Modeling and Control of a Continuous Stirred Tank Reactor Based on a Mixed Logical Dynamical Model

A novel control strategy for a continuous stirred tank reactor(CSTR)system,which has the typical characteristic of strongly pronounced nonlinearity,multiple operating points,and a wide operating range,is initiated from the point of hybrid systems.The proposed scheme makes full use of the modeling power of mixed logical dy- namical(MLD)systems to describe the highly nonlinear dynamics and multiple operating points in a unified framework as a hybrid system,and takes advantage of the good control quality of model predictive control(MPC) to design a controller.Thus,this approach avoids oscillation during switching between sub-systems,helps to relieve shaking in transition,and augments the stability robustness of the whole system,and finally achieves optimal(i.e. fast and smooth)transition between operating points.The simulation results demonstrate that the presented ap- proach has a satisfactory performance.

Development of Linearizing Feedback Control with a Variable Structure Observer for Continuous Stirred Tank Reactors

This paper deals with the design of an observer-based nonlinear control for continuous stirred tank reactors(CSTR).A variable structure observer is constructed to estimate the whole process state variables.This observer is basically the conventional Luenberger observer with an additional switching term used to guarantee the robustness against modeling errors.The observer is coupled with a nonlinear controller,designed based on input-output linearization for controlling the reactor temperature.The asymptotical stability of the closed-loop system is shown by the Lyapunov stability theorem.Finally,computer simulations are developed for showing the performance of the proposed approach.

Model identification of continuous stirred tank reactor based on QKLMS algorithm

The continuous stirred tank reactor(CSTR)is one of the typical chemical processes.Aiming at its strong nonlinear characteristics,a quantized kernel least mean square(QKLMS)algorithm is proposed.The QKLMS algorithm is based on a simple online vector quantization technology instead of sparsification,which can compress the input or feature space and suppress the growth of the radial basis function(RBF)structure in the kernel learning algorithm.To verify the effectiveness of the algorithm,it is applied to the model identification of CSTR process to construct a nonlinear mapping relationship between coolant flow rate and product concentration.In additiion,the proposed algorithm is further compared with least squares support vector machine(LS-SVM),echo state network(ESN),extreme learning machine with kernels(KELM),etc.The experimental results show that the proposed algorithm has higher identification accuracy and better online learning ability under the same conditions.

Bioleaching of chalcopyrite by mixed culture of moderately thermophilic microorganisms

A mixed culture of moderately thermophilic microorganisms was enriched from acid mine drainages(AMDs)samples collected from several sulphide mines in China,and the bioleaching of chalcopyrite was conducted both in shake flask and bioreactor.The results show that in the shake flask,the mixture can tolerate 50 g/L chalcopyrite after being acclimated to gradually increased concentrations of chalcopyrite.The copper extraction increases obviously in bioleaching of chalcopyrite with moderately thermophilic microorganisms supplemented with 0.4 g/L yeast extract at 180 r/min,74% copper can be extracted in the pulp of 50 g/L chalcopyrite after 20 d.Compared with copper extractions of mesophilic culture,unacclimated culture and acclimated culture without addition of yeast extract,that of accliniated culture with addition of yeast extract is increased by 53%,44% and 16%,respectively.In a completely stirred tank reactor,the mass fraction of copper and total iron extraction reach up to 81% and 56%,respectively.The results also indicate that it is necessary to add a large amount of acid to the pulp to extract copper from chalcopyrite effectively.

Determination of Heroin Based on Analyte Pulse Perturbation to an Oscillating Chemical Reaction

A new analytical method is proposed for the determination of heroin based on a sequential perturbation caused by trace amounts of heroin in the Cu(Ⅱ)-catalyzed oscillating reaction between hydrogen peroxide and sodium thiocyanate in an alkaline medium with the aid of a continuous-flow stirred tank reactor(CSTR). The method relies on the linear relationship between the change in oscillation period of the system and the concentration of heroin, with a detecting limit of 4.0×10^(-7) mol/L. The calibration curve fits a linear equation very well when the concentration of heroin is in the range of 2.0×10^(-6)_1.2×10^(-5) mol/L(r=0.9971). This method features good precision(RSD=0.98%). The influences of temperature, injection point, flow rate and reaction variables on the oscillation period were investigated in detail and a possible mechanism of the performance of heroin in the Cu(Ⅱ)-catalyzed oscillating reaction system is also discussed. The proposed method opens a new avenue for the determination of heroin.

PSO Based Multi-Objective Approach for Controlling PID Controller

CSTR(Continuous stirred tank reactor)is employed in process control and chemical industries to improve response characteristics and system efficiency.It has a highly nonlinear characteristic that includes complexities in its control and design.Dynamic performance is compassionate to change in system parameterswhich need more effort for planning a significant controller for CSTR.The reactor temperature changes in either direction from the defined reference value.It is important to note that the intensity of chemical actions inside the CSTR is dependent on the various levels of temperature,and deviation from reference values may cause degradation of biomass quality.Design and implementation of an appropriate adaptive controller for such a nonlinear system are essential.In this paper,a conventional Proportional Integral Derivative(PID)controller is designed.The conventional techniques to deal with constraints suffer severe limitations like it has fixed controller parameters.Hence,A novel method is applied for computing the PID controller parameters using a swarm algorithm that overcomes the conventional controller’s limitation.In the proposed technique,PID parameters are tuned by Particle Swarm Optimization(PSO).It is not easy to choose the suitable objective function to design a PID controller using PSO to get an optimal response.In this article,a multi-objective function is proposed for PSO based controller design of CSTR.

Multi-objective nonlinear model predictive control through switching cost functions and its applications to chemical processes

This paper proposes a switching multi-objective model predictive control(MOMPC) algorithm for constrained nonlinear continuous-time process systems.Different cost functions to be minimized in MPC are switched to satisfy different performance criteria imposed at different sampling times.In order to ensure recursive feasibility of the switching MOMPC and stability of the resulted closed-loop system,the dual-mode control method is used to design the switching MOMPC controller.In this method,a local control law with some free-parameters is constructed using the control Lyapunov function technique to enlarge the terminal state set of MOMPC.The correction term is computed if the states are out of the terminal set and the free-parameters of the local control law are computed if the states are in the terminal set.The recursive feasibility of the MOMPC and stability of the resulted closed-loop system are established in the presence of constraints and arbitrary switches between cost functions.Finally,implementation of the switching MOMPC controller is demonstrated with a chemical process example for the continuous stirred tank reactor.

Balanced multiple weighted linear discriminant analysis and its application to visual process monitoring

Visual process monitoring is important in complex chemical processes.To address the high state separation of industrial data,we propose a new criterion for feature extraction called balanced multiple weighted linear discriminant analysis(BMWLDA).Then,we combine BMWLDA with self-organizing map(SOM)for visual monitoring of industrial operation processes.BMWLDA can extract the discriminative feature vectors from the original industrial data and maximally separate industrial operation states in the space spanned by these discriminative feature vectors.When the discriminative feature vectors are used as the input to SOM,the training result of SOM can differentiate industrial operation states clearly.This function improves the performance of visual monitoring.Continuous stirred tank reactor is used to verify that the class separation performance of BMWLDA is more effective than that of traditional linear discriminant analysis,approximate pairwise accuracy criterion,max–min distance analysis,maximum margin criterion,and local Fisher discriminant analysis.In addition,the method that combines BMWLDA with SOM can effectively perform visual process monitoring in real time.

Reactive Flash Simulation of the Continuous Melt Transesterification Process of Polycarbonate

A model of the continuous melt transesterification process of bisphenol-A and diphenyl carbonate in a continuous stirred tank reactor to produce polycarbonate is presented. The model is developed by using the molecular species model of polycarbonate melt polycondensation and the modeling method of reactive flash. Liquid phase is treated as perfect mixed flow and the vapor phase is assumed following the ideal gas law. With this model, the continuous melt transesterification process of bisphenol-A and diphenyl carbonate is examined with respect to different orocess parameters.

Nonlinear model predictive control based on hyper chaotic diagonal recurrent neural network

Nonlinear model predictive controllers(NMPC)can predict the future behavior of the under-controlled system using a nonlinear predictive model.Here,an array of hyper chaotic diagonal recurrent neural network(HCDRNN)was proposed for modeling and predicting the behavior of the under-controller nonlinear system in a moving forward window.In order to improve the convergence of the parameters of the HCDRNN to improve system’s modeling,the extent of chaos is adjusted using a logistic map in the hidden layer.A novel NMPC based on the HCDRNN array(HCDRNN-NMPC)was proposed that the control signal with the help of an improved gradient descent method was obtained.The controller was used to control a continuous stirred tank reactor(CSTR)with hard-nonlinearities and input constraints,in the presence of uncertainties including external disturbance.The results of the simulations show the superior performance of the proposed method in trajectory tracking and disturbance rejection.Parameter convergence and neglectable prediction error of the neural network(NN),guaranteed stability and high tracking performance are the most significant advantages of the proposed scheme.

Identification of LPV Models with Non-uniformly Spaced Operating Points by Using Asymmetric Gaussian Weights

In this paper, asymmetric Gaussian weighting functions are introduced for the identification of linear parameter varying systems by utilizing an input-output multi-model structure. It is not required to select operating points with uniform spacing and more flexibility is achieved. To verify the effectiveness of the proposed approach, several weighting functions, including linear, Gaussian and asymmetric Gaussian weighting functions, are evaluated and compared. It is demonstrated through simulations with a continuous stirred tank reactor model that the oroposed aonroach nrovides more satisfactory aonroximation.

Stabilization of CSTR w ith Self-tuning Sliding Mode Controller Using T-S Fuzzy Linearization

A self-tuning reaching law based sliding mode control(SMC)theory is proposed to stabilize the nonlinear continuous stirred tank reactor(CSTR).T-S fuzzy logic is used to build a global fuzzy state-space linear model.Combing the traits of SMC and CSTR,three fuzzy rules can meet the requirements of controlled system.The self-tuning switch control law which can drive the state variables to the sliding surface as soon as possible is designed to ensure the robustness of uncertain fuzzy system.Lyapunov equation is applied to proving the stability of the sliding surface.The simulations show that the proposed approach can achieve desired performance with less chattering problem.

Output neighboring-extremal and NCO tracking control in the optimal operation of CSTR

A new optimizing framework of process operation is proposed to deal with optimizing op- eration of continuous stirred tank reactor （CSTR）. The optimization framework includes two layers： the first layer, necessary condition of optimally （NCO） tracking controller, calculates the optimal set-point of the process; and the second layer, output neighboring-extremal controller, calculates the input values of the controlled plant. The algorithm design and convergent analysis of output neighboring-extremal controller are discussed emphatically, and in the case of existing parametric uncertainty, the approach is shown to converge to the optimum atmost in two iterations. At last the approach is illustrated by simulation results for a dynamic CSTR.

Nonlinear model predictive control with guaranteed stability based on pseudolinear neural networks

A nonlinear model predictive control problem based on pseudo-linear neural network (PNN) is discussed, in which the second order on-line optimization method is adopted. The recursive computation of Jacobian matrix is investigated. The stability of the closed loop model predictive control system is analyzed based on Lyapunov theory to obtain the sufficient condition for the asymptotical stability of the neural predictive control system. A simulation was carried out for an exothermic first-order reaction in a continuous stirred tank reactor.It is demonstrated that the proposed control strategy is applicable to some of nonlinear systems.

An innovative design of septic tank for wastewater treatment and its performance evaluation： An applicable model for developing countries

A study was carried out to evaluate the treatment efficiency of modified model of septic tank（ST）for the treatment of domestic wastewater.The objective was to explore the possibility of increasing the removal efficiency,at household level,thereby reducing cost and treatment burden on city level treatment plants.For this purpose,a bench scale model of ST was prepared and operated continuously for 78 days at different detention times i.e.,48,24 and 12 h and at two reactor temperatures viz.15℃ and 25℃.Domestic wastewater was fed to the bench scale ST without pre-settling.Research was conducted under two different arrangements.Firstly,by installing baffles in the bench scale ST（called Run-1 setup）,and secondly by installing perforated plates between the baffles（called Run-2 setup）.Results demonstrated that Run-2 setup is better than Run-1 setup.Temperature significantly affects the efficiency.Detention time of 24 h was found feasible.Run-2 setup demonstrated a percentage BOD removal of 45%with effluent BOD of 113 mg·L^-1 at 15℃ and 85%removal with effluent BOD of 31 mg·L^-1 at 25℃.It is concluded that if a modified design of ST using Run-2 setup is provided at household level,the effluent coming out of the house will meet the National Environmental Quality Standards（NEQS）when reactor temperature is close to 25℃.Development authorities are suggested to change their by-laws and make modified ST mandatory for all households.This may significantly reduce the cost and footprint of city level wastewater treatment plants being planned.