Why is the control valve at the bottom of the atmospheric and vacuum distillation initial distillation tower adjusted using a manual operator instead of a control valve?
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Why is the control valve at the bottom of the atmospheric and vacuum distillation tower regulated using a manual operator instead of a control valve?
What does that mean? The expression isn’t very clear. Could you be more detailed?
Steam injection at the bottom of the initial distillation tower causes large fluctuations in the liquid level
The main concern is unstable liquid levels, which can lead to fluctuations. There are many factors that affect the liquid level at the bottom of the tower, and this makes it easy for large fluctuations to occur. If control valves are used for automatic regulation, it’s difficult to tune the PID parameters; it seems that the automatic control design isn’t very effective. By adjusting the control method, the stability can be greatly improved. So, the handheld controller is a very good choice.
This expression is a bit... . . . . . The liquid level at the top of the initial distillation tower fluctuates quite significantly; it can be adjusted gradually as operations start, depending on the characteristics of your raw materials. In the initial stage, manual control is usually used, while later on a PID control system can be employed – it depends on the skills of the instrumentation personnel.
I guess the manual controller is not used to control the liquid level at the bottom of the initial distillation tower, but rather to control the flow rate of the atmospheric furnace. Atmospheric pressure furnaces require a very stable flow rate.
If the liquid level is stable, automatic control can of course be used; otherwise, manual control is the only option.
The bottom of the initial distillation tower manual controller is used to balance the final temperature of heat exchange in various heat exchange processes at the bottom of this tower. The final flow rate is controlled based on the feed to the atmospheric pressure furnace; in any given process, only one set of automatic control valves can be used, as otherwise it will lead to significant fluctuations in operation, and in severe cases, pressure buildup and leaks in the system may occur.
What was said upstairs is correct; if control valves are used, instrument failures (such as instrument icing or interruption of instrument air supply) can lead to high pressure building up in the heat exchanger at the bottom of the tower, which may trigger a fire accident.