One of the interesting aspects of our growing hydrogen economy is the way that it is turning up in all sorts of new places and applications. Ammonia plants and refineries have been handling hydrogen for decades, but the proliferation of electrolyzers, fuel cells, and various residential uses has all sorts of people needing to learn a lot about hydrogen very quickly. For example, one common question: “How pure does hydrogen need to be to run this fuel cell properly?”
Such questions are understandable given the growing number of sources for hydrogen and all those intriguing colors. Is green hydrogen necessarily free of contaminants? Is blue hydrogen purer than gray? How do we determine purity, and are there relevant standards to apply? Looking at these and other questions about purity is the focus of my article in the September 2023 issue of H2 Tech, Ensure H2 Purity with Modern Gas Analyzers.
Regardless of the source, H2 purity is a necessary consideration for every application. The International Standard Organization’s ISO 14687 standard was created to correlate applications and uses with required H2 purity. It specifies the quality tolerances for H2 fuel, primarily focused on stationary, vehicular, and proton exchange membrane (PEM) fuel cell uses. Depending on the application, each gas grade defined an acceptable impurity allowance.
The article goes into greater depth on the grades and the allowable levels of contaminants. The contaminants noted are interesting in themselves as they differ from what we expect in natural gas. For example, argon, oxygen, and other odd gases are on the list, along with typical contaminants such as sulfur and ammonia. In any case, the question quickly emerges, how do we measure H2 purity?
The two main modern ways of measuring H2 purity are gas chromatography (GC) and continuous gas analysis. GC relies on a thermal conductivity, flame ionization, or micro flame photometric detector. Thermal conductivity detectors are mainly used to measure inert gases and most hydrocarbons, while flame ionization detectors are adept at measuring trace hydrocarbons, and micro flame photometric detectors specialize in measuring low-level sulfur species.
Problems emerge when looking at ISO 14687’s list of contaminants because some analyzers have a hard time measuring those gases. For example, a GC has trouble differentiating argon and oxygen when they’re mixed, but depending on the application, this limitation may not be a consideration. Emerson offers three analyzers that should be in the hydrogen purity analysis toolbox because either separately or in combination they can solve all the hydrogen purity measurement problems:
- Rosemount 700XA Gas Chromatograph
- Rosemount CT5800 Continuous Gas Analyzer
- Rosemount X-STREAM Enhanced XEFD Continuous Gas Analyzer
The article provides examples of actual applications calling for different requirements and matching the best analyzer technology to each.
As the world further reduces its dependency on fossil fuels, the need for uncontaminated H2 gas for power generation and storage will continue to increase. While no single-analyzer solutions are on the market to universally measure all possible H2 contaminants, the technologies are progressing quickly, helping processors ensure pure products for maximum reliability, uptime, and profitability.
For more information, visit Emerson’s Gas Analysis pages at Emerson.com. You can also connect and interact with other engineers in the Hydrogen Processing Groups at the Emerson Exchange 365 community.
