Synthesis Of Heat Exchanger Networks With Low Sensitivity Based On Bypass Optimal Control

Heat exchange network(HEN)is widely used in the process energy exchange system of large industrial enterprises such as oil refining,chemical industry and metallurgy.Since the 1960 s,the research on the synthesis of HEN has gradually attracted the attention of scholars.The synthesis of HEN general is based on technical and economic index as the goal,but during system operation,when operating conditions or system parameters deviates from the designed value,technical and economic indicators will deviates from its optimal value,then there is no guarantee of sustained energy efficiency.Therefore,scholars at home and abroad have been studying the changing conditions of the operating conditions,starting from the two dimensions of process design and optimizing control separately in recent years.Synthesis of low sensitivity HEN starts from the perspective of process design,in order to process operation stability as the research point,that makes the HEN can adapt to the change from the design condition and overcome slightly deviates from the value of design parameters and working conditions.But these methods usually focus on the effects of HEN economy when the operating condition changes,do not consider the moderating volatility and the control performance of the dynamic process.No online optimization is involved either.Bypass optimal control as a main effective method for HEN optimization and real-time online adjustment,can keep the HEN matching original conditions while improving system control degrees of freedom,effectively reduces the utilities consumption,and ensures that the entire network has good control performance.Many bypass optimization design and optimization control methods are usually carried out for a given HEN without consideration for the impact of system design.To balance the synthesis of the low sensitivity HEN and the bypass optimal control performance in the process system,a flexible HEN bypass optimization design method,which takes into account the control performance,is proposed in this paper.At first,the effects of the bypass on the sensitivity of the system is analyzed,thus relations of the sensitivity,control performance and economic characteristics are analyzed.Then the effects of local sensitivity to the bypass position setting and the effects of control action to the system sensitivity are analyzed respectively.And based on the analysis above,a kind of low heat exchange network sensitivity bypass optimal design method is put forward.Finally,the positions of the bypasses are determined by calculating the local sensitivity coefficient.According to the simulation result of the relationship of sensitivity,control performance and economic characteristics,the constraints of ?-are determined by looking for an inflection point.By using the ideas of integrated optimization for process design and control,turning multi-objective optimization into single target optimization problem by making economic performance as an optimal goal,control performance and sensitivity as constraints.Through dynamic optimization,the HEN synthesis result that meets the requirements of process design and the constraint of control performance at the same time is obtained.