Papers by Rosendo Monroy-Loperena
Industrial & Engineering Chemistry Research, 2000
In this work, an output-feedback control for the regulation of distillate purity via manipulation... more In this work, an output-feedback control for the regulation of distillate purity via manipulations of the reflux ratio in reactive batch distillation is designed. The approach is based on an approximate model of the composition dynamics and makes use of a reduced-order observer to estimate the modeling error. An input/output linearizing feedback is proposed where the estimated modeling error is included to achieve robust tracking of a composition reference. It is shown that the resulting controller has the structure of a proportional-integral derivative (PID) controller with antireset windup. The controller performance is tested using a simulation example including strong uncertainties in the reaction model. An interesting finding is that the required reflux ratio policy to reach asymptotically a constant reference resembles the reflux ratio policy obtained from posing an optimization technique (Mujtaba, I.
Industrial & Engineering Chemistry Research, 2000
The aim of this paper is to propose a novel proportional-integral-derivative (PID) control config... more The aim of this paper is to propose a novel proportional-integral-derivative (PID) control configuration based on an observer structure. Batch distillation is used as the base case study where the regulated output is the distillate composition. The proposed PID control law is derived in the framework of robust nonlinear control with modeling error compensation techniques. A reduced-order observer is proposed to estimate both the derivative of the regulated output and the underlying modeling error. These observations are subsequently used in a control loop to feedback variations of distillate composition (derivative feedback) and to counteract the effects of modeling errors. It is shown that, under certain conditions, the resulting control law is equivalent to a classical PID controller with an antireset windup scheme. Moreover, the tuning of the controller is performed very easily in terms of a prescribed closed-loop time constant and an estimation time constant. Numerical results are provided for binary and multicomponent separations. Sampled/delayed measurements and several sources of uncertainties are considered in order to provide a realistic test scenario for the proposed control design procedure.
Industrial & Engineering Chemistry Research, 2007
ABSTRACT The use of shortcut methods for the design of complex distillation systems provides prel... more ABSTRACT The use of shortcut methods for the design of complex distillation systems provides preliminary structures that need to be updated, typically by a recursive use of simulations. Although this procedure is generally effective, it can be time-consuming. In this work, collocation techniques are used as part of the design of Petlyuk distillation columns for the separation of ternary mixtures. Once a preliminary design is generated by a shortcut method, collocation techniques are applied to refine the location of the interconnecting and sidestream product stages, as well as the flowrate values of interlinking streams. The proposed method gives a proper distribution of stages for the Petlyuk system. The final designs are easily obtained with the proposed methodology, with a significant lower effort than that required when preliminary designs are corrected using recursive simulations.
Industrial & Engineering Chemistry Research, 2001
The dual composition control problem in a middle-vessel batch distillation column is studied in t... more The dual composition control problem in a middle-vessel batch distillation column is studied in this work. The control objective is to regulate the overhead purity by manipulating the reflux flow rate and the bottoms product composition by manipulating the boilup flow rate. By using estimators of the input-output modeling error, output-feedback compensators are designed that are shown to be equivalent to a PID controller with an antireset windup structure for the overhead purity regulator and a PI controller with an antireset windup structure for the bottoms composition regulator. Tuning issues are discussed, showing that they have straightforward physical meanings. The ability of the controllers to regulate the overhead product composition and the bottoms product composition in the face of unknown nonlinearities and sampled/delayed measurements is shown via numerical simulations on a dynamical model.
Industrial & Engineering Chemistry Research, 2001
Steady-state input multiplicities in vapor-liquid flash separation processes are common when a pr... more Steady-state input multiplicities in vapor-liquid flash separation processes are common when a product mole fraction is specified and places restrictions on the selection of controlled variables such that more than one set of conditions can produce the same result; if this happens, then potential problems during the process operation can arise. The equations that describe isobaric flash operation with a product composition specified are analyzed to propose a fast method for determining the existence of steady-state input multiplicities. The ability of the method is shown via numerical examples using homogeneous nonazeotropic multicomponent mixtures. The most attractive features of the proposed method are that it is easy to use, has a high reliability in determining the presence of steady-state input multiplicities, and requires only the separation factors of each component at the bubble and dew points at the pressure of the flash separation process.
Ingeniería, investigación y tecnología, 2010
En la lite ra tura se han plan teado estruc turas de control en para lelo para el control del dis... more En la lite ra tura se han plan teado estruc turas de control en para lelo para el control del diseño de plantas completas. En este trabajo, se consi dera el compor ta miento de una planta que consiste en un sistema de recir cu la ción, un reactor y dos columnas de desti la ción, cuyo obje tivo prin cipal es mejorar la capa cidad de recu pe ra ción del proceso contro lado ante pertur ba ciones externas. La idea es modi ficar las condiciones de opera ción del reactor y la segunda columna, a fin de distri buir el esfuerzo del control de compo si ción ante pertur ba ciones en la compo si ción de entrada. Para este fin, se propone una estruc tura de control para lelo donde la compo si ción sea contro lada mediante la mani pu la ción simul tánea de la velo cidad de vapor del rehervidor y la tempe ra tura del reactor. De esta forma, el uso de la tempe ra tura del reactor con una entrada de control secun daria redu cirá el compor ta miento osci la torio y la cantidad de flujo de vapor usado. Descrip tores: control planta completa, mate rial recir cu lado, control para lelo, control de compo si ción.
Fluid Phase Equilibria, 2022
A useful procedure for finding all the roots of the type of equation indicated in the title, typi... more A useful procedure for finding all the roots of the type of equation indicated in the title, typically used in vapor-liquid separations, is presented. The proposed procedure is the result of a matrix-based analysis to generate a Standard Eigenvalue Problem. The eigenvalues of the resulting matrix system are exactly the roots of the equation indicated in the title. Numerical experiments are presented to show the goodness of the proposed procedure.
Industrial & Engineering Chemistry Research, 2012
... Distillation Columns, with a Draw-Stream in the Middle-Vessel Rosendo Monroy-Loperena 1,2,∗ a... more ... Distillation Columns, with a Draw-Stream in the Middle-Vessel Rosendo Monroy-Loperena 1,2,∗ and José Alvarez-Ramírez 3 1. ROMON ... However, other control configurations can be derived along the same lines (see, for instance, Bezzo and Barolo 6 ). ...
Industrial & Engineering Chemistry Research, 2012
This work address the problem of round-off errors in the analytical solution (Cardano's Method) o... more This work address the problem of round-off errors in the analytical solution (Cardano's Method) of cubic equations of state inside the simulation of chemical processes in the low-temperature region, as it is the case of cryogenic processes involving hydrates calculations. It is proposed as a strategy that can be taken as an iterative refinement of the solution obtained by the analytical method and allows one to take advantage of the calculations fulfilled in the application of the analytical solution (Cardano's Method). Numerical experimentations are presented in order to show the application of the proposed strategy.
Industrial & Engineering Chemistry Research, 2012
Flash calculations are used extensively in computer-aided process simulation programs. Inherent t... more Flash calculations are used extensively in computer-aided process simulation programs. Inherent to flash calculations is the determination of the vapor−liquid split. Currently, to calculate the vapor−liquid split, the Rachford−Rice equation is the most accepted method. In this work, it is shown that the Rachford−Rice equation can be posed as a generalized eigenvalue problem, where each eigenvalue of the resulting system is exactly a root of the Rachford−Rice equation. In this way, an ad hoc strategy based on linear algebra is proposed for finding the vapor−liquid split. The main advantage of the proposed strategy is that the resulting linear system has an almost-diagonal structure and generates a discrepancy function with a more linear shape than that of the Rachford−Rice equation. In this way, the solution of the system is simple and computationally inexpensive. Numerical experiments show the reliability of the proposed solution strategy for calculating the vapor−liquid split.
Industrial & Engineering Chemistry Research, 2004
Internal model control (IMC) tuning rules have proven to yield acceptable performance and robustn... more Internal model control (IMC) tuning rules have proven to yield acceptable performance and robustness properties when used in the control of typical processes (e.g., distillation columns, chemical reactors). In general, analytical IMC tuning rules are derived for proportional-integral (PI)/proportional-integral-derivative compensators by matching an approximate process model to a low-dimensional reference model. In the case of time-delay processes, an approximate model is obtained by taking a finite-dimensional approximation to the delay operator by means of Pade or Taylor expansions. For some typical cases arising commonly in process control, including first-order plus time-delay plants, this paper studies the optimality of PI-IMC tuning rules to match the prescribed closed-loop behavior (i.e., the reference model response). To this end, optimal PI settings are computed by means of numerical optimization based on random search algorithms. Small deviations of IMC tuning from optimality are found for moderate time delays. However, significant deviations are displayed for large time delays, which motivate the use of tuning techniques based on numerical optimization to refine IMC settings.
Industrial & Engineering Chemistry Research, 1999
The proportional plus double-integral (PI 2) controller was proposed by Belanger and Luyben (Ind.... more The proportional plus double-integral (PI 2) controller was proposed by Belanger and Luyben (Ind. Eng. Chem. Res. 1997, 36, 5339-5347) as a low-frequency compensator. The objective of the additional double-integral compensation is to reject the effects of ramplike disturbances. The aim of this work is to provide a parametrization of the PI 2 controller gains in terms of a nominal closed-loop and disturbance estimation time constants. A reduced-order observer is constructed to estimate ramplike disturbances, which is subsequently coupled with a feedback loop to counteract the effects of the disturbance. It is shown that such control configuration is equivalent to a PI 2 compensator. Some robustness issues of the PI 2 compensator with respect to unmodeled dynamics and nonlinearities are discussed and illustrated with two numerical examples.
Industrial & Engineering Chemistry Research, 1999
An ethylene glycol column is studied in this paper, where the main objective is to describe the b... more An ethylene glycol column is studied in this paper, where the main objective is to describe the bifurcation diagram with respect to the reboiler boilup ratio. The bifurcation analysis reveals the existence of a unique equilibrium point at low reboiler heat inputs and three equilibrium points (two stable and one unstable) at high reboiler heat inputs. Moreover, the existence of input multiplicities at moderate and high product purity is also revealed.
Industrial & Engineering Chemistry Research, 2001
This paper presents a PI control configuration for a class of multi-input multi-output (MIMO) pla... more This paper presents a PI control configuration for a class of multi-input multi-output (MIMO) plants. The control design procedure consists of a modeling error estimator based on a reducedorder observer structure and a nominal feedback function. The estimated modeling error signals are used in the feedback loop to counteract the effects of uncertain parameters. It is shown that this design procedure leads to a classical multivariable PI control configuration with novel parametrization of the controller gains. An advantage of the proposed control design is that easy tuning procedures can be designed. In addition, several special two-input two-output PI control configurations with decentralized structure can be obtained. As an application example, the separation control in an integrated three-product (Petlyuk) distillation column is studied. Sufficient conditions to achieve decentralized regulation in terms of the steady-state gain matrix are provided. Numerical simulations are used to show the effectiveness of the proposed PI controller under measurement dead times and uncertain parameters.
Industrial & Engineering Chemistry Research, 2005
This paper studies the limitations in the operation and control of a continuous middle-vessel dis... more This paper studies the limitations in the operation and control of a continuous middle-vessel distillation column with a draw stream in the middle vessel. This separation layout can be of interest to cases where the most and less volatile components of fractions of a mixture are desired in high concentrations, as in the processing of some oil streams. It was found that to maintain distillate and bottoms products within specifications, large recycling rates can be required to compensate for the storage effects of the middle vessel. This is because, contrary to the case where a draw stream is not present, in the studied distillation column layout the middle vessel alters material balances. In this form, the middle vessel acts as both a dynamical damper to reduce bottoms and distillate control loops and an accumulator for intermediate fractions. That includes some residuals of nonseparated most and less volatile components. The control objective is to track prescribed product compositions of the most and less volatile components by means of manipulations of the reflux and vapor boilup rates. Given that the middle vessel introduces a sluggish controlled response, the recycling stream from the middle vessel to the column is taken as an additional control input to improve the operation of the column and the control performance. In this way, a rectangular control configuration is obtained, which is regularized (i.e., squared) with a habituating control parameter. It is shown that this habituating control configuration can satisfy the control objectives more easily because it provides a balance between the separation and mixing tasks provided by the distillation column and the middle vessel, respectively.
Industrial & Engineering Chemistry Research, 2004
The simple reactor/separator process with recycle has recently been used as a benchmark case to g... more The simple reactor/separator process with recycle has recently been used as a benchmark case to gain insights into the problem of plantwide control structure selection. This paper explores the use of a balanced control scheme aimed at improving the disturbance rejection capabilities of the controlled process. The idea is to change the operating conditions in both the reactor and the separator so that the composition control effort in the presence of production rate changes is distributed. To this end, a parallel control structure is proposed where the product composition is regulated by means of simultaneous feedback manipulations of the vapor boilup rate and the reactor temperature. In this way, the use of the reactor temperature as a secondary control input reduces the snowball effects reflected in large vapor boilup rate changes in response to relatively small production rate changes. Nonlinear simulations show that effective composition control can be obtained with moderate vapor boilup control efforts.
Industrial & Engineering Chemistry Research, 2003
It is shown that the well-known and extensively used bubble-point methods, such as the one propos... more It is shown that the well-known and extensively used bubble-point methods, such as the one proposed by Wang and Henke for simulating vapor-liquid multistage distillation problems, can be used efficiently for the simulation of other types of vapor-liquid multistage separation problems, such as absorption and reboiled-absorption processes, even when the thermodynamic properties are a strong function of the composition. Via numerical simulations, it is shown that a robust bubble-point temperature iteration scheme provides convergence stability in the whole bubble-point method. The proposed robust bubble-point temperature iteration scheme is a combination of an equation decoupling method and a simultaneous method. This hybrid bubblepoint temperature iteration scheme exploits the reliability of the equation decoupling method, which makes good convergence progress from a poor starting point. However, if the initial point in the bubble-point temperature calculation is good enough, only the equation decoupling method is used, to avoid excessive successive substitution steps when the separation factors are updated. As a consequence of the extension of the bubble-point method to simulate absorption cases, a didiagonal matrix with an off column is generated, when the interstage vapor rates are calculated. An efficient and simple algorithm derived from the Gaussian elimination method to solve the didiagonal matrix with an off column is presented. Results are reported for distillation, absorption, and reboiled-absorption processes, using the Soave-Redlich-Kwong equation of state.
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Papers by Rosendo Monroy-Loperena