Explainer: Storing LNG and other gases for energy

The ongoing energy crisis is causing potential power interruptions this week in many Australian states.

At a press conference following a meeting of all state and territory counterparts last week, federal energy minister Chris Bowen said that the country needed more transmission, more renewables, and more storage.

The economic and environmental benefits of renewable energy and improved grid infrastructure (transmission) are well established.

But what does storage entail? Batteries form part of the picture, but gas – also called fossil gas or natural gas – will likely be playing a role for the next few decades. By 2030, hydrogen fuel may well also be contributing to the grid’s energy security.

So how do you store a gas at scale? Cosmos investigates.

How is gas stored at scale?

Fossil gas is mostly made of methane, along with trace amounts of other hydrocarbons. It’s typically stored as a liquid, hence the acronym LNG, or liquefied natural gas.

“When you liquefy it, the volume reduces, about 600 times. So therefore, obviously, it’s easier to store a much more significant amount of it,” says Dr Behzad Fatahi, an associate professor of engineering at University of Technology Sydney.

To do this, the gas is cooled until it condenses at -162°C (methane’s boiling point) – and then usually a handful of degrees lower.

From there, it’s typically kept in storage tanks that can hold several hundred million litres at a time. These tanks are usually about 30 to 50 metres in height, and 80 to 100 metres in diameter.

“Inside you have got some sort of a steel tank – it’s a special cryogenic material – that can take the temperature of -162°C,” says Fatahi.

“And then outside of that also, you design a concrete tank, so that in case there is a leakage or something happening to the internal layer, that concrete layer can hold it.”

The steel in the inner chamber is usually around four centimetres thick, while the outer concrete layer is roughly a metre thick.

Is it dangerous to store this much gas?

Is it a good idea to keep that much liquefied flammable fuel in one place? Fatahi says that the temperature and the storage tank prevent most danger.

“The chances of having problems with storage of LNG is very low,” he says.

“Unless you build them in a very highly seismic area, for example, that you didn’t design for properly, or there has been a sabotage or external attack to the facilities, it’s very rare that there will be a safety issue.”

The thickness of both the inner and outer layers prevent danger from the exterior – accidents, natural disasters, or deliberate attacks – and leaks from the interior.

“They can resist a big force – an explosion or attack from outside – and also leakage from inside,” says Fatahi.

As with nuclear power stations, no system is completely safe from the most unexpected disasters – but LNG storage tanks are prepared for all the more predictable ones.

Does it leak methane?

Gas mining and transport operations are notorious for venting excess methane, a greenhouse gas with up to 30 times more global-warming potential than carbon dioxide, into the atmosphere. Do storage tanks pose the same climate risks?

If they’re built correctly, no, but poor maintenance can lead to faults and leakage, particularly as the gas enters and exits the tank.

According to a 2010 US Environment Protection Authority paper, for instance, storage tanks were responsible for 6% of all methane emissions in the US’s oil and gas sector.

The technology exists to capture this methane and prevent it from getting into the atmosphere, but it’s not always deployed – storage facilities need clear incentives to do so, and excess methane emissions are not always closely monitored or reported.

What about other gases?

“We really need to build more energy-storage facilities that can accommodate more versatile types of energy,” says Fatahi.

“Because each of these facilities, if we want to build them, we are talking about billions of dollars, right? It’s not cheap.”

Retired coal plants turn out to be good sites for future batteries, and there is talk of repurposing gas power plants to run on hydrogen. Can LNG storage be repurposed in the same way?

“It’s a bit of challenging question,” says Fatahi.

Hydrogen has some key differences to methane – it’s got a much lower boiling point of -253°C, for one, meaning far colder conditions are needed to keep it in pure form. Storing it as ammonia could mitigate this problem, but it will pose others – such as its corrosive nature.

“For sure, in terms of the material science, we can have materials that can store both hydrogen and LNG,” says Fatahi. “But we want to make them as cost effective as possible.”

Figuring out what is going to be economical and industrially feasible is the next big research challenge.

“This thinking needs to be done now, when we want to build these energy-storage facilities,” says Fatahi.

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