RU2777361C2 - Extrusion system with pressure adjustment device - Google Patents

Abstract

FIELD: gas industry.

SUBSTANCE: invention relates to an extrusion system for degassing of a mixture. The extrusion system includes first extruder (1), second extruder (2) located downstream from first extruder (1), and transfer zone (6) formed between them. Moreover, a pressure adjustment device is provided, using which pressure of mixture (5) is adjusted at an outlet of first extruder (1), as well as perforated plate (10), using which mixture (5) passed through transfer zone (6) is divided into several partial streams. At the same time, the transfer zone includes the first part of a pipeline, which is adjacent to the first extruder and has a decreased volumetric cross-section compared to the first extruder, wherein the second extruder has a degassing zone, and pressure in the second extruder, at least in the area of the degassing zone, is maximally lowered relatively to excessive pressure in the transfer zone.

EFFECT: improvement of degassing in an extrusion system.

12 cl, 2 dwg

Description

The invention relates to an extrusion system.

Extruders can be broadly classified into two types, which differ in process principles. Processing extruders serve mainly for shaping (usually single screw extruders), while preparation extruders serve for the chemical and/or physical modification (reacting, mixing, degassing, etc.) of substances (unidirectional, tightly interlocking twin screw extruders , rubber mixers, etc.).

One form of preparation extruders are the so-called degassing extruders, which are used in particular for the degassing of polymers and in particular elastomers.

The degassing process is divided, as a rule, into several stages. In this case, in the first extruder, volatile components, such as solvents, residual monomers or water, can be removed to a residual volatile component content of approximately 5% to 40%. This mixture of product and residual volatile components is then heated in the first extruder by the input of mechanical energy. Optionally, a highly volatile carrier may be added. The scavenger may, for example, be nitrogen, carbon dioxide or water, or mixtures thereof. The mixture of product, residual volatile components and, if necessary, scavenger is then fed into a second extruder, where the mixture is further degassed in the second extruder. A significant part of this further degassing is in the so-called transfer zone, ie the formation of the transition from the first to the second extruder. This transition is carried out in particular in such a way that, when entering the second extruder, it comes to a decrease in the pressure of the mixture, which has a positive effect on degassing.

Based on this prior art, the invention was based on the problem of further improving the degassing in an extrusion system corresponding to the generic concept.

This problem is solved by means of an extrusion system according to the independent claim. Preferred embodiments of the extrusion system according to the invention are the subject of the dependent claims and follow from the following description of the invention.

A generic extrusion system for degassing a mixture, comprising (at least one) a first extruder, (at least one) a second extruder located downstream of the first extruder, and (at least one) a transfer zone formed therebetween, is characterized according to the invention (at least one) pressure control device, with which the pressure at the outlet of the first extruder, i.e. at the inlet to the transfer zone, can be regulated.

By means of the pressure control device, the energy supply and thus the temperature of the mixture can be set, whereby a higher set pressure can result in a higher mixture temperature, and a higher temperature can lead to improved degassing.

Preferably, it is provided that the pressure is only set so high that the volatile components contained in the mixture do not boil off. The same may apply to possibly contained water, the boiling point of which may rise due to the increased pressure above the prevailing temperatures. Boiling of water can be prevented as a result. Further, high pressure can improve the dispersion of sparingly soluble scavengers, such as nitrogen or carbon dioxide.

In a preferred embodiment of the extrusion system according to the invention, it can also be provided that the pressure control device is controlled in such a way that the pressure at the outlet of the first extruder is greater than in the degassing zone of the second extruder adjacent to the transfer zone. As a result, a reduction in the pressure of the mixture is achieved, in particular at the entrance to the second extruder. Due to this pressure reduction, in particular in combination with the resulting increase in temperature in the transfer zone, the boiling pressure of the mixture can be lowered, which can lead to effective degassing of the mixture. Further, by reducing the pressure of the mixture, it can be achieved that, due to the expansion of the residual volatile components and the scavengers present if necessary, a foam is formed, which, due to the large surface, promotes degassing.

The expansion of the volatile components can preferably be supported by creating a maximally reduced pressure within the second extruder (at least in the region of the degassing zone) in relation to the (over) pressure in the transfer zone. In this case, the pressure in the degassing zone can preferably also be below atmospheric pressure. Most preferably, a vacuum can be generated in the transfer zone (in particular between 50 millibars and 900 millibars (absolute pressure)).

Since conventional degassing processes, in particular from polymers, are often limited by the available surface of the mixture, in a further preferred embodiment of the extrusion system according to the invention, means can be provided to increase the free surface of the mixture passed through the transfer zone. They may most preferably be provided at the outlet of the transfer zone.

The means for increasing the surface may advantageously have a perforated plate with a plurality of through holes, by means of which the mixture carried through the transfer zone is separated into several partial streams.

Another possibility for increasing the surface may be that the mixture is conducted in the transfer zone or at the entrance to the degassing zone of the second extruder through one or more slotted nozzles. These slit nozzles are characterized by large surface to volume ratios, which are preferably achieved due to the fact that the orifices of the nozzles are slit-like with a length that is many times greater than the width.

Of course, both measures can also be combined, i.e. by means of a perforated plate with a plurality of slot-like through-holes (slot nozzles), both separation of the mixture into several streams and a maximum surface area for the individual mixture streams can be achieved.

In order to prevent product deposits and to improve the removal of volatile components, it can further be provided that the second extruder is located (preferably vertically) above (with respect to the direction of gravity) the first extruder. As a result, a rapid or direct withdrawal of the degassed mixture from the transfer zone can be achieved and at the same time a largely free gas space in the degassing zone above the degassed mixture can be achieved, through which volatile components can be well removed. In this case, the removal of volatile components can be further improved if at least one degassing outlet leading (preferably vertically) upwards relative to the direction of gravity is provided in the degassing zone of the second extruder adjacent to the transfer zone. The mixture and the degassed components can in this case be carried out in countercurrent, in crossflow and/or in parallel flow. Thanks to this embodiment of the extrusion system according to the invention, the volatile components can be effectively separated from the degassed mixture; the simultaneous entrainment of particles of the degassed mixture can be largely prevented by the special conduction of the mixture and the volatile components.

In another embodiment of the extrusion system according to the invention, an effective separation of the degassed mixture from volatile components can be achieved due to the fact that the second extruder is located in relation to the direction of gravity (preferably vertically) below the first extruder, and in adjacent to the transfer zone a degassing zone of the second extruder is provided (along at least one) leading (preferably horizontally) to the side relative to the direction of gravity degassing outlet.

In a further preferred embodiment of the extrusion system according to the invention, an (at least one) closable outlet for discharging the mixture can be provided in the region of the transfer zone. It can serve, in particular, to take part of the mixture as a sample within the framework of technical control. Also, a portion of the mixture may be withdrawn through the closable outlet before it is transferred to the second extruder. This may be advantageous in particular when starting up or emptying the first extruder.

Preferably, it can be provided that the outlet can be closed by means of a pressure control device, wherein the pressure control device can preferably include (at least one) spool valve for this, which, by means of a relative movement (translational or rotational) of the valve body, more or less closes either (at least one) the opening of the transfer zone, or an outlet through which part of the mixture can be taken. In particular, when talking about a spool valve, we can talk about a (rotary) piston valve.

In a further preferred embodiment of the extrusion system according to the invention, it can be provided that the screw of the first extruder can be driven or driven at a higher angular velocity than the screw of the second extruder. Due to the relatively high rotational speed of the first extruder, a correspondingly high energy input into the mixture can be achieved in order to increase the temperature and thereby degas.

In particular, with such a design of the extrusion system, it can also be provided that the average volumetric cross section of the first extruder is smaller than the average volumetric cross section of the second extruder. Due to the relatively large volumetric cross-section of the second extruder, on the one hand, the input of mechanical energy can be kept low, and on the other hand, a relatively large gas space can be provided.

The extrusion system according to the invention is suitable in particular for degassing polymers and in particular elastomers.

The invention is explained below in more detail on the basis of the exemplary embodiment shown in the drawing.

The drawing shows:

fig. 1 is a schematic side view of an embodiment of an extrusion system according to the invention in a first functional position; and

fig. 2 is a part of the extrusion system according to FIG. 1 in the second functional position.

Shown in FIG. 1 and 2, the extrusion system serves to degas the polymers and includes a first extruder 1 and a second extruder 2 adjoining the first extruder 1 downstream. The extruders 1, 2 in each case include one or more extruder screws 3, 4, which the possibility of bringing into rotation by a drive not shown are installed in the extruder housings.

In the annular production spaces between the extruder screws 3, 4 and the extruder housings, the mixture 5 (product) is transported by rotation of the extruder screws 3, 4, made with helical coils. This is where degassing occurs.

In the first extruder 1, volatile components, such as in particular solvents, residual monomers or water, are removed to a residual volatile component content of about 5% to 40%. In this case, the mixture 5 of the product (polymer) and volatile components is heated by the supply of mechanical energy and - in connection with the still explained pressure control device in the transfer zone 6 between the two extruders 3, 4 - is compacted.

In the dispersion zone 7 adjacent to the rear end of the extruder screw 3, a highly volatile carrier is added to the mixture. This can be, for example, nitrogen or carbon dioxide.

The mixture 5 then enters, moved by the screw 3 of the first extruder 1, into the transfer zone 6. In this case, the pressure increase caused by the extruder 1 is set in such a way that the outlet pressure of the extruder 1 is at least so high that the volatile components contained in the mixture 5 do not boil. The transfer zone 6 is a piping system through which the mixture 5 is transferred from the first extruder 1 to the second extruder 2 in a controlled manner. and also a second part of the pipeline, which in the radial direction of the first part of the pipeline (relative to its longitudinal axis) adjoins it. The opening of the transition from the first to the second part of the pipeline can be more or less closed by means of a pressure control device in the form of a spool valve. To do this, the valve body 8 is moved by means of a piston 9 by a drive device not shown inside the first part of the pipeline.

The flow of the mixture from the first extruder 1 into the second extruder 2 is accompanied by a decrease in pressure, which, on the one hand, is based on a decrease in the volumetric cross-section of the first part of the pipeline compared to the first extruder 1 and on the narrowing of the free cross-section of the transition hole, if necessary, due to partial overlap by the body 8 valve. On the other hand, a funnel-shaped expansion of the section of the second part of the pipeline is provided.

At the rear end of the funnel-shaped expansion, a perforated plate 10 is provided, which has a plurality of holes through which the mixture 5 is extruded. In this case, the flow of the mixture 5 is divided into a plurality of partial flows. The partial flows are characterized by a significantly higher surface-to-volume ratio compared to the total flow prevailing in front of the perforated plate 10. This large surface-to-volume ratio in turn has a positive effect on the volatilization of the mixture 5 and thus on its degassing.

Partial streams of the mixture 5 enter the degassing zone of the second extruder 2. In this case, the mixture 5 foams due to the expansion of the volatile components, which in turn leads to an increase in the surface and thus to an improvement in the outgassing. This almost instantaneous expansion of the volatiles is caused by a relatively large difference between the pressure in the degassing zone of the second extruder 2 and the pressure in the second pipeline section of the transfer zone 6 . To this end, the atmosphere is largely evacuated inside the second extruder 2 .

The first extruder is located in relation to the direction of gravity below the second extruder. The mixture 5 is thus introduced from below and in a direction radial to the screw 4 of the second extruder 2 into the second extruder 2. As a result, the mixture 5 is located almost exclusively in the lower section of the degassing zone of the second extruder 2 and is discharged from there directly by the screw 4 of the extruder. In the upper portion of the degassing zone, a gas space thus remains, which is substantially free of the mixture 5 and through which volatile components can be well discharged. The evacuation of the volatile components takes place on one side via a degassing outlet 11, which is provided at the rear end 5 in the direction of flow of the degassed mixture and therefore also behind the area in which the mixture 5 is introduced into the second extruder 2. The degassing outlet 11 extends in a vertical, radial direction from body of the second extruder 2. Due to this arrangement of the degassing outlet 11, the volatile components flow in the opposite direction to the direction of the main flow of the mixture 5 direction.

In the extrusion system shown, it is provided that, on the further stroke of the second extruder 2, another further degassing is carried out by means of a so-called excess screw 12.

The first part of the pipeline of the transfer zone also includes an outlet 13, through which part of the mixture 5 can be discharged. This can be carried out in particular for sampling within the framework of technical control. In normal operation of the extrusion system, the outlet 13 is closed by the valve body 8 of the pressure control device. To take a sample, the valve body 8 is moved so that through the axial or transverse opening of the valve body 8 a connection is established between the outlet 13 and the mixture-receiving part 5 of the first part of the pipeline of the transfer zone 6. In this case, the wall section of the valve body 8 closes the transition hole from the first to the second part of the pipeline of the transfer zone 6 (see Fig. 2).

LIST OF REFERENCES

1 extruder

2 extruder

3 screw extruder

4 screw extruder

5 mix

6 transmission zone

7 dispersion zone

8 valve body

9 piston

10 perforated plate

11 degassing outlet

12 excess worm

Issue 13

Claims (15)

1. An extrusion system for degassing the mixture (5), including the first extruder (1) located downstream of the first extruder (1), the second extruder (2) and the transfer zone (6) formed between them, characterized in that a pressure control device is provided, by means of which the pressure of the mixture (5) is regulated at the outlet of the first extruder (1), as well as a perforated plate (10), with the help of which the mixture (5) passed through the transfer zone (6) is divided into multiple partial streams, moreover, the transfer zone includes the first part of the pipeline, which is adjacent to the first extruder and has a reduced volumetric cross section compared to the first extruder, and moreover, the second extruder has a degassing zone, and the pressure in the second extruder, at least in the region of the degassing zone, is reduced as much as possible in relation to the overpressure in the transfer zone. 2. Extrusion system according to claim 1, characterized in that the pressure control device is controlled in such a way that the pressure of the mixture (5) at the outlet of the first extruder (1) is greater than in the degassing zone of the second extruder (2) adjacent to the transfer zone (6). ). 3. Extrusion system according to claim 1 or 2, characterized in that the perforated plate (10) is intended to increase the surface of the mixture (5) passed through the transfer zone (6). 4. Extrusion system according to claim 3, characterized in that the perforated plate (10) has one or more slotted nozzles. 5. Extrusion system according to claim 2, characterized in that the second extruder (2) is located in relation to the direction of gravity above the first extruder (1). 6. An extrusion system according to claim 5, characterized in that in the degassing zone (6) adjacent to the transfer zone of the second extruder (2), a degassing outlet (11) leading upward relative to the direction of gravity is provided. 7. Extrusion system according to claim 2, characterized in that the second extruder (2) is located in relation to the direction of gravity below the first extruder (1), and in the degassing zone adjacent to the transfer zone, the second extruder (2) is provided leading to the side or downwards relative to the direction of gravity degassing release. 8. An extrusion system according to claim 2, characterized in that a closable outlet (13) is provided in the region of the transfer zone to withdraw the mixture (5). 9. An extrusion system according to claim 8, characterized in that the outlet (13) is closable by means of a pressure control device. 10. An extrusion system according to any one of claims 1 to 9, characterized in that the pressure control device includes a spool valve. 11. Extrusion system according to claim 10, characterized in that the volumetric cross section of the first extruder (1) is smaller than the volumetric cross section of the second extruder (2). 12. An extrusion system according to claim 11, characterized in that the screw (3) of the first extruder (1) is capable of being driven at a higher angular velocity than the screw (4) of the second extruder (2).

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