Method for recycling flue gas carbon dioxide for alumina production wastewater treatment

Abstract

The invention discloses a method for recycling flue gas carbon dioxide for aluminum oxide production wastewater treatment. The method comprises the following steps: adding wastewater into a gas dissolving reaction tank, pressurizing and conveying flue gas containing carbon dioxide into the gas dissolving reaction tank through a fan, reacting carbon dioxide with water to generate carbonic acid, reacting carbonic acid with meta-aluminate radicals in the wastewater to generate aluminum carbonate, and immediately reacting aluminum carbonate with water to generate aluminum hydroxide. Aluminum hydroxide generated by the reaction gathers suspended particles in water into large particles and precipitates the large particles, and supernate obtained after reaction precipitation flows into a backwater pool. The method has the beneficial effects that the flocculants required to be input in the wastewater treatment process are greatly reduced, the method has important significance in controlling the sewage treatment cost, the production benefits of enterprises can be effectively improved, and the advantage of greatly reducing the coagulant aid cost in the wastewater treatment process is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment methods, and particularly relates to a method for treating wastewater in alumina production by recycling carbon dioxide in flue gas. BACKGROUND

[0002] In the process of alumina production, a large amount of carbon dioxide is generated in the process of carbonation and decomposition of sodium aluminate solution, calcination of limestone and calcination of aluminum hydroxide, and the concentration of the carbon dioxide is 10%-20%. The purified carbon dioxide is discharged into the atmosphere through a flue, and the carbon dioxide is one of the main greenhouse gases. It has an important influence on the energy balance of the earth's climate system, and its increase is closely related to the phenomenon of global warming. On the other hand, the wastewater and the backwater of the red mud reservoir in the process of alumina production contain a large amount of strong alkaline aluminum metal, and the content of metavanadate is 300 mg / L-500 mg / L. If not properly disposed, it will have a great impact on the soil and water system.

[0003] A Chinese utility model patent with the publication number CN204111491U discloses an aluminum industry wastewater treatment system, which comprises a regulating pool for collecting aluminum industry wastewater, a first PH regulating pool, a mixed reaction pool, an inclined plate sedimentation pool, a second PH regulating pool, an intermediate pool, a recycled water pool and a water supply mechanism. A first lifting pump is arranged in the regulating pool to pump the wastewater into the first PH regulating pool. A second lifting pump is arranged in the first PH regulating pool to pump the wastewater into the mixed reaction pool through a first discharge pipeline. An alkali adding device is arranged on the first discharge pipeline. The mixed reaction pool is further provided with a flocculant adding mechanism and a coagulant adding mechanism. The present utility model fully utilizes the workshop resources to neutralize and treat the alkaline wastewater and the acidic wastewater, mixes the acidic and alkaline wastewater and the anode oxidation wastewater to neutralize each other, achieves the purpose of treating waste with waste, and effectively reduces the treatment cost.

[0004] Currently, the produced wastewater and the backwater of the red mud reservoir enter a produced wastewater regulating pool, a certain polyacrylamide and polyaluminum chloride are added, and the wastewater is filtered in an integrated wastewater treatment device. The backwash sludge enters a sludge pool, and the clear water enters a recycled water pool. The process flow diagram is shown in FIG. 1. Inorganic salts such as aluminum salts, iron salts and calcium salts are needed to be added as coagulants. The coagulants can form charged ions or colloids in water, and have an electric neutralization or adsorption effect with suspended particles, so as to make the particles aggregate and settle. In the continuous production process, a large amount of coagulants are consumed, which leads to high production cost and has a great impact on the production efficiency of the enterprise. Therefore, the current wastewater treatment process has the defect of high cost of coagulants. Figure 1 SUMMARY

[0005] ​To solve the above technical problems, the present application aims to provide a flue gas carbon dioxide recovery method for alumina production wastewater treatment, which comprises the following steps: adding wastewater into a dissolved gas reaction tank, pressurizing and conveying the flue gas containing carbon dioxide to the dissolved gas reaction tank by a fan, reacting carbon dioxide with water to generate carbonic acid, reacting the carbonic acid with the aluminate in the wastewater to generate aluminum carbonate, immediately reacting the aluminum carbonate with water to generate aluminum hydroxide, and gathering the suspended particles in the water into large particles and precipitating by the aluminum hydroxide generated in the reaction, and flowing the supernatant into a backwater tank after the reaction and precipitation.

[0006] To achieve the above-mentioned application purposes, the technical solutions adopted by the present application are as follows: A flue gas carbon dioxide recovery method for alumina production wastewater treatment, comprising the following steps: S1, adding wastewater into a dissolved gas reaction tank; S2, pressurizing and conveying the flue gas containing carbon dioxide to the dissolved gas reaction tank by a fan; S3, introducing the flue gas containing carbon dioxide into the dissolved gas reaction tank, reacting carbon dioxide with water to generate carbonic acid, and the chemical reaction formula is: reacting the carbonic acid with the aluminate in the wastewater to generate aluminum carbonate, immediately reacting the aluminum carbonate with water to generate aluminum hydroxide, and the reaction formula is: S4, gathering the suspended particles in the water into large particles and precipitating by the aluminum hydroxide generated in the reaction; S5, flowing the supernatant into a backwater tank after the reaction and precipitation, and discharging the precipitate into a sludge tank.

[0007] As a preferred, in the step S2, the following step is further included: temporarily reducing the temperature by a heat exchange device.

[0008] As a preferred, in the step S2, the following step is further included: reducing the temperature of the flue gas containing carbon dioxide from 60-150℃ to less than 40℃.

[0009] As a preferred, in the step S2, the following step is further included: carrying out dust removal and purification treatment on the flue gas containing carbon dioxide.

[0010] As a preferred, in the step S5, the following step is further included: monitoring the turbidity of the supernatant flowing into the backwater tank.

[0011] As a preferred, in the step S5, the following step is further included: ​According to the turbidity interlocking control of the supernatant, the air supply flow of the fan is increased when the turbidity of the supernatant increases.

[0012] As preferred, in the step S2, the following steps are further included: The carbon dioxide-containing flue gas is waste gas generated in the carbonation and decomposition of sodium aluminate solution, limestone calcination and calcination of aluminum hydroxide in the aluminum production process.

[0013] As preferred, in the step S2, the following steps are further included: After the carbon dioxide-containing flue gas is depressurized and energy dissipated by the dissolved gas release device, the carbon dioxide is rapidly and uniformly released into the wastewater in the form of fine bubbles for reaction.

[0014] Compared with the prior art, the present application has the following beneficial technical effects: The wastewater treatment method utilizes the carbon dioxide-containing flue gas that needs to be discharged, uses the flue gas to produce carbonic acid in the wastewater, and then reacts with the meta-aluminate in the alumina production wastewater to produce aluminum carbonate, and then the aluminum carbonate reacts with water to produce aluminum hydroxide, so that the aluminum hydroxide can be used as a flocculating agent to aggregate suspended particles in water into large particles, and then solid-liquid separation is realized, achieving the function of wastewater treatment, greatly reducing the flocculating agent needed in the wastewater treatment process, having important significance in controlling sewage treatment cost, effectively improving enterprise production efficiency, and achieving the advantage of greatly reducing the cost of coagulant in the wastewater treatment process. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a process flow diagram of the conventional wastewater treatment process in the background art of the present application; Figure 2 is a process flow diagram of a flue gas carbon dioxide recovery method for alumina production wastewater treatment in an embodiment of the present application. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solution and advantages of the present application clearer, the present application will be further described in detail below in conjunction with embodiments, but the scope of protection claimed by the present application is not limited to the following specific embodiments.

[0017] REFERENCE Figure 1 A flue gas carbon dioxide recovery method for alumina production wastewater treatment, comprising the following steps: S1, adding wastewater to the dissolved gas reaction tank, the wastewater being wastewater generated in the alumina production process and wastewater generated from the red mud reservoir.

[0018] S2, the flue gas containing carbon dioxide is pressurized and transported to the dissolved gas reaction tank by a fan; the flue gas is cooled by a heat exchange device during transportation. The temperature of the flue gas containing carbon dioxide is reduced from 60-150℃ to less than 40℃. The flue gas containing carbon dioxide is subjected to dust removal and purification treatment. The flue gas containing carbon dioxide is the waste gas generated in the process of carbonation and decomposition of sodium aluminate solution, calcination of limestone and calcination of aluminum hydroxide in the production process of aluminum oxide. After the flue gas containing carbon dioxide is depressurized and energy dissipated by the dissolved gas release device, the carbon dioxide is rapidly and uniformly released into the wastewater in the form of fine bubbles for reaction.

[0019] S3, the flue gas containing carbon dioxide is introduced into the dissolved gas reaction tank, and the carbon dioxide reacts with water to generate carbonic acid, and the chemical reaction formula is: , the carbonic acid reacts with the met aluminates in the wastewater to generate aluminum carbonate, and the aluminum carbonate immediately reacts with water to generate aluminum hydroxide, and the reaction formula is: .

[0020] S4, the aluminum hydroxide generated by the reaction aggregates the suspended particles in the water into large particles and precipitates.

[0021] S5, after the reaction and precipitation, the supernatant flows into the backwater tank, and the precipitate is discharged into the sludge tank. The turbidity of the supernatant flowing into the backwater tank is monitored. The air supply flow of the fan is controlled according to the turbidity of the supernatant. When the turbidity of the supernatant increases, the air supply flow of the fan is increased.

[0022] Taking the daily wastewater treatment capacity of 8500m³ / d as an example, compared with the polyacrylamide and polyaluminum chloride flocculation treatment process, the treatment reagent cost is reduced. The cost comparison is as follows: Table 1 cost table of adding traditional flocculants

[0023] Table 2 cost table of using the wastewater treatment method

[0024] As shown in Tables 1 and 2, the wastewater treatment method can reduce 13300 yuan per year under the condition of daily wastewater treatment capacity of 8500m³ / d, which greatly reduces the flocculant procurement cost in the wastewater treatment process.

[0025] Table 3 turbidity and removal rate comparison table after wastewater treatment

[0026] As shown in Table 3, the wastewater treated by the wastewater treatment method has lower turbidity and higher removal rate, and has better removal effect.

[0027] The embodiment has the following advantages: In step S3, since the chemical bond (oxygen bond) between aluminum, carbon, and oxygen in the produced aluminum carbonate is too weak, the generated aluminum carbonate will immediately react with water to generate aluminum hydroxide, so that the aluminum hydroxide can be used as a flocculant to aggregate suspended particles in water into large particles through charge neutralization, adsorption bridging, and multi-ligand coordination, thereby realizing solid-liquid separation. In this process, a small amount of polyacrylamide water-soluble polymer flocculant can also be added according to actual needs to further enhance the treatment effect, improve the clarity and stability of the water quality, facilitate the adjustment of the effluent water quality, and avoid the problem of substandard water quality due to insufficient carbon dioxide in the flue gas.

[0028] The wastewater treatment method utilizes the flue gas containing carbon dioxide that needs to be discharged, uses the flue gas to produce carbonic acid in the wastewater, and then reacts with the meta-aluminate in the alumina production wastewater to produce aluminum carbonate, and then the aluminum carbonate reacts with water to generate aluminum hydroxide, so that the aluminum hydroxide can be used as a flocculant to aggregate suspended particles in water into large particles, thereby realizing solid-liquid separation, achieving the function of wastewater treatment, and greatly reducing the flocculant needed in the wastewater treatment process, which is of great significance in controlling the cost of sewage treatment and can effectively improve the production efficiency of enterprises, thereby achieving the advantage of greatly reducing the cost of coagulant in the wastewater treatment process.

[0029] Since the aluminum hydroxide in the wastewater treatment method is generated by reaction in the wastewater, the in-situ generated aluminum hydroxide is more uniformly distributed in the wastewater and has a larger total surface area, so it can have a higher reaction speed and wastewater purification effect.

[0030] The solubility of gas generally increases with the decrease of temperature, and a low-temperature environment is conducive to the dissolution of more carbon dioxide in water. Reducing the temperature of the flue gas containing carbon dioxide can increase the solubility of carbon dioxide in the wastewater, improve the efficiency of generating carbonic acid in the wastewater, and thus promote the reaction of carbon dioxide and water to generate carbonic acid, so that the subsequent reaction with meta-aluminate is more sufficient.

[0031] If the temperature is too high, the solubility of carbon dioxide decreases and the reaction is not sufficient; if the temperature is too low, the reaction rate may be too slow, affecting the treatment efficiency. After a large number of experiments and actual application verification, a temperature of less than 40°C can ensure good reaction effect.

[0032] Removing dust and impurities from the flue gas prevents dust and impurities from being adsorbed on the surface of aluminum hydroxide, affecting its performance as a flocculant.

[0033] Using a filtering device to remove solids from the liquid can reduce the influence of solid particles on the reaction and avoid interference with the aggregation process of aluminum hydroxide and suspended particles.

[0034] Turbidity is an important indicator to measure the content of suspended particles in supernatant, and real-time monitoring of turbidity can understand the effect of wastewater treatment in time to ensure that the effluent quality meets the requirements.

[0035] The air supply flow of the fan directly affects the amount of carbon dioxide into the dissolved air reaction tank, and further affects the generation amount and flocculation effect of aluminum hydroxide. When the supernatant turbidity is monitored to increase, it indicates that the content of suspended particles in water is high. At this time, increasing the air supply flow of the fan can increase the amount of carbon dioxide into, promote more aluminum hydroxide to be generated, thereby improving the flocculation effect and reducing the turbidity of supernatant. The interlocking control mechanism can adjust the process parameters in time according to the actual treatment effect, and ensure the stable operation of the wastewater treatment system and the compliance of the effluent quality.

[0036] Recycling the waste gas that needs to be discharged into the atmosphere not only reduces the emission of carbon dioxide and reduces the impact on the environment, but also provides a cheap source of carbon dioxide for wastewater treatment. The utilization of waste gas resources is realized, and the dual effects of energy saving and emission reduction and waste treatment are achieved.

[0037] Uniform distribution of fine bubbles in wastewater can make the reaction more complete and stable, which is conducive to the generation of aluminum hydroxide and the aggregation and precipitation of suspended particles, and further improves the effect of wastewater treatment.

[0038] According to the disclosure and teaching of the above description, those skilled in the art of the present application can also make changes and modifications to the above embodiments. Therefore, the present application is not limited to the specific embodiments disclosed and described above, and some modifications and changes of the application should also fall within the protection scope of the claims of the present application. In addition, although some specific terms are used in the specification, these terms are only for convenience of explanation and do not constitute any limitation on the application.

Claims

1. A method for recovering carbon dioxide from flue gas for use in the treatment of wastewater from alumina production, characterized in that, Includes the following steps: S1. Add wastewater to the dissolved gas reaction tank; S2. The flue gas containing carbon dioxide is pressurized and transported to the dissolved gas reaction tank by a blower; S3. Carbon dioxide-containing flue gas is introduced into the dissolved gas reaction tank. The carbon dioxide reacts with water to produce carbonic acid. The chemical reaction formula is: Carbonic acid reacts with aluminate ions in wastewater to form aluminum carbonate, which then immediately reacts with water to form aluminum hydroxide. The reaction equation is as follows: ; S4. The aluminum hydroxide produced by the reaction aggregates suspended particles in the water into large particles and causes them to precipitate. S5. After the reaction and sedimentation, the supernatant flows into the return water tank, and the sediment is discharged into the sludge tank.

2. The method for treating alumina production wastewater by recovering carbon dioxide from flue gas according to claim 1, characterized in that, Step S2 further includes the following steps: It is cooled down by heat exchange equipment midway through the process.

3. The method for treating alumina production wastewater by recovering carbon dioxide from flue gas according to claim 2, characterized in that, Step S2 further includes the following steps: The temperature of the carbon dioxide-containing flue gas decreased from 60℃-150℃ to less than 40℃.

4. The method for treating alumina production wastewater by recovering carbon dioxide from flue gas according to claim 1, characterized in that, Step S2 further includes the following steps: Dust removal and purification treatment is carried out on flue gas containing carbon dioxide.

5. The method for treating alumina production wastewater by recovering carbon dioxide from flue gas according to claim 1, characterized in that, Step S5 further includes the following steps: The turbidity of the supernatant flowing into the return water tank is monitored.

6. The method for treating alumina production wastewater by recovering carbon dioxide from flue gas according to claim 5, characterized in that, Step S5 further includes the following steps: The blower's airflow is controlled by interlocking the turbidity of the supernatant. When the turbidity of the supernatant increases, the blower's airflow is increased.

7. The method for treating alumina production wastewater by recovering carbon dioxide from flue gas according to claim 1, characterized in that, Step S2 further includes the following steps: The carbon dioxide-containing flue gas is the waste gas generated in the carbonation decomposition of sodium aluminate solution, limestone calcination, and aluminum hydroxide roasting stages of the alumina production process.

8. The method for treating alumina production wastewater by recovering carbon dioxide from flue gas according to claim 1, characterized in that, Step S2 further includes the following steps: The carbon dioxide-containing flue gas is depressurized and de-energized by the dissolved gas release device, and the carbon dioxide is rapidly and evenly released into the wastewater in the form of fine bubbles to react.

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