Note: Descriptions are shown in the official language in which they were submitted.
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MULTIPLE DR><JM MIXING SYSTEM
s This invention deals with ,the field of mixing plants for
aggregate and the like and in particular such a plant that
employs an inner and an outer drum rotating together.
l0 H~ACKGROUND
Aggregate typically is sized into categories such as fine,
medium and course, or some similar divisions. Different
applications and uses of aggregate often require specific
1s proportions of different sized aggregate, which proportions
are achieved by mixing aggregate from the different categories
to achieve the proper and substantially uniform mix. As well,
aggregate tends to segregate itself when handled, as the
larger pieces roll to the sides of a pile. Mixing the
Zo required proportions nearest the point of final use can be
beneficial in maintaining the proper mix.
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In some instances, the properly proportioned aggregate mix is
further mixed with another material. For example, to make
asphalt for road paving, liquid asphalt is added to an
aggregate mix, and sometimes there is the further addition of
a proportion of recycled asphaltic material. Similarly, to
make pre-mixed dry concrete, cement is added to an aggregate
mix.
Single drum mixers are commonly used for such mixing, with the
materials to be mixed introduced into one end and tumbled
together as they pass through the drum. In addition to mixing
the aggregate, it is usually desired to dry the aggregate as
well. The drying is generally accomplished by directing a
flow of heated air into the drum. Where moisture content of
is different materials varies, it would be desirable to have one
or more of the mix materials dried at a slower rate or heated
to a different temperature than another mix material.
When exposed to high heat, liquid asphalt may be damaged and
z0 the quality of asphalt may be reduced. Remo~ring the point at
which asphalt is introduced into the mix from the direct path
of the heated air improves the quality of asphalt produced.
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A significant problem with such systems is that the fine
material carried out With the air not only causes pollution,
but the fines are also lost from the mix. These fines are
material that has been conveyed into the mixer and dried. Any
such material that does not go into the mix is a loss, and
must be replaced with further aggregate material, at added
cost.
Dual drum mixers are also known in the prior art. Prior U.S.
io Patent No. 4, 600, 379 to Elliot is directed to a mixer with
concentric dual drums, as does U.S. Patent No. 4,262,429 to
Avril. These devices are directed towards reduced energy use
and pollutants such as fines or combustion gases.
~s A device which would provide more versatility with respect to
adding, drying and heating the various components of a mix
would be beneficial. Such a de~rice that also reduced the
fines exhausted from the~mixer would be further advantageous.
io
SUD~~QPrRY OE THE INVENTION
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It is an object of the present invention to provide a drying
and mixing plant that provides improved selection of points
for insertion of material into a mix and improved selection of
drying rates through such selection.
It is a further object of the present invention to provide a
drying and mixing plant that captures the fine aggregate
material usually carried out of the plant by the exhaust air,
for use and retention in the material mix, thereby also
iu reducing the filtration capacity needed to remove these fines
from the air.
The invention accomplishes these objects providing a drying
and mixing plant for particulate material comprising an inner
i5 drum, a middle drum and'an outer drum, each having an input
end for receiving particulate material and an output end for
discharging particulate material, said drums attached
concentrically to form a substantially horizontal drum
assembly having a top side and a bottom side, wherein said
2o drums rotate together, said assembly thereby forming a first
annular chamber between said inner and middle drums and a
second annular chamber between said middle and outer drums;
said drums located such that a first particulate material
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discharged from said output end of the inner drum is received
at a mid-point of said middle drum and is then carried to said
output end of the middle drum and received by said input end
of the outer drum and carried through said second annular
s chamber to said output end of the outer drum and discharged
from said drum assembly through a material outlet; a drive
operatively connected to said drum assembly and operative to
rotate said drum assembly; a hot air source directing a hot
air stream into said input end of the inner drum; a first
io shroud enclosing said first annular chamber at said input end
of the middle drum, said first shroud providing access for a
second particulate material to enter said input end of the
middle drum; a second shroud enclosing said second annular
chamber at said output end~of the outer drum, said second
is shroud providing access in the bottom thereof for particulate
material to be discharged through said material outlet: a
third shroud enclosing said input end of the outer drum said
third shroud providing access for a third particulate material
to enter said outer drum; an exhaust vent operatively
2o connected to one of said second or third shrouds for directing
said hot air stream out of said drum assembly; and impellers
mounted on the inner ,surface of each drum for moving
particulate material along said drums and for lifting
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particulate material and dropping same to fall through said
hot air stream: where in operation, particulate material
travels in the same direction through said inner and middle
drums, opposite to Lhe direction of travel of particulate
material through said outer drum and said second annular
chamber, all particulate material introduced into said drums
thereby becoming mixed.
The disclosed mixer allows for insertion of different
>lo materials at the input ends of each drum. Particulate
materials such as aggregate or recycled asphalt could be
sorted and put into the apparatus at the desired location.
First material introduced into the input end of the inner drum
will be subject to the highest temperatures and fastest
drying. Second material introduced into the input end of the
middle drum will be carried first through the first chamber
where it will be heated by radiant heat from the inner drum,
and then will enter the path of the hot air stream and be
mixed with the hotter first material from the inner drum. The
i0 second material will not be exposed to the hot air stream as
long as the first material, and will receive less drying.
This first mixed material will then be discharged into the
outer drum and be carried in the opposite direction through
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the second chamber to the material outlet.
A third material could be introduced into the input end of the
outer drum and be mixed with the first mixed material to form
s a second mixed material. This third material will receive
even less drying as it i's exposed to heat for less time than
the other materials.
The hot air stream may be directed out of the apparatus at the
1o input end of the outer drum, through the thixd shroud. The
hot air stream then does not pass through the second chamber
and the third material then receives heat only by radiant heat
from the middle drum, and absorption of heat from the first
mixed material. Alternatively the hot air stream may be
is directed out of the apparatus at the output end of the outer
drum, through the second shroud. The hot air stream then
passes through the second chamber, and further dries and heats
the second mixed material and thus the third material.
2o As well a material could be inserted somewhere along the
second chamber between the middle and outer drums. This is
most applicable to liquid materials which could be inserted
through a conduit extending through the third shroud and
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ending at the chosen location in the second chamber. For
example, liquid asphalt, could be introduced at this point,
with the hot air stream directed through the third shroud,
thus substantially reducing the temperature in the second
chamber and reducing damage to the asphalt.
With the exhaust vent operatively connected zo the second
shroud, and the exhaust vent operatively connected to the top
portion of the second shroud, the invention could further
io comprise means to direct the hot air stream in the second
chamber downwards towards the bottom of the second chamber as
the hot air stream leaves the second chamber and enters the
second shroud. The meahs could comprise an annular baffle
attached to the exterior surface of the middle drum at a mid-
is point of the middle drum, the baffle extending radially into
said second chamber and directing the hot air stream towards
the inner surface of the outer drum; and a semi-circular
baffle attached to the second shroud and extending into the
top portion of the second chamber, the baffle angled to direct
2o the hot air stream from the top side of the second chamber
towards the bottom thereof.
Thus the hot air stream is forced to the bottom of the second
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shroud and must rise to the,top portion to enter the exhaust
vent. More of the larger tines will then fall into the mix.
This effect can be accentuated if the airflow path through the
second shroud and the exhaust vent has a cross-sectional area
greater than the cross-sectional area of the second chamber,
whereby the velocity of the hot air stream is reduced as the
hot air stream exits the second chamber into the second
shroud. Reducing the velocity of the hot air stream will
allow more of the fines to settle out re-enter the mix.
~o
A liquid material, such as liquid asphalt, could be introduced
into the outer drum at a point inside the second chamber.
Moving the injection point down the second chamber somewhat
would reduce the temperature that the asphalt is exposed to,
i5 and reduce burning.
Further, the asphalt could be introduced through a plurality
of nozzles oriented to direct a spray of liquid material
across a majority of the cross-section of the second chamber.
The majority of the fines would pass through the spray and be
2o coated with asphalt, thereby becoming heavier and more likely
to fall down into the mix.
The hot air stream thus passes through the second chamber
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before exiting the drum assembly through the exhaust vent.
The second mixed material would be subjected to higher
temperatures, and more drying. The annular baffle at the mid-
point of the middle drum directs the hot air stream towards
s the outer drum where it can be deflected by the semi-circular
baffle would direct it down and into the mix.
DESCRIPTION OF THE DRAWINGS
1D
While the invention is claimed in the concluding portions
hereof, preferred embodiments are provided in the accompanying
detailed description which may be best understood in
conjunction with the accompanying diagrams where like parts in
>-s each of the several diagrams are labeled with like numbers,
and where:
Figure 1 is a cut-away side view of an embodiment for
mixing asphalt and aggregate, with the exhaust vent
ao located so that the hot air stream does not pass through
the chamber between the middle and outer drums;
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Figure 2 is a cut-away side view of an embodiment for
mixing asphalt and aggregate, with the exhaust vent
located so that the hot air stream passes through the
chamber between the middle and outer drums;
Figure 3 is an end view of the semi-circular baffle.
Figure 4 is an end view of the nozzle ring.
to
DETAILED DLSCRIPTION OF THE ILLUSTRATED EL~ODIMENTS
Figure 1 shows one preferred embodiment of the invention. A
drying and mixing plant for particulate material comprises an
is inner drum 1, a middle drum 2 and an outer drum 3, each having
an input end la, 2a, 3a for receiving particulate material and
an output end 1b, 2b, 3b for discharging particulate material.
The drums 1, 2 ands 3 are attached concentrically by drum
brackets 4 to form a substantially horizontal drum assembly 5
ao having a top side Sa and a bottom side Sb. The drum assembly
5 is supported on the frame 6 at drive wheel 7 and support
wheels 8. Drive wheel 7 is rotationally driven by motor 9, and
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the drum assembly 5 is thereby rotated.
The drum assembly 5 forms a first annular chamber 10 between
the inner and middle drums 1, 2 and a second annular chamber
s 11 between the middle and outer drums 2, 3. The drums 1, 2
and 3 are located such that a first particulate material 20
(indicated by the circular "o" particles in the figures),
introduced into the input end la of the inner drum 1 on first
conveyor 17, and then dischargEd from the output end lb of the
io inner drum 1 is received at a mid-point of the middle drum 2
and is then carried to the output end 2b of the middle drum 2
and received by the input end 3a of the outer drum 3 and
carried through the second annular chamber 11 to the output
end 3b of the outer drum 3 and discharged from the drum
is assembly 5 through a material outlet 12. The direction of
flow of the particulate material is dictated by the pitch on
the impellers 13 located on the inner surface of the drums 1,
2 and 3. The impellers 13 also lift the particulate material
and drop same through the hot air stream 15. Such impellers
zo are well known in the prior art and many are suitable for use
in the drums 1, 2 and,3..
A hot air source 14 comprises a conventional burner and blower
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and directs a hot air stream 15 into the input end la of the
inner drum 1. The direction of flow of the hot air stream 15
is indicated by the arrows in the figures. A first shroud 16
encloses the first annular chamber 10 at the input end 2a of
the middle drum 2. The first shroud 16 provides access for
a second particulate material 21 (indicated by the cross
figures "x" in the figures) to enter the input end Za of the
middle drum 2 via second conveyor 18. A second shroud 19
encloses the second annular chamber 11 at the output end 3b of
~o the outer drum 3 and provides access in the bottom thereof for
particulate material to be discharged through the material
outlet 23. This is a vibrating, air-blocking type outlet
which prevents air from escaping. A finished product conveyor
24 takes the mixed particulate material to storage,
is transport or the like as required.
A third shroud 25 encloses the input end 3a of the outer drum
3 and provides access for a third particulate material to
enter the outer drum 1 through access hatch 26. zn the
Zo embodiment illustrated in Figure 1, this hatch 26 is sealed
with hatch cover 27, while Figure 2 shows an embodiment with
a third material 22 (indicated by the square figures "o" in
the figures) being introduced through the hatch 26.
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An exhaust vent 28 is operatively connected to the third
shroud 25 for directing the hot air stream 15 out of the drum
assembly 5. With the exhaust vent 28 so located, the hot air
stream 15 simply travels essentially straight through the drum
s assembly 5 from the hot air source 14 to the exhaust vent 28.
It can be seen that material inside the first and second
chambers 10, 11 is not exposed to the hot air stream 15, and
thus receives less drying than the material that is in the
inner drum 1 and the latter half of the middle drum 2. The
io embodiment also includes a liquid injection nozzle 29 which
protrudes somewhat into the second chamber 12, supported on a
pipe 30. Fox liquid asphalt injection, this location would be
preferred because it is not in the hot air stream 15, and so
is not subject to damage from burning. Liquid asphalt is
is supplied to the nozzle 2.9 by conventional pressuri2ed source
40.
In operation particulate material 20 and 21, travels in the
same direction through the inner and middle drums 1 and 2,
ao opposite to the direction of travel of particulate material
20, 21 through the outer drum 3 and the second annular chamber
12. All particulate material introduced into the drums thereby
becomes mixed.
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Alternatively the exhaust vent 28 may be connected to the top
portion of said second shroud 19 as illustrated in Figure 2,
wherein the hot air stream 15 passes through the second
chamber 11 before exiting the drum assembly 5. The
embodiment further comprises means to direct the hot air
stream 15 in the second chamber 11 downwards towards the
bottom of the second chamber 11 as it leaves the second
chamber 11 and enters the second shroud 19. The means
utilized comprises an annular baffle 31 attached to the
yo exterior surface of the middle drum 2 at a mid-point thereof
extending radially into the second chamber 11 and directing
the hot air stream 15 towards the inner surface of the outer
drum 3. A semi-circular baffle 32, as illustrated in Figure
3, is attached to the second shroud 19 and extends into the
is top portion of the second chamber 11. The semi-circular
baffle 32 is angled to direct the hot air stream 15 from the
top side of the second chamber 11 towards the bottom thereof.
The semi-circular baffle 32 catches the air stream that is
accelerated along the inner surface of the outer drum 3 by the
zo annular baffle 31 and directs it towards the bottom of the
second chamber as the hot air stream 15 enters the second
shroud 19.
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The hot air stream 15 is forced to the bottom~of the second
shroud 19 and must therefore rise a greater distance to the
top portion of the second shroud 19 to enter the exhaust gent
28. More of the larger fines will then fall into the mix.
This effect is accentuated by the fact that the airflow path
through the second shroud 19 and the exhaust vent 28 has a
cross-sectional area greater than the cross-sectional area of
the second chamber 11. The velocity of the hot air stream 15
is thus reduced as it exits the second chamber 11 into the
io second shroud 19. Reducing the velocity of the hot air stream
will allow more of the fines to settle out re-enter the mix,
thereby reducing waste of material and expulsion of material
into the air.
is Also illustrated in Figure 2 is a third particulate material
22 being introduced into the input end 3a of the outer drum 3
through access hatch 26. The third material 22 is mixed with
the first and second materials 20, 21 as the material passes
through the second chamber 11.
Liquid material 33, such as 2tsphalt, is also introduced to the
particulate material just inside the second chamber 11 through
a plurality of nozzles 34 mounted on nozzle ring 35 attached
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to frame 6 and oriented to direct a spray of liquid material
33 across a majority of the cross-section of the second
chamber 11, as illustrated in Figure 4. The majority of the
fines pass through the spray and are coated ~rith the liquid
s material 33, thereby becoming heavier and more likely to fall
down into the mix.
The invention thus provides greatly increased flexibility in
the heating and drying of various particulate materials. The
addition of liquid materials is facilitated, and provision is
made for utilizing the liquid material to reduce the expulsion
of material into the exhaust air stream.
The foregoing is considered as illustrative only of the
is ~ principles of the invention. Further, since numerous changes
and modifications will readily occur to those skilled in the
art, it is not desired to limit the invention to the exact
construction and operatidn shown and described, and
accordingly, all such suitable changes or modifications in
2o structure or operation which may be resorted to are intended
to fall within the scope of the claimed invention.
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