EP4596097A1

EP4596097A1 - Limiting foam generation during mixing of ingredients

Info

Publication number: EP4596097A1
Application number: EP25153256.0A
Authority: EP
Inventors: Hans Henrik Mortensen; Lars MOSGAARD; Morten Kristensen
Original assignee: Tetra Laval Holdings and Finance SA
Current assignee: Tetra Laval Holdings and Finance SA
Priority date: 2024-01-30
Filing date: 2025-01-22
Publication date: 2025-08-06
Also published as: WO2025162782A1

Abstract

A control arrangement is configured to perform a method of operating a mixing apparatus (10) to produce a mixture. In the method, a set of ingredients containing air is supplied to a mixing chamber (11A) of the mixing apparatus, and a mixing device (12) in the mixing chamber is operated, during a mixing procedure, to produce the mixture from the set of ingredients. During the mixing procedure, an evacuation arrangement (20B) is operated to establish a sub-atmospheric gas pressure in the mixing chamber to draw out at least part of the air from the mixture. During the mixing procedure, foam generation in the mixing chamber is controlled by adjusting the sub-atmospheric gas pressure in the mixing chamber based on a sensor signal (S1) that indicates if foam is present at one or more levels in the mixing chamber.

Description

Technical Field

The present disclosure generally relates to mixing of ingredients, for example during manufacture of products for human ingestion, and in particular to a technique of controlling foam generation during such mixing.

Background

Foaming and air entrapment are common phenomena encountered in mixing processes. In many applications, it is an unavoidable side-effect of mixing, shearing and powder incorporation. The higher the agitator or blade speed, the better the mixing but also the greater the amount of foam created and the more the air entrained within the resulting mixture.
Excessive foam formation can interfere with the mixing operation by artificially raising batch volume, causing prolonged cycle time, difficult handling, reduced productivity, product loss and extensive clean-up. Entrapped air that remains in the finished mixture can cause structural problems, clouding, discoloration, voids, instability and other undesired qualities depending on the product and end use.
One technique of reducing foam generation is to add chemical defoamers, also known as anti-foam agents. However, chemical defoamers are expensive and are often unsuitable for human ingestion. Further, the mixing may be performed to generate a mixture in strict adherence to a predefined recipe that does not include or leave room for addition of a chemical defoamer.
It is desirable to provide an alternative technique of limiting foam generation during mixing of ingredients.

Summary

It is an objective to at least partly overcome one or more limitations of the prior art.
One such objective is to provide a technique of limiting foam generation during mixing of ingredients.
Another objective is to provide such a technique that reduces the amount of entrapped air in the resulting mixture.
Yet another objective is to provide such a technique for use in manufacture of products for human ingestion.
One or more of these objectives, as well as further objectives that may appear from the description below, are at least partly achieved by a method of method of operating a mixing apparatus to produce a mixture, and a system for producing a mixture according to the independent claims, embodiments thereof being defined by the dependent claims.
A first aspect of the invention is a method of operating a mixing apparatus to produce a mixture. The method comprises: supplying, to a mixing chamber of the mixing apparatus, a set of ingredients containing an amount of air; operating, during a mixing procedure, a mixing device in the mixing chamber to produce said mixture from the set of ingredients; and operating, during the mixing procedure, an evacuation arrangement to establish a gas pressure that is sub-atmospheric in the mixing chamber to draw out at least part of said amount of air from the mixture. The method further comprises: obtaining, during the mixing procedure, a sensor signal indicative of foam being present at one or more levels in the mixing chamber; and controlling the evacuation arrangement, during the mixing procedure, to adjust the gas pressure in the mixing chamber based on the sensor signal to control foam generation within the mixing chamber.
A second aspect of the invention is a system for producing a mixture. The system comprises: a mixing apparatus comprising a mixing chamber, a mixing device in the mixing chamber, and one or more inlets for a set of ingredients containing an amount of air; an evacuation arrangement fluidly connected to the mixing chamber; and a control arrangement configured to, during a mixing procedure, operate the mixing device to produce the mixture from said ingredients and operate the evacuation arrangement to establish a gas pressure that is sub-atmospheric in the mixing chamber to draw out at least part of said amount of air from the mixture. The system further comprises a sensor arrangement, which is associated with the mixing chamber and configured to generate a sensor signal indicative of presence of foam at one or more levels in the mixing chamber, and the control arrangement is configured to operate the evacuation arrangement to adjust the gas pressure in the mixing chamber based on the sensor signal to control foam generation within the mixing chamber.
These aspects provide a simple technique of limiting the generation of foam during mixing of a set of ingredients, while allowing air to be removed from the mixture as it is being generated in the mixing chamber. The technique thereby reduces the amount of entrapped air in the resulting mixture. The adjustment of gas pressure in dependence of foam level serves to counteract the tendency of excessive and uncontrolled foam generation when mixing is performed in a sub-atmospheric environment. The technique is particularly suited for mixing of ingredients that are known to generate significant amounts of foam during mixing, for example ingredients that include a powder or a powder-based liquid. The technique may also be particularly suitable for use in manufacture of products for human ingestion, where it might not be possible to add a chemical defoamer to limit foam generation.
Still other objectives and aspects, as well as features, embodiments and technical advantages will appear from the following detailed description as well as from the drawings.

Drawings

FIG. 1 is a block diagram of an example system for mixing a set of ingredients.
FIGS 2A-2B are section views of a mixing apparatus with foam level sensing in accordance with first and second examples, respectively.
FIG. 3 is a flow chart of an example method of operating a system for mixing a set of ingredients.
FIG. 4A is a perspective view of an example mixing apparatus, FIG. 4B is a side view of the mixing apparatus in FIG. 4A, FIG. 4C is a perspective view of an internal structure of the mixing apparatus in FIG. 4A, and FIG. 4D is a section view of mixing apparatus in FIG. 4A.
FIG. 5 is a flow chart of an example method of operating the system in FIG. 1.
FIG. 6 is a graph of example data for the system in FIG. 1 when operated in accordance with the method in FIG. 5.

Description

Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments are shown. Indeed, the subject of the present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure may satisfy applicable legal requirements.
Well-known functions or constructions may not be described in detail for brevity and/or clarity. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
Like reference signs refer to like elements throughout.
Before describing embodiments in more detail, a few definitions will be given.
As used herein, "foam" refers to an aggregation of bubbles formed by gas being trapped inside a liquid barrier, typically a thin film of liquid.
As used herein, "vacuum" or "vacuum pressure" refers to a pressure below atmospheric pressure ("sub-atmospheric pressure"), where a pressure of 0 Pa corresponds to a prefect or full vacuum, and a pressure between 0 Pa and atmospheric pressure is a partial vacuum.
As used herein, "vertical direction" refers to the direction of gravity.
As used herein, a "high-shear mixer" comprises a rotatable element, for example in form of a rotor, impeller, paddle, propeller, vane, turbine etc., such that the rotatable element has a peripheral speed of at least 10 m/s, at least 15 m/s, or at least 20 m/s. The rotatable element may in some implementations be surrounded by a stator for increasing the high-shear mixing effect. If present, the stator is arranged to create a close-clearance gap between itself and the rotatable element, to form a high-shear zone for the materials being processed as the materials exit the rotatable element. The rotor and stator combined together are often referred to as a mixing head, or generator. A high-shear mixer may comprise more than one generator.
The present disclosure relates to a novel technique of mixing a set of ingredients in a mixing apparatus, where the set of ingredients contains air. The air may be embedded or dissolved in one or more of the ingredients. For example, all powdery materials contain air, which is embedded within individual grains of the powdery material. Liquids also typically contain dissolved air unless they have been pre-processed for air removal. Air may also be entrained with a powdery material as it is supplied to the mixing apparatus. Such entrained air is present between the individual grains of the powdery material and acts as a transportation fluid.
As noted in the Background section, it is desirable to reduce or minimize the amount of air in the resulting mixture. To this end, in the technique disclosed herein, the mixing of the ingredients is at least partly performed in a sub-atmospheric environment, to draw out air that is released from set of the ingredients while the ingredients are being mixed or blended into a resulting mixture. Thereby, at least part of the air that was introduced with the set of ingredients is removed, to produce a resulting mixture with a reduced air content.
Within the present disclosure it is assumed that the set of ingredients includes at least one liquid ingredient, which contains or is water. The presence of the liquid ingredient will lead to generation of foam, as the contained air interfaces with the liquid during the mixing process. The foam will accumulate on top of the forming mixture in the mixing apparatus. As noted in the Background section, excessive foam generation is highly undesirable. The foam generation is aggravated by the sub-atmospheric environment in the mixing device and increases with decreasing pressure in the mixing apparatus.
Foam generation is also affected by the composition of the set of ingredients that are mixed. For example, the amount of foam is likely to increase with increasing protein content in the set of ingredients. It has also been found that proteins from various plant sources are more prone to produce foam than dairy proteins. Likewise, the amount of foam is likely to increase with decreasing fat content in the set of ingredients. Given the current trend of producing products with high protein content, for example for use as dietary supplement or bodybuilding supplement, it is foreseen that foam generation will be an increasing complication in manufacturing of products for human ingestion. There is also a trend to decrease the amount of fat in these types of products, as well as other products for human ingestion, and a trend towards plant-based products. Even in products with medium or high fat content, there is a trend towards adding all or most of the fat, for example vegetable oil, towards the end of the manufacturing process, when a preparatory mixing procedure has been completed. In view of these trends, a technique for limiting or controlling foam generation during mixing in a sub-atmospheric environment is highly desirable.
In the following description, a set of ingredients is supplied to a mixing apparatus, which is operated to produce a final mixture of the set of ingredients. The final mixture is the mixture that is output from the mixing apparatus for downstream processing. In some embodiments, the final mixture is a homogeneous mixture that has the same proportions of its components throughout. The liquid mixture of ingredients within the mixing apparatus is denoted "process liquid" in the following.
FIG. 1 is a block diagram of a mixing apparatus 10 in a system for producing a final mixture of a set of ingredients. In the illustrated example, the set of ingredients includes a powder ingredient and a liquid ingredient. In FIG. 1, the power ingredient is designated by P, and the process liquid within the apparatus is designated by M. Foam formed during mixing is designated by F. The mixing apparatus 10 comprises a vessel, tank or container 11, which defines a mixing chamber 11A. A mixing device 12 is arranged inside the mixing chamber 11A and is operable to generate the final mixture. As indicated, the mixing device 12 may comprise a rotatable element such as a rotor, blade or impeller. In some embodiments, as shown, the mixing device 12 is arranged at the bottom of the mixing chamber 11A, for example with its rotational axis aligned with a central vertical axis of the mixing chamber 10A, as shown, or shifted therefrom. In other embodiments, the mixing device 12 is spaced from the bottom of the mixing chamber 11A. A drive unit 12A, for example an electrical motor, is coupled to the mixing device 12 to rotate the rotatable element inside the mixing chamber 11A. In some embodiments, the mixing device 12 is or comprises a high-shear mixer with a variable or fixed shear.
The mixing apparatus 12 comprises ports or openings 13, 14, 15 for establishing fluid communication with the mixing chamber 11A. Port 13 defines an inlet for the liquid ingredient, port 14 defines an inlet for the powdery ingredient P, and port 15 defines an outlet for the final mixture. An inlet pipe 21 is connected to port 13 to direct the liquid ingredient into the mixing chamber 11A. A powder supply arrangement or sub-system 20A is connected to port 14 to supply the powdery ingredient P from a source 22 through a supply pipe 23 into the mixing chamber 11A. In the illustrated example, the supply arrangement 20A further comprises an inlet valve 24 and a flow meter 25 in the supply pipe 23. The flow meter 25 is configured to provide an output signal S4. An outlet pipe 26 is connected to port 15 to transfer the final mixture from the mixing chamber 11A.
In the illustrated example, the powdery ingredient P is driven into the mixing chamber 11A by a vacuum pressure inside the mixing chamber 11A. The vacuum pressure is established by an evacuation arrangement or sub-system 20B (below), which is connected to an evacuation port 16 in a top portion of the tank 11. In some embodiments, the inlet valve 24 is operable to change the flow resistance, continuously or in steps, to vary the flow rate of the powdery material P into the tank 11. In other embodiments, the inlet valve 24 is an on/off valve, which is switchable between open and closed states.
A sensor arrangement 17 is associated with the tank 11 to detect presence of the foam F at one or more levels in the vertical direction of the mixing chamber 11A. The sensor arrangement 17 is configured to provide an output signal S1. The sensor arrangement 17 may be a single foam-detecting component or an aggregation of such components. It to be understood that the signal S1 may include a plurality of subsignals, for example one from each foam-detecting component (probe). Examples of sensor arrangements are given below with reference to FIGS 2A-2B.
In the illustrated example, the system 1 further includes a sensor 18 for measuring the level of dissolved oxygen (DO) in the process liquid M within the mixing chamber 11A. The sensor 18 provides an output signal S3 indicative of DO level, in any conventional measurement unit such as mg/L, ppm, percent saturation, etc. The sensor 18 may be any conventional DO sensor, for example operating by electrochemical or optical detection. Examples of electrochemical detection include polarographic detection and galvanic detection, and examples of optical detection include intensity-based detection and lifetime-based detection.
The evacuation arrangement 20B includes an evacuation pipe 27, which is connected to the evacuation port 16, and an evacuation device 28, which is arranged in the evacuation line 27. In some embodiments, the evacuation device 28 comprises one or more vacuum pumps and/or one or more vacuum ejectors. Devices for generating vacuum are well-known in the art and will not be described further. In the illustrated example, the evacuation arrangement 20B further comprises an evacuation valve 29, which is switchable between open and closed states, and a pressure sensor 29' for sensing the gas pressure in the mixing chamber 11A. The pressure sensor 29' need not be arranged in the evacuation line 27, as shown, but may have any suitable location for sensing the gas pressure in the mixing chamber 11A, for example in a dedicated port (not shown) in the top portion of the tank 11 or in the evacuation device 28.
The system 1 further comprises a control arrangement 30. The control arrangement 30 is configured to generate control signals C1, C2, ..., Cm for controlling the operation of the system 1. In the illustrated example, control signal C1 is supplied to the drive unit 12A of the mixing device 12, control signal C2 is supplied to the evacuation device 28, control signal C3 is supplied to the inlet valve 24, and control signal C4 is supplied to the evacuation valve 29. For example, control signal C1 may set the speed of the rotating element of the mixing device 12 and/or the shearing imposed by the mixing device 12 on the process liquid M in the mixing chamber 11A. Control signal C2 may set the gas pressure ("vacuum level") inside the mixing chamber 11A. The control device 30 is also be configured to receive input signals S1, S2, ..., Sn. In the illustrated example, input signal S1 is received from the sensor arrangement 17, input signal S2 is received from the pressure sensor 29', input signal S3 is received from the DO sensor 18, and input signal S4 is received from the flow meter 25.
The control arrangement 30 may be implemented by hardware components, or a combination of hardware components and software instructions. The software instructions may be executed by processing circuitry 31 in conjunction with computer memory 32 in the control arrangement 30. The software instructions may be supplied to the control arrangement 30 on a computer-readable medium, which may be a tangible (non-transitory) product (for example, magnetic medium, optical disk, read-only memory, flash memory, etc.) or a propagating signal. For example, the control arrangement 30 may comprise a generic or specialized computer device. In one embodiment, the control arrangement 30 is a PLC.
Although not shown in FIG. 1, the control arrangement 30 may further comprise an MMI (Man Machine Interface), which is configured so that the system may be controlled by an operator and so that information may be presented to the operator about the operation of the system. The MMI may, for example, comprise one or more of a display, a touch screen, a mouse, a keyboard, a track pad, buttons, sliders, switches and knobs, allowing control data and/or instructions to be inputted by the operator.
As shown in FIG. 1, generation of foam F is a common consequence of the mixing process when the set of ingredients contains air. As explained above, the foam generation is likely to be enhanced by the vacuum pressure in the mixing chamber 11A and may be further enhanced for certain types of ingredients. The foam F will accumulate above the process liquid M in the mixing chamber 11A. As will be described with reference to FIG. 3, the control arrangement 30 is configured to operate the system 1 to control the generation of foam in the mixing chamber 11A, at least based on signal S1 from the sensor arrangement 17.
Although not mentioned in the foregoing, the skilled person understands that the system 1 may be operated to ensure that the process liquid M does not exceed a maximum level in the mixing chamber 11A, for example based on a signal from a level sensor (not shown) for detecting presence of liquid at the maximum level in the mixing chamber 11A. The volume above the maximum level in the tank 11 is commonly known as "headspace". In some embodiments, to allow for an increased volume of foam F, the headspace may be increased compared to a conventional mixing apparatus, by enlarging the vertical extent of the tank 11 and/or by lowering the maximum level.
The system 1 in FIG. 1 may be operated to generate the final mixture by batch processing or continuous processing. In batch processing, a batch of ingredients are supplied to and processed by the mixing apparatus 10 for a time period to produce the final mixture, whereupon the final mixture is drained from the mixing chamber 11A, before a new batch of ingredients is supplied to the mixing apparatus 10. In continuous processing, the final mixture is continuously extracted from the mixing apparatus 10 and ingredients are supplied continuously or intermittently to the mixing apparatus 10. In some embodiments of continuous mixing, process liquid is continuously or intermittently extracted from and re-introduced into the chamber 11A, to increase the residence time of the process liquid in the chamber 11A. In the example of FIG. 1, a recirculation pipe (not shown) may fluidly connect the outlet pipe 26 and the inlet pipe 21. The recirculation of process liquid may be controlled via a pump or a regulating valve in the recirculation pipe.
In some embodiments, the final mixture is a final product which is only further processed for distribution. For example, a final product for human ingestion may be processed by heat treatment and packaging. In other embodiments, the final mixture in an intermediate product, which is processed into the final product by addition of one or more further ingredients, for example flavoring, salt, vegetable oil, etc. Examples of final products for human ingestion include beverages, yoghurt, cheese, ice cream, sauces, condiments, etc. Examples of final products that are likely to result in excessive foam generation during a mixing procedure include nutritional drinks, medical food, protein shakes, infant formulas, meal replacement drinks, sports drinks, high-protein flavored milks, high-protein beverages, milk bases for high-protein yoghurt and cheese.
In some embodiments, the final product has a protein content in the range of 4-20 wt% (percentage by weight). In some embodiments, the final product has a fat content in the range of 0-6 wt%. For these ranges of protein content and fat content, foam generation during mixing may be significant.
The source of the protein may be one or more dairy-based powders, for example a milk powder such as a whole milk powder or a skim milk powder, or a milk protein concentrate or an isolated powder such as a whey, casein or caseinate powder. Alternatively or additionally, the source of the protein may be one or more plant-based powders, for example powders of grains, nuts, beans or peas such as powders of oat, almond, soy, pea, rice, hemp or algae. Alternatively or additionally, the protein originates from insects, biomass from bacteria, fungus or yeast, protein derived from a fermentation process, or synthetic protein, for example from self-producing animal cells.
It is also conceivable to use the system 1 in FIG. 1 to manufacture final products that are not intended for human ingestion such as paint, liquid detergents, etc.
The sensor arrangement 17 for detecting foam in the mixing chamber 11A may be arranged and configured in different ways.
FIG. 2A shows a first example, in which the sensor arrangement 17 is arranged on a side wall of the tank 11 to detect presence of foam. The sensor arrangement 17 is configured to sense one or more parameters that differ between foam and air, and possibly between foam and liquid. Examples of parameters include capacitance, impedance, density or viscosity. In some embodiments, the sensor arrangement 17 senses capacitance between a pair of electrodes to detect presence of foam at a particular level. The capacitance will differ depending on the medium between the electrodes, making it possible to distinguish between air and foam, as well as between foam and process liquid, if desired. Techniques for sensing capacitance, as well as other relevant parameters are well-known in the art. It is also conceivable to adapt vibrating tuning forks, which a conventionally used for liquid level detection, for foam level detection.
FIG. 2B shows a second example, in which the sensor arrangement 17 is arranged at the top of the mixing chamber 11A to detect the level of foam. As indicated by dashed arrows, the sensor arrangement 17 may include a range detector that measures the distance to the foam by emitting a probe signal and detecting a corresponding response signal. The probe signal may be electromagnetic radiation in any suitable wavelength range. In one example, the probe signal is a microwave signal. Alternatively, the probe signal may be an ultrasound signal. In some embodiments, the sensor arrangement 17 includes an imaging device, for example a camera, which captures two-dimensional images of the interior of the chamber 11A, including the foam, and determines the level of the foam based on the images. For example, the respective image may show the foam and a scale on the side wall in the chamber 11A, so that the top of the foam can be related to a particular level in the chamber 11A.
The sensor arrangement 17 may be configured to detect presence of foam at any number of levels. If plural levels are detectable, the levels may be either discrete or continuous. Discrete levels may be detected by spatially separated probes. These probes may, for example, be arranged in the vertical direction to sense any of the above-mentioned parameters. Continuous levels may, for example, be detected by the above-mentioned range detector or imaging device (cf. FIG. 2B).
In the examples of FIGS 2A-2B, the sensor arrangement 17 is configured detect and signal presence of foam at three levels L1-L3 in the vertical direction. The first level L1 is a top-most level that is set to define the maximum allowable level for foam. The second level L2 is a bottom level that may be used to define a start level for foam control. The third level L3 is an intermediate level between L1 and L2. The third level L3 may be used to define a switching point for the foam control. The use of the third level L3 will be described further below with reference to FIG. 5. Any number of intermediate levels L3 may be defined.
FIG. 3 is a flow chart of an example method 300 of operating a mixing apparatus 10 to produce a mixture of a set of ingredients. The method 300 will described with reference to the system in FIG. 1 and may be performed by the control arrangement 30. In step 301, the set of ingredients is supplied to the mixing apparatus 10 to form the process liquid M inside the chamber 11A. As noted above, the set of ingredients contains air, which also enters the chamber 11A in step 301. In step 302, a mixing procedure 310 is started, in which the mixing device 12 is operated to mix the process liquid M into the final mixture. In step 303, the evacuation arrangement 20B is operated to evacuate air from the chamber 11A. The evacuated air includes at least part of air that might be present in the chamber 11A at start of the method 300, as well as at least part of the air that enters the chamber 11A with the set of ingredients in step 301. Step 303 is performed to establish a vacuum pressure in the chamber 11A throughout the mixing procedure 310. Steps 301-303 may be performed in any order and have any duration, depending on implementation. For example, step 301 may be performed continuously or intermittently, step 303 may be initiated before or concurrently with step 302, step 301 may be at least partly performed during the mixing procedure 310, etc.
In the example of FIG. 1, the method 300 may involve opening the evacuation valve 16, starting the evacuation device 28 and starting to supply the liquid ingredient to the chamber 11A, for example by starting a supply pump (not shown). The liquid ingredient may be supplied at a known flow rate. The evacuation arrangement 20B is operated based on the pressure signal S2 to establish a target vacuum pressure in the chamber 11A. The mixing device 12 is started, and the inlet valve 24 is opened, causing the vacuum pressure to draw the powder ingredient P into the chamber 11A. The flow rate of the powder ingredient P may be controlled via the inlet valve 24, based on the signal S4 from the flow meter 25, to achieve a target relation between the flow rates or supplied amounts of the liquid and powder ingredients. The mixing device 12 is kept operating throughout the mixing procedure 310. The mixing of ingredients may be improved when at least part of the liquid ingredient and at least part of the powder ingredient are supplied while the mixing device 12 is operating. If batch processing is performed, the final mixture may be extracted from the chamber 11A via port 15 at the end of the mixing procedure 310. If continuous processing is performed, the final mixture may be continuously extracted from the chamber 11A via port 15 during the ongoing mixing procedure 310.
The method 300 further includes steps 304-305. In step 304, the signal S1 from the sensor arrangement 17 is obtained. As noted, the signal S1 is indicative of foam level in the chamber 11A, specifically if foam is present at one or more levels in the chamber 11A. In step 305, the evacuation arrangement 20B is operated to adjust the gas pressure in the chamber 11A, based on the signal S1, to control the generation of foam in the chamber 11A. This means that the gas pressure in the chamber 11A is selectively increased or decreased in dependence of the presence of foam as detected by the sensor arrangement 17. As noted above, the generation of foam is likely to increase with increasing vacuum level in the chamber 11A. As used herein, "increasing vacuum level" implies that the absolute gas pressure is decreased. Thus, in some embodiments, the gas pressure in the chamber 11A may be increased to counteract foam generation, when deemed necessary based on the signal S1.
In some embodiments, as indicated by dashed lines in FIG. 3, step 305 includes a step 305A, in which the gas pressure is adjusted to avoid foam being present at a first level in the chamber 11A. The first level may correspond to a top-most level for foam in the chamber 11A (cf. L1 in FIGS 2A-2B). Step 305A does not imply that foam cannot be present at the first level, but rather that corrective action is taken whenever foam is detected at the first level to drive the level of foam downwards in the chamber 11A. As noted, the corrective action may involve operating the evacuation arrangement 20B to increase the gas pressure in the chamber 11A. It is understood that step 305A is applicable irrespective of the number of levels that the sensor arrangement 17 is capable of sensing. A more advanced implementation of step 305, resulting in more precise control of the foam generation, may be achieved by adding one or more further levels beneath the first level and by selectively adjusting the gas pressure in dependence of the presence of foam at the further level(s).
An example of a more advanced procedure for foam control, which may be part of step 305, is shown in FIG. 5. Here, it assumed that the presence of foam can be detected at the levels L1-L3 in FIGS 2A-2C. The procedure in FIG. 5 comprises steps 501-515. The procedure 305 adjusts the gas pressure in the chamber 11A to find the minimum gas pressure that results in foam being at an acceptable level within the chamber 11A.
The procedure 305 repeatedly performs a step 501 of checking if a termination signal has been received. If so, the procedure 305 continues to step 515, in which the foam control is terminated. The termination signal may be generated by an operator via the above-mentioned MMI, or be automatically generated by another step of the method 300, for example when the mixing procedure 310 is terminated (FIG. 3).
If no termination signal is received in step 501, step 502 is performed to check if the signal S1 indicates presence of foam at the bottom level, L2 ("LOW"). If not, the foam is below L2 and an action is taken in step 503 to decrease the gas pressure. The procedure then returns to step 501. In a non-limiting example, the gas pressure is decreased by 75-125 mbar. As shown, a delay period ΔT1 may be introduced by step 504 after step 503, to allow the gas pressure in the chamber 11A to stabilize and/or to allow the foam level to stabilize after the change in gas pressure. In a non-limiting example, ΔT1 is in the range of 10-20 seconds.
If foam is present at L2 in step 502, step 505 is performed to check if the signal S1 indicates presence of foam at the intermediate level, L3 ("MID"). If not, the foam is between L2 and L3, and an action is taken in step 506 to decrease the gas pressure. As indicated, the pressure change in step 506 is smaller than the pressure change in step 503. This is made to reduce the rate of foam growth in the chamber 11A as the foam approaches L3, compared to when the foam is below L2. In a non-limiting example, the gas pressure is decreased by 25-75 mbar. The procedure then returns to step 501, optionally after the delay period ΔT1 (step 504).
If foam is present at L3 in step 505, step 507 is performed to check if the signal S1 indicates presence of foam at the top-most level, L1 ("HIGH"). If not, the foam is between L3 and L1, and an action is taken in step 509 to increase the gas pressure. This is made to decrease the foam level as the foam approaches L1. In a non-limiting example, the gas pressure is increased by 25-75 mbar. The procedure then returns to step 501, optionally after the delay period ΔT1 (step 504). As shown, the procedure may include a step 508, between steps 507 and 509, that checks if the current gas pressure, P, given by the pressure sensor (cf. 29' in FIG. 1), is below a maximum pressure level, Pmax. If P < Pmax, then it is safe to increase the pressure, and the procedure proceeds to step 509. Otherwise, the procedure bypasses step 509, so that no change is gas pressure is performed. The rationale for step 508 is to avoid that the gas pressure in the chamber 11A gets high enough to drive process liquid into the powder supply arrangement 20A. In a non-limiting example, Pmax is in the range of 500-700 mbar. If liquid enters the supply pipe 23 or even the source 22, there is risk of clogging, which in turn may result in significant downtime of the system.
If foam is present at L1 in step 507, step 510 is performed to increase the gas pressure. Since the foam has reached the top-most level L1, which should be avoided, the pressure increase in step 510 may be larger than the pressure increase in step 509. The larger pressure increase aims at causing a large and fast reduction in foam level. To avoid the above-mentioned risk of pushing liquid into the power supply arrangement 20B, the supply valve 24 ("POWDER VALVE") is closed in step 511, which may be performed shortly after step 510 as shown. Alternatively, step 511 may be concurrent with or performed before step 510. As shown, a delay period ΔT2 may be introduced by step 512 after step 510, to allow the gas pressure in the chamber to stabilize and/or to allow for the foam level to stabilize after the change in gas pressure. In a non-limiting example, ΔT2 is in the range of 20-40 seconds. Then, step 513 is performed to check if the signal S1 indicates presence of foam at the top-most level, L1 ("HIGH"). If so, the procedure returns to step 510. Otherwise, if foam is absent at L1, step 514 is performed to open the supply valve 24, whereupon the procedure 305 proceeds to step 502.
The result of the procedure 305 is schematically illustrated in FIG. 6 for a specific use case. In FIG. 6, curve 601 represents the signal S1, which attains values 33, 66 and 100 at levels L2, L3 and L1, respectively (left scale), and curve 602 represents the vacuum level in the chamber 11, given as absolute pressure in mbar (left scale). Thus, standard pressure is 1013 mbar (101.3 kPa), and full vacuum is 0 mbar (0 Pa). Further, curve 603 represents the actual foam level in the chamber 11A, with index 700 corresponding to L2, index 900 corresponding to L3, and index 1000 corresponding to L1 (right scale). It is to be noted that curve 603 is not given by the sensor arrangement 17 but is a simulated development of foam level for the use case. Finally, curve 604 represents the feed rate of the powder ingredient in relative units (right scale). It is seen that, in this example, the feed rate (curve 604) depends on the vacuum level in the chamber (curve 602). The dots indicate time points when a data sample is obtained from the signal S1 and evaluated in the procedure 305 of FIG. 5. Dotted vertical lines indicate time points t1-t8 at which there is a change in the sensor signal S1. Before t1, the gas pressure is decreased at a large steps (curve 602), in accordance with step 503. As seen from curve 603, this causes the foam level to increase rapidly. From t1 to t2, the gas pressure is decreased in smaller steps (curve 602), in accordance with step 506. This results is a slower increase in foam level (curve 603). From t2 to t3, the gas pressure is instead increased in smaller steps (curve 602), in accordance with step 509 (FIG. 5). As seen from curve 603, the foam level continues to increase in this time period. Therefore, when the foam level reaches L1 (HIGH) at t3, step 510 is performed to increase the gas pressure in large steps (curve 602), and step 511 is performed to close the supply valve 24, causing the powder feed rate to be 0 (curve 604). As seen from curve 603, at t4 after a few repetitions of step 510, absence of foam is detected at L1 (HIGH) and presence of foam is detected at L3 (MID). From t4 to t5, the gas pressure is increased in accordance with step 509 (curve 602). At t5, presence of foam is only detected at L2 (LOW), causing the gas pressure to be decreased in accordance with step 506 until t6, at which foam is detected at L3 (MID). This causes the gas pressure to be increased in accordance with step 509 (curve 602), until t7 when foam is again only detected at L2 (LOW). It is realized that the procedure 305 automatically finds the lowest gas pressure that is capable of maintaining an acceptable foam level in the chamber 11A.
The procedure 305 in FIG. 5 embodies various generic solutions for foam control.
According to one solution, the evacuation arrangement 20B is operated to increase the gas pressure in the chamber 11A when the signal S1 indicates that the foam is approaching a first level (cf. step 509). The first level may be L1 in FIGS 2A-2B.This solution, which is applicable whenever the sensor system 17 is capable of providing an appropriate signal S1, serves to slow down the growth of foam in the chamber 11A to reduce the risk that the foam level exceeds L1.
According to one solution, the evacuation arrangement 20B is operated to decrease the gas pressure in the chamber 11A when the signal S1 indicates that the foam is absent at a second level below the first level (cf. steps 503, 506). The second level may be L2 or L3 in FIGS 2A-2B. This solution allows the mixing apparatus 10 to be operated with a low gas pressure in view of foam generation, which will reduce the amount of remaining air in the final mixture.
According to one solution, the evacuation arrangement 20B is operated to decrease the gas pressure in the chamber 11A at a lower rate when the signal S1 indicates that the foam is present between the second level and a third level, which is located between the first level and the second level, compared to when the signal S1 indicates that the foam is absent at the second level (cf. steps 503, 506). The second level may be L2, and the third level may be L3 in FIGS 2A-2B. This solution serves to slow down the growth of foam in the chamber 11A to reduce the risk that the foam level exceeds L1.
According to one solution, the evacuation arrangement 20B is operated to increase the gas pressure in the chamber 11A at a higher rate when the signal S1 indicates that the foam is present at the first level, compared to when the signal S1 indicates that the foam is approaching the first level (cf. steps 506, 509). This solution serves to rapidly decrease the foam level when foam is found to be present at L1.
According to one solution, a supply line into the chamber 11A is closed when the signal S1 indicates that the foam is present at the first level (cf. step 511). This solution is applicable when a powdery ingredient is supplied to the chamber 11A via the supply line (cf. 22 in FIG. 1) and serves to prevent that liquid is driven from the chamber 11A into the supply line by the increase in gas pressure within the chamber 11A.
According to one solution, the supply line is opened when the signal S1 indicates that the foam is absent at the first level. This serves to restore the supply of the powdery ingredient when the foam level has again decreased in the chamber 11A.
According to one solution, the evacuation arrangement is operated to refrain from increasing the gas pressure when the signal S1 indicates that the foam is approaching the first level (cf. step 507) and when a measured gas pressure in the chamber 11A is above a predefined maximum value (cf. step 508). The measured gas pressure may be obtained from a pressure sensor associated with the chamber 11A or the evacuation arrangement 20B. This solution serves to prevent the gas pressure from being too high in the chamber 11A during foam control.
FIGS 4A-4D show a detailed example a mixing apparatus 10 in a system for producing a final mixture of a set of ingredients. The system in FIGS 4A-4D includes components that have already been described with reference to FIG. 1. For brevity of presentation, the following description will focus on differences compared the system in FIG. 1. As seen in FIG. 4B, the sensor arrangement 17 comprises a set of discrete sensors or probes 17A, 17B , 17C, which are arranged in the side wall of the tank 11 at different heights in the vertical direction. With reference to FIGS 2A-2B, sensor 17A may define level L1, sensor 17B may define level L3, and sensor 17C may define level L2. As seen in FIG. 4A, the mixing apparatus 10 comprises two ports 24 for supply of powdery ingredient(s), each with a respective inlet valve 24. The mixing device 12 is a high-shear mixer, which is arranged at the bottom of the mixing chamber 11A. The drive unit 12A is spaced from and connected to the mixing device 12 by a transmission device 12B, for example a transmission belt (FIG. 4B). The outlet port 15 is arranged in the bottom of the chamber 11A adjacent to the mixing device 12 (FIGS 4A-4D). The evacuation valve 29 is connected to the evacuation port 16 in the top (lid) of the tank 11. The evacuation valve 29 is configured to prevent passage of process liquid into the evacuation line 27, by automatically directing the process liquid to an overflow outlet 29" (FIGS 4A, 4C). Thereby, the evacuation line 27 and the evacuation device 28 are safeguarded, if a malfunction causes the tank 11 to be completely filled with process liquid. As seen in the section view of FIG. 4D, the tank 11 comprises an outer jacket 11', which may be configured for heating and/or cooling of the walls of the mixing chamber 11A. The illustrated mixing apparatus 10 is also associated with a CIP system (Clean-In-Place) 50, which includes tubing, nozzles, valves, etc. The CIP system 50 is standard equipment and will not be described in further detail.
The mixing apparatus 10 includes a dynamically operable baffle device 40, which is seen in FIGS 4C-4D. The baffle device 40 is dynamically operable in the sense that is rotatable within the chamber 11A. The baffle device 40 comprises one or more baffle plates 41, which are rigidly connected to an elongated main rod 42 by cross-bars 43. The main rod 42 defines a rotation axis A2 along its extent. The main rod 42 is coupled to a drive unit 44, for example an electric motor, which is operable to rotate the main rod 42. The baffle plates 41 are arranged to be perpendicular to their direction of movement when the main rod 42 is rotated around the rotation axis A2. The baffle device 40 may include any number of baffle plates 41, for example 2-4. The baffle plates 41 may be evenly distributed around the rotation axis A2. In some embodiments, the width of the respective baffle plate 41, in a radial direction to the rotation axis A2, is typically 1/10 to 1/12 of the width (diameter) of the chamber 11A.
When installed in the chamber 11A, the baffle device 40 defines a set of vertically and radially extending baffle plates 41. The baffle device 40 is provided to enhance top-to-bottom circulation and mixing in the chamber 11A. The baffle device 40 may be particularly useful when the mixing device 12 is configured to generate a vortex rotation of the mixture inside the chamber 11A around the rotation axis A1 of the rotatable element in the mixing device 12. The vortex may introduce massive amounts of air if the vortex tip reaches an inlet of the mixing device 12. The baffle device 40 is capable of reducing or eliminating vortex formation. In the illustrated example, to achieve this objective, the baffle device 40 is arranged with its rotation axis A2 parallel to the vertical rotation axis A1 of the mixing device 12. The rotation axes A1, A2 may or may not be aligned.
The baffle device 40 is operable to adjust its impact on the flow and mixing within the chamber 11A, denoted "baffling effect" herein. The highest baffling effect is obtained by rotating the baffle device 40 in opposite direction compared to the mixing device 12 ("anti-rotation"), where the baffling effect increases with increasing rotational speed of the baffle device 40. A medium baffling effect is obtained by holding the baffle device 40 in static position (zero rotational speed). The lowest baffling effect is obtained by rotating the baffle device 40 in the same direction as the mixer device 12 ("co-rotation") but at a lower speed than the mixing device 12. A negative baffling effect is obtained by rotating the baffle device 40 in same direction as the mixing device 12 ("co-rotation") at the same or higher speed than the mixing device 12.
By adjusting the baffling effect of the baffle device 40, it is possible to achieve optimal circulation and mixing within the chamber 11A, as well as minimum vortex formation and air incorporation. It is currently believed that the dynamically operable baffle device 40 is at least suitable for use in a mixing apparatus with a mixing chamber volume of 250-20,000 L, a mixing device with a diameter of 100-600 mm and operated at speed of 100-3,000 rpm, and for viscosities of 1-100,000 cP (mPa.s).
In some embodiments, the rotation of the baffle device 40 is controlled throughout the mixing procedure within the chamber 11A. As different ingredients are added, the viscosity, as well as the need for shear and turbulence, might change. Mixing and vortex formation is also influenced by liquid viscosity and liquid height in the chamber 11A as well as by design, speed, and location of the mixing device 12 in the chamber 11A.
For a given configuration of the mixing apparatus 10, an increased baffling effect may be required with increasing speed of the mixing device 12, with decreasing viscosity of the process liquid, or with decreasing liquid level in the chamber 11A.
Reverting to FIG. 3, the method 300 may comprise a step 306 of operating the baffle device 30, during the mixing procedure 310, in dependence of at least the rotational speed of the mixing device 12. As understood from the foregoing, step 306 may involve adjusting the rotational speed and/or the rotational direction of the baffle device 40. In some embodiments, step 306 is achieved by use of a predetermined function that yields optimal rotation of the baffle device 40 depending on the current speed of the mixing device 12, and optionally based on the current viscosity of the process liquid (measured or estimated) and/or the current liquid level in the chamber 11A (measured or estimated).
In some embodiments, if the mixing procedure is divided into sub-procedures, settings of rotational speed and/or rotational direction may be defined and fixed for the respective sub-procedure. The settings may differ between sub-procedures. The settings may be defined during commissioning of the mixing apparatus 10.
In some embodiments, the rotational speed and/or the rotational direction may be adjusted based on direct or indirect measurement of the circulation within the chamber 11A and/or the vortex size. The circulation may, for example, be measured by pitot tubes, hot-wires, Laser Doppler Anemometry (LDA) or Particle Image Velocimetry (PIV). Examples of direct vortex measurement include imaging or sonar methods. Examples of indirect vortex measurement include measurement of current, torque or power consumption of the drive unit 44 for the baffle device 40 and/or for the drive unit 12A for the mixing device 12. For example, presence of a vortex may be detected when the current, torque or power consumption is below a threshold value associated with a current liquid level in the chamber 11A, a current rotational speed of the mixing device 12, and a current viscosity of the process liquid. Threshold values for different operating conditions may be determined by experiments and/or simulations.
As shown in FIG. 3, the method 300 may include a step 307 of obtaining a sensor signal (DO signal) S3 indicative of dissolved oxygen in the process liquid within the chamber 11A, and a step 308 of operating the system based on the DO signal S3. The DO signal S3 may be provided by the DO sensor 18 in FIG. 1, or a plurality of DO sensors. By steps 307-308, the system can be operated towards a target value of dissolved oxygen in the final mixture. Recalling that the operation of the mixing apparatus 10 aims at removing air from the process liquid, it is realized that steps 307-308 may enable more accurate control of the mixing procedure. Step 308 may involve adjusting the operation of various components of the system, as represented by steps 308A-308E, which may be used singly or in any combination. According to step 308A, the rotational speed of the mixing device 12 is adjusted. If the DO value of the process liquid is above a predefined limit, for example the above-mentioned target value, the rotational speed of the mixing device 12 may be reduced. According to step 308B, the gas pressure in the chamber 11A is adjusted. If the DO value of the process liquid is above the predefined limit, the gas pressure may be decreased. According to step 308C, the flow rate of the powdery ingredient into the chamber 11A is adjusted. If the DO value of the process liquid is above the predefined limit, this flow rate may be reduced. According to steps 308D-308E, the rotation of the baffle device 40 is adjusted. If the DO value of the process liquid is above the predefined limit, the baffle device 40 may be operated to increase the baffling effect, for example by reversing the rotational direction (step 308) from co-rotation to anti-rotation, or by increasing the rotational speed in anti-rotation (step 307).
Although the foregoing description presents mixing of a liquid and a powder, it is equally applicable to mixing of ingredients that are all in liquid form. Further, any number of ingredients may be processed into the final mixture within the mixing apparatus. The ingredients may be added to the mixing apparatus jointly and/or in sequence.
The technique presented herein may be particularly suitable when air in entrapped or embedded in at least one of the ingredients, since it allows at least part of this air to be removed during processing. As noted above, powdery material is known to have air embedded within its individual grains. When a powdery material is mixed or blended with a liquid to form a powder-based liquid, a major portion of the air embedded in the powder will remain in the powder-based liquid, unless the powder-based liquid is processed for air removal. Thus, the technique presented herein is particularly suited for mixing a set of ingredients that comprises a powder and/or a powder-based liquid.
While the subject of the present disclosure has been described in connection with what is presently considered to be the most practical embodiments, it is to be understood that the subject of the present disclosure is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and the scope of the appended claims. Further, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results.
Some of the described embodiments are reiterated in the following.
In one embodiment, the mixing device (12) is a high-shear mixer.
In one embodiment, the sensor signal (S1) is obtained from a sensor arrangement (17) comprising at least one of a capacitance sensor, a range detector, or an imaging device.
In one embodiment, the sensor arrangement (17) is configured to detect the presence of foam at a first level (L1) in the mixing chamber (11A), and wherein the control arrangement (30) is configured to operate the evacuation arrangement (20B) to adjust the gas pressure to avoid foam being present at the first level (L1).
In one embodiment, the control arrangement (30) is configured to operate the evacuation arrangement (20B) to increase the gas pressure in the mixing chamber (11A) when the sensor signal (S1) indicates that the foam is approaching the first level (L1).
In one embodiment, the sensor arrangement (17) is configured to detect the presence of foam at a second level (L2) below the first level (L1) in the mixing chamber (11A), and wherein the control arrangement (30) is configured to operate the evacuation arrangement (20B) to decrease the gas pressure in the mixing chamber (11A) when the sensor signal (S1) indicates that the foam is absent at the second level (L2).
In one embodiment, the sensor arrangement (17) is configured to detect the presence of foam at a third level (L3) between the first level (L1) and the second level (L2), and wherein the control arrangement (30) is configured to operate the evacuation arrangement (20B) to decrease the gas pressure in the mixing chamber (11A) at a lower rate when the sensor signal indicates that the foam is present between the second level (L2) and the third level (L3), compared to when the sensor signal (S1) indicates that the foam is absent at the second level (L2).
In one embodiment, the control arrangement (30) is configured to operate the evacuation arrangement (20B) to increase the gas pressure in the mixing chamber (11A) at a higher rate when the sensor signal (S1) indicates that the foam is present at the first level (L1), compared to when the sensor signal (S1) indicates that the foam is approaching the first level (L1).
In one embodiment, the system further comprises a supply line (23) configured to transfer a powder among said ingredients into the mixing chamber (11A), wherein the control arrangement (30) is configured to close the supply line (23) when the sensor signal (S1) indicates that the foam is present at the first level (L1).
In one embodiment, the control arrangement (30) is configured to open the supply line (23) when the sensor signal (S1) indicates that the foam is absent at the first level (L1).
In one embodiment, the system further comprises a pressure sensor (29'), which is configured to provide a second sensor signal (S2) indicative of measured gas pressure in the mixing chamber (11A), wherein the control arrangement (30) is configured to operate the evacuation arrangement (20B) to refrain from increasing the gas pressure when the measured gas pressure, given by the second sensor signal (S2), is above a predefined maximum value.
In one embodiment, the system further comprises a further sensor (18), which is configured to provide a third sensor signal (S3) indicative of dissolved oxygen in the mixture within the mixing chamber (11A), wherein the control arrangement (30) is configured to perform, when the dissolved oxygen is above a predefined limit, at least one of: reducing (308A) a rotational speed of the mixing device (12), operating (308B) the evacuation arrangement (20B) to decrease the gas pressure in the mixing chamber (11A), operating (308C) a flow controller (24) to reduce a flow rate of the powder into the mixing chamber (11A), reducing (308D) a rotational speed of baffle device (40) that comprises at least one vertical baffle plate (41) and is arranged for rotation within the mixing chamber (11A), or changing (308E) a direction of rotation of the baffle device (40).
In one embodiment, the mixing device (12) is configured to generate a vortex rotation of the mixture inside the mixing chamber (11A) around a first vertical axis (A1), wherein the system further comprises a baffle device (40) that comprises at least one vertical baffle plate (41) and is arranged for rotation around a second vertical axis (A2) inside the mixing chamber (11A), and wherein the control arrangement (30) is further configured to operate, during the mixing procedure, the baffle device (40) to rotate around the second vertical axis (A2) inside the mixing chamber (11A) to reduce the vortex rotation of the mixture inside the mixing chamber (11A).
In one embodiment, the control arrangement (30) is further configured to adjust a speed and/or direction of rotation of the baffle device (40) in dependence of a rotational speed of the mixing device (12).
In one embodiment, the set of ingredients comprises a liquid and a powder, and wherein the control arrangement (30) is configured to provide for supply of at least part of the liquid and at least part of the powder during the mixing procedure.
In one embodiment, the mixing device (12) is a high-shear mixer.
In one embodiment, the sensor arrangement (17) comprises at least one of a capacitance sensor, a range detector, or an imaging device.

Claims

A method of operating a mixing apparatus (10) to produce a mixture, said method comprising:
supplying (301), to a mixing chamber (11A) of the mixing apparatus (10), a set of ingredients containing an amount of air,

operating (302), during a mixing procedure, a mixing device (12) in the mixing chamber (11A) to produce said mixture from the set of ingredients,

operating (303), during the mixing procedure, an evacuation arrangement (20B) to establish a gas pressure that is sub-atmospheric in the mixing chamber (11A) to draw out at least part of said amount of air from the mixture,

obtaining (304), during the mixing procedure, a sensor signal (S1) indicative of foam being present at one or more levels in the mixing chamber (11A), and

controlling (305) the evacuation arrangement (20B), during the mixing procedure, to adjust the gas pressure in the mixing chamber (11A) based on the sensor signal (S1) to control foam generation within the mixing chamber (11A).
The method of claim 1, wherein said one or more levels comprise a first level (L1) in the mixing chamber (11A), and wherein the evacuation arrangement (20B) is operated to adjust the gas pressure to avoid foam being present at the first level (L1).
The method of claim 2, wherein the evacuation arrangement (20B) is operated to increase the gas pressure in the mixing chamber (11A) when the sensor signal (S1) indicates that the foam is approaching the first level (L1).
The method of claim 2 or 3, wherein said one or more levels comprise a second level (L2) below the first level (L1) in the mixing chamber (11A), and wherein the evacuation arrangement (20B) is operated to decrease the gas pressure in the mixing chamber (11A) when the sensor signal (S1) indicates that the foam is absent at the second level (L2).
The method of claim 4, wherein said one or more levels comprise a third level (L3) between the first level (L1) and the second level (L2), and wherein the evacuation arrangement (20B) is operated to decrease the gas pressure in the mixing chamber (11A) at a lower rate when the sensor signal indicates that the foam is present between the second level (L2) and the third level (L3), compared to when the sensor signal (S1) indicates that the foam is absent at the second level (L2).
The method of any one of claims 2-5, wherein the evacuation arrangement (20B) is operated to increase the gas pressure in the mixing chamber (11A) at a higher rate when the sensor signal (S1) indicates that the foam is present at the first level (L1), compared to when the sensor signal (S1) indicates that the foam is approaching the first level (L1).
The method of claim 6, wherein said ingredients comprises a powder, and wherein a supply line (23) for the powder into the mixing chamber (11A) is closed when the sensor signal (S1) indicates that the foam is present at the first level (L1).
The method of claim 7, wherein, after being closed, the supply line (23) for the powder is opened when the sensor signal (S1) indicates that the foam is absent at the first level (L1).
The method of any one of claims 2-8, further comprising, when the sensor signal (S1) indicates that the foam is approaching the first level (L1), obtaining (508) a second sensor signal (S2) indicative of measured gas pressure in the mixing chamber (11A), and operating the evacuation arrangement (20B) to refrain from increasing the gas pressure when the measured gas pressure is above a predefined maximum value.
The method of any preceding claim, further comprising: obtaining (307), during the mixing procedure, a third sensor signal (S3) indicative of dissolved oxygen in the mixture within the mixing chamber (11A), and performing (308), when the dissolved oxygen is above a predefined limit, at least one of: reducing (308A) a rotational speed of the mixing device (12), operating (308B) the evacuation arrangement (20B) to decrease the gas pressure in the mixing chamber (11A), operating (308C) a flow controller (24) to reduce a flow rate of the powder into the mixing chamber (11A), reducing (308D) a rotational speed of a baffle device (40) that comprises at least one vertical baffle plate (41) and is rotated within the mixing chamber, or changing (308E) a direction of rotation of the baffle device (40).
The method of any one of claims 1-9, wherein the mixing device (12) is configured to generate a vortex rotation of the mixture inside the mixing chamber (11A) around a first vertical axis (A1), wherein said method further comprises: operating (306), during the mixing procedure, a baffle device (40) comprising at least one vertical baffle plate (41) to rotate around a second vertical axis (A2) inside the mixing chamber (11A) to reduce the vortex rotation of the mixture inside the mixing chamber (11A).
The method of claim 11, further comprising adjusting (306) a speed and/or direction of rotation of the baffle device (40) in dependence of a rotational speed of the mixing device (12).
The method of any preceding claim, wherein the set of ingredients comprises a liquid and a powder, and wherein at least part of the liquid and at least part of the powder are supplied during the mixing procedure.
The method of any preceding claim, wherein the mixture has a protein content of at least 4 wt%, and a fat content of at most 6 wt%.
The method of any preceding claim, wherein the mixture is for human ingestion.
A system for producing a mixture, said system comprising:
a mixing apparatus (10) comprising a mixing chamber (11A), a mixing device (12) in the mixing chamber (11A), and one or more inlets (13, 14) for a set of ingredients containing an amount of air,

an evacuation arrangement (20B) fluidly connected to the mixing chamber (11A), and

a control arrangement (30) configured to, during a mixing procedure, operate the mixing device (12) to produce the mixture from said ingredients and operate the evacuation arrangement (20B) to establish a gas pressure that is sub-atmospheric in the mixing chamber (11A) to draw out at least part of said amount of air from the mixture,

wherein the system further comprises a sensor arrangement (17), which is associated with the mixing chamber (11A) and configured to generate a sensor signal (S1) indicative of presence of foam at one or more levels in the mixing chamber (11A),

wherein the control arrangement (30) is configured to operate the evacuation arrangement (20B) to adjust the gas pressure in the mixing chamber (11A) based on the sensor signal (S1) to control foam generation within the mixing chamber (11A).