EP1690592A1

EP1690592A1 - Mixing device and method including an injection nozzle

Info

Publication number: EP1690592A1
Application number: EP05003182A
Authority: EP
Inventors: Christian Schmied; Thomasganesh Puram Meierhans; Hector A. Sullivan
Original assignee: Nestec SA
Current assignee: Nestec SA
Priority date: 2005-02-15
Filing date: 2005-02-15
Publication date: 2006-08-16

Abstract

The invention concerns an apparatus for mixing a first fluid material (B) with a second fluid material (A), comprising a duct (11) having an inlet (12) for the first fluid material (B) and an outlet (14) for the mixture of the fluid materials (A and B) and an injection device (20) for introducing the second fluid material (A) into the duct, characterised in that said duct comprises an injection zone which successively comprises a first, second and third cross-sections, said second cross-section being smaller than said first and third cross-sections in order to generate a turbulent flow at least downstream of said second cross-section and in that the injection device comprises nozzle means arranged in said injection zone, said nozzle means being situated upstream of said second cross-section and being arranged to inject the second fluid material (A) in a direction counter to the flow of the first fluid material (B) from the inlet (12) to the outlet (14) of the duct (11).

Description

FIELD OF THE INVENTION

This invention relates to a process and apparatus for mixing two fluid materials. Mixing of two fluid materials, which may be of different viscosities and may be required to be mixed in equal or unequal amounts, is a common requirement in many industries including food processing and various chemical process industries. In particular the invention relates to a process and apparatus in which one fluid material is injected into a flow of another fluid material with which it is to be mixed.

BACKGROUND TO THE INVENTION

A common method of mixing two fluid materials is by a static in-line mixer. The two materials are made to flow down a duct which contains chicanes and/or baffles which divert the flow of the materials so that they are continually separated and recombined. One example of a static in-line mixer is the 'Primixer' sold by Primix BV, which contains a number of twisted helical elements. After a 180° rotation by one element, the next element is twisted to cause rotation in the reverse direction, and its leading edge is also rotated 90°. Another example is shown in US-5865537, which describes a device for mixing a high viscosity fluid with a low viscosity fluid and has a main line for carrying the the high viscosity fluid having inbuilt static mixing units and a branch line which is routed from the main line to the inlet of the main mixer, with a static auxiliary mixer at the end of the branch line.
US-4441823 describes a static mixer for liquids in which the mixing elements are a multiplicity of slotted orifice plates. When dispersing small volumes of water into oil, water is injected transversely into the oil upstream of the orifice plates.
DE-3611589 describes a static mixer comprising a tube through which the liquids flow in the same direction. An injection apparatus opens out in the narrowest cross-section of a venturi-tube-shaped pipe section of the mixer. The flow medium is injected into the process stream via at least one annular gap, principally in cross-flow to the process stream.
GB-2022430 describes an apparatus for mixing cement and coal slurry in which a liquid or suspension flows through a divergent portion of a passage followed by a convergent portion. An inlet for fluent material to be mixed with the suspension converges with and projects into the divergent portion.
One disadvantage of the known static mixers is that the mixing elements extend over a great length and require a high pressure to force the materials through the mixer. A reduction in the load passing through the mixer can affect the operation of the mixer. Moreover, some materials are sensitive to high pressure and can not be mixed in this type of mixer. A further disadvantage is the difficulty of cleaning the corners of the chicanes, which can pose a hygiene problem, especially in the food and pharmaceutical industries.

SUMMARY OF THE INVENTION

An apparatus for mixing a first fluid material (B) with a second fluid material (A), comprising a duct having an inlet for the first fluid material (B) and an outlet for the mixture of the fluid materials (A and B) and an injection device for introducing the second fluid material (A) into the duct, characterised in that said duct comprises an injection zone which successively comprises a first, second and third cross-sections, said second cross-section being smaller than said first and third cross-sections in order to generate a turbulent flow at least downstream of said second cross-section and in that the injection device comprises nozzle means arranged in said injection zone, said nozzle means being situated upstream of said second cross-section and being arranged to inject the second fluid material (A) in a direction counter to the flow of the first fluid material (B) from the inlet to the outlet of the duct. According to a preferred embodiment of the apparatus of the invention, the duct has substantially a constant cross section and said cross-second section is formed by means of an obstacle arranged within the duct. Advantageously, the injection device comprises a nozzle portion and a cowl portion, and the cowl portion is positioned downstream of the nozzle portion with respect to the direction of flow of the first fluid material (B) and protrudes inwardly from one side of the duct beyond the nozzle portion to form a constriction in the duct.
The invention also concerns a process of mixing a first fluid material (B) with a second fluid material (A), comprising passing the first fluid material (B) through a duct and injecting the second fluid material (A) into the duct, characterised in that it comprises the steps of:

creating an obstacle within the duct so as to generate a turbulent flow in the obstacle region, and
injecting the second fluid material (A) in a direction counter to the flow of the first fluid material (B).

BRIEF DESCRIPTION OF THE DRAWINGS

Other features of the present invention will appear hereinafter in the detailed description of one embodiment, given by way of non-limiting example with reference to the annexed drawings in which:

Figure 1 is a lengthwise section of a mixing apparatus according to the invention;
Figure 2 is an enlarged lengthwise section of a portion the mixing apparatus of Figure 1 in the region of the injection device;
Figure 3 is a perspective view of the injection device shown in Figure 2 showing its position within the duct;
Figure 4 is a bottom view of the portion of the mixing apparatus shown in Figure 2;
Figure 5 is a cross-section of the mixing apparatus of Figure 1, looking downstream at the line 5...5;
Figure 6 is a schematic lengthwise section of a portion the mixing apparatus of Figure 1 in the region of the injection device, showing the turbulent flow believed to occur within the mixer.

The mixing apparatus comprises a duct in the form of a tube 11. The tube has a threaded inlet 12 which can be attached to a feed pipe for a fluid material B and a threaded outlet 14 to which a pipe for conveying the mixed product can be attached. The tube 11 has a convergent portion 16 adjacent the inlet 12 and a divergent portion 17 adjacent the outlet 14, but the tube 11 has a constant cross-section over the main part of its length except in an injection zone where the cross-section varies.
An injection device 20 is joined in injection zone, for example by soldering or welding, to the tube 11. The injection device 20 comprises a nozzle portion 21, a cowl portion 22 and an inlet pipe 23 to which a fluid material A can be fed under pressure. The pipe 23 is conveniently arranged to be substantially perpendicular to the tube 11, although it can be at a different angle if desired. The inlet pipe 23 leads to a pipe portion 24 of narrower cross-section which is angled with respect to the longitudinal direction of tube 11. Preferably the pipe portion 24 is angled in a direction towards the inlet 12 of tube 11, i.e. counter to the flow of fluid material B in tube 11, and towards the centre of tube 11. The pipe portion 24 terminates in a nozzle 25 through which the fluid material A can be injected into the tube 11.
In the example shown, the nozzle portion 21 is integral with a cowl portion 22 which covers the junction of pipe portion 24 and the upper part of feed pipe 23. The cowl portion 22 is preferably wedge-shaped and tapers from its widest point 32. The widest part or crest 32 of the wedge-shaped portion 22 is adjacent to the nozzle portion 21. The crest 32 extends into the tube 11 to about half the diameter of the tube 11, for example 40 to 60% of the diameter of the tube. The crest 32 preferably extends right across the tube 11 in the direction perpendicular to both tube 11 and pipe 23, as seen in Figure 5, although other shapes of crest can be used. The cross-sectional area of the tube available for liquid flow at crest 32 is thus constricted to about half, generally from about 35 to 65%, most preferably 50%, of the total cross-sectional area of the tube. The downstream part 33 of the wedge-shaped portion 22 tapers smoothly in a wedge shape from the crest 32 to the downstream edge 34 of the wedge where the wedge meets the wall of the tube 11. The downstream portion 33 of wedge 22 preferably tapers at an angle of between 10° and 50° to the wall of the tube 11, most preferably about 30°.
Tube 11 thus comprises an injection zone which successively comprises a first, second and third cross-sections. The second cross-section, which is formed at crest 32 of cowl portion 21, is smaller that the first and third cross-sections respectively disposed on either side of crest 32. This configuration of successive cross-sections generates a turbulent flow at least downstream of the second cross-section when fluid material B flows in tube 11. Nozzle portion 21 is arranged in the injection zone, and is situated upstream of the second cross-section so as to inject the second fluid material A in a direction counter to the flow of the first fluid material B from the inlet 12 to the outlet 14 of the duct 11.
In use, a fluid material B is fed to the tube 11 through inlet 12, and a fluid material A is pumped through feed pipe 23 to the nozzle 25 at sufficient pressure that the fluid material A is injected into the flowing material B. The mixing apparatus of the invention is particularly suitable for mixing an additive A in a minor proportion into a fluid B forming a major proportion of the mixed product. For example a flavouring material A can be mixed into a fluid food product B such as yogurt, concentrated milk or sweetened condensed milk or the like. When honey is injected as material A into concentrated milk, we have found that injection pressures in the range 4 to 10 bar are suitable to give consistent injection and thorough mixing according to the invention. The materials A and B can each be single phase or multiphase materials. As depicted in Figure 5, turbulence occurs where the injected material A meets the main flow of material B, causing thorough mixing of A and B. The constriction in tube 11 formed by the crest 32 of wedge-shaped portion 22 causes an acceleration of the liquid flowing through tube 11 at this point. After this constriction there is a rapid pressure drop as the cross-section of the tube increases along the tapering portion 33 of wedge 22, resulting in turbulent flow promoting further mixing of A and B and a self-cleaning effect ensuring that material adjacent the wall of tube 11 or adjacent the wedge-shaped portion 27 of injection device 20 is carried along the tube to the outlet.
The mixing thus induced allows formation of a homogenous mixture of fluids A and B even when A and B are poorly miscible. The mixing apparatus of the invention does not need the chicanes or baffles used in conventional static mixing apparatus. The mixing apparatus mixes efficiently whether the flow of material B in tube 11 is turbulent or laminar flow.
Compared to a conventional static mixing apparatus, the apparatus of the invention has no crevices or dead spaces where unmixed material can accumulate. The mixing apparatus can be extremely compact. Mixing can be achieved in a distance as short as 2 or 3 times the diameter of the tube 11. Moreover, the pressure required to force the main flux of material B through the mixing apparatus is less than is required in conventional static mixing apparatus.
The form of the mixing apparatus of the invention reduces greatly problems concerned with hygiene often encountered in mixing processes in the pharmaceutical and food industries. The mixing apparatus comprising injection device 20 and tube 11 can readily be detached by unscrewing at inlet 12 and outlet 14. The mixing apparatus can then readily be sterilised. This allows use of the mixing apparatus in sterile aseptic processing.

Claims

An apparatus for mixing a first fluid material (B) with a second fluid material (A), comprising a duct (11) having an inlet (12) for the first fluid material (B) and an outlet (14) for the mixture of the fluid materials (A and B) and an injection device (20) for introducing the second fluid material (A) into the duct, characterised in that said duct comprises an injection zone which successively comprises a first, second and third cross-sections, said second cross-section being smaller than said first and third cross-sections in order to generate a turbulent flow at least downstream of said second cross-section and in that the injection device comprises nozzle means arranged in said injection zone, said nozzle means being situated upstream of said second cross-section and being arranged to inject the second fluid material (A) in a direction counter to the flow of the first fluid material (B) from the inlet (12) to the outlet (14) of the duct (11).
A mixing apparatus according to Claim 1, characterised in that said duct has substantially a constant cross section and in that said cross-second section is formed by means of an obstacle arranged within the duct.
A mixing apparatus according to Claim 1 or 2, characterised in that the injection device (20) comprises a nozzle portion (21) and a cowl portion (22), and the cowl portion (22) being positioned downstream of the nozzle portion (21) with respect to the direction of flow of the first fluid material (B) and protruding inwardly from one side of the duct (11) beyond the nozzle portion (21) to form a constriction in the duct.
A mixing apparatus according to Claim 3, characterised in that the cowl portion (22) is a wedge-shaped portion which tapers smoothly from the point (32) at which the wedge protrudes furthest into the duct (11) to the downstream edge (34) of the wedge where the wedge meets the wall of the duct.
A mixing apparatus according to Claim 4, characterised in that the wedge-shaped portion (22) tapers at an angle of between 10° and 50° to the wall of the duct (11).
A mixing apparatus according to any of Claims 1 to 5, characterised in that the nozzle outlet (25) is offset from the centre of the duct (11) and is directed counter to the flow of the first fluid material (B) from the inlet (12) to the outlet (14) of the duct and angled towards the centre of the duct.
A process of mixing a first fluid material (B) with a second fluid material (A), comprising passing the first fluid material (B) through a duct (11) and injecting the second fluid material (A) into the duct, characterised in that it comprises the steps of:
- creating an obstacle within the duct so as to generate a turbulent flow in the obstacle region , and

- injecting the second fluid material (A) in a direction counter to the flow of the first fluid material (B).