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Questions and Answers
Which one of the following is the correct equation for calculating excess air?
What is the total air supplied for combustion if the excess air is 4 kg and the theoretical air is 10 kg?
Which of the following factors does NOT affect the required excess air for combustion?
According to the text, what is the effect of too much excess air in combustion?
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According to the text, what is the effect of not enough excess air in combustion?
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According to the text, how much air is required to supply 1 kg of oxygen for combustion?
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According to the text, how much air is required for the complete combustion of 1 kg of carbon?
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Which one of the following equations represents the air-fuel ratio (AF)?
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If the air-fuel ratio for perfect combustion of methane is 17.2, how much air is required to burn 16 kg of methane?
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What is the percent excess air supplied if the air-fuel ratio for methane combustion in a particular boiler is 20.64?
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What is the mass of nitrogen in the flue gases if 2.054 kg of excess air is supplied?
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According to the text, what is the mass of air required for the combustion of 1 kg of hydrogen?
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According to the text, what is the mass of air required for the combustion of 1 kg of sulfur?
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According to the text, what is the theoretical air required for the combustion of carbon, hydrogen, and sulfur?
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If the safe operation of a furnace requires 20% excess air and the theoretical air required is 10.27 kg per kg of fuel, what is the excess air in kg/kg fuel?
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Study Notes
Excess Air Calculation
- The equation for calculating excess air is expressed as: Excess Air = (Actual Air - Theoretical Air) / Theoretical Air × 100%
- If excess air is 4 kg and theoretical air is 10 kg, the total air supplied for combustion is: Total Air = Theoretical Air + Excess Air = 10 kg + 4 kg = 14 kg
Factors Affecting Excess Air
- Factors that do not affect required excess air include fuel type, combustion temperature, and burner design.
Effects of Excess Air in Combustion
- Too much excess air can lead to lower combustion efficiency and higher heat losses due to increased flue gas volume.
- Insufficient excess air can cause incomplete combustion, leading to the formation of carbon monoxide and unburned hydrocarbons.
Air Requirement for Combustion
- To supply 1 kg of oxygen for combustion, approximately 4 kg of air is needed.
- The complete combustion of 1 kg of carbon requires about 3.67 kg of air.
Air-Fuel Ratio (AF)
- The air-fuel ratio is defined by the equation: AF = Mass of Air / Mass of Fuel.
- For perfect combustion of methane with an air-fuel ratio of 17.2, burning 16 kg of methane requires: Air = AF × Mass of Fuel = 17.2 × 16 kg = 275.2 kg of air.
Excess Air Percent Calculation
- The percent excess air supplied for methane combustion with an air-fuel ratio of 20.64 can be calculated as: Percent Excess Air = ((Actual AF - Theoretical AF) / Theoretical AF) × 100%.
Nitrogen in Flue Gases
- If 2.054 kg of excess air is supplied, the mass of nitrogen in the flue gases can be deduced from the composition of air, generally assumed to be about 79% nitrogen.
Mass of Air for Other Fuels
- The mass of air required for the combustion of 1 kg of hydrogen is approximately 34 kg.
- The mass of air required for the combustion of 1 kg of sulfur is about 10 kg.
Theoretical Air Requirements
- The theoretical air required for the combustion processes of carbon, hydrogen, and sulfur varies based on the stoichiometric calculations for each element.
Safe Operation and Excess Air
- If safe operation of a furnace requires 20% excess air, and the theoretical air required is 10.27 kg per kg of fuel, then excess air can be calculated as follows: Excess Air = Theoretical Air × 0.20 = 10.27 kg × 0.20 = 2.054 kg/kg fuel.
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Description
Table 7 - Air Required for Combustion of Hydrogen Quiz: Test your knowledge on the calculation of air required for the combustion of hydrogen. Learn how to determine the mass of air needed for complete combustion and understand the relationship between oxygen and combustion air.
