Getting a sense of hydrogen

What is a hydrogen sensor?

Hydrogen is the lightest and most abundant element in the universe, and one would think that developing a device to measure its concentration in a gas or liquid would be simple. Unfortunately, this is not the case; it took many years of research and development – from the early days when canaries were used to detect explosive gases in mines. The first sensor of the modern age was developed in 1926 by Dr. Oliver Johnson of Standard Oil Co. His design measured the heat created by the presence of combustible gases in air. This thermal conductivity technology is still used today, along with a range of new gas sensor technologies that have been developed over the last 100 years. Each of these technologies (e.g. gas chromatography, catalytic bead, laser gas analysis, solid-state, etc.) were developed to address unmet gas sensing needs, and there are many issues to consider when applying these technologies to hydrogen sensing.

What to consider when selecting a hydrogen sensor for industrial applications?

Industrial sensing applications generally have challenging performance and operational requirements that must be met over a range of environmental and other conditions. Care must be taken to ensure that the selected sensor and underlying technology works for the intended use, for example:

• Sensor performance may seem like a straightforward specification, but the devil is in the details. For example, a quoted measurement accuracy of 0.1% could be the maximum error, or it could be the one sigma error, or it could only be valid at room temperature and one atmosphere of pressure. Also, the quoted accuracy specification may only be met after calibration for a specified period before drifting out of specification.
• If other gases are present in the stream being measured, they could impact sensor accuracy. For example, carbon monoxide (CO) in a hydrogen stream can corrupt the hydrogen measurement when using certain gas sensing technologies. One must understand the gas stream make-up and consider using a hydrogen-specific sensor to avoid cross-gas sensitivities.
• From a total cost of ownership perspective, sensors should be selected to minimise or avoid calibration, maintenance and service if possible. Some hydrogen sensor technologies have consumables, such as calibration gases, that must be periodically replaced. Also common is the need for sensor calibration to maintain long-term accuracy. One should understand the calibration interval and the associated costs, especially for remote or hazardous locations, or whether the system needs to be shut down for this maintenance. Beyond the upfront cost of the sensor and its installation/connectivity, one should consider the total cost – including the cost of training operation support professionals.
• If the sensor is not reliable, sending a service team to an oil platform or remote pipeline location takes a great deal of time, effort and expense. Sensor technologies requiring numerous mechanical parts and components, such as gas extraction systems to measure hydrogen in liquids, are often not well-suited for these applications. One should strive for a long life, with a goal of over 10 years.
• Hydrogen is an explosive gas, and a small spark can cause it to explode within certain concentration levels. There are certifications, such as ATEX, to ensure that sensors work safely in hazardous environments. Sensor compliance to these certifications is critical to ensure safe operation.

Where are hydrogen sensors being used now?

The largest hydrogen user today is refining and chemical production. One such application is hydrocracking, which uses hydrogen sensors to ensure efficient processing. One of the challenges of oil processing applications is gas streams that can contain multiple other gases, such as hydrogen sulfide (H₂S). These gases can reduce the measurement accuracy if the sensor is not a hydrogen-specific design. Also, the sensor needs a fast response time to ensure tight process control when concentration levels fluctuate, in order to achieve optimal process efficiency.

Another common application for hydrogen sensors is area safety monitoring for the detection and mitigation of hydrogen build-up in a closed environment. For example, in data centres and utilities, battery back-up systems are used to provide instantaneous back-up power. Cost-effective energy storage solutions such as lead acid batteries are commonly used, and can release hydrogen during recharging. A similar application is hydrogen fuel cell forklifts that could potentially leak. In both applications, hydrogen sensors are generally mounted in the ceiling to trigger alarms and enable fans to evacuate hydrogen at concentrations well below the lower explosion limit of approximately 4%.

One hydrogen sensor application that many people are unaware of is transformer monitoring to improve electrical grid reliability. Power on the grid is distributed using large transformers that convert high voltage to a lower voltage for end users. These devices are filled with oil to keep them cool and provide electrical isolation. If there are faults or overheating in the transformer, the oil will break down into hydrogen and other gases. If faults persist for too long, the transformer can explode and cause a fire, or injure people. Hydrogen sensors are used to continuously measure hydrogen levels in the oil to determine the need for maintenance or to take the transformer offline.

1. ‘The Hydrogen Economy Will Soon Be Ready For Take Off, Including Planes And Power Plants’, Forbes, (6 November 2022), https://www.forbes.com/sites/kensilverstein/2022/11/06/the-hydrogen-economy-will-soon-be-ready-for-take-off-including-planes-and-power-plants/?sh=7779619c4451

Written by David Meyers, H2scan, USA.

This article was originally published in the Spring 2023 issue of Global Hydrogen Review magazine. To read the full article, simply follow this link.

Read the article online at: https://www.globalhydrogenreview.com/special-reports/14042023/getting-a-sense-of-hydrogen/