Blue hydrogen — produced from natural gas with carbon capture and storage — is often criticised because it is not inherently a zero-emission solution. It is only possible to capture up to 98% of the CO2 emitted in the process of methane reforming, although levels of around 90% are often more realistic.

However, what is less well reported is that the entire blue hydrogen value chain will produce a lot of additional greenhouse gas emissions unless efforts are purposely taken to reduce them.

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Almost every stage of the process — from extracting natural gas to transporting it, compressing the hydrogen, and capturing the CO2 and moving it to storage — has the potential for CO2 emissions, either directly or indirectly from the use of fossil-fuel power, while leakage of methane (a potent greenhouse gas in itself) is also a constant risk.

And if liquefied natural gas (LNG) is used, additional emissions are even more likely, as LNG is often transported overseas by highly polluting oil-powered vessels, while additional energy is required for liquefaction and regasification.

So to make blue hydrogen a truly low-carbon solution, all the electricity used throughout the value chain should come from renewable sources; CO2 emissions from gas flaring must be eliminated; while stringent monitoring will also be needed to ensure minimal leakage of methane — which is 84 times more potent a greenhouse gas compared to carbon dioxide over a 20-year period.

Henrik Solgaard Andersen, vice-president of low-carbon technology at Norwegian oil giant — and global blue hydrogen leader — Equinor, tells Recharge: “These [emission-reduction solutions] must be implemented in the gas industry to make blue hydrogen a long-term option.

“Otherwise upstream emissions will kill the concept [of blue hydrogen].”

He explains: “I’m always honest saying that if we talk about a weakness of blue hydrogen it’s the upstream emissions. So it's key that the natural gas you're providing for blue hydrogen has low emissions and that means both in terms of CO2 and methane leakages.”

The Dane says that strict regulations in Norway have required Equinor to spend a lot of time and money on reducing its upstream methane and CO2 emissions, including powering some of its offshore platforms from shore using hydroelectricity and recycling excess gas down to the reservoir, rather than flaring (ie, burning) it.

Henrik Solgaard Andersen, vice-president of low-carbon technology at Equinor. Photo: Equinor

“That means, in fact, the offshore emissions [at such platforms] are close to zero, and that’s the same type of solutions you need when you’re sourcing other types of natural gas,” he says. “So when you are, let’s say, using Russian gas, that needs to be compressed all the way from Yamal [in northwest Siberia] to the UK; you need to use renewable power when you do the recompression, otherwise you would just add a lot of CO2 emissions.

“And when you are importing LNG, you need to make sure the LNG production has CCS [because the liquefaction process separates out any CO2 present in the natural gas] like we do in Norway at Snøhvit.”

Andersen says that reducing upstream emissions is not “rocket science” — all gas companies could reduce them if they chose to, but that would require them to accept additional costs.

“We have electrified a lot of our offshore installations, so we're using a lot of renewable power to drive all our rotating equipment on offshore platforms; we are implementing CCS. When it comes to maritime sectors we also — because we are running a lot of vessels globally — are looking into replacing that with less carbon intensive fuels, of course, [over the] long term, ammonia or biofuels. In methane leakage, we have implemented a lot of different methodologies and processes to avoid leakages, both during start-ups and shutdowns and critical operations where these things can happen.

“These are not rocket science. It's more like a cost issue. People must be willing to take that potential extra cost to implement it.”

Methane leakage is one of the largest sources of direct greenhouse gas emissions from the natural-gas industry. For example, Russian gas giant Gazprom recently admitted releasing 2.7 million cubic metres of methane into the atmosphere due to a pipeline leak, and a further 900,000 cubic metres from “planned maintenance” in May and June this year.

Why can’t all the CO2 be captured in blue hydrogen production?

Influential energy analyst Michael Liebreich, the founder of Bloomberg New Energy Finance, recently told Recharge that capturing only 90% of emissions from blue hydrogen production “ain’t good enough”, and that this should be 100% or in the “high-90s”.

Andersen explains that 100% carbon capture from methane reforming is not physically possible.

“In these blue hydrogen processes, there will always be some CO2 remaining because they are catalytic processes,” Andersen explains. “So they are driven by what we call catalytic equilibrium, reaction equilibrium, and you can never get 100% conversion, that is more or less impossible when it comes to the laws of nature. But we believe with the best technology, we can achieve maybe up to 97-98%.”

He puts it in more simple terms by explaining the difficulties of capturing carbon dioxide from the flue gas at a natural-gas-fired power plant. “The pressure is very low and the CO2 concentration is very low… so it’s very difficult. It's like finding a needle in a haystack. And the more [CO2] you take out, the smaller the needle gets to find the rest [of the CO2]. And finally, you can't get it.

“In a blue hydrogen plant, it's high-pressure CO2. So we have many more needles initially, and that's why you can capture much more CO2 in a blue hydrogen plant compared to a post-combustion plant, because the pressure is so high, so you can get down to [97-98%].”

According to a recent report by the UK’s Hydrogen and Fuel Cell Association, entitled The Case for Blue Hydrogen, the standard method of grey hydrogen production from natural gas — steam methane reforming (SMR) — can only capture 90% of CO2 emissions. A slightly more expensive process, known as autothermal reforming (ATR), which requires the addition of pure oxygen, can capture 98%, it says.

Andersen explains that Equinor has not yet decided which of these two process it would use to produce blue hydrogen, but it would probably go with ATR.

“What we see is that for smaller scale and medium scale sizes, SMR will be the best solution. But when it comes to bigger scale, towards the 1GW [size], ATR is the more cost efficient solution.”

He says Equinor could source oxygen from its green hydrogen projects — which split water molecules into oxygen and hydrogen, which would reduce overall costs. But producing oxygen in other ways would require additional energy that would also need to be carbon-neutral in order to avoid adding emissions to the value chain, he points out.

How blue hydrogen could become net zero

Andersen says that even though blue hydrogen is not intrinsically a net-zero solution, it could become one through the addition of carbon-neutral biogas, which is produced by fermenting plant matter inside huge tanks known as anaerobic digesters.

“One concept we have been working on, which we published a year and a half ago, is to add biogas — a carbon-neutral component — into the natural gas. So when you capture [the CO2 that was absorbed by the plant matter as it grew], it becomes carbon-negative. Maybe [adding] 5% in total will also cover potential upstream emissions.”

Potential emissions from the CCS process

It is often overlooked that capturing and storing CO2 requires a lot of energy — which can, perversely, add carbon emissions if that power is sourced from fossil-fuel generation.

Carbon is captured by passing flue gas, or in the case of blue hydrogen, syngas — a mixture of hydrogen, carbon monoxide and carbon dioxide — through a spray of chemical solvent known as an amine, which absorbs the CO2.

The now CO2-rich solvent is then heated, which releases the carbon dioxide in a highly concentrated form. It is then compressed, cooled, dried and condensed to a pressure of 200 bar, before it is then pumped to a storage reservoir where it will be sequestered in perpetuity. The solvent can then be recycled and re-used thousands of times.

As Andersen explains, this entire process requires large amounts of both heat and power.

“When you are stripping out that CO2 [from the solvent], you need a low-temperature heat — 134°C, which is in fact an advantage because using low-grade [electric] heaters is a very nice way of creating high energy efficiency. But still there will be a need for power. Compressing CO2 to 200 bar will require a lot of power. Recycling that solvent requires a lot of power, and there are different ways it can be sourced — from renewable power or we can produce it internally in the process when we’re producing blue hydrogen.

“An ATR is what we call an exothermic reaction, it generates heat, almost like some kind of a combustion process. So when you’re adding oxygen and natural gas, it burns and it raises the heat inside the reactor.”

In total, he says, the amount of energy needed in the blue hydrogen production process is equal to 5-10% of the energy content of hydrogen.