JPH05141865A - Separation/recovery method of carbon dioxide gas - Google Patents

Abstract

PURPOSE:To inexpensively separate and recover carbon dioxide gas with a high yield and a high purity by directly bubbling stock gas including carbon dioxide gas in a refrigerant of a fluid lower than a boiling paint and lower than solidification temperature of the carbon dioxide gas for heat exchange thereof, and solidifying and recovering the carbon dioxide gas. CONSTITUTION:Feed stock gas is directly bubbled for heat exchange from a stock blow-off nozzle 7 into n-butane 8 as a refrigerant of a fluid lower than a boiling point thereof at temperature lower than solidification temperature of carbon dioxide gas, e. g. at a temperature lower than -78.5C at atmospheric temperature. Hereby, the carbon dioxide in the stock gas is cooled into solid carbon dioxide gas and is precipitated in the fluid n-butane 8 utilizing a specific gravity difference. The n-butane 8 is temperature controlled at a temperature lower than its boiling temperature, and hence is not vaporized and is kept as a liquid refrigerant. The solid carbon dioxide gas precipitated in the n-butane 8 is rendered to solid-liquid separation by degassing, and hereby the solid carbon dioxide gas is recovered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating and recovering carbon dioxide from fuel gas or combustion exhaust gas containing carbon dioxide such as blast furnace gas and converter gas.

[0002]

2. Description of the Related Art Conventionally, as a method for separating and recovering carbon dioxide, there is almost no example of a method for separating and recovering carbon dioxide at a low temperature.
There is only a cryogenic distillation process from the point of view for Recovery. Enhanced Oil Recover
A typical low temperature distillation process for ry is Ry
an / Holmes method, Controlled Fr
The ese zone method and the like have been proposed. On the other hand, a method for producing dry ice by bubbling carbon dioxide gas into liquefied natural gas (LPG), liquid nitrogen or the like (Japanese Patent Publication No. 60-42).
No. 163), in the circulation and reuse method of argon in the argon-oxygen blowing method, carbon dioxide which is an impure component is removed by deep-cooling treatment (liquefaction separation of carbon dioxide), or -1.
A method of removing carbon dioxide gas as dry ice by exchanging heat with a cold source of about 00 ° C. in a heat exchanger (JP-A-52-28)
No. 750) has been proposed. An adsorption separation method is known as a method for separating and recovering carbon dioxide gas from a fuel gas containing carbon dioxide gas or combustion exhaust gas.
Many proposals have been made such as Japanese Patent No. 2204 and Japanese Patent Laid-Open No. 61-187932.

[0003]

[Problems to be Solved by the Invention] Ryan / Hol
mes method, Controlled Freeze Z
The one method is not versatile because it is for a special purpose, and because the low temperature distillation method is adopted as the basic separation technology, the system is complicated, and it is costly to simply separate and recover carbon dioxide gas. It is not economically feasible. The method for producing dry ice disclosed in Japanese Patent Publication No. 60-42163 uses carbon dioxide gas as a heat source for vaporizing liquefied natural gas and the like, and bubbling carbon dioxide gas into the liquefied natural gas causes latent heat of vaporization of the liquefied natural gas. Etc.,
Dry ice is produced while vaporizing liquefied natural gas. In this method, carbon dioxide cannot be separated and recovered from the fuel gas containing carbon dioxide or the combustion exhaust gas. If fuel gas or combustion exhaust gas containing carbon dioxide in liquefied natural gas is bubbled, carbon dioxide can be recovered as dry ice, but a large amount of nitrogen, etc., having a lower boiling point than liquefied natural gas is mixed into liquefied natural gas. Then, the value of liquefied natural gas will be impaired.

Further, the method of removing carbon dioxide gas disclosed in JP-A-52-28750 is a method of removing carbon dioxide gas, which is an impurity in argon gas, by cryogenic separation of carbon dioxide gas. In order to liquefy, a pressure of at least the triple point pressure of carbon dioxide (5.28 kg / cm ² abs) or higher is required, and in consideration of the concentration of carbon dioxide described in JP-A-52-28750, the minimum But 15kg / c
A pressure of about m ² abs is required, and at the same time, it is necessary to compress argon gas as well, which is not practical from the viewpoint of power cost. Furthermore, the method of removing carbon dioxide gas as dry ice by exchanging heat with a cold source of about −100 ° C. requires a very large heat transfer area because the heat transfer coefficient of gas is poor, and Since the gas becomes dry ice and adheres to the heat transfer surface, the heat transfer rate is reduced and the method of removing carbon dioxide gas has poor thermal efficiency. Further, JP-A-61-157322 and JP-A-1-17220.
The PSA method disclosed in Japanese Patent No. 4 etc. has a carbon dioxide concentration of 20%
It is said that the yield of carbon dioxide is low in the low concentration range below a certain level, and the equipment becomes larger as the concentration becomes lower, which makes it unprofitable as a business (Chemical equipment, August 1989 issue,
"CO2 recovery from waste gas by adsorption (PSA)").

An object of the present invention is to provide a method for separating and recovering carbon dioxide gas, which uses carbon dioxide-containing fuel gas or combustion exhaust gas as a raw material gas and can recover carbon dioxide gas in high yield at low cost.

[0006]

Means for Solving the Problems The present inventors have conducted various test studies in order to achieve the above object. As a result, the raw material gas is blown into a refrigerant such as a liquid hydrocarbon cooled to a temperature below the boiling point to cause bubbling, and the carbon dioxide gas is solidified by directly exchanging heat, and the liquid hydrocarbon can be separated without being vaporized. Found and arrived at this invention.

That is, according to the present invention, a raw material gas consisting of a fuel gas containing carbon dioxide gas or a combustion exhaust gas is directly bubbled into a liquid refrigerant having a solidification temperature of carbon dioxide gas or lower and a boiling point to cause heat exchange, The carbon dioxide gas is cooled and solidified without being vaporized, and then recovered.

[0008]

In the present invention, since the raw material gas containing carbon dioxide is bubbling directly into the liquid refrigerant having a boiling point lower than the solidification temperature of carbon dioxide, for example, -78.5 ° C or less at atmospheric pressure for heat exchange. The carbon dioxide gas in the raw material gas is cooled to become solid carbon dioxide gas, and is precipitated in the liquid refrigerant due to the difference in specific gravity. Since the temperature of the refrigerant is adjusted below the boiling point, it is maintained as a liquid refrigerant without vaporization. The solid carbon dioxide gas precipitated in the refrigerant can be extracted and solid-liquid separated to recover the solid carbon dioxide gas. The yield of the recovered solid carbon dioxide depends on the temperature of the liquid refrigerant,
The lower the temperature, the higher the yield. The reason for this is that the carbon dioxide gas leaking from the liquid refrigerant leaks only by the saturated vapor pressure (sublimation pressure) at the temperature of the liquid refrigerant. As an example of the carbon dioxide gas yield, when the carbon dioxide gas concentration in the raw material gas is 20% and the temperature of the refrigerant is −110 ° C., the carbon dioxide gas yield is about 77%, and the carbon dioxide gas concentration is 40% even under the same temperature condition. %, The carbon dioxide gas yield is about 89%. The separated solid carbon dioxide gas has an atmospheric pressure of −78.5 ° C.
By heating above, carbon dioxide gas in a gas form can be produced. In addition, three key pressures (5.28 kg / cm
Liquid carbon dioxide can be produced by heating and melting under a pressure of ² abs) or more.

The refrigerant used in the present invention is required to be capable of solidifying carbon dioxide at a temperature lower than the boiling point of the refrigerant, and has a liquid density smaller than that of solid carbon dioxide so that solid carbon dioxide can be easily precipitated. is necessary. As the refrigerant suitable for this condition, in addition to hydrocarbons such as methane, ethane, propane and butane, liquefied natural gas and the like can be used, but it is desirable to use one having a large difference in boiling point and melting point, n-butane (boiling point -0.5
° C, melting point -135 ° C, i-butane (boiling point -11.7)
(° C, melting point-159.6 ° C) and the like are suitable. Liquid nitrogen can be used, but it is difficult to bring it below the boiling point,
Not suitable as this refrigerant.

Examples of the raw material gas containing carbon dioxide gas used in the present invention include fuel gas such as blast furnace gas containing carbon dioxide gas, converter gas, and combustion exhaust gas. In addition to these exhaust gases, all exhaust gases containing carbon dioxide and having a boiling point or melting point of other gas components lower than that of carbon dioxide can be used as the raw material gas. When the fuel gas is used as the raw material gas, the carbon dioxide gas in the fuel gas is removed and the calorific value rises. Therefore, the fuel gas is returned to the original line and burned. When combustion exhaust gas is used as the raw material gas, the off gas is released into the atmosphere after the carbon dioxide gas is recovered.

For separating the liquid refrigerant and the solid carbon dioxide gas, a usual solid-liquid separation method such as filtration or centrifugal separation can be applied. The solid carbon dioxide gas thus separated usually contains some liquid refrigerant, and the separation from the liquid refrigerant differs depending on the vaporization temperature of the solid carbon dioxide gas and the liquid refrigerant. When the temperature is lower than the vaporization temperature of the liquid refrigerant, the solid carbon dioxide gas is vaporized. When the vaporization temperature of the solid carbon dioxide is higher than the vaporization temperature of the liquid refrigerant, the liquid refrigerant is vaporized, and then the solid carbon dioxide is vaporized and separated and recovered.

Most of the cold heat used in recovering carbon dioxide gas as solid carbon dioxide gas can be recovered by exchanging heat of the exhaust gas after solid carbon dioxide gas separation with the raw material gas and using it for cooling the raw material gas. Further, the cold heat generated when the solid carbon dioxide gas is vaporized can be used as the cold heat for solid carbon dioxide gas separation by forming a refrigeration cycle, and the carbon dioxide gas can be separated and recovered at low cost.

[0013]

EXAMPLE FIG. 1 is a vertical cross-sectional view of a test apparatus used in Examples, and FIG. 2 is an explanatory view of the bubble column of FIG. As shown in FIG. 1, the upper part of the cold storage tank 1 is sealed with a liquefied nitrogen gas container 2, the upper and lower parts are communicated with each other, and a separating plate 3 is provided in the central portion, and a bubble tank 6 is divided into an ascending tank 4 and a descending tank 5. And the bubble tank 6
1m hole diameter as raw material injection nozzle 7 in the lower part of the rising tank 4
m, outer diameter 12.7 obtained by punching raw material injection holes with 22 holes
mm, thickness 1.59 mm Teflon pipe 7 is provided, and n-butane 8 having a temperature of −102 to −107 ° C. as a liquid refrigerant has a liquid depth of 2 to the upper surface of the raw material injection nozzle 7.
It was prepared to be 00 mm. And carbon dioxide gas 20Vo
1% and nitrogen gas 80 vol% mixed gas 9 at a temperature of −65 to −75 ° C. from the material injection nozzle 7 to 30 Nl.
Blows in at a rate of / min.

The mixed gas 9 blown into the liquefied n-butane 8 in the rising tank 4 is liquefied while rising in the rising tank 4.
Cooled by direct heat exchange with butane 8. As a result, the carbon dioxide gas in the mixed gas was solidified, and the off gas was diffused from the upper part of the bubble tank 6 as it was. The solid carbon dioxide gas solidified in the rising tank 4 went up in the rising tank 4, was inverted at the upper part of the separation plate 3, and went down in the falling tank 5 to be deposited on the bottom pyramid portion of the bubble tank 6. The average carbon dioxide yield in this case is 65.
It was 2%. Further, the cumulative amount of carbon dioxide gas blown and the carbon dioxide gas yield, the cumulative amount of carbon dioxide gas blown, and the liquid temperature of n-butane 8 in the upper portion A and the lower portion B of the ascending tank 4 and the intermediate portion C of the descending tank 5 and the cumulative carbon dioxide gas amount The blowing amount and the differential pressure of the raw material blowing nozzle 7 were measured. The results are shown in FIGS. In addition,
The actual yield of carbon dioxide was calculated from the results of carbon dioxide analysis by gas chromatography in the blown mixed gas and off gas.

FIG. 3 shows a comparison between the theoretical yield and the actual yield.
The theoretical yield is based on the assumption that if the carbon dioxide gas exchanges heat sufficiently in the liquid refrigerant, the carbon dioxide gas leaking from the liquid refrigerant leaks by the saturated vapor pressure (sublimation pressure) at the temperature of the liquid refrigerant. It is the value obtained by As shown in FIG. 3, the theoretical yield indicated by the solid line and the measured yield indicated by the broken line are in good agreement. This indicates that the heat exchange is sufficiently performed even at a liquid depth of about 200 mm, and that the method of bubbling the liquid to perform the heat exchange has a very high heat exchange efficiency. As shown in FIG. 5, the differential pressure of the raw material injection nozzle 7 changes from 0.55 to 0.6 kg / cm ² , and the raw material gas supply pressure may be low at such a differential pressure that does not pose a problem. I understand. Further, as shown in FIG. 4, n-butane 8 which is a liquid refrigerant in the bubble tank 6 is also used.
The liquid temperature of the liquid was stable at around -105 ° C in both the upper part A shown by the solid line of the ascending tank 4, the lower part B shown by the alternate long and short dash line (overlap with the upper part A) and the middle part C of the descending tank 5 shown by the broken line. .. The solid carbon dioxide gas deposited on the pyramid at the bottom of the bubble tank 6 was about 50% slurry when extracted at the end of the test. After this was subjected to solid-liquid separation, carbon dioxide was vaporized to be separated and recovered, and the purity was 98.8%, the recovered amount was 3166 g, and the calculated carbon dioxide blowing amount was 4871 g.
The yield was 65.0%.

Example 2 In the same manner as in Example 1, the temperature of the liquid refrigerant n-butane was changed to −
When the same experiment was carried out at 110 ° C., the yield of carbon dioxide gas was about 77%.

Example 3 Carbon dioxide concentration in the raw material gas was adjusted to 4 by the same method as in Example 2.
When the same experiment was carried out by increasing it to 0%, the yield of carbon dioxide gas was about 89%.

[0018]

As described above, according to the method of the present invention, carbon dioxide can be separated and recovered from the raw material gas containing carbon dioxide at a high yield and a high purity at a low cost. Also,
Since it is handled at a low temperature, the gas volume can be reduced, and the equipment can be downsized, so the equipment cost can be reduced. Further, when a fuel gas containing carbon dioxide gas is used as the source gas, carbon dioxide gas in the fuel gas is removed, so that there is an advantage that the calorific value of the fuel gas increases.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a test apparatus used in an embodiment of the present invention.

FIG. 2 is an explanatory view of a bubble column in FIG.

FIG. 3 is a graph showing the relationship between the cumulative amount of carbon dioxide gas blown and the carbon dioxide gas yield in the example.

FIG. 4 is a graph showing the relationship between the cumulative carbon dioxide gas injection amount and the liquid temperature of n-butane in the upper part of the ascending tank and the middle part of the descending tank in the same example.

FIG. 5 is a graph showing the relationship between the cumulative carbon dioxide gas blowing amount and the raw material blowing nozzle differential pressure in the same example.

[Explanation of symbols]

 1 Cold Storage Tank 2 Liquefied Nitrogen Gas Container 3 Separation Plate 4 Rising Tank 5 Falling Tank 6 Bubble Tank 7 Raw Material Injection Nozzle 8 n-Butane 9 Raw Material Gas

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeshi Fujisaki 1850 Minato, Wakayama, Wakayama Joint oxygen company Wakayama factory (72) Inventor Yasuo Tomiyama 1850, Minato, Wakayama, Wakayama Joint oxygen company Wakayama factory Within

Claims (1)

[Claims] 1. A raw material gas composed of a fuel gas containing carbon dioxide gas or a combustion exhaust gas is directly bubbled into a liquid refrigerant whose temperature is equal to or lower than the solidification temperature of carbon dioxide gas and lower than the boiling point to cause heat exchange, and A method for separating and recovering carbon dioxide gas, which comprises recovering after solidifying carbon dioxide gas without vaporizing the refrigerant.