The issue of measuring the ammonia level in liquid ammonia spherical tanks using external-type level gauges
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Hello, everyone on this forum. I have a question for you all； When measuring the liquid ammonia level in the spherical tank used by our company for storing liquid ammonia, two different types of level gauges are employed for this purpose; one of them is an external-type level gauge used to measure the level of liquid ammonia in the spherical tank. It mainly consists of a level measuring probe installed at the bottom of the liquid ammonia spherical tank, a side calibration measuring probe mounted on the equator of the liquid ammonia spherical tank, and the instrument main unit. The inlet and outlet for liquid ammonia are both located in the bottom area of the spherical tank. In recent years, every time ammonia is introduced into the bottom of the liquid ammonia sphere tank, the level sensor located at the bottom of the tank, near the inlet where the ammonia enters, causes excessive fluctuations in the liquid level due to the incoming ammonia. This severely affects the accuracy of the measurements; as a result, the reading from the external level gauge drops to around the set blind zone and remains there for about 10 minutes. It triggers a level alarm. Since the level sensor installed at the bottom of the liquid ammonia sphere tank can only meet the measurement requirement that its sensing plane be parallel to the liquid surface inside the tank when it is positioned at the bottom, it is not possible to bypass the ammonia inlet location by moving this level sensor. How can an external-type level gauge carry out measurements normally as before?
Can’t you make the liquid ammonia flow in more slowly?
During feeding, the liquid ammonia flows at a high velocity, creating a jetting effect that draws in the surrounding material and reduces the pressure in that area. Adding a baffle to the feed inlet should basically solve this problem.
It is not recommended to install a baffle at the feed inlet. An external-type level gauge is a type of ultrasonic level gauge; its measuring probe measures the liquid level by emitting and receiving ultrasonic waves. The presence of baffles can affect the transmission of these ultrasonic waves, resulting in significant measurement errors or even preventing proper operation.
An on-site level gauge should be installed for reference calibration.
As soon as ammonia enters, the reading of the external-type level gauge drops to near the set blind zone; this reduced reading remains at that level for about 10 minutes before returning to normal.
Ammonia is introduced at normal speed; the process requirements dictate that it cannot be slower than this.
It worked normally during the first two years after it was installed in 2013, but gradually started showing the aforementioned abnormal issues thereafter. Recently, we moved the measuring head to inspect the area where it makes contact with the bottom of the spherical tank; the metal surface showed normal luster. We routinely polished the metal surface in that contact area, reapplied the bonding agent to the measuring surface, and used 587 adhesive to seal the sealing ring and cover. After power was applied and ammonia was introduced, the liquid level measurement readings and outputs were normal; however, after two days it reverted to its previous behavior – as soon as ammonia was introduced, both the readings and outputs dropped to around the set blind zone value and remained there for about 10 minutes.