JPH10230131A - Method for absorption removal of carbon dioxide in air - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently absorb and capture carbon dioxide in the air with lime water by a method wherein saturated lime aqueous solution or calcium hydroxide aqueous solution of a specific concentration is continuously made to flow down in a thin layer form of a specific film thickness bringing that in contact with the air, or sprayed by circulation. SOLUTION: In the case where carbon dioxide in the air is eliminated by absorption, saturated lime aqueous solution, or calcium hydroxide solution of at least 3×10<-4> N (normal) concentration (hereinafter, referred to as lime water) is continuously made to flow down in a thin film form of about 5-10mm or lower bringing that in contact with the air, or sprayed in circulation in a thin film form. Thereby, carbon dioxide in the air is effectively eliminated by absorption with a dynamic film surface of lime water. In that case, a concentration of the lime water is not limited to a saturated state, and about 9.5 or higher pH may suffice. For the lime to be used, both of slaked lime (calcium hydroxide) and quick lime (calcium oxide) may suffice.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air conditioner including air cleaning.
It is related to industrial technologies such as ventilation, air pollution prevention and environmental protection, and wastewater treatment.

[0002]

2. Description of the Related Art Conventional air conditioning and ventilation technologies and devices
It is limited to thermodynamic temperature and humidity adjustment, dust removal and germicidal removal of circulating air, and it has been considered impossible to reduce or remove carbon dioxide in the air. By the way, drowsiness is often experienced in large conference rooms, etc., and it is common knowledge that the physiological phenomenon is caused by the relative increase in the amount of carbon dioxide relative to the amount of oxygen in the air. I have.
As technical measures against industrial smoke pollution and so-called air pollution, passive measures such as removal of odorous components and sulfur oxides or limitation of emission sources have been limited, and artificial removal of carbon dioxide has been largely omitted. I couldn't. In addition, there is no practical technique for effectively utilizing atmospheric carbon dioxide for neutralizing alkaline water in wastewater treatment using lime.

[0003]

The composition of ordinary air is as follows (Iwanami Dictionary of Physical and Chemical Sciences, Third Edition, 1971).
23.01% oxygen, 75.51% nitrogen, 1.2 argon
86%, carbon dioxide 0.04%, and others. (Each% by weight). Among these mixed components, the concentration of carbon dioxide tends to fluctuate depending on the human environment, so that it is necessary to maintain an appropriate concentration for healthy human activities. The importance of reducing carbon dioxide on a global scale is generally pointed out.

[0004] On the other hand, carbon dioxide becomes carbonic acid when dissolved in water, and the action of carbonic acid as an acid is milder than that of mineral acids such as sulfuric acid and hydrochloric acid. And even if the carbonate of the neutralized product causes secondary decomposition, there is no harm like sulfur compounds and chlorine compounds. Furthermore, even though the relative concentration of carbon dioxide in the air is low, the amount of resources is infinite.
Therefore, the significance of utilization development as unused resources is significant.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a "method for treating wastewater with lime milk" which was separately invented as a method for decolorizing brown factory wastewater normally discharged as treated water (Japanese Unexamined Patent Publication No.
294 693) in a post-treatment, based on a new experimental finding that atmospheric carbon dioxide was found to be useful in the neutralization step. That is, the neutralization of the saturated lime water of about pH 12.5 is also achieved by trapping carbon dioxide in the atmosphere,
It was first identified that the two conditions, time and water surface area, were the major controlling factors. In addition to confirming that the neutralization is due to the carbon dioxide trapped in the lime water, it has been found that the amount of carbon dioxide dissolved in the lime water is steady in an alkaline region having a pH of about 9.5 or more. Was done.

"Necessary neutralization days; y [d]" due to the incorporation of atmospheric carbon dioxide and "relative surface area of saturated lime water;
x [cm ² / l] ”, the following empirical formula was derived. log y = a log x + b [Formula 1] In Formula 1, a and b are constants determined by geographical conditions and the like, and a is always a negative coefficient. Specifically, the a and b values for the point A (about 360m above sea level) are-
0.993 and 3.31, Otsu (about 590m above sea level)
The a, b values for are -0.955 and 2.77.

Further, in the logarithmic graph relating to the equation 1, when the two x, y coordinates relating to the insteps A and B overlap the same point, the numerical value is about 130 cm ² / l, 16 days.
This was data within the range of the actual measurement. This relative surface area corresponds to a circular water tank having an effective water depth of 7.7 m and a diameter of 12.9 m. From this, in order to shorten the required neutralization days of saturated lime water, that is, to increase the trapping efficiency of atmospheric carbon dioxide, the relative surface area should be significantly increased by some means. .

On the other hand, in the stationary [OH ⁻ ] decrease period,
It has also been found that the rate of capture and reaction of atmospheric carbon dioxide by saturated lime water is about 5.6 g (CO ₂ ) per 1 m ² per day. It also has the same effect in the alkaline region, usually at a pH of about 9.5 or higher.

In view of the above, it is necessary to increase the relative surface area of lime water in contact with air as much as possible. As a means for this, lime water is spouted into the air in the form of a thin film having an average thickness of 1 mm or less and circulated. Thereby, carbon dioxide in the air can be efficiently collected and absorbed.
Further, neutralization can be achieved in a short time. It is useful to make the surface area of the lime water film as large as technically possible. As a means of absorbing carbon dioxide when the purpose of neutralization is not always intended, a method in which lime water is continuously flowed in a thin layer form is effective, and its circulation system is also effective.

[0010]

The carbon dioxide in the air reacts with the lime water as shown in equation (2). Ca (OH) ₂ + CO ₂ → CaCO ₃ + H ₂ O [Equation 2] Since calcium carbonate (CaCO ₃ ), which is a reaction product, forms a sparingly soluble precipitate, the reaction of Equation 2 proceeds to the right. In addition, the fact that the solubility of oxygen coexisting in the air in water is much smaller than that of carbon dioxide, which also has an advantageous effect on accelerating the reaction of Formula 2.

[0011] When the lime water surface is in a static state, the dissolution of atmospheric carbon dioxide into saturated or nearly saturated lime water, according to the results of the present inventors, shows that the relative surface area is 1 cm ² / l per day. Approximately 1 × 10 ⁻⁵ [OH ⁻ ]
It is equivalent to N (specified density). Converting this further,
As described above, the rate of trapping and absorbing carbon dioxide in air on the surface of lime water is about “5.6 g (CO ₂ ) / m ² · da.
y ".

In the case of a dynamic state in which lime water is ejected in a thin film or a thin layer, it is difficult to grasp an accurate numerical value. The time efficiency is remarkably improved, as shown in the following embodiments. That is, the size of the total area of the thin film liquid level with respect to the volume of the lime water is the controlling factor.

[0013]

Example 1 A bucket of saturated lime water (14 liters (1)) was placed in a bucket having an inner diameter of 276 mm and a capacity of about 20 liters, and was spouted horizontally into a thin film at a height of 50 cm using a micro water pump. A circulating jet was made by a method in which the end of a water stream was buffered and flowed down onto a smooth metal plate suspended to about 15 cm. In this case, the amount of lime water circulation is about 5 l / mi.
n, the head from the spout to the lower liquid surface was about 15 cm, and the horizontal film surface was slightly curved, but the width of the film surface was approximately 10 cm in width and 10 cm in length. The thickness was 1 mm, and the water temperature (February) was 0 to 3 ° C. The speed of carbon dioxide absorption was indirectly evaluated by the time required for neutralization based on the pH measurement. As a result, the completion of neutralization was recognized within 24 hours.

In the trial, the calculated value of the required neutralization days when the lime water was left standing statically was 4
8 days. In other words, it can be said that the absorption of carbon dioxide by the above method was approximately 50 times as efficient as in the case of static. Incidentally, the cumulative total area (relative surface area) of the dynamic membrane surface is about 3,571 cm ² / l, and the calculated value of the required neutralization days when the same equation is applied is 0.60 days (about 15 hours). It was calculated.

[0015]

Embodiment 2 A drum having an inner diameter of 567 mm and a capacity of about 200 liters is filled with 160 liters (1) of saturated lime water,
Using a small submersible pump, lime water is discharged in a thin rectangular shape from a position about 3 m in height, and an inclination angle of about 8
The lime water was continuously flowed down by a method of flowing into a drum via a 0 ° sheet trough and refluxing. In this case, the lime water flow rate is about 50 l / min, the head from the discharge port to the lower liquid level is about 2 m, and the area of the water film that falls like a small waterfall in the air is:
Roughly 30 cm wide, 40 cm long and 5 mm thick,
The water temperature (October-November) was 7-22C. Similarly to the above, the speed of carbon dioxide absorption was indirectly evaluated based on the time required for neutralization based on the pH measurement. As a result of the repeated trials,
The number of days required for neutralization was 5 to 9 days, with an average of 7 days.

In the trial, the calculated value of the required number of neutralization days when this lime water was left standing statically was calculated as
3 days. Even in the case of this method, about ten times the efficiency is obtained. Incidentally, the cumulative area (relative surface area) of the dynamic membrane surface was about 625 cm ² / l, and the calculated value of the required number of neutralization days when the same equation was applied was calculated to be 5.1 days.

[0017]

Since the present invention is configured as described above, it has the following effects.

The carbon dioxide in the air can be effectively absorbed by the dynamic surface of the lime water. At that time, the concentration of the lime water is not limited to the saturated state,
What is necessary is just 9.5 or more. The same effect can be obtained regardless of whether the lime used is slaked lime (calcium hydroxide) or quick lime (acid or calcium).

The rate of capturing and absorbing carbon dioxide in the air on the surface of static saturated lime water is about 5.6 g (CO ₂ ) / m ^2.
Measured as day. On the other hand, in the present invention, lime water circulated and ejected in the form of a thin film captures and absorbs carbon dioxide in the air at least 50 times more efficiently than carbon dioxide absorption from a static lime water surface. it can. This efficiency can be further improved by increasing the area of the water film surface and reducing the film thickness.

According to the method of the present invention, alkaline lime water can be neutralized in a short time. Therefore, this can be easily applied to wastewater treatment.

The evaluation of the collection and absorption of carbon dioxide, the management of its water quality, and the measurement of its function can be easily performed by pH measurement.

Physicochemical and mechanical means of the present invention,
The operation is a simple method in principle, and the size of the hardware can be set arbitrarily. Except for the fact that lime or lime water is an alkaline substance, it is unlikely to cause any harm to the human body and is a chemical substance that does not hinder daily handling. Therefore, application to various industrial fields is easy.

Claims (2)

[Claims] 1. A saturated lime solution or 3 × 10 ^-4
An aqueous solution of calcium hydroxide having a concentration of N (normative) or higher (hereinafter collectively referred to as lime water) is brought into contact with air while
A method of efficiently absorbing carbon dioxide in the air by forming a thin layer having a thickness of about 10 mm or less and continuously flowing down, or forming a thin film and circulating water sprinkling. 2. A method of actively absorbing and neutralizing carbon dioxide in the air by a treatment method in which alkaline lime water having a pH of 12.5 or close thereto is formed into a thin film, and is subjected to running water or circulating water spraying / spraying.