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Combined Combined

CycleCycle

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TurbineTurbine

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POWER GENERATION

Thermal Power Plants as the name suggests, these power plants convert heat energy into electrical energy. The workingfluid of these plants is mostly steam and they work on theRankine cycle.

Hydro Power Plants these plants use the kinetic energy of flowing water to rotate the turbine blades, hence convertingkinetic energy into electrical energy.

Nuclear energy Uses nuclear energy for producing steam whichruns the turbine.

Solar energy Solar cells, solar heater. and

Wind energy to generate power.

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Combined Cycle

Gas TurbineAn important field of study for power plants is thatof the combined plant. A broad definition of thecombined power plant is one in which a higher (upper

or topping) thermodynamic cycle produces power, butpart or all of its heat rejection is used in supplying heatto a lower or bottoming cycle.

The upper plant is frequently an open circuit gas

turbine while the lower plant is a closed circuit steamturbine; together they form a combined cycle gasturbine (CCGT) plant.

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Principle :The Joule-Brayton (JB) constant pressure closedcycle is the basis of the cyclic gas turbine power plant, with steady flow of air (or gas) through acompressor, heater, turbine, cooler within a closed

circuit .

The turbine drives the compressor and a generator delivering the electrical power, heat is supplied at aconstant pressure and is also rejected at constantpressure. The temperature-entropy diagram for thiscycle is also

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Usually, a gas turbine plant operates on opencircuit, with internal combustion. Air and fuel pass

across the single control surface into thecompressor and combustion chamber, respectively,and the combustion products leave the control surfaceafter expansion through the turbine.

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Modifications of gas turbinecycles to achieve higher

thermal efficiency.There are several modifications to the basic gas turbinecycle that may be introduced to raise thermal efficiency.

Two objectives are immediately clear. If the top temperaturecan be raised and the bottom temperature lowered, then theratio T = (T min /T max ) decreased and, as with a Carnotcycle, thermal efficiency will be increased (for given p). The

limit on top temperature is likely to be metallurgical whilethat on the bottom temperature is of the surroundingatmosphere.

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Steam Power plant

Nuclear power plant

Combined gas cycle plant

100 35

8

57

0

31

69

100

15

49

36

100Gas cycle plant

68

32

0

100

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Efficiency:A gas turbine generator generates electricity and

the waste heat is used to make steam to generateadditional electricity via a steam turbine; this last stepenhances the efficiency of electricity generation. Most

new gas power plants in North America and Europeare of this type. In a thermal power plant, high-temperature heat as input to the power plant, usuallyfrom burning of fuel, is converted to electricity as oneof the outputs and low-temperature heat as another output. As a rule, in order to achieve high efficiency,the temperature difference between the input andoutput heat levels should be as high as possible

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The Brayton cycle is a thermodynamic cycle that describes the workings of the gasturbine engine, basis of the jet engine and others. It is named after George Brayton(18301892), the American engineer who developed it, although it was originallyproposed and patented by Englishman John Barber in 1791. It is also sometimesknown as the Joule cycle . The Ericsson cycle is similar but uses external heat andincorporates the use of a regenerator.

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The Rankine cycle is a thermodynamic cycle which converts heat into work. Theheat is supplied externally to a closed loop, which usually uses water as the workingfluid. This cycle generates about 80% of all electric power used throughout the world,[1] including virtually all solar thermal, biomass, coal and nuclear power plants. It is

named after William John Macquorn Rankine

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Regenerative Rankine cycle

The regenerative Rankine cycle is sonamed because after emerging fromthe condenser (possibly as a subcooledliquid) the working fluid is heated bysteam tapped from the hot portion of the cycle. On the diagram shown, thefluid at 2 is mixed with the fluid at 4(both at the same pressure) to end upwith the saturated liquid at 7. TheRegenerative Rankine cycle (with minor variants) is commonly used in realpower stations.

http://en.wikipedia.org/wiki/File:Regenerative_rankine_cycle.jpg

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In this variation, two turbineswork in series. The first accepts vapour from the boiler at high pressure. After the vapour has passed through the firstturbine, it re-enters the boiler and is

reheated before passing through asecond, lower pressure turbine. Amongother advantages, this prevents thevapour from condensing during itsexpansion which can seriously damagethe turbine blades, and improves theefficiency of the cycle.

Rankine cycle with reheat

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