Temperature difference control
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There is an ethylbenzene-styrene distillation column, and the styrene content is required to be no higher than 0.08%. Currently, the ethylbenzene content is controlled by adjusting the gas temperature difference between the packing layer above the feed inlet and the packing layer below it. I would like to know the relevant knowledge regarding this temperature difference control as well as the principles behind its effectiveness
Temperature difference control reduces to some extent the impact of pressure changes on control parameters, thereby improving control accuracy
The temperature difference is generated by taking advantage of the different thermal conductivity values of gases; the composition ratio is calculated based on the magnitude of this difference
Generally, the temperature difference is determined using the tower top temperature and the sensor plate temperature
For the temperature difference control of the tower, I think it should be controlled by a sensitive plate.
It is recommended to draw a schematic diagram showing the temperature measurement points, the packing section, and the feed location, which will aid in problem analysis. Personal understanding: The control principle should be similar to that of the sensitivity plate control. At a constant total pressure, the top temperature is a direct reflection of the composition of the distillate; however, during high-purity separation, the temperature change is minimal in a relatively high section of the tower, either at the top or at the bottom. In this way, by the time a noticeable change occurs in the tower top temperature, the fluctuations in the composition of the distillate have already exceeded the allowable limits. Ethylbenzene-styrene was subjected to vacuum distillation at 8 kPa; when the ethylbenzene content in the overhead distillate decreased from 99% to 90%, the bubble point temperature changed by only 0.7°C. When performing high-purity separation, it is generally not possible to control the quality of the distillate by measuring the temperature at the top of the tower. Measuring the temperatures at the upper and lower ends of the filler is intended to identify the points where temperature changes are significant as a function of composition changes, which facilitates control. The above are my personal opinions. Discussion is welcome.