Is it just a matter of not being worth it? I see cooling towers releasing what appears to be a ton of steam, pretty high up. If that steam were captured at the top and allowed to condense, wouldn’t that result in a ton of water with a lot of gravitational potential energy? That water could then be released and used to power water turbines. Maybe I’m overestimating the amount of water being released as steam, or underestimating how much is needed to spin a water turbine to get a meaningful result, but it seems like wasted energy to me.
It’s not worth it. The energy you would generate is proportional to the vertical drop and the mass of water. If it were a river’s worth of water then you could generate a significant amount of power, but there just isn’t that much water mass in the steam.
You can use the leftover low-pressure steam for other purposes. For example, some places have combined heat and power (CHP) plants that use the steam to heat buildings, or run industrial operations that need a lot of heat energy. Though that requires you to live or work next to a power plant, which many people don’t like.
Yup. By the time it’s released, most of the energy has already been extracted from the steam. In the boiler, it was high temp and high pressure, then once it’s gone through the turbine(s) it’s cooler and low pressure, not really energetic enough to turn another turbine.
I’m talking about capturing the vapor, letting it condense, and then dropping the condensed water from its capture point. It’s not about exploiting the remaining energy from heat & pressure contained in the steam, but exploiting the gravitational potential energy created from all that water vapor rising and coming out the top of the cooling towers. Kinda like how we create energy batteries by pumping water uphill into a reservoir for later use, except we wouldn’t have to use any additional energy to pump it uphill.
So you want rainpower, but worse? Water batteries are a thing, but the amount of water in that vapor is miniscule compared to the amount required to generate enough energy to make that kind of infrastructure even remotely worth it.
You can get a hell of a vertical drop for free though. A typical nuclear cooling tower, for instance, is about 500ft and thats not the limit to how high the water vapor will travel. Even a couple thousand gallons at that height is a lot of potential energy that could be recaptured, and it appears that large nuclear plants release several million gallons of water per day.
They don’t release that much as steam, though.
The majority of water discharged from nuclear plants is cooling water, which stays in liquid form the whole way. It’s just rather warmer on the way out than in.
I went looking for some number for fun. (Every work day needs a good distraction, right?)
The nuclear plant that provides some of my electricity supposedly intakes 24 million gallons of water per day. As far as I can tell, that is entirely to make up for cooling water that is released as steam. There is a lot more cooling water present in the system which is recaptured and reused.
24M gallons/day = 16,667 gallons/minute. That’s a significant amount of water. However, it’s several orders of magnitude less than the flow through the smaller hydro power dams in my area. A few that I looked at have average turbine discharges in the ballpark of 6,000,000 gallons/min.
So for the cost (and vast regulatory headaches) of adding a secondary generation unit onto a nuclear cooling tower, you can just dam a nearby river and get 360x the energy.
Edit: I was way off on that 24M gallon/day number. After more reading, it looks like only around 2% of that water becomes steam leaving the cooling towers. So condensing the steam would give us a flow rate of 333 gallons/min of liquid water. That’s barely enough flow to operate a water slide at a theme park, let alone generate significant electricity through a turbine.
They are not evaporating 24M gallons a day. Most of that will be returned to the body of water it is pulled from but a few degrees warmer. There’s strict limits on how much the plant can warm a river or lake because of concerns about killing fish so plants will have cooling towers in parallel.
That makes a lot more sense. I thought the number seemed huge, but everything I could find said they have closed-loop cooling at this particular facility.
More importantly, if water is in steam form it still has pressure (and therefore energy).
Nuclear power plants are designed to cool down (aka capture) as much energy as possible before releasing the water back into the wild.
Short answer you are correct it’s not worth it. The massive cost of a bigger tower and gravity turbine aren’t worth the tiny energy you get.
This video covers the basics of how cooling towers work to reuse as much of the energy as is reasonable.
The energy generated by such a construction would be proportional to the mass of water that falls (as is basically every other form of energy generation), which is a problem because the m here is way too small to be worth it. The steam looks like a lot because you’re going by volume, but gases in general are just really light. To get an idea of how light, steam at 125C will shrink to 1/1800 of its volume when it’s condensed into water. In other words, a 1-meter cube of steam would become an 8cm cube of water. You can find this out by plugging the numbers into the ideal gas law, but either way there’s just not enough steam up there to be worth it.
I’d guess because it does not produce enough power to justify the cost of creating the condenser/turbine, otherwise, they probably would have.
How would you cool the water to condense it?
Getting it to cool efficiently is actually a very interesting challenge. Certainly more challenging that I thought before watching this https://youtu.be/tmbZVmXyOXM
Even assuming you had 100% efficient, and totally free energy capture systems for the evaporative clouds you see coming off the cooling towers… You probably wouldn’t use them because of the need of the primary system for time based cooling.
Any capture and recycling system will slow down the cooling rate of the primary system, if your goal is to use the primary system to maximum efficiency then that cooling rate can not be slowed down. .
Because efficiency. The amount of power generated from the water fall would be minuscule compared to the power generated from the stream.
Any engineering effort going into making this process more efficient would be better off making the steam generation more effective.
Short answer is because it isn’t worth the effort.
