5 replies to this topic

[Chem32]

Dear sir,

 

If we decrease the excess air, will the stack temperature reduce?

 

[Bobby Strain]

You should not care. What you will do is reduce fuel consumption.

 

Bobby

[Neelakantan]

the stack temperature would tend to rise, assuming complete combustion is already achieved.

neelakantan

[ankur2061]

Sarathkumar,

 

The major concern related to excess air is the increase of NOx emissions from the stack with higher percentage of exces air and with environmental emission regulations getting stringent by the day, excess air needs to be controlled within limits.

 

Ideally the excess air should be between 3-7% above the stoichiometric requirement.depending on the type of burner. O2 analyzers installed in the flue gas exit duct can be utilized for excess air trimming to maintain the optimum O2 level in the flue gas.

 

Regards,

Ankur.

[PKS]

Mr. Sarath

 

Excess air is used to ensure complete combustion and as above said by Mr. Ankur, it shall be within the stipulated limits (approx. between 3-7% as above said in Ankur's post)

 

1) I want to add here that, if we push air in excess of the stipulated limit, it may lead to overall energy loss from the Fired heater, hence more fuel is to be burnt to maintain, the Coil Outlet Temperatures.

 

2) Excess air, if reduced below the required, may lead to incomplete combustion, which in-turn may lead to inefficient operation of the fired heater.

 

3) In some rare or frequent cases (Operations people best to tell) of incomplete combustion there are chances of "After Burning" in the convection section, which may lead to increase in stack temperature, means reducing excess air below required may increase the stack temperature.

 

Hope it helps!!  

 

Thanks

PKS

[Chem32]

Thanks all of you for your replies.

Edited by sarathkumar, 29 May 2014 - 09:07 AM.