Stream splitting apparatus

An apparatus for splitting a stream of material into two or more streams. The apparatus includes a cylindrical housing with an axial inlet and two or more radial outlets which are axially spaced from each other. The apparatus includes an impeller which has a central shaft with a plurality of blades extending radially therefrom defining two or more sets of material receiving chambers. Each set of material receiving chambers has guide means directing any material which enters the chambers in that particular set outward through a specific outlet. Due to the rapid rotation of the impeller, each set of material receiving chambers receives material from the inlet at a predetermined ratio of flow rates relative, and guides that material outward through a particular outlet. The device is particularly useful for splitting a stream of particulate material into two separate streams having equal flow rates, even if the flow rate at the inlet to the stream splitter is inconsistent.

BACKGROUND OF THE INVENTION 
This invention relates generally to the flow of material, and more 
particularly to an apparatus for splitting a stream of material into two 
or more streams. 
It is often desirable to split a stream of particulate material into two or 
more streams each having the same average flow rate. In the mechanical 
pulping industry, stream splitters are used in order to feed equal amounts 
of pulp or wood chips into each side of a central rotating disc in one 
type of refiner. When a stream splitter is used, it is important to feed 
equal quantities of material in each side of the refiner in order that the 
refiner operates at its maximum capacity. Furthermore, equal feed in each 
stream will provide for similar thrust and fiber development on each side 
of the refiner. 
A typical stream splitter for a stream of particulate material has a Y-type 
divider blade. It is both difficult and expensive to achieve an equal 
split using this type of device, because in order to get equal flow to 
each side, the incoming stream either must be 100% full, or perfectly 
centered, with uniform material density and velocity throughout. 
Otherwise, the more densely packed or faster side of the "Y" receives more 
material than the other side. 
It is known that a material stream can be accurately split by providing 
equal opposing discharge openings on a simple screw conveyor. However, in 
order for equal splitting to result, the following three conditions must 
be met. First, the screw must rotate fast enough for centrifugal force to 
keep the material on the barrel of the conveyor, in order to distribute it 
equally to both outlets. Second, the outlets must be exactly 180.degree. 
apart. Third, any restriction to flow through the outlets must be the same 
for each outlet. If material encounters more resistance at one outlet or 
the other, the material will move to the outlet of least resistance, and 
the split will not be equal. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide an apparatus and method for 
splitting a stream of material into two streams having equal volume flow 
rates. 
Another object of the invention is to provide an apparatus and method for 
splitting a single feed stream into multiple streams which have 
predetermined average flow rate ratios relative to one another. 
Another object of the invention is to provide a stream splitter which will 
operate consistently over a wide range of feed stream flow rates. 
Yet another object of the invention is to provide an apparatus and method 
for efficiently splitting a stream of particulate material. 
A further object of the invention is to provide a stream splitting 
apparatus which has a relatively simple design. 
Other objects will be in part obvious and in part pointed out more in 
detail hereinafter. 
The invention in a preferred apparatus form includes a stationary housing 
having a first wall with a material inlet for receiving a stream of 
conveyed material, an opposite second wall, a side wall connecting the 
first and second walls, and axially spaced first and second material 
outlets. The housing contains an impeller which includes a central shaft 
and a plurality of blades extending radially from the shaft defining 
therebetween and with the first, second, and side walls at least two 
different sets of material receiving chambers in the housing. The first 
and second sets of material receiving chambers are configured to receive 
material at a predetermined ratio of average overall flow rates from the 
material inlet. Preferably, the first and second sets of material 
receiving chambers receive equivalent average volume flow rates. The 
impeller also includes guide means in the plurality of material of 
receiving chambers for guiding material in the first set of material 
receiving chambers through only the first material outlet, and for guiding 
material in the second set of material receiving chambers through only the 
second material outlet, as the impeller rotates. The apparatus also 
includes drive means on the shaft for attachment to a source for 
rotationally driving the impeller. 
Each set of material receiving chambers constitutes at least one material 
receiving chamber. In a particularly preferred form, the blades define at 
least four material receiving chambers of approximately equal size, i.e. 
two sets of material receiving chambers, each of which includes two 
chambers. In this case, the first set of material receiving chambers 
preferably consists of a pair of non-adjacent material receiving chambers. 
Preferably, although not necessarily, the blades form an even number of 
material receiving chambers in the housing. 
In a particularly preferred form, each guide means comprises a 
frustoconical segment. This configuration facilitates smooth flow of the 
material through the impeller. 
Each blade in the impeller preferably includes a generally rectangular 
inner portion connected to the shaft and a co-planer, trapezoidal outer 
portion which diverges from the rectangular inner portion. 
Each guide means preferably has a pair of opposite terminal edges connected 
to the outer portions of adjacent blades. The terminal edges are mounted 
diagonally on the outer portions of the blades relative to the axis of the 
housing, at an angle of about 45.degree.-60.degree. relative to the axis 
of the housing. 
In a preferred construction of the apparatus, each guide means also 
includes a pie-shaped segment opposite to the inlet opening in the 
housing. The pie-shaped segment is part of a flat, circular segment which 
is coaxial with the impeller shaft and abuts both the downstream edge of 
the inner portion of each blade and the downstream edges of the 
frustoconical segments in the material receiving chambers which direct 
material out the first outlet. The pie-shaped segments also facilitate 
smooth flow of the material through the impeller. 
Another preferred form of the invention is a method of splitting a stream 
of material into at least two streams having a predetermined ratio of 
volume flow rates. The method comprises feeding the material into a stream 
splitting apparatus of the type described above. 
The invention accordingly comprises the several steps and the relation of 
one or more of such steps with respect to each of the others and the 
article possessing the features, properties, and the relation of elements 
described in the following detailed disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings and in particular to FIGS. 1-4, a first 
embodiment of a stream splitting apparatus is shown and is designated as 
10. The stream splitter includes an impeller 12 having a housing 11 which 
has a cylindrical outer shape and has indented front and back walls 13, 
16, respectively which conform to the shape of the impeller 12, which is 
disposed therein. The front wall 13 has a central, axial inlet 14 for 
introducing material into the housing in an axial direction. The back wall 
has the shape of a pie plate. The inlet 14 is fluidly connected to a 
horizontal screw-type feeder 17 having four equally spaced flights 19, the 
end of each flight 19 being welded or otherwise attached to the impeller 
12 in a manner which is further described below, in order that the screw 
conveyor 17 and impeller 12 rotate at the same rate. Other types of 
feeders also can be used in conjunction with the impeller 12 of the 
invention. A cylindrical side wall 18 connects the front and back walls 
13, 16 of the housing around their peripheries. The side wall 18 includes 
an upstream outlet 20 and a downstream outlet 22, which are axially spaced 
and are side-by-side, diverging in a Y-shaped configuration. The housing 
11 is of relatively simple construction, and preferably is designed to 
support a system which operates at a pressure of about 4-5 bars. 
The feeder 17 has a feeder inlet 21 for receiving approximately equal 
amounts of feed into each of the four flights 19. This configuration is 
particularly useful when a screw conveyor is used which has the same 
number of flights as there are impeller blades. In this manner, the 
impeller takes the place of more conventional radial paddles at the 
discharge of a screw conveyor. In this case, initial splitting occurs when 
material enters the screw conveyor. Soon thereafter, the impeller directs 
the split material along two different paths. If unequal feeding is 
desired, the flights can be unequally spaced at inlet 21. In the preferred 
embodiment, after a particular flight receives material, the material 
received therein cannot move to an adjacent flight. 
The impeller 12, which controls the discharge path of material, is shown in 
detail in FIGS. 2 and 3. The impeller 12 is driven by a central shaft 26, 
which is driven by conventional drive means 28, shown in FIG. 1. The shaft 
26 preferably is, but need not necessarily be, the same shaft as drives 
the screw-type feeder 17. The impeller 12 has four thin, radially 
extending blades 30, each of which forms a right angle with the two 
adjacent blades. The width cf the blades extends in a direction which is 
parallel to the axis of the shaft. Each blade 30 has an inner portion 32 
which is rectangular and extends perpendicularly to the axis, and a 
co-planar outer portion 34 which diverges obliquely to the axis from the 
outer end cf the rectangular inner portion 32. The diverging outer portion 
34 preferably, but not necessarily, is of a substantially trapezoidal 
shape, with the shorter of the two parallel sides being integrally 
connected to the outer side of the inner portion 32. The diverging outer 
portion 34 is configured to direct material alternately upstream and 
downstream from the inner portion. 
The blades 30 define four material receiving chambers of substantially 
equal size, including a first set of chambers each designated as 36 and a 
second set of chambers each designated as 37, which receive particulate 
material from the central inlet 14 in the housing 11. The material 
receiving chambers 36 are opposite each other and receive material which 
subsequently is directed out through upstream outlet 20. The material in 
chambers 36 moves along the path designated by arrows A in FIGS. 3 and 4. 
Material is removed from chambers 36 when the chambers 36 are individually 
aligned with outlet 20. The material receiving chambers 37 are opposite 
each other and receive material which subsequently is directed out through 
downstream outlet 22 when chambers 37 are individually aligned with outlet 
22. Thus, material in chambers 37 moves along a path designated by arrow B 
in FIGS. 3 and 4. Each of the four flights 19 of the screw feeder 17 is 
connected to a different blade 30 in order to feed into a single one of 
the chambers 36, 37. 
Thin, frustoconical guide members 38, 39 are positioned in material 
receiving chambers 36, 37, respectively, and are connected to adjacent 
blades 30. The guide members reduce the total volume of each material 
receiving chamber by about 20% relative to the volume of such chambers if 
the guide members were not present. The guide members assure that material 
in a particular chamber exits only through one of the housing outlets 20, 
22. More specifically, guide members 38 direct material in the material 
receiving chambers 36, in which they are disposed, outward through 
upstream outlet 20. Guide members 39 direct material in the material 
receiving chambers 37 outward through downstream outlet 22. 
Guide members 38 also are connected to a circular, flat rear plate 40 of 
the impeller 12. The plate 40 has a diameter which corresponds to the 
radial dimension of the inner portion of the blades. The rear plate 40 
also acts as a guide in each material receiving chamber for directing flow 
in the material receiving chambers 36, 37 outward through outlets 20, 22, 
thereby keeping material in the material receiving chambers 36 from 
entering into material receiving chambers 37 at a location downstream from 
the impeller guide members 39. In each chamber 36, 37, the rear plate 40 
has a shape which corresponds to a quadrant of a circle or, more 
generally, the shape of a pie piece. 
As shown in FIG. 4, the guide members 38, 39, when mounted on the blades, 
form a circular outer diameter for the impeller when viewed from an 
upstream position, the outer diameter corresponding to the diameter of the 
inner surface of the side wall 18 of the housing. In each material 
receiving chamber 36, 37, the concave side of the frustoconical guide 
members 38, 39 is the side which is in contact with the particulate 
material. As shown in FIG. 3, ends 41, 43 of the guide members 38, 39 
respectively, are angled at about 45.degree.-60.degree. relative to the 
axis of the impeller. The downstream end corners 44 of guide members 38 
are positioned at the downstream point of intersection between the inner 
and outer portions 32, 34 of blades 30. The upstream end corners 46 of 
guide members 38 are positioned at the center of the outermost side 48 of 
the outer portions of blades 30. The guide members 39 face in an opposite 
direction, in order that the upstream end corners 50 of guide members 39 
are positioned at the upstream point of intersection between the inner and 
outer portions of blades 30. The downstream end corners 52 of guide 
members 39 are positioned at the center outermost sides 49 of the outer 
portions of blades 30. The housing 11 forms walls of the material 
receiving chambers which are opposite, and generally parallel, to the 
guide members 38, 39 in order that the material receiving chambers 36, 37 
have a bent or angled shape. 
The stream splitter 10 of the invention operates in the following manner. 
Particulate material is chopped or ground prior to being fed into the 
feeder 17. The chopped material is fed through feeder inlet 21 into feeder 
17. Approximately equal amounts of material enter each flight 19 in the 
feeder 17. Material in feeder 17 is conveyed to the impeller 12 through 
central inlet 14 of housing 11. At inlet 14, the material from the flights 
enters the four material receiving chambers 36, 37 of the rotating 
impeller 12 in a one-to-one relationship, i.e. all of the material from a 
particular flight 19 enters the same material receiving chamber. The 
impeller 12 receives material continually by force feeding or, in the 
event the impeller is disposed horizontally, by gravity feeding through 
the top, as discussed further below. Typically, the impeller will rotate 
at a rate of about 200 to 600 revolutions per minute (rpm) and will split 
a feed stream which has a volume flow rate of about 25 to 150 cu. 
ft./minute. The stream splitting apparatus can be sized and operated under 
conditions sufficient to handle a desired capacity. Sizing will depend in 
part on whether the apparatus is to be used to process fiber or chips. As 
a result of the rotational speed of the impeller, the material is 
centrifugally driven to the outer perimeter of the material receiving 
chambers 36, 37, and as each chamber passes the outlet 20 or 22 to which 
it is connected, the material exits from the apparatus through outlet 20 
or 22. 
The embodiment of FIG. 1 is particularly advantageous in that it has a 
single shaft and is therefore of a simpler design than the double screw 
feeders which are often used in conjunction with stream splitters. 
The apparatus of FIG. 1 can be revised to split the stream into a greater 
number of separate streams. For example, if the feed screw includes six 
flights, the impeller includes six chambers, and three outlets are axially 
spaced from each other, the impeller can be designed such that the 
material from two opposite chambers is directed to one of three outlets. 
It is noted that such a revision would require modification of the 
configuration of the guide members in the impeller 12. 
In accordance with a second embodiment of the invention shown in FIG. 5, 
the stream splitter 10' includes a screw-type feeder 17' with a single 
flight 19' having an exit and which is slightly spaced from, and is not 
connected to, impeller 12'. Flight 19' is formed on shaft 26', which is 
driven by drive means 28'. Impeller 12' is mounted on axial shaft 27, 
which is driven by separate impeller drive means 29. Preferably the 
impeller 12' is driven at a higher speed than the screw-type feeder 17'. 
The feed screw flight ends at the central inlet 14' of the impeller 12'. 
In the embodiment shown in FIG. 5, the impeller 12' rotates fast enough to 
provide that, statistically, on an overall basis, each of the chambers 
receives an equivalent volume of material, at approximately the same flow 
rate. The requirement for exactly splitting the volume of the inlet stream 
in a continuous manner is satisfied by the rapid pulse-like switching 
between two alternating outlets from the apparatus in a pulse-like manner. 
Whether the central inlet 14' is full, half empty, or only one quarter 
full, each chamber will receive an overall quantity of material which is 
substantially identical to that received by each of the adjacent chambers. 
If there is fluctuation of the incoming flow rate, the split ratio will 
still be constant because the pulse like switching rate is much faster 
than typical incoming volume flow fluctuations. Each surge of incoming 
flow will be chopped into many small equal pieces and sent in two 
directions. Thus, the flow rate at the impeller inlet can be increased or 
decreased without effecting the equal splitting of the inlet stream. 
Another embodiment of the invention, which is shown in FIG. 6, involves 
gravity dropping feed material into a horizontally disposed impeller 12". 
In this embodiment, no screw-type feeder is needed, and the feed is 
introduced into the impeller 12" through conduit 53, which provides for 
downward vertical feed into the impeller 12". The walls of conduit 53 are 
connected to the impeller housing 11'. The impeller is connected to axial 
shaft 27', which is driven by impeller drive means 29'. The impeller 12" 
itself has the same construction as impellers 12 and 12' of the first and 
second embodiments. Thus, half of the feed material exits through upstream 
outlet 20', flowing as shown by arrow A' in FIG. 6, and the other half of 
the material exits through downstream outlet 22', having a flow path 
indicated by arrow B' in FIG. 6. This embodiment is advantageous in that 
it dispenses with the need for a screw-type feeder. 
Yet another preferred embodiment of the stream splitting apparatus is shown 
in FIG. 7. In this embodiment, material is fed into inlet 21" of 
screw-type feeder 17" having a single flight 19". The flight is connected 
to shaft 26", which is driven by drive means 28". The material drops 
vertically from the screw-type feeder 17" at the exit end, and enters a 
second screw-type feeder 58 having four flights 59. Each flight is welded 
to one of the blades 30" of an impeller 12'". Both the screw-type feeder 
58 and the impeller 12'" are connected to an axial shaft 27" which is 
driven by impeller drive means 29". In this embodiment, splitting of the 
stream occurs at the entrance to screw-type feeder 58. The impeller 12'" 
has the same configuration as the impellers of the other three 
embodiments, and includes blades 30". Half of the feed into feeder 58 
exits through upstream outlet 20", following a path shown by A", and the 
other half of the material exits through downstream outlet 22" following a 
path shown by the arrow designated as B". 
In the preferred embodiments of the invention, adjacent material receiving 
chambers are of equal size. However, it is within the scope of the 
invention to have adjacent chambers, one of which is larger than the other 
in order to provide for an unequal split. 
While it is preferable to split a stream into two or more streams having 
equal volume flow rates, it is also within the scope of the invention to 
alter the size of the chambers, or change the configuration of the guide 
members in the chambers, such that unequal proportions of the material 
exit through each of the outlets. For example, if one (but not the other) 
of the material receiving chambers 36 was altered to be identical to 
material receiving chamber 37, i.e. such that it includes guide member 39, 
3/4 of the volume material would then exit through the downstream outlet 
22, while only 1/4 of the material would exit through the upstream outlet 
20. 
One of the advantages of the apparatus of the invention is that it is 
insensitive to downstream pressure fluctuations. The guide members 38, 39 
and blades 30 of the present invention prevent material from moving from 
one material receiving chamber to another after the material has entered 
the impeller. The only way inter-chamber movement could occur would be if 
the material were to move upstream from inlet 14 after having entered the 
impeller 12. Such backflow would not occur even if the downstream pressure 
of the material entering the impeller is greater than the upstream 
pressure of the material at the inlet 14, because the centrifugal force of 
the spinning blades throws the material to the outer portion of the blades 
with 10 to 150 times gravity. 
When it is desirable to split the inlet feed equally into two outlet 
streams, it is preferable that an even number of chambers be formed and 
that each chamber have an identical size. However, as is apparent to one 
having ordinary skill in the art, variation in the number of blades, the 
number of chambers and chamber sizes is possible. 
As will be apparent to persons skilled in the art, various modifications 
and adaptations of the structure above described will become readily 
apparent without departure from the spirit and scope of the invention, the 
scope of which is defined in the appended claims.