Quaise Energy has been dazzling us lately with its bleeding-edge plans to tap super-deep, superheated steam as a global power source. Now, the company's reaching back over a century to adapt yesterday's technology for tomorrow's energy.
Quaise Energy can't be accused of being unambitious. Geothermal power has a tremendous potential for providing humanity with unlimited energy for the foreseeable future, but it suffers from the fact that it's only really practical in a few places where the sources of subterranean heat are close enough to the surface to be easily tapped.
What Quaise Energy wants to do is get around this by going straight to the source. In other words, instead of waiting for the heat to come to us, we go to the heat. Using a traditional rotary drill bit and a gyrotron-powered energy beam to burrow up to an incredible 12.4 miles (20 km) to a region in the Earth's crust that is heated to 500 °C (932 °F).
Not only would this make geothermal power accessible in almost any place that isn't a high mountain chain, it also brings a bonus. At this depth and that heat, water is heated and squashed to the point where it is supercritical. That is, when the temperature is above 373.9 °C (705.2 °F) and the pressure is over 218 atmospheres, the water enters a state where it is neither a liquid nor a gas. Instead, it behaves as a single homogeneous fluid and shifts from being an almost-liquid to an almost-gas depending on the current conditions.
When in a supercritical state, water has lower viscosity than liquid water, yet higher than steam, allowing for improved flow dynamics in turbines and heat exchangers. It also has lower thermal conductivity than liquid water but higher than that of dry steam, aiding heat transfer. It expands very rapidly when depressurized, and its specific heat capacity changes dramatically near the critical point, allowing for efficient energy absorption. This gives it higher thermal efficiency and the ability to hold 10 times more energy than regular water or steam.
If that isn't enough, it can even clean the pipes it's flowing through thanks to its ability to dissolve salts and other impurities.
All of this sounds spectacular, but like consuming a delicious meal there's still the point where you have to eat the broccoli. I don't know why people use broccoli as a metaphor for something unpleasant. Personally, I rather like it – especially when stir fried in clarified butter with a bit of oyster sauce, but there you are.
In the case of Quaise Energy, the broccoli is getting this supercritical water to do useful work. That's not very hard. Supercritical water is commonly used in power generation and industrial processes, so the technology is well established. The problem is how to deal with a supercritical power source that's so deep it's over twice the height of Mount Everest. Not only that, current geothermal systems are designed to operate at much lower temperatures of between 100 to 250 °C (212 to 282 °F).
Worse, getting supercritical water to the surface has its own difficulties.
What happens is that the higher heat content of supercritical water is cancelled out by the decreased mass flow rate due to the phase changes in the sort-of-liquid-gas. However, if the water that reaches the surface is as low as 350 °C (662 °F), you still get an efficiency order of magnitude higher than conventional geothermal power plants.
The question is, how to make it work? For the answer, Quaise went back to the first geothermal plant, Larderello 1, that opened in Italy in 1914. Instead of having one loop with water going into the Earth and then returning steam to the surface, this used two loops of water with one collecting the heat deep underground and the second swapping the heat from the first to bring it to the turbines on the surface.
This heat exchanger system was used because the water coming up was highly corrosive, so the exchanger protected the generating gear. Similar exchangers are used for geothermal power today, but the low temperatures mean that the upper loop uses organic chemicals with lower boiling points like benzene, pentane, butane, and isopentane. Because it uses much hotter water, Quaise wants to swap these out and go back to water like the earliest plants.
According to the company, this approach would not only be a major step to making their system practical, it would also be lower cost and more environmentally friendly as it eliminates toxic chemicals.
"The applications are diverse, from power plants to regional heating to domestic ground-source heat pumps, and there are a lot of fresh new eyes on the field," said Daniel W. Dichter of Quaise Energy. "There’s a renaissance happening in geothermal right now."
Source: Quaise Energy