TW201801786A - Treatment method for reducing carbon dioxide emissions by using microalgae culture to reduce the emission of carbon dioxide for waste water - Google Patents

Abstract

The present invention relates to a treatment method of reducing carbon dioxide emissions with high efficiency. The method comprises the following steps of: absorbing exhaust gas containing carbon dioxide by using an alkaline aqueous solution having a concentration lower than 20 weight percentage to obtain a weakly acidic aqueous solution rich in carbonate ions and bicarbonate ions; utilizing the characteristics of photosynthesis carbon fixation of microalgae to add the weakly acidic aqueous solution to the microalgae culture tank to provide the carbon source needed for microalgae photosynthesis. The present invention effectively absorbs carbon dioxide by an alkaline aqueous solution, and then uses the microalgae culture for photosynthesis to solve the problems of ineffectiveness in poor absorption of carbon dioxide by fresh water or seawater, and environmental pollution caused by the direct discharge of waste water, thereby effectively reducing the emission of carbon dioxide.

Description

Treatment methods to reduce carbon dioxide emissions

The present invention relates to a method for purifying exhaust gas, and more particularly to a method for reducing carbon dioxide emissions in exhaust gas.

Due to the large amount of industrial development of greenhouse gas emissions, the global warming problem is becoming increasingly serious, and the continuous rise in global temperature is enough to affect the survival of global species. Therefore, how to reduce greenhouse gas emissions has become a common goal worldwide. Various solutions have been developed to reduce carbon dioxide emissions, such as improving fuel efficiency or carbon dioxide capture and adsorption. Related patents include TW201100532 and TW201317045.

In the prior art, a method of reducing carbon dioxide content is to use fresh water or seawater as a flushing agent, and use water washing technology to flush exhaust gas containing carbon dioxide, so as to try to dissolve part of the carbon dioxide gas in the freshwater or seawater. However, as described in Journal of Chemical and Engineering Data , 1970, 15 (1) , p 67-p 71, carbon dioxide gas can only dissolve 2.403 grams of carbon dioxide per 100 grams of fresh water at 25 ^° C and 20 atmospheres, and the carbon dioxide gas Only 0.11 grams of carbon dioxide can be dissolved per 100 grams of seawater at 25 ^° C and 1 atmosphere, so it is difficult to obtain the desired washing effect regardless of whether the fresh water or seawater is used to flush the exhaust gas, and the carbonated water produced after washing is directly discharged without treatment To rivers or seawater, it will also cause environmental acidification pollution.

In view of the technical shortcomings of the prior art, the purpose of the present invention is to improve the problem of ineffective carbon dioxide absorption in general freshwater or seawater and the environmental pollution caused by the direct discharge of wastewater, thereby efficiently reducing the amount of carbon dioxide emissions.

To achieve the foregoing object, the present invention provides a treatment method for reducing carbon dioxide emissions, which includes the following steps: collecting exhaust gas containing carbon dioxide; absorbing carbon dioxide in the exhaust gas with an alkaline aqueous solution having a concentration of less than 20% by weight, and obtaining a A weakly acidic aqueous solution containing carbonate ions, bicarbonate ions, and metal ions; and adding the weakly acidic aqueous solution to a microalgae culture tank containing microalgae for photosynthesis, thereby reducing carbonic acid in the weakly acidic aqueous solution Concentration of root ions and bicarbonate ions to obtain a treated wastewater.

According to the present invention, the technical means of using an alkaline aqueous solution having a concentration of less than 20% by weight can greatly improve the problem of poor results when absorbing carbon dioxide using fresh water or seawater in the prior art, and can save water consumption of the alkaline aqueous solution. To achieve the effect of saving water.

More preferably, the step of collecting the exhaust gas containing carbon dioxide and the step of absorbing the carbon dioxide in the exhaust gas with an alkaline aqueous solution having a concentration of less than 20% by weight to obtain the weakly acidic aqueous solution include: collecting the exhaust gas containing carbon dioxide; The exhaust gas containing carbon dioxide is pre-processed to obtain a pre-treated exhaust gas, the pre-treated exhaust gas contains carbon dioxide; the alkaline aqueous solution with a concentration of less than 20% by weight absorbs the carbon dioxide in the pre-treated exhaust gas to obtain the Weakly acidic aqueous solution; wherein the pretreatment is a dust collection treatment, a desulfurization treatment, a denitration treatment, a temperature reduction treatment, or a combination thereof.

Preferably, the alkaline aqueous solution is an aqueous solution containing a group IA element metal ion, an aqueous solution containing a group IIA element metal ion, or a combination thereof; more preferably, the alkaline aqueous solution is a sodium hydroxide aqueous solution, a calcium hydroxide aqueous solution, hydrogen An aqueous potassium oxide solution, an aqueous ammonia solution, or a combination thereof; even more preferably, the alkaline aqueous solution is an aqueous sodium hydroxide solution.

Preferably, the concentration of the alkaline aqueous solution is less than or equal to 10% by weight; more preferably, the concentration of the alkaline aqueous solution is greater than or equal to 3% by weight and less than or equal to 5% by weight; even more preferably The concentration of the alkaline aqueous solution is higher than or equal to 3 weight percent and lower than or equal to 3.5 weight percent.

Preferably, the weakly acidic aqueous solution has a pH value of 5 or more and 7 or less. More preferably, the weakly acidic aqueous solution has a pH value of 5 or more and 6 or less.

Preferably, the microalgae are Botryococcus braunii , Chlorella sp. , Crypthecodinium cohnii , Cylindrotheca sp. , Dunaliella primolecta , etc. Isochrysis sp. , Monalanthus Salina , Nannochloris sp. , Nannochloropsis sp. , Neochloris oleoabundans , Nitzschia sp. , Phaeodactylum tricornutum , Schizochytrium sp. , Tetraselmis suecica , or a combination thereof. Even more preferably, the microalgae are chlorella, Dunaliella, Isochrysis, micro green algae, neo green algae, and Schizochytrium.

Preferably, the microalga cultivation tank is a closed microalga cultivation tank. Compared with the use of open microalgae culture tanks, the closed microalgae culture tanks have the advantages of lower land demand and being less affected by weather changes. Therefore, the method of the present invention has the advantages of higher productivity and stability of microalgae, higher carbon fixation efficiency, and higher algal fat content of the microalgae.

More preferably, the weakly acidic aqueous solution is added to the microalgae-containing microalgae breeding tank for photosynthesis in order to reduce the concentration of carbonate ions and bicarbonate ions in the weakly acidic aqueous solution to obtain the treated wastewater. The steps include: adding the weakly acidic aqueous solution to a microalgae culture tank containing microalgae for photosynthesis, thereby reducing the concentration of carbonate ions and bicarbonate ions in the weakly acidic aqueous solution to obtain a first treatment solution, and the first treatment The acid-base value of the solution is greater than 8; the weakly acidic aqueous solution is added to the first treatment solution to obtain a second treatment solution, and the acid-base value of the second treatment solution is greater than or equal to 6 and less than or equal to 7, so The second treatment solution contains carbonate ions, bicarbonate ions and metal ions; in the microalga cultivation tank containing microalgae and the second treatment solution, the microalgae performs photosynthesis, thereby reducing the second treatment solution Concentration of carbonate ions and bicarbonate ions to obtain the treated wastewater. Even better, the microalgae breeding tank is a fully automatic microalgae culture tank, which can detect the pH value of the first treatment solution, water flow speed, temperature, algae density, and light intensity, etc. When the time comes, the weakly acidic aqueous solution is automatically replenished in the first treatment solution, thereby ensuring that the microalgae in the microalgae cultivation tank can continuously perform photosynthesis.

Preferably, the weakly acidic aqueous solution is added to the microalgae-containing microalgae culture tank for photosynthesis, so as to reduce the concentration of carbonate ions and bicarbonate ions in the weakly acidic aqueous solution to obtain the treated wastewater. After the step, the treated wastewater is subjected to subsequent treatment to obtain a supernatant and a sediment of algae mud containing microalgae, wherein the supernatant contains hydroxide ions and metal ions; and The algae slime containing microalgae is dried to obtain a dried algae powder, wherein the subsequent treatment is a precipitation treatment, a filtration treatment, or a combination thereof. The dried algae powder can be directly applied to raw materials of food, feed, fertilizer or used directly as fuel. More preferably, the alkaline aqueous solution having a concentration of less than 20% by weight is a supernatant collected by subsequent treatment of the treated wastewater; and is absorbed by the alkaline aqueous solution having a concentration of less than 20% by weight as described above. The step of obtaining carbon dioxide in the exhaust gas to obtain the weakly acidic aqueous solution includes: absorbing carbon dioxide in the exhaust gas with the supernatant to obtain the weakly acidic aqueous solution. More preferably, the supernatant is an alkaline aqueous solution having a concentration of less than or equal to 5 weight percent. More preferably, after the aforesaid step of drying the algae slime containing microalgae to obtain the dried algae powder, the method comprises: using the wall breaking treatment of the dried algae powder to obtain an algae oil and an algae block; This algal oil is transesterified to obtain a biodiesel. The algae block can be used as animal feed or fertilizer.

According to the present invention, the step of treating the dried algae powder by breaking the wall to obtain algae oil and algae block can be performed by ultrasonic vibration wall-breaking extraction method, plasma wall-breaking extraction method or supercritical wall-breaking extraction method. , But it's not limited to this. According to the present invention, the step of transesterifying the algal oil to obtain a biodiesel can be completed by a sodium hydroxide alkalinization reaction method, a high-temperature supercritical transesterification reaction method, or an enzyme-catalyzed transesterification reaction method, but it is not limited to this.

The treatment method of the present invention has the advantages of greatly increasing the solubility of carbon dioxide with an alkaline aqueous solution having a concentration of less than 20% by weight, effectively absorbing carbon dioxide, and reducing the amount of water originally using fresh water or seawater as a solvent; and the weakly acidic aqueous solution contains carbonic acid Root ions, bicarbonate ions and metal ions, the weakly acidic aqueous solution is added to a microalgae culture tank containing microalgae for photosynthesis, so that the microalgae can accelerate the use of carbonate and bicarbonate ions in the weakly acidic aqueous solution for biological Carbon fixation. According to this, the technical means of the present invention can improve the problem of poor absorption of carbon dioxide by freshwater or seawater in general and the environmental pollution caused by the direct discharge of wastewater, thereby achieving a high efficiency in reducing carbon dioxide emissions.

According to the present invention, one kilogram of microalgae can absorb about 2.28 kilograms of carbon dioxide, and its effect is far better than that of planting trees to purify carbon dioxide. In addition, the carbon dioxide absorbed by the microalgae cultivation can also produce biodiesel for energy, and the algae block can be used as animal feed or fertilizer, so that the products of the present invention can be effectively used.

Please refer to FIG. 1. First, the exhaust gas containing carbon dioxide is collected, and after being treated by dust collection, denitrification, denitration, and temperature reduction, it is discharged into a carbon dioxide absorption device, and the carbon dioxide absorption device contains hydrogen at a concentration of 3.5% by weight. The sodium oxide aqueous solution absorbs carbon dioxide in the exhaust gas by using a cyclic spraying method to obtain an aqueous sodium hydrogen carbonate solution (ie, a weakly acidic aqueous solution) containing carbonate ions, bicarbonate ions, and sodium ions, and the treated exhaust gas. The pH value of the aqueous sodium hydrogen carbonate solution is about 5 to 6.

Here, 38.5 kg of carbon dioxide can be absorbed by using 1000 kg of a 3.5 weight percent sodium hydroxide aqueous solution. In an equivalent amount of exhaust gas, the content of carbon dioxide in the treated exhaust gas is reduced from 45 ppm to 0.03 ppm and discharged. It can be seen that the absorption of carbon dioxide by using an aqueous sodium hydroxide solution containing a concentration of 3.5% by weight can indeed help reduce carbon dioxide emissions.

Next, the 1000 kg sodium bicarbonate aqueous solution that absorbed saturated carbon dioxide was collected and added to a microalga cultivation tank containing 8500 kg of microalgae, and the microalgae were supplied for photosynthesis, thereby reducing the carbonate ion and Concentration of bicarbonate ions and get a treated wastewater.

After the treated wastewater is filtered and precipitated, a supernatant liquid and algae slurry containing microalgae can be obtained; the supernatant liquid contains hydroxide ions and sodium ions, which can be recovered and introduced into the carbon dioxide absorption equipment again. To absorb carbon dioxide in the exhaust gas; and the algae mud sediment is dried to obtain dried algae powder. The dried algae powder can be directly used as a raw material for food, feed, fertilizer or directly used as a fuel. The dried algae powder can be reused and broken. After the wall treatment, an algae oil and an algae block are obtained, and the algae block can be used as animal feed or fertilizer; the algae oil can be transesterified to obtain biodiesel.

In a specific embodiment, the microalgae cultivation tank is a fully-automatic closed microalgae cultivation tank, and the fully-automatic closed microalgae cultivation tank is further provided with an acid-base value detector, a water flow speed detector, a temperature detector, and algae. Density detector and illuminance detector, which can automatically detect the pH value of the aqueous solution of the microalgae cultivation tank. When the pH value exceeds 8, the sodium bicarbonate solution will be automatically adjusted to maintain the photosynthesis of the microalgae. The efficiency of the effect, and the microalgae in the fully-automatic closed microalgae cultivation tank, compared with the open microalgae cultivation tank, the production capacity is higher, and it is less affected by weather changes.

The treatment method of the present invention absorbs carbon dioxide with an alkaline aqueous solution, which effectively improves the problem of poor solubility of carbon dioxide in the exhaust gas from freshwater or seawater. The obtained weakly acidic aqueous solution is added to a microalga cultivation tank for photosynthesis, which solves the problem of carbonated water directly. The problem of environmental pollution caused by emissions. Not only that, after the photosynthetic reaction wastewater obtained by the treatment method of the present invention is filtered and precipitated, the supernatant can be recycled and reused, and the dried algae powder obtained by filtering and drying the algal slurry can further be used as environmental protection. Energy raw materials.

The above description is only for the convenience of describing a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The scope of the claimed rights of the present invention should mainly be described in the scope of patent application.

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FIG. 1 is a schematic flowchart of a treatment method for reducing carbon dioxide emissions according to the present invention.

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Claims (17)

A treatment method for reducing carbon dioxide emissions, comprising the following steps: collecting exhaust gas containing carbon dioxide; absorbing carbon dioxide in the exhaust gas with an alkaline aqueous solution having a concentration of less than 20% by weight, and obtaining a weakly acidic aqueous solution, the weak The acidic aqueous solution contains carbonate ions, bicarbonate ions, and metal ions; and the weakly acidic aqueous solution is added to a microalgae culture tank containing microalgae for photosynthesis, thereby reducing the carbonate and bicarbonate ions in the weakly acidic aqueous solution. Concentration to get a treated wastewater. The processing method according to claim 1, wherein the step of collecting the exhaust gas containing carbon dioxide and the step of absorbing the carbon dioxide in the exhaust gas with an alkaline aqueous solution having a concentration of less than 20% by weight to obtain the weakly acidic aqueous solution include: collecting Carbon dioxide-containing exhaust gas; pre-treating the carbon dioxide-containing exhaust gas to obtain a pre-treated exhaust gas, the pre-treated exhaust gas containing carbon dioxide; absorbing the pre-treated exhaust gas with the alkaline aqueous solution having a concentration of less than 20% by weight Carbon dioxide in the exhaust gas to obtain the weakly acidic aqueous solution; wherein the pretreatment is a dust collection treatment, a desulfurization treatment, a denitration treatment, a temperature reduction treatment, or a combination thereof. The processing method according to claim 1, wherein the alkaline aqueous solution is an aqueous solution containing a group IA element metal ion, an aqueous solution containing a group IIA element metal ion, or a combination thereof. The method according to claim 3, wherein the alkaline aqueous solution is an aqueous sodium hydroxide solution, an aqueous calcium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous ammonia solution, or a combination thereof. The method according to claim 4, wherein the alkaline aqueous solution is an aqueous sodium hydroxide solution. The method according to claim 1, wherein the concentration of the alkaline aqueous solution is less than or equal to 10 weight percent. The processing method according to claim 6, wherein the concentration of the alkaline aqueous solution is higher than or equal to 3 weight percent and lower than or equal to 5 weight percent. The method according to claim 1, wherein the weakly acidic aqueous solution has a pH value of 5 or more and 7 or less. The processing method according to claim 8, wherein the weakly acidic aqueous solution has a pH value of 5 or more and 6 or less. The processing method according to claim 1, wherein the microalgae are phytoplankton, chlorella, dinoflagellum, cylindrum, Dunaliella, isochrysis, monoenteric algae, micro green algae, pseudococcus, Neo-green algae, diamond-shaped algae, Phaeodactylum tricornutum, Schizochytrium spp., Schizochytrium or a combination thereof. The processing method according to claim 1, wherein the microalgae cultivation tank is a closed microalgae cultivation tank. The processing method according to claim 1, wherein the weakly acidic aqueous solution is added to the microalgae-containing microalgae cultivation tank for photosynthesis, thereby reducing the concentration of carbonate and bicarbonate ions in the weakly acidic aqueous solution to obtain The step of treating the treated wastewater includes: adding the weakly acidic aqueous solution to a microalgae culture tank containing microalgae for photosynthesis, thereby reducing the concentration of carbonate ions and bicarbonate ions in the weakly acidic aqueous solution to obtain a first treatment Solution, the pH value of the first treatment solution is greater than 8; adding the weakly acidic aqueous solution to the first treatment solution to obtain a second treatment solution, the pH value of the second treatment solution is greater than or equal to 6 and Less than or equal to 7, the second treatment solution contains ions, bicarbonate ions, and metal ions; in the microalga cultivation tank containing the microalgae and the second treatment solution, the microalgae performs photosynthesis, thereby reducing The concentration of carbonate ions and bicarbonate ions in the second treatment solution to obtain the treated wastewater. The method according to claim 12, wherein the microalgae cultivation tank is a fully automatic microalgae cultivation tank. The treatment method according to claim 1, wherein the weakly acidic aqueous solution is added to the microalgae-containing microalgae culture tank for photosynthesis, thereby reducing the concentration of carbonate ions and bicarbonate ions in the weakly acidic aqueous solution, so as to After the step of obtaining the treated wastewater, the method includes the following steps: obtaining a supernatant and a microalgae-containing algae mud precipitate, wherein the supernatant contains hydroxide ions and Metal ions; and drying the microalgae-containing algae mud sediment to obtain a dried algae powder; wherein the subsequent treatment is a precipitation treatment, a filtration treatment, or a combination thereof. The processing method according to claim 14, wherein the alkaline aqueous solution having a concentration of less than 20% by weight is a supernatant collected by subsequent treatment of the treated wastewater; The percentage of the alkaline aqueous solution absorbs carbon dioxide in the exhaust gas, and the step of obtaining the weakly acidic aqueous solution includes: absorbing the carbon dioxide in the exhaust gas with the supernatant, and obtaining the weakly acidic aqueous solution. The method according to claim 15, wherein the supernatant is an alkaline aqueous solution having a concentration of less than or equal to 5 weight percent. The processing method according to claim 14, wherein after the aforesaid step of drying the algae mud precipitate containing microalgae to obtain the dried algae powder, the method comprises: using the dried algae powder to break the wall to obtain a Algal oil and an algae block; the algal oil is transesterified to obtain a biodiesel.