It is simply untrue to suggest that radar is an unsuitable technology for providing accurate and reliable level measurements of liquefied gases. In fact, modern non-contacting radar transmitters excel in such applications and provide significant advantages over inferior servo gauges.

Have you ever wondered why some tank terminals are still relying on servo gauges to provide level measurements in liquefied gas tanks? Well, it could be due to a belief within some quarters that all radar devices are unsuitable for use in applications involving liquefied natural gas (LNG), liquefied petroleum gas (LPG) and other natural gas liquids, such as ethane. However, this is simply untrue, as I explain in an article in Tank Storage magazine, ‘Debunking the Myth About Radar and Liquefied Gases’.

Some organizations fear that a combination of vapor in the tank and weak signal reflection can impact the performance of radar instruments in liquefied gas applications. Consequently, they continue to use inferior servo gauges to provide level measurements, despite the disadvantages of this older and less reliable technology.

Yes, it is true that the vapors often produced in liquefied gas tanks can affect the propagation speed of radar waves, which can then impact the accuracy of some radar level gauges. Temperature and pressure variations, causing changes in vapor saturation degree, can also affect radar signal behavior and measurement accuracy. In addition, the typically low dielectric constant of liquefied gases results in weaker radar signal reflections, making it more difficult for some radar level gauges to distinguish the level signal from background noise.

However, as I point out in the article, well-engineered non-contacting radar devices such as the Rosemount™ 5900S Radar Level Gauge from Emerson overcome these issues and maintain excellent measurement accuracy and reliability. Far from being unsuitable, non-contacting radar devices are already being successfully used on more than 10,000 LNG and LPG tanks globally, and during four decades of service on such tanks, no Emerson radar installation has experienced any accuracy- or reliability-related problems due to the presence of vapor. The article states:

…Non-contacting radar level gauges can compensate for the presence of vapour in liquefied gas tanks – and the effect of the vapour on the radar waves – by utilising an integrated pressure transmitter. This sensor measures the vapour pressure inside the tank, and the gauge can then calculate the influence of vapour on the microwave propagation speed by combining the pressure measurement with information about the liquefied gas type and mixture. Compensating for the effect of vapour in this way enables level readings to be automatically corrected, ensuring excellent measurement accuracy of ±0.5 millimetres (0.020 inches) in the case of the Rosemount 5900S. An integrated pressure sensor also helps to determine the vapour saturation degree. This data then enables the tank gauging system to dynamically compensate for variations in signal speed caused by changing tank conditions, thereby maintaining measurement accuracy.

The Rosemount 5900S Radar Level Gauge from Emerson features an integrated Rosemount 2051 Pressure Transmitter. Pressure measurements are vital in enabling the device to maintain level measurement accuracy in liquefied gas tanks by compensating for the presence of vapor and the effects of vapor pressure changes.

To overcome the challenge of liquefied gases having a low dielectric constant, the Rosemount 5900S leverages frequency modulated continuous wave (FMCW) technology, with a sensitivity more than 30 times greater than devices using older pulse modulation techniques. This maximizes signal strength and enables superior measurement accuracy and reliability. The article continues:

…A wide dynamic range enables these devices to detect both strong and weak radar signal reflections effectively and process them reliably. Superior signal processing algorithms enable noise to be suppressed and filtered, enhancing the detection of weak echoes and producing a more robust and reliable measurement.

The Rosemount 5900S can easily operate for 20 years without requiring maintenance or adjustment. This helps to maximize tank availability, which is crucial when storing liquefied gases.

I then discuss how non-contacting radar level gauges use antennas specially designed to optimize measurement accuracy and address the challenges posed by liquefied gas applications:

…These robust antennas are designed to ensure optimal transmission and reception of radar signals, even when the dielectric constant is low, and to withstand low temperatures, enabling them to operate effectively in cryogenic conditions.

The article adds that radar signals should be guided within a still-pipe, as this reduces signal dispersion and helps to amplify the radar echo from the surface of the liquefied gas, further optimizing signal strength and measurement accuracy.

A vital consideration when selecting level measurement technology for liquefied gas applications is the need for reliability. I explain that devices with excellent reliability are vital, as this helps to increase safety and optimizes the operational availability of tanks. This is a critical requirement because tank downtime can result in financial losses, impact demand fulfilment, disrupt supply chains and affect inventory management. The article continues:

…In stark contrast to servo gauges, non-contacting radar level gauges deliver outstanding reliability, even in the most challenging applications. Because these instruments are non-contacting there are no wetted parts, and combined with a lack of moving parts, this minimises their maintenance requirements. Non-contacting radar level gauges used in liquefied gas applications will therefore have a very long service life, and can easily operate for 20 years without any need for maintenance or adjustment, which helps to reduce their total cost of ownership. The design of these devices enables their availability to usually reach close to 100% during their long lifespan.

To learn more about Emerson level measurement solutions for all large storage tanks, visit www.Emerson.com/RosemountTankGauging.