A steam power station uses 2 kg of coal per kWh of electrical energy generated. What is the calorific value of coal if the overall efficiency of the plant is 20%?

Concept

The efficiency of a coal is given by:

\(η={Output \space energy \over Input \space energy}\times 100\)

Let CV be the calorific value of coal in kcal/kg. The total energy input from n kg of coal:

Total Input Energy = n × CV

\(η={Output \space energy \over n\times CV}\times 100\)

Calculation

Given, η = 20% = 0.2

Coal consumption = 2 kg per kWh

Output energy = 1 kWh = 860 kcal (since 1 kWh = 860 kcal of useful energy)

\(0.2={860\over 2\times CV}\)

CV = 2150 kcal/kg