U.S. Department of Energy
Washington, DC. USA
Operating your boiler with an optimum amount of excess air will minimize heat loss up the stack and improve combustion efficiency. Combustion efficiency is a measure of how effectively the heat content of a fuel is transferred into usable heat. The stack temperature and flue gas Oxygen (or Carbon Dioxide) concentrations are primary indicators of combustion efficiency.
Natural Resources and Office of Energy
Typically, reducing O2 in the flue gas by 1 percent- for example, from 5 percent to 4 percent- increases boiler efficiency by about 2.5 percent.
Controlling excess air is the most important tool for managing the energy efficiency and atmospheric emissions of a boiler system.
As graph shows, the effect of air temperature on excess air in the flue gas can be dramatic.
Nitrogen oxides (NOx) include various nitrogen compounds like nitrogen dioxide (NO2) and nitric oxide (NO). These compounds play an important role in the atmospheric reactions that create harmful particulate matter, ground-level ozone (smog) and acid rain.
NOx forms when fuels are burned at high temperatures. The two major emissions sources are transportation vehicles and stationary combustion sources such as electric utility and industrial boilers. Power plants account for 21% of the NOx that is emitted world-wide.
National emissions of NOx have actually increased over the past 30 years by about 19 percent.
What are the harmful effects of NOx emissions?
NOx emissions contribute to the formation of fine particles and ozone smog that cost society billions of dollars annually from illnesses and deaths.