41.In a fire tube boiler how are tubes secured in a tube sheet and why? In a water tube boiler how are tubes secured in a tube sheet and why? In a water tube boiler why are only some of the tube ends beaded? BOW 2-3-4
In a fire tube boiler they are rolled then beaded to prevent heat damage and to keep them from pulling out.
In a water tube boiler hey are rolled then flared to keep them from pulling apart.
For drainage of the top drums and to prevent air pockets in the lower drums.
- Is it necessary to brace or stay a flat surface? Name three types of stays. SPO 6 BOW 2-3-4
YES. To overcome the force on heads and flat surfaces. Where there are no tubes, braces and stays must be provided to prevent bulging of the boiler plate.
Through bolt, Stay bolt, Diagonal stay,
Gusset stay, Girder stay, Jaw stay, T stay, J stay, Y stay, Crowfoot stay, Palm stay, Head brace, Screw, Vertical bar stay, Roof stay, End brace
- Describe a through stay. Why are hollow stay bolts used on water legs? SPO 6 BOW 2-3-4
A THROUGH stay runs from one tube sheet to the other or from one flat surface to another.
A rod threaded on both ends is held in place with nuts on the inside tightened against nuts on the outside of the plates. A small hole is drilled into the stay bolt so if it failed, a leak will develop and be detected at once.
- Describe a diagonal and gusset stay. Where would each be used? SPO 6 BOW 2-3-4
A DIAGONAL stay is made of flat material similar to the boiler shell and is attached directly to the boiler shell and head or tube sheet.
A GUSSET stay consists of boiler plate riveted to the shell and head or tube sheet by means of angle iron. They are more rigid.
Both are used to brace right angle surfaces.
- Why are handholes and manholes made oval instead of round? What are the minimum sizes for manhole and handhole openings? SPO 6-7-8 BOW 2-3-4
So they can be inserted into and removed from their respective openings in the boiler. MANHOLE = 11x15 or 10x16. HANDHOLE = 2-3/4 x 3-1/2
- What is thermal efficiency and what is a good percentage? SPO 7-8 LPB 2-3 BOW 3
It is the ratio of heat supplied by the fuel to heat absorbed by the boiler.
A good percentage is 85%
- How do you determine boiler capacity and what is boiler heating surface? SPO 6-7-8
Total heating surface determines the capacity of the boiler.
Heating surface is any area that has hot gases on one side & boiler water on the other and is MEASURED FROM THE FIRE SIDE.
- What is furnace volume? Is furnace volume measured in square feet or cubic feet? SPO 6-7-8 BOW4
Furnace volume is the space available for complete combustion of the fuel before the products of combustion enter the heat absorbing sections of the boiler. This varies with the type of fuel used.
It is measured in cubic feet.
- What is superheated steam? Does its temperature rise? SPO 6-7-8 BOW 2-3-4
It is steam that has been heated to a higher temperature but its pressure remains the same.
Yes. Its temperature does rise.
- Define flash point, ignition point, and pour point. SPO 7-8 LPB 3 BOW 2-3-4
FLASH POINT is the lowest temperature at which vapors of a substance will make a flash of flame but not continue to burn when exposed to an open flame.
IGNITION POINT is the lowest temperature at which vapors of a substance will ignite and burn continuously when exposed to an open flame.
POUR POINT is the lowest temperature at which liquid will flow.
- Define combustion. SPO 6-7-8 LPB 2-3
Combustion is a CHEMICAL REACTION between oxygen and combustibles. It is the process of rapid OXIDATION by which heat stored in fuel is liberated
- What is Rate of combustion? Do air and fuel have any relationship in figuring the rate of combustion? SPO 6-7-8 BOW 3-4
The rate of which heat is released from a fuel.
YES. When oxygen and combustibles are mixed in definite proportions, at an elevated temperature and given proper time, they will combine completely
- Define primary air, secondary air and excess air. Is secondary air necessary in a boiler and why? SPO 6#» LPB M BOW 2-3-4
PRIMARY AIR enters the furnace with the fuel and determines the rate of combustion.
SECONDARY AIR creates a turbulence around the fuel to complete the burning process.
EXCESS AIR is more than what is theoretically needed for complete combustion.
YES. Secondary air is introduced above the fuel bed to burn combustible gases.
- What are the three T’s of combustion? SPO 6-7-8 LPB 2-3 B0W24-4
Time Temperature Turbulence
- Define PSI, PSIG and PSIA SPO 6-7-8 LPB 2-3 BOW 2-3-4
POUNDS PER SQUARE INCH – Pressure exerted on a surface
POUNDS PER SQUARE INCH GAUGE – Pressure that is read on a gauge
POUNDS PER SQUARE INCH ABSOLUTE – Gauge reading plus atmospheric pressure.
- Could too much secondary air have a bad effect on the efficiency of a boiler? SPO 6-7.8 LPB 3 BOW 2-3-4
YES. Excess secondary air will not enter into the reaction and will pass through the furnace wasting heat out of the stack.
- What percent of air is oxygen by volume and what percent by weight? SPO 6-7-8
By Volume, Oxygen is 21%
By Weight, Oxygen is 23%
- Define perfect, complete and incomplete combustion. SPO 6-74 LPB 2-3 BOW 2-3-4
PERFECT COMBUSTION - The burning of all the fuel using only the theoretical amount of air.
COMPLETE COMBUSTION – The burning of all the fuel using more than the theoretical amount of air.
INCOMPLETE COMBUSTION – When a portion of the fuel remains unburned because of insufficient amounts of air.
- What is excess air? SPO 6-7-8 LPB 2-3 BOW 2-3-4
The amount of air that is above what is theoretically needed for complete combustion.
- In a flue gas analysis, what do you consider a good percent of C02? SPO 6-7-8 LPB 3 BOW 2-34
12% to 15% with 20% ideal, but mostly unattainable
