| Mass exchange networks (MENs) and heat exchange networks (HENs) are among the most important contributors of process industries to realize the objective of energy conservation and emission reduction. According to the nature of mass transfer processes involving multiple components, MEN synthesis methods are proposed to handle the incompatible multi-component system problem at first in this thesis; then the simultaneous synthesis strategies for MEN and HEN are explored, with regarding the minimum total annual cost (TAC) of combined mass and heat exchange network as target. The main contents and results of this thesis are as follows:(1) To handle the incompatible problem that caused by the diverse solubility of components in multi-component systems, the synthesis though of setting tray numbers of mass exchange units as variables are proposed. Merge this thought into the interception method and the superstructure method, then the mixed integer non-linear program (MINLP) mathematical model of the former method can be significantly linearized and able to be solved by general solution software in case of using several simplification activities, including interceptors’ discretization, mass transfer equations’linearization and operation options’ pre-setting; the latter method can execute the global optimization and find the optimal solutions through its combination with genetic-simulated annealing algorithm (GASA). An example from literature is separately investigated using the proposed two methods. The obtained true concentration values can demonstrate the rationality and the application of the proposed methods in dealing with MEN synthesis problem of multi-component systems.(2) A method is presented for purpose of synthesizing the MEN and HEN in a single component system simultaneously. In this method, MEN and HEN in a combined mass and heat exchange network are designed using mass pinch technology (MPT) and pseudo T-H diagram approach (PTHDA), respectively. Based on the sub-networks coupling model in literature, the lean bypass streams, which are employed for sake of getting a more comprehensive tradeoff between the costs of MENs and HENs, are considered firstly in the method. Then, a simultaneous synthesis strategy is proposed based on the formation of steam existence matrix and stream temperature difference contribution value matrix. During the synthesis process, the existence feature, the hot or cold nature, as well as the corresponding variable value of any process stream can be identified through the product of these two matrices. This strategy is a guarantee for the simultaneous synthesis, especially in the case of hot/cold properties of heat exchange streams are unable to be predicted in advance. An example from literature is used to verify the proposed method, and the two cases of no bypass involved and having bypass involved are both investigated for comparison. Results indicate that the optimal network and TAC results of former case are both about the same with those obtained in literature; the optimal TAC of latter case is19.9%and21.2%lower than that of literature and former case, respectively. These comparison results can not only show the effectiveness of proposed method, but also can demonstrate the possibility of obtaining a better solution by involving bypass streams.(3) For multi-component systems, a superstructure-based method is proposed for their combined mass and heat exchange networks synthesis. In this method, MENs are designed with the pre-introduced superstructure method, HENs are supposed to be obtained using a new network representation called indistinct HEN superstructure. Indistinct HEN superstructure is possible to provide all possible network options in the case of hot/cold streams are unable to be pre-indentified. It is the basis of synthesis strategy which can ensure the simultaneous design of MENs and HENs. At last, the results of a single-component example and a multi-component example have demonstrated the effectiveness of this proposed method. |
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