Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to a gas liquid mass
transfer column of -the type used in deuterium-hydrogen exchange
or the like.
Columns of this type are used in distillation, extrac-
tion, absorption and exchange processes and in par-ticular, in
enriching of one phase with an isotope. In all such processes
the phases which are to be mixed with each other must be
brought into a thorough contact with each other i~ the process
is to be rapid and satisfactory.
Columns are known in which the passage of the gaseous
phase in the system is caused by temperature differential
resulting in a pressure difference. Gravity is normally used
for causing the flow of the liquid phase throughout the system.
In the columns of this type, the onl~ way of achieving a large
throughput is to increase the cross section of the column. If,
for instance, the rate of flow of the gaseous phase were
increased in known systems, the separating effect of gravity
would cease to be adequate to meet the requirements of appro-
- priate separation of the two phases; in particular, when there
is little difference between the specific weight of the liquid
and the gaseous phase, the descending particles of liquid may
become drawn along by the gas flow.
In exchange columns of the above type to which the
invention relates, the volume ratio between the liquid and gas
phases in the reaction chamber can be selected independent of
the throughput ratio determined by the process, to meet the
desired mass-transfer rate.
In such case forces which are a multiple of gravity
have to be used to separate the phases, since the liquid is
circulated several times through the reaction chamber of each
exchange unit.
The amount of the substance transferred in the exchange
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columns is increased by increasing the overall area of contact
between the two phases.
It is known to provide sieve tray columns wherein a
woven wire fabric is disposed in the bubble bed above the ;~
sieve tray, in order to reduce agglomeration of gas bubbles
passing through the bed. ~owever, the liquid speed in such
columns is limited as the amount of liquid per transfer stage
is determined by the volume of liquid flowing through the column.
Consequently, it is impossible to achieve any considerable
turbulence in the bubble bed so that the increase in the contact
surface is not satisfactory. Moreover, the size of the gas
bubbles produced is increased by increasing the volume of gas
supplied to the bed; eventually the gas bubbles may become so
large that the wixes of the bubblebreaking system fail to break
the bubbles up.
It is an object of the invention to provide relativel~
inexpensive means whereby the area of contact between the phases
is considerably increased.
According to the invention, a gas-liquid mass-transfex
column is provided which comprises a plurality of vertically
spaced exchange units for a counter-flow mass-transfer, wherein
the passage of the liquid descending between adjacent units is
boosted by a pump so that the pressure of the liquid in a
lower unit is hi~her than the static pressure corresponding ~ ;
to the respective height of liquid colurnn between the adjacent
units. Each of such exchange units has at least one reaction
chamber surrounded by a level charnber for the liquid phase.
Means for circulating the liquid from said level chamber
through the associated reaction chamber form a further part of
the column. Each of the exchange units has a bottom plate
with at least one nozzle for introducing the gas phase into
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the reaction chamber. The top of the reaction chamber commu-
nicates with a separating chamber. A substantial portion of
the inside of the reaction chamber comprises a gas and liquid
permeable packing, the packing being made of solid material.
In one embodiment of the present invention the packing
comprises at least one member made of a wire-like material of ~`
a generally uniform structure. The wire-like material is pre-
ferably a woven or knitted wire structure. In an even more
preferred embodiment, the packing includes at least one layer
of fleece comprised of fiber-type wires. The packing is pre-
ferably of the type of a coil or roll of the wire-fabric-like
material, whose outside diameter generally corresponds to the
inside diameter of the reaction chamber so that when the roll
is placed inside the chamber, the wire-like material fills a
substantial portion of the volume of the chamber.
The invention will now be described by way of preferred
embodiments with reference to the accompanying schematic
drawings.
In The Drawings:
Figure 1 is a schematic vertical section of a part of
an exchange column including one embodiment of the present
invention;
Figure 2 is a section similar to Figure 1 but showing
another embodiment of the present invention;
Figure 3 is a perspective view of one embodiment of ~;
the packing; and `
Figure 4 is a detailed perspective view of an embodiment
of wire fabric used introducing the packing of Figure 3.
Referring now to Figure 1, reference numeral 1 shows
a column comprising a plurality of exchange units 2 which are
disposed one above the other in a pressurized tube. The column
of this kind is used in deuterium exchange between hydrogen and
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methylamine.
The exchange units 2 are each of the type of a reac-
tion chamber 3, equidistantly spaced across the column. Opera
tively associated with each chamber 3 is a jet pump ~ compris-
ing a nozzle 4a and a diffuser 4b. The nozzles 4a are disposed
in bottom plates secured in a gas-tight fashion to the column
1. A gas and liquid pervious packing consisting of a plurality
of coils as shown in Figure 3, is disposed in each of the
chambers 3. The coils 5 are of the same diameter as the
diameter of the respective chambers 3 and are stacked loosely
on each other. As best seen from Figures 3 and 4, the coils 5
are each formed from a sheet 5a of woven fabric provided with
obliquely oriented corrugations.
Each of the chambers 3 is open at the top to communi- -
cate with an associated separation chamber 6 wherein the gas
is separated from the liquid whereupon the gas is discharged
upwards through a tube 7 and via nozzles 4a enters the next
exchange unit located above.
Surrounding the reaction chambers is a liquid chamber
8 from which a pump 9 is arranged to convey liquid through a
line 10 into the liquid chamber 8 of the exchange unit 2
located immediately below the former. The jet pump continuously
circulates liquid from the level chamber 8 through the res-
pective reaction chamber 3 wherein the liquid contacts the gas.
The gas bubbles strike the wires of the coils 5 at high speed
with the resulting breaking of the bubbles into an increased
number of same.
The embodiment of Figure 2 differs from that of Figure
1 by the used type of counter flow mixing. While the different
exchange units 2 of Figure 1 have jet pumps which circulate
through the respective reaction chambers 3 a volume of liquid in-
dependent of the total liquid throughput of the column, the
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embodiment shown in Figure 2 comprises an improvement wherein
pumps 11 feed li~uid from the liquid chambers into the reaction
chambers and the gas flows between consecutive exchange units
through nozzles 12 into the reaction chambers. In Figure 2,
the structural elements corresponding to those of Figure 1 are
referred to with the same reference numerals, each having an
apostrophe.
As mentioned above, Figures 1 and 2 show only portions
of the entire respective columns. The column heads and bottoms
are not shown as they are not essential for proper understanding
of the principles of this invention. The gas entering the bottom
of the column can be compressed e.g~ by means of a compressor
(not shown) which can be placed inside the column and below the
bottom plate thereof. The required total pressure drop across
the column can be provided by a pressure vessel (not shown)
which, in a particularly advantageous embodiment, is simul-
taneously used for storage of the compressed phase in an overall
system of which the gas-liquid exchange column is a part.
It will be appreciated that the invention is based ~;
on an inventive recognition of the fact that by combining the -;~
features of known bubble beds in the type of the column as
described above, the exchange rate can be considerably improved.
This is due to the fact that by repeated circulation of the
liquid through reaction chambers according to the present
invention, relatively high turbulence can be produced in the
reaction chambers resulting in considerable reduction of the ~
size of gas bubbles, in reduced agglomeration of gas bubbles, ~ i
with the resulting possibility of considerable increase in
mass-transfer rate.
Those skilled in the art will readily appreciate fur-
ther embodiments of the present invention differing from the
above preferred embodiments but still falling within the scope
of the accompanying claims.
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