WO2013182268A1

WO2013182268A1 - Scrubber column and method for scrubbing a raw gas

Info

Publication number: WO2013182268A1
Application number: PCT/EP2013/001419
Authority: WO
Inventors: Gerhard Alzner; Manh-Hung Nguyen
Original assignee: Linde Aktiengesellschaft
Priority date: 2012-06-06
Filing date: 2013-05-14
Publication date: 2013-12-12
Also published as: DE102012011329A1

Abstract

Scrubber column for scrubbing a raw gas containing C₂H₂ using a scrubbing agent comprising DMF for removing C₂H₂ from said raw gas, comprising: a first tray (10) for receiving the scrubbing agent (W), wherein multiple flues (11) extend from the first tray (10) and are respectively covered over by an assigned cap (12) such that, together with the respectively assigned cap (12), the respective flue (11) defines a through-opening (D) in the first tray (10) that is designed to introduce raw gas (G) from an underside (U) of the first tray (10) through the first tray (10) into scrubbing agent (W) located on the first tray (10). According to the invention, each free peripheral end region (111) of the flues (11) protrudes into the respectively assigned cap (12). The invention also relates to a method for scrubbing a raw gas (G) using a DMF-containing scrubbing agent (W) for the removal of acetylene (C₂H₂).

Description

description

Washing column and process for washing a raw gas

The invention relates to a wash column according to the preamble of claim 1 and a method for washing a raw gas with a N, N-dimethylformamide ((CH ₃ ) ₂ N-CHO or C ₃ H ₇ NO, DMF short) containing detergent to C ₂ H ₂ to remove from the raw gas.

Such a washing column forms e.g. a part of an acetylene recovery plant (ARU), which can be integrated, for example, in an ethylene recovery plant. Such wash columns have at least one first floor

Receiving or accumulating in the wash column initiated detergent, wherein depart from the first floor several chimneys, which are each roofed by an associated bell. The said bells each form a downwardly facing opening or downwardly open curvature, which is bounded by a bell edge. The chimneys further form together with their bells each have a through opening of the first floor, through which raw gas from an underside of the first floor forth through the first floor can be introduced into stationary on the first floor detergent, so that the raw gas in phase contact with the detergent can occur. Here, acetylene in the raw gas is dissolved in the detergent (DMF).

However, scrubbing for C ₂ H ₂ removal from a crude gas by DMF tends to foam. Such foaming tendency can be counteracted, for example, by bottoms (flat-bubble trays) equipped with Linde flat bells, in which the chimneys each end with their upper peripheral free ends below the bell rim of the respective associated bell. The chimneys are in particular comparatively short (so-called chimney stump). Such flat bells are described in detail, for example, in "Linde Reports from Technology and Science No. 28/1970 and 15/1970".

At low gas load, however, as may be the case, for example, when starting up an (ethylene) plant, the abovementioned flat-bubble trays tend to be activated when the detergent is activated (DMF) cycle to rain through, leaving the head above the column

withdrawn raw gas is not yet released to the desired extent contained therein C ₂ H ₂ and must be flared accordingly. This means a loss of the product to be produced ethylene.

On this basis, the object of the present invention is therefore to provide a scrubbing column and a method for scrubbing a raw gas, which counteracts the aforementioned disadvantage. This problem is solved by a washing column having the features of claim 1.

Thereafter, it is provided that the chimneys are each with a free circumferential (upper) end portion in the respective associated bell in, ie, the chimneys are each along a perpendicular to the first floor extending longitudinal axis of the wash column from the first floor, with one along the longitudinal axis uppermost peripheral edge of the respective chimney is arranged along said longitudinal axis above the respective bell edge. Such a chimney bell configuration is also referred to as a chimney bell. In the case of an intended state of the washing column, said longitudinal axis preferably runs along the vertical (that is, the individual bottoms of the washing column preferably extend horizontally).

With the use of such Kaminhalsglocken can be a forced contact between the gaseous phase (raw gas) and the liquid during the start-up

Phase (detergent) are generated because such Kaminhalsglocken tend to rain rather than the said flat bells. This will be the

Crude gas with sufficient advantage also during start-up washed sufficiently and the said overhead gas is sufficiently free of acetylene, the subsequent process without (ethylene) loss can be further supplied and must not be flared accordingly.

Of course, according to another embodiment, the wash column may be a

Have a plurality of said equipped with chimney cowls first floors, along the longitudinal axis (cylinder axis) of the washing column or a jacket of the Washing column are arranged one above the other in a jacket space surrounding the jacket. For damming the detergent, which is preferably introduced into the column in an upper region (head) of the column, so that it can act on the individual (first) soils, the individual (first) floors have weirs, via which the detergent through downcomers the soil can flow to underlying soil. The raw gas is introduced into the jacket space in a lower region of the wash column or of the jacket of the wash column and passes in countercurrent to the detergent (from bottom to top) through the passage openings of the (first) bottoms, so that a phase contact between the raw gas and the the individual (first) floors befindlichem detergent is prepared, wherein C ₂ H _{2 is dissolved} in the detergent (DMF), so that at the top of the column, the purified from C ₂ H ₂ raw gas can be withdrawn, while the loaded detergent from the bottom of the Pulled off wash column and can be fed to a regeneration. In a variant of the invention, in addition to the at least one first floor

(At least) provided below or above the first floor second floor provided, which is formed in contrast to the first floor with flat bells. That is, from the said second floor turn off several chimneys, which are each roofed by an associated bell, so that the respective chimney defines together with the respective bell associated with a through hole of the second bottom, which is adapted to raw gas from a bottom of the second bottom through forth in the second floor through standing detergent in the second floor, so that the raw gas can come into phase contact with the detergent, wherein the chimneys respectively along the perpendicular to the second bottom extending longitudinal axis of the wash column depart from the second bottom, and a top edge along the longitudinal axis of the respective chimney is arranged below a bell edge of the respective associated bell. That is, the respective fireplace is - unlike the chimney cowbells described above - not in the respective associated bell or is not of the said

Bell ring embraced. Rather, viewed perpendicular to the longitudinal axis a

Gap between the top (circumferential) edge of the chimney and the bell edge.

Preferably, the chimneys of the second floor along said

Longitudinal axis a shorter length than the chimneys of the first floor. The chimneys of the second floor are therefore also referred to as Kaminstümmel, the Length of that stump stump may be smaller than the extent of the associated bells from the bell rim to the bell tip (along said longitudinal axis). Furthermore, the chimneys of the second floor preferably each have in a along the longitudinal axis extending cross section (viewed from the outside) a concave curvature (ie, a concave curved surface line), so that the respective fireplace upwards, ie, away from the associated second floor , rejuvenated. In order to keep the pressure loss dP across the bottoms of the wash column as low as possible (in the case of several soils), in one embodiment of the invention

provided that the first floors (chimney neck cap trays) and the second trays (flat bubble-cap trays) alternate with each other, because the pressure loss dP _F iachgiocken via a second ground is less than the pressure drop dP _Ka minhaisgiocken via a first floor. In this case, the washing capacity of half the number of plates (1/2 tray forced contact, 1/2 soils through rain) due to the reduced Auswaschnutwendigkeit in

Starting operation (low gas, less pollutants, less necessary power) advantageously sufficient. Concerning the chimney cowls of the first floors, it is provided according to a variant of the invention that the chimneys of the first floor associated bells each have a circumferential bell edge, wherein the respective bell at its bell edge a plurality of slit-shaped, along the

Having longitudinal axis oriented recesses (cutouts).

Alternatively, however, the bell rim of the respective bell may also have a circular course without such recesses, so that there is a circumferential gap between the bell rim and the first floor from which the chimney associated with the chimney exits.

In the event that the bells have said slot-shaped recesses, it may further be provided that edge portions of the

Glockrandes, each between two adjacent slot-shaped

Recesses extend (so to speak, along the longitudinal axis considered forming the lowest edge portions of the bell edge) to the respective first Floor, from which the respective bell associated chimney, are pulled down. In this case, therefore, there is no continuous circumferential gap between the bell rim and said first floor. Alternatively, those between two adjacent slot-shaped

Recesses extending edge portions of the respective bell edge along the longitudinal axis spaced to be arranged to the respective first floor. In this case, there is a circumferential gap between said first floor and the bell rim of the respective bell.

Finally, of course, there is also the possibility that all floors of the

Washing column, through which the raw gas is passed, are formed as first floors, ie, from each of the first floors go from several chimneys, each of which is covered by an associated bell, so that the respective fireplace together with the respective bell associated with a passage opening of the defined respective first soil, which is adapted to raw gas from one

Underside of the respective first floor forth through the respective first floor through in standing on the respective first floor detergent, said chimneys are each with a free circumferential end portion in the respective associated bell inside.

Preferably, the lowest bottom of the wash column is always a first bottom. Furthermore, the problem of the invention by a method for washing a C ₂ H ₂ -containing raw gas with a DMF having detergent for removing C ₂ H ₂ from that raw gas having the features of claim 8 is achieved.

Thereafter, the inventive method comprises the steps of: loading a first floor (and possibly other floors) with said detergent, and

Passing raw gas through formed in the first bottom

Through openings, which are each formed by a projecting from the first floor fireplace and the respective fireplace roofing bell, the respective chimney is with a free circumferential end portion in the respective associated bell into it, so that that raw gas in phase contact with on the first floor befindliches detergent occurs and contained in the crude gas C ₂ H _{2 is dissolved} in the detergent.

To carry out the process according to the invention, in particular the device according to the invention (washing column) can be used.

In a variant of the method according to the invention, it is provided that the raw gas before or after passing through those through holes of the first floor is passed through through holes of a second floor (which is disposed below or above the first floor), so that that raw gas in phase contact with on the second floor befindliches detergent occurs and dissolved in the crude gas C ₂ H _{2 is dissolved} in the detergent, wherein the

Through openings of the second floor are each formed by a projecting from the second floor fireplace and the respective fireplace roofing bell, the chimneys respectively along the said longitudinal axis of the wash column depart from the second floor, and along the longitudinal axis of the uppermost peripheral edge of the respective fireplace along the longitudinal axis is arranged below a bell edge of the respective associated bell (Linde flat bell). Preferably, the crude gas (see above) for the dissolution of C ₂ H _{2 is} alternately passed through first floors (chimney cowl plates) or through the through holes and second floors (flat bubble trays) or through their through holes, on the one hand to reduce rainfall and on the other hand, the pressure drop to decrease (see above).

Of course, there is also the possibility that only first trays are used, that is, the raw gas is only passed through chimney cowls from bottom to top through the (first) trays (see above). Preferably, the lowest bottom of the scrubbing column, through which raw gas is directed upwards, is always around a first tray.

As a result, the solution according to the invention has the advantages that a tendency of the wash column to rain through can be reduced by using chimney cowl floors. At the same time, furthermore Pressure losses through the use of alternating soil types (see above) are lowered. The flat bells used for this purpose are also cheaper. This allows the production of a head gas (of crude gas purified from C ₂ H ₂ ) which satisfies the desired specification, in particular already when starting the washing column or the ethylene plant. Therefore, no off-spec head gas must be flared, which reduces product losses (ethylene).

Further details and advantages of the invention will be explained by the following description of exemplary embodiments with reference to the figures.

Show it:

Fig. 1 is a schematic sectional view of an inventive

Washing column;

2 - 5 alternative embodiments of shaft walls of the in the figure 1

shown washing column; 6 shows a chimney with a bell arranged above it (Linde flat bell);

Fig. 7 is a side view of a chimney cowl;

FIG. 8 is a perspective view of the chimney cowl of FIG. 7; FIG.

9 shows a sectional view of the chimney cowl according to FIGS. 7 and 8;

Fig. 10 is a side view of another chimney bell with a smooth edge; Fig. 1 1 is a perspective view of the chimney cowl of FIG. 10;

FIG. 12 is a sectional view of the chimney cowl according to FIGS. 10 and 11;

Fig. 13 is a side view of another chimney bell with serrated

Edge; a perspective view of the chimney cowl of FIG. 13; a sectional view of the chimney cowl according to Figures 13 and 14; and

Fig. 16 are schematic representations of different recesses of

Fireplace neck bells. FIG. 1 shows a scrubbing column 1 which has a jacket 2 extending along a longitudinal axis L, wherein the longitudinal axis L runs along the vertical Z relative to a state of the scrubbing column 1 arranged as intended. The jacket 2 of the washing column 1 defines a jacket space in which along the

Longitudinal axis L alternately first and second bottoms 10, 20 are arranged one above the other. In the figure 1 are exemplarily a first floor 10 and one below

arranged second bottom 20 shown (the order may also be reversed). Preferably, the lowermost tray in the wash column 1 is formed as a first bottom 10 (chimney cowl bottom). The bottoms 10, 20 each extend over at least part of the cross section of the jacket space perpendicular to the longitudinal axis L of the wash column 1 and serve to accumulate a DMF containing

Detergent W, which is fed in the region of the head 1 of the washing column 1 in the shell space and the bottoms 10, 20 acted upon from above. The individual floors 10, 20 may each have at least one weir 5, 6, so that the

Detergent W at the respective weir 5, 6 accumulate and can flow through the weir 5, 6 through an adjacent downcomer shaft 3, 4 arranged underneath floors 10, 20. According to Figure 1, said downcomers have an angle

Shaft walls 3a, 4a, so that the respective downcomer 3, 4 tapers towards the bottom. Alternative shapes of downcomers are shown in FIGS. 2 to 5 by way of example with reference to the downcomer 4. After that, the

Shaft walls 4a according to Figure 2 be formed offset (the shaft wall 4a has a step on a lower portion, so that the downcomer 4 tapers). According to FIG. 3, the respective shaft wall 4a can run straight downwards. According to FIG. 4, the downcomer can furthermore be designed as a "truncated downcomer", the downcomer 4 being bounded at the bottom by a shaft bottom 7a, which defines a gap with the shaft wall 4a, through which it passes the detergent W can escape from the downcomer 4, wherein from the shaft bottom 7a an overflow weir 7b goes upwards, which is arranged in front of that gap and this projects beyond the top ("seal pan"). Finally, the downcomer 4 according to FIG. 5 can be designed as a "truncated downcomer" with outlet openings 4c. That is, the downcomer 4 is down through a

Shaft bottom 4b closed, in which the said outlet openings 4c are formed. These may e.g. be round, square or oval, etc. formed.

In countercurrent to the detergent W, a crude gas G containing C ₂ H ₂ is introduced into the scrubbing column 1, which is formed by at the bottoms 10, 20

Through openings D, D 'in the mantle space of the washing column 1 flows upwards and is in each case introduced into the standing on the respective bottom 10, 20 detergent W. In this case, C ₂ H ₂ in the detergent W due to DMF in solution and accumulates in the raw gas G accordingly. The purified from C ₂ H ₂ crude gas G can then be withdrawn as overhead from the wash column 1.

In particular, at low gas load, as e.g. during the startup of an (ethylene) plant is the case to prevent rainfall of at least some soils, the column 1 according to the invention first floors 10, whose

Through holes D are as so-called chimney cowls 1 1, 12 are equipped, ie, the first floors 10 have a plurality of chimneys 1 1, which along the longitudinal axis L of the first floors 10 (upwards) depart, said chimneys 1 1 with a upper circumferential free end portion 1 1 1 in the respective, the

relevant fireplace 11 roofing bell 12 protrude so that an upper peripheral edge 110 of the respective chimney 1 1 along the longitudinal axis L above a bell edge 120 of the respective associated bell 12 is arranged.

In order to additionally keep the pressure loss in the wash column 1 low, first and second plates 10, 20 are alternately arranged in the wash column 1 one above the other, the second plates 20 using flat bells 21, 22. Although flat bells 21, 22 tend to rain through in the start-up phase described above, this can be compensated to a sufficient extent by the first bottoms 10. Preferably, the same number of first and second bottoms 10, 20 are used. According to FIG. 6, in the case of the second trays 20, the chimneys 21 leaving the second trays 20 along the longitudinal axis L lie with their upper peripheral edge 210 below the bell rim 220 of the respective roofing bell 22, so that, as seen from the side, a distance A between the trays said upper

surrounding edge 210 of the respective chimney 21 and the bell edge 220 of the respective associated bell 22 consists. Furthermore, the outgoing along the longitudinal axis L chimneys 21 of the second bottoms 20 are significantly shorter along the

In addition, the chimneys 21 of the second floors 20 have with respect to the chimneys 1 1 of the first floors 10, which are preferably formed hollow cylindrical, a circumferential wall with a concave cross-section curvature (surface line) so that the chimneys 21 of the second bottoms 20 taper upwards (along the longitudinal axis L). The bells 22 of the chimneys 21 of the second floors 20 may further along the said longitudinal axis L have a greater extent (from the bell edge 220 to the bell tip 222) as the chimneys 21 of the second floors along the longitudinal axis L. Further, the bell 22 of the second floor 20 may be connected to the respective second floor 20 via webs 40 protruding from the bell edge 220. Various configurations for chimneys 11 and bells 12 of the first floors 10 (chimney cowl bottoms 1 1, 12) are shown in FIGS. 7 to 15. According to FIGS. 7 to 9, the chimneys 1 1 emerging from the first floors 10 are respectively roofed over by an associated bell (chimney hood) 12 or

each having a plurality of slot-shaped recesses 13 at a lower bell edge 120, via which the respective bell 12 rests on the associated first floor 10, whose upper edges 131 each have a distance A from the longitudinal axis L to a circumferential upper edge 10 each roofed fireplace 1 1 have. Preferably, the distance A or the length H of the chimneys 1 1 along the longitudinal axis L is dimensioned (length between about 30-150 mm), that after correct dimensioning of the weirs 5, 6 (this example, both in the first and the second bottoms 10, 20 be 50mm high) a forced guidance of the gaseous phase (raw gas) G through the liquid phase

(Detergent) W takes place. As an alternative to the gas slots 13, according to FIGS. 10 to 12, the circumferential bell rim 120 may be circular and spaced along the longitudinal axis L relative to the associated bottom 10, resulting in a circumferential gap passing through the bell rim 120 and the associated first floor 10 is limited. The gap has along the longitudinal axis L a height H 'above said first floor 10, wherein the bell edge 120 along the longitudinal axis L has a distance A to the upper peripheral edge 1 10 of the associated chimney 1 1. Preferably, the distance A or the length of the chimneys 1 1 along the longitudinal axis L in turn so dimensioned (length between about 30-150mm) that, if possible, an overlap of said gap with the liquid phase W after correct dimensioning of the weirs 5, 6 is ensured.

According to FIGS. 13 to 15, the bells 12 according to FIGS. 3 to 5 may be formed, wherein additionally the edge portions 131 of the bell rim 120 extended between two recesses 13 are spaced along the longitudinal axis L to the associated first bottom 10, so that in addition a peripheral gap between the bell rim 120 and said first floor 10 results. The bell rim 120 then has correspondingly a stepped (jagged) course. In this case, the slot-shaped recesses 13 along the

Longitudinal axis L a height H ", whereas the upper edges 130 of the recesses 13 also have a height H '+ H" above the associated first floor 10. Again, the distance A between the upper edges 130 and the upper peripheral edge 110 of the associated chimney 1 1 is preferably dimensioned so that the above-described forced operation of the gaseous phase G is ensured by the liquid phase W.

Finally, the slot-shaped recesses 13 can assume any geometric shape or contour. FIG. 16 shows some possible examples

Configurations. Thereafter, the recesses 13 may be formed as rounded slots (Figure 16, left) or have a semi-circular contour (Figure 16, center left). Furthermore, the recesses 13 can have obliquely upwardly extending edges (FIG. 16, middle right) or simply rectangular (FIG. 16, right). LIST OF REFERENCE NUMBERS

1 wash column

2 coat

3, 4 downcomer

3a, 4a shaft wall

4b shaft bottom

4c outlet openings

7a shaft floor

7b overflow weir

5, 6 weir

10 First floor

11 fireplace

12 bell

13 recess

20 Second floor

21 fireplace

22 bell

40 footbridge

110 Upper peripheral edge

111 Free surrounding edge area

120 bell edge

130 upper edge

131 edge section

210 Upper peripheral edge

220 bell edge

222 bell tip

L longitudinal axis

U bottom

U 'bottom

Z vertical

Claims

Patent claims

Washing column for washing a raw gas containing C ₂ H ₂ with a washing agent containing DMF for removing C ₂ H ₂ from that raw gas, with:

- a first floor (10) for holding the detergent (W), with several chimneys (11) extending from the first floor (10), each of which is covered by an assigned bell (12), so that the respective chimney (11) together with the respectively assigned bell (12), a through opening (D) of the first base (10) is defined, which is designed to allow raw gas (G) from an underside (U) of the first base (10) through the first base (10 ) through to introduce detergent (W) standing on the first floor (10), characterized in that the chimneys (11) each have a free circumferential end region (111) in the respectively assigned bell (12).

Washing column according to claim 1, characterized in that a second tray (20) arranged below or above the first tray (10) is provided for receiving said detergent (W), with several chimneys (21) from the second tray (20). go off, which are each covered by an assigned bell (22), so that the respective chimney (21) together with the respective assigned bell (22) defines a through opening (D ¹ ) of the second floor (20), which is designed to To introduce raw gas (G) from an underside (U') of the second base (20) through the second base (20) into detergent (W) standing on the second base (20), the chimneys (21) each running along one The longitudinal axis (L) of the washing column (W) extending perpendicular to the second tray (20) extends from the second tray (20), with an uppermost circumferential edge (210) of the respective chimney (21) along the longitudinal axis (L) along the longitudinal axis ( L) is arranged below a bell edge (220) of the respectively assigned bell (22).

3. Washing column according to claim 2, characterized in that the chimneys (1 1) of the first tray (10) and the chimneys (21) of the second tray (20) each run along the longitudinal axis (10) running perpendicular to the trays (10, 20). L) protrude from the respective floor (10, 20), the chimneys (21) of the second floor (20) having a shorter length (H) along the longitudinal axis (L) than that

Chimneys (1 1 ) of the first floor (10).

4. Washing column according to one of claims 2 to 3, characterized in that the chimneys (21) extending from the second floor (20) taper along the longitudinal axis (L).

5. Washing column according to one of claims 2 to 4, characterized in that the washing column (1) has a plurality of first and second trays (10, 20) which are arranged one above the other, with the first and second trays (10, 20) alternating one another .

6. Washing column according to one of the preceding claims, characterized

characterized in that the chimneys (1 1) of the first floor (10)

assigned bells (12) each have a circumferential bell edge (120), the respective bell (12) having one on its bell edge (120).

Has a plurality of slot-shaped recesses (13), or wherein the bell edge (120) runs around the associated chimney (1 1) in a circle.

7. Washing column according to claim 6, characterized in that the respective bell (12) runs between adjacent recesses (13).

Edge sections (131) of the bell rim (120) are pulled down to the first floor (10) or those edge sections (131) are arranged at a distance from the first floor (10).

8. Washing column according to one of the preceding claims, characterized

characterized in that a lowest tray of the washing column (1) is a first tray (20).

9. Washing column according to claim 1, characterized in that the

Washing column has several trays, all trays of the washing column being designed as first trays (10).

10. Process for washing a raw gas containing C ₂ H ₂ with a DMF

having washing agent for removing C ₂ H ₂ from that raw gas, in particular using a washing column according to one of

preceding claims, comprising the steps: - loading a first tray (10) of a washing column (1) with the

said detergent (W),

- Passing C ₂ H ₂ -containing raw gas (G) through through openings (D) formed in the first floor (10), each of which passes through a chimney (1 1) projecting from the first floor (10) and the respective chimney (1 1 ) roofing bell (12) are formed, the respective chimney (1 1) with a free circumferential edge area (11 1) standing into the respectively assigned bell (12), so that that raw gas (G) is in phase contact with on the first Detergent (W) located in the bottom (10) occurs and C ₂ H ₂ contained in the raw gas (G) is dissolved in the detergent (W).

1 1. The method according to claim 10, characterized in that the raw gas (G) before or after passing through those through openings (D) of the first tray (10) through through openings (D ') of a second tray (20) of the washing column (1 ) is passed through, so that that raw gas (G) in

Phase contact with detergent (W) located on the second base (20) occurs and C ₂ H ₂ contained in the raw gas (G) is dissolved in the detergent (W), with those through openings (D ') of the second base (20) each passing through one a chimney (21) projecting from the second floor (20) and a bell (22) covering the respective chimney (21) are formed, the chimneys (21) each extending along a longitudinal axis (L) running perpendicular to the second floor (20). second floor (20), with an uppermost circumferential edge (210) of the respective chimney (21) along the longitudinal axis (L) below one

Bell edge (220) of the respectively assigned bell (22) is arranged.

12. The method according to claim 1 1, characterized in that the raw gas (G) is passed alternately through first and second trays (10, 20).

13. The method according to claim 12, characterized in that a lowest tray of the washing column (1) is a first tray (10).

14. The method according to claim 10, characterized in that C ₂ H ₂ -containing

Raw gas (G) is passed through several trays of the washing column (1), all trays of the washing column (1) being designed as first trays (10).