A method for carbon sequestration by concentrated brine mineralization

Abstract

The application discloses a method for carbon capture and storage by concentrated brine mineralization, comprising the following steps: introducing a carbon dioxide source into pure water, stirring under pressure until the carbon dioxide is dissolved in the pure water to obtain a carbonic acid solution; under the pressure, adding liquid alkali into the carbonic acid solution to adjust the pH to obtain a high-pressure carbonic acid alkali solution; under normal pressure, mixing the high-pressure carbonic acid alkali solution with concentrated brine containing calcium ions, and aging at 25-40 DEG C to obtain a reaction slurry; and performing solid-liquid separation, washing and drying to collect calcium carbonate. The method can remove 97% of the calcium ions in the concentrated brine separated by nanofiltration, significantly reduces the calcium hardness of the effluent, creates favorable conditions for effluent reuse, and realizes the fixation of about 0.4 tons of carbon dioxide for every ton of calcium carbonate product, realizes the high-value mineralization utilization of carbon dioxide in flue gas, and simultaneously solves multiple problems such as calcium resource waste, high energy consumption in concentrated brine treatment, and limited utilization of carbon dioxide in the field of carbon capture.

Description

Technical Field

[0001] This invention relates to the fields of technology, energy technology, and energy water treatment technology, and more particularly to a method for mineralizing and fixing carbon in concentrated brine. Background Technology

[0002] The treatment of high-salinity brine (typically with total dissolved solids (TDS) >10,000 mg / L and hardness (calculated as CaCO3) of 500-2000 mg / L) generated during wastewater treatment has become a major challenge in the industry. Currently, brine is mainly treated through evaporation crystallization or deep well reinjection, which are not only energy-intensive (typically 20-60 kWh / m³), but also pose significant challenges. 3 The high cost and the resulting mixed salts make them difficult to utilize as resources, leading to a waste of calcium resources.

[0003] Meanwhile, the carbon dioxide captured by steel companies using carbon capture technology is mostly used for coal gas utilization, which restricts the development of concentrated brine resource utilization and end-of-pipe carbon capture in steel companies. Therefore, there is an urgent need to develop a treatment method that synergistically treats concentrated brine and reduces carbon dioxide emissions, in order to solve the problems of calcium resource waste, generation of mixed salts and waste liquid, high costs, and limited carbon capture pathways in existing processes. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for mineralizing and fixing calcium carbonate in concentrated brine. This method utilizes the hardness of concentrated brine and the synergistic carbon fixation of carbon dioxide in flue gas to prepare calcium carbonate. Through a process route of high-pressure carbon dioxide dissolution-alkalization conversion-chemical precipitation, it achieves efficient removal and resource recovery of calcium ions from concentrated brine and high-value carbon fixation utilization of CO2 in flue gas.

[0005] To achieve the above objectives, the present invention is accomplished through the following technical solutions.

[0006] A method for mineralizing and fixing carbon in concentrated brine includes the following steps:

[0007] Step 1, High-pressure carbon dioxide dissolution: Pass carbon dioxide gas into pure water and stir at a pressure of 2~5 MPa until the amount of carbon dioxide dissolved in pure water reaches 2.76~6 g / L to obtain a carbonic acid solution. In step 1, the carbon dioxide source includes carbon dioxide produced by pressure swing adsorption (PSA) carbon capture of flue gas, and the pure water includes reverse osmosis permeate with a conductivity of <10 μS / cm.

[0008] In step 1, the volume concentration of carbon dioxide in the carbon dioxide gas source is ≥95%.

[0009] In step 1, carbon dioxide gas is introduced into pure water for 10 to 30 minutes to allow the carbon dioxide to dissolve fully in the pure water, with a dissolved amount of 2.76 to 6 g / L.

[0010] In step 1, the temperature of the pure water is 15~25℃.

[0011] Step 2, Alkalization Conversion: Under the pressure conditions described in Step 1, liquid alkali is added dropwise to the carbonic acid solution to adjust the pH to 10.2~10.5, thereby obtaining a high-pressure carbonic acid alkali solution; In step 2, liquid alkali is added dropwise to the carbonic acid solution to dissolve the CO2 (H2CO3, HCO3-). - ) converted into CO3 2- .

[0012] In step 2, the CO3 in the high-pressure carbonate solution 2- The concentration is 1.7~5 g / L.

[0013] In step 2, the liquid alkali is a mixture of alkali metal hydroxide and water, and the concentration of the alkali metal hydroxide in the liquid alkali is 30~40wt%, including sodium hydroxide and potassium hydroxide.

[0014] Step 3, precipitation reaction: Under normal pressure, the high-pressure carbonic acid solution is mixed evenly with concentrated brine containing calcium ions and aged at 25~40℃ for 30~60 minutes to obtain a reaction slurry. The concentrated brine is the calcium enrichment side concentrate after the concentrated water of the reverse osmosis device is desalted by nanofiltration membrane. In step 3, the concentration of calcium ions in the concentrated saline solution is 800~1000 mg / L.

[0015] In step 3, the high-pressure alkaline carbonate solution is reduced to atmospheric pressure and mixed with concentrated brine containing calcium ions. The mixture is then reacted at 25-40°C for 30-60 minutes to allow the CO32- content in the high-pressure alkaline carbonate solution to decrease. 2- With Ca in concentrated salt water 2+ The reaction produces calcium carbonate.

[0016] In step 3, the operation of mixing the high-pressure alkali carbonate solution with the concentrated brine containing calcium ions is as follows: calculate the total volume of the concentrated brine required according to the chemical reaction equation of calcium carbonate, first mix the high-pressure alkali carbonate solution with concentrated brine accounting for 30~35% of the total volume of concentrated brine to control the initial concentration of calcium ions and reduce supersaturation, and then slowly add the remaining concentrated brine to maintain a stable supersaturation, so that the crystals can grow in an orderly manner.

[0017] In the above technical solution, the slow dripping time is 20~30 minutes.

[0018] In step 3, the ripening is carried out under stirring to promote crystal perfection and remove impurities, and the stirring rate is 100~150 rpm.

[0019] Step 4, post-processing: solid-liquid separation, washing, drying, and collection of calcium carbonate.

[0020] In step 4, the reaction slurry is separated into solid and liquid components by centrifugation. The filtrate (i.e., mother liquor) after solid-liquid separation contains sodium carbonate, which can be used as an alkalizing agent in the alkali solution in step 2.

[0021] In the above technical solution, the centrifugal separation equipment is a horizontal screw centrifuge or a disc centrifuge, and the separation factor for solid-liquid separation is controlled between 150 and 300.

[0022] In step 4, the washing is a three-stage countercurrent water wash. The first-stage washing liquid used in the three-stage countercurrent water wash is the filtrate collected after solid-liquid separation. The second-stage washing liquid and the third-stage washing liquid are both pure water. The total mass ratio of the first-stage washing liquid, the second-stage washing liquid and the third-stage washing liquid to the solid precipitate is 3:1.

[0023] In step 4, the drying is flash drying, and the inlet temperature of the flash drying is 120~140℃.

[0024] In step 4, the filtrate (i.e., mother liquor) after solid-liquid separation and the washing liquid generated after washing can both be returned to the circulating water system for reuse.

[0025] The reaction principle is as follows: High-pressure carbon dioxide dissolution: CO2 + H2O = H2CO3 Alkaliization transformation: H2CO3 + 2NaOH → Na2CO3 + 2H2O; HCO3 - +OH - →CO3 2- +H2O Precipitation reaction: Ca 2+ +CO3 2一 =CaCO3↓ The method of this invention relies on the concentration of calcium and magnesium ions by a nanofiltration membrane and precise pH control for the purity control of calcium carbonate. It utilizes the nanofiltration membrane in the nanofiltration equipment to achieve high retention of calcium and magnesium ions in the concentrate from the reverse osmosis unit; and based on the difference that magnesium hydroxide begins to precipitate significantly at pH > 10.5, while calcium carbonate can precipitate completely at pH > 8.5, the pH of the precipitation reaction is controlled between 10.2 and 10.5 to achieve selective precipitation of calcium ions.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The method of the present invention can achieve a calcium ion removal rate of more than 95% in the concentrated brine after nanofiltration separation, significantly reduce the calcium hardness of the effluent, and create favorable conditions for the reuse of effluent.

[0027] (2) The method of the present invention can fix about 0.4 tons of carbon dioxide for every 1 ton of calcium carbonate product produced, realizing the high-value mineralization and utilization of carbon dioxide in flue gas.

[0028] (3) The method of the present invention utilizes the carbon dioxide dissolution pressure and pH adjustment and other necessary conditions to achieve carbon fixation, which can simultaneously solve multiple problems in concentrated brine treatment, such as calcium resource waste, mixed salt problem, high energy consumption, and limited carbon dioxide utilization in the field of carbon capture. Moreover, it does not rely on specific equipment, is simple to operate, and has low cost.

[0029] (4) In the method of the present invention, the filtrate after solid-liquid separation can be used as makeup water for the enterprise's circulating water, reducing the risk of scaling. The concentrated brine in this method comes from the saline wastewater, which is a pain point in the enterprise's water treatment, and the flue gas also comes from the carbon dioxide captured by the lime kiln of the steel enterprise, thus realizing resource utilization. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the process flow for concentrated brine mineralization and carbon fixation according to the present invention. Figure 2 The image shows the morphology of calcium carbonate obtained by the concentrated brine mineralization and carbon fixation method in Example 1. Detailed Implementation

[0031] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0032] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0033] In the following embodiments, the instruments and equipment used and their specifications are configured as follows. High-pressure melting vessel: V=10L, design pressure 6 MPa, 316L stainless steel material, with magnetic stirring (0~300 rpm); High-pressure metering pump: flow rate 0~100 L / h, pressure resistance 6 MPa; Precipitation reactor: V=10L, atmospheric pressure, with jacketed temperature control, variable frequency stirring (0~200 rpm); Horizontal decanter centrifuge: LW350 model, separation factor 250; Flash dryer: evaporation capacity 150 kg / h, bag filter dust collector.

[0034] In the following examples, the CO2 solubility was calculated using Henry's Law, and its theoretical saturation value at 3.5 MPa was 5.1 g.

[0035] In the following examples, the carbon dioxide source used is carbon dioxide produced by pressure swing adsorption (PSA) carbon capture of blast furnace gas, with a volume concentration of 95%, a gas source temperature of 25°C, and a gas source pressure of 3.5 MPa.

[0036] In the following examples, the concentrated brine used was the calcium enrichment concentrate from the concentrated water of the reverse osmosis unit after salt separation by nanofiltration membrane. The total dissolved solids (TDS) concentration in the concentrated brine was 18,500 mg / L, and the pH of the concentrated brine was 7.8. The concentrated brine contained Ca... 2+ The concentration was 900 mg / L, Mg 2+ The concentration was 180 mg / L.

[0037] In the following examples, the pure water used is reverse osmosis permeate with a conductivity of <10 μS / cm.

[0038] In the following examples, the first-stage washing liquid used in the three-stage countercurrent water washing is the filtrate from solid-liquid separation (i.e., mother liquor), and the second-stage and third-stage washing liquids are both pure water. The total mass ratio of the first-stage washing liquid, the second-stage washing liquid, and the third-stage washing liquid to the solid precipitate is 3:1.

[0039] In the following embodiments, the flash dryer drying settings are: inlet temperature 135°C and outlet temperature 75°C.

[0040] Example 1 A method for mineralizing and fixing carbon in concentrated brine, the process flow is as follows: Figure 1 As shown, it includes the following steps: Step 1, High-Pressure Carbon Dioxide Dissolution: The carbon dioxide gas source is pressurized to 3.5 MPa by a compressor, and then fed into a high-pressure dissolution vessel containing 2.5 L of pure water at a flow rate of 20 L / h. Under the pressure of 3.5 MPa, the mixture is stirred at a water temperature of 18~22℃ until the amount of CO2 dissolved in pure water reaches 4.8 g / L (the amount of CO2 dissolved is monitored and recorded in real time during the stirring process. When the amount of dissolved CO2 reaches 4.8 g / L, it is 94% of the theoretical saturation value. The gas-water contact time is 20 min), and a carbonic acid solution is obtained. Step 2, Alkalization Conversion: Under the pressure conditions of Step 1, start the high-pressure metering pump and add liquid alkali dropwise to the carbonate solution in the high-pressure dissolving vessel at a flow rate of 1.6 L / h to convert the dissolved CO2 (H2CO3, HCO3-) into alkali. - ) converted into CO3 2- Adjust the pH to 10.5 (pH monitored in real time, time taken 5 min), stir for 10 min to ensure complete conversion, and obtain a high-pressure alkaline carbonate solution (the CO3 content in the high-pressure alkaline carbonate solution was measured).2- The concentration of the solution is 3.84 g / L. The solution is a mixture of alkali metal hydroxide and water. The alkali metal hydroxide is sodium hydroxide, and the concentration of sodium hydroxide in the solution is 32 wt%.

[0041] Step 3, Precipitation Reaction: Calculate the total volume of concentrated brine used based on the chemical reaction equation for calcium carbonate. First, slowly release the high-pressure carbonate solution from the high-pressure dissolving vessel into the precipitation reactor using a pressure reducing valve. Then, add 2.5L of concentrated brine with a calcium ion concentration of 900mg / L (approximately 33% of the total volume of concentrated brine) over 5 minutes (to avoid CO2 flash loss). Mix thoroughly at 0.1 MPa atmospheric pressure and 80 rpm stirring speed to control the initial calcium ion concentration and reduce supersaturation. Then, add 4.9L of concentrated brine over 10 minutes using a metering pump. Crystals form in an orderly manner. The temperature is controlled at 32±2℃ during the dropwise addition process. After the dropwise addition is complete, a mixed solution is obtained. The mixed solution is then aged at 35℃ for 30 minutes with a stirring speed of 100 rpm to obtain a reaction slurry with a solid content of approximately 0.061%.

[0042] At the end of the maturation process, samples of the reaction slurry were taken and tested. The Ca content in the supernatant after settling was measured. 2+ At a concentration of 20 mg / L, the calcium ion removal rate was 97%.

[0043] Step 4, Post-processing: Set the separation factor to 250 and the feed rate to 20L / h. Pump the reaction slurry to a horizontal screw centrifuge for solid-liquid separation. The solid precipitate (i.e., filter cake) and filtrate (i.e., mother liquor) are separated. The filter cake has a moisture content of 35%. The filter cake is washed with countercurrent water in three stages and dried in a flash dryer for 3-5 seconds. After drying, it is collected by a cyclone separator and a bag filter to obtain calcium carbonate.

[0044] After three-stage countercurrent washing, the filter cake was determined to be calcium carbonate, with a mass of 16.28 g. Its morphology is shown in the figure below. Figure 2 As shown, the calcium ion removal rate was 97%. The purity of calcium carbonate was 92.5% (detected by titration).

[0045] The filtrate contains NaHCO3, and because of its low calcium ion content, it can be reused as circulating water.

[0046] Comparative Example 1 A method for mineralizing and fixing carbon with concentrated brine is basically the same as the method in Example 1, except that the CO2 dissolution pressure is different in step 1. The operation of step 1 is as follows: In step 1, the carbon dioxide gas source is pressurized to 0.1 MPa by a compressor, and then introduced into a high-pressure dissolution vessel containing 2.5 L of pure water at a flow rate of 20 L / h. Under the pressure of 0.1 MPa, the mixture is stirred at a water temperature of 18~22℃ until the amount of CO2 dissolved in the pure water reaches 1.38 g / L (the amount of CO2 dissolved is monitored in real time during the stirring process. When the amount of dissolved CO2 reaches 1.24 g / L, it is 89% of the theoretical saturation value (the theoretical value is 1.38 g / L at 0.1 MPa, and the gas-water contact time is 240 min), thus obtaining a carbonic acid solution.

[0047] The reaction slurry from step 3 was sampled and tested. The calcium ion removal rate was 44%, and the liquid alkali consumption was 14.2 g. The data from Example 1 and Comparative Example 1 were compared, and the results are shown in Table 1.

[0048] Table 1

[0049] Comparative Example 2 A method for mineralizing and fixing carbon with concentrated brine is basically the same as the method in Example 1, except that step 3 is performed directly after obtaining the carbonic acid solution (pH=6.5~7.0) in step 1, instead of step 2.

[0050] Samples of the reaction slurry from step 3 were tested, and calcium ions were not removed.

[0051] The data of Example 1 and Comparative Example 2 were compared, and the results are shown in Table 2.

[0052] Table 2

[0053] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for mineralizing and fixing carbon in concentrated brine, characterized in that, Includes the following steps: Step 1, High-pressure carbon dioxide dissolution: Pass carbon dioxide gas into pure water and stir at a pressure of 2~5 MPa until the amount of carbon dioxide dissolved in pure water reaches 2.76~6 g / L to obtain a carbonic acid solution. Step 2, Alkalization Conversion: Under the pressure conditions described in Step 1, liquid alkali is added dropwise to the carbonic acid solution to adjust the pH to 10.2~10.5, thereby obtaining a high-pressure carbonic acid alkali solution; Step 3, precipitation reaction: Under normal pressure, the high-pressure carbonic acid solution is mixed evenly with concentrated brine containing calcium ions and aged at 25~40℃ for 30~60 minutes to obtain a reaction slurry. The concentrated brine is the calcium enrichment side concentrate after the concentrated water of the reverse osmosis device is desalted by nanofiltration membrane. Step 4, post-processing: solid-liquid separation, washing, drying, and collection of calcium carbonate; The concentration of calcium ions in the concentrated brine is 800~1000 mg / L; CO3 in high-pressure carbonic acid solution 2- The concentration is 1.7~5 g / L The procedure for mixing high-pressure alkali carbonate solution with concentrated brine containing calcium ions is as follows: Calculate the total volume of concentrated brine required based on the chemical reaction equation of calcium carbonate. First, mix the high-pressure alkali carbonate solution with concentrated brine accounting for 30-35% of the total volume of concentrated brine, and then slowly add the remaining concentrated brine.

2. The method according to claim 1, characterized in that, The carbon dioxide source includes carbon dioxide produced from flue gas through a pressure swing adsorption carbon capture process, the pure water includes reverse osmosis permeate with a conductivity of <10 μS / cm, and the volume concentration of carbon dioxide in the carbon dioxide source is ≥95%.

3. The method according to claim 1, characterized in that, The carbon dioxide gas source is introduced into pure water for 10 to 30 minutes to allow the carbon dioxide to dissolve fully in the pure water, with a dissolved amount of 2.76 to 6 g / L. The temperature of pure water is 15~25℃.

4. The method according to claim 1, characterized in that, The liquid alkali is a mixture of alkali metal hydroxide and water, and the concentration of the alkali metal hydroxide in the liquid alkali is 30~40wt%, including sodium hydroxide or potassium hydroxide.

5. The method according to claim 1, characterized in that, The high-pressure alkaline carbonate solution is reduced to atmospheric pressure and mixed with concentrated salt water containing calcium ions, and reacted at 25~40℃ for 30~60 minutes.

6. The method according to claim 1, characterized in that, The slow dripping time is 20-30 minutes; the stirring speed is 100-150 rpm.

7. The method according to claim 1, characterized in that, The reaction slurry is separated into solid and liquid components by centrifugation. The filtrate after solid-liquid separation contains sodium carbonate, which is used as an alkalizing agent in the alkali solution in step 2. The centrifugal separation equipment is a horizontal screw centrifuge or a disc centrifuge, and the separation factor for solid-liquid separation is controlled between 150 and 300.

8. The method according to claim 1, characterized in that, The washing process is a three-stage countercurrent water washing. The first-stage washing liquid used in the three-stage countercurrent water washing is the filtrate collected after solid-liquid separation. The second-stage washing liquid and the third-stage washing liquid are both pure water. The total mass ratio of the first-stage washing liquid, the second-stage washing liquid and the third-stage washing liquid to the solid precipitate is 3:

1. The filtrate after solid-liquid separation and the washing liquid generated after washing are both returned to the circulating water system for reuse.

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