Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to packing elements for use in
mass transfer towers.
Contact elements partially enclosing a space for fluid
~l~w have found wide uses in mass tr~nsfer devices such as
scrubber tdwers, absorption columns, distillation columns and
the like. One example of a popular form of packing element is
based on the cylindrical type described in U.S. Patent 3,266,~87
to Eckert where contact fin~ers are punched out of the cylin-
drical wall and bent inwardly into the space de:Eined by the
cylinder. The type of packing descrihed in the Eckert patent
works w~ll in the smaller sizes of packings. ~owever for the
larger size packings, which are becoming increasingly important
for ~crubber towers adapted to hand].e tremendous volumes of gas, ..
uah as encountered in the scrubbing of p~wer plant ~tack gases,
the effic~enay ~alls o~f as the diame~er of the packing element
~: is increased. I~ is believed that this fall-off in efficiency
result~ ~rom the fa~t that, with ~he larger diameter of packing
; ~lement, the g~s ha~ a tendency to flow axially o~ the pa~king
~lement a~d parallel to the elem~nt sur~aces. In this circum-
~anb~ th~ contact betweon the gas and ~he wetted surfaae~ of
the flnger~ extending in~o the fluid ~low spao~ is not ~3 com-
ple~e as desired. In:the pr~ ent lnvention the effici~ncy of the
packing element is substantially increased by twi~sting some
o~ the inwardly projecting fingers so that their surfaces
.
~, 25 each form an angle at between 4 and 45 to the axis of the
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enclosed fluld flow space This imparts a turbulence ~o
the gas flowing along the axis of the space so as to provide
more intimate contact between the flowing gas and the wetted
surfaces projecting into this-enclosed space as well as
increasing contact with the wetted surface of the wall defln-
ing the space.
In accordance with the present invention the fingers
extending towards the axis of the fluid flow space are
twisted sufficiently to obtain some turbulence, but not enough
to provide aerodynamic shielding of the back surfaces of the
fingers~ In .ccordance with the pres~nt invention the~e is
provided a generally cylindrical packing element, portions of
the surface bèing cut from the cylinder to form fingers which
are directed inwar~ly towar~s the cylinder axis, the surface
~f some of said fingers being bent at an angle of between 4 and
45 to the axis of the cylinder/ each such inwardly directed
finger having a transverse dimension extending along less than
35% of the axis of the packing ~lem~.nt, whereby the inwardly
: directed fingers create turbulent flow wi`thin the element of
gases flowing past the finge~s and generally parallel to the
axis. The exact amount of angle will depend on a number of
faators including the spacing of the fingers, ~he amoun~ of
penetration of the fingers into the empty ~pace, the width
of the fingers parallel to the axis, the flow rate of the gas
In one packing alement, having a diameter of about 3-1j2",
it was found that a 10 angle seemed to give the highest
~ficiency. The efficiency started to fall off as the.angle
was increased to about 16 until it was about equal to the
efficiency with the surfaces parallel to the axisO As far
as is known, prior packing elements of the type described
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in the above mentioned Eckert patent ha~e been made with
surfaces either parallel to the axis of the cylindrical
packing element or normal to the axis as shown in French
patent 542,902. ~See Figs. 5,7 and 8). The only packing
elements described in the prior art known to applicant having
an inclined internal surface are the old spiral type rings,
However these spiral rings were entirely different since
their interior surfaces were not formed by fingers which were
punched from the cylinder itself and bent inwardly, rather
their spiral surfaces were completely enclosed by
imperforate cylinders.-- A structure similar in performance
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to ~he old "~piral rings" is shown in Fig. 3 of British patent
1,385,672. Another type of prior art packing is illustrated in
~rman DA5 1~029,346 published May 8,1958. This shows a saddle
ale~ent having fingers punched from the surface and bent inwardly
to the ~pace partially defined by the curved saddle surface. In
~hi~ D~S, however, the angle between the finger surfaces a~d the
axis o~ ga~ flow approximateq 90. While the recently issued U.S.
~at~n~ 3,957d931 contains ~he cryptic sta~emen~ (col. 5 lines 13-
14) that ~Ithese tabs may be angled to the longitudinal axis of
~ha cylindric~l mem~er" there i~ no discussion of specific angle~
or how they are mea~ured or the effect of the angulation.
~he invention will now be described, by way of example,
~th re~erenc:e to the accompanying drawings, in which:
. Fig. 1 i~ a side view of one embodiment of the packing
aleme~t having three rows o~ finger~ punched from its surface
an~ b~n~ inwardly.
Fig. 2 is a ~ ard sectional view along line 2-2
o~ ~g. 1 looking parallel to the axis of the cylinder~
Fig. 3 i~ a diagr~mmatia perspec~ive view of another
o~bodiment of thQ invention.
Referr~.ng now to Fig. 1 the packing element, which is
gen~r~lly lndiaat~ at 10, i~ ~ormed of a ~ylindrical surfa~e 12
~xo~ ~hi~h a number of ~lnger~ 14 and 14a are cut and bent in~
w~rdly o ~xtend into th~ interior spa~e 13 de~lned by the
oylindri~al surf~ae 12~ A~ ind~a~ed on Fig. 1 ~he finger 14
r~d by a roughly rectangular cut. ~ha surface ~ finger
14 will have a 10 angl~ "a" with respect to the axis. The hinge
llno 167 along which the ~.inger 14 is bent inwardly, also con
~ ntly ha~ ~h~ ~ame 10 angle "b" wi~h the axis A. Thus the
~ao ~l~wing do~n th~ cylinder parallel to the axis A is deflected
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somewhat by the surfaees 14 to create turbulence which increases
the amount of interaction between the flowing gas and the liquid
on the wetted surfaces on the fingers 14 and the interior surface
of the cylinder 12.
As viewed from the top (~ig. 2) the projected area of
the bent fingers 14 intercepts an appreciable amount of the cross-
sectional area of the empty space 13, thus substantially in-
creasing the chance of interaction of the gas with the liquid on
a wetted surface during travel of the gas down the inside of
the packing element. In Fig. 2 it is seen that fingers 14a are
not twisted with respect to the axis.
Tests of packings made in accordance with the present
invention by using humidification of air as a performance test
showed considerable improvement over standard commercially
available packing elements made in accordance with the prior art
techniques where the finger surfaces were essentially parallel
to the axis of the cylinder. It was found that a 3-l/2" diameter
ring packing element (90 millimeters) had a heat transfer effi-
ciency equal to the 2" prior art packing element even though the
pressure drop across a bed of the 3-l/2" packing elements of the
present invention was considerably less than the pressure drop
across a bed of similar height of the 2" packing elements. In a
~referred embodiment of the invention, the packing element made
in accordance with Fig. l is formed of cylindrical elements
approximately 3.54" high (90 millimeters) by 3.54" (90 milli-
meters) in diameter. Each element has ~hree rows of fingers with
eight fingers in each row of the approximate relative dimension
shown in Figs. l and 2. The center row of fingers 14a is parallel
to the cylinder axis and the finger of the top and bottom rows
are twisted so that the surface of these fingers forms an angle of
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approximately 10 with respect to the axis of the cylinder. In
Fig. 2 the bottom row of bent fingers is not visible since they
would be shielded by the top row.
With the dimensions of the approximate size shown in
Fig. 1 when the angle is somewhat greater than 15 (e.g. about
16) the performance falls off somewhat.
While actual tests have not b~en run with a narrower
flnger it is believed, on the basis of theoretical considerations,
that when the width of the finger in the axial direction is about
5~ of the total axial length of the packing element the angle
"a" can be up to 45 and still provide improved performance. In
this lattPr case there will not be so much "shadowing" of the
back side of the finger, i.e. the side which is down stream
of the flowing gas. However, when the width of the
finger extends between about 25% and 50% of the axial length of
the packing element, then the angle is preferably between 4
and 8~ with respect to the axis of the element. In the preferred
embodiment illustrated in Figs. 1 and 2, the transverse dimension
of the finger extends along about 17% to 20~ of the axial length
of the packing element and the angle of the finger is ~referably
around 10 for improved performance.
While a preferred embodiment of the inv~ntion has been
described above wherein the finger is more or less rectangular
and is bent at a constant angle to the axis, considerable
departure from this simple structure can be achieved without
departing from the spirit of the inventionO For example the
angle of the surface can change along the length, being rel-
atively shallow near the cylinder wall and increasing towards
the free end. Similarly the shape of the finger can be triangular,
ellip~ical, or any other shape that furnishes an inwardly
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extending surface having an angle oE 4 to 45 to the axis
of the cylinder.
Another embodiment of the invention is based on a
saddle of the type shown in the above mentioned DAS 1,029,346
and is formed from a single saddle shaped piece of metal (or
plastic) as illustxated in Fig. 3. Each finger 20, cut from
the saddle 22, and bent inwardly towards the flow axes 24 and
24a (ther will be two axes) is bent so that the finger surface
forms an angle of between 4 and 45 with respect to the flow
lQ axis adjacent the finger. In general the narrower the finger
the higher can be the angle, as discussed above.
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