4. In a boiler trial, the following observations were obtained: Mass of feed water =1520kg/h; Temperature of feed water =30C; Dryness fraction of steam =0.95; Pressure of steam =8.5 bar; Coal burnt / hour =200kg; Calorific value of coal =27300kJ/kg of coal; Ash and unburnt coal collected =16kg/h; Calorific value of ash and unburnt coal =3780kJ/kg; Mass of flue gases =17.5kg/kg of coal; Temperature of flue gases =330C; Boiler room temperature =17C; Mean specific heat of flue gases =1kJ/kgK. Estimate the thermal efficiency of the boiler and draw the heat balance sheet