Solving for the liquid level in an ammonia tank using a differential pressure transmitter
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The company has two ammonia tanks, each 15.7 meters in height, and each is equipped with two level measurement systems: one based on differential pressure and the other on radar. The radar is an E+H240 horn with a guide wave tube. The differential pressure measurement uses a Yokogawa transmitter with a range of 0-160 KPA. It was only today that I realized that the range within the differential pressure transmitter hasn’t changed; it has simply been adjusted to 2-158. The instrument displayed in the control room is a Bently XMT gauge, but its range is 0-26.6 meters – I don’t understand this. Please help.
I only know that the specific gravity of liquid ammonia is 0.6. 160 kPa is equivalent to 16 meters of water column; 16/26.6 = 0.6015, which is pretty much the same.
This is related to the density of ammonia; to determine whether the setting is accurate, it is necessary to calculate the density of ammonia.
The installation location of the differential pressure transmitter also affects the range; let’s take a look at a diagram.
The range of the differential pressure transmitter should allow for negative drift, and the specific range should be calculated based on the liquid filled in the gas-phase isolation tank.
2-158 is your operating range, while 0-160 is the factory-calibrated range of the gauge
For clear water at a level of 15.7 meters, the pressure is 154 kPa; ammonia has a lower density, so the pressure of ammonia at a height of 15.7 meters is lower than that of clear water. Shanghai Ligé 2880189604
Is it a pressure-bearing device? If it is a pressure-bearing device, then liquid ammonia is stored in it, and the calculation method is as follows: The density of liquid ammonia is roughly around 0.6; 0.6 is used in this calculation (this value varies with temperature, ranging from 0.7 to 0.5). For 15.7 meters of liquid ammonia, the maximum static pressure is approximately 92 kPa. Strictly speaking, the upper limit of the instruments on site should be set to 92 kPa using a manual controller. The lower limit depends on the distance between the flange where the pressure transmitter is installed and the bottom of the tank; if that distance is 10 cm, then the lower limit would be around 0.6 kPa (calculated using P=ρgh). Therefore, the range of the instruments should be set between 0.6 kPa and 92 kPa. The range of the differential pressure transmitter is 0-160, which is sufficient. The readings of 0-26.6 shown in the control room are incorrect; you can modify the display range in the DCS screen to 0-15.7. If it is not a pressure-bearing device, then a new calculation is required. The concentration of industrial ammonia solution is generally 30%, with a density of around 0.9; the static pressure at 15.7 meters is approximately 138 kPa. The rest of the calculations follow the same approach. I hope this helps you