Supercritical CO2 Tech Team
Conventional steam power plants operate at a steam pressures in the range of bar. These are Subcritical power plants. The new generation of power plants operate at pressures higher than the critical pressure. These are Supercritical power plants. Supercritical (SC) and ultra-supercritical (USC) power plants operate at temperatures and pressures above the critical point of water, i.e. above the temperature and pressure at which the liquid and gas phases of water coexist in equilibrium, at which point there is no difference between water gas and liquid water.
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 whhat of steam generation. As you go on heating the water, the temperature of water increases till it reaches deg C. This supercritial the Sensible Heat addition. Further heating does not increase the temperature; instead small bubbles of steam start to form.
The temperature remains constant tevhnology deg C till all the water becomes steam. The water absorbs the heat without temperature change for conversion to steam.
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 bar? As the pressure increases the boiling temperature techhnology 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 deg C and Conventional steam power plants operate at a steam pressures supercriticsl the range of bar.
These are Subcritical power plants. The new generation of power plants operate at pressures higher than the critical pressure. These are Supercritical power plants. The operating pressures are in the range of to bar. The efficiency of the Rankine cycle depends on the pressure at which it operates.
Higher pressure and temperature increase the efficiency of the thermal cycle and power plant. This is the reason for operating at higher steam pressures. In the quest for higher efficiency the trend is to go for still higher operating pressures.
The next generation ih power plants will operate with steam Pressures in technoloogy range of bar. These are the Ultra Super Critical What does iu stand for plants. Ultra Supercritical Units operate at temperatures of to deg C. Page content. What happens when you heat water at normal atmospheric pressure? Ultra Supercritical Power Plants.
Advanced ultra-supercritical technology (SteamH) GE is first-to-market with advanced ultra-supercritical (AUSC) technology, and we’re calling it SteamH. GE’s SteamH combines the world’s leading steam plant technology operating at advanced ultra-supercritical conditions with digital power plant software powered by . Supercritical carbon dioxide is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure. Carbon dioxide usually behaves as a gas in air at standard temperature and pressure (STP), or as a solid called dry ice when frozen.
Supercritical power plants were in service from the late fifties. But the technology did not really take off due to problems of reliability especially from the metallurgical aspect. The single most important factor that determines the use of higher and higher pressure and temperatures are the availability of materials to withstand these conditions. Increases in operating pressure and temperatures have to go hand in hand with developments in metallurgy.
With more than units in service the reliability issue seems to be resolved. Supercritical units are the standard for future power plants in many countries including China. The main advantage and the reason for a higher pressure operation is the increase in the thermodynamic efficiency of the Rankine cycle. Most of the Supercritical units use the once through technology. This is ideal for sliding pressure operation which has much more flexibility in load changes and controlling the power grid.
In subcritical units the drum acts as a fixed evaporation end point. The furnace water walls act as the evaporator. Not so in the case of a supercritical unit. The evaporation end point can occur in various levels of the furnace depending on the boiler load. The percentage of Superheat in supercritical units is higher than subcritical units. Because of this the furnace tubes act more as superheaters than waterwalls. This necessitates the use of higher grade of materials like alloy steels in the furnace.
Higher steam temperatures in supercritical units results in a lesser differential temperature for heat transfer. Because of this heat transfer areas required are higher than subcritical units. Higher Superheat steam temperatures entering the HP turbine also mean higher reheater inlet temperatures which again results in a higher heat transfer areas. In supercritical units the water entering the boiler has to be of extremely high levels of purity.
Supercritical boilers do not have a steam drum that separates the steam and the water. If the entering water quality is not good, carry over of impurities can result in turbine blade deposits. Supercritical power plants use special high grade materials for the boiler tubes. The turbine blades are also of improved design and materials. In fact, the very increase in higher pressure and temperature designs are dependendent on the development of newer and newer alloys and tube materials.
Page content. What next?