Watertube Boilers

Question 1

In a longitudinal straight tube boiler the downcomer fed

a) “cool” water to the steam drum
b) “hot” water to a riser
c) “cool” water to a rear header
d) “cool” water to a front header
e) “hot” water to the water tubes

Answer 1

c) “cool” water to a rear header

Question 2

A packaged watertube boiler having two mud drums is the

a) “O” type
b) “D” type
c) three drum bent-tube type
d) “A” type
e) Sterling type

Answer 2

d) “A” type

Question 3

High pressure watertubes

a) are always smaller than firetubes
b) are elliptical in cross-section
c) are always straight
d) can be of various bent configurations
e) require pumps for circulation

Answer 3

d) can be of various bent configurations

Question 4

Bent tube watertube boilers

a) cannot have the furnace water-lined
b) make more efficient use of the furnace
c) are externally fired
d) cannot be fitted with heat recovery components
e) have poor utilization of floor space

Answer 4

b) make more efficient use of the furnace

Question 5

A cross drum straight tube boiler
a) could not have higher capacity than a longitudinal drum
unit
b) was usually only of single pass design
c) could have more inclined tubes than a longitudinal drum
unit
d) is a very popular design in today’s plants
e) was internally fired

Answer 5

c) could have more inclined tubes than a longitudinal drum

unit

Question 6

Watertube boilers are better suited to higher pressures
than firetube boilers, because they:
1. incorporate a bent tube design
2. are larger than firetube boilers
3. do not have flat surfaces subjected to pressure
4. usually have smaller diameter tubes
5. have smaller diameter drums
a) 1, 2
b) 1, 3, 5
c) 2, 3, 5
d) 1, 2, 5
e) 1, 3, 4, 5

Answer 6

e) 1, 3, 4, 5

Question 7

The use of bent tube boiler designs allows the furnace wall
to be lined with tubes, thereby exposing more of the heating
surface to
a) convection heat
b) conducted heat
c) radiant heat
d) residual heat
e) latent heat

Answer 7

c) radiant heat

Question 8

The bent tube boiler design allows the tubes to be attached
radially on the outside of the
a) furnace
b) superheater
c) economizer
d) shell or drum
e) air preheater

Answer 8

d) shell or drum

Question 9

Since furnace pressure is often positive on a packaged
watertube boiler, in order to prevent flue gas leakage
a) an induced draft fan is incorporated
b) smoke stacks are made taller
c) an economizer is used
d) a steel casing forms a seal for the furnace
e) sootblowers cannot be used

Answer 9

d) a steel casing forms a seal for the furnace

Question 10

Excessive vibrations caused by inadequate support of a watertube boiler can result in

a) insulation failure
b) water level control problems
c) tube failure
d) drum fracture
e) combustion control problems

Answer 10

a) insulation failure

Question 11

A problem with a D-type watertube packaged boiler is

a) excessive vibration
b) ceiling height requirements
c) refractory maintenance for the external furnace
d) its need to be top supported
e) its poor water circulation

Answer 11

a) excessive vibration

Question 12

A unit which would most likely utilize a cyclone furnace
would be the
a) Sterling watertube boiler
b) steam generator
c) packaged watertube boiler
d) "D" type boiler
e) three drum bent-tube boiler

Answer 12

b) steam generator

Question 13

Large steam generating units may have their superheaters
located:
1. beneath the furnace
2. in the convection zone
3. in the main waterwall header
4. in the radiant zone
5. in the downcomer pipe
a) 2, 4
b) 4, 5
c) 1, 3
d) 1, 2, 5
e) 3, 4, 5

Answer 13

a) 2, 4

Question 14

Large steam generators

a) are bottom supported
b) are fired by pulverized coal only
c) have sluggish water circulation
d) are usually of the water tube type
e) have beaded tubes

Answer 14

d) are usually of the water tube type

Question 15

Large steam generating units are usually built so that high
pressure, high temperature, and dry steam can be generated in
order that
a) more fuel can be fired
b) large steam turbines can be used to drive electrical generators
c) higher furnace temperatures can be attained
d) less water treatment is necessary
e) stack temperatures can be maintained at a high level
to prevent condensation

Answer 15

b) large steam turbines can be used to drive electrical generators

Question 16

A steam generator economizer is usually located

a) between the air preheater and ID fan
b) between the primary and secondary superheaters
c) after the reheater
d) in the furnace section
e) between the air preheater and primary superheater

Answer 16

e) between the air preheater and primary superheater

Question 17

The most economical fuel to burn in a steam generator is

a) natural gas
b) crushed coal
c) heavy fuel oil
d) pulverized coal
e) crude oil

Answer 17

d) pulverized coal

Question 18

Economizers

a) increase the boiler efficiency
b) are installed before the superheater
c) increase the steam temperature
d) increase the air temperature
e) increase the flue gas temperature

Answer 18

a) increase the boiler efficiency

Question 19

Air heaters in a boiler

a) are installed between the superheater and the economizer.
b) reduce the temperature of the flue gases going to the stack.
c) help the boiler from freezing during the winter period.
d) increase the flue gas temperature.
e) maintain a steady higher temperature in the stack

Answer 19

b) reduce the temperature of the flue gases going to the stack.

Question 20

Air heaters are implemented in steam generating units in order
to:
1. recover heat from the hot flue gases
2. improve boiler thermal efficiency
3. produce dryer steam
4. heat the feedwater
a) 1, 2
b) 2, 3
c) 1, 2, 4

Answer 20

a) 1, 2

Question 21

Combustion air for the burners is preheated in the
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ by hot flue gases.
a) economizer
b) air heater
c) superheater
d) windbox
e) furnace

Answer 21

b) air heater