BE1019198A3 - GAS PURIFICATION PROCESS COMPRISING CO2 AND CORRESPONDING DEVICE. - Google Patents

Abstract

The invention relates to a method for cleaning gases comprising CO2 using phototrophic organisms and the corresponding device. According to the invention, such a method comprises the following steps: a) supply (801) of water from a water source; b) capturing and washing (802) the gas in an absorber comprising at least a portion of the water so as to obtain an aqueous solution of CO2; c) from at least a portion of the water, preparing (803) an aqueous solution comprising nutrients; d) injection (804) into a photobioreactor comprising the phototrophic organisms of at least a portion of the aqueous solution of CO2 and at least a portion of the aqueous solution comprising the nutrients; e) illumination (805) of the contents of the photobioreactor with light radiation; steps (b) and (c) can be inverted or simultaneous.

Description

Process for purifying gas comprising CO2 and corresponding device 1. Field of the invention

The present invention relates to the treatment of gases comprising carbon dioxide, especially combustion gases containing a significant portion of carbon dioxide.

2. Solutions of the prior art

Regulations aimed at limiting greenhouse gas emissions are increasing. The regulations in question are most often accompanied by penalties for those who do not comply with the requirements. Significantly, the requirements are more and more restrictive. Industries in particular, which constitute an important source of emission of these gases, are led to find solutions making it possible to reach the conditions satisfying these regulations.

By nature some industries that consume large quantities of fossil fuels also produce large quantities of flue gas containing these gases whose emission is regulated. All industries in whose productions the implementation of fusion calcination, heat treatment of any kind are concerned. Among these are thermal power plants, iron and steel, glass production, refining of petroleum products, cement plants, lime production ...

At present, research has focused on techniques to reduce gas emissions in two ways: by limiting the consumption of fossil fuels on the one hand, and by capturing and / or storing gases. issued on the other hand.

The first way (limiting consumption) has been to use energy sources that do not generate flue gas. These sources, however, are generally more expensive and often only shift emissions to upstream industries. This is the case of electrical energy when it is produced in thermal power plants for example.

The second way is to have means to limit the release of gas into the atmosphere. Solutions consist in capturing and storing these gases insofar as this solution is industrially possible. This is practiced, for example, on certain sites producing natural gas or oil, or even mines. The gases are, for example, reintroduced into the underground pockets from which the extracted fuels originate.

The removal of gases such as carbon dioxide can also be the subject of treatments that lead to fixing this gas in a chemical form without impacting the environment, for example in the form of calcium carbonate. The products of this transformation are not of significant value. The overall cost is therefore relatively large.

Other solutions consist of using photosynthetic algae in reactors called "photobioreactors". Such organisms synthesize their organic matter by exploiting light (from the Sun) and by fixing carbon dioxide (hereinafter referred to as CO2). In addition to CO2, their needs are water and nutrients present for example in the soil. The products obtained are organic matter also called "biomass", and oxygen (hereinafter referred to as O2) also called "metabolic oxygen". The photosynthesis reaction can be summarized by the following chemical equation: n CO2 + η H2O (CTLOjn + η O2 (equation 1).

The traditional scheme of algae culture is then the following: water enriched with nutrients is introduced into the photobioreactor. In addition, CO2 is introduced into the photobioreactor and the photobioreactor receives a light radiation, which provides the necessary energy for the reaction. In these systems, CO2 comes from either atmospheric air or CO2-rich gases (pure CO2, flue gas, synthetic air, etc.).

In the case of CO2-rich gases, the injection of these gases is carried out in a compressed form. Indeed, this compression is necessary to overcome the back pressure of the culture water, but it represents an energy cost of the order of 10% or more of the energy produced by the algal biomass.

To avoid this energy-consuming compression, patent application No. US2008178739A1 proposes a solution according to which the algae are grown in a horizontal plane surmounted by a synthetic atmosphere enriched with CO2. However, this solution has two disadvantages. First, the temperature of the gases must be limited to avoid destroying the algae culture by heating the water beyond a critical value, which depends on the strain used. Moreover, in such a device, the gas / water contact surface must be sufficiently large to allow good diffusion of CO 2 in the water. This last characteristic constitutes the major disadvantage of such a device.

3. OBJECTIVES OF THE INVENTION The object of the invention is notably to overcome these disadvantages of the prior art.

More specifically, an object of the invention, in at least one of its embodiments, is to provide a process for purifying CO2-rich gases or fumes, for example a flue gas, by means of phototrophic organisms in a photobioreactor, which is less expensive in energy than conventional methods. By "phototrophic", we mean thereafter any organism capable of photosynthesis.

Another object of the invention, in at least one of its embodiments, is to implement such a method to achieve this CO2 injection without gas compression.

Another objective of the invention, in at least one of its embodiments, is to implement such a method according to which the quantity of CO2 injected into the photobioreactor can be controlled independently of the amount of CO2 present in the gas.

Another object of the invention, in at least one of its embodiments, is to implement such a technique that allows to obtain a better purification performance and this for a lower cost than conventional solutions.

4. Disclosure of the Invention The invention relates to a method of purifying gas comprising CO2 by means of phototrophic organisms, comprising the following steps: a) supply of water from a source of water; b) capturing and washing the gas in an absorber comprising at least a portion of the water so as to obtain an aqueous solution of CO2; c) from at least a portion of the water, preparing an aqueous solution comprising nutrients; d) photobioreactor injection comprising the phototrophic organisms of at least a portion of the aqueous CO2 solution and at least a portion of the aqueous solution comprising the nutrients; e) illumination of the photobioreactor contents by light radiation.

Of course, steps (b) and (c) can be implemented in any order, they can be implemented simultaneously or be implemented in parallel. Moreover, the portion of the water used in step (b) and the portion of the water used in step (c) may be distinct, or totally or partially merged.

The term "photobioreactor" any type of container or lagoon, whether closed or open (a closed lagoon may be, for example, a lagoon covered with a greenhouse), which allows the cultivation of phototrophic organisms.

The general principle of the invention is based on the introduction into the photobioreactor of an aqueous solution of CO2 obtained from the gas comprising CO2, and not on the direct introduction of the gas into the photobioreactor.

Thus, thanks to the method according to the invention, it is not necessary to perform a gas compression, which allows substantial savings in energy.

Advantageously, according to this method, the capture of CO2 from the gas comprising CO 2, carried out during step (b), is decoupled from the injection of the solution obtained into the culture medium during step (d). . The expression "culture medium" designates the overall aqueous solution contained in the photobioreactor (comprising at least a portion of the aqueous nutrient solution and at least a portion of the aqueous CO2 solution) as well as the phototrophic organisms contained in the photobioreactor. .

Thus, the invention is based on a completely new and inventive approach to CO2 capture and CO2 input for fixation by phototrophic organisms.

Preferably, the process may comprise a step of regulating the level of CO 2 in the overall aqueous solution contained in the photobioreactor: the CO 2 concentration in the photobioreactor can be adjusted independently of the production of the gas comprising CO 2. Thus, by following the needs of the phototrophic organisms, an optimal crop yield of the phototrophic organisms is obtained, so that the consumption of CO 2 is maximal, which makes it possible to increase the efficiency of the purification process according to the invention.

Advantageously, the above-mentioned regulation step comprises a step of temporarily storing at least a portion of the aqueous CO2 solution. Since the injection of CO2 into the culture medium can be decoupled from its uptake from the gas comprising CO 2, the instantaneous flow rate of CO 2 injected into the photobioreactor can be controlled independently of the CO2 flow rate present in the gas comprising CO 2. Thus, the invention allows continuous gas treatment, even if the supply of CO2 to the culture medium is not continuous.

According to a preferred embodiment of the invention, the gas comprising CO2 can come from industrial processes. Thus, the invention may also relate to lime kilns or glass furnaces, and in particular to oxy-combustion furnaces.

According to an advantageous implementation of the invention, the water contained in. the photobioreactor is recycled to generate at least a portion of said water source. Thus, the amount of water needed is minimal.

According to a variant of the invention, each of steps (b) and (c) can be divided into a sequence of substeps, said substeps of steps (b) and (c) being interposed.

According to an embodiment according to the invention, step (d) comprises the following steps: premixing said at least one portion of the aqueous CO2 solution with said at least one portion of the aqueous solution comprising the nutrients ; injection of the resulting solution of the premix into the photobioreactor.

For example, the nutrient composition of the culture medium can be adjusted independently of its CO2 content, the aqueous nutrient solution and the aqueous CO2 solution being all the same prepared. This preparation in parallel followed by a premixing allows a single injection of liquid into the photobioreactor, which can save time and reduce disturbances in the culture medium.

According to an advantageous variant of the invention, recovery by extraction of at least a portion of the metabolic oxygen produced by the phototrophic organisms in the photobioreactor can be envisaged.

According to the invention, the term "phototrophic organisms" may designate by way of examples and in a nonlimiting manner algae, micro-algae, bacteria. The invention also relates to mixtures of one or more species of the aforementioned organisms.

According to the invention, the aqueous CO2 solution comprises CO 2 which can be in three forms: dissolved CO 2, hydrogen carbonate (hereinafter referred to as HCO 3 -), carbonate (hereinafter designated CO32 '). , the CO2 brought into the photobioreactor during step (d) is in at least one of these three forms.

According to a particular embodiment, the invention also relates to a gas purification device comprising CO2 by means of phototrophic organisms comprising: a) means for supplying water from a source of water; b) means for capturing and washing the gas in an absorber comprising at least a portion of the water so as to obtain an aqueous solution of CO2; c) means for preparing, from at least a portion of the water, an aqueous solution comprising nutrients; d) photobioreactor injection means comprising the phototrophic organisms of at least a portion of the aqueous CO2 solution and at least a portion of the aqueous solution comprising the nutrients; e) means for illuminating the content of the photobioreactor with light radiation.

The advantages of the devices are the same as those of the processes: they are not detailed further.

According to a preferred embodiment of the invention, the device comprises means for regulating the CO2 level in the overall aqueous solution contained in the photobioreactor.

Advantageously, the regulating means comprise means for temporarily storing at least a portion of the aqueous CO2 solution.

According to an advantageous embodiment of the device according to the invention, the gas comprising CO2 comes from an oxy-combustion furnace.

Advantageously, the device comprises means for recycling the water contained in the photobioreactor in order to generate at least a portion of said source of water.

According to a preferred embodiment, the means b) and c) are activated in a determined sequence according to which the activations of the means b) and c) are intercalated.

According to a variant of the invention, the means d) comprise: means for premixing said at least one portion of the aqueous CO2 solution with said at least a portion of the aqueous solution comprising the nutrients; means for injecting the resulting solution of the premix into the photobioreactor.

According to an advantageous embodiment of the invention, the device comprises means for extracting at least a portion of the metabolic oxygen produced by the phototrophic organisms in the photobioreactor.

According to a variant of the invention, the phototrophic organisms comprise at least one of the following organisms: an algae; a micro-algae; a bacteria.

According to one embodiment according to the invention, the means d) comprise means for supplying the CO2 photobioreactor in dissolved form.

5. List of Figures Other features and advantages of the invention will appear more clearly on reading the following description of preferred embodiments, given as simple illustrative and non-limiting examples, and the appended figures, among which: Figure 1 shows a synoptic of the traditional process of algae culture; FIG. 2 illustrates an embodiment of the process according to the invention in which the preparation of the aqueous solution of nutrients (step (c)) is carried out before obtaining the aqueous solution of CO2 (stage (b)); FIG. 3 illustrates an embodiment of the method according to the invention in which the obtaining of the aqueous solution of CO2 (step (b)) is carried out before the preparation of the aqueous solution of nutrients (step (c)); FIG. 4 illustrates an embodiment of the method according to the invention in which the injection of CO2 necessary to obtain an aqueous solution of CO2 (step (b)) and the injection of the nutrients necessary for the production of an aqueous solution of nutrients is carried out (step (d)) simultaneously or intercalated, in the same portion of water; FIG. 5 illustrates an embodiment of the process according to the invention in which the obtaining of the aqueous solution of CO2 (stage (b)) and the preparation of the aqueous solution of nutrients (stage (c)) are carried out in parallel and injecting the aqueous CO2 solution and injecting the aqueous nutrient solution into the photobioreactor during step (d) may be simultaneous, sequential or intercalated; FIG. 6 illustrates an embodiment of the process according to the invention for obtaining the aqueous solution of CO2 (step (b)) and the preparation of the aqueous nutrient solution (step (c)) are carried out in parallel, and the solutions obtained are premixed to obtain a single solution comprising CO2 and nutrients, which is then injected into the photobioreactor; FIG. 7 gives the variations in concentration of the different forms of CO2 present in the aqueous solution of CO2 as a function of the pH; Figure 8 shows a block diagram of the claimed process.

6. Description of at least one embodiment of the invention

With Figure 1 is illustrated the traditional scheme of algae culture in photobioreactors. Water 103 enriched with nutrients 104 is introduced into the photobioreactor 105. Moreover, CO2 101 is introduced into the photobioreactor 105. In addition, the photobioreactor 105 receives a light radiation 102, which provides the necessary energy for the reaction. . In this system, the CO2101 is introduced directly into the photobioreactor 105.

The general principle of the invention is based on the decoupling of the uptake of CO2 from the gas, absorbed during step (b), from its injection into the culture medium during step (d). This decoupling is illustrated in FIGS. 2 to 6, which shows that, contrary to FIG. 1, the CO2 201; 301; 401; 501; 601 is not introduced directly into the photobioreactor 205; 305; 405; 505; 605.

FIG. 2 shows a purification method according to a first embodiment: nutrients 204 are introduced into a portion of water coming from a water source 203 so as to obtain an aqueous solution comprising nutrients . Then this aqueous nutrient solution is enriched in CO2 201 from gases comprising CO2, and the resulting aqueous solution is introduced into the photobioreactor 205 which comprises phototrophic organisms.

In FIG. 3, the CO2 301 is introduced into a portion of water 303 so as to obtain an aqueous solution of CO2. Then this aqueous solution of CO2 is enriched in nutrients 304, and the resulting aqueous solution is introduced into the photobioreactor 305 which comprises phototrophic organisms.

The passage from FIG. 2 to FIG. 3 is obtained by reversing the steps for obtaining the aqueous CO2 solution (step (b)) and the step of preparing the aqueous nutrient solution (step (c)). ).

FIG. 4 is the limiting case between FIGS. 2 and 3. According to a variant of the embodiment illustrated in FIG. 4, the nutrients 404 and the CO2 401 can be introduced simultaneously into the same portion of water 403, and then the solution The resulting aqueous solution is introduced into photobioreactor 405. Steps (b) and (c) are then simultaneous and "fused". According to another variant of the embodiment shown in FIG. 4, the injection rate 409 of the nutrients in the portion of water and the injection rate 408 of the CO2 in the same portion of water can be jerky, so that that in fact each of the steps of obtaining the aqueous solution of CO2 and preparing the aqueous solution of nutrients are cut into substeps, said substeps thus being "interleaved".

According to one embodiment shown in FIG. 5, the step of obtaining the aqueous solution of CO2 (step (b)) and the step of preparing the aqueous solution of nutrients (step (c)) can be carried out in parallel. There is shown a particular case where there is a water reserve 503 (for example a tank) between the water source 500 and the photobioreactor 505. In the embodiment shown, parallel to the capture of the gas and the preparation of the aqueous solution of CO2 501 with a portion of water of the water reserve 503, an aqueous solution comprising nutrients 504 is prepared with a portion of water of the water reserve 503 different from the first portion of water. water. Each of the solutions is separately injected into photobioreactor 505 comprising the phototrophic organisms. Here again, the injections may be successive (injection 508 of the aqueous solution of CO2 before injection 509 of the aqueous solution comprising nutrients, or injection 509 of the aqueous solution comprising nutrients before injection 508 of the aqueous solution of CO2), or the injections may be simultaneous (508 and 509 are performed at the same time), or the injections may be interspersed (the arrows 508 and 509 representing jerky flow rates).

The embodiment illustrated in FIG. 6 can be considered as a special case of the embodiment shown in FIG. 5, in which the aqueous solution of CO2 601 and the aqueous solution comprising nutrients 604 are prepared in parallel, then prepared. mixed and finally injected into the photobioreactor 605 comprising the phototrophic organisms.

In all cases, the content of the photobioreactor is illuminated by a light radiation 202; 302; 402; 502; 602 which provides the energy necessary for the photosynthesis reaction. The products obtained are organic matter called "biomass" 206; 306; 406; 506; 606 and oxygen O2 207; 307; 407; 507; 607. Biomass and oxygen can be extracted from the culture medium and recovered.

After cultivation, the phototrophic organisms can be harvested continuously or by spot samples, for example by traditional methods such as flocculation followed by filtration and drying. The removal of at least a portion of the culture medium and its treatment to recover the biomass may be called "biomass extraction". These samples can lead to water losses which will be preferentially offset by the addition of make-up water.

Illumination by light radiation 202; 302; 402; 502; 602 can be provided by a source of natural light, that is to say by the Sun.

The lighting can also be artificial, for example with lamps comprising a halogen bulb or a bulb based on light emitting diodes ("LEDs").

Preferably, the water source is controlled to ensure that the amount of harmful elements (especially toxic) phototrophic organisms is below a predetermined threshold. For the alga Chlorella vulgaris, for example, values derived from "Tolerance of Chlorella vulgaris for metallic and non-metallic ions" by E. Den Dooren De Jong, Antonie van Leeuwenhoek, vol. 31, pp. 301-313 (1965), and repeated in the following table:

The water source may be city water, river or canal water, rainwater, demineralized water, or bubbled city water. of air for removing one or more toxic elements for certain strains of phototrophic organisms, such as for example chlorine.

It is possible to set up a water recycling system as illustrated in FIG. 5. During the extraction of at least a portion of the biomass 506 by taking a portion of the culture medium included in the photobioreactor 505, a portion of water 510 can be recovered. After cleaning, this portion of water can be returned to the water reserve 503. Indeed, it can implement to do this a pump 511 connected between the photobioreactor 505 and the water reserve 503. This recycling system saves water. Only the losses of water, due for example to evaporation, or to the extraction of biomass, can then be compensated by providing a portion of water called "make-up water" 512.

According to the invention, the CO2 necessary for photosynthesis is supplied to the culture medium in the form of an aqueous solution of CO2.

Dissolving the gaseous CO 2 O 201; 301; 401; 501; 601 in water 203; 303; 403; 503; 603 corresponds to Equation 2:

(equation 2)

She obeys the law of Henry resumed in Equation 3:

(1 equation 3) where [CO2 (dissolved)] refers to the concentration of dissolved CO2 in water, HCo2 the Henry constant for CO2, and pco2 (gas) the CO2 partial pressure of the gas phase.

Then the dissolved CO2 reacts with H2O water to form HCO3 'and CCb2'. And the dissolution responds to the equilibrium given by the following equations (4) and (5): (equation 4)

(equation 5)

The aqueous CO2 solution comprises CO2 that can actually be found in three forms: dissolved CO2 (703), hydrogen carbonate HCO3 '(704), and carbonate CO32' (705). The majority form is a function of pH (as shown in Figure 7). This figure shows the concentration of the different forms of CO2 that may exist in the aqueous CO2 solution as a function of the pH: the abscissa axis 701 gives the pH values, and the ordinate axis 702 gives the concentration ( in pmol / kg) of each form of CO2 present in the solution.

The necessary CO2 201; 301; 401; 501; 601 can come from industrial gases, such as flue gases from glass furnaces or lime kilns, which emit a lot of CO2.

Oxy-combustion furnaces, which use pure oxygen as the oxidant (rather than just air), produce gases that are particularly rich in CO2 and depleted of secondary products, which makes treatment easier. Indeed, having a concentrated CO 2 can increase the yield of the process according to the invention, and this at least for two reasons: On the one hand, if the CO 2 partial pressure is high, then the concentration of dissolved CO 2 is high. after equation 3 and the yield of the dissolution of CO2 gas in 1 water ([CO2 dissolved] / [CO 2 gas supplied]) will be large.

On the other hand, with a high partial pressure of CO2, for a unit rate of CO2 (lkg / h for example), the total gas flow will be less important. So with CO2-rich gases, the volume of gas to be treated will be lower than for CO2-poor gases. This may allow for example to reduce the volume of equipment, including that of the device for dissolving CO2 in water.

The gases comprising the CO 2 can be cleaned before the step of dissolving CO2 gas 201; 301; 401; 501; 601 in water 203; 303; 403; 503; 603. The absorber used to capture these gases may consist of two parts that may or may not be separate: a cleaning device and a device for dissolving gaseous CO2 in water. For example, the pollution control methods traditionally employed in the glass or lime industry may be used: the gases comprising CO 2 may pass through a bag filter, on an electro-filter which makes it possible to remove particles, for example heavy metals (such as Hg, Cr, Ni, Zn, Pb), then on a DeSOx device (to remove the sulfur oxides) and on a DeNOx catalyst (to remove the nitrogen oxides).

Finally, in the invention, the gas comprising CO2 is no longer in direct contact with the culture medium. However, the oxygen production by photosynthesis takes place only in this medium. If it is considered that an aqueous solution is injected into the culture medium comprising as sole gas dissolved pure CO2 and that it is totally absorbed by the phototrophic organisms (according to Equation 1) or that the CO2 not consumed by the phototrophic organisms remains in solution, so the only gas leaving the photobioreactor will be metabolic ΓΟ2. If the photobioreactor is closed, we can consider recovering this metabolic O2 207; 307; 407; 507; 607.

The temperature of the culture medium depends on the species of phototrophic organism used. For Chlorella vulgaris algae for example, it is around 28 ° C. It is then necessary to cool the gas including CO2. As an indication, the temperature of the gases at the outlet of a glass furnace is of the order of 220 ° C and the temperature of the gases at the outlet of a lime kiln is of the order of 150 ° C.

This can be done by traditional techniques, for example through a heat exchanger, the cold source can be the source of water 500. The heat exchanger can also be the device 513 for dissolving gaseous CO2 in water himself.

Conversely, the heat of gases including CO2 can be used to heat the culture medium if it is too cold (eg in winter).

The dissolution of gaseous CO2 502 in the water explained above can be achieved by means of various devices 513 for dissolving gaseous CO2 in water, among which mention may be made of a bubble column, a stirred tank (magnetic for example) , a plate column (perforated or cap), a packed column (co- or countercurrent), a Venturi, a spraying column, a film column.

The use of a "Amazon" type film column (marketed by the company Toussaint-Nyssenne) makes it possible, in addition to the dissolution of CO2 in the water, the elimination of dust, and the exchange of heat.

After this step, an aqueous solution of CO2 is thus obtained. Advantageously according to the invention, the phototrophic organisms are never in direct contact with the gaseous CO2. Thus phototrophic organisms are not subject to shocks from gas bubbles and are not stressed.

The decoupling of the capture of CO2 from the gas, carried out during step (b), of its injection into the culture medium during step (d) also makes it possible to carry out a storage of the CO2 reserve present in water in dissolved form, for example in a buffer tank 514 (shown in FIG. 5) inserted between the device 513 for dissolving gaseous CO2 in water and the photobioreactor 505. Thus, the contribution of CO2 to the medium of culture can be regulated according to the needs. For example, it is conceivable to insert, between the buffer tank 514 and the photobioreactor 505, a pump 515 whose flow rate is adjustable, which makes it possible to adjust the amount of CO2 in the culture medium. It is also possible to dilute the culture medium by adding make-up water 512. The CO2 requirements can be estimated by measuring the concentrations of HCO3 · and CO3 ', for example with an "Applikon" type automatic titrator (marketed by Metrohm).

Another advantage of storing CO2 in the form of an aqueous solution lies in its routing to photobioreactors 205; 305; 405; 505; 605. It is indeed easier to transport liquids than gases (transport by simple gravity for example), especially since the distance to be traveled is large (especially in the case of a field of about photobioreactors of several hectares). This translates into substantial cost savings.

In addition, a filtration after the dissolution of CO2 gas in water decoupled from the injection into the culture medium, for example with a filter 516 (placed between the device 513 for dissolving gaseous CO2 in water and the photobioreactor 505, or, where appropriate, between the buffer tank 514 and the photobioreactor 505), makes it possible to recover insoluble salts (such as CaCCb, MgCCb, etc.) and thus prevent their contact with the phototrophic organisms. In a traditional process such as that shown in Figure 1, these salts would have precipitated in the culture medium and mixed with the phototrophic organisms.

In the same way that one can regulate the supply of CO2 501 in the culture medium, the supply of nutrients 504 can be controlled. Nitrates are traditionally used as an indicator of the average level of nutrients, this control can be done by means of a measurement of the amount of nitrates in the overall aqueous solution. The additional supply of nutrients can then be achieved using a metering pump 517 placed between the nutrient store 504 and the photobioreactor 505.

A particular example of a gas purification device comprising CO2 using phototrophic organisms according to the invention is now described.

Culture tests were carried out with algae of the order Chlorococcales, family: Chlorellaceae, genus: Chlorella, species: vulgaris (hereinafter referred to as "Chlorella vulgaris") in an open glass photobioreactor of dimensions 85 * 5 * 280 cm (ie a volume of 119L) made with 12mm thick glass sheets glued, the seal being provided by an O-ring. The photobioreactor is in a greenhouse and is filled with 112L

demineralized water enriched with nutrients so as to obtain an M8 culture medium whose composition in macro- and micronutrients is indicated in the following tables:

The temperature of the reactor is ideally maintained around 27.5 ° C (+/- 2.5 ° C), which is the optimum temperature for Chlorella vulgaris, by means of a thermally insulated greenhouse with air conditioning and heat exchanger. internal heat to the photobioreactor.

Illumination is provided by natural light (ie in Belgium: 125W / m2 / year on average by counting the hours of night).

In this example, the supply of CO2 to the culture medium is carried out in the form of an aqueous solution containing hydrogen carbonate ions HCO3 ', in this case for example with an aqueous solution of NaHCCb. The use of such a solution makes it possible to simulate the dissolution of CO2 gas in water and results in an aqueous solution of CO2 which can be assimilated to that which would be obtained by the process according to the invention.

The step of dissolving gaseous CO 2 in deionized water was also carried out with a 513 bubbler-pilot device made of glass, 10 cm in diameter and 54 cm in height; its working volume is 4 L. The tests were carried out with a working volume of 3 L. A gas flow of 600mL / min containing 33% of CO2 in the air (which can be assimilated to the composition of the gases from an oxy-combustion glass furnace) is introduced by 16 holes 1.5 mm in diameter. The velocity of the gas through a hole is about 0.35 m / s. A mixer with 4 vertical blades rotates at a speed of 12000 rpm to destroy coalescing bubbles and reduce their diameter.

The yield of the dissolution, obtained by calculating the ratio [dissolved CO2] / [DC> 2 introduced] is of the order of 55%.

By neglecting the degassing of the dissolved CO2 (at the level of the photobioreactor 505, and possibly at the level of the buffer tank 514) and assuming that the phototrophic organisms are synchronized with the device 513 for dissolving CO2 gas in the water, ie the whole of the CO2 dissolved in water by the aforementioned device is consumed by the phototrophic organisms, then the efficiency of the process of absorption of CO2 by phototrophic organisms is the efficiency of the dissolution of CO2 gas in water.

Under the conditions described above, the concentration of algae stabilizes at 1 g / l. To extract biomass 506, a portion of the culture medium can be sampled (punctually or continuously) and then subjected to a treatment comprising filtration, flocculation and drying steps.

The volume of water can be kept constant by the addition of make-up water 512 in the photobioreactor 505 to compensate for the losses due to evaporation and samples of culture medium.

In summary, one can compare the composition of the combustion gas of a glass furnace after a traditional treatment currently used in the glass industry without purification process by phototrophic organisms, with the composition of this gas after treatment by the process purification according to the embodiment of the invention described above.

Traditional treatment consists of a simple cleaning of the gas. First this gas passes electro-filters to remove dust and undergo DeSOx treatment to remove sulfur oxides (for example by adding CaCC> 3 in aqueous medium, depending on the reaction: CaCC> 3 + SO 2 CaSO 3 + CO 2) then the resulting gas passes over a DeNOx catalyst to remove the nitrogen oxides (for example by injecting NH3 in the form of NH4OH on a ceramic honeycomb matrix which catalyzes the degradation reaction of the nitrogen oxides to H 2 O , O2 and N2.

The values are listed in the following table:

In this example, the gas purification process comprising CO2 according to the invention makes it possible to reject 50% less CO2 in the atmosphere than by the conventional method.

In connection with FIG. 8 is described a gas purification process comprising CO2 using phototrophic organisms. This method comprises a step 801 for supplying water from a water source; a step 802 for capturing and washing the gas in an absorber comprising at least a portion of the water so as to obtain an aqueous solution of CO2; a step 803 of preparing, from at least a portion of the water, an aqueous solution comprising nutrients; a photobioreactor injection step 804 comprising the phototrophic organisms of at least a portion of the aqueous CO2 solution and at least a portion of the aqueous solution comprising the nutrients; a step 805 for illuminating the contents of the photobioreactor with light radiation.

Of course, the invention is not limited to the embodiments mentioned above.

In particular, the skilled person may provide any variant in the choice of the species of algae or micro-algae or more generally phototrophic organism. In addition to the Chlorella vulgaris mentioned here, it is possible, for example and without limitation, to use Chlorella sorokiniana, Dunaliella tertiolecta, Dunaliella salina or Haematococcus pluvialis. A mixture of several species can also be used. The phototrophic organism may also be a bacterium, such as for example a cyanobacterium, such as Spirulina platensis.

The invention applies of course, also to closed reactors, and lagoons (open or closed).

Likewise, the invention is not limited to a batch culture and also applies to a continuous culture.

In addition, the invention does not apply solely to the treatment of flue gases from glass or lime furnaces, but also to any type of gas or fumes including CO2, such as air, gases or combustion fumes, for example industrial.

Claims (11)

A method of purifying gas comprising CO2 using phototrophic organisms comprising the steps of: a) supplying (801) water (203; 303; 403; 503; 603) from a water source b) capturing and washing (802) the gas in an absorber comprising at least a portion of the water so as to obtain an aqueous solution of CO2; c) from at least a portion of the water, preparing (803) an aqueous solution comprising nutrients (204; 304; 404; 504; 604); d) injecting (804) into a photobioreactor (205; 305; 405; 505; 605) comprising the phototrophic organisms of at least a portion of the aqueous CO2 solution and at least a portion of the aqueous solution comprising the nutrients ; e) illuminating (805) the contents of the photobioreactor with light radiation (202; 302; 402; 502; 602); and (c) which can be inverted or simultaneous. 2. Method according to claim 1, characterized in that it comprises a step of regulating the CO2 content in the overall aqueous solution contained in the photobioreactor (205; 305; 405; 505; 605). 3. Method according to claim 2, characterized in that the regulating step comprises a step of temporarily storing at least a portion of the aqueous solution of CO2. 4. Process according to claim 1, wherein the gas comprising CO 2 (201; combustion. 5. Method according to any one of claims 1 to 4, characterized in that the water contained in the photobioreactor (205; 305; 405; 505; 605) is recycled in order to generate at least a portion of said source of water. 6. Method according to any one of claims 1 to 5, characterized in that each of steps (b) and (c) is divided into a sequence of substeps, said substeps of steps (b) and (c) being interspersed. 7. Method according to any one of claims 1 to 6, characterized in that step (d) comprises the following steps: premixing said at least a portion of the aqueous solution of CO2 with said at least a portion an aqueous solution comprising the nutrients; injection of the resulting solution of the premix into the photobioreactor. 8. Process according to any one of claims 1 to 7, characterized in that it comprises a step of extracting at least a portion of the metabolic oxygen (207; 307; 407; 507; 607) produced by phototrophic organisms in the photobioreactor (205; 305; 405; 505; 605). 9. Process according to any one of claims 1 to 8, characterized in that the phototrophic organisms comprise at least one of the following organisms: an algae; a micro-algae; a bacteria. The process according to any one of claims 1 to 9, wherein the CO2 (201; 301; 401; 501; 601) is supplied to the photobioreactor (205; 305; 405; 505; 605) in step ( (d) in dissolved form. 11. A gas cleaning device comprising CO2 by means of phototrophic organisms comprising: a) water supply means (203; 303; 403; 503; 603) from a source of water; b) means for capturing and washing the gas in an absorber comprising at least a portion of the water so as to obtain an aqueous solution of CO2; c) means for preparing, from at least a portion of the water, an aqueous solution comprising nutrients (204; 304; 404; 504; 604); d) photobioreactor injection means (205; 305; 405; 505; 605) comprising the phototrophic organisms of at least a portion of the aqueous CO2 solution and at least a portion of the aqueous solution comprising the nutrients; e) means for illuminating the content of the photobioreactor with light radiation (202; 302; 402; 502; 602).