Agitated tank with improved uniformity of air bubble distribution and method thereof

Abstract

The present invention relates to an agitator tank for uniformly dispersing gas bubbles in a liquid. The agitator tank includes a liquid container, a gas injection system, at least one impeller, and at least one baffle. The at least one impeller is rotatable about at least one axis of rotation and includes one or more blades extending a maximum distance R from the corresponding axis of rotation of the impeller. One or more of the at least one impellers are shaped and oriented to induce an axial flow of the liquid toward the gas injection system, and the minimum distance from the at least one baffle to the at least one axis of rotation is at most 1.2R for any of the at least one impeller.

Description

[Technical Field]

[0001] The present invention relates to the field of bioreactor devices, and in particular to bioreactors that can achieve uniform dispersion of gas bubbles using low rotational speeds, and methods for producing such dispersion using low rotational speeds. [Background technology]

[0002] The prior art is known for a variety of agitation and aeration systems for stirred tanks, each incorporating agitators with different geometries. Such systems consume a great deal of energy because they must operate with high agitator rotation speeds or the torque required to maintain such rotation speeds is very high to achieve an adequate level of mixing. Examples of agitation systems are summarized in the following patent documents:

[0003] US Patent No. 5,949,999 describes a bioreactor for mammalian cell culture based on an axial agitator combined with an element having the outer radial profile of an axial impeller that rotates in the closest part of the side wall of the reactor.

[0004] US Patent No. 5,949,999 describes an agitation system consisting of discrete vertical baffles close to the sidewall of the vessel.

[0005] US Pat. No. 5,649,999 describes a compound stirring system including at least one upper impeller and one lower impeller, the upper impeller being of the axial flow type.

[0006] US Pat. No. 5,699,499 describes an agitated reactor for cultivating microorganisms and cells, in which the impeller that circulates the fluid has holes on its surface for injecting gas into the reactor.

[0007] The ability to achieve uniform mixing using the above agitation systems is sometimes reduced as some fluid recirculation cells form, making it difficult to achieve complete mixing in a short time, a situation typical of radial impellers such as the Rushton type.

[0008] In other agitation systems mentioned above, the high azimuthal velocity component of the fluid around the agitator axis induced by the impeller rotation makes it difficult to disperse the bubbles throughout the volume of the agitated tank. Some systems have vertical baffles close to the sidewalls of the vessel, but these systems cannot effectively reduce the azimuthal velocity component. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Patent Application No. 2019168177(A1) [Patent Document 2] KR1020160039907A [Patent Document 3] U.S. Patent Application No. 2019078045(A1) [Patent Document 4] WO2019126660A1 Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, there is a need for an agitation system for a stirred tank that can uniformly distribute gas bubbles in a liquid while rotating the agitator at a slow speed and reducing the azimuthal velocity component. [Means for solving the problem]

[0011] A first aspect of the present invention relates to an agitator tank for uniformly dispersing gas bubbles in a liquid. The agitator tank includes a liquid container, a gas injection system, at least one impeller, and at least one baffle. The liquid container includes first and second ends defining axial ends of the container and one or more sidewalls extending between the axial ends. The gas injection system is located proximate to the first end of the container. The at least one impeller is rotatable about at least one rotation axis and includes one or more blades extending a maximum distance R from the corresponding impeller rotation axis. The at least one baffle is axially displaced from the at least one impeller and is fixed relative to the container in an orientation to reduce azimuthal flow generated by the at least one impeller. One or more impellers of the at least one impeller are shaped and oriented to induce an axial flow of liquid toward the gas injection system, and a minimum distance from the at least one baffle to the at least one axis of rotation is at most 1.2R for any of the at least one impeller.

[0012] In a preferred embodiment, at least one baffle is bent or curved anywhere between the minimum distance from the at least one baffle to the at least one axis of rotation and 1.2R to the at least one axis of rotation of any of the at least one impeller, thereby converting azimuthal flow of the liquid to axial flow.

[0013] In another preferred embodiment of the first aspect of the present invention, the minimum distance from the at least one baffle to the at least one axis of rotation of any of the at least one impeller is at most 1.1R.

[0014] In another preferred embodiment of the first aspect of the present invention, the minimum distance from the at least one baffle to the at least one axis of rotation is at most R of any of the at least one impeller.

[0015] In another preferred embodiment of the first aspect of the present invention, a gap is provided between the at least one baffle and the one or more side walls.

[0016] In another preferred embodiment of the first aspect of the present invention, the at least one impeller is a single impeller, the single impeller configured to induce at least an axial flow of liquid toward the gas injection system. Optionally, the single impeller is also configured to induce a radial flow from the axis of rotation of the single impeller to one or more side walls. More preferably, one or more, preferably all, of the blades of the single impeller comprise surfaces having a mean pitch angle of 10° to 60°, even more preferably 15° to 50°, the mean pitch angle being defined as the average angle formed between the chord line and a plane perpendicular to the axis of rotation of the impeller.

[0017] In another alternative preferred embodiment of the first aspect of the present invention, the at least one impeller comprises a plurality of impellers axially displaced relative to one another, the plurality of impellers comprising a first impeller closest to the gas injection system and one or more second impellers further away from the gas injection system, the first impeller shaped to induce at least a radial flow of liquid from the axis of rotation of the first impeller toward the one or more side walls, and the one or more second impellers shaped to induce at least an axial flow of liquid toward the first impeller.

[0018] In a more preferred embodiment, one or more, preferably all, of the blades of the first impeller have surfaces with an average pitch angle of between 50° and 90°, and / or one or more, preferably all, of the blades of the one or more second impellers have surfaces with an average pitch angle of between 10° and 60°, preferably between 15° and 50°, where the average pitch angle is defined as the average angle formed between the chord line and a plane perpendicular to the axis of rotation of the impeller in which the blade is located. In another more preferred embodiment, the minimum distance between two adjacent impellers is less than 3R of any of the above impellers.

[0019] In another more preferred embodiment, the minimum diameter of the second impeller is greater than 0.3 times the square root of the vessel cross-sectional area perpendicular to the axis at the height of the second impeller, preferably greater than 0.45 times the square root of the vessel cross-sectional area perpendicular to the axis at the height of the second impeller.

[0020] In another preferred embodiment of the first aspect of the invention, the maximum diameter of one or more of the at least one impeller shaped and oriented to induce axial flow of liquid towards the gas injection system is less than or equal to 0.75 times the square root of the vessel cross-sectional area perpendicular to the axis at the height of the at least one impeller.

[0021] In another preferred embodiment of the first aspect of the present invention, at least one baffle is folded or curved to redirect azimuthal flow of the liquid to axial flow. In certain embodiments, at least one baffle is folded or curved to redirect azimuthal flow of the liquid to axial flow, and more preferably, at least one baffle (150) comprises a second planar surface (158) that has a particular angle (152) relative to the axis of rotation (160). In even more preferred embodiments, the second planar surface forms an average angle of 10° to 45° with respect to the main plane of the baffle. In another even more preferred embodiment, at least one baffle defines a curved surface having an average arch of 10° to 45°.

[0022] In another preferred embodiment of the first aspect of the present invention, the minimum distance from the at least one baffle to the at least one axis of rotation is less than R of any of the at least one impeller.

[0023] In another preferred embodiment of the first aspect of the present invention, the gas injection system comprises an injection orifice, and the average distance from the injection orifice to the first end is less than the distance R of the first impeller.

[0024] In another preferred embodiment of the first aspect of the present invention, the gas injection system is a sparger including a plurality of orifices each located radially between the axis of rotation of the impeller closest to the first end of the vessel and one or more side walls, and further wherein the average distance between the orifices of the sparger and the axis of rotation of the impeller closest to the first end of the vessel is greater than 0.7R for the impeller closest to the first end of the liquid vessel.

[0025] In another preferred embodiment of the first aspect of the present invention, the agitator tank is configured to have a height (H) of the liquid that the agitator tank is configured to contain inside the liquid container and an average diameter ( <d>) is greater than 1.5, a plurality of impellers are provided, and <d>) is greater than 2, there are more than two impellers. The liquid height (H) is the distance from such free liquid surface to the first end of the agitator tank, and is the average diameter ( <d>) is the average square root of the cross-sectional area of ​​the container perpendicular to the axis along the liquid container.

[0026] In another preferred embodiment of the first aspect of the present invention, the at least one impeller comprises a hub having a radius greater than 0.2R, preferably greater than 0.3R.

[0027] A second aspect of the present invention refers to a method for uniformly dispersing gas bubbles in a liquid in an agitator tank, wherein the agitator tank is an agitator tank according to any of the embodiments of the first aspect of the present invention, the method comprising: a) generating at least an axial flow towards a first end of the agitator tank by one or more impellers of at least one impeller above the gas injection system, and preferably also generating a radial flow (135) by said first impeller; b) reducing the azimuthal flow generated by one or more of the impellers by at least one baffle; and c) injecting gas into the fluid with a gas injection system proximate the first end of the vessel.

[0028] To enable the present disclosure to be better understood and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying schematic drawings. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a schematic side view of an agitator tank according to at least one embodiment of the present invention. [Figure 2A] 1 is a schematic top view of a gas injection system according to at least one embodiment of the present invention. [Figure 2B] FIG. 1 is a schematic top view of another gas injection system according to at least one embodiment of the present invention. [Figure 2C] FIG. 1 is a schematic top view of another gas injection system according to at least one embodiment of the present invention. [Figure 3A] FIG. 1 is a schematic side view of an agitator tank incorporating baffles according to at least one embodiment of the present invention. [Figure 3B] 3B is a schematic radial cross-sectional view of the baffle of FIG. 3A taken along line AA. [Figure 4A] 1 is a schematic side view of an impeller configured to induce radial flow through a vessel in accordance with at least one embodiment of the present invention; FIG. [Figure 4B] FIG. 4B is a schematic top view of the impeller shown in FIG. 4A. [Figure 5A] 1 is a schematic side view of an impeller configured to induce axial flow according to at least one embodiment of the present invention; [Figure 5B] FIG. 5B is a schematic top view of the impeller shown in FIG. 5A. [Figure 6] 1 is a schematic side view of a blade according to at least one embodiment of the present invention. [Figure 7] FIG. 1 illustrates a simulated fluid flow in an agitator tank according to at least one embodiment of the present invention. [Figure 8] FIG. 1 shows a comparison of mass transfer coefficients for an agitator tank in accordance with at least one embodiment of the present invention and a standard stirred tank. [Figure 9] 1 is a schematic illustration of a method for obtaining a uniform bubble distribution according to at least one of the embodiments of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0030] definition The term "radial" when referring to an impeller is preferably understood to mean an impeller configured to generate more radial flow than axial flow.

[0031] The term "axial flow" when referring to an impeller is preferably understood to be an impeller configured to generate more axial flow than radial flow.

[0032] The term "mixed type" when referring to an impeller is preferably understood to mean an impeller configured to generate both axial and axial flow.

[0033] The term "proximal" with respect to one of the container ends is preferably understood as an element closer to such end than to the other end of the container, preferably closer in the quadrant of the container closer to such end.

[0034] The term "pitch angle", when referring to an impeller, is preferably understood to be the average angle formed between the chord line and a plane perpendicular to the axis of rotation of said impeller.

[0035] The term "sparger" is preferably understood as a gas injection system comprising a plurality of orifices configured to inject such gases through such orifices.

[0036] A first aspect of the present invention refers to a stirred tank for uniformly dispersing gas bubbles in a liquid. Note that an agitator tank is sometimes referred to as a stirred tank. As shown with respect to FIG. 1 , the stirred tank comprises a liquid container 100 having a first end 110 and a second end 112 defining axial ends of the container 100, and one or more sidewalls 115 extending between the axial ends 110, 112. The agitator tank also comprises a gas injection system 120 located proximate the first end 110 of the container 100, and at least one impeller 130, 140 rotatable about at least one axis of rotation 160 (i.e., in embodiments where two or more impellers are provided, the axes of rotation of each impeller may be the same or different). At least one impeller 130, 140 includes one or more blades 130a, 130b, 130c, 140a, 140b, 140c that extend a maximum distance R from the axis of rotation 160 of the corresponding impeller 130, 140. At least one baffle 150 is provided, the baffle being axially displaced from the at least one impeller 130, 140 such that the baffle does not contact either of the impellers 130, 140 as they rotate. The at least one baffle 150 is fixed relative to the vessel 100 in an orientation to reduce the azimuthal flow generated by the at least one impeller 130, 140. It should also be noted that the at least one baffle 150 may reduce the azimuthal flow differently, for example, by simply reducing the flow by impeding or changing the direction of the flow. One or more of the at least one impellers 130, 140 are shaped and oriented to induce an axial flow of liquid toward the gas injection system 120, and the minimum distance D from the at least one baffle 150 to the at least one axis of rotation 160 is at most 1.2R for any of the at least one impeller.

[0037] It should be understood that, according to certain preferred embodiments, when the baffle 150 has a portion that is axially displaced from at least one impeller 130, 140, it is displaced from such at least one impeller 130, 140 even if other portions of the baffle 150 are not axially displaced.

[0038] While the liquid container 100 of FIG. 1 includes two baffles 150, 150′, it should be noted that any number of baffles may be provided, and other embodiments may include only one baffle. The one or more baffles may have any suitable shape, and may be the same or different from one another. The baffle 150 may extend the entire length of the container 100 between the first axial end 110 and the second axial end 112, although in other embodiments, the baffle 150 may extend only a portion of the entire length. The liquid container 100 also includes an optional second impeller 140, although other embodiments in accordance with the present invention may not include a second impeller or may include three or more impellers. Similarly, while the first and second impellers 130, 140 each have four blades, other embodiments may include any other suitable number of blades. Furthermore, although the first end 110 of the liquid container 100 is shown as having a rounded shape, this feature is optional and other embodiments according to the first aspect of the invention may have any other suitable shape. Accordingly, the different figures should be considered for illustrative purposes only and are not intended to limit the scope of the invention.

[0039] It is further noted that second end 112 of container 100 may be open to the space outside container 100 or may be closed. In some embodiments, an openable or removable lid is fitted to second end 112 of container 100 to close container 100. Gas injection system 120 may take any suitable shape and may include any number of orifices for discharging gas.

[0040] In some embodiments, the impellers may be mounted on a single rotatable shaft 170 configured to be driven by a motor, as shown in FIG. 1, or may be mounted on separate shafts. The separate shafts may have the same or different axes of rotation. The axes of rotation may be displaced and / or tilted relative to one another. One or more of the axes of rotation may be centered relative to the sidewall 115 of the vessel 100 or off-center relative to the sidewall 115.

[0041] The interior shape of the liquid container 100 can take several forms. In some embodiments, for example, the liquid container 100 is cylindrical with a defined base diameter and height, while in other embodiments, the liquid container 100 is cubic or rectangular. In the case of a cylinder, the first and second ends 110, 112 can be defined by two circular planes on opposite faces. Note that elliptical, irregular, or oblique versions of a cylinder can also be defined, in which case the two planes on opposite faces of the container can take on an elliptical or irregular shape. Externally, the liquid container can take on the same or a different shape from the interior shape of the liquid container. Because the first and second ends define the axial ends of the container, the rotation axis 160 of either of the impellers can be any axis that passes through both the first and second ends 110, 112 of the liquid container, or any other suitable axis that enables one or more impellers to induce fluid flow of the present invention. Preferably, the axis of rotation 160 of either of the impellers 130, 140 is essentially located at the center of the first and second ends 110, 112 of the vessel.

[0042] As shown in FIG. 1 , in some embodiments, gas injection system 120 is connectable to gas source 170 through gas conduit 127 configured to fluidly connect gas from the gas source to gas injection system 120. Note that the gas source can be a gas tank or reservoir, a gas generator such as a compressor, or any other source of gas capable of providing gas to gas injection system 120 in a controlled manner. The gas can be any suitable gas required for whatever reaction agitator tank 100 is configured to perform. Note also that gas conduit 127 can take several forms and can be mounted in different ways in a liquid container, and the design shown in FIG. 1 should be considered only representative of such forms. For example, the conduit can be mounted inside vessel 100, can extend along or inside sidewall 115, or can extend outside vessel 100 along sidewall 115.

[0043] Gas injection system 120 may have any suitable shape and any number of orifices for discharging gas. As shown in FIGS. 2A-2C, gas injection system 120 is a device configured to introduce gas bubbles into a liquid. Gas injection system 120 may have several shapes. For example, gas injection system 120 may have a circular or toroidal shape, as shown in FIG. 2A, or a square toroidal shape, as shown with reference to FIG. 2B, or a more complex shape, such as a star-shaped sparger with multiple cylindrical gas injectors arranged in a radial array, as shown with reference to FIG. 2C. Gas injection system 120 may also have the shape of multiple cylindrical gas injectors arranged parallel to one another. It should be noted that one skilled in the art may implement different possible configurations for gas injection systems known in the art.

[0044] At least one impeller 130, 140 includes at least one blade. At least one impeller 130, 140 preferably includes two or more blades. At least one impeller 130, 140 has a defined first axis of rotation 136. One or more of the at least one impeller 130, 140 is shaped to generate an axial flow 145 relative to the axis of rotation of the one or more impellers 130, 140, as shown with respect to Figures 5A and 5B.

[0045] FIG. 3A shows a schematic side view of an agitator tank incorporating a baffle 150 according to at least one embodiment, illustrating fluid flow of liquid during use of the agitator tank. Note that the vessel 100 of FIG. 3 includes an optional second baffle 150′ and a second impeller 130. The impeller 140 generates an axial flow 145 and an azimuthal flow 155 as a by-product of the rotation of the impeller 140. The azimuthal flow 155 is defined as flow around the axis of rotation with an azimuthal direction of the impeller, as shown in FIGS. 4A and 4B. Azimuthal flow is counterproductive for a stirred tank where uniformity of bubbles is desirable because it causes bubbles to coalesce near the axis of rotation due to the centripetal force generated. Therefore, azimuthal flow 155 is undesirable, and reducing the azimuthal flow 155 enhances uniform distribution of bubbles. At least one baffle 150 is configured to reduce the azimuthal flow 155. Note that in embodiments where the second impeller 140 is not present, at least one baffle 150 is configured to reduce azimuthal flow 155 from the impeller. Note that the second flat surfaces 158, 158′ are optional.

[0046] Baffles 150 at least partially perpendicular to the azimuthal flow 155 of an impeller reduce the azimuthal flow 155 generated by such an impeller. Those skilled in the art will note that there are several ways to configure baffles to reduce azimuthal flow. As shown in Example 2, the presence of baffles significantly reduces the azimuthal flow of fluid caused by impeller rotation, while Example 3 demonstrates that the presence of baffles increases mass transfer due to more uniform air bubble distribution within the agitator tank. In some embodiments, as shown in FIG. 3A, the baffles are further configured to divert the azimuthal flow 155 into an axial flow 145′. This can be further seen with respect to FIG. 3B, which shows a schematic cylindrical cross-section of the baffle of FIG. 3A taken along line AA as a cross-section formed by a cylindrical surface concentric with the axis of rotation of at least one impeller.

[0047] Note that the term partially vertical is understood as a surface having an angle that includes a component perpendicular to the azimuthal flow 155. Thus, any baffle having a surface that is not parallel to the azimuthal flow is partially vertical. Note that by design, any surface that is not parallel to the flow reduces such flow by changing the direction of the flow, and therefore, a surface that is partially perpendicular to the azimuthal flow 155 reduces the azimuthal flow 155.

[0048] The baffles 150 may be secured to the liquid container 100 in different ways. The baffles may be secured to the sidewall 115 of the liquid container 100 and / or to the first and / or second ends 110, 112 of the liquid container 100. Note that the baffles 150 may be secured directly or through arms (not shown). The baffles 150 may be integral with the container 100 or may be attached to the container by fastening means such as screws, clamps, or welding or adhesives. In any of the embodiments having multiple baffles 150 as shown in FIG. 1 , the baffles may be secured to the liquid container 100 at different locations relative to the axis of rotation of one of the impellers 130, 140 and / or the first and second ends of the liquid containers 100, 112. Each of the one or more baffles may be configured to reduce azimuthal flow generated by the one or more impellers. Additionally, multiple baffles may have different shapes and sizes, which may be determined by the impeller having the azimuthal flow 155 that the baffle is configured to reduce. For example, a baffle may have a different shape and / or size if it is configured to reduce the azimuthal flow of an impeller with larger blades compared to another baffle configured to reduce the azimuthal flow of an impeller with smaller blades. This may be true for any parameter related to the impeller, such as the flow generated by the impeller, its location within the agitator tank, the size of the blades, etc. One skilled in the art will appreciate that impellers may be characterized by numerous other parameters and corresponding baffles may be designed according to these parameters.

[0049] In a preferred embodiment, the minimum distance from the at least one baffle to the at least one axis of rotation of any of the at least one impeller 130, 140 is at most 1.1R. Advantageously, this allows the baffle to help reduce the azimuthal flow 155 generated by the at least one impeller 130, 140.

[0050] In another preferred embodiment, the minimum distance from the at least one baffle to the at least one axis of rotation is at most R of any of the at least one impeller 130, 140. Advantageously, this further helps the baffle to reduce the azimuthal flow 155 generated by the at least one impeller 130, 140.

[0051] In another preferred embodiment, the minimum distance from the at least one baffle to the at least one axis of rotation is less than R of the at least one impeller, whereby the baffle 150 overlaps with at least one blade of one or more impellers 130, 140 (i.e., overlaps when viewed along the axis of rotation of one of the impellers). Note that in Figure 1, the baffle 150 includes a protruding portion 151 whose distance to the at least one axis of rotation 160 is less than R, whereby the baffle overlaps with at least one blade of the at least one impeller 130.

[0052] In another preferred embodiment, the at least one baffle 150 is bent or curved anywhere between the minimum distance from the at least one baffle 150 to the at least one axis of rotation 160 and 1.2R to the at least one axis of rotation 160 of any of the at least one impeller, thereby converting the azimuthal flow of liquid into axial flow 145. Advantageously, having a bent or curved portion anywhere between the minimum distance from the at least one baffle 150 to the at least one axis of rotation 160 and 1.2R to the at least one axis of rotation 160 of any of the at least one impeller allows the baffle 150 to not only reduce the azimuthal flow 155 generated by the at least one impeller 130, 140, but also convert the azimuthal flow 155 into axial flow 145, further increasing efficiency. The azimuthal flow 155 is generated by the at least one impeller anywhere between the impeller's axis of rotation and 1.2R of the impeller. Therefore, having such folded or curved portions in such areas to convert azimuthal flow 155 to axial flow 145 makes the agitator tank more efficient.

[0053] In certain more preferred embodiments, at least one baffle 150 is bent or curved anywhere between R and 1.2R up to at least one axis of rotation 160 of any of the at least one impeller, thereby converting the azimuthal flow of the liquid to axial flow 145. Alternatively, at least one baffle 150 is bent or curved anywhere between 1.1R and 1.2R up to at least one axis of rotation 160 of any of the at least one impeller, thereby converting the azimuthal flow of the liquid to axial flow 145. Because the azimuthal flow 155 is primarily generated at the ends of the blades of the at least one impeller 130, 140, having at least one baffle 150 bent or curved anywhere between R and 1.2R or 1.1R and 1.2R up to at least one axis of rotation 160 of any of the at least one impeller further improves the efficiency of the agitator tank.

[0054] In an even more preferred embodiment, at least one baffle 150 is Any location between the minimum distance from the at least one baffle 150 to the at least one axis of rotation 160 and 1.2R to the at least one axis of rotation 160 of any of the at least one impeller; or any position between R and 1.2R up to at least one axis of rotation 160 of any of the at least one impeller; or bent or curved at any location between 1.1R and 1.2R up to at least one axis of rotation 160 of any of the at least one impeller; Thereby, at least one baffle 150 has a second plane 158 that has a particular angle 152 relative to the axis of rotation 160, and / or at least one baffle 150 defines a curved surface, which covers any position between a plane perpendicular to the axis of rotation 160 and a plane parallel to the axis of rotation 160.

[0055] In a more preferred embodiment, the angle 152 of the second plane of the baffle 150 forms an average angle of 10° to 45° with the main plane of the baffle 150. Advantageously, this increases the reduction of the azimuthal flow 155. By establishing an inclination angle with the rotational axis of at least one impeller, the baffle more efficiently increases its interaction with the azimuthal flow 155, further reducing the azimuthal flow 155 and advantageously generating an axial flow 145'. For example, as shown in FIG. 3B, the baffle includes a section 158 that defines the second plane of the baffle 150. This section 158 has an angle 152 relative to the main plane of the baffle 150, which in this case is a plane perpendicular to the azimuthal flow. As shown in FIG. 3B, which shows a cross-sectional radial view of baffle 150 along AA, baffle 150 with a second plane 158 at an angle 152 relative to the plane containing the axis of rotation redirects azimuthal flow 155 to generate axial flow 145′.

[0056] In another more preferred embodiment, the curved surface comprises a mean arch of between 10° and 45°. It should be noted that different radii can be used to achieve an arch between 10° and 45°, and the invention is not limited in this respect. Advantageously, this allows the baffle 150 to generate a desired recirculation flow by using a portion of the undesired azimuthal flow 150 to divert a portion of the azimuthal flow 155 of the liquid into a downward axial flow 145. Those skilled in the art will appreciate that the bends or curves can be any suitable shape configured to divert the azimuthal flow into a downward axial flow. In some embodiments, as shown in FIG. 3B , the radially inward portion of the baffle 150 comprises the described folded or curved section, while the radially outer portion of the baffle 150 does not undergo such a bend or curve, so that the azimuthal flow is diverted into a downward axial flow only at radially inward locations where downward flow is desired.

[0057] In another particularly more preferred embodiment, at least one baffle 150 comprises a surface having a tangent plane that forms an angle of at least 5° with one or more axes of rotation 160. Advantageously, this enables the baffle to convert azimuthal flow 155 of liquid into axial flow 145. As can be noted by those skilled in the art, a difference of at least 5° with one or more axes of rotation 160 has a significant effect on the fluid dynamic function of the baffle 150.

[0058] In another particularly preferred embodiment, the at least one baffle 150 has an essentially longitudinal shape defining a primary baffle plane that forms an angle of at least 5° with the one or more rotation axes 160. Advantageously, this enables the baffle to convert the azimuthal flow 155 of the liquid into an axial flow 145. As can be appreciated by those skilled in the art, a difference of at least 5° with the one or more rotation axes 160 has a significant effect on the fluid dynamics of the baffle 150. In another preferred embodiment, a gap 154 ​​is provided between the at least one baffle 150 and the one or more side walls 115. Thus, the at least one baffle 150 primarily reduces the azimuthal flow at a location where the azimuthal flow is greatest, i.e., at an intermediate distance between the at least one rotation axis 160 and the side wall 115 at a distance R. The distance R corresponds to the extension of the blades of the at least one impeller 130. 3A, at least one baffle 150 leaves a gap 154 ​​in the sidewall 115. Advantageously, this makes more efficient use of the baffle 150 surface by concentrating the azimuthal flow reduction of the baffle 150 surface where the azimuthal flow is greatest.

[0059] In a preferred embodiment, the gas injection system 120 includes multiple orifices 122, each located radially between the impeller's rotation axis 160 closest to the vessel's first end and one or more sidewalls 115. The gas injection system 120 can be a sparger, such as a ring sparger. The orifices 122 are the injection points for gas into the liquid vessel 100 and thus form bubble generation points. The radial location of the orifices 122 ensures that the gas is injected farther from at least one of the rotation axes 160. This is preferred because any azimuthal flow occurring in the flow tends to send gas bubbles toward the rotation axis, and therefore, more uniform distribution of the gas bubbles is achieved when the gas bubbles are injected away from the rotation axis. The sparger 120 includes a set of orifices 122 through which the gas bubbles are introduced into the liquid. Note that these sets of orifices 122 are distributed differently across the surface of the sparger. These may be evenly or unevenly distributed across the surface of sparger 120. It should be noted that one skilled in the art may achieve different distributions using different spargers to achieve the desired gas injection. For example, the set of orifices 122 may be unevenly distributed by considering the distance from gas injection system 120 to the sidewall of liquid container 100 and / or the distance from gas injection system 120 to first and second ends 110, 112 of liquid container 100. For example, orifices 122 may be more densely distributed closer to the sidewall of liquid container 100 and closer to first end 110 of liquid container 100. The set of orifices 122 may be equal-sized orifices or a set of different-sized orifices and may be evenly or unevenly distributed across the surface of sparger 120. Also, note that the sparger 120 may be a dedicated system as shown in FIG. 1, or may be defined within the liquid container, for example, by defining a set of orifices on the first end 110 through which the gas is injected.The term sparger may therefore be understood as any gas injection system comprising multiple orifices for such gas injection.

[0060] More preferably, the sparger 120 of the preferred embodiment includes uniformly distributed orifices 122. As shown in Figures 2A-2C, the sparger 120 may include orifices for injecting gas into the liquid that are uniformly distributed on its surface. Advantageously, a uniform arrangement of orifices on the surface of the sparger further improves the uniformity of gas bubbles within the vessel.

[0061] In a more preferred embodiment, the average distance between the orifice of the sparger 120 and the axis of rotation 160 of the impeller closest to the first end 110 of the liquid vessel 100 is greater than 0.7R for the impeller closest to the first end 110 of the liquid vessel 100. Even more preferably, at least 75% of the gas flow is injected at a distance greater than 0.7R from the axis of rotation 160 of the impeller closest to the first end 110. Advantageously, this prevents gas bubbles from being sucked toward the axis, which would reduce the uniformity of the gas bubbles in the vessel.

[0062] In another preferred embodiment of any of the foregoing embodiments, at least one impeller 130 is a single impeller, and the single impeller is shaped to induce at least an axial flow 145 of liquid toward gas injection system 120, and in some cases, the single impeller 130 is also shaped to induce a radial flow 135 from the axis of rotation 136 of the single impeller 130 to one or more side walls 115. When only one impeller 130 is provided, that impeller is shaped to induce at least an axial flow 145 of liquid toward gas injection system 120. This ensures that the generated liquid flow circulates toward gas injection system 120 closer to axis of rotation 136 of the single impeller 130 and away from gas injection system 120 closer to one or more side walls. Because gas bubbles generally migrate upward toward the surface of the liquid, an upward flow of liquid is permitted in the outer radial portion of vessel 100. The downward flow generated by the single impeller at a radially inner location of the vessel 110, combined with the natural upward flow of bubbles radially away from the single impeller, induces a circulatory flow of fluid within the vessel 100. One or more baffles 150 inhibit the generation of azimuthal flow to ensure uniform radial distribution of the bubbles.

[0063] Thus, in use, the flow generated by the single impeller 130 interacts with gas provided by the gas injection system 120, reaches the first end 110 of the vessel 100, and returns to the second end 112 of the vessel along a path proximate one or more side walls 115 (i.e., along a radially outward path of the vessel 100). Optionally, the single impeller 130 is also shaped to induce a radial flow 135 from the axis of rotation 136 of the single impeller 130 to one or more side walls 115, which further induces an outward radial flow from the axis of rotation 160 towards one or more side walls 115, thereby promoting a desired circulatory flow of gas bubbles in the fluid.

[0064] As shown in FIG. 5A, the single impeller 130 may have a pitch angle 142. The pitch angle 142 affects the flow 145 generated. A larger pitch angle 142 configures the single impeller 130 to have a more mixed type of flow. Generally speaking, the smaller this angle, the more axial flow 145 there is (i.e., the flow generated has a smaller radial flow component). In a more preferred embodiment, one or more, preferably all, of the blades of the single impeller have surfaces with an average pitch angle between 10° and 60°. The average pitch angle is defined as the average angle formed between the chord line and a plane perpendicular to the impeller's axis of rotation. Therefore, the average pitch angle <α> can be expressed as follows:

[0065]

number

[0066] where α(r) is the pitch angle of the section generated about the axis of rotation of said impeller by a cylindrical surface of radius r.

[0067] As shown with respect to Figure 6, the chord line is defined as the line connecting the leading and trailing edges of the blade for a determined cut equidistant to the axis, and the pitch angle at a particular radius r of the blade is defined as the angle formed between the chord line at such radius and a plane perpendicular to the axis of rotation of the impeller, which is the direction of rotation. main <r<r max By integrating this angle along the blade with respect to and averaging the values ​​weighted by the distance to the axis of rotation r, the average pitch angle <α> can be calculated.

[0068] More preferably, the average pitch angle of the surfaces is between 15° and 50°. Advantageously, this ensures that the flow 145 of a single impeller 130 has a large downward axial flow component and a small radial flow component. Note that each blade of the impeller may have a different average pitch angle 142, and the pitch angle 142 of each blade may vary arbitrarily across the radius of the blade, or the blades may be designed to vary depending on the distance from the blade to one of the ends of the vessels 110, 112 and / or according to the distance from the blade to the axis of rotation 160.

[0069] In an alternative preferred embodiment of any of the foregoing embodiments, as shown with respect to FIG. 1 , the at least one impeller comprises a plurality of impellers axially displaced relative to one another, the plurality of impellers comprising: a first impeller 130 closest to the gas injection system 120, the first impeller 130 configured to induce at least a radial flow 135 of liquid from the axis of rotation of the first impeller 130 to one or more side walls 115; and one or more second impellers 140 remote from the gas injection system 120, the second impellers 140 configured to induce at least an axial flow 145 of liquid toward the first impeller 130.

[0070] Thus, first impeller 130 is longitudinally displaced from gas injection system 120 toward second end 112 and positioned between gas injection system 120 and one or more second impellers 140. Advantageously, in use, this agitator tank can generate circulatory flow in longer vessels, i.e., vessels where axial ends 110, 112 are further apart. Only first impeller 130 needs to generate radial flow that displaces axial flow from one or more second impellers 140 toward the sidewall, because first impeller 130 is the lower impeller.

[0071] The one or more second impellers 140 are longitudinally displaced towards the second end of the liquid container 112 and are positioned between the first impeller 130 and the second end of the liquid container 112. Advantageously, in use, this configures the one or more second impellers 140 to be the upper impellers that promote axial flow 145 such that a single circulation loop is achieved along the length of the liquid container 100.

[0072] The one or more second impellers 140 include at least one impeller. Each of the one or more second impellers 140 may include any number of blades. The one or more second impellers 140 define at least a second axis of rotation 146, which may be the same or different (translating or tilted) relative to each other and the same or translating / tilting relative to the first impeller. Note that the one or more second impellers 140 may include one, two, three, or more impellers (140, 140', 140''). In embodiments with multiple second impellers, each second impeller may include a different number of blades or an equal number of blades. It should be noted that the first and second rotational axes 136, 146 of the first impeller and one or more second impellers, respectively, may be different from one another. Each second impeller 130 includes at least one blade. Preferably, each second impeller 130 includes two or more blades.

[0073] The first impeller 130 is configured to generate a radial flow 135 relative to the axis of rotation of the first impeller 130, as shown with reference to FIGS. 4A and 4B, and the one or more second impellers 140 are configured to generate an axial flow 145 relative to the axis of rotation 146 of the one or more second impellers, as shown with reference to FIG. 5A. Note that the respective radial and axial flows 135 and 145 may exclude axial and radial flows, respectively. In some other embodiments, the first impeller 130 and the one or more second impellers 140 may be configured to generate primarily radial and axial flows, respectively, with the majority of the flow being radial and axial, respectively, but with small axial and radial flows also being generated. The impellers may also generate mixed flows that include similar amounts of radial and axial flows. In preferred embodiments of all embodiments, the tank comprises such a first impeller and one or more second impellers, the first impeller being configured to generate more radial flow than axial flow, and the one or more second impellers generating more downward axial flow than radial flow.

[0074] In use, the impellers 130, 140 are interposed in the free path of gas from the gas injection system 120 to the fluid surface, and the flow formed by the impellers 130, 140 is a recirculating flow defined by a radial flow 135 formed by the first impeller 130 and an axial flow 145 toward the gas injection system 120 formed by the one or more second impellers 140. In use, the first end of the vessel 110 is located at the bottom, so that the gas injection system 120 is located below all of the impellers 130, 140 of the liquid vessel 100. Thus, the free path of gas from the gas injection system 120 defines a free path through the impellers 130, 140. The combination of the first radial impeller 130 and one or more second axial impellers 140 above the first impeller 130 generates a circulating flow that flows toward the gas injection system 120 closer to at least one of the rotation axes 136, 146 and flows in a reverse direction from the gas injection system 120 toward the surface of the liquid closer to one or more side walls 115 of the liquid container 100. The first radial impeller 130 modifies the axial flow 145 generated by the one or more second impellers 140 so that the flow direction is from the rotation axis of the first impeller 130 toward the one or more side walls 115. The one or more second impellers 140 are configured to generate a flow 145 toward the first impeller 130 and thus toward the first end of the vessel 110, and the first impeller 130 is configured to generate a radially outward flow 135 from the axis 136, thereby generating a circulating flow according to the present invention.

[0075] As shown in FIG. 4A, the impeller of the first impeller 130 can have a pitch angle 132. The pitch angle 132 affects the generated flow 135, with a smaller pitch angle configuring the first impeller 130 to have a more mixed type of flow. The larger the pitch angle 132, the more radial the flow 135. In a more preferred embodiment, the blades of the first impeller have surfaces with an average pitch angle of 50° to 90° along a portion of the blade surface. Advantageously, this ensures that the flow 135 of the first impeller 130 is at least radial. Note that each of the blades can have a different average pitch angle 132, and the pitch angle 132 of each blade can vary depending on the distance across the surface of the blade to one of the ends of the vessels 110, 112 or to the axis of rotation 160.

[0076] As shown in FIG. 4B , the blades of the first impeller 130 may have curved surfaces with different exit angles 4 along the length of the blades. More preferably, the exit angle decreases as the blades move away from the axis of rotation 136. Advantageously, this allows the radial flow 135 of the liquid to increase as the liquid moves away from the axis of rotation 136. The blades of the first impeller 130 may also have a surface 3 affixed to the blades at their closest major portion to the gas injection system 120. The surface 3 prevents air bubbles from being sucked in by the impeller 130, and therefore the generated azimuthal flow 135 contains fewer air bubbles because the air bubbles can only escape from the end of the impeller 130, which is closer to the sidewall of the liquid container 100.

[0077] As shown in FIG. 5A , an impeller of the one or more second impellers 140 can have a pitch angle 142. The pitch angle 142 influences the generated flow 145, with larger pitch angles configuring the one or more second impellers 140 to have a more mixed type of flow, and smaller angles configuring the flow 145 to be more axial. In another more preferred embodiment, one or more, preferably all, of the blades of the one or more second impellers have surfaces with an average pitch angle between 10° and 60°. More preferably, the average pitch angle of the surfaces of the one or more second impellers is between 15° and 45°. Advantageously, this ensures that the flow 145 of the one or more second impellers 140 is at least axial. Note that each of the blades can have a different average pitch angle 142, and the pitch angle 142 of each blade can vary depending on the distance through the surface of the blade to one of the ends of the vessel 110, 112 or to the axis of rotation 160. Additionally, in embodiments where the agitator tank includes multiple second impellers 140, 140', the pitch angle 142 may vary between each second impeller 140, 140'.

[0078] In a preferred embodiment of any of the aforementioned embodiments, at least one baffle 150 is bent or curved to redirect the azimuthal flow 155 of liquid into an axial flow 145'. As shown with reference to FIGS. 3A and 3B, at least one baffle 150 may include a second plane 158 having a specific angle 152 with respect to a plane containing the axis of rotation 160 and / or may define a curved surface that covers any position between a plane perpendicular to the axis of rotation 160 and a plane parallel to the axis of rotation 160. In a more preferred embodiment, the curved surface includes a mean arc of 10° to 45°. Note that different radii can be used to achieve an arc of 10° to 45°, and the invention is not limited in this respect. Advantageously, this allows the baffle 150 to generate a desired recirculation flow by using a portion of the undesired azimuthal flow 150 to redirect a portion of the azimuthal flow 155 of liquid into a downward axial flow 145. Those skilled in the art will appreciate that the bends or curves can be any suitable shape configured to redirect azimuthal flow into downward axial flow. In some embodiments, as shown in FIG. 3B , the radially inward portion of baffle 150 comprises the described folded or curved section, while the radially outward portion of baffle 150 does not undergo such a bend or curve, so that azimuthal flow is redirected into downward axial flow only at radially inward locations where downward flow is desired. As shown in FIG. 3B , which shows a cross-sectional radial view of baffle 150 along line AA, baffle 150 with second plane 158 at angle 152 relative to a plane containing the axis of rotation redirects azimuthal flow 155 to generate axial flow 145′.

[0079] In use, as shown in FIG. 3A , when the agitator tank includes a first impeller and two or more second impellers, the agitator tank is configured to generate an axial flow 145 with at least one second impeller 140 moving liquid toward the first impeller 130. However, due to the rotation of the at least second impeller 140 about its axis 160, an azimuthal flow 155 is generated. To reduce the azimuthal flow, baffles 150, 150′ are provided, each having a second flat surface 158, 158′ at an angle 152 relative to a plane containing the axis of rotation, which, together with the main plane of the baffle 150, 150′, converts the azimuthal flow 155 into an axial flow 145′. Note that the second flat surfaces 158, 158′ are optional.

[0080] In a more preferred embodiment, the angle 152 of at least a portion of the baffle 150 forms an average angle of 10° to 45° with the major plane of the baffle 150. Advantageously, this increases the reduction of the azimuthal flow 155. By establishing an inclination angle with the rotational axis of at least one impeller, the baffle more efficiently increases its interaction with the azimuthal flow 155, further reducing the azimuthal flow 155 and advantageously generating an axial flow 145'. For example, as shown in FIG. 3B, the baffle includes a section 158 that defines a second plane of the baffle 150. This section 158 has an angle 152 relative to the major plane of the baffle 150, which in this case is a plane perpendicular to the azimuthal flow.

[0081] It should be noted that at least one baffle 150 is preferably at least partially perpendicular to the azimuthal flow 155 of the set of impellers in a different manner. For example, at least one baffle 150 may extend radially toward the axis of rotation and define a plane intersecting the axis of rotation of one set of impellers that is absolutely perpendicular to any generated azimuthal flow 155. In embodiments where a section 158 having an angle 152 is defined, this section 158 may also extend radially toward the axis of rotation.

[0082] The at least one baffle 150 may optionally have different shapes and angles along its length. However, the at least one baffle 150 may be designed to have different shapes and angles depending on the distance from a particular section of the baffle to the axis of rotation of an impeller configured to reduce azimuthal flow and / or the distance from the baffle to the first and second ends 110, 112 of the liquid container 100. The at least one baffle 150 may have different shapes on each side, with one parameter for the side facing the azimuthal flow and another parameter for the other side not facing the azimuthal flow. Thus, the direction of rotation of the impeller may also be taken into consideration. For example, the baffle 150 may have a greater longitudinal extension closer to the axis of rotation and a smaller longitudinal extension closer to the sidewall of the container, and / or the baffle 150 may have an angle that increases or decreases as it approaches one of the ends 110, 112 of the liquid container 100. It should be noted that when multiple baffles 150 are present, the baffles 150 may differ from one another. For example, the baffles 150 may have different shapes, numbers of sections 158, and angles 152 based, for example, on the distance to the impeller having the azimuthal flow 155 that the baffle 150 reduces, the distance to the ends 110, 112 of the liquid container 100, and / or the distance to the axis of rotation 160 of the impeller.

[0083] In another preferred embodiment, the gas injection system comprises an injection orifice, and the average distance from the injection orifice to the first end should be less than the distance R of the first impeller. Advantageously, this ensures a more uniform distribution of the bubbles, since, as mentioned above, any azimuthal flow created in the flow will tend to send bubbles towards the axis of rotation.

[0084] In another preferred embodiment, the minimum distance between two adjacent impellers is less than 3R of any of the above impellers. When two adjacent impellers are too far apart, there is a risk that the flow generated by one impeller will not reach the other impeller, thus creating a volume where no flow is generated or where undesirable local circulating flow is generated. By setting the impellers 130, 140 so that the minimum distance between each two adjacent impellers is less than 3R of any of the above impellers, the agitator tank is configured to reduce or eliminate stagnation areas, i.e., areas with no flow between the impellers or areas with undesirable local circulating flow. This is because the flow generated by one set of impellers effectively reaches the other set, thereby creating a unique flow.

[0085] In another preferred embodiment, the minimum diameter of the second impeller 140 is greater than 0.3 times the square root of the vessel cross-sectional area perpendicular to the axis at the height of the second impeller. More preferably, the minimum diameter of the second impeller 140 is greater than 0.45 times the square root of the vessel cross-sectional area perpendicular to the axis at the height of the second impeller.

[0086] Because the second impeller(s) 140 are of the axial flow type, the axial flow generated by the second impeller(s) 140 directs the bubbles in the axial direction towards the adjacent set of impellers 130 or 140. If the diameter of the second impeller(s) 140 is too small, the bubbles will not be effectively directed towards the adjacent set of impellers 130 or 140; instead, some local circulating flow will be generated in the volume between the generated axial flow 145 and the flow generated in the opposite direction by the first impeller 130 closer to the surface of the vessel 100. Therefore, advantageously, having a minimum diameter of the second impeller 140 greater than 0.3 times the diameter TD ensures effective direction of the bubbles to the adjacent set of impellers 130 or 140.

[0087] In another preferred embodiment, the at least one impeller does not move more than 50% of the horizontal cross-sectional area of ​​the reactor vessel perpendicular to the axis at the height of the at least one impeller 130, 140 axially downward, while allowing the other 50% to move in the opposite direction, creating a recirculation flow. However, because the blade's influence reaches a position beyond the blade's extreme radius, the impeller does not need to cover 50% of the horizontal cross-sectional area of ​​the reactor, and preferably has a maximum of 45%. Advantageously, by limiting the maximum diameter of the at least one impeller 130, 140, the at least one impeller 130, 140 enables the creation of a recirculation flow according to the present invention, with the axial flow generated by the at least one impeller 130, 140 being generated toward the first end of the vessel, and the recirculation flow being completed axially upward and radially outward of the vessel 110 closer to one or more side walls 115.

[0088] Therefore, the circular area

number

number

number

[0089] Thus, in this preferred embodiment, the maximum diameter of one or more of the at least one impellers 130, 140 shaped and oriented to induce an axial flow 145 of liquid toward the gas injection system 120 is less than or equal to 0.79 times the square root of the vessel cross-sectional area perpendicular to the axis at the height of the at least one impeller 130, 140.

[0090] More preferably, to avoid the effect of the blades interfering with the axial flow through the wall, the impellers shaped and oriented to induce an axial flow 145 of liquid towards the gas injection system 120 can be defined to cover at most 45% of the area of ​​the horizontal cross-sectional area of ​​the reactor vessel cross section perpendicular to the axis at the height of at least one impeller 130, 140. Thus, the circular area

number

number

number

[0091] Thus, in this preferred embodiment, the maximum diameter of one or more of the at least one impellers 130, 140 shaped and oriented to induce an axial flow 145 of liquid toward the gas injection system 120 is less than or equal to 0.75 times the square root of the vessel cross-sectional area perpendicular to the axis at the height of the at least one impeller 130, 140.

[0092] It is further noted that since the minimum distance from the at least one baffle to the at least one axis of rotation is at most 1.2R of any of the at least one impellers, in this more preferred embodiment, the minimum distance from the at least one baffle to the at least one axis of rotation is at most 1.2 × 0.75 / 2 = 0.45 times the square root of the vessel cross-sectional area perpendicular to the axis at the height of the at least one impeller 130, 140. Thus, the at least one baffle is configured to reduce azimuthal flow in the region where most azimuthal flow is generated, which region is closest to the maximum radius of the impeller. The agitator tank then generates the desired recirculation flow described above with minimum azimuthal flow, resulting in maximum efficiency of the agitator tank.

[0093] In another preferred embodiment, the agitator tank comprises multiple impellers when the ratio between the height (H) of the liquid that the agitator tank is configured to contain in the liquid container and the average diameter (D) of the side wall(s) is / are greater than 1.5, and three or more impellers when said ratio (H / D) is greater than 2. Advantageously, this ensures that when the agitator tank has an elongated shape, the number of impellers is accordingly constant, thereby resulting in a uniform flow between the first end 110 of the liquid container and the liquid level.

[0094] The liquid height (H) is the distance from such free liquid level to the first end of the agitator tank. It should be noted that the agitator may not contain any liquid, but is configured to agitate the liquid and mix it uniformly with air, and is configured to work with a specific amount of liquid. Therefore, it should be understood that those embodiments in which the container does not contain any liquid are included in this preferred embodiment, as long as the container is configured to contain liquid having such a height (H) inside the liquid container, thereby satisfying the stated ratio.

[0095] The mean diameter (D) is the square root of the cross-sectional area of ​​the container perpendicular to the axis along the liquid container. The mean diameter can be expressed as:

number

[0096] In another preferred embodiment, at least one impeller comprises a hub with a radius greater than 0.2 R, preferably greater than 0.3 R. Advantageously, this avoids bubbles accumulating close to the axis below 0.2 R, ensuring greater uniformity.

[0097] To further reduce the formation of dead volume, i.e., a volume where the liquid velocity is much slower than the average velocity within the stirred tank, typically less than 10%, or where localized recirculation flows are generated, the end shape of the liquid container 100 can be curved. For example, if the ends 110, 112 have a straight angle when they meet the side of the container, localized recirculation flows can be generated. In a preferred embodiment, the first end of the container 110 has a rounded shape, which eliminates a peak at the interface between the first end 110 and one or more side walls 115 and prevents the formation of stagnant water areas. This creates a surface that allows for the formation of a recirculation flow of liquid closer to the first end 110 of the container 100. Advantageously, during use, this reduces the formation of dead ends at the first end 110 of the container 100.

[0098] In another preferred embodiment, the agitator tank further comprises a rounded sidewall element at the height (H) of liquid that the agitator tank is configured to accommodate inside the liquid container 100, the rounded sidewall element being configured to replicate the sidewall of a liquid container having a curved shape. Advantageously, the rounded sidewall element allows the sidewall to be adapted to be rounded at such height, thus mimicking the rounded ends 110, 112 and reducing the formation of dead ends near the second end 112 at the height (H) of liquid that the agitator tank is configured to accommodate. This therefore creates a surface that allows for the formation of a circulating flow of liquid on the surface of the liquid. More preferably, the rounded sidewall element is configured to be longitudinally displaceable along the liquid container between the first end 110 and the second end 112. Advantageously, this allows the rounded sidewall element to be adapted to the different heights (H) of each of the liquids that the agitator tank may be configured to accommodate inside the liquid container 100. Thus, before filling the liquid container 100, the user can set the rounded sidewall element to the height of the liquid that the liquid container 100 contains or will contain, so that the container is configured to reduce local recirculation flow on the surface of the liquid near the second end 112.

[0099] It should be noted that the agitator tank, including any of the elements that make up the agitator tank, may be made of different materials. In a preferred embodiment of any of the embodiments of the first aspect of the present invention, the agitator tank comprises a material selected from any of a metal, such as steel, and / or a thermoplastic.

[0100] A second aspect of the present invention refers to a method for uniformly dispersing gas bubbles in a liquid in an agitator tank, the agitator tank being any of the agitator tanks of the first aspect of the present invention.

[0101] As shown with reference to FIG. 9 , the method first includes step 1010 of generating at least an axial flow toward a first end of the agitator tank by one or more impellers of at least one impeller above a gas injection system near the bottom of the vessel. The rotation axis is defined by the first and second ends of the vessel, which are the bottom and top ends of the vessel during use. The axial flow preferably forms a vertically downward flow from the one or more impellers toward the gas injection system near the rotation axis of the first impeller and a vertically upward flow from the gas injection system near the sidewall of the vessel toward the opposite end of the vessel. More preferably, step 1010 further includes generating a radial flow by the first impeller. The radial flow preferably generates a flow from the rotation axis of the one or more impellers toward the sidewall of the vessel. When the flow is above the sparger and near the bottom of the vessel, it interacts with any of the gas bubbles provided by the gas injection system.

[0102] The method then includes the optional step 1020 of generating a radial flow with the nearest impeller above the gas injection system. Advantageously, this further encourages the downward axial flow generated by the axial flow to be transferred radially toward the sidewall of the liquid container and then flow upward toward the surface of the liquid, providing a circulating flow within the gas injection system with one or more second impellers above the first impeller. Thus, in use, the container contains an axial flow that flows vertically from above the one or more second impellers toward the first impeller. Whenever multiple second impellers are used, each second impeller provides an axial flow to the adjacent impeller below it.

[0103] The method further includes a step 1030 of reducing azimuthal flow generated by one or more of the impellers with at least one baffle axially displaced from at least one set of impellers and fixed in an orientation relative to the vessel, the baffle comprising a surface oriented at least partially perpendicular to the azimuthal flow generated about any of the vessel's axes of rotation.

[0104] Finally, the method includes a step 1040 of injecting gas into the fluid with a gas injection system proximate the first end of the vessel.

[0105] The injection is preferably performed using an orifice located radially between the axis of rotation of the impeller closest to the first end of the vessel and one or more side walls, and more preferably is uniformly distributed throughout the gas injection system surface. The gas injection system is a sparger. More preferably, the at least one impeller is a single impeller, the single impeller configured to induce at least one axial flow of liquid toward the gas injection system. Optionally, the single impeller is also configured to induce a radial flow from the axis of rotation of the single impeller to one or more side walls.

[0106] (Example) Example 1: Investigation of the effect of baffles on azimuthal velocity material and method To investigate the effect of baffles on the azimuthal velocity, a fluid simulation was performed using a virtual stirred tank. To do so, computational fluid dynamics (CFD) analysis was performed using ANSYS-Fluent software. The virtual stirred tank was defined as follows: A reactor vessel with an internal height of 1600 mm and an internal diameter of 550 mm The standard configuration includes three Rushtons with six blades per impeller, equally spaced impellers with a diameter of 175 mm, with axial distances from the first end of the agitator tank of 105 mm, 505 mm, and 905 mm. The configuration according to the invention consists of four impeller sets with a diameter of 275 mm (one radial impeller as in Figure 4B, located 105 mm from the first end + three equally spaced axial impellers as in Figure 4A, distance between impeller centers 400 mm, six blades for the radial impellers, four blades per axial impeller, pitch angle 132 of each plain blade is 30°). The gas generation system consisted of a 10 mm diameter sparger with 15 equally spaced orifices spaced 1 mm apart, with an axial distance of 90 mm to the first end of the bioreactor and a radial distance of 150 mm from the axis of the radial impeller. Gas flow rate = 0.8 vvm (reactor volume per minute)

[0107] Three different configurations were investigated. Agitated tank without baffles. A stirred tank having vertical plain baffles attached to the side walls. A stirred tank with baffles according to the invention as shown in FIG. 3B, angle 152 is 30°, minimum distance to the axis of rotation is 130 mm.

[0108] Each model was exposed to the same fluid and gas environment, specifically using the following parameters: Fluid: Water, viscosity 0.001kg m-1 s-1, temperature 20℃ Gas: Air, output fluid 0.8vvm

[0109] result FIG. 7 shows the simulated fluid flow in an agitator tank according to the present invention.

[0110] [Table 1]

[0111] The result is that adding baffles reduces the azimuthal velocity, and baffles according to the present invention further reduce the azimuthal velocity, thus increasing the uniformity of the bubble distribution within the tank.

[0112] Example 2: Investigation of the effect of baffles on uniformity material and method To investigate the effect of baffles on the uniformity of bubble distribution, a fluid simulation was performed using a virtual stirred tank. To this end, CFD was performed using ANSYS-Fluent software. The virtual stirred tank was defined in the same way as in Example 1.

[0113] Three different configurations were investigated. As a reference, a stirred tank containing a Rushton impeller and standard vertical baffles. A stirred tank according to the invention with standard vertical baffles. A stirred tank and baffles according to the present invention.

[0114] Each model was exposed to the same fluid and gas environment, specifically using the following parameters: Fluid: Water, viscosity 0.001kg m-1 s-1, temperature 20℃ Gas: Air, output flow rate 0.8 vvm. The stirred tank with a Rushton impeller was simulated at a rotation speed of 500 rpm, while the other two models were operated at 400 rpm. The oxygen transfer constant (k La ) and k for stirred tanks with Rushton impellers La was used as a reference.

[0115] result [Table 2]

[0116] The results showed that even at lower rotational speeds, both the impeller according to the invention and the baffle according to the invention significantly increased the oxygen transfer constant, up to 39% compared to a standard stirred tank with a standard agitator, indicating that the invention improves the uniformity of the distribution of gas bubbles in the stirred tank compared to conventional stirred tanks.

[0117] Example 3: Computational Fluid Dynamics (CFD) Comparison of Stirred Tanks According to the Invention vs. Conventional Stirred Tanks material and method To demonstrate the advantages of the stirred tank according to the present invention, a fluid simulation was performed using a virtual stirred tank, for which CFD was performed using ANSYS-Fluent software.

[0118] The stirred tank A according to the present invention is defined as follows: A reactor vessel with an internal height of 280 mm and an internal diameter of 150 mm The configuration according to the invention consists of two impeller sets (one radial impeller with 70 mm diameter as in Figure 4B, located 35 mm from the first end + one axial impeller with 70 mm diameter as in Figure 4A, distance between impeller centers 105 mm, 6 blades for the radial impeller, 4 blades per axial impeller, pitch angle 132 of each plain blade is 30°). The gas generation system is a 6 mm diameter sparger with six equally spaced orifices spaced 1 mm apart, axially 25 mm to the first end of the bioreactor and radially 25 mm from the axis of the radial impeller. Gas flow rate = 0.8 vvm (reactor volume per minute)

[0119] As a conventional tank, a stirring tank B having the following characteristics was fabricated. A reactor vessel with an internal height of 280 mm and an internal diameter of 150 mm This configuration has two Rushtons with six blades per impeller, equally spaced impellers with 50mm diameter, and axial distances of 55mm and 155mm from the first end of the stirred tank. The gas generating system and its gas flow rate were identical to those of Stirred Tank A.

[0120] Both models were exposed to the same fluid and gas environment, specifically using the following parameters: Fluid: Water, viscosity 0.001kg m-1 s-1, temperature 20℃ Gas: Air, output flow rate varied from 2 to 8 l / m. The agitator rotation speed was varied from 300 to 1000 rpm.

[0121] The oxygen transfer constants (k) of both models at different rotational speeds (rpm) and with different gas flow rates measured in liters per minute (lpm) were calculated. La ) were compared.

[0122] result As shown in FIG. 8, reactor A, which corresponds to a tank with an agitation and aeration system according to the invention, has a higher k in all cases than reactor B, which corresponds to a tank with a standard agitation and aeration system. La Tank A achieved a higher k at a much lower rotation speed. La It is noteworthy that the oxygen transfer constant is higher when the bubbles are more uniformly distributed, since regions of high bubble concentration (usually near the impeller axis) cause bubble coalescence and reduce the contact surface between the gas and the liquid. On the other hand, regions of low bubble concentration also have less contact surface between the gas and the liquid. [Explanation of symbols]

[0123] 100 liquid containers 110 first end 112 second end 115 Side wall 120 Gas injection system, sparger 122 Orifice 127 Gas Pipe 130, 140, 140', 140'' impeller 132 pitch angle 130a, 130b, 130c, 140a, 140b, 140c blades 135 Radial Flow 136 First Rotation Axis 142 pitch angle 145, 145' axial flow 146 Second Rotation Axis 150, 150' baffle 151 Projection part 152 Specific Angle 155 Azimuthal flow 158, 158' Second plane 160 Rotational Axis< / d> < / d> < / d>

Claims

1. An agitator tank for uniformly dispersing air bubbles in a liquid, A liquid container (100) comprising first and second ends (110, 112) defining axial ends of the container (100) and one or more side walls (115) extending between the axial ends; a gas injection system (120) located proximate the first end (110) of the vessel (100); at least one impeller (130, 140) rotatable about at least one axis of rotation (160) and comprising one or more blades (130a, 130b, 130c, 140b, 140c) extending a maximum distance R from the axis of rotation (160) of the corresponding impeller (130, 140); at least one baffle (150) axially displaced from the at least one impeller (130, 140) and fixed relative to the vessel in an orientation to reduce azimuthal flow (155) generated by the at least one impeller (130, 140); Equipped with one or more of the at least one impeller (130, 140) are shaped and oriented to induce an axial flow (145) of the liquid toward the gas injection system (120), and a minimum distance from the at least one baffle (150) to the at least one axis of rotation (160) is at most 1.2R of any of the at least one impeller (130, 140); 10. An agitator tank, comprising: a first impeller (130, 140) configured and oriented to induce an axial flow (145) of the liquid toward the gas injection system (120), the first impeller (130, 140) having a maximum diameter that is less than or equal to 0.75 times the square root of a vessel cross-sectional area perpendicular to the axis at a height of the first impeller (130, 140).

2. 2. The agitator tank of claim 1, wherein the at least one baffle is bent or curved at any location between a minimum distance from the at least one baffle to the at least one axis of rotation and 1.2R to the at least one axis of rotation of any of the at least one impeller, thereby converting azimuthal flow of the liquid to an axial flow.

3. 3. The agitator tank of claim 1 or 2, wherein the minimum distance from the at least one baffle (150) to the at least one rotation axis (160) is at most 1.1 R of any of the at least one impeller (130, 140).

4. 4. The agitator tank according to claim 1, wherein the minimum distance from the at least one baffle to the at least one axis of rotation is at most R of any of the at least one impellers.

5. The agitator tank of any one of claims 1 to 4, wherein an air gap is provided between the at least one baffle (150) and the one or more side walls (115).

6. 6. The agitator tank of claim 1, wherein the at least one impeller is a single impeller (130), the single impeller (130) being configured to induce at least an axial flow (145) of the liquid towards the gas injection system (120).

7. 7. The agitator tank of claim 6, wherein the single impeller (130) is also configured to induce radial flow (135) from the axis of rotation (160) of the single impeller to the one or more side walls (115).

8. 8. The agitator tank according to claim 6 or 7, wherein one or more, preferably all, of the blades of the single impeller (130) are provided with a surface having a mean pitch angle of between 10° and 60°, preferably between 15° and 50°, said mean pitch angle being defined as the mean angle formed between a chord line and a plane perpendicular to the axis of rotation (160) of the impeller.

9. The at least one impeller comprises a plurality of impellers axially displaced relative to one another, the plurality of impellers comprising: a first impeller (130) closest to the gas injection system (120), the first impeller (130) being shaped to induce at least a radial flow (135) of the liquid from the axis of rotation (160) of the first impeller (130) to the one or more side walls (115); one or more second impellers (140) remote from the gas injection system (120), the second impellers (140) configured to induce at least an axial flow (145) of the liquid toward the first impeller (130); 6. The agitator tank of any one of claims 1 to 5, comprising:

10. 10. The agitator tank of claim 9, wherein one or more, preferably all, of the blades of the first impeller (130) have surfaces with an average pitch angle of between 50° and 90°, the average pitch angle being defined as the average angle formed between a chord line and a plane perpendicular to the rotation axis (160) of the impeller in which the blade is located.

11. 11. The agitator tank according to claim 9 or 10, wherein one or more, preferably all, of the blades of the one or more second impellers (140) comprise surfaces having an average pitch angle of between 10° and 60°, preferably between 15° and 50°, said average pitch angle being defined as the average angle formed between a chord line and a plane perpendicular to the axis of rotation (160) of the impeller in which said blade is located.

12. 12. The agitator tank according to any one of claims 9 to 11, wherein the minimum distance between two adjacent impellers is less than 3R of any of said impellers.

13. 13. The agitator tank of any one of claims 9 to 12, wherein the minimum diameter of the second impeller (140) is greater than 0.3 times the square root of the vessel cross-sectional area perpendicular to the axis at the height of the second impeller (140).

14. 14. The agitator tank of any one of claims 9 to 13, wherein the minimum diameter of the second impeller (140) is greater than 0.45 times the square root of the vessel cross-sectional area perpendicular to the axis at the height of the second impeller (140).

15. 15. The agitator tank of any one of claims 1 to 14, wherein the at least one baffle is bent or curved so as to convert the azimuthal flow of the liquid into an axial flow.

16. 16. The agitator tank of claim 15, wherein the at least one baffle (150) comprises a second plane (158) that has an angle (152) relative to a plane containing the axis of rotation (160).

17. The agitator tank of claim 16, wherein the second plane (158) forms an average angle (152) of between 10° and 45° with respect to the main plane of the baffle (150).

18. The agitator tank of claim 15, wherein the at least one baffle (150) defines a curved surface having a mean arch of between 10° and 45°.

19. 19. The agitator tank of any one of claims 1 to 18, wherein the minimum distance from the at least one baffle (150) to the at least one rotation axis (160) is less than an R of any of the at least one impeller.

20. 20. The agitator tank of any one of claims 1 to 19, wherein the gas injection system (120) comprises an injection orifice, and an average distance from the injection orifice to the first end (110) is less than a distance R of the first impeller.

21. 21. The agitator tank of any one of claims 1 to 20, wherein the gas injection system (120) is a sparger comprising a plurality of orifices each positioned radially between the axis of rotation (160) of the impeller closest to the first end (110) of the vessel (100) and the one or more side walls (115).

22. 22. The agitator tank of claim 21, wherein an average distance between the orifice of the sparger and the axis of rotation of the impeller closest to the first end of the vessel is greater than 0.7R for the impeller closest to the first end of the liquid vessel.

23. 23. The agitator tank according to any one of claims 1 to 22, wherein the agitator tank comprises a plurality of impellers when the ratio between the height (H) of the liquid that the agitator tank is configured to contain inside the liquid container (100) and the average diameter (<D>) of the one or more side walls (115) is greater than 1.5, or comprises more than two impellers when the ratio (H / <D>) is greater than 2, the height (H) of the liquid being the distance from a free liquid surface to the first end (110) of the agitator tank, and the average diameter (<D>) is the average of the square roots of the areas of the vessel cross sections perpendicular to the axis along the liquid container (100).

24. 24. The agitator tank according to any one of the preceding claims, wherein said at least one impeller comprises a hub with a radius greater than 0.2R, preferably greater than 0.3R.

25. 22. A method for uniformly dispersing air bubbles in a liquid in an agitator tank, the agitator tank being an agitator tank according to any one of claims 1 to 21, the method comprising: a) generating at least an axial flow (145) toward the first end (110) of the agitator tank by one or more impellers (140) of at least one impeller (130, 140) above the gas injection system (120), and preferably also generating a radial flow (135) by the first impeller; b) reducing the azimuthal flow (155) generated by one or more of the impellers by the at least one baffle (150); and c) injecting the gas into the fluid via the gas injection system (120) proximate the first end (110) of the vessel (100).

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