Method and device for mixing gases in liquids

Abstract

A device for mixing gases and liquids comprises a container (10) and a mixer (18) extending into the container (10) and rotating about a rotational axis (A), which mixer has a rotationally symmetrical shape except for a predetermined imbalance point (32). The imbalance point created during manufacturing is either a recess or an additional applied mass. The missing mass or the additional mass amounts to at least 1% of the dead mass of the mixer (18). Furthermore, a method for mixing gases is also presented.

Description

[0001] The invention relates to a device and a method for mixing gases in liquids.

[0002] Mixing or even dissolving gases in liquids has many uses. For example, dissolving ozone in aqueous solutions containing organic and inorganic substances provides highly effective oxidation of these substances. The targeted and efficient addition of oxygen and the dissolution of this oxygen or atmospheric oxygen in wastewater is one of the most important principles of today's aerobic water treatment plants.

[0003] Other possible applications include bleaching processes, stripping processes or any other form of enrichment and increase of the dissolved fraction of a gas in a liquid.

[0004] Aquaculture, which is becoming increasingly important for supplying a constantly growing world population with healthy proteins, also requires a large proportion of a sufficient and efficient supply of oxygen to the fish in order to ensure economical production with high fish health.

[0005] Mixing solutions already containing gas and other liquids is important in the chemical industry, among other things for the production of different substances and groups of substances. Uniform mixing can increase the safety of specific manufacturing processes, as it prevents excessively high concentrations of certain substances at specific points, thus preventing adverse processes such as exothermic reactions from occurring.

[0006] Various methods for mixing gas in liquids are known. For example, US Pat. No. 4,007,920 describes a rotating disc with axial holes used to mix air located on the surface of the disc with water located on the underside of the disc.

[0007] EP 2 125 174 B1 describes a mechanical cavitation element used to mix gas with liquid. This occurs by introducing the gas directly onto the surface of the cavitation element and by moving this cavitation element. This prior art describes how the gas enters the liquid through the cavitation process. In a second stage, ultrasound is applied to the gas and liquid, reducing the size of the generated gas bubbles. This ultimately achieves a sonochemical dissolution of the gas in the liquid.

[0008] The object of the invention is to improve the mixing of gases in liquids or the mixing of gas-containing liquids in other, less gas-containing or non-gas-containing liquids with a single apparatus in order to have as little gas loss as possible.

[0009] This object is achieved by a device for mixing gases in liquids, comprising a container and a mixer which projects into the container and rotates about a rotational axis. The mixer has a rotationally symmetrical shape except for at least one predetermined imbalance point. This mixer has a missing or additional mass compared to an otherwise identical, ideally rotationally symmetrical mixer designed without the imbalance point. The missing or additional mass amounts to at least 1% and preferably a maximum of 5% of the mixer's dead mass and imparts an imbalance to the mixer when it rotates about the rotational axis. The mixer has a shaft section which is connected to a rotary drive and a mixer body which is positioned in the container and which sits on the shaft section and has a diameter which is larger than the shaft section.

[0010] The device according to the invention, with its definition of imbalance and missing mass, is based on a brand-new, i.e., unused mixer. This mixer is set in rotation at a relatively high speed in the container and is deliberately designed to experience lateral deflection due to an imbalance, so that movements overlap and the movement of the outer surface of the mixer body does not follow a purely circular path.

[0011] The applicant's research has shown that this imbalance significantly improves the mixing quality due to the additional movement caused by the imbalance.

[0012] The mobility can be achieved either by a correspondingly “soft” bearing or by an elasticity of the shaft section or a combination of these.

[0013] The device according to the invention leads to an improved mixing of gases in liquids due to the additional frequency and vibration forced by the imbalance.

[0014] The imbalance is deliberately created during the mixer manufacturing process by the specific and clearly defined removal or addition of mass at one or more points in the mixer body area. The resulting harmonic oscillation can be adjusted in terms of amplitude and frequency by changing the speed.

[0015] The mixing of gases is so effective, as extensive testing has shown, that the gas can also be dissolved in the liquid. The device is therefore a device for introducing, mixing, and also dissolving (general term: mixing) gas in liquid.

[0016] After gas is added, which should preferably occur near the mixer body, a so-called transfer zone develops near the surface of the mixer body. This is caused by the formation of a film or interface between the gaseous, gas-containing, and liquid phases present. The reason for this transfer zone is the kinetic energy at the surface of the mixer body. The created interface influences the partial pressure prevailing at this point. Due to the additional movement caused by the imbalance, the kinetic energy at the surface is higher, so the partial pressure rises and an increased gas transfer rate is achieved.

[0017] The rotationally symmetrical mixer body creates a suction effect on its surface, known as the hydrodynamic paradox, and the Magnus effect. These two effects ensure that the added phase, in this case the gas, is sucked toward the surface of the moving body. This means that when the gas is introduced into the liquid near the mixer body, it is sucked onto the surface where it is then mixed into the liquid.

[0018] As already mentioned, mixing can go so far that the gas dissolves in the liquid, e.g., ozone or oxygen dissolves in the liquid. This results in the formation of extremely fine micro- and nanobubbles with a diameter of 120 nm to 10 µm.

[0019] The container can be a tank, a vessel, a basin, each of which can be closed or open, or even a channel through which the liquid flows.

[0020] For example, in a channel, the mixer body can be arranged in a bypass or a main channel in order to enrich a partial flow or the entire flow of liquid with gas.

[0021] An embodiment of the invention provides that the missing or additional mass compared to a mixer without the imbalance but otherwise identical, ideally rotationally symmetrical, is at least 2% of the mixer's own mass and / or that the mixer body has a completely closed outer contour and / or is designed without any steps.

[0022] A completely closed outer contour means that there are no through-holes, as is sometimes the case in prior art. The mixer body has a recess to prevent the formation of imbalance due to the removal of material.

[0023] If the outer contour of the mixer body is designed without steps, this means that it has a continuous curvature in every direction, without edges or steps, in order to avoid flow separation.

[0024] According to a preferred embodiment, the mixer body has a spherical, discus or bell shape, which have proven to be very advantageous in tests.

[0025] The container is in particular a flow-through container, with an inlet opening for liquid and an opposite outlet opening for liquid mixed with gas, as well as a gas inlet upstream of the mixer located between the inlet opening and the outlet opening.

[0026] In particular, the gas inlet can be directed toward the surface of the mixer body. Due to the very high mixing capacity of the device according to the invention, it is possible to operate it in continuous operation.

[0027] The surface of the mixer body is preferably with a roughness in the range of Rz 2 to Rz 6.3.

[0028] As it turns out, roughness plays a significant role in determining the capacity of the device.

[0029] The mixer body can be surface coated, i.e. it can have a metal coating, a plastic or ceramic coating or it can also be coated with composite materials.

[0030] According to a variant of the invention, the container and the bearing of the mixer allow the angle at which the axis of rotation protrudes into the container to be adjustable, because this also makes different effects possible.

[0031] A further special feature is that one or more drive units are provided that impose a superimposed oscillatory or vibratory motion on the mixer, in addition to the rotation around its axis of rotation, in a radial, oblique to the axial, or axial direction. This means that, in addition to the rotational motion and the additional movement caused by the imbalance, one or more additional motion patterns are implemented that further improve the mixing capacity of the device. One example is the aforementioned vibratory motion, in which the shaft section, for example, is moved axially up and down, preferably at a frequency of over 20 Hz.

[0032] The rotary drive is designed to drive the mixer at a rotation speed in a range between 10 and 10,000 rpm. Generally speaking, a smaller maximum diameter of the mixer body requires higher rotation speeds than a very large diameter. Such large-volume mixer bodies are used, for example, in wastewater treatment plants.

[0033] Preferably, the rotational speed to which the rotary drive is adjustable is regulated so that the maximum rotational speed in the outermost quarter of the mixer body is between 5 m / sec and 160 m / sec. Since the rotational speed increases with the radius, this value is measured at the point corresponding to 75% of the maximum diameter of the mixer body, because the beginning of the outermost quarter is the slowest-moving area of ​​the outermost quarter. The aforementioned speed range is important for achieving sufficient mixing effects with liquids, especially water.

[0034] The imbalance should be corrected by a localized, machine-based surface removal on the mixer body at the manufacturer's site or by attaching a local additional weight to the rest of the mixer body. As mentioned, this refers to the manufacturing of the device.

[0035] A further improvement is achieved by the inclusion of vibration sensors that detect the vibrations occurring in the mixer body, allowing the speed to be controlled based on these vibrations. This also allows the optimal operating point to be controlled and maintained. Furthermore, the device can be checked for damage. If, for example, vibration changes or recurring vibration peaks occur, it may be possible to conclude that a change in the bearing of the shaft section or other emerging damage is present. This allows for proactive damage detection.

[0036] The above-mentioned problem is also solved by a method for mixing gas in liquids, which is characterized by the following steps: Introducing liquid and gas into a container, and Mixing of gas and liquid in the container by means of a mixer which rotates about an axis of rotation and has a shaft section coupled to a rotary drive and a mixer body attached to the shaft section, which has a rotationally symmetrical shape except for a predetermined imbalance point, wherein the imbalance point has a missing or additional mass compared to an otherwise identical, ideally rotationally symmetrical mixer designed without the imbalance point, which mass amounts to at least 1% of the dead mass of the mixer and imparts an imbalance to the mixer when rotating about the axis of rotation.

[0037] As already explained, the mixer body should be brought to a speed between 10 and 10,000 revolutions / min, and the gas should be moved in the container until microbubbles or nanobubbles are generated, which have a diameter between 120 nm and 10 µm.

[0038] According to a further variant, the mixer body is driven in addition to the rotary movement in such a way that it performs a superimposed oscillatory movement or vibration movement, namely more precisely in a radial direction, oblique to the radial direction or axial direction, in order to mix the gas and the liquid.

[0039] To increase throughput, the process can be carried out in a single channel.

[0040] As already explained, the vibrations of the mixer body during operation can be recorded using a vibration sensor and, depending on this, the speed of the mixer body can be adjusted or damage can be detected.

[0041] Finally, it is advantageous if the flow rate is monitored and controlled by sensors in order, on the one hand, to ensure that the liquid and gas are not left in the vicinity of the mixer body for too long and to increase the throughput, and, on the other hand, to ensure that the flow rate is just long enough to achieve the desired mixing or dissolution of the gas in the liquid.

[0042] Further features and advantages of the invention will become apparent from the following descriptions and the accompanying drawings, to which reference is made. In the drawings: - Fig. 1 a schematic view of a first variant of the device according to the invention for carrying out the method according to the invention, - Fig. 2 a schematic view of a second variant of the device according to the invention for carrying out the method according to the invention, - Fig. 3 a third variant of the device according to the invention for carrying out the method according to the invention, - Fig. 4 a fourth variant of the device according to the invention for carrying out the method according to the invention, - Fig. 5 a fifth variant of the device according to the invention and for carrying out the method according to the invention, - Fig. 6 a sixth variant of the device according to the invention and for carrying out the method according to the invention, - Fig. 7 a seventh variant of the device according to the invention and for carrying out the method according to the invention, - Fig. 8 an eighth variant of the device according to the invention and for carrying out the method according to the invention, - Fig. 9 is a perspective view of a variant of the mixer body of the device according to the invention, - Fig. 10 shows a further variant of the mixer body of the device according to the invention, - Fig. 11 another variant of the mixer body of the device according to the invention, and - Fig. 12 an additional variant of the mixer body of the device according to the invention.

[0043] In Fig. Figure 1 shows a device for mixing gases in liquids. The device comprises a container 10, here in the form of a pipe, with an inlet opening 12 at one end and an outlet opening 14 at the opposite end.

[0044] The arrows indicate the flow direction.

[0045] The channel 16 formed by the tube does not necessarily have to be completely filled with liquid, it can also be only partially filled with liquid, preferably at least 2 / 3.

[0046] The liquid must have a viscosity so that it can still flow.

[0047] It can come from a tank or a basin and be supplied.

[0048] A mixer 18, which is rotatable about a rotational axis A, extends into the channel 16. The mixer body 20 preferably extends completely into the liquid and is attached to a shaft section 22. The shaft section 22 is coupled to a rotary drive 24, which can drive the mixer 18 to a rotational speed of 10 to 10,000 revolutions / min.

[0049] The rotary drive 24 does not have to be able to operate over the entire rotational range; it is sufficient if it can operate at a corresponding speed or a corresponding speed range, depending on the dimensions of the mixer body 20 and the liquid and the gas to be mixed.

[0050] Upstream of the mixer body 20, a gas inlet 26 is provided for gas to be mixed in, which is positioned and projects into the channel 16 so far that the gas is entrained by the flow of the liquid and strikes the outer surface of the mixer body 20.

[0051] The gas comes from a container 28 which is coupled to the gas inlet 26 via a line 29.

[0052] The mixer body 20 has a rotationally symmetrical shape relative to the rotation axis A.

[0053] However, it has an unbalance point 32 already provided by the manufacturer and determined by planning, which gives the mixer body 20 an overall unbalance.

[0054] This imbalance point 32 can be created by deliberately removing material by means of a production machine or by deliberately and specifically applying a pre-designed additional weight that is matched to the size and mass of the mixer body 20 and is attached to the rest of the mixer body 20, in particular by soldering, gluing, welding or a mechanical connection.

[0055] Optionally, the mixer body 20, the shaft section 22 or the rotary drive 24 can be coupled to a further drive unit 34, which ensures that during the rotation of the mixer body 20, an oscillation or vibration movement is also imposed on it in a radial, oblique to the axial or in the axial direction A.

[0056] This movement overlays both the rotational movement and the wobbling movement caused by the imbalance.

[0057] In order for the imbalance to actually lead to an additional movement or an additional component of the movement of the mixer body 20, the imbalance point is designed such that the mass missing or the additional mass added by it amounts to at least 1% of the mixer's own mass, compared to an otherwise identical and ideally rotationally symmetrical mixer designed without the imbalance point.

[0058] The bearings of the mixer 18 and those of the rotary drive 24 as well as the bending stability of the shaft section 22 must be coordinated in such a way that this not insignificant imbalance actually leads to an additional lateral movement of the mixer body.

[0059] The lateral movement should preferably be greater than 0.5 mm, especially greater than 1 mm, in order to achieve an effective effect.

[0060] Preferably, the aforementioned missing or additional mass is at least 2% of the mixer's own mass. To determine either the volume of the missing mass or that of the additional mass, an ideally rotationally symmetric mixer is used as a reference, in which the rotational symmetry covers the missing portion or truncates the additional mass to determine the missing or additional mass, respectively.

[0061] An imbalance whose missing mass or the additional mass which amounts to more than 5% of the dead mass appears to have little practical use in view of the resulting bearing problems and additional strength problems.

[0062] In the embodiment according to Fig. 1, the mixer body 20 is disc-shaped, with the central axis of the disc in the rotation axis A.

[0063] The following describes the process for mixing the gas into the flowing liquid.

[0064] A liquid, e.g., water, is fed to channel 16 via inlet opening 12, with channel 16 being at least two-thirds full with water. At the same time, a gas, e.g., ozone, is transported via container 28 to gas inlet 26. The corresponding gas bubbles 40 are still relatively large in this area, but are shown exaggeratedly large.

[0065] The flow entrains the gas introduced upstream of the mixer body 20 and divides it into small gas bubbles on the surface of the mixer body 20, which rotates at high speed, forming extremely fine micro- and nanobubbles. These bubbles then mix homogeneously in the liquid, as can be seen by the small circles shown near the outlet opening 14.

[0066] To optimally control the gas mixture, a vibration sensor 48 can be provided, which detects the vibration of the mixer body 20 at a suitable location and transmits the corresponding recorded values ​​to a controller. These detected vibrations can be used to determine whether the mixer body 20 is moving in the desired manner, either due to the imbalance or due to the additional movement imposed by the drive unit 34.

[0067] The embodiment according to Fig. 2 essentially corresponds to the Fig. 1, so only the differences need to be discussed below.

[0068] Instead of a disc-shaped surface, the mixer body 20 in this embodiment has a spherical surface with a recess that creates an imbalance point 32.

[0069] The rotation axis A is not aligned vertically, but at an angle α to the vertical, which causes an oblique upward movement direction of the liquid and the gas.

[0070] Alternatively, the mounting of the mixer 18, for example, on the container 10, can be designed such that the angle α at which the rotational axis A extends into the container 10 is adjustable, possibly even in two dimensions. Tests have shown that this influences the mixing properties.

[0071] Here, too, additional movements in addition to the imbalance can be generated by a separate drive unit 34. To increase clarity, Fig. 2 neither this additional drive unit 34 nor the rotary drive 24 are shown.

[0072] The path of the gas here is first horizontal, more precisely parallel to the upper and lower walls of the container 10 and then obliquely upwards due to the inclination of the axis of rotation A.

[0073] As shown by the circles, the cross-section of the gas bubbles decreases with increasing gas path length, so that the mixture is best at the upper right end of the container 10. An outlet opening 14 may also be provided here if the entire end face of the channel 16 does not form the outlet opening 14.

[0074] The variant according to Fig. 3 essentially corresponds to the Fig. 1, here too the unbalance point 32 is reached by material removal.

[0075] However, the inlet opening 12 and the outlet opening 14 only form part of the opposing end walls. The gas inlet 26 is oriented in the direction of flow.

[0076] This modified gas outlet is also available in the variant according to Fig. 4 are executed accordingly, which otherwise corresponds to the variant Fig. 2 corresponds.

[0077] In the variant according to Fig. 4 it can also be seen that the outlet opening 14 is arranged at the upper end of the container 10 downstream of the mixer body 20, i.e. approximately in the direction in which a radial plane to the axis of rotation A also runs.

[0078] The inlet opening 12, however, is located approximately at the level of the mixer body 20.

[0079] In the variant according to Fig. 5, the container 10 is a kind of tank with an overflow 50.

[0080] The mixer body 20 is a hemisphere or a hollow hemisphere, with an imbalance at an imbalance point 32, which is formed by an additional weight, in the form of an additional body, on the surface of the hemisphere.

[0081] Below the mixer body, the inlet opening 12 and, aligned therewith, the outlet opening 14 are provided.

[0082] The gas inlet 26 is directed directly onto the hemisphere surface.

[0083] The embodiment according to Fig. 6 has a mixer body 20 in the form of a cylinder with flattened portions provided on the circumference and a horizontal axis of rotation A. The flattened portions are exaggerated here and serve to form unbalance points 32.

[0084] In the variant according to Fig. 7 are in contrast to the Fig. 3 the inlet opening 12 and the outlet opening 14 are offset in height.

[0085] The line 30 projects from the end wall, on which the inlet opening 12 is provided, in the direction of flow into the interior of the container 10, which is cylindrical here, and ends shortly before, i.e. shortly upstream of the mixer body 20, which is disc-shaped here.

[0086] The variant according to Fig. 8 largely corresponds to the Fig. 3, however, a cone, possibly a solid cone or a cone hollow from below, is used as the mixer body 20, with an unbalance point 32 formed by a recess.

[0087] Further forms of mixer bodies 20 are shown in the Fig. 9 to 12 shown. Fig. 9 shows a mixer body 20 with a ring shape, the upper side of which has a closed circumferential groove 60, wherein in the center a conically tapered pin or a conically tapered sleeve extends in the direction of the axis of rotation A.

[0088] The unbalance point 32 can be a recess or a separately attached body.

[0089] The mixer body according to Fig. 10 is a hemisphere with centrally encircling grooves 64. These grooves further increase the surface area of ​​the mixer body 20.

[0090] The mixer body 20 after Fig. 11 has an annular bead which forms the outer circumference, with a coaxial recess 66 extending from the upper side and a pin-shaped elevation 68 being provided in the center, which forms the transition to the shaft section.

[0091] Several unbalance points 32 can be provided here.

[0092] The variant according to Fig. In contrast to all previous mixer bodies, mixer body 20 does not have a completely closed outer contour, as the mixer body has several through-openings 70 that imbalance it. The shape of mixer body 20 is that of a hemispherical shell with a sleeve 72 protruding from the interior, which terminates in a curve 74 at the bottom of the shell.

[0093] For all embodiments of the mixer body 20, the surface has a roughness in the range of Rz 2 and Rz 6.3 and / or can be surface coated.

[0094] This surface coating consists of, for example, metal, plastic, ceramic or a composite material.

[0095] For all mixer bodies 20, it also applies that they can either be driven only by a rotary drive or can also experience a superimposed movement with the aid of one or more additional drive units.

[0096] The surface of the mixer body 20 does not necessarily have to be smooth or very smooth, it can also be porous, but the imbalance is caused by the imbalance point 32. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 4 007 920

[0006] EP 2 125 174 B1

[0007]

Claims

[1] Device for mixing gases in liquids, comprising a container (10) and a mixer (18) which projects into the container (10) and rotates about an axis of rotation (A), said mixer having a rotationally symmetrical shape except for at least one predetermined imbalance point (32), said mixer having a missing or additional mass compared to an otherwise identical, ideally rotationally symmetrical mixer (18) designed without the imbalance point (32), which mass amounts to at least 1% of the dead mass of the mixer (18) and imparts an imbalance to the mixer (18) when rotating about the axis of rotation (A), wherein the mixer (18) has a shaft section (22) which is connected to a rotary drive (24), and a mixer body (20) which is positioned in the container (10), which mixer body is seated on the shaft section (22) and has a diameter which is larger than the shaft section (22). [2] Device according to claim 1, characterized bythat the missing or additional mass compared to an otherwise identical, ideally rotationally symmetrical mixer (18) without the unbalance point (32) is at least 2% of the dead mass of the mixer (18) and / or that the mixer body (20) has a completely closed outer contour and / or is designed without any steps. [3] Device according to claim 1 or 2, characterized by that the mixer body (20) has a spherical, discus or bell shape. [4] Device according to one of the preceding claims, characterized by that the container (10) is a flow-through container, with an inlet opening (12) for liquid and an opposite outlet opening (14) for the liquid mixed with gas and a gas inlet (26) upstream of the mixer (18) located between the inlet opening (12) and the outlet opening (14). [5] Device according to one of the preceding claims, characterized bythat the mixer body (20) has a roughness in the range of Rz 6.3 - Rz 2 and / or is surface coated. [6] Device according to one of the preceding claims, characterized by that the container (10) and the bearing of the mixer (18) are designed such that the angle at which the axis of rotation (A) projects into the container (10) is adjustable. [7] Device according to one of the preceding claims, characterized by that a drive unit (34) is provided which imposes on the mixer (18) in addition to the rotation about its axis of rotation (A) a superimposed oscillatory movement or vibration movement in a radial, oblique to the axial or in the axial direction. [8] Device according to one of the preceding claims, characterized by that the rotary drive (24) is designed so that it can drive the mixer (18) with a rotation in a range between 10 and 10,000 revolutions / min. [9] Device according to one of the preceding claims, characterized by that the imbalance is generated by a locally limited, mechanical surface removal on the mixer body (20) or by attaching a local additional weight to the rest of the mixer body (20). [10] Device according to one of the preceding claims, characterized by that a vibration sensor (48) is provided for determining the vibrations of the mixer body (20). [11] Process for mixing gas in liquids, characterized by following steps: Introducing liquid and gas into a container (10), and Mixing of gas and liquid in the container (10) by means of a mixer (18) which rotates about an axis of rotation (A) and has a shaft section (22) coupled to a rotary drive (24) and a mixer body (20) attached to the shaft section (22), which has a rotationally symmetrical shape except for a predetermined imbalance point (32), wherein the imbalance point (32) has a missing or additional mass compared to a mixer designed without the imbalance point (32), otherwise identical, ideally rotationally symmetrical mixer (18), which amounts to at least 1% of the dead mass of the mixer (18) and imparts an imbalance to the mixer (18) when rotating about the axis of rotation (A). [12] Method according to claim 11, characterized bythat the mixer body (20) is brought to a speed of between 10 and 10,000 revolutions / min and the gas is moved in the container until microbubbles or nanobubbles are generated which have a diameter between 120 nm and 10 µm. [13] Method according to claim 11 or 12, characterized by that the mixer body (20) performs a superimposed oscillatory or vibratory movement in addition to the rotary movement in order to mix the gas and the liquid. [14] Method according to one of claims 11-13, characterized by that the process takes place in a continuous flow in a channel (16). [15] Method according to one of claims 11-14, characterized by that the vibrations of the mixer body (20) are detected during operation by means of a vibration sensor system (48) and, depending thereon, the speed of the mixer body (20) is adjusted or damage is detected.

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