WO2017190504A1 - Rotating disc type photobioreactor for microalgae large-scale cultivation - Google Patents

Abstract

Provided is a rotating disc type photobioreactor for microalgae large-scale cultivation, comprising a reactor main body, a rotating shaft (5) throughout the entire reactor main body, rotating discs (4) vertically fixed on the rotating shaft (5) at intervals, a driving motor (1), a transmission system (2), an air pipe (6) provided at the bottom of the reactor, a carbon dioxide inlet valve (8), a carbon dioxide source (7), a water inlet (9), and a water outlet (10). The rotating discs (4) are partially submerged in a culture solution and partially exposed to the air. The driving motor (1) drives the rotating discs (4) to rotate slowly via the transmission system (2), so that microalgae cells adhered to and grown on the rotating discs (4) are alternatively fed into a liquid phase and a gas phase. The air pipe (6) is in communication with the carbon dioxide source (7) outside the reactor via the carbon dioxide inlet valve (8). The reactor is simple in structure and is convenient for operations such as inoculation, harvesting and the like. It takes a small area, has a modular design, is easy to amplify, and is suitable for the large-scale production of microalgae biomass and microalgae secondary metabolites. It is also suitable for removal of nutrient substances such as nitrogen and phosphorus in sewage.

Description

Rotary type photobioreactor for large-scale cultivation of microalgae Technical field:

The invention relates to the field of microalgae cultivation biotechnology, in particular to a rotary disk type photobioreactor for large-scale cultivation of microalgae.

Background technique:

Microalgae absorbs carbon dioxide and water for photosynthesis and can synthesize a large amount of biomass resources such as protein, fat, polysaccharide, vitamins and pigments. It is used in medicine, food, health products, aquatic bait, animal feed, water purification, biofuels, etc. Widely used, with important economic and social benefits. For example, in the field of food, microalgae can provide humans with a large number of single-cell proteins, vegetable oils, carotenoids, EPA, DHA and other food or food additives; in the field of medicine and health, microalgae can produce antibiotics, antioxidants, anti-cancer And antiviral drugs. Due to its high photosynthesis efficiency, high oil content, short growth period, high yield per unit area, and no occupation of cultivated land, microalgae has become a research hotspot for bioenergy production in recent years, for biodiesel, bioethanol, biogas. Research and development of bio-oil, etc. According to the composition of microalgae, about 1 ton of carbon dioxide can be absorbed per ton of microalgae biomass. Therefore, the large-scale production of microalgae bioenergy can not only effectively alleviate energy shortage, but also contribute to greenhouse gas emission reduction. In addition, compared with the conventional sewage treatment method, the microalgae can quickly absorb elements such as nitrogen and phosphorus in the sewage and convert it into biomass, which can be further biorefined.

Low-cost large-scale cultivation is the key to realizing the industrialization of microalgae, and it is also the bottleneck restricting the industrialization of microalgae. At present, the microalgae culture mainly adopts an open pool or a closed photobioreactor, and is basically a suspension culture mode, and the algal cells are dispersed in a large amount of medium water. In the suspension culture mode, the density of algae cells is low. For example, the cell concentration in the open cell is generally 0.5-1 g/L, and the cell concentration in the photobioreactor is 2-6 g/L. The suspension cultured microalgae must be subjected to steps such as concentration and dehydration to remove more than 90% of water during downstream processing. Generally, a two-step method is employed, firstly concentrating to a solid content of about 1% by precipitation, flocculation, air flotation, etc., and then centrifuging to a solid matter of about 20%. This process has the disadvantages of large equipment investment, energy consumption, and time consuming. Generally, the micro-algae harvesting cost of suspension culture accounts for about 20-30% of the total investment and operating costs. In addition, in suspension culture, due to mutual shielding of cells, light is attenuated severely in water, which limits the improvement of photosynthesis efficiency. Due to the large specific surface area required, the reactor area is increased, which restricts the industrial development of microalgae.

Microalgae attachment culture has attracted the attention of researchers as another culture mode in recent years, characterized in that microalgae cells adhere to the surface of solid or semi-solid materials for growth. Compared with suspension culture, the advantage of adherent culture is that the harvest is simple and the cost of microalgae harvesting can be greatly reduced. In addition, the adherent culture of microalgae can also improve light utilization efficiency, enhance CO ₂ mass transfer, increase cell residence time, and the like. The most representative microalgae attachment culture is the Algae Turf Scrubber-ATS system, in which the microalgae are attached to a horizontally placed slightly inclined attachment material, and the culture solution intermittently flushes the surface. In addition to the ATS system, a spray-type immobilized microalgae culture system has been invented in which microalgae cells are immobilized on the surface of a support material, and the desired culture medium is supplied to the cells by intermittent or continuous spraying to keep the cells moist.

Summary of the invention:

The object of the present invention is to overcome the deficiencies in the prior art and to provide a rotary-type photobioreactor for the large-scale cultivation of microalgae. The reactor has the advantages of simple structure, convenient inoculation and harvesting, high-efficiency utilization of light energy, and improvement of microalgae yield and yield. The reactor is modular in design and easy to be industrially amplified. It is suitable for large-scale production of microalgae biomass and microalgae secondary metabolites. It is also suitable for removing nutrients such as nitrogen and phosphorus in sewage. At the same time, the reactor realizes microalgae cells. Adhesive growth solves the problems of low efficiency, large floor space, large water consumption and difficult harvesting of photosynthesis in microalgae suspension culture.

The present invention is achieved by the following technical solutions:

A rotary-type photobioreactor for large-scale cultivation of microalgae, comprising a reactor main body, a rotating shaft running through the entire reactor main body, a rotating disc fixedly fixed on the rotating shaft at a certain interval, a driving motor, a transmission system, a vent pipe, a carbon dioxide intake valve, a carbon dioxide gas source, a water inlet, and a water outlet provided at the bottom of the reactor; the rotating disk is partially immersed in the culture liquid, partially exposed to the air; and the driving motor drives the rotating disk to rotate slowly through the transmission system. The microalgae cells attached to the rotating disk are alternately introduced into the liquid phase and the gas phase; the vent pipe is communicated with the carbon dioxide gas source outside the reactor through the carbon dioxide inlet valve, and at least the liquid portion of the reactor body is transparent. Material preparation.

The reactor body is a light transmissive material, and the light permeable material may be used only in the upper portion of the liquid surface in order to reduce the cost.

The light transmissive material is selected from the group consisting of glass, plexiglass, polycarbonate, and polymethyl methacrylate.

The rotating disc is made of a rigid adhesive material fixed on the rigid skeleton or directly made of a rigid adhesive material; the rigid skeleton refers to a skeleton made of a solid material such as steel or iron; and the attached material includes Rigid and flexible) refers to thin steel sheets, aluminum sheets, polyurethane plastics, polycarbonate, polystyrene, polyvinyl chloride, cotton, filter cloth, canvas, non-woven fabric, nylon, fiber fabric, and the like. The microalgae hangs on the surface of the attached material and grows rapidly to form a biofilm.

Further, the surface of the rotating disk may be planar or curved. For ease of harvesting, a flat design is preferred.

Further, the immersion rate of the rotating disk is between 20% and 40%, and the preferred immersion rate is 40%.

Further, the spacing between the rotating disks can be adjusted to any value as needed, and the preferred spacing is 30-150 mm.

Further, the rotating disk is provided with a biomass harvesting device to realize in-situ harvesting during the cultivation process, and the harvested biomass is highly concentrated. The biomass harvesting device can be a variety of mechanical scrapers, scrapers or vacuum suction devices.

The rotating shaft and the rotating shaft are connected between the rotating shaft and the driving motor through a transmission system.

Further, the transmission system is a chain-gear transmission or a belt-pulley transmission, and a gear or a pulley is connected to an output shaft of the driving motor, and a gear or a pulley is connected to each rotating shaft, and an output shaft and a motor of the driving motor are connected. The gears or pulleys on the rotating shaft are connected by a chain or a belt. When there are multiple reactor combinations or one reactor contains multiple rotating shafts, one driving motor can be used to drive multiple rotating shafts or one driving motor can drive one rotating shaft, as the case may be.

In order to provide sufficient CO ₂ to the reactor medium, orifices or nozzles are provided on the vent tube disposed at the bottom of the reactor, the vent tubes being selected from commercially available aeration hoses or variable orifice aeration hoses.

The snorkel can be one or more, as the case may be.

Further, the vent tube can maintain continuous ventilation or intermittent ventilation under light culture conditions. Intermittent ventilation can be controlled by monitoring the pH of the culture fluid. Since the pH of the culture solution rises due to the consumption of CO ₂ , when the pH of the culture solution exceeds the preset pH range, the intake valve switch can be opened to ventilate the reactor.

The bottom of the reactor can be designed as any of a flat bottom, a semi-circular shape, a tapered shape or a trapezoidal shape.

The invention also protects the use of the rotary-type photobioreactor for the large-scale cultivation of microalgae, the reactor is placed in an open environment or a closed environment; in an open environment, the reaction system can be directly placed in a desired water body. The water body includes but is not limited to lakes, rivers, runway pools, ditches, oxidation ponds, etc.; in a closed environment, the upper part of the reactor may be sealed, or the entire reactor body is placed in a closed container or greenhouse, closed The reactor requires an exhaust port.

The carbon dioxide gas source is selected from the group consisting of air mixed with CO ₂ , pure CO ₂ gas, industrial CO ₂ gas, one or more of flue gases, or liquid CO ₂ .

The reactor is placed under an artificial light source or directly exposed to natural light. The position of the light source should take into account the orientation of the disk surface, so that the disk surface can maximize the illumination.

The reactor of the present invention can be operated in a batch, semi-continuous or continuous flow depending on the actual situation. The supplemental culture solution may be various types of microalgae culture medium, or a solution containing various stress or induction factors, or various types of sewage, seawater, and the like.

The microalgae medium may be any medium suitable for the growth of microalgae well known in the art, such as BG-11 medium, SM medium, BBM medium, SE medium, etc., or may contain various stresses or inducements. A solution of factors such as nitrogen-deficient medium, high-salt medium, etc., or seawater, municipal sewage, industrial wastewater, livestock waste water, and any other natural water containing nitrogen and phosphorus.

The microalgae in the present invention includes, but is not limited to, Scenedesmus, Chlorella, Haematococcus pluvialis, Dunaliella, Nannochloropsis, Spirulina, etc., and secondary metabolites of microalgae include, but are not limited to, triglyceride, Astaxanthin, lutein, carotenoids, etc.

The reactor of the invention is also suitable for secondary treatment or tertiary treatment of sewage and nitrogen-rich sewage such as urban sewage, industrial wastewater, livestock waste water, etc., and the inoculated culture is a mixed culture, including microalgae, photosynthetic bacteria and isoxic bacteria. Any combination of nitrifying bacteria, fungi, and the like.

The invention has the following beneficial effects:

1) The reactor is simple in structure, easy to inoculate and harvest, etc. It has small footprint, modular design and easy to enlarge. It is suitable for large-scale production of microalgae biomass and microalgae secondary metabolites, and is also suitable for removing sewage. Nutrients such as nitrogen and phosphorus;

2) The application realizes the microalgae adhesion culture, does not need to maintain the suspension state, and therefore does not require a large stirring power or ventilation, and reduces the energy consumption; there is also no problem that the suspension culture cells are shielded from each other, because the present invention There is almost no suspended microalgae in the culture solution, and there is no problem of separation of the microalgae cells and the culture solution. Therefore, it is convenient to switch the induction conditions, such as inducing microalgae to produce oil, and only discharging the nitrogen-rich medium, and then injecting The nitrogen-deficient medium can be cultured; the problems of low photosynthesis, large floor space, large water consumption, and difficulty in harvesting of the microalgae suspension culture are solved.

3) The invention can be conveniently improved on the existing runway pool or the high-efficiency algae pond, and can effectively improve the microalgae culture efficiency of the existing system; compared with the conventional method, the microalgae cell growth of the present invention is attached. The film state can be directly harvested to obtain concentrated algae mud, which solves the problems of traditional suspension culture and the high energy consumption of dehydration. In addition, the solid residence time and hydraulic retention time can be inconsistent, which is more conducive to the growth of algae. It is easy to carry out continuous flow culture and solves the industrial bottleneck of microalgae technology.

4) The driving motor of the present application drives the rotating disk to rotate slowly, so that the microalgae cells attached to the rotating disk alternately enter the liquid phase and the gas phase, and the microalgae cells are easy to be mixed with nutrients (such as CO ₂ in the gas phase, in the liquid phase). Nitrogen and phosphorus) fully contact, greatly improving the efficiency of photosynthesis and nutrient utilization; since the disk surface is only partially immersed in water, the total water demand during the cultivation process and the amount of chemical reagents required for growth are reduced, saving the cultivation cost. .

BRIEF DESCRIPTION OF THE DRAWINGS:

1 is a schematic structural view of a rotary disk type photobioreactor for the microalgae scale culture of Example 1;

2 is a schematic structural view of a rotary disk type photobioreactor for the microalgae scale culture of Example 2;

Among them, 1, drive motor; 2, transmission system; 3, sealing cover; 4, rotating disc; 5, rotating shaft; 6, vent pipe; 7, CO ₂ gas source; 8, intake valve; 9, water inlet; 10, water outlet; 11, exhaust port; 12, paddle wheel; 13, partition; 14, baffle.

detailed description:

The following is a further description of the invention and is not to be construed as limiting.

Example 1: Rotary-type photobioreactor for large-scale cultivation of microalgae in a closed environment

The rotary-type photobioreactor for the microalgae scale culture of the present embodiment has a structure as shown in FIG. 1 , and includes a reactor main body, a detachable sealing cover 3 on the top of the reactor, and a rotating shaft penetrating the entire reactor main body. 5. A rotating disk 4 fixed vertically on the rotating shaft 5, a driving motor 1, a transmission system 2, a vent pipe 6 provided at the bottom of the reactor, a carbon dioxide intake valve 8, a carbon dioxide gas source 7, a water inlet 9, a water outlet 10, and An exhaust port 11 is provided on the sealing cover 3; the rotating disk 4 is partially immersed in the culture liquid, and partially exposed to the air; the driving motor 1 drives the rotating disk 4 to rotate slowly through the transmission system 2, so that the rotating disk 4 is attached. The growing microalgae cells alternately enter the liquid phase and the gas phase; the vent tube is in communication with a carbon dioxide gas source outside the reactor via a carbon dioxide intake valve, and the reactor body is prepared at least above the liquid surface as a light transmissive material.

The transmission system 2 is a chain-gear transmission or a belt-pulley transmission, and a gear or a pulley is connected to an output shaft of the drive motor 1, and a gear or a pulley is connected to each rotation shaft, and an output shaft and each of the drive motor are connected. The gears or pulleys on the rotating shaft are connected by a chain or belt.

The light transmissive material is selected from the group consisting of glass, plexiglass, polycarbonate, and polymethyl methacrylate.

a rotating disc is fixed every 30 to 150 mm on the rotating shaft; the rotating disc is made of a rigid adhesive material fixed on the rigid skeleton or directly made of a rigid adhesive material; the rigid skeleton is made of a solid material such as steel or iron. Skeleton; the attachment material (including rigidity and flexibility) is selected from the group consisting of thin steel sheets, aluminum sheets, polyurethane plastics, polycarbonate, polystyrene, polyvinyl chloride, cotton, filter cloth, canvas, non-woven fabric, nylon, and fiber fabric. Wait. The microalgae hangs on the surface of the attached material and grows rapidly to form a biofilm.

The liquid level of the reactor is below the center of the rotating shaft, and about 40% of the rotating disk is immersed in the culture solution, and the rotation speed of the turntable is between 1 and 20 rpm.

Further, the rotating disk is provided with a biomass harvesting device to realize in-situ harvesting during the cultivation process, and the harvested biomass is highly concentrated. The biomass harvesting device can be a variety of mechanical scrapers, scrapers or vacuum suction devices.

In order to provide sufficient CO ₂ to the reactor medium, a small orifice is provided in the vent tube disposed at the bottom of the reactor, the vent tube being selected from commercially available aeration hoses or variable orifice aeration hoses.

The supply of carbon dioxide can be automated. The pH of the culture solution is monitored by a pH sensor to control the intake valve 8 to be automatically opened and closed. For example, when culturing chlorella, when the pH of the culture solution is greater than 8, the intake valve is automatically opened, and the CO ₂ gas is slowly released into the reactor through the small hole in the vent pipe. When the pH value is less than 7.5, the intake valve is automatically closed. No more CO ₂ gas is introduced.

The CO ₂ gas source is one or more of air mixed with CO ₂ , pure CO ₂ gas, industrial CO ₂ gas, flue gas or liquid CO ₂ . Since the aeration is only for providing a carbon source, it is not necessary to maintain the suspension of the algae liquid, so the opening size and the gas flow rate of the vent pipe 6 can be small, which is advantageous for increasing the gas-liquid contact area and time, and greatly increasing the absorption rate of CO ₂ .

The top of the reactor is equipped with a detachable sealing cover 3 for easy inoculation, feeding, harvesting and other operations. The sealing cover 3 is provided with an exhaust port 11 to facilitate the discharge of O ₂ .

In this embodiment, the harvesting process may be manual or electric harvesting, and the harvesting mode is not specifically limited.

The specific use is as follows:

The medium was added to the rotary photobioreactor shown in Fig. 1, and the fresh medium was inoculated with a volume fraction of 10% microalgae seed solution, and the sealing cap 3 was covered. The reactor is placed under light conditions, the intake valve 8 is opened to introduce CO ₂ gas, and the driving motor 1 is started to rotate the rotating disk 4 slowly, and the aeration is carried out for 7 to 14 days, and the microalgae in the medium is gradually attached to the rotating disk 4 On the attached material, and growing on the attached material, the biomass of the microalgae in the liquid gradually decreases, the liquid becomes clear, and the microalgae is hanged. The microalgae on the surface of the rotating material attached to the rotating disk 4 is scraped off with a rubber scraper, and the remaining microalgae is used as a seed for the next round of growth, and fresh medium or nutrient elements are replaced at the same time for formal circulation growth. The algae mud is harvested every 5 to 10 days, and the mass concentration of the directly harvested algae is 10-20%, which is equivalent to the effect after suspension culture.

Example 2: Rotary-type photobioreactor for large-scale cultivation of microalgae in an open environment

This embodiment is a rotary disk type photobioreactor which is reconstructed on the basis of the existing runway pool. The schematic diagram of the reactor is shown in FIG. 2, including the reactor main body, the driving motor 1, the transmission system 2, and the bottom of the reactor. a vent pipe, a carbon dioxide intake valve, a carbon dioxide gas source, a water inlet, a water outlet; a rotating shaft 5 extending through the entire reactor body, a rotating disk 4 vertically fixed to the rotating shaft 5, a paddle wheel 12, a partition plate 13, The deflector 14. The drive motor 1 drives the paddle wheel 12 and the rotary disc 4 to rotate through the transmission system 2 at the same time. The rotating disk is partially immersed in the culture liquid and partially exposed to the air; the vent pipe is communicated with a carbon dioxide gas source outside the reactor via a carbon dioxide intake valve, and at least the liquid portion of the reactor body is a light transmissive material preparation. The transmission system 2 is a chain-gear transmission or a belt-pulley transmission, and a gear or a pulley is connected to an output shaft of the drive motor 1 and each transmission shaft, and an output shaft of the drive motor 1 and each of the rotation shafts The gears or pulleys are connected by a chain or belt. The reactor contains a plurality of rotating shafts 5, and a plurality of rotating shafts 5 are driven by a driving motor 1.

Since the microalgae mainly grow on the rotating disk 4, the microalgae in the liquid is extremely small, so the rotation speed of the paddle wheel 12 can be very low, and the paddle wheel 12 functions only in the circulation flow of the culture liquid, and does not need to keep the suspension of the microalgae. status.

Due to the suspension growth of microalgae in the traditional runway pool, the microalgae in the liquid are shielded from each other, and the penetration of light in the water body is extremely poor. Therefore, the traditional runway pools are shallow pools, and the water depth cannot exceed 30 cm. In the present invention, the microalgae are mainly attached to the rotating disk 4, and there are few microalgae in the liquid, and there is no problem that the light is attenuated sharply in the water body, so the water depth of the reactor can be unlimited.

A rotating disc 4 is fixed on the rotating shaft 5 every 30 to 150 mm, and the rotating disc 4 is made of a rigid adhesive material fixed on the rigid skeleton or directly made of a rigid adhesive material, which is made of steel and iron. A skeleton made of a solid material; the attached material (including rigidity and flexibility) includes but is not limited to thin steel sheets, aluminum sheets, polyurethane plastics, polycarbonate, polystyrene, polyvinyl chloride, cotton cloth, filter cloth, canvas, and non-woven fabric. , nylon, fiber fabrics, etc.

The specific use is as follows:

Adding a certain amount of medium to the runway pool, inoculating the fresh medium with a volume fraction of 10% microalgae seed solution, starting the drive motor 1 to slowly rotate the paddle wheel 12 and the rotating disc 4, and cultivating for 7 to 14 days, the suspension The microalgae in the middle adhered to the disk surface of the rotating disk 4 in a large amount, and the liquid became clear, and the microalgae was hanged. The microalgae on the surface of the rotating plate of the rotating disk 4 is scraped off with a rubber scraper, and the remaining microalgae is used as the seed for the next round of growth, and the fresh medium or nutrient elements are replaced at the same time to perform formal circulation growth every 5~. The algae mud was harvested once every 10 days, and the mass concentration of the directly harvested algae was 10-20%, which was equivalent to the effect after suspension culture in suspension.

Claims (9)

1. A rotary-type photobioreactor for large-scale cultivation of microalgae, comprising: a reactor main body, a rotating shaft penetrating the entire reactor main body, a rotating disc vertically fixed on the rotating shaft, a driving motor, and a transmission The system, the vent pipe disposed at the bottom of the reactor, the carbon dioxide intake valve, the carbon dioxide gas source, the water inlet, and the water outlet; the rotating disk is partially immersed in the culture liquid, partially exposed to the air; the driving motor drives the rotating disk through the transmission system Slowly rotating, the microalgae cells attached to the rotating disk alternately enter the liquid phase and the gas phase; the vent pipe is communicated with the carbon dioxide gas source outside the reactor via a carbon dioxide inlet valve, and at least the liquid portion of the reactor body is Preparation of light transmissive materials.
2. The rotary disk type photobioreactor for large-scale cultivation of microalgae according to claim 1, wherein the rotating disk is made of a rigid adhesive material fixed on a rigid skeleton or directly made of a rigid adhesive material; The material is selected from the group consisting of a thin steel plate, an aluminum plate, a polyurethane plastic, a polycarbonate, a polystyrene, a polyvinyl chloride, a cotton cloth, a filter cloth, a canvas, a non-woven fabric, a nylon, and a fiber fabric.
3. The rotary-type photobioreactor for large-scale cultivation of microalgae according to claim 1 or 2, wherein the surface of the rotating disk is flat, and the immersion rate of the rotating disk is 20% to 40%; The spacing between the discs is 30-150 mm.
4. The rotary disk type photobioreactor for large-scale cultivation of microalgae according to claim 1 or 2, wherein the rotating disk is provided with a biomass harvesting device, and the biomass harvesting device is a mechanical scraper, Scraper or vacuum suction device.
5. The rotary-type photobioreactor for scale culture of microalgae according to claim 1 or 2, wherein the rotating shaft and the rotating shaft are connected between the rotating shaft and the driving motor through a transmission system.
6. The rotary disk type photobioreactor for large-scale cultivation of microalgae according to claim 1 or 2, wherein the transmission system is a chain-gear transmission or a belt-pulley transmission, and an output shaft of the drive motor Gears or pulleys are connected to each other, and gears or pulleys are connected to each rotating shaft. The output shaft of the driving motor and the gear or pulley on each rotating shaft are connected by a chain or a belt; when there are multiple reactor combinations or one reactor When a plurality of rotating shafts are included, one driving motor drives a plurality of rotating shafts or one driving motor drives a rotating shaft.
7. A rotary disk type photobioreactor for large-scale cultivation of microalgae according to claim 1 or 2, The utility model is characterized in that the vent pipe is provided with a small hole or a nozzle, and the vent pipe is selected from an aeration hose or a variable orifice aeration hose.
8. The use of a rotary disk type photobioreactor for scale culture of microalgae according to claim 1, wherein the reactor is placed in an open environment or a closed environment; and the reactor is directly placed in an open environment as needed In a water body, the water body is selected from a lake, a river, a runway pond, a ditch or an oxidation pond; in a closed environment, a seal cap is placed on the upper part of the reactor, or the entire reactor body is placed in a closed vessel or greenhouse, and the closed reactor Set the exhaust port.
9. The use of a rotary disk type photobioreactor for microalgae scale culture according to claim 8, wherein the carbon dioxide gas source is selected from the group consisting of air mixed with CO ₂ , pure CO ₂ gas, industrial CO ₂ gas. One or more of the flue gases or liquid CO ₂ .

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