Installation for mixing a fluid in a fluid treatment and / or storage tank, and associated process

Abstract

Fluid mixing installation in a fluid treatment and / or storage tank, and associated method. The invention relates to a fluid mixing installation (12) (15) comprising: - a fluid treatment tank (18) including a side wall (22) including an internal surface (23); - a fluid mixing system (30) in the tank including an inlet (35) and an injection outlet (37). Each mixing system includes a downstream section (48) defining the injection outlet configured to inject a fluid jet along an injection direction (Dinj) forming an angle α greater than 30° with a radial direction (R) of the tank, in order to deflect the fluid jet towards the side wall of the tank and / or to limit the dispersion of the fluid jet away from the side wall of the tank. Figure for the abstract: 1

Description

Title of the invention: Installation for mixing a fluid in a fluid treatment and / or storage tank, and associated method

[0001] The present invention relates to a fluid mixing installation in a treatment tank.

[0002] Such an installation is for example intended to generate biogas, containing in particular biomethane, notably by anaerobic digestion.

[0003] Anaerobic digestion has a cellular processing capacity capable of eliminating a significant amount of organic matter, producing biogas. Biogas production is encouraged because the biogas can then be used in a biomethane production unit by separating the carbon dioxide and methane contained in the biogas (for example, by a membrane process), and / or as an energy source for generating electricity, heating buildings, and / or powering vehicles.

[0004] In this regard, it is known to introduce sludge from wastewater treatment into a tank of a sludge digester to conduct anaerobic digestion producing biogas.

[0005] Many parameters influence the yield of biogas production from sludge. In particular, the sludge must be stirred effectively in the digester, notably to reduce variations in temperature and organic matter concentration within the digester mass, and to increase the chances of contact between microorganisms and the materials to be degraded.

[0006] The mixing operation must also be efficient in order to guarantee a residence time in the digester that provides thorough mixing. For example, it must ensure sufficient mixing at the bottom of the digester to minimize the accumulation of deposits, so as not to lose usable volume, and sufficiently agitate the fluid to facilitate the continuous rise of biogas.

[0007] In known mixing devices, sludge is taken from the digester tank, then conveyed through vertical chimneys distributed around the central axis of the tank before being reinjected into the tank.

[0008] Such a mixing device is very reliable but does not give complete satisfaction, particularly when the concentrations of organic matter in the digester are very high.

[0009] Indeed, a high concentration of organic matter induces a high viscosity of the sludge to be treated and leads to a decrease in the average mixing speed of the sludge in the tank and consequently a decrease in biogas production yield.

[0010] To overcome this problem, it is known to pretreat the sludge chemically and / or thermally and / or biologically in order to reduce its viscosity before introducing it into the digester, which increases the cost and consumables related to the treatment of sludge.

[0011] Another solution is to increase the energy supplied to the mixing plant so that the mixing system can drive a high-viscosity fluid in motion at a speed and shear rate satisfactory for biogas production yield. However, this solution is energy-intensive and thus increases biogas production costs.

[0012] An object of the invention is therefore to provide a mixing installation which allows very efficient mixing of the fluid, in particular for high fluid viscosities, while limiting the chemical treatments applied to the fluid and without increasing the energy consumption of the installation.

[0013] To this end, the invention relates to a fluid mixing installation comprising:

[0014] - a fluid treatment and / or storage tank, the tank comprising a bottom and a side wall comprising an internal surface delimiting an internal volume containing the fluid, the internal volume having a vertical central axis;

[0015] - at least one fluid mixing system in the tank comprising a socket fluid inlet into the tank, at least one fluid injection outlet located lower than the inlet into the tank, and a fluid movement system disposed between the inlet and the injection outlet, the mixing system or systems having an upstream section for guiding the fluid through the side wall;

[0016] characterized in that the mixing system or each mixing system includes a downstream section protruding into the internal volume and defining the injection outlet, the downstream section being configured to inject a fluid jet extending along an injection direction forming an angle α, in projection in a plane perpendicular to the central axis, greater than 30° with a radial direction towards the central axis and passing through the center of the section of the downstream section taken at the intersection with the internal surface of the side wall, in order to deflect the fluid jet towards the side wall of the tank and / or to limit the dispersion of the fluid jet away from the side wall of the tank.

[0017] The downstream section or sections being configured to deflect the fluid jet towards the side wall of the tank and / or to limit the dispersion of the fluid jet away from the side wall of the tank, the fluid flow at the injection outlet is concentrated and directed towards the side wall.

[0018] Thus, the mixing energy of the fluid circulation flow is also concentrated and directed towards the side wall of the tank, and does not disperse from the injection outlet as would be the case in the absence of deflection / concentration of the fluid jet.

[0019] Concentrating the flow towards the side wall of the tank allows for the efficient transmission of flow energy over a greater distance. This induces greater shear in the fluid, reducing its average viscosity on the one hand and increasing the mixing speed on the other. Consequently, the fluid mixing within the tank is more homogeneous.

[0020] Thus, the installation allows efficient mixing of the viscous fluid, without requiring pretreatment of the fluid to reduce its viscosity and without increasing the energy power consumed.

[0021] According to other advantageous aspects of the invention, the mixing installation comprises one or more of the following features, taken individually or in any technically possible combination:

[0022] - the downstream section or sections comprise a portion coaxial with the upstream section of guidance;

[0023] - the downstream section or sections comprise a guidance element extending the portion coaxial downstream;

[0024] - at least one guiding element is a downstream sheath, the injection outlet being defined at the free end of the downstream duct, the downstream duct advantageously having a passage cross-section substantially equal to the cross-section of the injection outlet;

[0025] - the downstream sheath comprises a downstream region extending in a direction of deviation forming an angle [3 between 1° and 90°, preferably between 10° and 50°, with the coaxial portion projected into a plane perpendicular to the central axis, so as to direct the jet of fluid circulating in the downstream duct towards the side wall of the tank;

[0026] - the downstream sheath comprises an upstream region extending in the axial continuation of the coaxial portion;

[0027] - the upstream region has a length L1 between 1 cm and 50 cm, of preferably between 10 cm and 20 cm, or even more preferably between 10 cm and 15 cm;

[0028] - the downstream region has a length L2 between 1 cm and 100 cm, of preferably between 30 cm and 80 cm, preferably between 50 cm and 70 cm;

[0029] - the injection outlet is defined at the free end of the coaxial portion, at least a guiding element being a deflector arranged downstream of the injection outlet having a height, taken parallel to the central axis, greater than or equal to the height of the injection outlet;

[0030] - the deflector extends in a plane parallel to the central axis along a direction of deflection forming an angle ô between 1° and 45°, preferably between 1° and 20°, with the coaxial portion, projected into a plane perpendicular to the central axis;

[0031] - the mixing installation comprises at least two fluid mixing systems, the fluid inlet of at least one first fluid mixing system being disposed at a first height relative to the bottom, strictly greater than at least a second height of the fluid inlet of at least one second fluid mixing system;

[0032] - the first height is between 5% and 50% of a minimum height of one fluid inlet ports;

[0033] - the fluid mixing system in the tank includes a chimney defining a fluid circulation conduit between the fluid inlet and the fluid injection outlet, the chimney extending substantially vertically along the side wall of the tank in or out of the tank;

[0034] - the fluid movement system or systems is a mechanical agitator or a pump; and

[0035] - the fluid movement system or systems are arranged in the section upstream, upstream of the downstream section or is located upstream of the upstream section outside the tank.

[0036] The invention also relates to a method for mixing a fluid in an installation as described above, the method comprising the following steps, implemented by the mixing system(s): - Suction and movement of the fluid by the fluid movement system between the fluid inlet and the injection outlet, - generation of a fluid jet to be injected into the tank at the injection outlet, - diversion of the fluid jet by the downstream section towards the side wall of the tank and / or limiting the dispersion of the fluid jet away from the side wall of the tank.

[0037] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0038] [Fig-1] [Fig.1] is a perspective view of a fluid mixing installation according to the invention, comprising a fluid mixing system according to a first embodiment,

[0039] [Fig.2] [Fig.2] is a perspective view of a downstream section of the mixing system of [Fig.1] according to a first embodiment,

[0040] [Fig.3] [Fig.3] is a schematic representation of the dynamic viscosity of the fluid within the mixing installation of [Fig.1],

[0041] [Fig.4] [Fig.4] is a perspective view of a downstream section of the system of mixing of the [Fig. 1] according to a second embodiment, and

[0042] [Fig.5] [Fig.5] is a schematic representation of a mixing installation of a fluid according to another embodiment.

[0043] A mixing installation 12 for a fluid 15 is illustrated in [Fig.1].

[0044] The mixing installation 12 is, for example, a processing installation sludge from a water treatment unit, for example industrial water treatment, drinking water, or wastewater treatment.

[0045] The brewing installation 12 is, for example, also intended for the treatment of bio-waste, such as agricultural waste.

[0046] The average sludge concentration of fluid 15 is for example greater than 30 g / L, and can for example reach values ​​greater than 60 g / L.

[0047] The brewing unit 12 is specifically designed to carry out anaerobic fermentation or digestion to remove organic matter present in the fluid, producing biogas. The biogas includes, in particular, biomethane, produced by anaerobic digestion. The biogas is intended to be separated to produce biomethane and / or is intended to be used as a fuel.

[0048] More generally, the mixing installation 12 is intended for mixing a fluid 15 in the form of a liquid with a viscosity greater than that of water. The average viscosity of the fluid 15 in the installation is generally greater than 10 mPa.s, with areas reaching up to 1000 Pa.s.

[0049] The fluid 15 is preferably non-Newtonian, in particular shear-thinning, its viscosity decreasing as a function of the shear to which it is subjected.

[0050] The brewing installation 12 includes a tank 18 for the treatment and / or storage of the fluid 15.

[0051] The tank 18 comprises a bottom 20 and a side wall 22 advantageously comprising a plurality of bases 22A projecting on the bottom 20. The side wall 22, including its bases 22A, thus defines an internal surface 23 delimiting with the bottom 20 an internal volume 24 intended to contain fluid 15.

[0052] The internal surface 23 is the surface of the side wall 22 in contact with the fluid 15 when fluid 15 is received into the internal volume 24. Each base 22A defines a vertical face 22B included in the internal surface 23.

[0053] The internal volume 24 has a central vertical axis A-A' and is for example greater than 100 m3 and is in particular between 100 m3 and 20000 m3.

[0054] The tank 18 is provided with an injection inlet for the fluid to be treated into the internal volume 24 and an outlet for the treated fluid, advantageously located opposite the injection inlet, or at the lowest point of the bottom 20.

[0055] The mixing installation 12 includes at least one mixing system 30 for the fluid 15 in the tank 18. In the example of [Fig.1], the mixing installation 12 includes a plurality of mixing systems 30 angularly distributed in the tank 18 around the central axis A-A'.

[0056] Each mixing system 30 includes a chimney 33 defined between a fluid inlet 35 of fluid 15 and a fluid injection outlet 37 of fluid 15 into the tank 18, each chimney 33 being advantageously held in a base 22A.

[0057] In all that follows, the terms "upstream" and "downstream" are used with respect to the direction of flow of the fluid 15 from the inlet port 35 to the injection outlet 37.

[0058] In the example of [Fig.1], each chimney 33 extends substantially vertically in the tank 18 downwards and along the side wall 22 of the tank 18. Each injection outlet 37 is disposed in the tank 18 near the side wall 22 of the tank 18, generally projecting from the base 22A.

[0059] By "near" it is understood that the injection outlets 37 are advantageously located at a distance from the side wall 22 of less than 40%, in particular less than 20%, of the radius of the tank 18, that is to say, of the minimum distance separating the central axis A-A' at the point closest to the side wall 22.

[0060] In addition, the chimneys 33 are for example located at a distance from the side wall 22 less than 40%, in particular less than 20%, of the radius of the tank 18, that is to say the minimum distance separating the central axis A-A' at the point closest to the side wall 22.

[0061] In the particular example shown in [Fig.1], each chimney 33 is a hollow half-cylinder welded against the internal surface 23 of the side wall 22 of the tank 18 above the base 22A.

[0062] Advantageously, each inlet port 35 is located below the free surface of fluid 15 in the tank 18. For example, at least one inlet port 35 is located between 25 cm and 50 cm below the free surface of fluid 15 in the tank 18. Thus, fluid 15 present in the tank 18 is able to be drawn in through each inlet port 35, circulate through the circulation conduit 39, and be reinjected into the tank 18 through the injection outlet 37 in order to set the fluid 15 present in the tank 18 in motion. In other words, it is not necessary to continuously inject fluid 15 into the tank 18 to stir the fluid 15.

[0063] Each injection outlet 37 is located lower in the tank 18, along the vertical axis, than the corresponding inlet 35. Thus, each chimney 33 defines a conduit circulation 39 of fluid 15 exhibiting a top-down flow between the inlet port 35 and the injection outlet 37.

[0064] Each injection outlet 37 has, for example, a circular contour passage section with a diameter typically between 50 cm and 100 cm, preferably between 60 cm and 80 cm and more particularly between 60 cm and 70 cm.

[0065] In the example shown in Figures 1 and 2, each mixing system 30 has an upstream section 42 for guiding the fluid 15 through the side wall 22, in particular through the base 22A, and a downstream section 48 for guiding the fluid 15, located downstream of the upstream section 42 for guiding, protruding into the tank 18, from the base 22A to the injection outlet 37.

[0066] Each upstream section 42 is cylindrical here. Each upstream section 42 is located upstream of the injection outlet 37 in the chimney 33, and downstream of the inlet 35.

[0067] Each upstream section 42 extends the fluid circulation conduit 39 15 and extends through the side wall 22 of the tank 18, in particular through the base 22A to the internal surface 23 of the tank 18, from which it is extended by the downstream section 48.

[0068] In order to produce a fluid jet 44 from the fluid 15 circulating in each circulation conduit 39, the fluid 15 mixing system 30 includes a fluid 15 movement system disposed between the inlet port 35 and the injection outlet 37.

[0069] In particular, each fluid movement system 15 is disposed in the upstream section 42 of the corresponding chimney 33.

[0070] In the example of Figures 1 and 2, the fluid movement system 15 is a mechanical agitator 46. For example, the mechanical agitator 46 is located in the upstream section 42 of the chimney 33 and is powered by a motor, not shown, located in the upstream section 42 outside the tank 18. In other words, the motor is, for example, located in the part of the upstream section 42 situated outside the tank 18, on the other side of the side wall 22 and opposite the end opening into the tank 18. Thus, maintenance of the mechanical agitator 46 is facilitated for an operator who does not have to drain the tank 18 and enter the tank 18 in order to work on the motor of the mechanical agitator 46.

[0071] The injection of a jet of fluid 44 into the tank 18 helps to set the fluid 15 present in the tank 18 in motion and thus promotes the mixing of the fluid 15 inside the tank 18.

[0072] Each downstream section 48 is configured to inject the fluid jet 44 along an injection direction Dinj forming an angle α, in projection onto a plane perpendicular to the central axis A-A', greater than 30° with a radial direction R towards the central axis A-A' and passing through the center 48A of the section of the downstream segment 48 taken at the intersection with the internal surface 23 of the side wall 22 (here on the vertical face 22B of the base 22A), in order to deflect the fluid jet 44 towards the side wall 22 of the tank 18 and / or to limit the dispersion of the fluid jet 44 away from the side wall 22 of the tank 18, as shown in [Fig.3].

[0073] Each downstream section 48 includes, for example, a coaxial portion 49 with the upstream guidance section 42.

[0074] In the example of the figures, each downstream section 48 includes a fluid jet guide 50 44 extending the coaxial portion 49 downstream.

[0075] The coaxial portion 49 protrudes into the tank 18. It has a length less than the length of the upstream section 42. Advantageously, the upstream section 42 and the coaxial portion 49 can be formed in the same tube inserted into the base 22A and protruding from the face 22B of the base 22A.

[0076] Each guide member 50 is configured to deflect the fluid jet 44 towards the side wall 22 of the tank 18 and / or to limit the dispersion of the fluid jet 44 away from the side wall 22 of the tank 18.

[0077] Each guiding element 50 is for example reported on the coaxial portion 49 at its downstream end.

[0078] According to a first embodiment, represented in particular on [Fig.2], at least one guide element 50 is a downstream sheath 52 extending the upstream guide section 42 and the coaxial portion 49.

[0079] The injection outlet 37 is then defined at the free end 54 of the downstream sheath 52.

[0080] The downstream duct 52, for example, has a passage cross-section substantially equal at the section of passage of the injection outlet 37. Thus, the pressure losses during the passage of the fluid jet 44 from the injection outlet 37 to the downstream duct 52 are advantageously limited.

[0081] The downstream sheath 52 comprises an upstream region 56 extending parallel to the coaxial portion 49, and a downstream region 58 opening downstream through the free end 54.

[0082] The downstream region 58 extends along a deflection direction Ddev forming an angle [3] between 1° and 90°, preferably between 10° and 50°, and even more preferably between 20° and 30°, with the coaxial portion 49 projected into a plane perpendicular to the central axis A-A'. In other words, the downstream duct 52 is an angled duct, the downstream region 58 forming with the upstream region 56 an angle [3] projected into a plane perpendicular to the central axis A-A', so as to direct the fluid jet 44 circulating in the downstream duct 52 and exiting through the injection outlet 37 towards the side wall 22 of the tank 18 and / or so as to limit the dispersion of the fluid jet 44 away from the side wall 22 of the tank 18.

[0083] Thus, the fluid jet 44 is effectively injected into the tank 18 along the direction Ddev (coaxial with the direction Dinj) forming an angle equal to [3 with the coaxial portion and equal to a with the radial direction R.

[0084] The upstream region 56 has for example a length L1 between 1 cm and 50 cm, preferably between 10 cm and 20 cm, more preferably between 10 cm and 15 cm.

[0085] More generally, the length L1 must be sufficiently small in order to limit the dissipation of the energy of the fluid 15 during the circulation of the fluid 15 in the upstream region 56.

[0086] The downstream region 58 has for example a length L2 between 1 cm and 100 cm, preferably between 30 cm and 80 cm, even more preferably between 50 cm and 70 cm.

[0087] Such lengths L1 and L2 allow the fluid jet 44 to be guided and the energy of the fluid jet 44 to be concentrated over an adequate distance in order to avoid too rapid a dispersion of the energy of the fluid jet 44. Thus, a greater shear is induced in the fluid, which reduces its average viscosity on the one hand, and increases the mixing speed on the other.

[0088] The injected fluid jet 44 then forms a channel, as shown in [Fig. 3], for high-speed fluid 15, capable of entraining the fluid 15 present in the tank 18. The mixing of the fluid 15 is thus made more efficient and more homogeneous.

[0089] In a particular embodiment where the mixing installation 12 includes at least two mixing systems 30 of the fluid 15 and with reference to [Fig.1], the inlet 35 of the fluid 15 of at least a first mixing system 60, 62 of the fluid 15 is disposed at a first height H1, H2 relative to the bottom 20, strictly greater than at least a second height H3 of the inlet 35 of the fluid 15 of at least a second mixing system 64 of the fluid 15.

[0090] In particular, the first height Hl, H2 is between 5% and 50% of a minimum height H3 of one of the inlet sockets 35 of the fluid 15.

[0091] In the particular example of [Fig.1], all the inlet sockets 35 are located at different heights H1, H2, H3, taken from the bottom 20 of the tank 18.

[0092] Varying the height of the inlet ports 35 introduces an asymmetry in the flow, resulting in a higher shear stress. This helps to reduce the average viscosity of the fluid 15 in the tank 18 and allows for an increase in the average velocity of the fluid 15 in the tank 18, as will be shown in more detail later.

[0093] In one variant, shown in [Fig. 4], for at least one downstream section 48 or for each downstream section 48, the injection outlet 37 is defined at the free end of the coaxial section 49. The guiding element 50 of this downstream section 48 is a deflector 70 arranged downstream of the injection outlet 37.

[0094] The deflector or each deflector 70 is for example a plate disposed at a distance between 0 m and 1 m, preferably between 0 cm and 50 cm and advantageously at 0 cm, from the corresponding injection outlet 37, taken along the direction of the axis of the coaxial portion 49.

[0095] In an alternative, not shown, the deflector or each deflector 70 extends for example from upstream of the injection outlet 37. In other words, the deflector or each deflector 70 is for example positioned a few centimeters, for example 5 cm, upstream of the injection outlet 37 along the direction of the axis of the coaxial portion 49, and extends continuously to downstream of the injection outlet 37, such that the coaxial portion 49 and the deflector or each deflector 70 overlap over part of their length upstream of the injection outlet 37.

[0096] The deflector or each deflector 70 extends in a plane parallel to the central axis A-A', along a deflection direction Ddef forming an angle ô between 1° and 70°, for example between 1° and 45°, preferably between 1° and 20°, with the coaxial portion 49, projected into a plane perpendicular to the central axis A-A'.

[0097] The deflector or each deflector 70 extends at least in part the coaxial portion 49 guiding the fluid from the injection outlet 37 and is disposed between the injection outlet 37 and the central axis A-A', along the radial direction R. In other words, the deflector or each deflector 70 forms a barrier deflecting all or part of the fluid jet 44 injected downstream of the injection outlet 37 away from the central axis A-A', as shown in [Fig.4].

[0098] The deflector or each deflector 70 is here a non-tubular panel.

[0099] The deflector or deflectors 70 comprise, for example, a height, taken parallel to the central axis A-A', greater than or equal to the height of the injection outlet 37, and a width, taken along the deflection direction Ddef between 0.1 m and 3 m, preferably between 50 cm and 2 m.

[0100] Such a height allows the deflector 70 to effectively deflect the fluid jet 44, at least over part of its height, preferably over its entire height at the outlet of the injection outlet 37.

[0101] Such a width allows the fluid jet 44 to be guided advantageously away from the injection outlet 37 in order to concentrate the energy of the fluid jet 44 over an adequate distance and thus avoids too rapid a dispersion of the energy of the fluid jet 44. The injected fluid jet 44 then forms a channel, as shown in [Fig.3], of high-speed fluid 15, capable of driving the fluid 15 present in the tank 18 into motion.

[0102] Concentrating the flow towards the side wall of the tank allows for efficient energy transmission of the flow over a greater distance. Thus, a higher shear rate A significant amount of fluid is introduced, reducing its average viscosity on the one hand and increasing the mixing speed on the other. As a result, the fluid mixing in the tank is more homogeneous and efficient.

[0103] In a particular embodiment, schematically illustrated in [Fig.5], the chimney or each chimney 33 extends out of the tank 18, outside the side wall 22.

[0104] In this embodiment, the fluid movement system 15 includes, for example, an axial pump 72 disposed in the circulation conduit 39 upstream of the upstream section 42 which passes through the side wall 22.

[0105] Thus, the axial pump 72 is located outside the tank 18 and allows the pumping of the fluid 15 from the inlet 35 to the injection outlet 37, creating a circulation of the fluid 15 in the circulation conduit 39 in a direction substantially parallel to the central axis A-A'.

[0106] This embodiment has the advantage of facilitating the maintenance of the brewing systems 30, the tank 18 not necessarily having to be emptied in order to access the chimneys 33 or the pumps 72.

[0107] Independently of the embodiments described above, a method for mixing the fluid 15 in such a mixing installation 12 will now be described.

[0108] The process comprises the following steps, implemented by the brewing system(s) 30:

[0109] - aspiration and movement of the fluid 15 by the system fluid movement 15 between the fluid inlet 35 and the injection outlet 37.

[0110] Since the inlet ports 35 are arranged below the free surface of the fluid 15 in the tank 18, fluid 15 is naturally drawn in through the inlet ports 35 and flows through the chimneys 33 to the fluid 15 movement system.

[0111] The fluid movement system 15 (for example the mechanical agitator 46 of [Fig.2] or the axial pump of [Fig.5]), then generates a jet of fluid 44 suitable for injection into the tank 18 downstream of the injection outlet 37.

[0112] The downstream section or sections 48 (for example including the downstream duct 52 of [Fig.2] or the deflector 70 of [Fig.4]) deflects the fluid jet 44 towards the side wall 22 of the tank 18 and / or limits the dispersion of the fluid jet 44 away from the side wall 22 of the tank 18, as shown in [Fig.3].

[0113] Such a fluid mixing installation 12 of fluid 15 has many advantages.

[0114] Indeed, for sludge concentrations in fluid 15 exceeding 50 g / L, Installation 12 as described allows effective mixing of fluid 15, and therefore contributes to increasing biogas production yield.

[0115] In particular, the jet guide elements are configured to deflect the fluid jet towards the side wall of the tank and / or to limit the dispersion of the fluid jet to the gap in the side wall of the tank, the mixing energy carried by the fluid jet 44 is concentrated and directed towards the side wall.

[0116] Thus, the mixing energy is not dispersed from the injection outlet but guides and propels the fluid jet 44 downstream of the injection outlet 37 towards the side wall 22.

[0117] The circulation of the fluid flow 15 is then optimized, the induced shear stress field makes it possible to reduce the average viscosity of the fluid 15 in the tank and to increase the average velocity of the fluid 15 in the tank 18.

[0118] Thus, the installation 12 allows efficient mixing of the viscous fluid, even for high concentrations of the fluid 15 in sludge, without requiring pretreatment of the fluid to reduce its viscosity and without increasing the energy power consumed.

[0119] By way of example, approximate values ​​of the average velocity of fluid 15 in tank 18, as well as of the average viscosity of fluid 15 in tank 18, were measured by simulation and are grouped in the tables below, according to the different embodiments described above.

[0120] [Tables 1] Control case: With downstream sheath; With deflector and θ = 0°; With deflector and θ = 10°; With deflector and θ = 20°; With deflector and θ = 30°; Average fluid viscosity (Pa·s): 433, 300, 381, 368, 366, 416; Variation compared to the control case (%): -31, -12, -15, -15, -4; Average fluid velocity (m / s): 0.04, 0.06, 0.045, 0.045, 0.044, 0.037; Variation compared to the control case (%): +50, +12.5, +12.5, +10, -7.5

[0121] With reference to Table 1, results of the average viscosity of fluid 15 in the tank 18 and of the average velocity of fluid 15 in the tank were obtained following a "Computational Fluid Dynamics" model (in French, digital fluid dynamics, CFD).

[0122] For the simulation, the fluid used is a Herschel-Bulkley type fluid.

[0123] This type of fluid is a generalized model of a non-Newtonian fluid, in which the deformation undergone by the fluid is related to the stress in a non-linear manner. Three parameters characterize this relationship: the coherence factor K, the flow index p and the yield stress for the flow r.

[0124] The simulation was carried out with such a fluid having the following rheological parameters: k = 3.74; - q = 0.24; and - r = 3.3 Pa.

[0125] The simulation was carried out with a fluid sludge concentration of 70 g / L.

[0126] The simulations performed for the control case were carried out with a mixing plant model 12 having a volume of 7000 m³. The plant 12 comprises three mixing systems 30 for the fluid 15 having inlet ports 35 of similar height. The mixing systems 30 for the fluid 15 do not include a guide element 50.

[0127] Simulations with a guiding element 50 such as a downstream duct 52 and a deflector 70 were carried out with a mixing installation model 12 having a volume of 7000 m3 and comprising three mixing systems 30 of the fluid 15. Each mixing system 30 includes a guiding element 50 such as a downstream duct 52 or a deflector 70 disposed downstream of the injection outlet 37.

[0128] When the guiding element 50 is a deflector, the simulations were carried out for different inclinations of the deflector 70 relative to coaxial portion 49.

[0129] Thus, four simulations were carried out, corresponding respectively to the angle ô, taken between the coaxial portion 49 and the deflection direction Ddef in projection in a plane perpendicular to the central axis A-A', equal to 0°, 10°, 20° and 30°.

[0130] An analysis tool, such as for example the Star-CCM+ vl7.06.008 tool, was used to obtain, from the fluid and its rheological parameters and a CAD (computer-aided design) model of the mixing installation 12, the fluid velocity in the structure, its viscosity, the shear field lines as well as the shear stress values.

[0131] As can be seen in Table 1, the addition of the downstream sleeve 52 downstream of the three injection outlets 37 reduces the average viscosity by about 30% and increases the average velocity in the tank 18 by about 50%.

[0132] The sheath 52 makes it possible to modify the flow of the flux at the injection outlet 37 by concentrating it and directing it towards the wall of the tank, preferably so that the fluid moves tangentially to the wall 22 of the tank 18, licking the wall of the tank 18.

[0133] Similarly, the presence of a deflector downstream of the three injection outlets 37 makes it possible to reduce the average viscosity by a value of between 4% and 15% in depending on the angle ô of the deflector 70, and to significantly increase the average speed in the tank.

[0134] [Tables2] Control case With duct a val With duct downstream + reduction in the height of two inlet ports Average fluid viscosity (Pa.s) 433 300 200 Variation compared to the control case (%) / -31 -54 Average fluid velocity (m / s) 0.04 0.06 0.08 Variation compared to the control case (%) / +50 +100

[0135] With reference to Table 2, measurements of the average viscosity of fluid 15 in the tank 18 and of the average velocity of fluid 15 in the tank were carried out by simulation following the protocols described with reference to Table 1.

[0136] These simulations were carried out with a mixing installation 12 having a volume of 7000 m3 and comprising three mixing systems 30 of the fluid 15, each comprising a downstream duct 52.

[0137] Each mixing system 30 of the fluid 15 has an inlet 35 located at a distinct height from the bottom 20 of the tank 18. In particular, the first inlet 35 is disposed between 25 cm and 50 cm below the free surface of the fluid 15 in the tank, the second inlet 35 is disposed 2 m below the first inlet 35, and the third inlet 35 is disposed 4 m below the first inlet 35, i.e. 2 m below the second inlet 35.

[0138] It is noted that reducing the height of two of the inlet fittings 35 reduces the average viscosity by about 30% and increases the average velocity in the structure by about 50% compared to a mixing installation 12 with a downstream duct 52 but without difference in heights of the inlet fittings 35.

[0139] Thus, compared to the control solution (absence of a guiding element and uniform height of the inlet sockets 35), an overall reduction in average viscosity of approximately 55% and an increase in average velocity in the tank 18 of approximately 100% are observed.

[0140] In an alternative, not shown, at least one downstream section 48 or each downstream section 48 does not include a guiding element 50.

[0141] According to this variant, this downstream section 48, devoid of a guiding element 50, comprises only the coaxial portion 49 projecting into the tank 18, which extends the upstream section 42.

[0142] Thus, the upstream section 42 extends along the injection direction Dinj, forming the angle a greater than 30° with the radial direction R, as defined above.

[0143] In other words, the downstream section 48 is coaxial with the upstream section 42 up to the injection outlet 37.

Claims

Demands

1. Fluid (15) mixing installation (12) comprising: - a tank (18) for processing and / or storing the fluid (15), the tank (18) comprising a bottom (20) and a side wall (22) comprising an internal surface (23) delimiting an internal volume (24) containing the fluid (15), the internal volume (24) having a vertical central axis (A-A'); - at least one fluid mixing system (30) in the tank (18) comprising a fluid inlet (35) in the tank (18), at least one fluid injection outlet (37) located lower than the inlet (35) in the tank (18), and a fluid movement system (15) disposed between the inlet (35) and the injection outlet (37), the mixing system or each mixing system (30) having an upstream section (42) for guiding the fluid (15) through the side wall (22); characterized in that the mixing system or each mixing system (30) comprises a downstream section (48) projecting into the internal volume (24) and defining the injection outlet (37), the downstream section (48) being configured to inject a fluid jet (44) extending along an injection direction (Dinj) forming an angle α, in projection into a plane perpendicular to the central axis (A-A'), greater than 30° with a radial direction (R) towards the central axis (A-A') and passing through the center (48A) of the section of the downstream section (48) taken at the intersection with the internal surface (23) of the side wall (22), in order to deflect the fluid jet (44) towards the side wall (22) of the tank (18) and / or to limit the dispersion of the fluid jet (44) away from the side wall (22) of the tank (18).

2. Fluid mixing installation (12) according to claim 1, wherein the downstream section or each downstream section (48) comprises a coaxial portion (49) with the upstream guide section (42).

3. Fluid mixing installation (12) according to claim 2, wherein the downstream section or each downstream section (48) includes a guide element (50) extending the coaxial portion (49) downstream.

4. A fluid mixing installation (12) according to claim 3, wherein at least one guiding element (50) is a downstream duct (52), the injection outlet (37) being defined at the free end (54) of the downstream duct (52), the downstream duct (52) advantageously having a passage section substantially equal to the section of the injection outlet (37).

5. Fluid mixing installation (12) according to claim 4, wherein the downstream duct (52) comprises a downstream region (58) extending in a direction of deviation (Ddev) forming an angle [3] between 1° and 90°, preferably between 10° and 50°, with the coaxial portion (49) projecting in a plane perpendicular to the central axis (A-A'), so as to direct the fluid jet (44) circulating in the downstream duct (52) towards the side wall (22) of the tank (18).

6. Fluid mixing installation (12) according to claim 4 or 5, wherein the downstream duct (52) comprises an upstream region (56) extending in the axial continuation of the coaxial portion (49).

7. Fluid mixing installation (12) according to claim 6, wherein the upstream region (56) has a length L1 between 1 cm and 50 cm, preferably between 10 cm and 20 cm, more preferably between 10 cm and 15 cm.

8. Fluid mixing installation (12) according to claim any one of claims 5 to 7, wherein the downstream region (58) has a length L2 of between 1 cm and 100 cm, preferably between 30 cm and 80 cm, more preferably between 50 cm and 70 cm.

9. Fluid mixing installation (12) according to any one of claims 3 to 8, wherein the injection outlet (37) is defined at the free end of the coaxial portion (49), at least one guiding member (50) being a deflector (70) disposed downstream of the injection outlet (37) having a height, taken parallel to the central axis (A-A'), greater than or equal to the height of the injection outlet (37).

10. Fluid mixing installation (12) according to claim 9, wherein the deflector (70) extends in a plane parallel to the central axis (A-A') along a deflection direction (Ddef) forming an angle ô between 1° and 45°, preferably between 1° and 20°, with the coaxial portion, projected in a plane perpendicular to the central axis (A-A').

11. A fluid mixing installation (12) according to any one of the preceding claims, wherein the mixing installation (12) comprises at least two fluid (15) mixing systems (30), the fluid inlet (35) of at least one of the systems mixing (60, 62) of fluid (15) being disposed at a first height (H1, H2) relative to the bottom (20), strictly greater than at least a second height (H3) of the inlet (35) of the fluid of at least a second mixing system (64) of the fluid (15).

12. Fluid mixing installation (12) according to claim 11, wherein the first height (H1, H2) is between 5% and 50% of a minimum height (H3) of one of the inlet ports (35) of the fluid (15).

13. Fluid mixing installation (12) according to any one of the preceding claims, wherein the fluid (15) mixing system (30) in the tank (18) comprises a chimney (33) defining a circulation conduit (39) for the fluid (15) between the fluid inlet (35) and the fluid injection outlet (37), the chimney (33) extending substantially vertically along the side wall (22) of the tank (18) in the tank (18) or out of the tank (18).

14. Fluid mixing installation (12) according to any one of the preceding claims, wherein the fluid movement system or systems is a mechanical agitator (46) or a pump (72).

15. Fluid mixing installation (12) according to any one of the preceding claims, wherein the fluid movement system or systems is disposed in the upstream section (42), upstream of the downstream section (48) or is disposed upstream of the upstream section (42) outside the tank (18).

16. A method for stirring a fluid (15) in an installation (12) according to any one of the preceding claims, the method comprising the following steps, implemented by the stirring system or each stirring system (30): - suction and movement of the fluid (15) by the fluid movement system (15) between the fluid inlet (35) and the injection outlet (37), - generation of a fluid jet (44) to be injected into the tank (18) at the injection outlet (37), - deflection of the fluid jet (44) by the downstream section (48) towards the side wall (22) of the tank (18) and / or limitation of the dispersion of the fluid jet (44) away from the side wall (22) of the tank (18).

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