U.S. patent application number 14/561824 was filed with the patent office on 2015-04-02 for rotary atomizer having electro-magnetic bearings and a permanent magnet rotor.
The applicant listed for this patent is DEDERT CORPORATION. Invention is credited to Claude Bazergui.
Application Number | 20150093464 14/561824 |
Document ID | / |
Family ID | 47506569 |
Filed Date | 2015-04-02 |
United States Patent
Application |
20150093464 |
Kind Code |
A1 |
Bazergui; Claude |
April 2, 2015 |
ROTARY ATOMIZER HAVING ELECTRO-MAGNETIC BEARINGS AND A PERMANENT
MAGNET ROTOR
Abstract
An improved rotary disc atomizer for use in, for example, spray
dryers or congealers is disclosed. The rotary disc may be directly
mounted to the shaft of a high-speed electrical motor. The
high-speed electrical motor comprises a permanent magnet rotor and
electro-magnetic bearings. The electro-magnetic bearings may be
supported by one or more upper/lower bearing housings and used to
enable frictionless support of the shaft/rotor and rotary disc. The
atomizer system may further comprise a gas distributor enabled to
dynamically adjust the velocity at which the gas leaves the radial
vanes and meets with the atomized droplets.
Inventors: |
Bazergui; Claude;
(Pointe-Claire, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DEDERT CORPORATION |
Homewood |
IL |
US |
|
|
Family ID: |
47506569 |
Appl. No.: |
14/561824 |
Filed: |
December 5, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13548712 |
Jul 13, 2012 |
8931710 |
|
|
14561824 |
|
|
|
|
61507864 |
Jul 14, 2011 |
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Current U.S.
Class: |
425/8 |
Current CPC
Class: |
B01J 2/04 20130101; B05B
3/1035 20130101; B01D 1/18 20130101; F26B 3/12 20130101 |
Class at
Publication: |
425/8 |
International
Class: |
B05B 3/10 20060101
B05B003/10; F26B 3/12 20060101 F26B003/12 |
Claims
1. A rotary atomizer comprising: an electric motor, said electric
motor having a stator and a rotor; a shaft vertically installed;
one or more magnetic bearings, said one or more magnetic bearings
configured to provide frictionless radial and axial support to the
shaft; and a rotating disc installed at a lower end of the shaft,
said rotating disc configured to spray liquid into the form of fine
particles
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of commonly owned U.S.
patent application Ser. No. 13/548,712, filed on Jul. 13, 2012,
which claims priority to U.S. Provisional Patent Application No.
61/507,864, filed on Jul. 14, 2011, each of which are hereby
incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates generally to rotary disc
atomizers for use in spray dryers or congealers, and more
specifically to rotary atomizers having electro-magnetic bearings
and/or a permanent magnet rotor. The present invention also relates
to systems, methods, and apparatuses for adjusting gas stream
velocity during atomizer use and, more specifically, to systems,
methods, and apparatuses for dynamically adjusting gas stream
velocity.
BACKGROUND
[0003] Spray drying is a method of producing dry powder/particles
from a slurry or solution liquid by rapidly drying the liquid with
a hot gas stream. Spray drying is the preferred method of drying
many thermally sensitive materials such as foods and
pharmaceuticals. A consistent particle size distribution is a
reason for spray drying some industrial products, such as catalysts
and other chemicals. Typically, air is the heated drying medium;
however, nitrogen may be used if the liquid being atomized is a
flammable solvent (e.g., ethanol) or if the product is
oxygen-sensitive.
[0004] Generally speaking, spray dryers use an atomizer or spray
nozzle to disperse a liquid into a controlled-drop-size spray.
Common types of nozzle used in spray drying include rotary disc and
single-fluid pressure swirl nozzles. Alternatively, for some
applications, two-fluid or ultrasonic nozzles may be used.
Depending on the process and/or product needs, drop sizes from 10
to 500 micrometers may be achieved with the appropriate choices.
However, common applications are often in the 100 to 200 micrometer
diameter range.
[0005] A hot, drying gas stream (e.g., air, nitrogen, etc.) may be
passed as a co-current or counter-current flow to the atomizer
direction. The co-current flow method enables the particles to have
a lower residence time within the system, and the particle
separator (typically a cyclone device) operates more efficiently.
The counter-current flow method enables the particles to have a
greater residence time in the chamber and usually is paired with a
fluidized bed system.
[0006] A nano spray dryer offers new possibilities in the field of
spray drying. It allows production of particles in the range of 300
nm to 5 .mu.m with a narrow size distribution. High yields are
produced--up to 90%--and the minimum sample amount is 1 ml. In the
past, the limitations of spray drying were the particle size
(minimum 2 micrometers), the yield (maximum around 70%), and the
sample volume (minimum 50 ml for devices in lab scale). Recently,
minimum particle sizes have been reduced to 300 nm, yields up to
90% are possible, and the sample amount can be as small as 1 ml.
These expanded limits are possible due to new technological
developments to the spray head, the heating system, and the
electrostatic particle collector. To emphasize the small particle
sizes possible with this new technology, it has been described as
"nano" spray drying. However, the smallest particles produced are
typically in the sub-micrometer range common to fine particles
rather than the nanometer scale of ultrafine particles. For further
information on nano spray drying, see, for example, the Mar. 31,
2011 article entitled "Nano Spray Dryer--Experience Submicron Spray
Drying."
[0007] Numerous attempts have been made over the years to improve
rotary atomizer performance. For example, U.S. Pat. No. 7,611,069
to Clifford, et al., entitled "Apparatus and Method for a Rotary
Atomizer with Improved Pattern Control," discloses an apparatus and
method for forming and controlling a pattern for spraying surfaces
with a fluid using a rotary atomizer spray head having an air
shaping ring with shaping air nozzles inclined in a direction of
rotation of a bell cup to direct the air onto the cup surface near
the cup edge. U.S. Pat. No. 7,344,092 to Kim, entitled "Rotary
Atomizer, And Air Bearing Protection System For Rotary Atomizer,"
discloses a rotary atomizer and an air-bearing protection system
for the rotary atomizer to reduce the manufacturing cost. Kim
recognizes that high-speed rotation generates a lot of heat and
load upon the atomizer during continuous operation. In order to
remove this heat, lubricating equipment is commonly used, which
leads to complexity in the system structure and consequently to
difficulties in maintenance and an increase in the manufacturing
cost.
[0008] U.S. Pat. No. 6,551,402 to Renyer, et al., entitled "Rotary
Atomizer," discloses a system utilizing a rotary atomizer for
applying a liquid-based substance to particles. Renyer recognizes
that rotary atomizers typically require a high-speed rotational
force within the vicinity of moving particles (as with a continuous
flow process) and that machinery that utilizes rotary atomizers can
be somewhat complicated, requiring several moving parts which can
be subject to frequent breakdowns.
[0009] Despite the various advancements in and array of existing
atomizers and atomizing systems, current technology still requires
regular maintenance and repair, leading to unnecessary repair cost
and downtime. Thus, a need exists for an improved rotary atomizer
and atomizing system that requires minimal maintenance while
yielding increased revolutions per minute ("RPM") and providing the
ability to direct and adjust gas stream velocity.
SUMMARY OF THE INVENTION
[0010] The present application discloses a system and method for
improving rotary atomizer reliability while producing increased RPM
to yield an increased disc speed. The present application also
discloses a system and method for providing the ability to
dynamically direct and adjust gas stream velocity.
[0011] According to a first aspect of the present invention, a
rotary atomizer comprises an electric motor having a stator and a
permanent magnet rotor enabled to output a rotating force; a shaft
vertically installed and having a desired length, the shaft capable
of being rotated by the rotating force; one or more magnetic
bearings for enabling frictionless radial and axial support of the
shaft; and a rotating disc installed at a lower end of the shaft
for spraying liquid in the form of fine particles.
[0012] In some aspects of the present invention, the rotary
atomizer may further comprise cooling fins for directing cooling
air from a blower across the stator to pick up heat dissipated by
the stator. The cooling air may be expelled from the rotary
atomizer through an annulus gap between the rotating disc and a
feed distributor. Furthermore, the rotary atomizer's electric motor
may be enabled to rotate the shaft at a speed allowing for disc
peripheral tip speeds in excess of 900 feet per second ("ft/s").
For example, a 12-inch diameter disc could be rotated at about
18,000 RPM to yield a speed of about 940 ft/s. The rotary atomizer
may further comprise a compressed air connector for receiving
compressed air to be diverted into gaps between the shaft and the
one or more magnetic bearings and/or to a liquid cooling jacket for
removing excess electrical heat from the stator. A rotary atomizer
may further comprise friction back-up bearings enabled to impede
the shaft's rotation in the event of loss of magnetic
levitation.
[0013] According to a second aspect of the present invention, an
atomizer system comprises an adjustable outer cone; a fixed inner
cone configured to receive an atomizer; a chamber; and one or more
adjustable vertical members coupled to one or more height actuators
for dynamically adjusting the adjustable outer cone. In some
aspects, the atomizer system may further comprise one or more
radial swirl vanes.
[0014] According to a third aspect of the present invention, a
method for atomizing slurry material comprises feeding slurry
material to a rotary atomizer, wherein the rotary atomizer
comprises an electric motor enabled to rotate a shaft at a certain
speed (this depends on the size of the disc; a small 8-inch
diameter disc will need to rotate at 26,000 RPM); using the rotary
atomizer to output the liquid material in the form of atomized
droplets; and circulating the atomized droplets with process gas to
produce substantially dry particles. In some aspects, the method
may further comprise the step of dynamically adjusting gas stream
velocity using at least one vertical member coupled to an
actuator.
[0015] In certain aspects of the present invention, the adjustable
outer cone may be dynamically adjusted to yield a first gas stream
having a first velocity and a second gas steam having a second
velocity that is greater than the first velocity. The one or more
height actuators may comprise an actuator(s) chosen from a group
consisting of (i) electric actuators; (ii) hydraulic actuators;
(iii) pneumatic actuators; (iv) manual actuators; and (v)
combinations thereof. The atomizer may be a rotary atomizer
comprising a permanent magnet rotor and/or one or more
electro-magnetic bearings enabled to provide frictionless radial
and axial support of the shaft.
DESCRIPTION OF THE DRAWINGS
[0016] These and other advantages of the present invention will be
readily understood with reference to the following specifications
and attached drawings wherein:
[0017] FIG. 1 is a cutaway side view of a rotary atomizer according
to the present invention; and
[0018] FIG. 2 is a cutaway side view of an exemplary apparatus
utilizing a rotary atomizer according to the present invention.
DETAILED DESCRIPTION
[0019] Preferred embodiments of the present invention will be
described hereinbelow with reference to the accompanying drawings.
In the following description, well-known functions or constructions
are not described in detail because they may obscure the invention
in unnecessary detail. The present application discloses systems,
methods, and apparatuses for improving rotary atomizer reliability
while yielding higher RPM to yield an increased disc speed. The
present application also discloses a system and method for
providing the ability to dynamically direct and adjust gas stream
velocity.
[0020] FIG. 1 illustrates an exemplary rotary atomizer system 100
having improved reliability and enabled to yield increased RPM and
disc speed. Rather than employing an induction rotor such as those
used in existing rotary atomizer systems, the rotary atomizer
system 100 uses an electric motor having a permanent magnet rotor
104, resulting in a more efficient motor requiring less physical
space for a given power output. The electric motor, which receives
power via the power electrical receptacle 110, generally comprises
a motor housing 102, permanent magnet rotor 104, a stator 106, and
a shaft 108. A smaller motor size typically allows for closer
proximity of the disc to the lower motor bearing. For example, the
motor of the present invention is preferably between about 10
inches by 10 inches through about 72 inches by 72 inches. More
preferably, the motor can be approximately 25 inches by 25 inches
through about 45 inches by 45 inches. Most preferably, the motor
can be about 30 inches by 36 inches. In a preferred embodiment, the
motor is about 30 inches by 36 inches, has a power of approximately
330 horsepower, and has internal discs capable of spinning around
16,000 RPM. The motor is preferably constructed with aluminum which
is both resistant to corrosion and a good dissipater of heat. Other
materials such as stainless steel, or other metals or plastics are
envisioned. As a result of the ability to have closer proximity, a
motor can operate throughout its speed range while remaining below
the first critical speed of the shaft. Rotating shafts, even in the
absence of an external load, can deflect during rotation. The
combined weight of a shaft and disc can cause deflection that often
creates resonant vibration above a certain speed, known as the
critical speed. Thus, to function properly, the motor should be
operated at speeds less than the critical speed. Also, this motor
configuration permits use of a smaller disc diameter, which is
generally less costly and easier to manipulate, leaving sufficient
room around the motor for the placement of the liquid feed
tube(s).
[0021] A permanent magnet rotor provides numerous advantages over
its AC equivalents (e.g., induction or asynchronous motors). For
instance, permanent magnet rotors generally yield a higher speed
and higher torque output, while increasing power efficiency by
eliminating the need for unnecessary current that would otherwise
flow through the rotor windings of traditional induction motors.
Another benefit attributed to the use of permanent magnet rotors is
increased power density (i.e., the power that may be extracted from
a given space). Generally speaking, a permanent magnet motor
typically produces as much as 30% to 40% more power density than a
conventional and similar-sized AC asynchronous motor. An increase
in power density provides the opportunity to increase performance
without requiring additional space for a larger motor or,
alternatively, to reduce the motor size and weight while
maintaining the original performance. Decreasing motor power size
and consumption can lead to lower operating temperatures, thus
reducing the efforts needed to cool the motor and/or motor
system.
[0022] The electric motor system may further employ one or more
electro-magnetic bearings 112a, 112b, which may be supported by one
or more upper/lower bearing housings 116a, 116b to enable
frictionless support of the shaft 108, rotor 104, and disc 114.
However, in certain embodiments, bearing housings may not be
necessary. For example, a single housing may encompass both
bearings and a stator. A benefit of the magnetic bearings 112a,
112b is that they are contactless and thus do not require
lubrication or speed restrictions on the electric motor. The
magnetic bearings 112a, 112b may also provide both primary radial
and axial support for the shaft 108, rotor 104, and disc 114.
Therefore, the atomizer system of the present invention is able to
safely operate at higher RPM to yield increased disc speeds.
[0023] The atomizer 100 may further comprise a set of friction
back-up bearings 118a, 118b with a gap between the bearings' 118a,
118b inner surfaces and the shaft 108 during normal operation. In
the event of loss of magnetic bearing 112a, 112b operation, the
shaft 108 would contact the inner bearing 118a, 118b surfaces to
bring the rotor 104 to a safe stop.
[0024] Using a permanent magnet rotor 104 in conjunction with
frictionless magnetic bearings 112a, 112b permits the atomizer to
reach greater and more favorable operating RPM speeds, thereby
increasing spray drying efficiency while also reducing maintenance.
A favorable operating speed (RPM) will vary depending on the size
of the disc. Accordingly, discs are available in a plurality of
sizes; however, smaller disc sizes may be preferable because they
are generally less expensive and easier to manipulate. Therefore,
the atomizer disclosed herein will be described as having a disc
diameter of approximately 12.75 inches. However, it would be
obvious to one having skill in the art to install a disc with a
different diameter. For example, a smaller power atomizer may have
an 8-inch diameter disc, and a larger unit could have a 16-inch
diameter or larger disc.
[0025] As mentioned, the RPM necessary to reach a target peripheral
disc tip speed will vary depending on the size of the disc being
used. For example, to maintain a peripheral disc tip speed of 900
ft/s, a smaller 8-inch diameter disc will need to be rotated at
26,000 RPM while a larger 12-inch diameter disc will need to be
rotated at 18,000 RPM. Due to limitations on the motors and
frictional losses, current atomizers typically yield a disc
peripheral tip speed only up to 800 ft/s; however, the atomizer of
the present invention is advantageous in that it is capable of
producing more preferable speeds without needing to employ a larger
disc size (e.g., speeds greater than 800 ft/s; more preferably,
greater than 900 ft/s; even more preferably, 900-1,125 ft/s). For
instance, a peripheral disc tip speed of 1,000 ft/s may be readily
ascertained using the system of the present invention by rotating a
12.75-inch disc at a speed of about 18,000 RPM. Similarly, a
peripheral disc tip speed of 1,100 ft/s may reached by rotating a
12.75-inch disc at a speed of about 19,800 RPM or, alternatively,
by rotating a 16-inch diameter disc at about 15,750 RPM. These
higher rotational speeds permit higher throughput for a
given-diameter disc and achieve smaller particle sizes that do not
hit and/or become deposited on the chamber walls. By adjusting disc
size and RPM, a designer may achieve virtually any desired
peripheral disc tip speed using the following equation, where
TipSpeed is the peripheral disc tip speed in ft/s, D is the
diameter of the disc in inches, and s is the RPM of the disc.
TipSpeed = D ( .pi. ) ( s ) 1 12 1 60 Equation 1 ##EQU00001##
[0026] Electrical heat losses from the motor stator 106 may be
removed and/or regulated using cooling air 120. To promote
temperature regulation, the stator housing 102 may have cooling
fins 122 distributed evenly along its periphery. While the fins 122
are preferably evenly distributed, they may be adjusted to divert
air to, or away from, particular areas if one area requires
additional cooling. Above the fins 122 is a distributor with holes
that line up with each fin cavity. Cooling air from a blower enters
the distributor and exits through the holes, and then proceeds to
pick up the heat dissipated into the stator housing fins 122. The
same cooling air 102, now heated, may be directed and expelled to
the outside of the atomizer cone housing through an annulus gap
between the feed distributor 124 and the rotating disc 114. The
feed, which may be a slurry (e.g., particles and fluid), may be fed
to the disc 114 by way of the feed tube 132. The feed tube 132 may
be supported by the feed tube support plate 134.
[0027] The rotating disc 114 can function as a pump impeller, thus
creating a suction pressure at its central annulus opening. This
phenomenon has the tendency to entrain process gas along with
partially dried atomized feed droplets from the surroundings. This
negative effect causes feed product to deposit and build up on the
disc top surface, resulting in disc imbalance and possible blockage
between the disc top surface and the feed distributor bottom
surface, and preventing the disc from rotating properly.
[0028] Therefore, the cooling air 120 may serve a second function
of acting as a clean gas barrier between the suction pressure of
the disc 114 and the atomized droplets, thus preventing the ingress
of particles while supplying the rotating disc 114 with clean
air.
[0029] An alternative, or supplemental, motor cooling method may be
to have a coolant passage jacket 130 surrounding the stator 106,
whereby coolant may be supplied either as a once-through or as a
recirculated loop with a heat exchanger to remove the excess
electrical heat from the stator.
[0030] Further cooling of the motor may be accomplished by
supplying cooled compressed air (or air from a high-pressure
blower) into the gaps between the shaft 108 and magnetic bearings
112a, 112b, and the rotor 104 and stator 106. This air may be
introduced at the top of the motor assembly via an air connector
126 and may be expelled at the bottom through a labyrinth shaft
seal 128 and into the disc 114. This now pressurized non-contact
shaft seal 128 prevents the ingress of liquid feed from the disc
114 into the motor cavity.
[0031] Referring now to the system 200 of FIG. 2, the atomizer 100
of FIG. 1 may be positioned in the fixed inner cone 212 at the
center of a gas distributor 202 to evenly distribute either heated
or cooled process gas around the atomized droplets 204 produced by
the rotating disc. Because the atomizer 100 of FIG. 1 may be
constructed to be the same size and dimension of more traditional
atomizers, the atomizer 100 may be coupled to existing gas
distributors 202, thereby enabling users to easily upgrade existing
atomizer systems without the need to make modifications. Included
as part of this distributor 202 of FIG. 2 is a series of radial
vanes 206 that can impart a swirl pattern to the process gas 208a,
208b. The swirl pattern may be used to ensure proper flow patterns
of the gas and droplets through the spray chamber. A notable design
parameter in an air distributor system of FIG. 2 is the ability to
dynamically adjust the velocity at which the gas stream leaves the
radial vanes 206 and meets with the atomized droplets 204. For
example, a low gas velocity 208a could allow for larger droplets to
travel in a more horizontal trajectory and hit the wall, whereas a
high gas velocity 208b could have the opposite effect of forcing
the gas along with the droplets in a downward trajectory, keeping
the walls clean, but considerably reducing the residence time
(i.e., the amount of time the particles are airborne) in the
chamber 210.
[0032] Determination of the appropriate gas velocity is dependent
upon the nature of the feed and the size of the droplets required.
In prior systems, changing the gas velocity required physical
removal and replacement of components in the gas distributor.
However, as disclosed herein, the process gas velocity may be
dynamically adjusted while the spray dryer/congealer is in
operation, allowing for immediate feedback with no equipment
downtime. For instance, an ideal gas velocity would typically be
the minimum velocity required, for a desired particle size, to
disperse the particles into a chamber without hitting the walls.
The dynamic adjustments may be either manually triggered by a user
(e.g., one monitoring the system) or controlled by a computer
system that measures one or more system parameters and responds by
adjusting the gas velocity pursuant to a computer algorithm.
[0033] The radial vanes 206 may be repositioned from their normal
conical discharge section to a cylindrical section above, thus
allowing the process gas to exit through two concentric cones. The
inner cone is fixed 212 and may be used to support the atomizer 100
and is typically insulated to prevent the often high temperatures
of the gas from affecting the atomizer casing. The outer cone 214
serves to contain the process gas and define its velocity by the
cross-sectional area between the two cones. This outer cone may be
supported by a series of vertical members 216 that can be varied in
height (i.e., lengthwise), thereby changing the vertical position
of the outer cone 214 with respect to the fixed inner cone 212.
This in turn will vary the cross-sectional area between the two
cones and ultimately vary the velocity of the process gas. A
smaller cross-sectional area will typically produce a higher gas
velocity 208b, while a larger area will result in a lower gas
velocity 208a.
[0034] Vertical members 216 may be adjusted using one or more
height actuators 218. The actuators 218 may be operated, for
example, using electric current, hydraulic fluid pressure, or
pneumatic pressure or may be operated manually. In applications
where adjustment precision is necessary, position feedback elements
may be used to actuate vertical members 216 to a predetermined
desired position for a particular product.
[0035] Although various embodiments have been described with
reference to a particular arrangement of parts, features, and the
like, these are not intended to exhaust all possible arrangements
or features, and indeed many other embodiments, modifications, and
variations will be ascertainable to those of skill in the art.
Thus, it is to be understood that the invention may be practiced
otherwise than as specifically described above. The above-cited
patents and patent publications are hereby incorporated by
reference in their entirety herein, because they provide additional
background information which may be considered relevant to the
present application.
* * * * *