Note: Descriptions are shown in the official language in which they were submitted.
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WEAR INSERT FOR USE IN A ROTARY ATOMIZER
FIELD OF THE INVENTION
The present invention relates to a wear insert for use in a rotating atomizer
wheel. The atomizer wheel may be arranged to be positioned within a chamber
for
use in connection with flue gas desulfurization. However, it should be
understood
that the wear insert of the present invention is not limited to use in
connection with
gas desulfurization. To the contrary, the wear insert of the present invention
is not
limited to flue gas desulfurization and can be utilized in spray drying
processes in a
broad range of other industries including pharmaceuticals, powdered milk,
coffee,
food products, and clay. For example, powdered milk results from passing
liquid
milk slurry through an atomizer wheel which flash evaporates the water from
the
slurry leaving a powdered milk product. The wear insert of the present
invention
provides a fan-shaped atomized spray exiting the wear insert having an
increased
width and a decreased depth which increases the efficiency of atomization,
reduces
usage of lime, improves desulfurization and increases wear insert life, among
other
benefits.
BACKGROUND OF INVENTION
Flue gas desulfurization systems are typically used in coal fired power
plants,
waste-to-energy plants and in incinerators. A typical desulfurization system
will
include a processing or treatment chamber wherein flue gases are subjected to
desulfurization treatment. Positioned inside that chamber is a high speed
rotating
atomizer wheel through which a desulfurization treatment slurry is dispersed
into the
chamber and the gas therein in order to initiate the desulfurization process.
Typically, the atomizer wheels are circular with a circumferential sidewall
that
includes nozzle openings that project through the circumferential sidewall.
Typically,
the atomizer wheels are between eight and fourteen inches in diameter.
Such a desulfurization system might typically be powered by drive systems
that include motors in the 160 to 1100 horsepower range that rotate the
atomizer
wheels at speeds of 8,800-10,000 rpm and upwards to 15,000 rpm. While these
wheels are rapidly rotating at these very high speeds, a slurry treatment
mixture,
typically of water, lime and other inert materials of upwards to 20%-40%
solids, is fed
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into the wheels at rates ranging typically between 40-200 gallons per minute.
Due to
the rotational velocity of the wheels, the slurry fed into the wheels is
accelerated and
expelled through wear inserts positioned around the circumference of the
rotating
wheels into the treatment chamber. The atomized mist of the treatment slurry
chemically reacts with the sulfur in the flue gases to form solid particles
that
precipitate from the flue gas. These solid particulates formed from the
chemical
reaction of the atomized treatment slurry and the flue gases are filtered out,
thereby
removing the sulfur from the flue gas.
A typical atomizer wheel that is the subject of the improvement of the present
invention is shown in U.S. Patent No. 6,659,375. Atomizer wheels of a similar
type
are also disclosed in U.S. Patent Nos. 5,370,310; U.S. Re. Pat. No. 30,963 and
U.S.
Pat. No. 5,356,075. In each of the atomizer wheels disclosed in these patents,
the
atomizer wheels are circular with a circumferential sidewall that forms a
hollow
center or annular space. Ejection orifices project through the circumferential
sidewall. A lid or cover plate fits over the annular space. In the lid is an
opening or
inlet through which slurry to be atomized passes into the annular space. The
atomizer wheel is positioned within a treatment chamber wherein atomized
slurry
from the wheel reacts with the gases in the chamber to desulfurize the gases.
The flow rate of slurry entering an atomizer wheel ranges from 40 to 200
gallons per minute. The number of wear inserts in an atomizer wheel range from
six
to forty and preferably range from eight to sixteen. The diameter of an
atomizer
wheel ranges from between six and fourteen inches, the smaller diameter
atomizer
wheels rotating at a faster rate (15,000 rpm) than the larger atomizer wheels.
Typically, smaller atomizer wheels are used for spray drying applications. Tip
velocity, i.e., the angular velocity at the exit end of the wear insert, can
range
between 525 feet per second and 625 feet per second. The amount of slurry that
can flow through a particular atomizer wheel is dependent upon the cross-
sectional
area of the internal passageway of the wear insert and the number of wear
inserts on
the atomizer wheel. Wear inserts for directing the flow of the atomized slurry
from
the atomizer wheel are well known in the art. These wear inserts are typically
made
of a wear-resistant sintered material such as boron carbide tungsten carbide,
silicone
carbide, aluminum oxide, and tetraboric carbide.
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SUMMARY OF THE INVENTION
A wear insert for use in a rotary atomizer for atomizing a slurry to form a
discharge spray. The wear insert comprises a hollow body having an open inlet
end
for receiving the slurry, an open outlet end for discharging the slurry, and a
longitudinal channel extending from the inlet end to the outlet end. The
longitudinal
channel includes a central axis and is provided for directing a stream of
slurry
therethrough from the inlet end to the outlet end. The longitudinal channel
includes
at least one substantially flat surface over which the slurry stream flows as
it is
directed through the longitudinal channel. The stream of slurry is atomized to
form a
discharge spray as it exits the outlet end.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a cross-sectional view of a wear insert of the present invention
situated within an atomizer wheel.
Fig. 2 is an elevational view of the outlet end of a prior art wear insert
during
use.
Fig. 3 is an elevational view of the outlet end of a wear insert of the
present
invention during use.
Fig. 4 is an elevational view of the outlet end of a wear insert of the
present
invention during use.
Fig. 5 is an elevational view of the outlet end of a prior art wear insert
during
use.
Fig. 6 is an elevational view of the outlet end of a prior art wear insert
during
use.
Fig. 7 is an elevational view of the outlet end of a wear insert of the
present
invention during use.
Fig. 8 is an elevational view of the outlet end of the prior art wear insert
during
use.
Fig. 9 is an elevational view of the outlet end of a wear insert of the
present
invention during use.
Fig. 10 is a graph comparing change in performance characteristics of the
inventive wear insert with those of the prior art.
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Fig. 11 is a chart comparing change in performance characteristics of the
inventive wear insert with those of the prior art.
DETAILED DESCRIPTION OF THE INVENTION
Referring now in detail to the various figures of the drawings wherein like
reference characters refer to like parts, there is shown in Fig. 1, a nozzle
10 of the
present invention positioned within an ejection orifice 14 located on the
circumference of the sidewall of a rotating atomizer wheel 18. During
operation, the
atomizer wheel 18 rotate in a counterclockwise direction as indicated by the
direction
arrow 20. Alternatively, the atomizer wheel may rotate in a clockwise
direction as
shown in other drawings. The ejection orifice 14 is an opening extending on a
radial
line (not shown) from the axis of rotation (not shown) of the circular
atomizer wheel
18. The nozzle 10 is comprised of two components: a wear insert 22 and a
structural or metallic protective cup 26.
The cup 26 is formed of any suitable metal and is usually formed of the same
material used to form the atomizer wheel 18, e.g., titanium or stainless
steel. The
cup 26 has a cylindrical outer diameter or outer surface 30, a cylindrical
bore or inner
surface 34, an open end 38 and a support wall 42. The outer surface 30 has an
0-
ring groove 46 and an annular mounting shoulder 50 which engages a shoulder 54
located on the ejection orifice 14 to hold the protective cup 26 within the
atomizer
wheel 18 during operation. Open end 38 is arranged to receive the wear insert
22
and the support wall 42 is arranged to engage and retain the wear insert 22
and
prevent it from being ejected during rotational movement of the atomizer wheel
18
during operation. The wear insert 22 slips into and is affixed within, e.g.,
glued, the
protective cup 26. An 0-ring 58 seated within the 0-ring groove 46 is provided
to
help seal the wear insert 22 and protective cup 26 within the atomizer wheel
18 and
lock it in place. The wear insert 22 is fabricated of any suitable very hard
substance,
e.g., silicon carbide or boron carbide. In an alternative embodiment, the wear
insert
22 may be retained within the ejection orifice 14 of the atomizer wheel 18
without the
use of the protective cup 26.
The wear insert 22 has a cylindrical outer diameter or outer surface 62 and
includes an inlet end 66, an outlet end 70 and a longitudinal channel 74
within the
wear insert 22 extending from the inlet end 66 to the outlet end 70. As shown
in Fig.
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1, the longitudinal channel 74 flares outwardly from a smaller cross-sectional
area at
the inlet end 66 to a larger cross-sectional area at the outlet end 70.
Alternatively,
the cross-sectional area of the longitudinal channel 74 can remain constant
from the
inlet end to the outlet end or can taper inwardly from a larger cross-
sectional area to
a smaller cross-sectional area from the inlet end to the outlet end, or can
include
other configurations. The support wall 42 of the cup 26 includes an axial
aperture 78
that is approximately equal in size to the outlet end 70 of the wear insert
22.
Referring now to Fig. 3, there is shown an elevational view of a wear insert
22
of the present invention at its outlet end 70. As shown in Fig. 3, the
longitudinal
channel 74 includes a central axis 142, and four substantially flat walls 82,
86, 90,
and 94, the walls being of approximate equal length from end to end and being
joined at their ends by rounded corners 98 approximating a square
configuration. It
is to be understood that the present invention is not limited to the
configuration
described and illustrated in the specification. Rather, the invention includes
configurations having at least one substantially flat wall. For example, the
longitudinal channel 74 could include four flat walls of unequal length
forming a
rectangle or quadrilateral. Alternatively, the longitudinal channel 74 could
include
five or more flat walls, e.g., forming a pentagon or hexagon, the walls having
equal
or unequal length. Alternatively, the longitudinal channel 74 could include a
single
flat wall with the remainder of the longitudinal channel cross-section being
rounded,
e.g., semicircular.
Referring now to Fig. 2, there is shown a prior art wear insert 102. Such
known wear inserts 102 include a guide tube 106 having a circular cross-
section
through which a slurry stream passes. On known wear inserts, the cross-
sectional
area of the guide tube remains constant from the inlet end to the outlet end.
Known
wear inserts may have other configurations. Rotational movement of the
atomizer
wheel 18 in which the wear insert 102 is affixed creates centrifugal forces
which
direct the slurry 122 to occupy only a portion of the cross-section of the
guide tube
106, i.e., the side surface the guide tube 106, as the slurry 122 flows across
the
guide tube 106 from the inlet end to the outlet end. The slurry 122 itself
comprises a
predetermined cross-sectional area and is shown filling only about 25% of the
cross-
sectional area of the guide tube 106 of the prior art wear insert 102. Thus,
the
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amount of slurry 122 flowing through the guide tube 106 of the prior art wear
insert
102 is less than full capacity. Wear is typically observed over time during
service
which is caused by the laminar and turbulent flow conditions of the slurry 122
along
the side surface of the guide tube 106. Such wear creates performance problems
due to the fact that geometrical changes in the wear insert tend to affect the
atomizer
spray efficiency.
The prior art wear inserts suffer from several drawbacks. As best shown in
Fig. 5, the centrifugal forces caused by rotation of the atomizer wheel 18
during
operation, cause large lime (and/or fly ash particles) 126 of the slurry to
settle out of
the water portion 130 of the slurry and to bunch together against the side
surface of
the guide tube 106 of the prior art wear insert 102. The largest numbers of
these
lime particles 126 settle at the mid-point of the side surface while fewer
particles
settling above and below the mid-point. In Fig. 5, thirty-four discrete lime
particles
126 are shown bunched together at the side surface of the guide tube 106, each
particle exerting a force in an amount of 1 F against the side surface due to
centrifugal force. At the mid-point of the bunch, the lime particles 126 are
stacked
three or four deep and exert a force against the side surface of the guide
tube 106 in
an aggregate amount of as much as 3F or 4F while above and below the mid-
point,
where lime particles 126 are stacked not as deep, a lesser aggregate force of
1 F or
2F is exerted.
Figs. 6 and 8 illustrate the manner in which the geometry of the prior art
wear
insert 102 changes over time as the lime particles 126 continue to exert
forces and
progressively wear away the side surface of the guide tube106. As best shown
in
these figures, as wear progresses, the stacking of lime particles 126 upon
themselves actually increases, thus accelerating the progression of wear. As
shown
in Fig. 6, the lime particles 126 have worn away the side surface of the guide
tube
106 of the known wear insert 102 to form a bulbous wear area indicated at 132.
As
shown in Fig. 8, over time, the lime particles 126 continue to wear away the
side
surface of the guide tube 106 of the prior art wear insert 102 to form a wear
cone
134. As wear builds on the side surface of the prior art wear insert 102, the
fan-
shaped atomized spray exiting the outlet end thereof becomes narrower and
deeper
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resulting in lower efficiency of desulfurization and requiring increased usage
of lime
and more frequent maintenance.
Referring again to Fig. 8, when the wear insert has reached a predetermined
level of wear, e.g., when the wear cone 134 has fully formed, or when a
predetermined period of time has expired, the atomizer wheel 18 is shut down
to
enable rotation of the wear insert 102 along its central axis 138 to a new
position to
distribute wear evenly around the remaining surface of the circular guide tube
106.
For example, the wear insert 102 can be rotated about its central axis 138 to
four
distinct service positions, 900 apart from each other. Alternatively, the wear
insert
102 can be rotated to three distinct service positions, 120 apart from each
other, or
to two service positions, 180 apart from each other. Once the wear insert is
rotated
a full 360 , it is removed and replaced with a new unworn wear insert. If the
rotation
is not performed in time, wear will progress and the rate of wear will
increase rapidly
due to the shape of the wear cone. Over time, wear can progress through the
wear
insert 102 and protective cup and can extend into the atomizer wheel which can
result in catastrophic failure.
Referring again to Fig. 3, in order to overcome the shortcomings associated
with the prior art wear inserts 102, the inventive wear insert 22 is provided
with a
longitudinal channel 74 having a plurality of flat side walls, 82, 86, 90, and
94. Figs.
3, 4, 7 and 9 illustrate the manner in which the geometry of the longitudinal
channel
74 of the inventive wear insert 22 changes over time as the lime particles 126
continue to exert forces against the flat side wall 82 of the longitudinal
channel 74.
As shown in Fig. 3, rotational movement of the atomizer wheel 18 in which the
inventive wear insert 22 is affixed forces the slurry 122 to occupy only a
portion of
the cross-section of the longitudinal channel 74, i.e., the flat side wall 82.
As shown
in Fig. 3, the same predetermined cross-sectional area of slurry 122 as is
shown in
the prior art wear insert 102 of Fig. 2 occupies an even smaller portion of
the cross-
section of the longitudinal channel 74 of the inventive wear insert 22. The
slurry 122
is more evenly distributed due to the geometry of the flat side wall 82.
Referring now to Fig. 4, the same thirty-four lime particles 126 are shown
evenly distributed, one-deep, across the length of a flat side wall 82 of the
longitudinal channel 74, each particle 126 exerting a force in the amount of 1
F
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against the flat side wall 82. Significantly, the lime particles 126 are not
stacked two,
three and four deep as they are in the prior art wear insert 102 of Fig. 5.
Thus,
forces causing wear are less and are distributed evenly along the length of
the flat
side wall 82.
Referring now to Figs. 7 and 9, due to the geometry of the flat side wall 82,
forces caused by lime particles 126 are distributed more uniformly across the
flat
surface and the progression of wear along flat side wall 82 occurs and a much
reduced rate, thus substantially increasing service life and reducing down
time of the
atomizer wheel 18 for replacing wear inserts. As shown in Figs. 7 and 9, the
progression of wear demonstrated by the inventive wear insert 22 is relatively
small
when compared with that of the prior art wear insert 102. The reduction in
length of
the flat side wall 82 of the inventive wear insert 22 due to wear is minimal
and the
amount of stacking of lime particles 126 occurs, if at all, only at the ends
of the flat
side wall 82 and is minimal. Like the prior art wear insert 102, the inventive
wear
insert 22 can be rotated about its central axis 142 to new positions to
distribute wear
evenly to remaining walls 86, 90 and 94 of the longitudinal channel 74.
As best shown in Fig. 10, due to the resulting geometry of the inventive wear
insert 22, the overall width of the atomized spray exiting the wear insert 22
is greater
than that produced by the prior art wear insert 102. Such greater width of
spray
results in greater efficiency of atomization which improves desulfurization.
Fig. 10
also demonstrates that the reduction in width of the atomized spray due to
increasing
wear on the inventive wear insert 22 over time is substantially less than that
caused
by wear on the prior art wear insert 102, resulting in longer life and greater
efficiency
and consistency of atomization which improves desulfurization. Likewise, as
best
shown in Fig. 11, the overall depth of the atomized spray resulting from the
geometry
of the inventive wear insert 22 is substantially less than that produced by
the prior art
wear insert 102, resulting in the same benefits as previously mentioned.
Moreover,
as demonstrated in this figure, the increase in depth of the atomized spray
caused
by wear on the inventive wear insert 22 is substantially less than that caused
by
wear on the prior art wear insert 102 resulting in a longer life of the wear
insert and
greater efficiency of atomization. While the invention has been described in
detail
and with reference to specific examples thereof, it will be apparent to one
skilled in
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the art that various changes and modifications can be made therein without
departing from the spirit and scope thereof.
An alternative embodiment 110 of the wear insert of the present invention is
shown in Fig. 12. This wear insert 110 includes a longitudinal channel 114
being in
the shape of a cone, the longitudinal channel 114 flaring outwardly from the
inlet end
118 to the outlet end 122. The resulting atomized spray is greater in width
and
lesser in depth than that produced by the prior art wear insert 102 due to the
flared
geometry of the longitudinal channel 114. Also, wear over time is reduced
because
forces causing wear are distributed over a greater surface at the outlet end
122 of
the wear insert 110.
