[0001] This invention relates to a method and apparatus for mixing a liquid and solids and
more particularly but not exclusively to the continuous mixing of a liquid and solids
in powder form.
[0002] According to one aspect of the present invention, there is provided a method of mixing
a liquid and solids, the method comprising feeding the solids into the liquid whilst
the liquid is swirling about the surface of a chamber which is converging downwardly
towards an outlet, the chamber comprising at least two frusto-conical portions thereof
disposed one above the other, the upper said portion having a substantially larger
included angle than that of the lower said portion.
[0003] According to a second aspect of the invention, there is provided apparatus for the
mixing of a liquid and solids by the method of the first aspect of the invention,
the apparatus comprising a chamber having a plurality of inlets for the liquid aligned
so as to induce swirling of the liquid at an upper end of the chamber and an outlet
at the lower end of the chamber, and means for feeding the solids into the upper end
of the chamber, the chamber comprising at least two frusto-conical portions thereof
disposed one above the other, the upper said portion having a substantially larger
included angle than that of the lower said portion.
[0004] Preferably, the liquid flows in turbulent flow about the portions. Desirably, the
included angles of the portions are such as to maintain the tangential component of
flow of the liquid thereon above a predetermined velocity.
[0005] In one form of the invention, the solids may comprise powder having an average particle
size between 5 and 500µm, for example micronised powder having an average particle
size of between 5 and 10µm.
[0006] The invention will now be further described by way of example only and with reference
to the accompanying drawings in which:
Figure 1 shows a schematic representation of a liquid/solids mixing apparatus;
Figure 2 shows to an enlarged scale a fragmentary portion of Figure 1;
Figure 3 shows to an enlarged scale a sectional view on the line III-III of Figure
1;
Figure 4 shows a sectional view on the line IV-IV of Figure 3, and
Figure 5 shows to an enlarged scale a fragmentary view on the line V-V of Figure 1.
[0007] Referring to Figure 1 a liquid/solids mixing apparatus 10 is shown and comprises
an inlet head assembly 12, and a collecting vessel 14. A powder feed 16 is arranged
to drop powder through the inlet head assembly 12 into a converging chamber 18. The
chamber 18 as shown more clearly in Figure 2 has an upper frusto-conical portion 20
joined to a lower frusto-conical portion 22 having an outlet 24 to the collecting
vessel 14. An inlet 26 for liquid discharges into the inlet head assembly 12. The
collecting vessel 14 discharges through an outlet 28 into a pipeline 30 connected
to a pump 32. The pump 32 has a product discharge line 34 with a branch line 35 for
recycling, when desired, mixed liquid and solids to the chamber 18.
[0008] In more detail and referring now to Figures 3 and 4, the inlet head assembly 12 comprises
parallel circular flanges 36, 38 respectively having between them a body member 40
defining an annular plenum chamber 42 into which the inlet 26 discharges. A plurality
of nozzles 44 (ten are shown) from the plenum chamber 42 are aligned substantially
tangentially to a cylindrical inlet chamber 46 to connect the plenum chamber 42 thereto.
The upper portion 20 is joined to the flange 38 below the inlet chamber, and a tube
48 from the powder feed 16 (not shown in Figures 2 and 3) extends through the inlet
chamber 46 to discharge into the upper portion 20. At the outlet 28 of Figure 1, a
vortex breaker 50 as shown in Figure 5 eliminates air flow associated with swirling
liquid, the vortex breaker 50 comprising a circular plate 52 having several (three
are shown) holes 54 therethrough for liquid flow.
[0009] In operation, liquid is injected through the inlet 26 into the plenum chamber 42
and is discharged through the nozzles 44 into the inlet chamber 46 at an angle thereto
so as to set up a swirling motion. From the inlet chamber 46 the liquid falls onto
the upper portion 20, and because of the relatively large angle defined by the upper
portion 20 the downward liquid flow is retarded which ensures that the entire surface
of the upper portion 20 is wetted by the liquid. From the upper portion 20 the swirling
liquid falls into the lower portion 22, and then whilst still swirling falls through
the outlet 24 into the collecting vessel 14. Powder fed from the powder feed 16 and
through the tube 48 falls onto the wetted surface of the upper portion 20 and the
lower portion 22, where it is entrained in the liquid thereon. The effect of the angular
shape of the upper portion 20 and the lower portion 22 is to overcome frictional effects
and maintain the tangential component of flow of the liquid as it falls in the chamber
18. Hence the swirling motion of the liquid is maintained as it falls in the chamber
18 into the vessel 14. The mixed liquid/powder is then discharged through the outlet
28 and the pipe 30 to the pump 32.
[0010] The rate of flow of the liquid is arranged to ensure that there are no dry areas
on the upper portion 20 and the lower portion 22 on which powder could collect. The
flow is also arranged to be turbulent in the chamber 18 to enhance entrainment of
the powder by the liquid. A typical liquid flow velocity of about 6.5 m/sec at a pressure
of 3 x 10⁵ Nm² has been suitable for some applications, in which the upper portion
20 defines an angle from the vertical of 30° (ie 60° included angle) and the lower
portion 22 an angle from the vertical of between 7 to 10° (14°-20° included angle).
[0011] The liquid may be organic, for example an organic solvent, or aqueous, for example
an acid or alkali solution. The powder may have an average particle size between 5
and 500µm, for example micronised powder having an average particle size of between
5 and 10 µm.
[0012] One advantage of the invention is that continuous mixing of the liquid and solids
occurs, and the absence of dry areas on the mixing surfaces inhibits the local build-up
of solids. If necessary the mixed liquid and solids may be recycled through the apparatus
via the branch line 35. A conventional screw feeder device (not shown) may be used
to feed powder to the powder feed 16.
EXAMPLES
EXAMPLE I
[0013] Mixing kieselguhr powder with water as follows:-
a) powder feed @ 90ℓ/hr ≡ 18kg/hr 420ℓ/hr water
b) as (a) but with 48ℓ/hr water
c) powder feed @ 200ℓ/hr ≡ 40kg/hr 420ℓ/hr water
d) as (c) but 195ℓ/hr water
EXAMPLE II
[0014] Pharmaceutical powders:
a) base powder at 22-44kg/hr organic solvent mix @ 120→240ℓ/hr
b) base powder @ 22-44kg/hr organic solvent @ 170→340ℓ/hr
EXAMPLE III
[0015] Flocculent Dispersal Aid:
granules @ 0.3 to 1.2kg/hr
water @ 195-390ℓ/hr
[0016] The liquids and solids of the above EXAMPLES were successfully mixed using the apparatus
of Figures 1 to 5.
1. A method of mixing a liquid and solids, characterised by feeding the solids into the
liquid whilst the liquid is swirling about the surface of a chamber (18) which is
converging downwardly towards an outlet (24), the chamber (18) comprising at least
two frusto-conical portions (20,22) thereof positioned one above the other, the upper
said portion (20) having a substantially larger included angle than the included angle
of the lower said portion (22).
2. A method as claimed in Claim 1, wherein the liquid flows in turbulent flow about the
portions (20,22).
3. A method as claimed in Claim 1 or Claim 2, wherein the included angles of the portions
(20,22) are such as to maintain the tangential component of flow of the liquid thereon
above a predetermined velocity.
4. A method as claimed in Claim 3, wherein the liquid has a flow velocity of about 6.5m/sec.
5. A method as claimed in Claim 3, wherein the liquid is injected into the upper portion
(20) at a pressure of about 3x10⁵Nm².
6. A method as claimed in Claim 3, wherein the solids comprise powder having an average
particle size of between 5 and 500µm.
7. A method as claimed in Claim 6, wherein the powder has an average particle size of
between 5 and 10µm.
8. A method as claimed in Claim 6, wherein the solids comprise kieselguhr or a flocculent
dispersal aid.
9. A method as claimed in Claim 8, wherein the liquid comprises water.
10. A method as claimed in anyone of Claims 1 to 7, wherein the solids comprise a pharmaceutical
compound.
11. A method as claimed in Claim 10, wherein the liquid comprises an organic liquid.
12. A method as claimed in Claim 11, wherein the organic liquid has a flow rate between
170 and 340ℓ/hr.
13. A method as claimed in any one of the preceding Claims, wherein mixed liquid and solids
from the outlet (24) are recycled through the chamber (18).
14. Apparatus for the mixing of a liquid and solids by the method as claimed in Claim
1, characterised by a chamber (18) having a plurality of inlets (44) for the liquid
aligned so as to induce swirling of the liquid at an upper end of the chamber (18)
and an outlet (24) at the lower end of the chamber (18), and means (16,48) for feeding
the solids into the upper end (46) of the chamber (18), the chamber (18) comprising
at least two frusto-conical portions (20,22) thereof disposed one above the other,
the upper said portion (20) having a substantially larger included angle than that
of the lower said portion (22).
15. An apparatus as claimed in Claim 14, wherein the inlets (44) are arranged to be supplied
from an annular plenum (42) defined about the chamber (18).
16. An apparatus as claimed in Claim 14 or Claim 15, wherein the outlet (24) is connectable
to an inlet of a vessel (14) for collecting solids and liquid mixed in the chamber
(18).
17. An apparatus as claimed in Claim 16, wherein a vortex breaking means (50) is disposed
at an outlet (28) from the vessel (14).
18. An apparatus as claimed in any one of Claims 14 to 17, wherein the solids feeding
means (48) extends to below the inlets (44) but terminates above the upper portion
(20).
19. An apparatus as claimed in any one of Claims 14 to 18, wherein the upper portion (20)
has an included angle of about 60°C.
20. An apparatus as claimed in any one of Claims 14 to 19, wherein the lower portion (22)
has an included angle of between 14° and 20°.
21. An apparatus as claimed in any one of Claims 14 to 20, wherein the inlets (44) are
aligned so as to be substantially tangential to the upper end (46) of the chamber
(18).
22. An apparatus as claimed in any one of Claims 14 to 21, wherein pump means (32) are
connectable with the vessel outlet (28) so as to extract mixed liquid and solids from
the vessel (14).
23. Apparatus as claimed in Claim 22, wherein the pump means (32) is arranged to discharge
through discharge duct means (34), and branch duct means (35) are connectable to the
discharge duct means (34) for recycling mixed liquid and solids to the chamber (18).