The four circuits of the thermal power plant make a complete picture when put together helping to generate electricity out of fuels such as coal which is the most widely used fuel. The calorific value of coals depends on the quality of the coal and the place from where it is mined.
Let us perform a simple calculation regarding the amount of coal required in a power plant.
Let us assume an imaginary thermal power plant which has a capacity of 1000 MW and try to find the amount of coal required for its consumption. Also assume that the boiler operates at an efficiency of 75% and the heat supplied per kg of steam be around 500 kcal per kg and that the amount of steam required per kWh is nearly 5 kgs. Further let us assume that the type of coal used in the plant has a calorific value of 5000 kcal/kg
Then the quantity of coal required per hour would be given by
Weight of Coal Required ==> Capacity * Steam Requirement * Heat Delivered/Calorific Value of Coal * Efficiency of Boiler
==> {1000 * 1000 * 5 * 500}/{5000 * 0.75 * 1000} = 666 tons/hr
Normally it is a practice to store coal for upto one month usage in case the power plant is situated at a sufficient geographical distance from the coal source so that in case of any disruption of the transportation system, the region is not immediately affected. You can calculate that in case the above plant requires such a facility, we would require space to store and handle nearly 480, 000 tons of coal.
Coming back to the actual operation this coal is then fed to the combustion chamber of the boiler where steam is generated giving rise to hot exhaust gases and ash which are handled by their respective circuits. The steam turbine is driven by the steam which converts this thermal energy into the mechanical energy and is coupled with an electric generator to convert it to electrical energy.
The electricity generated through the generator coupled to the turbine is then fed to the main grid via a system of transformers and other electrical equipment and is usually taken to far off places via high voltage transmission lines before it is actually supplied in the domestic or industrial sectors at their respective voltage levels.
Hence we see that how the energy hidden within the ordinary coal is harnessed through the use of a thermal power plant to light our homes and industries.
