Answer to Question #291511 in Chemical Engineering for vithu

Question

A natural gas-fired boiler operates with 20% excess air. Air is fed at 25 °C and contains 21% O2 and 79% N2 on a volume basis. Natural gas composition: 92.6% CH4, 3.6% C2H6, 0.8% C3H8, 0.3% C4H10, 2.6% N2, 0.1% CO2; GCV: 38.6 MJ/m3 . Molecular weights of C, H, O, N are 12 g, 1g, 16 g and 14 g respectively.

(i) During an energy audit, it was proposed to convert this boiler to a condensing boiler. Do you think it is a viable option? Why? In your discussion, consider the main aspects you should look at during the design and operating phases of a condensing boiler.

(ii) Calculate the amount of condensate formed if a condensing section is added to the boiler so that the flue gas exit temperature is 45 °C. Stack pressure is 1.013 bar.

(iv) Calculate the percentage total energy loss with the flue gas and condensate. The specific heat of the dry flue gas and condensate are 1.2 kJ/m3 K and 4.2 kJ/kg K respectively. Assume the molar volume of the gases as 22.4 m3 /kmol

Answer 1

Answer is given below: