Thermal Power Plants what are they?How do they Work?

GAS TURBINE POWER PLANTS

WORKING  PRINCIPLE

Compressed air is mixed with fuel and burned under constant pressure conditions. The resulting hot gas is allowed to expand through the turbine and perform work

MAIN COMPONENTS

Compressor : sucks in air form the atmosphere and compresses it to pressures in the range of 15 to 20 bar (1.5-2 MPa). The compressor consists of a number of rows of blades mounted on a shaft. The pressurized air from the first row is further pressurized in the second row and so on. The shaft is connected and rotates along with the main gas turbine.

Combustion chamber : Burn the fuel and produce high pressure high velocity gas (what is similar to the  furnace in the boiler). The hot gas leaves the chamber at the temperature of  14000C -15000C.  The chamber and the subsequent sections are made of special alloys and designs that can withstand this high temperature. The fuel may be kerosene,  Jet fuel  or natural gas

Power turbine :  Extract the energy from the hot gas and turn it.

PROBLEMS

• Compressor is to be started before the plant starts. This need power from the outside
• Pressure losses throughout  the system
• Exhaust velocity is not used
• Energy escape from the system
• Efficiency of the simple gas turbine is very low

HOW TO MAKE IT MORE EFFICIENT?

• Regeneration
• Reheating
• Intercooling

COMBINED-CYCLE POWER PLANT

WORKING PRINCIPLE

• The heat exhaust from the gas turbine is used to heat the water in the boiler.
• Steam is produced and flow to the steam turbine which is coupled with generator.
• Two generators are in operation: one using gas turbine, other   using steam turbine
• This increases the overall efficiency of the power plant

THERMAL POWER PLANTS

Entropy : This is a thermodynamic property that can be used to determine the energy available for useful work in a thermodynamic process

First Law of thermodynamic: The algebraic sum of the work transfer is proportional to the algebraic sum of heat transfer

entropy =Energy/ Temperature

Second law of thermodynamics: Heat cannot, on its own flow from a body of lower temperature to higher temperature

It’s impossible to construct a heat engine which perform one complete cycle and delivers work exchanging heat from a single source.

Enthalpy : This is a measure of total energy of a thermodynamic system

H = U + pV

U-internal Energy of the system

p-pressure of the boundary system

V-volume of the system

RANKINE CYCLE