Mining giant Rio Tinto is planning to use green hydrogen to help decarbonise its operations, but it would only consume H2 where it is generated to avoid leakage of the indirect greenhouse gas, investors were told on Wednesday.
“Hydrogen use will be impacted by leakage from storage and transport facilities; an estimated 1% per day is lost when stored in liquid form, and hydrogen has a global warming potential 5-16 times that of carbon dioxide over 100 years, making it potentially more damaging to use than burning natural gas,” chief scientist Nigel Steward told the company’s investor summit in London.
“Therefore, our intention is to consume hydrogen close to its point of generation.”
Mainstream liquid hydrogen (LH2) storage tanks, such as those used by Nasa, are said to lose 1-5% of their H2 every day from boil-off. This term refers to the portion of the stored liquid hydrogen that is warmed by ambient air until it reaches boiling point (at minus 252.9°C) and becomes a gas. Because hydrogen gas takes up more space than liquid H2, and because it has nowhere to expand into when inside a solid metal tank, this boil-off will quickly start to compress and increase the pressure inside the tank. If the boil-off is not vented, the pressure will grow until the tank ruptures.
However, it is possible, at added expensise, to capture and reliquefy boil-off gas, and there are several tank companies offering storage vessels that promise to eliminate almost all boil-off from LH2.
Steward also told investors on Wednesday that “there is a lot of hype about green hydrogen”.
“At the moment, [green] hydrogen is very expensive and will require a technological breakthrough to be economically viable.
“It is a very energetic material to produce; approximately four times more per tonne than aluminium, but it can provide a great deal of energy back to decarbonise some hard-to-abate industry sectors. There will be very high power requirements to generate sufficient hydrogen to meet future demand; however, the electrolyser supply chain to deliver green hydrogen is not yet well established and it will take time before it will be a material contributor to decarbonisation.”
Nevertheless, he explained: “We expect to use [green hydrogen] as a reductant for zero-carbon steel making, for ilmenite [titanium ore] reduction... and for calcining our alumina refineries [ie, part of the process of extracting aluminium from bauxite ore].”
“In these cases, we exploit hydrogen’s unique chemical properties, rather than using it as an energy carrier.”
Steward added that Rio Tinto has invested in a start-up called Electric Hydrogen, which aims to reduce the cost of green hydrogen by a factor of three “through better process design and system engineering, as well as scientific breakthrough”.
London-based Rio Tinto, the world’s biggest iron-ore producer, last year announced a $7.5bn plan to slash its greenhouse gas emissions in half by 2030.