Ricardo Aguilar-López

Integral observers for uncertainty estimation in continuous chemical reactors: algebraic-differential approach

In this paper, the on-line estimation of reaction heat in continuous stirred tank reactors, from noisy temperature measurements is addressed. An alternative representation of the original system is proposed in order to transform the output system disturbance on a system disturbance; this allows using a high gain-type observer without noise amplification problems. The uncertainty observer developed consists of integral (I)-type action and it is related with differential-algebraic concepts, where the observability condition for the uncertainty estimation from temperature measurements can be corroborated easily and the observer structure is simple enough to leads a feasible implementation. The structure of the proposed observer is robust against noisy measurements and model uncertainties. The performance of the observer is illustrated with numerical experiments.

On the dynamic optimization of methane production in anaerobic digestion via extremum-seeking control approach

This paper proposes an extremum-seeking control approach based on sliding mode to achieve the dynamic optimization of methane outflow rate in anaerobic digestion processes. Open-loop analysis for a two-population model shown that the system becomes unstable due at the accumulation of volatile fatty acids (VFA). Then the controller is designed to achieve the regulation of VFA concentration close to the optimal set-point while maximizing the methane production. The control law is based on a variable-structure feedback to iteratively extremize the methane outflow rate and converges to the neighborhood of the optimum with sliding mode motions. In contrast with previous works on extremum-seeking control with sliding mode, the control scheme includes an observer-based uncertain estimator which computes the unknown terms related to the growth kinetics and the inlet composition. Practical stabilizability for the closed-loop system around to unknown optimal set-point is analyzed. Numerical experiments illustrate the effectiveness of the proposed approach.

Monitoring in a predator-prey systems via a class of high order observer design

The goal of this work is the monitoring of the corresponding species in a class of predator-prey systems, this issue is important from the ecology point of view to analyze the population dynamics. The above is done via a nonlinear observer design which contains on its structure a high order polynomial form of the estimation error. A theoretical frame is provided in order to show the convergence characteristics of the proposed observer, where it can be concluded that the performance of the observer is improved as the order of the polynomial is high. The proposed methodology is applied to a class of Lotka-Volterra systems with two and three species. Finally, numerical simulations present the performance of the proposed observer.

An Integral High-Order Sliding Mode Control Approach for Stick-Slip Suppression in Oil Drillstrings

Abstract In this paper a novel sliding mode control law combined with a cascade control scheme is proposed for the suppression of stick-slip oscillations in oil drillstrings. It is assumed that the parameters of the system are uncertain and external disturbances are present. Numerical simulations on a generic simple model of stick-slip oscillations are provided to illustrate the control performance.

Sliding-mode Observer for Uncertainty Estimation in a Class of Chemical Reactor: A Differential-Algebraic Approach

The problem of the on-line estimation of the reaction heat in a continuous stirred tank reactor from temperature measurements is addressed in this paper. The proposed uncertainty observer is based on differential algebraic techniques, such that the algebraic observability condition of the uncertainty from noisy temperature measurements is easily verified and the observer structure is very simple, which lead to feasible implementation. The observer proposed is robust against noisy measurements and sustained disturbances. The good performance of the observer is shown by means of numerical simulations and is compared with a nonlinear Luenberger-type observer.

Impact of Production Objectives on Adiabatic FCC Regenerator Control

Abstract In adiabatic FCC regenerators, the classical approach of design and control of continuous stirred tank reactors identify stable steady states. This kind of reactors is a particular case of lumped parameter nonlinear systems. The easiness of regulation of the steady operating states depends on the relationship between system dynamics and control scheme. There have been several attempts for the evaluation of this relationship by systematic approaches, however the nonlinearities of these systems have troubled the evaluation goals. In partially controlled systems, such as chemical reactors, dynamic interactions among process variables might exhibit unexpected responses to control actions when the system is operating in some particular regions. These responses depend on the selection of control and manipulable variables. In this work, a methodology for the evaluation of control strategies is used to identify possible troubles when production objectives and process dynamics are noncompatible. The methodology is easy to understand and to apply to nonlinear lumped parameter systems that present control affine structure. Because the proposed methodology is independent of the kind of control used and the full process model is evaluated, it is possible to study the system behavior at any operating condition. An adiabatic FCC regenerator is used as example of the methodology application; three common production objectives are evaluated. Recommendations for the selection of operation objectives are given.

Evaluation of hydrocarbons and organochlorine pesticides and their tolerant microorganisms from an agricultural soil to define its bioremediation feasibility

The concentrations of hydrocarbons and organochlorine pesticides (OCPs), nutrients and tolerant microorganisms in an agricultural soil from a locality in Tepeaca, Puebla, Mexico, were determined to define its feasibility for bioremediation. The OCPs detected were heptachlor, aldrin, trans-chlordane, endosulfán I, endosulfán II, 1,1,1-bis-(4-chlorophenyl)-2,2-trichloroethane (4,4′-DDT), 1,1-bis-(4-chlorophenyl)-2,2-dichloroethene (4,4′-DDE) and endrin aldehyde, with values of 0.69–30.81 ng g−1. The concentration of hydrocarbons in the soil of Middle Hydrocarbons Fraction (MHF), C10 to C28, was 4608–27,748 mg kg−1 and 1117–19,610 mg kg−1 for Heavy Hydrocarbons Fraction (HHF), C28 to C35, due to an oil spill from the rupture of a pipeline. The soil was deficient in nitrogen (0.03–0.07%) and phosphorus (0 ppm), and therefore it was advisable to fertilize to bio-stimulate the native microorganisms of soil. In the soil samples, hydrocarbonoclast fungi 3.72 × 102 to 44.6 × 102 CFU g−1 d.s. and hydrocarbonoclast bacteria (0.17 × 105 to 8.60 × 105 CFU g−1 d.s.) were detected, with a tolerance of 30,000 mg kg−1 of diesel. Moreover, pesticideclast fungi (5.13 × 102 to 42.2 × 102 CFU g−1 d.s.) and pesticideclast bacteria (0.15 × 105 to 9.68 × 105 CFU g−1 d.s.) were determined with tolerance to 20 mg kg−1 of OCPs. Fungi and bacteria tolerant to both pollutants were also quantified. Therefore, native microorganisms had potential to be stimulated to degrade hydrocarbons and pesticides or both pollutants. The concentration of pollutants and the microbial activity analyzed indicated that bioremediation of the soil contaminated with hydrocarbons and pesticides using bio-stimulation of native microorganisms was feasible.

Temperature Regulation via PI High-Order Sliding-Mode Controller Design: Application to a Class of Chemical Reactor

The main issue of this paper is the synthesis of a robust control law for regulation purposes, which is applied to a class of chemical reactor which exhibits highly nonlinear and oscillatory behavior. The considered methodology employs the typical structure of Proportional-Integral controllers, where the corresponding integral term is now proposed as an integral high order sliding-mode compensator, which deals with the intrinsic nonlinearities of the system to be regulated. A theoretical frame is provided to demonstrate that the proposed controller produces semi-global practical stability; performance of the proposed methodology is assessed via comparison with other controllers.

Tracking Trajectories in a Continuous Anaerobic Bioreactor Employing a Nonlinear Proportional Controller

This work is related to the tracking of sulfate concentration trajectories in a continuous anaerobic bioreactor, where Desulfovibrio alaskensis is considered for different operation purposes. A new design of a class of nonlinear proportional control law with an adaptive gain was proposed. The proposed controller was applied to the mathematical bioreactors model with the kinetics experimentally corroborated; this describes the dynamics of biomass, sulfate and sulfide concentrations. The open-loop stability conditions of the optimum set points and the corresponding closed-loop performances were analyzed. The proposed control law is able to track trajectories, despite sustained disturbances. An Internal Model Control (IMC) Proportional-Integral Controller was implemented for comparison purposes and the corresponding performances were illustrated via numerical experiments.

Reduction of Cr(VI) utilizing biogenic sulfide: an experimental and mathematical modeling approach

AbstractThe aim of this work was to analyze the performance of a wastewater system for Cr(VI) and sulfate compounds reduction via mathematical modeling. The considered process is coupled to chemical reactors to achieve its tasks. The first stage of the considered process is a biological sulfate-reducing reactor, by which sulfate compounds can be reduced to biogenic sulfide; then, in the second stage, the above-mentioned biogenic sulfide is fed to a second reactor in which the Cr(VI) is reduced, allowing high Cr(VI) concentration removal. The kinetic model of the biological sulfate-reducing process and the Cr(VI) reduction via biogenic sulfide reactions were experimentally corroborated and employed as a benchmarck for the wastewater process analysis via numerical simulations to achieve several feasible operation conditions, under the system’s constraints. The mathematical model was extended to a continuous operation, where numerical experiments were carried out predicting an excellent removal of 99% of Cr(...