Download - 4 Steam Distribution
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Steam DistributionSteam DistributionWith An Emphasis on Costs and DangersWith An Emphasis on Costs and Dangers
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STEAM DISTRIBUTION OBJECTIVES.STEAM DISTRIBUTION OBJECTIVES.
•• Make sure dry saturated steam leave the boilerMake sure dry saturated steam leave the boiler
•• The distribution main is laid out correctlyThe distribution main is laid out correctly
•• The distribution main is sized correctlyThe distribution main is sized correctly
Steam DistributionSteam Distribution
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•• The distribution main is properly insulatedThe distribution main is properly insulated
•• Expansion joints are Expansion joints are strategically strategically placedplaced
•• The distribution main is adequately trappedThe distribution main is adequately trapped
Steam DistributionSteam Distribution
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Steam DistributionSteam Distribution
•• Dry saturated steam arrives at usage pointDry saturated steam arrives at usage point
•• Pressure reduction is properly Pressure reduction is properly applied at usage pointapplied at usage point
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Steam DistributionSteam Distribution
InsulationInsulation
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Steam Pipe InsulationSteam Pipe InsulationUseful Heat Escapes From Bare Pipes And Can Burn Personnel
Well Insulated Pipes Contain Heat Energy
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Steam Pipe InsulationSteam Pipe Insulation
TT00
TTii
TTpp
TTii
TT00
TTpp
TTss
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Steam Pipe InsulationSteam Pipe Insulation
Pipe Size
Economic Insulation
Radiation Losses(1) (kW/m)
Thickness Insulated Uninsulated 1/2” 15mm 125 692 2” 25mm 243 1820
4” 40mm 298 2942 12” 50mm 588 7614
(1) Comparison of Radiation Losses(1) Comparison of Radiation Losses(Pipe Surface Temperature at 150(Pipe Surface Temperature at 15000C)C)
Insulation has a very short payback period and makes the plant safer
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Steam DistributionWhat’s in the steam pipe?
•• SteamSteam•• Condensate on the bottom of the pipeCondensate on the bottom of the pipe•• Condensate as a mistCondensate as a mist•• Air and other incondensable gasesAir and other incondensable gases•• Pipe scale and dirtPipe scale and dirt
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Steam Distribution
Simple Pipe RulesSimple Pipe Rules
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Steam System DesignSteam System Design-- PipingPiping• Pipes should slope at a gentle downward
angle away from the boiler.
Steam LinesInclination
1:100 to 1:200
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Strainer in a Steam PipeStrainer in a Steam Pipe
Correctly Fitted Strainer
Incorrectly Fitted Strainer
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Steam System Design Steam System Design -- PipingPiping
• Eccentric reducers are used rather than concentric reducers
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Steam System Design Steam System Design -- PipingPiping• Equipment supply lines should be connected to
the top of steam mains, not the bottom.
This prevents condensate entering the system to be heated
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Steam System Design Steam System Design -- PipingPiping
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Steam System Design Steam System Design -- PipingPiping• Equipment supply lines are connected to
the top of steam mains, not the bottom.
This prevents condensate entering the system to be heated
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Steam System Design Steam System Design -- PipingPiping
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Steam Distribution
Water HammerWater Hammer
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Water HammerWater Hammer
Water hammer can cause severe damage to equipment !!!
Gaskets can blow, Pipes can explode!
Operators might be seriously injured or die!!
WHY?
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Water HammerWater Hammer
•• Hydraulic ShockHydraulic Shock:– Opening Valves too Quickly.– Blocked, Locked, or Insufficient Traps.– Stall by Modulating Pressures.
•• Thermal ShockThermal Shock:– Live or Flash Steam Contacting Subcooled
Condensate.
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Water HammerWater Hammer
Collapsing steamCollapsing steam
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Water HammerWater Hammer
Steam contacts with subSteam contacts with sub--cooled condensatecooled condensate
Flash Steam
Receiver filled with water
Vent
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Water HammerWater Hammer
WellWell SpacedSpaced Pipe HangersPipe Hangers
Hangers spaced too wideHangers spaced too wide
The pipe sags allowing condensate to collect
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Water HammerWater Hammer
•• High velocity steam tends to lift the condensate asHigh velocity steam tends to lift the condensate asit passes down the pipe. it passes down the pipe.
•• Should the condensate be allowed to plug the pipeShould the condensate be allowed to plug the pipea disaster is likely.a disaster is likely.
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Water Water HammerHammer
Hydraulic shock
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Water Water HammerHammer DamageDamage
Tube of a heat exchanger damaged by water hammer.
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Steam DistributionSteam Distribution
Condensate DrainageCondensate Drainage
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Steam DistributionSteam DistributionCondensate Collection PointsCondensate Collection Points
STEAMSTEAM
Bottom of large riserBottom of large riser
Every 30 to 50 metersEvery 30 to 50 meterson horizontal runs on horizontal runs 100 to 160 feet100 to 160 feet
Before valvesBefore valves
Bottom ofBottom oflarge fallslarge falls
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Steam System Design• Collection pockets should be piped to a
trap system as shown.
Optional DrainValve
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Steam DistributionSteam DistributionCondensate Collection PointsCondensate Collection Points
STEAM
Every 30 to 50 meters
Bottom of large riser
Before valves
Bottom oflarge falls
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Steam Main Design
TLV Steam Trap Set
TLV Air Vent
• Steam traps and condensate collecting points should be provided at the bottom of a lift.
• Air venting should also be at the top of the lift.
Trapping should occur at each lift point in the steam systemTrapping should occur at each lift point in the steam system
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Steam DistributionSteam DistributionCondensate Collection PointsCondensate Collection Points
STEAM
Every 30 to 50 meters
Bottom of large riser
Before valves
Bottom oflarge falls
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Erosion DamageErosion DamageClosed valves can back up condensateClosed valves can back up condensate
Valve ClosedValve Closed
Pneumatic Control Pneumatic Control ValveValve
CondensateCondensateBacks upBacks up
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Photo of Actual Valve ErosionPhoto of Actual Valve Erosion
Condensate mixed with steam can wreck valves Condensate mixed with steam can wreck valves
Erosion DamageErosion Damage
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Erosion DamageErosion DamageClosed valves can back up condensateClosed valves can back up condensate
Condensate drain pot
TLV Free Float trap set
Pneumatic Control Valve
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Condensate DrainageCondensate DrainageTrap SetTrap Set
SightSightGlassGlass
CheckCheckValveValve
StopStopValveValve
StopStopValveValve
StopStopValveValve
ToTocondensatecondensate
recoveryrecovery Steam trapSteam trap
Steam trap bySteam trap by--passpassFrom SteamFrom Steamequipmentequipment
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Steam DistributionSteam DistributionCondensate Collection PointsCondensate Collection Points
STEAM
Every 30 to 50 meters
Bottom of large riser
Before valves
Bottom oflarge falls
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Steam Main Design
TLV Steam Trap Set
TLV Air Vent
• Steam traps and condensate collecting points should be provided at the bottom of a lift.
• Air venting should also be at the top of the lift.
Trapping should occur after each drop point in the steam systemTrapping should occur after each drop point in the steam system
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Steam DistributionSteam DistributionCondensate Collection PointsCondensate Collection Points
STEAM
Trap at Trap at all low pointsall low points
At endAt endof linesof linesBefore andBefore and
afteraftervertical loopsvertical loops
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Steam Main Design
TLV Steam Trap Set
TLV Air Vent
• Steam traps and condensate collecting points should be provided at the bottom of a lift.
• Air venting should also be at the top of the lift.
Trapping should occur at each lift point in the steam systemTrapping should occur at each lift point in the steam system
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Steam DistributionSteam DistributionCondensate Collection PointsCondensate Collection Points
STEAM
At all low pointsAt all low points
At endAt endof linesof linesBefore andBefore and
afteraftervertical loopsvertical loops
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Steam Main DesignVertical Expansion LoopVertical Expansion Loop
Vertical expansion loopsVertical expansion loopsShould have traps before Should have traps before
And after the loopAnd after the loop
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Steam DistributionSteam DistributionCondensate Collection PointsCondensate Collection Points
STEAM
At all low pointsAt all low points
At endAt endof linesof linesBefore andBefore and
afteraftervertical loopsvertical loops
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Steam Main DesignDraining and Venting the
Terminal Point of a Steam Main
12 3
1 4 5
3
6
6
1 Globe Isolation Valve
2 TLV Air Vent
3 TLV Check Valve
4 TLV Free Float Trap
5 TLV Sight Glass
6 TLV Ball valve
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Steam Distribution
Air and Air and NonNon--condensable Gasescondensable Gases
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Effects of AirEffects of Air
What was a smallWhat was a smallleak during the dayleak during the day
Is a path for air to enter the pipeIs a path for air to enter the pipeduring shut down periodsduring shut down periods
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Effects of Air in Steam EquipmentsEffects of Air in Steam Equipments
• Reduced Heat Transfer.• Lower (suppressed) Temperature.• Uneven Heating (Cold Spots).• Corrosion.
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Reduced Heat TransferReduced Heat Transfer
• Is Air is an Insulator or a Thermal Conductor?
• Air is an GOOD Insulator and a POOR Thermal Conductor.
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Effects of AirEffects of AirAIR AND NONAIR AND NON--CONDENSABLE GASES IN PERSPECTIVECONDENSABLE GASES IN PERSPECTIVE
•• It’s not the Ceramic tiles on the nose of the NASA Shuttle that It’s not the Ceramic tiles on the nose of the NASA Shuttle that stops it melting on restops it melting on re--entry, it the air trapped inside the tiles.entry, it the air trapped inside the tiles.
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Effects of AirEffects of Air
•• It’s not the glass fiber material used for pipe insulation that It’s not the glass fiber material used for pipe insulation that contains the heat in the pipe, it’s the air trapped in the glasscontains the heat in the pipe, it’s the air trapped in the glass fiber fiber material.material.
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Effects of AirEffects of Air•• And the same goes for all insulating materials from a Polar BearAnd the same goes for all insulating materials from a Polar Bears s
fur to the ceramic shuttle tiles, the air trapped inside does alfur to the ceramic shuttle tiles, the air trapped inside does all the l the insulating.insulating.
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Effects of AirEffects of Air•• Now relative to steam, a film of air 0.024mm thick on the heat Now relative to steam, a film of air 0.024mm thick on the heat
transfer surface of a steam vessel has the same resistance to transfer surface of a steam vessel has the same resistance to heat transfer,heat transfer,
as a 400mm block of copper !!!as a 400mm block of copper !!!
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Thermal Conductivity ComparisonMaterial Thermal
Conductivity (1)Comparison
to Air AIR 0.024 -
WATER 0.58 24 times greater
CARBON STEEL
54 2250 times greater
COPPER 401 16708 times greater
(1) Unit is W/m/K(1) Unit is W/m/K
Effects of AirEffects of Air
High thermal conductivity means good thermal conductor.Low thermal conductivity means good thermal insulator.
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Temperature GradientTemperature Gradient
121C
99C
STEA
M
Water BeingHeated
MET
AL
HEA
TIN
G S
UR
FAC
E
Con
dens
ate
Film
Wat
er F
ilm
Air
Film
Max. Temp.Drop
Without air better heat transfer
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Lower TemperatureLower Temperature
• Total Pressure = Sum of Partial Pressures. P (total) = P (steam) + P(air)
• Partial Pressure is proportional to Partial Volume.
• Actual Steam Pressure is less than the Total Mixer Pressure.
• Less Steam Pressure Means lower Temperature.
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Lower TemperatureLower Temperature
5 5 barGbarG Vapor MixtureVapor Mixture80% Steam + 20% Air80% Steam + 20% Air
Pressure = 0.80 x 5 + 0.20 x 5Pressure = 0.80 x 5 + 0.20 x 5= 4 = 4 barGbarG + 1 + 1 barGbarG
(steam) (air)(steam) (air)
Temp. of Steam at 5 Temp. of Steam at 5 barGbarG = 158 = 158 00CCTemp. of Vapor mixture is = 15Temp. of Vapor mixture is = 152 2 00CC(equivalent to steam at 4 (equivalent to steam at 4 barGbarG))
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Uneven Heating SurfacesUneven Heating Surfaces
• Air Is Pushed to Remote Corners Where It Forms Pockets in the Steam Equipment.
• Results in Uneven Temperature or Cold Spots at the Heat Transfer Surface.
• Cold Spots Mean Unequal Expansion of the Tubes and Resultant Stresses Can Lead to Joint Failure.
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CorrosionCorrosion
• H20 + CO2 = H2CO3
• Carbonic Acid (H2CO3 )Is Very Corrosive Especially at Below 160 F or 70 C.
• High Replacement Cost for Steam Equipment (Copper Tubes).
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Sources of Air/ NonSources of Air/ Non--condensable Gasescondensable Gases
• Residual Steam Condenses and an Initial Vacuum May Be Formed
• Air Is Drawn to Steam Space Through Valve Packing, Joint Gaskets, Minute Leaks.
• Air & Non-condensable Enter Via Feed Water. O2 & CO2 Are Released During Steam Formation.
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Effects of AirEffects of Air
So now it’s clear air and nonSo now it’s clear air and non--condensable gases arecondensable gases areunwelcome guest in any steam system !!!unwelcome guest in any steam system !!!
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Affect of Air In a Steam ProcessAffect of Air In a Steam ProcessMeatworks Renderer/CookerMeatworks Renderer/Cooker
TLV Air Vent
Steam is turned on
Jacket Trap Set
Steam Jacket
Jacket Steam
Paddle Steam
PaddleTrap Set
Mixing Paddle Air is pushed to theend and trapped
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Steam DistributionSteam DistributionTilting PanTilting Pan
TLV Air Vent
Air pushed into top of jacket
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QUESTIONSQUESTIONS??
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