Plant-wide optimization and control of an industrial diesel hydro-processing plant

• Empirical models to predict sulfur content of the feed, D86 curve of the feed and T95 value of the diesel product are developed.
• A cascaded MPC structure is used to implement the results of economic plant wide steady-state optimization.
• Supervisory MPC computes the optimal set-point trajectories for FeedT95 and the exit temperatures of the reactor beds.
• Local regulatory MPCs are designed to track the set-points supplied by the Supervisory MPC.
• Simulations show that desired sulfur removal is achieved and the product Diesel meets its end properties in an economically optimal and safe operation.

Diesel hydro-processing (DHP) is an important refinery process which removes the undesired sulfur from the oil feedstock followed by hydro-cracking and fractionation to obtain diesel with desired properties. The DHP plant operates with varying feed-stocks. Also, changing market conditions have significant effects on the diesel product specifications. In the presence of such a dynamic environment, the DHP plant has to run in the most profitable and safe way and satisfy the product requirements. In this study, we propose a hierarchical, cascaded model predictive control structure to be used for real-time optimization of an industrial DHP plant.

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