![]() ![]() Fuels - Combustion Air and Flue Gases Combustion air and flue gas for common fuels - coke, oil, wood, natural gas and more.Boiler - Efficiency Combustion gross and net calorific value.Combustion Boiler house topics, fuels like oil, gas, coal, wood - chimneys, safety valves, tanks - combustion efficiency.The chemical equation for methane burned with 25% excess air can be expressed asĬH 4 + 1.25 x 2(O 2 + 3.76 N 2) -> CO 2 + 2 H 2O + 0.5 O 2 + 9.4 N 2 Excess Air and O 2 and CO 2 in Flue GasĪpproximated values for CO 2 and O 2 in the flue gas as result of excess air are estimated in the table below: The additional air is termed excess air, but the term theoretical air may also be used. If more air is supplied some of the air will not be involved in the reaction. The chemical equation for stoichiometric combustion of methane - CH 4 - with air can be expressed asĬH 4 + 2(O 2 + 3.76 N 2) -> CO 2 + 2 H 2O + 7.52 N 2 if air content is less than the stoichiometric ratio - the mixture is fuel-richĮxample - Stoichiometric Combustion of Methane - CH 4.if air content is higher than the stoichiometric ratio - the mixture is said to be fuel-lean.Typical values of excess air are indicated for various fuels in the table below. This excess air level also provides protection from insufficient oxygen conditions caused by variations in fuel composition and "operating slops" in the fuel-air control system. To avoid inefficient and unsafe conditions boilers normally operate at an excess air level. 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. "On-ratio" combustion used in boilers and high temperature process furnaces usually incorporates a modest amount of excess air - about 10 to 20% more than what is needed to burn the fuel completely. Process heating equipment are rarely run that way. ![]() When burned all fuel and air is consumed without any excess left over. The stoichiometric ratio is the perfect ideal fuel ratio where the chemical mixing proportion is correct. To determine the excess air or excess fuel for a combustion system we starts with the stoichiometric air -fuel ratio. With unburned components in the exhaust gas such as C, H 2, CO, the combustion process is uncompleted and not stoichiometric. Stoichiometric or Theoretical Combustion is the ideal combustion process where fuel is burned completely.Ī complete combustion is a process burning all the carbon (C) to (CO 2), all the hydrogen (H) to (H 2O) and all the sulphur (S) to (SO 2). ![]()
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