Microalgae cultivation and drying integrated system and method thereof

Abstract

The present application relates to the technical field of microalgae biofuel preparation, and more particularly to a microalgae cultivation and drying integrated system and method thereof, wherein the system comprises a microalgae cultivation device, a compound parabolic concentrator and a microalgae drying device, the compound parabolic concentrator is installed above the microalgae cultivation device, and the microalgae drying device is installed at the focal point of the compound parabolic concentrator; the compound parabolic concentrator transmits sunlight of a first wavelength to the microalgae cultivation device, and reflects sunlight of a second wavelength to the microalgae drying device. The present application uses a compound parabolic concentrator as an optical interface, transmits sunlight of a first wavelength to the microalgae cultivation device below, and reflects sunlight of a second wavelength to the microalgae drying device at the focal point, organically combines the microalgae cultivation and drying processes, realizes efficient matching and utilization of the solar spectrum, and is conducive to improving the process continuity and resource utilization efficiency.

Description

Technical Field

[0001] This invention relates to the technical field of microalgae biofuel preparation, and more specifically, to an integrated system and method for microalgae cultivation and drying. Background Technology

[0002] Microalgae are a type of aquatic microorganism with high photosynthetic efficiency and rapid growth. The lipids synthesized by microalgae are mainly composed of triglycerides, and their carbon chain length and structural composition are similar to those of terrestrial plant lipids. After transesterification, they can be used to produce fatty acid methyl esters, the main component of biodiesel. Furthermore, microalgae fix carbon dioxide through photosynthesis during their growth, achieving a peak photosynthetic efficiency of 5%–7%. Under the same light conditions, the biomass yield of microalgae is far higher than that of terrestrial plants. Based on these outstanding advantages, such as high lipid content, high photosynthetic efficiency, and no competition for land with food crops, microalgae are considered one of the ideal raw material sources for biofuel production. The process of producing biofuel from microalgae typically includes two core stages: cultivation and drying. First, the microalgae are multiplied and accumulate biomass through a cultivation system. After harvesting, fresh algae with extremely high water content are obtained. The harvested algae must then be dehydrated and dried for subsequent storage and fuel refining.

[0003] In existing technologies, the microalgae industry generally adopts a system architecture where "cultivation" and "drying" are independent. After completing the cultivation stage and obtaining the harvested algae, the algal solution needs to be transferred from the cultivation site to a dedicated drying facility for drying. Cultivation and drying are two different physical stages, with independent equipment configurations, operation management, and spatial layouts. This physically separate process architecture brings multiple problems: the algae need to be loaded, transported, and unloaded during the transfer process, adding extra operational steps and labor costs; the distance between the cultivation site and the drying equipment prevents effective heat integration and utilization, requiring the drying equipment to heat the wet algae independently, resulting in low energy efficiency; and the separation of the cultivation system and drying equipment in spatial layout, each occupying independent site resources, leads to low overall land use efficiency. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology that uses a process architecture that separates cultivation and drying physically, and to provide an integrated system and method for microalgae cultivation and drying, which is beneficial to improving process continuity and resource utilization efficiency.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: An integrated microalgae cultivation and drying system is provided, comprising a microalgae cultivation device, a composite parabolic concentrator, and a microalgae drying device. The composite parabolic concentrator is installed above the microalgae cultivation device, and the microalgae drying device is installed at the focal point of the composite parabolic concentrator. The composite parabolic concentrator transmits sunlight of a first wavelength to the microalgae cultivation device and reflects sunlight of a second wavelength to the microalgae drying device.

[0006] Furthermore, the first wavelength is 400nm to 700nm, and the second wavelength is less than 400nm or greater than 700nm.

[0007] Furthermore, the composite parabolic concentrator includes a substrate and a beam-splitting film. The beam-splitting film is deposited on the side of the substrate away from the microalgae cultivation device. The beam-splitting film includes a transition layer, alternating beam-splitting film layers, and a protective layer sequentially stacked on the substrate.

[0008] Furthermore, the substrate is made of ultraviolet fused silica glass, the transition layer is made of tantalum pentoxide, the alternating spectral splitting film is composed of alternating layers of silicon dioxide and titanium dioxide, and the protective layer is made of aluminum oxide.

[0009] Furthermore, the microalgae cultivation device is designed as a rectangular open structure, and the material of the microalgae cultivation device is plexiglass, borosilicate glass, or transparent polyethylene terephthalate.

[0010] Furthermore, the microalgae drying device includes a mounting bracket and a drying container. The mounting bracket is installed at the focal point of the composite parabolic concentrator, and the drying container is detachably connected to the mounting bracket.

[0011] Furthermore, the drying container is semi-circular, with an opening at the top, and is made of glass.

[0012] Furthermore, the composite parabolic concentrator is a symmetrical linear composite parabolic concentrator; a rectangular coordinate system is established with the central vertical axis of the composite parabolic concentrator as the Y-axis and the top surface of the microalgae drying device as the X-axis, and the contour equation of the composite parabolic concentrator is as follows: when hour , ; when hour, ,in, ; In the formula, This represents the x-coordinate of the composite parabolic concentrator; This represents the y-coordinate of the composite parabolic concentrator; This represents the equivalent radius of the microalgae drying device; This indicates the profile rotation angle of the composite parabolic concentrator; This indicates the maximum receiving half-angle of the composite parabolic concentrator; This represents the correction factor.

[0013] Furthermore, the bottom of the drying container is provided with a transparent hydrophobic film for directional discharge of water vapor; the transparent hydrophobic film is made of polydimethylsiloxane or polytetrafluoroethylene.

[0014] This invention also provides an integrated method for microalgae cultivation and drying, applied to the aforementioned integrated microalgae cultivation and drying system, comprising the following steps: During the day, the composite parabolic concentrator transmits sunlight of the first wavelength to the microalgae cultivation device, where the microalgae grow through photosynthesis. The composite parabolic concentrator also reflects and concentrates sunlight of the second wavelength to the microalgae drying device, drying the algae slurry placed inside the device. At night, the microalgae are left in the microalgae cultivation device; the dried algae are taken out of the microalgae drying device, and the next batch of algae slurry to be dried is placed in the microalgae drying device for continued drying the next day.

[0015] Compared with the prior art, the beneficial effects of the present invention are: A composite parabolic concentrator is used as the optical interface to transmit sunlight of the first wavelength to the microalgae cultivation device below, promoting the growth of microalgae within the device. Simultaneously, sunlight of the second wavelength is reflected to the microalgae drying device located at the focal point, achieving photothermal conversion and drying the algae slurry within the drying device. This organic combination of microalgae cultivation and drying processes achieves efficient matching and utilization of the solar spectrum, which is beneficial for improving process continuity and resource utilization efficiency. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the integrated microalgae cultivation and drying system of the present invention. The arrows in the diagram indicate the direction of sunlight irradiation. Figure 2 This is a schematic diagram of the drying container in the integrated microalgae cultivation and drying system of the present invention. In the diagram, the thick arrow indicates the direction of sunlight and the thin arrow indicates the direction of water vapor discharge.

[0017] In the attached diagram: 100, microalgae cultivation device; 200, composite parabolic concentrator; 300, microalgae drying device; 310, drying container; 311, transparent hydrophobic film; 400, sunlight; 410, transmitted light; 420, reflected light; 500, water vapor. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The present invention will be further described below with reference to specific embodiments. The accompanying drawings are for illustrative purposes only, representing schematic diagrams only, not actual pictures, and should not be construed as limiting this patent. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0019] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," and "right" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms describing positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting this patent. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances. Furthermore, if the embodiments of the present invention involve descriptions such as "first" and "second," these descriptions are only for descriptive purposes and should not be construed as indicating or implying their relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. In addition, the meaning of "and / or" in the text is that it includes three parallel options. Taking "A and / or B" as an example, it includes option A, option B, or an option that satisfies both A and B.

[0020] Example 1 This embodiment is the first embodiment of an integrated microalgae cultivation and drying system, such as... Figure 1As shown, the device includes a microalgae cultivation device 100, a compound parabolic concentrator 200 (CPC), and a microalgae drying device 300. The compound parabolic concentrator 200 is mounted above the microalgae cultivation device 100, and the microalgae drying device 300 is mounted at the focal point of the compound parabolic concentrator 200. The compound parabolic concentrator 200 has spectrally selective transmission and reflection functions. It transmits sunlight of a first wavelength (410) to the microalgae cultivation device 100, driving the photosynthesis and growth of the microalgae. It also reflects sunlight of a second wavelength (420) to the microalgae drying device 300, providing the heat energy required for drying.

[0021] The inventors discovered that microalgae photosynthesis primarily relies on the absorption of blue light (400-450 nm) and red light (640-725 nm). Light energy in other wavelengths is often lost through absorption, conversion into heat, transmission, or reflection, severely limiting the overall efficiency of light energy utilization. Furthermore, microalgae exhibit significant light absorption characteristics in the near-infrared spectral region, and water also has a high absorption rate in this band, further enhancing the light absorption and heat generation effect of the algal slurry. Therefore, the first wavelength is 400 nm to 700 nm, and the second wavelength is either less than 400 nm or greater than 700 nm. This achieves an efficient, tiered distribution of sunlight (400 nm) between the cultivation and drying functional areas.

[0022] The composite parabolic concentrator 200 includes a substrate and a beam-splitting film. The beam-splitting film is deposited on the side of the substrate away from the microalgae cultivation device 100. The beam-splitting film includes a transition layer, alternating beam-splitting film layers, and a protective layer sequentially stacked on the substrate. The substrate is made of ultraviolet fused silica glass, the transition layer is made of tantalum pentoxide, the alternating beam-splitting film layers are composed of alternating layers of silicon dioxide and titanium dioxide, and the protective layer is made of aluminum oxide. In some embodiments, the thickness of a single film layer is 60 nm to 100 nm, and the total coating thickness is 500 nm to 800 nm. This structure enables high transmission of photosynthetically active radiation with wavelengths from 400 nm to 700 nm into the microalgae cultivation device 100; ultraviolet light with wavelengths below 400 nm, near-infrared light with wavelengths above 700 nm, and infrared light are highly reflected and focused by the CPC parabolic concentrator to the microalgae drying device 300 at the focal point, thereby completing the full-spectrum cascade distribution and utilization of solar energy.

[0023] In this embodiment, the maximum receiving half-angle of the composite parabolic concentrator 200 is set. The composite parabolic concentrator 200 has an overall length of 2.81 m and a width of 0.32 m, with a light-receiving opening width of 0.1764 m. The microalgae drying device 300 is semi-circular in shape, with an equivalent radius of 1.90 cm. The CPC's focusing ratio is set to 2-3, and its surface is coated with multi-layered beam-dispersing films. Through optimized film system design, the transmittance in the 400 nm-700 nm wavelength range is not less than 0.9, while the reflectance at wavelengths outside this range is all above 0.9. The drying container 310 of the microalgae drying device is made of transparent glass with a broadband transmittance of 1 (or close to 1).

[0024] This embodiment presents an integrated microalgae cultivation and drying system, which, compared to traditional solar drying methods, exhibits higher photothermal conversion efficiency, more uniform temperature distribution, and a significantly better water evaporation rate. The solar spectral energy incident per unit area is simultaneously and efficiently used for both photosynthetic cultivation and thermal drying of the microalgae, thus breaking the high energy consumption pattern caused by the separation of cultivation and drying processes in traditional methods.

[0025] Example 2 This embodiment is a second embodiment of an integrated microalgae cultivation and drying system. Similar to the first embodiment, the difference lies in that the microalgae cultivation device 100 is a rectangular open-top shape, meaning the entire device is a cuboid with rounded corners and an opening at the top. The device 100 is made of plexiglass, borosilicate glass, or transparent polyethylene terephthalate (PET). Specifically, transparent PMMA plexiglass can be used. In some embodiments, the microalgae cultivation device 100 can also integrate carbon dioxide inlet and outlet, algae-water mixture inlet and outlet, and connect to components such as an algae sampler, water pump, and water inlet for convenient microalgae cultivation. The microalgae cultivation device 100 has external dimensions of 500-120 mm in length, 300-600 mm in width, and 200-250 mm in height, with an internal effective liquid depth of 150-200 mm. The microalgae cultivation device 100 can be horizontally installed below the CPC using a bracket, with a vertical distance of 50-200 mm between them. This integrated microalgae cultivation and drying system can be set up in multiple groups, with the multiple groups arranged in a modular, parallel configuration along an east-west direction.

[0026] The microalgae drying device 300 includes a mounting bracket and a drying container 310. The mounting bracket is installed at the focal point of the composite parabolic concentrator 200, and the drying container 310 is detachably connected to the mounting bracket. By setting up the mounting bracket and the drying container 310, after the algae slurry is dried, the drying container 310 containing the dried algae can be directly removed and replaced with a drying container 310 containing algae slurry to be dried, which is beneficial for the drying cycle.

[0027] like Figure 2 As shown, the drying container 310 is semi-circular with an opening at the top. The drying container 310 is used to hold the algae slurry to be dried. The drying container 310 is made of glass, specifically a low thermal conductivity material, to reduce downward heat loss. Utilizing the high light absorption characteristics of the algae slurry in the infrared band, it receives high-density infrared radiation reflected and focused by the CPC, effectively absorbing light and generating heat, thus heating the bottom of the algae slurry. The top of the drying container 310 is open and exposed to sunlight 400, directly irradiating and heating the upper surface of the algae slurry, thereby creating a temperature field distribution with coordinated heating from both the top and bottom surfaces. This achieves synergistic heating of the algae slurry from both sides, improving temperature uniformity and evaporation rate.

[0028] The composite parabolic concentrator 200 is a symmetrical linear composite parabolic concentrator. A rectangular coordinate system is established with the central vertical axis of the composite parabolic concentrator 200 as the Y-axis and the top surface of the microalgae drying device 300 as the X-axis. The microalgae drying device 300 is a perfect semicircle. The contour equation of the composite parabolic concentrator 200 is as follows: when hour , ; when hour, ,in, ; In the formula, The x-coordinate represents the composite parabolic concentrator 200; The y-coordinate represents the composite parabolic concentrator 200; This represents the equivalent radius of the microalgae drying device 300; This indicates the profile rotation angle of the composite parabolic concentrator 200; This indicates the maximum receiving half-angle of the composite parabolic concentrator 200; This represents the correction factor.

[0029] The bottom of the drying container 310 is provided with a transparent hydrophobic film 311 for directional discharge of water vapor 500, that is, the transparent hydrophobic film 311 is placed between the algae slurry and the drying container 310. The transparent hydrophobic film (311) is made of polydimethylsiloxane (PDMS) or polytetrafluoroethylene (PTFE). By setting the transparent hydrophobic film 311, an additional evaporation and discharge channel for water vapor is opened at the bottom of the algae slurry, thereby significantly improving the overall evaporation efficiency. The transparent hydrophobic film 311 is characterized by its ability to effectively allow water vapor to pass through while simultaneously blocking the penetration of liquid water and microalgae.

[0030] Considering the requirements for infrared transmittance, hydrophobic properties, structural strength, and temperature resistance, the thickness of the transparent hydrophobic film 311 ranges from 0.25 mm to 1.5 mm, with the specific value determined based on actual engineering needs. This thickness range ensures that the film maintains high transmittance in the infrared band above 700 nm, while also possessing good hydrophobicity, flexibility, and high-temperature resistance. It is not easily deformed or damaged during long-term use and can stably achieve the functions of directional water vapor discharge at 500 nm and blocking liquid water backflow.

[0031] In this embodiment, the high-density infrared radiation reflected light 420, which is focused by CPC reflection, and sunlight 400 work together on the algal slurry, causing the temperature of the algal slurry to rise rapidly and the water to evaporate continuously. The generated water vapor 500 is discharged outward through the transparent hydrophobic film 311, while the solids in the algal slurry are gradually concentrated and dried, finally obtaining dried algae with a water content that meets the requirements of subsequent refining.

[0032] Example 3 This embodiment is a first embodiment of an integrated method for microalgae cultivation and drying, applied to the integrated microalgae cultivation and drying system provided in Embodiment 1 or Embodiment 2, and includes the following steps: During the daytime, the composite parabolic concentrator 200 transmits sunlight of the first wavelength to the microalgae cultivation device 100, where the microalgae undergo photosynthesis and grow. The composite parabolic concentrator 200 also reflects and concentrates sunlight of the second wavelength onto the microalgae drying device 300, while sunlight 400 directly illuminates the top of the microalgae drying device 300, drying the algae slurry inside. Overall, the addition of the CPC beam-splitting structure does not adversely affect microalgae cultivation; on the contrary, it avoids overheating caused by direct absorption of infrared light by the microalgae in the cultivation area, thereby improving cultivation efficiency.

[0033] At night, the microalgae remain in the microalgae cultivation device 100; the dried algae are removed from the microalgae drying device 300, and the next batch of algae slurry to be dried is placed in the microalgae drying device 300 for continued drying the next day. This operation can be achieved in various ways. When applied to the integrated microalgae cultivation and drying system provided in Example 2, two drying containers 310 can be configured for each CPC, and the algae slurry samples to be dried can be placed in each of the two drying containers 310. During the drying operation, only one drying container 310 is placed at the CPC focal point. After sunset, the heat supply stops, the dried drying container 310 is removed, and the second drying container 310 is placed at the focal point for drying the next day. The algae powder extraction process can be carried out at night, and the new algae slurry is placed in the first drying basin for drying the next day. Through the above cycle, continuous daily microalgae drying and algae powder extraction can be achieved.

[0034] This embodiment presents an integrated method for microalgae cultivation and drying, which integrates the microalgae cultivation device 100 and the microalgae drying device 300 into the same system, sharing the same solar energy 400 resource. This achieves the segmented and functional tiered utilization of the full spectrum of solar energy 400, significantly improving the overall energy efficiency and land use efficiency of the system.

[0035] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0036] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An integrated system for microalgae cultivation and drying, characterized in that, The device includes a microalgae cultivation device (100), a composite parabolic concentrator (200), and a microalgae drying device (300). The composite parabolic concentrator (200) is installed above the microalgae cultivation device (100), and the microalgae drying device (300) is installed at the focal point of the composite parabolic concentrator (200). The composite parabolic concentrator (200) transmits sunlight of a first wavelength to the microalgae cultivation device (100) and reflects sunlight of a second wavelength to the microalgae drying device (300).

2. The integrated microalgae cultivation and drying system according to claim 1, characterized in that, The first wavelength is 400nm to 700nm, and the second wavelength is less than 400nm or greater than 700nm.

3. The integrated microalgae cultivation and drying system according to claim 2, characterized in that, The composite parabolic concentrator (200) includes a substrate and a beam-splitting film. The beam-splitting film is deposited on the side of the substrate away from the microalgae cultivation device (100). The beam-splitting film includes a transition layer, alternating beam-splitting film layers and a protective layer sequentially stacked on the substrate.

4. The integrated microalgae cultivation and drying system according to claim 3, characterized in that, The substrate is made of ultraviolet fused silica glass, the transition layer is made of tantalum pentoxide, the alternating spectral dispersive film is composed of alternating layers of silicon dioxide and titanium dioxide, and the protective layer is made of aluminum oxide.

5. The integrated microalgae cultivation and drying system according to claim 1, characterized in that, The microalgae cultivation device (100) is designed as a rectangular open shape, and the material of the microalgae cultivation device (100) is plexiglass, borosilicate glass or transparent polyethylene terephthalate.

6. The integrated microalgae cultivation and drying system according to any one of claims 1 to 5, characterized in that, The microalgae drying device (300) includes a mounting bracket and a drying container (310). The mounting bracket is installed at the focal point of the composite parabolic concentrator (200), and the drying container (310) is detachably connected to the mounting bracket.

7. The integrated microalgae cultivation and drying system according to claim 6, characterized in that, The drying container (310) is semi-circular, and the top of the drying container (310) is provided with an opening. The material of the drying container (310) is glass.

8. The integrated microalgae cultivation and drying system according to claim 7, characterized in that, The composite parabolic concentrator (200) is a symmetrical linear composite parabolic concentrator; a rectangular coordinate system is established with the central vertical axis of the composite parabolic concentrator (200) as the Y-axis and the top surface of the drying container (310) as the X-axis. The contour equation of the composite parabolic concentrator (200) is as follows: when hour, ; when hour, ,in, ; In the formula, The x-coordinate represents the composite parabolic concentrator (200); The y-coordinate represents the composite parabolic concentrator (200); The equivalent radius of the microalgae drying device (300) is indicated; The outline rotation angle of the composite parabolic concentrator (200) is indicated; This indicates the maximum receiving half-angle of the composite parabolic concentrator (200); This represents the correction factor.

9. The integrated microalgae cultivation and drying system according to claim 7, characterized in that, The bottom of the drying container (310) is provided with a transparent hydrophobic film (311) for directional discharge of water vapor (500); the transparent hydrophobic film (311) is made of polydimethylsiloxane or polytetrafluoroethylene.

10. A method for integrating microalgae cultivation and drying, characterized in that, Applied to the integrated microalgae cultivation and drying system as described in any one of claims 1 to 9, Includes the following steps: During the day, the composite parabolic concentrator (200) transmits sunlight of the first wavelength to the microalgae cultivation device (100), where microalgae grow through photosynthesis. The composite parabolic concentrator (200) reflects and concentrates sunlight of the second wavelength to the microalgae drying device (300) to dry the algae slurry placed in the microalgae drying device (300). At night, the microalgae are left in the microalgae cultivation device (100); the dried algae are taken out from the microalgae drying device (300), and the next batch of algae slurry to be dried is placed in the microalgae drying device (300) for continued drying the next day.

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