Abdulwahab 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.

Modelling, Simulation and Sensitivity Analysis of a Fatty Acid Methyl Ester Reactive Distillation Process Using Aspen Plus

Reactive distillation, being an intensified process of combining reaction and distillation in a single vessel, is an ongoing research. This work considered the use of this novel process to investigate how the purity of a fatty acid methyl ester (oleic acid methyl ester – methyl oleate), which is an alternative fuel that has a potential economic bedrock, vary with variations in reflux ratio and reboiler duty with the aid of Aspen Plus model of the process. The column employed in developing the model of the process was a RadFrac type having 29 stages, which was divided into five sections, namely condenser (top), rectifying, reaction, stripping and reboiler (bottom) sections. After the development, the model was simulated using UNIversal QUAsiChemical model (UNIQUAC) base method. In order to investigate the sensitivity of the system, reflux ratio and reboiler duty were varied from 2.0-5.5 and 1350-1800 W, respectively. The results obtained from the steady-state simulation of the process revealed that the developed Aspen Plus model of the system was table because it was able to converge when simulated. Furthermore, it was discovered from the sensitivity analysis carried out that a methyl oleate having a mole fraction of approximately 0.7627 could be obtained from the process when the reflux ratio and the reboiler duty were 2.0 and 1800 W respectively. Also, it was observed that the mole fraction of methyl oleate was sensitive to both reflux ratio and reboiler duty because the variations in them (reflux ratio and reboiler duty) resulted in corresponding variation in the methyl oleate mole fraction obtained from the system.

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.

Kinetics and Isotherm Studies of Liquid Phase Adsorption of Cationic Dye onto Chitosan Synthesized from Crab Shells

The use of cheap and eco-friendly adsorbents studied as an alternative to activated carbon for removal of dyes from wastewater is the focus of this paper. Chitosan, which was produced from food industry waste (crab shells), was synthesized, characterized and utilized as adsorbent to remove cationic dye, basic blue, from wastewater by adsorption. Characteristics of the synthesized chitosan biosorbents was established using scanning electron microscope (SEM), and Fourier Transform Infra-Red (FTIR) spectroscopy. Experiments were conducted in batch forms to investigate the effects of contact time, initial dye concentration and adsorbent dosage. Kinetic and isotherm analysis of the adsorption process were also carried out. The results obtained revealed that removal efficiency of the chitosan was increased as the contact time and chitosan biosorbent dose were increased, but a decrease with increasing initial concentration of basic dye was observed. The pseudo-second order reaction model was found to describe the biosorption process best, with chemisorption as the rate limiting step. The maximum colour removal efficiencies of chitosan at dosage of 4 g for time duration of 90 min was found to be 91.88% of the dye from a solution of 80 ppm. The pseudo-second order kinetic model was also seen to agree very well with the dynamic behaviour of the adsorption of basic blue on chitosan under different contact time, initial dye concentrations and adsorbent dosages. The dynamic behaviour of adsorption of basic blue onto chitosan has the model fitness in the following order: pseudo-second order > Elovich model > pseudo-first order. The Elovich equation was found to be the best fit equilibrium isotherm for the sorption of basic blue onto chitosan based on linearized correlation coefficient. Moreover, the equilibrium isotherm has its model fitness to be in the order of Elovich model > Langmuir model > Freundlich model.

Cascade PID Control of a Reactive Distillation Process for Biodiesel Production: A Comparison with Conventional PID Control

The combination of chemical reaction and distillation, which is analogous to inserting a chemical reactor into a distillation column, is a phenomenon that can be accomplished using a single piece of equipment known as a reactive distillation column, and the phenomenon is, thereby, referred to as reactive distillation process. Because of this combination, a lot of benefits such as improving reaction conversion, suppressing side reactions and utilizing heat of reaction for mass transfer operation can be achieved. However, this combination has made the control of this process a little bit challenging because of some disturbances that normally affect its smooth running. Therefore, cascade control method, being a type that can be used to handle any disturbance before it affects the main process, is applied in this work to carry out the control of a biodiesel reactive distillation process using proportional-integral-derivative (PID) control algorithm. The responses of the process towards the applications of step changes to the input variable (reboiler duty) of the process revealed that it was stable because it could attain steady states. Also, the closed-loop simulations showed that cascade PID controller was better for the control of the process than the conventional PID controller owing to the fact that the responses of the cascade PID control system, upon the application of step changes to the set-point value of the controlled variable, were found to get to the desired setpoint faster and in a better way than those of the conventional PID control system. Moreover, the superiority of the cascade PID controller over the conventional one was demonstrated by the estimation of the integral absolute error (IAE) and integral squared error (ISE) of the cascade control system, which were obtained to be less than those of the conventional PID control system.

Inferential Control of Fuel Additive Purity via Reactive Distillation Process

In this work, the control of the mole fraction of a fuel additive being produced in a reactive distillation column has been carried out using proportional-integral-derivative (PID) control. The fuel additive considered in this case was isopropyl alcohol, which was produced from the reaction between propylene and water. To accomplish the work, a ChemCAD model of the process was first developed and simulated to convergence before it was converted to dynamic type from which the dynamic responses of the system were generated and used, with the aid of MATLAB, to develop a transfer function model having the reboiler duty, the reflux ratio and the temperature of the bottom product as the input, the disturbance and the output variables of the process, respectively. The obtained transfer function model was used to develop the open-loop and the closed-loop Simulink models of the process that were also simulated. The closed-loop simulation was carried out with the objective of achieving a fuel additive product with a mole fraction of 0.97, and this was done using a PID controller that was applied inferentially via the product temperature. The results obtained showed that the control of the fuel additive mole fraction could be achieved inferentially, with PID controller tuned with Cohen-Coon and Simulink approaches, using product temperature.

Kinetics, Optimization and Proximate Analysis of Drying Moringa Oleifera Seeds in A Tray Dryer

This study examined the drying behaviour, optimum drying conditions and proximate analysis of Moringa oleifera seeds in a tray dryer. Thirteen (13) experimental data sets were generated using Box-Behnken design of design expert at varying temperature, contact time and fan speed on response surface methodology. Data generated from the experiment were fitted into existing models to determine the best fit using Excel Solver. Experimental data was used to simulate mathematical model developed using Box-Behnken design with the objective of minimizing the moisture content of the moringa seed within the lower and upper bound of 25-50°C (drying temperature), 30-100 mins (contact time) and 0.5-2.5 m/secs (fan speed). It was shown that the moisture ratio decreases with increasing drying time in all the plots with equilibrium moisture content being achieved within the range of 60-90 minutes at different operating conditions. However, the experiments with temperature (50°C) and fan speed (2.5 m/s) exhibited lowest moisture ratio with varying time. Also, the drying rate decreased continuously throughout the drying period in all the graphs with no constant rate period at any of the operating conditions. Wang and Singh model best described the drying behaviour of the moringa oleifera seeds in a tray dryer with R2 and χ2 values of 0.9991 and 0.00017 respectively at drying temperature of 50°C, fan speed of 0.5 m/s and contact time of 65 min. The moringa seeds that were dried at temperature 37.5°C, contact time 65 mins and fan speed of 1.5 m/s have moisture content of 17.71% with highest crude carbohydrate of 75.49%. A minimum moisture content of 16.7390% was obtained at drying temperature of 25°C, contact time of 75 mins and fan speed of 2.5 m/s using the developed optimization model that gives an excellent prediction with R2 value of 0.9918.

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.