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SUPER CRITICAL THERMAL POWER PLANTS

Supercritical Thermal Power Plants in India

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With technological advancements in the area of power generation, the world too has it easy. With increased awareness

on carbon and its side effects, the importance of reducing carbon emissions and increasing the overall efficiency of

thermal power plants have become utmost concerns in the mind of scientists. Supercritical thermal power plants

stemmed from this concern for the environment.

Supercritical thermal power plants have greater power output and higher efficiency levels. Supercritical thermal power

plants also have the best pollution control technology.

Supercritical thermal power plants function at a very high temperature of 580 degree centigrade and pressure of 23 MP

a. This results in a heat efficiency of 45% as compared to the 40% generated by sub - critical coal fire plants.

Supercritical thermal power plants have many advantages like:

Improved efficiency in plant functioning

Reduced fuel costs

Less environmental pollution due to less CO2 emission

Plant cost less than other coal thermal power plant technologies

Low NO x, SO x and emission of other particles

Can be integrated with CO2 capture technology.

In a supercritical thermal power plant, the drum boilers are replaced by once-through boilers, which increase the

efficiency by at least 3% without any extra cost. These boilers are also better designed to withstand frequent load

variations. A wide range of fuels have been tried and tested in once- through boilers in a supercritical power plant. The

pollution levels are reduced by burning much less coal per megawatt-hour. The kilowatt-hour produced per kg of coal

burnt in a supercritical power plant increases with fewer emissions.

As more and more plants adopt supercritical thermal power plant technology, they benefit tremendously by improving

the lower heating value from 40% to more than 45% and also by reducing the emissions of CO2, NO x, SO x and

particulate

matters.

Supercritical is a thermodynamic term that explains the state of a substance where there is no distinction between the

liquid and gaseous state. When water is heated beyond boiling point, the temperature remains constant at 100 degree C

until all the water is converted to steam. Further heating will increase the temperature of the steam. Increase in pressure

increases the boiling temperature and the latent heat of vaporisation decreases. As you keep on increasing the

temperature and pressure, it leads to a stage where the latent heat of vaporisation is zero and the boiling stops. Water

directly becomes steam. This is Critical Pressure and Critical Temperature.

Supercritical thermal power plants operate at pressures much higher than critical pressure. The operating pressures are

in the range of 230 to 265 bar. The efficiency of a supercritical power plant is determined by how much of the energy

that is fed into the process is converted into electrical energy. If the energy input in a supercritical power plant remains

constant, increasing the temperature and pressure will increase the output. Supercritical thermal power plants work onthis theory.

Supercritical thermal power plants can use various turbine designs, which can give more output due to its elevated

temperature and pressure. However, special care has to be taken while selecting materials for the high-pressure turbine

section and the wall of the turbine.

Supercritical thermal power plants perform better with good steam conditions. Steel with 12% chromium content gives

up to 30 MP a/600C/620C steam condit ions. Austenite, an expensive material gives up to 31.5 MP a/620C/620C.

Nickel based alloys give 35 MP a/700C/720C providing a power efficiency of up to 48%.

The pressure and temperature can be increased further more in Ultra Supercritical Steam Condition. Raising the

temperature to 760C and pressure to 42 MP a, the thermal efficiency can be increased by about 4%.

Now, supercritical thermal power plants are set up as integrated plants with CO2 capture facilities. CO2 had been tried

and tested by many countries to increase oil production in the oil fields.

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