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Modelling and MPC for a Primary Gas Reformer Open Access


Other title
Model Predictive Control
Primary Gas Reformer
Mathematical Modelling
Type of item
Degree grantor
University of Alberta
Author or creator
Sun, Lei
Supervisor and department
Forbes, Fraser (Chemical and Materials Engineering)
Huang, Biao (Chemical and Materials Engineering)
Examining committee member and department
Liu, Jinfeng (Chemical and Materials Engineering)
Forbes, Fraser (Chemical and Materials Engineering)
Huang, Biao (Chemical and Materials Engineering)
Department of Chemical and Materials Engineering
Process Control
Date accepted
Graduation date
Master of Science
Degree level
In the steam methane reforming process, improvement of the reformed gas outlet temperature control performance can lead to a larger hydrogen production rate, while ensuring safe process operation. In this work, a side fired primary gas reformer is investigated. The three objectives of this work are: 1) to develop a process model that describes the dynamic relationship between the temperature of the reformed gas (process output) and the process variables consisting of manipulated and disturbance variables; 2) to develop optimization strategies for manipulating side-fired burners in order to provide smooth heat flux profiles that can prolong tube life and uniform reformed gas outlet temperatures; 3) to design predictive controllers that regulate the production process accurately. As a first step, dynamic models for a generic primary gas reformer are developed by using homogeneous-phase one-dimensional reaction kinetics equations to describe the chemical reactions inside the reforming tubes and computing the external heat transfer to the tubes by radiation and convection. The model consists of a set of 1) coupled non-linear hyperbolic Partial Differential Equations (PDEs), which describe the product conversion rate and temperature profiles along each fixed bed catalytic tube reactors inside the furnace; 2) Ordinary Differential Equations (ODEs), which describe the temperatures of combustion gas and refractory walls; and 3) Algebraic Equations (AEs), which describe the heat flux profiles along the refractory walls towards tube reactors. These dynamic models lay a foundation for system optimization and optimal control design. Mixed Integer Non-Linear Programming (MINLP) technique is used with the process model to determine optimal steady state operation condition. The objective is to find the optimal operating conditions for the side wall burners to maintain uniform reformed gas outlet temperatures within a certain range and to provide approximately flat profiles of radiant heat flux to the tubes. Four objective functions are proposed and their performances are compared. Constant disturbance effects that may cause uneven distribution in the system is also studied. Model Predictive Control (MPC) application using both early-lumping (a conventional MPC) and late-lumping (Characteristic-based MPC) approximations is studied for the outlet temperature control of the primary gas reformer. Set-point tracking and disturbance rejection performances of the two MPC controllers are evaluated. It is demonstrated that both predictive controllers are capable of providing satisfactory performance, while CBMPC yields a much shorter convergence time. Difference between the two controllers are further discussed.
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