Hydrogen is regarded as the energy source of the future, as it is expected to initially supplement fossil fuels in the medium term and then replace them completely. One of the decisive factors will be whether the safety issues surrounding this highly explosive gas can be tackled.
The safety of pipelines, storage facilities and connection points is crucial for the development of the hydrogen infrastructure. This is because the invisible and odorless gas is highly flammable and explosive. The Fraunhofer Institute for Physical Measurement Techniques IPM in Freiburg has developed sensor and measurement systems that reliably detect even the smallest quantities of hydrogen. Leaks of all kinds can thus be detected quickly.
The research work was part of the TransHyDE hydrogen lighthouse project of the Federal Ministry of Education and Research together with the Project Management Jülich (PTJ). Here, partners from science and industry are developing solutions for the transportation and storage of the gas. Dr. Carolin Pannek and the team at Fraunhofer IPM led the Safe Infrastructure sub-project.
As hydrogen is used in very different scenarios and applications, the Fraunhofer researchers have developed three different sensor systems.
Sensor systems for a wide range of applicationsUltrasonic sensor with photoacoustic effect
Functional principle of the ultrasonic sensor: The LED light generates an ultrasonic wave in the gas. If hydrogen enters the housing, a resonance shift occurs. A MEMS microphone registers this shiftLightcan excite gas to vibrate and thus generate a sound wave. The researchers use this photoacoustic effect for their ultrasonic sensor. A light source shines into the device and generates a resonant sound wave in the gas with a frequency in the ultrasonic range. When hydrogen enters the housing through a membrane, there is a resonance shift, i.e. a change in the sound.
The altered sound is registered by MEMS microphones (MEMS, microelectromechanical systems). In this way, hydrogen escaping from tanks or pipes can be detected, for example. "The sensor could be used to check containers, pipes or connectors. It would also be conceivable to distribute several devices in a room in a similar way to smoke detectors and link them together to form a sensor network," explains Pannek.
But the ultrasonic sensor can do even more. It works so precisely that it even registers if there are molecules of other substances in the hydrogen, i.e. if it is minimally contaminated. Fuel cells that generate electricity in trucks, for example, require high-purity hydrogen. The smallest impurities could damage the sensitive membranes. This is where the sensor checks whether the hydrogen is really pure.
Laser spectrometer
An alternative to the costly storage of hydrogen as a gas in high-pressure containers or as a liquid at minus 253 °C in cryogenic tanks is the use of ammonia (NH3) as a carrier matrix. Storage and transportation are then much easier. However, as ammonia is extremely toxic, leaks must be detected quickly and reliably. Fraunhofer IPM has developed a laser spectrometer for the remote detection of ammonia. It absorbs the wavelength of ammonia, reacts immediately and shows the result on a display. "Specialists can hold the compact device in their hand and check pipes or tanks from a safe distance of up to 50 meters. Mounted on robots or drones, it inspects industrial plants or flies over pipelines," says Fraunhofer project manager Pannek.
Hydrogen can be stored and transported in the form of ammonia (NH3). The Fraunhofer IPM laser spectrometer absorbs the wavelength of ammonia, reacts immediately and shows the result on a display
Raman spectroscopy
The third measuring system is a further development of Raman spectroscopy. The Raman shift - named after an Indian physicist - is caused by the interaction between light and matter. The light reflected by the matter has a different wavelength than the incident light. This gives every material a spectroscopic fingerprint.
Fraunhofer IPM has many years of experience in the design and construction of Raman systems. For the TransHyDE project, the researchers have developed a filter-based Raman sensor that selectively detects hydrogen in complex media. The device works with low-cost components such as an inexpensive CMOS camera (complementary metal oxide semiconductor), is mobile and can therefore serve as a flexible test station for quantifying hydrogen. The system is used, for example, in the energy industry for the production of hydrogen.
Flexible use, consulting for H2 projects
All sensor systems are designed to be so flexible that they can be adapted to very different scenarios. If required, the Fraunhofer experts can advise industrial customers, energy suppliers or operators of hydrogen projects on questions relating to safe use. Fraunhofer expert Pannek is convinced: "The starting signal for the expansion of the hydrogen economy can be given."
