Reducing Foam Formation in a Cooling Water Outfall.pdf

R&R Consult, together with our long-term partner Tetra Engineering, was tasked with analyzing severe foam formation and pressure pulsations in the cooling water outfall of a 1 000 MW CCGT plant in the Middle East.

Why do power plants use open outfalls?
A single pipe to discharge cooling water would be impractical and cause excessive pressure loss. Open outfalls and drop shafts are used to reduce pressure, dampen water hammer, and ensure that the massive cooling water flow is discharged safely and in an environmentally controlled manner.

The challenge:
In this case, cooling water was falling freely from a drop shaft, entraining large amounts of air and causing foam, pulsations, and unstable operation.

How CFD helped:
Using an advanced transient two-phase Volume of Fluid model, we simulated the process and tested multiple design modifications – without the need for expensive prototypes.

The result:
Installing simple baffle blocks immediately downstream of the drop shaft reduced air entrainment by 47 %, leading to much more stable operation – with minimal extra investment.

🔹 Benefits of CFD in this project:

Fast and detailed evaluation of complex hydraulic phenomena

Significant savings in testing and development costs

A robust, documented design that ensures both efficiency and reliability

1. REDUCING FOAM FORMATION IN A COOLING WATER OUTFALL
Sohngårdsholmsvej2, DK 9000 Aalborg www.R-R-Consult.com www.LinkedIn.com/company/R&R-consult [email protected]

2. REDUCING FOAM FORMATION IN A COOLING WATER OUTFALL
A1000MWCCGTinthemiddleEasthadreportsoffoamgenerationand
pressureissuesatitscoolingwaterdischargepoint.R&RConsultwas
commissionedbyTetraEngineeringtomodelthefluiddynamicsinthe
outfallsystem.Thecauseoftheproblemappearedtobeafreefallofthe
coolingwaterinaweirlocatedupstreamoftheoutfalltocontrolthe
systempressure.
Withouttheneedforphysicaltests,R&RConsultdevelopedaCFDmodel
capableofsimulatingvariousdesignalterations.oneofwhich
successfullyreducedtheairentrapmentinthedischargedwaterby47%.
TheCFDanalysisincludedatwo-phasemodeltoassesstheinitialamount
ofairinthedischargedwaterdownstreamoftheweir,andsubsequently
simulatedtheeffectsofmultipledesignchanges.TherequiredCFDmodel
wasatransient(timedependent),two-phaseVolumeofFluidmodel,
whichvisualizedthewater/airinterfaceundervariousoperating
conditions.
Water flow through the weir
TheCFDsimulationshowedpressurepulsationsandconsiderable
entrainmentofambientair,whichexplainedthefoamgeneration.
Volume fraction of water in the weir cross section
Sohngårdsholmsvej2, DK 9000 Aalborg www.R-R-Consult.com www.LinkedIn.com/company/R&R-consult [email protected]

3. Sohngårdsholmsvej2, DK 9000 Aalborg www.R-R-Consult.com www.LinkedIn.com/company/R&R-consult [email protected]
REDUCING FOAM FORMATION IN A COOLING WATER OUTFALL
Simulatingthesystemnumericallyhasseveralgreatadvantages:itlimits
timeandcostsandallowsanimmediateandhighlyaccurateevaluationof
designalterations.Themostpromisingdesignchangewastoinstall
baffleblocksaftertheweirfreefalltoincreasethesettlingtimeandto
separatetheairfromthewaterbeforetheoutlet.Differentdesignsand
locationsofthebaffleblockwereinvestigated.
Asimilarmodellingapproachofquicklyanalyzingdesignchangesthrough
CFD,canbeappliedinvariousengineeringfieldsandprocessessuchas
productdevelopment,systemscalingandoptimization.
Thebaffleblocksreducedpressurepulsationsandairentrapment.The
mostsuccessfuloftheinvestigateddesignsreducedtheairentrapment
inthedischargedwaterby47%.
Example of baffle blocks
Volume fraction of water in the weir cross section with baffle blocks
Link to CFD animation of water surface