How an underground cavern could aid in green steel production
Swedish energy giant Vattenfall has recently unveiled a man-made underground cavern that could be used to store green hydrogen, forming the backbone for future green steel projects.
The plan is to store green hydrogen for use in the HYBRIT joint venture formed alongside SSAB and LKAB, the cavern is planned to be put into operation during the summer of 2022.
Read more: Steeling the future: Using hydrogen to make green steel
Vattenfall has announced that roughly half of the cave has been completed since construction started in May 2021.
The plant has been designed to allow for smoother production by storing green hydrogen when other forms of power generation are abundant to help alleviate shortages should supply falter, although production could commence without the need for storage should it need to.
When completed, the pilot will be around 100 m3 and could eventually store up to 100,000–120,000 m3 of hydrogen - roughly 100GWh - enough to power a mill for a few days on its own.
The HYBRIT venture led to the creation of the world's first fossil-free steel back in 2021. One of the venture's partners, SSAB, later pledged a line of fossil-free products would hit shelves by 2026.
Steel is currently the most carbon-intensive material in the world, accounting for roughly 8% of total emissions, and forms an essential part of the construction and engineering sector and presents a major decarbonisation challenge for both.
Typically made using coal and coke, switching to green steel could reduce Sweden's net emissions by up to 10% and Finland's by around 7%, with steel being a massive sector in both nations.
As such, a number of projects have sprung up in recent years in order to rapidly decarbonise the sector. The new storage could help store a large amount of hydrogen, ultimately playing its role in reducing active carbon emissions from the sector.
“The hydrogen storage facility has a stabilising effect on the electrical system: it reduces the risk of the system overloading. We want to develop HYBRIT technology so that it is in line with the future electricity system with more weather-dependent electricity generation,” Mikael Nordlander, Development Manager for Vattenfall’s industrial partnerships, said in a statement.
The concept is known as a lined rock cavern (LRC) and has seen use in Sweden for decades. Concepts for similar projects have been drafted in both the public and private sectors to store both natural gas and hydrogen.
“The hydrogen atom and the hydrogen gas molecule are the smallest that exist, which brings special challenges. We want to see that the storage facility can cope with variations in pressure and can keep up when electricity generation varies", Susanne Rostmark, research leader at HYBRIT partner LKAB, said.
Vattenfall reports that much of the systems needed for storage have been constructed in the cavern. Rock caverns and connecting tunnels have been constructed in the rock and a ventilation shaft has been drilled from the top of the rock down to the upper part of the rock cavern.
At the tail-end end of 2021, a compressor that will be used to pressurise the hydrogen gas for storage was lifted into place.
Read more: Operations begin at Sweden's HYBRIT fossil-free steel plant
In addition, pipelines that will transport the hydrogen gas into the caverns have also been laid.
The coalition estimates that as much as 15 TWh of capacity will be needed to achieve its production goals for green steel per year, which will require rapid transition and require necessary permits and grants to be confirmed faster.
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