Static mixer for tube reactor

Abstract

The present invention relates to a static mixer for a tube reactor comprising one or more reactor tubes. The static mixer comprises a unit positioned inside one or more of the reactor tubes. The invention also relates to a tube reactor and a photobioreactor comprising such a static mixer. In particular, the invention relates to a static mixer (1) for a liquid comprising a first end, an inlet end (2), and a second end, an outlet end (3), which liquid flows in direction from the inlet end to the outlet end (3) during operation, wherein the static mixer (1) comprises at least two walls (4) which walls (4) at the inlet end (2) each extends radially between a central position of the static mixer (1) and a peripheral position of the static mixer (1) dividing the liquid flow into at least two separate flows, and which walls (4) extend in a longitudinal direction corresponding to the overall flow direction and comprise means (7) configured to provide at least two vortices at the outlet end (3) of the static mixer (1).

Description

[0001] Static mixer for tube reactor

[0002] The present invention relates to a static mixer for a tube reactor comprising one or more reactor tubes. The static mixer comprises a unit positioned inside one or more of the reactor tubes.

[0003] In particular, the tube reactor may be a photobioreactor comprising a two or more reactor tubes and optionally comprising one or more modules for culturing a phototrophic microorganism in a closed environment.

[0004] Background of the invention

[0005] Algae are photogenic microorganisms which grow by consuming carbon dioxide (CO2) using the mechanism described as photosynthesis. Algae are a diverse group of phototrophic microorganisms that play an important role in the biosphere and algae are characterized by a high growth rate potential compared to other typical photosynthetic organisms. They are increasingly used in agriculture, for food and feed, environmental protection, medicine and energy production.

[0006] Many systems have been described and used for production of algae and often products derived from this production have a low efficiency, low productivity and low yields due to suboptimal production process parameters, or the production facilities require large areas causing difficulties in up- or down-scaling of the production capacity.

[0007] Parameters of a production process, such as nutrients supplied during production, concentration of nutrients, pH, inorganic carbon supply including CO2and hydrogen carbonate and temperature may be important. However, high productivity of good-quality algae, optimal growth rate and high productivity of algae products also depends on factors like distribution and availability of light.

[0008] Algae are a potential source of renewable energy and a raw material for production of biofuels, cosmetics, and a significant source of food and feed. Unfortunately, the production method presently available are very energy-intensive making production of algae uneconomical, with low productivity and a large climate-footprint and facing difficulties in up- or down-scaling of the production capacity.

[0009] A photobioreactor is used for growing photosynthetic microorganisms, like algae, and providing products e.g. for human consumption or animal or pet consumption which is possible due to the hygienic and controlled manner in which production takes place. A photobioreactor according to the invention may easily be adapted to optimize production for a specific microorganism or to optimize purity of a product by controlling light, flow and temperature. The photobioreactor may be used for production of products for human consumption, products for animal or pet consumption, aqua culture feed, which product may comprise unsaturated fatty acids such as fish oil containing omega-3, omega-6 or omega-9 fatty acids, or proteins or pigments such as carotenoids, or biofuels.

[0010] Use of static mixers in tubular photobioreactors has been known and was probably first suggested by Molina Grima in 1999 (See Molina Grima, E., F. G. A. Fernandez, F. G. Camacho and M. Y. Chisti (1999). "Photobioreactors: light regime, mass transfer, and scaleup." Journal of Biotechnology 70(1-3 (list of articles in this issue)): 231-247.) as a means to enhance radial dispersion, mathematically coupled to the flow regime without elaborating further on the method. Static mixers were tested in outdoor inclined tubular reactors as a means to improve mass transfer and light-darkness exchange in order to avoid mid-day photoinhibition (See Ugwu, C. U., J. C. Ogbonna and H. Tanaka (2005). "Light / dark cyclic movement of algal culture (Synechocystis aquatilis) in outdoor inclined tubular photobioreactor equipped with static mixers for efficient production of biomass."

[0011] Letters 27(2) 75-78).

[0012] Known static mixers for tubular photobioreactors are a helical mixer extending in the complete length of the tubular reactor or as a twisted axial baffler mixer which also extends in the complete length of the tubular reactor. The pressure drop originating from mounting helical mixers exhibits large differences between the different mixer designs and reduction of the pressure drop is subject to development efforts. In general, the pressure drop and hence energy consumption is linearly proportional to the number of static mixer elements in a tube. For a comparison of functionality of different mixers, it is therefore essential that the number of mixing elements is chosen to allow a useful comparison; that is the number of mixers, necessary to create a required and identical mixing effect.

[0013] CN 105664749 B discloses a static mixer which static mixer is referred to as a triangular tube wall vane static mixer. This invention provides a triangular tube wall blade type static mixer comprising a unit cylinder body and a blade fixedly mounted on the inner wall of the cylinder, the blade is a triangular tube wall formed by cutting a cylinder body. The three triangular wall blades positioned at the same axial position are evenly distributed on the inner wall at 120° for the fluid material to be separated into three general regions that are not completely interrupted from each other. Specifically, the triangular tube wall blade has a bottom edge, a vertical side perpendicular to the bottom edge, and an arc edge connecting the bottom edge and the vertical edge end, the vertical edge being aligned with the axis of the cut cylinder. In the same plane, the arc edge is welded to the inner wall of the cylinder. The arc edge is welded to the inner wall of the cylinder. When cutting, the bottom edge is a circular arc from the circle end surface of the cylinder, and the vertical edge and the arc edge are cut along the radial direction of the cylinder body, and the formed cutting surface (vertical surface, curved surface) is formed with the cut cylinder body. The wall surface is vertical, and the projection of the triangular tube wall formed by cutting is a triangle. After the expansion, the arc edge is an arc, and the arc can fit directly with the inner wall of the cylinder to facilitate welding. Contrary to the present invention, this static mixer does not comprise means to divide the incoming flow in separate flows and provide a plurality of vortices, instead of dividing the incoming flow, the three blades unit the flow forming a single vortex at the outlet of the static mixer.

[0014] Thus, there is a need in the industry for improved systems and methods for growing microorganisms such as photogenic microorganisms like algae, to improve productivity and make the production of algae and products derived therefrom more economically interesting. Summary of the invention

[0015] Thus, an object of the present invention relates to providing a static mixer providing an optimal radial distribution of suspended organisms, particles, or components in a tubular reactor while minimizing the pressure loss through the tubular reactor. Also, the static mixer according to the invention takes up a lot less volume than the known static mixers.

[0016] The invention relates to a static mixer (1) for mixing a liquid comprising a first end, an inlet end (2), and a second end, an outlet end (3), which liquid flows in direction from the inlet end to the outlet end (3) during operation, wherein the static mixer (1) comprises at least two walls (4) which walls (4) at the inlet end (2) each extends radially between a central position of the static mixer (1) and a peripheral position of the static mixer (1) dividing the liquid flow into at least two separate flows, and which walls (4) extend in a longitudinal direction corresponding to the overall flow direction and comprise means (7) configured to provide at least two vortices at the outlet end (3) of the static mixer (1).

[0017] Thus, a first aspect of the invention relates to a static mixer (1) for a liquid comprising a first end, an inlet end (2), and a second end, an outlet end (3), which liquid flows in direction from the inlet end to the outlet end (3) during operation, the static mixer (1) comprises at least two flow dividing walls (4), wherein each wall (4) at the inlet end (2) extends radially between a central position of the static mixer (1) and a peripheral position of the static mixer (1) dividing the liquid flow into at least two separate flows, and each wall (4) extends in a longitudinal direction corresponding to the overall flow direction and comprise means (7) configured to provide at least two vortices at the outlet end (3) of the static mixer (1).

[0018] When the inlet flow is split into two or more flows which two or more flows rotate around a centre differing from the centre of the tubular reactor, then a radial displacement of particles is created inside the tubular reactor.

[0019] The two or more flow dividing walls (4) may be joined at least at one position at the central position of the static mixer or fixed to each other or a common central part (12), or the two or more flow dividing walls (4) may be joined at two or more position at the central position of the static mixer or fixed to each other or a common central part (12). Preferably, the two or more flow dividing walls (4) may be joined or fixed to each other at the central position at the inlet end (2) of the static mixer or fixed to each other or a common central part (12) at the inlet end (2) of the static mixer.

[0020] According to an embodiment of the first aspect of the invention, the static mixer (1) may comprise at least four walls (4) extending both radially between a central position of the static mixer (1) to a peripheral position of the static mixer (1) dividing the liquid flow into at least four separated flows, and longitudinally in the overall flow direction comprising means (7) configured to provide at least four vortices at the outlet end (3) of the static mixer (1).

[0021] According to an embodiment of the first aspect of the invention, the static mixer (1) may comprise at least six walls (4) extending radially between a central position of the static mixer (1) to a peripheral position of the static mixer (1) dividing the liquid flow into at least six separated flows, and extending longitudinally in the overall flow direction comprising means (7) configured to provide at least six vortices at the outlet end (3) of the static mixer (1).

[0022] According to an embodiment of the first aspect of the invention, at least two vortices may share a common tangential flow direction in an area where the two vortices are closest to each other.

[0023] According to an embodiment of the first aspect of the invention, the static mixer (1) may be prepared from metal or polymer e.g. by moulding or printing.

[0024] According to an embodiment of the first aspect of the invention, the static mixer (1) may comprise a central rod (12) to which central rod (12) each wall (4) is fixed at the inlet end (2) and / or at the outlet end (3).

[0025] According to any embodiment of the first aspect of the invention, the static mixer (1) comprises a first part (8) and a second part (9) where the first part (8) is positioned closest to the inlet end (2) and the second part (9) extends from the end of the first part (8) being opposite the inlet end (2) and to the outlet end (3). The end of the first part (8) being opposite the inlet end (2) may have a reduced cross-section relative to the inlet end (2). Then, the cross-section of the static mixer (1) may be increased from the inlet of the second part (9) to the end of the curved sections (10, 11).

[0026] According to an embodiment of the first aspect of the invention, each wall (4) of the first part (8) of the static mixer may twist or curve in the longitudinal direction from the inlet end (2) and to the end of the first part (8) opposite the inlet end (2). The second part (9) may comprise a first section (10) curving towards the central position (5) of the static mixer (1) and a second section (11) curving away from the central position (5) of the static mixer (1). Each wall (4) may be twisted / curved, along the longitudinal direction, by an angle a in any of the ranges [0°, 15°] + k-36Qo, or [15°, 30°] + k-36Qo, or [30°, 45°] + k-36Qo, or [45°, 600]+k-360°, or [60°, 750] + k-36Qo, or [75°, 90°] + k-36Qo, or [90°, 105°] + k-36Qo, or [1050, 1200]+k-3600, or [120°, 135°] + k-36Q0, or [135°, 150°] + k-36Q0, or [150°, 1650]+k-3600, or [1650, 180°] + k-36Q0, or [180°, 195°] + k-36Q0, or [195°, 210°] + k-3600, or [210°, 225°] + k-36Q0, or [225°, 240°] + k-36Q0, or [240°, 255°] + k-36Q0, or [2550, 2700]+k-3600,or[270°, 285°] + k-36Q0, or [285°, 300°] + k-36Q0, or [300°, 3150]+k-3600, or [315°, 330°] + k-36Q0, or [330°, 345°] + k-36Q0, or [345°, 360°] + k-360°; where k-360° represents any arbitrary number of full rotations, with k being any positive integer, the twisting / curving proceeds from the inlet end (2) to the end of the first part (8) opposite the inlet end (2).

[0027] According to an embodiment of the first aspect of the invention, two neighbouring walls (4) may have a common shape / structure along surfaces facing each other and the two neighbouring walls (4a, 4b) may be joined along the common surface, this way the static mixer (1) may comprise three pairs of neighbouring walls (4a, 4b) equally distributed around the central position of the static mixer (1).

[0028] A second aspect of the present invention relates to a tube reactor comprising a static mixer (1) according to the first aspect, wherein the tube reactor comprises at least one tube or pipe (20) having an inlet (21) at a first end and an outlet (22) at a second end wherein liquid flow from the inlet (21) to the outlet (22) during operation.

[0029] According to an embodiment of the second aspect of the invention, the outer periphery of the static mixer (1) may be smaller than the inner cross-sectional dimension of the tube (20), and optionally the periphery at the inlet end (2) of the static mixer may fit closely into the tube (20) and thereby keep the static mixer (1) in a chosen radial position inside the tube (20).

[0030] According to an embodiment of the second aspect of the invention, the static mixer (1) may be fixed relative to the tube (20), optionally either by the walls (4) of the static mixer (1) at the periphery being in contact with the inner surface of the tube (20) or by the static mixer (1) being fixed to a central tube (20).

[0031] According to an embodiment of the second aspect of the invention, more than one static mixer (1) may be positioned in one reactor tube (20), and the distance between two consecutive static mixers (1) in the axial direction may be at least 0,20 m, or at least 0,50 m, or at least 0,80 m, and / or the distance between two consecutive static mixers (1) may be at maximum 4,0 m, or 3,0 m or 2,0 m, or at maximum 1,5 m, or at maximum 1,1 m.

[0032] A third aspect of the present invention relates to a photobioreactor comprising an array of tubes (20) where each tube (20) comprises transparent wall(s) and is subjected to light from a light source extending in the axial or longitudinal direction of each tube (20), preferably in the complete length of the tube (20), and in at least one of the tubes (20), and optionally in all of the tubes (20), is / are placed a static mixer (1) according to the first aspect.

[0033] According to an embodiment of the third aspect, at least one light strip may be positioned between at least two reactor tubes (20) transmitting light through the transparent wall of the reactor tube (20) in a part of or the full length of the reactor tube (20), optionally two or more light strips are position e.g. equally distributed around, each reactor tube (20).

[0034] According to an embodiment of the third aspect, one or more light strips may be positioned at one or more radial positions around a tube where neighbouring vortices create a common tangential flow.

[0035] Brief description of the figures

[0036] Figure 1 shows a side view of first embodiment of a static mixer according to the invention,

[0037] Figure 2 shows a side view of the same embodiment as fig. 1 in which view the static mixer is rotated 45 degrees,

[0038] Figure 3 shows a view from the outlet end of the same embodiment as fig. 1,

[0039] Figure 4 shows a view from the inlet end of the same embodiment as fig. 1,

[0040] Figure 5 shows a tube of a tubular reactor in which a static mixer has been placed,

[0041] Figure 6 illustrates a streamline diagram just downstream of the outlet end of an embodiment of a static mixer as shown in fig. 1, Fig. 7 is a diagram showing the average radial velocity as function of axial position in the longitudinal direction of a tube of a tube reactor for a static mixer shown in fig. 1,

[0042] Fig. 8 shows a cut-through view of a photobioreactor in which a static mixer according to the invention may be applied,

[0043] Fig. 9 shows a detailed view of a photobioreactor according to fig.8.

[0044] Detailed description of the invention

[0045] Definitions

[0046] Prior to discussing the present invention in further details, the following terms and conventions is defined:

[0047] In general - when this expression is used to describe a feature, the described feature can be used with all embodiments of the invention, even if the mentioning of the feature is done in the detailed description of the invention.

[0048] It should be noted that embodiments and features described in the context of one of the aspects of the present invention also apply to the other aspects of the invention.

[0049] The invention relates to a static mixer 1 to be used as mixer in a flow of liquid or a liquid suspension in a tube or pipe. The static mixer 1 comprises a first end also named an inlet end 2 and a second end also named an outlet end 3 and the liquid is transported from the inlet 2 end to the outlet end 3 during operation. The velocity of the liquid flow before the static mixer 1 is normally low enough for the flow to be laminar at the inlet end 2, however, the liquid flow may also be turbulent at the inlet end 2 during operation.

[0050] The static mixer 1 has a maximum outer perimeter, and this maximum outer perimeter fits relatively closely to the inner surfaces of the tube or pipe in which it is positioned.

[0051] The static mixer 1 comprises at least two walls 4 and at the inlet end 2, each wall 4 extends radially between a central position 5 of the static mixer 1 and a peripheral position 6 of the static mixer 1 dividing the liquid flow into at least two separate flows. "71 central position" need not be but may be a central point of a circle or rectangle or oval, "a central position" may however also be an outer perimeter or circumference of a central unit such as a cylindrical unit or a unit having a polyangular or rectangular or oval outer circumference which may be used for fixing the position of the static mixer 1 as illustrated in the embodiment of figs. 1-4 where the walls 4 are fixed to a central unit in form of a central rod 12. In general, a central unit may be solid i.e. it does not allow a flow through the central unit, or the central unit may have one or more through-going or blind openings allowing a flow through or into the central unit either in a longitudinal or cross-sectional direction. Each wall 4 then extends from either the point or from the outer surface of the central unit.

[0052] Each of the walls 4 also extends in an axial or a longitudinal direction which axial or longitudinal direction corresponds to the overall flow direction and each wall 4 comprises means 7 and / or is shaped and functions as bafflers or blades or guides configured to provide at least two vortices at the outlet end 3 of the static mixer 1. The direction of the overall flow is defined as a straight line from the inlet end 2 to the outlet end 3.

[0053] A purpose of a static mixer according to the invention is to create radial movement in the flow direction inside the tube or pipe in form of two or more vortices which is formed at the outlet end 3 of the static mixer 1, thereby creating a radial displacement of the liquid flow and of particles or components suspended or dissolved in the liquid.

[0054] Each of the two or more vortices extends over a fraction of the cross-section of the tube or pipe in which the static mixer 1 is positioned, normally each vortex extends over 50% or less of the cross-section of the tube or pipe. This means that particles or components circulated with a vortex will be moved between a periphery of the tube or pipe and the centre of the tube or pipe, and if the tube or pipe is surrounded by e.g. heat members or light sources the transport between intense energy addition at the periphery and relative low energy addition near the centre can be used to optimise average light transfer or mass transfer inside each tube of a tube reactor.

[0055] Normally two neighbouring vortices share a common tangential flow direction in the contact area between them. A common tangential flow direction between two neighbouring vortices is self-reinforcing and supports a continued circulation after the outlet end 3 of the static mixer 1. This means the radial displacement via the vortices created by the static mixer 1 may be maintained for a longer time after the flowing liquid has left the static mixer 1, and instead of having a static mixer 1 extending through the entire length of the tube or pipe of a tubular reactor, the static mixer 1 may have form of one or more units placed with a distance, normally the distance between two consecutive static mixers 1 are at least 3 times the length of one static mixer 1, or at least 5 times the length of a static mixer 1, or at least 10 times the length of a static mixer 1. The optimal distance may however depend on the flow velocity, the cross-sectional size such as the diameter of the tube, the viscosity of the liquid or suspension, etc.

[0056] Normally, the static mixer 1 may be shaped as a unit having a relation between maximum length lmaxand maximum cross-section cmaxsuch as a maximum cross-sectional diameter of between 1.0 - 3.0, preferably of between 1.2 - 2.0.

[0057] The means 7 configured to provide at least two vortices at the outlet end 3 of the static mixer 1 normally comprise curved surfaces of the walls 4.

[0058] To prevent creation of turbulent flow, which is normally combined with increased pressure loss, it is an advantage to avoid surfaces in the longitudinal direction comprising angular bends, only curved bends should be applied, and / or only curved bends over 45 degrees. "A curved bend" is a smooth continuous bends where it is possible to determine a tangent for all points whereas "an angular bend" has a sharp point where it is not possible to determine a tangent.

[0059] Only exception in respect of angular bends in the flow direction of the static mixer 1 may be at the inlet and outlet ends 2, 3 where the liquid flow is split into separated flows, the point or part of a wall 4 close to or attached to the central position may present a narrow obstacle having an angular bend. However, the influence of such obstacle is reduced by keeping the part narrow, and optionally pointing in the direction of the inlet end 2.

[0060] A simple not shown embodiment of a static mixer 1 may comprise two walls 4, the means 7 configured to provide two vortices may comprise two radially curved, sickle-shaped walls 4 which mirror each other around the centre position, the two walls 4 also curve in the longitudinally direction forcing the liquid towards the periphery. As the walls 4 mirror each other, two vortices rotating towards or away from each other will be created at the outlet end of the static mixer 1.

[0061] A more complex embodiment of a static mixer comprising six walls 4 is shown in figures 1-5 where fig. 1 shows a side view of the embodiment, fig. 2 also shows a side view of the same embodiment turned around 60 degrees, fig. 3 shows a partial front view of the embodiment, and fig. 4 shows a partial back-view of the embodiment.

[0062] According to the embodiment illustrated in figs. 1-4, each wall 4 comprises a first part 8 near the inlet end 2 and a second part 9 near the outlet end 3. From the inlet end 2 to where the first part 8 meet the second part 9, each wall 4 twist 90 degrees according to the embodiment shown in figs. 1-4 and is reduced in cross-section. The incoming liquid flow is at the inlet end 2 split in six separate flows as two neighbouring walls 4 more or less isolate each separated flow as the flow is approximately laminar near the inlet end 2. A first separated flow is an internal flow which flows along the central portion of the static mixer 1, whereas a second flow - neighbouring the first flow on both sides - is an external flow which is directed away from the central portion by a smooth curving outer surface of two neighbouring walls 4 of the first part 8.

[0063] The second part 9 of each wall 4 comprises a first wing or section 10 curving toward the central portion and a second wing or section 11 curving outwards towards the periphery. Both the first and the second wing or section has a curved bend around 45 degrees, in each their direction. The curving and distribution of the first and second wings or sections means that the fluid is either dragged towards the surface of the pipe or dragged into the centre of the pipe, thus creating an additional alternating pattern, along the axial direction, of outwards (towards the surface) and inwards (towards the centre) flows, the shape and position of the wings or sections as well as the initial separation of the flows may be said to be the means 7 providing the vortices. As a result, the first and second wings or sections create six vortices at the outlet end 3 of the static mixer 1 and all six vortices share a common tangential flow direction with both neighbours i.e. any pair of two adjacent walls 4 imposes a circular motion in opposite direction, that is, clockwise and counterclockwise. The combination of this effects for the static mixer 1 with 6 walls leads to a pattern of six helical trajectories in alternating clockwise - counterclockwise direction.

[0064] The circular movements of the liquid are maintained after of the static mixer as the fluid advances in the axial direction downstream of the static mixer 1 and the combination of the circular and axial motions causes the fluid elements to follow a helical trajectory after the static mixer 1. In general, the distance up to which these patterns are maintained after the mixer can reach 3 to 20 times the length of the static mixer 1 depending on the flow velocity.

[0065] Fig. 5 shows how a static mixer 1 according to the invention may be positioned inside a tube 20 of a tubular reactor. A tubular reactor normally comprises a multiplicity of identical tube e.g. having same diameter and same length. The tube shown in fig. 5 has an inlet end 21 near which inlet end 21 the static mixer 1 is positioned, and an outlet end 22.

[0066] Fig. 6 shows a streamline diagram illustrating the radial flow inside the tube 20 just downstream of the outlet end 3 of the static mixer 1. Streamline velocity is indicated by the colour of the streamlines; the colour of the figure illustrates there are relatively high velocity in the contract zones between the vortices where the tangential flow direction is indicated with arrows. A very distinct type of movement / displacement may be obtained where straight laminas of flow fig.6 : radial zones of higher (marked - red) flow velocity, extending from a central position to a peripheral position, interchanged with straight laminas of flow in the opposite direction.

[0067] Fig. 7 shows a diagram of the average radial velocity (m / s) inside a tube 20 as a function of the axial position where "0" indicates the inlet end 2 of the static mixer 1 (the static mixer 1 used is the embodiment of fig. 1-4). The measurement is prepared at a constant flow velocity of 0.5 m / s and the maximum average radial velocity is obtained around 0.08 m which is at the outlet end 3 of the static mixer 1. From this maximum for average radial velocity decreases until it reaches 0 at a position between 0.8 and 0.9 m.

[0068] The reactor tubes 20 may have an outside diameter of at least 10 mm, such as at least 20 mm, such as at least 30 mm, e.g. at least 40 mm, such as at least 45 mm, e.g. at least 50 mm, such as at least 60 mm, e.g. at least 70 mm, such as at least 80 mm, e.g. at least 90 mm, such as at least 100 mm, e.g. at least 150 mm, such as at least 200 mm, e.g. at least 250 mm, such as at least 300 mm, and an outside diameter of at most 100 mm, such as at most 90 mm, e.g. at most 80 mm, such as at most 70 mm, e.g. at most 60 mm, such as at most 50 mm, e.g. at most 45 mm.

[0069] The static mixer 1 according to the invention may advantageously be used in a photobioreactor comprising a multiplicity of tubes where each tube may be in surrounded by or in contact with two, three, four or more light strips being equally distributed around the perimeter of a reactor tube and extending in the longitudinal direction of the tube, normally in the full length of each tube. The tubes constituting a photobioreactor may comprise an array of tubes 20 forming a tube module. In a photobioreactor comprising one or more tubes, the energy efficiency is significantly increased when using a static mixer according to the invention compared to the energy efficiency occurring at a simple turbulent flow in a tubular photobioreactor.

[0070] Phototrophic microorganism to be produced in such a photobioreactor may comprise one or more phototrophic algae and / or one or more phototrophic bacteria and / or a mixed culture comprising one or more phototrophic algae and one or more phototrophic bacteria. A phototrophic microorganism or phototrophs may be microorganisms that use light as their source of energy to produce ATP and carry out various cellular processes and they may anabolically convert carbon dioxide (CO2) into organic material and cultivation products. The one or more phototrophic algae may be selected from Chlorella vulgaris, Scenedesmus quadricauda, Scenedesmus obliquus, Nannochloris atomus, Nannochloropsis oceanica, Nannochloropsis oculata, Nannochloropsis gaditana, Chlorococcum littorale, Pseudochlorococcum sp., Haematococcus pluvialis, Dunaliella tertiolecta, Neochloris oleoabundans, Phaeodactylum tricornutum, Thalassiosira weisflogii, Thalassiosira pseudonanna, Skeletonema costatum, Nitzschia closterium, Nitzschia pusilia, Stichococcus bacillaris, Tetraselmis suecica, Pavlova lutheri, Chaetoceros calcitrans, Isochrysis galbana, Rhodomonas baltica, Porphyridium cruentum, Botryococcus braunii, Emiliana huxleyi, Spirulina platensis, Synechococcus sp., Synechocystis sp., Euglena gracilis, Parietochloris incisa, or a combination hereof.

[0071] Fig. 8 illustrates such a photobioreactor tube module comprising 114 photobioreactor tubes 20. Each photobioreactor tubes 20 may be connected to one or more other photobioreactor tube(s) 20 as one end of a first photobioreactor tube 20 is connected to one end of a second photobioreactor tube 20, e.g. by using a manifold or a U-shaped tube. This way the reactor tubes 20 constituting the photobioreactor tube module may be arranged either on top of each other and / or beside each other.

[0072] If the photobioreactor tubes 20 are round or cylindric or at least partly round or cylindric, the interspace between the photobioreactor tubes 20 may form an approximately polygonically shaped space 23 between the photobioreactor tubes surrounding the space 23. The polygonically shaped space 23 provided by according to the shown embodiment of fig. 8 may comprise four sides 23a, 23b, 23c, and 23d. A light source (not shown in fig. 8) may be placed in this polygonically shaped space 23 or as one or more sheaths surrounding each of the photobioreactor tubes 20 and placing the at least one light source between the at least two sheaths and the photobioreactor tube 20 and facing the photobioreactor tubes (directing the light into the photobioreactor tube 20). The photobioreactor tube module may comprise a surrounding frame 24 and the frame 24 may be provided with a light source illuminating the outer periphery of the photobioreactor tubes 20. Reference A relates to a subset of the photobioreactor tube module comprising four photobioreactor tubes 20 shown in figure 9.

[0073] Fig. 9 shows a subset A of the photobioreactor tube module shown in fig. 8. The subset A of tubes in a photobioreactor tube module illustrates how at least one light source 25 may be positioned inside the polygonically shaped space 23 provided by the four surfaces 23a, 23b, 23c, and 23d. The distance between an outer surface of a specific photobioreactor tube 20 and the light source 25 may be less than 4 cm, such as less than 3 cm, e.g. less than 2 cm, such as less than 1 cm, e.g. less than 0.1 cm, such as less than 0.05 cm, e.g. less than 0.01 cm, such as 0 cm.

[0074] The distance between the outer surface of a photobioreactor tube 20 and the light source 25 have shown to affect the intensity and the efficiency of the light source and is normally kept at small as possible. The length (in straight direction) of a photobioreactor tube in a module may be at least 0.1 m, such as at least 0.2 m, e.g. at least 0.3 m, such as at least 0.4 m, e.g. at least 0.5 m, such as at least 0.75 m, e.g. at least 1.0 m, such as at least 2 m, e.g. at least 3 m, such as at least 4 m, e.g. at least 5 m, such as at least 7.5 m, e.g. at least 10 m, and the length (in straight direction) of the one or more photobioreactor tubes may be at most 15 m, such as at most 13 m, e.g. at most 11 m, such as at most 10 m.

[0075] Two or more adjacent and / or parallel photobioreactor tubes 20 of a module may be placed with a distance 10 cm or less between an outer surface of one photobioreactor tube 20 to the outer surface of another and adjacent photobioreactor tube 20; such as 9 cm or less; e.g. 8 cm or less; such as 7 cm or less; e.g. 6 cm or less; such as 5 cm or less; e.g. 4 cm or less; such as 3 cm or less; e.g. 2 cm or less; such as 1 cm or less; e.g. 0.5 cm or less; such as 0.1 cm or less; e.g. the outer surface of one photobioreactor tube is in contact with the outer surface of another and adjacent photobioreactor tube.

[0076] It may be desirable to increase the intensity of the light transmitted by the light source, and then increase the radial movement of the liquid inside the reactor tube 20 so that the algae travelling in the longitudinal direction of the reactor tube with the liquid move through a less light intense centre of the reactor tube 20. Also, as the flow through the relatively narrow reactor tubes 20 is normally laminar, it is advantageous to use a static mixer 1 as algae travelling near the centre of the reactor tube 20 otherwise will stay near the centre without any enforced radial movement where the light intensity is relatively low.

Claims

Claims1. A static mixer (1) for a liquid comprising a first end, an inlet end (2), and a second end, an outlet end (3), which liquid flows in direction from the inlet end to the outlet end (3) during operation, the static mixer (1) comprises at least two flow dividing walls (4), characterized in that- each wall (4) at the inlet end (2) extends radially between a central position of the static mixer (1) and a peripheral position of the static mixer (1) dividing the liquid flow into at least two separate flows, and- each wall (4) extends in a longitudinal direction corresponding to the overall flow direction and comprise means (7) configured to provide at least two vortices at the outlet end (3) of the static mixer (1).

2. A static mixer (1) according to claim 1, wherein the static mixer (1) comprises at least four walls (4) extending both radially between a central position of the static mixer (1) to a peripheral position of the static mixer (1) dividing the liquid flow into at least four separated flows, and longitudinally in the overall flow direction comprising means (7) configured to provide at least four vortices at the outlet end (3) of the static mixer (1).

3. A static mixer (1) according to any previous claim, wherein the static mixer (1) comprises at least six walls (4) extending radially between a central position of the static mixer (1) to a peripheral position of the static mixer (1) dividing the liquid flow into at least six separated flows, and extending longitudinally in the overall flow direction comprising means (7) configured to provide at least six vortices at the outlet end (3) of the static mixer (1).

4. A static mixer (1) according to any previous claim, wherein at least two vortices share a common tangential flow direction in an area where the two vortices are closest to each other.

5. A static mixer (1) according to any previous claim, wherein the static mixer (1) comprises a central rod (12) to which central rod (12) each wall (4) is fixed at the inlet end (2) and / or at the outlet end (3).

6. A static mixer (1) according to any previous claim, wherein each wall (4) of a first part (8) of the static mixer twists / curves in the longitudinal direction from the inlet end (2) and to the end of the first part (8) opposite the inlet end (2).

7. A static mixer (1) according to claim 6, wherein the static mixer (1) comprises a second part (9) extending from the end of the first part (8) opposite the inlet end (2) and to the outlet end (3), which second part (9) comprises a first section (10) curving towards the central position (5) of the static mixer (1) and a second section (11) curving away from the central position (5) of the static mixer (1).

8. A static mixer (1) according to claim 6, wherein each wall (4) is twisted / curved, along the longitudinal direction, by an angle a in any of the ranges [0°, 15°] + k-360°, or [15°, 30°] + k'360°, or [300, 450]+k-360°, or [45°, 60°] + k-360°, or [60°, 75°] + k-360°, or [75°, 900]+k-360o, or [90°, 105°] + k-360°, or [105°, 120°] + k-360°, or [120°, 135°] + k'360°, or [1350, 150°]+k-360°, or [150°, 165°] + k-360°, or [165°, 180°] + k-360°, or [1800, 1950]+k-3600, or [195°, 210°] + k-360°, or [210°, 225°] + k-360°, or [225°, 2400]+k-3600, or [240°, 255°] + k-36Q0, or [255°, 270°] + k-36Q0, or [270°, 285°] + k-3600, or [285°, 300°] + k-36Q0, or [300°, 315°] + k-36Q0, or [315°, 330°] + k-36Q0, or [330°, 345°] + k-360°, or [345°, 360°] + k-360°; where k-360° represents any arbitrary number of full rotations, with k being any positive integer, the twisting / curving proceeds from the inlet end (2) to the end of the first part (8) being opposite the inlet end (2).

9. A static mixer (1) according to claim 6, 7 or 8, wherein two neighbouring walls (4) have a common shape / structure along surfaces facing each other and the two neighbouring walls (4a, 4b) are joined along the common surface, this way the static mixer (1) comprises 3 pairs of neighbouring walls (4a, 4b) equally distributed around the central position of the static mixer (1).

10. A tube reactor comprising a static mixer (1) according to any of the claims 1-9, wherein the tube reactor comprises at least one tube or pipe (20) having an inlet (21) at a first end and an outlet (22) at a second end wherein liquid flow from the inlet (21) to the outlet (22) during operation.

11. A tube reactor according to claim 10, wherein the outer periphery of the static mixer (1) is smaller than the inner cross-sectional dimension of the tube (20), and optionally the periphery at the inlet end (2) of the static mixer fits closely into the tube (20) and thereby keep the static mixer (1) in a chosen radial position inside the tube (20).

12. A photobioreactor comprising an array of tubes (20) where each tube (20) comprises one or more transparent walls and is subjected to light from a light source which extend in the axial or longitudinal direction of each tube (20), and in at least one of the tubes (20), and optionally in all of the tubes (20), is / are placed a static mixer (1) according to any of the claims 1-9.

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