Hydrogen has long played a key role as an industrial feedstock in petroleum refining, fertilizer production, and chemical manufacturing. However, conventional methods of producing hydrogen generate substantial carbon dioxide emissions.
In recent years, there's been growing demand for clean hydrogen—produced without greenhouse gas emissions—and that demand is expected to grow significantly over the next 10 to 20 years as part of a broader shift toward climate-conscious energy solutions.
A recent analysis by McKinsey and Co.1 found that global demand for clean hydrogen is likely to reach over 250 million tons per year by 2050.
Should leading countries achieve vital net-zero CO2 commitments via appropriate policies, it is expected that global demand for hydrogen will increase further to almost 400 million tons annually.
It is also anticipated that hydrogen production methods and end uses will broaden and diversify in line with this increase in demand.
This dramatic growth in hydrogen production and use prompts a need for accurate and cost-effective hydrogen flow measurements able to support a wide range of applications (Figure 1).
This article outlines those emerging end uses, as well as providing insight into current flow-measurement solutions for hydrogen gas.
Typical H2 End-Use Markets
The most commonly encountered end-use markets for hydrogen include petroleum refining, fertilizer, and the chemical industries. These application areas constitute the majority of current demand.
In 2022, the International Energy Agency (IEA) reported that current H2 demand had reached 95 million tons, concentrated in the manufacture of chemicals, agricultural fertilizers, and transportation fuels.
Petroleum Refining
The most significant current demand for hydrogen stems from the hydrocracking and hydrotreating of petroleum refinery processes.
The hydrocracking process catalytically breaks carbon-carbon bonds and hydrogenates to convert heavy oil fractions to lower-molecular-weight hydrocarbons suitable for use in fuels such as diesel. Hydrotreating removes heteroatoms like sulfur from hydrocarbon molecules.
The petroleum refining sector accounts for the greatest demand for hydrogen currently. Image Credit: Sierra Instruments
Ammonia Manufacturing
A considerable amount of hydrogen is employed in the production of ammonia for a range of use cases, including synthetic fertilizers. This is done via the Haber-Bosch process, using atmospheric nitrogen (N2) from air-separation units.
The Haber-Bosch process creates ammonia by combining H2 with N2 over a finely dispersed iron catalyst accompanied by promoters.
Chemical Production
Hydrogen is a key component in a number of important industrial chemicals, including hydrochloric acid, hydrogen peroxide, methanol, cyclohexane, and oxo-alcohols. H2 is also employed in the manufacture of some pharmaceutical products and vitamins.
Oil Hydrogenation
Hydrogen is utilized in the production of hydrogenated oils used in food production. This helps to prevent oxidation and to raise the smoke point of cooking oils.
Metals
Some applications in the metallurgical industry involve hydrogen being mixed with inert gases to generate a reducing atmosphere, for example, heat-treating of steel and welding.
Emerging Hydrogen Markets
Traditional uses of hydrogen are likely to continue for the foreseeable future, but increases in demand are likely to be driven by emerging markets linked to the ongoing clean-energy transition.
Power Generation
It is expected that hydrogen will see growing use as a fuel for power generation facilities. H2 will likely be blended with natural gas to power commercial and residential energy supply and heating applications.
Industrial Heating
It is possible to utilize hydrogen alongside specialized burners for industrial boilers and furnaces, with H2 functioning as a combustion fuel.
Transportation
Hydrogen is used to power the electrochemical reactions in a hydrogen fuel cell, which can be used in vehicles with no CO2 emissions. H2 can also be used as a feedstock with captured CO2, facilitating the manufacture of synthetic vehicle fuels such as diesel, gasoline, and sustainable aviation fuel.
Generator Cooling
Hydrogen can be used to cool conductors in power plant generators due to its high heat capacity and low density.
Power-to-X
Hydrogen can function as an energy storage medium for surplus renewable energy acquired via solar and wind sources. This surplus energy can be used to power water electrolysis, generating hydrogen as an energy carrier with no carbon emissions.
Rocket Fuel
Hydrogen can be used as a rocket propellant, a key consideration in the expanding commercial space industry.
Hydrogen Production Methods
There are multiple viable approaches to hydrogen production, but steam-methane reforming (SMR) of natural gas remains the most commonly employed method. Hydrogen is also created via the gasification of coal in some areas.
It is expected that the future will feature more diverse hydrogen production methods. For example, conventional SMR processes can be coupled with carbon capture, utilization, and storage (CCUS) technologies to help mitigate SMR’s associated CO2 emissions.
A great deal of attention is also being given to the use of water electrolysis to produce hydrogen, with electrolysis processes powered by nuclear and/or renewable energy resulting in no release of CO2.
Methane pyrolysis is also garnering significant interest, with methane decomposed using thermal energy, plasma, or catalysts to produce hydrogen with a solid carbon by-product. Some methane pyrolysis processes produce carbon black, while other processes result in graphite or various other types of solid carbon.
A further emerging hydrogen production method sees naturally occurring hydrogen extracted directly from the Earth’s crust.
Hydrogen Application Considerations
The applications outlined thus far are not without their challenges, however. The economic conditions surrounding hydrogen production and its unique inherent properties present a number of specific challenges.
For instance, green hydrogen production via renewable energy is currently around four times more expensive than production via SMR, depending on the cost of natural gas and electricity. Minimal waste is key to cost-effectiveness for green hydrogen producers, handlers, and end users.
Hydrogen applications also tend to feature simultaneous engagement with its gas and liquid phases, potentially making it difficult to quantify gas moving into or out of a piece of equipment or specific process. The wide range of pressures and temperatures found in H2 applications is also unique among industrial gases.
Hydrogen’s small molecular size allows its molecules to permeate into solid metals, potentially reducing the amount of mechanical stress needed to produce cracking in the metal. This can lead to embrittlement over time in the metal in storage tanks or steel piping used for hydrogen storage or transport, respectively.
Hydrogen Flow Measurement
Emerging hydrogen applications have varying demands in terms of gas handling, but every application necessitates robust and accurate flow measurement. This is necessary in order to:
- Confidently determine quantities of gas flowing into or out of process or research equipment
- Help limit waste and optimize gas usage
- Support end users to optimize processes and ensure safety
Sierra Instruments (Monterey, California) is in a unique position to offer accurate flow measurement solutions suitable for a diverse array of hydrogen applications.
The company’s technical expertise, market experience, and broad range of product offerings make it the go-to organization for flow measurement in emerging hydrogen applications and a ‘one-stop-shop’ for flow measurement.
The following examples of hydrogen flow measurement highlight the importance of determining flow in these areas, outlining the specific Sierra solutions for measuring flow in these H2 applications.
Challenge 1: Flow Measurement in Hydrogen Fuel Cells
Fuel cells convert the chemical energy in hydrogen molecules into electrical energy to power a motor in both stationary and mobile applications. If hydrogen is produced using renewable energy (Figure 1), hydrogen fuel cells can be a zero-emission technology. This is because the only by-product of the reaction is water.
Figure 1. Fuel cells convert the chemical energy in hydrogen molecules into electrical energy. Image Credit: Sierra Instruments
In a polymer electrolyte membrane fuel cell (PEMFC), the electrolyte membrane enables ion conduction between two electrodes, and it must stay hydrated to maintain high proton conductivity—crucial for efficient fuel cell performance.
If the inlet gases (hydrogen and oxygen) aren’t properly humidified, the membrane can dry out, leading to increased resistance losses and potential damage. Factors such as temperature, water flow rate, and gas flow rate all influence the relative humidity (%RH) inside the cell, which directly impacts its efficiency.
Industrial thermal mass flow meters are a powerful and cost-effective option for acquiring these measurements. An immersible thermal mass flow meter maintains a constant temperature differential between a heating element and a reference RTD (resistance temperature detector).
Power is applied to the heated element, and molecules remove heat from the heated element as fluid passes by it. Because higher fluid flow removes more heat, more power is necessary to maintain the constant delta-T. In this instance, the amount of power applied to the heating element will be proportional to the mass flow rate.
When working with thermal mass flow meters, flow measurements are not impacted by changes in density, temperature, viscosity, or pressure. This type of instrument can also accurately detect low gas flows.
Fuel-Cell Flow Measurement Solution
It is necessary to measure the flow of hydrogen and H2 gas blends with high accuracy and low drift over time in order to maintain optimal fuel-cell efficiency.
The QuadraTherm series from Sierra is ideally suited to this challenge due to its capacity to measure a wide range of flow rates, including very low flow. This robust instrument can achieve gas mass flow rate accuracies of +/-0.5 % of reading—representing the most accurate thermal flow meter accuracy currently on the market.
The QuadraTherm’s distinct design features powerful four-sensor technology with three platinum temperature sensors and one patented DrySense mass velocity sensor. These sensors allow the QuadraTherm to offer extreme precision with ‘percent of reading’ confidently rivaling Coriolis flow meter technology’s accuracy.
Flow measurement is critical in testing the performance of hydrogen fuel cells and electrolyzers, among other hydrogen R&D efforts. Image Credit: Sierra Instruments
Challenge 2: Flow Measurement for Hydrogen in Research and Development Applications
The transition to zero-GHG-emissions energy has been accompanied by a notable increase in research and development activity in this area. As research and development in the production, storage, and use of hydrogen continues, there is a linked need to reliably and accurately measure hydrogen gas flow.
Gas output in electrolyzer development must be analyzed in order to ascertain system performance under a range of conditions. Flow measurement is key to evaluating fuel cell efficiency and leakage.
Beyond hydrogen itself, research and development in hydrogen-related technologies also necessitate the accurate flow measurement of related gases to evaluate and improve technology, for example, natural gas and ammonia.
R&D Flow Measurement Solution
MEM-based mass flow meter and controller sensors are comprised of two or three temperature sensors and a heater.
Vapor deposition involves the depositing of an extremely small molecular layer on a thin membrane. MEMS-based mass flow controllers feature a bypass that moves a defined percentage of the total gas flow through the sensor. The sensor’s bore is relatively large, meaning that the pressure drop is relatively low.
The MEMS chip introduces heat into the medium with a constant heating output when in the presence of flow. These two temperature sensors are arranged symmetrically prior to and following the heating element in order to detect a shift in the temperature profile toward the downstream sensor.
Both sensing elements measure the same temperature if there is no flow, and the measured signal is immediately digitized to provide a direct mass flow reading because the sensor is part of the MEMS electronic circuit.
Sierra offers a range of mass flow meters and controllers that are able to meet the needs of complex, smaller-scale development applications. This range includes its SmartTrak capillary products, Redy Series MEMS-based flow meters, and the d·flux multiparameter flow series based on differential pressure.
The SmartTrak series is a digital, multi-gas mass flow controller able to offer stable, accurate, repeatable gas mass flow, while the Redy Series features no moving parts and is provided with a no-drift warranty.
RedySmart Mass Flow Meters and Controllers. Image Credit: Sierra Instruments
d·flux Multiparameter Mass Flow Meters and Controllers. Image Credit: Sierra Instruments
Challenge 3: Flow Measurement in General Cooling Applications in Power Plants
Hydrogen can be used in power plants to cool the copper windings used in electricity generators. The cooling fans of generators can move significantly more hydrogen than air using the same amount of power. Flow measurement is, therefore, key to maintaining generator efficiency.
Power-Plant Cooling Applications Solution
Sierra vortex flow meters are ideally suited to accommodating high-pressure flows up to 1500 psia.
These volumetric flow meters feature an obstruction in the flow path that creates vortices in the flow, resulting in differential pressure areas that prompt the sensor to oscillate at a specific frequency, proportional to the actual velocity in the pipe.
Unique built-in temperature and pressure compensation features facilitate the mass flow measurement of hydrogen.
The InnovaMass series of vortex meters from Sierra includes both 240s inline and 241s insertion configurations. These products are able to measure up to five process variables with high accuracy: volumetric flow, mass flow, density, pressure, and temperature, all with a single process connection.
The model 241s is able to measure three key process variables through one process connection: velocity, temperature, and pressure (VTP). This enables the real-time calculation of true mass flow, offering very high system accuracy because everything is calibrated together.
Because VTP is measured directly and the Reynolds number is calculated dynamically, the effects of flow profile variations in large pipes are automatically accounted for in the real-time mass flow measurements.
This approach enables reliable measurements in large pipes—up to 72 inches in diameter—whereas installing an inline airflow meter at that scale would be prohibitively expensive.
Future Outlook and Concluding Remarks
Hydrogen flow measurement is also proving to be of key significance in the rapidly expanding commercial space industry. Hydrogen is seen as a viable rocket propellant in these applications, with flow measurement central to the maintenance of the appropriate hydrogen-to-oxygen ratios required in combustion to ensure optimal thrust.
Sierra continues to innovate, bringing pioneering new flow measurement products to the market.
The Sierra d·flux is a new, especially relevant product for hydrogen flow measurement. The d·flux is able to provide flow rate measurement and control up to 3124 slpm (standard liters per minute) in hydrogen applications, with five sensor options ensuring precision accuracy:
- A1 Core: ± 0.5 % of user full scale ± 1 % of measured value
- B1 Prime: ± 0.3 % of user full scale ± 0.7 % of measured value
- B2 Prime high accuracy: ± 0.3 % of user full scale ± 0.5 % of measured value
- Hydrogen Applications (Prime Hydrogen Sensor)
- B3 Prime H2: ± 0.3 % of user full scale ± 0.7 % of measured value
- B4 Prime H2 high accuracy: ± 0.3 % of user full scale ± 0.5 % of measured value
- User full scale = ~70-100 % standard range
Partnering with a reputable flow measurement company can ensure successful flow solutions for all aspects of hydrogen applications.
Sierra Instruments boasts 30 years of experience in hydrogen flow applications, with an array of hard-won expertise that can offer significant benefits to its partners. The company offers a comprehensive portfolio of products and can serve as a ‘one-stop shop’ for all hydrogen flow monitoring requirements.
Example Calculation for Fuel Cell Membrane Hydration
In a PEM fuel cell, a portion of the exhaust gas—primarily water vapor—is recycled to help humidify the inlet gases.
To maintain optimal fuel cell performance, it’s essential to accurately monitor the flow rates of all three gases involved. Any changes in temperature, water flow rate, or gas flow rate can impact the overall % RH, which is critical for efficient operation.
The Gibbs free energy equation (ΔG = ΔH − T× ΔS) is an equation of state describing the relationship between changes in Gibbs free energy (ΔG) and changes in enthalpy (ΔH) and entropy (ΔS). Gibbs free energy is expressed in Kelvin and dependent on temperature (T).
The NIST (National Institute of Standards and Technology) Chemistry Webbook offers a formula search tool (Chemical Formula Search) containing phase-change data for fluid properties and thermochemical data. It also includes Antoine parameters for the fluids, some of which have multiple equations for different temperatures.
Antoine Equation Parameters:
log10(P) = A − (B / (T + C))
P = vapor pressure (bar)
T = temperature (K)
Incorporating additional mathematics to include the thermal expansion of combined gases/fluids, with an addition of a % of relative humidity, reveals that % RH is vapor partial pressure over saturation vapor pressure.
The table below features an example of the impact of temperature on % RH concentration, with % RH affected by decreasing the temperature from 150 °C to 100 °C.
Sierra MEMS sensors are guaranteed not to drift, so leveraging Sierra’s MEMS technology for gas delivery eliminates any uncertainty in flow accuracy.
Example of Relation Temperature has on %RH Concentration
Source: Sierra Instruments
| Fluid |
Water |
| Grams per mole |
18.05 |
| Grams per hour |
12000.00 |
| Operating temperature °C |
150.00 |
| Carrier Gas flow (SLPM) N2 |
150.00 |
| Saturation vapor pressure @ Operating Temp (torr) |
3807.687834 |
| Total gas/vapor volume at operating temperature |
619.84 |
| Vapor/Gas (%) |
560.9388 |
| Vapor partial pressure (torr) |
560.9388 |
| Relative humidity |
14.73% |
Source: Sierra Instruments
| Fluid |
Water |
| Grams per mole |
18.05 |
| Grams per hour |
12000.00 |
| Operating temperature °C |
100.00 |
| Carrier Gas flow (SLPM) N2 |
100.00 |
| Saturation vapor pressure @ Operating Temp (torr) |
758.1065246 |
| Total gas/vapor volume at operating temperature |
478.24 |
| Vapor/Gas (%) |
71.27743% |
| Vapor partial pressure (torr) |
641.4968 |
| Relative humidity |
84.62% |
References and Further Reading
- Gulli, C., et al. McKinsey & Company (2024). Global Energy Perspective 2023: Hydrogen outlook | McKinsey. (online). Available at: https://www.mckinsey.com/industries/oil-and-gas/our-insights/global-energy-perspective-2023-hydrogen-outlook.
Acknowledgments
Produced from materials originally authored by Sierra Instruments.
This information has been sourced, reviewed and adapted from materials provided by Sierra Instruments.
For more information on this source, please visit Sierra Instruments.