What is the min Oxygen percentage should be maintained in boiler, furnace.

What is the min Oxygen percentage should be maintained in boiler for continues combustion process in full load?

O2% in the flue gas after the combustion is called Excess Air (i.e. Excess O2%). This is a way to ensure combustion is complete with sufficient air. Hence O2 in the flue gas is maintained approx 1% at Full load. Understand the combustion process & refer the Optimum combustion zone in the below slides. Hope it is clear.

Minimum 1% needs to be maintain in Full load condition of boiler.

First we should ensure the load condition of boiler. Based on the boiler load, Fuel and air flow needs to be adjusted. So that we will get a proper combustion.

Some times what happens in full load condition of boiler, Readings will go to "0% "of O2 Due to carbon presence in the smoke.

This we can ensure visually through by seeing the Duct smoke itself.

If the smoke colour is observed with "Black" then we suggest customer to increase the air flow rate also this type of problem occurs due to lesser air flow rate and carbon presence in combustion. By increasing the airflow rate carbon presence in the combustion will get reduced.......

Incase smoke colour is observed with "White" it will be due to 50% of load or lesser than the load that time readings will be more than 5% of O2.

Incase Boiler load, Air and fuel flow rate is normal then the smoke colour will observed with "Blue" colour.

Seeing physically we can ensure the combustion of boilers.

Combustion not only based on the feed rate of fuel and air flow, It also depends on Calorific Value of "Fuel".

So Depends on the calorific value of fuel combustion and efficiency of boiler also will varies....