Ceramic recuperators (made of SiC) is economical, only when used for preheating combustion air above __________ °C.

Ceramic recuperators compared to metallic recuperators for the same duty

A

Are lighter

B

Occupy more space

C

Are less costly

D

Have higher pressure differential between flue gas & air side

Ceramic recuperators used for waste heat recovery from high temperature flue gas going out of the furnace is made of

A

Fireclay

B

Silicon carbide

C

Corrundum

D

Siliceous fireclay

Ceramic recuperators are generally made of

A

Silicon carbide

B

Calcium carbide

C

Fireclay bricks

D

High alumina bricks

Metallic recuperators are not used for waste heat recovery, if the hot flue gas temperature is above __________ °C, because corrosion prevails at higher temperatures.

A

350

B

750

C

1050

D

1250

Preheating of combustion air is done to

A

Increase the adiabatic flame temperature

B

Increase the calorific value of the fuel

C

Complete the combustion of fuel

D

Reduce its requirement for effecting the complete combustion

Regenerators compared to the recuperators for the same duty

A

Occupy more space

B

Are less costly

C

Are of smaller size

D

All of the above

Regenerators as compared to recuperators for the same duty

A

Store smaller quantity of waste heat

B

Are lighter & compact

C

Involve higher initial cost

D

All of the above

The thermal efficiency of an air/fuel gas preheating recuperator may be as high as __________ percent.

A

50

B

65

C

85

D

99

Preheating of __________ the flame temperature.

A

The gaseous fuel before combustion decreases

B

Combustion air decreases

C

Either the fuel or the air or both, increases

D

Either the fuel or the air does not affect

Preheating temperature of medium viscosity furnace oil for better atomisation through burner is about __________ °C.

A

50

B

70

C

90

D

140

Ceramic recuperators (made of SiC) is economical, only when used for preheating combustion air above __________ °C.

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