On Course in Deep Cold
Published on : Tuesday 04-07-2023
Whether at sea or on land: 80-GHz radar level measurement makes cryogenic applications safe and secure, says Claudia Homburg.
LNG and LPG are promising fuel sources for low-emission transportation in the future: Providing an alternative to the heavy fuel-oil powering ocean-going ships and the diesel fuel on our roads. When new LNG-powered container and cruise ships and ferries are launched in the coming years, extremely cold-tolerant level sensors will also be needed on board.
Liquefied natural gas is booming – especially in the shipping and cruise industries. The new generation of container and cruise ships are extraordinary, and not just because of their unprecedented sizes. It is their new propulsion concepts that make them so remarkable. Astonishingly, some of them are now crossing the oceans using natural gas as fuel. But it is not only ship operators who are recognising the ecological as well as the growing economic advantages of liquefied natural gas (LNG) and liquefied petroleum gas (LPG) over conventional fuels. LNG is also becoming more attractive for truck fleets. When liquefied by cooling to minus 162 °Celsius, natural gas reaches an impressive density of 450 kilograms per cubic metre: That’s 600 times denser than its original state as a gas. At the same, its volume is reduced by the same factor: 600. An LNG ship can transport significantly more energy from point A to point B than a comparable oil tanker.
Safety first
When handling liquefied gas, safety comes first. The substance is not only extremely cold, but also flammable and explosive. Automation systems therefore play a special role in storage and delivery at the filling terminals. Reliable sensor data, in turn, ensures the quality and reliability of the automation systems. Comprehensive evaluation of the data helps to reduce potential risks. This provides security, as well as the information that allows optimal utilisation of processes in order to reduce time and costs.
It is not only the extreme temperatures that make life difficult for measuring instruments when they are used at sea or in the regasification process. All petrochemical products are difficult to measure, mostly due to their typically small dielectric constants. The smaller the DK value, the more challenging it is to get an exact level measurement with radar. Whatever level and pressure measurement technology is deployed, because it is the only thing that can provide a reliable and accurate overview in such applications, it must therefore be optimally designed in many different regards.
Mechanically decoupled
The 80-GHz radar sensor VEGAPULS 6X is ideally suited for non-contact measurement of liquefied gas, as it measures the level independently of temperature, pressure and density. From the top of the housing to the measuring antenna, it is robustly constructed and equipped with high quality components, right down to the last detail. The key element is its durable stainless steel construction, which thermally decouples the sensitive electronics inside the housing. Thanks to the more reliable shielding from the process, the sensor can be used down to process temperatures of -196 °C. In addition to cryogenic applications, the specially protected housing and front-flush antenna cover of PTFE are also suitable for reliable measurement of aggressive media, whether acids, alkalis or abrasive substances.
Dynamics in view
The excellent dynamics of this high-frequency radar sensor also makes a difference. Because liquefied gases only weakly reflect emitted signals, due to their small DK values, the sensors have to be able to reliably detect even the smallest of reflection signals. With a sector-leading 120 decibels of sensitivity, the 80-GHz radar sensors from VEGA do this particularly well. Due to their high dynamic range, they are repeatedly setting new standards in the detection of tiny signals. This is especially true in the level measurement of hydrocarbons. The sensors measure virtually all media in the petrochemical industry, from crude oil to cryogenic liquefied gases, with high reliability despite their poor reflective properties.
Focussed all the way down to the tank floor
Cryogenic vessels are usually very well insulated. Typical for liquified gas applications is the requirement that sensors be separable from the process, via a suitable armature or fitting, without interrupting the process. This requirement is mandatory for liquified gas tanks on land. Radar level sensors thus have to be mounted on a ball valve and measure through it. One of the strengths of VEGAPULS 6X is its exceptional focussing. Due to this, the influence of the ball valve on the signal is significantly lower. In fact, the ball valve doesn’t cause any interfering reflections at all. The 80-GHz radar sensor measures the level exactly, completely bypassing vessel internals, and is not affected to condensate and buildup as well.
In the wake of innovation
VEGA’s level and pressure measurement technology is based on many years of experience in developing products for use in process, storage and cargo tanks. Today, VEGA is able to keep up with the demands of the booming, worldwide LNG market by providing sophisticated instrumentation for cryogenic applications. The VEGAPULS 6X sensor ensures maximum security in the production, processing, storage and delivery of LNG / LPG. Its robust design is based on experience with the previous generation of radar sensors. Those earlier sensors, which operated in the frequency range of 26 GHz, mastered the difficult process conditions on the high seas for over 10 years. However the new 80-GHz technology has surpassed these previous achievements. Like no other radar sensor, VEGAPULS 6X handles media with low dielectric values so reliably that DK values concerns can finally be dispensed with – even in maritime applications.
Comprehensive safety concept
When it comes to safety, VEGAPULS 6X offers decisive technical innovations: most importantly, a comprehensive safety concept. Functional safety is guaranteed, as the instrument conforms with all the requirements of Safety Integrity Level. The certified sensor has exceptional SIL characteristics and provides the necessary operational safety to minimise risks in safety-related applications. Another increasingly important focus is “cybersecurity”. In this regard VEGAPULS 6X, in conformity with IEC 61511, meets the strictest requirements for secure communication and system access control. It thus guarantees comprehensive security for the process and the control system.
An important third aspect of its extensive safety features is its self-diagnosis system. It continuously monitors the function of the sensor and recognises if it has been impaired in any way, thus contributing significantly to higher plant availability and sensor performance.
Central to these important features is a new, second generation radar chip created by VEGA. Because there was no chip available on the market that would have met all requirements, the research and development team set to work to design one themselves, from scratch. “The result pretty much encapsulates our entire radar experience from three decades,” says VEGA product manager Jürgen Skowaisa, praising this achievement. “In its scope and functionality, the chip is unique in the whole world.” It is especially characterised by its low energy consumption, high sensitivity, scalable architecture and universal applicability. The radar antenna system and the chip are connected directly to each other, without any cable, for maximum performance.
An industry changes its course
As a marine fuel, liquified gas still occupies only a tiny corner of the market. Most ocean-going container giants still use a mixture of heavy oil and diesel oil, because converting to LNG would be too expensive. But legislation is getting stricter and, in the shipping industry, LNG is considered the fuel of the future. With a whole host of advantages: with reduced (almost zero) particulates and considerably lower greenhouse gas emissions. In the event of any release, neither LNG nor LPG damage the quality of the ocean water, nor are they toxic to aquatic organisms. As long as the gas is not ignited by a spark, there’s a good chance that it will simply dissipate and evaporate.
Even at sea, some measured values are more important than others for the safe operation of processes – particularly in the case of ice-cold and combustible transport goods. Continuous measurement of levels and process pressures as well as the monitoring of multiple stages of the liquefaction process are becoming increasingly important, especially when it comes to improving the operational safety of a ship’s “critical systems”. On this basis, applications in any tank must be more efficient and safer. At sea, safety is not a condition that can be taken for granted – it is a permanent, deliberate and continuous process.
Conclusion
Almost all petrochemical products have a particularly low dielectric constant and are therefore a challenge for level measurement technology. VEGAPULS 6X radar sensors measure contactlessly and highly focussed. Due to their temperature decoupling from the process, they operate reliably even with extreme process temperatures as low as -196 °C. The measuring results are not affected by icing or condensation on the antenna system. The specially protected housing of VEGAPULS 6X and the front-flush antenna cover of PTFE is ideal not only for cryogenic applications. Aggressive media, whether acids, alkalis or abrasive substances, can also be measured very reliably with the instrument. From the top of the housing to the front end of the measuring probe, the sensors are robustly constructed and equipped in every detail with high-quality parts. Their core component is a structure made of resistant stainless steel, which ensures reliable decoupling of the sensitive electronics in the sensor housing. VEGAPULS 6X sensors are equipped with an all-round security package and, in addition to SIL, have the strict cybersecurity certification according to IEC 62334. They measure with a particularly high dynamic range and can thus detect even the smallest signals, so that even media with poor reflective properties are reliably detected.
Claudia Homburg is Marketing Manager, VEGA Grieshaber KG.
