DE8700639U1 - Column for mass and/or heat exchange and for carrying out chemical reactions in cocurrent or countercurrent - Google Patents

Description

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Gebrüder Sulzer Aktiengesellschaft, Winterthur, Switzerland

Column for mass and/or heat exchange and for carrying out chemical reactions in cocurrent or countercurrent flow. -- &mdash;

The invention relates to a column for mass and/or heat exchange and for carrying out chemical reactions in cocurrent or countercurrent according to the preamble of patent claim 1.

Such columns with packing bodies with an ordered structure are known, for example, from Swiss patents 398 503, 627 263, 578 370, EP-PS 70 917 and DE-PS 25 22 106.

Furthermore, columns with such packing bodies are also described in the article "Liquid-liquid extraction in columns with regular packings" by R. Billet and J. Mackowiak in the journal "Verfahrenstechnik" 15 (1981) on pages 898 to 904.

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Packing bodies with an ordered structure are characterized by a particularly low flow resistance and a high empty volume fraction.

In multiphase flow, large-scale circulation flows can easily occur, particularly in extraction columns and gas-liquid/bubble columns, which lead to axial mixing of the phases and thus to a deterioration in mass and heat exchange. It should be noted that such circulation flows occur more frequently with larger column diameters and are difficult to control. In addition, the disperse phase flows through the packing bodies relatively unhindered and is insufficiently dispersed. The hold-up (volume fraction) of disperse phase is relatively low. This results in a smaller mass transfer area, since fewer and larger droplets are formed.

The invention is based on the object of improving the mass or heat exchange in processes as they relate to the invention compared to the known designs of columns without significantly reducing the load, regardless of the size of the columns.

This object is achieved according to the invention with the features specified in the characterizing part of claim 1.

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35

Although the invention is intended to include the formation of an intermediate plate with a single through-opening, an advantageous embodiment of the invention is that a number of through-openings can be arranged above the intermediate plate. The through-openings can be circular, slot-like, square or triangular, for example.

Furthermore, the openings can all have the same cross-section, e.g. with a diameter of 5 to 15 mm.

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However, it is also possible to provide passage openings of different shapes and dimensions in the intermediate plates. This can be used in particular when the throughputs of the disperse and continuous phases are very different. In this case, the phase with the smaller throughput will preferably flow through the smaller holes and the phase with the larger throughput will preferably flow through the larger holes. The area of the free cross-section formed by the passage openings is advantageously in the order of 40 to 60% of the plate cross-section, as can be proven experimentally.

15

In the following, surprising results and advantages of a column designed according to the invention compared to a known column with ordered packing bodies without intermediate plates or compared to a known sieve plate column are explained using the table below and a diagram shown in Fig. 1.

columns, Here all these extraction ^/< with the material

system toluene / acetone / water.

30

In these investigations, toluene was the disperse phase D, water the continuous phase C and acetone the component passing from the continuous phase to the disperse phase, i.e. mass transfer direction C-^D.

35

While the measured values for a column with packing bodies without intermediate plates and for a sieve plate column of Figure 3 from the article "Performance and cost comparison of various apparatus designs for liquid-liquid extraction" by J. Stichlms·ir in the journal Chemie-Ingenieur-Technik, 52nd year / Issue 3 / March 1980,

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The load range indicated in Fig. 3 and the sizes given in the table are experimentally determined values.

As can be seen from the table, Fig. 1 and from the magazine "German Chemical Engineering", Edition 3, 1984, page 182, with the material system mentioned and the mass transfer direction C ■> D, a column with packings chnG intermediate plates (SMV) only achieves a separation efficiency of approx. 0.8 to 1.0 separation stages/m (HETS = 1 to 1.25 m ) at a maximum loading of approx. 90 (m ³ /m ² h).

Surprisingly, it has now been shown that by installing the intermediate plates according to the invention, the number of separation stages/m increases to 3 to 4 (HETS = 0.25 to 0.3 m ) and the maximum load B _m "
(see table and Fig. 1 (SMV Z)).

only to approx. 60 to 70 (m /m h)

20

This result is surprising and unpredictable compared to the assumptions based on the state of the art.

25

For example, in a sieve plate column for systems with high interfacial tension, the hole diameters of the sieve plates should not exceed 2 mm with a free cross-section formed by the totality of the holes of approx. 5% of the sieve plate cross-section (cf. the magazine "Chemie-Ingenieur-Technik", 57 (1985) No. 7, pp. 567 to 581).

The maximum load for these known installations is

3 2 (SE in Fig. 1) also only at 30 to 45 (m /m h) and the height of a theoretical separation stage (HETS) is also 1 to 1.25 m (cf. the magazine "Chemie-Ingenieur-Technik", 52 (1980), No. 3, pages 253 to 255 or Fig. 1).

A common parameter for characterizing the performance of an extraction column is the residence time

Characteristic value

HETS

min B

Max

As can be deduced from the diagram shown in Fig. 1, (y · approx. 72 (s) for a sieve plate column, approx. 40 (s) for a column with ordered packing bodies without intermediate plates, but only 18 (s) for a column designed according to the invention, whereby all measured values apply to an extraction factor e = 1.

As a consequence of the measured values given above, it can be seen that the volume of a column designed according to the invention can be reduced by a factor of approximately 4 compared to a known sieve plate column and by more than a factor compared to a column with ordered packings without intermediate plates.

In addition, a column designed according to the invention can be cascaded (dividing the column into separate sections according to the plate spacing or the packing layer height). This suppresses axial mixing effects and circulation flows.

Backmixing effects are known to be recorded by the Bodenstein number Bo. If large Bodenstein numbers are achieved, this means that only small amounts of backmixing are present. Measurements in a column with a diameter of 0.8 m and a height of 5 m with a water/air system, where air is the disperse phase, have shown that the Bodenstein number / m (column length / Bo) in a column with ordered packing without intermediate plates is 1.6 and in a column with intermediate plates it is approx. 3.

The increase in the

Separation performance can be explained by the fact that a coalescence layer of the disperse phase appears to form in an ordered packing below or above an intermediate plate with subsequent redispersion in the adjacent packing layer.

10

To prevent undesirable edge penetration, an advantageous development of the invention consists in that the individual intermediate plates are sealed in their edge area against the casing tube of the column. Embodiments of this seal are described in the characteristics of claims 8 and 9.

Although the above considerations and examples are directed in particular at extraction columns, the invention can also be applied to columns in which, for example, rectification or absorption processes take place. In these processes, as is known, there are two continuous phases in the mass transfer. The downward-flowing liquid film is dammed and local bubbling areas with very intensive mass transfer are formed.

The invention also includes columns with packing layers consisting of random packings (e.g. Raschig rings). However, the application according to the invention to columns in which the packing layers each consist of at least one packing body with an ordered structure, e.g. as described and shown in the patent documents cited in the introduction, is particularly advantageous. In such packing bodies, a pronounced cross-mixing component occurs during operation.

While in sieve tray columns, an uneven distribution of the phases over the column cross-section can develop in the empty sections between the sieve trays during operation, as well as a pronounced circulation flow,

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This is avoided in a column according to the invention, which in itself consists of a combination of the features of columns with packing layers and of columns with sieve bottoms with free spaces. 5

The invention is explained below using embodiments shown in the drawing.

Pig. 2 shows the elevation of an extraction column with ordered packings and intermediate plates, which are inserted between successive packing bodies.

Fig. 3 to 5 show examples of the design of intermediate plates and

Fig. 6 to 9 show different embodiments of sealing the sieve tray with the jacket tube of a column.

The extraction column 1 shown schematically in Fig. 2 has in its upper and lower parts feed nozzles 2 and 3 for a continuous phase C and a disperse phase D. In the exchange part, packing bodies 4 with an ordered structure, as described and shown for example in the patent documents mentioned at the beginning, are arranged. Perforated intermediate plates 5 are arranged between the packing bodies 4 according to the invention.

Fig. 3 shows a schematic representation of an intermediate plate 6, which, as can be seen in detail in Fig. 3a, is provided with holes of the same size 7 in a uniform distribution,

Fig. 4 shows an intermediate plate 8 which is provided with larger and smaller holes 9 and 10.

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Fig. 5 shows an intermediate plate 12 provided with a central opening 11.

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10

Fig. 6 and 6a show a perforated intermediate plate 13 arranged above a packing body 4, between which and the casing tube 1 of a column a slotted ring 14 is arranged for sealing. The ring 14 can be made of sheet metal, plastic or wire mesh, for example. The slotted ring elements 15, 16 are bent inwards, 15 and outwards, IS, like flaps for sealing.

15

Fig. 7 to 9 show further variants for sealing with the column wall 1. 3o For sealing in Fig. 7, the intermediate plate 15' is bent up in the shape of a collar in its edge region, whereby this seal could also be designed as a separate, collar-like element which is connected to the intermediate plate 15 ^' .

Fig. 8 and 9 each show two different embodiments of a seal.

25

According to Fig. 8 on the right, the intermediate plate 16 is brought up to the jacket pipe wall 1, whereby a ring 17 consisting of an elastic material is pressed against the jacket pipe wall by means of an element 18.

30

In Fig. 8 on the left, the plate 16" has fork-like bends 18' in its edge area, which press a hose 19 made of an elastic material against the casing pipe wall.

35

Fig. 9 right and left show variant seals in which a plate 20 or 20" is sealed with the casing pipe wall 1 by means of a slotted hose or thin pipe 21 or 22.

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Table

Extraction factor e = 1

only ordered
Packing body
H = 5 m ordered
Packing body
and Between
plates
H = 15 m n _t ( - J C ■&diams; D C * D HETS ( m ) 5 j
50 B _m=v (m / 2 _U )
max m &eegr; 1/0 0.3 \~j · ( S ) 90 60 40 18

= Number of theoretical plates

Max
where

Max
S'

Height of a theoretical separation stage maximum load of both phases together,

T d

Max

= volume flow of solvent&mdash;■r&mdash; ) = volume flow of receiver ( = column diameter ( m )

= minimum residence time per separation stage ( s )

NTSM = Theoretical number of separation stages/m B = load (m ³ /m ² h) SE = Sieve tray column SMV ⁼ Column with packing bodies

SMVZ ⁼ Column with packing bodies and intermediate plates

Claims (9)

Expectations 1. Column for mass and/or heat exchange and for carrying out chemical reactions in cocurrent or countercurrent, wherein at least one of the substances brought into contact with one another is dispersed, wherein the column has a jacket tube, 5 in which at least two packing layers are arranged, and wherein the packing layers preferably consist of packing bodies with an ordered structure of layers which are formed from guide surfaces, such that flow channels are formed which are inclined against the jacket tube axis, wherein the flow channels of adjacent layers cross each other, characterized in that between the packing layers (4) intermediate plates (5, 6, 3, 12, 13, 15', 16', 16", 2o, 2&ogr; ¹ ) with at least one passage opening (7, 9, 1o, 11) covering the column cross-section are loosely inserted. 2. Column according to claim 1, characterized in that above the intermediate plate (5, 6, 8, 13, 15', 16', 16", 2o, 2o') a number of passage openings (7, 9, 1o) are arranged distributed. 3. Column according to claim 2, characterized in that the passage openings (7, 9, 10) have a diameter of 5 to 15 mm. 4. Column according to claim 2, characterized in that the passage openings (7) have the same cross-section. 5. Column according to claim 2, characterized in that the passage openings (9, 1o) have different cross-sections. 6. Column according to claim 2, characterized in that the passage openings (7, 9, 10, 11) are designed as circular holes, slots, squares or triangles. 7. Column according to claim 1 and 3, characterized in that the free cross section formed by all the passage openings (7, 9, 10, 11) is 4o to 6o? of the plate cross section. 8. Column according to claim 1, characterized in that the intermediate plates (13, 15') have bent flaps or collars (15, 16) in their edge region for sealing with the jacket tube wall. 9. Column according to claim ?, characterized in that in the edge region of the intermediate plates (16 ¹ , 16", 2o, 2o ·) a sealing ring (17, 19, 21, 22) is inserted for sealing with the jacket tube wall (1).