1. Seawater DeSalinationprojects
_________
Hagay Shemer, Tianjin Project Engineer, IDE Technologies
___
Execution of a
Chinese desalination
project at minus 20°C
THE BEIJING power station, built on an area of
2.2 km2
, is located along the Yellow Sea, approximately
60 km north of Tianjin and some 220 km from the
capital Beijing, in the Chinese province of Hebei.
The 4,000 MW power station required an
investment of 26 billion Yuan (US$ 4 billion) and is
owned by SDIC – a government investment company
established in 1995, and considered the largest
government-owned holding company in China, with
a current asset value estimated at approximately
US$ 13 billion. The company operates under the
Chinese Energy Ministry.
The coal-based station is located in the hub of
an industrial zone that is undergoing accelerated
development and is considered one of the most
advanced in China.
The power station was built using an
Ultra-Supercritical Power Generation design, a
technology originally developed in Europe and
Japan in the 1990s. The technology is based on
increasing the pressure and temperature in the steam
boiler to above critical values, thus achieving high
efficiency with reduced coal consumption.
In 2010, IDE Technologies completed the
construction of a 100,000 m3
/d seawater desalination
plant utilizing multi-effect distillation (MED)
evaporation technology, within the area of the power
station. This plant serves the boiler feed water needs
of the power station, as well as the supply of drinking
water to the local population. Following the success
of the first project, in 2010 IDE won the bid for the
second stage of the project with a capacity identical
to that of the first stage. The total capacity of the two
facilities will be 200,000 m3
/d, making this the largest
seawater desalination site in China.
Project GoalS
In the inspirational slogan “Recycled Economy”, the
Chinese envisaged an ecological circle where natural
resources are utilized while protecting the environment.
The vision combines inexpensive power production
with seawater desalination for the benefit of industry
and the community. Potable water is produced together
with salt and other essential minerals, such as bromide,
magnesium chloride and magnesium sulfate.
As the project is located in an area that suffers a
severe water shortage, the desalination facility provides
an important source of drinking water to the large
municipal system of Tianjin, with its population that
exceeds 15 million inhabitants.
How do you design a thermal desalination plant
where the driven force is steam with a wide range
of pressures? And how can the project cope
with hostile environmental conditions such as
temperatures that drop below minus 20°C? This
article describes how IDE Technologies overcame
the challenges of building a multi-effect distillation
plant in China, the largest seawater desalination
plant in the country to date.
Project Data (1st
stage)
Parameter Units ValUes
Plant production m3
/d 100,000
Number of units unit 4
Plant dimensions m x m 160x125
Product water capacity
per unit
m3
/d 25,000
Brine salinity TDS in mg/L, % 6.7
Brine temperature °C 68
Amount of steam (@ 0.5
Mpa) required for the plant
t/h 260
GOR (gain output ratio) – 16 – 13
Power consumption
for the process
kWh/t product 1.3
| 18 | Desalination & Water Reuse | May-June 2011
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2. ProjectS
May-June 2011 | Desalination & Water Reuse | 19 |
DeSalination ProceSS
Existing MED plants utilize horizontal tubes made of
aluminum alloy and falling-film evaporative condensers
in a serial arrangement, to produce a multiple quantity
of distillate from a given quantity of input steam. This
is achieved through repetitive steps of evaporation and
condensation, each at a lower temperature and pressure.
Any number of evaporative condensers (effects)
may be incorporated in the plant’s heat-recovery
sections, depending upon the temperature and cost of
the available low-grade heat and the optimal trade-off
point between investment and steam economy
Technically, the number of effects is limited only
by the temperature difference between the steam and
seawater inlet temperatures (defining the hot and
cold ends of the unit) and the minimum temperature
differential allowed on each effect. The MED process
operation is based on counter-current flow of the
evaporating vapor against the seawater feed. The
feed is first introduced into the cool group of effects,
where it is partially evaporated by the vapor received
from the adjacent hotter effect. The remaining feed in
each effect, now slightly warmed and concentrated, is
pumped into the next hotter group of effects.
The thermal efficiency of the process is considerably
improved by routing the motive steam through a
thermo-compressor, which recompresses and recycles
a substantial amount of the vapor generated in the
lower temperature effect back to the first effect, thus
increasing the performance ratio of the unit.
Summary the tianjin desalination plant constitutes a landmark in
the world desalination industry for its implementation of an
integrative system that combines power production, seawater
desalination and the production of edible salt. project execution
was on schedule and met high local quality standards, thus
serving as an economic model of sustainable development.
View of the MED
plant in Tianjin
raw (Feed) Water Quality(1)
ser. no. Parameter ValUe Units
1 Temperature(2)
-1 °C
2 Salinity 3.35 %
3 pH 8.11 –
4 Suspended solids 254 mg/l
5 Turbidity 20 NTU
(1)
Seawater data from the power station site (2)
Winter time

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3. | 20 | Desalination & Water Reuse | May-June 2011
Giant Minneapolis
potable water plant
becoming UF testbed
THE ColumBIA Heights Membrane
Filtration Plant (MFP), Minneapolis,
USA, one of the largest ultrafiltration (UF)
potable water plants in the world, increased
its size by 14% last summer as the result of
four new UF units being put into service.
These expanded the plant’s capacity from
70 MGD (265,000 m3
/d) to 79 MGD
(299,000 m3
/d).
A few months earlier in 2010, the
council of the City of Minneapolis
authorized city officials to enter into a
collaborative partnership with the Dow
Chemical Company to allow the council
and the membrane manufacturer to
discuss opportunities for Dow to evaluate
treatment technology and developmental
products at city facilities.
As a result, in January 2011, the
city authorized field testing of a Dow
UF pilot unit and related items at
Columbia Heights.
HiStory of columbia HeiGHtS
The Columbia Heights MFP, which
commenced operations in 2005, is sited
next door to the original Minneapolis
ProjectS
Since the performance of a thermo-compressor is a
function of the motive steam pressure and the required
compression ratio, and given that in the Tianjin
installation the motive steam pressure is not constant,
two thermo-compressors are installed. When the
motive steam pressure is 0.12 MPa, the fixed
thermo-compressor recycles vapor from the sixth effect.
When the motive steam pressure is 0.5 MPa, the
variable thermo-compressor recycles vapor from the
ninth effect.
tianjin meD aDvantaGeS
The Tianjin MED unit offers significant advantages
working with varying pressures (0.3-6.0 bara), which
have a significant impact on the viability of constant
water production with high purity:
• The MED units can operate at 110% – 40% capacity
under variable steam pressures
• The MED units work under extreme ambient
temperatures of 40° to minus 20°C; seawater
temperatures vary in the range 33° to minus 1°C
• Tianjin’s 14 effect units show an extraordinary GOR
(Gain Output Ratio) in the range of 13 – 16
• The MED yield is 50%
The produced water is used directly for industrial
processes (boiler feed water), or blended with locally
available brackish water for urban consumption.
The MED plant at Tianjin has superior
technological characteristics compared with other
systems for seawater applications. These characteristics,
resulting from operation under variable motive
steam pressures at a low temperature design,
provide simple and long term operation under
remarkably stable conditions.
DeSalinateD Water Quality
The plant supplies distilled water containing less than
10 mg/l Total Dissolved Solids (TDS), and with a pH
of approximately 6.
oPeration anD maintenance
The plant requires only 15 people for operation; local
employees have been trained for the purpose.
uniQue featureS of tHe Plant
The design, supply and erection of the plant combined
a number of significant challenges, including harsh
terrain conditions characterized by low ambient and
seawater temperatures in the winter (minus 20°C and
1°C respectively) and low quality seawater.
As opposed to most operating desalination facilities
in the world, where the brine water is returned to the
sea, the brine from the Tianjin plant is directed to
evaporation ponds for the production of edible salt. 
The uS city of minneapolis has become a key site in the history of ultrafiltration
(uF) membrane technology for drinking water. Its recently expanded Columbia
Heights membrane Treatment Plant is one of the largest uF drinking water plants in
the world and is currently being used by Dow Water & Process Solutions as a test-bed
for new uF membranes.
_________
robin Wiseman,
Editor D&WR
___

tianjin’s 14
effect units
show an ex-
traordinary
Gor
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