Boiler
Feed
Water
Treatment
The natural water contains solid, liquid and gaseous impurities and. therefore this water cannot be used for the generation of steam in the boilers. The impurities present in the water should be removed before its use for steam generation.
The necessity for reducing the corrosive nature and quantity of dissolved and suspended solids in feed water has become increasingly important with the advent of high pressure critical and super critical boilers.
With
the
introduction
of
once
through
boilers,
the
problem
pf
removing
the
dissolved
solids
has
b
come
more
important
because,
even
very
small
quantities
of
dissolved
and
suspended
solids
in
feed
water
pass
through
the
turbine
and
condenser.
The
effects
of
these
solids
are
the
corrosion
and
erosion
of
boiler
tubes,
turbine
blades
and
condenser
tubes,
These
solids
further
blockage
the
boiler
tubes
and
result
is
tube
failure
due
to
over
heating.
Therefore.
it
is
necessary
to
polish
the
condensate
or
condenser
leakage
compensating
feed
water
to
remove
any
contamination
caused
by
corrosion
Although
a
considerable
volume
of
knowledge
is
now
available
even
then
the
internal
boiler
corrosion
remains
a
problem,
especially
in
plants
operating
at
60
kgf/cm2
The
external
water
is
used
as
a
make
up
to
the
feed
water
system
in
order
to
counter
balance
the
loss
of
working
medium
throughout
the
cycle
from
blow
down,
leaks
etc.
This
loss
varies
from
1
to
3%
during
normal
operation
and
5%
during
start-up
period
The
total
make
up
water
required
per
hour
for
a
400
MW
capacity
plant
is
of
the
order
of
100
to
150
tons
per
hour.
Therefore,
it
is
absolutely
necessary
to
have
a
separate
water
softening
plant
to
polish
the
water
taken
from
outside
source
(well,
lake
or
river)
to
counterbalance
the
losses
in
the
system.
The
most
probable
reason
of
condensate
contamination
is
leakage
since
the
system
is
not
sufficiently
tight
under
normal
load
conditions
or
because
of
cyclic
operating
conditions
such
as
frequent
start
up
and
stop.
Another
cause
of
contamination
is
condenser
tube
leakage. Condenser
cooling
water
is
generally
oxygen
saturated
and
contains
enormous
quantity
of
solids.
Therefore,
the
condenser
tube
leakage
introduces
oxygen
and
solids
in
the
feed
water
system.
This
leakage
can
seriously
upset
operating
conditions
where
the
condenser
cooling
water
system
consists
cooling
towers
because
of
further
concentration
of
salt
in
cooling
water
due
to
evaporation
over
cooling
towers.
Even
small
leaks
in
condenser
permit
a
surprising
amount
of
low
quality
cooling
water
to
contaminate
high
purity
condensate
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