Problems with the automatic control valve for hydrogen main pipe reflux
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In chlor-alkali production, we use Roots blowers. The hydrogen reflux control valve PICA0400 operates in automatic mode when everything is functioning properly, with the valve gradually closing. What causes this? Could it be because of this: the pressure shown by his transmitter is lower than the actual pressure at that location, which causes the valve to close gradually? I earnestly request your guidance. Also, is it related to whether there is a PID or not? This post was last edited by Ai Zhi Yuan on 2009-4-11 21:50.]
In automatic mode, the controller’s output is calculated based on the deviation between the measured value and the set value. The valve gradually closes, which may be normal adjustment; when the pressure of the returning hydrogen exceeds the set value, the valve closes to reduce the pressure. But if it remains at a low level for an extended period (with a large deviation), there might be a problem. There are two possible reasons: 1. The transmitter is faulty, resulting in distorted and exaggerated readings; check whether there is an issue with the transmitter’s IOP ； 2. If the control valve is faulty, check for leaks there; inspect the positioner as well as the air supply lines.
It doesn’t close quickly; it gradually slows down as it closes. There is a problem with the transmitter; it seems there is water accumulation, and the pressure displayed by the transmitter is 0.2 KPa lower than the actual pressure. However, this transmitter also includes the inlet pressure of the Roots blower; its valve remains stable and is not affected by water accumulation in the transmitter. One more question: This transmitter has two pressure inputs. While the system is running, can I switch everything to manual control in order to perform calibration or drain air from this transmitter, without affecting the system’s pressure? This post was last edited by Ai Zhi Yuan on 2009-4-12 08:19]
Sure. Set both pressure control valves to manual control, but be sure to monitor changes in pressure (there should be local pressure gauges on site). When making adjustments, do so slowly and avoid opening or closing the valves abruptly to prevent excessive pressure fluctuations. This is because there is a certain delay in the response of the control valves (around 3 seconds), and the effects of the adjustments may not become apparent until after some time has passed.
Thank you. Since we are responsible for supplying hydrogen to the hydrochloric acid process, it’s necessary to maintain the pressure; so let’s talk about this after the plant stops operating