Following energy conversion processes takes place in coal based thermal power plant
- Conversion of heat energy in to production of steam in boiler.
- Conversion of kinetic energy in steam in to mechanical energy by rotating the steam turbine.
- Converting this mechanical energy of rotation of steam turbine in to electrical energy by rotating the generator by steam turbine.
Working Principle of Coal Based Thermal Power Plant
Thermal power station works on the principle of Rankine cycle which is explained as below along with methods for improving the efficiency of Rankine cycle.
In Rankine cycle working fluid is vaporized to do the work by expansion, after expansion heat is removed to convert it back in to liquid form so that same fluid can be re-circulated in closed cycle.
In coal based thermal power plant Water is used as a working fluid because of its low cost and relatively large value of enthalpy of vaporization
Water at state 1 is pumped in boiler at state point 2 but note that it is not at the saturation temperature corresponding to boiler pressure
Heat must be added to change water at 2 to saturated water at ‘ a ‘( sensible heat)
Then further heat is added to convert it from liquid state to gaseous state i.e. to convert water in to steam from ‘a ‘to state 3 (Latent heat)
This steam at state 3 is passed through turbine where steam expands and rotates the turbine and comes to state 4 in the steam form
To convert back this steam at state 4 to water at State 1, heat from the steam is removed in condenser so that the water could be re-circulated. This process leads to heat loss.
Efficiency = output / input. Here output is work done by steam in turbine and input is heat added in boiler
- Super heating the steam by addition of super heater in boiler and increasing the boiler pressure
- Reducing the pressure of condenser to reduce the heat loss
- Addition of re heater in boiler and addition of intermediate pressure turbine and low pressure turbine
- Addition of low pressure heaters in condensate cycle
- Addition of high pressure heaters in the boiler feed water cycle