Environmental Engineering Reference
In-Depth Information
It simultaneously causes further evaporation from the external seawater film and the
process is repeated from effect to effect down the plant. The heat input from the accumulator
is thus used over and over again in successive evaporation/condensation heat exchangers in
each effect to produce more product and new vapor, thereby obtaining a maximum quantity
of fresh water with minimum heat input. The vapor generated in the last effect (18
th
) is
condensed in a seawater-cooled condenser and part of the seawater is used as feedwater to the
stack. The remaining seawater is rejected to the sea and carries most of the heat away from
the process.
Figure 7. The MED evaporator.
3.2. Design Features
Table 2 shows the design conditions and specifications at the time of the original
planning of the test plant. At the planning stage, no detailed solar radiation data was available
for Abu Dhabi city and the only data available was that for nearby Kuwait. Therefore the data
for Kuwait was used with the annual mean daily solar radiation on horizontal surface taken as
5000 kcal/m
2
day. Based on the measurements at the test plant made during 1985 and
subsequent years, the annual average daily values were found to be slightly higher than this
value (5270 kcal/m
2
day for 1985).
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