Which measurements ensure safety and purity of hydrogen gas in storage and transport?

There are several storage and transport methods possible for hydrogen gas, depending on the final use. All of these methods need careful planning and control to ensure gas quality and safety, and, not surprisingly, precision measurements of the gas at critical points play an important role.

As well as being highly flammable, hydrogen molecules are very small which makes preventing leaks especially challenging. Because of this the two main concerns for anyone involved in transporting or storing hydrogen are:

• Preventing or detecting leaks of hydrogen
• Avoiding the risk of an explosion through oxygen or air mixing with hydrogen

The third concern is shared with the transport or storage of any industrial gas:

• Ensuring purity of the hydrogen

Hydrogen purity analyzers and trace impurity analyzers are an essential tool to help operators to monitor the integrity of their pipelines and other systems and for users to check on the purity of hydrogen in their processes. Trace oxygen analyzers are used to detect tiny amounts of oxygen present in hydrogen to alert operators to potential leaks in the system and provide an early warning before the level of oxygen poses a risk of explosion.

In any industry where large amounts of industrial gas are stored or transported, there is also a risk to personnel working in confined spaces in the area, such as control rooms. In the event of leaks, the levels of oxygen in the room could drop to dangerously low levels leading. For this reason, ambient oxygen monitors are essential to protect staff from risk of asphyxiation.

How is hydrogen gas stored and transported?

Processing Hydrogen for transport or storage can add varying levels of impurities depending on the conditioning technique. For instance, an oil compressor can typically add 1-3ppm of residual oil, likewise hydrogen sulphide or humidity contamination from a salt cavern will affect the chemical integrity of Hydrogen. Gas impurities can creep in and reduce the gas purity whenever Hydrogen is handled whether it is being stored or transported.

Hydrogen needs to be available in the right place, at the right time, but not only that it requires enough pressure at the right purity level and in sufficient quantity. Acceptable impurity levels are application dependent and measuring them is crucial to ensure Hydrogen retains its purity along the supply chain.

Below, we list the main storage and transportation methods for hydrogen along with the key analysis and measurement techniques needed to ensure safety and quality at each stage.

Storing hydrogen in underground caverns

Hydrogen gas is pumped into caverns, depleted oil fields or salt domes which provide a ready-made underground storage facility. This method is often used by companies using the hydrogen for power generation or to inject into the national transmission grid.

Key concerns:

The hydrogen will become saturated with moisture and will need drying before use, which will be a major cost to the operator. It may also become contaminated with trace chemicals from the cavern. Trace moisture analyzers with suitable hazardous area certification measure the moisture content of the gas before and after the drying process to ensure maximum energy efficiency.

Hydrogen purity analyzers will give an indication of the level of purity. If exact information on the types and levels of each impurity is needed, then an industrial gas chromatograph is recommended.

Storing hydrogen in pressurized tanks

The hydrogen is stored a compressed gas at high pressure between 5,000 to 10,000 psi. This reduces the volume of the gas and is a cost-effective method to use.

Key concerns:

At these pressures the hydrogen must be dry to avoid liquid water forming in the tank – accurate trace moisture measurements to monitor the dryers before pressurization optimise the energy used for drying. Intrinsically safe or explosion-proof dew-point transmitters together with suitable sampling systems are recommended.

Compressing the gas may introduce traces of oil into the gas. Depending on the level of purity required for the final application, reliable hydrogen purity analyzers or trace impurity analyzers allow operators and end users confirm the quality of the gas provided.

Ensuring there are no leaks in the tank is of critical importance. Because the hydrogen is stored at high pressure it will leak out of the tank and can be detected with an ambient H2 monitor. Leaks will also occur where there is loose-fitting pipework which would allow ingress of moisture or air. Hydrogen purity analyzers installed at the point of provide confirmation of hydrogen purity.

Storing hydrogen in cryogenic tanks

Hydrogen is stored as a liquid at -253 °C. This further reduces the volume, but maintaining the low temperature make this method a more expensive option.

Key concerns:

As before, the gas must be dried before liquefaction to avoid ice forming and damage to equipment. After the re-gasification and before use, hydrogen purity analyzers provide assurance of the gas quality.

Storing hydrogen in solids or as chemical compounds:

Hydrogen can also be stored by absorption or adsorption on to a solid, or by storing in a solid chemical form, which gives the hydrogen high density which makes it easier to find suitable storage space. This method is being explored for use in storing hydrogen for fuel cells.

Key concerns:

Chemical compounds are not stable and hydrogen gas will be released as the solid degrades. Safety is the key concern with storage, and ambient monitors are needed to monitor for hydrogen: both Oxygen and Hydrogen ambient monitors are required.

Transporting hydrogen gas in pipelines

Gaseous hydrogen is transported via a pipeline. This method is most usually used for short distances due to the small size of the hydrogen molecule and the need to monitor for and prevent leaks. For transport over longer distances, hydrogen is sometimes mixed with natural gas and transported in the same pipeline and either used as fuel in the power grid, or separated before use as pure hydrogen.

Key concerns:

Detecting leaks in the pipeline is the main concern for safety – if hydrogen is leaking into the atmosphere there is a risk of explosion. However, there is also a quality concern: if air and moisture ingress into the pipeline then the gas purity level drops.

Online trace moisture and process binary gas analyzers will monitor both the purity of the hydrogen and also provide an early warning for leaks if air is detected in the pipeline.

When the hydrogen has been mixed with natural gas for transport, trace impurities analyzers and hydrogen purity analyzers will confirm the purity of gas after separation.

Transporting hydrogen in gas bottles or in chemical/solid form

Transporting hydrogen by road or rail as a compressed gas in bottled form is the most common form of transport.

Key concerns:

As with any bottled gas, confirming the quality at point of use is essential for most processes. This can easily be done using by using a binary gas analyzer calibrated for pure H2 and a fixed or portable hygrometer to check for moisture levels.

Get expert, application specific advice

This post has briefly covered the common storage and transport methods together with the most common concerns. Each site and application are different, and our experts are happy to advise you on the most effective solution to meet your specific needs, whether this is an off-the-shelf instrument or a custom-designed analyzer package. Why not get in touch with your question today?