EP2440648A2

EP2440648A2 - Photobioreactor, in particular for growing and developing photosynthetic and heterotrophic micro-organisms

Info

Publication number: EP2440648A2
Application number: EP10734769A
Authority: EP
Inventors: Edouard Kabakian
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-06-09
Filing date: 2010-06-09
Publication date: 2012-04-18
Also published as: FR2946362A1; WO2010142870A3; US20120122199A1; WO2010142870A2; CN102459561B; TN2011000633A1; BRPI1009018A2; FR2946362B1; CN102459561A

Abstract

The invention relates to a photobioreactor, in particular for growing and developing photosynthetic micro-organisms such as microalgae and cyanobacteria. The photobioreactor includes at least one reflector (101) arranged on one side of the photobioreactor and tubes arranged in a plurality of layers which follow one another in a direction (N) normal to the reflector at a central region thereof, each layer comprising a plurality of tubes. The tubes (1, 16, etc.) are preferably rectilinear and extend in a direction orthogonal to the normal direction (N), the reflector is cylindrical with a circular or oval section, and the layers are cylindrical with a circular or oval section and concentric.

Description

Photobioreactor, especially for the growth and development of photosynthetic and heterotrophic microorganisms

The present invention relates to a photobioreactor, in particular for the growth and development of photosynthetic and heterotrophic microorganisms such as microalgae or cyanobacteria.

Microalgae and cyanobacteria are aquatic organisms ranging in size from micron to hundred microns in size, using light as a source of energy to fix carbon dioxide (CO ₂ ). Like terrestrial plants, microalgae and cyanobacteria can accumulate the carbon absorbed in the form of lipids, which makes it possible to consider using them to produce biofuels. Such a use is all the more promising as microalgae and cyanobacteria exhibit a very high photosynthetic yield and cell growth rate (one to several tens of times higher than those of terrestrial oilseeds such as rapeseed, sunflower, etc.) and the fraction of biomass that can be used directly is maximal (on the contrary, terrestrial plants release part of the carbon absorbed towards lignocellulosic molecules, more difficult or impossible to valorize).

In order for the production of usable lipids (essentially triglycerides) to be maximal, microalgae and cyanobacteria should be subjected to alternating cycles of growth and oil production. Growth is achieved by feeding the microalgae with carbon dioxide and nitrogen at a medium to low light intensity; oil production is stimulated by stress generated by nitrogen deficiency and / or a sudden increase in light intensity. When conditions are optimized, microalgae and cyanobacteria can accumulate a quantity of lipids up to 80% of their dry weight.

There are currently two ways of producing microalgae and cyanobacteria: open-pit culture, in "race-field" ponds, and cultivation in a closed transparent enclosure called photobioreactor. Open cultures offer lower yields, require significant water input to compensate for evaporation, and are sensitive to contamination. Photobioreactors can offset higher costs with higher productivities, thanks to greater control over conditions access to nutrient resources, exposure to light and transfer of CO2 from the gas phase to the liquid phase.

There are two main types of photobioreactor: flat photobioreactors and tubular photobioreactors. The flat photobioreactors are essentially composed of two parallel transparent panels between which a thin layer of culture medium flows along a baffled path. Flat photobioreactors are today neglected because of the leakage problems they encounter, their propensity for soiling (due to baffles) and the large number of units that would be necessary to implement to consider an industrial exploitation and commercial.

The tubular photobioreactors comprise one or more transparent tubes of various lengths and diameters (or widths). We distinguish :

column-type photobioreactors, consisting of a large upright column whose diameter generally varies between 30 and

60 cm;

planar photobioreactors comprising a plurality of rigid tubes, generally of smaller diameters (less than 15 cm), arranged side by side and connected in the manner of a coil, the tubes all extending in the same horizontal inclined plane or vertical;

the triangular photobioreactors comprising a plurality of triangular tubes arranged side by side, the photobioreactor consequently having the shape of a triangular prism;

- helical photobioreactors, constituted by a single long tube wound helically around a vertical structure;

- The photobioreactors whose tubes are formed in a rigid double-walled extruded panel.

The geometry of the photobioreactor depends on the exposure of microorganisms to light. The tubular photobioreactors allow great flexibility in size and volume and can be easily equipped with agitation and circulation devices of various types, depending on the microalgae or cyanobacteria grown.

However, the known tubular photobioreactors have the disadvantage of a large footprint, which limits the yield to the hectare obtained.

The invention aims to overcome this disadvantage by proposing a tubular photobioreactor with innovative geometry, whose footprint is reduced for a yield equivalent to or greater than that offered by a known photobioreactor of the same volume of culture.

To this end, the invention proposes a photobioreactor comprising a plurality of reaction tubes, characterized in that it comprises at least one reflector arranged on one side of the photobioreactor and in that the tubes are arranged according to a plurality of layers which follow one another in a direction normal to the reflector taken in a central region thereof, each sheet having a plurality of tubes.

Preferably, the tubes are arranged in the photobioreactor so that each tube is not completely obscured by another tube in this normal direction. The photobioreactor according to the invention is intended to be installed outdoors so that the reflector extends below the tubes and reflects the sun's rays towards them. Preferably, it is installed so that the normal direction previously defined coincides substantially with the direction of the zenith. The invention therefore lies in the combination of the use of a reflector and the vertical superposition of tube sheets. The photobioreactor according to the invention has a small footprint compared to known tubular photobioreactors (triangular or planar).

Preferably, all the tubes of the photobioreactor according to the invention are connected in series with each other. Alternatively, all the tubes are connected in parallel. Alternatively, the photobioreactor comprises several groups of tubes, the tubes of the same group being connected in series, the groups being connected in parallel.

Advantageously, all the tubes of the photobioreactor according to the invention are rectilinear and extend in the same direction orthogonal to the normal direction to the reflector. The tubes therefore extend horizontally when the photobioreactor is installed so that the direction normal to the reflector substantially coincides with the direction of the zenith.

Advantageously, the reflector is cylindrical in section arcuate or oval (for example parabolic or semi-elliptical), and the tubes extend parallel to the generatrix of the reflector. Thus, each tube receives substantially the same light intensity along its entire length when the photobioreactor is installed so that the tubes extend in a north-south direction or in north-south planes. According to a preferred arrangement, the plies are all cylindrical of circular or oval section, and concentric. Tablecloths "follow" the race of the sun.

Advantageously, the photobioreactor according to the invention has at least two tubes of different diameters interconnected. The flow rate of the culture medium is constant from one tube to another within the photobioreactor, the circulation speed is increased in the tube or tubes of reduced diameter. This acceleration of the culture medium prevents sedimentation and flocculation of microorganisms.

Preferably, the tubes of one and the same sheet have identical diameters and the diameter of the tubes decreases from one sheet to the next from the periphery to the center of the photobioreactor. Note that the term "diameter" here refers generally to the largest transverse dimension of each tube (it is a diameter in the usual sense of the term only when the tube has a circular cross section, being specified that the invention is not limited to circular section tubes). Such an arrangement not only makes it possible to accelerate the culture medium in the tubes extending in the central part of the photobioreactor, but also to optimize exposure of the tubes to light. Indeed, the quantity and the quality of the light actually available for each microorganism in a tube depends not only on the incident luminous flux striking the tube but also on the diameter of said tube: the irradiance is attenuated exponentially inside the tube depending on the depth of culture medium (for a given cell concentration), due to a phenomenon known as self-shading and resulting from the absorption and diffusion of light by microorganisms. In the photobioreactor according to the invention, the tubes located in the central portion of the photobioreactor may be partially hidden, in the direction of incident light rays, by the tubes located in the peripheral portion of the photobioreactor. They therefore receive an incident light flux which, depending on the time of day, may be less than that striking the peripheral tubes. To compensate for this more low exposure, the central tubes advantageously have a smaller diameter, which limits energy losses by self-shading within the tube. Preferably, the difference in diameter between the peripheral and central tubes is chosen so as not to completely compensate for the difference in exposure of said tubes, in order to create zones of lower irradiance and zones of greater irradiance. A sudden increase in irradiance can indeed stimulate the production of lipids in microorganisms. However, it is not excluded to choose to adjust the diameters of the peripheral and central tubes so as to obtain a substantially uniform irradiance linearly (along the tubes) throughout the photobioreactor.

Advantageously, the diameter and the number of tubes for each sheet are chosen so that the tubes occupy between 35% and 50% of the surface of the sheet (the sheet passing through the central axes of the tubes). In other words, 50% to 65% of the incident light rays pass from a web to the next web from the periphery to the center of the photobioreactor. Such an arrangement optimizes both the size of the photobioreactor and the sun exposure of the tubes located in the central portion of the photobioreactor.

Advantageously, the photobioreactor according to the invention comprises at least one device, preferably a pump or possibly a gas injector, for the axial circulation of a culture medium inside each tube. Furthermore, it comprises at least one deflector, preferably helical, for each tube, which deflectors promote mixing and homogenization of the culture medium. It is possible to replace the pump and the deflectors (fixed) by propeller-type stirring means, turbine, etc., in a plurality or in each of the tubes, since these means are not likely to injure the microorganisms. The use of baffles has the advantage of preserving cell integrity.

Preferably, the tubes are connected in series by connecting bends arranged on two opposite end faces of the photobioreactor. Advantageously, the connecting bends are arranged so that at most three (or possibly four) tubes of the same sheet are consecutive. In other words, the culture medium passes several times from one sheet to another during a complete cycle; it is thus exposed to different sun exposures, at different speeds of circulation, etc., in an alternative manner. Also preferably, the connecting bends are arranged so that the path traveled by the circulating culture medium is as horizontal as possible when the photobioreactor is installed so that the direction normal to the reflector substantially coincides with the direction of the zenith and / or that the tubes extend horizontally.

To better control the synthesis occurring in the photobioreactor tubes according to the invention, it is proposed in an alternative embodiment that at least some tubes are each equipped with at least one diffuser for introducing products inside. said photobioreactor tubes. It is thus possible to introduce as examples in the photobioreactor CO2, NOx, nutrients, organic carbon, etc.

To better control also the synthesis in the photobioreactor, at least one artificial lighting for illuminating the reaction tubes is advantageously provided. This then allows to illuminate the photobioreactor tubes also when there is no sun, or insufficient daylight.

In the preferred embodiment in which the tubes are arranged in concentric layers, the artificial lighting is preferably placed in the center of the sheets, for better efficiency. A preferred embodiment provides that the reflector is a selective wavelength reflector, i.e. reflecting light in a range of wavelengths and allowing light to pass outside said range of wavelengths. wave. In such a case, the energy of the light passing through the reflector is advantageously recovered by at least one photovoltaic sensor disposed under the reflector. The energy then recovered at the level of the photovoltaic sensors can then be used for the energy supply of the artificial lighting.

Finally, it can be provided that the photobioreactor further comprises a protective cover, which can for example be used to provide a night thermal protection. Other details and advantages of the present invention will appear on reading the following description, which refers to the attached schematic drawings and relates to preferred embodiments, provided as non-limiting examples. On these drawings:

FIG. 1 is a schematic view of a main part of a photobioreactor according to the invention,

FIG. 2 is a schematic cross-sectional view of the tubes and the reflector of the photobioreactor of FIG.

The photobioreactor according to the invention illustrated in FIGS. 1 and 2 is observed in a position corresponding to its position of use. The terms "vertical", "horizontal ¹ ", "above", "below", "lower", "upper", etc., refer to this position.

The photobioreactor illustrated comprises a lower reflector 101 intended to be oriented towards the sun. This reflector is cylindrical of parabolic section or arcuate. Above this reflector extends a plurality of tubes 1 to 44 cylindrical. All the tubes are parallel to the generatrix of the reflector 101. Each tube 1 to 44 is about 6 meters long, and the tubes extend facing each other transversely. Each tube 1 to 44 is carried at each of its ends by a support plate 102, 103. These two only plates are used for fixing and supporting all the tubes. Each tube

1 to 44 has a circular cross section, in order to limit deposits likely to form on the inner wall of the tube. Each tube 1 to 44 is made of a synthetic material, such as a polycarbonate, preferably non-stick or provided with an internal non-stick coating to prevent or limit the formation of deposits on the inner wall of the tube.

The reference N indicates a normal direction to the reflector 101 contained in a median longitudinal plane thereof (the term "median" means that the plane intersects the reflector in two equal parts). According to the invention, the tubes are arranged in successive layers in this normal direction above the reflector 101. In the illustrated example, the photobioreactor comprises three cylindrical sheets of circular section. These sheets are also concentric, their common center rising about 3 meters from the ground.

Such a configuration makes it possible to accommodate a maximum number of tubes per unit area on the ground, while ensuring optimum irradiance for each of the tubes.

More specifically, the illustrated photobioreactor comprises:

an outer ply 104 (cylindrical of circular section) of radius R1 of the order of 182 cm, this ply 104 comprising sixteen tubes referenced 1 to 16, all having an internal diameter of the order of 34 cm; an intermediate ply 105 (cylindrical of circular section) of radius R2 of the order of 142 cm, this ply 105 comprising fifteen tubes referenced 17 to 31, all having an internal diameter of the order of 28 cm;

an inner ply 106 (cylindrical of circular section) of radius R3 of the order of 92 cm, this ply 106 comprising thirteen tubes referenced 32 to 44, all having an internal diameter of the order of 22 cm.

The tubes of the intermediate ply 105 are wedged angularly with respect to the tubes of the outer ply 104 at a wedging angle which is chosen so as to maximize the amount of light reaching the tubes of the intermediate ply. For this purpose, the tube 17 is preferably centered angularly with respect to the tubes 1 and 16. Similarly, the tubes of the inner ply 106 are wedged angularly with respect to the tubes of the outer plies 104 and intermediate plies 105 at a wedging angle which is chosen to maximize the amount of light reaching the tubes of the inner sheet. In the illustrated example, the tube 33 is centered angularly with respect to the tubes 18 and 19. The arrangement of the set of tubes is further chosen so that a significant portion of the incident light rays passes through all the layers. and reaches the reflector 101 for the reflection of said rays to the tubes.

In the configuration illustrated, the photobioreactor according to the invention has a sunlit surface of the order of 235 m ² and occupies a floor area of 35 m ² , a multiplying coefficient of 6.7. It can also receive a volume of culture medium of 17,210 liters.

On each circular layer, the tubes are separated by an arc of a circle equal in length to the diameter of the tubes of the layer increased by a multiplying coefficient of between 1.11 and 1.15.

The tubes are connected in series by means of connecting bends 45-49 projecting from the support plates 102, 103 (towards the outside of the photobioreactor). For the sake of clarity, only the elbows on the side of the support plate 102 are shown. The connecting bends are arranged so as to make it possible to circulate a culture medium in the following way: tube 1, tube 2, tube 3, tube 19, tube 18, tube 17, tube 32, tube 33, tube 34, tube 20, tube 4, tube 5, tube 6, tube 22, tube 21, tube 35, tube 36, tube 37, tube 23, tube 7, tube 8, tube 9, tube 25, tube 24, tube 38, tube 39, tube 40, tube 26, tube 10, tube 11, tube 12, tube 28, tube 27, tube 41, tube 42, tube 29, tube 13, tube 14, tube 30, tube 43, tube 44, tube 31, tube 15, tube 16. This path is advantageously defined so as to limit the vertical circulation of the medium. of culture. The entry of the culture medium into the photobioreactor takes place in the upper part of the photobioreactor via the tube 1; the medium also comes out at the top through the tube 16, to be filtered or reintroduced into the tube 1 for an additional cycle.

Consequently, on the side of the support plate 102 are provided the following elbows: a bend 45 connecting the tubes 2 and 3, an elbow connecting the tubes 19 and 18, an elbow connecting the tubes 17 and 32, an elbow connecting the tubes 33 and 34, an elbow connecting the tubes 20 and 4, an elbow connecting the tubes 5 and 6, an elbow connecting the tubes 22 and 21, an elbow connecting the tubes 35 and 36, an elbow connecting the tubes 37 and 23, an elbow connecting the tubes 7 and 8, an elbow connecting the tubes 9 and 25, an elbow connecting the tubes 24 and 38, an elbow connecting the tubes 39 and 40, an elbow connecting the tubes 26 and 10, an elbow connecting the tubes 11 and 12, an elbow connecting the tubes 28 and 27, an elbow connecting the tubes 41 and 42, an elbow connecting the tubes 29 and 13, an elbow connecting the tubes 14 and 30, an elbow connecting the tubes 43 and 44, a connecting elbow the tubes 31 and 15.

On the side of the support plate 103 are therefore provided the following bends: a bend connecting the tubes 3 and 19, an elbow connecting the tubes 18 and 17, an elbow connecting the tubes 32 and 33, an elbow connecting the tubes 34 and 20, an elbow connecting the tubes 4 and 5, an elbow connecting the tubes 6 and 22, an elbow connecting the tubes 21 and 35, an elbow connecting the tubes 36 and 37, an elbow connecting the tubes 23 and 7, an elbow connecting the tubes 8 and 9, an elbow connecting the tubes 25 and 24, an elbow connecting the tubes 38 and 39, an elbow connecting the tubes 40 and 26, an elbow connecting the tubes 10 and 11, an elbow connecting the tubes 12 and 28, a elbow connecting the tubes 27 and 41, an elbow connecting the tubes 42 and 29, an elbow connecting the tubes 13 and 14, an elbow connecting the tubes 30 and 43, an elbow connecting the tubes 44 and 31, an elbow connecting the tubes 15 and 16.

In an alternative embodiment, the order of travel in the tubes may also be as follows: tube 1 and then 6, 7, 5, 2, 41, 40, 3, 4, 8, 12, 13, 14, 15, 11, 9, 10, 16, 17, 18, 19, 24, 23, 20, 21, 22, 27, 26, 25, 30, 31, 32, 29, 28, 33, 34, 35, 36, 37, 38, 39, 42, 43 and finally tube 44 output. The elbows are then adjusted accordingly to allow a flow of biomass in the photobioreactor according to this path. Each tube is equipped with at least three diffusers (not shown) with variable flow, arranged at the support plate 102, 103 at the inlet (in the direction of circulation of the medium) of said tube, namely: a first diffuser adapted to to release CO ₂ in the tube, a second diffuser capable of releasing nitrogen oxides (NOx) into the tube in order to provoke nitrogen stresses temporarily and in a timely manner, a third diffuser for the delivery of nutrients (trace elements and silica in particular). Each tube may also be equipped with a fourth diffuser for the delivery of organic carbon if the culture medium contains heterotrophic microorganisms carbon. As a variant, only certain tubes are equipped with one or more diffusers (CO ₂ , NOx, nutrients or organic carbon). A specific diffuser can also be provided for the operation of the photobioreactor in heterotrophic mode. Such a diffuser is for example provided with a rod, whose length may be of the order of 25 cm (illustrative but not limiting), to deliver nutrients to the central inlet of each tube.

The photobioreactor further comprises a variable flow pump (not shown) for the circulation of the culture medium. The illustrated photobioreactor having a volume of about 17 m ³ , the pump is advantageously chosen so as to ensure a flow rate of between 17 and 105 m ³ / h, that is to say between one and six complete cycles per hour. . The flow rate of the medium varies from single to double between the tubes 1 to 16 of the outer ply 104 and the tubes 32 to 44 of the inner ply 106. Note that the photobioreactor may optionally comprise several pumps, if necessary.

Each tube incorporates two helical baffles 50 (helical blade shape or, in a variant not shown, in the form of screws), one located at the inlet of the tube and the other located at its outlet. The baffles may alternatively be incorporated in the connecting bends. The shape (angle of attack, pitch, length, diameter, rounded edge ...) and the material of the deflectors are chosen so as not to hurt the microorganisms. These deflectors promote the mixing of the culture medium.

Preferably, the photobioreactor also comprises a buffer tank at the outlet, arranged to receive the culture medium exiting the tube 16. The volume of this buffer tank may be of the order of 1000 liters. It is preferably located at the same height as the exit of the tube 16 in order to avoid any loss of load that would be related to the difference in level. This buffer tank can also serve as a bypass tank for connecting two photobioreactors together, in series or in parallel. In its upper part, the buffer tank is advantageously provided with a membrane permeable to oxygen and impermeable to carbon dioxide. If necessary, if necessary, a pump may also or alternatively be provided to ensure a partial vacuum in the buffer tank to evacuate the oxygen released by the microorganisms.

Such a photobioreactor is intended to be installed so that the normal direction N coincides substantially with the direction of the zenith and that the tubes 1 to 44 extend in directions (horizontal) north-south, in order to capture a maximum of energy bright throughout the course of the sun. It is also possible to slightly tilt the photobioreactor so that the incident light rays are orthogonal to the axes of the tubes in the middle of the day (when the sun is at the highest). The photobioreactor according to the invention is particularly intended for the biofuel industry (for the development of microalgae rich in lipids) as well as for the food industry and the cosmetics and pharmaceutical industry.

Under certain conditions, artificial lighting 51 (Figure 2) can be provided. In the preferred embodiment shown in the drawings, that is to say in the case where the tube plies are concentric circular plies, the lighting advantageously takes place in the center of these plies. This artificial lighting 51 preferably extends parallel to the tubes of the photobioreactor for better illumination of said tubes. This artificial lighting 51 is in this case a centrifugal lighting that comes to substantially illuminate the less well-lit areas. This artificial lighting 51 also makes it possible (or alternatively) to create in other zones a concentration of light, thus stimulating photosynthetic microorganisms. For the cultivation of heterotrophic algae, that is to say which depend on organic substances for their growth and their diet, artificial lighting 51 can also be used to interrupt the nocturnal cycle and improve fixation of organic matter in heterotrophic.

It is also proposed here a power supply of this artificial lighting 51. The reflector 101, in a variant embodiment, is a selective reflector that reflects light in the range of wavelengths used by the microorganisms to effect photosynthesis and which allows the light to pass outside this range of wavelengths. The light then passing through the reflector 101 is then advantageously captured by a panel 52 of photovoltaic sensors placed under the reflector 101.

Generally, microorganism-friendly light has a wavelength between 400 and 700 nm ( ^10-9 m), which is about 45% of the light emitted by the sun, so the reflector is transparent to the waves. outside of this wavelength range, it is therefore 55% of the solar energy that is potentially available for the panel 52 and therefore the production of electricity.

The energy thus recovered can be used directly by the artificial lighting 51 and thus illuminate the tubes at an angle different from the direct sunlight angle or reflected by the reflector 101. An alternative embodiment can also provide a storage energy recovered by the panel 52, in a battery (not shown) and then be used at will for lighting the tubes.

To better control the temperature in the photobioreactor, it is proposed to associate one, preferably several, tarpaulin (s).

For example, nighttime temperature, or even daytime temperature on certain winter days, may be too low for microorganisms. In this case, the tarpaulin used is for example made of a transparent synthetic material passing light rays useful for photosynthesis and further having a calorific value and insulating.

To limit temperature losses on cool or cold nights, a thick and dark tarpaulin can be considered.

It is also possible to cover the photobioreactor with two tarpaulins.

For example in winter, the photobioreactor can be covered in the day by a tarpaulin made in a transparent film (type greenhouse) to maintain the temperature inside the system and at night, this tarpaulin can be doubled by a thicker tarpaulin.

On the other hand, for days when the temperature is too high, a ventilation system can be used for temperature regulation. In the variant embodiment with a panel 52 of photovoltaic sensors, the ventilation system can also be supplied with electrical energy directly by the panel 52 or by means of accumulators.

The photobioreactor is also preferably protected against UV (ultraviolet). A first protection can be obtained by the choice of materials for the production of the tubes. A second protection proposed here is to protect the photobioreactor by a transparent UV antireflective tarpaulin, this tarpaulin being for example arranged in an arc on the photobioreactor following the rotation of the sun. The invention may be subject to numerous variations with respect to the illustrated embodiment, provided that these variants fall within the scope delimited by the claims.

For example, the outer ply 104 could comprise seventeen tubes (34 cm in diameter) and have a radius of 192 cm. Alternatively, the photobioreactor could have the following characteristics:

a first cylindrical ply of circular section and radius of the order of 200 cm, this ply comprising twenty-five tubes of 22 cm internal diameter; a second cylindrical sheet of circular section and radius of the order of 160 cm, this sheet comprising twenty-five tubes of 18 cm internal diameter;

a third cylindrical sheet of circular section and radius of the order of 124 cm, this sheet comprising twenty-five tubes of 14 cm internal diameter;

a fourth cylindrical sheet of circular section and radius of the order of 92 cm, this sheet comprising twenty-one tubes of 12 cm internal diameter.

This embodiment provides 301 m ² of illuminated area and occupies a floor area of 35 m ² , a multiplying factor of 8.62, for a volume of culture medium of 13 250 liters (if the length of the tubes is 6 m).

In areas of strong sunlight, it may be appropriate to provide five concentric layers, from 92 cm to 225 cm radius, with tubes of 11 cm to 24 cm in diameter. In general, the invention is not limited to the number of plies, rays of plies, number of tubes, diameters and length of tubes described and illustrated.

The various characteristic dimensions of the photobioreactor must be chosen in particular according to the sunshine of the place of installation of the photobioreactor and the cultivated variety of microorganisms.

The invention is also not limited to circular section plies. It extends for example to flat sheets.

Claims

A photobioreactor comprising a plurality of reaction tubes, characterized in that it comprises at least one reflector (101) arranged on one side of the photobioreactor and in that the tubes are arranged in a plurality of layers (104-106). which follow each other in a normal direction (N) to the reflector taken at a central region thereof, each web (104, 105, 106) having a plurality of tubes (1-16, 17-31, 32-44).

2. photobioreactor according to claim 1, characterized in that all the tubes (1-44) are rectilinear and extend in a direction orthogonal to the normal direction (N) to the reflector.

3. Photobioreactor according to one of claims 1 or 2, characterized in that the reflector (101) is cylindrical section arcuate or oval and that the tubes (1-44) extending parallel to the generator reflector.

4. Photobioreactor according to one of claims 1 to 3, characterized in that the layers (104-106) are cylindrical, of circular or oval section, and concentric.

5. Photobioreactor according to one of claims 1 to 4, characterized in that the tubes (1-16; 17-31; 32-44) of the same ply (104; 105; 106) have identical diameters, and in that the diameter of the tubes decreases from one ply to the next from the periphery towards the center of the photobioreactor.

Photobioreactor according to one of claims 1 to 5, characterized in that the diameter and the number of tubes (1-16, 17-31, 32-44) for each web (104-106) are selected so as to that the tubes occupy between 35% and 50% of the surface of the sheet.

7. Photobioreactor according to one of claims 1 to 6, characterized in that it comprises at least one deflector (50) for each tube (1-44).

8. Photobioreactor according to one of claims 1 to 7, characterized in that all the tubes (1-44) are connected in series with each other.

9. Photobioreactor according to one of claims 1 to 8, characterized in that connecting bends (45-49) are arranged between the tubes and so that at most three tubes of the same sheet are consecutive.

10. Photobioreactor according to one of claims 1 to 9, characterized in that it comprises: - An outer layer (104) of cylindrical circular section and radius (R1) of the order of 182 cm, this web having sixteen tubes (1-16) all having an internal diameter of about 34 cm;

- An intermediate layer (105) of cylindrical circular section and radius (R2) of the order of 142 cm, this web comprising fifteen tubes (17-31) all having an internal diameter of about 28 cm;

- An inner sheet (106) of cylindrical circular section and radius (R3) of the order of 92 cm, this sheet comprising thirteen tubes (32-44) all having an internal diameter of about 22 cm.

11. Photobioreactor according to one of claims 1 to 10, characterized in that at least some tubes are each equipped with at least one diffuser for introducing products within said photobioreactor tubes.

12. Photobioreactor according to one of claims 1 to 11, characterized in that it comprises at least one artificial lighting (51) for illuminating the reaction tubes.

13. Photobioreactor according to claims 4 and 12, characterized in that it comprises an artificial lighting (51) placed in the center of the webs.

Photobioreactor according to one of claims 1 to 12, characterized in that the reflector (101) is a reflector with selective wavelengths, that is to say, reflecting light in a range of wavelengths. and allowing the light to pass outside said wavelength range, and in that the photobioreactor further comprises at least one photovoltaic sensor (52) disposed under the reflector (101).

Photobioreactor according to claims 12 and 14, characterized in that the photovoltaic sensors (52) are used for the energy supply of the artificial lighting (51).

16. Photoreactor according to one of revendicatons 1 to 15, characterized in that it further comprises a protective cover.