Design and optimization of temperature controller for high pressure rated modified CSTR system

Abstract

Continuous stirred tank reactor (CSTR) system is the need of the hour to mimic and maintain deep-sea conditions such as pressure, temperature, pH, etc. in the laboratory to study environmental effects. Design and optimization of a temperature controller for such reactor system are important areas in process control to offer a diverse range of research outputs. This paper attempts to identify suitable controller and tuning methods to optimize the system performance for a hyperbaric reactor system. CSTR maximum pressure and temperature ratings are 350 bar and 275 0 C respectively. In environmental CSTR systems, temperature control is an absolute challenge due to the strong on-line non-linearity, reactor vessel thickness to withstand high pressure and polytetrafluoroethylene (PTFE) liner to avoid corrosion while handling sea water. Various strategies are being employed to achieve highly precise temperature control by using proportional-integral (PI), proportional-derivative (PD) and proportional-integralderivative (PID) controllers for analysis purposes depending on requirement of the systems. A suitable control strategy was explored to develop an environmental CSTR system for deep-sea applications using real time on-line open loop temperature curve. First order plus dead time (FOPDT) process model was chosen to derive transfer function from the real time on-line system curve at atmospheric pressure and 310 C temperature condition. MATLAB SIMULINK tool was used for various controller simulation and result comparison. Although our attempt using PID or PI algorithms as an individual controller to obtain set precise temperature within the loop was convenient to tune, the cumulative error noticed in the loops made it impossible to handle oscillating poles and zeroes in case of modified options like environmental CSTR. During the course of the study, a number of tuning methods such as Ziegler-Nichols, Cohan-Coon, Chien-Hrones-Reswick and Wang-Juang-Chan tunning methods for suitable PD controller was also examined to optimize the temperature controller for environmental CSTR system. A simulation result on the environmental CSTR system is presented to show the efficiency of the various controllers and tuning rules. Performance indices for various tuning methods of the controller with and without PTFE liner are also calculated, compared, analyzed and presented, and a winning method using PD controller is identified.