphical methods require assumptions for ease of implementation, some of which may be difficult to justify.

Huang and coworkers presented a mathematical programming solution of the combined problem of water allocation and treatment by solving nonlinear problem (NLP). Recently, Bagajewicz and Savelski showed how to reduce a nonlinear program to a linear program (LP), by inserting the maximum outlet concentration conditions. The mathematical programming methods are effective in optimizing large-scale systems but can be difficult to interpret, giving designers fewer insights compared with graphical methods. Works by others are also in the two kinds.

Water networks mentioned above are designed using strategies similar to those used in the design of networks of heat exchangers, with pipes connecting the unit processes.

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When the entire plant involves only a few processes, the networks are simple and water savings at or near the maximum are achieved. However, for a large petrochemical or chemical complex, with many unit processes, the piping network becomes very complicated and hard to design and control. Moreover, the change of water flow rate or water quantity in one unit process will influence other unit processes. If using freshwater to adjust the change, the water-saving effect will decrease. To solve the problem, Feng and Seider (2001) introduced a new structure and its design methodology for water networks. The new structure uses one or more internal water mains (or reservoirs) to simplify the network. These water mains simplify operation and the control of water quality, as well as the design strategy. However, their work involved only single contaminant.

Design methodology for water networks with internal water mains H, Ma, X. Fenf_and K. Cau, ” A Rule-based methodology for water network with internal water mains 2007, Zhi- Yong Liu, Yi Yang, Lin-Zhan Wan, Xi Wang and Kai- Hu, ” A heuristic design procedure for water-using networks with multiple contaminants 2009a, He, H.N.; Wan, L.Z.; Liu, Z.Y. A simple design for water network with multi-contaminant internal water mains. CIESC Journal, 2010[19], Xiao Yanfan, Yan Pengli, Zhi Yongliu, Chun Hui Panb. A new design method for water using networks of multiple contaminates with the concentration potential concepts. Chemical Engineering Science, 2012, Wei Nansu; Giu Hanli, Zhiyong Liu, Chunohui Pan. A new Design Method for Water Using Net Work of Multiple Contaminants with Single Inter Water Main, Journal of Cleaner Production, 2012.

Recycling for Water Networks with Internal Water Mains by Using Concentration Potential Concepts. Chemical Engineering Science, 2013. When dealing with the multiple contaminant problems, the design methodology for single contaminant cannot be used anymore. In multiple contaminant system, the key contaminant of each unit is different which is related to the water source to the unit. Therefore, the inlet and outlet flow rate allocation of each unit is difficult to specify because its freshwater consumption is close related to the choice of its sources. Due to the complexity, the design for water networks with single contaminants based on internal mains cannot be extended to that of multiple contaminant systems. In this paper, the design methodology for multiple contaminant systems is presented. Emphasis on the location of the first internal water main. Generally, water networks having just one internal main determined by the presented method can obviously reduce water consumption, approaching the minimum value.