Gassing device

Abstract

The invention relates to a gassing device for gassing a liquid medium, said gassing device comprising a gas supply (1), a control unit (3), a gas modulation unit (4), and a bubble diffuser (5). The gas supply (1) is designed to supply a gas to the control unit (3), the gas modulation unit (4) and the bubble diffuser (5); the control unit (3) is designed to control the gas volume flow or the pressure of the gas supplied to the gas modulation unit (4) and to supply same to the gas modulation unit (4) in such a way that the gas is supplied to the gas modulation unit (4) at a constant gas volume flow and / or a constant gas pressure; and the gas modulation unit (4) is designed to vary the gas volume flow and / or the pressure and to supply same to the liquid medium via the bubble diffuser (5) provided with at least one opening (7) so that at least one bubble (6) forms at the opening (7) of the bubble diffuser (5) in the liquid medium.

Description

[0001] Fumigation device

[0002] The present invention relates to a gassing device for gassing a liquid medium.

[0003] In many industrial processes, a gas must be dissolved or dispersed in a liquid. For this purpose, small gas bubbles are typically used to improve heat and mass transfer. This is particularly true in the fields of chemistry, biochemistry, mining, environmental process engineering, or food production, for example, in wastewater treatment,

[0004] Similar processes are used in mineral processing, yeast production, or cooling processes. Unfortunately, generating small bubbles is a major challenge in these cases. The energy balance in particular is often disadvantageous; for example, DE 202017 002548 Ul discloses a corresponding gassing arrangement aimed at achieving a better energy balance. A disadvantage, however, is the lack of flexibility in the arrangement. With prior art processes, it is often not possible to control the formation of the bubbles (and thus also the bubble sizes). Conventional membrane gassers or aerators, for example, generate gas bubbles with a diameter of approximately 2 mm. Due to the membrane-based mode of operation, only a rough control of the gas bubble size is possible through the size of the perforations in the membrane.

[0005] An obvious solution to this problem is to use smaller openings. However, the problem is that the greater dynamics associated with smaller openings lead to the so-called "bubble-in-rush" effect, in which new bubbles form so quickly at the opening where the bubble forms that the initially formed bubble cannot yet detach and merges with the subsequent bubble, thus increasing the bubble size.

[0006] The present invention is therefore based on the object of proposing a gassing device which avoids the disadvantages mentioned, with which bubbles which are as small as possible and have little scatter in bubble size can be reliably produced in a controlled manner.

[0007] This object is achieved according to the invention by a device according to claim 1. Advantageous embodiments and further developments are described in the dependent claims.

[0008] A gassing device for gassing a liquid medium, typically a liquid, i.e. a substance which is in the liquid state, has a gas supply, a control unit, a gas modulation unit and a bubble diffuser. The gas supply is designed to supply a gas to the control unit, the gas modulation unit and the bubble diffuser, wherein the control unit is designed to control the gas volume flow or the pressure of the gas supplied to the gas modulation unit such that the gas is supplied to the gas modulation unit at a constant gas volume flow and / or a constant gas pressure. The gas modulation unit is designed or constructed to control the gas volume flow and / oror to vary the pressure of the gas and to supply it to the liquid medium via the bubble diffuser provided with at least one opening, so that at least one bubble forms in the liquid medium at the opening of the bubble diffuser.

[0009] A constant gas pressure or a constant gas flow rate allows for more uniform bubble formation, and bubble parameters such as size and frequency of formation can be more easily adjusted, depending on other parameters. The gas modulation unit provides an easy-to-use and flexible means for this purpose. Furthermore, undesirable phenomena such as "bubble in rush" can be avoided, and smaller bubble diameters than with previous methods can be generated, typically in the submillimeter range. Furthermore, the generated bubbles exhibit only a small size deviation from one another. In the context of this document, the term "gassing" refers to the introduction of gases into a liquid medium; in the case of aeration, this refers to the introduction of air or oxygen into a liquid medium.

[0010] The gas modulation unit typically modulates the gas with an acoustic wave in the frequency range from 150 Hz to 180 Hz in order to enable efficient and reliable bubble formation. The gas modulation unit can have at least one electrically controllable actuator, in particular an electroacoustic transducer and / or at least one electroacoustic actuator, for example a loudspeaker or a pneumatic oscillator, in order to reliably modulate or vary the pressure of the gas or the gas volume flow in such a way that targeted bubble formation is enabled. The actuator and in particular the electroacoustic transducer or actuator is preferably operated at a frequency of less than 1 kHz, particularly preferably in the frequency range from 150 Hz to 250 Hz, in particular 150 Hz to 180 Hz. The actuator (in particular the transducer orThe actuator (actuator) can be configured to generate a pressure amplitude, whereby the maximum pressure value can be up to 30 percent above the critical pressure, i.e. up to 30 percent above the minimum pressure necessary to spontaneously form bubbles in the respective liquid. Generally speaking, the actuator can be configured to generate a pressure gradient sufficient to form bubbles. As an alternative to an electroacoustic transducer and / or electroacoustic actuator, the actuator can, for example, be a pneumatic actuator and / or be configured to generate or release compressed air. Furthermore, alternatively, the actuator can generally be configured to generate mechanical vibrations that can be transferred to the gas for the purpose of the modulation disclosed here.

[0011] The gas modulation unit and the bubble diffuser can be designed as a single piece, i.e., consisting of a single part or combined into a single component. This is also referred to as a monolithic or integral design, and enables a particularly compact and mechanically stable construction. This results in a particularly compact design. Alternatively, it is also possible to design both units as two parts, i.e., two components connected by the gas supply or gas supply unit, in order to create the most flexible arrangement possible.

[0012] The gas supply is typically designed as a tube that connects the aforementioned units from a gas source. To enable a targeted gas flow, an openable and closable valve can also be arranged on the gas supply, usually between the gas source and the control unit. The gas supply is typically designed with a round cross-section, although an oval, rectangular, or square cross-section can also be provided in other embodiments.

[0013] The bubble diffuser can have multiple openings to generate multiple bubbles as precisely as possible. The openings can be identical in size and shape, but at least one of the openings can also have a different shape and / or size than the others.

[0014] If multiple openings are used, at least one electrically controllable actuator, in particular an electroacoustic transducer and / or an electroacoustic actuator, can be arranged at each of the openings so that bubbles can be generated specifically at each of these openings, thus creating different bubble patterns. Preferably, the respective transducer or actuator is arranged within the bubble diffuser directly below the associated opening. These transducers or actuators can be controlled individually, for example, via the control unit, the gas modulation unit, and / or an electrical control unit.

[0015] The electrical control unit can generally control several units, i.e. the gas source, the valve, the control unit and / or the gas modulation unit and is typically designed as a computer.

[0016] Preferably, an acoustic damping unit is arranged in the bubble diffuser, which serves and is designed to prevent acoustic back reflections (for example of the gas pressure wave) from the end of the gas supply line and thus enables more efficient bubble generation.

[0017] It can be provided that the control unit is configured to forward the gas to the gas modulation unit at a gas pressure that is lower than a critical pressure for bubble generation for the respective medium, preferably up to 20 percent lower than a critical pressure for bubble generation for the respective medium. This ensures that bubbles are only generated when a corresponding modulation of the gas pressure takes place by the gas modulation unit. In particular, it can be provided that the gas is forwarded to the gas modulation unit at a gas pressure that, as described above, is lower than a critical pressure for bubble generation for the respective medium, and in addition, a pressure amplitude is generated by the converter or actuator, whereby the maximum pressure value can be up to 30 percent above the critical pressure, i.e.by up to 30 percent above the minimum pressure required to spontaneously form bubbles in the respective liquid. Instead of a constant and controlled gas pressure, a constant volume flow that is modulated can also be used, which is usually preferred in industrial processes such as biological wastewater treatment. This results in an increased frequency of bubble formation. The constancy of the gas pressure and / or volume flow can relate to a duration of the gas supply or can occur within this duration. Additionally or alternatively, it can occur at least over a period of several tens of minutes or even several hours. The constancy can occur within the framework of standard tolerances. It can, for example, include temporary deviations (for no more than 10 minutes, no more than 2 minutes, or no more than 30 seconds) of no more than 10% or no more than 5%.

[0018] The gas modulation unit can comprise a signal generator or be connected to a signal generator designed to apply periodic, particularly harmonic, modulations of adjustable amplitude and frequency to the gas volume flow or gas pressure through the gas modulation unit. Such periodic, particularly harmonic, or, in other words, sinusoidal, modulations can support or enable bubble formation in a targeted manner and adapted to the respective liquid medium.

[0019] The following measures have proven advantageous for reliable controllability of bubble formation: A respective period of modulation comprises a first time portion with a pressure above a critical pressure for bubble generation for the respective liquid medium and a subsequent second time portion with a pressure below the critical pressure, wherein: a) the time portions are different from one another (i.e. their duration differs from one another); and / or b) the amounts of the differences of the (maximum) amplitudes of each time portion to the critical pressure are different from one another; and / or c) the integrals of the pressure over time within the time portions or, in other words, over the duration of the time portions are different from one another.

[0020] Regarding variant a), the first time portion can be longer (for example, at least one and a half times or at least twice as long) than the second time portion. Regarding variant b), the difference in the amplitude of the first time portion from the critical pressure can be greater (for example, at least one and a half times or at least twice as large) than the difference in the amplitude of the second time portion from the critical pressure.

[0021] Regarding variant c), the integral of the pressure over the duration of the first time portion may be greater than the integral of the pressure over the duration of the second time portion (for example, at least one and a half times or at least twice as large).

[0022] All of the above optional embodiments of variants a) - c) enable particularly reliable control of bubble formation in terms of size and frequency.

[0023] The at least one opening typically has a size of 0.5 mm to 1 mm. The opening is preferably round, but in further embodiments, an elliptical, rectangular, square, or octagonal opening can also be used. The specified size refers to the diameter or length of the opening.

[0024] Alternatively or additionally, it can also be provided that a funnel-shaped feed is provided in the bubble diffuser below the opening, which decreases in diameter in the direction of the opening so that the gas is focused in the direction of the opening.

[0025] A gassing tank comprises a gassing device with the described properties. The gassing device is arranged below a liquid level in the gassing tank, provided the tank is filled with the liquid or liquid medium, and is connected to the gas source, which is typically located outside the gassing tank. The gassing tank, which can also be referred to as a gassing container, can be open on one side or closed and equipped with means for gas recovery.

[0026] In a method for generating bubbles in a liquid medium, a gas is passed through the gas supply, the control unit, the gas modulation unit and the bubble diffuser in the gassing tank filled with the liquid medium and having the described properties by the gassing device arranged below a surface of the liquid medium and having the said properties, wherein the control unit controls the gas volume flow and / or the pressure of the supplied gas such that the gas is supplied to the gas modulation unit with a constant gas volume flow and / or a constant gas pressure, wherein the gas modulation unit provides the gas with a gas pressure modulation and supplies it to the bubble diffuser provided with at least one opening, such that at least one bubble forms at the opening of the bubble diffuser and is supplied to the liquid medium.

[0027] The method can therefore be carried out with the described gassing tank or the described gassing device, ie the gassing tank and the gassing device are designed to carry out this method.

[0028] The described gassing device, the described gassing tank and / or the described method can be used for wastewater treatment, i.e. the liquid medium is wastewater and the gas used is oxygen or air, which is preferably introduced into an activated sludge tank. Alternatively or additionally, the gassing device or the method can also be used to introduce ozone into a liquid-filled tank for trace elimination, for oxygen supply in aquaculture or fish farming, for cleaning membrane filters, for flotation in raw material extraction in mining and in mining recycling, for reducing noise emissions during offshore work by forming at least one bubble curtain, for drug delivery or for mixing and mass transfer in chemical processes.

[0029] Embodiments of the invention are illustrated in the drawings and are explained below with reference to Figures 1 to 17.

[0030] Shown are: Fig. 1 a schematic side view of a gassing device;

[0031] Fig. 2 is a view corresponding to Fig. 1 of an embodiment of the gassing device with a one-piece gas modulation unit and bubble diffuser;

[0032] Fig. 3 is a schematic representation of a formation of a bubble at an opening by an electroacoustic modulator;

[0033] Fig. 4 is a view corresponding to Fig. 3 with several bubbles forming;

[0034] Fig. 5 is a view corresponding to Fig. 3 showing the formation of bubbles by a modulated gas volume flow;

[0035] Fig. 6 is a view corresponding to Fig. 5 with several bubbles;

[0036] Fig. 7 is a view corresponding to Fig. 3 of an embodiment in which bubbles are generated independently of one another at the openings;

[0037] Fig. 8 is a view corresponding to Fig. 1 of an embodiment with a standing wave in the bubble diffuser;

[0038] Fig. 9 is a schematic plan view of a gassing device with a meandering pipe;

[0039] Fig. 10 a gassing device in side view with funnel-shaped openings;

[0040] Fig. 11 is a schematic three-dimensional view of a gassing tank;

[0041] Fig. 12 is a diagram of a modulation of a gas pressure;

[0042] Fig. 13 Diagrams of different phases of bubble generation;

[0043] Fig. 14 a diagram of the frequency dependence of bubble size and bubble formation frequency;

[0044] Fig. 15 is a diagram of a frequency dependence of the bubble size for different frequencies of an acoustic signal;

[0045] Fig. 16 Images of bubble formation and

[0046] Fig. 17 is another diagram of a modulation of a gas pressure according to an embodiment of the invention.

[0047] Figure 1 shows a schematic side view of a gassing device or bubble generation device in which a gas to be used for bubble generation is supplied from a gas source (not shown in Figure 1 for reasons of clarity) via a gas supply 1, which can also be referred to as a gas supply device. The gas supply 1 can be opened and closed via a valve 2. The control unit 3 controls a gas volume flow or gas flow and / or a gas pressure in such a way that a gas modulation unit 4 is supplied with a constant gas volume flow or a constant gas pressure from the control unit 3 via the tubular gas supply 1. If the gas volume flow is kept constant, however, typically only the frequency of bubble formation can be controlled; with a constant gas pressure, the bubble size can also be controlled.The gas modulation unit 4 provides the gas with gas pressure modulation or gas volume flow modulation, i.e. it varies the gas pressure as the pressure of the gas and / or the gas volume flow, and the gas is fed from the gas modulation unit 4 to a bubble diffuser 5 via the gas supply 1, which in this embodiment is referred to as gas supply line 15 and continues after the gas modulation unit 4. In the embodiment shown in Figure 1, the bubble diffuser 5 is plate-shaped and has a circular surface into which several openings are made. A number of bubbles 6 then form at the openings and are released into a liquid. In the embodiment shown, the gas modulation unit 4 and the bubble diffuser 5 are designed as two separate components, i.e. two spatially spaced components that are connected to one another via the gas supply 1.The modulations are damped by a damping unit 14, which is arranged at the end of the gas supply line 15 and prevents acoustic reflections in the direction of the gas modulation unit 4.

[0048] Figure 2 shows, in a view corresponding to Figure 1, an embodiment in which the gas modulation unit 4 and the bubble diffuser 5 are designed integrally, i.e. are arranged within a common housing. Recurring features are provided with identical reference numerals in this figure as well as in the following figures. In addition, a gassing basin 16 is shown which is open on one side on a side facing away from the gassing device and is filled with a liquid 8 or a substance in its liquid phase. The gassing device is arranged below the liquid level, i.e. below the liquid surface, wherein in the illustrated embodiment only the gas modulation unit 4 and the bubble diffuser 5 designed as a single piece therewith are arranged within the gassing basin 16, whereas the valve 2 and the control unit 3 are arranged outside the gassing basin 16.In further embodiments, however, the control unit 3 and the valve 2 can of course also be arranged within the gassing tank 16, only the gas source usually remains outside.

[0049] In the embodiment shown in Figure 2, the gas modulation unit 4 is provided with an electroacoustic actuator 9, which extends over the entire length of the gas modulation unit 4 below the openings 7 and is housed in a gas-tight housing except for the gas supply 1 and the openings 7. This actuator 9 generates gas pressure fluctuations that lead to the formation of bubbles at the openings 7.

[0050] In a similar way, Figure 4, in a view corresponding to Figure 3, shows an embodiment in which a plurality of openings 7 are arranged next to one another, at each of which a bubble 6 is formed. Below each opening 7, a separate electroacoustic actuator 9 is arranged, wherein the electroacoustic actuators 9 can be controlled independently of one another as modulators. For this purpose, for example, a computer can be used which controls the gas modulation unit 4 (and thus also the electroacoustic modulators 9) and the control unit 3. Figure 5, in a view corresponding to Figure 3, shows one of the openings 7, although this time the bubble generation is not generated by an electroacoustic actuator 9, but rather by a modulation of the gas pressure, i.e. a gas pressure wave 10 propagates in the gas modulation unit 4.A corresponding arrangement with several openings 7, at each of which a bubble 6 is generated, is shown in Figure 6 in a view corresponding to Figure 3.

[0051] By arranging a separate electroacoustic actuator 9 below each of the openings 7, any desired bubble pattern can be generated, as shown in Figure 7. While bubbles 6 are formed at two of the openings 7 in the embodiment shown in Figure 7, a corresponding control at the central opening 7 does not produce a bubble 6. In this case, even at adjacent openings 7, bubbles are not generated simultaneously.

[0052] Furthermore, it may also be provided to form a standing wave 11 within the gas modulation unit 4, as shown in Figure 8 in a view corresponding to Figure 1. The formation of the standing wave, i.e., the relevant frequency range, naturally depends on the length or width of the bubble diffuser 5. Due to the length of the bubble diffuser 5, the standing wave 11 forms within the housing, thereby increasing the energy efficiency of the gas modulation unit 4. The acoustic wave can be guided parallel or perpendicular to the openings 7.

[0053] In addition, the efficiency can also be increased by designing the gas supply 1 in a meandering shape or by providing a pipe 12 perforated with openings 7 or a correspondingly perforated channel downstream of the gas modulation unit 4. In the illustrated embodiment, the openings 7 are all arranged on the same side of the pipe 12, i.e. their surface normals all point in the same direction. Figure 9 shows a plan view in the left-hand part of an upper side of the bubble diffuser 5 with the openings 7, and in the right-hand part the layer below it with the perforated pipe 12. A pressure wave guided along the pipe 12 continuously forms bubbles 6 along the path traveled, so that bubbles 6 are released from neighboring openings 7 at a specific time interval, and a spatially and temporally predetermined pattern of gas injection is realized.This reduces undesirable interactions such as the merging of individual bubbles generated one after the other at the same opening 7.

[0054] Figure 10 discloses a side view of another embodiment in which the gas supply 1 opens into a cavity of the gas modulation unit 4, which now modulates the supplied gas from below. Funnels 13 or funnel-shaped structures are provided below the openings 7 as perforations in a plate, which focus the gas onto the openings 7. By locally focusing pressure waves, the electrical energy required to generate the bubbles 6 can be reduced compared to a situation in which the pressure wave strikes the perforated plate directly.

[0055] Figure 11 shows a schematic three-dimensional view of the aeration tank 16, with the aeration device arranged therein comprising a plurality of bubble diffusers 5 and a meandering connection between them. This allows gas bubbles to be introduced into the liquid 8, for example wastewater, contained in the aeration tank 16, over a large area, with a liquid column with a height typically in the range of 4 m to 5 m lying above the openings 7, although smaller and larger liquid columns are also possible. In biological wastewater treatment, air or pure oxygen is typically used as the gas; however, depending on the application, other gases can also be introduced, for example ozone for trace elimination, biogas or sewage gas, or carbon dioxide for membrane cleaning.Further application examples include oxygen supply in aquaculture or fish farming, flotation in raw material extraction in mining and mining recycling, reduction of noise emissions during offshore work by forming at least one bubble curtain, for drug delivery or for mixing and mass transfer in chemical processes.

[0056] Typically, the gassing device is operated continuously, but bursty emission of pressure waves can also be provided. In further embodiments, in addition to the control unit 3 as a pressure control unit, which sets the pressure level to a specific level, an acoustic damper or acoustic damping unit 14 can also be provided, which prevents reflection of acoustic waves at the end of the bubble diffuser 5, the gas supply 1, or the pipe 12. Furthermore, it can be provided to connect the gas modulation unit 4 to a signal generator, or the gas modulation unit 4 can already include the signal generator, so that harmonic signals, i.e. sinusoidal waves, with adjustable amplitude and frequency are generated. An electrical or electronic amplifier can also be provided to amplify the signals from the signal generator.

[0057] The size of the resulting bubbles 6 is determined by several parameters, namely the size of the openings 7, the frequency of the pressure of the modulated signal, the signal amplitude and the pressure difference between the gas in the gas supply 1 or parts connected thereto and a critical pressure level which applies to the bubble formation in the respective liquid 8.

[0058] It can be provided that the gas is maintained at a static pressure level that is 20 percent below this critical level, i.e. 20 percent below the minimum pressure at which bubbles 6 begin to form. The control unit 3 is typically designed to maintain this level with an accuracy of 1 percent. As shown in Figure 12, a continuous sinusoidal pressure signal generated by the signal generator and transmitted via an amplifier to a loudspeaker of the gas modulation unit 4 can generate an acoustic pressure wave that propagates along the gas supply 1 and / or the pipe 12. The resulting oscillating instantaneous pressure value is shown in Figure 12 as its time curve. Figure 12 shows three periods of an exemplary signal in which the original signal from the signal generator is compared with pressure variations.The pressure wave exhibits gas compression for half a period, followed by relaxation for the remainder of the period. The maximum acoustic pressure gradient is sufficient to cause spontaneous formation of a bubble 6 as soon as the critical pressure is exceeded. The diameters of the generated bubbles 6 can typically be adjusted between 0.01 mm and 5 mm.

[0059] For example, with a pressure wave of a frequency of 165 Hz and a pressure of 0.6 kPa below the critical pressure (which in this example corresponds to 103.5 kPa), bubble formation can be achieved because the local pressure level below one of the openings 7 is brought to a pressure level above the critical pressure by the pressure wave, and thus spontaneous bubble formation begins, in which a bubble forms within a few milliseconds.

[0060] Figure 13 shows a diagram of the different phases of bubble formation. The standardized pressure, which is therefore not assigned a unit, is plotted against time. Figure 13a) shows the gassing device at low acoustic frequencies. When the first acoustic wave reaches opening 7 in this first operating mode, a sufficiently large pressure difference is created to produce bubbles 6.

[0061] Due to the low frequency, bubble 6 has enough time to grow, and the buoyancy force becomes significant. The detachment of bubble 6 from opening 7 is also due to the buoyancy force. The initial detachment of bubble 6 occurs at time td<0.5t p , ie at a time when the pressure difference due to the acoustic wave is positive. t pwhere td denotes the duration of a complete period of the pressure wave, and td denotes the time required for the bubble 6 to detach from the opening 7. In this first operating mode, the start of bubble formation can be controlled, but not the bubble size.

[0062] Figure 13b) shows a second operating mode, in which the bubble formation occurs between 0.5t p <td<0,75t ptakes place. During bubble formation, the bubble 6 expands and contracts successively, eventually forming a small bubble 6. In this case, the detachment is determined by hydrodynamic forces. In this second operating mode, the bubble size and frequency of bubble formation can be determined by adjusting the properties of the acoustic wave. For example, in a frequency range of 168 Hz to 182 Hz of the acoustic wave, bubble sizes between 0.5 mm and 0.7 mm can be generated. If the pressure difference is increased, the frequency tends to become lower, for example, 154-612 Hz, and the bubble size is 1.1-1.5 mm.

[0063] Figure 13c) represents a third operating mode in which neither the bubble size nor the bubble formation frequency can be controlled. The bubble formation time is 0.75t. p <td<t p. In this operating mode, the waiting time for detachment is too short for the bubble 6 to detach from the opening 7. Finally, Figure 13d) shows a fourth operating mode for high frequencies of the acoustic wave. In this case, the frequency is selected too high and the bubble 6 cannot detach from the opening 7. In principle, however, a continuous formation of bubbles 6 with defined properties can occur at any frequency, provided the initial pressure level is adjusted accordingly. For this reason, the control unit 3 is used to provide a constant gas pressure or a constant gas volume flow, so that the first operating mode or the second operating mode can be achieved by adjusting the modulation parameters by the gas modulation unit 4.However, it is also true that the operating modes depend on the gas and liquid 8 used, as well as the size of the openings 7, the liquid column above the openings 7, the amplitude and frequency of the acoustic wave, and finally, the response of the gassing device to the intended frequency range. Figure 16 accordingly illustrates the bubble formation in the various operating modes, with Figure 16a) showing the first operating mode, Figure 16b) the second operating mode, Figure 16c) the third operating mode, and Figure 16d) the fourth operating mode.

[0064] Figure 14 shows, by way of example, the variation of the bubble size in the left part of the figure and the bubble frequency in the right part of the figure with the signal frequency in the second operating mode. The size of the opening 7 in the illustrated embodiment is 0.81 mm. The hydrostatic pressure level is kept constant at 200 mm above the opening 7, and the measurement is carried out at atmospheric pressure. In addition, the amplitude of the acoustic signal is kept constant. Independent of the pressure difference, the maximum achievable bubble size is reached at 161 Hz, whereas the frequency of bubble generation depends on the frequency of the acoustic signal. In a particularly advantageous manner, the frequency of the acoustic signal can be tuned to the resonance frequency of the gassing device used, as shown in a corresponding diagram in Figure 15.

[0065] Fig. 17 shows another diagram of a pressure modulation that can be generated according to one embodiment. In this case, the pressure modulation occurs periodically, but not necessarily harmonically (e.g., not sinusoidally). Instead, the pressure curve p plotted over time t describes a kind of sawtooth profile, although the actual pressure curve may be somewhat less sharp-edged than the illustrated variant due to inertia effects and other imperfections.

[0066] A period of pressure modulation consists of two time components tA and tB. Figure 17 shows two periods and the corresponding temporal end points TI and T2 as examples, whereby the number of periods can be increased as desired.

[0067] Each period comprises a pressure modulation to a level above a critical pressure Pcrt and to a level below it. Within a first time period tA, the pressure initially increases above the critical pressure Pcrt to an amplitude Al. Subsequently, the pressure decreases, reaching an amplitude A2 below the critical pressure Pcrt within a second time period tB.

[0068] It has been shown that an initial rapid pressure increase to a level significantly above the critical pressure Pcrt is beneficial for rapid and reliably controllable bubble formation. With the subsequent pressure reduction during the time period tB, which, however, is shorter in time than the time period tA and deviates less from the critical pressure Pcrt in magnitude, the already partially formed bubble is reliably detached, its size finally being determined.

[0069] The respective differences Dl, D2 of the amplitudes Al, A2 of the time components tA, tB to the critical pressure Pcrt are plotted in Fig. 17 and differ noticeably from one another. For example, the difference Dl is at least twice as large as the difference D2. Fig. 17 also shows that the integral of the pressure p over time t (i.e., the area between the pressure modulation curve and the time axis) is greater over the duration of the first time component tA than over the duration of the second time component tB. Thus, an energy input corresponding to this integral and area is greater during the first time component tA than during the second time component tB.

[0070] Only features of the various embodiments disclosed in the exemplary embodiments can be combined with one another and claimed individually.

[0071] List of reference symbols:

[0072] 1 gas supply

[0073] 2 valve

[0074] 3 Control unit

[0075] 4 Gas modulation unit

[0076] 5 Bubble diffuser

[0077] 6 Bladder

[0078] 7 Opening

[0079] 8 Liquid

[0080] 9 Actuator

[0081] 10 Gas pressure wave

[0082] 11 standing wave

[0083] 12 perforated pipe

[0084] 13 funnels

[0085] 14 Damping unit

[0086] 15 Gas supply line

[0087] 16 fumigation tanks

Claims

Claims: A gassing device for gassing a liquid medium comprising a gas supply (1), a control unit (3), a gas modulation unit (4) and a bubble diffuser (5), wherein the gas supply (1) is configured to supply a gas to the control unit (3), the gas modulation unit (4) and the bubble diffuser (5), the control unit (3) is configured to control the gas volume flow or the pressure of the gas supplied to the gas modulation unit (4) in such a way that the gas is supplied to the gas modulation unit (4) with a constant gas volume flow and / or a constant gas pressure, and the gas modulation unit (4) is configured to vary the gas volume flow and / or the pressure and supply it to the liquid medium via the bubble diffuser (5) which is provided with at least one opening (7), so that at least one bubble (6) forms at the opening (7) of the bubble diffuser (5) in the liquid medium.A gassing device according to claim 1, characterized in that the gas modulation unit (4) has at least one electrically controllable actuator, in particular at least one electroacoustic transducer and / or at least one electroacoustic actuator (9). A gassing device according to claim 1 or claim 2, characterized in that the gas modulation unit (4) and the bubble diffuser (5) are integrally designed. A gassing device according to one of the preceding claims, characterized in that the bubble diffuser (5) has several openings (7) at each of which at least one electrically controllable actuator, in particular an electroacoustic transducer and / or an electroacoustic actuator (9), is arranged for forming different bubble patterns. A gassing device according to one of the preceding claims, characterized in that an acoustic damping unit (14) is arranged in the bubble diffuser (5), which is designed to prevent back reflections. A gassing device according to one of the preceding claims, characterized in that the control unit (3) is configured to direct the gas to the gas modulation unit (4) at a gas pressure that is up to 20 percent lower than a pressure critical for bubble generation for the respective liquid medium.A gassing device according to any of the preceding claims, characterized in that the gas modulation unit (4) comprises or is connected to a signal generator configured to apply periodic modulations of adjustable amplitude and frequency to the gas volume flow or gas pressure through the gas modulation unit (4). A gassing device according to claim 7, wherein the modulations are harmonic. A gassing device according to claim 7 or 8, wherein each period of the modulation comprises a first time component (tA) with a pressure above a pressure critical for bubble generation for the respective liquid medium and a subsequent second time component (tB) with a pressure below the critical pressure, wherein: a) the time components (tA, tB) are different from each other; and / or. b) the magnitudes of the differences (D1, D2) of the amplitudes (Al, A2) of each time fraction (tA, tB) from the critical pressure are different from each other; and / or c) the integrals of the pressure over the duration of the time fractions (tA, tB) are different from each other. A fumigation device according to option b) of claim 9, wherein the magnitude of the difference (D1) of the amplitude (Al) of the first time fraction (tA) from the critical pressure is greater than the magnitude of the difference (D2) of the amplitude (A2) of the second time fraction (tB) from the critical pressure. A fumigation device according to option c) of claim 9, wherein the integral of the pressure over time within the first time fraction (tA) is greater than the integral of the pressure over time within the second time fraction (tB). A fumigation basin with a fumigation device according to any one of the preceding claims.A method for generating bubbles in a liquid medium, wherein in the aeration basin filled with the liquid medium according to claim 12, a gas is guided through the gas supply (1), the control unit (3), the gas modulation unit (4) and the bubble diffuser (5) by the aeration device arranged below a surface of the liquid medium according to one of claims 1 to 11, wherein the control unit (3) controls the gas volume flow and / or the pressure of the supplied gas such that the gas is supplied to the gas modulation unit (4) at a constant gas volume flow and / or a constant gas pressure, wherein the gas modulation unit (4) provides the gas with a gas volume flow modulation and / or a gas pressure modulation and supplies it to the bubble diffuser (5) which has at least one opening (7), so that at least one bubble (6) is formed at the opening (7) of the bubble diffuser (5), which is supplied to the liquid medium. Use of a gassing device according to one of claims 1-11, a gassing basin according to claim 12 and / or a method according to claim 13 for wastewater treatment, in particular for the introduction of air or oxygen into an activated sludge basin or for the introduction of ozone into a basin for trace elimination, for oxygen supply in aquaculture or fish farming, for cleaning membrane filters, for flotation in raw material extraction in mining and in mining recycling, for reducing noise emission in offshore work by forming at least one bubble curtain, for drug delivery or for mixing and mass exchange in chemical processes.

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