MechChem Africa September-October 2022

Level measurement for extreme conditions Clemens Hengstler, product manager for Radar at Vega, presents the case for using solutions from Vega for level measurement in LNG/LPG processes.

at sealing points and connection points in the ball valve and their multiplication within the throat of the ball valve. This makes reliable measurement impossible, especially in liquids with low dielectric values and in the upper area of the tank, where the sensor needs to detect overfilling. Becauseof theconsiderably better signal focusing with the Vegapuls 64, the influence of the ball valve ismuch smaller and generates almost no disturbing signals. Another advantage is that the new sensor can be installed on existing shut-off devices, which keeps rebuilding and retrofitting costs to a minimum. Critical applications, where the previous technology was problematic can easily be upgraded to the new 80-GHz technology to increasemeasurement reliabil ity, thereby increasing plant availability and reducing maintenance requirements. With smaller, horizontal LPG tanks, there is a further advantage, the Vegapuls 64 can be installed directly onto the tank without a bypass tube, saving additional costs. In addi tion, 80 GHz technology has a positive effect when measuring liquids with low dielectric values at the bottom of a vessel. Normally, radar signals are reflected at the surface of the medium. In the case of media with small dielectric values, however, some of signal penetrates the medium and is reflected by the underlying container bottom. As a conse quence, twosignals are received: one fromthe liquid surface and one from the tank bottom. The lower the dielectric value of the medium and the lower the level, the larger the signals from the tank bottom. With the previous 26-GHz sensors, these two signals overlapped and mixed together, especially at low levels and, in the region of only a few cm, the smaller level signalwasmadealmost invis ible by the larger tank bottom signal. Due to the significantly shorter wave length of the 80-GHz signals from Vegapuls 64, the signals that pass through the medium aremore strongly attenuatedby themedium. As a result, the reflection from the bottom of the vessel is significantly weaker making the signal from the liquid much stronger. The result is that even filling levels of a few mm can still be measured reliably and accurately, allowing the full tank volume to be better utilised. If the storage tanks are on a ship, one of the first questions asked is where the sensor can be installed to bypass many internal instal lations. A typical ship tank has pumps that require piping for the hydraulic feed, the return feed and for conveyed product – and there are often two pumps, one for the large quantities and another for residual liquid. All internal fixtures and equipment gener Intelligent solutions for processes at sea

Top: The Vegaswing 66 is a universal vibrating level switch that it is now suitable for use at extreme process temperatures and pressures. Bottom The guided wave radar sensor Vegaflex 86 is proven in many complex processes such as liquefaction units.

A cross the individual LNG/LPG production stages – from lique faction and storage, shipping, vaporising and pipe conveying, to further processing or consumption as an energy carrier – there are numerous measuring points where safe, reliable level measure ment is required. But the installation situation and the process conditions present significant difficul ties, while the unusual properties of the products themselves, do not make the task easier. LNG has a low density and an ex tremely lowdielectric constant. These physical properties also change de pending on the product composition, the supplier or theplaceof origin, mak ing many measuring principles unable to return reliable and precise values. Very lowtemperatures alsonarrow down the suitable choice. Mechanical measuring techniques often malfunc tion, for example, andaremaintenance intensive. Sensors based on radar technology are therefore preferred and Vega has already installed more than 500 000 radar sensors worldwide, many of them in LNG/LPG applications. The 80 GHz VEGAPULS 64 The new VEGAPULS 64 offers a radar level measurement solution thatworks better than

ever, particularly in difficult installation situ ations. Operating at 80 GHz instead of the usual 26 GHz allows the focused radar beam to be three times narrower, which enables the beam to get past internal tank compo nents. Standpipes often used to be installed in storage tanks/spherical tanks to facilitate measurement using radar but these reduce measurement accuracy and are extremely laborious and expensive to install. Thenew80-GHzVegapuls64radar sensor canbemounteddirectlyontoa tankwithout a standpipe. Thismakesmeasurementmore re liable and accurate, and themeasuring points less expensive to plan and set up. In addition, Vegapuls 64 is suitable for poorly reflective media, such as liquids with low dielectric values like LPG/LNG. Vegapuls 64 also has an exceptionally large dynamic range, offers wider range ap plications for the sensors, and higher mea surement certainty. This means that media with poor reflective properties can now be measuredmuchmore accurately thanbefore. Typical for the LPG/LNG industry is the strict requirement that every sensor be sepa rable from the process without interrupting the process or shutting down any part of the productionequipment. For a radar sensor, this means that itmust bemountedon a ball valve to enable the radar sensor and the process to separated. Installation on a ball valve was never recommended for radar sensors, because the ball valve itself causes large interfering reflections inthecloserange, due toreflection

24 ¦ MechChem Africa • September-October 2022