METHOD FOR TREATING GAS

Abstract

The present invention provides a method for treating a gas, comprising: step (A): collecting a gas comprising carbon dioxide and fine particulate matter; step (B): rinsing the gas with water to obtain a rinsed gas; and step (C): contacting the rinsed gas with a basic solution in a way of co-current flow to absorb the carbon dioxide in the rinsed gas by the basic solution to obtain a treated gas and a weak basic solution; wherein the pH value of the basic solution is between 9 and 14, and the pH value of the weak basic solution is between 8 and 8.5. The method can reduce the content of both fine particulate matter and carbon dioxide.

Claims

1. A method for treating a gas comprising: step (A): collecting a gas comprising carbon dioxide and fine particulate matter; step (B): rinsing the gas with water to obtain a rinsed gas; and step (C): contacting the rinsed gas with a basic solution in a way of co-current flow to absorb the carbon dioxide in the rinsed gas by the basic solution to obtain a treated gas and a weak basic solution; wherein the pH value of the basic solution is between 9 and 14, and the pH value of the weak basic solution is between 8 and 8.5.

2. The method according to claim 1, wherein said step (C) is conducted at the temperature below 90 C.

3. The method according to claim 1, wherein the basic solution is sodium hydroxide solution.

4. The method according to claim 3, wherein the method comprises step (D): adding the weak basic solution to a microalgae culture tank containing microalgae.

5. The method according to claim 3, wherein the method comprises step (E): evaporating the moisture content in the weak basic solution to obtain a solid sodium hydrogen carbonate.

6. The method according to claim 1, wherein step (C) includes: step (C1): preliminarily contacting the rinsed gas with the basic solution in the way of co-current flow, to absorb the carbon dioxide in the rinsed gas by the basic solution to obtain a preliminary treated gas and a first weak basic solution; and step (C2): again contacting the preliminary treated gas with the basic solution in the way of co-current flow to absorb the carbon dioxide in the preliminary treated gas by the basic solution to obtain the treated gas and a second weak basic solution, wherein the weak basic solution comprises the first weak basic solution and the second basic weak solution.

7. The method according to claim 1, wherein in step (C), the total contacting time of the basic solution with the rinsed gas is more than 5 seconds.

8. The method according to claim 1, wherein in step (C), the concentration of the basic solution is between 1 wt % to 2 wt %.

9. The method according to claim 1, wherein in step (C), the flow rate ratio of the basic solution to the rinsed gas is between 1:200 and 1:800.

10. The method according to claim 4, wherein the microalgae in step (D) is Botryococcus braunii, Chlorella sp., Crypthecodinium cohnii, Cylindrotheca sp., Dunaliella primolecta, Isochrysis sp., Monalanthus Salina, Nannochloris sp., Nannochloropsis sp., Neochloris oleoabundans, Nitzschia sp., Phaeodactylum tricomutum, Schizochytrium sp., Tetraselmis suecica, Arthrospira maxima, Arthrospira platensis, or any combination thereof.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] First, in step (A), a gas comprising carbon dioxide and fine particulate matter was collected. Said gas was an emitted waste gas collected from the high-temperature boilers of steelmaking, and comprised average 159 g/m.sup.3 carbon dioxide and average 35.42 mg/m.sup.3 fine particulate matter, PM 2.5. Besides, the temperature of said gas was higher than 400 C.

[0028] Next, in step (B), the gas was rinsed with water to obtain a rinsed gas. This makes the PM2.5 in said gas deposit and, in the meantime, makes the partial carbon dioxide dissolve in the water. The collected gas, with an average carbon dioxide concentration of 52.5 kg/hr detected by a carbon dioxide monitor (New Guardian, Edinburgh Sensor), with a flow rate of 330 m.sup.3/hr, was rinsed by the water, below 50 C., with a flow rate between 2 m.sup.3/hr and 3 m.sup.3/hr for 5 seconds, which makes the temperature of said gas decrease to lower than 50 C.

[0029] Then, through step (C1): the rinsed gas, having a flow rate of 330 m.sup.3/hr, was preliminarily contacted with a 2 wt % sodium hydroxide solution, having a flow rate of 500 L/hr, in the way of co-current flow. The preliminary contact was a circulation spray lasting for five seconds. In the meantime, the flow rate ratio of the basic solution to the gas was 1:600. Said circulation spray refers to the rinsed gas sprayed by a circulated sodium hydroxide solution in a chamber, so that the carbon dioxide in the rinsed gas was absorbed by the sodium hydroxide solution, to obtain a preliminary treated gas and a first sodium hydrogen carbonate solution; and step (C2): the preliminary treated gas, having a flow rate of 330 m.sup.3/hr, was again contacted with the 2 wt % sodium hydroxide solution, having a flow rate of 500 L/hr, in the way of co-current flow. Besides, the term again contacting refers to a circulation spray lasting for 5 seconds, resulting in a second sodium hydrogen carbonate solution and an again treated gas. After that, step (C2) was repeated once, in order to obtain the third sodium hydrogen carbonate solution and a treated gas. The first sodium hydrogen carbonate solution, second sodium hydrogen carbonate solution and third sodium hydrogen carbonate solution, obtained from the three stages of contacting, were collected together into a storage pool. Therefore, in step (C), the rinsed gas was separately contacted with 2 wt % sodium hydroxide solution for three times sequentially, so that the carbon dioxide in the gas was mostly absorbed by the sodium hydroxide solution. Finally, a treated gas was obtained. The content of carbon dioxide and the fine particulate matter of said treated gas was largely reduced compared to the original waste gas.

[0030] In step (C), when the sodium hydroxide solution contacted the carbon dioxide, the acid-base neutralization reacted immediately. Besides, by contacting the rinsed gas with the basic solution in the way of co-current flow, the contacting time of the sodium hydroxide solution with the carbon dioxide was extended. Therefore, the acid-base neutralization can fully react.

[0031] It can be found from the detecting results of the treated gas, that the carbon dioxide was reduced for more than 45 kg/hr in total compared to the original collected gas in the step (A), having 52.5 kg/hr carbon dioxide and a flow rate of 330 m3/hr, according to the carbon dioxide monitor (New Guardian, Edinburgh Sensor). Among others, the averages of removing efficiency of the carbon dioxide and PM 2.5, which were detected 5, 10, 20, 25, 30 minutes after the treatment of the present embodiment, are shown in the following table 1.

TABLE-US-00001 TABLE 1 The removing efficiency of carbon dioxide and PM 2.5 Concentration Concentration Average detected at the inlet detected at the outlet removing Average carbon dioxide PM2.5 carbon dioxide PM2.5 flow efficiency of removing Time concentration Concentration concentration concentration rate carbon efficiency of (minute) (g/m.sup.3) (mg/m.sup.3) (g/m.sup.3) (mg/m.sup.3) (m.sup.3/hr) dioxide PM2.5 5 152.09 34 23.89 1.3 330 86.93% 96.28% 10 157.14 34.5 19.28 1.3 330 15 160.51 37.5 19.26 1.3 330 20 161.63 35.5 20.57 1.3 330 25 159.95 36 20.64 1.4 330 30 162.76 35 21.07 1.3 330 Average 159.01 35.42 20.79 1.32 330

[0032] According to the results of the table 1, the removing efficiency of PM 2.5 of every 5 minutes of the present invention can reach 95%, and that of carbon dioxide can almost reach 90%.

[0033] Then the sodium hydrogen carbonate solution obtained in step (C) was further processed through step (D): adding the sodium hydrogen carbonate solution to the microalgae culture tank comprising microalgae. The partial sodium hydrogen carbonate solution obtained from said step (C) was added into the culture tank containing microalgae in order to provide the carbon source for the photosynthesis of the microalgae. The growing microalgae was processed to produce the functional products, animal feeds, or biodiesel. Among others, the microalgae can be Botryococcus braunii, Chlorella sp., Crypthecodinium cohnii, Cylindrotheca sp., Dunaliella primolecta, Isochrysis sp., Monalanthus Salina, Nannochloris sp., Nannochloropsis sp., Neochloris oleoabundans, Nitzschia sp., Phaeodactylum tricomutum, Schizochytrium sp., Tetraselmis suecica, Arthrospira maxima, or Arthrospira platensis. The carbon dioxide was consumed after the photosynthesis of the microalgae in the culture tank, so that the hydroxide ion was released from the sodium hydrogen carbonate solution. Therefore, the aqueous solution, in the culture tank, can be concentrated after collecting microalgae, and the pH value can be adjusted by adding partial solid sodium hydroxide to the concentrated aqueous solution from the culture tank in order to be used as a basic solution in step (C), and thus achieves the effect of the circulation utilization. The method of said concentration may utilize solar exposure or the remaining heat on the chimney for emitting waste gas, generated by burning or burning oil, to evaporate the water content, or may utilize the molecular sieve to remove the water content.

[0034] Besides, the partial sodium hydrogen carbonate solution obtained in step (C) was further processed through step (E): evaporating the water content in the sodium hydrogen carbonate to obtain solid sodium hydrogen carbonate.

[0035] The above embodiments are only preferred embodiments of the present invention, not intended to limit the present invention in any aspect. The scope of the right asserted from the present invention shall be based on the claims.