Device and method for culturing microalgae in wastewater and pyrolyzing to prepare high-quality bio-oil

Abstract

The present invention relates to the field of environmental protection and biomass energy technology, and in particular provides a device and method for culturing microalgae with wastewater and pyrolyzing to prepare high-quality bio-oil. The device includes a microalgae culture box, a solid-liquid separation device, a water quality detection device, a drying device, a crushing device, a stirring device, and a catalytic pyrolysis purification system. The outlet of the microalgae culture box is connected to the inlet of the solid-liquid separation device through a pipeline, the liquid outlet of the solid-liquid separation device is connected to the water quality detection device, the solid outlet of the solid-liquid separation device is connected to the inlet of the drying device, the outlet of the drying device is connected to the inlet of the crushing device, the outlet of the crushing device is connected to the inlet of the stirring device, and the outlet of the stirring device is connected to the inlet of the catalytic pyrolysis purification system. The present invention aims to reduce the cost of microalgae cultivation, improve the quality of bio-oil, and realize the resource utilization of wastewater.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection and biomass energy, and in particular provides a device and a method for culturing microalgae in wastewater and pyrolyzing them to prepare high-quality bio-oil. Background Art

[0002] With the growing global energy demand and the improvement of environmental protection awareness, the search for clean and renewable alternative energy has become a major issue facing society. As a biological resource with fast growth rate, high photosynthesis efficiency and the ability to accumulate a large amount of lipids, microalgae have shown great application potential in the field of biofuels in recent years. In particular, Chlorella, due to its unique biological characteristics and wide adaptability, is regarded as one of the important raw materials for the third generation of biofuels. However, traditional microalgae biofuel production technology faces many challenges. First, the cost of microalgae cultivation is high, especially the preparation of culture medium and the supply of nutrients have become key factors restricting its commercial application. Secondly, the bio-oil obtained by pyrolysis of microalgae often contains high oxygen and nitrogen content, resulting in low calorific value and poor stability, which is difficult to meet the standards of high-quality fuel. In addition, the rich proteins and other non-lipid components in microalgae are prone to produce harmful substances during the pyrolysis process, further reducing the quality of bio-oil.

[0003] In response to the above problems, researchers have begun to explore new ways to use wastewater as a culture medium for microalgae, promoting the growth of microalgae through nutrients in wastewater, and realizing the resource utilization of wastewater. In addition, the application of exogenous induction methods has also significantly improved the lipid accumulation efficiency of microalgae, providing possibilities for improving the quality and efficiency of bio-oil. However, how to accurately control microalgae culture conditions through intelligent means, and how to combine efficient catalytic pyrolysis technology to further improve the quality of bio-oil, are still hot spots and difficulties in current research.

[0004] Therefore, the present invention proposes a method for cultivating microalgae by using wastewater, optimizing the cultivation conditions in combination with an intelligent monitoring system, promoting lipid enrichment of Chlorella, and using efficient catalytic pyrolysis technology to reduce the oxygen and nitrogen content in bio-oil and improve the fuel performance of bio-oil. This method can not only reduce the cost of microalgae cultivation and realize the resource utilization of wastewater, but also significantly improve the quality of bio-oil, providing strong support for the commercial application of microalgae-based biofuels. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a device and method for culturing microalgae with wastewater and pyrolyzing to prepare high-quality bio-oil, aiming to reduce the cost of microalgae cultivation, improve the quality of bio-oil, and realize the resource utilization of wastewater.

[0006] The present invention is implemented in this way. It provides a device for culturing microalgae in wastewater and pyrolyzing to prepare high-quality bio-oil, comprising a microalgae culture box, a solid-liquid separation device, a water quality detection device, a drying device, a crushing device, a stirring device, and a catalytic pyrolysis purification system. The outlet of the microalgae culture box is connected to the inlet of the solid-liquid separation device through a pipeline, the liquid outlet of the solid-liquid separation device is connected to the water quality detection device, the solid outlet of the solid-liquid separation device is connected to the inlet of the drying device, the outlet of the drying device is connected to the inlet of the crushing device, the outlet of the crushing device is connected to the inlet of the stirring device, and the outlet of the stirring device is connected to the inlet of the catalytic pyrolysis purification system.

[0007] Preferably, the water quality detection device is provided with two outlets, one outlet is connected to a discharge pipeline, and the other outlet is connected to the microalgae culture box through a circulation pipeline.

[0008] Further preferably, a catalyst inlet is provided on the stirring device; and the catalytic pyrolysis purification system comprises a pyrolysis reactor, a condensation bottle, a glass bottle and an air bag which are connected in sequence through pipelines.

[0009] More preferably, the number of the condensation bottle and the number of the glass bottle are both two.

[0010] Further preferably, a heater and a cooler are provided on the outer wall of the pyrolysis reactor.

[0011] The present invention provides a method for culturing microalgae with wastewater and preparing high-quality bio-oil by pyrolysis. Based on the above-mentioned device for culturing microalgae with wastewater and preparing high-quality bio-oil by pyrolysis, the method comprises the following steps:

[0012] Step 1: wastewater pretreatment;

[0013] Step 2: adding the pretreated wastewater and microalgae into the microalgae culture box for culture, and monitoring and adjusting the parameters of the culture environment;

[0014] Step 3: After the microalgae grow to the logarithmic phase, the microalgae culture solution is discharged into the solid-liquid separation device for solid-liquid separation;

[0015] Step 4: Discharging the separated microalgae into the drying device for drying, and then discharging the separated microalgae into the crushing device for crushing to form microalgae powder;

[0016] Step 5: Discharging the microalgae powder into the stirring device, adding the metal-loaded HZSM-5 catalyst into the microalgae powder, and stirring and mixing;

[0017] Step 6: the microalgae powder mixed with the catalyst is discharged into the catalytic pyrolysis purification system, catalytically pyrolyzed in an inert atmosphere at a high temperature to generate bio-oil, the bio-oil is collected and the bio-oil is tested for indicators;

[0018] Step 7: Test the quality of the wastewater separated by the solid-liquid separation equipment in step 3, and recycle or safely discharge it.

[0019] Preferably, in step 1, the wastewater is urban sewage, industrial wastewater or agricultural wastewater, and the wastewater pretreatment is to remove solid impurities, organic pollutants and heavy metal ions in the wastewater by one or more of physical, biological and chemical methods.

[0020] Further preferably, in step 2, the parameters of the culture environment are adjusted according to the following standards: culture temperature 28±1°C, light intensity 5000Lux for 24 hours uninterrupted continuous illumination, concentrations of wastewater plant hormones, antibiotics and heavy metals maintained below 0.5mg / L, wherein the content of antibiotic CTC is maintained at 0.2mg / L.

[0021] Further preferably, in step 5, the metal-loaded HZSM-5 catalyst is Ni / HZSM-5, and the mass ratio of Ni / HZSM-5 to microalgae powder is 1:2.

[0022] Further preferably, in step 6, the pyrolysis temperature is 600° C., and the oxygen content, nitrogen content and calorific value of the bio-oil are detected.

[0023] Compared with the prior art, the advantages of the present invention are:

[0024] 1. The present invention solves the problem of high cost of microalgae cultivation in traditional microalgae biofuel production technology. By using pretreated industrial wastewater, agricultural wastewater or urban sewage as culture medium, the nutrients in the wastewater are fully utilized, the cost of culture medium preparation and nutrient supply is reduced, and at the same time, the resource utilization of wastewater is realized, reducing environmental pollution.

[0025] 2. The present invention monitors various parameters of the culture environment in real time through intelligent monitoring, accurately regulates the culture conditions of microalgae, promotes the lipid enrichment of Chlorella, and automatically adjusts the concentrations of plant hormones, antibiotics and heavy metals in the wastewater, as well as the light intensity according to monitoring feedback, to provide the best growth environment for Chlorella, promote its growth and induce lipid enrichment, thereby improving the lipid accumulation efficiency of microalgae.

[0026] 3. The present invention effectively reduces the oxygen and nitrogen contents in microalgae pyrolysis bio-oil, improves its calorific value and stability, adopts catalytic pyrolysis technology, combined with metal-loaded HZSM-5 catalyst, especially Ni / HZSM-5 catalyst, and exhibits excellent performance in denitrification and deoxygenation reactions, significantly reducing the oxygen and nitrogen contents of bio-oil and improving the calorific value, thereby meeting the standards of high-quality fuel and improving the fuel performance of bio-oil. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments:

[0028] Figure 1 A schematic diagram of the structure of the device for culturing microalgae with wastewater and pyrolyzing to prepare bio-oil provided by the present invention (where the heater and cooler are located in a cutaway view);

[0029] Figure 2 The composition distribution of bio-oil from pyrolysis of Chlorella vulgaris under different experimental conditions;

[0030] Figure 3 The element content of bio-oil from pyrolysis of Chlorella under different experimental conditions, where (a) is the mass ratio of catalyst to Chlorella powder is 1:1; (b) is the mass ratio of catalyst to Chlorella powder is 1:2; (c) is the mass ratio of catalyst to Chlorella powder is 1:5;

[0031] Figure 4 The calorific value distribution of bio-oil from pyrolysis of Chlorella under different experimental conditions. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0033] This application first explored the optimal growth conditions and catalytic pyrolysis conditions of microalgae. For the growth conditions, plant hormones (2,4-D, GAs, NAA), antibiotics (CTC, OTC, STZ) and heavy metals (Cu, Fe, As) were added to the Chlorella culture at 0.2 and 2 mg / L, respectively. No substance was added to the control group. All treatments were repeated three times, and the calorific value of algae powder was calculated according to the following formula:

[0034]

[0035] The results showed that after the introduction of additives, the lipid content of Chlorella was significantly increased compared with the control group. This was because the stress caused by exogenous stimulation caused the stress response of Chlorella, thereby changing the metabolic pathway of lipid production and promoting the accumulation of cell lipids. After treatment with 0.2 mg / L CTC, the lipid content of Chlorella was as high as 16.3%, which was 1.5 times that of the control group. This induced stimulation will cause metabolic resources to tilt towards lipid synthesis rather than cell proliferation, resulting in limited biomass increase.

[0036] The investigation of catalytic pyrolysis conditions was carried out as follows: 5 g of Chlorella powder sample was weighed, and the catalyst and algae were added at a mass ratio of 1:1, 1:2 and 1:5. The quartz boat containing the experimental material was placed in the main heating zone of the reactor. Before starting heating, the gas valve was opened to pass the gas to check whether the air tightness of the device was good. The experimental carrier gas was high-purity N2 with a fixed flow rate of 100 mL / min through a gas mass flow meter, and purged for 30 minutes to ensure that the experimental environment was in an inert atmosphere. The program set the heating rate to 10℃ / min, from room temperature to the final pyrolysis temperature of 600℃, and stayed at this temperature for 20 minutes. After the reaction was completed, the system was turned off and cooled to room temperature. The condensable gas produced by pyrolysis was collected in a condensation bottle through an ice-water mixture. The pyrolysis liquid phase product was obtained by suction filtration and rotary evaporation. The bio-oil sample was further filtered using a syringe filter (0.45μm) to remove any possible particles and collected in a sealed glass bottle for analysis. The non-condensable gas was collected in the air bag. The bio-oil and biochar products obtained by pyrolysis were weighed to determine the yield. The elemental composition of the bio-oil samples was then analyzed using a CHNS / O elemental analyzer, and the HHV was calculated according to the above formula. The chemical composition of the bio-oil samples was analyzed using a gas chromatography-mass spectrometer GC-MS.

[0037] refer to Figure 2 , there are two groups of direct pyrolysis, namely the Chlorella group and the CTC group. It can be seen that the content of nitrogen-containing compounds in the CTC group is significantly reduced, while the content of aromatic hydrocarbons has increased to a certain extent, but the content is very small. This is because the Chlorella in the CTC group has less protein content and more lipid content. In the catalytic cracking reaction, the difficulty of generating aromatic hydrocarbons is fat>polysaccharide>protein, that is, protein has the lowest selectivity for aromatic hydrocarbons, resulting in a low content of aromatic hydrocarbons in the pyrolysis oil. By comparing the bio-oil produced by catalytic pyrolysis with the CTC group, it can be found that the addition of the catalyst has significantly changed the product distribution of the bio-oil. Specifically, in the bio-oil samples produced by catalytic pyrolysis, the content of nitrogen-containing and oxygen-containing compounds is generally reduced, especially when the catalyst ratio is 1:2, the effect is most significant.

[0038] Elemental composition is an important property of liquid fuels and is usually closely related to the energy density of pyrolysis oil. Figure 3, from the overall point of view, the content of carbon element occupies a dominant position. With the addition of catalyst, the content of C and H elements increases, while the content of O and N elements in the catalytic pyrolysis group is significantly reduced compared with the direct pyrolysis CTC group. This is consistent with the change trend of nitrogen-containing and oxygen-containing compounds in the bio-oil composition in the GC-MS analysis results, indicating that a series of reactions such as decarbonylation, decarboxylation, dehydration, and denitrification occurred during the pyrolysis process, effectively removing O and N elements. Especially when using Ni / HZSM-5 catalyst, the deoxygenation and denitrification effect is the best. It can be observed that when the addition ratio is 1:2, the oxygen content is 9.8% and the nitrogen content is 3.6%, which is 30.5% and 30.8% lower than that of the CTC group respectively; the calorific value is increased from 34.47MJ / kg to 38.45MJ / kg. The reduction of oxygen content usually means that the oxygen-containing compounds such as acid and phenol in the pyrolysis oil are reduced, thereby improving the stability and quality of the pyrolysis oil, and the reduction of nitrogen content can effectively control the emission of pollutants produced by combustion. In addition, the higher carbon and hydrogen content and lower nitrogen and oxygen content also mean that these products have higher calorific value. Figure 4 The shown also proves this point.

[0039] Taking into account the yield, calorific value and component distribution of bio-oil, it was found that Ni and Cu modified catalysts performed better, while Fe modified catalysts had the worst effect, and the pyrolysis effect was not as good as that of direct pyrolysis; in addition, the bimetallic loaded catalyst did not show the expected effect, and its ability to catalyze pyrolysis to improve the quality of bio-oil was not as good as that of single metal catalysts. In summary, when the catalyst addition ratio was 1:2, under the Ni / HZSM-5 working condition, the properties of bio-oil fuel prepared by pyrolysis were optimal.

[0040] Based on the above experimental results, the present application provides a device and method for culturing microalgae in wastewater and pyrolyzing to prepare high-quality bio-oil. The specific embodiments are as follows:

[0041] In the following three embodiments, the microalgae are all Chlorella vulgaris.

[0042] Embodiment 1,

[0043] This embodiment provides a method for culturing microalgae in wastewater and pyrolyzing to produce high-quality bio-oil. Figure 1 A device for culturing microalgae and pyrolyzing wastewater to prepare high-quality bio-oil, the method comprising the following steps:

[0044] Step 1: wastewater pretreatment;

[0045] Municipal sewage is selected as the culture medium. First, the suspended solids and larger particles in the sewage are removed by physical filtration. Then, biological treatment methods are used to use microbial flora to degrade organic pollutants and reduce chemical oxygen demand (COD) and biochemical oxygen demand (BOD). At the same time, chemical precipitation is used to remove heavy metal ions to ensure that the content of harmful substances in the wastewater meets safety standards.

[0046] Step 2: Add the pretreated wastewater and microalgae species together into the microalgae incubator 100 for cultivation, monitor the temperature of the culture environment, light intensity and the concentration of nutrients (such as nitrogen, phosphorus, etc.) in the wastewater in real time, and automatically adjust the concentration of plant hormones (2,4-D, GAs, NAA), antibiotics (CTC, OTC, STZ) and heavy metals (Cu, Fe, As) in the wastewater to below 0.5 mg / L by adding or diluting according to the monitoring feedback, wherein the content of the antibiotic CTC is maintained at 0.2 mg / L, providing the best growth environment for the microalgae, promoting its growth and lipid enrichment, and automatically adjusting the light intensity to ensure that the microalgae can carry out efficient photosynthesis under a light intensity of 5000 Lux.

[0047] Step 3: When the microalgae grows to the logarithmic growth phase (20 days), the culture solution is removed by using the solid-liquid separation device 200, and the culture solution is centrifuged at a speed of 3500 r / min for 5 minutes, and then the microalgae cells are separated efficiently and accurately by using nano-membrane separation technology;

[0048] Step 4: The separated microalgae are sent to the drying device 400 for freeze drying. The drying temperature and time are automatically adjusted according to the humidity and temperature of the algae mud to ensure that the algae mud is dried evenly and with the lowest energy consumption. During the freeze drying process, the temperature is controlled at about -40°C and the drying time is 12 hours. The dried algae mud is sent to the crushing device 500 for crushing. The crushing process is precisely controlled to make the algae powder particle size uniform and the particle size is controlled at about 100 meshes, providing high-quality raw materials for subsequent catalytic pyrolysis.

[0049] Step 5: discharge the microalgae powder into the stirring device 600, add the metal-loaded Ni / HZSM-5 catalyst to the microalgae powder, the mass ratio of the catalyst to the microalgae powder is 1:2, stir and mix, and take another part of the microalgae powder for direct pyrolysis;

[0050] Step 6: The microalgae powder mixed with the catalyst is discharged into the pyrolysis reactor 710 of the catalytic pyrolysis purification system 700, and nitrogen is introduced at a flow rate of 100 mL / min, and purged for 30 minutes to ensure that the experimental environment is in an inert atmosphere. The heater 750 is controlled by a program to increase the temperature at a rate of 10°C / min, and the temperature is increased to 600°C and maintained for 20 minutes for catalytic pyrolysis. The bio-oil generated by catalytic pyrolysis is collected, and its oxygen content, nitrogen content and calorific value are detected by chemical analysis. The elemental composition is analyzed by an element analyzer, and the calorific value is calculated according to the relevant formula. The results show that compared with the microalgae bio-oil directly pyrolyzed, the oxygen content of the bio-oil is reduced by 35%, the nitrogen content is reduced by 32%, and the calorific value is increased by 12%, meeting the standard of high-quality biofuel. The cooler 760 is used to cool down after the reaction is completed.

[0051] After the reaction is completed, the catalytic pyrolysis purification system 700 is turned off and cooled to room temperature. The condensable gases produced by pyrolysis are collected in the condensation bottle 720 through an ice-water mixture, and the pyrolysis liquid phase products are obtained by means of suction filtration and rotary evaporation. The bio-oil sample is further filtered using a syringe filter to remove any particles that may be present, and collected in a sealed glass bottle 730 for analysis, and the non-condensable gases are collected in the air bag 740.

[0052] Step 7: Detect the wastewater separated by the solid-liquid separation device 200 in step 3, and the detection indicators include harmful substance content, COD, BOD and other indicators. The results show that the removal efficiency of harmful substances in the wastewater reaches more than 90%, and the water quality meets the national discharge standards and is discharged through the discharge pipeline 310.

[0053] Embodiment 2,

[0054] This embodiment provides a method for culturing microalgae in wastewater and pyrolyzing to produce high-quality bio-oil. Figure 1 A device for culturing microalgae and pyrolyzing wastewater to prepare high-quality bio-oil, the method comprising the following steps:

[0055] Step 1: wastewater pretreatment;

[0056] Industrial wastewater is selected as the culture medium, and chemical treatment methods such as chemical precipitation and oxidation-reduction are used to remove heavy metal ions and some organic pollutants in the wastewater. Then, biological treatment methods such as biofilm reactors are used to further degrade organic pollutants, providing a safe and stable growth environment for microalgae;

[0057] Step 2: Add the pretreated wastewater and microalgae species together into the microalgae incubator 100 for cultivation, monitor the temperature, light intensity and concentration of nutrients (such as nitrogen, phosphorus, etc.) in the culture environment in real time, and automatically adjust the concentration of plant hormones (2,4-D, GAs, NAA), antibiotics (CTC, OTC, STZ) and heavy metals (Cu, Fe, As) in the wastewater to below 0.5 mg / L by adding or diluting according to the monitoring feedback, wherein the content of the antibiotic CTC is maintained at 0.2 mg / L, providing the best growth environment for the microalgae, promoting its growth and lipid enrichment, and automatically adjusting the light intensity to ensure that the microalgae can carry out uninterrupted and efficient photosynthesis 24 hours a day under a light intensity of 5000 Lux.

[0058] Step 3: When the microalgae grows to the logarithmic growth phase (20 days), the culture solution is removed by using the solid-liquid separation device 200, and the culture solution is centrifuged at a speed of 3500 r / min for 5 minutes, and then the microalgae cells are separated efficiently and accurately by using nano-membrane separation technology;

[0059] Step 4: The separated microalgae are sent to the drying device 400 for drying. According to the preset drying curve and the real-time feedback of the humidity and temperature data of the algae mud, the operating parameters of the drying device are dynamically adjusted, such as the temperature is controlled at about 60°C, and the wind speed is adjusted according to the actual situation to ensure the best drying effect. The dried algae mud is sent to the crushing device 500 for crushing. The crushing process is accurately controlled to make the algae powder particle size uniform and the particle size is controlled at about 80 meshes, providing high-quality raw materials for subsequent catalytic pyrolysis;

[0060] Step 5: discharge the microalgae powder into the stirring device 600, add the metal-loaded Cu / HZSM-5 catalyst to the microalgae powder, the mass ratio of the catalyst to the microalgae powder is 1:2, stir and mix, and take another part of the microalgae powder for direct pyrolysis;

[0061] Step 6: The microalgae powder mixed with the catalyst is discharged into the pyrolysis reactor 710 of the catalytic pyrolysis purification system 700, and nitrogen is introduced at a flow rate of 100 mL / min, and purged for 30 minutes to ensure that the experimental environment is in an inert atmosphere. The heater 750 is controlled by a program to increase the temperature at a rate of 10°C / min, and the temperature is increased to 600°C and maintained for 20 minutes for catalytic pyrolysis. The bio-oil generated by catalytic pyrolysis is collected, and its oxygen content, nitrogen content and calorific value are detected by chemical analysis. The elemental composition is analyzed by an element analyzer, and the calorific value is calculated according to the relevant formula. The results show that compared with the microalgae bio-oil directly pyrolyzed, the oxygen content of the bio-oil is reduced by 30%, the nitrogen content is reduced by 31%, and the calorific value is increased by 10%, which meets the requirements of high-quality biofuel. The cooler 760 is used to cool down after the reaction is completed.

[0062] After the reaction is completed, the catalytic pyrolysis purification system 700 is turned off and cooled to room temperature. The condensable gases produced by pyrolysis are collected in the condensation bottle 720 through an ice-water mixture, and the pyrolysis liquid phase products are obtained by means of suction filtration and rotary evaporation. The bio-oil sample is further filtered using a syringe filter to remove any particles that may be present, and collected in a sealed glass bottle 730 for analysis, and the non-condensable gases are collected in the air bag 740.

[0063] Step 7: Detect the wastewater separated by the solid-liquid separation device 200 in step 3, and the detection indicators include harmful substance content, COD, BOD and other indicators. The results show that the removal efficiency of harmful substances in the wastewater reaches more than 85%, and the water quality meets the national discharge standards and is discharged through the discharge pipeline 310.

[0064] Embodiment 3,

[0065] This embodiment provides a method for culturing microalgae in wastewater and pyrolyzing to produce high-quality bio-oil. Figure 1 A device for culturing microalgae and pyrolyzing wastewater to prepare high-quality bio-oil, the method comprising the following steps:

[0066] Step 1: wastewater pretreatment;

[0067] Agricultural wastewater is selected as the culture medium, and a combination of physical precipitation, chemical neutralization and biodegradation treatment methods is used to remove suspended matter, heavy metal ions and organic pollutants in the wastewater. Physical precipitation is used to remove larger particles and suspended matter, chemical neutralization adjusts the pH value of the wastewater, and biodegradation uses microbial flora to decompose organic matter so that the wastewater meets the requirements for the growth of microalgae.

[0068] Step 2: Add the pretreated wastewater and microalgae species together into the microalgae incubator 100 for cultivation, monitor and adjust the temperature of the culture environment to (28±1)°C, the light intensity to 5000Lux (24h uninterrupted continuous light) and the concentration of nutrients in the wastewater in real time, and automatically adjust the concentration of plant hormones, antibiotics and heavy metals to below 0.5mg / L by adding or diluting the monitoring data, wherein the content of antibiotic CTC is maintained at 0.2mg / L, providing optimal growth conditions for microalgae.

[0069] Step 3: When the microalgae grows to the logarithmic growth phase (20 days), the culture solution is removed by using the solid-liquid separation device 200, and the culture solution is centrifuged at a speed of 3500 r / min for 5 minutes, and then the microalgae cells are separated efficiently and accurately by using nano-membrane separation technology;

[0070] Step 4: The separated microalgae are sent to the drying device 400 for freeze-drying treatment. Intelligent low-heat constant temperature drying equipment is used. The intelligent control system automatically adjusts the drying temperature and time according to the humidity, temperature and drying progress of the algae mud to ensure that the drying process is efficient and the energy consumption is minimized. The drying temperature is controlled at about 80°C, and the drying time is adjusted according to the actual situation. The dried algae mud is sent to the crushing device 500 for crushing treatment. The crushing process is accurately controlled to make the algae powder particle size uniform and the particle size is controlled at about 90 meshes, providing high-quality raw materials for subsequent catalytic pyrolysis;

[0071] Step 5: discharge the microalgae powder into the stirring device 600, add the metal-loaded Co / HZSM-5 catalyst to the microalgae powder, the mass ratio of the catalyst to the microalgae powder is 1:2, stir and mix, and take another part of the microalgae powder for direct pyrolysis;

[0072] Step 6: The microalgae powder mixed with the catalyst is discharged into the pyrolysis reactor 710 of the catalytic pyrolysis purification system 700, and nitrogen is introduced at a flow rate of 100 mL / min, and purged for 30 minutes to ensure that the experimental environment is in an inert atmosphere. The heater 750 is controlled by a program to increase the temperature at a rate of 10°C / min, and the temperature is increased to 600°C and maintained for 20 minutes for catalytic pyrolysis. The bio-oil generated by catalytic pyrolysis is collected, and its oxygen content, nitrogen content and calorific value are detected by chemical analysis means. The elemental composition is analyzed by an element analyzer, and the calorific value is calculated according to the relevant formula. The results show that compared with the microalgae bio-oil without catalytic pyrolysis, the oxygen content of the bio-oil is reduced by 33%, the nitrogen content is reduced by 30%, and the calorific value is increased by 11%, reaching the standard of high-quality biofuel. The cooler 760 is used to cool down after the reaction is completed.

[0073] After the reaction is completed, the catalytic pyrolysis purification system 700 is turned off and cooled to room temperature. The condensable gases produced by pyrolysis are collected in the condensation bottle 720 through an ice-water mixture, and the pyrolysis liquid phase products are obtained by means of suction filtration and rotary evaporation. The bio-oil sample is further filtered using a syringe filter to remove any particles that may be present, and collected in a sealed glass bottle 730 for analysis, and the non-condensable gases are collected in the air bag 740.

[0074] Step 7: Detect the wastewater separated by the solid-liquid separation device 200 in step 3, and the detection indicators include harmful substance content, COD, BOD and other indicators. The results show that the removal efficiency of harmful substances in the wastewater reaches more than 88%, and the water quality meets the national emission standards, and is recycled through the circulation pipeline 320.

[0075] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for culturing microalgae in wastewater and pyrolyzing to produce high-quality bio-oil, characterized in that: The device used in the method comprises a microalgae culture box (100), a solid-liquid separation device (200), a water quality detection device (300), a drying device (400), a crushing device (500), a stirring device (600), and a catalytic pyrolysis purification system (700); the outlet of the microalgae culture box (100) is connected to the inlet of the solid-liquid separation device (200) through a pipeline; the liquid outlet of the solid-liquid separation device (200) is connected to the water quality detection device (300); the solid outlet of the solid-liquid separation device (200) is connected to the inlet of the drying device (400); the outlet of the drying device (400) is connected to the inlet of the crushing device (500); the outlet of the crushing device (500) is connected to the inlet of the stirring device (600); and the outlet of the stirring device (600) is connected to the inlet of the catalytic pyrolysis purification system (700); The method comprises the following steps: Step 1: wastewater pretreatment; Step 2: adding the pretreated wastewater and microalgae together into the microalgae culture box (100) for culture, monitoring and adjusting the parameters of the culture environment, and using Chlorella vulgaris as the microalgae; The parameters of the culture environment were adjusted according to the following standards: culture temperature 28±1℃, light intensity 5000Lux 24h uninterrupted continuous illumination, the concentrations of plant hormones, antibiotics and heavy metals in the wastewater were maintained below 0.5mg / L, and the content of antibiotic CTC was maintained at 0.2mg / L; Step 3: After the microalgae grow to the logarithmic phase, the microalgae culture solution is discharged into the solid-liquid separation device (200) for solid-liquid separation; Step 4: the separated microalgae are discharged into the drying device (400) for drying, and then discharged into the crushing device (500) for crushing to form microalgae powder; Step 5: discharge the microalgae powder into the stirring device (600), add the metal-loaded HZSM-5 catalyst into the microalgae powder, and stir and mix; the metal-loaded HZSM-5 catalyst is Ni / HZSM-5, and the mass ratio of Ni / HZSM-5 to microalgae powder is 1:2; Step 6: the microalgae powder mixed with the catalyst is discharged into the catalytic pyrolysis purification system (700), catalytically pyrolyzed in an inert atmosphere at a high temperature to generate bio-oil, the bio-oil is collected and the bio-oil is tested for indicators; Step 7: Detect the quality of the wastewater separated by the solid-liquid separation device (200) in step 3, and recycle or safely discharge it.

2. The method for culturing microalgae with wastewater and pyrolyzing to produce high-quality bio-oil according to claim 1, characterized in that: The water quality detection device (300) is provided with two outlets, one outlet is connected to a discharge pipeline (310), and the other outlet is connected to the microalgae culture box (100) via a circulation pipeline (320).

3. The method for culturing microalgae with wastewater and pyrolyzing to produce high-quality bio-oil according to claim 1, characterized in that: A catalyst inlet is provided on the stirring device (600); the catalytic pyrolysis purification system (700) comprises a pyrolysis reactor (710), a condensation bottle (720), a glass bottle (730) and an air bag (740) which are connected in sequence through pipelines.

4. The method for culturing microalgae with wastewater and pyrolyzing to produce high-quality bio-oil according to claim 3, characterized in that: The number of the condensation bottle (720) and the number of the glass bottle (730) are both two.

5. The method for culturing microalgae with wastewater and pyrolyzing to produce high-quality bio-oil according to claim 3, characterized in that: A heater (750) and a cooler (760) are provided on the outer wall of the pyrolysis reactor (710).

6. The method for culturing microalgae with wastewater and pyrolyzing to produce high-quality bio-oil according to claim 1, characterized in that: In step 6, the catalytic pyrolysis temperature is 600° C., and the oxygen content, nitrogen content and calorific value of the bio-oil are detected.

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