On-site instrument failure analysis (one question per week) – Question 8 (answers released)
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This post was last edited by Yiding on 2009-11-15 03:02. Abnormal temperature readings during the heating up process of the synthesis tower. a) Process description: In a certain ammonia plant’s synthesis tower, there is a thermocouple sleeve about 10 meters long, with multiple thermocouples inserted inside it. b. Fault symptoms: During the vehicle’s heating process, an abnormal temperature reading was observed. Initially, the temperature readings at all measurement points increased accordingly; after some time, the temperatures at the lower measurement points continued to rise, remaining around 200°C. However, the temperature reading at the highest measurement point stayed around 100°C without changing. According to analysis, the actual temperature at that point is definitely above 130°C. Answer revealed: c. Analysis and judgment – The temperature reading at the uppermost temperature sensing point remains around 100°C, which indicates that there is moisture accumulation in that area. When this moisture is heated, it evaporates upward and then condenses into small water droplets once it reaches the upper part; these droplets fall back inside the casing, and this process repeats itself, causing the temperature reading at the upper sensing point to stay around the boiling point (100°C). The cause of this fault is that the protection conduit was not treated before installation or the treatment was inadequate, as well as the high temperature of the gas inside the sleeve. d. Treatment method: Lift the multi-point thermocouple so that the upper temperature sensing point is at a certain distance above the top of the casing; the water vapor inside is carried out of the casing and then evaporates outside. Repeating this process several times, if there is not much water vapor present, normal operation can generally be restored; otherwise, all the thermocouples need to be removed, and a thin nylon tube should be inserted at the bottom of the conduit to fill it with dry nitrogen, thereby gradually displacing the water vapor.
If the temperatures at all other points continue to rise, while the temperature reading at the very top remains around 100, this indicates that there is nothing wrong with the gauge； ““The temperature readings at each monitoring point increased accordingly in the initial stage,” which indicates that there are no issues with the thermocouples at those points as well ； In other words, there are no issues with the entire measurement circuit. The only explanation is that there is water inside the thermocouple sleeve; at the beginning of operation, when the temperature was below 100 degrees, the temperature reading was normal ； Once the temperature exceeds 100 degrees, the water inside the sleeve evaporates into steam when heated. This steam rises upward along the thermocouple sleeve; as it approaches the upper end of the sleeve, the water vapor cools down and turns into condensed water. Since the temperature of the water never exceeds 100 degrees, the temperature reading at the highest measurement point remains around 100 degrees.
It might be caused by a short circuit at the cold end of the thermocouple.
The temperature rise is normal, and the bottom temperature is also normal. Only the top one is abnormal; generally, it is assumed that water has entered the sleeve. As a result, the measured temperature can only remain around 100 degrees.
I agree with the explanations from those above; it must be that water has gotten inside!
There must be water inside the thermocouple sheath
The judgment on the 1st floor was very accurate. Agree
You should observe for a while longer and see
The temperature reading at the very top is around 100 degrees, while the temperature is higher at the lower levels. The moisture heats up and evaporates upward; it then cools down in the upper areas and turns back into water droplets that fall back down. This process repeats itself, resulting in the temperature in the upper areas remaining around the boiling point. This fault may be caused by high gas humidity inside the sleeve prior to installation