Liquid level measurement in low-temperature storage tanks
Thread Content
Low-temperature storage tanks, with temperatures ranging from -190 to -70°C, using liquid nitrogen or other substances as the medium. Currently, only side mounting flanges are provided on the tank; it is planned to use a diaphragm differential pressure transmitter with double flanges for measuring the liquid level. I would like to ask everyone: 1. Here, which is more suitable for a differential pressure transmitter – one with a capillary or one without? What are the differences? 2. How should the pressure guide pipes be arranged?
With such low temperatures, will the silicone oil be able to withstand it? Ethylene glycol: –50 ~ 100°C
The measurement performance with double flanges is poor; guided wave radar is recommended
Double-flange transmitters have some issues regarding temperature resistance; it is advisable to use pressure guiding tubes to transmit pressure, as this results in lower overall costs and better performance.
1. At -170°C, that capillary with double flanges will freeze up and turn into several hard rods... :P 2. Using pressure induction and temperature rise for measurement is the correct approach. When pressure is applied to the diaphragm, is it at room temperature? 3. Stop at that point. Whoever sends a large WeChat red envelope to my brother to bribe him will have my brother teach them how to install pressure pipes. :lol
Using a pressure tap is fine; it’s cost-effective. If double flanges are required, the flanges on the equipment need to extend further out for heating before they can be used.
For liquid nitrogen, a regular differential pressure transmitter is used to measure the liquid level; the pressure guide tube is led out for measurement after vaporization, and we have found this approach to work very well. The same principle is also used in air separation to measure parameters such as pressure and differential pressure inside the cryogenic tank.
Personally, I think the magnetic float level gauge is quite good; both the temperature and pressure readings meet the requirements. Shanghai Huarong HRUHZ magnetic flap/magnetic float level gauges. The BM26/BM26G and BM26(G) models feature a metal tube structure with a scale; magnetic flaps or floats are used to indicate the level or interface. It is possible to install level transmitters and level switches, and these gauges are suitable for measuring the level or interface in open or closed pressure vessels. Depending on the user’s needs, the BM26 (G) can be equipped with a 4-20mA remote signal output transmitter, a switch signal transmitter, and a digital level indicator. The design of these special floats features high temperature, high pressure, and low density; titanium materials, 316L steel, as well as anti-corrosion materials such as PTFE lining are used, and X-ray inspection is employed to ensure that the products meet all requirements in various application scenarios. Overall features: Simple structure, robust and reliable, stable operation. Magnetic flip plates and magnetic floats are sealed inside glass tubes. Large-scale markings for easy reading. The measuring medium is securely separated from the display and signal output. A 4-20mA level transmitter can be installed, as well as a level switch sensor. Various corrosion-resistant materials are available, such as 304, 316, 316L, titanium, and Hastelloy. Multiple installation options and connection methods are available. Features of BM26: Maximum nominal pressure ≤ 5.0 MPa; maximum medium temperature ≤ 400°C; minimum medium temperature –200°C; medium density ≥ 0.5 g/cm3. Suitable for interface measurement (density difference ≥ 0.1 g/cm3)
For the pressure measurement using the pressure tap, the temperature at the gauge should be around -20 degrees Celsius. Do you manufacture small storage tanks for quick cooling applications, or are you involved in vertical or horizontal tanks? The technical insights on CIMC Group’s website seem to cover the layout of pressure pipes. Suntain focuses on large tanks, Nantong specializes in quick cooling tanks, while Anrico deals with tank trucks.
It is better to use pressure transduction tubes, but attention should be paid to the material of these tubes as well as to proper insulation. Using double flanges directly can lead to many problems due to low temperatures, such as sudden changes in measurement values and no readings at all
The level measurement of liquid nitrogen and liquid oxygen tanks at the site is carried out using pressure transmitters combined with differential pressure transmitters; this method is simple and practical, requires low costs, and makes it easy to analyze and diagnose faults. Make sure the hydraulic pipe on the lower side is at a certain distance from the cryogenic tank, so that the pressure guide pipe can vaporize fully near the transmitter side, thereby preventing damage to the diaphragm box due to freezing.