Abstract
This work reports the integration of Real Time Optimization and Model Predictive Control in the multi-layer control structure of an existing Crude Distillation Unit (CDU) of an oil refinery. The MPC considers output control zones and targets for the inputs or outputs. Both the infinite horizon and the finite output horizon controllers were tested. The plant results show that the infinite horizon controller tends to perform similarly or better then the finite horizon MPC when the CDU system needs to operate at quite different conditions. Although the dynamic layer based on the infinite horizon controller is nominally stable for any set of tuning parameters, in practice, it is observed that the interaction between the layers of the control structure associated to model uncertainty may result in oscillations in some variables that fail to converge to the optimum operation point. This problem can be solved with the retuning of the intermediary layer (target calculation layer), which indicates that the frequent tuning of the MPC is recommended and should be performed in conjunction with tuning of the intermediary layer.
Highlights
The crude oil distillation unit (CDU) is one of the key process systems of the oil industry
In the operation of the CDU, the quality specifications of the products has to be maintained, and several process variables are to be kept inside well defined ranges despite the disturbances that affect the process. This results in the consideration of complex control structures that aim at the reduction of the variability of the intermediary products in order to reach an operation point, which is close to equipment constraints to maximize their utilization and the economic benefit
This work reports some practical results related to the multi-layer integration of Real Time Optimization (RTO) and MPC in the industrial Crude Distillation Unit of the oil refinery at Capuava (Brazil)
Summary
Abstract - This work reports the integration of Real Time Optimization and Model Predictive Control in the multi-layer control structure of an existing Crude Distillation Unit (CDU) of an oil refinery. The dynamic layer based on the infinite horizon controller is nominally stable for any set of tuning parameters, in practice, it is observed that the interaction between the layers of the control structure associated to model uncertainty may result in oscillations in some variables that fail to converge to the optimum operation point. This problem can be solved with the retuning of the intermediary layer (target calculation layer), which indicates that the frequent tuning of the MPC is recommended and should be performed in conjunction with tuning of the intermediary layer.
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