1 Boilers Mms
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Transcript of 1 Boilers Mms
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UTILITY STEAM GENERATOR
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BOILER
Process equipment that
are use to generate
steam
Closed vessel in whichwater, under pressure, is
transformed into steam
by the application of
heat
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Three factors required to generate steam:
1) A suitable vessel or container to hold thewater, transfer the heat to the water, and
collect the steam.
2) Water is heated above its boiling point andforms steam.
3) Heat is needed to change water into
steam and the most common sources forgenerating heat are oil, gas, and coal.
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FUEL: oil, gas and coal
AIR: oxygenHEAT: ignition
Proper adjustment to
produce an efficient flame
that has a BLUE COLOR
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HEAT TRANSFER MODE IN THE BOILER:
Radiation
Convection
Conduction
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Types Of Steam Saturated Steam
Steam at temperature of boiling point of water which
corresponds to its pressure.
Superheated Steam
Steam heated top a temperature higher than the
boiling point temperature corresponds to its pressure.It can not exist in contact to water and resemble asperfect gas.
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Water-tube boilersFire-tube boilers
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Fire-tube boilers
1. Exit Gases
3. Water inlet
2. Steam Outlet
4. Combustion Chamber
5. Tubes
1 2 3
45
Rely on hot gases circulating through the boiler inside tubes that are
submerged in water.
These gases usually make several passes through the tubes.
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ADVANTAGES OF FIRE-TUBE BOILERS:
Relatively inexpensive
Easy to clean
Compact in size
Easy to replace tubes
Well suited for space heating and industrial process applications
DISADVANTAGES OF FIRE-TUBE BOILERS:
Not suitable for high pressure applications 250 psig and above
Limitation for high capacity steam generation
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Fire tube boiler has an internal combustion chamberwithin a vessel containing the water.
A series of horizontal tubes pass through the vessel
and are surrounded by water to bring the hotcombustion gases in contact with the water.
The hot gases are directed back and forth through the
tubes to use as much heat as possible before venting
through an exhaust.
Steam is formed as a result of contact with the tubes
and thus rises to the top of the vessel and is ready for
designated use.
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The Steam Drum
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ADVANTAGES OF WATER-TUBE BOILER:
Available in sizes that are far greater than the firetube design.
Able to handle higher pressures up to 5,000 psig
Recover faster than the fire-tube Have the ability to reach very high temperatures
DISADVANTAGES OF WATER-TUBE BOILER:
High initial capital cost Cleaning is more difficult due to the design
No commonality between tubes
Physical size may be an issue
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Steam bubbles are formed in the heated riser.
The resulting steam water mixture is lighter than the
solid column of water in the unheated portion of the
tube and is, therefore, displaced and steam is releasedinto the steam drum.
In the drum, the bubbles rise to the waters surface and
steam is released into the vapor space.
This circuit is made over and over again as new
feedwater enters the drum at the same rate that steam
is produced from the drum.
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1Steam drum;
2Water drum;
3 Furnace;
4
Boiler bank tubes;
5 Feeders and risers tubes;
6Superheater;
7Desuperheater;
8 Economizer;
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Insulation, lagging and refractories.
MAIN PARTS OF USG
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PO4 Dosing SH St
WATER DRUM
STEAM DRUM
SUPERHEATER
ECONOMIZER
BFW PUMP
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Some Important Boiler Problems:
SCALE LOSS OF FEED WATER
TUBE BREAKAGE SOOT
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Boiler Scale Formation
Scale is formed on boiler tube heating surfaces bythe depositing of impurities in the feed water in theform of a more or less hard adherent crust. Suchdeposits are due to the fact the water loses itssoluble power at high temperatures or becausethe concentrations become so high, due toevaporation, that the impurities crystallize andadhere to the boiler surfaces
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Effect of Boiler Scale
1/8-inch (3mm) of scale can cause a 2.0-3.0%loss in fire-tube boilers and water tube boilers.
A second but more serious effect from scale isthe overheating of boilertube metal, causing
eventual tube failure. In modern boilers with highheat-transfer rates, even extremely thin layers ofscale will cause a serious elevation in thetemperature of tube material
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Boiler Scale
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Corrosion Related Problems
Corrosion is due to the acidity/or oxidizingproperties of the feed water
Pitting Corrosion
Which consists of isolated spots of activecorrosion
caused by Oxygen attack
General CorrosionProduced by an acid attack mainly due to thepresence ofCO2 which dissolve in water
forming
carbonic acid (H2CO3)
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Pitting Corrosion
Dissolved oxygen interacts with boiler componentsurfaces, forming pits on the metal surface.
These pits may eventually grow large enough topenetrate the metal, forcing a boiler shutdown.
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Pitting Corrosion
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Treatment Processes
External treatment
Internal treatment
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Internal Treatment
1-Sodium Phosphate
It buffers the boiler water pH to minimize the
potential for boiler corrosion.
It precipitates small amounts of calcium or
magnesium into a soft deposit which can then
accumulate in mud drums or steam drums
rather than as hard scale. It helps to promote the protective oxide film
on boiler metal surfaces
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This type of program causes sludge to formand therefore requires continuousblowdown. Deposition problems are
possible in the higher heat transfer areas ofthe boiler. On the positive side, phosphate-polymer programs can essentially handleany feed water hardness and be cost
effective. This is particularly true of thenew synthetic polymers.
2-Phosphateand Polymers
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BlowdownTreatment
Blowdown is a very important part of anywater treatment program. Its purpose is tolimit the concentration of impurities in theboiler water.
The right amount of blowdown is critical: toomuch results in energy loss and excessivechemical treatment cost; too little andexcessive concentrations of impurities build
up. It can range from 1% (based on feedwater
flow) to as much as 25%.
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By definition, bottom blowdown is intermittentand designed to remove sludge from the areas ofthe boiler where it settles. The frequency of bottomblowdown is a function of experience and plantoperation. Bottom blowdown can be accomplishedmanually or electronically using automaticblowdown controllers
1-Bottom Blowdown
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Frequently used in conjunction with manualblowdown, continuous blowdown constantly removesconcentrated water from the boiler. By design, it is inthe area of highest boiler water concentration. Thispoint is determined by the design of the boiler and isgenerally the area of greatest steam release.
Continuous blowdown allows for excellent controlover boiler water solids. In addition, it can remove
significant levels of suspended solids. Anotheradvantage is that the continuous blowdown can bepassed through heat recovery equipment.
2-Continuous Blowdown
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For the sake of clarity, certain definitions arerequired:
1. Steam Purity-The amount of solid, liquid orvaporous contamination in the steam. Steampurity is normaily reported as total solids in partsper billion (ppb).
2. Steam Quality-The amount of moisture in thesteam. It is the weight of dry steam in the mixtureof steam and water droplets. It is reported as apercentage.
Carryover
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Carryover is generally considered to be anycontaminant that leaves a boiler steam drum withthe steam. It can be in solid, liquid or vaporous
form. With higher operating pressures, highersuperheat temperatures and the need for puresteam in certain processes, greater emphasis isplaced on controlling the factors that minimizecarryover.
Carryover Problem
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Some of the effects of carryover are:
1. Deposition in regulators and valving
2. Deposition in superheaters3. Deposition in control valves and turbines
4. Process contamination
Carryover Effects
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PROTECTION AND SECURITIES
BOILER START-UP \ SHUTDOWN AND PROTECTION SYSTEM IS KNOWN AS
BMS (BURNER MANAGEMENT SYSTEM)
PROTECTIONS
LOW WATER LEVEL (ALARM / TRIP).
LOW FUEL GAS PRESSURE.
HIGH FUEL GAS PRESSURE.
FLAME DETECTORS OR FLAME FAILURE.
LOW AIR FLOW.
FD FAN FAILURE (LOW SPEED)
LOW INSTT. AIR PRESSURE.
STEAM DRUM HIGH PRESSURE.
CPU OR I-O FAILURE.
SAFETY VALVES.
HIGH FURNACE PRESSURE.
OTHER INTERLOCKS ( DEPENDS UPON LIMITATION/ DESIGN FEATURES )