Development and assessment of a Manual and Automated PID Controllers for the Optimum Production of Ethylene Glycol in a CSTR

Abstract

Industrially, one of the techniques used to enhance the optimum production of petrochemicals is the configuration of process control units such as gas chromatography (G.C. Analyzer) for concentration and thermocouple for temperature in the production system. This research focused on the application of the principles of mass and energy conservation in the development of dynamic or unsteady state models for predicting the behaviour of the system or process involved in the production of ethylene glycol from a reaction involving oxidation of ethylene to ethylene oxide which further undergoes hydrolysis to produce ethylene glycol in a continuous stirred tank reactor (CSTR). The high mathematical complexities of the mass and energy balance models of the Process as a result of the reaction kinetic scheme of the non-elementary reaction of the process which integrates both linear and non-linear terms into the models were resolved by applying the principles of Taylor’s series expansion, Laplace Transform, partial fraction and matrix appropriately in the development of the dynamic models. Process simulation tool Simulink was utilized in the configuration of closed-loop systems (thermocouple and G. C. Analyzer) at the feed point of the reactor for process variables (temperature and concentration) control during the process using proportional, integral and derivative (PID) as the controller parameters. The results of the process behaviour as shown in the temperature and concentration profiles versus time show that the use of manual tuning of different controller parameters (PID) of (0, 1 and 0), (0, 2 and 3) and (1.5,0.5 and 0) for temperature control and (3,0 and 0), (0,1 and 2) and (4,1 and 2) for concentration. The system experienced a high level of fluctuations and would not attain its stability or steady state even at process time above 16seconds. Whereas, the use of automatic tuning of desired controller gains of (1.361, 1.056 and 0.4109) for KP, KI and KD (PID) for temperature and pressure with tuning of 143.9 times requires a maximum time of 8 seconds for the system to attain stability. Ths study showed that automated tuning of the controller resulted in better performance characteristics for optimum production of ethylene glycol in a non-isotheral continuous stirred tank reactor within the shortest possible time.