All fuels consist mostly of atomic Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Sulfur (S),minerals (ash) and water (H2O).
If too much air than what is required for completing combustion were allowed to enter, additional heat would be lost in heating the surplus air to the chimney temperature. This would result in increased stack losses. Less air would lead to the incomplete combustion and smoke. Hence, there is an optimum excess air level for each type of fuel.
if air content is higher than the stoichiometric ratio - the mixture is said to be fuel-lean.
if air content is less than the stoichiometric ratio - the mixture is fuel-rich.
Fuel combustion means to let the molecular Oxygen (O2) in air react with the combustible components of a fuel. As an example the fuel Carbon (C) reacts with O2 of the air to generate Carbon Dioxide (CO2). If the reaction is incomplete Carbon Monoxide (CO), a deadly gas, is generated.
Excess Air, EA = mass of air in kg to combust one kg of fuel/stoichiometric air(Kg air/Kg fuel)
For complete combustion of every one kg of fuel oil 14.1 kg of air is needed. In practice, mixing is never perfect; a certain amount of excess air is needed to complete combustion.
1 Kg of coal will require 7 – 8 kg of air depending upon the hydrogen, carbon, oxygen, nitrogen and sulphur content for complete combustion.
1 Kg of Natural gas will require 9 – 10 kg of air.
Recommended excess air level at full boiler load is given below:
For fuel oil - 10 - 20%
For Natural gas - 10 - 20%
For stoker coal - 35 – 40%
For pulverized coal - 20 – 25%
For optimum combustion of fuel oil, the CO2 or O2 in flue gases should be maintained at 14 – 15.5 % in case of CO2 and 2 – 3.5 % in case of O2.
If an insufficient amount of air is supplied to the burner, unburned fuel, soot, smoke, and carbon monoxide exhausts from the boiler - resulting in heat transfer surface fouling, pollution, lower combustion efficiency, flame instability and a potential for explosion.
If too much air than what is required for completing combustion were allowed to enter, additional heat would be lost in heating the surplus air to the chimney temperature. This would result in increased stack losses. Less air would lead to the incomplete combustion and smoke. Hence, there is an optimum excess air level for each type of fuel.
if air content is higher than the stoichiometric ratio - the mixture is said to be fuel-lean.
if air content is less than the stoichiometric ratio - the mixture is fuel-rich.
Fuel combustion means to let the molecular Oxygen (O2) in air react with the combustible components of a fuel. As an example the fuel Carbon (C) reacts with O2 of the air to generate Carbon Dioxide (CO2). If the reaction is incomplete Carbon Monoxide (CO), a deadly gas, is generated.
Excess Air, EA = mass of air in kg to combust one kg of fuel/stoichiometric air(Kg air/Kg fuel)
For complete combustion of every one kg of fuel oil 14.1 kg of air is needed. In practice, mixing is never perfect; a certain amount of excess air is needed to complete combustion.
1 Kg of coal will require 7 – 8 kg of air depending upon the hydrogen, carbon, oxygen, nitrogen and sulphur content for complete combustion.
1 Kg of Natural gas will require 9 – 10 kg of air.
Recommended excess air level at full boiler load is given below:
For fuel oil - 10 - 20%
For Natural gas - 10 - 20%
For stoker coal - 35 – 40%
For pulverized coal - 20 – 25%
For optimum combustion of fuel oil, the CO2 or O2 in flue gases should be maintained at 14 – 15.5 % in case of CO2 and 2 – 3.5 % in case of O2.
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