Questions about differential pressure level gauges
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An LNG storage tank, whose mechanical level gauge shows a stable reading at all times. However, the data from the differential pressure level transmitter fluctuates (for example, it reads 2500 mm of water column in the morning, but becomes 3200 mm in the afternoon). Excuse me, what’s going on with the expert?
The installation plan still needs to be shown
It is caused by the change in temperature between morning and afternoon, which leads to changes in the density of the medium
The pressure and temperature of liquefied natural gas have a significant impact on its liquid level. The physical properties of the medium are not clear.
Changes in temperature-induced variations in medium density, self-density, and the density of the upper gas layer
1. Since the liquid level in the morning is only 2.5 m, and with a temperature difference of 20°C between the ambient conditions in the morning and evening throughout the day, this can be considered the extreme value. Under such circumstances, the vaporization of condensate in the storage tank due to temperature changes, as well as fluctuations in the density of the liquid phase, should not cause excessive fluctuations in the liquid level: (3.2–2.5)÷2.5 = 28%, which represents a 28% increase in the liquid level – that’s too much. 2. The error in the gauge reading is likely due to an unreasonable layout of the pressure-taking pipes in the differential pressure gauge. The original poster might as well draw a schematic diagram of the piping system, indicate the dimensions, note the pipe diameters, take a photo and post it so that everyone can take a look. .
When using liquid nitrogen for pre-cooling my LNG storage tank, the liquid nitrogen is stored inside the tank; it showed 450 mm right after unloading, but after six or seven hours it showed 0 mm, with no signs of leakage.