4 steam distribution

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Copyright 200Copyright 20022 byby 11

Steam DistributionSteam DistributionWith An Emphasis on Costs and DangersWith An Emphasis on Costs and Dangers


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




•• 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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InsulationInsulation


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


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


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


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


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• 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 Distribution

Water HammerWater Hammer

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Water hammer can cause severe damage to equipment !!!

Gaskets can blow, Pipes can explode!

Operators might be seriously injured or die!!

WHY?



•• 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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Collapsing steamCollapsing steam



Steam contacts with subSteam contacts with sub--cooled condensatecooled condensate

Flash Steam

Receiver filled with water

Vent

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WellWell SpacedSpaced Pipe HangersPipe Hangers

Hangers spaced too wideHangers spaced too wide

The pipe sags allowing condensate to collect



•• 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


Water Water HammerHammer DamageDamage

Tube of a heat exchanger damaged by water hammer.

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Condensate DrainageCondensate Drainage


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



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



STEAM



Before valves


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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


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


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



Before valves



Steam Main Design

TLV Steam Trap Set

TLV Air Vent



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

Trap at Trap at all low pointsall low points

At endAt endof linesof linesBefore andBefore and

afteraftervertical loopsvertical loops


Steam Main Design

TLV Steam Trap Set

TLV Air Vent



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

At all low pointsAt all low points




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

At all low pointsAt all low points




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


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.


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.



•• 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.


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


High thermal conductivity means good thermal conductor.Low thermal conductivity means good thermal insulator.


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.


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.


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.



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


Steam DistributionSteam DistributionTilting PanTilting Pan

TLV Air Vent

Air pushed into top of jacket

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Thank you,Thank you,do you now have anydo you now have any

QUESTIONSQUESTIONS??

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