Application Analysis of Several Level Gauges for Liquid Ammonia Storage Tanks

Thread Content

In chemical plants, liquid ammonia accounts for the vast majority of usage, and its intake and output from storage tanks is also frequent. Liquid ammonia is highly corrosive and volatile, which results in a high incidence of chemical accidents. To effectively control the liquid ammonia level in storage tanks, using stable and safe level gauges for measuring this level can help eliminate the safety risks associated with the use of liquid ammonia. This article analyzes the application issues of several common level measurement instruments for liquid ammonia storage tanks, thereby providing a basis for the selection of such instruments. Analysis of the key application aspects of several liquid ammonia tank level measurement instruments 1. Key application aspects of the sonar-based external level gauge. The ELL sonar-based external level gauge is an instrument that uses the principle of sonar ranging and \"micro-vibration analysis\" technology to measure the liquid level from outside the container. It requires no holes to be made in the tank wall or the use of flanges; it involves no need for welding or cleaning of the tank, and there is no contact with the liquid or gases inside the tank. It can be installed and maintained online, making it a completely non-contact, isolated type of instrument. 2. Key application points of differential pressure transmitters: One end of a differential pressure transmitter is connected to the liquid phase, while the other end is connected to the gas phase; the principle of hydrostatics can be utilized to measure the liquid level in ammonia storage tanks. When using this measuring device, it is necessary to strictly control its installation height; it should generally be installed below the pressure-taking interface of the liquid level in the container being measured, in a location that is easy to maintain and observe, and also close to the pressure-taking components. Given the low boiling point and easy vaporization of liquid ammonia, a double-flange differential pressure transmitter is required to ensure the stability of the measurement signal. If this device is used, its installation will be limited only by the length of the capillary. Specifically, it is necessary to take appropriate protection and insulation measures, and to ensure that the bending radius of the capillary is greater than 50 mm. When using this measuring instrument, if the installation elevation changes, the output value of the device will be affected. 3. Key points for the application of magnetic flap level gauges: The operation of magnetic flap level gauges is based on the law of buoyancy and magnetic principles, and they need to be connected to storage tanks via flanges. During the measurement process, the dual-color cylindrical magnetic float inside the device changes under the influence of the magnetic field, and the point where the floats meet indicates the actual liquid level in the tank. During the installation of the equipment, it is necessary to avoid magnetic materials around it, and the heat tracing temperature should be determined based on the properties of the medium. When the opening connection between the gas and liquid phases is large, a flange needs to be installed in the middle of the level gauge. During equipment calibration, it is necessary to use a magnet corrector to turn the magnetic column white, then open the gas-phase shut-off valve and the liquid-phase shut-off valve in sequence, while observing the rise and fall of the liquid level. 4. Key points for the application of cable-guided wave radar level gauges: The operation of cable-guided wave radar level gauges is based on the time-of-flight principle; it involves sending and receiving high-frequency pulse signals in order to measure the distance from a reference point to the surface of liquid ammonia. When installing this device, it is necessary to avoid the liquid ammonia inlet in order to prevent false reflections from occurring on the device. When installing the sensor, it should not be placed at the center of the tank, and it is necessary to keep the sensor away from the tank walls. When installing a cable-type probe, it is necessary to keep the distance between the probe and the smooth metal wall at more than 50 mm; the distance from the tip of the probe to the bottom of the container should be more than 80 mm, while the diameter of the short tube must not exceed 80 mm. Furthermore, due to the installation location, the bias amount of the cable probe may increase. Application effects of several liquid ammonia tank level measurement instruments 1. Sonar-type external level gauge: The external level gauge measures the liquid level inside the tank continuously and accurately from outside the tank, with no contact at all with the liquid and gases inside the tank, thus enabling true isolated measurement. Therefore, the features are as follows: (1) Isolated contactless level measurement technology is very safe. (2) Installation and commissioning, thereby reducing construction costs and maintenance expenses. (3) More reliable and durable; the measurement probe and the main unit have no mechanical moving parts, and they are tightly sealed to isolate them from the outside environment, preventing wear or corrosion. (4) Passed the \"Functional Safety Integrity\" level certification by the Shanghai Instrumentation and Automation System Testing Institute, obtaining a SIL3 certificate. 2. Application effects and faults of differential pressure transmitters. In terms of their application effects, differential pressure transmitters are characterized by easy calibration and a wide range of applications. At the same time, these devices have a lower price, offering good cost-performance advantages. However, when installing this device, installation holes need to be reserved. At the same time, since the density of the equipment is closely related to changes in the density of the medium, the measurement process will cause the material of the instrument’s diaphragm to be corroded by corrosive media. After long-term operation, the equipment is prone to membrane box deformation problems. During operation, if faults such as no indication, excessive or insufficient indication, or unchanged indication occur, it is also necessary to check the power supply, safety barrier, circuit board, diaphragm capillary, and pressure tap valve; furthermore, the equipment components should be replaced as appropriate and the pressure tap valve of the equipment should be opened promptly. 3. Application effects and faults of magnetic flap level gauges. By using magnetic flap level gauges, it is possible to measure the level and interface of any type of fluid, and these devices are characterized by easy installation and intuitive operation. However, when there are too many impurities in the medium, the magnetic columns will not flip, and the measurements will become invalid. At the same time, using this device can easily lead to the jamming of the magnetic columns, which will prevent remote indication from being possible. Moreover, this device is relatively inexpensive, and installation holes need to be prepared during installation. In operation, magnetic flap level gauges are prone to problems such as no signal output from the transmitter, no change in the output signal, and an inability to adjust the range to the desired value. During application, it is necessary to check the supply voltage, cables, terminal connections, and safety barriers. 4. Application effects and faults of cable guided-wave radar level gauges. Cable guided-wave radar level gauges feature direct contact with the medium and a small measurement blind zone, resulting in high measurement accuracy. However, this device is not suitable for measuring pressure vessels, and it is relatively expensive; installation requires the provision of mounting holes at the top of the device. In terms of application-related failures, this device may experience issues such as incorrect DCS system configuration, faults with cable probes, and unstable DCS display values. During application, field measurements need to be carried out before calibration, and the practice of checking whether the DCS configuration data matches the actual measurement results should be abandoned in order to obtain accurate data. Before measurement, it is necessary to clean the probe and appropriately increase the height of the empty tank in order to eliminate the effect of echoes. END Conclusion In summary, various level measurement instruments can be used for measuring the liquid level in liquid ammonia storage tanks. Different instruments have distinct characteristics; they produce varying effects during use and can lead to different types of equipment failures. Therefore, the measurement personnel must also select appropriate level measurement instruments based on the actual conditions, in order to carry out the operation of the equipment more effectively.