Simultaneous Synthesis Of Controllable Heat Exchanger Networks Considering Uncertain Parameter

Heat exchanger network is composed of many heat exchangers connected in series and parallel pattern,and the internal interaction of the network is complicated.In order to ensure that the designed heat exchanger network is feasible in practical industrial applications,it needs to have both high controllability and sufficient flexibility to resist the impact of uncertain factors on the system.To the best of knowledge,the research on controllable heat exchanger networks mainly focuses on the optimization of control structure,ignoring the influence of network structure on controllability In addition,controllability and flexibility are two important aspects that affect the operability of the system.Ignoring its synergy will lead to the heat exchanger network performance deviations in actual operation.The complex mechanism between network structure synthesis and control structure selection makes it difficult to synchronize these two aspects.In order to solve these problems,this thesis carried out a study on the simultaneous optimization of controllable heat exchanger network synthesis considering uncertain parameters.The content of this thesis mainly includes the following three sections:(1)In order to consider the influence of network structure and control structure on controllability,and explore the resulting complex relationship between economy and controllability,a multi-objective method for heat exchanger networks synthesis considering economy and controllability is proposed.To figure out the problem that the control structure selection can only be based on a known network structure,an extended disturbance propagation and control model based on the superstructure is proposed to quantify the system deviation,which can realize the automatic design of the control structure.The total annual cost and the relative gain matrix number are selected as the economic goal and controllability goal respectively;The optimization problem type is determined according to the minimum temperature difference interval,and the relationship between economy and controllability objective is analyzed.If the change trend of total annual cost is opposite to that of relative gain matrix number,the ε-constraint method is used to solve the multi-objective problem;Otherwise,the problem can be simplified as a single-objective optimization solution.The results of the case studies show that the method in this thesis can effectively divide the problem types and simplify the problem,and the heat exchanger matching is the main factor affecting the controllability of heat exchanger network.(2)In order to simultaneously consider the economy and controllability of heat exchanger networks synthesis,and the simultaneous optimization of network synthesis and control structure selection,a simultaneous synthesis method for controllable heat exchanger networks is proposed.The controllability rules are proposed to synthesize the heat exchanger network considering the controllability factors.Based on the controllability rules and the shared bypass strategy,the network structure synthesis and control structure selection are realized simultaneously.Comparing the result of case study 1 with the result of smallest relative gain matric number in Chapter 2,and comparing case study 2 with the literature,the proposed method is able to effectively improve the controllability.(3)In order to make the system have the ability to resist the disturbance of uncertainty,a method for simultaneous synthesis of controllable heat exchanger network considering uncertain parameters is proposed to realize the optimization of controllability and flexibility.Based on the area of the heat exchanger,the internal mechanism of flexibility and controllability is investigated.On the basis of the synthesis method in Chapter 3,the strategy of preferentially increasing the area of the heat exchanger is proposed and a collaborative optimization model of flexibility and controllability is established.The results of the case studies show that the method in this thesis can improve the controllability of the heat exchanger network on the premise of meeting the flexibility requirements of the system.