Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Title of the invention
Insert for an atomizer wheel and atomizer wheel comprising a number
of such inserts
Field of the invention
The present invention relates to an insert for an atomizer wheel for a
spray dryer, said insert having a longitudinal axis and comprising an inner
end
face, an outer end face, an external surface and an internal surface defining
a
channel having a centre axis and extending between an inlet at the inner end
face and an outlet at the outer end face. The invention furthermore relates to
an atomizer for a spray dryer comprising a number of such inserts.
Background of the invention
In the atomization of slurries such inserts are inserted into the atom-
izer wheel in order to guide the slurry feed out of the atomizer for forming
droplets for the further drying and/or absorption process. During atomization,
the internal structures of the atomizer wheel, including the inserts, are ex-
posed to wear which, depending on the slurry to be atomized, may even be
very heavy. However, this wear is normally restricted to certain well-defined
areas of the atomizer wheel or inserts.
In general, the wear on different parts of the atomizer wheel arises
during rotation of the wheel, where owing to the centrifugal forces and the
nature of the feed, the feed affects the internal parts with a force that
causes
heavy abrasion. Parts exposed to abrasion from feed are therefore made ab-
rasion-resistant and replaceable.
A series of improvements have been suggested in order to enhance
the abrasion-resisting properties of the internal structures of the atomizer
wheel, in order to prevent the ongoing deformation and possibly fracture, e.g.
as disclosed in US patents Nos 3,640,467 and 4,684,065 (Niro).
Disclosed in both documents are inwards-protruding inserts which
ensure that a layer of liquid will deposit on the internal wall of the wheel
dur-
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ing the rotation and hereby prevent wear. Owing to the centrifugal forces the
heavier parts of the layer, i.e. the suspended solid material, is separated
from
the liquid in the layer and deposited directly on the wall so as to fill the
area
surrounding the inwardly extending portions of the inserts. In this way the in-
ner surface of the wheel rim is protected against abrasion from the feed,
since
during operation a layer of feed solids will settle on the inside wall to a
thick-
ness determined by the length of the protrusion, consequently the abrasion
will take place on the sedimented layer itself and not on the inside wall of
the
wheel.
However, it has turned out that these inserts during atomization of
some abrasive slurries experience extremely high wear on the foremost parts,
seen in the tangential or rotational direction, which has entailed that not
only
the wear-resistant lining but also the steel bushing show sign of wear. It is
believed that this effect is due to the fact that whirl formation prevents the
formation of a protective layer locally at the front end of the inserts.
Further improvement of these inserts has therefore been developed
for e.g. disclosed in European patent No. EP 1 184 081 B1 (Niro), where each
insert is provided with a transition surface in the inwards protruding part of
the
insert, thereby directing the flow of the feed along the transition surface to
the
inner side of the external wall thereby avoiding wear on the bushing. It is be-
lieved that the wear on the bushings in this way is limited since the whirl
formed in front of the insert is controllably led past the front of the
insert, dur-
ing rotation to form a coherent layer of protective material on the inner side
of
the external wall.
In the prior art, it has furthermore been suggested to mount the in-
serts so that they can be turned, as they are gradually being worn, in order
to
increase their overall lifetime. However, turning of the inserts requires that
the
apparatus is shut down. The need to frequently turn the inserts results in
manufacturing stops, which are time-consuming and costly due to time pe-
nods without any manufacturing. Furthermore, in order to meet demands set
in for instance environmental regulations, start-and-stop and downtime should
generally be reduced to a minimum.
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Summary of the invention
With this background it is an object of the present invention to pro-
vide an improved insert for use in an atomizer wheel, which has increased
resistance properties, and which furthermore limits the need for rotation and
replacement of the inserts.
In a first aspect, this object is met by an insert of the kind mentioned
in the introduction, which is furthermore characterized in that at least the
inlet
is offset from the longitudinal axis such that the centre axis of the channel
is
offset from the longitudinal axis of the insert.
By this design, an enlarged portion containing an increased amount
of material is formed in one segment near the inlet of the insert. In this man-
ner, it has shown possible to increase the lifetime of the insert without the
need for scheduled starts and stops having as its purpose to rotate the insert
to shift the inlet segment exposed most heavily to the wear.
From the inlet, the channel may in principle extend in any suitable
manner, provided sufficient material is present in order to secure operation.
In
a simple embodiment of the insert according to the invention, said outlet is
offset from the longitudinal axis.
In one embodiment, the centre axis of said channel is substantially
parallel with the longitudinal axis of the insert. This insert thus has
substan-
tially the corresponding flow as a traditional insert having a centrally posi-
tioned channel.
The position and the dimensions of the inlet, and of the outlet and
other parts of the channel, may be varied according to for instance the mate-
rial, the field of application, and dimensions of the insert. In one
embodiment,
the inlet lies entirely outside the longitudinal axis, but alternatively, an
overlap
between the inlet and the longitudinal axis may be provided.
The cross-section of the inlet is preferably chosen from the group of
different shapes comprising circular, elliptical, oval, ovoid, quadratic and
rec-
tangular.
The channel may have a uniform cross-section from said inlet to said
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outlet.
Although the shape may be varied throughout, it is possible also to
vary the dimensions of the channel, for instance by providing the channel with
a cross-section that decreases or increases from said inlet towards said out-
let.
In order to optimize the flow conditions around the inlet and the out-
let, the channel may have the shape of a funnel in at least one of said inlet
or
outlet.
In an advantageous embodiment, said inlet is symmetrical about at
least one axis other than radial.
Alternatively to embodiments, in which the centre axis of the channel
is parallel with the longitudinal direction of the insert, the centre axis of
said
channel may form an angle in the interval 0 to 30 with the longitudinal direc-
tion of the insert.
Alternatively or additionally, the centre axis of said channel may form
an angle with a plane extending in a radial direction of said insert in the
inter-
val 0 to 30 .
Preferably, the external surface is of a substantially tapered shape.
However, as an alternative, the external surface may be of a cylindrical
shape.
The overall resistance against wear and tear, and the flow conditions,
are increased in an embodiment, in which the insert comprises a gripping re-
cess extending from said inner end face to the external surface.
The gripping recess comprises a first transition surface extending at
angle from the inner end face to a second transition surface extending at an
angle from said first transition surface towards said external surface face.
As the insert itself is asymmetrical about the longitudinal axis, the
gripping recess may be formed asymmetrically relative to the longitudinal axis
of the insert.
In a second aspect of the invention, an atomizer wheel for a spray
dryer for atomizing slurries of abrasive material is provided. The atomizer
wheel comprises a wheel hub and a substantially cylindrical external wall de-
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fining an annular chamber of a substantially bowl-like cross-sectional shape
coaxially surrounding said hub, a plurality of ejection apertures, each extend-
ing in a substantially radial direction, distributed over the circumference of
said external wall, and a plurality of inserts arranged in said ejection aper-
5 tures,
each insert being formed in accordance with the first aspect of the in-
vention.
In order to increase the overall lifetime of the atomizer wheel, the
atomizer wheel may furthermore comprise a bushing mounted externally of
the corresponding insert in each ejection aperture.
In further aspects of the invention, use of an insert and an atomizer
wheel comprising such inserts in accordance with the first aspect is provided
for spray drying absorption for flue gas cleaning.
In the following the invention will be described in further detail by
means of embodiments thereof and the appended drawings.
Brief description of the drawings
Fig. 1 is a partial sectional side view of an atomizer wheel in an em-
bodiment of the invention;
Fig. 2 is a sectional top view of the atomizer wheel shown in Fig. 1;
Fig. 3 is a perspective view of an insert for an atomizer wheel in a first
embodiment of the invention;
Fig. 4 is a top view of the insert of Fig. 3;
Fig. 5 is a cross-sectional view of the insert of Figs 3 and 4, along the
line V-V in Fig. 4;
Fig. 6a is a schematic top view of an insert in a second embodiment of
the invention;
Fig. 6b is a cross-sectional view of the insert of Fig. 6a, along the line
K-K in Fig. 6a;
Fig. 7a is a schematic bottom view of a third embodiment of an insert
according to the invention,
Fig. 7b is a cross-sectional view of the insert of Fig. 7a, along the line
A-A in Fig. 7a;
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Figs 8a and 8b are views corresponding to Figs 7a and 7b, respec-
tively, of a fourth embodiment of an insert according to the invention, the
cross-sectional view taken along the line F-F;
Figs 9a and 9b are views corresponding to Figs 7a and 7b, respec-
tively, of a fifth embodiment of an insert according to the invention, the
cross-
sectional view taken along the line C-C;
Fig. 10a is a schematic top view of a sixth embodiment of an insert ac-
cording to the invention,
Fig. 10b is a cross-sectional view of the insert of Fig. 10a;
Figs 11a and 11 b are views corresponding to Figs 10a and 10b, re-
spectively, of an insert in a seventh embodiment of the invention; and
Figs 12 to14 are schematic top views of further embodiments of an in-
sert according to the invention.
Description of preferred embodiments
In Figs 1 and 2, an embodiment of an atomizer wheel 1 for atomizing
slurries of abrasive material is illustrated, where the atomizer wheel 1
comprises a wheel hub 2 defining an axial direction of the atomizer wheel,
and a substantially cylindrical external wall 3 defining an annular chamber 4
of a substantially bowl-like cross-sectional shape coaxially surrounding the
hub 2, which is delimited by a cover 8 and a bottom portion 10. The slurries
to
be atomized are provided concentrically around the hub 1 through an
aperture 9 in the cover 8. The circumference of the external wall 3 of the
atomizer wheel 1 is provided with a number of ejection apertures 5, through
which a supplied slurry is ejected outwards in atomized form during operation
into a surrounding drying chamber in which the fine particles formed by the
atomization are dried so that their content of solids drops down to the bottom
of the drying chamber, possibly in the form of a fine powder.
As shown most clearly in Fig. 2, the ejection apertures 5 each extends
in a substantially radial direction of the atomizer wheel and are distributed
over the circumference of said external wall. In the embodiment shown, the
atomizer wheel is adapted to rotate in a counter-clockwise direction.
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In order to prevent wear on the atomizer wheel 1 itself, inserts 20 fitting
into the ejection apertures 5 are inserted in the individual ejection
apertures 5.
In the embodiment shown, each insert 20 is in turn fitted into a steel bushing
6; however, in some fields of application, it is also conceivable to fit the
inserts 20 directlly into the wall of the atomizer wheel. As indicated and as
will
be described in further detail below, a longitudinal direction of the
respective
inserts 20 coincides with the radial direction of the atomizer wheel.
Figs 3 to 5 illustrate a first embodiment of the insert 20 adapted to fit
into a corresponding ejection aperture 5 in an atomizer wheel, for instance an
atomizer wheel having the overall properties shown in Figs 1 and 2.
The insert 20 has a longitudinal axis I and comprises an inner end face
21, an outer end face 22, an external surface 23 and an internal surface 24
defining a channel 35 extending between an inlet 25 at the inner end face 21
and an outlet 26 at the outer end face 22. As the inner end face 21 has a
larger extension than the outer end face 22 in the first embodiment, the
external surface 23 is of a substantially tapered overall shape. Furthermore,
is
is noted that In the embodiment shown in Figs 3 to 5, the channel 35 has a
uniform cross-sectional shape from the inlet 25 to the outlet 26, however with
varying dimensions.
Referring in particular to Fig. 5, the channel 35 has a centre axis c. As
indicated in the above, the longitudinal axis I of the insert 20 substantially
coincides with the radial direction of the atomizer wheel 1 in the mounted
position of the insert in the atomizer wheel. The centre axis c of the channel
35, however, is eccentric to or offset from the longitudinal axis I of the
insert
20 and hence relative to the radial direction of the atomizer wheel 1 in the
mounted position.
In the first embodiment shown in Figs 3 to 5, the offsetting is provided
in that the inlet 25 and the outlet 26 are both offset from the longitudinal
axis I
of the insert, such that the centre axis c of the channel 35 is offset from
the
longitudinal axis I of the insert 20 in parallel therewith. The offset marked
by
"ecc" in Figs 4 and 5 is thus the same throughout the channel 35, from the
inlet 25 (cf. the distance between lines 27 and 28 denoting the longitudinal
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axis I and the centre axis c, respectively, in Fig. 4) to the outlet 26. The
range
of the offset may vary according to other parameters of the insert, such as
the
overall dimensions of the insert, shape of the channel 35, thickness of the
wall between the external surface 23 and the internal surface 24, etc.
Typically, however, for an insert having an overall diameter at the inner end
face 21 of 30 to 40 mm, and a diameter of 20 to 30 mm at the outer end face
22, the offset typically lies in the range 2 to 5 mm. In the first embodiment,
the
inlet 25 overlaps the longitudinal axis I of the insert 35. However, it is
also
conceivable to offset the inlet opening to such an extent that no overlap is
provided and the inlet lies entirely outside the longitudinal axis.
As a consequence of the offset inlet 25, the insert 20 is provided with
an enlarged portion at the inner end face 21 containing a larger amount of
material between the external surface 23 and the internal surface 24 in one
segment of the insert 20 than in the opposite. Referring back to Fig. 2, when
in use, an insert 20 of this kind thus meets the slurry at the uppermost
portion
of the internal surface 24 positioned at the trailing edge of the inlet 25,
when
seen in the tangential direction of the atomizer wheel, which is thus the edge
that is worn more heavily due to abrasion. As the amount of material in this
area is increased due to the offset inlet 25, the lifetime of the insert is
increased.
In the first embodiment, a further feature is present which is particularly
efficient in ensuring minimal wear on the bushings of the atomizer wheel,
namely that the insert 20 has at the inner end face 21 a gripping recess,
generally designated 30, which extends from the inner end face 21 to the
external surface 23, best illustrated in Fig. 5. In the embodiment shown, the
gripping recess 30 comprises a first transition surface 31 extending at angle
from the inner end face 21 to a second transition surface 32 extending at an
angle from the first transition surface 31 towards the external surface 23.
The
gripping recess and transition surface(s) may take other forms as well, as
described in further detail in the above-mentioned European patent No. EP 1
184 081 B1. Thus, it is also conceivable that the gripping recess 30 may
comprise more than two portions, or only one portion thus forming a bevelled
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gripping recess. The gripping recess 30 may also be designed as any suitable
surface or combination of surface portions having an all in all concave shape.
As indicated, the gripping recess 30 in the embodiment shown is
asymmetrical relative to the longitudinal axis I of the insert 20. This is
primarly
due to the fact that there is no need for a gripping recess, or transition
surface(s), at the trailing side of the insert. It has turned out that a shape
of
the enlarged portion extending substantially in parallel with the tangential
direction of the atomizer wheel provides for an advantageous flow pattern
such that flow of slurry meeting the following insert in the circumferential
direction is not adversely affected.
When inserted into the atomizer wheel in Figs 1 and 2, the gripping
recess 30 of the insert 20 faces the slurry in the counter-clockwise rotation
of
the atomizer wheel 1, which entails that the direction of the flow of the
slurry
to be atomized is changed by virtually 90 degrees and is thus led past the
bushing 6 and further onto the internal surface 24, thereby minimizing the
wear on the bushing. However, in other embodiments of the insert according
to the invention, there is not necessarily a gripping recess, or the gripping
recess may have other configurations.
Independently of the provision of a gripping recess, the transition
between the inner end face 21 and the internal surface 24 may as shown be
provided as a bevelled or chamfered edge, which is believed to postpone the
point in time when the abrasion leads to noticeable wear on the trailing edge
of the inlet 25 and hence the enlarged portion, as a sharp edge will be more
prone to wear and tear. The chamfered edge needs not extend throughout
the circumference but may be formed only in a sector covering for instance
20-50 .
In the first embodiment shown in Figs 3 to 5, the shape of the inlet 25
is substantially elliptical. By forming the inlet other than for instance
circular, a
larger surface subjected to the load of the slurries is provided. This, in
turn, is
believed to have an advantageous effect on the lifetime of the insert. The
elliptical shape of the inlet 25 is present throughout the channel 35; however
as is most apparent from the cross-sectional view of Fig. 5, the first portion
of
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the channel 35 is substantially straight, whereas the remaining portion
towards the outlet 26 is narrowed. The shape may in principle be varied in
any suitable manner as will be described in further detail below; however, it
is
preferred that inlet is symmetrical about at least one axis other than radial.
5 Other features, and variations thereof, will now be described.
Referring to Figs 6a and 6b, a second embodiment of the insert 120
according to the invention is shown. Elements having the same or analogous
function as in the embodiment of Figs 3 to 5, carry the same reference
numerals to which 100 is added. In the second embodiment the inlet 125 of
10 the insert 120 lies substantially entirely outside the longitudinal axis I
and
extends towards the outlet 126 with decreasing cross-section of the channel.
The shape of the channel 135 through the inlet 25 towards the outlet 26 forms
an angle a with the longitudinal direction / of the insert. The angle
typically lies
in the interval 0 to 30 , here approximately 20 . In this embodiment, the
channel 135 also forms an angle 11 with a plane extending in a radial
direction
of the insert, which is indicated in Fig. 6b. This angle also typically lies
in the
interval 0 to 30 , here approximately 30 .
Notice is taken regarding the embodiment illustrated in Figs 6a and 6b
that a gripping recess corresponding to gripping recess 30 is absent, which
does not exclude the option of incoorporating a gripping recess in this
embodiment as well.
The inlet 125 is substantially circular and so is the oulet 126. The
cross-sectional shape of the channel 135 is uniformly circular and the
dimensions diminish from the inlet 125 to the outlet 126.
Figs 7a and 7b illustrate a third embodiment of the invention, where
200 is added to reference numerals of elements having the same or
analogous function as in the embodiment of Figs 3 to 5. In Fig. 7a the inlet
225 lies entirely outside the longitudinal axis as in the previously described
embodiment. However, contrary to the previous embodiment the channel has
a uniform cross-sectional dimension from the inlet 225 to the outlet 226,
extending in parallel with the longitudinal axis, best illustrated in Fig. 7b.
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Figs 8a and 8b illustrate a fourth embodiment of the invention, where
300 is added to reference numerals of elements having the same or
analogous function as in the embodiment of Figs 3 to 5. The insert is in this
embodiment provided with a gripping recess 330 at the inlet 325, while having
an uniform cross-section of the channel, best illustrated in Fig. 8b. As shown
in Fig. 8b, the insert 320 has a substantially cylindrical external shape, as
the
external surface 323 takes the form of a cylindrical surface. This shape is
not
as such preferred, as the insert 320 is dependent on shoulders on the
bushing or on the atomizer wheel itself. Even more important, the cylindrical
shape does not entail the positive engagement provided by the tapered
external shape of the other embodiments, which in turn does not entail the
security against unintentional release of the inserts from the atomizer wheel
in
the case of failure of the bushing or other retaining elements.
In a fifth embodiment illustrated in Figs 9a and 9b, with 400 added to
reference numerals of elements having the same or analogous function as in
the embodiment of Figs 3 to 5, the centre axis of the channel forms an angle
in the interval 0 to 30 with the longitudinal direction of the insert, while
having
an increasing cross-section from the inlet 425 to the outlet 426.
In a sixth embodiment of the invention, illustrated in Fig. 10a and 10b,
the channel has the shape of a funnel extending with the narrow end from the
inlet 525 to the outlet 526, best illustrated in Fig. 10b, while still
maintaining a
larger surface area of the external wall 523.
Alternatively, in a seventh embodiment the funnel shape of the channel
extends with the widest end from the inlet 625 to the outlet 626, while still
maintaining the larger surface area of the external wall 623, best illustrated
in
Fig. 11a-b.
Furthermore, the shape of the inlet and the outlet and other parts of the
channel of the insert may differ in different embodiments, as illustrated in
Fig.
12 trough Fig. 14, by the cross-section of the channel, seen from the inlet
725, 825, 925, being chosen from the group of different shapes comprising
circular, elliptical, oval, ovoid, quadratic and rectangular.
The different kind of embodiments of an insert may be used for spray
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drying absorption for flue gas cleaning or industrial off gasses, from for
exam-
ple power plants and metal industries, respectively. Finally, the insert may
be
inserted into an atomizer wheel used for the same purpose of spray drying
absorption for flue gas cleaning. The flue gas may emanate from for instance
power plants, industrial off gases, e.g. from metal industries. The invention
is
also useful for drying of abrasive feeds in general, e.g. in the chemical
indus-
try or in the mining industry.
The invention should not be regarded as been delimited to the em-
bodiments shown and described in the above, but various modifications and
combinations may be carried out without departing from the scope of the ap-
pended claims.
