Optimization Design Of Water-using Network Based On The Petri Nets In Batch Processes With Single Contaminant

As a water crisis becomes more and more serious and the problem of environmental protection has been paid more attention, more and more researchers have carried through the study on the water saving and emission reduction. And how to use the process integration to realize water saving and emission reduction in the process industry, which needs lots of the fresh water and lets out lots of the wastewater, has become a research focus for researchers. As the important part of process industry, batch process and its water-using network also have got more and more researcher’s attention, and the water integration in batch process can be conducive to water saving, emission reduction and improving production capacity. The study of water-using network in batch processes was formerly based on mathematical programming method andwater pinch technology. The mathematical programming method not only has a complex model but it also is difficult to get the optimal solution due to no-linear and integrality constraints and the non-convexity of the problem. While the water pinch technology is vivid and visual, but its calculation is more tedious and lack of effective mathematical tools to analyze.A Petri net, which is a graphical modeling tool and also a formal mathematics tool, not only can build intuitionistic and pellucid model but it also has a variety of analytical techniques. So the system can be analysed by Petri nets (PN), not only the static structure but also the dynamic behavior. So a new approach based on PN was presented to build the PN models for scheduling optimization and water-using network in the thesis, respectively. And then through combining the above two models, the PN model for water-using network considering the scheduling was built.(1) Optimization design of water-using network in continuous processes with single contaminant. The water integration technique in batch processes is often derived from continuous processes, which can be regarded a special batch process. So, the Petri nets model for water-using network in continuous processes with single contaminant was firstly built. Based on the water pinch technology, the Petri nets model for water pinch analysis was built to determine the minimum fresh water, and then the Petri nets model for water-using network’s synthesis, based on the basic principles of water network design, were built, respectively. And the feasibility and effectiveness of the proposed approach were valicated through one example.(2) Optimization design of water-using network in batch processes. Based on the Petri nets model for water-using network in continuous processes and water cascading analysis technique, the water-using network in batch processes with single contaminant was designed in this thesis. In allusion to the water-using network with/without storage in batch processes, firstly, the model for pinch analysis was established based on Timed Petri net (TPN), which is developed by adding time factor into PN. And then, according to the autonomous learning mechanism of PN and the principles of designing and matching, the synthesis model for water-using network was built. At last, the feasibility and effectiveness of the proposed approach were valicated through two examples.(3) Optimization design of water-using network in batch processes, taking the scheduling into account. A Petri net can describe the phenomena directly, such as the parallelism, asynchronous phenomenon, conflicts phenomenon and so on. So it is a simple and effective modeling tool to model and analyse the discrete event systems. The Petri nets model for scheduling was built in this thesis, which was solved by the reachability tree and simulation algorithm. And then the PN models for water pinch analysis and the scheduling in batch processes were combined to achieve the comprehensive consideration. The feasibility and effectiveness of the proposed approach were valicated through one example.