FR2696753A1 - Device for cleaning the pipelines of a photobioreactor and photobioreactor provided with this device. - Google Patents

Abstract

Device for cleaning photobioreactor tubes and photobioreactor comprising said device. The object of the invention is the effective cleaning of the inner walls of photobioreactor tubes, including tubes of square or rectangular cross-section. The device must also circulate the liquid culture medium inside the photobioreactor. The object is attained using a device comprising at least one mobile cleaning element (15) having a magnetosensitive core covered with a material chemically stable in relation to the culture medium and magnetic driving means (19) capable of propelling the mobile element (15) inside the photobioreactor tubes (3) for cleaning of the inner walls thereof.

Description

DEVICE FOR CLEANING THE PIPES OF A
PHOTOBIOREACTOR AND PHOTOBIOREACTOR PROVIDED WITH THIS DEVICE
The present invention relates to a device
cleaning the lines of a photobioreactor, as well as the photobioreactor provided with this device.

For several years now, we have been carrying out
cultures of photosynthetic microorganisms, inside
laughter of photobioreactors. These allow
the production of all photosynthetic matter, i.e. any form of life likely to develop
and to carry out a photosynthesis reaction in a suitable nutritive liquid medium, in the presence of solar radiation and carbon dioxide. Cultured microorganisms are, for example, microalgae
(Porphyridium cruentum) or cyanobacteria (chloruel, spirulina, scenedesmus, etc ...).

The main parameters of the culture of
these microorganisms are temperature, light,
pH, CO2 and 2 pressures in the culture medium, as well as the composition of the nutrient medium.

 Consequently, the photobioreactors currently known consist of a set of tubes transparent to light, made for example of plastic and inside which circulates a liquid culture medium loaded with microorganisms.

These tubes can be flexible and arranged in the form of a raft, above a large body of water such as a lagoon, a pond, the sea or a swimming pool and serving as a source of cooling of the liquid culture medium. An example of this type of photobioreactor is described in the document.
FR-A-2 621 323.

 The tubes can also be rigid.

They are then produced for example in plastic panels transparent to light radiation and extruded so as to form parallel longitudinal cells. Such an example of photobioreactor is described in documents FR-A-2 564 855 and FR-A-2 662 705. These panels then rest on a hard surface and preferably inclined so as to present an angle of 900 relative to the sun. .

 In order to develop properly, and to carry out photosynthesis, these microorganisms need the presence of CO2 in the culture medium.

To this end, photobioreactors are generally provided with a carbonator making it possible to ensure a sufficient transfer of CO2 to the liquid culture medium, so that the biological demand for CO2 is always satisfied.

 The culture device also requires the presence of means for continuously circulating the culture medium between the tubes of the photobioreactor and said carbonator. These means are for example a pump.

 In addition, photobioreactors also require cleaning devices because they tend to clog quickly, if no special precautions are taken. In fact, micro-algae naturally tend to adhere to the internal walls of the photobioreactor tubes.

The deposits thus formed considerably reduce the transparency to light of the upper wall of the tubes, (that is to say, the wall directed towards the sun), and therefore cause less efficient use of solar energy. In addition, these deposits make the dispersion of cells inside the medium less homogeneous. Finally, the connecting parts such as the elbows, for example, between the different straight tubes of the device further increase the risks of sedimentation and therefore of contamination of the culture medium. This explains why it is necessary to provide devices for cleaning the tubes of the photobioreactor.

 Already known in the prior art, from document FR-A-2 576 034, an example of a cleaning device making it possible to circulate balls inside the cylindrical tubes of a photobioreactor, under the action of a pump. However, this device is not completely satisfactory because it does not allow effective cleaning of tubes whose section is square or rectangular, since the corners are not reached by the balls.

 Also known from the prior art, a photobioreactor comprising a gas lift device for simultaneously charging the culture medium with CO2 and ensuring the circulation of this liquid medium, so as to avoid stagnation and therefore the formation of deposits inside the tubes.

 We also know from an article by M.R.

TREDICI et al. , 1991, "A vertical alveolar panel for outdoor mass cultivation of microalgae and cyanobacteria", Bioresource Technology 38, a photobioreactor comprising a panel where the culture is circulated by air diffusion in the vertical alveoli of rectangular section.

 I.A.J. RATCHFORD et al. in "Performance of a flat plate, air lift reactor for the growth of high biomass algal cultures", Journal of Applied Phycology 4: 1-9, also describes the performance of a panel whose cells of rectangular section are connected in series and where culture circulates under the action of an external device such as an air lift. However, this type of air circulation device, if it allows the culture medium to circulate, does not allow effective cleaning of the internal wall of the cells of the photobioreactor.

 Therefore, the solution adopted in practice to avoid deposits, often consists in choosing microorganisms having a weak tendency to adhere to the walls, which restricts the field of possible applications.

 Consequently, the object of the invention is to remedy these drawbacks. It aims in particular to produce a device making it possible to effectively clean the internal walls of the pipes of a photobioreactor. The invention also makes it possible to provide this cleaning even when the section of the pipes is square or rectangular.

 To this end, the invention relates to a device for cleaning the pipes of a photobioreactor, this device comprising at least one movable cleaning element, intended to circulate inside said pipes; storage means and drive means of said movable cleaning elements.

 According to the characteristics of the invention, this mobile cleaning element comprises a magneto-sensitive core covered with a material which is chemically stable vis-à-vis the culture medium and the drive means comprise at least one magnet capable of propel this mobile element in the photobioreactor pipes so that this element cleans the internal walls of these pipes.

 This cleaning device is simple to implement and easy to manufacture at low cost. The magnetic drive means are efficient and allow cleaning elements to be sent to the pipes at selected intervals.

 Advantageously, the movable cleaning element has dimensions corresponding substantially to those of the section of the pipes of the photobioreactor and ensures the circulation of the culture medium in said pipes.

This characteristic of the invention makes it possible to ensure two functions with a single device. In the prior art, (see in particular the patent application
FR-A-2 576 034), the balls ensured the cleaning of the walls while the pump ensured the circulation of the nutritive medium and the balls being therein. In 1 invention, on the contrary, it is the mobile cleaning elements which, after having been propelled by the magnetic drive means, drive out the culture medium before them by a piston effect.

 According to a first embodiment of the invention, the drive means comprise a launching pipe in the form of an open circular loop, connected at one end to the storage means and at its other end to the inlet of the photobioreactor and at least one rotary arm, the end of which is provided with at least one magnet, this arm being arranged in the vicinity of the launch pipe, so that the rotation of the magnet causes the displacement of a movable magneto element -sensitive, inside said launch pipe, towards the entrance of the photobioreactor.

 Thanks to these characteristics, the photobioreactor no longer requires either a pump or a gas lift, which constitutes an advantageous simplification of the circuit for circulating the culture medium. In addition, the reduction in mechanical stresses created essentially by the pump and the reduction in turbulence generated by the gas lift makes it possible to envisage the culture of fragile cells. This embodiment of the drive means also has the advantage of being more compact than the second embodiment.

 According to a second embodiment of the invention, the drive means comprise a straight launching pipe, connected at one of its ends to the inlet of the photobioreactor and at its other end to the storage means, and a belt without thin, rotating, arranged parallel to the longitudinal axis of said launch pipe. This belt is provided with at least one magnet which, during the rotation of said belt, moves along the launch pipe, causing the displacement of the mobile, magneto-sensitive cleaning element, inside said belt. launch pipe, from one end to the other thereof.

 Thus, the culture medium is set in motion without shearing effort and without turbulence.

Furthermore, this second embodiment requires a smaller number of cleaning elements than that using the rotary arm.

 The invention also relates to a photobioreactor for the cultivation of photo-synthetic microorganisms comprising a series of pipes mounted in series, produced in a TS ... material transparent to light radiation and inside which said microorganisms are suspended in a culture medium. liquid, this photobioreactor being equipped with the aforementioned cleaning device.

The invention will be better understood on reading the following description of an embodiment of the invention, given by way of illustrative and nonlimiting example, this description being made with reference to the accompanying drawings, in which
FIG. 1 is a diagram representing a first embodiment of the cleaning device according to the invention, mounted in a photobioreactor,
FIG. 2 is a perspective view of part of the cleaning device in FIG. 1,
FIG. 3 illustrates a second embodiment of the cleaning device according to the invention, and
- Figure 4 is a partial sectional view along line IV-IV of Figure 3.

 According to the first embodiment of the invention illustrated in Figure 1, the photobioreactor consists of an extruded panel 1, made of a material transparent to light radiation, such as polymethyl methacrylate, polycarbonate or polyvinyl chloride, by example, inside which are arranged a number of pipes 3 parallel to each other. These pipes have a section in the shape of a parallelogram, preferably square or rectangular. As illustrated in FIG. 4, each pipe 3 has an upper wall referenced 5 and a lower wall referenced 7.

The top wall is the wall facing the sun, while the bottom wall is the one facing the ground.

 Although this is not illustrated in FIG. 4, it is also possible, as described in patent application FR-A-2 662 705, to produce a panel comprising two superposed layers of pipes, the upper pipes serving for the circulation of the culture medium and the lower pipes used for the circulation of a thermal regulation fluid.

 The panel 1 has at each of its two ends, a connecting piece 9, preferably made of material transparent to light radiation and having internally a series of semi-cylindrical cavities 11 of the same thickness as the pipes 3. These cavities 11 are intended to connect two by two the ends of two neighboring pipes 3, so as to form a coil inside which circulate, in one direction, the liquid culture medium and the cultivated microorganisms.

 Several of these panels 1 can be arranged side by side and interconnected by connecting pieces 13 so as to form a pipe of a greater total length.

 The cleaning device according to the invention comprises at least one movable cleaning element 15 and preferably several, intended to circulate inside the pipes 3. The cleaning device also comprises storage means 17 and drive means 19 of said movable elements 15.

The movable cleaning element 15 is intended to circulate in pipes 3 whose section is preferably rectangular and for this purpose, it has the shape of a thin disc whose height H corresponds substantially to the thickness
E of the pipes 3, to the nearest functional clearance and whose diameter D also corresponds substantially to the width L of the pipes 3, (see FIGS. 4 and 1).

This movable element internally comprises a core 21 made of a magneto-sensitive material, that is to say a material capable of being attracted by a magnet. This core 21 is covered with a layer 23 of a material which is chemically stable vis-à-vis the culture medium, that is to say generally an elastic polymer, of the polyethylene type. The movable elements 15 thus produced advantageously have a density greater than that of the culture medium in which they circulate.

 Advantageously, at least one of the two circular faces of this mobile element 15, or even both, or even the lateral faces of this element, are covered with a layer 25 of a material with a low coefficient of friction, such as PTFE (polytetrafluoroethylene).

 The disc shape of the movable elements 15 is particularly suitable for circulation in the cavities or elbows 11. However, if photobioreactors with cavities 11 and / or pipes 3 of different shapes were used, it would be possible to adapt consequently the shape of the mobile elements 15.

 As illustrated in FIG. 1, the output 27 of the photobioreactor is connected directly by a connecting pipe 29, to the storage means 17. These consist of a pipe 18 defining an inclined plane. The width L1 of the pipe 18 is approximately twice the width L of the pipes 3, so that the liquid culture medium circulating inside this pipe 18 is not braked by the mobile elements 15.

After having circulated inside the pipes 3 of the photobioreactor, the mobile cleaning elements 15 descend by gravity to the base 31 of the inclined pipe 18, then stack one behind the other along the slope. The fact that the elements 15 are of a density slightly greater than that of the culture medium facilitates this movement.

The base 31 is connected to the drive means 19.

 These storage means 17 further comprise a loading channel 33 closed by a plug 35. This loading channel 33 opens into the inclined pipe 18 and makes it possible to introduce the mobile elements 15, into the circulation of the photobioreactor, as well as the medium liquid culture.

 In the embodiment of the invention illustrated in FIG. 3, the storage means 17 are identical but are not connected to the photobioreactor in exactly the same way. The base 31 is connected to the drive means 19 ', while the output 27 of the photobioreactor is connected, via a connecting pipe 36 to the top of the inclined pipe 18.

 The drive means 19 comprise one or more magnets capable of propelling a mobile magneto-sensitive element 15 in the pipes 3 of the photobioreactor. Thus, during its passage, not only does the element 15 clean the internal walls 5, 7 of the pipes 3 but it displaces in front of it a certain volume of liquid culture medium to ensure the circulation thereof.

 A first embodiment of these drive means 19 is illustrated in FIG. 1.

 These drive means 19 comprise a launch pipe 37 whose section is identical to that of the pipes 3. This launch pipe 37 has the shape of an open circular loop. It is connected on the one hand to the base 31 of the storage means 17 and on the other hand to its other end, to a rectilinear connection pipe 39 which is connected to the inlet 41 of the photobioreactor.

 As illustrated in FIGS. 1 and 2, at least one rotary arm 43 is mounted in the vicinity of the launch pipe 37. This rotary arm pivots about an axis 45 placed at the center of the circle defined by the launch pipe 37. L ' shaft 45 is rotated by a motor not shown. The rotary arm 43 has at its free end at least one magnet 47 which can be either a permanent magnet or an electromagnet. In Figure 2, there is only one magnet 47 and it is located under the launch pipe 37, but it could also be above it.

The length of the arm 43 corresponds to the radius of the circle defined by said pipe 37 so that the magnet 47 is constantly moving above or below this pipe 37, (depending on the embodiment). It would also be possible to have several rotary arms 43 distributed around the axis 45 or to have a fork arm carrying several magnets.

 Each rotation of the arm 43 makes it possible to drive a mobile cleaning element 15. In addition, the mobile element 15 arriving at the outlet of the launch pipe 37, escapes the magnetic field of the magnet 47 and continues its race. in the connecting pipe 39, (Wire arrow). Note that the length of the launch pipe 37 corresponds to the distance between two successive moving elements 15.

The choice of this length, the length of the rotary arm 43 and the number of arms makes it possible to adapt the distance between two consecutive elements. After having circulated inside the photobioreactor, the elements 15 return to standby in the inclined pipe 18 of the storage means 17.

 The second embodiment of the drive means 19 ′ is illustrated in FIG. 3. This drive means is adapted on the first pipe 3 for entering the photobioreactor. This pipe 3 is called launch pipe and bears the reference 49. This launch pipe is connected at one of its ends to the base 31 of the storage means 17 and at its other end to a cavity 11, itself connected to the second line 3, that is to say at the input 41 proper of the photobioreactor.

 An endless belt 51 placed parallel to the longitudinal axis of this launch pipe 49 passes outside and above the wall 5 (see FIG. 4). This belt 51 is rotated around two pulleys 53 'and 53 "which appear better in FIG. 4. These pulleys are placed substantially at the two ends of the launch pipe 49. One of the pulleys 53' is provided with a axis 55 driven in rotation by a motor 57 (see FIG. 1). The other pulley 53 "rotates freely around an axis 58.

 The endless belt 51 is provided with at least one permanent magnet 59, but preferably at least two, spaced regularly in order to ensure good circulation of the culture medium. These magnets 59 are fixed on the external face of the belt 51 placed opposite the upper wall of the launching tube 5. The upper wall 5 of the launching pipe 49 preferably comprises on its external face an anti-friction coating 5a of the type PTFE (polytetrafluoroethylene).

When the motor 57 is running, the endless belt 51 starts to rotate in the direction of the arrow
F2 and when a magnet 59 arrives above the base 31 of the storage means 17, it attracts by its magnetic field, one of the mobile cleaning elements 15, magneto-sensitive which is stored there. The magnet 59 moves the element 15 inside the launch pipe 49 to the opposite end of the latter.

When the magnet 59 begins to pivot around the pulley 53 ', the magneto-sensitive mobile element 15 escapes the magnetic field of the magnet and continues its race inside the pipes 3. The magnet 59 returns (arrow F3), but being far enough away from the upper wall 5 not to act on a new element 15 driven towards the pulley 53 '(direction F2).

 It will be noted that the endless belt 51 could also be placed under the lower wall 7 of the launch pipe 49.

 The choice of the number of magnets 59 and their spacing on the belt 51 determines the interval between two successive moving elements 15, flowing in the pipes 3.

The minimum number N of mobile cleaning elements 15 required to ensure continuity of pumping and movement of the culture medium inside the lines 3 of the photobioreactor is as follows
N = (L.na) / e,
L representing the total length of the lines 3 of the photobioractor and the connecting line 36 or 39, e representing the length of the launch line 37 or 49, depending on the embodiment and na representing the number of active magnets of the device d 'drive 19, 19'. In the case of the drive device 19, using the rotary arm, this number na is identical to the total number of magnets, on the other hand in the case of the device 19 ', using the belt 51, this number na only corresponds to half the total number of magnets.

A numerical example will be given below, for purely illustrative purposes. The photobioreactor of FIG. 1 comprises forty-two pipes 3, with a unit length of 1.7 m each. I1 is equipped with a drive device provided with a single magnet 47. The length of the launch pipe 37 is 0.75 m and that of the connection pipe 39 is 2.2 m. The minimum number N of mobile elements 15 required is
N- (L.na) / e or N = (1,7.42 + 2.2). 1 / 0.75 = 98.

The same photobioreactor equipped with the drive device illustrated in FIG. 3 comprising two drive magnets 59 fixed on the belt 51, (but only one active magnet), a launch pipe 49 with a length of 1.7 m and a 2.2 m connecting pipe 36, requires a minimum number
No. of moving parts 15 of
(1.7.42 + 2.2). 1/7 = 43.

 This device makes it possible to obtain a speed of circulation of the culture medium of between 5 and 50 cm / s.

Claims (17)

 1. Device for cleaning the pipes (3) of a photobioreactor, this device comprising at least one movable cleaning element (15) intended to circulate inside said pipes (3) of the storage means (17) and of the means drive (19, 19 ') of said mobile cleaning elements (15), characterized in that this mobile cleaning element (15) comprises a magneto-sensitive core (21) covered with a chemically stable material (23) -with respect to the culture medium and in that the drive means (19, 19 ') comprise at least one magnet (47, 59) capable of propelling this mobile element (15), in the pipes (3) of the photobioreactor so that this element (15) cleans the internal walls (5, 7) of these pipes.  2. Cleaning device according to claim 1, characterized in that the mobile cleaning element (15) has dimensions corresponding substantially to those of the section of the pipes (3) of the photobioreactor and ensures the circulation of. culture medium in said pipes.  3. Cleaning device according to claim 1 or 2, characterized in that the drive means (19) comprise a launch pipe (37) in the form of an open circular loop, connected at one of its ends to the means of storage (17) and at its other end at the inlet (41) of the photobioreactor and at least one rotary arm (43) the end of which is provided with at least one magnet (47), this arm (43) being disposed in the vicinity of the launch pipe (37) so that the rotation of the magnet (47) causes the displacement of a movable magneto-sensitive element (15) inside said launch pipe (37), towards the entrance (41) of the photobioreactor.  4. Cleaning device according to claim 1 or 2, characterized in that the drive means (19 ') comprise a straight launch pipe (49), connected at one of its ends to the inlet (41) of the photobioreactor and at its other end to the storage means (17), and an endless belt (51), rotatable, arranged parallel to the longitudinal axis of said launch pipe (49), this belt (51) being provided with '' at least one magnet (59) which during the rotation of said belt moves along the launch pipe (49), causing the displacement of the mobile cleaning element (15), magneto-sensitive, to inside said launch pipe, from one end to the other thereof.  5. Cleaning device according to claim 4, characterized in that the belt (51) provided with at least one magnet (59) moves along the external face of the upper wall (5) of the launch pipe ( 49).  6. Cleaning device according to claim 4 or 5, characterized in that the belt (51) moves around two pulleys (53 ', 53 ") arranged at the two ends of the launch pipe (49), one (53 ') of these pulleys being driven in rotation by a motor (57).  7. Cleaning device according to claim 3 or 4, characterized in that the magnet (47, 59) is a permanent magnet.  8. Cleaning device according to claim 3, characterized in that the magnet (47) is an electromagnet.  9. Cleaning device according to claim 1, 3 or 4, characterized in that the storage means (17) comprise an inclined pipe (18) whose width (L1) is greater than or equal to twice the width (L ) pipes (3) of the photobioreactor, the base (31) of which is connected to the drive means (19, 19 ') and the top of which is connected to the outlet (27) of the photobioreactor.  10. Cleaning device according to claim 9, characterized in that the storage means (17) comprise a loading channel (33) for the introduction into the culture medium, mobile cleaning elements (15), this channel opening into said inclined pipe (18).  11. Cleaning device according to claim 1, characterized in that the chemically stable material (23) is a polyethylene.  12. Cleaning device according to claim 1 or 11, characterized in that the mobile cleaning element (15) is at least partially covered with a material (15) with a low coefficient of friction.  13. Cleaning device according to claim 12, characterized in that the material (15) with a low coefficient of friction is polytetrafluoroethylene.  14. Cleaning device according to claim 1, 11, 12 or 13, characterized in that the mobile cleaning element (15) has a density greater than that of the culture medium in which it circulates.  15. Cleaning device according to claim 1, 11, 12, 13 or 14, characterized in that the movable cleaning element (15) has the shape of a disc.  16. Cleaning device according to claim 3 or 4, characterized in that the minimum number (N) of mobile cleaning elements (15) necessary corresponds to the ratio between the product of the number (na) of active magnets (47, 59) of the drive device (19, 19 ') by the total length (L) of the pipes (3) of the photobioreactor and of the connection pipe (36, 39) and the length (e) of the launch pipe ( 37, 49).  17. Photobioreactor for cultivating photosynthetic microorganisms comprising a series of pipes (3) mounted in series, made of a material transparent to light radiation and inside which said microorganisms are suspended in a liquid culture medium, characterized in that that it comprises a cleaning device according to any one of the preceding claims.