Model Predictive Control of Non-Isothermal Dispersive Chemical Tubular Reactors with Recycle Flow

• Author / Creator

  Khatibi, Seyedhamidreza

• Tubular reactors have widespread applications in petrochemical, biochemical and pharmaceutical unit operations. The design of a control law, which accounts for stabilization of the concentration and the temperature of the chemical component during the reaction in an isothermal/non-isothermal tubular reactor with axial dispersion, is still challenging issue in process engineering. The mathematical models for this kind of chemical unit operation is represented by distributed parameter systems (DPS) models. The major issue of DPS models is that they take the form of partial differential equations (PDEs) or a mixed set of PDEs and ordinary differential equations (ODEs). The complexity of DPS models lies in spatial approximation in order to obtain finite-dimensional models amenable for corresponding controllers/observers.

  Moreover, in process engineering, recycle-loop are typically used around the reactor to reduce the hot-spot temperature while maintaining the component conversion at the desired level. Unfortunately, a recycle-loop may bring the system instability, thereby introducing a controller, which also accounts for instability and physical limitations of the process is essential.

  This work provides a model predictive control as well as observer design for dispersive chemical tubular reactors with recycle flow. The discrete version of the DPS is constructed by energy preserving Cayley-Tustin transformation. Along the same vein, the DPS is kept without any model reduction or spatial approximation.

  First, we explore a model predictive control and a discrete observer design for a coupled axial dispersion reactor and continuous stirred tank reactor (CSTR) given by a cascade ODE-PDE system (a case study for polymerization process) in which the regulator design accounts for stability and physical limitations of the process implemented by input/state constraints.

  Next, the proposed design is extended to a non-isothermal tubular reactor with recycle flow described by a class of convection-diffusion-reaction PDEs with a nonlinear reaction term (a case study for chemical and bio-processing). Based on the different mass and heat Peclet values the system can exhibit multiple equilibria than can be stable or unstable. The objective is to design a model predictive controller and discrete observer for the linearized system around the unstable steady state profile. The controller can provide state stabilization, constraints satisfaction and input disturbance rejection. Finally, the performance of the both controllers are assessed via numerical simulations.

• Subjects / Keywords

  • Model predictive control
  • Coupled PDEs system
  • Tubular reactor
  • Recycle systems
  • Distributed parameter systems
  • Discrete observer
  • Coupled PDE–ODE system

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-09n5-xc59

• License

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