Environmental Engineering Reference
In-Depth Information
8,546 hours which translate into an availability of 97.6%. Thus, the test plant has a very good
adaptability to weather conditions.
(3) Establishment of a method for cleaning of solar collectors
One of the early worries about the test plant was whether there was an easy and
economical method for removing fouling material (dust) due to sandstorms and polluted air.
In an effort to solve this problem, an investigation was made of solar installations in the
Middle East, and based on the results of this investigation, a preliminary test was made for
collector cleaning. As a result, high-pressure water spray gun was adopted as the method of
cleaning the solar collectors. This method worked very well. A cleaning once a month
reduced the heat loss from the solar collectors from the planned 10% to 5.2%. The annual
amount of water used for this purpose was about 0.2% of the total water production. The
applicability of this cleaning method to practical plants was therefore demonstrated.
(4) Comparison of the test plant results with that of the basic design
(a) Improved effective use of solar radiation
It was difficult to make an accurate comparison of the effective use of solar radiation
between the test plant and the basic design because the weather conditions were different.
Nevertheless, the table below shows that the ratio of solar radiation used for water production
to the total solar radiation obtained using the simulation program (47.5%) increased markedly
over the value that was predicted by the basic design (36.0%).
Table 22. Plant energy balance
Energy quantity
Basic design
Simulation
Total solar radiation on tilted surface
100%
100%
Heat loss due to fouling
10%
5.2%
Heat loss from solar collectors
42.7%
36.3%
Quantity of
collected heat
Heat loss from collector piping
5.3%
6.9%
Heat loss from heat accumulators
2.4%
3.8%
Heat loss from evaporator
2.6%
0.3%
Heat quantity used for
desalination
36.0%
47.5%
The reasons for this marked increase are:
•
The heat loss due to dust deposition was reduced by almost half, although the heat
loss from the solar collectors was actually larger than was planned in the basic
design.
•
The quantity of collected heat was larger than was planned in the basic design
because it was possible to collect heat at lower temperature.
•
The number of evaporator starts and stops was considerably reduced over the
planned number, which in turn reduced the heat loss from the evaporator.
•
mprovements made on the test plant: Motor-operated valves, check valves, etc. were
installed at the inlet and outlet of the solar collectors to make provision for power
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