High
Pressure
Boilers
The demand for the higher power outputs from the boiler and associated plant is increased in the last ten years. It is a common practice to use high pressure and temperature steam in power plants to increase: the efficiency of the plant and to reduce the cost of electricity production. In the last to years, the operating pressures and temperatures of boilers have risen, and this has been possible because of developments of materials. For the given steam conditions and boiler size, there is not much variation in efficiency between different types and the widest scope left to the designer only in increasing plant economy by making use of high temperature flue gases.
When
steam
is
needed
at
pressures
30
kg/cm2,
and
individual
boilers
are
required
to
raise
less
than
about
30
tons
of
steam
per
hour,
shell
boilers
arc
considerably
cheaper
than
water
tube
boiler
and
are
equally
satisfactory
it.
all
other
respects.
Above
these
limit
shell
boilers
(generally
factory
built)
are
difficult
to
transport
if
not
impossible.
There
arc
no
such
limits
to
water
tube
boilers.
These
can
be
site
erected
from
easily
transportable
parts,
and
moreover
the
pressure
parts
are
of
small,
diameter
and
therefore
can
be
thinner.
The
geometry
can
be
varied
to
suit
a
wide
range
of
situations,
and
furnace
is
not
limited
to
cylindrical
form.
Therefore,
water
tube
boilers
are
generally
preferred
for
high
pressure
and
high
output,
whereas
shell
boilers
for
low
pressure
and
low
output.
The
modern
high
pressure
boilers
used
for
power
generations
are
for
steam
capacities
30
to
650
ton3/hr
and
above
with
a
pressure:
up
to
160
kgf/cm2
and
maximum
steam
temperature
of
about
540
Degree
Celsius
One
of
the
largest
boiler
plants
in
the
world
is
in
U.K.
used
to
the
Central
Electricity
Generating
Board.
This
boiler
was
designed
for
1700
tons
of
steam
generation
per
hour
at
a
pressure
of
160
kg/
cm2
and
a
temperature
of
560
Degree
Celsius
with
one
reheat
to
560°C burning 220 tons of coal per hour
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