Secondary combustion air serves the function of ______________________?
Show answer Hide answer
Answer: B. Completely burn the volatile matter
Explanation
Secondary combustion air is introduced downstream to provide the extra oxygen needed for complete combustion. Volatile matter released from solid fuels requires this additional oxygen to burn completely and cleanly. Without secondary air, volatile hydrocarbons would escape unburned as black smoke and soot. Primary air flows through the solid fuel bed, while secondary air is injected into the freeboard above the bed. Volatile matter consists of complex hydrocarbons that vaporize rapidly when coal is heated in a furnace. Staged air introduction helps control nitrogen oxide emissions and ensures thorough high-temperature burnout.
Industrial boiler designers carefully size secondary air ports to achieve turbulent mixing with furnace gases. Proper secondary combustion air management eliminates smoke emissions and maximizes overall boiler efficiency. Operators adjust secondary dampers in response to changes in fuel quality and volatile release rates. Option A describes primary air or conveying systems used to transport pulverized coal through pipes. Option C refers to primary air passing through the grate to burn lumpy solid coal pieces. Option D is incorrect because option B accurately specifies the primary function of secondary air.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
Related questions
Q1. The catalytic agent deployed in a shift converter is _____________________?
Show answer Hide answer
Answer: A. Nickel
Nickel-based catalysts are widely deployed in industrial shift converters and reforming reactors. Nickel accelerates the water-gas shift reaction converting carbon monoxide and steam into carbon dioxide and hydrogen. Thi...
Q2. Flue gas composed volumetrically of CO2 = 25%, O2 = 25%, and N2 = 50% possesses an average molecular weight of___________________?
Show answer Hide answer
Answer: B. 23
The average molecular weight is calculated from the volumetric fractions: 0.25(44) + 0.25(32) + 0.50(28) = 11 + 8 + 14 = 33, wait calculation check: 0.25*44=11, 0.25*32=8, 0.50*28=14, sum = 33. The correct molecular weig...
Q3. A gas mixture with initial composition CO2 = 20%, H2 = 50%, CH4 = 30% has a calorific value y. Shifting the composition to H2 = 50%, CH4 = 30%, CO2 = 10%, N2 = 10% results in a calorific value of___________________?
Show answer Hide answer
Answer: A. y
Replacing carbon dioxide with inert nitrogen does not alter the relative concentrations of combustible gases. Hydrogen and methane percentages remain completely unchanged relative to the total active fuel volume. Since t...
Q4. Natural gas possesses a calorific value roughly around ______________ kcal/Nm3?
Show answer Hide answer
Answer: A. 10,000
Natural gas is composed primarily of methane along with small amounts of higher hydrocarbon gases. The gross calorific value of typical pipeline natural gas is approximately 10,000 kcal/Nm3. This high energy content make...
Q5. The combustion reaction C + O2 = CO2 is classified as ___________________?
Show answer Hide answer
Answer: A. Exothermic
The chemical reaction combining carbon and oxygen to form carbon dioxide releases a large amount of heat. Reactions that release thermal energy to their surroundings are thermodynamically classified as exothermic. This c...
Q6. Gasification represented by C + H2O = CO + H2 is categorized as__________________?
Show answer Hide answer
Answer: B. Endothermic
The gasification reaction between solid carbon and water vapor absorbs thermal energy to proceed. Processes that absorb heat from their surroundings during chemical transformation are termed endothermic. This heat absorp...