Abstrict A rotary solids crusher has three product exits for selectively
removing product particle sizes produced by secondary, tertiary,
or fine grind crushing. In the fine grind mode, the crusher has
an unobstructed vertical attrition chamber from which air-entrained
particles exit at high velocity, and are subsequently classified
by particle size using the energy inherent in the rapidly moving
stream to effect settling; e.g., by gravity or in centrifugal separators.
Claims I claim:
1. In an apparatus for crushing solid particles having a housing,
inlet means for passing material to be crushed into an impact reduction
chamber, an impact reduction chamber within the housing, an impact
rotor having impact hammers at its periphery, drive means to rotate
the impact rotor, a fluidizing rotor removably mounted near the
bottom of the impact reduction chamber, and drive means to rotate
the fluidizing rotor, the improvement therein which comprises an
attrition chamber extending from the impact reduction chamber vertically
above the impact rotor, first product exit means located at the
bottom of the impact reduction chamber, second product exit means
located in a lower portion of the housing opposite the inlet means
and generally adjacent to the first product exit means, third product
exit means located at an upper portion of the attrition chamber,
and first, second, and third closure means to selectively close
the first, second, and third product exit means.
2. The apparatus of claim 1 also comprising air inlet means for
permitting air flow into the impact reduction chamber, and control
means for selectively varying the air flow into the chamber.
3. The apparatus of claim 1 wherein the attrition chamber is unobstructed
and has a vertically decreasing cross-sectional area at an upstream
portion thereof such that air traversing the attrition chamber increases
in velocity along said chamber.
Description BACKGROUND OF THE INVENTION
This invention relates to rotary crushers for pulverizing solid
materials, and to a method and system for classifying the pulverized
product. In particular, it relates to a rotary crusher having the
capability with very little adjustment to provide relatively uniform
product particle sizes ranging from rather large chunks to very
fine powders. The invention also features a collection system for
finely ground material which permits the crusher exhaust to assist
in the recovery and classification of finely ground material.
Commercial crushers are required to perform a wide variety of crushing
chores. For example, it may be desired to reduce the size of ordinary
rock from 6"+ to -3/4" for use as paving aggregate. Alternatively,
to prepare mineral-containing ore for chemical processing it may
be desired to crush chunks of ore to a product size of approximately
30 mesh. In other instances, such as the pulverizing of coal for
use in utility boilers, or cement manufacture, product particle
sizes of 100 to 200 mesh may be required. At the present time, no
single available crusher can satisfy the wide variety of product
distributions and product sizes which may be desired without extensive
modification. Accordingly, there is a substantial demand for a crusher
which is sufficiently flexible to provide utility for a large number
of feed materials and product size and distribution.
Rotary crushers of the general type disclosed herein have been
described in my existing U.S. Pat. Nos. 3887141; 4037796; and
4077574. These patents disclose a crusher having an impact rotor
positioned within a reduction chamber and having a plurality of
hammerheads around its periphery. Ore entering the reduction chamber
is directed tangentially against the hammers and hurled against
the sides of the reduction chamber. The internal walls of the reduction
chamber are lined with shatterbars which assist in reduction of
the ore to a finer particle size. As particles fall to the bottom
of the chamber, they are swept back into the downstream side of
the reduction chamber by a rapidly moving fluidizing rotor located
beneath the impact rotor. Air enters the reduction chamber through
inlets in its side, and crushed particles are swept upwardly through
a vertical classification chamber to permit removal of particles
within certain size ranges. As shown in U.S. Pat. No. 4037796
particle diverter plates and air deflector flaps are used within
the classification chambers to direct particles of various sizes
into their proper classification.
With the prior art devices, particle size distribution is relatively
fixed by the crusher design. While some flexibility exists to produce
a very finely pulverized product by adjusting rotor speed, air flow,
and classification chamber height, these mills can handle only a
relatively narrow variety of feeds and product size distribution
requirements. It has been found that with relatively minor modifications,
the crusher described in U.S. Pat. No. 4037796 can be designed
to do the work of three separate crushers; i.e., having product
particle sizes corresponding to ranges generally referred to as
secondary, tertiary, and fine grinding. In addition, it has been
discovered that energy generated by the rotating hammers can be
used to classify finely ground materials into a plurality of desired
product distributions.
The crusher and classification system of the invention are characterized
by the crusher having three separate and independent product takeoff
points, including 2 exits used for very light crushing operations
(i.e., where the product particle size is relatively large). In
addition, the crusher is characterized by an offset unimpeded vertical
attrition chamber, containing no deflectors or product removal means,
where the attrition of rising small particles with falling larger
particles creates further particle comminution. In addition, product
classification from the exhaust from the crusher is effected through
the use of the energy contained in the air/particle stream to assist
in classifying the product. This classification may be accomplished
by thrusting the product stream into a centrifugal separator, such
as a cyclone collector, wherein the larger particles exit the bottom
of the unit and smaller particles are carried across the top thereof.
Alternatively, the product exit stream may be directed horizontally
across a series of bins, with the larger particles falling by gravity
into the bins nearest the exit, and smaller particle sizes falling
at a greater distance from the exit.
BRIEF SUMMARY OF THE INVENTION
In a system for crushing solid particles having a housing, a particle
inlet chute, an impact reduction chamber within the housing, an
impact rotor having impact hammers at its periphery, a drive motor
to turn the impact rotor at high velocity, a motor driven fluidizing
rotor removably mounted near the bottom of the impact reduction
chamber, the improvement therein which comprises an unobstructed
attrition chamber having, at a lower section thereof, a vertically
decreasing cross-sectional area, said attrition chamber extending
vertically above the impact rotor, first product exit means located
at the bottom of the impact reduction chamber, second product exit
means located in a side of the housing opposite the inlet chute,
and third product exit means at the upper end of the attrition chamber.
In another embodiment of the invention, a particle crushing/classifying
system comprises a crusher housing, a particle inlet chute, an impact
reduction chamber containing a motor driven impact rotor, a fluidizing
rotor, an unobstructed vertical attrition chamber having at least
along a portion thereof a vertically decreasing cross-sectional
area, product exit means in communication with the attrition chamber
oriented to thrust an air/particle product stream in a substantially
horizontal plane, and a plurality of crushed particle collection
bins located at various distances from the exit to permit classification
of particles by gravity flow into the various bins.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is best understood with reference to the drawings
in which:
FIG. 1 is a perspective exterior view of the feed system, rotary
crusher, multiple bin classification system, and dust collector
(i.e., fine grinding mode);
FIG. 2 is a side cross-sectional view of the crusher and bin collection
system;
FIG. 3 is a side elevational cross-section view of the crusher
in secondary crushing mode;
FIG. 4 is a side elevational cross-sectional view of the crusher
in tertiary crushing mode; and
FIG. 5 is a schematic diagram of a fine-grind collection system
using the centrifugal separators.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Referring first to FIG. 1 rotary mill or crusher 2 is fed coarse
material by belt feeder 4. The belt feeder is elevated on support
structure 3 and is upwardly inclined, dumping the coarse feed material
into the opening of feed chute 5 in the crusher.
The crusher has three distinct modes of operation as shown in FIGS.
2 through 4. Conventional primary crushing, which reduces large
rocks to -6", is not done in the crusher of the invention.
The secondary mode, used on relatively large size feed to effect
a relatively small reduction (e.g. from 6" to 3/4") is
shown in FIG. 3. In this mode, the fluidizing rotor is removed,
and feed passes through the inlet chute into the impact reduction
chamber 89 impacts with the rotor 63 shatter bar 66 and other
particles, and exits from the bottom of the impact reduction chamber
into a pit 79 beneath the crusher.
In the tertiary crushing mode, shown in FIG. 4 fluidizing rotor
14 is in place at the bottom of the impact reduction chamber. Trap
door or hatch 82 is opened, and crushed product exits through opening
88. In this mode, feed particles having an average size of about
11/2" can be ground to product sizes varying from about 1/8"
to 30 mesh.
The fine grind mode is shown in FIG. 2 wherein the impact rotor
63 and fluidizing rotor 70 are both actuated, air ducts 16 (see
FIG. 1) are opened, and the product is further reduced in attrition
chamber 90 prior to passing through header 21 and exits at high
velocity and in a horizontal direction into the multi-bin classification
system. In the fine grind mode as shown in FIG. 2 product size
is generally from 30- to about 200 mesh, and can be further decreased
by increasing the height of the attrition chamber. Addition of a
36" vertical section between the top of the attrition chamber
and header 21 generates a product between 30 mesh and 200 mesh,
and addition of a further 24" chamber creates a product size
between 100 mesh and 300 mesh.
Details of the internal construction of the mill of the invention
are best seen in FIGS. 3 and 4. Coarse product enters the exit chute
and passes through flexible curtain 60 secured at its upper edge
to the mill housing. The outer housing wall 61 has an impact rotor
63 mounted on the interior thereof in an impact reduction chamber
89. A diverter bar 62 located at the end of the chute reverses the
direction of the incoming feed material, directing the material
into the entry side of the impact reduction chamber. Rotor 63 is
carried on a shaft 15 which traverses the impact reduction chamber
and penetrates the housing wall; it is driven by an engine 7 (see
FIG. 1). The rotor, which has hammers 65 mounted at its periphery
on support blades 64 revolve rapidly in a counter-clockwise direction.
The support blades are preferably constructed in a manner so as
to sweep a substantial amount of air to create a high velocity of
air upwardly through the attrition chamber toward the collection
bins.
Feed particles entering the entry section of the impact reduction
chamber fall by gravity against the rotating hammers and blades,
and are thrust outwardly against a series of transverse shatterbars
66 each of which has a pointed apex 67 to shatter the ore and
reduce the particle size. Particles impacting on the shatterbars
and the rotor hammers will also impact the remainder of the wall
lining 68 of the impact reduction chamber, causing further size
reduction.
In the secondary reduction mode, fluidizing rotor 70 is removed
via hinged rotor cover 71 which is attached to the external portion
of inner housing wall 69 and flange 78 by hinge 72. The hinged joint
is rotatable around hinge pin 73. When the rotor is in place, the
rotor cover is closed as shown in FIG. 4. Closure is effected by
swinging the cover to the closed position, sliding an L-shaped retaining
bracket 76 over threaded lug 74 and fastening the assembly with
nut 77. Seal is effected between the rotor cover and lip 81 which
depends from the exterior of the crusher housing. With the rotor
cover open and the rotor removed, particles may be reduced in size
about 8-10 fold very quickly and with a minimal expenditure of energy.
Product is collected in pit 79 and can be removed by conventional
means.
The tertiary crushing mode is shown in FIG. 4. Ore enters the impact
reduction chamber 89 through feed chute 5 and impacts the rotor
hammers and the shatterbars in the same manner as heretofore described.
In the crusher described herein, small particles tend to accumulate
in the bottom portion of the impact reduction chamber. To keep the
small particles moving throughout the chamber, the fluidizing rotor
unit rotates rapidly and throws the particles back into the impact
reduction chamber. The fluidizing rotor comprises a shaft 14 having
radially extending removable bars or blades 80 extending along the
length of the shaft within the housing. As shown, the fluidizing
rotor normally rotates in a counterclockwise direction, but may
be reversed if desired. A more detailed view of the blades and hammers
for the impact rotor, and of the fluidizing rotor, are found in
my U.S. Pat. No. 4037796. These designs are conventional, and
no invention in a specific rotor design is claimed herein.
In the tertiary mode (FIG. 4), hatch 82 mounted on external housing
wall 61 is shown in the open position. The hatch is hingedly mounted
at 83 with pin 84 and can be swung downwardly to provide product
exit means 88 downstream (i.e., on the opposite side of the impact
reduction chamber from the feed inlet) of fluidizing rotor. Closure
of the hatch is similar to closure of the rotor cover, and is best
seen in FIG. 3. An L-shaped retaining bracket 85 fits over threaded
lug 86 with a flange of the bracket extending over the end of the
hatch 82 to maintain it in closed position. A fastening nut 87 completes
the closure of the unit. Crushed particles exiting the tertiary
product exit are crushed to particle sizes intermediate the secondary
and fine-grind modes.
In operation of the crusher of the invention both the secondary
and tertiary modes, a cover 96 is bolted on the unit at the top
of attrition chamber 90 in the manner shown in FIG. 4. FIG. 3 shows
an additional extension on the top of the attrition chamber which
is not normally used except in the fine-grind reduction mode. In
addition, the air vents 16 are closed when operating in the secondary
and tertiary modes.
The remaining, and generally most important, operating configuration
is the fine crushing configuration shown in FIGS. 1 and 2. As shown
in FIG. 2 rotor 70 is in place, and hatch 88 is in the closed position.
In this mode of operation, crusher rotor 63 operates at very high
speeds, e.g., rotor tip speeds of up to about 9000 feet per minute,
and the fluidizing rotor is actuated to jettison particles which
settle by gravity at the bottom of the impact reduction chamber.
Particles are swept by a very high air flow upwardly into attrition
chamber 90 which is a vertical chamber having a vertically decreasing
cross-sectional area formed by inner housing walls 68 69 and 91.
Importantly, the attrition chamber does not contain any diverters
or other objects which impede the upward flow of air and particles.
Attrition occurs in the attrition chamber by intercontact of rising
and falling particles, and by impact of the particles against the
chamber walls. Slanted wall 91 which extends at an angle of approximately
45.degree. to horizontal, deflects particles back toward the center
of the attrition chamber and toward the mainstream of the rapidly
moving vertical air flow. Because of the vertically decreasing cross-section
of the attrition chamber, air velocity increases as the air rises
approximately inversely proportional to the cross-sectional area.
Accordingly, air velocity is maximized at the upper end 97 of the
slanted wall of the attrition chamber. As shown in FIG. 3 additional
vertical sections such as section 92 may be bolted to the top of
the attrition chamber to increase the path of travel of the crushed
particles and concomitantly decrease particle size. Depending upon
the number of vertical sections bolted on, product particles may
range in size from about 50 mesh to -200 mesh.
Actual experience has demonstrated that particles will be in the
range of 1/8" to 30 mesh when the attrition chamber is configured
as shown in FIG. 2. Addition of a 36" vertical extension to
the attrition chamber changes the product size range to about -30
mesh to about -100 mesh. The further addition of a 24" vertical
chamber changes the product size range from about -100 mesh to -200
mesh.
At the top of the attrition chamber is a header 93 having a horizontal
hinged cover 94 connected at hinge 95. This cover is either closed
by a frictional closing or an explosion bolt such that, in the event
of an explosion when grinding potentially dangerous products such
as coal, the cover acts as a relief valve to release the pressure
and prevent damage to expensive components of the crusher and collection
system.
Product exits the header, optionally through a screen 98 (shown
in FIG. 2) which may knock back any exiting particles larger than
a desired size and are thrust into a collection system at very high
velocities. At this point, particle velocities may be in the range
of 4000 to 8000 f.p.m.; more particularly 5000 to 6000 f.p.m. Whereas
in prior art systems the product particles are collected together
and separated subsequently by mechanical means (e.g., screening).
The collection system of the invention preferably takes advantage
of the high air and particle stream velocity to assist in classifying
the product. For example, the stream may be used as feed to a conventional
cyclone separator, where product enters tangentially and is centrifugally
separated, with heavier particles exiting the bottom of the separator
and larger particles being carried over into an additional separating
means or storage bin. Alternatively, particles may jet into the
separation system shown in FIGS. 1 and 2.
As best shown in FIG. 2 the air particle stream passes through
optional sieve 98 at high velocity into a series of collection bins
22 23 and 24 which are positioned adjacent to each other at increasing
distances from the attrition chamber exit. Finely divided particles
in the product stream shoot across the top portions of the bins
and fall by gravity into the lower funnel shaped portions 25 26
and 27 of the bins. Heavier larger particles drop closest to the
attrition chamber outlet, i.e., in bin 25; intermediate sized particles
drop into bin 26 and fine particles will carry over into bin 27.
By this method of classification, energy produced in the crusher
is in effect recovered by using the energy to perform a classification
function.
Each of bins 22 23 and 24 have a cylindrical neck opening at the
bottom thereof, identified as product exits 50 51 and 52. A series
of vertical dust suction tubes 47 48 and 49 extend downwardly
into the funnel shaped portions of the bins and into the necks of
the bins to collect dust-type particles in the vicinity of the bin
exit. Each of the suction tubes are fastened by an adjustable collar
44 45 and 46 which may be loosened to adjust the height of the
suction tube in the bin. The suction tubes are connected by flexible
extendable couplings 34 35 and 36 to horizontal duct sections
31 32 and 33 which connect to a dust collection system best seen
in FIG. 1. The dust collection system consists of a header 37 into
which all of the horizontal tubes extend, a funnel shaped portion
38 and a vertical duct leading from the bottom neck portion of
section 38 to a suction fan 40 having a variable speed drive which
creates a constant flow of air from the collection bins through
the header, the suction fan, and into bag house 42 through line
41. The bag house is a conventional dust collection vehicle; any
known system for removing extremely fine particles from an air stream
may also be used. In general, the fines collected in the bag house
may be used or discarded; in crushing limerock, or in the recovery
of silver, lead, and zinc, the fines are used or processed, whereas
in gold ore recovery, they are usually discarded.
The drive mechanism for the crusher is shown in FIG. 1. Drive engine
7 having control stick 8 drives the fluidizing rotor and the impact
reduction rotor through a series of belts and pulleys. Drive belts
9 and 10 transmit rotational motion to pulley 12 attached to the
shaft 14 of the fluidizing rotor, and belt 11 transmits power to
pulley 13 attached to the drive shaft 15 of the crusher rotor. Of
particular importance to the tertiary crushing mode are identical
air inlets 16 on opposing sides of the crusher housing which have
a damper control 17 for a butterfly valve in the air inlet tube.
When the butterfly valve is opened, air is sucked into the crusher
at high speeds, and the air velocity through the impact reduction
chamber and the attrition chamber is increased to very high rates.
The rapidly revolving crusher rotor acts as a giant fan, creating
a tremendous velocity of air and particles through the attrition
chamber and into the classification chambers. Velocity is controlled
to a large extent by controlling the quantity of air passing through
the air inlet tubes. Air passes upwardly through the header, shown
in FIG. 1 having an outer wall 21 and into the three bins spaced
at various distances from the product exit. An access door 30 is
located in the center bin 23 to permit maintenance.
For any given crusher, the fineness of crushing depends on the
type of material being crushed, the rotor tip speed, and the air
velocity. Air velocity is controlled by adjustment of the air intake
flaps 17. The following table illustrates specific examples of crushing
in the fine grind mode at various air and rotor speeds.
______________________________________ Air Rotor Velocity Tip Speed
Particle Material f.p.m. f.p.m. Size Range ______________________________________
Mineral-bearing Quartz 4000 6000 1/8"- 30 mesh Limerock 4000
6000 30-60 mesh Galena 4000 6000 30-100 mesh Quartz 5000 7500 30-60
mesh Limerock 5000 7500 60-100 mesh Galena 5000 7500 100-150 mesh
Quartz 7000 9000 60-100 mesh Limerock 7000 9000 100-200 mesh Galena
7000 9000 100-200 mesh Coal 7000 9000 100-250 mesh ______________________________________
As the rotor tip speed approaches about 12000 f.p.m., the air
intake for the equipment tested begins to become relatively constant.
During operation in the fine crushing mode, product passes through
the necks 50 51 and 52 of the collection bins where it may be
collected in any suitable container, such as barrels or hoppers,
or on conveyor belts which may carry the materials to other containers,
such as freight cars. Because of the dust collection system, these
heavier particles falling through the bin necks are generally relatively
dust free.
Depending on the height of the attrition chamber, it has normally
been found from operating experience that material having a size
range from about -30 mesh to +50 mesh is normally collected in the
first bin 22. In the second bin, particle size ranges from approximately
-50 to about -150 mesh; extremely fine particles, i.e., +150 mesh,
are picked up in the third bin. The dust particles are sucked up
through the tubes 47 48 and 49 for final collection at the bag
house. By adjusting the depth of the tube in the bin neck and by
controlling the speed of the suction of the updraft fan 40 the
size of particles drawn into the dust collection system may be controlled.
An alternative to the three bin collection system is a solid/gas
cyclone. These are conventional, commercially available units which
may be equipped with a suction tube having an adjustable depth and
a variable speed suction fan in the same manner as is shown in the
collection bins in FIGS. 1 and 2. Similarly, the fine particles
are drawn through the suction tube and collected in a bag house.
As an alternative to the single blower system shown in FIG. 1 each
of the suction tubes 31 32 and 33 may be attached to separate
suction fans and separate cyclones. By adjusting the height of each
of the tubes and the amount of air drawn through the tubes, additional
classification of extremely fine particles may be accomplished.
Another embodiment of the invention shown in FIG. 5 is a crusher
100 operating in the fine-grind mode with recovery effected in a
series of cyclones 102 104 and 106. Product exits the crusher
and enters the first cyclone, with the particles traversing the
interior perimeter of the cyclone and gravitating toward the lower
opening. Coarse product drops through the opening, and finer product
and air are sucked through the verticle tube via variable-speed
suction fan 110. Similar separations are made in cyclones 104 and
106 with variable speed fans 112 and 114 controlling product size.
Very fine dust is sent to bag house 108.
This method is particularly useful where a number of different
product gradations are needed, e.g., for fertilizer lime; by controlling
fan speed, product size distribution can be closely controlled.
In addition, this control can be used to substantially reduce the
size of the bag house which is normally required to handle all of
the fines.
Many modifications to the invention within its spirit and scope
will be apparent to those skilled in the art; the description of
the specific embodiment herein should not be construed as limiting.
Accordingly, the invention should be defined only by the following
claims. |