(61p) Energy Flow Redistribution for Optimal Operation of Heat Exchanger Networks
AIChE Annual Meeting
2023
2023 AIChE Annual Meeting
Computing and Systems Technology Division
Interactive Session: Systems and Process Operations
Tuesday, November 7, 2023 - 3:30pm to 5:00pm
This work focuses on the optimal operation of heat exchanger networks using a concept of energy flow redistribution (EFR). The EFR methodology uses the structure of the HEN to direct the energetic impact of a disturbance along a favorable (e.g. minimum utility) path. Specifically, when a disturbance enters the HEN, the duties of the process-to-process heat exchangers are adjusted, using internal degrees of freedom like exchanger bypass or stream split fraction, such that the net impact on the utility exchangers is minimized. To this end, the governing equations of an individual heat exchanger and energy balance for the entire HEN are restructured to explicitly quantify the effect of disturbance on the overall performance of the HEN, and subsequently back-calculate the change needed in the values of the manipulated inputs (utility flow, exchanger bypass or stream split fraction) to achieve optimal operation. Additional operational constraints, such as limits on utility usage, absence of bypass on any exchanger can also be incorporated. The EFR strategy can be implemented in an openloop (similar to RTO) or closed-loop (similar to economic MPC) configuration as shown in the figure below.
Using multiple illustrating examples, it is shown that the proposed approach successfully handles commonly encountered (measured and unmeasured) disturbances (such as feed flowrate or temperature, target specifications) as well as plant-model mismatch (exchanger fouling or complex flow patterns), and achieves better performance as compared to the existing methodologies. The proposed approach offers additional benefits such as flexible configuration (in terms of degrees of freedom and performance objective) and ability to incorporate trade-off between optimality, flexibility and computational efficiency.
References:
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[3] Jaschke J and Skogested S, Optimal operation of heat exchanger networks with stream split: Only temperature measurements are required, Comput. Chem. Eng., 70, 35-49, 2014.