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Coimbra, Portugal

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Brasio A.S.R.,University of Coimbra | Romanenko A.,Ciengis SA | Santos L.O.,University of Coimbra | Fernandes N.C.P.,University of Coimbra
Bioresource Technology | Year: 2011

The transesterification reaction models available in the literature are valid only for one particular mixing condition. In this work, a modeling strategy is presented in order to predict the effect of mixing conditions in the transesterification process. The proposed methodology was applied to independent sets of experimental data available in the literature that show the dependency of the transesterification reaction on the frequency of rotation of the stirrer. The accuracy of the developed models corroborates the validity of the proposed modeling approach. © 2011 Elsevier Ltd.


Brasio A.S.R.,University of Coimbra | Brasio A.S.R.,Ciengis SA | Romanenko A.,Ciengis SA | Fernandes N.C.P.,University of Coimbra
AIP Conference Proceedings | Year: 2012

The work concerns the system identification of industrial processes via the Sequential Quadratic Programming algorithm. The proposed approach, testing scenarios, and the system identification results are discussed. The tool is tested with two datasets, the first one collected in loco from an industrial process and the second one generated with a plant simulator of a continuous stirred tank reactor, a system widely used in industry. In both cases, the resulting models capture well the process dynamics. © 2012 American Institute of Physics.


Brasio A.S.R.,University of Coimbra | Brasio A.S.R.,Ciengis SA | Romanenko A.,Ciengis SA | Fernandes N.C.P.,University of Coimbra
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2014

Stiction is a major problematic phenomenon affecting industrial control valves. An approach for detection and quantification of valve stiction using an one-stage optimization technique is proposed. A Hammerstein Model that comprises a complete stiction model and a process model is identified from industrial process data. Some difficulties in the identification approach are pointed out and strategies to overcome them are suggested, namely the smoothing of discontinuity points. A simulation study demonstrates the application of the proposed technique. © 2014 Springer International Publishing.


Brasio A.S.R.,University of Coimbra | Brasio A.S.R.,Ciengis SA | Romanenko A.,University of Coimbra | Fernandes N.C.P.,University of Coimbra
Applied Mathematics and Information Sciences | Year: 2015

System identification plays an important role in the development of process simulators and controllers. The ability to determine correctly the model parameters directly affects the model quality and, therefore, the model based controller performance. This work details the development of a system identification approach and its computational implementation based on sequential quadratic programming (SQP) in which first and second order linear systems, represented in state-space, are identified from simulated and from real industrial process data. Both single-input single-output and multivariable processes are considered. The resulting optimization problem may become not trivial to solve as one of the examples illustrates. It is shown how a rescaling of the decision variables or the use of a priori process knowledge may be used in order to overcome the difficulties and to improve the quality of the results. © 2015 NSP.


Brasio A.S.R.,University of Coimbra | Brasio A.S.R.,Ciengis SA | Romanenko A.,Ciengis SA | Fernandes N.C.P.,University of Coimbra
IFAC Proceedings Volumes (IFAC-PapersOnline) | Year: 2015

Stiction is a persistent control valve problem in the process industry responsible for oscillations and, consequently, losses of productivity. Its early detection and separation from other oscillation causes is an important issue in the industrial context. One of simple and effective approaches to detect stiction has been proposed by Yamashita that employed a pattern recognition principle. While its performance is good in flow control loops, it fails to properly diagnose other types of processes. The present work details a new approach that enables the application of the Yamashita pattern recognition principle to level and other integrating process control loops. A simulation study demonstrates its capabilities in clean and noisy environments and analyzes the impact of the noise on the diagnostic performance. © 2015, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved.


Brasio A.S.R.,Ciengis SA | Romanenko A.,Ciengis SA | Leal J.,Ciengis SA | Santos L.O.,University of Coimbra | Fernandes N.C.P.,University of Coimbra
Journal of Process Control | Year: 2013

The economic performance of an industrial scale semi-batch reactor for biodiesel production via transesterification of used vegetable oils is investigated by simulation using nonlinear model predictive control (NMPC) technology. The objective is to produce biodiesel compliant to the biodiesel standards at the minimum costs. A first-principle model is formulated to describe the dynamics of the reactor mixture temperature and composition. The feed oil and mixture composition are characterized using a pseudo-component approach, and the thermodynamic properties are estimated from group contribution methods. The dynamic model is used by the NMPC framework to predict the optimal control profiles, where a multiple shooting based dynamic optimization problem is solved at every sampling time. Simulation results with the economic performance of an industrial scale semi-batch reactor are presented for control configurations manipulating the methanol feed flow rate and the heat duty. © 2013 Elsevier Ltd.


Brasio A.S.R.,University of Coimbra | Brasio A.S.R.,Ciengis SA | Romanenko A.,Ciengis SA | Fernandes N.C.P.,University of Coimbra
Industrial and Engineering Chemistry Research | Year: 2014

In the process industry, it is crucial to ensure safety, high product quality, strict environmental compliance, and optimum economics. Among other important factors, this calls for high performance of the control loops. One of the main root causes for poor performance is control valve malfunctions. In particular, stiction is a long-standing valve problem in the process industry, causing limit cycles with a negative impact on process performance. Therefore, it is important to detect this phenomenon as early as possible, to distinguish it from other oscillation causes, to determine the correct maintenance measures, and, if applicable, to apply proper stiction compensation. The present survey covers the field of stiction modeling, detection, and compensation, encompassing main research directions and significant contributions that have been reported in the literature. The relationship among different approaches is outlined showing their strengths and weaknesses. The review is complemented with a description of academic and commercial software packages that incorporate stiction diagnosis. Finally, a view on possible future research directions is provided. © 2014 American Chemical Society.


Brasio A.S.R.,University of Coimbra | Brasio A.S.R.,Ciengis SA | Romanenko A.,Ciengis SA | Fernandes N.C.P.,University of Coimbra | Santos L.O.,University of Coimbra
Journal of Process Control | Year: 2016

Typically, the large-scale production of biodiesel involves continuous operation plants. Also, the final biodiesel product has to comply with specifications imposed by standards of quality in order to be marketable. These quality constraints must be satisfied during the production at the minimum possible operating cost, in order to make the process economically viable. In this context, a nonlinear model predictive controller (NMPC) is applied to control the oil transesterification section of a continuous biodiesel plant. The controller determines the optimal profiles of the process variables using a nonlinear mechanistic model of the whole transesterification section. The model describes the dynamics of the composition and temperature of the liquid mixture in the reactors and in the decanters, as well as of the decanters interface level. The capability of the proposed NMPC strategy to improve the process economic performance and to enforce the final biodiesel specifications is demonstrated by simulation. © 2016 Elsevier Ltd

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