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.

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.

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.