Selecting the right hydrogen mass flow controller

Unique requirements

Hydrogen is nature’s smallest and simplest element. As a result of these properties, hydrogen gas molecules are extremely small relative to all other types of gas particles. Due to this, compared to other gases, hydrogen gas has unique flow properties such as being more prone to leakage during storage or transportation. Because the diffusivity of hydrogen is higher than ordinary gases, sealing/gasketing materials for a hydrogen mass flow controller must be selected more cautiously. In order to smoothly transition to a global hydrogen economy, hydrogen systems must be built to be extremely leak resistant.   Moreover, hydrogen is also highly combustible and has the highest rating on the NFPA 704 flammability scale since ignition can occur at any volumetric ratio of hydrogen to air exceeding 4%. For example, ignition is often an issue of concern when purging hydrogen gas since too much air present can result in explosions. As a matter of fact, hydrogen-air mixtures ignite with 1/10 the effort to ignite gasoline-air mixtures. Therefore, hydrogen systems must use special fittings and follow unique regulations which are not specific to other gases.  Additionally, hydrogen has several more chemical attributes which make it unique from other gases such as high levels of oxidation in ambient environments. Hydrogen embrittlement is another intrinsic property of hydrogen which occurs over time due to incompatibility with many common building materials. As a result, hydrogen flow systems must emphasize a high level of material compatibility with hydrogen.   Due to all these special properties of hydrogen, choosing the optimal hydrogen flow controller for a specific application or industrial process varies depending on operating conditions. As a result, Alicat offers a range of flow controllers which are specialized to accommodate the different operating conditions in specific hydrogen applications and processes within hydrogen production, transportation, storage, and the fuel cell industry. Product features such as custom valve sizing, port sizing, and PID tuning allow Alicat devices to provide optimal flow control of hydrogen. 

Using Alicat devices to control hydrogen

Alicat mass flow controllers have been used in the fuel cell industry for over 20 years. Compared to other mass flow controller technologies such as thermal, Alicat’s laminar flow and Coriolis-based products offer advantages such as: 

• Wider turndown ratios 
• More instantaneous start-up times 
• Superior control stability 
• More extensive communication options  
• Faster control speeds 

Alicat’s mass flow and pressure devices are widely used by the hydrogen industry for applications such as fuel cell and electrolysis test stands, back pressure regulation, leak testing, transportation, storage, and more.   In the following, we discuss some of the common best use scenarios for several Alicat devices, highlighting the main conditions in which to select one device or another for specific types of hydrogen applications. In addition to the advice suggested, always verify the specific operating conditions for your application with our team of application engineers in order to make the proper device selection.  

When to choose an MC-Series as a hydrogen flow controller 

For low flow and low pressure applications in which hydrogen does not need to be regulated within a class 1 div 1 environment, such as hydrogen leak testing when using a mix of less than 5.7% hydrogen or in small-scale research systems flowing miniscule amounts of hydrogen gas, Alicat’s MC-Series is the optimal hydrogen flow controller.   Examples of MC-Series hydrogen applications:

• Research fuel cell testing
• Fuel cell test stands
• Hydrogen fueling stations
• Hydrogen leak testing
• PEM and AEM fuel cells
• Low flow electrolysis systems

MC-Series devices offer customization options which are particularly useful for hydrogen flow control. Because hydrogen flows differently from other gases due to its small size, MC-Series custom valve sizing allows for selection of smaller orifices which are more optimal for hydrogen flow control and measurement.   MC-Series devices can also be customized for class 1 div 2 areas such as hydrogen fueling stations where “flammable gases, flammable liquid–produced vapors, or combustible liquid–produced vapors are, or may be present, in the air, in quantities sufficient to produce explosive or ignitable mixtures” and “these flammable materials are handled, processed, or used in the defined hazardous location, but not normally present in concentrations high enough to be ignitable.”   Lastly, high accuracy calibration improves the precision of flow control from 0.6% of reading or ±0.1% of full scale, whichever is greater, down to only 0.5% of reading or ±0.1% of full scale.   MC-Series features and specs: 

• 0.5 SCCM full scale to 5,000 SLPM full scale with a turndown of 0.01% – 100% of full scale 
• NIST-traceable accuracy up to ±0.5% of reading or ±0.1% of full scale 
• Repeatability ±0.1% of reading + 0.02% of full scale 
• Control response times as fast as 30 ms 
• A range of analog, serial, and industrial protocol communication options  

When to choose a CODA KC-Series as a hydrogen flow controller 

For higher pressure, higher required accuracy, liquid, and low flow hydrogen applications that are not classified as class 1 div 1 or class 1 div 2, Alicat’s CODA KC-Series is the optimal choice for a hydrogen mass flow controller.  Examples of CODA KC-Series hydrogen applications:

• Solid oxide fuel cells
• Liquid fuel cells
• High operating pressures
• Fuel cell test stands
• Diesel-hydrogen injection
• Hydrogen leak testing
• High flow electrolysis systems

Compared to MC-Series, Alicat’s CODA KC-Series is more suitable for extremely low flow applications with a full scale down to just 40 g/h as well as higher pressure applications which require up to 4000 PSIG.   For liquid applications which use hydrogen as an input or output such as microbial and microfluidic fuel cells, CODA KC-Series provide superior flow regulation features such as serial and analog communication options for automation and accuracy up to 0.2% of reading and ±0.05% of full scale, whichever is greater.   CODA KC-Series features and specs: 

• 40 g/h full scale to 100 kg/h full scale with a turndown of 2% – 100% of full scale
• NIST-traceable accuracy up to ±0.5% of reading or ±0.05% of full scale
• Repeatability ±0.05% of reading + 0.025% of full scale
• Control response times as fast as 500 ms