Boiler performance (Part 2) - Boiler efficiency, Boiler trial and Heat balance

In these notes Boiler efficiency, Boiler trial and Heat balance related with Boiler performance are explained.

1. Boiler performance (Part 2) - Boiler efficiency, Boiler trial and Heat balance Presentation by: Avdhesh Tyagi Asst. Prof. Department of Mechanical Engineering G. L. Bajaj Institute of Technology & Management, Greater Noida Disclaimer: The materials provided in this presentation and any comments or information provided by the presenter are for educational purposes only . Nothing conveyed or provided should be considered legal, accounting or tax advice.

2. Name of Subject: Applied Thermodynamics Subject Code: KME401 Department of Mechanical Engineering G. L. Bajaj Institute of Technology and Management, Greater Noida, Uttar Pradesh College code: 192 Affiliated to Dr. A.P.J. Abdul Kalam Technical University (Formerly UPTU Lucknow ). Unit 3 Topic covered: Boiler efficiency, Boiler trial and Heat balance

3. Boiler efficiency It is defined as the ratio of heat actually utilized in steam generation to the heat supplied by the fuel during same time duration. Mathematically Where CV = Calorific v alue of fuel in kJ/kg If Boiler, superheater and economizer are considered as single unit, above formula gives the overall efficiency of boiler plant.  

4. Heat balance sheet A heat balance sheet represents the complete account of heat supplied by 1 kg of dry fuel and the consumption of this supplied heat. The heat supplied is used for steam generation in boiler and the remaining heat is lost. Various heat losses are: Heat lost in dry flue gases Heat lost in moisture in fuel Heat lost due to steam in flue gases Heat lost due to unburnt carbon in ash pit Heat lost due to incomplete combustion Heat lost due to convection, radiation and other unaccounted losses (By difference)

5. Heat balance sheet Heat supplied by fuel Supplied percentage Heat distribution (kJ) Percentage (%) 100% Heat used in steam generation  X1 Heat lost in dry flue gases  X2 Heat lost in moisture present in fuel  X3 Heat lost due to steam in flue gases   X4 Heat lost due to unburnt carbon in ash pit   X5 Heat lost due to incomplete combustion  X6 Heat lost due to convection, radiation and other unaccounted losses (By difference)   X7 = 100 – ( X1+X2+X3+X4+X5+X6) Overall heat supplied 100% Overall heat distribution X1+X2+X3+X4+X5+X6+X7=100 % Heat supplied by fuel Supplied percentage Heat distribution (kJ) Percentage (%) 100% Heat used in steam generation  X1 Heat lost in dry flue gases  X2 Heat lost in moisture present in fuel  X3 Heat lost due to steam in flue gases   X4 Heat lost due to unburnt carbon in ash pit   X5 Heat lost due to incomplete combustion  X6 Heat lost due to convection, radiation and other unaccounted losses (By difference)   X7 = 100 – ( X1+X2+X3+X4+X5+X6) Overall heat supplied 100% Overall heat distribution X1+X2+X3+X4+X5+X6+X7=100 %

6. Boiler trial Boiler trial refers to running the boiler under test conditions for assessment of its performance. The objectives of a boiler trial are: To determine the steam generation capacity of the boiler. To determine the thermal efficiency of the plant while working at a certain pressure. To prepare the heat balance sheet for the boiler . During trial the boiler is generally run for 4 to 6 hours duration so as to attain steady state .

7. Boiler trial Duration of boiler run for attaining steady state changes from boiler to boiler (Oil fired and coal fired types ). Observations are taken after the boiler attains steady state for a duration ranging from 10 to 15 minutes. Measurements are made for fuel supply, combustion analysis, steam generation rate and its quality/state, flue gas and their analysis, temperature and pressure at salient locations and all other measurements as required for heat balance sheet preparation .

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