Steam gener ator
The Theory of Producing Steam
• Water
boils and evaporates at 100°C under atmospheric
pressure.
• By higher pressure, water evaporates at higher temperature e.g. a pressure of 10 bar equals an evaporation temperature
of 184°C.
• During the evaporation process, pressure and temperature
are constant, and a substantial amount of thermal energy is
used for bringing the water from liquid to vapor phase.
• When all the water is evaporated, the steam is called dry
saturated.
• In this condition the steam contains a large amount of latent
heat.
• Further heating of dry saturated steam will lead to increase in
temperature of the steam.
• Superheated steam.
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Steam generator versus steam boiler
• Opposite the pr inciple of the steam boiler s,
• the water in the steam generators evaporates inside
the tube winded up into serial connected tube coils.
• The feed water is heated up to the evaporation
temperature and then evaporated.
• The intensity of the heat, the feed water flow and the
size/length of the tube are adapted, so that the water is
exactly fully evaporated at the exit of the tube.
• This ensures a very small water and steam volume
(content of the pressure vessel).
• Thus there are no buffer in a steam generator, and is it
temporary overloaded.
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The advantages using a steam gener ator
compare to conventional steam boiler s.
• Easy to operate - normally no requirement for
boiler authorization
• Rapid start-up and establishing full steam
pressure Compact and easy to adapt in the
existing machinery arrangement
• Price attractive - especially at low steam rates.
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Steam Generation Theory
• Within the boiler, fuel and air are force into the
furnace by the burner.
• There, it burns to produce heat.
• From there, the heat (flue gases) travel throughout
the boiler.
• The water absorbs the heat, and eventually absorb
enough to change into a gaseous state - steam.
• Bellow is the basic theoretical design of a modern
boiler.
• Boiler makers have developed various designs to
squeeze the most energy out of fuel and to
maximized its transfer to the water.
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Types of Boilers
1. Fire Tube Boiler
2. Water Tube Boiler
3. Packaged Boiler
4. Fluidized Bed (FBC) Boiler
5. Stoker Fired Boiler
6. Pulverized Fuel Boiler
7. Waste Heat Boiler
8. Thermic Fluid Heater (not a
boiler!)
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Fire Tube Boiler
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Fire Tube Boiler
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•Packaged Boiler
• Comes in complete package
• Features
• High heat transfer
• Faster evaporation
• Good convective heat transfer
• Good combustion efficiency
• High thermal efficiency
• Classified based on number of passes
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Packaged Boiler
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Water Tube Boiler
• Used for high steam
demand and
pressure
requirements
• Capacity range of
4,500 – 120,000
kg/hour
• Combustion
efficiency enhanced
by induced draft
provisions
• Lower tolerance for
water quality and
needs water
treatment plant 10
Water Tube Boiler with Superheater
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Water Tube Boiler Operation
• Water enters the boiler, preheated, at the top.
• The hot water naturally circulates through the
tubes down to the lower area where it is hot.
• The water heats up and flows back to the steam
drum where the steam collects.
• Not all the water gets turn to steam, so the process
starts again.
• Water keeps on circulating until it becomes steam.
• Meanwhile, the control system is taking the
temperature of the steam drum, along with
numerous other readings, to determine if it should
keep the burner burning, or shut it down.
• would not be very efficient.
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• As well, sensors control the amount of
water entering the boiler, this water is
know as feed water.
• Feed water is not your regular drinking
water.
• It is treated with chemicals to neutralize
various minerals in the water, which
untreated, would cling to the tubes
clogging or worst, rusting them.
• This would make the boiler expensive to
operate because it
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• On the fire side of the boiler, carbon deposit
resulting from improper combustion or
impurities in the fuel can accumulate on the
outer surface of the water tube.
• This creates an insulation which quickly
decrease the energy transfer from the heat to
the water.
• To remedy this problem the engineer will
carry out soot blowing. At a specified time
the engineer uses a long tool and insert it
into the fire side of the boiler.
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• This device, which looks like a lance, has a tip at the
end which "blows" steam.
• This blowing action of the steam "scrubs" the outside
of the water tubes, cleaning the carbon build up.
• Water tube boilers can have pressures from 7 bar to as
high as 250 bar.
• The steam temperature's can vary between saturated
steam, 100 degrees Celsius steam with particle of
water, or be as high as 600 - 650 degrees Celsius,
know as superheated steam or dry steam
• The performance of boiler is generally referred to as
tons of steam produced in one hour.
• In water tube boilers that could be as low as 1.5 t/hr
to as high as 2500 t/hr.
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