Economic MPC of an Industrial Diesel Hydrotreating Plant

Abstract

This work addresses the control and optimization of an industrial diesel hydrotreating unit (HDT) with MPC (Model Predictive Control). Initially, it is given a brief description of the diesel hydrotreating process, which is studied here and the requirements for the control system of this type of industrial plant are discussed. In order to best explore the capabilities of the MPC in the HDT unit a new MPC algorithm is proposed. In the controller considered here, the control objective function is extended with an economic objective that aims at to the increase of the conversion of the raw feed to the hydrotreated product, specially the most valuable streams, and to the minimization of catalyst degradation due to thermal instabilities. With the extended control objective, both control and optimization are performed simultaneously. In a simulation environment, it is shown that the proposed control algorithm is able to stabilize the industrial plant and to increase the profitability of its operation.

Assessing plant design with regard to MPC performance

“…Also recent research has shown that process economics can be optimized directly in the dynamic control problem, which can take advantage of potentially higher profit transients to give superior economic performance. Examples of this approach include Amrit et al (2013) and Strutzel et al (2013). The optimization is performed by changing the manipulated process inputs when the process finds itself within its control bounds, and degrees of freedom are available to be employed in optimization tasks.…”

“…The state-space formulation for this plant is presented in Strutzel et al (2013) and is built upon the transfer functions that can be obtained from the analytical form of the step response of the system, a convenient and common way of obtaining the models of a chemical plant. Therefore, this formulation was selected for use in the case study discussed in this section.…”