Blue hydrogen as clean as green if emissions minimised: study

Blue hydrogen can have a similar climate impact to green hydrogen provided that methane emissions from the natural gas used to produce it are kept low and enough CO₂ from the process is captured, a new scientific study published in September argues.

On the climate impacts of blue hydrogen production, a study by academics in the UK, the US, Canada, Switzerland, Germany, Italy and the Netherlands, looks at the degree to which blue hydrogen can be clean under the right conditions.

"Our analysis sheds light on the relevant issues and provides a balanced perspective on the impacts of climate change associated with blue hydrogen," the study paper explains. "We show that such impacts may indeed vary over large ranges and depend on only a few key parameters: the methane emission rate of the natural gas supply chain, the CO₂ removal rate at the hydrogen production plant, and the global warming metric applied."

As long as state-of-the-art reforming is used, with high CO₂ capture rates and a low methane intensity for the feedstock gas, blue hydrogen "is compatible with low-carbon economies and features climate change impacts in line with green hydrogen from electrolysis supplied with renewable electricity."

The paper also stresses that "neither current blue nor green hydrogen production pathways render full 'net-zero' hydrogen without additional carbon dioxide removal."

Green hydrogen uses an electrolyser powered by renewable energy to split water into its elemental components. Blue hydrogen uses a process called stream reforming to draw the product out of natural gas feedstock, though it requires carbon capture and storage to capture emitted CO₂.

The study's conclusions stands in contrast with a controversial one published last month that estimated that blue hydrogen might even result in higher greenhouse gas (GHG) emissions than burning conventional gas.

The latest study estimated that current carbon capture technology can "allow removal rates at the hydrogen plant of above 90%," adding that rates of "close to 100% are technically feasible, slightly decreasing energy efficiencies and increasing costs, but have yet to be demonstrated at scale."

To compete with green hydrogen on climate credentials, the study concludes that blue hydrogen should have a lifecycle GHG footprint of no more than 2-4 kg CO₂ equivalent/kg. This can only be achieved with CO₂ capture rates of 93% and methane emission rates of about 1% global warming potential (GWP) over 100 years, or 0.3% GWP over 20 years, by reducing known and fugitive methane emissions across the supply chain.