Roxana Both

Dynamic modeling and validation of 2-ethyl-hexenal hydrogenation process

Abstract The paper evaluates, by modeling and simulation, 2-ethyl-hexenal hydrogenation process in catalytic trickle bed three-phase reactors. The mathematical model consists of balance equations for gas and liquid phases. Reaction rate equations, transport models and mass balances were coupled to generalized heterogeneous models which were solved with respect to time and space with algorithms suitable for partial differential equations. The importance of mass transfer resistance inside the catalyst pellets as well as the dynamics of the different phases being present in the reactor is revealed. The dynamic mathematical model presented can be used to analyze and understand the interaction of various processes that take place inside the hydrogenation reactor and also to make preliminary calculation of experimental parameters. Another important use of the mathematical model is to determine the optimal operation conditions and to design the control system. The model is implemented in Matlab and tested in simulations achieving successful results.

Microcontroller Implementation of a Multivariable Fractional Order PI Controller

Fractional order calculus has been used intensively to control various types of processes. The main approaches towards fractional order controllers focus on the single-input-single-output systems. The general design procedure consists in a frequency domain specification of various performance criteria followed by optimization routines. The implementation issues regarding fractional order controllers are based on Oustaloup approximations and are centered on SISO processes. The present paper addresses the problem of implementing on a microcontroller a fractional order multivariable controller for time delay processes. The paper presents a tuning algorithm for determining the parameters of the multivariable fractional order controller and the implementation issues. The multivariable time delay process is implemented in Matlab Simulink environment. The experimental results show that the fractional order multivariable controller implemented on a simple microcontroller provides similar results to that obtained by simulation, even under uncertainty conditions.

Fractional order models for a cryogenic separation column

The chemical processes developed in the 13C-isotope separation plant are very complex and many details are not yet known in totality. The authors are concerned with the problem of developing effective and readily useful techniques for modeling and control of the isotope separation plant. In the present paper is presented a variant of continuous linear model. Recent studies show that fractional control methods are widely used and that non integer models describe completely the distributed systems behavior. Based on these studies the authors propose two fractional models of the isotope separation plant. The results are validated and compared by simulation, based on experimental data.

RGA analysis and decentralized control for a wastewater treatment plant

A vital process in wastewater treatment is the biological treatment with activated sludge. In Romania, there are still plenty of cases where the biological treatment stage is operated manually, leading to inefficient operation and implicitly to higher operational costs, increased difficulty in maintaining the quality of the effluent and less disturbance rejection capabilities. In our paper, we show that using a medium-fidelity first principle model and by carrying out an RGA analysis, a decentralized control strategy using PI controllers can be easily developed and tested before implementation, the control strategy giving good results in disturbance rejection and trajectory tracking.

Fractional and integer order control. Application to DC motor speed control

Sustainable engineering implies the active management of engineering resources, by cutting down expenses and ensuring the premises for further development. Advanced control strategies offer increased robustness, high reliability and efficiency, but they require fast computation times and powerful numerical resources. Hence, the trend in control engineering should be directed towards developing and employing cheap, reliable and energy-efficient devices that support the implementation of the advanced control strategies. This would eventually lead to a more sustainable use of the available technological resources and a decrease of the energy consumption. The present paper offers a comparison between a fractional order control algorithm and a traditional PI controller for a DC motor. The results show that the fractional order controller has the pros of the advanced control methods, offering increased robustness, while the cons related to the computation requirements are avoided through a simple implementation technique that is similar to that of a classical PI controller.

Models for the AC locomotives regenerative braking

Railway has been playing a significant role in passenger and cargo transportation. Electric railway systems are of growing importance with recent augments on energy saving and environmental friendly. The advantages of electrical railway compared to other transportation systems are cheaper sources of energy, lightweight locomotives, easier maintenance and a lower cost per passenger. Advances in power electronics allow trains to employ regenerative braking, resulting in a safer, more economical means of transport, with reduced maintenance and increased comfort. Estimating the regenerative braking process requires a complex model of the electrical and mechanical components, related to the mechanical behavior of the train, mechanical-electrical conversion in the traction motor operated as a generator, electrical equations of the power distribution system and of the power equipment in the traction substations.

Monitoring and control of liquid nitrogen level of the 13 C separation column using NI PXI-1031

This paper is a step forward by making real time control system design to monitor and control process variables to ensure its smooth operation and desired reliability. Liquid nitrogen level in the condenser is a core component of isotopic separation process to obtain (13C), so is needed a special focus on monitoring and control. The goal of the work is to design a controller for the liquid nitrogen in the condenser of (13C) isotope separation column using NI-PXI 1031 (PCI eXtensions for Instrumentation) from National Instruments. The designed ON-OFF controller is implemented in LabVIEW and are discussed the advantages and disadvantages.

Fractional order controller design for 13 C separation column

Controller design for an isotope separation column is recognized as a difficult and challenging problem, especially when the controller used is of fractional order. The objective of this work is to find out optimum settings for a fractional PIλ controller in order to fulfill three different robustness specifications of design for the compensated system, taking advantage of the fractional order, λ. Since this fractional controller has one parameter more than the conventional PI controller, one more specification can be fulfilled, improving the performance of the system and making it more robust to plant uncertainties, such as gain and time constant changes. For the tuning of the controller, an iterative optimization method has been used based on a nonlinear parametric minimization routine‥

Fractional order PD control of an isotope separation columns cascade

Cryogenic isotope separation columns are unique equipments used to produce enriched substances in the isotope of interest for many industrial applications. The control of an isotope separation column is a difficult and challenging task, being a highly nonlinear plant with large time constants and time delays. A single column can enrich only to a low level of concentration, so column cascades are used for high purity final products. A cascade of three isotope separation columns due to the interdependencies between them represents an even more difficult process to control. Due to the fact that in prior studies fractional order controllers have been successfully implemented for a single isotope separation column, the present paper addresses the development of a control system for the isotope separation column cascade using fractional order PD controllers. As design parameters were imposed the phase margin, gain crossover frequency and robustness of process gain variations. The simulation results, evaluated using the nonlinear mathematical model of the process, including all process input effects, prove the efficiency of the method.

Model validation, simulation and control for ammonia synthesis column

Ammonia synthesis is a very important process in the national economy and the column synthesis with the additional expensive equipments justify the necessity of the mathematical modeling, model validation and control system implementation. The work presents some problems of the ammonia synthesis model based on fundamental equations from physics and chemical engineering. After a model linearization some control conventional system are presented and validated.