Chapter 7AUXILIARY MACHINERY
distiller condenser vacuum. The vacuum is
dependent upon the temperature and quantity of
the circulating water, and the proper operation
of the air ejectors. Too low an overboard
discharge temperature of the distiller condenser
circulating water is accompanied by efficiency
losses in the distilling plant. The overboard
discharge temperature should be kept as high as
possible, without exceeding the desired 20°F
temperature rise through the distiller condenser.
In addition, limiting the quantity of circulating
water tends to prolong the service life of the tubes
and tube sheets. When troubles occur which are
not caused by improper operating procedures, an
inspection should be made of the condenser cir-
culating water system to determine the cause of
faulty operation.
Preventive maintenance procedures should be
carried out to ensure that the circulating water
pump is maintained in good material condition.
The maintenance and repair procedures for this
pump are similar to those for the other pumps
of the plant.
Routine procedures should be carried out to
ensure the proper setting and maintenance of the
back-pressure regulating valve. If this valve is not
functioning properly,
the valve should be
disassembled, the valve parts replaced, and the
necessary repairs to the valve made, before its
faulty operation interferes with the operation of
the distilling plant.
To ensure that the condenser circulating water
system is clean and free from scale and foreign
matter, the piping should be inspected at regular
intervals. The operators of the distilling plant
should inspect and clean the strainers, in accord-
ance with the PMS, to prevent accumulations of
foreign matter from interfering with the
proper operation of the plant.
Improper Drainage
Failure of the distilling plant to produce
designed output when the pressure above the
orifice is 5 psig and the first-effect tube nest
vacuum is several inches of mercury always
indicates improper drainage of the distiller con-
denser or of one of the evaporator tube nests
subsequent to the first effect. Complete flooding
of the flash chamber gage glass is also a positive
indication of improper draining of the condenser,
but the fact that the level appears to be in the gage
glass or below is not necessarily an indication of
improper drainage because air leaks at the gage
glass fittings may indicate a false liquid level.
A temperature difference of more than 5 °F
to 10°F between the last-effect shell temperature
and the temperature of the distillate at the
distillate cooler inlet is another indication of
improper drainage; however, the fact that the
temperature difference is within the proper range
does not necessarily indicate proper drainage.
Scale deposits are unlikely to form in the
distilling condenser tubes if the plant is properly
operated and a full flow of circulating water is
maintained. However, if scale deposits do occur,
the tubes must be cleaned.
Venting of the vapor side of the distiller con-
denser is continuously accomplished by the air
ejector. Venting of the saltwater side of this and
other units of the distilling plant need not be con-
tinuous. While starting the plant, and once every
watch thereafter, the vents on all saltwater heads
should be opened until all air is expelled and a
solid stream of water appears, then the vents
should be closed.
Constant Brine Density
The concentration of brine in the evaporators,
to a certain extent, has a direct bearing on the
quality of the distillate, and since varying quan-
tities of brine discharged overboard may affect
the operating conditions, the quantity of brine
discharged and the brine density must be kept as
constant as possible.
If the brine concentration is too low, there will
be a loss in capacity and economy. If the brine
concentration is too high, there will be an increase
in the rate of scaling of the evaporator heating
surfaces, and the quality of the distillate will be
impaired.
The brine density, which should never exceed
1.5/32, is dependent mainly on the quantity of
brine pumped overboard and the amount of
freshwater being produced. The density must be
checked frequently during each watch and
adjusted to the required density. On older distill-
ing plants, the brine density is adjusted by means
of a hand-controlled valve located in the discharge
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