Ch 56 Boiler Draft Equipment

A way of increasing natural draft is to

a) incorporate a forced draft fan

b) have the outside air temperature increase

c) install an induced draft fan

d) increase stack height

e) decrease the amount of excess air

When draft is produced by natural means,

a) hot air surrounding the boiler increases draft

b) fans can control the flue gas flow

c) a short stack will increase draft

d) the diameter of the stack will improve the draft

e) cooler air surrounding the boiler increases draft

Primary air

a) is supplied in the combustion zone

b) is the same as excess air

c) is supplied on all types of burners

d) is pre-mixed with the fuel before being admitted to the furnace

e) enters the furnace before the fuel

A more durable chimney for power plant application is the

a) brick chimney

b) reinforced concrete chimney

c) steel chimney

d) insulated steel chimney

e) guy wire supported chimney

Chimneys are commonly lined with

a) concrete

b) common brick

c) clay

d) mortar

e) insulation

The advantage of a steel stack over a reinforced concrete stack is that a steel stack

a) is more durable

b) requires less maintenance

c) is a lower cost

d) has a longer life

e) is more resistant to abrasive flue gases

Relative to draft, a steam jet is very popular

a) on railway steam locomotives

b) as a fuel atomizer

c) as a forced draft unit

d) for increasing furnace pressure

e) for decreasing draft during cold weather

What are the advantages of mechanical draft?

1. dependent on atmospheric air temperatures

2. independent of the chimney temperature

3. better draft regulation

4. can be regulated accurately

a) 1, 2, 3, 4

b) 1, 2, 3

c) 1, 3, 4

d) 2, 3, 4

e) 3, 4

In a balanced draft system the air heater is placed:

1. between ID fan and stack

2. between ID fan and boiler

3. between forced draft fan and boiler

4. on inlet ducting to forced draft fan

a) 1, 2, 3

b) 2, 3, 4

c) 2, 3

d) 1, 4

e) 1, 3, 4

The most efficient operation of a fan demands that

a) the speed be only sufficient enough to supply the required amount of air

b) inlet damper controls are used

c) outlet damper controls are used

d) constant speed electric motors are used

e) gaseous fuels be fired

Balanced draft

a) means furnace pressure is maintained at some desired value

b) means air flow is always constant

c) requires an FD and ID fan, never just an FD fan

d) can be accomplished with just a chimney

e) means air and fuel quantities are the same per unit time

An induced draft fan

a) is physically smaller than a forced draft fan

b) has less expensive materials of construction than an FD fan

c) handles only air

d) discharges air to the windbox

e) operates at much higher temperatures than an FD fan

A pressurized furnace is usually associated with

a) balanced draft

b) induced draft

c) natural draft

d) packaged boilers with FD

e) large steam generators

Induced draft may be accomplished by a:

1. steam jet

2. fan

3. windbox

4. forced draft fan

a) 1, 2

b) 2, 3, 4

c) 2, 4

d) 2, 3

e) 3, 4

In a balanced draft system, the forced draft fan is

a) larger than the induced draft fan

b) the same size as the induced draft fan

c) smaller than the induced draft fan

d) designed to handle hot combustion gases

e) subjected to the products of combustion and high temperatures

In a forced draft system, the furnace pressure is

a) above atmospheric pressure

b) below atmospheric pressure

c) at atmospheric pressure

d) measured in psi

e) not a factor

With an axial flow fan the air flow

a) is at right angles to the windbox

b) is at right angles to the shaft

c) does not come in contact with the driving motor

d) is the most efficient

e) is parallel to the shaft

A boiler with only an induced draft fan

a) will have a negative furnace pressure

b) does need an airtight furnace

c) needs a very long stack

d) will have a positive furnace pressure

e) cannot maintain a stable fire

Boiler combustion is regulated by

a) varying the speed of an ID fan

b) controlling or regulating the fuel flow

c) varying the speed of an FD fan

d) controlling or regulating the air flow

e) controlling the air and fuel flow

The simplest way of measuring draft is with

a) an inclined manometer

b) a Bourdon tube device

c) a flexible diaphragm device

d) a hydrometer

e) a bellows measuring device

The most efficient operation of a fan occurs when

a) draft is balanced

b) draft is FD only

c) draft is ID only

d) speed is just enough to meet the demand

e) speed is at maximum

When the least amount of energy is desired to drive a fan with variable output control, the type of control used would most likely be

a) variable speed coupling

b) inlet damper control

c) outlet damper control

d) register control

e) variable speed driver

Inlet damper control on a fan

a) is less complicated than an outlet damper control

b) requires more power to drive the fan when the vanes are closed

c) can only be used when the fan is driven by a steam turbine

d) is used on forced draft fans only

e) requires less power to drive the fan at reduced loads

Proper draft is important to the plant operator because it

a) produces efficient combustion

b) delivers the products of combustion to a high altitude

c) reduces the volume of ash and slag

d) prevents toxic gases from leaking out of the system

e) satisfies the codes

With a fan outlet damper control

a) the fan air pressure decreases with a decrease in air flow

b) the fan air pressure increases with a decrease in air flow

c) it is placed in the suction side of fan

d) fan output is difficult to control

e) flue gas velocity will rise

When an air heater is used in a boiler

a) the forced draft fan supplies hot gases to the heater

b) the induced draft fan supplies combustion air to the air heater

c) it increases the efficiency of the boiler

d) the boiler usually has only a forced draft fan

e) a balanced draft system cannot be incorporated

Draft measuring instruments can be used to measure:

1. wind box pressure

2. steam pressure

3. air heater flue gas pressure

4. furnace pressure

5. feedwater pressure

a) 1, 2, 3

b) 3, 4, 5

c) 1, 2, 3, 4

d) 1, 3, 4

e) 3, 4, 5

When a diaphragm draft gauge is used to measure furnace draft

a) furnace draft connections are on both sides of the diaphragm

b) it can only be used on a balanced draft system

c) it can only be used on a forced draft system

d) it can only be used for positive pressures

e) the furnace draft connection is on one side of the diaphragm

Adequate openings for combustion air must be provided in enclosed boiler rooms. These openings

a) may include doors and windows

b) should be located at the top of the room near the ceiling

c) should be located at the bottom of the room near the floor

d) are a standard size for all boilers

e) are only for high pressure boilers

Inclined "U" tubes may be used to measure:

1. fan discharge pressure

2. fan suction pressure

3. air heater flue gas pressure

4. air heater flue gas temperature

a) 1, 2, 3

b) 3, 4

c) 1, 4

d) 2, 3, 4

e) 4

If a "U" tube is connected to the discharge of a forced draftfan the

a) connection to the fan will have a higher liquid level than the open end

b) open end will have a higher liquid level than the connection to the fan

c) liquid level will be the same in both sides of the "U" tubed) liquid will be drawn into the forced draft stream

e) liquid will expand

The inclined tube manometer operates

a) on a different principle than the "U" tube manometer

b) so that only positive pressure can be measured

c) so that only a vacuum can be measured

d) on the same principle as a "U" tube manometer

e) by displacing a compressed gas

Define draft

Two kinds of air supplied to the furnace are?

What's the difference between natural and mechanical draft?

What is aspirating air?

3 ways to increase air or exhaust flow?

Purpose of Forced draft (FD fan)

Purpose of Induced draft (ID fan/High stack)

Balanced draft

5 ways to control the flow of air or flue gas

Does FD fan or ID fan require more power?