Simulation Of Control System In Divided Wall Column And Control Experimental Study Of Vapour Splitter Based On Temperature Monitoring

Divided wall column has many advantages in reducing equipment investment and energy savings and it has become a hot topic. The vapour split between the two sides of the divided wall is a very important parameter. While the vapour split is not used as a manipulated variable because of the difficulty of adjustment. A vapour splitter which could adjust the vapour split flexibly and make the vapour distribute uniformly was put forward by Hebei University of Technology. Good performance was obtained through experimental and simulation results. In this article the following research was done according to the divided wall column which contained the vapour splitter:The vapour split was used as a manipulated variable innovatively and was applied as a part to make up the temperature control strategy of divided wall column. Separation of ternary mixtures of ethanol, n-propanol, and n-butanol was chosen as an example to evaluate the performance of the temperature control scheme using Aspen Dynamics software. The scheme consisted of five temperature control loops in which three loops were located in the public rectifying section, side-stream section and public stripping section and two other loops were controlled by vapour split and liquid split respectively. The responses of the mass fraction of three products in the face of ±10% step changes of feed flow rate and the same step changes of ethanol and n-propanol and n-butanol in feed flow was investigated. Although the complicated relationship between temperature and concentration resulted in the deviation of stable value of concentration and initial value, the purities of three products achieved stability after a certain time. The simulation results showed that the control scheme could effectively overcome disturbances of the feed flow rate and composition which indicated that the vapour split could act as an effective manipulated variable.The controllability of the vapour splitter using the control system based on temperature monitoring in divided wall packed column was investigated by using the direct contact evaporating heat transfer of air-water. The water temperature was using as the controlled variable and the vapour split was using as the manipulated variable. The water temperature was examined and translated into electric current signal of 4-20 mA by Pt100 temperature transmitting instrument. Then the signal was entered into PLC through EM235.The pulse signal was exported to the stepper motor driver after the temperature signal was compared and operated. The blade of the vapour splitter was drived by the stepper motor until the examined temperature reached the range the set temperature range. The responses of the temperature control system under different water temperatures, different water flow rates and different air velocities were investigated. The experimental results showed that the measured temperature could reach different target temperatures which indicated that thevapour splitter had good controllability in actual operation. The results laid a sound foundation for the practical application of the vapour splitter.