Why Thermal Conductivity Sensors are Good Hydrogen Leak Detectors

From heavy-duty trucks to buses and automobiles, along with aircraft and ships, hydrogen-generated power is gaining popularity in transportation for several reasons such as zero emissions, fast refueling, long range, and high efficiency. When compared to the greenhouse gases emitted by conventional fossil-fuel-based internal combustion engines (ICE), hydrogen fuel cells produce only water vapor as an exhaust emission. Although cost and infrastructure remain hurdles in adoption, technological advancements are further improving efficiencies while the rising drive for decarbonization continues to attract interest and investment in hydrogen as a clean alternative to fossil fuels.

With the widespread adoption of hydrogen-powered transportation, there is a tremendous need for detecting hydrogen leaks in these systems. Leaks are common in hydrogen power systems primarily because hydrogen molecules are extremely small and have high diffusivity, allowing them to escape through materials and seals. Additionally, hydrogen can cause hydrogen embrittlement, a process where it infiltrates and weakens materials like steel over time, creating more opportunities for leaks. Hydrogen is also highly flammable, and is a colorless, odorless, and tasteless gas that can quickly create a dangerous and risky situation. It must be detected instantly whenever and wherever a leak occurs.

While there are numerous methods to detect hydrogen leaks, such as electrochemical sensors and catalytic bead sensors, the most effective and accurate method is thermal conductivity detection (TCD) sensors. These work by precisely measuring the thermal properties of hydrogen as it passes through the sensor, comparing it to the thermal properties of air.

Notable features of HLD sensors

Key features that make TCD sensors attractive for gas leak detection, especially hydrogen leak detector (HLD) sensors, include stability under varying conditions like shock and vibration, fast response times of less than 2 seconds, high accuracy, and high sensitivity. Honeywell Sensing & Productivity Solutions’ HLD-111-111-001 sensor (Figure 1) implements advanced compensation algorithms to detect low hydrogen leakage and deliver accurate solutions without manual intervention for 10 years.

Figure 1: Honeywell’s HLD-111-111-001 sensor uses thermal conductivity detection to reliably and accurately monitor hydrogen leaks. (Image Source: Honeywell Sensing & Productivity Solutions)

Additionally, TCD-based HLD sensors are less susceptible to contamination from chemicals that might interfere with other sensor technologies. Unlike chemical sensors that degrade with time or catalytic sensors that are susceptible to poisoning from compounds like sulfur, HLD sensors do not use reactive materials, leading to a much longer lifespan and greater reliability.

TCD sensors also have a start-up time of less than one second, and have an operating temperature range from -40°C to +85°C (-40°F to +185°F).

Key benefits of TCD sensors as hydrogen leak detectors

There are several benefits in using thermal conductivity detection sensors for monitoring hydrogen leaks. Besides ensuring a high degree of accuracy, they offer a long operational life. HLD sensors are developed to operate for up to 10 years without manual intervention and calibration, reducing maintenance costs and downtime. Unlike other gas sensors, thermal conductivity-based HLD sensors do not require oxygen to provide efficient and stable detection. HLD sensors can work in an inert or oxygen-deficient atmosphere where other types of sensors like catalytic beads, would fail.

HLD sensors also have very fast response times, which are crucial for safety in applications like automotive or fuel-cell systems. High sensitivity and accuracy allow these sensors to detect very small hydrogen leaks before they pose a safety risk. Fast leak detection enables quick corrective actions, preventing escalation of a hazardous situation. In addition, they are reliable and durable for tough industrial conditions, and support hydrogen safety standards and industry regulations.

Finally, due to simpler construction, they are lower in cost and can be fabricated using high-volume, repeatable solid-state sensing elements, making them an economical option for widespread deployment.

Typical HLD applications

Typical applications for TCD sensors include fuel cell electric vehicles (FCEVs), hydrogen refueling stations, hydrogen generators, industrial applications like chemical processing, metal refining, and semiconductor manufacturing, hydrogen storage and distribution, and marine applications.

Like other EVs, FCEVs use electricity to power electric motors, which they generate using a fuel cell powered by hydrogen. Consequently, hydrogen leaks in the fuel system can pose a safety hazard and reduce vehicle efficiency. By continuously monitoring the FCEV’s hydrogen tanks, pipelines, and fuel cell stacks, the HLD sensors detect leaks to prevent dangerous situations and maintain hydrogen fuel efficiency (Figure 2).

Figure 2: TCD-based HLD sensors deployed in fuel-cell-powered electric vehicles prevent hazardous situations such as leaks and maintain hydrogen fuel efficiency. (Image source: Honeywell Sensing & Productivity Solutions)

Likewise, hydrogen-powered EVs depend on high-pressure storage tanks and refueling stations, where leaks can present significant safety risks. TCDs ensure that by continuously monitoring the refueling infrastructure for leaks, EV makers can mitigate ignition risks. Concurrently, placing these sensors across hydrogen dispensers and storage systems enhances operational efficiency and safety, thereby minimizing downtime and building consumer confidence in hydrogen refueling infrastructure.

Similarly, hydrogen generators are essential for on-site hydrogen production in industrial, medical, and energy applications. For the safety of users around these generators, HLD sensors are placed in key locations to detect minimal leaks and prevent hazards such as gas buildup, fire, or explosion (Figure 3).

Figure 3: Hydrogen generators use HLD sensors for user safety. (Image source: Honeywell Sensing & Productivity Solutions)

Other industries, such as chemical processing, metal refining, semiconductor manufacturing, and warehouse logistics, are also tapping the benefits of hydrogen power. For instance, hydrogen fuel cell forklifts are increasingly being used in warehouses due to fast refueling capabilities and zero emissions. Workplace safety is ensured by placing HLD sensors in key locations and real-time monitoring for leaks around forklifts and fueling stations (Figure 4). By using HLD sensors, warehouse operators are ensuring safe operations of hydrogen-powered forklifts while maintaining operational efficiency and preventing costly downtime.

Figure 4: HLD sensors ensure safe operation of hydrogen-powered forklifts. (Image source: Honeywell Sensing & Productivity Solutions)

Delivering a sensitive, stable, and reliable solution

Honeywell Sensing & Productivity Solutions’ HLD series of sensors employs thermal conductivity detection techniques to deliver high sensitivity, stability, and reliability for many applications across multiple industries, including automotive, transportation, industrial safety, and residential power. These sensors incorporate a proprietary algorithm to compensate for factors like temperature, pressure, and humidity, ensuring accurate readings across a wide range of operating conditions. As a result, they can detect leaks as low as 50 parts per million (ppm) with an accuracy of ±10%, and do so within two seconds. Because of their unique properties, HLD sensors also prevent false readings due to the presence of other environmental gases, such as carbon monoxide or hydrocarbons.

HLD sensors may be customized to meet application needs, such as being lightweight and having an auxiliary output. Solutions may be tailored to exact specifications for improved time-to-market, lower total system cost, and enhanced reliability. HLD sensors are also available in both a rugged polycarbonate housing for protection and ease of use with a fire rating of UL94V0 and an ingress protection level of IP67, and in a no-housing (PCB only) version for custom integration.

Conclusion

Hydrogen is gaining popularity in many industries as a promising clean energy alternative for achieving sustainable energy goals due to its potential to reduce greenhouse gas emissions and reliance on fossil fuels. Honeywell Sensing & Productivity Solutions supports this transition through its highly accurate and reliable HLD sensor series for mitigating safety concerns and building customer confidence in hydrogen fuel cells.