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)
24
Peak mean tangential velocity ___________________________
SPIV: Initial swirl intensity
Axial Velocity
Angular Velocity
Degree of swirl (G) = Peak mean axial velocity
25
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
26
(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
28
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
30
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
31
Centerline peak height and terminal rise height significantly reduce with swirling
Effective when G > 0.2
Terminal rise height with Swirl Valve
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.
shortening of the outfall pipe length
SWRO plant
Brine outfall pipe
Negatively buoyant jet