Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 94/26377 PCT/GB94/01007
21 62572
CONTACTO~ CONSTRUCTION
This invention is concerned with a contactor
construction. More particularly it is concerned with the
construction of à liquid/liquid or solid/liquid mass trans-
fer contactor, and such contactors are useful in large scale
solvent extraction techniques and other similar mass trans-
fer operations.
One known form of liquid/li~uid and solid/liquid
contactor is the multi-compartmented cylindrical rotor
contactor known as the Graesser Contactor, manufactured and
sold by the Applicants.
This known form of contactor which finds wide
applications in solvent extraction and in other mass trans-
fer operations is shown fully assembled in Figure 1, par-
tially dismantled in Figure 2 and its method of operation is
- depicted schematically in Figure 3.
The known Graesser Contactor, of the type illus-
trated in Figures 1-3, works on what is termed in the art as
a "raining bucket" principle enabling inti~ate ~ixing of a
liquid feed and applied solvent over a plurality of theoret-
ical stages of mass transfer but within a single apparatus.
The Graesser Contzctor shown in Figures 1 and 2 is
a horizontal cylindrical machine having an outer shell 1, a
centrally located spindle 2 connected via drive train 3 to a
relatively low power motor 4. Because of the size and
weight of the contactor it is conveniently mounted on rigid
supports 5 forming part of a mounting platform. The outer
shell is provided with a number of take-offs 6 either for
removing liquid from intermediate stages within the contac-
tor or which can be useful as gas vents, during a mass
transfer operation.
As shown in Fi~ure 2, the rotor assembly 8 com-
prises a pair of end plates 9 (only one of which is shown in
this drawing) connected to a plurality of axially spaced
cylindrical plates 10 between which are located "scoops" 11
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W094/26377
which serve to collect solid or liquid from the feedstock
and cause this to be mixed with an applied solvent or other
extraction medium. Accordingly a plurality of adjacent
compartments are formed within the interior of the contac-
tor, the first compartment of which is defined by the space
between end plate 9 and its immediately adjacent cylindrical
plate 10.
The method of operation of the known Graesser
contactor is shown in simplified form in Figure 3. A liquid
or liquid/solid feedstock enters feed inlet 7 and can be
applied on a continuous basis to approximately fill one half
of the volume of the interior of the contactor. The feed-
stock ~hen treated exits as raffinate at outlet 7a. A
solvent (or other liquid) is applied at solvent inlet 6a and
exits the contactor via outlet 6b containing the material
extracted from the feedstock. The feedstock is designated
12 and the solvent designa.ed 11, one compartment being
defined by the space 13 between adjacent axially spaced
plates 10. The scoops (not shown in Figure 3 but visible in
Figure 2) cause a relatively gentle mixing as between feed-
stock 12 and solvent 11 without excessive agitation, bub-
bling or frothiness. Such is possible by use of ~ relative-
ly low powered motor 4 to drive the spindle 2 and hence the
rotor assembly 8.
Graesser Contactors are established items of
industrial hardware and have found considerable commercial
application in the treatr.,ent/extraction of phenolic liquors
and effluents, tar acid extractions from carbonisation
distillates, extraction of products from aqueous reaction
mixtures, desalination of organic reaction products by water
washing, purification of herbicides and other similar ex-
traction techniques useful in the chemical industry, water
and effluent treatment, agricultural, food and pharmaceuti-
cal industries. Such contactors with gentle (low rpm)
mixing techniques hav~ been used in separation techniques
otherwise requiring distillation, evapcration, crystallisa-
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~ 094/2~77 2 1 6 2 5 7 2 PCT/GB94/01007
tion, zone refining 2nd leaching processes.
Early applications of the Graesser Contactor werein a liquid-liquid mode with the flows of both phases taking
place in the interfacial gaps between the shell and the
compartmental dividing plates. Whilst the upper phase is
usually the solvent phase and the lower phase the solute
phase examples exist of where the densities are reversed.
Flow design is related to the pressure drop across each of
the interfacial areas, znd the summation of each of the
pressure drops.
Originally, the Graesser Contactor was used in
extractions fro~ slurries in the aqueous phase; or other
denser phase. These slurries were passed entirely through
the lower peripheral gap (spacing between rotor periphery
and interior surface of cylindrical housing) - aided by
eccentricity of the rotor to increase the lower gap at the
expense of the upper.
As the demands for greater percentages of solids
in the slurry continued, and more difficult materials were
used e.g.
(A) Larger size particles (Gravels-Metals),
(B) More Cohesive raterials (Clays), and
(C) More entwining material (vegetable matter),
modifications were needed to the assembly, to handle the
higher solids material more effectively.
This was done by piercing the compartmental divid-
ing plates alternatel~ behind each pair of buckets (scoops)
- thus passing solids corpartment to compartment ~ithout
allowing by-passing since the material could only pass one
dividing plate without being lifted and dropped through the
other phase. This system has been used, but there remains
room for further ir,provements.
-~owever, the Graesser Contactor is increasingly
used for environmental clean-ups, and for highly cohesive
industrial materials often bound together by bitumens. All
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this has lead to a need ~or a contactor of the Graesser type
having a 'drive mechanism' for solids movement but which
nevertheless minimises disturbance of the solvent phase.
Other desirable features of such a 'drive
mechanism' include adjustability to reduction from the
maximum drive available and it should preferably be
proportional to the speed of revolution of the rotor.
According to this invention we provide a
liquid/liquid or solid/liquid contactor comprising a
substantially hollow cylindrical outer shell, and a rotor
assembly mounted for rotation within the interior of said
shell, the rotor assembly including a plurality of axially
spaced generally circular plates, the spacing between
adjacent plates defining a compartment of the rotor, a
peripheral clearance provided between the periphery of each
said plate and the internal surface of said shell,
characterised in that at least one elongate
solids movement assisting bar is located between at least
two adjacent plates at or near their periphery.
It is preferred to use one or even several
assisting bars extending from one end plate of the rotor to
the other end plate, thus allowing more effective solids
movement whilst permitting the solid movement to be
proportional to the rotor speed.
The number of assisting bars can be increased or
decreased if they are removable and the inter-compartmental
partitions e.g. plates~as specified above may have slots or
similar notches cut in them, at or near their periphery,
into which the bars can be placed or withdrawn. The bars
can extend diagonally across the or each compartment defined
by the rotor assembly and the shell. For example six "sets"
of diagnonal bars can be used although a practical maximum
might be ten "sets" wherein a "set" is one bar which extends
between the two end plates of a rotor, but which is itself
made up of a number of end-linked, smaller assisting bars
having protuberances which engage notches in the plates at
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~ 094/2~77 2 1 6 2 5 7 2 PCT/GB94/01007
the ends of the smaller bars.
The or each assisting bar can be constructed of
metal, preferably corrosion resistant metal such as
stainless steel or the like, but it could be constructed of
strong, essentially inert plastics material such as PTFE,
carbon fibre, or polypropylene. It has been found
convenient for the bars to be constructed of metal, allowing
the provision of a series of connected metal strips or
blades placed in suitably sized notches located at the
peripheral surface of dividing plates of the rotor assembly.
The bar or bars may be in the form of a metal
strip or helically wound blade extending across a plurality
of compartments. A number of assisting bars can
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W094/2~77 2 1 6 2 5 7 2 PCT/GB94/01007
be employed within the interior of the contactor, in radial-
ly-spaced location. A continuous assisting bar can be
comprised of a series of end-linked smaller bars, wherein
one such smaller bar extends across the two plates ~efinin~
between them a co~part~ent.
Best results are likely to be obtained with a
solids/liquid rotor, optionally including piercings.
In order that the invention including further
preferred and optional features may be illustrated, more
easily appreciated, and readily carried into effect, embodi-
ments of the invention are now described with reference to
the accompanying drawings by way of non-limiting example
only and wherein:
Figs. 1-3 show a conventional for3 of contactor
and have already been described,
Figure 4 shows an internal view of a modified
contactor according to the invention,
Figure 5 is a side elevation of the rotor assembly
shown in Fi~ure 4,
Figs Sa - 5c show enlarged details of the connec-
tion between assisting bars respectively along the lines f-
f, e-e and d-d noted on Figure 5,
Figure 6 shows an end elevation of one plate
member, such as an end plate used in the rotor assembly, and
Figs 6a - 6c show enlarged details of assisting
bars located in peripheral plate notches along the lines f-
f, e-e and d-d s~own in Figure 5.
Referring to the drawings Figures 1-3 have already
been described for purposes of background information and
for identifying or.e preferred form of contactor which may be
modifieq by use of one or more assisting bars, and so pro-
vide a Contactor capable of better solids movement according
to the present invention.
Figure 4 shows an isometric view of part of the
interior section of a contactor, modified by inclusion of a
solids movement assisting bar 15. The bar 15 is comprised
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of a series of inter-connected smaller such bars ~here
individual bars extend bet~een a pair of adjacent plates lO
(and/or s,lo) of the rotor assembly 8.
The rotor assembly shown includes an end plate 9,
and a series of adjacently spaced plates lO ~hich are joined
by connecting rods 14. In practice the connecting rods 14
may be attached to bucket-like scoops as in a conventional
Graesser Contactor. Each of the plates 9, lO has a series
of radially spaced inwardly directed, peripherally located
and radially spaced notches 16. The assisting bar is in
the form of a helically wound metal blade. A number of
smaller bars are welded together at their abutting ends, to
form the helical blade 15. Each smaller bar has a
protu~erance at its end (15e - see Figs 6a-c) which fit
into co-operating notches 16.
Figure 5 shows the arrangement, in elevation, of
the rotor assembly where a plurality of solids movement
assisting bars 15 are deployed. Each compartment of the
rotor assembly being defined by adjacent plates lO, or by
an end plate 9 and its adjacent plate 10, includes a plural-
ity of peripherally spaced assisting bars, but the bars can
be removed to reduce their number.
Joining locations, 15a, 15b and 15c (Figure 5) are
shown in Figures 5a to 5c. Figure 5b shows a detail of the
optionally welded joint designated 15b bet~een bars 15 at
the notch 16 along the line e-e shown in Figure 5. Joint
15a between bars 15, shown in Figure 5a is a detail of the
arrangement shown in Figure 5a. Similarly, the joint 15c is
shown in Figure 5c. It will be appreciated that the includ-
ed angle between two bars may be varied. Whereas Figures 5a
and 5c show an included angle of the order 36O, the included
angle in the arrangement shown in Figure 5b can be of the
order 72, for example.
Figure 6 shows a plate 10, which could be an end
plate 9, having ten equi-distantly spaced, inwardly directed
rectangular notches 16, some of which have been
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designated 16A, 16B, 16C, 16D and 16E. In one
embodiment,the abutting projections 15e (see Figs 6a-6c) can
be located in notches of adjacent plates designated 16A to
16C whereas in another embodiment of a contactor, for exam-
ple the type shown in Figure 6c, incorporati~g a metal strip
15d of thicker section than the element to which it is
joined, may extend fro~ notch 16A in the first plate, there-
after to notch 16B, to notch 16C, to notch 16D and then to
notch 16E before reaching another notch designated 16A.
Finally Figures 6a-6c show one way of connecting
bars 1~ and locating their projecting protrusions 15e within
a notch 16 of a plate lO or end plate 9. The ~ars might be
welded or only ter,porarily fastened together at the protru-
sions 15e and, if necessary or desirable, in appropriate
position within the notch 16.
In use, the assisting bar or bars may extend
across compartments of the rotor assembly whilst still
leaving an operating clearance between the outermost periph-
eral sur~ace o~ the or each assisting bar and the
interior surface of the shell of the contactor. Such
an arrangement can improve control of solids flow.
The bars can be fabricated from readily available
materials and can be affixed to appropriate plates of the
rotor assembly. Considerable performance enhancements may
be achieved with a modified contactor according to this
invention.
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