Environmental Engineering Reference
In-Depth Information
failure during the day. If a power failure occurs, this installation automatically drains
out the solar collector water, preventing water hammer due to overheated collector
water.
For the test plant, there was no choice but to reduce the collector absorber area when
dealing with peak radiation intensity during summer time. If all the collectors installed are to
be fully used, however, it is suggested that a three-way proportional control valve is to be
added between the evaporator and the heat accumulators and to mix some of the return
heating water from the evaporator with the hot water from the accumulator to prevent the
evaporator from overloading.
(b) Development of computer simulation program
A simulation program was prepared based on the results of the research operation of the
test plant. It is a substantially improved version of the simulation program over that used in
the basic design. The results of running this new program showed water productions of 102%
and 97.4% of the test plant's actual performance for January and June 1985, respectively, and
there was good agreement.
The simulation program is used to calculate the water production for data input into it,
and involves the weather conditions at the plant concerned, such as solar radiation, ambient
temperature and seawater temperature; and the specifications and capacities of the major
individual plant components - capacity (100 to 2,000 m
3
/day), maximum brine temperature
(60 to 80
o
C), number of effects (13 to 32) for the evaporator, for example; and the operating
conditions of the plant (eg. Flow rate and temperature of the heating water). If this simulation
calculation is repeated for various sets of data, the optimum combination for the geographical
area concerned, including the specifications and capacities of solar collectors, heat
accumulator and evaporator, can be determined. Other data can also be obtained that may be
useful in the selection of pump capacities, piping lengths, angles of absorber plates of solar
collectors, etc. Therefore, the simulation program can be used to facilitate precise conceptual
design of solar plants of similar design.
(c) Water production costs
•
The collector cost has a vital contribution to the cost of water. For a plant capacity of
1000 m
3
/day, the cost of water is 2.24 $/m
3
for a collector cost of 200 $/m
2
and is
3.35 $/m
3
for a collector cost of 600 $/m
2
.
For a plant capacity of 130 m
3
/day which is identical to that of the test plant, the cost
of water is quite sensitive to the number of effects and to a lesser degree on the cost
of collector with the cost of water varying between 8 $/m
3
and 4 $/m
3
.
•
•
The difference between the cost of water from a solar MED plant and the
corresponding cost from a conventional MED plant can be in favor for high fuel cost
and low collector cost situation indicating that the cost of water from a solar MED
plant can be cheaper than that of a conventional MED plant under these conditions.
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