Design and Control for Liquid-Liquid Extraction Unit

Abstract

The aims of the study are to select and design a column for liquid-liquid extraction of acetic acid from aqueous solution and develop a control strategy of the system. liquid-liquid equilibrium data were found experimentally,then the tie lines data were correlated by Hand’s method with correlation coefficient near unity. All column dimensions were calculated, Number of theoretical stages , Number of actual stages, column height, Column diameter, Total plate area, Column cros-sectional area and Down comer area were equal to 3 ,5 ,3m ,2m ,22.44 m2 ,26.4 m2 and 3.96 m2 respectively. The characteristic equation, the Open Loop Transfer Function (OLTF) and the overall transfer function were obtained for stability analysis and tunning. The methods used for tunning and stability analysis were direct substitution, routh array, root locus and bode diagram to determine ultimate gain(ku), the frequency(ω) and ultimate period(pu).the response of system was plotted by inserting the obtained stable parameters into Ziegler-Nichols table. MATLAB was used to determine the system stability analysis and tunning. The results of this study were for two loops. The level of liquid in column control loop1 the average of ultimate gain ku is equal to 23.55 and the average of ultimate period pu is equal to 28.84 sec, for concentration of raffinate control loop2 the average of ultimate gain ku is equal to 19.766 and the average of ultimate period pu is equal to 3.929 sec, and this results were introduced into the Ziegler-Nichols table to calculate the optimum parameters for (P,PI and PID) controllers ,then the system was simulated and parameters of rise time, overshoot, decay ratio and settling time were obtained. These methods are proved to be identical in the results and each of them is qualified to be used for tunning and stability analysis without loss of accuracy. It is found that the digital format can be used for developing the liquid-liquid extraction control system .it is recommended that the control strategy must be developed and further studied using more advanced methods such as high performance control and distributed control system.