Combustion Theory – Efficiency


Understanding Combustion Efficiency

The efficiency of a burner-boiler combination is simply the amount of useful energy leaving the system expressed as a percentage of the chemical energy in the fuel entering the system.

Why should I care about efficiency?

Accounting for the loss of useful energy is an important step in evaluating overall cost.

For instance, a change in efficiency by as little as 5% can have a major impact on the operational expense of a facility. The larger the facility’s consumption of fuel and electricity, the more drastic the cost.

General rules of conservation of energy are:

  • Fuel energy “in” equals heat energy “out.”
  • Energy leaves in steam or in losses.
  • Efficiency + 100% minus all losses.

The typical efficiency of a boiler is 80% to 85%. The remaining 15% to 20% is lost. These losses usually fall in the following percentages:

  • 15% typical “stack loss.”
  • 3% radiation loss.
  • 1% to 2% miscellaneous loss.

The table below shows you how to calculate your cost with your efficiency as the variable.


Operator / Install Tips

Since a burner must be set up to operate cleanly under worst-case conditions, you must provide enough excess air in order to burn any additional fuel that the metering device at the burner may introduce.

You should also ensure that there is sufficient excess air available on a hot, humid summer day. Remember: there is no way to prevent heat and humidity, but with the proper control systems, you should be able to control fuel flow precisely and efficiently.

Other posts in this series:

  • Understanding Local Law 87 – and laws like it
  • Combustion Theory: The Basics
  • Combustion Theory: Variables – Account for variations in oxygen and fuel
  • Combustion Theory: Efficiency – Calculate efficiency and losses
  • Combustion Theory: FGR – See how flue gas recirculation reduces NOx
  • Combustion Theory: Combustion Controls – Learn how cutting-edge tech can cut your emissions
  • Combustion Systems: Design – Basic principles to follow when designing your combustion system
  • Combustion Systems: Troubleshooting: Burner problems and their causes
  • Combustion Control: Strategies – Linkage vs. Linkageless, and why you should care

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