In August 2021, the paper How green is blue ­hydrogen? hit the academic press. Co-authored by Professor Howarth of Cornell University, the paper makes the case that reforming natural gas alongside carbon capture and storage (CCS) to produce blue hydrogen can generate more than 20pc more greenhouse gas (GHG) emissions than the direct use of natural gas.

This conclusion follows an analysis of two blue hydrogen plants, one in the US and one in Canada, and—importantly—is based on two key assumptions: fugitive methane emissions from natural gas production are set at 3.5pc following analysis of US leakage statistics, and power for the CCS process is supplied from gas-fired generation. In addition, the two plants reviewed utilise steam methane reforming (SMR) technology, which is less efficient and has lower carbon-capture rates than autothermal reforming (ATR).

But our sensitivity analysis—which assessed fugitive methane emissions, alternative CCS efficiencies and power supplies, and the use of ATR—found that European blue hydrogen GHG emissions can be 78-95pc lower than the direct use of natural gas, a radically different conclusion from the perspective offered by Howarth.

Our analysis highlights the importance of the industry’s moves to minimise fugitive methane emissions in the natural gas supply chain—a key factor in reducing emissions from blue hydrogen production.

Methane emissions

Howarth adopts two pivotal assumptions for his analysis of methane emissions and their global warming potential (GWP). The first is that fugitive methane leakage can be as high as 3.5pc of total production. The second is that he uses a 20-year GWP timeframe for the impact of methane.

A 3.5pc leakage rate appears to be a consensus among analyses of US gas production. However, an assessment of UK, Dutch and Norwegian methane leakage shows that northwest European fugitive emissions can be much lower.

3.5pc – Methane leakage rate used by Howarth study

For the UK, we applied a 0.32pc figure based on the Oil and Gas Climate Initiative (OGCI), a figure supported by the UK Oil and Gas Authority. Under such leakage rates, emissions drop to 13.9g CO₂e/kWh of hydrogen from the 152g CO₂e/kWh in the Howarth paper.

For the Netherlands and Norway, a 0.03pc leakage figure was used, based on data from the paper On the climate benefit of coal-to-gas shift in Germany’s electric power sector and information provided to ICIS by Norwegian producer Equinor on Norwegian fugitive emissions. This results in 1.3g CO₂e/kWh.
When speaking to ICIS, Howarth noted that fugitive emissions rates in Europe should be the object of further study.

The second assumption, a 20-year basis for GWP of methane, is a factor under debate. Methane emissions are more regularly considered under a 100-year GWP, which reduces their impact to a multiple of 25, compared with the multiple of 86 used by Howarth.

Applying a 100-year metric to Howarth’s fugitive US-based methane emissions results in 44.1g CO₂e/kWh, down from 152g CO₂e/kWh. Further, when applying the 100-year metric to UK, Dutch and Norwegian equivalents, emissions drop to 4g CO₂e/kWh for the UK and 0.4g CO₂e/kWh for the Netherlands and Norway.

Howarth notes that the Climate Leadership and Community Protection Act of 2019, a piece of legislation introduced by the State of New York, mandates the use of a 20-year timeframe. He also highlights that the latest synthesis report from the Intergovernmental Panel on Climate Change, known as AR6, states the need to consider a timescale shorter than 100 years.

However, members of the scientific community remain split on the use of a 20-year metric. David Joffe, head of carbon budgets at the UK’s Committee on Climate Change, noted on Twitter when discussing the paper that such a metric ignores climate impacts beyond 20 years, emphasising methane at the expense of CO₂, “which remains important in 2042 (& 2060 & 2080)”.

Whether a 20-year or a 100-year timeframe is used, the higher values for fugitive methane emissions from US gas production should not hinder progress of blue hydrogen in cases where upstream and midstream operations are less damaging to the environment.

Power generation

An often forgotten aspect of the concept of blue hydrogen is power supply and demand for the CCS process.

Howarth’s paper assumes that CCS power is derived from burning natural gas, which itself emits CO₂ and results in fugitive upstream emissions. CCS for blue hydrogen requires carbon capture from the SMR stream and the flue stream. Howarth’s paper assumes energy demand of 625kWh/t CO₂ for the SMR stream and 975kWh/t CO₂ for the flue stream.

However, a review of the articles A comparison of the energy consumption for CO₂ compression process alternatives and A preliminary assessment of the initial compression power requirement in CO₂ pipeline CCS technologies outlined that CCS processes could have much lower power demand, falling to 120kWh/t CO₂.

An often forgotten aspect of the concept of blue hydrogen is power supply and demand for the CCS process

How that power supply is generated is also a key factor. As noted, the paper outlines that gas-fired power generation results in emissions of 400g CO₂e/kWh. In comparison, transmission system operator data for the UK showed the power mix over 2020 contained an average of 185g CO₂e/kWh. Equally, Norwegian average power emissions were substantially lower, at 9g CO₂e/kWh, due to notably higher renewable capacity on the grid.

Sensitivity analysis

Beyond renewable capacity, it is worth considering power emissions reduction as a result of CCS applied to combined-cycle gas turbines.

The Howarth paper applies capture rates of 85pc to the SMR emissions stream and 65pc to the flue gas stream. But Jon Gibbons, CCUS professor from the University of Sheffield, says capture rates can be higher than 95pc for SMR units that are purpose-built to have low carbon emissions.

Paul Deane, from the University of Cork in Ireland, expands on Gibbons’ point, saying that “the authors take a very pessimistic view on capture rates of CO₂ and do not investigate ATR for hydrogen production, which would lead to different outcomes”.

Howarth said, when speaking to ICIS, that no hydrogen has been commercially produced using ATR, adding that the process may not be adopted in the future.

But the UK has several blue hydrogen projects aiming to utilise ATR technology by 2030, and data gathered from the Hynet Phase 1 report for the Department for Business, Energy, and Industrial Strategy hydrogen supply competition suggests the capture rate for the process can be as high as 98pc.

This is because the CO₂ is contained in the process stream and so is at high pressure and concentration, as confirmed by technology provider Johnson Matthey.

However, ATR requires power for the air separation unit needed to produce the pure oxygen used to drive the endothermic reaction. Comparatively, steam generated in the SMR configuration can be used to provide low-carbon power supply for the overall production process with the potential to export. This can offset some of the advantages of ATR over SMR, depending on the carbon intensity of the power supply.

Potential issues

The results of this sensitivity analysis on blue hydrogen production in Europe aim to provide a data-driven basis for the value of blue hydrogen as one of the viable routes to decarbonisation. Indeed, given appropriate conditions, producing and using blue hydrogen for either heat or power generation looks to be greatly preferable to the unabated use of natural gas.

However, Howarth’s conclusions are important as they outline how blue hydrogen can be dangerous for the environment if certain parameters are not taken into consideration, and therefore provides the energy industry with a clear indication of the potential issues that brownfield SMR plants equipped with CCS present.

Jake Stones is lead hydrogen reporter for market intelligence service ICIS. Jamie Hamilton is a PhD candidate at UK university Imperial College London. This article is an abridged version of a longer piece of analysis that can be found on the ICIS website.

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Authors: Jake Stones, Jamie Hamilton