Gas retention type partitioned carbon supplement system of microalgae raceway pond and use method

Abstract

This invention discloses a gas retention-type zoned carbon supplementation system for microalgae raceway ponds and its usage method, belonging to the technical field of microalgae cultivation. It includes a raceway pond module and a carbon supplementation module, with the carbon supplementation module placed in the algae culture channel. The carbon supplementation module is connected to a gas buffer tank located outside the raceway pond module, and the gas buffer tank is connected to a circulating air pump, which is connected to a carbon-containing gas source tank. Through the full contact between the carbon supplementation module and the flowing algae culture, unabsorbed exhaust gas is recycled and reused, improving carbon dioxide utilization, reducing exhaust gas emissions and pH fluctuations. This invention is suitable for open or semi-open microalgae raceway ponds. It is applicable to Spirulina, Chlorella, Scenedesmus, Dunaliella salina, Haematococcus pluvialis, Micrococcus microcarpa, and other microalgae suitable for cultivation in open or semi-open raceway ponds, especially for large-scale microalgae cultivation and carbon dioxide emission reduction projects using pure carbon dioxide, air-carbon dioxide mixtures, fermentation exhaust gas, industrial exhaust gas, or coal-fired flue gas as carbon sources.

Description

Technical Field

[0001] This invention relates to the technical field of microalgae cultivation, and more particularly to a gas retention-type partitioned carbon supplementation system for microalgae raceway ponds and its usage method. Background Technology

[0002] Currently, microalgae are a class of photosynthetic microorganisms capable of synthesizing biomass using light energy and inorganic carbon sources. Their cells are rich in proteins, polysaccharides, pigments, polyunsaturated fatty acids, and other bioactive substances, making them valuable in food, feed, health products, bioenergy, wastewater treatment, and carbon dioxide emission reduction. With the development of carbon emission reduction and biomanufacturing technologies, low-cost, large-scale, and stable microalgae cultivation systems have become an important equipment foundation for the industrialization of microalgae and the biological fixation of carbon dioxide.

[0003] Large-scale microalgae cultivation facilities mainly include closed photobioreactors and open culture tanks. Closed photobioreactors have advantages such as low pollution risk, controllable parameters, and high yield per unit volume, but they also have problems such as large equipment investment, complex cleaning and maintenance, and high energy consumption for temperature control and circulation. Open culture tanks, especially raceway tanks, remain the main facility form for the industrial cultivation of microalgae such as Spirulina, Chlorella, Dunaliella, and Scenedesmus due to their simple structure, low construction cost, convenient maintenance, and suitability for large-scale construction.

[0004] A typical microalgae raceway pool consists of the pool body, a partition wall, and a paddlewheel. The partition wall divides the pool into two interconnected algal culture channels, and the paddlewheel drives the algal culture to circulate along the annular channels. Under light conditions, microalgae cells absorb inorganic carbon sources such as carbon dioxide or bicarbonate for photosynthesis and release oxygen. Raceway pools can operate in open-air environments or can be equipped with transparent arched canopies, photovoltaic shading structures, or other semi-open structures to reduce the impact of wind, sand, rain, low temperatures, and external pollution.

[0005] Carbon sources are one of the major nutrient sources required for microalgae photosynthesis and a key factor influencing microalgae cultivation costs and carbon dioxide fixation efficiency. In open raceway tanks, common carbon supplementation methods include directly introducing carbon dioxide gas or a mixture of gases containing carbon dioxide into the culture medium, or adding inorganic salts such as bicarbonate and carbonate. For processes using carbon dioxide gas as the carbon source, gas-liquid mass transfer efficiency directly determines carbon source utilization, culture medium pH stability, and microalgae biomass rate.

[0006] Traditional running track pools are typically shallow, ranging from 10cm to 50cm in depth. While this shallow water layer facilitates light penetration and reduces circulation resistance, it also results in shorter ascent paths and residence times for carbon dioxide bubbles in the culture medium, leading to insufficient gas-liquid contact time. Direct aeration at the bottom of the running track pool causes unabsorbed carbon dioxide to rapidly escape into the air, wasting carbon resources. Increasing the aeration rate or carbon dioxide concentration, on the other hand, can easily cause a sudden drop in local pH, bubble coalescence, increased foam, and higher energy consumption.

[0007] In existing technologies, to improve the carbon dioxide utilization rate of open runway pools, various solutions have been proposed, including trap-type carbon replenishment devices, submerged hood-type carbon replenishment devices, escape prevention hoods, microporous aeration, bypass carbon replenishment tanks, combined functional reactors, and integrated cultivation and concentration devices. These technologies, by extending gas residence time, increasing gas-liquid contact area, or employing bypass devices to improve carbon source utilization efficiency, can alleviate the problem of low carbon dioxide absorption efficiency in runway pools to some extent.

[0008] Regarding the aforementioned technologies, the applicant found that existing carbon supplementation technologies still have shortcomings. First, some in-situ carbon supplementation devices require alterations to the bottom or flow channel structure of the raceway pool, potentially increasing flow resistance or affecting the existing impermeable layer, hindering low-cost retrofitting of existing raceway pools. Second, some covers or escape-prevention structures reduce the effective light-receiving area after covering the liquid surface, affecting algal photosynthesis. Third, most carbon supplementation devices only focus on single-point or single-area carbon supplementation and cannot adjust the pH according to differences in different locations within the raceway pool, easily leading to localized acidification while other areas remain in a state of carbon source deficiency.

[0009] In the raceway tank, the algal solution circulates along a circular flow channel. As carbon dioxide is absorbed, the pH of the culture medium decreases. With continued flow and photosynthesis, the inorganic carbon source is consumed, and the pH gradually rises again. Therefore, in actual production, a spatial pH gradient often exists in different channels and locations within the raceway tank. Using a single carbon replenishment point or timed, quantitative carbon replenishment makes it difficult to precisely match the carbon dioxide requirements of microalgae in different areas.

[0010] Furthermore, when flue gas, fermentation exhaust gas, or industrial waste gas is used as a carbon source, the concentration, flow rate, and impurity composition of carbon dioxide in the gas fluctuate. Directly introducing flue gas into the raceway pond not only results in insufficient carbon dioxide utilization but may also lead to pH fluctuations in the culture medium, gas escape, and increased heat and moisture losses due to excessive aeration. Therefore, open raceway ponds urgently require an engineered system that can extend the residence time of carbon dioxide in the shallow algal solution, recover undissolved waste gas, and adjust the carbon supplementation intensity based on pH feedback zones.

[0011] For the large number of traditional raceway ponds that have already been built, the most valuable way to modify them is not to rebuild the entire raceway pond, but to add carbon supplementation modules, exhaust gas recovery pipelines and sensor control systems locally without changing the main structure, partition walls, impellers and basic algae culture channels of the raceway pond. This will improve the carbon source utilization efficiency and the stability of the culture process. Therefore, it is urgent to develop a gas retention-type zoned carbon supplementation system for microalgae raceway ponds. Summary of the Invention

[0012] This invention addresses the shortcomings of existing technologies by providing a gas retention-type zoned carbon replenishment system for microalgae raceway ponds and its usage method.

[0013] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0014] A gas retention-type zoned carbon supplementation system for a microalgae raceway pond includes a raceway pond module. The raceway pond module includes a raceway pond body with a partition wall in the middle. At least one impeller is installed inside the raceway pond, and the rotation of the impeller forms an annular flow channel for algae culture within the raceway pond body. At least one carbon supplementation module is installed inside the raceway pond module and placed in the algae culture channel. The carbon supplementation module is connected to a gas buffer tank located outside the raceway pond module. The gas buffer tank is connected to a circulating air pump, and the circulating air pump is connected to a carbon-containing gas source tank.

[0015] Furthermore, the carbon supplementation module includes a gas retention hood and a microporous aeration belt. The gas retention hood is inverted inside the algal culture channel, and the microporous aeration belt is placed at the bottom of the gas retention hood, facing or close to the bottom of the algal culture channel. The top of the gas retention hood has a tail gas collection port, and a tail gas recovery pipe is connected to the tail gas collection port. The tail gas recovery pipe is connected to the gas buffer tank.

[0016] Furthermore, the gas retention hood is at least one of the following structures: inverted U-shape, arc shape, semi-circular shape, arch shape, flat hood shape, or box-shaped hood shape. A gap for algae liquid flow is maintained between the lower edge of the gas retention hood and the bottom or side wall of the algae liquid culture channel. The algae liquid passes through the gas-liquid contact area below the gas retention hood under the drive of the paddle wheel.

[0017] Furthermore, the microporous aeration belt is at least one of the following: microporous aeration tube, microporous aeration disc, microporous ceramic strip, microporous membrane tube, microporous silicone tube, or perforated aeration belt.

[0018] Furthermore, the exhaust gas recovery pipe is equipped with a one-way valve, a steam trap, a condensate collector, a filter, or a gas-liquid separator.

[0019] Furthermore, the raceway module includes a controller, and at least one pH sensor is installed in the algae culture channel, with the pH sensor electrically connected to the controller.

[0020] Furthermore, the carbon-containing gas source tank is connected to the circulating air pump and the carbon replenishment module respectively through a carbon replenishment pipeline. Several solenoid valves are installed on the carbon replenishment pipeline, and the solenoid valves are electrically connected to the controller.

[0021] Furthermore, the gas buffer tank is equipped with a pressure sensor, a safety relief valve, and a drain outlet.

[0022] Furthermore, the gas in the carbon-containing gas source tank is at least one of the following: pure carbon dioxide, a mixture of air and carbon dioxide, fermentation tail gas, biogas purification tail gas, coal-fired flue gas, gas-fired flue gas, industrial tail gas, or pre-treated carbon dioxide-containing waste gas.

[0023] A method for using a gas retention-based zoned carbon supplementation system in a microalgae raceway pond includes the following steps:

[0024] S1 adds culture medium and inoculates microalgae into the raceway pool body, and starts the paddle wheel to make the algal solution circulate along the algal solution culture channel.

[0025] S2 activates the pH sensor and controller to monitor the pH value of algal solution in different areas of the raceway pool in real time.

[0026] When the pH value of the algal solution in a certain area is higher than the set upper limit, the controller opens the solenoid valve of the corresponding carbon replenishment pipeline, so that the carbon-containing gas in the carbon-containing gas source tank enters the lower part of the gas retention hood through the microporous aeration belt.

[0027] S4 carbon-containing gas is retained in the gas retention hood and comes into contact with the algal solution flowing through the area, while carbon dioxide is absorbed by the culture medium.

[0028] The unabsorbed exhaust gas from S5 enters the gas buffer tank through the exhaust gas collection port and exhaust gas recovery pipe, and is then pumped to the carbon replenishment pipeline by the circulating gas pump.

[0029] S6 When the pH value of the algal solution in a certain area is lower than the set lower limit, the controller closes the solenoid valve of the corresponding carbon supplementation pipeline.

[0030] S7 repeats the above-mentioned partitioned carbon replenishment process until the algal culture reaches the set cell concentration or the harvest time is reached.

[0031] In summary, compared with the prior art, the beneficial effects of the above technical solution are:

[0032] 1. The present invention aims to overcome the problems of short carbon dioxide gas-liquid contact time, large tail gas loss, significant local pH fluctuation and rough control of carbon replenishment points in the existing microalgae raceway carbon replenishment process. By setting carbon replenishment modules in different areas of the raceway module and collecting and recycling the unabsorbed tail gas, the carbon dioxide absorption efficiency and the overall carbon replenishment uniformity of the raceway are improved.

[0033] 2. The present invention provides a carbon supplementation method using the above system, which utilizes pH sensors distributed in different areas of the runway pool module to detect the pH of the culture medium in real time, selectively opens the solenoid valve of the corresponding carbon supplementation module according to the pH signal of each area, and sends the unabsorbed tail gas in the gas retention hood into the gas buffer tank through the tail gas recovery pipe, and then returns it to the main carbon supplementation pipe or carbon supplementation branch through the circulating air pump, so as to realize the multiple utilization of carbon dioxide.

[0034] 3. This invention extends the residence time of carbon dioxide in the shallow raceway pool by using a gas retention hood, significantly reducing gas escape caused by direct aeration. A tail gas reuse loop is formed through a tail gas collection port, tail gas recovery pipe, gas buffer tank, and circulating air pump, improving the overall utilization rate of carbon dioxide. Multiple pH sensors and multiple solenoid valves enable zoned feedback carbon supplementation, reducing the problem of excessively low local pH or insufficient carbon source in some areas. The carbon supplementation module can be locally installed in the existing raceway pool flow channel without requiring overall changes to the main structure of the raceway pool, facilitating low-cost retrofitting of existing raceway pools. The system is suitable for various carbon-containing gas sources such as pure carbon dioxide, mixed gas, fermentation tail gas, and industrial flue gas, exhibiting good engineering adaptability.

[0035] 4. The core of this invention does not lie in using microporous aeration alone or using a hood alone to prevent escape, but in integrating the microporous aeration belt, gas retention hood, exhaust gas collection port, exhaust gas recovery pipe, gas buffer tank, circulating air pump, zoned pH sensor, solenoid valve and controller into a gas retention zoned carbon replenishment system suitable for microalgae raceway ponds, thereby realizing retention, recovery, circulation and zoned feedback control of the carbon replenishment process. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the overall structure of the gas retention zone carbon replenishment system of the present invention;

[0037] Figure 2 This is a schematic cross-sectional view of the carbon supplementation module of the present invention in the algal culture channel.

[0038] Figure 3 This is a schematic diagram of the exhaust gas recovery and recirculation carbon replenishment pipeline structure of the present invention;

[0039] Figure 4 This is a schematic diagram of the pH zone feedback control operation of the present invention.

[0040] Explanation of reference numerals in the attached figures:

[0041] 1. Raceway pool body; 2. Partition wall; 3. Paddle wheel; 4. Algae culture channel; 5. Carbon supplementation module; 6. Microporous aeration belt; 7. Gas retention hood; 8. Exhaust gas collection port; 9. Exhaust gas recovery pipe; 10. Gas buffer tank; 11. Circulating air pump; 12. Carbon-containing gas source tank; 13. pH sensor; 14. Solenoid valve; 15. Controller. Detailed Implementation

[0042] The principles and features of the present invention are described below with reference to all the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0043] This invention discloses a gas retention zoned carbon replenishment system for a microalgae raceway pond and its usage method.

[0044] Reference Figures 1 to 4 As shown, a gas retention-type partitioned carbon supplementation system for a microalgae raceway pond includes a raceway pond body 1, a partition wall 2, a paddle wheel 3, an algae culture channel 4, a carbon supplementation module 5, a microporous aeration belt 6, a gas retention hood 7, an exhaust gas collection port 8, an exhaust gas recovery pipe 9, a gas buffer tank 10, a circulating air pump 11, a carbon-containing gas source tank 12, a pH sensor 13, a solenoid valve 14, and a controller 15. The partition wall 2 is installed inside the raceway pond body 1, dividing the raceway pond body 1 into two interconnected algae culture channels 4. The paddle wheel 3 is installed in the algae culture channels 4 to drive the algae culture to circulate along the algae culture channels 4.

[0045] Carbon supplementation modules 5 are disposed in one or more sections of the algal culture channel 4, preferably in straight sections, before bends, after bends, or in areas where the pH rises rapidly. Each carbon supplementation module 5 includes a microporous aeration band 6 disposed at or near the bottom of the algal culture channel 4, and a gas retention hood 7 covering the microporous aeration band 6. The microporous aeration band 6 is connected to a carbon-containing gas source tank 12 and is used to release carbon dioxide or a carbon dioxide-containing gas mixture in the form of small bubbles to the area below the gas retention hood 7.

[0046] The gas retention hood 7 has an inverted U-shape, arc shape, semi-circular shape, arch shape, flat hood shape, or box-shaped structure. A gap is maintained between the lower edge of the gas retention hood 7 and the bottom or sidewall of the algal culture channel 4 to allow the algal solution to pass through the gas-liquid contact area below the gas retention hood 7 under the drive of the paddle wheel 3. After being released from the microporous aeration zone 6, the bubbles remain below the gas retention hood 7. The algal solution flow shears and disturbs the bubbles and the retained gas phase, thereby prolonging the gas residence time and improving the carbon dioxide absorption rate.

[0047] A tail gas collection port 8 is installed at the top or high position of the gas retention hood 7, and the tail gas collection port 8 is connected to the tail gas recovery pipe 9. Gas that is not absorbed by the culture medium accumulates in the gas retention hood 7, enters the tail gas recovery pipe 9 through the tail gas collection port 8, and is then transported to the gas buffer tank 10. The gas buffer tank 10 is connected to the carbon supplementation main pipe or carbon supplementation branch through the circulating air pump 11, so that the tail gas can re-enter the microporous aeration belt 6 or be mixed with fresh carbon-containing gas source tank 12 for reuse in carbon supplementation.

[0048] The carbon-containing gas source tank 12 can be pure carbon dioxide, a mixture of air and carbon dioxide, fermentation tail gas, biogas purification tail gas, coal-fired flue gas, gas-fired flue gas, industrial tail gas, or pre-treated carbon dioxide-containing waste gas. A main carbon replenishment pipe and branches are provided between the carbon-containing gas source tank 12 and each carbon replenishment module 5. A solenoid valve 14 is installed on each carbon replenishment branch, and the solenoid valve 14 is electrically connected to the controller 15.

[0049] pH sensors 13 are installed in different sections of the algal culture channel 4. Preferably, at least one pH sensor 13 is installed upstream, downstream, or in the same area of ​​each carbon supplementation zone. The pH sensor 13 is electrically connected to the controller 15 and is used to detect the pH value of the culture medium in the corresponding area in real time. The controller 15 controls the opening and closing of the solenoid valve 14 of the corresponding carbon supplementation branch according to the feedback signal of the pH sensor 13, and controls the start / stop or operating frequency of the circulating air pump 11.

[0050] The raceway pool body 1 is divided into multiple control zones along the algae flow direction. Each control zone includes at least one pH sensor 13 and at least one carbon supplementation module 5. The controller 15 determines whether to activate the corresponding carbon supplementation module 5 based on whether the pH value of a control zone is higher than a set upper limit; when the pH of the zone drops to a set lower limit, the controller 15 closes the corresponding solenoid valve 14. The carbon supplementation modules 5 in different zones can operate independently, or they can operate sequentially or in a pulse manner according to the algae flow direction.

[0051] The microporous aeration zone 6 can be a microporous aeration tube, a microporous aeration disc, a microporous ceramic strip, a microporous membrane tube, a microporous silicone tube, or a perforated aeration zone. The micropore diameter is preferably from 1 μm to 200 μm, more preferably from 4 μm to 100 μm; the gas release intensity is preferably from 0.01 VVM to 0.5 VVM. The microporous aeration zone 6 can be arranged along the width of the algal culture channel 4, along the direction of algal flow, or multiple zones can be arranged in parallel.

[0052] The lower edge of the gas retention hood 7 is 1 cm to 15 cm above the bottom of the algae culture channel 4, preferably 3 cm to 10 cm. The height of the top of the gas retention hood 7 above the liquid surface is determined according to the operating water depth and the gas retention space. It is preferable that the gas retention hood 7 is completely or mostly below the liquid surface to avoid reducing the effective light-receiving area of ​​the liquid surface.

[0053] The gas trap 7 can be made of transparent or semi-transparent materials, such as acrylic, polycarbonate, fiberglass, transparent PVC, or transparent PP, or opaque materials such as stainless steel, PE, and FRP. Transparent or semi-transparent materials are preferred to minimize light obstruction. The gas trap 7 can be fixed to the bottom or side wall of the algae culture channel 4 using brackets, pressure plates, clips, bolts, or counterweights, and can be disassembled for cleaning.

[0054] The exhaust gas recovery pipe 9 is equipped with a one-way valve, a steam trap, a condensate collector, a filter, or a gas-liquid separator to prevent algal liquid from flowing back into the gas buffer tank 10 and the circulating air pump 11. The gas buffer tank 10 may be equipped with a pressure sensor, a safety relief valve, and a drain outlet to ensure the safety and stability of the exhaust gas recovery process.

[0055] The controller 15 can be a PLC controller 15, a microcontroller controller 15, an industrial computer, a data acquisition control cabinet, or a remote monitoring system. The controller 15 can record data from each pH sensor 13, the opening and closing status of the solenoid valve 14, the operating status of the circulating air pump 11, the flow rate of the carbon-containing gas source tank 12, the amount of exhaust gas recovered, and the pressure of the gas buffer tank 10. It can also perform zoned carbon replenishment, pulse carbon replenishment, exhaust gas circulation carbon replenishment, and abnormal alarms according to the set program.

[0056] like Figure 1 As shown, in the gas retention partition carbon supplementation system of the present invention, the partition wall 2 is located in the middle of the racetrack pool body 1, dividing the racetrack pool body 1 into two algae culture channels 4 connected end to end. The impeller 3 is located in one of the algae culture channels 4, so that the algae solution circulates along the racetrack pool body 1.

[0057] The carbon supplementation module 5 can be installed in the straight section, the section before the bend, or the section after the bend in the algal culture channel 4. For example... Figure 1 As shown, two carbon replenishment modules 5 are installed in the main body 1 of the raceway pool, located on the straight sections of the two algae culture channels 4 respectively. Each carbon replenishment module 5 includes a microporous aeration belt 6 and a gas retention hood 7. The microporous aeration belt 6 is located at or near the bottom of the algae culture channel 4, and the gas retention hood 7 covers the microporous aeration belt 6, with a gap maintained between the lower edge of the gas retention hood 7 and the bottom of the algae culture channel 4 for algae to pass through.

[0058] The carbon-containing gas source tank 12 is connected to the microporous aeration belt 6 via carbon replenishment pipelines (main carbon replenishment pipe and each carbon replenishment branch). Each carbon replenishment branch is equipped with a solenoid valve 14, and the controller 15 controls the opening and closing of the solenoid valve 14 based on the feedback signal from the pH sensor 13. The gas released by the carbon replenishment module 5 is retained below the gas retention hood 7 and comes into contact with the algal liquid flowing through this area. Unabsorbed exhaust gas enters the exhaust gas recovery pipe 9 through the exhaust gas collection port 8. The exhaust gas recovery pipe 9 transports the exhaust gas to the gas buffer tank 10, which is connected to the main carbon replenishment pipe or carbon replenishment branch via the circulating air pump 11.

[0059] like Figure 2As shown, the carbon supplementation module 5 is installed inside the algal culture channel 4, and the algal culture solution flows in the direction of the arrow within the channel 4. A pH sensor 13 is located upstream or near the carbon supplementation module 5 to detect the pH of the culture solution before it enters the carbon supplementation area. The carbon-containing gas source tank 12 enters the microporous aeration zone 6 via a solenoid valve 14. The microporous aeration zone 6 releases small bubbles, which are confined below the gas retention hood 7 as they rise, forming a gas-liquid contact zone. The gas phase and bubble clusters within the gas retention hood 7 are sheared and disturbed by the algal culture solution flow, and carbon dioxide continuously dissolves and enters the culture solution.

[0060] The gas retention hood 7 can be a transparent acrylic arched cover, with a length of 0.5m to 5m, a width of 0.2m to 3m, and a height of 0.05m to 0.5m. For an algae culture channel 4 that is 3m wide, a gas retention hood 7 with a width of 1m to 2.5m can be installed to prevent complete blockage of the channel. The gas retention hood 7 can be fixed to the bottom of the tank by side supports or by counterweights, facilitating subsequent disassembly, cleaning, and maintenance.

[0061] The microporous aeration zone 6 can be made of microporous silicone tubing, microporous aeration coil, ceramic microporous strips, or perforated aeration tubes. The pore size of the microporous aeration zone 6 is preferably from 4 μm to 100 μm, and the gas flow rate is preferably from 0.01 VVM to 0.2 VVM. The bubbles released through the microporous aeration zone 6 are small in size and have a large gas-liquid interface area, which, under the constraint of the gas retention hood 7, can significantly prolong the contact time of the bubbles in the culture medium.

[0062] The exhaust gas collection port 8 is located at the top of the gas retention hood 7 or at a high position within the hood. The exhaust gas collection port 8 can be a short pipe connector, flange connector, quick-connect connector, or threaded connector. The exhaust gas collection port 8 connects to the exhaust gas recovery pipe 9, which is preferably made of corrosion-resistant flexible tubing, PVC pipe, PP pipe, or stainless steel pipe. The exhaust gas recovery pipe 9 may be equipped with a check valve and a gas-liquid separator to prevent backflow of the culture medium into the gas buffer tank 10.

[0063] like Figure 3 As shown, the carbon-containing gas output from the carbon-containing gas source tank 12 enters the carbon replenishment module 5 via the solenoid valve 14. Unabsorbed exhaust gas in the carbon replenishment module 5 enters the gas buffer tank 10 via the exhaust gas collection port 8 and the exhaust gas recovery pipe 9. The exhaust gas in the gas buffer tank 10 is then pumped back to the main carbon replenishment pipe or branch line by the circulating air pump 11, mixed with fresh carbon-containing gas, and re-enters the carbon replenishment module 5. The controller 15 is connected to the pH sensor 13, the solenoid valve 14, and the circulating air pump 11 via the dashed signal line to achieve feedback control.

[0064] The gas buffer tank 10 can be a metal tank, fiberglass tank, plastic tank, or flexible air bladder, and preferably equipped with a pressure sensor, drain valve, and safety pressure relief valve. The circulating air pump 11 can be a diaphragm pump, Roots blower, small blower, or corrosion-resistant gas circulating pump. To prevent water vapor in the exhaust gas from condensing in the pipeline and affecting the operation of the air pump, a condensate collector or gas-liquid separator can be installed before the inlet of the gas buffer tank 10.

[0065] like Figure 4 As shown, the raceway pool body 1 is divided into regions A, B, C, and D along the direction of algae flow. Each region is equipped with at least one carbon replenishment module 5 and at least one pH sensor 13. Solenoid valves 14 are installed on the carbon replenishment branches of each carbon replenishment module 5. Each pH sensor 13 and solenoid valve 14 is connected to a controller 15. The controller 15 independently controls the corresponding solenoid valve 14 based on the detection results of the pH sensor 13 in each region, thus achieving zoned carbon replenishment.

[0066] In zone control mode, if the pH of zone A is higher than the set upper limit, while the pH of zones B, C, and D remains within the appropriate range, controller 15 only opens the solenoid valve 14 corresponding to zone A, enabling the carbon supplementation module 5 of zone A to operate. When the pH of zone A drops to the set lower limit, controller 15 closes the solenoid valve 14. Other zones supplement carbon independently according to the same logic. This method can avoid local over- or under-carbon supplementation caused by synchronous carbon supplementation across the entire pool.

[0067] In sequential carbon replenishment mode, the controller 15 performs short-duration pulse carbon replenishment in the order of region A, region B, region C, and region D, based on the algal solution flow direction and pH spatial distribution. For example, each region is replenished with carbon for 30 seconds to 5 minutes, then stopped for 1 to 30 minutes before the pH is detected again, and the timing of the next round of carbon replenishment is adjusted according to the rate of pH change. Sequential carbon replenishment mode is suitable for scenarios with limited gas source flow or where it is desirable to reduce instantaneous ventilation.

[0068] Example 1:

[0069] A two-module raceway pool zonal carbon supplementation system. A traditional raceway pool, 100m long, 6m wide, with a single flow channel width of 3m and a liquid depth of 20cm to 35cm, is used as the raceway pool body 1. A partition wall 2 is located in the middle, and a paddle wheel 3 drives the algal liquid flow at a velocity of 20cm / s to 35cm / s. A carbon supplementation module 5 is installed in each of the two straight algal liquid cultivation channels 4. The carbon supplementation module 5 is 2.0m long, 2.0m wide, and 0.25m high. The gas retention hood 7 is made of transparent acrylic material, and the microporous aeration belt 6 uses microporous silicone aeration pipes with an aeration pore diameter of approximately 20μm.

[0070] In this embodiment, the carbon-containing gas source tank 12 contains a mixed gas of 5% to 15% carbon dioxide. The gas enters the carbon replenishment main pipe after being depressurized and filtered. Each carbon replenishment branch is equipped with a solenoid valve 14, which is controlled by a controller 15. The top of the gas retention hood 7 is equipped with a tail gas collection port 8. The tail gas recovery pipe 9 delivers the tail gas to a 100L gas buffer tank 10. The outlet of the gas buffer tank 10 is connected to a circulating air pump 11, and the outlet of the circulating air pump 11 is connected back to the carbon replenishment main pipe.

[0071] During operation, when the pH sensor 13 upstream of the carbon replenishment module 5 detects a pH higher than 10.0, the controller 15 opens the corresponding solenoid valve 14, setting the gas flow rate to 0.05VVM to 0.2VVM; when the pH in the corresponding area drops to 9.6, the controller 15 closes the solenoid valve 14. The circulating air pump 11 starts when the pressure in the gas buffer tank 10 is higher than the set value, returning the recovered tail gas to the carbon replenishment main pipe; it stops when the pressure is lower than the set value.

[0072] Example 2:

[0073] Carbon supplementation method for Spirulina culture. Spirulina platensis was cultured using a two-module zoned carbon supplementation system as described in Example 1. The culture medium was Zarrouk medium, the inoculation density was 0.3 g / L (dry weight), the initial water depth was 25 cm, and the algal flow rate was 25 cm / s. During cultivation, the pH range was controlled between 9.5 and 10.2. Carbon supplementation module 5 was activated when the pH of any zone exceeded 10.2, and stopped when the pH of that zone fell below 9.6. Carbonate, nitrogen source, and trace element concentrations were monitored daily and supplemented accordingly.

[0074] After continuous cultivation for 6 to 8 days, the dry weight concentration of Spirulina can reach 1.3 g / L to 1.7 g / L, and the algal cell yield per unit area can reach 14 g / m² / d to 18 g / m² / d. Compared with direct bottom aeration for carbon supplementation, this system can significantly reduce carbon dioxide loss in the exhaust gas; compared with single carbon supplementation point control, the pH fluctuation range of different channels is smaller, and the pH spatial distribution of the culture medium is more uniform. The above data are reference data based on the cultivation conditions and engineering operation logic design of similar racetrack pools. In actual production, adjustments can be made according to the on-site gas source concentration, flow rate, algal species, and climatic conditions.

[0075] Compare with Example 1:

[0076] Traditional direct aeration for carbon supplementation. This method uses the same raceway tank, algae strain, culture medium, inoculation density, and flow rate as Example 2, but omits the gas retention hood 7, exhaust gas collection port 8, exhaust gas recovery pipe 9, gas buffer tank 10, and circulating air pump 11. Instead, a carbon dioxide-containing mixed gas is directly introduced into the raceway tank through a regular aeration pipe at only one location. In this method, the gas rises a short distance in the shallow water layer, resulting in a large number of bubbles dissipating after reaching the surface, leading to low carbon dioxide utilization. The pH drops rapidly near the carbon supplementation point, while the pH in areas far from the point may remain relatively high.

[0077] Compare with Example 2:

[0078] A single-hood enclosure without exhaust gas recovery and carbon replenishment is used. The same raceway pool and algae species as in Example 2 are employed. A gas retention hood 7 and a microporous aeration belt 6 are installed in a carbon replenishment zone, but the exhaust gas is directly discharged through the top of the hood without being recovered by the gas buffer tank 10 and the circulating air pump 11. Compared to traditional direct aeration, this method can extend the gas residence time, but unabsorbed exhaust gas is still emitted, resulting in lower carbon source utilization efficiency than the exhaust gas recovery and circulation method of this invention.

[0079] Example 3:

[0080] A four-zone pH feedback carbon supplementation system is used. A raceway pool, 120m long, 8m wide, and with a single flow channel width of 4m, is divided into four zones (ABCD) along the algal flow direction. Each zone is equipped with one carbon supplementation module 5, two pH sensors 13, and one solenoid valve 14. The carbon supplementation module 5 is 1.5m long, 3.0m wide, and 0.20m high, and its gas retention hood 7 is made of transparent polycarbonate material. The controller 15 uses a PLC to collect data from the eight pH sensors 13 and control the four solenoid valves 14 and the circulating air pump 11.

[0081] In this embodiment, pH control in each region is determined by a combination of average and difference values. If the average pH of the two pH sensors 13 in a certain region is higher than the set upper limit, the controller 15 opens the solenoid valve 14 in that region. If the average pH is lower than the set lower limit, the solenoid valve 14 in that region is closed. If the pH difference between the upstream and downstream of that region is greater than 0.3, the controller 15 extends the carbon replenishment time or increases the pulse frequency to improve the uniformity of carbon replenishment in that section.

[0082] Example 4:

[0083] A method for carbon supplementation in Chlorella cultivation. Chlorella was cultured using the four-zone carbon supplementation system described in Example 3. The culture medium was BG11, with an inoculation density of 0.2 g / L (dry weight), a water depth of 20 cm, and an algal flow rate of 25 cm / s to 40 cm / s. The carbon-containing gas source tank 12 contained a mixture of air and carbon dioxide, with a carbon dioxide volume fraction of 1% to 5%. The pH range for each zone was controlled between 6.8 and 7.8. Carbon supplementation module 5 was activated when the pH of any zone exceeded 7.8, and was stopped when the pH fell below 7.0.

[0084] After continuous cultivation for 5 to 7 days, the dry weight concentration of Chlorella reached 0.8 g / L to 1.2 g / L, and the yield per unit area reached 16 g / m² / d to 20 g / m² / d. Compared with single-point carbon supplementation, the pH fluctuation range in each area was reduced, and the supply of inorganic carbon in the culture medium was more stable. Since most of the gas retention hood 7 is located below the liquid surface and is made of transparent material, it has minimal light obstruction.

[0085] Example 5:

[0086] Application of flue gas carbon supplementation. Flue gas from coal-fired or gas-fired combustion is pretreated by dust removal, cooling, desulfurization, or other necessary pretreatment processes and used as a carbon-containing gas source tank 12. After entering a gas buffer or mixing device, the flue gas enters the carbon supplementation module 5 through a solenoid valve 14. A pH sensor 13 is used to determine the carbon supplementation needs of each area, and a controller 15 adjusts the flue gas introduction time based on the pH signal. The exhaust gas enters the gas buffer tank 10 through the exhaust gas collection port 8 and the exhaust gas recovery pipe 9, and a circulating air pump 11 delivers the exhaust gas back to the carbon supplementation pipeline.

[0087] In flue gas carbon supplementation applications, oxygen, carbon dioxide, sulfur oxides, nitrogen oxides, or pressure monitoring instruments can be installed on the gas buffer tank 10 or the tail gas recovery pipe 9. When the concentration of pollutants in the gas exceeds the set threshold, the controller 15 can close the flue gas inlet valve and switch to pure carbon dioxide or air-carbon dioxide mixture. Alternatively, it can activate the bypass exhaust or purification device to protect microalgae cells from short-term high-concentration pollutant gas impacts.

[0088] Example 6:

[0089] A combination of in-situ and out-of-situ carbon replenishment. In existing raceway pools, if a bypass carbon replenishment tank or culture concentration device is already installed, the carbon replenishment module 5 of this invention can be used in parallel. During periods of strong daylight and rapid pH increase, the in-situ gas retention carbon replenishment module 5 is activated first; at night or during periods of low light, the bypass carbon replenishment tank can be activated for low-flow carbon replenishment. The controller 15 determines the operating priority of in-situ or bypass carbon replenishment based on data from the pH sensor 13, temperature sensor, and turbidimeter.

[0090] Example 7:

[0091] Modular upgrade approach. For existing racetrack pools, the carbon supplementation module 5 can be designed as a movable module. The microporous aeration belt 6, gas retention hood 7, and exhaust gas collection port 8 are pre-installed on a bottom bracket, which is fixed inside the algae culture channel 4 by counterweights or clamps, without damaging the pool bottom. The carbon-containing gas source tank 12, gas buffer tank 10, circulating air pump 11, and controller 15 are installed on the outside of the racetrack pool. The carbon supplementation branch is connected to the microporous aeration belt 6 via a hose, and the exhaust gas recovery pipe 9 is connected to the gas buffer tank 10 via a hose. This method is suitable for the rapid upgrade of existing racetrack pools.

[0092] Example 8:

[0093] Operational Safety and Maintenance. During system operation, controller 15 periodically records pH, carbon supplementation duration, number of times solenoid valve 14 opens, operating time of circulating air pump 11, and pressure of gas buffer tank 10. When the pressure of gas buffer tank 10 exceeds the safety limit, controller 15 closes the corresponding solenoid valve 14 or opens the safety relief valve; when the pH sensor 13 signal is abnormal, the system can switch to a timed low-flow carbon supplementation mode and trigger an alarm. The gas retention hood 7 and the microporous aeration belt 6 can be periodically disassembled and cleaned to prevent algal sludge, carbonate deposition, or biofilm blockage.

[0094] Example 9:

[0095] Carbon supplementation efficiency reference evaluation. Comparing the same raceway pool, the same algal species, and the same total carbon dioxide input, the gas retention-type zoned carbon supplementation system of this invention, due to the installation of the gas retention hood 7 and the exhaust gas recovery and circulation, can improve the effective utilization rate of carbon dioxide compared to direct bottom aeration. For practical engineering, the carbon dioxide absorption rate can be calculated by measuring the carbon dioxide concentration in the inlet and exhaust gases, the gas flow rate, and the change in inorganic carbon in the culture medium; the carbon supplementation effect can also be evaluated by pH stabilization time, the increase in algal cells per unit carbon dioxide input, and the yield per unit area.

[0096] In the above embodiments, the number of carbon replenishment modules 5 is not limited by the drawings and can be one, two, four or more. For large runway pools, multiple carbon replenishment modules 5 can be distributed along the flow channel direction or arranged in parallel along the width of the flow channel in the same section. Multiple gas retention hoods 7 can share a single gas buffer tank 10 and circulating air pump 11, or multiple gas buffer tanks 10 and circulating air pumps 11 can be arranged in groups.

[0097] The pH sensor 13 in this invention can also be used in combination with a dissolved inorganic carbon sensor, a carbon dioxide sensor, a turbidimeter, a temperature sensor, a dissolved oxygen sensor, or a liquid level sensor. The controller 15 can further optimize the timing of carbon replenishment based on a multi-parameter model. For example, when the pH is high, dissolved oxygen is high, and light intensity is strong, the system can increase the carbon replenishment frequency; when light intensity is weak or temperature is low, the system can decrease the carbon replenishment frequency to avoid unnecessary gas consumption.

[0098] This invention can be combined with technologies such as raceway pool water depth control, photovoltaic power supply, wind power supply, bypass harvesting and concentration, online nutrient salt supplementation, transparent covering structure and physical filtration for pests and diseases to form a low-cost microalgae cultivation engineering system suitable for different climate zones, different algae species and different carbon source conditions.

[0099] The above-described specific embodiments show that the present invention extends the gas residence time by using the gas retention hood 7, reduces carbon dioxide emission by using the exhaust gas collection port 8 and the exhaust gas recovery pipe 9, enables exhaust gas reuse by using the gas buffer tank 10 and the circulating air pump 11, and enables zoned feedback carbon supplementation by using the pH sensor 13, the solenoid valve 14 and the controller 15. Therefore, it can improve the carbon source utilization efficiency and cultivation stability of open or semi-open microalgae raceway ponds.

[0100] Reference Figures 1 to 4 As shown, the present invention also provides a method for using a gas retention-type zoned carbon supplementation method in a microalgae raceway pond, comprising the following steps:

[0101] S1 adds culture medium and inoculates microalgae into the raceway pool body 1, and starts the paddle wheel 3 to make the algal solution circulate along the algal solution culture channel 4.

[0102] S2 activates pH sensor 13 and controller 15 to monitor the pH value of algal solution in different areas of the raceway pool body 1 in real time;

[0103] S3 When the pH value of the algal solution in a certain area is higher than the set upper limit, the controller 15 opens the solenoid valve 14 of the corresponding carbon replenishment pipeline, so that the carbon-containing gas in the carbon-containing gas source tank 12 enters the lower part of the gas retention hood 7 through the microporous aeration belt 6.

[0104] S4 carbon-containing gas is retained in the gas retention hood 7 and comes into contact with the algal liquid flowing through the area, while carbon dioxide is absorbed by the culture medium.

[0105] The unabsorbed exhaust gas from S5 enters the gas buffer tank 10 through the exhaust gas collection port 8 and the exhaust gas recovery pipe 9, and is then pumped to the carbon replenishment pipeline by the circulating gas pump 11.

[0106] S6 When the pH value of the algal solution in a certain area is lower than the set lower limit, the controller 15 closes the solenoid valve 14 of the corresponding carbon supplementation pipeline;

[0107] S7 repeats the above-mentioned partitioned carbon replenishment process until the algal culture reaches the set cell concentration or the harvest time is reached.

[0108] In the above methods, for Spirulina culture, the upper limit of pH setting is preferably 9.8 to 10.5, and the lower limit of pH setting is preferably 9.2 to 9.8; for Chlorella, Scenedesmus or Microcystis globulus culture, the upper limit of pH setting is preferably 7.5 to 8.5, and the lower limit of pH setting is preferably 6.8 to 7.5; for Dunaliella salina culture, the pH setting range can be adjusted according to the salinity of the culture medium and the target growth conditions.

[0109] In the above method, the controller 15 can determine the carbon source consumption intensity of each area based on the pH rise rate. When the pH rise rate of a certain area is higher than the set threshold, the controller 15 can activate the carbon replenishment module 5 in that area in advance or increase the carbon replenishment frequency; when the pH value changes slowly or the pressure of the recovered tail gas in the gas buffer tank 10 is high, the controller 15 can prioritize using the circulating air pump 11 to transport the recovered tail gas, thereby reducing the gas consumption of the fresh carbon-containing gas source tank 12.

[0110] In the above method, the carbon-containing gas source tank 12 can supply gas continuously at a low flow rate or intermittently with pulses. During pulsed gas supply, the solenoid valve 14 opens and closes according to a set cycle, causing a phased gas retention and absorption process within the gas retention hood 7. Pulsed carbon supplementation can reduce energy consumption and gas escape caused by continuous aeration, while also helping to maintain the pH stability of the culture medium.

[0111] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A gas retention-type partitioned carbon supplementation system for a microalgae raceway pond, comprising a raceway pond module, the raceway pond module comprising a raceway pond body (1), a partition wall (2) provided in the middle of the raceway pond body (1), and at least one impeller (3) provided in the raceway pond, wherein the rotation of the impeller (3) forms an annular flow channel (4) for algae culture within the raceway pond body (1), characterized in that: The raceway pool module is equipped with at least one carbon replenishment module (5). The carbon replenishment module (5) is placed in the algae culture channel (4). The carbon replenishment module (5) is connected to a gas buffer tank (10) placed outside the raceway pool module. The gas buffer tank (10) is connected to a circulating air pump (11). The circulating air pump (11) is connected to a carbon-containing gas source tank (12).

2. The gas retention zoned carbon replenishment system for a microalgae raceway pond according to claim 1, characterized in that: The carbon supplementation module (5) includes a gas retention hood (7) and a microporous aeration belt (6). The gas retention hood (7) is inverted inside the algal culture channel (4). The microporous aeration belt (6) is placed at the bottom of the gas retention hood (7) and faces or is close to the bottom of the algal culture channel (4). The top of the gas retention hood (7) is provided with a tail gas collection port (8). A tail gas recovery pipe (9) is connected to the tail gas collection port (8). The tail gas recovery pipe (9) is connected to the gas buffer tank (10).

3. The gas retention zoned carbon replenishment system for a microalgae raceway pond according to claim 2, characterized in that: The gas retention hood (7) is at least one of the following structures: inverted U-shape, arc shape, semi-circular shape, arch shape, flat hood shape or box shape. The lower edge of the gas retention hood (7) and the bottom or side wall of the algal culture channel (4) retain an algal flow gap. The algal liquid passes through the gas-liquid contact area below the gas retention hood (7) under the drive of the paddle wheel (3).

4. The gas retention zoned carbon replenishment system for a microalgae raceway pond according to claim 2, characterized in that: The microporous aeration belt (6) is at least one of the following: microporous aeration tube, microporous aeration disc, microporous ceramic strip, microporous membrane tube, microporous silicone tube, or perforated aeration belt.

5. The gas retention zoned carbon replenishment system for a microalgae raceway pond according to claim 2, characterized in that: The exhaust gas recovery pipe (9) is equipped with a one-way valve, a steam trap, a condensate collector, a filter, or a gas-liquid separator.

6. The gas retention zoned carbon replenishment system for a microalgae raceway pond according to claim 1, characterized in that: The raceway module includes a controller (15), and at least one pH sensor (13) is provided in the algae culture channel (4). The pH sensor (13) is electrically connected to the controller (15).

7. The gas retention zoned carbon replenishment system for a microalgae raceway pond according to claim 6, characterized in that: The carbon-containing gas source tank (12) is connected to the circulating gas pump (11) and the carbon replenishment module (5) respectively through the carbon replenishment pipeline. Several solenoid valves (14) are provided on the carbon replenishment pipeline, and the solenoid valves (14) are electrically connected to the controller (15).

8. The gas retention zoned carbon replenishment system for a microalgae raceway pond according to claim 1, characterized in that: The gas buffer tank (10) is equipped with a pressure sensor, a safety relief valve and a drain outlet.

9. A gas retention-type zoned carbon replenishment system for a microalgae raceway pond according to claim 1, characterized in that: The gas in the carbon-containing gas source tank (12) is at least one of the following: pure carbon dioxide, air and carbon dioxide mixture, fermentation tail gas, biogas purification tail gas, coal-fired flue gas, gas-fired flue gas, industrial tail gas, or pre-treated carbon dioxide-containing waste gas.

10. A method for using a gas retention-type zoned carbon supplementation system in a microalgae raceway pond, characterized in that, Includes the following steps: S1 adds culture medium and inoculates microalgae in the raceway pool body (1), and starts the paddle wheel (3) to make the algal solution circulate along the algal solution culture channel (4); S2 activates the pH sensor (13) and controller (15) to monitor the pH value of algal solution in different areas of the raceway pool body (1) in real time; S3 When the pH value of the algal solution in a certain area is higher than the set upper limit, the controller (15) opens the solenoid valve (14) of the corresponding carbon supplementation pipeline, so that the carbon-containing gas in the carbon-containing gas source tank (12) enters the gas retention hood (7) below through the microporous aeration belt (6). S4 carbon-containing gas is retained in the gas retention hood (7) and comes into contact with the algal liquid flowing through the area; carbon dioxide is absorbed by the culture medium. The unabsorbed exhaust gas from S5 enters the gas buffer tank (10) through the exhaust gas collection port (8) and the exhaust gas recovery pipe (9), and is pumped to the carbon replenishment pipeline by the circulating gas pump (11). S6 When the pH value of the algal solution in a certain area is lower than the set lower limit, the controller (15) closes the solenoid valve (14) of the corresponding carbon supplementation pipeline; S7 repeats the above-mentioned partitioned carbon replenishment process until the algal culture reaches the set cell concentration or the harvest time is reached.

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