Environmental Engineering Reference
In-Depth Information
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Immediate plant shutdown for motor relay tripping, too low seawater flow,
or the like.
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Gradual plant shutdown for too high first effect evaporator temperature, too
high brine concentration, or the like.
8.2.4. Modification of the System for Injecting Anti-scale Chemical
The original plan called for a single system for injecting the scale preventing chemical
“Belgard EV” into seawater feed. However, because the injection pump has failed during
unmanned operation of the plant and it was feared that the plant could have been subjected to
scaling, it was decided to modify the injection system to include the standby system as a
secondary injection system. In case the primary injection system fails, the secondary system
automatically turns on.
8.2.5. Modification of the Method of Feeding Sealing
Water to the Priming Vacuum Pump
Because the seawater level is lower than the level of the seawater intake pump, when the
plant is not in operation, the seawater in the suction line of this pump drains back by gravity
to the sea and the line is full of air. The priming vacuum pump, which is a water ring sealed
vacuum pump, is used to prime (start) the seawater intake pump by insuring that this pump
and its suction line is full of water. Seawater was initially used for the sealing water, but since
the primary vacuum pump is operated at plant startup only, seawater inside the pump and
sealing tank has caused considerable amount of rust and made the water brown. It was
therefore decided that fresh water be used for the sealing water instead of seawater.
9. Simulation Program and its Validation
9.1. Simulation Program
9.1.1. Outline
The performance of a solar desalination plant that uses solar energy as the heating source
for a seawater evaporator is affected by the amount of solar radiation, ambient temperature
and other climatic conditions. These conditions are extremely unstable and are subject to
constant change. This means that computer-based simulation is indispensable if, to cope with
these changes, the system operation states are to be grasped and the amount of product water
annually is to be forecast.
As shown with the basic design, computer simulation was used to investigate the
operating characteristics even at the planning stage of the test plant. However, it was not
possible to grasp with any accuracy the climatic conditions when design was commenced and
forecasted values based on experience to date were used even for the performance of the
various components.
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