How should the pressure difference in a distillation tower be controlled?
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If the pressure difference is to be controlled as shown in the diagram, then how do PT1101A and PT1101B transmit signals to the controller PIDC1101 for negative feedback calculation?
First of all, it’s not PIDC1101; it should be PDIC1101, where PD stands for pressure difference. It is speculated that low-pressure steam from the reboiler is used to adjust the amount of steam rising in the tower, thereby regulating the pressure difference between the bottom of the tower and the top.
This post was last edited by jlj913 on 2022-1-4 at 11:18. There are two PT sensors for detecting the variable, but what we actually need is the pressure difference. How should these two PT sensors be transmitted to the controller for processing? What type of control is this?
Use a differential pressure transmitter with a capillary; do not use two pressure transmitters, as the differential pressure signal is very small and there is a timing difference in the transmission of the two pressure signals.
This post was last edited by Hao Liang Zhi Le on January 5, 2022, at 09:39. First, the 4~20mA signals from the two pressure transmitters are sent to the DCS, where they are subtracted from each other. The resulting value is then provided to the PDIC differential pressure controller as a measurement signal. This signal is compared with the set differential pressure value; after PID calculations, an adjustment signal is generated and sent to the low-pressure steam control valve. If a differential pressure transmitter is used, the two pressure sampling points must not be too far apart; otherwise, an overly long pressure conduit will hinder accurate measurement ； If a double-flange capillary differential pressure transmitter is used, the capillary length must not be too long. Therefore, using two pressure transmitters can avoid these problems.
For differential pressure, perform subtraction in the DCS first, and then use an intermediate variable to feed it into the PID as the controlled parameter.
This is the automatic (interlocked) control of the steam flow rate and pressure difference in the tower bottom reboiler; steam is used to regulate the amount of evaporation and the reflux volume, thereby controlling the pressure difference.
Interlocking is interlocking, and regulation is regulation; they are two different things.
What is the purpose of the interlock between this pressure difference and the steam control valve?