WO2021124179A1

WO2021124179A1 - Biogas or biomethane production assembly with stirrer position detection device

Info

Publication number: WO2021124179A1
Application number: PCT/IB2020/062083
Authority: WO
Inventors: Matteo Paolo MAZZERO; Nicola PADOAN
Original assignee: Ies Biogas Srl
Current assignee: Ies Biogas Srl
Priority date: 2019-12-18
Filing date: 2020-12-17
Publication date: 2021-06-24
Anticipated expiration: 2022-06-18
Also published as: IT201900024490A1

Abstract

The present invention relates to a biogas or biomethane production assembly (1) comprising : - at least one tank (2), such as for example a fermenter or storage tank, which receives material (10) such as manure, slurry, poultry manure, dairy whey, vegetable waste, agricultural by- products inoculated with bacterial load for the formation especially of digestate and biogas; said tank (2) comprising a tank bottom (37); - at least one stirrer or mixer (3); - at least one stirrer support and movement device (4) for moving said stirrer or mixer (3) at least along a substantially vertical direction defining a vertical axis (Z-Z); - at least one lifting winch or winch (21); wherein there is further comprised - a position sensor (34) which detects at least one indication of minimum and maximum height (35, 36) of the position with respect to said tank bottom (37) of the stirrer or mixer (3).

Description

DESCRIPTION

Biogas or biomethane production assembly with stirrer position detection device

Cooperative Classes: A01C3/026 (EP); B01F7/00741 (EP); C02F3/1294 (EP); C02F2103/20

(EP); Y02W10/15 (EP).

[001] FIELD OF THE INVENTION

[002] The object of the present invention is a biogas or biomethane production assembly, a plant for the production of biogas or biomethane comprising said assembly and a method for the production of biogas.

[003] PRIOR ART

[004] Biogas is one of the most widely used alternative sources for the production of renewable energy. Biogas is the result of the degradation by numerous bacteria of various organic substances, in the absence of oxygen (a process called anaerobic digestion).

[005] The energy contained in the chemical bonds is then released and mainly stored in methane (CH4) which, together with carbon dioxide (C02) is the main constituent of biogas. Other substances, present in a lower percentage, are carbon monoxide, nitrogen, hydrogen, hydrogen sulfide.

[006] Biogas has a high calorific value and may be converted into electricity and heat. The residue of the fermentation is digestate, a liquid material, completely odorless and with a high agronomic value, with improved features with respect to the starting material.

[007] Biogas is a non-fossil renewable energy source which ensures energy autonomy and the gradual reduction of the current state of air pollution and therefore of the greenhouse effect.

[008] Biomethane is a gas derived from biogas which has undergone a refining and purification process or upgrading, bringing the concentration of methane CH4 to exceed 98%.

[009] Like natural gas (fossil methane), biomethane may be used as a biofuel for motor vehicles; it may be introduced into the national distribution grid; transported and stored for subsequent energy production, even in places very far from the production site.

[0010] The process transforming waste into biogas, and therefore into biomethane, is briefly described below. [0011] Inside a suitable container, the fermenter, various natural substances are conveyed, such as, for example, manure, slurry, poultry manure, dairy whey, vegetable waste, agricultural by-products.

[0012] Crops such as maize silage, wheat, sorghum, grain, in combination with slurry and manure, are excellent raw materials. Furthermore, waste from the agri-food industry may also be used.

[0013] In the fermenter, in the absence of oxygen and at a controlled temperature, a large number of bacteria degrades the organic substance. The result of this degradation is threefold: biogas, heat and digestate, i.e., natural liquid fertilizer.

[0014] Biogas may be, in turn, converted into electricity, by virtue of a cogenerator, and sold to the national grid. A part is converted into further heat.

[0015] The heat is used for heating some premises of the company, such as stables and offices (or even for an industrial process), as well as for the fermentation process itself.

[0016] Digestate, the quality of which is far superior to manure, is used as a natural fertilizer in farm crops.

[0017] In document US10479970, a solution of a container is disclosed, in particular a fermenter for a biogas plant, in which a mixer is arranged in the container which may be removed by means of an inspection opening provided in a container wall. In particular, this solution shows a mixer attached to a mixer rod supported by the container wall. The mixer connection is essentially configured as a vertical shaft. The mixer is mounted vertically on the shaft by moving with a slide; this facilitates the use of the mixing effect of the mixer at different levels in the container.

[0018] Document US9828578 describes a fermenter for biogas plants, including a submerged motorized stirrer which may be vertically adjusted by means of a motor. During the operation of the biogas production plant, the fermenter is filled, up to one level, with the substrate to be fermented, with the stirrer blades completely immersed in the substrate. According to this known solution, a non-contact level indicator is provided, placed on the lid, by means of which the substrate level is detected and a corresponding level measurement signal is generated as an actual level signal. In addition, a control device is provided, to which the level measurement signal is sent and which controls the vertical adjustment motor for the submerged motor stirrer, so that, when a lower level is detected, the stirrer is lowered and the stirrer blades continue to be completely immersed in the substrate.

[0019] Document DE3345643 describes a device for treating liquids, preferably located in containers, in particular manure. In particular, a device is described which may act as a pumping device for recirculating manure, and in a short time, by disassembling the conduits, it is possible to mount blades to have a stirring device capable of mixing and crushing the different layers of manure being transformed into digestate. Said device is mounted for a different height adjustment thereof, by means of a raising and lowering device.

[0020] These known solutions, although satisfactory from various points of view, do not allow to optimize the efficiency of the mixer, which is sometimes limited in the action thereof to the single substrate in which the stirrer itself is temporarily located, forcing excessively frequent vertical movements of the stirrer or the acceptance of the constitution on the surface of a cap layer which slows down and disturbs the formation of biogas. In particular, since the material of the outermost layer tends to create a cap, the action of the mixer ends up limiting the effects thereof to the material which is located near the stirrer, substantially at the level occupied at that moment by the mixer.

[0021] Therefore the need is felt to improve the mixing of the material contained in the fermentation tank, for a better use of the different substrates having different tendencies to flotation or sedimentation.

[0022] In particular, the need is felt to frequently move the stirrers or mixers and, at the same time, to humidify the surface layer of the material which tends to form a cap.

[0023] Furthermore, the need is felt to have a clear reference of the positioning of each stirrer or mixer.

[0024] OBJECT OF THE PRESENT INVENTION

[0025] It is one of the main objects of the present invention to solve the issues encountered in the solutions of the prior art and allow to satisfy the permanent felt needs and propose a solution which improves the efficiency of the stirrers so as to more uniformly mix the material or, in other words, the organic substance and the bacterial load which is being transformed into digestate.

[0026] Furthermore, it is the object of the present invention to allow to quickly identify the exact position of the stirrer immersed in the organic substance to be treated.

[0027] SOLUTION

[0028] These and other objects are achieved by means of an assembly according to claim 1 , a plant according to claim 5, as well as a method according to claim 7. The dependent claims relate to advantageous or preferred embodiments.

[0029] By virtue of the proposed solutions, with the appended claims, it is possible to provide an assembly with an automatic movement system for raising and lowering the stirrer or mixer, with confirmation of the exact position thereof, for example on the outer wall of the tank.

[0030] Furthermore, by virtue of the proposed solutions, with the appended claims, it is possible to provide a system applicable to all types of conventional submersible stirrers and mixers with lifting winch.

[0031] By virtue of the proposed solutions, with the appended claims, it is possible to provide an assembly managed by a system for controlling the position of the cable for moving the stirrer or mixer, which is preferably only possible with the stirrer or mixer switched off and the diagnosis of a sliding arrest.

[0032] By virtue of the proposed solutions, with the appended claims, it is possible to provide an assembly which allows an improved moving and mixing of the material inside the tank and, at the same time, to obtain a spraying of the surface layers for the hydration of the floating substrates so as to favor the cap breaking action by keeping a constant jet always incident to the mixer propeller.

[0033] DRAWINGS

[0034] To better understand the invention and appreciate the advantages thereof, some non limiting examples of embodiments will be described below with reference to the accompanying Figures, in which:

Figure 1 shows a diagrammatic view of a biogas production plant;

Figure 2 shows an axonometric view of a detail from the outside of a tank of a fermenter at a stirrer support and movement device;

Figure 3 shows an axonometric view of the detail of Figure 2 from inside the tank of a fermenter;

Figure 4 shows a diagrammatic sectional view of a detail of an assembly according to the present invention;

Figure 5 shows in a diagrammatic section the detail of the assembly of Figure 4 in which the stirrer or mixer is placed near the bottom of the tank;

Figure 6 shows in a diagrammatic section the detail of the assembly of Figure 4 in which the stirrer or mixer is placed near the upper edge of the tank;

Figures 7 to 9 show a top view of the detail of the assembly of Figure 4 in which the stirrer or mixer is placed in three different angular positions, orthogonal to the tank wall, oriented towards the left of the Figure and towards the right of the Figure.

[0035] DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION [0036] With reference to the Figures and in accordance with a general embodiment, a biogas or biomethane production assembly 1 comprises at least one tank 2, such as for example a fermenter or storage tank for material 10 such as manure, slurry, poultry manure, dairy whey, vegetable waste, agricultural by-products inoculated with bacterial load so as to mainly produce biogas and digestate.

[0037] Said assembly 1 further comprises at least one stirrer or mixer 3; in which said stirrer or mixer 3 is mounted on a stirrer support and movement device 4.

[0038] Said stirrer or mixer 3 is adapted to generate a flow of material contained in said tank 2 according to a prevailing stirrer flow direction X-X.

[0039] Advantageously, said assembly 1 further comprises at least one spray gun 5 adapted to direct a jet of fluid according to a prevailing gun jet direction Y-Y.

[0040] Said spray gun 5 is placed at the top of said stirrer support and movement device 4 and is adjustable in position so as to be able to direct the jet of fluid according to said prevailing gun jet direction Y-Y incident to said prevailing stirrer flow direction X-X.

[0041 ] In accordance with an embodiment, said spray gun 5 is placed at the top of said stirrer support and movement device 4 and is adjustable in position so as to be able to direct the jet of fluid according to said prevailing gun jet direction Y-Y in a direction substantially perpendicular to said prevailing stirrer flow direction X-X.

[0042] In accordance with an embodiment, said assembly comprises a hydrating liquid tank 6 adapted to contain a hydrating liquid 7.

[0043] Said at least one spray gun 5 is fluidly connected with said hydrating liquid tank 6 by means of a hydrating fluid conduit 8 in which a hydrating fluid pump 9 is provided.

[0044] In accordance with an embodiment, the jet of said spray gun 5 is directed to hydrate the floating layers of said material 10 so as to favor the breaking action of a floating cap which tends to form on this material.

[0045] In accordance with an embodiment, said assembly comprises a recirculation circuit 11 adapted to take said material 10 from the bottom of the tank 2 and bring it to a different point of the tank 2; in which said recirculation circuit 11 comprises a recirculation pipe 12 in which a recirculation pump 13 is inserted.

[0046] In accordance with an embodiment, said at least one spray gun 5 is fluidly connected with said recirculation pipe 12.

[0047] In accordance with an embodiment, said recirculation pump 13 comprises a device adapted to reduce the size of the solid parts of said material 10 by means of a cutting or crushing action, so that the fluid material 10 or in chopped parts are pumped by the recirculation pump and introduced at least in part into said at least one spray gun 5 to create a high-speed jet which generates a vigorous mixing of the material 10. In accordance with an embodiment, the recirculation pump 13 may be installed in recirculation of the tank 2 itself, avoiding the provision of a grinding device.

[0048] In accordance with an embodiment, said at least one spray gun 5 is rotatably supported by said stirrer support and movement device 4 so as to follow the movement of said stirrer or mixer 3.

[0049] In accordance with an embodiment, said at least one spray gun 5 is connected to a synchronization device 14 which synchronizes the movement of said at least one stirrer or mixer 3 with the movement of said at least one spray gun 5.

[0050] In accordance with an embodiment, said stirrer support and movement device 4 allows a rotation movement of said at least one stirrer 3 about a vertical axis Z-Z and/or a translation movement of said at least one stirrer 3 along a vertical axis Z-Z.

[0051 ] Said at least one spray gun 5 is connected to a synchronization device 14 which allows a rotation movement of said at least one spray gun 5 about a vertical axis Z-Z in synchronism with said at least one stirrer 3.

[0052] In accordance with an embodiment, said stirrer or mixer 3 is operatively connected to at least one stirrer motor 15.

[0053] Said stirrer motor 15 is operatively connected to a control device 16.

[0054] Said hydrating fluid pump 9 or said recirculation pump 13 is operatively connected to a pump motor 17.

[0055] Said pump motor 17 is operatively connected to said control device 16, so as to drive said pump motor 17 when said stirrer motor 15 is operated.

[0056] In accordance with an embodiment, said stirrer support and movement device 4 is operatively connected to at least one support device motor 18.

[0057] Said support device motor 18 is operatively connected to a control device 16.

[0058] In accordance with an embodiment, said spray gun 5 is operatively connected to at least one gun motor 19.

[0059] Said gun motor 19 is operatively connected to said control device 16 so as to control said gun motor 19 according to the position of said stirrer or mixer 3 to direct the jet of fluid according to said prevailing gun jet direction Y-Y incident to said prevailing stirrer flow direction X-X.

[0060] In accordance with an embodiment, said control device 16 is a feedback control device; in which said feedback control is operatively connected to a device for detecting the angular position of the stirrer or mixer 3 about an axis Z-Z. [0061 ] In accordance with an embodiment, said control device 16 is a feedback control device; in which said feedback control is operatively connected to a device for detecting the translation of the stirrer or mixer 3 along an axis Z-Z.

[0062] In accordance with an embodiment, said control device 16 is a feedback control device; in which said feedback control is operatively connected to a device for detecting the activation of the stirrer or mixer 3.

[0063] In accordance with an embodiment, said control device 16 is a feedback control device; in which said feedback control is operatively connected to a device for detecting the activation of the hydrating fluid pump 9.

[0064] In accordance with an embodiment, said control device 16 is a feedback control device; in which said feedback control is operatively connected to a device for detecting the activation of the recirculation pump 13.

[0065] In accordance with an embodiment, said stirrer support and movement device 4 comprises a support device motor 18 adapted to raise and lower said at least one stirrer or mixer 3 along a quadrangular section guide 20 by means of a winch 21 which moves a cable 22 connected at one end to a carriage 23 sliding along said quadrangular section guide 20 to which said at least one stirrer or mixer 3 is fixed. In accordance with an embodiment, instead of said winch, a pulley system is used, installed on a mechanical jack with trapezoidal rod, which in the accompanying Figures is always indicated with reference 21. Therefore, below, where "winch" is indicated, a "mechanical jack with which transmission pulleys cooperate" is also meant. In accordance with an embodiment, said jack cooperates with a load cell capable of detecting whether overthrust or overpull is occurring on the jack, (for example, due to the stirrer or mixer with difficulty in descending or the mixer with difficulty in ascending).

[0066] In accordance with an embodiment, said quadrangular section guide 20 is supported by said tank 2 rotatably about the vertical arranged axis or vertical axis Z-Z thereof.

[0067] Said quadrangular section guide 20 is operatively connected to an angular position reducer 24 which moves the angular position of the quadrangular section guide 20 about the vertical axis Z-Z thereof.

[0068] In accordance with an embodiment, said angular position reducer 24 is controlled by means of a crank 25, for example, by a manual operation by a user.

[0069] In accordance with an embodiment, a support plate 25 is connected to the top of the quadrangular section guide 20 by means of an angular lifting mechanism 27.

[0070] Said support plate 25 supports said spray gun 5. [0071 ] In accordance with an embodiment, said spray gun 5 is hung on or supported by hooks

28 connected to said support plate 25.

[0072] In accordance with an embodiment, said angular lifting mechanism 27 is controlled by means of a crank 25, for example, by a manual operation by a user.

[0073] In accordance with an embodiment, said tank 2 comprises an operator support walkway

29 located near said crank 25.

[0074] In accordance with an embodiment, said tank 2 comprises a tank wall 30; in said tank wall 30 there is a conduit seat 31 for the passage of said hydrating fluid conduit 8 and/or recirculation conduit 12.

[0075] In accordance with an embodiment, in said seat 31 there is a coupling 32 to which one end of a flexible tube 33 is connected on a side inside the tank 2 connected on the opposite end to said spray gun 5. Said hydrating fluid conduit 8 and/or recirculation conduit 12 is externally connected to said coupling 32.

[0076] In accordance with a general embodiment, a biogas or biomethane production assembly 1 comprises at least one tank 2, such as for example a fermenter or storage tank, which receives material 10 such as manure, slurry, poultry manure, dairy whey, vegetable waste, agricultural by-products inoculated with bacterial load for the prevailing formation of said biogas and digestate. Said tank comprises a tank bottom 37.

[0077] Said assembly 1 further comprises at least one stirrer or mixer 3.

[0078] Said assembly 1 further comprises at least one stirrer support and movement device 4 for moving said stirrer or mixer 3 at least along a substantially vertical direction defining a vertical axis Z-Z.

[0079] Said assembly 1 further comprises at least one lifting winch or winch 21.

[0080] Said assembly 1 further comprises a position sensor 34 which detects at least one indication of minimum and maximum height 35, 36 of the position with respect to said tank bottom 37 of the stirrer or mixer 3. In accordance with an embodiment, said position sensor is an encoder.

[0081] In accordance with an embodiment, said position sensor 34 is at least a fixed or movable graduated scale 38 bearing at least an indication of minimum and maximum height 35, 36 of the position with respect to said tank bottom 37 of the stirrer or mixer 3.

[0082] In accordance with an embodiment, said stirrer support and movement device 4 comprises a support device motor 18 adapted to raise and lower said at least one stirrer or mixer 3 along a guide 20 by means of a winch 21 which moves a cable 22 connected at one end to a carnage 23 sliding along said guide 20 to which said at least one stirrer or mixer 3 is fixed.

[0083] Said position sensor 34 is associated with said cable 22 or said winch 21 or with said support device motor 18.

[0084] In accordance with an embodiment, a rod 39 is connected by one of the ends thereof to said cable 22 and said rod 39 supports or forms said graduated scale 38. In accordance with an embodiment, said rod 39 is a stem of a jack.

[0085] In accordance with an embodiment, said tank 2 comprises a tank wall 30. A support bracket 47 protrudes from said tank wall 30. Said support bracket 47 supports said support device motor 18. Said support bracket 47 comprises a through seat for the rod 48 in which said rod 39 is received. Said support bracket 47 comprises an indicator or forms an indicator for said rod 39.

[0086] In accordance with an embodiment, said stirrer or mixer 3 is operatively connected to a control device 16.

[0087] Said stirrer support and movement device 4 comprises a support device motor 18 adapted to raise and lower said at least one stirrer or mixer 3.

[0088] Said support device motor 18 is operatively connected to said control device 16 so as to actuate said support device motor 18 only when the stirrer is turned off.

[0089] The present invention further relates to a biogas or biomethane production plant 40, comprising at least one assembly 1 according to any one of the embodiments described above.

[0090] In accordance with an embodiment, said plant 40 comprises at least one biogas collection device 41 operatively connected to said tank 2 for the collection of biogas produced by said tank 2.

[0091] Said plant 40 further comprises at least one biogas treatment device 42 operatively connected to said at least one biogas collection device 41 for the treatment of biogas and/or the concentration of methane CH4.

[0092] Said plant 40 further comprises at least one cogeneration device 43 operatively connected to said at least one biogas treatment device 42 for generating electricity and as a hot fluid by-product 44.

[0093] Said plant 40 further comprises at least one heating conduit 45 which conveys said hot fluid 44.

[0094] Said plant 40 further comprises at least one heating device 46 operatively connected to said tank 2 for heating said tank 2 and accelerating the biogas production process. [0095] The present invention also relates to a method for the production of biogas, comprising the steps of: providing at least one assembly according to any one of claims 1 to 8; stirring the material 10 according to at least one prevailing stirring flow direction X-X; sprinkling the material 10 from above the free surface thereof according to at least one prevailing jet direction Y-Y incident to said prevailing stirring flow direction X-X.

[0096] The present invention also relates to a method for the production of biogas, comprising the steps of: providing at least one assembly according to any one of the embodiments previously described; raising or lowering said stirrer or mixer 3 along a vertical axis Z-Z; detecting at least one indication of minimum and maximum height 35, 36 of the position with respect to the tank bottom 37 of the stirrer or mixer 3.

LIST OF REFERENCES

1 Biogas or biomethane production assembly

2 tank

3 stirrer or mixer

4 stirrer support and movement device

5 spray gun

6 hydrating liquid tank

7 hydrating liquid

8 hydrating fluid conduit

9 hydrating fluid pump

10 material such as manure, slurry, poultry manure, dairy whey, vegetable waste, agricultural by-products inoculated with bacterial load

11 recirculation circuit

12 recirculation pipe

13 recirculation pump

14 movement synchronization device

15 stirrer motor

16 control device

17 pump motor

18 support device motor

19 gun motor

20 quadrangular section guide

21 winch or pulley system installed on a mechanical jack with trapezoidal rod

22 cable

23 carriage

24 angular position reducer

25 crank 26 support plate

27 angular lifting mechanism

28 hooks

29 operator support walkway

30 tank wall

31 conduit seat

32 coupling

33 flexible tube

34 position sensor, for example an encoder

35 minimum height

36 maximum height

37 tank bottom

38 graduated scale

39 rod or jack stem

40 biogas or biomethane production plant

41 biogas collection device

42 biogas treatment device

43 cogeneration device

44 hot fluid

45 heating conduit

46 heating device

47 support bracket

48 rod through seat

X-X prevailing stirrer flow direction

Y-Y prevailing gun jet direction

7 7 vertical axis

Claims

1. A biogas or biomethane production assembly (1 ) comprising

- at least one tank (2), such as for example a fermenter or storage tank, which receives material (10) such as manure, slurry, poultry manure, dairy whey, vegetable waste, agricultural by products inoculated with bacterial load for the formation especially of digestate and biogas; said tank (2) comprising a tank bottom (37);

- at least one stirrer or mixer (3);

- at least one stirrer support and movement device (4) for moving said stirrer or mixer (3) at least along a substantially vertical direction defining a vertical axis (Z-Z);

- at least one lifting winch or winch (21); wherein there is further comprised

- a position sensor (34) which detects at least one indication of minimum and maximum height (35, 36) of the position with respect to said tank bottom (37) of the stirrer or mixer (3).

2. A biogas or biomethane production assembly (1 ) according to claim 1 , wherein

- said position sensor (34) is at least a fixed or movable graduated scale (38) bearing at least an indication of minimum and maximum height (35, 36) of the position with respect to said tank bottom (37) of the stirrer or mixer (3).

3. A biogas or biomethane production assembly (1 ) according to claim 1 or 2, wherein

- said stirrer support and movement device (4) comprises a support device motor (18) adapted to raise and lower said at least one stirrer or mixer (3) along a guide (20) by means of a winch (21) which moves a cable (22) connected at one end to a carriage (23) sliding along said guide (20) to which said at least one stirrer or mixer (3) is fixed; and wherein

- said position sensor (34) is associated with said cable (22) or said winch (21 ) or with said support device motor (18); and/or wherein

- a rod (39) is connected by one of its ends to said cable (22) and said rod (39) supports or constitutes said graduated scale (38); and/or wherein

- said tank (2) comprises a tank wall (30); a support bracket (47) protrudes from said tank wall (30); said support bracket (47) supports said support device motor (18); and wherein

- said support bracket (47) comprises a rod through seat (48);

- said support bracket (47) comprises an indicator or constitutes an indicator for said rod (39).

4. A biogas or biomethane production assembly (1 ) according to any one of the preceding claims, wherein

- said stirrer or mixer (3) is operatively connected to a control device (16); and wherein

- said stirrer support and movement device (4) comprises a support device motor (18) adapted to raise and lower said at least one stirrer or mixer (3); and wherein

- said support device motor (18) is operatively connected to said control device (16) so as to actuate said support device motor (18) only when the stirrer or mixer (3) is turned off.

5. A biogas or biomethane production plant (40), comprising - at least one assembly according to any one of claims 1 to 4.

6. A biogas or biomethane production plant (40) according to claim 5, comprising

- at least one biogas collection device (41) operatively connected to said tank for the collection of biogas produced by said tank (2);

- at least one biogas treatment device (42) operatively connected to said at least one biogas collection device (41) for the treatment of biogas and/or the concentration of methane (CH4);

- at least one cogeneration device (43) operatively connected to said at least one biogas treatment device (42) for generating electricity and as a hot fluid by-product (44);

- at least one heating conduit (45) which conveys said hot fluid (44);

- at least one heating device (46) operatively connected to said tank (2) for heating said tank (2) and accelerating the biogas production process.

7. A method for the production of biogas, comprising the steps of: - providing at least one assembly according to any one of claims 1 to 4;

- raising or lowering said stirrer or mixer (3) along a vertical axis (Z-Z);

- detecting at least one indication of minimum and maximum height (35, 36) of the position with respect to the tank bottom (37) of the stirrer or mixer (3).