Boiler Energy efficiency tip of the day (Excess O2)

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Boiler-1 Energy efficiency tip of the day (Excess O2)

  1. All combustion requires the correct measure of oxygen; too much or too little can cause undesirable effects. However, the error is almost always intentionally on the high-side (too much oxygen) because the main effect on the high side is low efficiency.
  2. Too little air results in carbon monoxide formation, sooting and even explosion if accumulated soot and other non-combusted suddenly get enough oxygen to rapidly burn.
  3. When boiler burners are manually tuned on a periodic basis, they are typically adjusted to about 3% excess oxygen which is about 15% excess air. This is because there are many ambient and atmospheric conditions that can affect oxygen/air supply. For example, colder air is denser and contains more oxygen than warm air; wind speed affects every chimney/flue/stack differently; and barometric pressure further affects draft.
  4. Therefore, an excess oxygen/air setting at the time of tuning assumes there will still be enough oxygen available for complete combustion when conditions worsen.
  5. From an efficiency standpoint, the excess O2 means there is more air in the combustion stream than there needs to be. That air also contains moisture, and it all is heated and then lost up the stack.
  6. The amount of excess O2 is about directly proportional to the efficiency lost; that is, 3% excess O2 means 3% efficiency drop.
  7. Although it may be possible to monitor and adjust the burner on a daily basis, it is not practical and efficient way to control.
  8. Automatic O2 systems continuously monitor the flue gases and adjust the burner air supply. They are generically called ‘O2 Trim Systems’.
diagram to show the excess air ratios for a combustion process

diagram to show the excess air ratios for a combustion process

Link to download the presentation slide

Magdy Aly

Energy manager, Energy efficiency consultant Passionate to help others to save Energy and Environment.

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3 Responses

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