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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Industrial & engineering chemistry research 33 (1994), S. 2453-2466 
    ISSN: 1520-5045
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 38 (1992), S. 1729-1743 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Practical guidelines are required for the design and operation of complicated catalytic packed-bed reactors. Primary among design considerations is the avoidance of operating regions of high parametric sensitivity, in which small changes in operating conditions can lead to thermal runaway in the reactor. Existing criteria for predicting these regions rely on complex mathematical formulations for differential sensitivity between input and output variables. The present work centers on the development of practical design criteria for avoiding reactor instability and temperature sensitivity in multitubular packed-bed reactors. A set of simple guidelines is proposed for the sizing of reactors and proper selection of operating conditions. The implications of these open-loop sensitivities for a controlled reactor are investigated. It is shown through simulation studies that violation of the proposed criteria leads to control problems and difficulty in operating at the design point.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 425-439 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The optimal control structure has been introduced as a design tool to measure the control-law nonlinearity of a given process design. In this context, control-law nonlinearity is the optimal degree of nonlinear compensation in the controller, a system property distinct from open-loop nonlinearity and determined by a performance objective and the region of operation as well as the nature of the open-loop system. This approach is extended to the analysis of multivariable systems with output feedback through the application of an extended Kalman filter. Coherence estimation is used as a practical method to measure continuous, open-loop multivariable system nonlinearity. The CSTR with van de Vusse kinetics, a system that features output feedback and a controllaw nonlinearity that changes with operating points, is analyzed. The optimal control structure approach with coherence estimation correctly indicates changes in the controllaw linearity between different operating points and changes as the regions of operation change around a particular operating point.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An application of a linear-programming based model-predictive control strategy to the paper-machine cross-direction (CD) control problem is presented. The objective of CD control is to maintain flat profiles of variables of interest by minimizing worst-case deviations from setpoints (defects). These control problems can have as many as 200 actuatiors (inputs) and 400 sensor measurements (outputs). This large size coupled with the stringent real-time requiremnt of computing a control move in a few seconds poses a very challenging control problem. The LP-based strategy is particularly well suited for solving such classes of control problems. This strategy has demonstrated its ability to solve large-scale control problems (over 100 inputs and 100 outputs) in real time and exhibits robustness to model uncertainty.
    Additional Material: 22 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1763-1784 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A nonlinear model-predictive control scheme based on the autoregressive-plus Volterra model is proposed. A “plant-friendly,” yet persistently exciting, input sequence is designed for model identification. A second feature of this work is that the control action is determined by solving a less computationally burdensome nonlinear programming problem than the optimization problems associated with Newton-type controllers and polynomial ARMA model nonlinear MPC. A third contribution is that semiglobal closed-loop stability conditions are derived and are shown to be less conservative than those previously published. The control scheme is shown to outperform a feedback strategy using proportional integral control and a linear model-predictive control design for the control of two polymerization reactor case studies. The complex features of the latter case study [multivarible (3 × 3), recycle loop, high-order (24) dynamics] motivate the applicability of this approach for industrial problems.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 3175-3192 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A model of a continuous digester was developed as an extension of the well-known Purdue model. A lumped-parameter approximation is used to describe the flow transport mechanism of the digester, and a model based on the fundamental principles of mass and energy is derived. Mass bases and volume fractions are defined to allow fewer simplifying assumptions in the model derivation than in previous model versions. The steady-state profiles and dynamic responses of the digester model are compared with a previous version of the Purdue model, and the significant differences between the two models are highlighted. The digester model is also compared to the Weyerhaeuser benchmark digester model, and a parametric sensitivity analysis to several model parameters is performed. Physical explanations are given for the demonstrated model behaviors. Model implementation is straightforward, making it useful for process control, optimization and design studies.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 703-714 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The trade-off between model accuracy and computation tractability for model-based control applications is well known. While nonlinear models are needed to capture the detailed behavior of many chemical processes, the resultant structures may not lead to straightforward control implementation. The current work advocates the use of low-order nonlinear models based on wave propagation that are mathematically concise and capture the essential nonlinear behavior of a process. In this work, differential geometry is invoked to achieve input-output linearization of a high-purity distillation column based on a traveling-wave model. A Kalman filter is used to recursively update the parameter values. Comparison with a linear controller based on a two-time constant model shows that the nonlinear controller outperforms the linear controller in tight control of both the overhead and the bottoms composition.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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