Blue hydrogen should not be considered a green fuel and, depending on the circumstances of its production, may actually have a greater impact on global warming than natural gas, a new study has suggested.
The authors of the paper concluded there is “no role for blue hydrogen in a carbon-free future,” stating it is “best viewed as a distraction” that may delay urgently needed action to decarbonise energy.
The study produced by researchers from Cornell University and Stanford University in the US and published in the journal Energy Science and Engineering examined the full lifecycle emissions of so-called blue hydrogen produced by reforming methane and capturing the carbon emissions. These include methane leakages during the production and transport of the natural gas that is used as a feedstock.
The researchers’ baseline estimate for the total greenhouse gas emissions from the production and combustion of blue hydrogen is 139 grams of carbon dioxide equivalent per megajoule compared to 111 grams for natural gas.
This estimate assumes that 85 per cent of the carbon dioxide produced during the steam methane reformation (SMR) process is captured.
Robert Howarth, report co-author and professor of ecology and environmental biology at Cornell University told Utility Week this is higher than greatest rate of almost 79 per cent achieved at the only two operational blue hydrogen production plants at Alberta in Canada and Texas in the US: “We assumed that the technology could get better so perhaps they can get up to 85 per cent. That was out baseline case which is better than what they’ve actually demonstrated. Industry says you might get as high as 90 per cent. It’s possible. Who knows?”
The baseline estimate also assumes the carbon capture process is powered using electricity mainly generated using natural gas and that natural gas is also used to power the SMR process itself, with no carbon being captured from the flue gases.
Howarth said these flue gases could also be captured – albeit at lower rates of 55 to 65 per cent – and that the capture processes could be powered by renewables.
However, Howarth said this would have a relatively limited impact on overall greenhouse gas emissions as the lion’s share of the total comes from methane leakages during the production and transport of the natural gas that used as both a feedstock and a fuel for the reformation process, as is the case for both of the existing blue hydrogen plants.
“They use natural gas because it’s already the feedstock and it’s cheaper than using electricity generally,” he explained. “But in theory there’s no reason why they couldn’t use renewable electricity to power the SMR as well as the CO2 capture. We don’t know how much electricity would be needed if you were to do that because no one’s built a plant, no one’s designed a plant, so we don’t know what the efficiency of electricity is for the SMR process.”
But even if this was the case, the study found the greenhouse gas emissions would still amount to 53 grams of carbon dioxide equivalent per megajoule, with the fugitive methane emissions from the production and transport of the feedstock accounting for 42 grams and the residual carbon emissions from the SMR process accounting for 6 grams. The rest would come from carbon dioxide emissions from feedstock production.
“That’s substantially lower than grey hydrogen, substantially lower the normal blue hydrogen, it’s lower than natural gas but it’s not trivial,” said Howarth.
“It’s still half of what it would be for natural gas. And we don’t know how much renewable electricity you’re using but presumably it’s a lot. You could instead just use the renewable electricity directly to electrolyse water to get the hydrogen and skip the methane part.”
He said the SMR process could also be powered using the hydrogen it produces, but this would obviously come with the associated greenhouse gas emissions.
Howarth noted that the emissions estimates from the study are far more sensitive to the assumptions around methane leakage and its impacts than to those on carbon capture rates as methane is a much more powerful greenhouse gas than carbon dioxide.
The figures given above all assume a methane leakage rate of 3.5 per cent during the production and transport of natural gas, primarily based on a synthesis by Howarth of 20 different studies on the production of natural gas in 10 major fields in the US. Notably, this includes the production of shale gas.
Howarth described this as being at the top of a reasonable range. He said the study also looked at rates of 4.3 per cent, 2.54 per cent and 1.54 per cent as part of its sensitivity analysis based on from findings from other studies, but said he considers the lowest of these to be “unreasonable,” remarking: “I don’t think there’s anyway in hell it’s that low.”
The study acknowledged that methane has a half-life in the atmosphere of only 12 years or so, but said it is still 86-times more powerful as warming agent per unit of mass over the 20-year timeframe used in the calculation of the baseline estimate.
Howarth said this choice of timeframe would have been considered more controversial in the past but is less so now, particularly following the publication of the latest report from UN’s climate change panel on Monday (9 August): “They very definitely say you should be looking at shorter timeframes so I’m more confident in that now than I was even a week ago.”
The study also noted that it assumes that captured carbon dioxide can be stored indefinitely – “an optimistic and unproven assumption”.
Commenting on the report’s findings, David Cebon, professor of mechanical engineering at the University of Cambridge, said: “This landmark paper sheds light on the key unknown in the UK’s hydrogen debate: the greenhouse gas footprint of blue hydrogen. The calculation method is rigorous, the assumptions are all solid and the results are stark.
“Blue hydrogen cannot be considered ‘low-carbon’ or a ‘clean’ solution. In fact, this paper shows that producing blue hydrogen is significantly worse than burning fossil fuels for heat, such as gas or coal, in the first place.”
Juliet Phillips, senior policy advisor at the environmental thinktank E3G, said: “A climate-safe future demands a rapid and steep reduction in greenhouse gases, but today’s new report warns that fossil fuel derived blue hydrogen is far from a truly zero emissions fuel. There is no time left to waste in second rate solutions to the climate emergency.
“Worryingly, the UK government has so far allocated around 75 per cent of public investments in hydrogen towards this fossil-based fuel. We encourage the UK government to rethink its risky strategy of pursuing a ‘twin track’ approach of supporting both blue and green hydrogen, and instead focus on becoming a global leader in green hydrogen sourced from renewables.”