How to Measure and Control Moisture in Hydrogen Fuel Cells

Why dew-point measurement is key to the quality of hydrogen fuel

The demand for hydrogen fuel cells is rapidly evolving.  According to research analysts Vision Research, the market looks set to reach a global net worth of around USD 60 billion by 2030, an increase of 60 % CAGR.  Decarbonizing transport in all its forms is a key focus, with developments underway for hydrogen-powered trains, ships, planes and road vehicles.  The latter – especially commercial vehicles – are predicted by management consultancy McKinsey to represent one of the fastest growth areas, with an anticipated 850,000 hydrogen-fuelled heavy-duty trucks being on European roads by 2035.  The consultancy estimates that these will require at least 4,800 hydrogen refuelling stations across the continent. 

The adoption of hydrogen as a source of clean energy is vital if we are to decarbonize and reach global net zero targets.  However, there is considerable debate over the different methods of generating and distributing hydrogen, as they vary in terms of the level of carbon emissions they generate.  Of equal importance, if hydrogen fuel is to be generally accepted, is the need to ensure that the gas delivered to the point of use meets the highest quality and safety standards and is free of potential contaminants – nobody wants to see hydrogen vehicles failing due to contaminated fuel. 

Hydrogen contamination

Hydrogen can either be produced at central generating stations, typically using methane steam reforming, or close to the point of use, with electrolyzers being used either to convert the chemical energy of hydrogen to produce electricity, or to generate hydrogen from water for dispensing to vehicles.  In each case, there are inherent risks caused by contaminants that include particulate matter, trace gases such as carbon dioxide, nitrogen and hydrogen sulphide, and moisture.  These can affect the efficiency and reliability of the generation systems – particularly Proton Exchange Fuel Cells – and the purity of the hydrogen that is produced.

Moisture measurement & ISO 14687-2

Water may be the critical raw material for electrolysis, but if water vapor is carried over into the hydrogen gas it will create significant problems, within distribution, storage and on-board vehicle systems.  For example, it can condense and cause corrosion on metal surfaces, while at low temperatures it can freeze and block pipes and valves in distribution systems or affect the operation of compressors and the functions of on-board vehicle tank units and fuel cell components.  In aerosol form it can also act as a transport medium for water-soluble impurities and as a solvent for elements such as sodium, potassium and calcium. 

Hydrogen generation or refuelling stations normally incorporate gas drying units, together with the potential for moisture measurement, or dew-point, monitoring sensors.  These are essential to ensure that gas purity is maintained at a predetermined level, and to meet the needs of infrastructure and refuelling operators.  In Europe, this is currently specified as part of the ISO standard 14687-2, which states that the maximum permissible concentration of water in hydrogen used for road vehicles and produced from polymer electrolyte membrane fuel cells (PEMFC) should not exceed 5 μmol mol-1 at the dispenser nozzle. 

Dew-point measurement technology

Measuring moisture dew point accurately and consistently in hydrogen fuel cells and refuelling stations isn’t always straightforward.  The complexity of the systems, varying operating pressures and temperatures and the evolution of new and commercially viable generating equipment place considerable demands on the performance, accuracy and consistency of dew-point monitoring and measurement instruments. 

Devices such as Michell Instruments’ Easidew Dew Point Transmitters have been developed to meet the needs of demanding applications and are widely used in traditional compressed natural gas processing and distribution networks.

The latest Easidew transmitters are intrinsically safe, with ATEX and IECEx ratings, and can be used optionally at operating pressures up to 52.5 MPa (525 Barg).  Michell have the design knowledge and capability to work with ultra-high pressures and qualified pressures beyond 100 MPa (1000 Barg). This makes the Easidew ideal in hydrogen refuelling stations where they can be fitted on-line, between the drying and final compression stages, to measure gas quality immediately before it is dispensed.  It is also extremely accurate, repeatable, robust, compact and easy to install, and is supported by a comprehensive range of technical, application and recalibration services.   

The importance of hydrogen quality assurance 

The use of Easidew Dew-Point Transmitters and high-performance analyzers from Michell Instruments is essential for effective control of the quality of hydrogen at all stages of production, distribution and use.  These instruments ensure production efficiency, consistency and reliability.  Just as importantly, they also provide the security and peace of mind that is essential to guarantee the widespread commercial and consumer acceptance of hydrogen as the fuel of the future. 

With over 45 years’ experience in the development of innovative precision instruments, we are the application experts in dew-point and gas measurements for all hydrogen applications. If you would like to discuss your requirements, please contact our team today.

Sources

Vision Research Reports

McKinsey & Company

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Industrial Dew-Point Transmitters, Dew-Point Sensors and Trace Moisture Sampling Systems