CBST 6009 - Combustion and Draft (Chp 13)

Question 1

Insufficient air for combustion will result in:

1. Sulfur monoxide in the flue gases
2. High oxygen reading in flue gases
3. Lower than normal oxygen reading in flue gases
4. High CO in flue gases
5. Higher than normal flue gas temperature

A) 1, 2, 3
B) 1, 3, 5
C) 3, 4, 5
D) 1, 3, 4
E) 2, 3, 4

Answer 1

D) 1, 3, 4

1. Sulfur monoxide in the flue gases
2. Lower than normal oxygen reading in flue gases
3. High CO in flue gases

Question 2

Combustion of a fuel in a boiler furnace:

A) Should be performed with a minimum of excess air
B) Is perfect if there is no moisture in the stack gases
C) Requires a higher air-fuel ratio than a diesel engine
D) Requires a higher air-fuel ratio than a gas turbine
E) Requires mechanical draft

Answer 2

A) Should be performed with a ‘‘MINIMUM OF EXCESS AIR”

Question 3

Proper draft is important to the plant operator because it:

A) Satisfies the codes
B) Delivers the products of combustion to a high altitude
C) Prevents toxic gases from leaking out of the system
D) Produces efficient combustion
E) Reduces the volume of ash or slag

Answer 3

D) Produces efficient combustion

Question 4

In a forced draft system, the furnace pressure is:

A) Below atmospheric pressure
B) Measured in psi
C) Above atmospheric pressure
D) At atmospheric pressure
E) Not a factor

Answer 4

C) ‘‘Above’’ atmospheric pressure

Question 5

A pressurized furnace is usually associated with:

A) Packaged boiler with forced draft
B) Natural draft
C) Balanced draft
D) Large steam generators
E) Induced draft

Answer 5

A) Packaged boiler with forced draft

Question 6

The combustible elements in fuels are:

1. Carbon
2. Sulphur
3. Ash
4. Nitrogen
5. Hydrogen

A) 1, 2, 5
B) 2, 3, 5
C) 1, 4, 5
D) 1, 2, 3
E) 3, 4, 5

Answer 6

A) 1, 2, 5 (Carbon,Sulphur,Hydrogen)

Question 7

Inlet damper control on a fan:

A) Is used on forced draft fans only
B) Is less complicated than an outlet damper control
C) Can only be used when the fan is driven by a steam turbine
D) Regulates the amount of air entering the fan
E) Requires more power to drive the fan when the vanes are closed

Answer 7

D) ‘‘Regulates’’ the amount of ‘‘air entering the fan’’

Note: Entering the Fan

Question 8

An induced draft fan:

A) Is physically smaller than a FD (forced draft) fan
B) Operates at much higher temperatures than an FD fan
C) Handles only air
D) Has less expensive materials of construction than an FD fan
E) Discharges air to the windbox

Answer 8

B) Operates at much higher temperatures than an FD fan

Question 9

A continuous flow of air and gas through a boiler is produced by a:

A) Flow difference
B) Specific gravity difference
C) Velocity difference
D) Pressure difference
E) Viscosity difference

Answer 9

D) Pressure difference

Question 10

The refining process for fuel oils involves separating the crude oil into end products, which have distinguishing characteristics such as specific gravity, viscosity, and:

A) Odour
B) Solids content
C) Boiling point
D) Colour
E) Heating value

Answer 10

C) Boiling point

Question 11

Combustion air openings are required by code. Combustion air can be said to be:

A) Atomising air
B) All air which contributes to the completion of combustion
C) Excess air
D) All air which enters the boiler furnace including high excess air
E) All air which contacts the raw fuel before the burner

Answer 11

B) All air which contributes to the completion of combustion

Question 12

What are the “advantages” of mechanical draft?

1. Dependent on atmospheric air temperature
2. Independent of the chimney temperature
3. A smaller chimney can be used
4. More definite draft control is possible

A) 1, 3, 4
B) 1, 2, 3, 4
C) 3, 4
D) 1, 2, 3
E) 2, 3, 4

Answer 12

E) 2, 3, 4

“independent, smaller, definite”

Question 13

The draft through a natural draft furnace is increased by:

A) Decreasing the height of the stack
B) Reducing the firing rate
C) Increasing the temperature of the stack
D) Warming the outside air
E) Decreasing the furnace temperature

Answer 13

C) Increasing the temperature of the stack

Question 14

Carbon monoxide is both combustible and:

A) Expensive
B) Grey in colour
C) Inert
D) Non-compressible
E) Undesirable

Answer 14

E) Undesirable

Question 15

CO₂ is the chemical symbol for:

A) Carbon monoxide
B) Carbon
C) Carbonic acid
D) Hydrocarbon
E) Carbon dioxide

Answer 15

E) Carbon dioxide

Question 16

A boiler with only an “induced draft fan”:

A) Will have a positive furnace pressure
B) Cannot maintain a stable fire
C) Will have a negative furnace pressure
D) Does need an airtight furnace
E) Needs a long stack

Answer 16

C) Will have a NEGATIVE furnace pressure

Question 17

Carbon, which is “not combined with hydrogen”, is referred to as:

A) Loose carbon
B) Non-united carbon
C) Mono-carbon
D) Fixed carbon
E) Separate carbon

Answer 17

D) Fixed carbon

Question 18

The main disadvantage of oil in comparison to coal is that it:

A) Does not burn as cleanly
B) Requires more storage space
C) Is more expensive
D) Is harder to control its flow to the furnace
E) Requires more handling equipment

Answer 18

C) Is more expensive

Question 19

Boiler combustion is regulated by:

A) Varying the speed of an ID fan
B) Controlling or regulating the fuel flow
C) Controlling or regulating the air flow
D) Varying the speed of an FD fan
E) Controlling the air and fuel flow

Answer 19

E) Controlling the air and fuel flow

Question 20

Soot can be caused by:

A) Too much nitrogen in the air
B) High temperature combustion air
C) Insufficient combustion air
D) Too much combustion air
E) Too high a boiler pressure

Answer 20

C) Insufficient combustion air

Question 21

The main components of natural gas supplied to the consumer are:

A) Ethane and butane
B) Methane and carbon
C) Methane and ethane
D) Methane and propane
E) Propane and butane

Answer 21

C) Methane and ethane

Question 22

If a “U” tube is connected to the discharge of a forced draft fan the:

A) Open end will have a higher liquid level than the connection to the fan
B) Liquid level will be the same in both sides of the “U” tube
C) Liquid will be drawn into the forced draft stream
D) Connection to the fan will have a higher liquid level than the open end
E) Liquid will expand

Answer 22

A) Open end will have a “higher liquid level” than the connection to the fan

Question 23

The amount of air required to supply just enough oxygen for complete combustion is called the:

A) Primary air
B) Secondary air
C) Exact air
D) Theoretical air
E) Perfect air

Answer 23

D) Theoretical air

Question 24

Which of the following advantages does oil have over coal as a boiler fuel?

1. Requires less storage space
2. Requires less handling equipment
3. Burns more cleanly
4. More abundant than coal

A) 3, 4
B) 2, 3, 4
C) 1, 3, 4
D) 1, 2, 4
E) 1, 2, 3

Answer 24

E) 1, 2, 3

less storage, less handling, more cleanly

Question 25

Natural draft is produced in a boiler furnace when:

A) Gases are heated; they tend to contract so that each cubic metre has more mass
B) Hot flue gases are condensed
C) Gases in the stack have less mass than an equal column of outside colder air
D) The dampers are fully closed
E) Gases in the stack have more mass than an equal column of outside colder air

Answer 25

C) Gases in the stack have less mass than an equal column of outside colder air

Question 26

Furnace explosions may be caused by:

A) Failure of boiler safety valve
B) High steam pressure
C) Scale and sludge buildup
D) Insufficient purge
E) Overheating of surfaces due to low water level

Answer 26

D) Insufficient purge