A topological aeration system for large scale microalgae photobioreactors

Abstract

This invention discloses a topological aeration system for large-scale microalgae photobioreactors, belonging to the field of microalgae cultivation equipment. The invention includes a gas source, a gas distribution network, and multiple aerators. The gas distribution network adopts a multi-level topological structure to distribute the gas source gas in a graded and uniform manner to each aerator. The aerators have aeration holes with a diameter of 0.5 mm and a hole spacing of 1.5 mm. This invention solves the problems of uneven gas distribution and low mass transfer efficiency in existing technologies through the synergistic design of macroscopic topological network layout and microscopic aerator structural parameters. It can form uniform bubbles in large-scale reactors, significantly improving the gas-liquid contact area and mass transfer efficiency, making it suitable for large-scale microalgae cultivation.

Description

Technical Field

[0001] This invention relates to the field of microalgae cultivation equipment technology, and in particular to a topological aeration system for large-scale microalgae photobioreactors. Background Technology

[0002] Microalgae, due to their high photosynthetic efficiency, short growth cycle, and rich content of high-value-added products such as oils and proteins, have shown enormous application potential in fields such as bioenergy, food, feed, and medicine. Achieving efficient, low-cost, and large-scale cultivation of microalgae is key to their industrial application. Photobioreactors are the core equipment for large-scale microalgae cultivation, and the aeration system is crucial. Its role is not only to supplement the carbon dioxide required for microalgae photosynthesis but also to achieve mixing and mass transfer of the gas-liquid-solid three-phase system within the reactor through bubble agitation, reducing algal cell sedimentation and promoting microalgae growth.

[0003] However, when scaling up laboratory or pilot-scale reactors to industrial production scale, traditional aeration systems reveal numerous problems. First, the transition from single-point, single-hole aeration in laboratory cultivation to multi-site, multi-hole aeration in large-scale cultivation easily leads to uneven gas distribution. Second, increasing the aeration rate to compensate for gas unevenness results in a shortened bubble travel time within the reactor, affecting carbon dioxide mass transfer efficiency and significantly increasing energy consumption.

[0004] Therefore, there is an urgent need in the existing technology for an aeration system that is designed for large-scale scenarios, can achieve uniform gas distribution, efficient mass transfer, and low energy consumption. Summary of the Invention

[0005] The purpose of this invention is to provide a topological aeration system for large-scale microalgae photobioreactors to solve the problems of uneven gas distribution, low carbon dioxide mass transfer efficiency and high energy consumption in the prior art.

[0006] To achieve the above objectives, the present invention provides a topological aeration system for a large-scale microalgae photobioreactor, comprising a gas source, a gas distribution network, and multiple aerators; the gas distribution network is connected to the gas source and is composed of gas pipelines with a multi-level topological structure; the multiple aerators are dispersedly arranged within the photobioreactor and connected to the end pipelines of the gas distribution network; the surface of each aerator is provided with multiple micropores for releasing gas, the pore diameter of each micropore is 0.5 mm, and the spacing between adjacent micropores is 1.5 mm.

[0007] Preferably, the gas source includes a carbon dioxide cylinder and an air pump, and the gas source is used to provide gas containing carbon dioxide.

[0008] Preferably, the gas distribution network includes a main pipeline, multiple primary branch pipelines, and multiple secondary branch pipelines. The main pipeline is connected to the gas source, the primary branch pipelines are connected to the main pipeline via five-way connectors, and the secondary branch pipelines are connected to the primary branch pipelines via Y-shaped tees, forming a multi-level tree-like topology.

[0009] Preferably, the aerator is a disc aerator, and the horizontal distance between adjacent aerators is 1.6 to 2.1 times the diameter of the aerator.

[0010] Preferably, the aerator includes a stainless steel outer shell and an air outlet membrane, and the micropores are formed on the air outlet membrane.

[0011] Preferably, a rotor flow meter is also provided between the gas source and the gas distribution network to regulate the gas flow rate entering the gas distribution network.

[0012] Preferably, the rotor flow meter controls the carbon dioxide concentration of the introduced gas to be 5% and the aeration rate to be 0.008 vvm.

[0013] Preferably, the diameters of the main pipe, the first-level branch pipe, and the second-level branch pipe are matched step by step so that the gas flow deviation of each aerator is within a preset range.

[0014] Preferably, the diameter of the aerator is 20cm.

[0015] Preferably, the stainless steel is 304 stainless steel.

[0016] Compared with the prior art, the present invention has the following advantages and technical effects: The topological aeration system for large-scale microalgae photobioreactors provided by this invention effectively solves the problems of uneven gas distribution, low mass transfer efficiency, and high energy consumption in large-scale microalgae cultivation by employing a multi-level topological gas distribution network and combining it with precise parameter design of the aerator's microstructure. On one hand, the multi-level tree-like topological gas distribution network, combined with pipe diameter optimization, achieves a macroscopically uniform distribution of gas supply to each aerator, mitigating the scale-up effect. On the other hand, precisely controlling the aerator's pore size and spacing to 0.5 mm and 1.5 mm, respectively, generates uniform and stable microbubbles even at lower aeration rates, significantly improving gas-liquid mass transfer efficiency and reducing energy consumption. Simultaneously, optimizing the spacing between adjacent aerators ensures the uniformity of the internal flow field of the reactor, providing a uniform and stable environment for microalgae growth. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention.

[0018] Figure 1 This is a schematic diagram of a topological aeration system for a large-scale microalgae photobioreactor according to the present invention.

[0019] Figure 2 This is a schematic diagram of the distribution of the air outlet membrane holes in the aeration system of the present invention.

[0020] Figure 3 This is a graph showing the specific growth rate variation of the aerator membrane under different pore sizes.

[0021] Figure 4 This is a graph showing the specific growth rate variation of the aerator membrane under different pore spacing conditions according to the present invention.

[0022] Figure 5 This is a cloud map showing the liquid phase velocity distribution across the axial section of the reactor of this invention.

[0023] In the diagram: 1. Gas source; 2. Carbon dioxide cylinder; 3. Air pump; 4. Rotor flow meter; 5. Gas distribution network; 6. Main pipeline; 7. Primary branch pipeline; 8. Secondary branch pipeline; 9. Five-way valve; 10. Aerator; 11. Y-type tee. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The described embodiments are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] like Figures 1 to 5 As shown, the present invention provides a topological aeration system for a large-scale microalgae photobioreactor, including a gas source 1, a gas distribution network 5, and multiple aerators 10; the gas distribution network 5 is connected to the gas source 1, and the gas distribution network 5 is composed of gas pipelines with a multi-level topological structure; multiple aerators 10 are dispersedly arranged in the photobioreactor and connected to the end pipeline of the gas distribution network 5; multiple micropores for releasing gas are opened on the surface of the aerators 10, the pore diameter of the micropores is 0.5 mm, and the pore spacing between adjacent micropores is 1.5 mm.

[0026] By setting up a gas distribution network 5 composed of gas pipelines with a multi-level topology, the gas from gas source 1 can be distributed step by step, effectively balancing the gas pressure and flow rate of each branch, and overcoming the problem of large differences in gas supply between the near and far aerators in the traditional single-pipe gas supply method. At the same time, by limiting the micropore diameter and pore spacing of aerator 10 to 0.5 mm and 1.5 mm respectively, stable-sized bubbles (1-3 mm) can be generated under normal gas supply pressure, avoiding excessive bubble collision and merging. Good gas-liquid mixing and mass transfer effects can be maintained even at a low aeration rate, thus achieving uniform gas distribution and efficient mass transfer at both macroscopic and microscopic levels.

[0027] The scheme was further optimized. Gas source 1 includes carbon dioxide cylinder 2 and air pump 3. Gas source 1 is used to provide gas containing carbon dioxide.

[0028] By setting up carbon dioxide cylinder 2 and air pump 3, the ratio of mixed gas can be flexibly adjusted and the concentration of carbon dioxide introduced into the reactor can be precisely controlled to meet the carbon source requirements of microalgae photosynthesis. At the same time, air pump 3 provides sufficient carrier gas to ensure the generation of bubbles and the mixing disturbance within the reactor.

[0029] The scheme is further optimized. The gas distribution network 5 includes a main pipeline 6, multiple primary branch pipelines 7 and multiple secondary branch pipelines 8. The main pipeline 6 is connected to the gas source 1. The primary branch pipelines 7 are connected to the main pipeline 6 through a five-way connector 9. The secondary branch pipelines 8 are connected to the primary branch pipelines 7 through a Y-shaped tee 11, forming a multi-level tree-like topology layout.

[0030] By employing a multi-level tree-like topology layout consisting of a main pipe 6, primary branch pipes 7, and secondary branch pipes 8, and combining it with connectors such as five-way connectors 9 and Y-type tees 11, a progressively uniform gas distribution is achieved. This tree-like structure allows gas to originate from gas source 1, undergo multi-level branching, and effectively balance path length and flow resistance. This ensures that multiple aerators 10 located at different positions in the reactor receive gas with essentially consistent flow rates and pressures, macroscopically eliminating uneven gas supply and laying a uniform gas supply foundation for large-scale cultivation.

[0031] Further optimization of the scheme: the aerator 10 is a disc aerator, and the horizontal distance between adjacent aerators 10 is 1.6 to 2.1 times the diameter of the aerator 10.

[0032] By setting the horizontal spacing between adjacent aerators 10 to 1.6 to 2.1 times their diameter, the bubble plume generated by a single aerator 10 can fully cover its surrounding area and smoothly connect with the working area of ​​adjacent aerators 10. This arrangement creates uniform turbulence across the entire cross-section of the reactor, avoids the existence of mixing dead zones, and achieves macroscopically uniform distribution of gas and nutrients, providing a stable and uniform environment for light, nutrients, and gas-liquid mixing for microalgae.

[0033] The aerator 10 is further optimized to include a stainless steel shell and an air outlet membrane with micropores on the air outlet membrane.

[0034] By using a stainless steel shell and air outlet membrane, the aerator 10 has good corrosion resistance and structural strength, enabling it to work stably in the microalgae culture medium environment for a long time, thus ensuring the reliability and service life of the aeration system.

[0035] To further optimize the scheme, a rotor flowmeter 4 is also installed between the gas source 1 and the gas distribution network 5 to regulate the gas flow rate entering the gas distribution network 5.

[0036] By installing a rotor flow meter 4 between the gas source 1 and the gas distribution network 5, the total gas flow rate into the system can be accurately measured and controlled, thereby dynamically adjusting the gas demand according to the different growth stages of microalgae, achieving precise gas supply, and avoiding gas waste or insufficient supply.

[0037] Further optimization of the scheme: the rotor flow meter 4 controls the carbon dioxide concentration of the introduced gas to 5% and the aeration rate to 0.008vvm.

[0038] By precisely controlling the carbon dioxide concentration of the introduced gas at 5% using a rotor flow meter 4 and the aeration rate at 0.008 vvm, optimal carbon source supply can be provided for microalgae photosynthesis, while avoiding excessively high aeration rates that lead to short bubble residence time and increased energy consumption. Under these parameters, combined with the aerator 10 structure of this invention, energy-saving operation can be achieved while ensuring efficient mass transfer.

[0039] The scheme was further optimized by matching the diameters of the main pipeline 6, the first-level branch pipeline 7, and the second-level branch pipeline 8 step by step, so that the gas flow deviation of each aerator 10 is within the preset range.

[0040] By progressively matching and optimizing the pipe diameters of the main pipe 6, the primary branch pipe 7, and the secondary branch pipe 8, the fluid resistance of each level of pipe can be further balanced, ensuring the hydraulic balance of the entire gas distribution network 5. This allows the air supply flow deviation of the aerator 10 to be controlled within a preset small range regardless of its position in the reactor, further improving the uniformity of gas distribution.

[0041] The design was further optimized so that the diameter of aerator 10 is 20cm.

[0042] Setting the diameter of the aerator 10 to 20 cm is a preferred size for large-scale photobioreactors. This size of aerator 10 facilitates a matrix arrangement at the bottom of large reactors, and combined with a spacing factor of 1.6 to 2.1, it can achieve good coverage and engineering economy.

[0043] The design has been further optimized, and the stainless steel used is 304 stainless steel.

[0044] Using 304 stainless steel as the material for aerator 10 provides excellent corrosion resistance and good machinability, ensuring that aerator 10 can work stably for a long time in an environment with certain salinity and pH in microalgae culture solution. It is also easy to precisely machine micropores with pore size and spacing that meet the design requirements.

[0045] The topological aeration system for large-scale microalgae photobioreactors provided by this invention is implemented as follows: First, based on the size and shape of the reactor, multiple disc aerators 10 are evenly arranged at the bottom of the reactor according to the principle that the horizontal spacing between adjacent aerators 10 is 1.6 to 2.1 times their diameter. Then, a gas distribution network 5 is constructed: the main pipe 6 is connected to the gas source 1 equipped with a rotor flowmeter 4. The main pipe 6 branches into multiple primary branch pipes 7 through multiple five-way connectors 9. Each primary branch pipe 7 then branches into secondary branch pipes 8 through Y-type tees 11. The ends of the secondary branch pipes 8 are connected to the aerators 10, forming a tree-like topology. The pipe diameters of each pipe are designed to be matched step-by-step to ensure hydraulic balance. During the cultivation process, the carbon dioxide cylinder 2 and air pump 3 in the gas source 1 provide a mixed gas containing 5% CO2. After the total flow rate is precisely controlled to 0.008 vvm by the rotor flowmeter 4, it enters the gas distribution network 5. The gas is distributed stepwise through the main pipe 6, the primary branch pipe 7, and the secondary branch pipe 8, and finally uniformly delivered to each aerator 10. The gas escapes through micropores with a diameter of 0.5 mm and a spacing of 1.5 mm on the aerator 10, forming a large number of uniform and stable microbubbles within the reactor. These microbubbles rise to form bubble plumes, driving the surrounding liquid to form a circulating flow. Due to the optimized spacing of the aerators 10, the plume zones are smoothly connected, forming a uniform mixing flow field across the entire cross-section of the reactor, achieving efficient carbon dioxide dissolution and uniform suspension of algal cells.

[0046] This system achieves significant technical results through the synergistic effect of a macroscopic topological gas distribution network and microscopic aerator structural parameters. Macroscopically, the multi-level tree-like gas distribution network 5, combined with pipe diameter matching design, completely solves the problem of uneven gas supply in large-scale reactors, ensuring highly consistent gas supply to each aerator 10 and mitigating scale-up effects. Microscopically, precisely controlling the pore size of the aerator 10 to 0.5 mm generates microbubbles with a diameter of 1-3 mm under normal pressure, significantly increasing the gas-liquid contact area and improving carbon dioxide mass transfer efficiency. Simultaneously, controlling the pore spacing to 1.5 mm effectively suppresses bubble coalescence, maintaining high-efficiency mass transfer even at a low aeration rate of 0.008 vvm, significantly reducing operating energy consumption. Furthermore, optimizing the spacing between adjacent aerators 10 to 1.6–2.1 times the diameter ensures that the bubble plume from a single aerator 10 effectively covers its effective area and smoothly connects with adjacent areas, forming a uniform turbulent field across the reactor cross-section. This provides a stable and uniform growth environment for microalgae, effectively improving the culture density, growth rate, and yield of microalgae. Experiments show that using the aeration parameters of this system significantly improves the specific growth rate of microalgae.

[0047] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Example 1 Experiment on optimization of microporous structure parameters of aerator membrane.

[0048] This example aims to determine the optimal pore size and pore spacing of aerators for large-scale microalgae photobioreactors, providing a basis for the design of topological aeration systems.

[0049] The experiment used a bottom-aerated microalgae photobioreactor with an effective volume of 400 ml. The bottom of the reactor was equipped with a replaceable perforated plate. The gas supply system included a CO2 cylinder, an air pump, a pressure gauge, and a mass flow meter. The mixing ratio of CO2 and air was controlled by the mass flow meter.

[0050] Experimental conditions: Light intensity 80 μmol / (m 2 •s), culture temperature 25℃, gas containing 5% CO2, aeration flow rate 100mL / min; the experimental algal species was Chlorella vulgaris FACHB-31.

[0051] First, we investigated the effect of pore size on microalgal growth: With a fixed hole spacing of 2.5 mm, comparative experiments were conducted using aeration plates with hole diameters of 0.3 mm, 0.5 mm, and 1 mm to determine the specific growth rate of microalgae. The results are as follows: Figure 3 The results show that the microalgae have the highest specific growth rate when the pore size is 0.5 mm.

[0052] Based on this, the effect of pore spacing on microalgal growth was investigated: With a fixed orifice diameter of 0.5 mm, comparative experiments were conducted using aeration plates with orifice spacings of 1 mm, 1.5 mm, 2 mm, and 2.5 mm. The results are as follows: Figure 4 This indicates that the microalgae have the highest specific growth rate when the pore spacing is 1.5 mm.

[0053] Example 2 Aerator spacing determined based on CFD simulation.

[0054] This embodiment uses computational fluid dynamics (CFD) simulation to determine the optimal spacing of aerators within the reactor.

[0055] A two-dimensional axisymmetric model was established, with a reactor diameter of 30cm and a height of 30cm; a disc aerator with a diameter of 10cm was set at the bottom center; the outlet membrane had an aperture of 0.5mm and a hole spacing of 1.5mm. A dual Euler multiphase flow model was adopted, with the liquid phase as the main phase and the gas phase as the dispersed phase; the standard k-ε model was used for the turbulence model. Boundary conditions: The gas inlet is a velocity inlet with a flow rate of 0.1vvm; the top is a degassing boundary; the wall is a no-slip boundary. The mesh uses a triangular grid, with localized refinement in the aerator region, resulting in a total mesh count of approximately 50,000; transient calculations yielded a convergence residual of 10. -3 .

[0056] Simulation results are as follows Figure 5 As shown, after the gas escapes from the aerator, it forms a bubble plume, which drives the liquid phase to form an upward flow and a circulating flow. Using a liquid phase velocity ≥ 0.05 m / s as the criterion for determining the effective mixing area, the effective mixing radial range was measured to be 10 cm outward from the center of the aerator, with an effective mixing diameter of approximately 20 cm. Within the air flow rate range of 0.05–0.2 vvm, the effective mixing diameter is 1.6–2.1 times the aerator diameter.

[0057] Considering both the uniformity of the flow field and the mixing and coverage effect, the horizontal spacing between adjacent aerators in this invention is determined to be twice the diameter of the aerator. This ensures a uniform flow field distribution within the reactor and guarantees effective mixing and mass transfer throughout the entire process.

[0058] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A topological aeration system for large-scale microalgae photobioreactors, characterized in that, It includes a gas source (1), a gas distribution network (5), and multiple aerators (10); the gas distribution network (5) is connected to the gas source (1), and the gas distribution network (5) is composed of gas pipelines with a multi-level topology; multiple aerators (10) are dispersed in the photobioreactor and connected to the end pipeline of the gas distribution network (5); multiple micropores for releasing gas are opened on the surface of the aerators (10), the pore diameter of the micropores is 0.5 mm, and the pore spacing between adjacent micropores is 1.5 mm.

2. The topological aeration system for large-scale microalgae photobioreactors according to claim 1, characterized in that, The gas source (1) includes a carbon dioxide cylinder (2) and an air pump (3), and the gas source (1) is used to provide gas containing carbon dioxide.

3. The topological aeration system for large-scale microalgae photobioreactors according to claim 1, characterized in that, The gas distribution network (5) includes a main pipeline (6), multiple primary branch pipelines (7) and multiple secondary branch pipelines (8). The main pipeline (6) is connected to the gas source (1). The primary branch pipelines (7) are connected to the main pipeline (6) through a five-way connector (9). The secondary branch pipelines (8) are connected to the primary branch pipelines (7) through a Y-shaped tee (11), forming a multi-level tree-like topology layout.

4. The topological aeration system for large-scale microalgae photobioreactors according to claim 1, characterized in that, The aerator (10) is a disc aerator, and the horizontal distance between adjacent aerators (10) is 1.6 to 2.1 times the diameter of the aerator (10).

5. The topological aeration system for large-scale microalgae photobioreactors according to claim 1, characterized in that, The aerator (10) includes a stainless steel shell and an air outlet membrane, with the micropores formed on the air outlet membrane.

6. The topological aeration system for large-scale microalgae photobioreactors according to claim 1, characterized in that, A rotor flow meter (4) is also provided between the gas source (1) and the gas distribution network (5) to regulate the gas flow rate entering the gas distribution network (5).

7. The topological aeration system for large-scale microalgae photobioreactors according to claim 6, characterized in that, The rotor flow meter (4) controls the carbon dioxide concentration of the introduced gas to be 5% and the aeration rate to be 0.008vvm.

8. The topological aeration system for large-scale microalgae photobioreactors according to claim 3, characterized in that, The diameters of the main pipe (6), the first-level branch pipe (7), and the second-level branch pipe (8) are matched step by step so that the gas flow deviation of each aerator (10) is within a preset range.

9. The topological aeration system for large-scale microalgae photobioreactors according to claim 1, characterized in that, The aerator (10) has a diameter of 20 cm.

10. The topological aeration system for large-scale microalgae photobioreactors according to claim 5, characterized in that, The stainless steel is 304 stainless steel.

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