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
13 Apr 2014
SWRO Desalination Brine
chlorine
coagulant
coagulant aid
elevated salinity;
suspended particles concentration
pretreatment chemicals;
antiscalants;
antiscalant
sodium bisulfite
Brine
NaOH
antiscalant
2
Source: Tampa Bay Water (2013),
Tampa Bay Seawater Desalination
Plant;
Environmental impacts on marine ecosystem
Outfalls
+A
+C
A
+B
500m
B
Figure: Desalination Plant Maspalomas II, Spain
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);
C
3
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;
Environmental impact
Potential salinity impacts on marine species
Mortality rate analysis:
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
LC50 (lethal concentration, 50%)
Source: WateReuse Desalination Committee (2011), Seawater concentrate management;
5
Environmental impact
Toxicity of antiscalants
Source: Tobias Bleninger (2010), Marine outfall systems;
6
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
Negatively
buoyant jet
Brine outfall
pipe
Source: WateReuse Association, 2011, Seawater Desalination Costs white paper.
POSEIDON water (2013), Sea Water Reverse Osmosis Cost Trend;
Submerged brine discharge
8
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
Duckbill Valve
Adelaide Desalination plant, Australia
Source: Youtube, Marine life near Adelaide Desalination Plant
outfall diffuser;
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
11
12
Densimetric Froude Number
Geometrical parameter and dilution coefficients
Dimensional analysis
U
___________
Fr = ____________
√ g(ρb- ρa)/ρa D
x
S
____
, ___ = constant
D·Fr Fr
(for a specific θ)
•
Fr
Densimetric Froude Number
•
U
Jet exit velocity
•
ρb
Brine density
•
Ρa
Ambient density
•
D
Discharge diameter
•
x
Geometrical parameter
•
S
Dilution (c0/c)
Inclined brine discharge with different degrees
13
30 degree
45 degree
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
Shallow coastal waters: Bohai Bay, East China Sea
14
Tianjin
10m
100 km
100 km
Shanghai
Figure: Bathymetric and satellite map of Bohai Bay & East China Sea
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;
Singapore Desalination Plant at Tuas
15
Civil Engineering Magazine
ASCE
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
SWRO plant
Negatively
buoyant jet
Brine outfall
pipe
shortening of
the outfall pipe length
Experimental setup for SPLIF and SPIV
17
SPLIF: Scanning Planar Laser Induced Fluorescence
SPIV: Stereoscopic Particle Image Velocimetry
Figure: Schematic diagram for the experiment setup
PLIF: Concentration distribution map
Figure: Experimental PLIF images for a fully submerged inclined dense jet
Figure: Calibrated instantaneous concentration distribution
18
Experimental setup for Scanning LIF
19
Scanning PLIF System
(a)
Image acquisition frequency: up to 200Hz
20
Scanning PLIF Results
(b)
(a)
(c)
(d)
Figure: (a) Time averaged side view; (b) Front view; (c) Spatial concentration
distribution; (d) Iso-surface, Dilution=20;
21
Horizontal pure jet for system verification
(a) Dilution along the jet centerline
(c) Concentration fluctuation along the centerline
22
(b) cross-sectional
concentration profile
(d) Concentration e-width growth rate
SPIV: stereo vision
 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 2dimensional displacements pairs to 3D displacements.
Figure: Fundamental principle of SPIV (DANTEC)
23
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SPIV: Initial swirl intensity
Axial Velocity
Angular Velocity
Peak mean tangential velocity
Degree of swirl (G) = ___________________________
Peak mean axial velocity
SPIV: Initial swirl intensity
(a)
Figure: The distribution of (a) tangential velocity and (b) axial velocity at the nozzle exit
Peak mean tangential velocity
___________________________
Degree of swirl (G) =
Peak mean axial velocity
25
(b)
26
(a) Non-swirling, G=0
(b) Swirling, G=0.22
(c) Swirling, G=0.33
27
(a) Non-swirling, G=0
(b) Swirling, G=0.22
(c) Swirling, G=0.33
PLIF: Mixing characteristics
Concentration decay along the centerline
28
Expansion/growth rate of the brine plume width
 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
Scanning PLIF: Spatial concentration distribution
(a) Non-swirling, G=0
(b) Swirling, G=0.22
(c) Swirling, G=0.33
29
Scanning PLIF: Lateral spreading
30
(a) Non-swirling, G=0
(b) Swirling, G=0.22
(c) Swirling, G=0.33
 The swirl enhances the lateral spreading
of the brine plume, i.e. the entrainment of
the ambient water
c/cm
y/D
3
5
7
9
(x-x0)/D
11
13
Terminal rise height with Swirl Valve
31
 Centerline peak height
and terminal rise height
significantly reduce with
swirling
 Effective when G > 0.2
32
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.
SWRO plant
Negatively
buoyant jet
Brine outfall
pipe
shortening of
the outfall pipe length