What is a Supercritical Power Plant?
Modern thermal power plants operate at very high pressures greater than the Critical pressure of steam. This article explains the concept of Supercritical power plants. "Steam is no stronger now than it was a hundred years ago, but it is put to better use.“ – Ralph Waldo Emerson To increase the efficiency of steam power plants the basic method is to improve the thermal efficiency by increasing the operating pressure. To understand what a Supercritical power plant is you have to understand the basics of steam generation. What happens when you heat water at normal atmospheric pressure? There are three stages.
As you go on heating the water, the temperature of water increases till it reaches 100 deg C. This is the Sensible Heat addition.
Further heating does not increase the temperature; instead small bubbles of steam start to form. The temperature remains constant at 100 deg C till all the water becomes steam. The water absorbs the heat without temperature change for conversion to steam. At atmospheric pressure the Latent Heat of vapourisation is 2256 kJ/kg.
Further heating called superheating will increase the temperature of the steam. How high one can go depends on the withstanding capacity of the vessel. What happens when the water is at a higher pressure, say, at 100 bar? Then the boiling takes place at 311 deg C and the latent heat of vaporisation is 1318 kJ/kg. If the water pressure is 200 bar then the boiling takes place at 366 deg C and the latent heat of vaporisation is 584 kJ/kg. As the pressure increases the boiling temperature increases and the latent heat of vaporisation decreases. A further increase in pressure and temperature leads us to a point at which the latent heat of vaporisation is zero, or there is no boiling. Water directly becomes steam. This is the Critical Pressure and the Critical Temperature. For steam this occurs at 374 deg C and 220.6 bar. Conventional steam power plants operate at a steam...
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