The excess air required for the combustion of pulverised coal is of the order of about __________ percent.

Combustion of pulverised coal as compared to that of lump coal

A

Develops a non-luminous flame

B

Develops a low temperature flame

C

Can be done with less excess air

D

Provides a lower rate of heat release

Combustion of pulverised coal compared to the lumpy coal

A

Provides better control of furnace temperature

B

Facilitates combustion with lower excess air

C

Provides higher thermal efficiency & flame temperature

D

All of the above

In case of pulverised coal fired steam boiler, the secondary air serves the main purpose of

A

Transportation of coal

B

Drying of coal

C

Combustion of coal by supplying it around the burner

D

Preheating the primary air

The main function of primary air in pulverised coal fired burner is to

A

Burn CO to CO₂

B

Dry and transport the coal

C

Have proper combustion by supplying it around the burner

D

Preheat the tertiary air used for complete combustion of CO to CO₂

Function of secondary air in pulverised coal firing is to

A

Transport the coal to the burner

B

Dry the coal

C

Ensure efficient burning of coal around the burner

D

Reduce primary air requirement

Use of excess of combustion air in the combustion of fuels results in

A

Heat losses

B

Long flame

C

Condensation of water vapour from the fuel gas

D

None of these

Limestone powder is injected during pulverised coal burning in boilers to __________ the flue gases.

A

Reduce SO₂ content in

B

Catalytically convert SO₂ to SO₃ in

C

Increase the dew point of

D

None of these

Combustion of pulverised fuel

A

Requires larger combustion chamber than rich gaseous fuel

B

In a metallurgical furnace does not contaminate the product in the furnace by ash from fuel

C

Suppresses the discharge of fine dust and grit into atmosphere

D

All of the above

Which of the following is the most important deterrants to an extended use of pulverised coal in boiler firing?

A

Ash disposal problem

B

Excessive fly ash discharge from the stack

C

Higher power consumption in its transportation

D

Erosion of induced draft fan blades

The advantages of firing pulverised coal in the furnace lies in the fact that, it

A

Permits the use of high ash content coal

B

Permits the use of low fusion point ash coal

C

Accelerates the burning rate and economises on fuel consumption

D

All of the above

The excess air required for the combustion of pulverised coal is of the order of about __________ percent.

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