NOx Emissions
NOX Emissions
- A fuel cell uses the chemical energy of hydrogen or another fuel to cleanly and efficiently produce electricity. If hydrogen is the fuel, electricity, water, and heat are the only products (source). However, when hydrogen gas (H2) is combusted, as in a power plant, this is not the case. While H2 does not generate carbon dioxide when combusted, it is not an emissions-free.
- Burning hydrogen can lead to nitrogen oxide (NOx) emissions up to six times that of methane (source 1, source 2)
- NOx does significant damage to the respiratory system over time. In areas affected by smog, symptoms including coughing, increased rates of asthma, and comorbidities with other respiratory illness develop. (source). This impact is readily apparent in many frontline communities dealing with heavy NOx emissions emitted by nearby high-polluting peaker power plants. These communities have developed historical health disparities and vulnerabilities because of constant NOx exposure.
- Air pollution controls to limit NOx emissions in gas turbines do exist. To comply with Clean Air Act regulations, most power plants limit their NOx emissions either through a catalytic reaction, dilution of the fuel mix with water or steam, or using newer low-NOx technology such as a dry low NOx (DLN) combustion system. None of these systems have been proven to work with a hydrogen blend or 100% hydrogen fuel. Due to the fundamental differences between hydrogen and methane, existing NOx reduction methods are only effective at controlling NOx at very low levels of hydrogen blending.
- The world’s first dry low NOx, 100% H2 power generation system was developed in July 2020. However, even with dry low NOx technology, this pilot project still produces NOx levels like that of a newer natural gas plant (source).
- The bottom line: the slew of H2 proposals for new and existing natural gas plants will create new sources of NOx for decades to come, with frontline communities bearing the brunt.
Additional Resources:
- Investigations on performance and emission characteristics of an industrial low swirl burner while burning natural gas, methane, hydrogen-enriched natural gas and hydrogen as fuels (Cellek, Pınarbaşı, 2018)
- Nitrogen Oxides Impacts On Public Health And The Environment (US EPA, 1997)
- Hydrogen for Power Generation: Experience, Requirements, and Implications for Use in Gas Turbines (GE Power, 2021)
- Hydrogen Power Generation Handbook (Mitsubishi Power, 2020)
- Hydrogen substitution for natural gas in turbines – Opportunities, issues, and challenges (EPRI, 2021)
- Hydrogen Gas Turbines (ETN Global, 2020)
- Decarbonized Hydrogen in the US Power and Industrial Sectors: Identifying and Incentivizing Opportunities to Lower Emissions (Resources for the Future, 2020)
Pipelines
Pipelines
- If steel is exposed to hydrogen at high temperatures, hydrogen will diffuse into the alloy and combine with carbon to form tiny pockets of methane. This methane does not diffuse out of the metal and cracks the steel. This process, called “hydrogen embrittlement,” means that hydrogen cannot simply be stored and transported with existing infrastructure. (source)
- Steel makes up more than a quarter-million miles natural gas transmission systems in the U.S. Because of the embrittlement issue, any plans to use existing natural gas assets with hydrogen would require replacement of these pipelines.
- Pipeline replacement is not cheap. Plans currently underway in the City of Chicago to replace all its natural gas pipes will cost each utility customer $750 per year by 2040. (source)
- In addition to pipeline replacement, if natural gas was to be replaced with hydrogen, all end user appliances would have to be replaced as well. Appliances currently built to run on natural gas, such as stoves, would not be able to run on hydrogen. (source)
Additional Resources:
- Hydrogen embrittlement (Murakami, Metal Fatigue, 2019)
- Department of Energy Hydrogen Program Plan (US DOE, 2020)
- Assessing The Viability Of Hydrogen Proposals: Considerations For State Utility Regulators And Policymakers – Full Report and Summary (Energy Innovation, March 2022)
Poor Efficiency
Poor Efficiency
- With current electrolyzers, green hydrogen’s efficiency, from production back to energy through combustion, is around 30%, which means 70% of the renewable energy put into producing green hydrogen is lost across the full cycle of production and use (source).
- Next generation electrolyzers could have an efficiency cycle of 80% — which will only bring green hydrogen’s total efficiency to around 45%. (source).
- To replace all current industrial consumption of grey hydrogen – produced by fossil-fuels without carbon capture – with green hydrogen would require 3,500 TWh of renewable energy, the amount of renewable energy currently produced by the entire European Union (source).
- Because of the massive inefficiency of electrolysis, green hydrogen production has the potential to divert renewable energy away from directly offsetting fossil fuel emissions.
Additional Resources:
- Green hydrogen production: Landscape, projects, and costs (Wood Mackenzie, 2019)
- The Real Promise of Hydrogen (Boston Consulting Group, 2019)
- Green Hydrogen: A Guide to Policy Making (IRENA, 2020)
Storage
Storage
- When steel is exposed to hydrogen at high temperatures, hydrogen will diffuse into the steel and cause tiny cracks. These tiny cracks can lead to leaks and an increased likelihood of explosion (source).
- This makes storage a major concern for hydrogen. While other methods such as salt caverns, have been proposed, these do not make sense in dense urban areas (source).
- Hydrogen’s competitiveness and value in a renewable energy future resides in its ability to be stored and readily available to deploy at any given time. However, the storage infrastructure needed for a hydrogen revolution does not yet exist.
- While a build-out of hydrogen-ready storage is entirely possible, couching a transition to hydrogen that utilizes existing natural gas assets ignores chemical differences in hydrogen that make that infeasible.
Additional Resources
- Corrosion Control in the Oil and Gas Industry (Papavinasam, 2014)
- Hydrogen substitution for natural gas in turbines – Opportunities, issues, and challenges (EPRI, 2021)
- Decarbonized Hydrogen in the US Power and Industrial Sectors: Identifying and Incentivizing Opportunities to Lower Emissions (Resources for the Future, 2020)
Water
Water
- Electrolysis requires up to 9 tons of water per ton of hydrogen produced (source).
- Because electrolysis breaks down water into constituent elements, this water needs to be purified. Most industrial water purification processes require, at minimum, a ratio of 2:1 wastewater to pure water, effectively doubling the amount of water required. This means each ton of green hydrogen produced requires 18 tons of water total (source).
- The high water demands of green hydrogen mean that producers will need to source water that hasn’t already been allocated. One option for sourcing this water is desalination, another water- and energy-intensive process (source).
- This analysis excludes the additional water used in as a cooling fluid in most power plants. Most combined cycle natural gas plants currently use up to 300 gallons of water per megawatt-hour of electricity produced (source).
Additional Resources:
- Water Resource Considerations for the Hydrogen Economy (K&L Gates, 2020)
- Fundamentals of Pressure-Driven Membrane Separation Processes (Cui, Jiang, Field, 2010)
- Power to Gas: Hydrogen for Power Generation (GE Power, 2019)
- How it Works: Water for Natural Gas (Union of Concerned Scientists, 2010)
- Decarbonized Hydrogen in the US Power and Industrial Sectors: Identifying and Incentivizing Opportunities to Lower Emissions (Resources for the Future, 2020)
