On the road to more climate-friendly mobility, hydrogen is gaining in importance as a new fuel. However, refuelling with hydrogen is more complex than with petrol and diesel. Unlike other gases, hydrogen heats up as it expands, resulting in pressure and temperature changes during refuelling that need to be monitored precisely. That's why Heinrichs Messtechnik GmbH, a subsidiary of the Kobold Group, has developed the TMU-W 004 mass flow meter, which ensures precise metering despite variations in pressure and temperature. This device is the first of its kind to be certified to the international standard OIML R 139 2018, and therefore approved for hydrogen filling stations. A compact, sturdy housing protects the sensors and measuring loops, which use the Coriolis effect for highly accurate flow measurement. Remote electronics convert sensor signals into a mass flow reading, and also measure fluid temperature. The TMU-W 004, suitable for high-pressure applications up to 1000 bar, is already in use in the filling stations of the listed company Nel Hydrogen.
Hydrogen as a fuel is gaining ground in Europe, thanks in part to government stimulus packages. "For passenger cars, hydrogen refuelling is generally carried out at 700 bar. This high pressure is necessary to generate the energy density required for good measurement conditions, explains Guido Thometzki, CEO of Heinrichs Messtechnik GmbH. During this process, the temperature must not exceed +85°C, otherwise the tank lining may be damaged."
As the tank expands and heats up during filling, the hydrogen is cooled before it reaches the tank. This high-pressure environment, together with the small size of the hydrogen molecule, represents a major constraint on accurate hydrogen flow measurement.
With this in mind, Heinrichs Messtechnik GmbH, a subsidiary of the Kobold Group, has modified its proven Coriolis mass flow meter for high-pressure gas applications, and now offers the TMU-W 004, a version specially designed for hydrogen measurement. This flowmeter enables precise measurement of the quantity of hydrogen transferred to the vehicle's tank during filling. This enables precise invoicing of the quantity filled, which is a prerequisite for refueling at public hydrogen filling stations. It covers a measurement range from 0.133 kg/min H2 to 4 kg/min H2.
During the development phase, the use of sophisticated engineering tools enabled numerous simulations to be carried out on the flowmeter structure as well as on the fluid itself, leading to optimal layouts and dimensions for all mechanical and electromechanical components. As a result, the device has become the first and so far only flowmeter in the world to be certified to the international standard OIML R 139 2018, which covers hydrogen flow measurement systems for vehicles. Norwegian listed company Nel Hydrogen is already successfully using the TMU-W 004 at its filling stations.
Special sensor arrangement delivers precise results
The TMU W004 flowmeter has been designed to be much more compact than its predecessors, so that it can be optimally integrated into hydrogen filling stations. Inside the compact, distortion-resistant housing are two parallel U-shaped measuring tubes. "An excitation system causes the measuring tubes to vibrate at their natural frequency. As the fluid flows through these tubes, the Coriolis effect causes a phase shift between these frequencies," explains Mr Guido Thometzki. "Optimally placed sensors in the measuring tubes detect this phase shift and send it as an electrical signal to the electronics for complete signal processing. From these signals, the current mass flow rate is calculated.
The specific architecture of the device - i.e. the shape of the measuring tubes and the ideal positioning of the sensors on the tubes - together with the further harmonization of other components such as the bellows, make this a particularly sensitive and precise flowmeter, despite the thick walls of the measuring tubes. This robustness of the measuring tubes is necessary to withstand the high pressure of 1000 bar (the test pressure is actually 1500 bar). The sturdy, fully-welded casing, for added rigidity, provides ample protection for the sensitive measuring equipment inside.
The actual volume is then processed from an electronic pulse output. "The user also obtains information on the temperature of the fluid, and possibly its density. This data can be used to control the compressor that pumps the hydrogen, for example by switching to a higher volume or, conversely, by interrupting pumping."adds Guido Thometzki. The electronics feature a two-line LCD display which directly indicates the selected values. The electronics are easy to configure using the four front-panel keys. Among the various functions available, the user can define physical units, displayed quantities, outputs and analyze faults. The transmitter is available as a process version (round waterproof housing) or as a rack-mounted version for installation in a control cabinet. Both types of enclosure are pressure-resistant and intrinsically safe, to prevent fire or explosion in the event of a gas leak.
Simulations and flow tests ensure measurement accuracy
For the development, manufacture and calibration of its meters, Heinrichs Messtechnik GmbH has used numerous simulation and optimization methods to guarantee the accuracy and reliability of its devices under every conceivable condition. "Devices for measuring high-pressure gases such as hydrogen, like the new TMU-W 004 for hydrogen filling stations, are naturally no exception, explains Guido Thometzki. On the contrary, when developing the TMU-W 004 in particular, we used state-of-the-art simulation methods specially developed for fluid mechanics and structural design, such as FEM (finite element method), CFD (computational fluid dynamics) and FSI (fluid structure interaction)." It was only in this way that the TMU-W 004 was able to meet the seemingly contradictory requirements of the highest precision and extreme reliability when measuring high-pressure gas flows. Measurement accuracy also had to remain high despite pressure and temperature fluctuations during filling. "The fact that the TMU-W 004 not only meets the requirements of OIML R 139 2018, but far exceeds them with its accuracy class of 1.5 for hydrogen, shows, above all what the TMU-W 004 development team has achieved," says Dr Thomas Chatzikonstantinou, Technical Director of Heinrichs Messtechnik GmbH, in conclusion.
Heinrichs Messtechnik GmbH, founded in Düsseldorf in 1911, has been developing and selling flowmeters for over a hundred years. From the outset, one of its main markets was the chemical and petrochemical industries. Since the 1960s, the company has been developing and marketing all-metal float flowmeters. In the mid-1980s, Heinrichs was the first company in Europe to build a mass flowmeter using the Coriolis effect, and in the years that followed it constantly expanded its range. Today, the company has customers in many sectors, including chemicals, oil & gas, energy, plant construction and mechanical engineering. In 2008, Heinrichs joined the Kobold Group, giving it access to an extensive sales network through the Group's international subsidiaries. Heinrichs develops and manufactures all its products in-house at its Cologne headquarters.
Visit the site:
www.kobold.com