Saidat Olanipekun Giwa

Application of Model Predictive Control to Renewable Energy Development via Reactive Distillation Process

Reactive distillation is a process that combines chemical reaction and separation in a single piece of equipment (distillation column). The process has a lot of benefits especially for those reactions occurring at conditions suitable for the distillation of the process components, and these result in significant economic advantages. However, owing to the complexities resulting from the integration of reaction and separation, its control is still a challenge to process engineers because it requires a control method that is robust enough to handle its complexities. Therefore, in this work, model predictive control (MPC) has been applied to a reactive distillation process used for developing a renewable energy known as biodiesel. The control algorithm of the MPC was formulated with the aid of MPC toolbox of MATLAB/Simulink in which the closed-loop models of the process were developed and simulated. The analysis of the results obtained from the simulations carried out for the optimization of the tuning parameters revealed that, among the tuning parameters considered, integral absolute error of the control system was less affected by the control horizon because its p-value was greater than 0.05 based on 95% confidence level. Furthermore, the simulation of the closed-loop system of the process using model predictive control tuned with control horizon of 11, prediction horizon of 18, weight on manipulated variable rate of 0.05 and weight on output variable of 2.17, which were the optimum parameters obtained using Excel Solver, showed that the system was well handled by the controller under servo control because it was able to get settled at desired mole fractions within 60 min. However, the settling time recorded in the case of regulatory control system of the process with the same controller was found not to be encouraging. Therefore, it is recommended that further work should be carried out on this subject matter in an attempt to obtain tuning parameters that will make the settling time of the closed-loop system of the process under regulatory control simulation very reasonable.

Control of a Reactive Distillation Process Using Model Predictive Control Toolbox of MATLAB

This research work has been carried out to investigate the application of the Model Predictive Control Toolbox contained in MATLAB in controlling a reactive distillation process used for the production of a biodiesel, the model of which was obtained from the work of Giwa et al.1. The optimum values of the model predictive control parameters were obtained by running the mfile program written for the implementation of the control simulation varying the model predictive control parameters (control horizon and prediction horizon) and recording the corresponding integral squared error (ISE). Thereafter, using the obtain optimum value of 5 and 15 for control horizon and prediction horizon respectively as well as a manipulated variable rate weight of 0.025 and an output variable rate weight of 1.10, various steps were applied to the setpoint of the controlled variable and the responses plotted. The results given by the simulations carried out by varying the model predictive control parameters (control horizon and prediction horizon) for the control of the system revealed that optimizing the control parameters is better than arbitrary choosing. Also, the simulation of the developed model predictive control system of the process showed that its performance was better than those used to control the same process using a proportional-integral-derivative (PID) controller tuned with Cohen-Coon and Ziegler-Nichols techniques. It has, thus, been discovered that the Model Predictive Control Toolbox of MATLAB can be applied successfully to control a reactive distillation process in order to obtain better performance than that obtained from a PID controller tuned with Cohen-Coon and Ziegler-Nichols methods.

System Identification and IMC-Based PID Control of a Reactive Distillation Process: A Case Study of n-Butyl Acetate Production

The identification of a reactive distillation system for the production of n-butyl acetate from the esterification reaction between acetic acid and n-butanol has been carried out in this research work. In order to achieve the aim of the research work, a prototype plant of the process was developed using ChemCAD from which dynamics data were generated upon applications of step changes to the reboiler duty and the reflux ratio, which were the input variables of the system. Thereafter, the transfer function of the process, later represented in Simulink environment, was formulated using the dynamics data and with the aid of MATLAB. The simulation of the transfer function model of the system was also carried out for open loop by applying step changes unto the input variables using the developed Simulink model of the system. Thereafter, the closed-loop control system developed also in Simulink environment was simulated by applying step changes to the set-point variable, which was the bottom mole fraction of n-butyl acetate. The results obtained from the simulation of the prototype plant of the reactive distillation process showed ChemCAD to be a powerful tool for steady state and dynamics prototype plant development. Furthermore, good representation and stability were also observed to exist in the system from the formulation and the simulation of the transfer function model of the process, which were carried out with the aid of MATLAB/Simulink. Moreover, the selection of appropriate closed-loop time constant contained in the tuning parameter formulas of IMC-based control system showed that the value suggested by Rivera et al. [1] was very good for this system, compared to those of Chien and Fruehauf [2] and Skogestad [3], because it could give closed-loop dynamic response with comparatively very low values of integral squared error (ISE), integral absolute error (IAE) and integral time absolute error (ITAE) for both proportional-integral (PI) and proportional-integral-derivative (PID) control systems. In addition, the comparison made between the IMC-based tuning approach and other ones (Cohen-Coon, Tyreus-Luyben and Ziegler-Nichols) considered in this work made it known that IMC-based tuning technique was the best among all those considered because its ISE, IAE and ITAE were found to be the lowest for both PI-and PID-controlled cases simulated.

Textile Wastewater Treatment Using Sodom Apple (Calotropis procera) - Aided Tamarind Seed as a Coagulant

Water contamination seems unavoidable as many human activities involve the use of water in one way or the other. Chemical coagulants, especially aluminium based, which are widely used in treatment of wastewater or contaminated water have been associated with some health issues. Research on the use of plant based coagulants in water treatment now draws a lot of attentions, not only because the natural coagulants are presumed safe but also because of their biodegradable nature. In this present study, efforts have been made to evaluate the effectiveness of locally available tamarind seed powder as natural coagulant and Sodom apple (Calotropis procera) as coagulant aid for the treatment of textile wastewater. The tests were carried out using the conventional jar test apparatus at various pH and coagulant dosage with no aid added. Also, three sets of jar test experiments were performed at constant values of coagulant dosage and pH (which were found to be favourable in the first experiments) by varying the dosage of liquid and solid coagulant aid as well as time. The results obtained show that pH slightly affected the pollutants removal efficiency of the unaided coagulation. The neutral pH was found to be favourable with turbidity and colour removal of 22.25% and 30.36% respectively. The optimum mixing time of turbidity removal efficiency was found to be 2 min with rapid mixing of 30 seconds and 1½ min of slow mixing with turbidity and colour removal of 69.48% and 60.53% respectively. The optimum dosage was found to be 4.0 g of coagulant and 1.0 g of coagulant aid for turbidity, total dissolved solid and colour removal efficiency.

Steady-State Modelling and Simulation of a Reactive Distillation Process for n-Butyl Acetate Production Using CHEMCAD

This work has been carried out to demonstrate the application of a process simulator known as CHEMCAD to the modelling and the simulation of a reactive distillation process used for the production of n-butyl acetate, with water as the by-product, from the esterification reaction between acetic acid and n-butanol. The esterification reaction, which is generally an equilibrium type, was modelled as two kinetic reaction types in the reaction section of the column used, which had 17 stages with the middle section (stages 6 – 12) being the reaction section. A reflux ratio of 3 and reboiler duty of 78 kJ/min as well as 30 mL/min of each of the reactants with 99% molar purity were used for the simulation of the column. The results obtained revealed that the developed model was a valid one because there was a very good agreement between the results and the theoretical knowledge of a distillation column based on the fact that the desired (which was the heavy) product (n-butyl acetate) was found to have the highest mole fraction in the bottom section of the column while the by-product of the process (water) was discovered to have a mole fraction higher than that of n-butyl acetate in the top (condenser) section of the column. Therefore, CHEMCAD has been applied to the steady-state simulation of the reactive distillation process used for the production of n-butyl acetate from the esterification reaction of acetic acid and n-butanol successfully.

Dynamic Simulation of a Reactive Distillation Process for n-Butyl Acetate Production Using CHEMCAD

The dynamic simulation of a reactive distillation process developed with the aid of CHEMCAD for the production of n-butyl acetate has been carried out in this research work. Originally, the by-product of the process was water. The developed model of the system was first simulated for steady state using a reflux ratio of 3 and a reboiler duty of 1.4 kW in order to have initial values for the mole fractions of the components involved. The model was converted to a dynamic type by activating the “Dynamics” in the “Convergence” tab of the “Run” menu of CHEMCAD. The dynamic model of the system was run using different (positive and negative) step changes applied to the input variables, which were reflux ratio and reboiler duty, of the process. The results obtained from the steady-state simulation showed that only n-butyl acetate and unconverted acetic acid were existing in the reboiler section of the column initially. The dynamic simulation of the process showed that the system was a stable one because it could get settled after some running time of its dynamic model for all the step changes in the two input variables considered. It was also discovered from the simulations carried out that the dynamic responses of the system to negative step changes in reflux ratio were smoother than those obtained when positive step changes were applied to the same input variable. Moreover, the applications of negative step changes to the reboiler duty resulted in decreases in the mole fractions of n-butyl acetate present in the bottom section of the column while the applications of positive changes to the same reboiler duty gave rise to increases in the mole fraction values of the desired product that was collected through the reboiler section of the column. It was discovered from the results obtained that the higher the reboiler duty of the system that was applied in the production of n-butyl acetate from the esterification reaction involving acetic acid and n-butanol, the faster the system was approaching its dynamic steady state.