Natural gas is a component of our energy future, whether as a direct fuel source for power generation or to alleviate grid load in an increasingly electrified world through residential heating and industrial applications. It’s also continuously and naturally produced in methane form at dairy farms, in landfills, within wastewater and even emanating from wetlands.
It’s not a panacea: Naturally occurring methane is a greenhouse gas and — while it produces much less than coal when burned — the byproduct of its combustion, carbon dioxide, is also a greenhouse gas. How can the capture of methane at its various sources be incentivized while simultaneously reducing generation of CO2? One promising solution is to blend hydrogen — whose combustion byproduct is water — with natural gas into the interstate natural gas pipeline system.
In 2021, the Interstate Natural Gas Association of America (INGAA) Foundation solicited study proposals for the benefit of INGAA gas transmission pipeline operators and foundation members. Foundation members funded a concept that would become its “Comprehensive Study of Transportation of Hydrogen in Natural Gas Infrastructure.”
A committee of INGAA and INGAA Foundation members was created to direct production of a research study using existing data and and other studies from pure research organizations in the public domain. The resulting comprehensive study, with its five focus areas, is a road map for interstate gas transmission companies to use in evaluating the feasibility and impacts of hydrogen blends on their systems.
The Five Focus Areas
The finalized study, completed in 2022, is exclusively available to members of INGAA and its foundation; other interested parties can contact the foundation to request access. For anyone considering blending hydrogen into interstate natural gas pipeline systems — whether in transmission pipeline or as compressor fuel — it is valuable to understand the five primary work scope areas, which form the basis of the comprehensive study.
Operations and maintenance. 49 CFR Part 192 is the compliance document for gas pipeline systems. Subparts L (Operations) and M (Maintenance) contain the prescriptive code requirements for gas pipeline systems, including hydrogen-blended pipeline systems. These subparts contain many requirements, all of which must be reviewed when blending and transporting hydrogen. For example, §192.616 contains the requirements for public awareness plans, which have to be modified when blending and transporting hydrogen. Modifications include sending notifications to the affected public, excavators and local planning commissions. Line markers will need to be modified to identify hydrogen in the pipeline. Additionally, §192.615 Emergency Plans will require modifications to existing emergency plans to include hydrogen language and changes in emergency response protocols.
Safety. Safety is of paramount importance to transmission pipeline operators. The comprehensive study contains many hydrogen safety considerations. For example, natural gas has a relatively narrow flammable explosive range, from approximately 5% to about 15%, outside of which it won’t burn. In contrast, hydrogen’s range extends from 4% to 74%. This means pipeline operators will need to be highly responsive to emergency calls about leaks and use leak detection equipment calibrated for hydrogen blends. Safety codes in the U.S. and globally may require revisions to reflect the risks and associated mitigation measures. Awareness and safety training will be critical.
Quality, heat content, volume, compression and deblending. Hydrogen has a much lower Btu value than natural gas, so when hydrogen is blended with natural gas, the blend’s Btu value will be lower than that of pure natural gas. If appliances require a given amount of energy from natural gas, it will take more blended gas to get the same amount of energy. Hydrogen is harder to compress than natural gas, affecting capacity calculations and potentially requiring different compression equipment. When blended gas is delivered to a liquefied natural gas (LNG) facility, without deblending, the hydrogen in the blended gas will not liquefy at the same temperature as natural gas and will increase boil-off gas. The comprehensive study covers these and other related topics.
Pipeline and materials integrity. The comprehensive study, drawing on reference material from a variety of sources and research organizations, contains a discussion of the various pipe grades currently installed on transmission gas pipeline systems and other materials. The approximately 300,000 miles of transmission pipeline of INGAA members incorporates various pipe grades, not all of which can accept hydrogen blends. Hydrogen molecules are much smaller than methane molecules and can find cracks and anomalies in the pipe’s structure and internal coating and start to embrittle the pipe. It’s important for operators to consider the steel grade and quality of their pipelines for blended fuels. Materials integrity calls for evaluating the internal valves, fittings, regulators, meters and elastomers that may not be compatible with hydrogen blends. The effectiveness of sealing materials is of great importance for blended fuels.
Storage. Pipeline Research Council International (PRCI) and other organizations are releasing studies on the challenges of utilizing underground gas storage or converting storage fields to accept hydrogen. The comprehensive study contains a discussion of the types of existing underground storage for natural gas transmission systems, including salt caverns or depleted reservoirs. Salt caverns are very good for hydrogen but are few in number and mostly located along the Gulf Coast. The suitability of depleted reservoirs depends on impurities and water content in the storage field. Aquifer fields have been an effective option for natural gas because the water surrounding a formation prevents the gas from escaping, but water and hydrogen do not react well together. The comprehensive study examines design requirements, conversion of natural gas storage fields to hydrogen storage, and the surface equipment required for liquefied hydrogen.
Where We Stand Today
All of these factors will be of vital interest to operators considering the merits and possibilities of adapting natural gas infrastructure to support an evolution to a carbon-managed economy. Blended hydrogen is one method being explored to help achieve net zero carbon emissions goals. The INGAA Foundation’s comprehensive study provides a thorough evaluation of the current state of the research and a detailed review of the big-picture considerations, from economics to safety and more.
Adoption of hydrogen into energy portfolios will depend on secure and resilient infrastructure. Operators are already exploring the blends and pipe replacement programs that may be needed.
