Flexibility Analysis And Extended Application Of Nodal Unstructured Model Element Matching In Thermal System Integration

Heat integration system is an important part of chemical process system integration.By recovering the effective energy of process logistics,it can achieve the purpose of reducing the amount of public works and improving the efficiency of energy utilization.The nodal unstructured model quantifies the matching position of the element in the form of a node,which is beneficial to the representation and generation of the element.However,in the later stage of optimization,it is still difficult to avoid the situation of insufficient structural variation ability due to the reduced flexibility of unit matching.Therefore,from the perspective of improving the flexibility of heat exchange unit matching in the evolution process,this paper discusses the construction method of the node non-structural model,analyzes the reasons for the obstruction of heat exchange unit matching,and proposes corresponding improvement measures to improve the structural variation ability in the optimization process.At the same time,in view of the similarity between the heat exchange network synthesis problem and the mass exchange network synthesis problem,the research method in the heat exchange network is applied to the mass exchange network optimization,and a node unstructured model that conforms to the mass exchange network optimization is constructed.Exploring and improving the matching flexibility of the medium mass transfer unit to enhance the structural evolution capability.The specific research contents and innovation points are as follows:Firstly,the influence of the construction method of the nodal non-structural model on the structural optimization is analyzed from the perspectives of utility matching and heat exchanger matching.It is found that the processing mechanism of temperature crossing in the model ensures the matching of utilities at any position on the stream to a certain extent,but constraints that must occur in pairs can cause cost surges,affect optimization efficiency,and limit utility flexibility.In addition,in the later stage of optimization,it is difficult to eliminate heat exchangers and generate new heat exchangers effectively,resulting in insufficient structural variation ability and affecting the quality of optimization.Therefore,improving the matching flexibility of heat exchange units is an important means to expand the model solution domain and enhance the structural variation ability.Secondly,in view of the insufficient flexibility of utility matching,an extended node unstructured model that can be freely matched is proposed.Based on the idea of streamlining of utilities,two new utility streams are added to match the conventional streams to determine the generation of hot and cold internal utilities(utilities are generated inside streams).Realize that the internal utilities can be generated freely at any position of the stream,and are no longer limited by the constraints that need to be paired on the hot and cold streams,and can be generated independently at the cold or hot end,which improves the flexibility of utility matching.On this basis,the influence of the generation probability of internal public works set on the newly added stream on optimization is discussed,and the protection strategy of internal public works is proposed based on this,so as to give full play to the structural evolution potential of internal public works after generation.Subsequently,in view of the reduced matching flexibility of the upstream area heat exchanger in the later stage of optimization,the newly generated heat exchanger in the downstream area cannot be effectively generated,resulting in insufficient structural variation ability,a dynamic area taboo matching strategy is proposed.The core of the strategy is to restrict the matching of heat exchangers in the upstream area of the stream with competitive advantages and allow them to be freely matched,but after the heat exchanger matching is formed,it needs to be transferred to the downstream area immediately,to ensure the generation of heat exchange matching on the upstream area nodes,enhance the competitiveness of newly generated heat exchangers in the process of structural evolution,break the tendency of heat exchangers to concentrate in the upstream area of the stream,and promote the optimization of late structural variation capabilities.Finally,considering the similarity of mass exchange network and heat exchange network,a node unstructured model suitable for mass exchange network and an RWCE algorithm matching its optimization are established according to the research method of heat exchange network.At the same time,in view of the lack of structural evolution ability in the later stage of optimization,the dynamic taboo matching strategy is introduced into it,and it is found that although it has a certain perturbation effect on the structure,the improvement of the optimization quality is not obvious.Therefore,a random perturbation strategy with stronger structural perturbation ability is proposed to be applied to the optimization process.According to the optimization stagnation state,the structure is perturbed from the perspectives of mass exchange and matching relationship of the mass transfer unit.In this way,the vitality of structural evolution in the later stage of optimization is improved.In a word,based on the node non-structural model,this paper analyzes the optimization obstacles of the heat exchange unit in the evolution process,and puts forward corresponding improvement strategies to enhance the structural variation ability of the heat exchange network in the later stage of optimization.The research method of heat exchange network is introduced into the optimization of mass exchange network,which further promotes the development of mass exchange network and provides ideas for the expansion and application of node unstructured model in chemical process system.