Two-chamber balanced vessel for measuring drum liquid level
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Is P-to-L compensation necessary when using a two-chamber balanced container to measure the drum liquid level?
At different operating pressures within the steam drum, the density of saturated water and the density of saturated steam change. Refer to the manual. The density varies considerably within the range of 0.2 MPa to 16 MPa. When using a differential pressure transmitter in a balanced container to calculate the differential pressure, the densities of saturated water and saturated steam are used as input values. So using pressure correction for L is essentially density correction. I think it is necessary.
Due to differences in temperature, the density of liquids also varies, and this difference increases as temperature changes. To measure the liquid level accurately, compensation is necessary.
I’ve seen boilers with a capacity of 240 t/H that didn’t use compensation, and no problems ever arose!
The dual-chamber balanced container has a certain compensating effect; the density of the water inside the container can generally be taken as that at around 30 or 40 degrees to calculate the pressure difference. If there is still a discrepancy after the boiler is operating normally, adjustments can be made based on the actual liquid level – sometimes theoretical calculations yield inaccuracies. We also didn’t use P to compensate for L; I heard about it for the first time.
If the pressure inside the drum is stable, it’s not necessary. When the actual operating pressure of the drum differs from the design pressure, the densities of saturated steam and saturated water inside the drum at that operating pressure will deviate from those at the design pressure. If the actual operating pressure deviates very little from the design pressure, no compensation is necessary. However, at the beginning of operation, when no compensation is applied during the voltage increase process, there will definitely be a discrepancy between this liquid level and the level indicated by the local gauge. What you’re talking about is just balancing the density inside the container; you’ll understand it if you look at the calculation sheet.
Anyway, in actual production I indeed don’t use any compensation. However, the drum control of the vaporizer designed by Shell includes compensation.
It’s best to perform density compensation. Especially during driving, the liquid level display has a large deviation. It is not recommended to use this level gauge; it is more convenient to opt for magnetostrictive or guided-wave radar.