Process analysis for treatment of industrial plating wastewater: simulation and control approach (original) (raw)
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Non-Linear Control Applied to Electrochemical Process to Remove Cr (VI) from Plating Wastewater
In this work the process to reduce hexavalent Chromium (Cr(VI)) in an electrochemical continuous stirred tank reactor is optimized. Chromium (VI) is toxic and potentially carcinogenic to living beings. It is produced by many industries and commonly discharged without any pretreatment. This electrochemical reactor itself can not satisfy the Mexican environmental legislation, which manages a maximum discharge limit of Chromium of 0.5 mg L -1 . In order to comply with this restriction, a proportional non-linear control law is implemented. Through numeric simulations, it is observed that the proposed control law has an acceptable performance, because the setpoint concentration is reached no matter the inlet concentration. It is also observed that the stabilization time of the reactor with close loop is about 2.6 times less than with open loop.
Chemical …, 2009
In this article a simple feedback controller approach for the regulation of Cr(VI) from electrochemical mixed-flow reactors in series is presented. The control approach is based on simple step response models obtained experimentally during the operation of three electrochemical continuous reactors in series. Based on simple first-order model and first-order model plus input delay to account for dead times induced by the measurement of the Cr(VI) two controllers are derived. The proposed controllers are composed of two parts: an uncertainty observer to compensate uncertainties and neglected terms in the input-output models and an inverse dynamics feedback controller. Numerical simulations show good closed-loop performance and robustness properties.
Journal of applied research and technology, 2008
The goal of this work is to describe the design of a feedback controller to regulate the Hexavalent chromium (Cr (VI)) concentration in industrial plating wastewater in a tubular reactor. Cr(VI) is a major pollutant present in industrial wastewaters common to the metal and mineral processing as well as to plating industries. For control purposes, a dynamic model of a plug flow reactor with dispersion is developed in the form of partial differential equations (PDE) via applying classical conservation principles; this model is experimentally corroborated using laboratory data. The proposed controller is based on uncertainty observer to infer unknown terms as diffusive transport and Cr(VI) kinetic rate; also Generic Model Controller (GMC) is coupled with this estimation methodology to provide robustness against model uncertainties. The controller leads to nonlinear PID plus double integral action, where the tuning rules are given in terms of the observer and GMC gains. A theoretical frame is given in order to show the stability properties of the closed-loop system under the proposed controller. Numerical simulation illustrates performance of the methodology proposed; a comparison with observer based I/O linearizing controller and a well tuned PID controller is done, which allows concluding that the observer based Generic Model Controller exhibits better performance.
Several chemical industrial plants such as electroplating and metal finishing plants have used strong acids and strong bases in production lines. These acids and bases are then released from the production lines to a wastewater treatment system and then treated to achieve compliance with an effluent standard. It is well known that the pH control of a wastewater treatment process is one of the most challenging control problems due to high non-linearity and time-variance of the pH value during pH titration. A conventional PID controller and an on-off controller are rarely able to handle this non- linearity resulting in poor control performances. Therefore, advanced nonlinear control techniques are needed. This research presents simulation study of Globally Linearizing Control (GLC) together with an extended Kalman Filter to control pH of the wastewater treatment process of an electroplating plant. The GLC, one of the advanced nonlinear model-based control techniques, has been develope...
2007
This work is aimed at obtaining and calibrating a dynamical model of the electrochemical reduction of Cr(VI) in a tubular continuous reactor with a spiral wire shaped anode at different conditions of pH (1.0 to 2.0) and residence times. An industrial wastewater sampled from a Mexican electroplating industry with about 1000 mg dm −3 of Cr(VI) was used for the experiments. It was found that pH exerts a strong influence on the performance of electrochemical reduction of Cr(VI). Thus at a wastewater influent pH = 1.0 and a residence time in the reactor of 38.5 min it is possible to reduce the Cr(VI) concentration from 1000 to 0.37 mg dm −3. However at an influent pH higher than 1.5, an effluent Cr(VI) concentration lower than 0.5 mg dm −3 cannot be obtained. A more complete dynamic model was applied incorporating pH and the dispersion effects that affect the electrochemical Cr(VI) removal. The model, which adequately describes the performance of the electrochemical process, can be used to optimize the performance of this kind of reactor with more reliability.
Modeling an electrochemical process to remove Cr(VI) from rinse-water in a stirred reactor
Journal of Chemical Technology & Biotechnology, 2003
Experimental studies were developed in a batch reactor (16 dm 3 ), to obtain the kinetic model of Cr(VI) removal by means of an electrochemical process. An overall kinetic model was obtained and experimentally validated in a continuous stirred electrochemical reactor (16 dm 3 ) with synthetic and industrial wastewater. To develop the mathematical model of the continuous reactor in relation to the Cr(VI) and Fe(II) concentration in the solution, a classical mass balance procedure was performed. The Cr(VI) concentration in the electrochemically-treated waters was less than 0.5 mg dm À3 . In the electrochemical process the Cr(VI) reduction is caused by the Fe(II) released from the anode due to the electric current applied, by the Fe(II) released for the dissolution (corrosion) of the electrodes due to the acidic media, and by reduction at the cathode. During the process, reduction from Fe(III) to Fe(II) occurs. All of these different reactions cause a diminution in the quantity of sludge generated. Finally, it was found that due to the slow rate of reduction of Cr(VI) during the first part of the process it is necessary to develop a method of control to apply the process in a continuous industrial system.
Multi-model control of wastewater treatment reactor
In this contribution a possible approach for designing multiple blended controller for wastewater treatment reactor is presented. Velocity-based linearisation framework for analysis of non-linear systems is used to assist control design. Due to this analysis tool the design of relatively simple controller is possible. The design procedure enables use of knowledge from linear systems control design and achieving desired performance not just in equilibrium points where system can be linearised but in whole operating region. This approach has confirmed its advantages on the wastewater treatment reactor control problem in tracking and regulatory control of dissolved oxygen level.
Real-time modelling and simulation applied to the treatment of electroplating wastewater
Proceedings of the 15th IFAC World Congress, 2002, 2002
Eco-industrial processes require high reliability control and supervision methodologies, so as to achieve the best compromise possible between the process' efficiency, safety and economy. Industries often focus on the two first objectives mainly, since they are unwilling to "experiment" not yet validated and/or complex control methodologies if safety and/or efficiency of the process may be jeopardized. This work focuses on an industrial wastewater treatment process, including a cyanides oxidation stage and a neutralization stage, applied to the surface treatment effluents. The project involved the development and validation of a model which enables to simulate various pH-control strategies as well as faults in the CSTRs.
Hybrid Model of a Wastewater-Treatment Electrolytic Process
International Journal of Electrochemical Science
This work is focussed on the development of models which can be implemented in efficient control devices to properly schedule batch electrolysis processes for wastewater treatment. The main goal has been to develop a hybrid approach based on a phenomenological mathematical model and a neural network methodology, in order to improve the quality of the model designed for electrolysis process of wastewaters. A well-known phenomenological model for the electrolyses of wastewaters and different neural network architectures were used, along with homogenous and heterogenous transfer functions. The models were validated with the results of a series of experiments consisting of the electrochemical oxidation of phenol wastes in different process conditions. The best results were obtained designing a feed-forward neural network with tangent hyperbolic axon as homogeneous transfer function (relative error of 8 %).
Adaptive Feedback Controller for Dosage of Water Treatment Chemicals
IFAC Proceedings Volumes, 2004
This paper describes an adaptive feedback PI-type controller for dosing of water treatment chemicals. The controller is based on Linguistic Equation (LE) method. The adaptive feedback LE-controller suits well for chemical dosage in such processes where fast adaptation of the controller is required. The performance of adaptation is based on identification of process states. The adaptive model modifies control parameters according to this knowledge. As a result, the adaptive LEcontroller can operate at the large range of process conditions. The control strategy for a flotation application was developed. Tuning and testing of the controller were carried out in a dynamic simulator. The controller operates moderately well in the simulator.