13 Apr 2014

Swirl Valve for Brine Outfalls

of Seawater Desalination Plants

A/Prof Adrian Wing-Keung, LAW

Director, DHI-NTU Centre, NEWRI and School of Civil and Environmental Engineering Nanyang Technological University, Singapore

2 SWRO Desalination Brine

chlorine coagulant coagulant aid

antiscalant sodium bisulfite

NaOH antiscalant Source: Tampa Bay Water (2013),

Tampa Bay Seawater Desalination Plant;

Brine

elevated salinity; suspended particles concentration pretreatment chemicals; antiscalants;

3

Source: Google earth; Pérez Talavera, J.L. and Quesada Ruiz, J.J. (2001), Identification of the mixing processes in brine discharges carried out in Barranco del Toro Beach, south of Gran Canaria (Canary Islands);

Figure: Desalination Plant Maspalomas II, Spain

500m

+ A + B

+ C Outfalls A

B C

Environmental impacts on marine ecosystem

4

Environmental impact Potential salinity impacts on seagrass

Posidonia oceanica (L.)

Source: Sanchez-Lizaso et al. 2008; Gacia et al. 2007; Fernandez-Torquemada et al. 2005; Latorre 2005; Buceta et al. 2003; Tobias Bleninger (2010), Marine outfall systems; Photos: Manu San Felix;

5

Definition Mortality rate is a measure of the number of deaths per unit of time in a population, scaled to the size of that population (in %), in response to a specific cause. Mortality rate analysis Three marine species: Mysidopsis, mysid shrimp; Cyprinodon, sheephead minnow; Menidia, silverside minnow; Unit of time: 48 hrs continued exposure

Source: WateReuse Desalination Committee (2011), Seawater concentrate management;

LC50 (lethal concentration, 50%)

Mortality rate analysis:

Environmental impact Potential salinity impacts on marine species

6

Toxicity of antiscalants

Source: Tobias Bleninger (2010), Marine outfall systems;

Environmental impact

7 Submerged Brine Outfall

Full submergence of the brine plume is generally targeted as design requirement;

Discharge facility cost/Capital cost: 10~30% or even higher (WateReuse Association, 2011).

SWRO plant

Brine outfall pipe

Negatively buoyant jet

Source: WateReuse Association, 2011, Seawater Desalination Costs white paper. POSEIDON water (2013), Sea Water Reverse Osmosis Cost Trend;

8 Submerged brine discharge

9

Outfall types Multi-port diffuser: Alternate

Figure: Gold coast seawater desalination plant, Australia

Source: Tom Pankratz (2012), Seawater intakes and outfalls: An overview; WateReuse Desalination Committee (2011), Seawater concentrate management;

10

Multi-port diffuser: Rosette

Adelaide Desalination plant, Australia

Source: Youtube, Marine life near Adelaide Desalination Plant outfall diffuser;

Duckbill Valve

11 Submerged brine discharge

negatively buoyant jet, or dense jet;

terminal rise height, zt, and return point dilution, Sr;

Figure: Schematic side view of a typical inclined negatively buoyant jet in stagnant ambient

12

Densimetric Froude Number Geometrical parameter and dilution coefficients

S

Fr ___

= constant (for a specific θ)

Dimensional analysis

Fr = U √ g(ρb- ρa)/ρa D

____________ ___________

x

D·Fr ____

,

• Fr Densimetric Froude Number • U Jet exit velocity • ρb Brine density • Ρa Ambient density • D Discharge diameter • x Geometrical parameter • S Dilution (c0/c)

13 Inclined brine discharge with different degrees

Source: Shao, D. and Law, A.W.K. (2010), Mixing and Boundary Interactions of 30 and 45 degree Inclined Dense Jets; Journal of Environmental Fluid Mechanics

30 degree

45 degree

14 Shallow coastal waters: Bohai Bay, East China Sea

10m

Figure: Bathymetric and satellite map of Bohai Bay & East China Sea

Shanghai

Tianjin

100 km

Source: Dongyan Liu, Yueqi Wang (2013), Trends of satellite derived chlorophyll-a (1997–2011) in the Bohai and Yellow Seas, China: Effects of bathymetry on seasonal and inter-annual patterns; Cast view geospatial;

100 km

15

Civil Engineering Magazine ASCE

Singapore Desalination Plant at Tuas

16 Concept of Swirl Valve A non-return valve with the introduction of swirling at the nozzle

outlet, to increase the mixing of brine discharge, and to reduce the terminal rise height of brine plume in shallow coastal waters

Potential to shorten the outfall pipe and reduce capital cost;

Effect of the initial swirl intensity on the jet mixing behavior was experimentally studied

shortening of the outfall pipe length

SWRO plant

Brine outfall pipe

Negatively buoyant jet

17

Figure: Schematic diagram for the experiment setup

SPLIF: Scanning Planar Laser Induced Fluorescence SPIV: Stereoscopic Particle Image Velocimetry

Experimental setup for SPLIF and SPIV

18 PLIF: Concentration distribution map

Figure: Experimental PLIF images for a fully submerged inclined dense jet

Figure: Calibrated instantaneous concentration distribution

19

Experimental setup for Scanning LIF

20 Scanning PLIF System

(a)

Image acquisition frequency: up to 200Hz

21

(c) (d)

Figure: (a) Time averaged side view; (b) Front view; (c) Spatial concentration distribution; (d) Iso-surface, Dilution=20;

(a) (b)

Scanning PLIF Results

22 Horizontal pure jet for system verification

(a) Dilution along the jet centerline

(c) Concentration fluctuation along the centerline

(b) cross-sectional concentration profile

(d) Concentration e-width growth rate

23

Each camera plays the role of the human eye, looking at the flow field from different angles;

The software plays the role of the brain, relating the observed 2-dimensional displacements pairs to 3D displacements.

SPIV: stereo vision

Figure: Fundamental principle of SPIV (DANTEC)

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Peak mean tangential velocity ___________________________

SPIV: Initial swirl intensity

Axial Velocity

Angular Velocity

Degree of swirl (G) = Peak mean axial velocity

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Figure: The distribution of (a) tangential velocity and (b) axial velocity at the nozzle exit

(a) (b)

SPIV: Initial swirl intensity

Peak mean tangential velocity ___________________________ Degree of swirl (G) =

Peak mean axial velocity

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(c) Swirling, G=0.33

(a) Non-swirling, G=0

(b) Swirling, G=0.22

27

(c) Swirling, G=0.33

(a) Non-swirling, G=0

(b) Swirling, G=0.22

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Concentration decay along the centerline

Introduction of swirling substantially enhances the mixing of the brine discharge near the outfall

Enhanced mixing leads to faster concentration delay and wider expansion of the brine plume

Expansion/growth rate of the brine plume width

PLIF: Mixing characteristics

29 Scanning PLIF: Spatial concentration distribution

(c) Swirling, G=0.33

(a) Non-swirling, G=0

(b) Swirling, G=0.22

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3 5 7 9 11 13 (x-x0)/D

y/D

c/cm

Scanning PLIF: Lateral spreading

The swirl enhances the lateral spreading of the brine plume, i.e. the entrainment of the ambient water

(c) Swirling, G=0.33

(a) Non-swirling, G=0

(b) Swirling, G=0.22

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Centerline peak height and terminal rise height significantly reduce with swirling

Effective when G > 0.2

Terminal rise height with Swirl Valve

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Summary Concept of Swirling Valve can increase the mixing efficiency of the brine

discharge near the outfall;

The terminal rise height reduces significantly when G > 0.2;

The length of the outfall pipe can be shortened with swirling in shallow coastal waters, thereby reduces the capital cost of the desalination plant.

shortening of the outfall pipe length

SWRO plant

Brine outfall pipe

Negatively buoyant jet