Overfire burning is defined as the combustion phenomenon where_____________________?
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Answer: C. burning CO and unburnts in upper zone of furnace by supplying more air
Explanation
Overfire burning involves injecting additional secondary air into the upper furnace zones. This extra oxygen burns unburnt combustible gases and carbon monoxide escaping the main fuel bed. Completing combustion in the upper furnace improves overall boiler thermal efficiency and reduces emissions. Incomplete combustion in solid fuel furnaces often produces carbon monoxide and unburnt hydrocarbon gases. Furnace design must ensure adequate mixing of fuel gases with oxygen at high temperatures. Overfire air jets create turbulent mixing zones that promote complete oxidation reactions.
Industrial coal boilers utilize overfire air systems to comply with strict environmental emission regulations. Boiler operators adjust secondary air ports to optimize combustion efficiency and eliminate smoke. Preventing unburnt fuel losses maximizes the thermal energy extracted from solid fuel. Excess air supply refers to total combustion air rather than targeted upper furnace injection. Excess coal supply would worsen incomplete combustion rather than resolve unburnt gas issues. Fuel bed firing describes primary combustion occurring on grates rather than overfire burning.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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