A method for synchronously treating flue gas and wastewater from a steel plant using microalgae

Abstract

The present invention provides a method for synchronously treating flue gas and wastewater from a steel plant using microalgae, the method comprising: inoculating microalgae onto a culture medium containing wastewater, and simultaneously filling flue gas into a reactor for carbon fixation culture; the concentration of CO2 in the flue gas is 23%-28%. The present invention utilizes high-concentration CO2 in the flue gas of a hot blast furnace in a steel plant and wastewater after desulfurization by slag flushing water to culture microalgae, thereby shortening the transportation distance of wastewater; the desulfurized wastewater contains nutrients and trace elements necessary for the growth of microalgae, such as carbon, nitrogen, magnesium, calcium and other trace elements, and the temperature and pH of the desulfurized wastewater are suitable for the growth of microalgae, which can increase the growth rate of microalgae, realize carbon emission reduction of hot blast furnace flue gas, and improve CO2 utilization efficiency, while coupling the resource utilization of wastewater, which is conducive to reducing the cost of industrialized cultivation of microalgae.

Description

Technical Field

[0001] The invention belongs to the field of microalgae biotechnology, relates to microalgae cultivation technology, and in particular to a method for synchronously treating flue gas and wastewater from a steel plant by using microalgae. Background Art

[0002] With the development of industry and the increase in population, the concentration of greenhouse gases such as CO2 in the atmosphere has increased, and the greenhouse effect has attracted more and more attention. A series of problems in recent years, such as global warming, melting of polar glaciers, and rising sea levels, are all related to the greenhouse effect of CO2. Last year, carbon emissions from the steel industry accounted for about 15% of total carbon emissions, ranking first among all manufacturing industries. The carbon emission characteristics of each process in the steel industry show that the CO2 content in the flue gas of steel hot blast furnaces is the process with the largest emissions in the steel industry, accounting for 29-52% of total emissions.

[0003] Microalgae are single-celled microorganisms with photosynthetic pigments that can use sunlight, CO2 and water to photosynthesize biomass and grow. Microalgae growth requires a large amount of CO2, about 1.8 tons of CO2 are needed to produce 1 ton of microalgae biomass. CO2 fixation by microalgae can achieve a complete cycle of carbon elements, and has the advantages of high photosynthetic rate, fast reproduction, strong environmental adaptability, controllability and easy integration with other engineering technologies. At the same time, microalgae can produce many high value-added products after fixing CO2 through photosynthesis, which has certain economic value. CO2 in industrial flue gas can be directly supplied to algae growth. Using algae technology to treat flue gas has low cost, low energy consumption, and effective absorption of CO2 in waste gas, and has great potential for engineering promotion and application. Microalgae can also use growth nutrients from various wastewater sources to realize the idea of ​​"waste to energy" and minimize the use of fresh water, bringing higher benefits. Therefore, microalgae CO2 fixation technology has great industrialization potential due to its advantages such as environmental protection, economy, high efficiency, and compliance with the characteristics of natural cycles, and is expected to become a CO2 fixation method with considerable feasibility and economic value.

[0004] The cultivation process of microalgae consumes a lot of water and nutrients. How to control the wastewater produced by steel to provide water and nutrients to microalgae is one of the key points of the industrial utilization of microalgae carbon fixation. At present, the research on the utilization of industrial wastewater of microalgae in the steel industry started late, and there are few studies on the selection and breeding of algae strains and methods for efficient and stable utilization of wastewater resources. So far, only a few types of industrial wastewater have been involved. The resource utilization of wastewater of microalgae not only provides nutrients for algae and reduces the cost of microalgae cultivation, but also prevents nutrients from entering the water body and causing eutrophication.

[0005] Therefore, in order to reduce carbon emissions in the steel industry, a technology that uses microalgae to simultaneously treat flue gas for carbon fixation and couples wastewater resource utilization is developed to enhance the adaptability and carbon fixation rate of microalgae to steel hot blast furnace flue gas, strengthen the development of microalgae for wastewater treatment and resource utilization, and reduce the cultivation cost of microalgae. Summary of the invention

[0006] The purpose of the present invention is to provide a method for simultaneously treating flue gas and wastewater from a steel plant using microalgae. While artificially cultivating microalgae to fix CO2 in the flue gas of the hot blast furnace of the steel plant, an appropriate amount of wastewater after hot blast furnace desulfurization is added to the microalgae culture medium to provide energy substances for the cultivation of microalgae and reduce the cultivation cost of microalgae.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for synchronously treating flue gas and wastewater from a steel plant by using microalgae, the method comprising: inoculating microalgae onto a culture medium containing wastewater, and simultaneously charging flue gas into a reactor for carbon fixation culture;

[0009] The concentration of CO2 in the flue gas is 23%-28%, for example, it can be 23%, 24%, 25%, 26%, 27% or 28%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0010] The present invention utilizes microalgae to treat carbon fixation in flue gas from hot blast furnaces of steel plants and couples the resource utilization of wastewater after desulfurization. On the one hand, microalgae are used for biological carbon fixation in flue gas, and on the other hand, desulfurization wastewater is used to cultivate microalgae to reduce material costs and increase the accumulation of microalgae biomass. At the same time, the CO2 emission reduction in flue gas from hot blast furnaces of steel plants and the resource utilization of slag flushing water desulfurization wastewater are solved.

[0011] As a preferred technical solution of the present invention, the inoculation amount of the microalgae is 0.01-0.05 g / L, for example, it can be 0.01 g / L, 0.02 g / L, 0.03 g / L, 0.04 g / L or 0.05 g / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0012] Preferably, the microalgae comprises Chlorella.

[0013] Preferably, the reactor is a tubular photo-generating reactor.

[0014] As a preferred technical solution of the present invention, the culture medium includes improved BG11 culture medium.

[0015] Preferably, the improved BG11 medium is the standard BG11 medium minus the carbon source.

[0016] In the present invention, the improved BG11 culture medium does not contain a carbon source, and the carbon source all comes from CO2 in the flue gas.

[0017] As a preferred technical solution of the present invention, the flue gas is desulfurized flue gas.

[0018] Preferably, the concentration of CO2 in the flue gas after desulfurization is 23%-28%, for example, it can be 23%, 24%, 25%, 26%, 27% or 28%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] In the present invention, the method can fix high-concentration CO2 in flue gas, solving the problem of high-concentration CO2 emission in flue gas from steel plants.

[0020] Preferably, the NO in the flue gas after desulfurization x The concentration is ≤63mg / m 3 , for example, 40 mg / m 3 45mg / m 3 , 50mg / m 3 , 55mg / m 3 , 60mg / m 3 or 63 mg / m 3 The above values ​​are not limited to the above values, and other values ​​not listed in the above values ​​are also applicable.

[0021] Preferably, the concentration of SO2 in the flue gas after desulfurization is ≤6 mg / m 3 , for example, it can be 1 mg / m 3 , 2mg / m 3 , 3mg / m 3 , 4mg / m 3 , 5mg / m 3 or 6 mg / m 3 The above values ​​are not limited to the above values, and other values ​​not listed in the above values ​​are also applicable.

[0022] As a preferred technical solution of the present invention, the wastewater is wastewater after desulfurization using slag flushing water.

[0023] In the present invention, the waste water is the waste water after desulfurization using slag flushing water in the hot blast furnace of the steel plant.

[0024] Preferably, the volume ratio of the desulfurized wastewater to the culture medium is (1-3):8, for example, it can be 1:8, 1.5:8, 2:8, 2.5:8 or 3:8, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] Preferably, the components of the wastewater after desulfurization include calcium sulfite salt and / or magnesium sulfite salt.

[0026] As a preferred technical solution of the present invention, the temperature of the wastewater after desulfurization is 26-36°C, for example, it can be 26°C, 28°C, 30°C, 32°C, 34°C or 36°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] In the present invention, the temperature of the wastewater after desulfurization is 26-36° C., which meets the temperature requirement for microalgae carbon fixation culture. There is no need to heat the culture medium, thus reducing energy consumption.

[0028] Preferably, the pH of the wastewater after desulfurization is 6-7, for example, it can be 6, 6.2, 6.4, 6.6, 6.8 or 7, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 6-6.5.

[0029] In the present invention, the pH of the slag flushing wastewater before desulfurization of the steel plant is as high as 11, which cannot be used for the cultivation of microalgae. After desulfurization, the pH of the slag flushing desulfurization wastewater is 6-7, which is suitable for the cultivation of microalgae. There is no need to adjust the pH of the wastewater, which simplifies the operation.

[0030] As a preferred technical solution of the present invention, the charging amount of the flue gas after desulfurization is 7.5-25mL / min, for example, it can be 7.5mL / min, 10mL / min, 15mL / min, 20mL / min or 25mL / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Preferably, the carbon fixation culture uses N2 as a carrier gas.

[0032] Preferably, the N2 filling amount is 22.5-75 mL / min, for example, it can be 22.5 mL / min, 25 mL / min, 30 mL / min, 40 mL / min, 50 mL / min, 60 mL / min, 70 mL / min or 75 mL / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0033] As a preferred technical solution of the present invention, the carbon fixation culture also includes: the intensity of light is 5000-15000 Lux, the light-dark ratio is (12-24) h: (8-12) h, and after culturing for 10-15 days, algal cells are obtained by centrifugation.

[0034] In the present invention, desulfurized wastewater is added to a culture medium inoculated with microalgae species and flue gas components are introduced, and the microalgae are cultured and acclimated under light conditions until the algae cells tolerate the flue gas components and the algae cell concentration no longer increases, entering a stable growth period.

[0035] In the present invention, the intensity of the light is 5000-15000 Lux, for example, it can be 5000 Lux, 7000 Lux, 9000 Lux, 10000 Lux, 12000 Lux, 14000 Lux or 15000 Lux, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0036] In the present invention, the light-to-dark ratio is (12-24)h:(8-12)h, for example, it can be 12h:8h, 14h:9h, 16h:10h, 18h:11h, 20h:11h or 24h:12h, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] As a preferred technical solution of the present invention, the lighting is LED lighting.

[0038] Preferably, the centrifugal rotation speed is 9000-11000rpm, for example, it can be 9000rpm, 9200rpm, 9400rpm, 9600rpm, 9800rpm, 10000rpm, 10200rpm, 10400rpm, 10600rpm, 10800rpm or 11000rpm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] Preferably, the centrifugation time is 10-20 min, for example, 10 min, 12 min, 14 min, 16 min, 18 min or 20 min, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] As a preferred technical solution of the present invention, the method comprises: inoculating 0.01-0.05 g / L of microalgae into a modified BG11 culture medium containing wastewater, and simultaneously filling flue gas into a tubular photo-generating reactor for carbon fixation culture;

[0041] The flue gas is desulfurized flue gas; the concentration of CO2 in the desulfurized flue gas is 23%-28%, and the concentration of NO x The concentration is ≤63mg / m 3 , SO2 concentration ≤ 6mg / m 3 ;

[0042] The wastewater is wastewater after desulfurization using slag flushing water; the volume ratio of the desulfurized wastewater to the improved BG11 culture medium is (1-3):8; the temperature of the desulfurized wastewater is 26-36°C, and the pH is 6-7;

[0043] The carbon fixation culture conditions are as follows: the charging amount of the flue gas after desulfurization is 7.5-25mL / min, the charging amount of N2 is 22.5-75mL / min, the light intensity is 5000-15000Lux, the light-dark ratio is (12-24)h:(8-12)h, and after culturing for 10-15 days, the algae cells are obtained by centrifugation.

[0044] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] The present invention uses high-concentration CO2 in the flue gas of the hot blast furnace of the steel plant and the wastewater after desulfurization using slag flushing water to cultivate microalgae, thereby shortening the transportation distance of the wastewater; the desulfurized wastewater contains nutrients and trace elements necessary for the growth of microalgae, such as carbon, nitrogen, magnesium, calcium and other trace elements, and the temperature and pH of the desulfurized wastewater are suitable for the growth of microalgae, thereby increasing the growth rate of microalgae, achieving carbon emission reduction of the hot blast furnace flue gas, and improving the CO2 utilization efficiency, while coupling the resource utilization of the wastewater, which is beneficial to reducing the cost of industrial cultivation of microalgae. DETAILED DESCRIPTION

[0047] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0048] Example 1

[0049] This example simulates the flue gas ratio based on the hot blast furnace flue gas of a steel plant. The components of the hot blast furnace flue gas before desulfurization are CO2 25%, SO2 72mg / m 3 、NO x 64 mg / m 3 、Particulate matter 3mg / m 3 The flue gas components after desulfurization are CO2 25%, SO2 6mg / m 3 、NO x 63mg / m 3 、Particulate matter 3mg / m 3 .

[0050] The wastewater in this embodiment comes from a steel plant. After desulfurization using slag water, the main components of the wastewater are calcium and magnesium salts of sulfite. The temperature of the desulfurized wastewater is 35°C and the pH is 6.5. The desulfurized wastewater is used after sedimentation and filtration.

[0051] This embodiment provides a method for synchronously treating flue gas and wastewater from a steel plant using microalgae, the method comprising:

[0052] An inoculum of 0.02 g / L Chlorella is inoculated into a medium containing desulfurized wastewater and improved BG11 culture medium, and desulfurized flue gas is charged into a 300 mL tubular photoreactor at 25 ml / min for carbon fixation culture; the improved BG11 culture medium is a standard BG11 culture medium with the carbon source removed; the volume ratio of the desulfurized wastewater to the improved BG11 culture medium is 2:8, and the conditions for the carbon fixation culture are: the intensity of LED illumination is 7500 Lux, the light-dark ratio is 12h:12h, and after 10 days of cultivation, 0.02 g / L of algae cells are reserved, and the rest are centrifuged at a speed of 10,000 rpm for 15 min to obtain algae cells, and then the desulfurized wastewater and the improved BG11 culture medium are added to the tubular photoreactor at a ratio of 2:8 for continued cultivation.

[0053] Example 2

[0054] This example simulates the flue gas ratio based on the hot blast furnace flue gas of a steel plant. The components of the hot blast furnace flue gas before desulfurization are CO2 28%, SO2 70mg / m 3 、NO x 65 mg / m 3 、Particulate matter 3mg / m 3 After desulfurization, the flue gas components are CO2 28%, SO25mg / m 3 、NO x 61mg / m 3 、Particulate matter 3mg / m 3 .

[0055] The wastewater in this embodiment comes from a steel plant. After desulfurization using slag water, the main components of the wastewater are calcium and magnesium salts of sulfite. The temperature of the desulfurized wastewater is 30°C and the pH is 6. The desulfurized wastewater is used after sedimentation and filtration.

[0056] The method of using flue gas and wastewater to culture Chlorella for carbon fixation in this embodiment is the same as that in Example 1.

[0057] Example 3

[0058] The only difference between this embodiment and embodiment 1 is that, except that the pH value of the wastewater after desulfurization is 8, other conditions are the same as those in embodiment 1.

[0059] Example 4

[0060] The only difference between this embodiment and embodiment 1 is that, except that the pH value of the wastewater after desulfurization is 5, other conditions are the same as those in embodiment 1.

[0061] Example 5

[0062] The only difference between this embodiment and embodiment 1 is that, except that the temperature of the desulfurized wastewater is 20° C., other conditions are the same as those in embodiment 1.

[0063] Example 6

[0064] The only difference between this embodiment and embodiment 1 is that, except that the volume ratio of the desulfurized wastewater to the improved BG11 culture medium is 5:5, other conditions are the same as those in embodiment 1.

[0065] Example 7

[0066] The only difference between this embodiment and Embodiment 1 is that, except that the intensity of the LED illumination is 4000 Lux, other conditions are the same as those of Embodiment 1.

[0067] Example 8

[0068] The only difference between this embodiment and Embodiment 1 is that, except that the intensity of the LED illumination is 17000 Lux, other conditions are the same as those of Embodiment 1.

[0069] Comparative Example 1

[0070] The difference between this comparative example and Example 1 is that, except that the artificial simulated smoke component CO2 is 20%, other conditions are the same as those of Example 1.

[0071] Comparative Example 2

[0072] The difference between this comparative example and Example 1 is that, except that the CO2 component of the artificial simulated smoke is 32%, other conditions are the same as those of Example 1.

[0073] The carbon fixation rate, biomass concentration and carbohydrate content of the microalgae in the reactors of the above examples and comparative examples were measured, and the test results are shown in Table 1.

[0074] Table 1

[0075] Carbon fixation rate (g / L·d) Biomass concentration (g / L) Carbohydrate content (%) Example 1 1.2 2.7 68.4 Example 2 1.2 2.6 65.8 Example 3 0.5 1.3 32.4 Example 4 0.4 1.1 26.7 Example 5 0.9 2.4 53.8 Example 6 0.8 2.2 50.2 Example 7 0.7 1.5 45.3 Example 8 1.0 2.4 58.3 Comparative Example 1 0.8 2.1 50.7 Comparative Example 2 1.1 2.6 63.5

[0076] As shown in Table 1, the method provided by the present invention can realize the simultaneous treatment of flue gas and wastewater from steel plants by microalgae, shorten the transportation distance, and reduce the cost of industrial cultivation of microalgae. When the pH of the wastewater after desulfurization is too alkaline or too acidic, it affects the growth of algae cells and even causes apoptosis of algae cells, resulting in too slow growth of microalgae, thereby causing a decrease in carbon fixation rate, biomass concentration and carbohydrate content. When the temperature of the wastewater after desulfurization is too low, the growth rate of algae cells slows down under low temperature conditions, resulting in a decrease in carbon fixation efficiency. When too much wastewater after desulfurization is added, the necessary nutrients for the growth of microalgae are lacking, resulting in a lack of nutrients for algae cells and slow growth. In the carbon fixation culture process, when the intensity of LED light is too weak, due to insufficient light intensity, a photoinhibition effect is formed, and the photoinhibition phenomenon seriously hinders the growth of microalgae and the accumulation of biomass. When the light intensity is too strong, the growth of Chlorella under high light intensity is also inhibited, resulting in a decrease in carbon fixation rate, biomass concentration and carbohydrate content under higher / low light intensity.

[0077] By comparing Example 1 and Comparative Examples 1-2, it can be seen that when the CO2 concentration in the flue gas after desulfurization is too low, the amount of dissolved carbon in the culture medium is reduced, resulting in a small lack of carbon source and causing a decrease in efficiency; when the CO2 concentration in the flue gas after desulfurization is too high, the amount of dissolved carbon in the culture medium reaches saturation, and excess CO2 overflows from the culture medium, which has little effect on the carbon fixation rate, biomass concentration and carbohydrate content.

[0078] The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed structural features, that is, it does not mean that the present invention must rely on the above-mentioned detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for synchronously treating flue gas and wastewater from a steel plant using microalgae, characterized in that: The method comprises: inoculating microalgae onto a culture medium containing wastewater, and simultaneously injecting flue gas into a reactor for carbon fixation culture; The inoculation amount of the microalgae is 0.01-0.05 g / L; the microalgae is Chlorella vulgaris; The wastewater is desulfurized wastewater using slag flushing water; the temperature of the desulfurized wastewater is 32-36°C and the pH is 6.2-7; the components of the desulfurized wastewater include calcium sulfite salt and magnesium sulfite salt; The flue gas is desulfurized flue gas; the concentration of CO2 in the desulfurized flue gas is 25%-28%, and the concentration of NO x The concentration is ≤63 mg / m 3 , SO2 concentration ≤6 mg / m 3 ; The charging amount of the desulfurized flue gas is 7.5-25 mL / min; The volume ratio of the desulfurized wastewater to the culture medium is (1-3):8; the culture medium includes a modified BG11 culture medium; the modified BG11 culture medium is a standard BG11 culture medium with the carbon source removed; The reactor is a tubular photo-generating reactor; The carbon fixation culture uses N2 as a carrier gas; the N2 charging amount is 22.5-75 mL / min; the carbon fixation culture also includes: the light intensity is 5000-15000 Lux, the light-dark ratio is (12-24) h:(8-12) h, and after culturing for 10-15 days, algal cells are obtained by centrifugation.

2. The method according to claim 1, characterized in that The illumination is LED illumination.

3. The method according to claim 1, characterized in that The centrifugal rotation speed is 9000-11000 rpm.

4. The method according to claim 1, characterized in that: The centrifugation time is 10-20 min.