Tseung Kwan O Desalination Plant - Hong Kong...
Transcript of Tseung Kwan O Desalination Plant - Hong Kong...
Tseung Kwan O Desalination Plant
Ir CHAN Tak Yeung, Thomas
Chief Engineer / Consultants Management
Water Supplies Department, HKSARG
Dr. Srinivas (Vasu) Veerapaneni
Desalination Technology Leader
Black & Veatch Corporation
19 December 2016
The Hong Kong Institution of Engineers
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Outline
• Uprising Challenges and Strategic Measures
• Global Desalination Perspective
• The Desalination Plant Project
• Overview of Typical Desalination Plant Design
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Uprising Challenges and
Strategic Measures
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Is
Hong Kong a
WATER-SCARCE city?
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Water Rationing in the 1960s
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Three-pronged Supply
Local Yield199mcm(16%)
Dongjiang Water
772mcm(62%)
Seawaterfor Flushing
274mcm(22%)
2015 Demand
1245mcm
Dongjiang Water
Local Yield
Seawater
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WATER SECURITY “the capacity of a population to safeguard sustainable
access to adequate quantities of acceptable quality
water for sustaining livelihoods, human well-being, and
socio-economic development, for ensuring protection
against water-borne pollution and water-related
disasters, and for preserving ecosystems in a climate
of peace and political stability.”
(UN-Water, 2013)
8 Photo source: Hotblack/Morguefile
Who’s Next?
Climate Change Is
Happening
Thailand:
July 2015 California,
USA:
April 2015
Taiwan:
April 2015
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How Sensitive is our Water Resources?
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How Sensitive is our Water Resources?
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Hong Kong’s Challenge in Water Supply
Fluctuating local yield and Donjiang
water supply due to climate change
Keen competition for the
Dongjiang water resource
Increasing water demand and arising from
population and economic growth
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Total Water Management
Demand Management
- Water Conservation
Supply Management
- New Water Sources
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Water Conservation
Total Water Consumption
2%
8% 5%
31%
Non-domestic “Water Conservation
Starts from Home”
School Talk
Water: Learn and
Conserve – Teaching Kit
for Liberal Studies
“Save Water. Cherish the
World” Mobile Showroom
Roving Exhibition
Water Efficiency
Labelling Scheme
(WELS)
Flow Regulator
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Best Practice Guidelines for
– Catering
– Hotel
– Laundry Industry
Water Conservation
Total Water Consumption
2%
8% 5%
31%
Non-domestic
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New Water Sources
Local Yield(10-25%)
Dongjiang Water(41-56%)
Seawater for Flushing
(26%)
Desalination(6%)
Reclaimed Water(~1.5%)
Grey Water Recycling(~0.5%)
Note: Chart drawn based on average local yield of 295mcm
Seawater Desalination
(5% - 10%)
Proposed
Desalination Plant
Local Yield
Dongjiang Water
Seawaterfor Flushing
Three
Pronged
Supply
Six
Pronged
Supply
Water Reclamation
(2%+)
Grey Water Recycling
(~0.5%) Desalination
Water Reclamation
Grey Water Recycling
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Global Desalination
Perspective
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Global Desalination Trend
Proven: 150 countries have installed desalination plants around the world
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Desalination Technologies
Currently Available
Primarily two types:
Thermal Desalination
Membrane Desalination
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Principle of operation – Evaporate water and condense the vapors
Oldest desalination technology
One of thermal technologies - Multi-Stage Flash (MSF)
Thermal Desalination
B&V - 19
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Lok On Pai Desalination Plant
• Commissioned in October 1975
• Adopted multi-stage flash distillation
• Decommissioned in 1982 due to high operation cost.
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Pure water migrates from low conc.
vessel to high conc. vessel
Flow stops when
hydraulic head on
high conc. vessel is
equal to solution’s
osmotic pressure
If external P
greater than
osmotic pressure is
applied, “Reverse
Osmosis” occurs
(desalination).
Semi permeable membrane
Start with equal
volumes of
fresh water and
saline water
Saline waterFresh water
Natural
osmosis
Saline waterFresh water
water
Osmotic
equilibrium
osm
otic
pre
ssu
reP
Reverse
Osmosis
water
(a) (b) (c) (d)
Membrane Desalination
Reverse Osmosis (RO): Principle
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• , Aus
Gold Coast, Australia
Melbourne desalination plant, Australia
Examples of SWRO Plants
Source: Suez Environment
Source: Veolia
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• New water source not susceptible to climate
change
• Latest reverse osmosis technology
Seawater Desalination by RO
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The Desalination Plant
Project
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The Proposed Desalination Plant
2007 Pilot Plant Study
confirmed technical
feasibility of
desalination
technologies as a
reliable freshwater
source
2008 The HK Government
promulgated the Total
Water Management
Strategy which
recommended
seawater desalination
as a new alternative
water source
2015 Funding
was
approved
from the
LegCo’s
FC in
Jun
2015.
2000 - 2002 Feasibility study
of developing
desalination in
HK. Pilot Plant
Study
commenced in
2002.
2012 - 2015 Planning and investigation study
confirmed the technical and
environmental viability of
constructing a seawater reverse
osmosis desalination plant at TKO
Area 137
Nov 2015 Investigation Review,
Design and Construction
Consultancy Agreement
for the first stage of the
desalination plant
commenced.
2015 Environmental
Permit was
granted by
EPD
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Site Selection Considerations
Oceanic current with stable seawater quality in the eastern waters
Strategic supply network to other parts of the territory
TKO Area 137 is currently a public fill bank zoned “Other Specified Uses (Deep Waterfront Industry)”
High turbidity in the western waters due to tidal effects in the Pearl River Delta
Environmental impacts assessed to be acceptable
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9.5 km long fresh water
trunk main to convey the
fresh water produced at
the proposed
desalination plant
Tseung Kwan O Desalination Plant
-First Stage: 135 MLD = ~5% of the
daily fresh water demand in HK
-- Second Stage: expansion to 270
MLD = ~10% of the daily fresh water
demand in HK
Existing TKO fresh
water primary
service reservoir
350m
Submarine
outfall
250m
Submarine
intake
TKO Area 137
The Proposed Desalination Plant
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Overview of Typical
Desalination Plant Design
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Seawater RO Process Schematic
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Intake • One of the important components of the
desalination plant. In fact, treatment starts with
a well designed intake
• Two types of intakes possible: Open intake or
Subsurface Intake
– Subsurface intake – high water quality, but
not always feasible
– Submerged open intake selected for the
project due to its feasibility
• Most commonly used around the world
• Capable of providing large flows
• Good pretreatment essential as water
quality is influenced by many factors
• Off the littoral zone of the coast to
minimize environmental impacts
• Low influent velocity to prevent
impingement
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Open submerged intake at Fujairah, UAE
Open Submerged Intake
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2 tunnels (2.5 km long and 3.4 m diameter)
Intake at Sydney Desalination Plant
Source: Veolia
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2 tunnels – (2.2 km influent and 2 m effluent); 2.8 m ID
Open intake (submerged pipe, tunnel on land); Gold Coast
Source: Veolia
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Environmental Considerations for Intake
Intake structure of Perth Desalination Plant, Australia (Source:Water Corporation)
Intake Overseas Example (Perth Desalination Plant, Australia)
Seawater Intake
•Submarine pipe to be constructed by micro-tunnelling
•Design of intake structure to minimise potential impingement and entrainment of fish and larvae
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Environmental Considerations for Outfall
Marine life around brine discharge diffuser of Perth Desalination Plant, Australia (Source:Water Corporation)
Discharge Diffusers
•Submarine pipe to be constructed by micro-tunnelling
•Rapid dilution of brine to ambient level
•Confined mixing zone resulting in minimal impact to seawater quality
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Intake and Outfall of TKO Desalination Plant
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Objectives of Pretreatment
• Biofouling control
• Remove turbidity, suspended solids
– RO membranes are good at removing dissolved constituents. Particulate material can plug up membranes
• Address the following if present
– Oil and grease – RO membranes are not tolerant
– Algae – Can plug up pretreatment and foul RO membranes
• Typically, efficacy of pretreatment is measured in terms of silt density index (SDI)
• However, not all foulants captured by SDI
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• Most common issue for open intake system
• Shock chlorination most widely practiced
• Newer practices being tested
• Change in pH (if feasible for offshore line also)
• Biofilm monitors
• Use of newer oxidants that do not damage membranes such as chloride dioxide
• Use of biocides such as DBNPA*
• Osmotic backwash of RO membranes
Biofouling Control
*2,2-dibromo-3-nitrilopropionamide
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• Coagulation + Filtration (Perth, Ashkelon, Fujairah, Sydney, Gold Coast, etc.)
• Clarification used as necessary (Trinidad, Singapore, Hamma)
• Second stage filtration is also used in some facilities (Okinawa, Eni Gela-Sicily)
• Most commonly used coagulant is iron salt
• Attributed to broader pH range, discharge limitations
• Polymer – Almost all facilities used it at some point; Continuous usage not preferred – can irreversibly damage RO membranes
Pretreatment - Traditional
Iron coagulants have lower solubility over a broad pH range compared to Al
Pressure filters at Perth SWRO Source: water Corporation
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• Singapore – Coagulation, flocculation, dissolved air flotation/filtration (DAFF) to address algae and oil & grease
• Barcelona, Spain – Coagulation, flocculation, DAF, two stage filtration
• Beckton, UK – Coagulation, flocculation, lamella clarifiers, pressure filters and UF
• Fujairah II – coagulation, flocculation, DAF and media filtration
Recent Pretreatment Configurations
In-Filter DAF at a SWRO facility Source: Black & Veatch
Additional processes primarily to address severe water quality issues
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Algae
• Requires use of DAF
• Algal blooms occur periodically
• Need for treatment dependent on degree of reliability needed and also type and concentration of algae
– Not all are created equal
– Variations in morphology could have significant implications for treatment
– Not all algae concentrations can be estimated by chlorophyll measurements
– Dinoflagellates could be as large as 100 um and contribute minimally for chlorophyll
Source: Harmful algal blooms in coastal upwelling systems, Oceanography, 2005
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• MF/UF as SWRO pretreatment on the rise
• They are polymeric membranes with absolute pore sizes;
• Primary benefits
• No coagulant needed for several, depending on water quality
• Consistently good water quality
• Design issues
• Ability to deal with varying water quality
• Strainers (type and size) to be selected carefully
• Algae
• Interchageability between different suppliers
Microfiltration/Ultrafiltration (MF/UF) pretreatment
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• Cost still an issue
• Membrane life and replacement costs
• Largest plants with MF/UF are procured under alliance style agreement or DBO contractor has a UF product
• Adelaide, Perth II – Alliance style DBO plants in Australia
• Tuas II, singapore; Magta and Tlemcen, Algeria and Tianjin china – DBO contractor's own the product
MF/UF pretreatment
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UF pretreatment at 318,000 m3/day (84 MGD) SWRO
Source: Hyflux
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• Primary process for removal of ions
• Significant developments in membranes over last few decades
Reverse Osmosis
• In other words, an element with today’s rejection and permeability would have cost 150 times more 30 years ago
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1975 1980 1985 1990 1995 2000 2005 2010Year
Salt
pas
sa
ge (
%)
& M
em
bra
ne C
ost
($/g
allo
ns/d
ay)
0
3
6
9
12
15
18
21
24
Ele
men
t p
rod
ucti
vit
y (
gp
d/f
t2)
Salt passage Membrane Price/Flow Productivity (gpd/ft2)
Reference: Based on data by Truby et al., 2007
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RO Design parameters
• Recovery – Percent of water converted to permeate
• Flux – Quantity of water pushed through unit membrane
area
• Skid Size/Pumping arrangement
• Number of passes – how many times the water is treated
• Energy recovery devices
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Second pass • Typically required to meet specific water quality goals
– Boron concentration typical reason outside US • WHO guideline revised from 0.5 mg/L to 2,4 mg/L. • 2nd pass operated at pH of ~10 to convert uncharged boric acid to
charged borate
– Bromide • Formation of brominated DBPs when the desalinated water is mixed
with other water sources
– TDS limits (Chloride, sodium, etc.)
– Examples: • Perth:
– 90% of the SWRO permeate treated by 2nd pass – 0.1 mg/L bromide limit; Recently relaxed to 0.2 mg/L
• Ashkelon – 100% of the SWRO permeate treated by additional passes – 20 mg/L chloride and 0.4 mg/L boron limits
• Tuas – 80% of SWRO permeate at pH of 10 – boron limit of 0.5 mg/L
– Concentrate from second pass typically recycled to SWRO feed
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Boron speciation B rejection
1st pass
2nd pass
Source : Dow chemical
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Permeate collection for second
pass treatment
• Consider taking permeate from both ends of pressure
vessel
– Permeate from lead end of membrane can bypass second pass
treatment
– Permeate from lag end (higher concentrations of constituents)
further treated by second pass
– Depending on the water quality requirements, elements
separated (permeate tube blocked) after 2 or 3 elements
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Feed water to second pass
FeedP
erm
ea
te 2
To post treatment
Pe
rme
ate
1
Feed
concentrate
to waste
Fe
ed
co
nc
Pe
rme
ate
co
nc Good quality -
to post treatment
Poor quality (wrt B)
send to second RO
Concentrate to
waste
Permeate2 for
further treatment
Permeate1 to
post treament
• Permeate from lag elements of the SWRO system
could be used as feed to second pass RO
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Parameter Value
Boron ≤1.0 mg/L
Bromide ≤0.2 mg/L
RO of TKO Desalination Plant
• 2 passes RO to achieve the freshwater quality
objectives:-
• Low bromide concentration to ensure that disinfection
byproduct formation won’t increase when this water is
blended with other water that has organic carbon
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• Two types of devices to recovery energy
• I: Hydro-Mechanical Conversion
– Hydraulic energy in concentrate is converted
to mechanical and then back to hydraulic
energy
• Pelton Wheel
• TurboCharger
• II: Positive Displacement
– Hydraulic energy in concentrate is transferred
to feed water directly
• Work Exchanger
• Pressure Exchanger
• Other devices
Energy Recovery:
HP PUMP
MEMBRANES
PELTON
TURBINE
HP PUMP
MEMBRANES
PXBOOSTER
PUMP
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Post-treatment • RO permeate is corrosive
– low pH, low alkalinity, low TDS, low hardness, etc.
• Typical post-treatment: adjustment of pH,
alkalinity and hardness.
• Target: – match pH to that in distribution system – have reasonable alkalinity, positive LSI and
reasonable CCPP
• Raising pH: If feed water was acidified,
degassify to remove CO2. Add NaOH or Lime
• Typical chemicals: Lime, NaOH, CO2. Also,
use of corrosion inhibitors.
• Soda ash – not so common
• Calcite filters also an option
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Green Energy Initiative
Use of Landfill Gas from South East New Territories (SENT) Landfill
• Processed gas from SENT available at night time
• On depletion till around 2030
• Technical and financial viability being explored
SENT Landfill
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Moving Forward …
Ultimate Project Objective:
A state of the art desalination facility that provides a
strategic water source to Hong Kong at optimal cost
Save Water for the Future
Every Drop Counts
Thank You