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# Excess Air In Fired Heaters

6 replies to this topic
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### #1 Divid Kelin

Divid Kelin

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Posted 13 July 2021 - 01:07 AM

Hi guys ,
I need help how I can calculate the excess air required for fired heater natural draft?

### #2 latexman

latexman

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Posted 13 July 2021 - 06:10 AM

Total amount of air - Stoichiometric amount of air to burn the fuel = Excess air

### #3 Pilesar

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Posted 13 July 2021 - 06:25 AM

For an existing fired heater, the correct amount of excess air is found by observation and measurement. Observe the flame. Measure the carbon monoxide and oxygen in the flue gas. Adjust the air flow to optimize. To estimate the optimal amount of air during the design, use past experience for the type of burner and heater. The manufacturers may supply an expected range. If you are asking how to determine the flow rate of air required, you first calculate the theoretical amount of air for complete combustion of the fuel and the excess air is usually described as a percentage of that amount.
What help are you asking for? The formula, the math, the measurements, or what?

### #4 breizh

breizh

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Posted 13 July 2021 - 08:02 AM

Hi,

To support your calculation , a doc attached .

Note : For existing unit let you try an ORSAT  testing equipment  to optimize the combustion .

Good luck

Breizh

### #5 Pilesar

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Posted 13 July 2021 - 12:15 PM

https://www.cheresou...ir-calculation/

### #6 Divid Kelin

Divid Kelin

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Posted 14 July 2021 - 04:10 AM

Thanks for sharing
Yes I am looking for calculation
Heat duty 61G cal/hr
10% excess of air which corresponds to 2.09/1.7% vol. dry/wet basis O2 in flue gases
Dear Pilesar
The document which you sent is very useful but we have Fuel gas instead of Fuel oil

### #7 Pronab

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Posted 13 August 2021 - 01:59 AM

Since it is natural draft furnace, difficult to verify amount of excess air. Observe the burner flame color. There might be O2 analyzer in flue gas. It should be within 3% O2 in flue gas. Analyzer should work fine, otherwise depend on the flame color, and CO/O2in flue gas.