Note: Descriptions are shown in the official language in which they were submitted.
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PUMP
FIELD OF THE INVENTION
The invention relates to a pump for mixing two or more
mutually insoluble liquid phases together into a
dispersion, feeding the dispersion into a mixer and
then into a solvent extraction settler.
BACKGROUND OF THE INVENTION
A pump mixer is known in the prior art e.g. in
publication US 5662871 (the Dispersion Overflow Pump,
DOP ), with which two or more mutually insoluble
liquid phases are mixed with each other into a
dispersion. The pump feeds the dispersion via one or
several mixers into a solvent extraction settler.
This kind of pump includes a suction tank comprising a
bottom, which limits the internal space of the suction
tank in the downward direction. The suction tank
further includes a cylindrical vertical sidewall,
which limits the internal space of the suction tank in
the lateral direction. There is an opening for the
first inlet channel in the sidewall, through which the
first liquid phase is fed into the suction tank, and
for the second inlet channel, through which the second
liquid phase is fed into the suction tank. The suction
tank further includes an upper wall, which limits the
internal space of the suction tank in the upward
direction and in which upper wall there is a central
opening. Furthermore, the pump includes a pump
section, which comprises an blade wheel housing, which
is arranged on top of the suction tank so that the
above-mentioned upper wall forms the bottom of the
blade wheel housing, and where the central opening in
the upper wall forms the suction opening for the pump
section, and which blade wheel housing is limited
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laterally by a cylindrical sidewall. The pump section
further comprises a blade wheel, in which there is a
set of blades. The blade wheel is arranged so as to
mix into a dispersion the first phase and second phase
that are sucked into the internal space of the blade
wheel housing from the suction opening. The blade
wheel is fixed to the vertical drive shaft in order to
rotate the drive motor.
In this DOP pump of the prior art the blade wheel
housing is open at the top. The upper part of the
blade wheel housing sidewall opens conically upwards
so that the upper rim of the sidewall forms an
"overflow" rim, over which the dispersion is
discharged into the space surrounding the blade wheel
housing. The suction tank and pump section are
surrounded by an outer tank, which receives the
dispersion discharging from the blade wheel housing
into the space between the suction tank and the outer
tank. In this space the mixing power is kept at a
level at which the phases remain mixed. The remainder
of the kinetic energy is changed into potential
energy, with the purpose of moving the dispersion
forwards via the discharge channel opening in the
sidewall of the outer tank to the mixers and from
there on to the solvent extraction settlers.
This type of DOP pump construction of the prior art
acts as an excellent dispersion former.
However, in large-scale Cu extraction plants the DOP
pump construction of the prior art creates some
problems. With the construction described above the
size of the DOP pump will be large. For example, the
diameter of the outer tank that is required, which
determines the physical size of the equipment, may be
as much as the order of 6 - 7 m and the height over 4
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m. The physical size of the equipment is therefore
huge and causes large investment costs. There is a
large empty space on top of the pump section in the
outer tank, which is not needed apart from during
process start-up, because the shaft bushing of the
drive shaft through the lid of the outer tank is not
sealed tight. This increases the size of the equipment
and consequently the investment costs. The space for
liquid between the outer tank and the suction tank
increases the physical size of the equipment,
increases the investment costs of the equipment and
technically in terms of the process makes it difficult
to dimension (dispersion residence time). Since there
is a large volume of liquid in the DOP unit, which
must be kept mixed before the dispersion flows to the
mixers, the phases have to be over-mixed in the pump
section. This increases the formation of small
droplets in the pump that are hard to separate, and
raises the power consumption of the DOP unit. A large
unit and especially a large outer tank raise
transportation costs and hamper transport,
particularly for instance in mountain regions and in
Africa, where the dimensions of the outer tank often
exceed the permitted transportation dimensions. Since
the drive motor is located a long way from the blade
wheel, a long drive shaft is required. A long shaft
will bend particularly in large production units and
cause vibration in the blade wheel. Bending of the
shaft hampers the mechanical dimensioning of the shaft
and blade wheel.
PURPOSE OF THE INVENTION
The purpose of the invention is to eliminate the
above-mentioned drawbacks.
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In particular the purpose of the invention is to
disclose a pump, which is considerably smaller in
physical size and cheaper in price than earlier.
A further purpose of the invention is to disclose a
pump, which enables the dimensioning of the pump so as
to be transportable by ordinary means of
transportation without requiring special
transportation, and where the pump transportation
costs are reasonable.
A further purpose of the invention is to disclose a
pump where there is no need for a large empty space
nor an outer tank, and whose liquid volume is thus as
small as possible.
A further purpose of the invention is to disclose a
pump where the dispersion residence time is as small
as possible.
A further purpose of the invention is to disclose a
pump, whose power consumption is smaller than earlier.
In addition, it is the purpose of the invention to
disclose a pump where there is as little blade wheel
vibration as possible.
SUMMARY OF THE INVENTION
In accordance with the invention, the inner space of
the blade wheel housing is limited in the upward di-
rection by a cover plate, in which there is a central
shaft bushing for the drive shaft sealed with a me-
chanical shaft seal. The discharge channel opening is
in the sidewall of the blade wheel housing.
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In comparison with the DOP pump known in the prior
art, the pump accordant with the invention has many
advantages:
- No separate outer tank is required at all, because
the dispersion is removed directly from the blade
wheel housing of the pump section. This reduces the
physical size and cost of the equipment by over 50 %.
- The pump is always full of liquid. There is no empty
space inside the equipment nor is it needed. Thus
there is no need for the expensive and troublesome
butterfly valve intended for liquid level control of
the current DOP pump.
- The liquid volume of the pump is small i.e. the
mixer residence time dimensioning will be accurate and
easy to calculate.
- Over-mixing is not required since as soon as the
dispersion is formed, it is removed from the pump and
is almost immediately in the mixer. This improves
phase separation in the solvent extraction settler and
decreases the power consumption of the pump.
- A small-sized pump unit can be transported easily as
a whole to the site, for instance by normal road
transport. Several pumps with the new construction can
be transported in the same transportation, whereas the
current units require individual transportation
pallets.
- The blade wheel drive shaft is short, so it does not
vibrate, which facilitates the dimensioning of the
shaft and blade wheel and enhances mechanical
durability.
In some embodiments of the pump, the opening of the
discharge channel in the sidewall of the blade wheel
housing is tangential.
In some embodiments of the pump, the drive includes a
motor.
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In some embodiments of the pump, the drive includes a
gear, which is arranged between the motor and the
drive shaft.
In some embodiments of the pump, the output is in the
order of magnitude of 50 - 10 000 m3/h, the peripheral
speed of the blade wheel is of the order of magnitude
of 5 m/s and the overpressure of the dispersion in the
discharge channel is of the order of magnitude of 5 -
50 kPa. This overpressure causes the majority of the
hydrostatic pressure in the mixer that comes after the
pump. The overpressure required for the dispersion to
flow from the pump is 3 - 8 kPa.
LIST OF DRAWINGS
The invention is described in detail below by means of
example embodiments with references to the attached
drawings, where
Figure 1 presents a diagram of one arrangement
equipped with one embodiment of the pump accordant
with the invention, and
Figure 2 presents a diagram of a cross-section of one
embodiment of the pump accordant with the invention.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 presents a diagram of an arrangement
consisting of pump 1, two mixers 2 and solvent
extraction settler 3. There may be a different number
of mixers than two. Two or more liquid phases that are
insoluble in each other are mixed together into a
dispersion in pump 1. Pump 1 feeds the dispersion to
mixer 2, from where it is routed on to the second
mixer 2 and from there on via rise channel 24 to
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solvent extraction settler 3. The phases to be mixed
into a dispersion in the arrangement may be for
instance water and an organic solution. In dispersion
the extraction reaction transfers for example metals
from one phase to the other. The phases are separated
from each other in settler 3.
In Figure 2 the basic structure of pump 1 from Figure
1 is shown in more detail. Pump 1 includes suction
tank 4. The inner space of suction tank 4 is bounded
by bottom 5 in the downward direction. The inner space
of suction tank 4 is bounded by cylindrical, vertical
sidewall 6 in the lateral direction. The inner space
of suction tank 4 is bounded by upper wall 9 in the
upward direction. There is a central opening 10 in the
upper wall. Sidewall 6 of suction tank 4 has an
opening for first inlet channel 7 through which the
first liquid phase is fed into the suction tank, and
an opening for the second inlet channel 8, through
which the second liquid phase is fed into the suction
tank.
Further, pump 1 includes pump section 11, which is
immediately on top of suction tank 4. Pump section 11
includes blade wheel housing 12, which is arranged on
top of suction tank 4 so that upper wall 9 forms the
bottom of blade wheel housing 12, and in which upper
wall 9 central opening 10 forms a suction opening from
which the phases are sucked into blade wheel housing
12. Blade wheel housing 12 is bounded laterally by
vertical, cylindrical sidewall 13 as an upward
continuous extension of sidewall 6 of suction tank 4.
The opening of discharge channel 18 is perpendicular
or tangential in sidewall 13 of blade wheel housing
12. Blade wheel 14, in which there is a set of rotor
blades 15, is arranged in the inner space of blade
wheel housing 12 so that as the blade wheel rotates,
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the first phase and second phase sucked out of suction
tank 4 through suction opening 10 are mixed together
into a dispersion, which can be discharged along
discharge channel 18 to the mixer. The inner space of
blade wheel housing 12 is bounded in the upward
direction by cover plate 19, in which central shaft
bushing 21 is sealed with mechanical shaft seal 20,
through which vertical drive shaft 16 extends into
blade wheel housing 12 and blade wheel 14 is fixed to
the lower end of drive shaft 16. Drive 17 is arranged
to rotate drive shaft 16, which may consist of
electric motor 22 and reduction gear 23.
Pump 1 is particularly suitable for use in large-scale
Cu extraction plants.
As an example of pump size and key figures, it can be
mentioned that the output of pump 1 may be in the or-
der of 50 - 10 000 m3/h. Drive 17 may be adapted to
rotate blade wheel 14 at a peripheral speed of the or-
der of 5 m/s. The pressure of the dispersion in dis-
charge channel 18 may be of the order of 50 kPa.
As an example of the physical dimensions, if the outer
dimensions of a DOP unit with a structure accordant
with the prior art were a diameter of 6.7 m and a
height of 4.01 m, then correspondingly for a structure
accordant with the invention the diameter is 3.4 m and
the height 1.75 m. In comparison with a DOP unit of
the prior art, the equipment volume of a pump accord-
ant with the invention falls by 88 %, the diameter de-
creases by 49 % and the height decreases by 56 %. The
volume of the solution contained in the pump falls by
approx. 75 96.
The invention is not restricted only to the example
applications presented above, but many variations are
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possible while remaining in the framework of the in-
ventive concept defined in the patent claims.
