Steam Boilers Flashcards
Is Lancashire boiler stationary or movable ?
Stationary
Where is Lancashire boiler used ?
Sugar mills and textile industry
Why should water reserve be high for Lancashire boiler be high ?
Large quantity of steam is needed
Is the Lancashire boiler internally or externally fired ?
Internally fired
How many passes does it have for flue gases ?
3 passes
Why does Lancashire boiler have good steaming quality (allowing for the use of low quality coal) ?
Heats water from three sides
What is the shape of the main shell ?
Cylindrical
What is the cylindrical shell mounted on ?
A brick structure
How many base flue gas lines are there ?
One
How many side flue gas lines are there ?
Two
How many flue tubes does the main cylindrical shell have ?
Two flue tubes
Where are the flue gases generated ?
At the grate
How many grates are there ?
Each flue tube has one
In what manner is the grate supported by a bridge ?
So that ash and coal do not enter the tube
Where do the flue gases go ?
End of the tube and then down
What happens to the flue gases when they reach the front of the boiler ?
Get divided into two streams and pass through side flues
Where do the flue gases go after travelling through the side tubes ?
Expelled to atmosphere through chimney
What should be the water level in the boiler ?
Above the main flue tubes
How is the water heated ?
By the passage of outgoing flue gases
How is fuel combustion controlled ?
Dampers
What do dampers do ?
They reduce the flow of air by partial closing of the passage of the chimney
How are the dampers controlled ?
By chain and pulley block from outside
Where are superheaters kept, when they are provided ?
End of main flue tubes
What the mountings on top of the Lancashire boiler ?
Manhole, safety valve, steam collecting pipe
What are the mountings in front of the Lancashire boiler ?
Pressure gauge and water level indicator
What are the mountings provided at the bottom of the Lancashire boiler ?
Blow off cock
Where is the fusible plug mounted ?
Top of each main flue tube, just above the grate
Why is the efficiency of Lancashire boiler high ?
Because of mountings like economizer, superheater, large heat transfer area
Why is the surface area for the burning of coal reduced ?
The furnaces are inside the flue tubes
What is another disadvantage of Lancashire boiler ?
Occupies a considerable floor area, requiring extensive brick work
Is Babcock and Wilcox boiler a water tube or fire tube boiler ?
It is a water tube boiler
How many headers is the main drum of Babcock and Wilcox boiler connected to ?
Two inclined headers
What is the function of the inclined headers ?
Easy circulation
What are the drum, headers and tubes made up of ?
High quality steel
Why ?
To withstand high pressure and temperature
Why are the headers provided with holes ?
Cleaning, descaling
What does the mud box do ?
Collects sediments which are blown off regularly
Where is the furnace of the Babcock and Wilcox boiler kept ?
Below the front header
How are the flue gases passed ?
They move back, up and front of the water tubes
Why ?
To provide maximum surface area of heat transfer
Why is there a damper below the chimney ?
Control flue gas flow rate into boiler
How does water enter the header ?
From the drum
What happens after the flue gases heat the water ?
The density of water reduces
How does water get circulated ?
By thermosyphon action
What is thermosyphon ?
It is a physical effect and refers to a method of passive heat exchange based on natural convection, which circulates a fluid without the necessity of a mechanical pump.
Where is the superheated steam taken from ?
Main stop valve through superheated header
What is the boiler supported by ?
Metallic slings, or wrought iron girders, supported on pillars
What is the major advantage of Babcock and Wilcox boiler ?
High steam generation capacity
Why can the draft be easily controlled ?
Pressure drop through the boiler of the flue gases is negligible
Why does Babcock and Wilcox boiler have high initial cost ?
Considerable planning and management is required
What is another disadvantage, stemming from it’s big size ?
Most of the components have to be assembled on site
What are the three categories of boiler mountings ?
Safety mounting
Control mounting
Inspection mounting
What are safety mounting ?
Safety valve
Fusible plug
What are control mounting ?
Water level indicators Pressure guage Steam stop valve Blow off cock Feed check valve
What are inspection mountings ?
Manhole
Mudhole
What is the main function of steam stop or junction valve ?
Control flow of steam from boiler to steam pipe
What is used to operate the steam stop valve ?
A hand wheel
What connects the hand wheel to the valve ?
The spindle
What else does the spindle pass through ?
Gland or stuffing box
What does the gland or stuffing box do ?
Stop leakages
What is the main function of a blow off cock ?
Discharge a portion of water from boiler
Why ?
To blow out mud, scale, sediments formed on boiler surface
How is the blow off cock used during repairs ?
TO completely empty the boiler
Where is the blow off cock generally fitted on boilers ?
Bottom
What is a fusible plug ?
A hollow body with a hexagonal flange
What is a flange ?
Internal or external rim for strength
What is it made up of ?
Gun metal
Why does it have a hexagonal flange ?
So that it easily fits into the shell
What is the main function of the fusible plug ?
Protect the boiler from damage when water level is low
What happens when water level is low ?
The steam causes the fusible plug to melt
What happens after it has melted ?
The high pressure steam and water rush through the hole to extinguish the alarm
Are there any other benefits of this ?
It gives an audible warning
Where is it fitted ?
Over the combustion chamber, above the burning fuel
Where are Bourdon pressure gauges mounted ?
On top and in front of the boiler
Why ?
So that they are visible to the operator
What is the general capacity of a pressure gauge ?
About twice the maximum pressure the boiler is expected to handle
How does the Bourdon tube measure pressure ?
It expands in proportion to boiler pressure - atmospheric pressure
How are the pressure guages connected to the boiler ?
Through a siphon tube, connected to an elliptical Bourdon tube, and another siphon tube
How many water level indicators are provided in a normal boiler ?
Two
How are the glass tubes connected to the water and steam levels of the boiler ?
Through metallic tubes which have steam and water cocks
Why is there a parallel metallic tube to the glass tube ?
For safety in case of breakages
What are some boiler accessories ?
Feed pump Economizer Super heater Steam Seperator Air preheater
What is the difference in between a mounting and an accessory ?
Accessories are not compulsory by law (IBR act), but enhance efficiency
