Co-edited by Alicat & Crowcon
Amidst the global push for sustainable, carbon neutral energy sources, many corporations and countries are increasingly interested in alternative fuels. One such fuel is hydrogen, playing a vital role in the clean energy landscape as a green alternative to natural gas. This has resulted in a sudden increased interest in fuel cell and electrolysis technology.
One of the primary challenges facing both of these processes is hydrogen leakage. Hydrogen gas requires careful control on the input side of PEM fuel cell stacks and on the output side of electrolysis. Any leakage that occurs not only diminishes efficiency, but also raises costs and introduces potential hazards such as flammability and asphyxiation.
Here we discuss hydrogen leak detection in more detail and provide several solutions to help improve the safety and efficiency of fuel cell processes.
Why hydrogen leaks in fuel cells
H2 gas has a high propensity to leak due to its very small size and its low density (0.09 g/L at NTP of 0°C / 1 atm) which corresponds to a high buoyancy.
In fuel cell stacks, hydrogen is prone to leak from seals present at process connections near the H2 storage cylinders and associated flow paths. While it is nearly impossible to reach 100% gas containment in a fuel cell stack, reliable leak detection is essential for minimizing loss.
Detecting hydrogen leaks is critical to maintaining process & personnel safety
Not only does leakage decrease process efficiency, but it becomes a serious safety concern. Hydrogen has a Lower Explosive Limit (LEL) of just 4% volume, meaning even tiny quantities of H2 can cause explosions when mixed with atmospheric air. Even a spark of static electricity from a person’s finger is enough to trigger an explosion when hydrogen is present.
Since hydrogen is odorless, colorless, and tasteless, hydrogen leak detection is extremely difficult without the help of mechanical sensors. Monitoring H2 therefore demands specialized equipment to alert personnel of danger and prompt emergency response procedures.
Detecting hydrogen with traditional sensor technology
Traditional sensor technologies for flammable gas detection are pellistors. Their key disadvantage is that they require oxygen, making them unsuitable in some installations. Another challenge is that some applications put pellistors at risk of being poisoned or inhibited, leaving workers unprotected. These sensors are not fail-safe, and a failure will not be detected unless test gas is applied, commonly known as a bump test.
Detection with mass flow instruments
Hydrogen leak detection relies on in-line process instruments and careful monitoring of system inputs and outputs. For PEM electrolysis, one method involves comparing the mass flow rates of H2O input and hydrogen output to calculate the amount of leakage occurring during the process. Coriolis instruments are ideal for measuring and controlling the input H2O for such electrolysis systems.
For PEM fuel cell stack systems, one common hydrogen leak detection method involves employing a combination of hydrogen sensors alongside flow meters. A flow meter situated downstream of the H2 supply and measurements can be used in conjunction with hydrogen sensors to detect any leaks on the anode side of a PEM fuel cell stack.
Differential pressure based mass flow instruments enable rapid response times, allowing real time leak detection. Given their sensitivity, they are also able to measure very small leaks with high precision and accuracy. This can help identify points of leakage to improve overall process efficiency, decrease cost, and reduce risks of danger to operators.
Detection with MPS™ technology
Crowcon, another Halma company, also has a wide range of products for the detection of hydrogen. The Xgard Bright utilizes their latest technology, the Molecular Property Spectrometer (MPS™), to detect and measure ambient levels of hydrogen and other flammable gases with high-accuracy and precision in real time. Furthermore, the sensors do not require recalibration, significantly reducing total cost of ownership and limiting interaction with the units. The Xgard Bight ensures process operators are at no risk of being poisoned while also guaranteeing no false alarms.
Alicat, Crowcon, and the Halma family of brands are here to provide solutions to help create a safer, cleaner, healthier world.