U.S. patent number 3,582,244 [Application Number 04/882,837] was granted by the patent office on 1971-06-01 for device for volumetrically removing viscous liquids from vacuum operating equipments.
This patent grant is currently assigned to Snia Viscosa Societa Nazionale Industria Applicazioni Viscosa. Invention is credited to Franco Magnoni, Luigi Marafioti, Francesco Siclari.
United States Patent |
3,582,244 |
Siclari , et al. |
June 1, 1971 |
DEVICE FOR VOLUMETRICALLY REMOVING VISCOUS LIQUIDS FROM VACUUM
OPERATING EQUIPMENTS
Abstract
A device for volumetrically removing liquids from vacuum
operating equipments, particularly reaction vessels and equipments
for obtaining polymers, comprising a set of mutually engaging
pumping screws, a number of which extend to the inside of the
vacuum equipment for a given length, while the remaining screw or
screws extend only up to the bottom of said vacuum equipment. Said
set of screws is rotatably driven within a body tightly enclosing
the same.
Inventors: |
Siclari; Francesco (Milan,
IT), Marafioti; Luigi (Milan, IT), Magnoni;
Franco (Milan, IT) |
Assignee: |
Snia Viscosa Societa Nazionale
Industria Applicazioni Viscosa (Milan, IT)
|
Family
ID: |
11215299 |
Appl.
No.: |
04/882,837 |
Filed: |
December 8, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Dec 12, 1968 [IT] |
|
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24972A/68 |
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Current U.S.
Class: |
418/197;
418/85 |
Current CPC
Class: |
B29B
7/26 (20130101); F04C 13/002 (20130101); F04C
2/16 (20130101); F04C 2/165 (20130101) |
Current International
Class: |
B29B
7/26 (20060101); F04C 2/16 (20060101); B29B
7/02 (20060101); F04C 2/00 (20060101); F04C
13/00 (20060101); F01c 001/16 (); F01c
021/06 () |
Field of
Search: |
;418/197,201 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Croyle; Carlton R.
Assistant Examiner: Goodlin; Wilbur J.
Claims
We claim:
1. A device for volumetrically removing viscous liquids from vacuum
operated equipments, particularly for the continuous production and
processing of polymers, as e.g. polyesters and polyamides
(intermediate and final reaction vessels for the polymerization and
polycondensation, demonomerizers, finishers and the like),
characterized in that it comprises a pumping system having a
plurality of parallely fitted cylindric screws, mutually engaging
all along their generatrices and acting within a body tightly
enclosing the same, a number of said screws extending to the inside
of the environment wherefrom the liquid is to be removed, in such a
manner as said number of screws be completely exposed to the liquid
present in the environment, across their whole development of
360.degree., while the remaining screw or screws, along with said
body extend only up to the bottom of said environment, whereby the
thread channels of the exposed portions of said number of screws
can be completely filled with the liquid before said channels get
engaged with the threads of said remaining screws.
2. A device according to claim 1, wherein the components of said
pumping system are fitted within a tubular casing, that in turn
extends into said environment the extended casing length being
formed with side windows or passages, to allow the liquid to flow
in a substantially radial direction, into the space wherein said
uncovered screw portions lie.
3. A device according to claim 2, wherein said tubular casing is
closed by a plug or cap means against which a number of screws are
abutting, said plug or cap means being formed with windows or
holes, particularly designed to allow a free exhaust in an upward
direction of the volatile fractions that evolve from the liquid
when entering into and between the pumping means.
4. A device according to claim 1, wherein the components of said
pumping system are located inside an outlet passage of said
environment, which extends through at least a part of a heating
jacket associated to said processing environment, the useful length
of said mutually engaging screws being enclosed in said outlet
passage portion that extends through said jacket.
5. A device according to claim 1, wherein the rotary components of
said pumping system are driven by a shaft that extends out of the
pumping mechanism frame through sealing means having heat resisting
packings.
6. A device according to claim 5, wherein said sealing means
consist of a stuffing box fitted with asbestos fiber packings,
which can be saturated with a liquid buffer.
7. A device according to claim 1, wherein said pumping system
comprises a central screw, fitted coaxially to a driving shaft and
operatively connected therewith, said screw being directed and
operated in such a manner as to axially react in the outlet
direction of the liquid, and formed with thrust resisting shoulders
by which the outer structure of the device is acted upon; and two
driven screws symmetrically fitted on either sides of said central
screw which extend upwardly and axially react on an upper plug or
cap means provided in said environment.
Description
BACKGROUND
This invention concerns a device, essentially operating as a
pumping means, for continuously and meteredly removing medium and
high viscosity liquids, wherefrom gases and volatile fractions may
be given off, from equipments and portions thereof wherein a
subatmospheric pressure, or even a high vacuum is maintained. More
particularly, the invention concerns a device for a continuous
volumetric removal of the product from reaction vessels and
equipments wherein intermediate and final processes for obtaining
polymers, and in particular polyesters and polyamides, are carried
out.
As well known, in the production and continuous processing of such
polymerized materials, as well as during the completion of their
polymerizing process within reaction vessels and equipments,
wherein a subatmospheric pressure or even a high vacuum is usually
maintained, difficulties are encountered in carrying out a
continuous and volumetrically metered removal of the related
product. In fact, unfavorable physical properties, as e.g. a high
viscosity and in particular the ability to give off gaseous
fractions, are shown by the products obtained from such
intermediate and final processes. Said viscosity may attain even
very high values, of a few or even many hundreds of Poises.
Moreover, well defined thermal conditions should be maintained,
since a very narrow temperature range is usually defined, below
which the material cannot be kept in the required molten condition,
and above which decomposition phenomena occur.
The absence of pressure inside the environment wherefrom said
viscous materials are to be removed and the remarkable drags
encountered all along the pipings through which said materials are
conveyed to further processing equipments, require devices adapted
to perform a highly efficient pumping action for continuously
removing said materials from said equipments. Due to above reasons,
said extraction devices are in the form of different types of
mechanical pumps, e.g. rotary pumps, gear pumps, screw pumps and
the like.
Due to the abovestated and further reasons, such pumps operate
under unfavorable conditions, particularly with respect to priming
and to the ability of uniformly removing the material, with a
complete filling of their cavities and passages, In fact, it must
be kept in mind that the material which shows a high viscosity and
wherefrom gaseous fractions are continuously evolved, is slightly
forced to enter between the pumping elements. Sometimes the gravity
force only, which anyway acts on the ground of a very small head,
operates to assist the introduction of said material into the
pump.
Amongst heretofore known pumping means, the multiple screw pumps
ought theoretically to ensure the most favorable results, owing to
their inherent regular and uniform outflow and to their good
volumetric properties. On the other hand, the multiple screw pumps,
even when engineered and operated according to the most advanced
technical standards, show priming difficulties under the required
conditions, are not adapted to operate at rather high temperatures,
and above all at temperatures wholly uniform in all points thereof,
and cannot give high outlet pressures.
SUMMARY
An object of this invention is to provide a device for a continuous
volumetric removal of viscous fluids, wherefrom gaseous fractions
are evolved, from equipments of the abovestated type and for the
considered applications, by which the drawbacks and operating
restrictions of the heretofore known devices are obviated or at
least minimized.
More detailedly, this invention concerns a device for the stated or
strictly equivalent applications, comprising pumping means in the
form of a system consisting of a plurality of cylindric screws,
comparable to the pumping system of pumps having multiple parallel
screws, which counterrotate and mutually engage along their
generatrices, such system being engineered, particularly in its
inlet and priming part in such a manner as to ensure a complete
filling of thread channels, before the threads of the adjacent
screws or screw get engaged thereinto.
A further object of the invention is to provide a multiple screw
pumping device showing the abovestated features, which is
structurally and operatively associated with the equipment
wherefrom the product is to be removed, in such a manner that said
complete filling of thread channels can occur directly inside the
associated equipment, without any intermediate passage wherein
cavitation phenomena might occur and gaseous occlusions may be
formed and maintained.
Another object of the invention is to provide a pumping device
which in addition to the abovestated features can ensure a
substantially uniform temperature of the removed material along the
whole travel of said material therethrough.
According to the invention, the device is essentially characterized
in that it comprises a pumping system having a plurality of screws,
and preferably three cylindric and parallely fitted screws,
mutually engaging all along their generatrices, the inlet section
of said mechanism being located inside the environment wherefrom
said viscous liquid is to be removed and showing wide inlet ports
radially directed toward the screws, in front of which a number of
screws is wholly exposed and uncovered, while the remaining screws
start downstream of said inlet port, in order to allow the viscous
fluid to freely attain the uncovered initial portions of the
uncovered screws and to fill the spiral channels thereof across
their whole development of 360.degree. before engaging the thread
of the other screw or screws thereinto.
A three screws pumping system comprising one driving central screw
having a shaft extending to the outside of the device and connected
to driving means, and two driven side screws, is preferably
utilized. The side screws extend to the inside of the equipment
wherefrom the product is to be removed, while the driving screw
extends essentially from the bottom wall of said equipment.
Moreover, the pumping device is preferably fitted within a tubular
outlet passage, which passes through a hollow space surrounding the
environment and wherein a heating fluid is circulated, as already
well known. Such an arrangement ensures a heating of the pumping
system practically all along its whole axial length. The device
might comprise further jackets or heating means, extending to the
outside of the equipment and fitted with pipe connections and inlet
ports.
Sealing means, adapted to operate at relatively high temperature,
e.g. a stuffing box having ring-shaped packing glands made of
asbestos or like fibers are preferably provided on the orifice
through which the driving shaft of the pumping mechanism extends to
the outside.
DRAWINGS
FIG. 1 is a section of a device according to the invention, taken
on the symmetry plane wherein the axes of pumping system screws
lie, the structural details being somewhat simplified.
FIG. 2 is a fragmentary, enlarged and more detailed section of the
inlet end of the device, taken on a plane wherein the axis of
central screw lies, and orthogonal to plane of FIG. 1.
FIG. 3 is a front view of the device, and
FIG. 4 and FIG. 5 are cross-sectional views thereof, respectively
taken on the planes IV-IV and V-V of FIG. 2.
PREFERRED EMBODIMENT
The embodiment of FIG. 1 shows a device which is associated with a
polymerization reaction vessel or equivalent equipment, as e.g. a
demonomerizing reactor, which in considered embodiment comprises an
essentially vertical chamber. The casing 10 of said chamber is
wholly surrounded by a jacket 14, and through the thus defined
hollow space 13 a heating fluid, as e.g. diphenyl or the like, is
circulated, as well known by those skilled in the art. The outlet
passage of the equipment consists, as well known, of a tubular duct
15, which inlet end defines the outlet port 16 of the casing 10,
said duct being surrounded by the hollow space 13 and extending for
a short length from said outlet port of the reactor chamber casing
10.
The above arrangement of the device is to be assumed as a not
restrictive example only, since the device according to the
invention could be obviously associated, under conditions
equivalent to the abovespecified ones, also with equipments of a
different kind, e.g. with reaction vessels of the horizontal type,
or reactors, demonomerizing vessels and other equipments, in case
operated with screw feeders or the like, provided that they show an
outlet port located in the lowest point of the processing
environment, and wherein an amount 12 of the processed liquid to be
removed is maintained to show a given head 11.
According to an already known technical solution, the device
comprises a tubular casing 20, wherein a hollow body 21 is fitted,
said body 21 being formed with seats for the screws, in particular
a central screw 22 and two symmetrically located side screws 23,
which represent the movable components of the pumping system.
The central screw 22 is rigidly connected with a hub 24 extending
to the outside, which is in turn secured to, or at any rate
rotatively connected with, a shaft 25 which extends outwardly in
such a manner that its opposite end 26 can be connected, directly
or through already known transmission means, with a suitable
driving means (not shown).
As it can be seen in particular in FIGS. 1 and 2, the tubular
casing 20 of the pumping device extends for a given length into the
processing chamber and is formed with a plurality of wide side
windows 30, through which the liquid to be removed can freely enter
into said casing, essentially along the directions indicated by A
in FIG. 1.
The plug 31 of the casing 20 is in turn formed with further
orifices or passages 32 (see FIGS. 2 and 3) to enhance said free
access of liquid into the casing.
The hollow body 21, wherein the pumping system is fitted, along
with the central screw 22, terminate under the space wherein said
passages or side windows 30 are formed, whilst both side screws 23
extend upwardly into said space, the upper portions 23' thereof
being thus wholly exposed and immersed into the liquid filling the
upper section of said casing 20.
The liquid flows into said space under the action of gravity. Due
to the width of access passages, such flow is easily performed and
moreover the volatile fractions which could be given off by the
liquid, can be easily discharged from said space, even when such
phenomena occur directly adjacent to the screws. In particular, the
discharge of bubbles and gas pockets as formed by the evolution of
volatile fractions, is made easier through the upper orifices
32.
The liquid into said space will wholly fill the spiral channels of
the wholly exposed upper sections 23' of the side screws, whereby
it reaches the area wherein the central screw engages both the side
screws, in an amount exceeding the liquid which can be contained in
said channels after the engagement thereof by the central screw.
Thus, a complete volumetric filling of the pumping system and
therefore a uniformly metered removal are positively ensured. The
pumping action is uniformly exerted across the whole useful length
of the screws, which is substantially coincident with the screw
portions extending through the lower protrusion of the heating
hollow space 13, a good uniformity of the pumped liquid temperature
being therefore ensured.
Further, exposed lengths 23" of the side screws 23 extend from the
lower end of the body 21 (see FIG. 1) into a discharge chamber 40,
whilst the central screw is connected to its extension 24 by a
threadless core. The removed liquid is then fed from said discharge
chamber to a delivery duct 42, through an annular passage 41.
Also the walls defining said discharge chamber 40, as well as the
passage 41 and the duct 42, are advantageously fitted with jackets
41 and 52 respectively, to allow a heating fluid to circulate
through suitable pipe connections 53 and 54.
The casing 20 of the pumping device is preferably embodied in the
structure of the equipment, by rigidly securing a flange section
43, integral with the casing outer end, to a flange 44, that is on
turn integral with the equipment and in particular with the outer
end of the tubular end part 15 thereof.
The rotary assembly is located by virtue of a component 45, that is
formed e.g. with a flange 46, and whereon the central screw 22 is
supported through suitable axial bearings of gaskets, while the
side screws 23, which support pressure acts in an opposite
direction, rest against the upper plug or cap 31, e.g. through
axially abutting buffers 47 (see FIG. 2). The abutting surfaces of
said thrust block systems are similarly or equally dimensioned, to
ensure a good balance of working conditions.
As shown in FIG. 1, the component 45 extends outwardly by means of
a tubular length 48, inside which a row of ring-shaped packing
glands 49, made e.g. of asbestos fibers is fitted, so to form a
stuffing box that can be tightened by a stuffing nut 50.
Moreover a liquid buffer, which obviously shall neither react nor
mix itself with the processed polymer, can advantageously be fed,
e.g. through a duct 55, into the stuffing box, wherein it is kept
under a suitable pressure, applied e.g. by means of nitrogen gas,
and in case also cooled.
However, since the device according to the invention has been
described and shown as a not restrictive example only and merely to
demonstrate its essential features, it is to be understood that the
inventive idea can be carried out in many different embodiment to
better conform the same to the different assembly and operational
requirements, without departing from the true spirit and scope of
the invention.
* * * * *