Ellen Phiddian
Cosmos science journalist
Earlier this week, the Labor party floated a proposal to change the planned Kurri Kurri gas station, which will be operated by Snowy Hydro in the NSW Hunter Valley, over to green hydrogen power.
Under Labor’s suggestion, the plant would initially run on 30% hydrogen and 70% methane (also called natural gas or fossil gas), transitioning to 100% hydrogen by 2030. (The current plan is to run the plant on 10% hydrogen initially and ramp up to 30% hydrogen by 2030.)
There’s been plenty of discussion as to whether the plant is necessary at all, but leaving the economic and political considerations aside, there’s a technical question too.
Is it possible to run a methane plant on hydrogen?
The short answer is: yes, but there’s some technology that needs to change. The amount of changes required depends on the original plant, and how specifically it was set up for one gas in the first place.
Hydrogen (H2) and methane (CH4) can both be burned to produce electricity in the same way. The gas is combusted, and the burst of heat and expanding gas from combustion drives a turbine which generates electricity.
In fact, hydrogen and methane are similar enough that there are half a dozen projects around the country that aim to blend small amounts of hydrogen with domestic gas supply in stovetops and heaters. At least four of these are already operational – in Western Sydney, Jandakot, WA, Canberra, and Tonsley, SA, and they’re all changing their area gas supplies to between 2% and 10% hydrogen.
But there are some chemical differences between hydrogen and methane that make a complete switch to hydrogen more difficult – both in stovetops and gas turbine plants.
The first is the amount of energy hydrogen can produce when burned. By mass, hydrogen produces about twice as much energy as methane.
But methane is a much denser gas than hydrogen – a litre of methane has many more CH4 molecules than a litre of hydrogen has H2. By volume, hydrogen combustion makes about a third as much energy as methane.
This means that about three times as much hydrogen needs to be pumped through a turbine to make the same amount of electricity. So a turbine needs to be equipped for a higher flow rate than methane, which it may not have been designed to do – a range of accessories may need to change to handle the higher volume and/or speed of gas.
Hydrogen also has a faster flame speed – essentially, how rapidly the flame spreads through a volume of hydrogen once it’s been ignited. This means that the section that ignites the gas in a turbine – the combustor – might not be suitable.
There are also three key safety considerations. Hydrogen flame is much less bright, and can be hard to see. A plant needs flame detectors that can pick up hydrogen flame.
It’s also easier for hydrogen to leak than many other gases – H2 molecules are small, and the gas isn’t very dense, so it can get through seals that stop methane.
And finally, hydrogen is more flammable than methane: it ignites more easily and can spread faster. Traditional safety measures designed to prevent methane fires might not be as effective against hydrogen.
So, refitting a methane plant for hydrogen needs a change in technology and training of staff. The amount of change that needs to happen depends heavily on a plant – General Electric has a calculator that estimates the emissions and financial savings from transitioning various plants.
And blending – while a useful way to transition a plant – might not reduce emissions as much as one might think.
Because hydrogen produces less energy by volume, a plant that runs on 30% hydrogen does not produce 30% less CO2 than a methane plant.
To make the same amount of electricity, a 30% hydrogen plant will need to burn more fuel than a full-methane plant.
So, while using green hydrogen in these turbines does lower emissions, be wary of the numbers associated with blending.