WO2019158511A1

WO2019158511A1 - Method for cleaning perforated plates

Info

Publication number: WO2019158511A1
Application number: PCT/EP2019/053396
Authority: WO
Inventors: Oskar Stephan; Rainer Friehmelt; Hendrik MONSCHAU; Juergen Ettmueller; Silke Muckenfuß
Original assignee: Basf Se
Priority date: 2018-02-14
Filing date: 2019-02-12
Publication date: 2019-08-22

Abstract

The invention relates to a method for cleaning holes in perforated plates (1), said method comprising the following steps: (a) optionally analysing the holes (11) for determining contamination; (b) removing impurities by means of a laser (7) which is so powerful that impurities (9) evaporate and/or burn out of the holes (11) and off the surface of the perforated plate (1), at least in the region of the holes (11), and the material of the perforated plate (1) remains undamaged; (c) testing the cleaning effect of step (b); and (d) optionally repeating steps (b) and (c).

Description

Process for cleaning perforated plates

description

The invention is based on a method for cleaning holes in perforated plates.

Perforated plates are used, for example, in reactors for drop polymerization, which can be used, for example, for the preparation of poly (meth) acrylates. In these reactors, a monomer solution is dripped through the perforated plates into the reactor. Due to the reaction conditions, the holes in the perforated plates can become contaminated and clogged by the monomer solution. This makes it necessary to clean the holes regularly.

In order to obtain a uniform particle size in reactors, it is necessary to measure the holes after the cleaning in order to detect damage to the perforated plates and possibly not completely cleaned holes.

The holes can be cleaned, for example, mechanically or by using suitable cleaning agents. However, this has the disadvantage that in many cases a long exposure time is necessary. On the other hand, the disadvantage of a mechanical cleaning is that this can lead to damage to the hole geometry. This particular because of the small diameter of the holes on one side of the perforated plate.

Optical control is then performed, for example, by magnification and image acquisition. Suitable measuring methods include, for example, transmitted light images or incident light images, with which, on the one hand, contamination of the holes can be detected and, on the other hand, it can be detected whether the holes have been completely cleaned. Particularly suitable are combined transmitted light and Auflichtaufnahmen.

Disadvantage of the known method, however, is that it can not be ensured by the cleaning method used that all impurities are removed and on the other hand, a large amount of time is required by the independent implementation of the cleaning and measuring methods.

It was therefore an object of the present invention to provide a method with which perforated plates can be cleaned and measured, which requires less effort than previous methods and, moreover, enables a good cleaning of the perforated plates.

This object is achieved by a method for cleaning holes in perforated plates, fol lowing steps comprising:

(a) if necessary, analysis of the contamination detection holes (b) removal of impurities with a laser whose power is so great that impurities from the holes and from the surface of the perforated plate evaporate and / or burn at least in the area of the perforations and the material of the perforated plate remains undamaged,

(c) checking the cleaning effect of the step (b) and

(d) optionally repeating steps (b) and (c).

The analysis of the holes for the detection of the contamination and the examination of the cleaning effect makes it possible to perform a specific cleaning of the holes. With the removal of contaminants with a laser, a fast and effective cleaning is possible.

As a suitable device on which the cleaning of the holes of the perforated plate is performed, for example, a laser table can be used. It is important that the inserted laser has enough power to clean the holes.

By using a laser table to clean the holes in the perforated plate, it is possible either to move the perforated plate or the laser horizontally, so that horizontal perforations of the perforated plate or laser can clean all holes in the perforated plate. In order to be able to clean the holes over the entire thickness of the perforated plate, a vertical displacement is still required since the best cleaning performance is obtained at the focal point of the laser. Due to the vertical displaceability of the laser or the perforated plate, the laser's focus can be shifted along the axis of the hole. "Horizontally displaceable" or "vertically displaceable" refers in this case to the movement relative to the laser beam direction. " Horizontal "is perpendicular to the orientation of the laser beam and" vertical "is parallel to the alignment of the laser beam.

As a laser, with which it is possible to clean the holes of the perforated plates, it is possible to use diode lasers, ultrashort pulse lasers, UV lasers, excimer lasers or CO ₂ lasers, for example. The laser used depends on the size of the holes and the possible impurities. Particularly in the case of perforated plates, as used in reactors for dropwise polymerization for the preparation of poly (meth) acrylates, it is preferred to use a CO ₂ laser or an ultrashort pulse laser. These are suitable with regard to the wavelength as well as with regard to the laser power and focusability to remove residues from the holes.

The power of the laser should be selected so that it is sufficient to remove impurities from the holes and possibly also from the surface of the perforated plate, this usually being done by evaporation and / or burning of the impurities at the same time in that the laser does not damage the material of the perforated plate itself. Suitable materials for the perforated plates, in particular for those which can be used in reactors for droplet polymerization, are, for example, metals, in particular steel or stainless steel. Damage to the material of the dropletizer plate can be prevented by using a laser of a wavelength that is independent of the material of the dropletizer plate is not absorbed, but is completely reflected or its performance is not sufficient to damage the material of the perforated plate. In particular, damage can be caused by melting in the area of the laser's action. In order to prevent damage to the material of the perforated plate and at the same time provide a sufficiently large power with which impurities can be removed, the laser used preferably has a power of 1 to 5000 watts, more preferably in the range of 5 to 500 watts, and particularly preferably in the Range from 10 to 250 watts.

Laser powers in the above-mentioned ranges allow a rapid removal of the impurities, that is, a distance in a period of 0.1 to 75 s per hole. If lasers are to be used with a smaller power, the process time increases significantly. In addition, too low a performance may mean that this is not sufficient to remove the impurities even with long exposure times.

Due to the large number of holes, especially in perforated plates, as they are used in reactors for drop polymerization, a short process time per hole is desired, so that the laser power should be as large as possible, that is in the above-mentioned areas te.

Further improvement in cleaning performance can be achieved using pulsed lasers. Preferred pulse durations are in the range of 1 fs to 1 s, in particular in the range of 0.1 ns to 0.1 s. Especially with perforated plates, which are used in drop polymerization reactors for the production of poly (meth) acrylates, by using pulsed C0 ₂ lasers a further improved cleaning at lower power compared to non-pulsed lasers was observed.

To test the cleaning effect, an image analysis is carried out in one embodiment of the invention. For this purpose, a picture of the cleaned hole is taken and evaluated with a suitable image processing software. In order to carry out the image analysis, it is possible, for example, to equip the laser table additionally with an optical unit, usually a camera, with which appropriate recordings can be made. In this case, the optics and cameras currently also used for optical measurement by transmitted light and / or reflected light can be used.

Preferably, the laser for the cleaning of the holes and the optical unit for checking the cleaning effect are arranged in a measuring unit so that during the cleaning of a hole with the optical unit, the cleaning effect of the previously cleaned hole can be checked. In order to be able to clean all the holes of a perforated plate, it is either possible to move the perforated plate in the case of a non-displaceable measuring unit such that all the holes to be cleaned are first cleaned with the laser and subsequently tested with the optical unit or alternatively with the fixed perforated plate the measuring unit move horizontally in such a way that all holes can be cleaned and checked one after the other. In order not to treat all the holes with the laser, it is also possible to additionally perform an analysis of the holes for detecting the impurities before cleaning. For example, this can also be done visually by an image analysis. To analyze the holes before cleaning, the same measuring unit can be used, with which also the examination of the cleaning effect is carried out. Alternatively, however, it is also possible to provide an additional optical unit. The use of an additional optical unit has the advantage that fewer movements of the measuring unit or of the perforated plate to be cleaned are required, since it is possible to carry out the analysis for detecting the contamination at a first hole simultaneously with the first optical unit (step (step (FIG. a)), laser-cleaning at a second hole (step (b)), and cleaning-out at a third hole (step (c)). After carrying out these steps, either a displacement of the perforated plate around a hole or the measuring unit takes place around a hole, so that in a subsequent step a new hole for the detection of contamination is analyzed, the hole analyzed in the previous step is cleaned and the Hole, which was cleaned in the previous step, is checked. Of course, if the distance between the holes is too small to analyze, clean and inspect directly adjacent holes, it is also possible to leave one or more holes at a time between the individual steps, so that cleaning only takes two or more steps after the analysis and according to the test, only two or more steps after cleaning are carried out, the number of steps corresponding to the number of holes which is between the steps performed at the same time. For example, if there is one hole between the hole being analyzed, the hole being cleaned, and the hole being tested, cleaning will be done two steps after the analysis and two steps after cleaning and, correspondingly, with two holes in between, cleaning three steps after the test and analysis three steps after cleaning. However, it is preferred if there is no further hole between the hole to be tested, the hole to be cleaned and the hole to be analyzed, so that in the immediately following step the sample being analyzed is cleaned and the piece just cleaned is checked. If there are holes in between, it is alternatively possible to move the measuring unit or the perforated plate by several holes in each case in order to ensure that the analyzed hole is cleaned in the subsequent step and the cleaned one is checked in the subsequent step. In this case, after a first run, at least a second pass has to be carried out in which the previously uncleaned holes are analyzed, cleaned and tested.

The image analysis of the holes, which is used either to analyze the impurities or to test the cleaning effect, is also preferably used to investigate the wear of the holes. For this purpose, the analysis for testing the cleaning effect after carrying out the cleaning is preferably used. By examining the wear of the holes, it is possible to check whether the perforated plate has any damage or that it is impossible to remove contaminants even after repeated or prolonged cleaning. If the damage or the size or number of impurities that can no longer be removed exceeds a predetermined size, it is necessary to eject the perforated plate. exchange. On the other hand, testing for damage and the removal of impurities that can no longer be removed will prevent too early replacement.

In order to keep the measuring and cleaning unit, in which the optical units for analyzing the impurities and for testing the cleaning effect and the laser for cleaning, as compact as possible, it is possible to use the light of the laser also for illumination for image analysis to use. As a result, additional lighting means are saved. For example, to enable illumination with the laser, it is possible to use a diffuser in which the laser beam is widened. This can be arranged above or below the perforated plate to be cleaned. In an arrangement below the perforated plate, the laser beam passing through the hole to be cleaned strikes the diffuser and is reflected and scattered there, so that transmitted light is generated. In the case of scattering of the laser above the perforated plate, a branched-off beam is preferably scattered through the perforated plate, in which case an incident light for the recording is produced.

In addition or as an alternative to image analysis to detect impurities and to test the cleaning effect, it is also possible to use a laser measuring method.

For the most accurate possible measurement and targeted removal of impurities, it is further preferred if the diameter of the laser beam at the point of contact with the perforated plate has a diameter which preferably corresponds at most to the diameter of the holes of the perforated plate.

By using a laser in a laser measuring process, the power of which is so great that impurities from the holes and from the surface of the perforated plate evaporate and / or burn at least in the area of the holes, it is possible to measure simultaneously with the measurement of the holes also to perform a cleaning. In particular, this method also allows the efficiency of the cleaning to be detected and, if appropriate, immediately followed by a second cleaning and measuring step on the perforated plate to connect a second, in order to remove residual residues that were not removed in the first cleaning step. This is not possible in conventional methods, in which the cleaning and measurement take place independently of one another, since it is only in a measuring step following the cleaning step that it is possible to detect whether the cleaning has been successful.

With a laser measuring method, it is possible to detect the exact shape of the individual holes and in this way determine whether and how much the holes are contaminated or how great the wear is. If it is no longer possible to ensure that the drops produced by the perforated plate meet the desired specification in terms of drop size due to too frequent cleaning or excessive wear or material damage, it will be necessary to replace the perforated plate. In this case, the device with which the method for measuring and cleaning perforated plates is carried out can also be used to perforate the holes, for example for incoming inspection or for quality control. tätskontrolle only to measure, since in a new perforated plate no contamination by the use of the perforated plate can be expected.

If a laser measuring method is used, it is possible to finally decide whether to replace a perforated plate, following the procedure for measuring and cleaning the perforated plates, an image analysis, for example by reflected light and / or transmitted light, preferably by a Combination of reflected light and transmitted light shots. This once again visually determine the exact extent of wear or the impurities that can no longer be removed and thus decide whether it is finally necessary to dispose of the corresponding plate and replace it. However, such additional image analysis is only necessary if corresponding indications arise during the measurement with the laser measurement method. The image analysis serves as an additional control, in order to avoid unnecessarily early replacement of perforated plates due to measurement errors.

Regardless of whether the analysis of the holes for the detection of the impurities and the examination of the cleaning effect are carried out with an optical measuring method or with a laser measuring method, it is advantageous to use a laser table. When measuring with the laser, the measurement of the holes is carried out in the usual manner, as is carried out in commercial Lasermesstischen. Corresponding laser measuring tables have, in addition to the laser and a receptacle for the object to be measured, in the context of the present invention the perforated plate to be cleaned and measured, as a rule an evaluation unit with which the measured data can be displayed. If the analysis and testing is performed with an optical system, it is preferably integrated into the measuring unit with the laser.

In order to achieve a quick cleaning of the perforated plate, it is possible to perform step (b) on several holes simultaneously. For this purpose, either a plurality of lasers can be used or else a laser beam is divided by a suitable optics, for example mirrors or prisms, so that it reaches several holes at the same time. The simultaneous cleaning of several holes reduces the necessary number of cleaning steps, which reduces the total time required for cleaning accordingly. If the method is carried out so that several holes are cleaned simultaneously, it is furthermore advantageous if steps (a), (b) and (c) are carried out simultaneously on a respective group of holes.

Due to the laser power required for effective cleaning, the removal of contaminants is generally by combustion. This can cause a flame, which in turn can lead to damage to the material of the perforated plate. In order to reduce the formation of flames, it is therefore preferable if compressed air is applied to the perforated plate in the region of the laser during cleaning and measurement. This has the further advantage that the flame can not lead to measurement errors. In addition, it is possible through the commissioning Residue with compressed air during combustion to remove residues, especially ash, directly from the holes.

Since it can not be ruled out that residues remain in the area of the holes after the removal of impurities by the laser, it is also advantageous to place the perforated plate in a cleaning bath after irradiation with the laser for the purpose of removing impurities and for measuring. In the cleaning bath, the residue can then be removed from the perforated plate.

In this case, any cleaning bath known to the person skilled in the art can be used as cleaning bath. It is particularly preferable to use an ultrasonic bath as the cleaning bath. The additional ultrasound loosens the residue from the surface and makes it even easier to remove.

Suitable washing liquid in the cleaning bath are, for example, water, hydrogen peroxide, organic solvents or aqueous surfactant solutions. In the case of perforated plates which have been used for the preparation of poly (meth) acrylates, the use of a mixture of water and hydrogen peroxide is particularly preferred.

The method is suitable both for perforated plates having holes with a constant diameter and for those whose diameter varies. The method is particularly suitable for perforated plates with holes whose diameter is greater on one side of the perforated plate than on the other side of the perforated plate, so that along the axis of the diameter decreases from one to the other side. With holes of this type, it is particularly easy to form impurities in areas of diameter constrictions, which are then flushed on with subsequent liquid and block the holes at the outlet.

Since organic impurities can be removed particularly well with a laser without removing the material of the perforated plate, the method according to the invention is particularly suitable for the cleaning of perforated plates through which an organic material, for example a monomer solution, is transported. The method is particularly preferably used for perforated plates which are used to disperse a monomer solution in a dropwise polymerization reactor for the production of pulverulent polymer, the pulverulent polymer most preferably being a powdery poly (meth) acrylate.

Perforated plates which are used for the production of pulverulent polymer, in particular pulverulent poly (meth) acrylate, preferably have a hole diameter at the narrowest point in the range of 50 to 500 μm, more preferably in the range of 100 to 350 μm and in particular in the range of 150 up to 250 pm.

However, the method according to the invention can also be used for perforated plates from any other process, for example for plates with spinnerets for the production of organic fibers or for gas distribution plates, for example for fluidized beds. Embodiments of the invention are illustrated in the figures and are explained in more detail in the following description.

Show it:

FIG. 1 shows a schematic representation of the method according to the invention,

2 shows a sectional view through a perforated plate,

FIG. 3 shows a photograph of a contaminated hole in a perforated plate,

Figure 4 is a photograph of the hole of Figure 3 after cleaning.

FIG. 1 shows a schematic representation of the method according to the invention.

To investigate a perforated plate 1, a displaceable measuring device 3 is used. In order to obtain the displaceability of the measuring device 3, this can be performed, for example, on a rail 5. The measuring device 3 comprises a laser 7 whose power is sufficiently large to remove impurities 9 from holes 11 of a perforated plate 13.

Laser lasers 7 are, for example, diode lasers, ultrashort pulse lasers, UV lasers, excimer lasers or CO2 lasers, carbon dioxide lasers or ultrashort pulse lasers being particularly preferred for the purification of perforated plates used in reactors for the production of poly (meth) acrylates ,

The laser 7 emits a laser beam 15, with which the holes 11 in the perforated plate 1 are cleaned. In addition, the measuring device 3 has a camera 17. With the camera 17, the individual holes 1 1 are optically examined to check the cleaning effect. For this purpose, depending on the diameter of the holes 1 1, a suitable optics 19 is used, which is preferably designed so that only one hole 11 is detected enlarged. This allows a detailed recording of the hole 1 1 with the immediate vicinity of the perforated plate 1, so that it is clearly recorded by the optical detection, whether all impurities 9 were removed from the hole 1 1 and whether the perforated plate 1 is still intact or has been damaged , The arrangement of the camera 17 in the measuring device 3 is such that each hole is first cleaned with the laser 7 and then an optical control of the cleaned hole 1 1 is performed.

In order to evaluate the images recorded by the camera 17, the images are transmitted to an evaluation unit. The evaluation unit can either be part of the measuring device 3 or an external evaluation unit which is connected to the measuring unit 3. In this case, the data transmission from the measuring unit 3 to the evaluation unit can be either wired or wireless. The results determined by the evaluation unit are transmitted to an output unit at which the data is output for further evaluation. Depending on the data collected, it can then be decided whether a renewed cleaning should be carried out, the perforated plate 1 can be used again in the process or should be replaced.

In addition to the structure shown here with a camera 17, it is also possible to provide a second camera, which is positioned in front of the laser 7 in the direction of movement. With the second camera, the holes for the detection of impurities can be analyzed. In this case, cleaning only has to be carried out if impurities have also been detected in the hole during the analysis for the detection of impurities. This avoids that a still clean hole is cleaned with the laser, whereby a possible damage to the perforated plate 1 by the laser can be prevented or at least delayed.

A sectional view through a perforated plate, as it is used, for example, in a reactor for drop polymerization for the preparation of poly (meth) acrylates and for the purification of which the device according to the invention is particularly suitable, is shown in FIG.

In order to produce sufficiently small droplets for droplet polymerization for the preparation of poly (meth) acrylates, it is necessary to use perforated plates 1 whose holes 1 1 on the side on which the monomer solution exits have a diameter at the narrowest point in the range of 50 to 500 pm, preferably in the range of 100 to 350 gm and in particular in the range of 150 to 250 pm.

So that the holes do not clog immediately by monomer solution, it is preferred if the length with the exit diameter is as short as possible. In order to achieve this, the holes 11 are preferably formed as shown in FIG. The holes 1 1 each have a cylindrical part 19 with a larger diameter, for example in the range of 1 to 5 mm, to which a conical part 21 connects, in which the diameter decreases to the outlet diameter. Experience has shown that the impurities form, in particular, in the conical region and in the region which has the exit diameter. The laser 7 in particular then measures and cleans the area with the exit diameter.

example

FIG. 3 shows a photograph of a contaminated hole in a perforated plate which has been used in a drop polymerization reactor for the production of poly (meth) acrylate as superabsorber.

As can be seen from the photo in FIG. 3, during the operation of the reactor, contaminants 9 form in the holes 11 of the perforated plate 1. Position of poly (meth) acrylates, the impurities arise, for example by caking on the walls or by a partial polymerization of the monomer solution. In this case, the impurities can also be formed if, by partial polymerization of the monomer solution in other parts of the system, particles or caking are produced, which are entrained by the flow of the monomer solution and then get stuck in hole 11 due to the small outlet diameter. The impurities cause the hole to clog and no monomer solution to escape.

To remove the impurities, an ultrashort pulse laser with a pulse duration of 10 ps and a power of 5 watts was used. By irradiation with the laser, the impurities could be removed from the hole 11. For the power used, a time of 60 s was required. The successful cleaning can be seen in the photo in Figure 4, in which no impurities are recognizable. In order to achieve a shorter cleaning time per hole with a large number of holes, it is possible to use lasers with a larger power and preferably other types of lasers. For example, faster cleaning can be achieved by using a higher power CO2 laser instead of an ultra-short pulse laser.

Claims

claims

1. A method for cleaning holes in perforated plates (1), comprising the following steps:

(a) if necessary, analysis of the holes (1 1) to detect the contamination

(B) removal of impurities with a laser (7) whose power is so large that impurities (9) from the holes (1 1) and from the surface of the perforated plate (1) at least in the region of the holes (1 1 ) evaporate and / or burn and the material of the perforated plate (1) remains undamaged,

(c) checking the cleaning effect of the step (b) and

(d) optionally repeating steps (b) and (c).

2. The method according to claim 1, characterized in that a laser table is used to clean the holes.

3. The method according to claim 1 or 2, characterized in that the laser (7) is a diode laser, an ultrashort pulse laser, a UV laser, an excimer laser or a CO2 laser.

4. The method according to any one of claims 1 to 3, characterized in that the laser (7) has a power in the range of 1 to 5000 watts.

5. The method according to any one of claims 1 to 4, characterized in that the laser beam (15) at the point of contact with the perforated plate (1) has a diameter which corresponds maximally to the diameter of the holes of the perforated plate.

6. The method according to any one of claims 1 to 5, characterized in that for the analysis of the holes in step (a) and / or for examining the cleaning effect, an image analysis is performed.

7. The method according to any one of claims 1 to 6, characterized in that step (b) is carried out at several holes simultaneously.

8. The method according to any one of claims 1 to 7, characterized in that at the same time at a first hole or a first group of holes step (a), at a second hole or a second group of holes step (b) and at a third hole or a third group of holes step (c) is performed.

9. The method according to any one of claims 6 to 8, characterized in that the light of the laser is used for illumination for the image analysis.

10. The method according to any one of claims 1 to 5, characterized in that for the analysis of the holes in step (a) and / or to test the cleaning effect, a measurement is carried out with a laser.

1 1. A method according to claim 10, characterized in that the laser, with which the cleaning in step (b) is performed, is used for the measurement.

12. The method according to claim 1 1, characterized in that the measurement and the cleaning are carried out simultaneously.

13. The method according to any one of claims 1 to 12, characterized in that the

Perforated plate (1) in the area of the laser (7) is subjected to compressed air during cleaning and measuring.

14. The method according to any one of claims 1 to 13, characterized in that residues are removed from the perforated plate (1) after irradiation with the laser (7) in a cleaning bath.

15. The method according to claim 14, characterized in that the cleaning bath is an ultrasonic bath.

16. The method according to any one of claims 1 to 15, characterized in that the holes (11) have along their axis a portion of decreasing diameter

17. The method according to any one of claims 1 to 16, characterized in that the

Perforated plate (1) is a perforated plate for distributing a monomer solution in a drop polymerization reactor for the production of powdery polymer.

18. The method according to claim 17, characterized in that the powdered polymer is a poly (meth) acrylate.