Catalyst: Underground coal gasification

MARK HORSTMAN:

What's different about Queensland's new coal rush is it's all about getting the energy out of the coal without digging it up. This is a story about using coal for gas and two very different ways of doing it. One is UCG, or 'underground coal gasification'. It burns the coal underground. The other is CSG or 'coal seam gas'. It keeps the coal intact and sucks out gas instead. There are three pilot projects in Queensland. Carbon Energy is one of them.

ANDREW DASH:

UCG is very different from coal seam gas. Underground coal gasification extracts the energy in the coal itself, which means we can extract a very large amount of energy from a small footprint. In fact, 20 times the amount of energy you would do from a similar coal seam gas extraction process.

MARK HORSTMAN:

I've come to this paddock near Dalby because Carbon Energy is trialling its UCG technology here rain, hail, or shine, 24 hours a day, for 100 days. It doesn't look like much, but I'm standing in the middle of a coal mine, one of the only ones of its kind in the world. 200m beneath my feet is a coal seam that's 30m wide, 8m deep and runs for 600m down that way, where it's extracted at this end through these pipelines after the coal has been converted into gas. Here's how it works. It all happens underground, beneath the water table. The coal seam is ignited, and, under high temperature and pressure, the coal reacts with oxygen and water to become a mixture of gases. The reaction is controlled by injecting more air and steam, so about a metre of coal seam is consumed each day. The resulting gas is sucked out through another pipe. UCG marries the mechanics of longwall mining with the chemistry of gasification.

DR CLIFF MALLETT:

It's very similar to longwall mining, except instead of having a machine underground, there's a chemical reaction on the face. And by putting the hot gases across the coal face, the coal effectively dissolves in front of your eyes and turns into this energy-containing gas.

MARK HORSTMAN:

The gas is called Syngas, a flammable mixture of hydrogen and carbon monoxide. Every day, underneath this paddock, 150,000 tonnes of coal is being turned into gas.

ANDREW DASH:

It produces enough energy to run about 2,000-to-3,000 homes per annum if it were converted to electricity.

MARK HORSTMAN:

Injecting different mixes of steam and oxygen creates different hydrocarbons, making their underground reactor more like a chemical refinery than a power station.

DR CLIFF MALLETT:

To ensure that none of those chemicals escape out into the ground water.

WAYNE NEWTON:

We don't have the salt issue, but, with underground coal gasification, our issue is probably subsidence.

MARK HORSTMAN:

When a coal seam is removed underground, as UCG does, it can cause the rock layers above to crack and slump into the empty space left behind. That's been a problem with longwall mining in central Queensland and New South Wales, where croplands and rivers have been damaged.

DR CLIFF MALLETT:

Gasifying coal is easy if you can get the gases to it. The challenge has been about making sure we can manage the ground response and be sure that, environmentally, we are not causing any unintended impacts.