![The deepest hole we ever dug was 500 degrees at the bottom, could a more shallow hole that could boil water be used to power a steam engine? [GIF - 18KB]](https://pic8.co/sh/azB0pa.gif){kind=link}
You wouldn't need to get the steam back up, would you? Just have it do it's thing at the bottom and turn a generator. Cables running up the hole would carry electricity. Then, ideally, you could get an almost reflux still effect in the hole, with the water. but getting additional water down would be easy.
The steam itself doesn't directly drive a turbine. It's just what causes enough of a pressure differential to act on the turbine blades and make the whole thing move. If you put everything down at the bottom of the hole, then the temperature and pressure would be equal across the system, and nothing would happen.
So instead you pipe the steam up from the source (where the temperature and thus pressure is high) into the turbines (where the pressure is low).
If you put everything down at the bottom of the hole, then the temperature and pressure would be equal across the system, and nothing would happen.
That can't be entirely true. If I had a sealed reservoir full of water, with a pipe going down into the water, and I throw it on the stove(or inside an oven for that matter), it will boil and water will come out of the pipe.
A piece of pipe full of steam at 500F is one thing. Putting a generator and all the associated equipment at that level would be problematic, and servicing would be impossible.
Countries with high volcanic activity already do this, so it's just a matter of finding an area where you can pipe the water around. In the USA, the Yellowstone region would probably be perfect for this.
Plus wouldn't boiling water like that below sea level at a higher atmosphere up the boiling temp?
The boiling point would depend on the pressure in the tube, since it's not exposed to atmosphere. If you're pumping it into a geological area and collecting it with another tube, the calculations change. I don't have any real experience here.
Still would need a cooler, lower pressure place to exhaust the steam. The volume of water required would be large to get significant power from a turbine. People have done a lot of work in the field of "geothermal energy" and there's a fair amount written about it.
People have done a lot of work in the field of "geothermal energy" and there's a fair amount written about it.
If I wanted to actually put in the effort for this, would I be armchair engineering here?
Why do you have to exhaust the steam? Isn't piping that back into the cold instream a more efficient option?
Just pointing out that a turbine lowered into the borehole would need to have a low pressure side so there would be a pressure differential. You can certainly use incoming cool water to condense the steam to make a pressure differential. In doing so you create hot water which you can cycle back into the heat source preheated. However, keeping the water in a closed cycle means there is no need for incoming cold water for cooling. Somehow something has to escape from the borehole or you end up with a static system, so you would have to pump out the warmer condensed water.
Check out power plant descriptions and you'll see that there is always a movement of heat through the system. Some of the heat energy is converted to mechanical energy but some is removed at the condenser either via moving river water through or more often passing condenser cooling water through a cooling tower.
They really did a lot of work with this in the '60s and there are geothermal plants operating in a number of places where there is volcanic activity bringing heat close enough to the surface for it to be practical. There are probably some good online resources on what has been done and some ideas for increasing use in the future. (It's been years since I studied this but IIRC there was an issue with the exhaust containing some undesirable chemicals picked up from the volcanic activity and ground water percolating through igneous rock.)
That's not how it usually works.
What they do is, they run a pipe down the well deep enough that it will heat the water to near boiling then the pipe does a "U-turn" back up still liquid, but very hot. 99°C
Because the level is the same at the input (cold tank) as the output (hot tank), almost no energy is required for pumping. The water just levels out by itself.
Then a minuscule amount of natural gas is needed to finish boiling the water to turn it into steam to power the generator.
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