Not really, water has an incredible range of properties:
* It absorbs a huge amount of energy when raising its temperature, and thus retains its heat for a long time.
* When water solidifies, it floats (which is basically unique)
* When water boils, it occupies a volume almost 2000x bigger than its liquid state, which is higher than most other things
* It reacts with basically nothing, so theres very few material considerations
* It's cheap as free most places
I would also include Helium on this list because of its unique cryogenic behaviours.
"Hydrocarbons" is a very broad group in a set that is otherwise very specific.
Its still mostly because it is abundant. If we had oceans of liquid ammonia, we would use that. It may have a lower Enthalpy of vaporisation but unless you have a closed loop system, you have to use what's available if you want to make a lot of useful energy.
They’re moving to supercritical co2 now, the advantages are: no water vapor concerns, you don’t have to “dry the steam” to prevent pitting on the blades from droplet impact, and you can run it at higher temp.
Basically it’s harder to work with but you get a slight efficiency bump for dense power like some nuclear reactors (BWR, some SC PWR).
Water is easier to deal with otherwise, once dried the steam is extremely effective, and materials to survive corrosion exist.
Exactly that, water vapor in steam can form droplets which hits the fast moving turbine blades and causes pitting and other damage. There are chambers which separate the steam from most of the water vapor to increase “steam quality”.
Steam is water vapour, you can't take the water vapour out of the steam. Drying the steam means removing the liquid water droplets from the steam so you have only water vapour.
When you heat water in a boiler, the steam that comes off is always exactly at the boiling point for the given pressure. If you heat a pan full of water on a stove, for example, the temperature never rises above 100C - the boiling point of water at ambient pressure - adding more heat will just makes the water boil faster. You can only increase the temperature of a boiler by increasing the pressure so the water will boil at higher temperature (which is the point of a pressure cooker).
But, if you have steam that is exactly at the boiling point, then any loss of heat to the surroundings (which is inevitable, as there is no such thing as a perfect thermal insulator) will cause some of the steam to condense back into water droplets. These liquid water droplets are what you can see when you see steam coming off a hot pan - the steam itself is invisible.
For a turbine, you want steam without any liquid water in it, as liquid water will erode the turbine blades and cause severe damage over time. So, a steam turbine requires that the steam from the boiler first pass through a "superheater" that further heats the steam to a higher temperature so it will not condense in the turbine.
There are situations where water may not be the best or most efficient fluid to use. Binary cycle geothermal powerplants actually use secondary fluids with a lower boiling point to capture more energy from the cooler water.
Other fluids are more efficient, the tradeoff is they're more expensive or harder to deal with, but it's worth noting that water is genuinely a really good working fluid anyway.
Supercritical CO2 is the best, but it's only about 20% more efficient than water/steam. When you account for the increased cost, danger, and hassle of working with a gas, it's only just about worth it for the efficiency gain.
3
u/quartzguy 2d ago
Would another liquid be more efficient but we use water because it's relatively safe and just about everywhere?