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The critical point of water occurs at 374C at a pressure of 22.1 MPa (3,208 psi), where liquid water and steam become indistinguishable. Above that point (Super Critical and USC), the water does not need to boil to produce steam. So, not only do you need less coal to make that steam, you now also have a saving in water use as well, as it does

In other words, You pump for pressure and fire for steam temps. Yes, it is more efficient. I would take exception with the saves water statement. even the older tech. recylces the existing water from condenser to feedwater to boiler to turbine and back to condenser. USC water passes through one time but i'm sure not discarded because it must be treated to remove disolved solids that would destroy turbine blading at these pressures. very expensive to treat that much water to those levels of cleanliness, no reason to discard the water under either format. There are many super-critical plants out there

Finally a subject on FR that I actually know something about. I taught in and managed our community college’s Power Plant Operator program for several years.

Supercritical power plants are more efficient because of the characteristics of water under various pressures. If you take 32 degreee F water at normal atmospheric pressure and start dumping in heat, you will neeed to add 1 BTU per pound of water to raise the temperature 1 degree F.

In order to get it up to 212 degreees, you have to add a total of 180 BTU per pound of water. Then you have to keep adding heat until you have added another 970 BTUs/pound before the water will turn into steam. That is a total of 1150 BTUs/pound to get steam.

If you pressurize the water to 3206 psi, it takes 903 BTUs to warm the pound of 32 degreee water up to 212 degrees F but it instantly tunrns into steam. No sitting there adding more heat at 212 degrees to eventually turn it into steam.

The 3206 psi water saves you 247 BTUs per pound to get your steam. (1150- 903 = 247)

Where I sit, I could go up on the roof and on a clear day, see the water plumes from five power plants. Two of these are supercritical and have been in operation since the early 1980s. How many pounds of water are in the closed loop for these plants? I can give you an idea from this fact. The 1,300mw plant at one of these five sites only shut downs after a boiler tube water leak exceeds 8,000 gallons per hour. Yes, only when they start losing over 8,000 gallons per hour will they shut down and fix the boiler tube leak.