Safety Issues to Consider When Blending Hydrogen with Natural Gas

Hydrogen Blending Overview

As a continuation of our series of articles discussing Hydrogen (Hydrogen Production through Electrolysis and Be Careful When Blending Hydrogen and Methane), here we present an article to further discuss safety issues to consider when blending hydrogen in natural gas.

As discussed in our earlier articles, injecting hydrogen into the existing natural gas (NG) grid infrastructure is one of the main approaches countries and oil and gas companies are considering to reduce the greenhouse gas (GHG) footprint and move forward with decarbonizing the economy.  

“Blue” and “green” hydrogen are produced by steam reforming of methane and electrolysis of water, respectively. In green hydrogen production, in particular, carbon emissions are minimized as electricity is provided by renewable sources (wind, solar, geothermal, etc.). A significant quantity of renewable energy can be stored (indirectly) in existing natural gas distribution systems as H₂ is blended with natural gas produced by conventional or unconventional hydrocarbon sources. Actors in the energy industry are hesitant in committing to incorporate hydrogen in their operations, primarily due to safety concerns with H₂ handling and transportation.

Key Safety Issues

We can summarize the main concerns as,

• Metal embrittlement of pipelines, compressors, storage, etc. Hydrogen is known to reduce the mechanical strength of metals. Embrittlement stimulates the formation of fractures in some materials.
• Leakages in pipe joints, seals, etc. Molecular hydrogen is smaller than methane and could escape more easily from typical gas containment measures. 
• Wobbe indexes of admixtures are too low. This is an indirect measure of the heating value of gases. Pure H₂ has a Wobbe index of about 1220 Btu/SCF, whereas natural gas ranges from 1235 to 1396 Btu/SCF. Low Wobbe indexes in fuel gases affect combustion efficiency on devices that have been designed to burn natural gas.  
• Inherent safety concerns about the risk of explosion, fire management, and environmental impact. 

Figure 1: Green Hydrogen Production and Storage into an existing Natural Gas Network

Blending Recommendations

Concentrations as low as 5 to 7 mol% of H₂ in natural gas can contribute significantly to the decarbonization of industries. Contents as high as 10% to 12% in industrial combustion equipment, and as high as 25% in domestic burners have been documented, however, the feasibility of utilizing NG-H₂ admixtures must be assessed on a case basis. The European Gas Research Group (GERG) has provided a list of recommendations for this assessment:

• Evaluate the performance of gas leak detectors and other analytical techniques to measure gas composition. The presence of hydrogen in admixtures may involve retrofitting of measurement equipment to work accurately.
• Always follow the manufacture’s recommendations and seek their advice when operating gas turbines and gas engines with NG-H₂ admixtures. 
• Steel tanks, metallic, and elastomer seals have good tolerances to hydrogen contents of up to 2%. There is a constant flow of new information coming from studies where metal and seals tolerances are tested at higher H₂ contents. 
• Most research has focused on the performance of gas systems with up to 10 mol% of H₂. The main criteria to follow are the safety margins on the Wobbe index and Methane Number (MN: analogous to octane index in liquid fuels) for each gas system. 
• Blending hydrogen to natural gas must be made slowly to avoid transient H₂ concentration peaks and other disturbances that may occur. GERG recommends injection rates slower than 2% per minute.  

Canada has outlined that hydrogen is a promising step towards the decarbonization of many sectors of the economy (see the NRCAN Hydrogen Strategy for Canada). Close collaboration between different parties is vital in achieving this goal. 

 Recommended Literature

1. Ball, M., Basile, A., Veziroglu, T.N. (Eds.). Compendium of Hydrogen Energy, Volume 4: Hydrogen Use, Safety, and the Hydrogen Economy. Woodhead Publishing Series in Energy, Number 86. Elsevier, UK, 2016. 
2. Europen Gas Research Group. THyGA: Testing Hydrogen Admixture for Gas Application. Brussels, Belgium, 2020. Available at  https://www.gerg.eu/media-centre/publications/#thyga-newsletter-n1-october-2020. 
3. Orhan Akansua, S. et al. (2004). Internal Combustion Engines fuelled by natural gas-hydrogen mixtures. International Journal of Hydrogen Energy, 29. 
4. Klell, M. et al. (2012). Mixtures of hydrogen and methane in the internal combustion engine – synergies, potential, and regulations. International Journal of Hydrogen Energy, 37.
5. Anderson, M. et al. (2013). Co-firing with hydrogen in industrial gas turbines. SGC Report. 
6. Marchmont, C. et al (2012). Alstom gas turbine technology trends. In: Proceedings of ASME Turbo Expo, 2012 GT2012. Denmark. 
7. Wu et al. (2007). Siemens Power Generation Inc. Advanced gas turbine combustion system development for high hydrogen fuels. In proceedings of GT2007 ASME Turbo Expo 2007: Power for Land, Sea, and Air. 2007. Montreal, Canada. 
8. Natural Resources Canada. Hydrogen Strategy for Canada: Seizing the Opportunities for Hydrogen. A Call for Action. Ottawa, December 2020. Available at https://www.nrcan.gc.ca/sites/www.nrcan.gc.ca/files/environment/hydrogen/NRCan_Hydrogen-Strategy-Canada-na-en-v3.pdf