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Dipl.-Phys.
H. Müller-Holst |
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Multi
Effect Humidification |
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Technical
Description GOR-MEH Desalination Systems |
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Description
of the process
Figure
1 illustrates the operation of the system. The principle of the
innovative distillation process is based on the evaporation of water and
the condensation of water vapour to and from humid air. The humid air
flows in a circuit driven by natural convection between condenser and
evaporator (clockwise in Figure 1). Evaporator and condenser are located
in the same thermally insulated box.
In
the
evaporator the hot (80-85°C)
seawater, being heated e.g. in a solar collector, is distributed onto
vertically hanging fleeces made of Polypropylene and is slowly
trickling downwards. The air moves in countercurrent flow to the brine
through the evaporator and becomes saturated with humidity. Partial
evaporation cools the brine which leaves the evaporation unit concentrated
with higher salt content and a temperature of approx.
45°C.
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The
condenser unit is located
opposite to the evaporator. Here the saturated air condenses on a flat
plate heat exchanger made of Polypropylene (double webbed slabs). The
distillate runs down the plates and is trickling into a collecting
basin. The heat of condensation is mainly transferred to the cold sea
water flowing upwards inside the flat plate heat exchanger. Thus the
temperature of the brine in the condenser rises from 40°C at the inlet
to approx. 75°C at outlet. In
the next step the brine is heated up to the evaporator inlet temperature,
which is between 80 to 85°C. This heat can be performed e.g. by highly
efficient solar collectors, from a thermal storage tank or by waste heat.
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Advantages of the System
The outstanding advantages of the
MEH desalination system are:
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Low specific process
heat consumption of 60-90
kWhthermal per meter cube of fresh water
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Low temperature process
heat can be supplied by solar collectors, waste heat or other sources of
low temperature heat, ( e.g. geothermal)
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Raw water of any
salinity can be used (brackish, sea, even brine of other processes)
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No
chemical pretreatment needed
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Low auxiliary energy
demand (pumps) can be provided by photovoltaics
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Product water is
distillate (best quality product water)
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Modular set up -
Capacities of up to 5 m³ per day are considerable
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Simple and robust
construction, easy maintenance
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No corrosion because
all components in contact with brine are made of enhanced materials
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