CN112118903A

CN112118903A - Mixing device comprising a rotor and a stator

Info

Publication number: CN112118903A
Application number: CN201980032532.4A
Authority: CN
Inventors: M·洛弗格伦; N·埃利克松; R·韦廷德
Original assignee: Valmet AB
Current assignee: Valmet Technologies Oy; Valmet AB
Priority date: 2018-05-18
Filing date: 2019-04-09
Publication date: 2020-12-22
Also published as: SE1850579A1; SE542677C2; EP3793717A4; EP3793717A1; WO2019221652A1

Abstract

According to the present invention, a mixing apparatus (10) for mixing fluids is provided. The apparatus includes a housing (12) having a mixing chamber (14). At least one inlet opening (18) communicates with the mixing chamber (14), wherein the inlet opening (18) enables a fluid to be fed into the mixing chamber (14). At least one outlet (22) is disposed in the housing (12) and communicates with the mixing chamber (14). A rotor (24) is disposed in the mixing chamber (14) and is adapted to be connected to a drive shaft (28) for rotation therewith. The rotor (24) comprises a mixing element (32) arranged around and along an extension of the rotor (24), wherein the rotor (24) comprises a discharge end (34) arranged with a discharge element (36) for radially discharging the fluid. The stator (38) is arranged in the mixing chamber (14) and comprises a plurality of stator openings (40), the stator openings (40) allowing the mixed fluid discharged by the discharge element (36) of the rotor (24) to flow from the mixing chamber (14) radially through the stator openings (40) and further towards the at least one outlet (22), wherein tangential movement of the discharged fluid is prevented.

Description

Mixing device comprising a rotor and a stator

Technical Field

The present invention relates to a mixing device for mixing media or fluids having different density properties, and in particular to a mixing device for mixing a treatment medium into a fibre suspension, such as a lignocellulosic pulp suspension.

Background

In many industrial applications, such as in different chemical industries, it is necessary to mix or blend various chemicals with suspensions of different raw materials into a combination of raw materials, which is important for homogenizing media having different properties, such as different densities, to obtain a homogenous suspension. Such industries include paint manufacturing as well as pulp and paper making.

In the pulping and paper industry, there are several locations where different kinds of media are mixed into the pulp suspension using mixing equipment throughout the entire pulping line, i.e. the different process steps involved in converting wood chips or other fibrous raw materials into pulp. The treatment medium added to the fibre suspension may for example be used for heating, delignification or bleaching purposes. Typically, the treatment medium is gaseous or liquid.

When mixing the treatment medium into the fibre suspension, it is very important for the mixing result to obtain a homogeneous or homogeneous distribution.

Cylindrical mixers are provided in a wide range of configurations. For example, the rotor of the mixer may have a central axis aligned with or arranged perpendicular to the general flow direction of the medium. Also, both the outlet and the inlet of the mixer may be positioned axially with respect to the central axis of the rotor, or one of the inlet or the outlet may be positioned perpendicular to the central axis of the rotor. In many cylindrical mixer configurations, in particular where the outlet is arranged perpendicular to the inlet and the central axis of the outlet is perpendicular to the central axis of the rotor, or in tangential direction with respect to the rotor, there is a residual rotation of the medium (e.g. pulp suspension) flowing out of the mixer.

This residual rotation of the pulp suspension causes separation of the medium or fluid when the mixed media have different densities due to centrifugal forces, which is an undesirable phenomenon especially when gaseous media are mixed with media having higher densities such as pulp.

Accordingly, there is a need for an improved mixing apparatus for mixing media or fluids having different density characteristics, and in particular for mixing a treatment medium into a fiber suspension, such as a lignocellulosic pulp suspension.

Disclosure of Invention

It is an object of the present invention to provide an improved mixing device for mixing media or fluids having different density characteristics.

It is another object of the present invention to provide an improved mixing apparatus for mixing a process medium into a fiber suspension, such as a lignocellulosic pulp suspension.

These and other objects are achieved by the present invention by means of a mixing device for mixing media or fluids according to the claims.

According to one aspect of the invention, a mixing device for mixing a fluid, such as a gaseous medium, into a pulp suspension is provided. The mixing device comprises a housing having a mixing chamber with at least one inlet opening communicating with the mixing chamber. The inlet opening enables the fluid to be fed into the mixing chamber. The drive shaft may be connected to a drive means for rotating the drive shaft in operation, and the rotor is disposed in the mixing chamber and adapted to be connected to the drive shaft for rotation therewith. At least one outlet is disposed in the housing and communicates with the mixing chamber. At least one outlet communicates with the outlet conduit to enable discharge of the mixed fluid. The rotor has a rotor axis extending through the mixing chamber and concentric with the drive shaft, wherein the rotor comprises mixing elements arranged around the rotor and along the extension thereof. The rotor comprises a discharge end arranged with discharge elements for radially discharging the fluid. The stator is arranged in the mixing chamber and comprises stator openings allowing the mixed fluid discharged by the discharge element of the rotor to flow from the mixing chamber radially through the stator openings and further towards the at least one outlet, thereby preventing tangential movement of the discharged fluid.

The invention is based on the insight that by stopping or preventing a residual rotation of the fluid, e.g. a pulp suspension, by means of the stator, and thus a tangential movement of the fluid, during discharge of the fluid, it is possible to minimize the separation of the fluid with different density characteristics caused by centrifugal forces. This effect is also improved by uniformly radially discharging the fluid from the mixing zone within the mixing chamber.

According to an embodiment of the invention, the central axis of the outlet duct is displaced perpendicularly, e.g. radially, with respect to the central axis of the rotor in a direction towards the at least one outlet.

In an embodiment of the invention, the internal volume of the outlet conduit increases in proportion to the volume of the discharged fluid in the flow direction.

According to an embodiment of the invention, the stator is shaped as a tubular element.

In an embodiment of the invention, the stator opening is arranged radially adjacent to and outside the discharge element of the rotor in the flow direction.

According to an embodiment of the invention, the stator openings are distributed along the entire circumference of the stator to provide a symmetrical fluid discharge flow.

In an embodiment of the invention, the mixing elements of the rotor are protrusions having a curved or angled rear surface in the direction of rotation of the rotor.

According to an embodiment of the invention, the mixing elements of the rotor are distributed along substantially the entire longitudinal extension of the rotor.

In an embodiment of the invention, the discharge elements of the rotor are protrusions that are curved or angled in the flow direction.

According to an embodiment of the invention, the stator is surrounded in radial direction by a discharge space, which is defined by the inner wall of the housing, the discharge end of the rotor and the stator. The discharge space communicates with the outlet duct via the at least one outlet, wherein, during operation, fluid is forced through the stator opening and flows in the discharge space in a semicircular flow towards the at least one outlet and the outlet duct.

Further advantageous embodiments of the device according to the invention and further advantages of the invention emerge from the detailed description of the embodiments.

Drawings

The invention will now be described in more detail, for the purposes of example, by means of embodiments and with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic axial cross-section of a first preferred embodiment of the invention;

FIG. 2 shows a schematic partial cross-section of a first preferred embodiment of the invention;

FIG. 3 shows a schematic view of the mixing device and the outlet opening in a direction perpendicular to the central axis of the rotor and the shaft;

fig. 4 shows a schematic cross-sectional view of the mixing device in a direction along the extension of the central axis of the rotor and the shaft;

fig. 5 schematically shows the exterior of the housing of the mixing device according to the invention.

Detailed Description

In the drawings, similar or corresponding elements are denoted by the same reference numerals. Generally, in the figures, the arrows indicate the direction of fluid flow into and out of the mixing device in the mixing device.

For the purposes of this disclosure, the term "longitudinal" refers to the direction of the body, component or element along which it extends most. Further, when the term "longitudinal" is used in connection with an axis of a shaft or the like, the longitudinal axis corresponds to the axis of rotation of the shaft or the like.

Referring first to fig. 1, a mixing apparatus 10 includes a housing 12, wherein the interior thereof is referred to as a homogenization chamber or mixing chamber 14, each having an inlet conduit 16, the inlet conduit 16 having an inlet 18 into the mixing chamber 14. Furthermore, the mixing device 10 comprises an outlet duct 20, which outlet duct 20 has an outlet 22 from the mixing chamber 14, and a rotor 24, which rotor 24 is arranged axially to the flow direction from the inlet opening 18 and transversely to the flow direction to the outlet 22.

In this embodiment of the invention, as shown in fig. 5, the housing 12 is preferably of cylindrical, shell or spiral design. The housing 12 is also provided with an end or cap 26. The end cap 26 includes a substantially central opening for the shaft 28 of the rotor 24, with the necessary sealing, and possibly a carrier for the shaft 28.

As mentioned above, the generally cylindrical wall of the housing 12 is provided with the inlet 18 and the outlet 22. Preferably, the shape of the inlet opening 18 is such that the central axis and the axis of symmetry are the same as the central axis R of the rotor 24 and the shaft 28_RAre concentric.

In some embodiments of the invention, the outlet 22 is shaped as a rectangle as shown in FIG. 3. FIG. 3 is a view of the central axis R perpendicular to the rotor 24 and shaft 28_RSchematically illustrating the mixing apparatus 10 and the outlet 22.

According to a preferred embodiment of the invention, the outlet duct 20 is shaped such that the central axis R of the outlet duct 20_ouRelative to the central axis R of the rotor 24_RRadially in the direction towards the outlet 22 and such that the internal volume of the outlet conduit 20 increases in proportion to the volume of fluid discharged.

Thus, the rotor 24 is mounted to a shaft 28 in the mixing chamber 14 and rotates with the drive shaft 28. The shaft 28 is driven by a motor, such as an electric motor. The rotor 24 has a plurality of mixing elements 32 arranged around the rotor and along the longitudinal extension thereof.

Furthermore, the rotor 24 comprises a discharge end 34 arranged with a discharge element 36, the discharge element 36 being intended for being arranged with respect to a centre axis R of the rotor 24_RThe fluid is discharged in a substantially radial direction towards the outlet 22 and the outlet conduit 20.

The purpose of the mixing element 32 is to induce turbulence in the fluid or medium, thereby obtaining homogenization or mixing of the fluid or medium and avoiding, for example, separation of the gas from the medium. However, as the skilled person realizes, the shape and design of the mixing elements 32 and their number and exact position on the rotor relative to the inner wall of the housing, relative to the inlet opening, depend on the medium or media to be treated, the consistency of the medium or media, the gas content of the medium, the volume flow through the mixing chamber, the amount of gas added to the medium or media, to mention a few influencing parameters. In addition to causing turbulence, the mixing elements also cause the media to flow through the mixing chamber towards the end of the rotor, for example, wherein the flow rate of one or more media can be adjusted in particular by means of the rotational speed of the rotor.

According to certain embodiments, the mixing elements 32 may be distributed in a gradually shifted manner along the longitudinal extension of the rotor 24, such that each row of mixing elements 32 is relative to the central axis R of the rotor 24_RArranged in an inclined manner. Further, in certain embodiments, the mixing elements 32 are protrusions having a curved or angled rear surface in the direction of rotation of the rotor 24, while the discharge elements 36 are protrusions that are curved or angled in the direction of flow.

The stator 38 is arranged at the end of the mixing chamber 14 adjacent to the outlet 22. The stator 38 includes a plurality of stator openings 40, the stator openings 40 being arranged radially adjacent to the discharge element 36 of the rotor 24 and outside of the discharge element 36 of the rotor 24 in the flow direction (indicated by the arrows).

Preferably, the stator 38 is shaped as a tubular element arranged inside the housing, for example as an insert liner or attached to the housing by means of, for example, bolts or screws. The important purpose of the stator 38 and stator openings 40 is essentially to act as an end of the mixing zone within the mixing chamber 14 and to impede or prevent tangential movement of the discharge fluid as it enters or flows through the stator openings 40.

A general problem in prior art mixing devices is that the gas is separated from the medium during the outflow or discharge caused by the remaining rotation in the medium, because the centrifugal force has a different effect on the gas, for example compared to a liquid or slurry suspension. This is a significant problem when the gas is mixed with the slurry suspension.

Turning now to FIG. 4, it is shown at a central axis R along the rotor 24 and shaft 28_RI.e. the figures refer toOut of the central axis R of the rotor 24_RA schematic cross-sectional view of the mixing device in the direction of the extension of (a). As shown in fig. 4, the stator 38 is surrounded in the radial direction by a discharge space 42, which discharge space 42 communicates with the mixing chamber 14 via the stator opening 40 and with the outlet duct 20 via the outlet 22.

The discharge space 42 is bounded by the inner wall 44 of the housing 12, the discharge end 34 of the rotor 24, and the stator 38. In fig. 4, the flow of the medium is indicated by arrows B, C and D. The arrow B shows the flow of the medium in the mixing chamber 14, wherein the rotation of the rotor 24 causes turbulence and rotation of the medium, thereby homogenizing and mixing the medium, e.g. gaseous medium and slurry suspension. Arrow C shows the discharge of the medium through the stator opening 40, while arrow D shows the semicircular medium flow following the inner wall 44 of the housing 12 towards the outlet 22 and then further to the outlet duct 20. As shown in fig. 4, the volume and width of the discharge space 42 (considered as the distance between the stator 38 and the inner wall 44 of the housing 12) increase in the flow direction.

The invention should not be regarded as being limited to the embodiments shown, but may be modified and substituted in many ways by a person skilled in the art without departing from the scope of the appended claims.

Claims

1. A mixing device (10) for mixing fluids, comprising:

a housing (12) having a mixing chamber (14), at least one inlet opening (18) communicating with the mixing chamber (14), the inlet opening (18) enabling fluid to be fed into the mixing chamber (14),

a drive shaft (28) connectable to a drive device to rotate the drive shaft (28) in operation,

at least one outlet (22) provided in the housing (12) and communicating with the mixing chamber (14), the at least one outlet (22) communicating with an outlet duct (20) to enable discharge of the mixed fluid;

a rotor (24) arranged in the mixing chamber (14), the rotor being adapted to be connected to the drive shaft (28) for rotation with the drive shaft (28),the rotor (24) has a central axis (R)_R) A central axis extending through the mixing chamber (14) and concentric with the drive shaft (28), the rotor (24) comprising mixing elements (32) arranged around and along the extension of the rotor (24), wherein the rotor (24) comprises a discharge end (34) arranged with discharge elements (36) for radially discharging fluid; and

a stator (38) arranged in the mixing chamber (14), the stator comprising a plurality of stator openings (40), the stator openings (40) allowing the mixed fluid discharged by the discharge elements (36) of the rotor (24) to flow from the mixing chamber (14) radially through the stator openings (40) and further towards the at least one outlet (22), thereby preventing tangential movement of the discharged fluid.

2. Mixing device according to claim 1, wherein the central axis (R) of the outlet duct in the housing (12)_ou) Relative to the central axis (R) of the rotor (24)_R) Is vertically displaced in a direction towards the at least one outlet (22).

3. Mixing device according to claim 2, wherein the internal volume of the outlet duct (20) increases in proportion to the volume of the discharged fluid in the flow direction.

4. Mixing device according to any of the preceding claims, wherein the stator (38) is shaped as a tubular element.

5. Mixing apparatus according to any one of the preceding claims, wherein the stator opening (40) is arranged radially adjacent to and outside the discharge element (36) of the rotor (24) in the flow direction.

6. Mixing apparatus according to any of the preceding claims wherein the stator openings (40) are distributed along the entire circumference of the stator (38) to provide a symmetrical fluid discharge flow.

7. Mixing device according to any of the preceding claims, wherein the mixing elements (32) of the rotor (24) are protrusions having a curved or angled rear surface in the direction of rotation of the rotor (24).

8. Mixing device according to any one of the preceding claims, wherein the mixing elements (32) of the rotor (24) are distributed along substantially the entire longitudinal extension of the rotor (24).

9. Mixing device according to any of the preceding claims, wherein the discharge elements (36) of the rotor (24) are protrusions curved or angled in the flow direction.

10. Mixing apparatus according to any of the preceding claims, wherein the stator (38) is surrounded in radial direction by a discharge space (42), the discharge space (42) being delimited by an inner wall (44) of the housing (12), the discharge end (34) of the rotor (24) and the stator (38), the discharge space (42) communicating with the outlet duct (20) via the at least one outlet (22), wherein during operation fluid is forced through the stator opening (40) and flows in the discharge space (42) towards the at least one outlet (22) and the outlet duct (20) in a semicircular flow.