Environmental Engineering Reference
In-Depth Information
level. The air leakage into the pump would break the vacuum and drastically reduces the
pump flow.
The drain pump gave a lot of trouble. All the drains from the evaporator was collected
into a pit in which the pump suction line is immersed. A level switch is used to start and stop
the operation of the pump. This pump was found to be easily clogged with debris which
accumulates inside the pit and caused a relay trip due to motor over-current. To solve this
problem, a fine screen was installed on the tip of the suction line inside the pit to prevent the
trash from entering the pump. The screen has to be cleaned regularly and trash removed from
it. The product water pump was another source of problems and was responsible for plant
shutdown particularly in the first year of plant operation. Faulty bearings and a pump shaft
were replaced.
8.2.2. Inspection of the Evaporator
An overhaul was carried out at the end of one year of plant operation which consisted of:
•
The first effect, which is subject to high temperature and hence high possibility of
scaling was inspected after the first year of operation. An accumulation of silt (fine
sand) approximately 1 cm thick was found on the bottom of the 1
st
effect and was
removed.
•
Blackened spots were seen on the outer surface of the first effect tube bundle but
they remained the same as those at the start of plant operation and should cause no
problems.
•
Scale marks were seen on parts of the tube bundle of the first effect near the water
chambers at the heater inlet and outlet, but they did not represent any advanced state.
A re-inspection few months later revealed no advanced state.
No abnormal conditions were seen on the 18
th
effect.
•
8.2.3. Change in Operating Sequence
A modification was carried out in a part of the operating sequence so that the test plant
could be safely operated. This change brought about the following improvements in plant
operation:
•
If the intake strainer is clogged with foreign matter like seaweed, the seawater intake
pump will be stopped temporarily.
•
If the concentration of the discharged brine becomes too high, an alarm will be
triggered and the plant shut down. This is to prevent scale formation on the heat
transfer tubes if the flow of heating water increases more than necessary or if the
feedwater quantity is reduced.
•
If the product water quantity becomes too small, an alarm will be triggered and the
plant shutdown. This is to prevent the product water pump fro running at no load if
the temperature of the heating water drops enough to make water production too low.
•
The manner of emergency plant shutdown will be either of the two types given below
depending on the degree of emergency:
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