Australian Science Illustrated — Issue 54 2017

scienceillustrated.com.au | 69

Supercritical Fluid Generates

Extreme Quantities of Energy

At temperatures above 374 degrees, when the pressure is

more than 220 times that at Earth’s surface, water does

not turn into vapour, but rather into supercritical fluid.

At this stage, the water is so high-energy that the

molecules cannot bind to anything, rather they speed

about each other. But the high pressure compresses the

molecules, so they get a shape reminiscent of liquid

water – i.e. the water is a type of liquid gas. It can

dissolve other substances, like liquid, but also pass

through certain substances, like a gas. Concepts like

"bioling" and "condensing" don't really apply to

supercritical fluid.

L

iquid magma from Earth’s interior

rises to heat the rock to a

temperature of up to 500

degrees. The ground water is

heated and compressed into red-

hot, liquid gas. The extreme water rises

towards the surface, where its huge energy

content is used: supercritical fluid powers a

power plant, which lights lamps, charges

smartphones, and keeps the cookers of

50,000 Icelandic homes going.

In February 2017, Icelandic engineers

finished the drilling of a 4,659 m hole into the

area above a magma chamber. A hole, which

is to be the world’s hottest geothermal well

and generate unprecedented quantities of

eco-friendly electricity harvested directly

from the heat in Earth’s interior.

At this depth, the temperature and

pressure are so high that the ground water is

converted into a state, in which the water

contains much more energy than ordinary

warm underground water and vapour. So,

scientists believe that this one well can

generate 10 times as much electricity as an

ordinary geothermal well – approximately 50

megawatts per year.

The deep well has been drilled as part of

the Iceland Deep Drilling Project (IDDP), which

was initiated in 2000 by three Icelandic

energy companies aiming to drill much

deeper than the existing geothermal wells, of

which the deepest is almost 3 km.

ICELANDIC VAPOUR

BEAT WORLD RECORD

Iceland is the obvious place to experiment

with geothermal energy, as the country is

located on the Mid-Atlantic Ridge, where the

North American and Eurasian tectonic plates

meet. In between the plates, magma rises to

heat the underground, and the Icelandic

population has long taken advantage of the

phenomenon.

Today, 90 % of all Icelandic homes are

heated via geothermal energy. Power

generation is not as common as direct

heating, but Iceland is still the second to

none world leader. One third of the electricity

consumed by Icelandic households derives

from geothermal power plants.

Hot water and vapour extracted from the

ground have their limitations, however. Ideal

drilling locations are hard to find, drilling is

expensive, and lots of wells are required to

operate a geothermal power plant. The Krafla

plant, which is the smallest geothermal plant

in Iceland, pumps up vapour from 33 wells to

generate 60 megawatts of power, i.e. only 10

megawatts more that the IDDP expects to

generate from the new Reykjanes well.

The deep drilling idea originated by

accident. In 2009, engineers drilled a

geothermal well in the Krafla region. About 2

km into the ground, they accidentally drilled

a hole into a magma chamber. The hole was

sealed with a plug made of steel and

concrete. The plug was full of microscopic

holes, allowing the water vapour from the

Supercritical fluid is neither liquid nor evaporated, and it includes

lots of energy. In Iceland, a company has drilled down to the vapour of an

underground magma chamber to try to take advantage of the extreme water.

The World’s Deepest Well

Thousands of homes get power from

TEMPERATURE

PRESSURE

LOW

LOW HIGH

HIGH

Liquid (water)

Supercritical fluid

THE FOUR STATES OF WATER

CLAUS LUNAU

Solid (ice)

Gas (vapour)

By Esben Schouboe