Transcript  Introduction  Watertube boiler construction  Steam generation process  Watertube boiler classification  Raising steam.

 Introduction
 Watertube
boiler construction
 Steam generation process
 Watertube boiler classification
 Raising steam
 Boiler
= a closed pressure vessel in
which feed water is heated in order to
produce steam
 Watertube
boiler
 Firetube boiler
 Watertube
boiler is a type of boiler in
which water circulates in tubes heated
externally by the fire.
A.
Smoke uptake
B.
Economiser
a heat exchanger that
transfers heat from boiler
flue gases to boiler
feedwater
C.
Steam outlet
saturated steam from the
steam drum to the
superheater
D.
Cyclone
a device inside the drum
that is used to prevent water
and solids from passing
over with the steam outlet
E.
Stay tube
for superheater
F.
Stays
for superheater tubes
G.
Superheated steam outlet
H.
Superheater
a bank of tubes, in the
exhaust gas duct after the
boiler, used to heat the
steam above the saturation
temperature
I.
Superheater headers
distribution and collecting
boxes for the superheater
tubes
J.
Water Drum
K.
Burner
L.
Waterwall header
distribution box for
waterwall and downcomers
M.
Footing
N.
Waterwall
tubes welded together to
form a wall
O.
Waterwall header
distribution box for
waterwall and downcomers
P.
Back side waterwall
Q.
Boiler hood
R.
Waterwall header
collecting box for waterwall
and risers
S.
Riser
the water-steam emulsion
rises in these tubes toward
the steam drum
T.
Downcomer
a tube through which water
flows downward; these tubes
are normally not heated, and
the boiler water flows
through them to supply the
generating tubes
U.
Steam Drum
separates the steam from
the water
V.
Economiser header
distribution box for the
economizer tubes
 furnace
or
combustion chamber
 air
is supplied to the
boiler furnace - to
enable combustion of
fuel to take place
 burning
of fuel (LNG,
liquid fuels, etc.) to
release its energy heat is developed
 the
energy released
by the burning fuel in
the boiler furnace is
stored (as temp. and
pressure) in the
steam produced
 feed
water circulates
from the water drum
to the steam drum
and is heated in the
process
 some
of the feed
water passes through
tubes surrounding
the furnace, i.e.
waterwall and floor
tubes, where it is
heated and returned
to the steam drum
 steam
is further
heated and 'dried‘
(i.e. all traces of
water are converted
into steam) in the
superheater
 temperature
of
superheated steam
will be above that of
steam in the drum

an 'attemperator', i.e.
a steam cooler, may
be fitted in the
system to control the
superheated steam
temperature
 superheated
steam
then leaves the boiler
for use in system
 Where
main propulsion is steam
powered, one or more large watertube
boilers will be fitted to produce steam at
very high temperatures and pressures.
 On
a vessel with diesel propulsion, a
smaller (usually firetube type) boiler
may be fitted to provide steam for
additional ship services.
 uses
small diameter tubes, has a small
steam drum, enables the generation or
production of steam at high temperatures
and pressures
 weight
of the boiler is much less than an
equivalent firetube boiler
 steam
raising and steam generation
process is much quicker
 design
arrangements are flexible,
efficiency is high
 the
design facilitates good natural
circulation of feed water
 these
are some of the many reasons why
the watertube boiler has replaced the
firetube boiler as the major steam
producer
CLASSIFICATION
ACCORDING TO:
TYPES

Application


Pressure


Number of drums

main boiler – auxiliary
boiler (donkey boiler)
low-pressure b. ,
intermediate-pressure b. ,
high-pressure b.
single-drum b., two- drum
b., three-drum b.
CLASSIFICATION
ACCORDING TO:
TYPES

Tube inclination


Arrangement of gas flow

horizontal - vertical
single-flow b., double-flow
b.
 the
forced draught fan should be started
and air passed through the furnace for
several minutes to 'purge' it of any
exhaust gas or oil vapours
 the
air slides (checks) at every register,
except the 'lighting up' burner, should
then be closed
 the
operating burner can now be lit and
adjusted to provide a low firing rate with
good combustion
 the
fuel oil pressure and forced draught
pressure should be matched to ensure
good combustion with a full steady flame
 the
superheater header drains may be
closed once steam issues from them
 the
boiler must be brought slowly up to
working pressure in order to ensure
gradual expansion and to avoid
overheating the superheater elements
and damaging any material
 the
main and auxiliary steam lines should
now be warmed through then the drains
closed
 the
water level gauges should be blown
through and checked for correct reading
 when
the steam pressure is about
300kN/m2 (3 bar) below the normal
operating value the safety valves should
be lifted and released using the easing
gear

once at operating pressure, the boiler
may be put on load and the superheater
circulating valves closed
 all
other vents, drains and bypasses
should then be closed
 the
water level in the boiler should be
carefully checked and the automatic
water regulating arrangements observed
for correct operation