is using seawater (or river or lake) as a coolant to condense the steam exhausting from the turbines. The heat is directly transferred to the ocean and "lost" (Yes we accept the First Law, but as far as economical plant operation goes, the energy is lost).
Heat loss by condensation is the greatest heat loss in a steam plant because it is latent and since it occurs at such a low temperature that little heat can be recovered. Because the condensers operate in a vacuum, the turbine exhaust temperature is quite low, on the order of 105 deg F or so. As long as the steam is in a dry-vapor state the turbine can extract power from it. One of the problems is the increase in volume to the point where choking occurs in the exhaust duct. So that is a limitation as well.
In steam plants, one way to reduce heat loss is to extract steam at various points in the turbines to transfer heat to the water side of the cycle through boiler feed water heating. Because the steam is condensed in the feed heater, sensible as well as latent (the biggie) heat is transferred. Essentially we are cheating the condenser by doing this.
Ideally a boiler should just add latent heat to change feedwater into steam and superheat for extra energy.
The turbine operates by exchanging steam pressure and temperature for velocity through the rows of turbine blades. The weight and velocity of the steam imparts the rotating motion. As the pressure and temperature drop, the volume increases. The turbine design increases blade length in the stages to make room. We can also take steam off the turbine and reheat it to increase energy available in later stages.
= new reply since forum marked as read
