Note: Descriptions are shown in the official language in which they were submitted.
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i SOOT BLOWER
The present invention relates to a soot blower for cleaning the
surfaces of a heat exchanger.
In such soot blowers, when not actuated, the corrosive hot gases
carrying soot from the combustion of solid, liquid or gaseous fuels come into
contact with the soot blower lance and through the blower jet openings in the
lance can enter the lance tube, where they cause damage by corrosion or
fouling.
To reduce this problem an inert gaseous purging medium, for example,
air, is introduced beyond the soot blower valve when the blower is in -
operative, with the pressure of the pur~ing medium being greater than that of
the combustion gases in the heat exchanger. A stream of the inert purging
medium thus passes through the lanc~ into the heat exchanger, and prevents the
entry of the agressive gases at the jets. A sealing medium, for example, air,
is also blown into the wall casing surrounding the entry point of the lance
into the heat exchanger to provide a seal against escape of combustion gas to
the environment.
In heat exchangers, particularly those for power station boilers,
which are provided with several soot blowers, both the purging air and the
sealing air are drawn from a central blower system and distributed to the
individual soot blowers. This requires an expensive ducting system. The
relatively low pressure level of the central blower frequently makes it
necessary to use large-diameter ducts to reduce frictional losses. A special
control element is needed ahead of each soot blower to achieve even
distribution of the required amounts of air, a difficulty which is compounded
by the different frictional losses resulting from the unequal duct lengths to
the individual soot blowers. Finally, the connections at the soot blower
valve andfor at tha wall casing must be flexible to allow for movement of the
soot blower and the efects of expansion.
A further disadvantage of such central air systems, is that very
often the purging and sealing air is drawn from a blower which is normally
shut down when the heat exchanger is switched off so that the purging and
sealing is then no longer present. This means that the stove effect which
persists within the hot heat exchanger drives the undesirable combustion gases
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into the soot blower lance or from the wall opening of the heat exchanger into
the environment.
It is a further requirement to many manufacturers and operators of
heat exchangers that the quantity of air introduced at each soot blower should
be as low as possible and should not exceed a quite low maximum value even in
the event of those pressure variations which typically frequently occur on the
combustion gas side.
It is an object of the present invention to simplify the known system
for supplying a soot blower with pur~ing and sealing media.
Here described in preferred embodiment is apparatus with which it is
possible to dispense with the central blower and the expensive
air-distribution system, and where the purging and sealing media are generated
by a dedicated compressor on each separate soot blower. The compressor and
the distribution system are configured so that each soot blower continuously
receives the required quantity oE purging and sealing air. 'rhe required
coarse adjustments can be undertaken by the manufacturer.
More particularly, in accordance with one aspe~t of the invention
there is provided, a soot blower for cleaning heating surfaces of a heat
exchanger comprising,
a lance,
said lance being provided at its front end with jets and at its rear
end being connected through a soot blower valve to a feed line for a blowing
medium, said lance passing through a wall of the heat exchanger and being
sealed by a waLl casing where the lance passes into the heat exchanger,
a connector for a purging medium for said lance between the soot
blower valve and the jets of said lance,
a connector for a sealing medium on said wall casing,
an individual system for generatinB and distributing purging medium
and sealing medium for said soot blower connected to said respective
connectors,
and a checX valve between the soot blower valve and said purging
medium connector for preventing flow of blowing medium into said generating
and distributing system.
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In accordance with a second aspect of the invention there is
provided, a soot blower for cleaning heating surfaces of a heat exchanger,
comprising, a lance, which passes through the wall of the heat exchanger and
is sealed at this point by a wall casing, the lance being provided at its
front end with jets and at its rear end being connected through a soot blower
valve to a feed line for a blowing medium, and an individual system for
generating and distributing at least one medium selected from the group
consisting of, a purging medium for said lance, and a sealing medium for said
wall casing.
In drawings which illustrate embodiments of the invention;
Figure 1 is a side view of a novel soot blower assembly;
Fieure 2 is a detailed view of portion Y of Figure l;
Figure 3 is a detailed view of portion Z of ~igure 1.
In the drawines, a long tube helical soot blower is shown and with
w~ich the invention is described by way of example only. The inventive
subject matter also finds use in other types of soot blower.
The soot blower illustrated comprises a lance 1, having jets 2 at its
front end. The lance 1 is connected to a drive carriage 4 driven by motor 3,
which together with the lance 1, can be moved on a fixed carrier rail 5. The
motor 3 also rotates the lance 1 axially so that the jets 2 move along a
helical path. The end points of the path for the lance 1 are determined by
fixed limiter switches.
The lance 1 can be moved into a heat exchanger through an entry port,
the walls of such heat exchanger being defined by a wall tube 6. The entry
port is surrounded by a wall casin~ 7 so as to seal it off from the outside
atmosphere. When in the withdrawn position, the lance 1 is located with its
jets 2 within the wall casing 7.
The sliding lance 1 surrounds a fixed inner tube 8, the rear end of
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which has a connector for a blowing medium, for e~ample, steam. The quantity
of blowing medium is controlled by a soot blower valve 9 arranged on the soot
blower.
The inner tube 8 also has a connector 10 for a purging medium, for
example, air. The purge air connector 10 is arranged above the valve seat of
the soot blower valve 9, i.e., in the direction of flow of the blowing mediu~
beyond the soot blower valve 9. The lance 1 is supplied with purging air
through the purge air connector 10 and the inner tube 8, and when the
apparatus is not in soot blowing mode this purgin~ air e~its through the jets
2. ~ check valve 12 (Fig. 2) is arranged in one of the purge air lines 11
leading to the purge air connector 10, and is so adjusted that the blowing
medium cannot pass into the purge air line 11 when the soot blower valve 9 is
open.
The wall casing 7 is provided with a connector 13 for a sealing
medium, for example, air. The sealing air connector 13 is connected through a
fle~ible line 14 with a sealing air line 15 arranged on the soot blower. The
pressure of the purging air and of the sealing air is greater than pressure of
the gas within the heat exchanger.
~ The purging air and the sealing air are both generated by a dedicated
system for the soot blower which comprises, a compressor 16, united with the
soot blower as a unit. Electrical connector cable for the drive for the
compressor 16 and for the motor 3 of the soot blower drive system runs from a
central connector box.
As can be seen in Figures 1 and 2, the compressor 16 is arranged
adjacent the soot blower valve 9. An air line 17 is connected to the output
of the compressor 16 and passes to a T coupling 18. The sealing air line lS
branches off from the T 18 to the sealing air connector 13 on the wall casing
7 and the purge air line 11 is taken from T 18 to the purge air connector 10.
~ safety valve 19 ~Fi~. 2) is incorporated in the air line 17, the release
pressure of which corresponds to the rated pressure of the compressor 16. The
desi~n of the compressor 16 is preferably such that its delivery volume is
substantially independent of the back pressure on the combustion gas.
Compressors which operate on the positive displacement principle may be used,
such as piston or rotary piston compressors. The use of a by-pass compressor
is however particularly advanta~eous. This is capable of operation unaffected
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by back pressure in the pressure range of 0.99 - 1.02 bar, which is that of
interest in soot blower applications. The costs of such by-pass blowers are
considerably less than those of the previously named compressor types. By
using such a compressor configuration, it is possible to ensure that the
delivery volumes rise at worst only slightly if the back pressure on the
combustion gas is lower than the design point of the compressor 16. This is a
considersble advantage over the radial blowers used for known central air
systems, such blowers having operating points which are closely dependent on
the back pressure existing at the particular time.
A further advantage of the named compressors over conventional radial
blowers is that they can operate against relatively high back pressure, so
that larger frictional resistances within the soot blower can be overcome.
This allows the use o~ the air introduced into the soot blower to be used both
as purging air and as sealing air, in a soot blower of the long tube helical
type illustrated, and in which the jets 2 at the ends of the lance 1 are
within the wall casing 7 when not in operation. The air which flows from the
jets 2 on the one hand, prevents combustion gases entering the soot blower,
and on the other, seals the heat exchanger wall. It is thus possible to
dispense with the sealing air connector 13 on the wall casing 7. This
solution is particularly advantageous, because the fle~ible line 14
necessitated by the movement of the heat exchanger wall can be eliminated.
However, this version can only be used if the back pressure on the combustion
gas is low, so that one can accept the fact that no sealin~ air is delivered
whilst the soot blower is in the blowing mode. During blowing, the check
valve 12 is closed and the compressor 16 is shut down or vents through the
safety valve 19. However, for higher back pressures, as is illustrated,
separated purge air connectors 10 and sealing air connectors 13 are provided.
In the emoodiment shown in Figure 3, the compressor 16 is arranged
directly on the wall casing 7. Thus, the sealin~ air connector 13 is
connected rigidly to the wall casing 7. The air blown into the wall casing 7
can serve simultaneously as purging air and sealing air and ensure that the
combustion gases cannot escape directly to the environment or enter the soot
blower.
If separate supplies of purging air and sealing air are to be
provided, then, as is shown in Figure 3, the T-coupling 18 in the air line 17
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is provided with Q branch to the purge air line 15. A separate purging air
and sealing air supply is also necessary in those types of soot blower in
which the jets 2 remain in the heat exchanger when the soot blower is not in
operation, i.e., when the soot blower valve 9 is closed. In those types of
multi-jet soot blower which remain constantly in the gas flow, a supply of
purging air and sealing air can be selected as in each of the versions shown
in Figures 2 and 3.
The control for the compressor 16 can be such that the compressor
runs continuously, even during soot blower operation with the soot blower
vslve l9 open and the check valve 12 closed. Any overpressure is relieved by
the safety valve 19. In soot blowers acted upon only by purging air, the
control is such, however, that the compressor 16 is shutdown in the soot
blower drive mode. Thus the switching for the compressor 16 is effected in
accordance with operation of the travel limit switches for the soot blower.
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