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JULY/AUGUST 2019. DISCOVER 67
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Beyond Steam
The “age of steam” began more than 200 years ago, with James Watt’s invention of the
first efficient steam engine. But if a new technology now being tested pans out, steam’s
monopoly on our power grids might be over. NET Power, a company based in Durham,North Carolina, has built a fundamentally new type of power plant, one that runs on
carbon dioxide rather than steam. Remarkably, it can burn fossil fuels without emitting
any greenhouse gases.
The demonstration plant in La Porte, Texas, was completed last year. It burns
natural gas in pure oxygen rather than normal air, producing heated and pressurized
“supercritical” carbon dioxide to spin turbine blades. Supercritical materials combine
the properties of a gas and a liquid: They flow like liquids or fill an empty volume
like a gas. Since supercritical carbon dioxide is denser than steam, it packs a greater
punch per volume, transferring more energy to the blades. And after spinning those
blades, the supercritical gas can be piped into underground storage, capturing all of
the greenhouse gas without any special equipment. With water as the only emission,
these plants might play a key role in a low-carbon future.
Calliopes — also known as
steam organs — produce sounds
by forcing steam through whistle
pipes. A keyboard controls the
flow of hot gas into the pipes.
Iceland, which sits
atop the geologically
active Mid-Atlantic ridge
between tectonic plates,
generates about 27 percent
of its electricity from
geothermal energy. Deep
wells tap underground
reservoirs of pressurized
water, providing steam to
power turbines at Iceland’s
six geothermal plants.
Heron of Alexandria is thought
to have invented the first steam
engine in the first century A.D.
His aeolipile, or “wind ball,”
consisted of a sealed spherical
container filled with water and
heated over an open flame. Steam
jetting from two pipes on the
sphere’s surface made it spin.
Heron saw the device as a toy
without any practical applications.
FAST FACTS
If you’ve ever grabbed a self-service meal or eaten at a buffet, you’ve seen
a steam table, which keeps prepared food warm on the bottom and four
sides of a food pan. Steam transfers heat five times more efficiently than
water and 12 percent better than air.
Carbon dioxide takes on different forms based
on temperature and pressure, as shown in this
phase diagram. In the right conditions, the
substance can act like both liquids and gases
in its supercritical state.Liquid
Gas
Supercritical
Solid
Critical point