Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BLENDER WITH VIRTUAL BAFFLE OF PARTICULATE MATERIAL
BACICCROUND OF THE 1NYENTION
FIELD OF THE INlIENTION
This invention relates to blenders and more specifically
to methods and apparatus for thoroughly blending particulate
or granular materials, a portion of the unblended material
forming a toroidal block, constituting a virtual baffle to
the downward flow of any particulate material except that
passing through the blending tubes themselves.
DEFINITIONS
baffle--(noun) a plate, wall, screen, or other device to
deflect, check, or regulate Ilow.
virtual battle-°herein defined as a barrier, formed of
particulate material, in combination with a supporting
structural matrix, to the downward flow of particulate
material, except through blending tubes which penetrate the
barrier.
matrix--herein defined as blender walls, metallic plates and
cones, blending conduits, all coacting wixh the particulate
material to provide the virtual battle.
voussoir°-(diet.) one of the wedge-shaped pieties forming an
arch or vault. Used herein to graphically describe the cross
section of the virtual baffle, at some point on the toroid
or segment.
bridging--the tendency of particulate solids, flowing
downward through a channel with converging sides, to bridge
across the channel, blocking the channel, causing all of the
material flowing out of the blender to flaw through the
blending tubes.
toroidal block--herein, a toroidal mass of particulate
material, having a voussoir-like crossection, supported
betwe~:n the outer wall of the blender and the downwsrdly '
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converging metal baffles of FIGs. 6 and 9. Also called a
toroidal or annular "keystone joist.°'
DESCRIPT10N OF THE PRIOR ART
Prior to the advent of large scale use of polymers in
such applications as continuous film or filament production,
the needs of industry for precision blendinig of bwlk solids
products were met with mechanical tumbler, ribbon or screw
blenders. Capacities of these units ranged from less than
one cubic meter to over 100 cubic meters.
As the demand for plastics grew, it became apparent that
much larger blender volumes were necessary to allow
continuous production lines in plastics users' plants to
operate without frequent shutdowns caused either by (1)
variations in physical properties or (2) additive content
inherent in the producer's production processes. This Ied
to a demand for tumble blenders in the range of 700 cubic
meter capacity.
The high cost of large tumble blander installations
prompted industry-wide efforts to develop a blending
capability in storage silos to comply with the product
uniformity requirements of the polymer industry. A number
of designs resulted, some silo blenders having capacities in
the 3000 cubic meter range.
Efficient silo blenders are available today in two broad
categories:
A. Gravity Blenders
These designs generally use either external or internal
tubes having openings to allow solids in the bin to slow
from the main silo body to a separate blend chamber below
the silo. The tube openings in the main body of the silo
are randomly located so that material drained into the blend
chamber represents a typical composite of the material in
the main silo body.
B. Internally Recirculated Blenders
These units rely on an external source of air to pick up
material in the lower part of the silo body by an orifice
arrangement, and convey it to the upper part of the main
silo. The material flowing vertically down through the silo
is randomly sampled by the openings in the tubes and
agitated by inverted cones, resulting in homogenization of
the silo contents after a period of time.
SUSSTdTUTE SHEET
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The performance of both Gravity Blenders and Internally
Recirculated Blenders can be significantly improved by
recirculation while the blender is being filled.
As storage bins or hoppers are filled with granular or
particulate material, it often happens that an inhomogeneous
distribution of material occurs. There may be several
reasons for this result. In the first place, as material
flows into a hopper, the material beneath the inlet nozzle
piles up at the angle of repose of the materiel. In this
case the larger particles often roll dawn the peak toward
the sides of the hopper, leaving the finer particles in the
central region. Inhomogeneity can also occur when the
hopper is filled with different batches of the same material
because of variations of composition ai individual batches.
When material is drawn off through an outlet at the bottom
of the hopper, the material flows irorn the region directly
above the nozzle. Thus the material will not be
representative of the average characteristics of the
material in the hopper.
Prior art attempts at a solution to this segregation
problem typically included placing perforated blending tubes
vertically within the hopper. Such tubes have openings
spaced apart along their axes which allow material from all
levels within the hopper to enter the tubes. The lower
portion of the blending tubes communicate with the outlet
nozzle so that a more nearly homogeneous mixture of the
material issues iron the outlet of the hopper.
In spite of many efforts to completely blend the
particulate materiel, it is usually necessary in prior art
blenders to specially treat at least the final portion of
the discharge to achieve acceptable results. For example,
U.S. Patent No. 4,923,304, discloses that the first and last
few pounds are not used, but instead are withdrawn and later
remixed with fresh ingredients, and re-poured, with these
fresh ingredients, back into the dispensing apparatus.
CA 02087178 2002-11-25
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SUMMRRY OF THE INDENTION
Recording to the invention there is provided a
gravity blender having a cylindrical upper portion
operable to receive and store a mass of particulate
material, and a lower portion defining a downwardly
converging canical section sealed to the lower cylindrical
edge of the upper portion, the lower and upper portions
being centered on a single vertical axis. R plurality of
blending conduits extended downwards from the upper
portion and continue downwardly adjacent the converging
conical section, converging downwardly towards the
vertical axis of the blender apparatus, The blending
conduits have open lower ends which terminate in a
generally circular and horizontal pattern, the convergence
of the blending conduits and the conical walls of the
lower section creating and supporting in operation a
virtual baffle of particulate material in combination.
The virtual baffle consists of uousaoir-like accumulations
of particulate material in the converging channels between
the blending conduits and between the conical walls and
the blending conduits. The baffle of particulate material
remains in position until the blending tubes have begun to
release the final portions of the particulate material
through the blending tubes to blend with the particulate
material of the virtual baffle as bath pass into and
through the lower portion of the bin,
In combination with a conventional hopper and
conventional blending tubes, two embodiments disclosed
herein can effectively blend a batch of particulate
material, including the final portion of the batch. In a
third embodiment, the operation of the i'ull size blender
is simulated, in an adjustable
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laboratory size model, enabling experimentation with various
particulate densities, cosrpactabilities and annular gaps.
My invention does not r~u~ire _a separate blending
chamber. It utilizes the tendency of particulate solids,
flowing downward through a channel with converging sides, to
bridge across the channel, blocking the channel, causing all
of the material flowing out of the blender to flow through
the blending tubes. Thus my invention assures that all of
the material discharged from the blender represents a truly
typical composite of the blender contents.
The three preferred embodiments disclosed in this
specification rely upon the tendency of particulate solids,
in flowing downward through a channel with converging sides,
to bridge across the channel. Such bridging may occur in:
A. A toroidal block, having a voussoir-like
crosssection, as shown in the blender of FIG. 6, and
equivalent supporting structure for bridging by particulate
materials, as shown in FIGrs. 2, 4, ?, 8 and 10.
B. A similar toroidal block in the apparatus iw FIG. 9,
for confirming by empirical tests, the preliminary design
proportions for a blender specifically contoured for the
density, compactability, and other characteristics ~i the
particulate material, or materials, to be blended;
C. A voussoir-like construction for the support of
particulate material! as shown in the construction of FIGS.
7 and 11-13, in which the matrix of blending tubes, optional
inverted cones, and conical walls of the vessel prsvide a
matrix for the support of the virtual baffle of pe~rticulate
material.
The "bridging principle" and the "virtual baff~de"
concept employed in the preferred embodiments are
illustrated in the following drawings and explained in the
specification.
BRIEF DESCRIPTION OF THE DRAb'VINGS
FIG. 1 provides an elevational, sectional vi~v through
the center line of a typical blender of the prior art;
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FIG. 2 provides an elevational, sectional view through
the center line of one preferred embodiment of the gravity
blender of the present invention;
FIG. 3 provides a schematic diagram of the hopper,
piping and pumps, if required for extremely uniform blending
within the gravity blender of the present invention;
FIG. 4 provides a sectional view from the vertical
centerline through the exterior wall of the lower portion of
the hopper of an alternate embodiment of tine present
invention, including a detail of s blending tube snd a
conduit for exhaust gases, or for structural purposes;
FIG. 5 is a section of the conduit of FIG. 4,
illustrating the knifelike device for preventing
accumulation of particulate matter on the top surface of the
conduit;
FIG. 6 is a more detailed view of Embodiment A of the
present invention, as combined with terminations of the
conventional blending tubes;
FIG, 7 is a more detailed view oI alternate Embodiments
A and C of the present invention as combined with two convex
surfaces for better blending of virtually all of the
material to be blended;
FiG. 8 provides an elevational, sectional view through
the center line of a gravity blender of an alternate
embodiment A of the present invention, in which one basic
convex surface is combined with a cylindrical device,
developed further in FIG. I2-I3, for further blending;
FIG. 9, Embodiment B, provides a vertical, sectional
view through the center line of the test apparatus, which
substantially duplicates the conditions within, and
operations of blending of the present invention)
FIG. 10, Embodiment A, provides a sectional view from
the vertical centerline tl2rough the exterior wall of the
lower portion of the hopper of an alternate embodiment of
the present invention, including a detail of a blending
tube, but without a venting conduit for exhaust gases
FIB, 11, Embodiment C, provides a fragmented elevational
hemicylindricai inside view, through a section in the plane
including the vertical centerline of a blender, utilizing a
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virtual baffle of particulate material, supported partially
on a matrix of converging blending tubes, and equipped with
a small inverted cone. Two partial sectional details are
provided]
FIG. 11A is a fragmentary section just inside~the wall
1112, showing the ends 1114 of the blending tubes 1110
within the toroidal block 1130 of particu late materials
FIG. 11B shows various angles of cut off of the
discharge ends 1114 of the blending tubes 11101
FIG. 12, Embodiment C, provides an elevational
hemicylindrical inside view, through a section in the plane
including the vertical centerline of a blender, utilizing a
virtual baffle of particulate material, supported solely on
a matrix of converging blending tubes, without an inverted
Bone, but with a vertical tubular elementl Q nd
FIG. 13, Embodiment C, provides a generally horizontal
sectional view through the blender of FIG. 12, at
approximately the level of the virtual baffle of particulate
material, supported partially on a matrix of converging
blending tubes and the vertical tubular element 1240.
DESCRIPTION OF THE THREE PREFERRED EIgBODI115ENTS OF THE
INVENTION
In praviding a more detailed discussion of the three
preferred embodiment of the invention, reference will be
first made to components of the blending apparatus from the
prior art, insofar as they differ from, or combine with, the
new invention for improved and more efficient performance at
lower cost.
In FIG. 1 is shown a drawing fram Patent No. 3,268,215,
issued to T.A. Burton for a Blending Apparatus on August 23,
1966. Illustrative of this prior art are tank or hopper 10,
blending tubes 24, and separate receiver or collector r
manifold 2ff.
FIG. 2 shows the similarities and the differences
between the prior art of FIG. 1 and the present invention.
Similarities include a cylindrical housing 210 superimposed
upon and sealed to a conical structure 211. Downcomer tubes
224 however, terminate in perforations 227 through the
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inverted generally horizontal baffle 225, comprising part of
the present invention. This means of termination is a
significant improvement over the prior art shown in FIG. 1,
in which tubes 24 pass entirely through the hopper 10 and
terminate in receiver 28. In the annular area 226, between
the converging walls of baffle 225 and structure 2.11, the
accumulation of particulate matter forms a toroldal block to
the passage of the particulate matter accumulating above the
block.
The recirculating schemes of the prior art are shown in
FIG. 3, diagrams 302 and 303.
My invention, as shown in its alternate embodiments.
deals with the problem in novel fashion. In FIG. 2,,and as
more easily seen in FIG. 6, the blending tubes, of which
tube 602 is an example, terminate in apertures 603. These
apertures are formed in the convex surface 604. This means
of termination is a significant departure from the prior
art, as shown in FIG. 1, in which tubes 24 pass entirely
through the hopper 10 and terminate in receiver 28.
Returning to FIG. 6, it should be noted that convex
surface 604 is supported upon brackets 606, and is thus
spaced away from the exterior cone 610 by an annular gap
shown as 605. Now, if the surfaces 604, annular gaps 605,
and apertures 603, are designed as will be shown in
connection with the description of FIG. 9, the material to
be blended will begin to sill the hopper 601, but will form
a barrier at the annulus 605, past which barrier the
particulate material will not descend, until blending tubes
are evacuated.
As the blending operation being perfarmed on the batch,
or mixture, draws to a close, the level of the material will
fall below the seam line 60't, and then past a series of
apertures 608. The discharge of material from the M ender
will then Ilow preferentially from the blending tulaes 602,
with essentially zero flow through the annulus 605 between
the inverted cone and the vessel cone. Flow through this
annulus 605 cannot occur until the supply of maternal coming
from the blend tubes 602 is exhausted,
FIG. 9 is a diagram of the Test Apparatus, il'~ustrating
its similarity in construction to the blenders of the
present invention. Material 901 is cross hatched for
clarity. Material 902 is shown crosshatched at mother
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CA 02087178 2002-11-25
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angle. The inverted cone may be set in a position 911 and
provides a smaller annular gap 903 than were it raised to a
higher position, say 912.
Material 901 is first poured into the inverted cone,
upright cone and standpipe at the start of test, filling
volumes shown as underlined 1,2,3,4 and 5. Material 902 may
be then put in to sill the remainder of the vessel and will
fill to the annular surface 809, in "keystone fashion," as a
toroidal block, or as a vousaofr a! particulate material.
Material 902 will not flow out of the vessel until the
supply of Material 901 is exhausted. In order to make this
principle work:
e. The flow of material from the center nozzle must be
regulated b~ ual~e to a rate below that could cause
voids to Corm in material 801.
b. Flow properties of material 801 and 902 should be
similar.
The teat procedure, it properly performed, can provide
valuable information on the dimensions 903, 809, and other
critical factors in cull-size blender design.
FIG. 11 illustrates the use of an inverted battle
through which the blending tubes 1110 do not penetrate, but
which is positioned in such a manner that a voussoir of
particulate material is formed between converging surfaces
in close proximity to each other. In this blender,
particulate material is entrapped within the matrix of
conduits 1110 and small inverted cone 1113 mounted on
brackets 1106 within the cone of the outer wall 1112, The
density, particle shape, compactability, and a host of
indeterminate factors will cooperate to establish a toroidal
block of material 1130, thus creating a virtual baffle of
particulate material, supported partially on a matrix of
converging blending tubes 1110, a small inverted cone 1113,
and lower section wall 1112. It must be understood that
this drawing is purely illustrative of the inventive
concept, and that other variations are within the scope of
the following claims.
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FIG. 12 illustrates the accumulation of particulate
material 1230 in this blender, when entrapped within the
matrix of conduits 1210, and within the cone of the outer
wall 1212. This embodiment is not equipped with an inverted
cone 1113, but has instead a vertical tubular element 1240.
A voussoir of particulate material 1230 will be formed,
Creating a virtual baille, in the corm of a toroid~al block,
between and among Lhe structural members, including the
central tubular structure 1240. The diameter of the tube
1240 is drawn too large in comparison with the area 1233
provided Ior discharge of the particulate material, but the
concept is adequately presented.
The density, particle shape, eompactability, and a host
of indeterminate factors will cooperate to establish the
position, volume, and mass of material 1230. These
parameters will be those required to obtain a suitable
toroidal block, utilizing a virtual baffle of particulate
material, supported partially on a matrix of converging
blending tubes 1210 and vertical tubular element 1240. It
must be understood that this drawing is purely illustrative
of the inventive concept, and that other variations are
within the scope the following claims.
FIG. 13 provides a horizontal sectional view through the
blender of FIG. 12, at approximately the level of the
virtual baffle 1230 of particulate material, supported
partially on a matrix of converging blending tubes 1210.
Further support is provided by the vertical tubular
structure 1240.
CLARIFICATION OF DIFFERENCES BETWEEN BAFFLES OF
THE THREE PREFERRED EItiBODII4iENTS OF THIS INVENTION
In the embodiments disclosed in FIGS. 11-13, the blender
uses a number of blending tubes or channels which terminate
at the same elevation adjacent to a small inverted cone 1113
as shown in FIG. 11, or without an inverted cone as shown in
FIVs, 1l and 13.
Although as shown in FIG. 6, the converging blending
conduits provide only limited support to the blocking
accumulation of the particulate material, in FIG. 11 the
ma,~or past of the mass of particulate material is supported
by the converging matrix of conduits. In FIGs. 12 and 13,
the entire mass of particulate material is supported by the
converging matrix of blending conduits and the vertical
tubular element 1240,
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Thus a very useful blender can be constructed which can
be installed in silos at a much lower cost than blenders
that rely solely on separate blend chambers as shown in F1G.
1.
FIG. 11 illustrates an alternate embodiment and a more
economical method of construction than that of FIG. 7,
achieved by eliminating the large baffle 704, and the "hard"
terminations of the blending tubes in apertures in the sides
of cone 704.
The matrix of converging downcoming blending tubes 1110
are mounted close to the conical wall 1112. Blending tubes
1110 do not terminate in apertures or hubs in the surface of
cone 1113, but terminate in the approximate region
delineated as 1114, which has a variable vertical range as
shown by the two-headed arrow at 1123.
The base line of the lower end of cone 1113 may vary
above or below a typical position 1114, as shown by
bidirectional arrow 1123. If proper proportions are
selected' such a grid of blending tubes converging toward
plane 1114, in combination with the converging wall 1112 of
the lower bin section 1101, can support a voussoir 1130 of
particulate material, extending slightly downward or upward
cram reference plane 1114.
It is thus possible to achieve the blocking effect of
the impervious baffle 604 of FIG. 6 without the expense of
physically connecting (measuring, cutting and welding) the
blending tubes to apertures fn the surface of a large
baffle, and in some cases the small baffle 1113 may not be
needed. Please refer to FIG. 12.
In FIG. 11A, various terminations for the blending tubes
may be employed. The intent of this disclosure is to
illustrate the concept of a baffle primarily of particulate
material, simpler to build and less costly in material. The
specific terminations of blending.conduits, patterns of the
matrix, and use or nonuse of small convex cones are all .
minor variations contemplated in the general use of this
invention.
In FIG. 12 is shown an embodiment which does not use the
small inverted baffle or cone 1113, a preferred construction
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being the structural tubing 1240. With some particulate
materials, the conical wall 1112 in combination with the
blending tube matrix 1110, may support the toroidal blocking
mass of material 1120 without member 1240.
The section shown in FIG. 13 is typical of many usable
designs. The intent of this disclosure is to illustrate the
concept of a baffle primarily of particulate material, .
simpler to build and less costly in material. The specific
terminations of blending conduits, patterns of the matrix,
and use or nonuse of small convex cones are all minor
variations contemplated in the general use of this
invention.
S~SST~TUTE SHEET
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