Multiple Effect Distillation Process for Sea Water Desalination
S IDEM/ENTROPIE is the world leader in a water desalination through low temperature distillation process such as:
•Multiple Effect Distillation(MED)
•Multiple Effect Distillation with Thermal Vapour Compression(MED-TVC)
•Multiple Effect Distillation with Mechanical Vapour Compression(MED-MVC)
BASICS ON THE MED PROCESS
An MED evaporator consists of veral concutive cells(or effects)maintained
at decreasing levels of pressure(and temperature)from the first(hot)cell to the
last one(cold).Each cell mainly consists in a horizontal tubes bundle.The top of
the bundle is sprayed with a water make-up that flows down from tube to
tube by gravity(e sketch1).
Heating steam is introduced inside the tubes.Since tubes are cooled externally
by make-up flow,steam condens into distillate(fresh water)inside the tubes.
At the same time a water warms up and partly evaporates by recovering the
condensation heat(latent heat).Due to evaporation a water slightly
欢乐颂2谢童concentrates when flowing down the bundle and gives brine at the bottom of
the cell.The vapour raid by a water evaporation is at a lower temperature
than heating steam.However it can still be ud as heating media for the next
effect where the process is repeated.The decreasing pressure from one cell to
the next one allows brine and distillate to be drawn to the next cell where they
will flash and relea additional amounts of vapour at the lower pressure.
This additional vapour will conden into distillate inside the next cell.
This process is repeated in a ries of effects(Multiple Effect Distillation)
(e sketch2with3effects).In the last cell,the produced steam condens on a
conventional shell and tubes heat exchanger.This exchanger,called“distillate
condenr”is cooled by a-water.At the outlet of this condenr,part of the
warmed a-water is ud as make-up of the unit,the other part is rejected to
the a.Brine and distillate are collected from cell to cell till the last one from where they are extracted by centrifugal pumps
The thermal efficiency of such evaporator can be quantified as the number of kilos of distillate produced per one kilo of steam introduced in the system.Such number is called the Gain Output Ratio(GOR).
The GOR of the evaporator in sketch2can be enhanced by addition of a thermo-compressor between one of the cells and the hot one.Using LP or MP steam this static compressor will take part of the vapour raid in one of the cells and recycle it into higher pressure vapour to be ud as heating media for the first one.Sketch3shows the typical arrangement of an MED evaporator with thermocompression(MED-TVC).Whereas the GOR of the evaporator in sketch2 would be in the range of3(using LLP steam)the GOR of sketch3would rather reach6(using LP or MP steam).
When no steam is available,it is still possible to u the MED process with a Mechanical Vapour Compressor(MED-MVC).In such ca the vapour is recycled from the cold cell to the hot one by means of a centrifugal compressor driven by an electrical engine(Sketch4).The electrical consumption of such system is in the range of8to15kWh/m3.Due to current limitation in compressors technology the maximum capacity of MED-MVC units is5000m3/day.
SEA WATER DISCHARGE
股权合作协议Sketch1
Non-heated
awater
家常凉拌海带丝Distilled
water
Produced
Steam
Brine
Steam
introduced
MED&MED-TVC
>Very low electrical consumption(1.5kWh/m3)compared to other thermal process such as Multi Stage Flash(MSF)or membrane process(Rever Osmosis)
>Operate at low temperature(<70C°)and at low concentration(<1.5)to avoid corrosion and scaling
>Produce steadily high purity distillate
>Do not need complex pre-treatment of a water and tolerant to variations of a water conditions
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>Are highly reliable and simple to operate
>Reduce civil works cost thanks to reduced foot print
>Are simple to install with the packaged unit mounted on skids and delivered ready for u,after simple installation
>Have a low maintenance cost(No rotating parts except low pressure pumps)
>Operate24hours a day with minimum supervision
>Ideal for coupling with power plants,steam can be ud at any pressure from0.35to40bar abs >Can be adapted to any heat source including hot water
>Allow very high thermal efficiencies and savings in fuel costs
>Range up to15MIGD(68000m3/day)
MED-MVC
>Range up to5000m3/day
>Are environmentally clean:100%electrical process(no external heat source)
>Have high energy efficiency:electrical energy consumption ranging from8to15kWh/m3
>Sea water consumption is reduced with only make up water necessary
>Water spray through large opening nozzles or dismountable perforated plates:•Better water distribution-No risk of plugging
梦见房子漏雨•Allows final degasing of a water祝福祖国的歌曲
>Low vapour velocities:
•Low pressure loss
•Better quality of distillate(<2ppm TDS)
>Knitted stainless steel wire high efficiency demisters
>Tubes expanded in tube plates:guarantee of a constant purity of distillate
>Easy access to the evaporator internals
>High quality lected materials
>Factory asmbled and tested(for capacities<2500m3/day)on skid,
胡一凡with all auxiliaries,so that installation on site is minimized
>A complete range of standard MED-TVC and MVC units is available
up to3000m3/day.
ENERGY SOURCES FLEXIBILITY
MED can be powered by almost any kind of heat source:
>Very low Pressure(LLP)steam(0.35to1bar a):MED
>Low or medium Pressure(LP or MP)steam(over2bar a):MED-TVC
>Hot water sources above60°C:MED
>Electricity:MED-MVC
Steam or heat is available from:
>Steam turbines
>Gas turbine power plants(open and combined cycle)
>Diel generators
>Heat recovery on flue gas cleaning and waste incinerators
>Heat recovery on exothermal industrial process
>Geothermal waters
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