Underground Hydrogen Storage (UHS) in Aquifers
1. Since, hydrogen no more directly exists as a gas, how easy would it remain to separate hydrogen, either from water, or, from fossil fuels, despite its abundance in the universe?
2. Whether subsurface hydrogen(H2) storage has been tested in a commercial-scale environment – either in deep saline aquifers, or, in depleted oil/gas reservoirs (apart from salt caverns, practiced in Texas/UK), where, temporarily stored hydrogen has been produced back on demand?
3. Whether, saline aquifers, and/or, oil/gas reservoirs, towards H2 storage, is expected to ensure sustainability and resilience of the planned clean hydrogen economy in order to meet the global de-carbonization goal?
4. In the absence of H2 storage, in a thick, porous and permeable saturated subsurface formation (like a salt cavern), will we be able to satisfy required storage capacity and sufficient injectivity for acceptable well operating rates – either in saline aquifers, or, depleted oil/gas aquifers?
5. Whether, UHS is expected to provide storage capacity in order to balance seasonal supply and demand fluctuations; and also, to meet peak demand towards stabilizing the power grid?
6. How exactly to handle
(a) The enhanced physical risk of hydrogen leakage (higher tendency of H2 to spread laterally in a porous reservoir increases the probability of escape of the stored H2 either through the abandoned/leaky wells or through the leaking faults)?
(b) Reduced recoverability of stored H2 product – either in depleted oil/gas reservoirs, or, in deep saline aquifers – given the fact that the H2 remains associated with reduced viscosity and enhanced diffusivity (with reference to natural-gas)?
7. Unlike the minimum requirement of cushion gas in salt caverns, to what extent, cushion gas (employed to ensure sufficient pressure maintenance and adequate withdrawal rates) gets factored into the subsurface storage costs in saline aquifers and depleted oil/gas reservoirs?
8. Towards storing hydrogen in depleted oil/gas reservoirs, how easy would it remain to handle the dynamics of reservoir wettability (that impacts H2 injection and storage); viscous fingering (providing means for hydrogen loss); and the reactivity of H2 with the organic constituents of depleted oil/gas reservoirs (including kerogen, residual hydrocarbons and microbes – leading to H2 losses resulting from chemical or microbial interaction)?
9. Whether the greater compressibility of a cushion gas would really improve the H2 production rate @ the end of a production cycle
? 10. Whether the application of standard diffusion models would remain to suffice towards the estimation of the amount of H2 lost through dissolution into formation brine; and diffusing away from the aquifer of interest into the overlying caprock?
Suresh Kumar Govindarajan
Professor (HAG) IIT-Madras
https://home.iitm.ac.in/gskumar/
https://iitm.irins.org/profile/61643
25-July-2024
Suresh Kumar Govindarajan
The statement "Since hydrogen no more directly exists as a gas, how easy would it remain to separate hydrogen, either from water, or from fossil fuels?" touches on a critical aspect of hydrogen production and its separation from other compounds. Here’s a detailed discussion:
Hydrogen Production and Separation
1. Hydrogen from Water:
- Electrolysis:
- Process: Electrolysis involves passing an electric current through water to separate it into hydrogen and oxygen gases.
- Efficiency: The efficiency of electrolysis is a key factor. Modern electrolyzers can achieve efficiencies of around 70-80%.
- Renewable Energy: If powered by renewable energy sources (e.g., solar, wind), electrolysis can produce green hydrogen, which is environmentally friendly.
- Challenges: The cost of electricity is a major factor influencing the economic viability of electrolysis. The initial setup and maintenance of electrolyzers can also be costly.
2. Hydrogen from Fossil Fuels:
- Steam Methane Reforming (SMR):
- Process: SMR is the most common method of producing hydrogen. It involves reacting methane (natural gas) with steam at high temperatures to produce hydrogen and carbon monoxide. A subsequent reaction (water-gas shift reaction) converts carbon monoxide to carbon dioxide and more hydrogen.
- Efficiency and Cost: SMR is relatively efficient and cost-effective, making it the predominant method for industrial hydrogen production.
- Environmental Impact: The process releases significant amounts of CO₂, contributing to greenhouse gas emissions unless carbon capture and storage (CCS) technologies are used.
- Coal Gasification:
- Process: Involves reacting coal with oxygen and steam at high temperatures to produce a mixture of gases (syngas) from which hydrogen can be separated.
- Challenges: This method is less efficient and more polluting compared to SMR. It also requires substantial capital investment.
Technological and Economic Considerations
1. Advancements in Technology:
- Electrolyzers: Continuous improvements in electrolyzer technology (e.g., proton exchange membrane electrolyzers, solid oxide electrolyzers) are making the process more efficient and cost-effective.
- Carbon Capture: Advances in carbon capture and storage (CCS) can mitigate the environmental impact of hydrogen production from fossil fuels.
2. Cost Factors:
- Capital Costs: Initial setup costs for both electrolysis and fossil fuel-based hydrogen production can be high.
- Operational Costs: These include the cost of electricity for electrolysis and the cost of raw materials (natural gas or coal) for SMR and gasification.
- Economies of Scale: Larger production facilities can achieve lower per-unit costs, making hydrogen more affordable.
3. Environmental and Policy Considerations:
- Regulations and Incentives: Government policies and incentives for clean hydrogen production (e.g., subsidies, carbon taxes) can influence the economic viability and adoption rates of different hydrogen production methods.
- Sustainability: The choice of production method impacts the sustainability of hydrogen as an energy carrier. Green hydrogen (from electrolysis using renewable energy) is more sustainable compared to grey hydrogen (from SMR without CCS) or brown hydrogen (from coal gasification).
Conclusion
Separating hydrogen from water via electrolysis and from fossil fuels through methods like steam methane reforming remains feasible but involves distinct challenges and considerations. Technological advancements, economic factors, and environmental policies will play crucial roles in determining the ease and efficiency of hydrogen production. As the world moves towards cleaner energy sources, the focus is likely to shift more towards sustainable methods like electrolysis powered by renewable energy.
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