As a common feature with thermal power plants, cooling towers enable major water savings compared to straight through cooling methods. Even so, the big clouds of water vapor above them are a clear indication of how much cooling water is still effectively lost, with water vapor also having a negative impact on the environment. Using so-called plume abatement the amount of water vapor making it into the environment can be reduced, with recently a trial taking place at a French nuclear power plant.
This trial featured electrostatic droplet capture by US-based Infinite Cooling, which markets it as able to be retrofitted to existing cooling towers and similar systems, including the condensers of office HVAC systems. The basic principle as the name suggests involves capturing the droplets that form as the heated, saturated air leaves the cooling tower, in this case with an electrostatic charge. The captured droplets are then led to a reservoir from which it can be reused in the cooling system. This reduces both the visible plume and the amount of cooling water used.
In a 2021 review article by [Shuo Li] and [M.R. Flynn] in Environmental Fluid Mechanics the different approaches to plume abatement are looked at. Traditional plume abatement designs use parallel streams of air, with the goal being to have condensation commence as early as possible rather than after having been exhausted into the surrounding air. Some methods used a mesh cover to provide a surface to condense on, while a commercially available technology are condensing modules which use counterflow in an air-to-air heat exchanger.
Other commercial solutions include low-profile, forced-draft hybrid cooling towers, yet it seems that electrostatic droplet capture is a rather new addition here. With even purely passive systems already seeing ~10% recapturing of lost cooling water, these active methods may just be the ticket to significantly reduce cooling water needs without being forced to look at (expensive) dry cooling methods.
Top image: The French Chinon nuclear power plant with its low-profile, forced-draft cooling towers. (Credit: EDF/Marc Mourceau)
https://meche.mit.edu/news-media/vapor-collection-technology-saves-water-while-clearing-air
Or just search “plume catcher”.
Obviously you need to tow the water vapour outside the environment.
Yeah, water vapor having a negative impact on Earth? LOL. Try Mars. We owe our existence to 6 inches of top soil and the fact that it rains. Maybe for use in the desert to save water. Certainly better than those monster towers that seem to get destroyed a lot on the Tube.
Whoosh!
The logic behind, (not explained in the article) is that water vapor causes more greenhouse effect than even CO2. Since this water is pumped from a river or a lake (or the sea), naturally, only evaporation would have suck the water in the atmosphere, so only a minuscule fraction of what the tower is producing.
Thinking about heat itself, all electricity production made by mankind finishes in heat that’s increasing the Earth temperature. But compared to the heat received by the Sun, it’s peanuts. However, if you factor in the additional water vapor produced, it’s no more negligible. So you’re better to catch and condense this water as soon as possible to reduce the heating effect.
Though the sky is already about as “black” as it can get at the frequencies where water gas is absorbing sunlight. You’re not going to change the situation significantly simply by adding more water vapor as is.
What difference it makes is in cloud cover, because more moisture in the air adds to the formation of clouds, which retain heat – but also reflect sunlight away. The situation isn’t simple: where and when the clouds occur decides whether the effect is cooling or warming.
Personally I love those towers. I’ve had a chance to walk in a few of them and they are amazing pieces of engineering
I would but the front fell off…..
You gotta admit the reference was a bit obscure.
I will not be giving up my day job.
Cooling towers are a fascinating technology when you dig into the engineering and physics.
Liquid water droplets that escape the tower is water that didn’t evaporate and thus didn’t contribute to cooling — it’s an inefficiency, but often a deliberate one.
You could easily engineer the system to ensure all the water is used and leaves as vapor, and the plume exiting the tower would be invisible. You just need to “superheat” the air-water mixture so it’s above the dew point when it leaves the heat exchanger in the tower. But this requires the heat exchanger to be bigger (to add the superheat section) and worse: the incoming hot side of the coolant loop must be hotter, reducing the efficiency of the plant.
So it’s a tradeoff: run the cooling tower in superheat, reducing the water usage but reducing plant efficiency; Or spend a bit more in excess cooling water, increasing plant efficiency. Or the new solution: spend for capital equipment and ongoing costs to capture those rogue water droplets.
Wouldn’t the plume always be visible? I mean if the outgoing air is hot enough it might rise a bit further before it condenses, but there’s enough moisture in the air that as it mixes with the surrounding air it’ll still happen.
Unless maybe it was in a desert where the air was hot and dry enough that the humidity introduced wouldn’t change the dew point enough to matter. But then I suspect the efficiency would drop enough you’d need more water, which would put you back over the dew point.
Of course how high a plume rises before the water condenses to form a cloud depends on the ambient air humidity and temperature (and lapse rate), and also how much you want to spend on superheat.
The Palo Verde Nuclear Generating Station, 40 miles west of Phoenix, AZ, generates over 1,390 MW of electricity and evaporates approximately 100 million gallons of cooling water per-day or almost 70,000 gpm from 9 forced-draft cooling towers, each 300 feet in diameter. During the summer, there is no visible evaporation plume from any of the towers because of the hot, dry air, the plume temperature does not drop below the dew point. Electrostatic collection would not work during this time of year because there are no droplets to charge. During the winter, the dew point is reached, and the plumes rise thousands of feet into the sky and can be seen from downtown Phoenix. This condition might benefit from the electrostatic reclaim of charged droplets. Furthermore, most of the blowdown of concentrated cooling water from the cooling towers is directed to on-site evaporation ponds, while a fraction of this blowdown is directed back to the on-site precipitation chemical softening plant, where it treated to supplement cooling tower makeup water. Palo Verde is the largest industrial user of reclaimed municipal sewage water in the U.S. I would love to see a pilot study on one of the 9 towers at this location. If you are looking for a large-scale trial, you will not find a larger installation than this! I was the Chief Chemist of the Fossil Generation Division of Arizona Public Service Co. and then became the Calgon Heavy Industrial Division Account Manager of the Palo Verde Nuclear Generating Station.
So, make the cooling system less efficient? The whole point of open-circuit liquid cooling is to move heat out of the system. Recovering the water – and requiring power to do so – works against that. You want the cooling liquid to be, optimally, at ambient temperature or less to be able to absorb more thermal energy. So the recovered water does less work, being warmer, requiring a larger plant and an additional energy input for the electrostatic system… just doesn’t seem to be the right priority for the purpose of only mitigating plumes. It would make more sense to install additional passive stages in the cooling system so the plumes would reach ambient quicker, forming smaller visible plumes.
Heat engines are indeed more efficient the higher the difference in temperature, if you’re capturing water by the means described then it’s going to at least probably be warmer.
Capturing and reusing ‘warmer’ water may not be the point here, it is probably just to keep more eater in a liquid state on the ground and not in the atmosphere – dumped back into a lake to river, or simply down the drain where it (possibly) won’t contribute to global warming. If some other user downstream uses that captured water again, that’s a nett reduction in water consumption right?
As for the efficiency loss, well that would need to be quantified. The energy cost to run all that compressed air and high voltage ionizers, against the total output it’s probably a fraction of a 10th of a percent.
Cooling towers always blew my mind.
The entire purpose of a thermal plant is to create heat and convert said heat into electricity, yet there are these cooling towers involved whose entire purpose is to purposely throw some of that heat away.
I never really understood why the working fluids needed to be cooled at all, if you’re just going to send them back in and heat the m up again, but I’m an electrical guy, not a thermal expert.
I intellectually get that there is some point below which it becomes impractical to recover the heat, and there are many smart experts who have optimized the hell out of the process, but it still seems weird to just… throw away a large fraction of the product you just made.
It’s because you need a temperature difference to extract work out of heat.
Like you need a difference in height to make water fall down through water a turbine, you need a difference in temperature to make gases expand and flow through a gas turbine.
The reason is that no heat engine can extract all the heat into useful energy. Some always remains at the exit – just like a water wheel cannot take all the energy of a flowing river; the river would stop and so would the wheel.
So if the heat wasn’t thrown away, the temperature at the turbine exit would continue to climb until it reaches the temperature at the inlet, and then there would be no temperature difference, and therefore no flow of heat, and therefore the heat engine could not extract any energy.
A heat source will raise the temperature of the working fluid regardless of how hot it already is – the issue is that (1) there’s a limit on how hot equipment can get without melting, and (2) per Carnot’s theorem, the work done is inversely proportional to the absolute temperature, irrespective of the temperature difference.
If power plants ran hotter, they’d be easier to cool, but for maximum efficiency you want to get both the input and output temperature of the reactor / turbine / furnace etc. as low as possible. That’s why it’s worth spending money and energy on cooling systems.
Thermal transfer problems are commonly solved using electrical simulations by using the analog that temperature is voltage and heat is coulombs of charge. Since heat is Joules of energy, Amps of current is the electrical analog of Watts of heat flow.
You can make “heat reservoirs”, basically two capacitors, one charged and the other empty. One at high temperature, the other at low temperature. Connecting them together results in a current which represents the flow of heat from hot to cold. Now you can place a “heat engine” in the middle to do useful work, like turning a motor – at least until the two reservoirs equalize in temperature and the flow of heat stops.
To keep it going, you have to empty the cold reservoir and fill the hot reservoir again. Filling the hot reservoir is easy – you burn something and you get more heat. Emptying the cold reservoir is hard, because you can’t just “ground” it like you would in a normal electrical circuit – you have to drain the cold reservoir by connecting it to other reservoirs that are bigger and colder – you have to dump the heat into the environment somehow.
Explaining the workings of the heat engine using this electrical analog gets a bit mind-bending because of the substitution of current=energy, so I’m not going to attempt that. Sufficient to say, the normal assumption of power=volts x amps does not hold here so do not attempt that.
Correction: substitution of current=power
No. Current is not power. Not even with heat flow.
With heat flow it’s both the speed of heat transfer (I.e. current) and the temperature difference (Voltage) of the two vessels that count. And you multiply those two together to get the power.
Analogs are quite common in engineering. No matter if you have mechanical mass / spring systems, motors, fluid dynamics thermodynamic effects or electricity. The form of the formula’s are mostly the same and you can one system to simulate another. 100 years ago there were mechanical systems that did integration and fourier transformations. At some point Opamps were designed and used to do electrical simulations of other systems. These days most electronics is digital, but there may be a comeback for analog computers in AI. In AI, a node does not have to be very precise, but massive parallelism is a huge thing. And a variable amplifier combined with some I/O switching may be much more scalable then a processor core in a digital computer.
What is more polluting, water vapor or burning energy to recover the water. I didnt know water vapor was a big problem.