RU2683078C1 - Mixing device - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: invention is intended for processes of mixing in heterogeneous systems: for suspending, homogenisation of suspension, especially in large volumes, including with special requirements for gentle mixing, when tangential stresses in liquid should not exceed certain threshold, admissible from the point of view of prevention of particles destruction, for example, activated sludge. Mixing device can be used at chemical and hydrometallurgical production enterprises, food, pharmaceutical industry, in water treatment for maintenance of active sludge in suspended state, and also in those industries, where according to production conditions it is necessary to prevent formation of residue on bottom of apparatus and to maintain solid phase in suspended state, providing good mass transfer from particles to liquid. In a mixing device comprising a hub mounted on a rotating vertical shaft, on which blades with a disc are fixed, the disk is attached to the blades from below, the blades have a curved surface shape with a generatrix parallel to the shaft, on inner diameter of blade are equipped with bent flange for attachment to hub, and on outer diameter blades are equipped with horizontal platform for attachment to disc, wherein disk has central hole, and blade upper edge is made reducing from outer diameter of hub to outer diameter of disc, and lower edge of blade is made reducing from outer diameter of hub to diameter of hole in disc. Angle between tangent to blade surface at its attachment point to hub and tangent to hub is in range from 15 to 90°, and the angle between the tangent to the blade surface at the point with the largest diameter and the tangent to the disc surface is sharp, wherein the blades are attached to the hub and the disc by means of threaded fasteners.EFFECT: invention improves the quality of mixing, simplifies the design of the mixing device, simplifies transportation, assembly and installation, easily reconstructs the mixing device when changing properties of the mixed media, concentration of the solid phase, viscosity and density.1 cl, 8 dwg, 2 tbl

Description

The invention is intended for mixing processes in heterogeneous systems: for suspending, homogenizing a suspension, especially in large volumes, including with special requirements for gentle mixing, when the tangential stresses in the liquid should not exceed a certain threshold that is acceptable from the point of view of preventing particle destruction, for example activated sludge. The mixing device can be used at chemical and hydrometallurgical enterprises, food and pharmaceutical industries, in water treatment to maintain activated sludge in suspension, and also in those industries where, under production conditions, it is necessary to prevent the formation of sediment at the bottom of the apparatus and maintain the solid phase in suspended state, providing good mass transfer from particles to liquid.

Currently, mixing devices of various types are used. A significant proportion of them are mixers with a vertical rotating shaft, on which working bodies are fixed - blades, blades, combs, etc. [Shterbachek, P. Tausk. Mixing in the chemical industry. Per. from Czech, ed. I.S. Pavlushenko, L .: Goskhimizdat, 1963]. The main problem when mixing suspensions is the sedimentation of solid particles on the walls and bottom. One of the most common types for mixing suspensions are turbine mixers. This type of mixer operates on the principle of a centrifugal pump. The rotational motion of the blades is transmitted to the liquid, due to centrifugal forces, a strong radial flow occurs, which, in turn, ensures complete circulation of the entire volume of the mixed component. To prevent the formation of a funnel in the apparatus, reflective partitions are installed, which, in addition, contribute to the creation of a meridional circulation in the apparatus.

The disadvantages of turbine mixers include: 1) a high level of power consumption, especially in the presence of reflective walls (power criterion reaches 8.4) [Braginsky L.N., Begachev V.I., Barabash V.M. Mixing in liquid media. L .: Chemistry, 1984. 336 p.]; 2) an excessively high level of shear stresses near the mixer blades, which can lead to undesirable damage to particles (for example, activated sludge or microorganism cells). If you reduce the speed of the turbine stirrer to reduce hazardous effects on the particles, the quality of mixing is also reduced.

Known agitator hyperboloid type [German Patent DE 4218027 A1 from 05/30/1991. Hyperboloid-Ruehr- und Begasunssystem zum Ruehren, Mischen und Begasen in einoder mehrphasigen Fluiden; B01F7 / 26], containing the body of the mixer in the form of a hyperboloid of revolution, on the upper curved part of which the working bodies are made in the form of short low-profile blades, and the blades are also made on the lower part.

This agitator also works on the principle of a centrifugal pump, but, unlike turbine agitators, it is more economical because, thanks to its special, streamlined shape, it consumes less power. In addition, it provides gentle mixing without destroying the flakes formed during biological wastewater treatment.

The disadvantages of the known device include: 1) the high complexity of manufacture, especially with diameters greater than 0.5 m, typical of mixers used for treatment facilities; 2) the difficulty of transporting large mixers (1–2 m or more) due to the bulkiness of the non-separable structure; 3) too short blades do not allow to achieve high quality mixing in the apparatus.

Known mixer (analog device) of the hyperboloid type [German Patent DE 10 2005 016 948 B3. Ruehrvorrichtung und Verfahren zur Abwasserbehandlung; Claim 04/12/2005], containing the body of the mixer in the form of a hyperboloid of revolution, on the upper curved part of which the working bodies are made in the form of long low-profile blades, and on the lower part the blades are also made, while several small holes are made in the body of the mixer near the shaft. In the known invention, the height of the blades increases in the direction from the outer diameter to the shaft. Known agitator allows to achieve improved circulation in the apparatus and particle weighing.

The disadvantages of the analog device include the first two drawbacks inherent in the mixer described above: 1) the high complexity of manufacture, especially with diameters of more than 0.5 m, typical of mixers used in sewage treatment plants (a large mold is required for the manufacture of blades); 2) the difficulty of transporting large-sized mixers (1–2 m or more) due to the bulkiness of the non-separable structure. In addition, there is another drawback: 3) the inability to regulate the circulation flow through the holes in the body of the mixer due to the increase in their number or size, because this will reduce the mechanical strength of the mixer, and it may collapse during rotation.

Known agitator (prototype device) of a hyperboloid type [US Patent United States Design Patent US D735291 S. Fluid moving device; Claim 12/11/2013. Publ. 06/28/2014], containing the body of the mixer in the form of a hyperboloid of revolution, on the upper curvilinear part of which the working bodies are made in the form of long low-profile blades, and on the lower part the blades are also made, while several oblong holes are made in the body of the mixer near the shaft. The design of the known mixer allows to simplify the assembly of the mixer of large sizes, however, its shape involves the manufacture mainly of metal parts with subsequent fastening by welding, riveting or threaded fasteners, since it is the metal parts that will ensure the accuracy of the manufacture and assembly of the mixer of this design. Production from less durable materials, such as plastics, will lead to a significant increase in the thickness of parts and complication of molds, in addition, due to a decrease in manufacturing accuracy, assembly problems will arise. At the same time, the manufacture of an agitator from affordable metals (carbon steel, aluminum) is associated with the need to protect them from corrosion. In the case of the manufacture of a metal stirrer with subsequent protection (for example, by coating with a paint or plastic lining), problems arise with paint adhesion due to temperature fluctuations (which is especially important in countries with different climatic zones, for example, for Russia, where the equipment is transported in winter at minus 30 ° C, and the equipment operates in water at a temperature of + 5 ° C). In addition, the prototype mixer does not provide for the possibility of varying the orifice of the holes, which does not allow you to adapt the speed of circulation through them depending on the requirements of the process. An arbitrary increase in their size and / or number may lead to the destruction of the mixer. This circumstance limits the scope of the known device.

The objective of the invention is to improve the quality of mixing, simplifying the design of the mixing device, providing easier transportation, assembly and installation (which is especially important for large-sized mixers with a diameter of 1-2 m or more), expanding the functionality of the mixing device in order to adapt to various requirements of the process (due to the possibility of completing the same set of blades with disks with different diameters of the central hole), ensuring soft reconstruction stirring device when changing the properties of the stirred medium, the concentration of solids, viscosity, and density.

The solution of this problem is achieved by the fact that in a mixing device containing a hub mounted on a rotating vertical shaft, on which the blades with a disk are fixed, according to the invention, the disk is attached to the blades from below, the blades have a curved surface with a generatrix parallel to the shaft, on the inner diameter of the blade equipped with a bent shelf for attachment to the hub, and on the outer diameter of the blades are equipped with a horizontal platform for attachment to the disk, while the disk has a central hole, and the top I the edge of the blade is made decreasing from the outer diameter of the hub to the outer diameter of the disk, and the lower edge of the blade is made decreasing from the outer diameter of the hub to the diameter of the hole in the disk.

The solution to this problem is also achieved by the fact that in the mixing device, the angle between the tangent to the surface of the blade at the point of attachment to the hub and the tangent to the hub is made in the range from 15 to 90 °, and the angle between the tangent to the surface of the blade at the point with the largest diameter and tangent to the surface of the disk is made sharp, while the blades are attached to the hub and disk using threaded fasteners.

In FIG. 1 shows a General view of the proposed device (a is a perspective view,
b is a top view), in FIG. 2 - fixing the blades on the inner diameter using a bent shelf to the hub. In FIG. 3 shows a scapula in a perspective view. In FIG. 4 shows a diagram of the operation of the proposed device and the occurrence of circulating currents in the apparatus.

In FIG. 5 is a test diagram of the impellers of the proposed mixing device in a rectangular apparatus. In FIG. 6 using the photographs of the bottom of the apparatus, made from the bottom, presents the dynamics of the release of the bottom from the sediment when using the mixing device according to the invention (under the photographs are the moments of time from the beginning of the mixing process). In FIG. 7 is a diagram of measuring the area of sediment at the bottom during the mixing process, used as a criterion for the quality of mixing. In FIG. 8 shows a comparison of the results of suspension for 3 minutes of stirring in a rectangular apparatus using the proposed (a) and known (b) mixers (made in accordance with the known invention - an analog device).

The technical result of the invention is: increasing the efficiency of the apparatus with the mixer, simplifying the design of the mixer and reducing the cost of its manufacture, the possibility of transportation in a disassembled state and easy assembly at the place of use, the ability to produce not only from metal, but also from polymeric materials (which is especially important from the point of view of ensuring corrosion resistance), providing the ability to regulate the circulation flow through the Central hole in the mixer, made in dis e, which, ultimately, it allows to intensify the process of mixing and suspending in the apparatus.

This result is achieved due to the following factors.

Increasing the efficiency of the apparatus consists in increasing the proportion of particles passing into a suspended (suspended) state due to more intensive mixing, as well as due to the creation of meridional circulation in the apparatus due to the presence of a central hole in the disk of the mixer, the size of which is selected depending on the set of organization requirements mixing process. Moreover, when setting up the apparatus, a set of disks with different diameters of the central holes can be used, as well as, if necessary, with different external diameters in order to adapt to specific mixing conditions.

Simplification of the design of the mixer is achieved by simplifying the shape of the parts (the disk and the hub have an extremely simple shape, and for the manufacture of blades a mold of a fairly simple design is also required).

The reduction in the cost of manufacturing the mixer is achieved by reducing the overall material consumption of the device compared to the analog device and the prototype device. In addition, the collapsible design of the proposed device can significantly reduce the dimensions of the product during transportation, which is especially true for mixers with a size of 1-2 meters or more.

The design features of the proposed device make it possible to produce its main parts (blades, disc, hub) from polymer materials, which also helps to reduce the cost and increases the corrosion resistance of the mixer. Fasteners can be made from corrosion-resistant steels or other alloys, as well as from any other materials suitable for these purposes.

The ability to control the circulation flow through the central hole in the mixer made in the disk is achieved by using disks with different diameters of the central hole or by manufacturing a disk with a central hole that is optimal for the given process conditions (particle size and density, density and viscosity of the liquid , dimensions of the apparatus) diameter. The indicated optimum diameter is determined experimentally, by numerical simulation, or directly when setting up the installation at the place of use.

The claimed technical solution is new, has an inventive step and is industrially applicable.

The device comprises a hub 1 mounted on a rotating vertical shaft (not shown in FIGS. 1 and 2), blades 2 are fixed on the hub 1 with a disk 3 attached to them from below. The blades 2 have a curved surface shape with a generatrix parallel to the shaft, on the inner diameter, coinciding with the outer diameter of the hub 1, the blades 2 are equipped with a bent shelf 4 for attachment to the hub 1, and on an external diameter not exceeding the outer diameter of the disk 3, the blades 2 are equipped with a horizontal platform 5 for attachment to the disk 3, while in the disk 3 a cent cial opening 6. The upper edge 7 of the blades 2 operate by decreasing the outer diameter of the hub 1 to the outer diameter of the disk 3 and the lower edge 8 of the blades 2 operate by decreasing the outer diameter of the hub 1 to the diameter of the hole 6 in the disc 3, as shown in FIG. 1a and FIG. 3.

The angle α between the tangent to the surface of the blade at the point of attachment to the hub and the tangent to the hub (Fig. 1b) is in the range from 15 to 90 °, and the angle β between the tangent to the surface of the blade 2 at the point with the largest diameter and tangent to the surface of the disk 3 (Fig. 1b) are sharp, while the attachment of the blades 2 to the hub 1 and the disk 3 is carried out using threaded fasteners - bolts 9. The implementation of the angles α and β within the specified limits, as shown by studies, allows to achieve the absence of cavitation bubbles and reduce behind Rata energy mixing.

The proposed mixing device operates as follows. A mixing device is mounted on a vertical shaft, at the other end of which a drive is located, as shown in FIG. 4. When the shaft rotates, the torque is transmitted through the hub 1 to the blades 2 and the disk 3 attached to them. When the surface of the blades 2 interacts with the liquid in the apparatus, rotational motion is transmitted to it, a complex velocity field with three components arises in the apparatus: circumferential, radial and axial. The peripheral speed is an order of magnitude or more greater than the other two velocity components. As a result of rotational motion, centrifugal inertia forces arise in the apparatus, generating radial motion. Due to the rectangular shape of the apparatus (typical for sewage treatment plants) near the walls, the rotational movement substantially attenuates, partially turning into meridional (axial), which contributes to the creation of meridional circulation and the lifting of particles from the bottom of the apparatus, i.e. their weighing (suspension).

The same purpose is served by making holes 6 in the disk 3. In FIG. 4 shows the occurrence of circulation flows in the apparatus with liquid during operation of the proposed mixing device: the lower circulation current 9 in the lower part of the apparatus, along the bottom surface of the apparatus and the upper circulation current 10 in the upper part of the apparatus. The circulation flow 9 is more intense, since it is closed on a shorter path, and the expansion of the flow does not occur as much as for flow 10, i.e. the cross section of the flow is smaller, which means that the flow velocity is higher. As a result of the intense influence of the circulation flow 9 on the sediment particles, it erodes rapidly, most of the bottom surface is fairly quickly released from the particles, i.e. particles pass into a suspended (suspended) state. Moreover, due to the curved shape of the blades, the level of shear stresses in the liquid in the zone of their movement is significantly lower than for known mixing devices (for example, turbine or paddle mixers with radial or propeller blades), which allows gentle mixing of sensitive substances, for example, activated sludge.

An example of a specific implementation 1. This example describes a known solution.

The purpose of the experiments was to determine the effectiveness of mixing during the suspension of fine particles simulating activated sludge in water treatment systems. As a criterion for the mixing effect, the bottom area of the apparatus, free of sediment after stirring for 3 minutes, was taken. The ratio of the area completely freed from particles (i.e., the area over which the particles were completely suspended) to the total bottom area of the apparatus was considered as a criterion for mixing efficiency. In this case, the level of energy spent on mixing was maintained approximately the same (within the experimental error).

In a parallelepiped-shaped organic glass apparatus with dimensions (length × width × depth) 500 × 230 × 300 mm ³ (external dimensions indicated; the sheet thickness of the apparatus made of was 10 mm) at a distance of 15 mm from the bottom along the vertical axis of the apparatus installed hyperbolic mixer (Fig. 5), made according to the description of the mixer prototype (patent DE 10 2005 016 948 D3 2007.01.04). A stirrer with a diameter of 100 mm was driven by an IG-32GM type motor gearbox manufactured by NPF Elektroprivod at a speed of 230 rpm (3.83 rpm), the rated motor power was 4.22 watts. The agitator rotation speed was controlled by a DT2234B non-contact digital laser tachometer.

Particles of calcium carbonate (CaCO ₃ ) “Microcalcite LinCarb 20” (manufacturer - company LinCarb, Turkey) were used as a model medium simulating activated sludge. In the experiments, the dry powder was suspended in tap water with a concentration of 1 g / L. To determine and confirm the passport data on particle sizes, the prepared solution was previously examined using a Levenhuk 320 / D 320L microscope equipped with a ToupCam video eyepiece with a resolution of 5.1 MPix. It was found that "Microcalcite" is a one-dimensional flocculent particles with a diameter of from 40 to 48 microns, the average particle size was 42 microns, and their true density is 2670 kg / m ³ .

The preparation of the apparatus for the experiment was carried out as follows. The prepared suspension was poured into the apparatus, the exposure time to complete sedimentation of the particles to the bottom was 5 minutes. Next, the drive of the mixer was turned on and suspension began. A digital camera was installed under the bottom of the apparatus, with the help of which a video was recorded of the dynamics of erosion of sediment at the bottom. Photographs of the bottom of the apparatus with a mixer in dynamics are presented in FIG. 6.

After 3 minutes, control pictures were taken and the ratio of the bottom area of the apparatus with sediment S _OS to the total bottom area of the apparatus S _total (S _total = 480 × 210 = 100800 mm ² ) was analyzed. In measurements, the apparatus width, which was L = 210 mm, was used as the scale in the images. The photos were processed in the ToupView program, the calculation of the sediment area S _{os was} carried out according to the formula

,

,

where S _pix is the sediment area measured in the program, pixel ² ;

L is the true width of the tank, mm (L = 210 mm);

L _pix - capacitance width measured in the program, pixel.

The scheme for measuring the area of sediment at the bottom is shown in FIG. 7.

In the course of the experiments, the adequacy of the criterion “spot area of the layer at the bottom” as a characteristic of the suspension effect was checked; It is proved that the angle of repose of particles in water remains constant as solid particles transition from sediment to a suspended state. Those. additional experiments (by pumping the suspension with a volumetric pump) it was confirmed that the area covered by particles is a reliable criterion characterizing the number of sediment particles at the bottom of the apparatus. Also, by additional experiments, a verification of the area measurement technique was performed. By photographing and measuring the area of a square with a predetermined area, the error in determining the area was determined, which amounted to no more than 4%.

The experiments showed that when using the known device (analog device), the area of the sediment zone after 3 minutes of mixing is 64% of the total bottom area (Fig. 8b).

An example of a specific implementation 2. This example characterizes the invention in comparison with the known solution.

In the apparatus described in example 1, a mixing device according to the invention with a diameter of 100 mm is installed, the circuit of which is shown in FIG. 1-3. The diameter of the hole 6 was 20 mm.

The mixer was set in motion by the same gear motor as in Example 1. The remaining experimental conditions were the same as in Example 1.

The experiments showed that when using the proposed device, the area of the sediment zone after 3 minutes of mixing is 35% of the total bottom area, which is more than half the area with unweighted sediment for the known device.

Thus, as a result of the experiments, it was proved that the mixer according to the invention is more effective for erosion of sediment in rectangular apparatus.

The experiments in examples 1 and 2 were carried out three times, the results are presented in table 1.

The experiments showed that when using the proposed device at a concentration of 1 g / l, the area of the sediment zone after 3 minutes of mixing is 35% of the total bottom area, which is almost half the area with unweighted sediment for the known device (64%).

A comparison of the results presented in table 1 shows that when using the proposed mixing device, the area of sediment at the bottom is 1.84 times less than when using the known mixer. This result reflects the effectiveness of the proposed device.

An example of a specific implementation 3. This example reflects the influence of the diameter of the holes 6 in the disk 3 on the circulation speed, and, accordingly, on the mixing efficiency.

In the apparatus described in example 1, a mixing device according to the invention with a diameter of 100 mm is installed, the circuit of which is shown in FIG. 1-3. Agitators with three hole diameters of 6 were manufactured: 0 mm (without hole), 10 mm and 20 mm.

The remaining experimental conditions were the same as in example 2.

To increase the reliability, the experiments in example 3 for each diameter of the hole 6 were carried out three times, the results are presented in table 2. To compare the effectiveness of the mixer with the hole 6, the value of the area of sediment at the bottom of the apparatus for all three investigated cases is attributed to the area of sediment at the bottom of the apparatus for case d = 0 mm.

From table 2 it follows that an increase in the diameter of the hole 6 in the disk 3 from 0 to 10 mm leads to a decrease in the area of sediment at the bottom of the apparatus by 10.1% (compared with the diameter of the hole 0 mm), and an increase in the diameter of the hole 6 in the disk 3 to 20 mm leads to a decrease in the area of sediment at the bottom of the apparatus by 30.2% (compared with a hole diameter of 0 mm).

Thus, by changing the diameter of the hole 6 in the disk 3 in the present invention, it is possible to control the speed of the circulation flow through the central hole in the mixer disk, and ultimately the intensification of the process of suspension of solid particles.

Simplification of the design of the mixer reduces the cost of its manufacture, provides the possibility of transportation in a disassembled state and easy assembly.

Thus, the present invention improves the mixing efficiency, simplifies the design of the mixer and reduces the cost of its manufacture, provides the possibility of transportation in a disassembled state and easy assembly at the place of use, provides the ability to control the speed of the circulation flow through the Central hole in the disk of the mixer, and, ultimately , allows you to intensify the processes of mixing and suspension in the apparatus.

Table 1. The results of the suspension experiments using the known (analog device) and the proposed stirrers at h = 15 mm, the diameter of the hole 6 was 20 mm, the speed was 230 rpm.

Experience Number The area of sediment at the bottom when using the known mixer S _OS1 , pix ² The area of sediment at the bottom when using the proposed mixer S _OS2 , pix ² Attitude
S _OS1 / S _OS2 one 5882,00 3468.00 1.70 2 6226.00 3434.00 1.81 3 6697,00 3330.00 2.01 Average value 6268.33 3410.67 1.84

Table 2. The results of the experiments on the suspension when using and the proposed device when varying the diameter of the holes 6 in the disk 3. The rotation speed of the mixer 230 rpm

Series Experience Number in the series Hole diameter d, mm The sediment area at the bottom S _OS , pix ² The average value of the sediment area at the bottom S _OS , pix ² The coefficient of sediment area referred to the case d = 0 mm,
S _OS d / S _{OS 0} one one
2
3 0 4912
5563
5880 5451 1,000 2 one
2
3 10 4946
4971
4778 4898 0.899 3 one
2
3 twenty 3958
3456
4002 3805 0.698

Claims (2)

1. A mixing device comprising a hub mounted on a rotating vertical shaft, on which blades with a disk are fixed, characterized in that the blades have a curved surface shape with a generatrix parallel to the shaft, on the inner diameter of the blade equipped with a bent shelf for attachment to the hub, and on the outer the blade diameter is provided with a horizontal platform for attachment to the disk, while the central hole is made in the disk, and the upper edge of the blade is made decreasing from the outer diameter of the hub to the outer the diameter of the disk, and the lower edge of the blade is made decreasing from the outer diameter of the hub to the diameter of the holes in the disk. 2. The mixing device according to claim 1, characterized in that the angle between the tangent to the surface of the blade at the point of attachment to the hub and the tangent to the hub is made in the range from 15 to 90 °, and the angle between the tangent to the surface of the blade at the point with the largest diameter and tangent to the surface of the disk is made sharp, while the blades are attached to the hub and disk using threaded fasteners.

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