ANS- BOILER EFFICIENCY:Ratio between heat output and heat input,
it's called boiler efficiency.



FORMULA FOR BOILER 
EFFICIENCY:
                    Q*(H-h)/q*GCV
 
Q       : Quantity of steam (kg/hr)
q       : quantity of coal consumption(kg/hr)
H       : Enthalpy of steam(Kcal/hr)
h       : Enthalpy of fead water(Kcal/hr)
GCV     : Gross calorific value of coal