Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~81~70
This invention relates to a method and apparatus
for removing foreign material and fluid from a permeable
fabric.
In the pulp and paper i.ndustry, the cleaning
of paper-making felts and in particular press felts, has
always been important for the efficient operation of
paper machines. As the speed of the machines has increased
over the years and with the increasing costs of the factors
of production such as energy, it has become imperative
that more efficient ways to clean, condition and dewater
the felts used in the press section of the paper machine be
:Eound.
Presently, two methods are emp].oyed for the
cleaning of the felts, both methods working in conjunction
with water showers which spray water on the felts to
loosen any material therein. In the :E.irst method, the
felt is passed over a stationary sucti.on box at which
~ime the loosened dirt and water is sucked out o:E the Eelt.
In a second method, the :Eelt is p~ssed th.rough a ringer or
squeeze press; the rolls comprising the press or ringer
may or may not have a suction box incorporated therein.
In the method utilizing the stationary suction
box, the felt is essentially dragged across the face of
the box and due to the friction involved, a fair amount of
energy is consumed by the motors which drive the felts and
more energy is also consumed to provide the necessary vacuum.
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S70
As will be appreciated, the wear on the felt and suction
box covers is also substantial. The method utilizing the
ringer or squeeze press is more energy efficient due to
the rotating aspect of the press/suction rolls; however,
the equipment required is more elaborate and expensive
and the pressing action has been known to decrease the
effectiveness of the felt.
It is therefore an object of the present
invention to provide a method for the removal of foreign
material and fluid from a permeable fabric which is both
relatively efficient and does not require a high energy
expenditure.
It is a further object of the present invention
to provide a method and apparatus for a felt dewatering and
conditioning system for the pulp and paper industry which
will efficiently remove foreign material and water and
therefore ]ead to dryer paper leaving ~he press section of
the paper macll;nc which in turn will reduce the cncrgy
rcquired to furtller dry the paper.
According to one aspect of the present invelltion,
there is provided a method of removing a fluid from a
permeable fabric which includes the steps of directing a
jet of a gaseous material at the fabric and controlling the
velocity of the gaseous material such that it does not
penetrate the fabric while creating an area of low pressure
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sufficient to remove at least a portion of the fluid
within the fabric.
There is also provided an apparatus for
removing fluid from a fluid containing permeable fabric
comprising means to support the fabric in a desired
position, gas supply means, jet means which are connected
to the gas supply means and which are operative to direct
a jet of pressurized gas at the fabric, and control means
for controlling the velocity of the gas jet such -that a
substantial portion of the gaseous material does not
penetrate the permeable fabric wllile creating an area of
low pressure which is sufficient to remove at least a
portion of the fluid from within the fabric.
In greater detail, the method and apparatus of
the present invention are intended for llse with a fluid
containing Eabric wherein it is desirable to remove at
least a portion of the fluid from the fabric. The types
of fabric with which t:he prcsetlt :invelltion can bc used
are nunierous; all:houcJh one oE the prime applications is
considered to be in the dcwatering/conditioning of felt
used in paper-making, other permeable fabrics may also have
a desired material removed utilizing the method and
apparatus of the invention. It suffices to say that the
fabric is permeable and has a certain porosity in order
that it contain the fluid which is to be removed. Similarly,
although the invention may primarily find use in removal
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of a liquid from a liquid containing fabric, it may be
desirable to remove a gaseous material from a fabric
utilizing the present invention. Commercial possibilities
are numerous including operations such as the dry cleaning
of fabrics.
The present invention operates by directing a
jet of gas at an angle to a supported fabric such that the
gas impinges on the fabric and creates a zone of low
pressure whereby the fluid/material will flow out of the
fabric on at least one side of the jet. The term "low
pressure" refers to a pressure which is less than the pressure
existing within the fabric; this normal pressure will usually
be atmospheric pressure.
In -the practice of the present invention, the
velocity of the jet of gaseous material is adjusted such
that it does not flow through the Eabric to escape on the
other side; instead the major portion oE the gas does not
flow through but rather creates the dc?sired eEEect by not
passing through t:o the opposite side oE the fabric.
Naturally, the particular velocity employed in any particular
situation will depend upon the porosity of the fabric, the
loading of the fabric, the gaseous material, and other known
factors. Further factors which have a relationship will
be the distance between the gas jet (nozzle) and the fabric;
the width of the gas jet, the velocity of the gaseous material,
~81~70
the location of that part of the surface of the fabric
under the influence of the gaseous material, the velocity
at which the fabric and air jet may be moving with respect
to each other, etc.
The gas employed may be any which is suitable
for the particular application. In many applications, and
in particular where one is concerned with the conditioning
of felts as employed in the paper-making industry, air is
a suitable material.
The nozzle of the gas jet may take on many
different configurations and indeed, the nozzle may merely
comprise a slit which has been cut in a section of pipe.
A plurali-ty of nozzles may be employed to cover the entire
width of the fabric. As aforementioned, one simple embodi-
ment will utilize a pipe in which a plurali-ty of slits or
one long slit have been cut to cover the entire width of the
felt. Gas may be fed to the pipe from one or both ends or
at`intervals so as to minimize any press~rc drop.
In Llle pulp al~d l~aper ;lldustry, the felt has a
liquid sprayed onto the felt which assists in loosening foreiyn
material therein. Subsequently, the gas is directed at the
felt to remove the fluid and foreign material contained therein.
It has been found the removal of the foreign material is
extremely efficient with the practice of the present invention
and thus leads to a felt having a better performance.
1570
Having thus generally described the invention,
reference will be made to the accompanying drawings
illustrating embodiments thereof and in which:-
FIGURE 1 is a side elevational view of a
dewatering arrangement;
FIGURE 2 is a detail view of one embodiment of
a nozzle;
FIGURE 3 is a detail view of a portion of the
dewatering arrangement of Figure l;
FIGURE 4 is a graph illustra-ting relationships
between the distance of the nozzle from the fabric and
the pressure at the fabric surface;
FIGURF. 5 illustrates the relationship between
the pressure and its effect on a particular segment of the
fabric;
FIGURE 6 is a cross-sectional view o:E a nozzle
arrangement; and
~ FIGURE 7 is a slde elevatiollal view of an arrange-
men-t l:o support the nozzle and corltain the mo;sture removed
from the fabric.
Figure 1 is an elcva-tional view oE an arrangement
involved in applying the present invention to the removal
of foreign material/fluid from a fabric and in particular,
to the conditioning of a wet press felt on a paper machine.
There are many overall wet press arrangemnts; Figure 1
illustrates a small section of the overall system to show
1~:81570
where the present invention can be fitted in. As shown,
a descending section of the felt run may be chosen as this
may be more convenient for collecting and disposing of the
water extracted by the device; design considerations may,
however, make a horlzontal run more feasible.
Referring to Figure 1, a portion of a wet press
felt run is illustrated. A pair of felt guide rolls 10 and
12 are provided, felt guide rolls 10 and 12 being journalled
on suitable supports (not shown) and rotating as shown by
arrows 14 and 16 respectively. A shower pipe 18 is provided,
shower pipe 18 being connected to a source (not shown) of
water or other suitable fluid for spraying the felt to loosen
any clogging foreign material. Reference numeral 20 generally
designates a slotted air-jet nozzle or blow pipe as will be
discussed in greater detail hereinbelow; a -tray 22 is
provided to catch the water extracted from the Eelt and
thrown aside by the air jet. The wet press ~elt 24 is advanced
in khe direction ;nd;cated by arrows 26 over felt guide rolls
10 and 12.
Figure 2 illustrates lhe blow nozzle 20 in more
detail. Referring to Figure 2, nozzle 20 is a section of
pipe in which a narrow slit 28 has been made; the length
of the slit is approximately the width of the wet felt and
the width of the slit will depend on several factors which
will be discussed below. A connection 30 is provided to
which a gas supply is attached; depending on the length
5'7C)
and diameter of the pipe, it may be desirable to feed
air into the pipe from both ends (as well as at intermediate
points) so as to minimize any pressure drop and an uneven
air jet; alternatively or in conjunction with this, the
pipe may be tapered. A series of circular clamps 32 are
provided which, if necessary, can be used to adjust the
local width of the air slot and so maintain an even longitu-
dinal velocity profile for the air jet as it passes through
slot 28 (this adjustment can be made by a small set screw 34
set in the wall of the clamp with the end of screw 34
bearing against the outside wall of the pipe).
Figure 3 illustrates some of the parameters to
be considered and the relationships between them and the
pressure or vacuum developed at the surface of the fabric
where the jet impinges. Figure 4 shows the relationship
between the distance D and the air pressure condition at
the surface of l:he fabric where the jet impinges. Figure 5
shows the relationship between the d.istance L ~nd the air
pressures at that pOi.llt.
~s seen in Figure 3, W ;s the width of the slot
through which the air passes to form the air jet having a
velocity J whose energy source is the pressure P of the
air in the pipe nozzle. The distance of slot or jet exit
from the fabric is designated by D, and L is the location or
distance of that part of the surface of the fabric under the
influence of the air jet which is being examined; the fabric
is moving relative to jet 20 at a velocity S.
1570
The relationship shown in Figure 4 does not
give any absolute values as these will vary with the jet
velocity J (and -to some extent the geome-try of the jet)
and the location of the surface being examined i.e.,
the distance L from the center of the slit or the jet to
that part of the surface of the fabric being examined;
l~owever, it clearly shows that for a given J there is a
specific D where the pressure V in terms of vacuum is
maximum and it is at this point where maximum efficiency
is achieved. In yeneral the value of D for optimum V will
change very li-ttle as J is varied. It is not necessary to
locate and maintain the jet exit at this specific value
of D, fox as long as the jet is in the vicinity of this
value and the felt is free to move slightly, the felt will
automatically position itself at the specific distance as
the forces of pressure and vacuum balance each other out.
The value of D for optimum vacuum is usually in the order
of 2 mm. (0.079") or less.
At this speciEic D ~ox maximum V, applicant
Eound that V varled as L challyed. In fact, Eor the
orientation shown in Figure 3 where the air jet is at
right angles to the surface, directly at -the jet there
will be a pressure zone, and on either side of this there
will be a vacuum zone of equally decreasing intensity as
the value of L increases; this is shown in Figure 5. As
illustrated, the magnitude of the vacuum peak will be
1~81570
roughly in the order of one-half the pressure peak;
and the pressure peak will be close to P the pressure in
the pipe. The vacuum peak will occur when L is approximately
2.5 mm. In some cases it will be found preferable to
operate the jet at right angles to the fabrics; however, for
other cases, it might be desirable to operate the jet at
various angles to the fabric. For example, where the fabric
is moving past the air jet at a relatively high velocity
it was found desirable to turn the jet slightly towards the
oncoming felt (i.e. angled the jet against the felt travel);
this tended to increase the suction effect.
Generally, the higher the value of J the higher
the value of V; and since V is much more sensitive to J
than to the volume of air involved, it thereEore is generally
more desirable economically to operate the air jet with a
lower rather than a higher volume of air and to obtain the
high velocities ret~ulxed for op-timum V by using narrow slits
in the blow nozzle. Whi.le t:hcre is soJne practlcal relat]on-
shlp belween tlle vel.ocity oE tlle fabric S and the jet
velocity J it is only signiEicallt when S is fairly large;
that is, while the vacuum in the vicinity of the fabric
surface is independent of the velocity of the fabric, it is
obvious that if fabric is moving very quickly the vacuum
condition will have little time to have any effect on the
fabric and to extract the water embedded in the pores of the
fabric. The relationship between P the pressure of air in
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~'~81S70
the pipe and J is of course a fixed one, being influenced
only by the co-efficient of veloclty (which varies with
-the type of orifice and other conditions of operation).
As can be seen from the above discussion, the values that
can be assigned to the above parameters will depend on the
use of the invention and the economics involved. As mentioned
above the fabric or felt will automatically position itself
the required distance from the jet. Nevertheless, to prevent
gross vibration or flapping of the felt, guide roll 10
(Figure 1) which is normally not present ln conventional
felt runs, will avoid problems of that sort; lf necessary
under certain conditions, fur-ther guide rolls can be added.
Another improtant element of the invention that
has a bearing on the efficiency of its operation, is the
area/surface/volume jus-t under the gas jet. as it rebounds
from the fabric and begins ~o flow parallel to it. One
could, for example, visua].i~e a jet issuinc3 From a nozzle
buried in a Elat surEace over which the fabric is passlng;
such an arrallgement has gellexally not been Eound satis-
factory depending on the width of the flat surface. This
is partially because the mixture of gas and fluid (extracted
from the fabric), in order to escape, has to pass through
the thin volume delineated by the fabric and the flat
surface of the nozzle ( the height of this volume being
substantially constant at 2 mm.). A curved surface has been
found to be very satisfactory as it allows the gas (air)
~i~81570
to break away Erom the fabric and follow the curved surface.
An optimum shape for this surface will depend on such
variables as jet veloci-ty, volume, etc. From a constructlon
point of view, a circular curvature is very satisfactory
as an ordinary pipe can be used for the blow nozzle.
Following the same reasoning, a smaller diameter pipe nozzle
is preferable to a larger one; therefore to keep the diameter
as small as possible and to minimize the pressure drop of
the gas flowing in the pipe it is preferable to feed gas
into the pipe from several inlets where necessary. At the
other extreme one could use a nozzle where the sides of an
elongated orifice would be vertical and s-traight, i.e.,
perpendicular -to the fabric; for intermediary designs the
sides would be s-traight and tapered at some chosen angle
to the surface of the fabric.
In applications invo]ving -the conditloning of wet
press felts as shown in Figure l, the following was observed
after the blow nozzle 20 was properly posit;oned and the
air jet 20 and water spray jet ]8 were operated; the water
shower jet tended to penetrate the felt, loosen the foreign
material therein, and saturate the felt surface with water,
the air jet in turn sucked from the felt substantial
quantities of water (and foreign material) and this was
followed by the blow stage action of the jet which in turn
was followed by a second sucking action (see Figure 5).
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~81~70
All this resulted in the water (and foreign material) in
the form of a heavy spray being flung away from the felt
surface to be collected in tray 22 and carried away.
This rapid and sudden vacuum, and blow and vacuum action
of the air jet as it split into two streams (in comparison
to the single suction action of a conventional vacuum suction
box) tended to leave the felt surface in more absorptive
condition for removing water from the paper in the wet
presses. The felt surface hairs, for example, showed a
marked tendency to stand out rather than to lie flat and
matted. One substantial advantage of the device is in the
substantial drop in energy required to produce this cleaning
and conditioning action; for example a 100" wide felt
condition of the conventional vacuum type drawing 10" of Hg at
2000 cfm would require approximately 100 E~P, whereas the
present blow nozzle would perform the same operation for
substantially lcss energy expcnditure. In addition, since
th~ :Eelt is ridi.ng on a cush;on o:E ai.r, .little or no energy
is used in mov;.ng tlle fe.lt throu~h the suction zone, whereas,
much friction .is present and cnergy used up in carrying the
felt over a conventional suction box. Also since there is
no contact with any solid surfaces, there is li-ttle chance for
any pitch on the felt surface to be smeared to be smeared
across and into the surface of the felt, decreasing its
water absorption properties.
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~1570
Figure 2 illustrates a construction of the
blow nozzle where a slit was made in a pipe in its
longi-tudinal direction. Since this could be a difficult
operation in a long blow pipe, and also where the slit
might vibrate and operate as a reed, Figure 6 illustrates
a further method of construction where a cross-sectional
view of a blow nozzle is shown. A section of pipe 36 has
a rought slot 38 cut therein, the width of which is
several times wider than the final width of the jet orifice
and at least as long; this area of the pipe nozzle then acts
as a support for two strips of material 40 which lie on the
outside surface of the pipe nozzle to define the jet orifice
42. These strips may be made out of any convenient material
preferably, that which will define a uniform and sharp
orifice as well as be wear resistant should any erosive
material be dragged across the orifice by the felt, e.g.,
high density polyethylene; stainless steel. These orifice
strips may be preEormed to fit the curvature of the pipe or
be flexible enouc3h to conEorm; -they may be attached by sets
of counter-sunk screws 44 to pipe 36; by using slotted
holes for the screws these strips could be made adjustable.
In situations where the jet orifice 42 will be long, it
may be necessary to stabilize the jet width and the
mechanical integrity of the pipe by using tension rods 46
running across the pipe at suitable intervals along its
length. Threads and nuts (gaskets) 48 could be provided
at the ends so the tension (and orifice profile) could be
adjusted. For the overall support of the blow nozzle
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~8~570
and to keep it straight and true, various techniques are
possible and known in the art. One particular method is
described below in regard to providing a spray/mist
collec-ting device. For certain si-tuations, such as to
provide forslot non-uniformity, it may even be desirable
to arrange for the blow nozzle to oscillate back and forth
under the felt in the transverse direction.
It was also found that at high jet velocities,
the water removed from the felt tended to turn into a very
fine mist which in cer-tain applications might be found to
be undesirable should it be allowed to permeate the area.
Figure 7 illus-trates an apparatus to contain this mist
and spray and in addition provide a method of supporting
the pipe and adjusting it so that it will remain level
for its full length. This is, of course, a very important
feature for a long blow pipe which would tend to sage if
supported only at the two ends. While independent supports
along its legnth may be possible in certain applic~tions,
it is generally preEerable to provide one having rigid
cross-sectional characteristics.
Referring to Figure 7, 36 is a blow nozzle (the
details of which are illustrated in Figure 6) and 52 is
a trough-like container to keep the mist and spray from
permeating the area. Retaining bracket(s) 54 are spaced
at suitable intervals along the length of container 52
to give further rigidity to container 52. Rods 56 are
screw-threadedly engaged with brackets 54 while a pair
of nuts, screw-threadedly engaged with an opposite end
of rod 56 in conjunction with bracket 58, adds rigidity
and support to blow nozzle 36. Small diameter rods or
pipes 62 are provided over which the fabric will run the
tops of which will be essentially level with the top of
nozzle 36. Other sealing shapes/surface can be used;
however, since there can be contact with the fabric any
sharp edges that may touch the fabric should be avoided.
The trough will be sealed at both ends using conventlonal
techn.iques and may be subjected to either a slight gas
pressure or a slight vacuum depending on -the situation.
As was mentioned, since it is generally desirable to keep
the diameter of nozzle 36 on the small side, if nozzle 36
is sufficiently long to incur serious pressure drop losses,
the lower part of the trough can be used or a larger
diameter gas supply line (or seri.es of l.;.nes) wi.th which to
furnish nozzle 36 with the requi..red gas. To avoid too much
mist leak.ing past the various scaling areas the mist in
the trough can be continuously removed with an inexpensive
fan exhauster; liquid in the bottom of the trough can be
removed through a suitable trap. Where practical, after
de-misting, the gas (air) can be recycled to the pipe
nozzle through a blower which will maintain the required
pressure in the nozzle. The following is an example of the
above-described embodiments to a paper-making wet felt.
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1~8~570
A pipe nozzle approximately 16 inches long
similar to the one illustrated in Figure 2 was used.
The air pressure was kept at 15 psig and this corresponds to
an air-jet velocity (J) of approximately 1360 fps. The width
of the orifice slot (I~) was 0.010 inches. (See Figure 3).
D was 2 mm (.079 inch).
The invention was placed against a conventional
paper-making wet felt after it had been subjected to the
action of a conventional felt conditioner (of the stationary
suction box type) installed on a modern newsprint machine.
By measuring the moisture in the felt before and after
i-ts passage over the orifice slot of the present invention
it was found that the apparatus had removed between 10-20
grams of water per square meter and since no attempt had
lS yet been made to optimize its operation, it was evident that
the dewatering efficiency of the present invention was
greater than that representing prior art equipment. Moreover,
the cleanliness oE the felt has a great eEFect (for a
given Eelt) on a sheet dryness. Conscuqently, in the above
test, samples of the water extracted from the felt were
tested for % solids and for -the nature of the material
extracted. These tests showed the ~ solids to be 0.65 and
the material to be mainly groundwood and sulphite pulp debris
and fines with traces of felt hairs. Thus the cleaning
efficiency of the present invention was also found to be
greater than that of prior art equipment.
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~'~8~570
It is also obvious from the present disclosure
that for the invention to work the gas jet or at least a
substantial portion of the gas should not be able to
flow throuyh the fabric to escape on the opposite side.
Thus, to accommodate the porosity of the fabric one
merely has reduced the jet velocity to a point where it
does not flow through, but still has sufficient energy
to create the desired vacuum/sucking effect. A further
embodiment of the invention could involve a combination of
a straight bIowing operation on one side of the fabric
along with the present invention on the other side - i.e.,
the controlled low pressure wouid be used on one side of
the fabric and simultaneously a jet of gas would be allowed
to impinge on the other side of the fabric directly opposite
the gas jet of the present invention and penetrate the
fabric, so that by_controlling the force (and location)
of the two jets, one jet (that opposite the one that will
create a low pressure) would urge the fluid to the other
side where the low pressure effect would complete the
extraction of the Eluid and convert it into a spray/mist.
Similarly, if the fabric is fairly thick gas jets of the
present invention could be used to create a low pressure effect
on both sides of the fabric at the same time.
Because of the relatively high dewater/cleaning
efficiency of the present invention, it may not be
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1~815~0
necessary to opera-te -the device continuously. Thus
in the case of a full felt width nozzle the effect may
be used intermittently on some optimum cycle. Alternatively,
a short nozzle could be made to scan or travel across the
width of the felt inside a collecting pipe at some optlmum
speed/cycle or the slot itself could be full width and a
short section of the air jet itself could be made to scan
the felt. Since the use of one long slit weakens the pipe
(nozzle), a plurality of slits (i.e. with a stiffening space
between slits) can be used and the pipe can be made to
oscillate/travel transversely back and forth sufficiently
so that the travel will allow the jet to cover the fabric
under the unslit-ted space. Besides dewatering/cleaning
wet felt fabrics on a paper machine, one could also utilize
the invention to clean wet end wire fabrics also ut;lized
on paper machines thereby replacing messy high pressure
oscillating needles or fan showers. Other applications
include wire abrics on twin wire Eormers and the cleaning
of drier Eelts. It will be unders~ood that the above
described embodiments are or purposes of illustration
only and that changes and modifications may be made thereto
without departing from the spirit and scope of the invention.
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