chapter 1. steam boilers Flashcards
what is a boiler
is a closed vessel used for heating water to generate steam by direct application of heat from combustion fuels or electricity.
what is enthalpy
The total heat in steam from a specific point (usually 32°F)
what ASME means
American Society of Mechanical Engineers
what ASME does
governs and controls the construction and installation of boilers
Power boiler symbol
s
Boiler assembly symbol
a
Electric boiler symbol
e
Miniature boiler symbol
m
Pressure piping symbol
pp
Safety valve symbol
v
Heating boiler symbol
h
what is a Hot water supply boiler
a low pressure hot water heating boiler having a volume exceeding 120 gal., a heat input exceeding 200,000 Btu/hr, or an operating temperature exceeding 200°F that provides hot water to be used externally to itself
what is a Low pressure hot water heating boiler
a boiler in which water is heated at pressures not exceeding 160 psi and temperatures not exceeding 250°F
what is a Low pressure steam heating boiler
a boiler operated at pressures not exceeding 15 psi for steam
what is a Power hot water boiler (high temperature water boiler)
a boiler used for heating water or liquid to a pressure exceeding 160 psi or to a temperature exceeding 250°F
what is a Power steam boiler
a boiler in which steam or other vapor is generated at pressures exceeding 15 psi
what is a Small power boiler
a boiler with pressures exceed-ing 15 psi but not exceeding 100 psi and having less than 440,000 Btu/hr heat input
what is a A low pressure steam boiler
is a boiler that operates at a maximum allowable working pressure (MAWP) of not more than 15 psi.
what are the type boilers
firetube, watertube, and cast-iron sectional boilers
what is a A high pressure steam boiler
is a boiler that operates at a maximum allowable working pressure (MAWP) of more than 15 psi.
what is a power boiler
is a high pressure boiler that operates a MAWP of more than 15 psi
what is a boiler horsepower (BHP)
is the amount of energy equal to the evaporation of 34.5 lb of water/hr from and at a feedwater temperature of 212°F.
what is a firetube steam boiler
is a boiler in which hot gases of combustion pass through tubes that are surrounded by water.
what is a firetube boiler basic operating principal
The heat produced by gases of combustion passes through the tubes while water surrounds the tubes.
what are the 3 types of firetube boilers
horizontal return tubular boiler, scotch marine boiler, and vertical firetube boiler
a firetube boilers are designed for pressures up to a maximum of ______psi and approximately ______BHP
350 psi, 2000 BHP
name 5 advantages of firetube boilers
- can be factory assembled, thus giving better quality control
- initial cost is less than a watertube boiler
- requires little or no setting (brickwork)
- contains larger volume of water for a given size compared to a watertube boiler
- requires less headroom
Because of the large volume of water which boiler is most likely to produce an explosion
firetube boiler
water boil at what temperature
212°F at atmospheric pressure at sea level.
name 3 basic principles of boiler operation can
prevent serious accidents:
- Water will boil and turn to steam when it reaches 212°F at atmospheric pressure at sea level.
- The higher the steam pressure, the higher the boiling point of water in the boiler.
- As steam pressure in a boiler increases, there is a corresponding increase in temperature.
When a steam boiler is operating at 100 (psig), the temperature of the water and steam will be approximately
338
explain when the water flashes into steam
when there is a sudden drop in pressure from 100 psig to 0 psig without a corresponding drop in water temperature, the water at 338°F immediately flashes into steam
when water flashes into steam the volume increases by a factor of about
1600
When a steam boiler is operating at 100 (psig), the temperature of the water and steam will be approximately _____ , and what percentage of the water flashes into steam______% and the remaining water will cools at ____
338°F , 13%, 212°F
explain the Principles of Firetube Boiler Operation
When water is heated, it increases in volume and becomes less dense.
This warmer water, now less dense, rises and the cooler water drops to take its place.
As steam bubbles begin to form, this steam/water mixture becomes less dense, which greatly increases the natural circulation in the boiler.
The steam bubbles break through the surface and enter the steam space.
what is atmospheric pressure
is pressure at sea level at 14.7 psia
what is absolute pressure
is gauge pressure + atmospheric pressure (14.7)
what is heating surface
is the part of a boiler with water on one side and heat and gases of com-bustion on the other.
how can we increase the heating surface
by Adding tubes and placing an internal furnace within the boiler shell
When larger quantities of steam are generated, the thermal efficiency of a boiler
increases
Thermal efficiency
is the ratio of the heat absorbed by a boiler (output) to the heat available in the fuel (input) in-cluding radiation and convection losses.
Modern firetube boilers with improved design and heat transfer rates have achieved thermal efficiency rates as high as
90% to 95%.
what is a furnace
furnace is a location where the combus-tion process takes place
what other names does the furnace have
firebox or combustion chamber
how can we greatly increase the heating surface
by placing an internal furnace
what are the benefits of placing an internal furnace within the boiler shell
.greatly increases the heating surface.
.Increases heat absorption through radiant heat transfer.
.The boiler creates steam more quickly.
.increases boiler efficiency
what is a dry-back boiler
is a firetube boiler with a refractory-lined door or chamber at the rear or top of the boiler that directs the gases of combustion from the furnace to the first pass of tubes or from one section of tubes to another
what is a wet-back boiler
is a firetube boiler with three tube sheets and a water-cooled turnaround chamber, with a water leg formed between the rear tube sheet and the
chamber.
by inserting baffles on the fire side, firetube boilers how many pass boilers are
two-, three-, or four-pass boiler
how can we increase thermal efficiency on a firetube boiler
By in-creasing the number of passes and the number of fire tubes, the water can absorb more heat.
horizontal return tubular (HRT) boiler
is a firetube boiler that consists of a shell that contains tube sheets and fire tubes mounted over a firebox or furnace
describe a modern design of an HRT boiler
is a package boiler with a welded steel firebox that can be equipped with a gas or oil burner.
For older styles of HRT boilers the two methods used to support the drum are
columns with a suspen-sion sling or supporting brackets resting on metal plates in a brick setting
The tube sheets of an HRT boiler are supported with
through stays (braces) and diagonal stays
The feedwater pipe of an HRT boiler extends approximately __________ of the length of the drum
three-fifths
where does the feedwater pipe on an HRT boiler goes and why
It enters through the front tube sheet. This
helps to heat the feedwater and direct it to a cooler location in the boiler, which increases water circula-tion in the boiler.
on older HRT boilers The bottom blowdown line must pass through?
the firebox.
on older HRT boilers The bottom blowdown line must be protected by ?
a sleeve and refractory or by a wrapping of protective insulation.
Modern HRT boilers drums are welded instead of
riveted
A scotch marine boiler is
is a firetube boiler with an internal furnace.
on a scotch marine boiler the furnace is
completely surrounded by water.
why on a scotch marine boiler has more boiler efficency
because the furnace is surrounded by water which increase the heating surface
in a scotch marine boiler, where is the furnace located
inside the drum
vertical firetube boiler how many pass boiler is
one pass boiler
vertical firetube boiler
is a one-pass firetube boiler that has tubes in a vertical position
can a vertical firetube boiler use baffles?
no
The combustion chamber, or firebox, of a vertical firetube boiler is supported by
staybolts
in a vertical firetube boiler the water leg if formed by the construction of _______and ________
the inner and outer wrapper sheets
in a vertical firetube boiler the water leg is subject to overheating because
deposits of sludge and sediment accumulate
Sludge
is the soft, muddy residue produced from impurities in water that accumulates in low spots in a boiler
Sediment
is the hard, sandy particles of foreign matter that have precipitated out of water.
vertical firetube boiler advantage
require less floor space
A disadvantage of vertical firetube boilers is
require a high ceiling
A dry-top boiler
is a vertical firetube boiler with an
upper tube sheet that is dry
A dry-top boiler produces steam that is slightly superheated, which can cause tubes in the upper tube sheet to be
prone to leak
A watertube steam boiler
is a boiler that has water inside
the tubes with heat and gases of combustion around the tubes
Watertube boilers were designed to operate at pres-sures as high as
3206 psi
critical pressure of steam
3206 psi
Critical pressure
is the pressure at which the density of water and steam are the same
critical pressure boiler
is a boiler that operates at pressures as high as 3206 psi
which boiler carry a smaller volume of water
water tube boiler
Because of their construction, which boilers can carry extremely high steam pressures and temperatures
water tube boiler
mud drum is
is the lowest part of the water side of a watertube boiler
Principles of Watertube Boiler Operation
The heated water inside the tubes becomes less dense, causing it to rise.
The steam bubbles that form at the heating surfaces rise and finally break through the water surface in the steam drum.
The cooler water drops to the bottom.
Factors that cause water circulation in a watertube boiler
- the difference in the density between the denser liquid in downcomer tubes and the less-dense mixture of steam bubbles and liquid in hotter “steaming” riser tubes
- the difference in temperature between the fluid in the downcomer tubes and riser tubes
- the buoyancy of steam bubbles, which causes the bubbles to rise faster than the water surrounding them
A straight-tube boiler
is a watertube boiler with box headers connected together by straight, inclined water tubes.
Downcomers
are found on watertube, traight tube boiler to allow for cir-culation between the lower drum and the box header
tubes in straight-tube watertube boilers are expanded into the drums and headers and are slightly flared to prevent
leakage
bent-tube boiler is
is a watertube boiler with multiple drums connected by shaped tubes.
in a bent-tube boiler the rear tube bank acts as a_____ to the mud drum.
downcomer
A bent-tube boiler most of the steaming occurs in the rear tube bank or front tube bank
in the front tube banks
which water tube boiler operates at higher pressures ad higher steam capacities
bent-tube boiler
in a bent-tube boiler the de-sign eliminates the need for
headers.
Common bent-tube boiler configurations are
A, D, and O styles.
membrane boiler
is a watertube boiler that uses strips of metal alloy welded between the tubes to form a seal
A flex-tube boiler is
is a watertube boiler in which replaceable serpentine tubes are connected to the upper and lower drums and surround the firebox.
what allows the tubes on a flex-tube boiler to be replaceable
The tubes have a tapered bushing welded on the ends, which is fitted into the headers by a press fit
what allows the tubes on a flex-tube boiler to expand and contract in a vertical direction
the serpentine shape of the tubes
An electric boiler is
is a boiler that produces heat using electrical resistance coils or electrodes instead of burn-ing a fuel.
Stress
is pressure or tension applied to an object
Compressive stress is
is stress that occurs when two forces of equal intensity act from opposite directions and push toward the center of an object
Fire tubes in a firetube boilers are subjected to what stress
Compressive stress
when compressive stress occurs on a firetube boiler
when a vacuum develops within the boiler.
Tensile stress is
occurs when two forces of equal intensity act on an object, which pulls the object in opposite directions.
Boiler plates and stays are subjected to___ stress
tensile
Shear stress is
occurs when two forces of equal intensity act parallel to each other but in opposite directions.
why piping should be color coded
to indicate the contents of the pipes
Sinuous headers eliminate the need for
staybolts
Some of the early watertube boilers had box headers that required the use of staybolts to prevent
bulging.
on watertube boilers the steam drum is dished (concave) and therefore requires no
braces or stays
Baffles are used to
direct the gases of combustion so that they come in close contact with the boiler heating surface.
Baffles are constructed of
steel plates or refractory (firebrick)
what wil haappen if broken baffles are not replaced
the gases of combustion take a direct path to the stack..
increase chimney temperature and decrease in boiler efficiency and capacity.
what are wateralls for
to increase the life of the furnace refractory and increase the the steaming capacity of the boiler
what is a waterall
is a set of tubes that is placed in the furnace area of watertube boilers and used to increase the heating surface of boilers and the service life of refractory.
benefits of waterwalls are
Increased heating surface increases the steaming capacity of the boiler.smaller furnace volume per unit of output, higher heat absorption in the furnace area, and increased firing rate per unit of furnace volume.
The amount of steam generated using waterwalls is
expressed in
pounds of steam per hour per square foot (lb/hr/sq ft) of waterwall heating surface.
The amount of steam generated using waterwalls in a hand-fired coal boiler, is about
8 lb/hr/sq ft of waterwall heating surface
The amount of steam generated using waterwalls when using a stoker-fired boiler is about
12 lb/hr/sq ft of waterwall heating surface
The amount of steam generated using waterwalls when burning fuel oil, gas, or pulverized coal, is about
16 lb/hr/sq ft of waterwall heating surface.
A package boiler is
is a boiler that comes completely assembled with its own pressure vessel, burner, draft fans, and fuel train
A package boiler only requires connecting what
feedwater lines, steam lines, fuel lines, electrical connections, and a tie into the breeching and stack
The only limitations of package boilers are
the pounds of steam per hour capability and the size of the unit.
A field-erected boiler is
is a boiler that is assembled at the final site because of size and complexity
Flat tube sheets must be supported and require careful use of _______to ensure the shell can withstand the pressure.
stays
For both firetube and watertube boilers, the tubes are measured by their
outside diameters (OD).
Stays in firetube boiler construction are used to support flat surfaces and prevent
bulging
Describe the difference between package boilers and field-erected boilers.
a package boiler is a boiler that comes completely assembled.
and field-erected boiler is a boiler that is assembled at the final site because of size and complexity
A turbine is
is a machine that converts the en-ergy from the expansion of high-pressure steam into the mechanical energy of rotation
A generator is
is a device that converts mechanical energy, usually from a rotating shaft, into electrical energy by means of electromagnetic induc-tion.
Electromagnetic induction is
is the production of electricity as a result of a conductor passing through a magnetic field.
Cogeneration is
is the process of generat-ing electricity and then using the waste heat from the generating process for heating buildings, providing process heat, or further electrical generation.
The higher the steam pressure, the higher the ___ of the water in the boiler.
boiling point
In electrode electric boilers, heat is generated by electric current flowing from one electrode to another electrode through the
boiler water
A heat recovery steam generator (HRSG) is
is a boiler that uses heat recovered from a hot gas stream, such as hot exhaust gases from a kiln or from a gas turbine.
which boiler does not require a burner because it uses hot waste heat gases from another process
heat recovery steam generator
Cogeneration produces ___ and then uses the waste heat in a process or for heating
electricity
A ___ is a device that converts mechanical energy into electrical energy by means of electromagnetic induction.
generator
