Study On The Synthesis Of Water-Using Networks With Multi-Contaminant Involving Reuse

Water is one of the most important resources for agriculture, industry and many other applications. In recent years, stricter discharge policies and growing costs for effluent treatment have accelerated research to both freshwater consumption and wastewater production. In chapter 1, this thesis presents a brief review for the synthesis approaches of water-using networks in the literature.In chapter 2 of this thesis, mass-load-based procedures are proposed to target the minimum freshwater requirement and design water networks with single contaminant. The minimum freshwater requirement target and pinch point(s) can be determined simultaneously in the targeting procedure. A general design procedure is proposed based on the mass load allocation from source streams to demand streams. Then a mass-load-based approach for design water-using network with minimum total flowrate is presented, which may reduce the capital and operating costs. The stream number, the complexity of the network and capital cost can be reduced by adjusting the streams allocations in the network.In chapter 3, a multiple resources approach is proposed to determine the targets of the water-using networks with single contaminant involving regeneration reuse/recycling. The optimal regeneration amount and regenerated concentration are investigated in the target-analysis procedure. The multiple resources approach can also be used to design network of zero discharge problem with fixed flowrate system.In chapter 4, a heuristic procedure is proposed to design water-using networks with multiple contaminants. New concepts,the concentration-potentials of the demand (inlet) streams and those of the source (outlet) streams, are introduced. The concentration-potential of a demand stream reflects the possibility of the stream to reuse the source streams. The concentration-potential of a source stream reflects the possibility of the stream to be reused by the demand streams. The order of the concentration-potentials obtained agrees with that of the conventional concentrations. When deciding the performing order of the processes, the inlet-concentration-potential is taken as the most important factor. The process with the lowest inlet-concentration-potential should be performed first; the process with the highest inlet-concentration-potential should be performed last; the performing order of the other processes can be determined based on the current available source streams. The results show that the method proposed can give excellent designs whose freshwater consumptions are very close to the target values.