Note: Descriptions are shown in the official language in which they were submitted.
26~ .
The present invention relates ~o an apparatus for ex-
changing material between a downwarclly flowlng liquid and an up-
wardly flowing gas counterflow to the liquid. The conditions of
the exchange of material for which the apparatus according to
the present inven~ion is par~icularly suitable will be described
hereinafter.
When the solubility of a gas, participating in the ex-
change of material, is low in a liquid also participating in the
exchange of material and ~urther when the exchange of material
depends on a chemical reaction or on an isotope reaction in the
liquid phase and the kinetics of this reaction are slow as compar-
ed with the kinetics of the exchange of material of a dissolved
~as with the gas phase, then a lony residence time of the liquid
in contact with the gas is required. This can be attained at a
favourable cost when as large a proportion as possible of the
column volume is used for the liquid. Furthermore when process
conditions require the use of several trays, then they should be
disposed in as small a number of pressure vessels as possible
- while counterflow must be maintained and remixing flows must be
avoided.
Material-exchange columns whose trays ~re superposed in
a pressure vessel are known. In such a case the liquid ~lows
from one tray via an overflow to the next lower tray. The over-
~low is disposed in the gas cha,mber and is filled with liquid
merely in the lowest region of the seal. Because of the hydro-
dynamic conditions only approximately one quarter of the distance
betwee~ the trays, ill which the liquid i5 in contact with the
gas bubbles, can be used in these columns as the contact space.
Columns in wh:ich the liquid flows downwardly,primarily
on the surface of packings, agalnst the gas ~low through the in-
terstices of these packings are also known~ The proportion of
volume filled with liquid in the columns is even substantially
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"~ smaller than that in the Eirst case. Columns which are filled
almost completely with liquid and in which the gas to be contacted
wit.h this li.quid flows upwardly in -the form of bubbles are also
known.
The liquid is mixed in many dirèc-tions so that this
kind of column can at best satisfy only the function of a single
theoretical. tray.
Finally columns are known in which machines having a
mechanical, electric or an intensified hydraulic drive for inten-
sifying the exchange of material are known. In the last mentionedcase this occurs when the pressure drop on the gas side exceeds
the available hydros-ta-tic pressure of the liquid and pumps must
be used between -the trays in order -to convey the liquid. How-
ever, these types of columns are -too costly to acquire and main-
tain. Furthermore, in oprera-tion they can cause long interrup-
tions due to their susceptibi.lity to trouble.
Accordi.ng to the presen-t invention there is provided
an apparatus for exchanging material between a downwardly flowing
liquid and an upwarding flowiny gas counterflow to said liquid,
comprising a plurali-ty of perfora-ted trays superposed in a pres-
sure vessel, comprising connecting ducts for passing the liquid
to a next. lower -tray, the path of the li~uid at the end of said
connecting ducts being arranged to be directed upwardly to prevent
an undesired inflow of gas at said .end of the connec-ting ducts,
said connecting ducts being disposed in the region of the axis
o~ said pressure vessel. Suitably said connecting ducts comprise
a pair of semicircular surfaces extending around the axis of said
pressure vessel, said semicircular surfaces alternately connec-ting
two adjacent trays. Desirably the liquid pa-th from an ou-tlet
from said connec-ti.ng duct, which passes the liquid on from a next
iligher tray, to the inl.et in said connecting duct, whi.ch removes
the liquid to a next lowe~ tray, extends via concentrically dis-
posect and ~,e.ries-connected semi-cylindrical chambers and sai~
]:iquid path e~tends first from the region of said axis of -the
pressure vessel in the direction of the walls oE sa:id pressure
vessel and then in -the opposite direc-tion. Preferably the space
in which the liquid is in contact with -the gas bubbles is filled
with fine-mesh gauze wire.
The present invention also provides a tray for use in
such apparatus which comprises a perforated base; an inner con-
centric part acting as a connecting duc-t, with a connectiny inlet
tube for leading the liquid from an upstream tray to said -tray,
concentrically disposed and series-connec-ted semi-cylindrical
chambers formed by metal walls, an opening in said tray which is
the outle-t fox a connecting inle-t tube -to a downstream tray, the
metal wall, on the side of said opening, being lower than on the
side of the connecting inlet tube from the upstream tray, so tha-t
the liquid on said tray res-ts on a part of the perfora-ted base
of said tray before ~alling into said opening.
Thus, according to the present invention in an appara-
tus for exchanging material between a downwardly flowing liquid
and an upwardly flowing gas couhterflow to said liquid, the liquid
forms a hydrostatically continuous column extending from the top
level to the lowes-t tapping point whereby the ratio of -the resi-
dence time of the liquid to the volume content of the column is as
large as possible. This column is merely loosened up by ~as
bubbles in the regions of contact wi-th gas but it is not interrup-
ted anywhere. ~ bubble cap is formed below each of said trays
and within sai~ bubb]e cap ~he level of the liquid is displaced
downwardly by the gas whereby, as compared wi-th the level of the
liquid above the tray, a higher gas pressure is produced below
the tray, the difference o:E said pressures being used to overcome
-the pressure loss because of the gas flowing through the holes
of t.he tray and simu:ltalleously to preven-t the flow o.~ liquid
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througll these holes. The connectin~ ducts for passin~ the ].iquid
to the
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next lower tray are disposed outside said bubblP caps or they
cross said bubble caps. At the end of said connecting ducts the
path of the liquid is directed upwards, thus preventing an un-
desired entrance of gas at said end of the connecting ducts.
It is not sufficient to assure a long average residence
time of the liquid on each tray~ but in order to attain a good
tray fficiency, it is important that the divergence of this re-
sidence time remains small when considering increasingly smaller
portions of the -total liquid flow~ This condition cannot be sat-
isfied without a forced guidance of the liquid via sufficientlynarrow ducts distributed over the entire tray~ According to the
present invention this is achieved when said GOnneCting ducts are
disposed in the region of the axis of the aforesaid pressure ve~-
sel~ said connecting ducts consist of two semicircular surfaces
encompassing the axis of said pressure vessel, said semicircular
surfaces being alternately used for connecting two adjacent trays,
and the path of the liquid from the outlet from said connecting
ductl which supp1ies the liquid from the next higher tray, to the
inlet into said connecting duct, which supplies the liquid to
the next lower tray, extends via concentrically arranged and
series-connected semicylindrical chambers, said liquid path ex-
tending firstt from the region of said axis of the pressure vessel
in the direction of the walls of said pressure vessel and then
in the opposite direction.
The gas bubbles rising upwardly through the liquid should
be as small as possible and should preferably be divided repeated-
ly while rising. According to the present invention this is
achieved when the volumel in which the liquid is in contact with
the gas bu~bles~ is filled with fine-meshed gauze wire.
The present invention will be further described by way
of the accompanying drawings, in which:-
Fi~ure 1 is a vertical section along the lines A, B,
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62
C, D in Figure ~;
Figure 2 is a horizontal section along the line EF in
Fiyure l;
Figure 3 is a horizontal section along the line GH in
Figuxe l; and
Figure 4 is a horizontal section along the line J~ in
Figure 1.
Referring to Figure 1 three trays 1, 2 and 3 are shown
in the vertical section ABCD. The tray 2 is described hereafter.
The other trays, whose number is optional, are identical directly
or in mirror image.
From the gas chambers 4 below the tray 2 the gas passes
via the opening 5 to the liquid chamber 6, through which it flows
in the for~ of bubbles 7 on its way to the nex-t gas chamber 8 be-
low the tray 3.
The liquid from the tray 3 flows via the connecting duct
9 to the tray 2. Said duct can ~e seen in Figure 1 as well as
in Figures 2 and 3~ In the lower portion 10 of the connecting
duct g, which can also be seen in Figure 4, the direction of the
liquid path is reversed. The liquid flows to the liquid chamber
6 vertically upwards through the last portion 11 of the connecting
duct 9. The further horizontal path of the liquid is evident from
the arrows shown in Figure 2. This path ends in the space 12,
which extends as far as the connecting duct 13 to the next lower
tray 1.
Amon~ the partially cylindrical walls 14, 15, 16 and 17
disposed in the liquid chamber and shown in Figures 2, 3 and 4,
only the two walls mentioned first can be seen in Figure 1 because
of the manner in which the sections are represented. Walls pos-
3Q sibly visi~le behind the sectional areas are not shown in thedrawing to avoid a complicated representation~
The celltl-al flat partition 18 ~ivides the annuli into
chambers through which the liquid f:lows towards the outside and
to the inside. The pressure housing 19 forms the external en-
closure.
The num~er of concentric annuli formed by the partially
cylindrical walls is optional, depending on the dimensions of
the column and on the ~hroughput of liquid. The liquid chamber
6 is filled with gauze wire ~not shown in Figure 1).
The level 20 of the liquid in the liquid chamber adjusts
itself as a function of the gas throughput with the exception
of the uppermost tray, where this level must be adjusted either
by means of the flow of liquid to the column or by means of the
flow of liquid from the column.
