JP2004141858A - Dehumidification method of exhaust gas, and system therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of effectively separating and removing water vapor from exhaust gas, avoiding the condensation of the water vapor on the wall surface of a carbon dioxide solidification equipment and the surface of piping or the like even when the exhaust gas is cooled below the water vapor solidification temperature, and preventing the deterioration of heat transfer performance caused by the solidification of the water vapor on the surface of a heat exchanger tube of the equipment. <P>SOLUTION: The dehumidification method of exhaust gas and the dehumidification system for exhaust gas comprise condensing or solidifying water vapor contained in an exhaust gas by circulating the exhaust gas in a cooling medium so as to separate the water vapor. <P>COPYRIGHT: (C)2004,JPO

Description

【００３０】
【表２】

【００３１】
実施例２
除湿装置の方式として、本発明によるバブリング方式と従来の吸着剤方式（ＰＳＡ）とを使用して、ボイラー排ガス中のＣＯ_２固化・分離運転を行った。本運転におけるＣＯ_２固化装置の出口排ガス中のＣＯ_２分離率を比較して、表３に示す。その結果、ＣＯ_２固化装置７の入口排ガス中の水蒸気露点を低下させることにより、ＣＯ_２分離率が大きくなる。本発明によるバブリング方式除湿装置の効果が大きいことが明確である。
（運転条件）
１）ボイラー排ガス
排ガス量＝６０（Ｎｍ^３／ｈ）
排ガス組成
ＣＯ_２濃度＝３．９（％），Ｈ_２Ｏ濃度＝７．６（％）
Ｎ_２濃度＝７５．６（％），Ｏ_２濃度＝１２．９（％）
２）除湿装置
バブリング方式　：　温度＝−７０℃
【００３２】
【表３】

【００３３】
【発明の効果】
本発明に係る方法によれば、従来の除湿方法では処理できなかった露点まで、排ガス中の水蒸気を分離・除去できる。その結果、ＣＯ_２を固化させるために水蒸気の固化温度以下まで排ガスを冷却しても、装置の壁面や配管表面等への凝結により発生するトラブルを防止することができる。また、ＣＯ_２固化装置の伝熱管表面への水蒸気固化による伝熱性能低下を防止することができる。従って、本発明の二酸化炭素回収方法および回収システムは、工業上極めて有益である。
【図面の簡単な説明】
【図１】本発明の二酸化炭素回収方法を実施するのに好適なシステムの一例を模式的に示す図である。
【図２】実施例１において用いた除湿試験装置の構成を示す図である。
【図３】本発明の二酸化炭素回収方法を実施するのに好適なシステムの他の一例を模式的に示す図である。
【符号の説明】
１　　ボイラー
３　　凝縮器
５　　除湿装置
７　　二酸化炭素固化装置
８　　冷熱源（冷凍機など）
１１　冷媒／水分離装置
４，６，１６，３８　熱交換器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and a system for dehumidifying exhaust gas, and more particularly to a method and a system for cooling water vapor in combustion exhaust gas from a boiler or an incinerator to a dew point of zero degrees Celsius or less.
[0002]
[Prior art]
Conventionally, water vapor has been condensed and separated by directly spraying cooling water (sea water, tap water or industrial water) into the exhaust gas or by cooling it with an indirect heat exchanger to cool the exhaust gas. In this method, the exhaust gas can be cooled only to the temperature of the cooling water, so that water equivalent to the water vapor pressure at the cooling temperature remains. Even when this cooling water was cooled by a refrigerator, it could generally only be cooled to about 5 to 10 ° C. Therefore, about several percent of water vapor remains in the exhaust gas.
[0003]
Therefore, if the cooled exhaust gas is cooled to a low temperature at which the water vapor solidifies, the residual water vapor in the exhaust gas solidifies on the wall surface of the device, the wall surface of the piping, or the like, which hinders the operation of the device. In addition, when the exhaust gas is pressurized (about 600 KPa or more) and cooled to liquefy the carbon dioxide gas, residual water vapor in the exhaust gas is condensed in the liquefied carbon dioxide and the purity of the liquefied carbon dioxide is reduced.
[0004]
As another dehumidifying method other than the cooling method, there is a treatment method using an adsorbent (PSA, TPSA method, etc.). Even in this method, several hundred ppm or more of water vapor remains in the exhaust gas, which causes a trouble on the apparatus.
[0005]
There is also a dehumidification method using a membrane separation method, but even in this case, several hundred to several thousand ppm or more of water vapor remains in the exhaust gas, and if it is not separated to about 50 ppm or less, it may cause a similar trouble on the apparatus.
[0006]
On the other hand, as a method of cooling and solidifying and separating carbon dioxide in exhaust gas to a low temperature (-78.5 ° C. or lower) at which carbon dioxide is solidified, a CO ₂ recovery method and a natural gas liquefaction energy recycling method include: A method has been proposed in which the exhaust gas is cooled to a temperature lower than the temperature at which water vapor solidifies, and the carbon dioxide gas is solidified and recovered as dry ice (for example, see Patent Documents 1 and 2).
[0007]
Further, in order to effectively use the cold heat of liquefied natural gas, a system has been proposed in which carbon dioxide in exhaust gas is solidified and separated at a low temperature and then the solidified material is further processed (for example, see Patent Documents 3 and 4). .
[0008]
[Patent Document 1]
JP-A-4-77308
[Patent Document 2]
JP-A-8-269469
[Patent Document 3]
JP 2000-24454 A
[Patent Document 4]
JP 2000-317302 A
[Problems to be solved by the invention]
However, in order to separate the water vapor in the exhaust gas using the conventional method, it is difficult to reduce the dew point of the exhaust gas to −10 ° C. or less when using cooling water. In addition, in the case of the adsorption method, the dew point of the exhaust gas is about −30 ° C., and there is a problem that water vapor remaining in the exhaust gas cannot be sufficiently removed.
In view of the above problems, the present inventors have been able to separate and remove water vapor in exhaust gas up to a dew point that could not be removed conventionally, and cooled the exhaust gas to below the solidification temperature of water vapor to solidify CO _2. Also, intensive studies were conducted to develop a method capable of avoiding condensation on the wall surface of the apparatus, the surface of the pipe, and the like, and preventing a decrease in heat transfer performance due to solidification of steam on the heat transfer tube surface of the carbon dioxide solidifying apparatus.
[0013]
As a result, the present inventors have found that, after separating the water vapor contained in the exhaust gas using a specific cooling medium, the exhaust gas is cooled and the carbon dioxide gas is separated and recovered, whereby this problem can be solved at once. I found it. The present invention has been completed from such a viewpoint.
[0014]
[Means for Solving the Problems]
That is, the present invention provides a method for dehumidifying exhaust gas in which exhaust gas is circulated in a cooling medium to condense or solidify and separate water vapor contained in the exhaust gas, and condensed or solidified water vapor contained in the exhaust gas. The present invention provides an exhaust gas dehumidification system including a dehumidification device that separates waste gas. According to such a dehumidifying method of the present invention, for example, the exhaust gas is circulated in a cooling medium, and the steam contained in the exhaust gas is condensed or solidified to be separated. A method for recovering carbon dioxide in exhaust gas by providing a carbon dioxide gas separation and recovery step of directly or indirectly cooling the exhaust gas that has passed through the steam separation step and separating and recovering carbon dioxide in the exhaust gas in a liquid or solid state. Can also be provided.
[0015]
In the present invention, when the exhaust gas is cooled directly or indirectly to separate and recover the carbon dioxide gas in the exhaust gas in a liquid or solid state, the steam contained in the exhaust gas is circulated through the cooling medium at the preceding stage. And then condensed or solidified and separated.
Here, examples of the cooling medium include inorganic salts (such as sodium chloride and potassium chloride), bromine compounds (such as lithium bromide and bromide), ethers (such as dimethyl ether and methyl ether), and alcohols (such as methanol and ethanol). ), Silicon oil, a solution containing at least one selected from the group consisting of paraffinic hydrocarbons and olefinic hydrocarbons. In the steam separation step, it is preferable that the cooling medium is cooled to a temperature equal to or lower than a solidification temperature of steam.
[0016]
Specifically, for example, a solution containing dimethyl ether is suitably used as the cooling medium. In the steam separation step, the dimethyl ether is preferably used in a low temperature state having a boiling point or lower and a freezing point or higher.
Further, the present invention provides an exhaust gas dehumidifying method and a system thereof, in which exhaust gas is circulated in a cooling medium, and water vapor contained in the exhaust gas is condensed or solidified and separated, and has the dehumidifying effect. A dehumidifying device and a dehumidifying system that includes a carbon dioxide solidifying device that cools the exhaust gas directly or indirectly and separates and collects carbon dioxide in the exhaust gas in a liquid or solid state after the dehumidifier. Applicable.
Usually, a refrigerant / water separator for circulating a cooling medium and separating and recovering water is connected to the dehumidifier.
[0017]
The cooling medium remains in a liquid state at a temperature at which moisture solidifies to ice. Therefore, it has the function of transmitting the cold heat held by the cooling medium to the exhaust gas to cool the steam below the coagulation temperature. In the dehumidifier, the steam is once cooled to the coagulation temperature and solidified and separated from the exhaust gas as ice. Thereafter, it is necessary to separate the cooling medium and the ice, and in the refrigerant / water separator, the cooling medium and the ice are separated based on a difference in melting point.
According to the present invention, the steam in the exhaust gas can be separated and removed by the steam separation step up to a low-temperature dew point that cannot be treated by the conventional dehumidification method. As a result, even if the exhaust gas is cooled to a temperature equal to or lower than the solidification temperature of steam in order to solidify CO ₂ in the carbon dioxide gas separation / recovery step, it is possible to prevent troubles caused by condensation on the wall surface of the apparatus or the pipe surface. it can. Further, it is possible to prevent a decrease in heat transfer performance due to solidification of steam on the heat transfer tube surface of the CO ₂ solidification device.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, specific embodiments will be described with reference to the accompanying drawings, taking as an example a method of solidifying and separating carbon dioxide in a method and system for dehumidifying exhaust gas according to the present invention. FIG. 1 is a diagram schematically showing an example of a system suitable for carrying out the method of the present invention.
The present invention is a system for directly or indirectly cooling combustion exhaust gas from a boiler or an incinerator and separating and recovering carbon dioxide in the exhaust gas in a liquid or solid state. In the recovery method of the present invention, first, in a steam separation step, exhaust gas is circulated in a cooling medium to separate or condense or solidify steam contained in the exhaust gas. Next, in the carbon dioxide gas separation and recovery step, the exhaust gas that has passed through the steam separation step is directly or indirectly cooled, and the carbon dioxide gas in the exhaust gas is separated and recovered in a liquid or solid state.
[0019]
In the present embodiment, when the steam contained in the exhaust gas is allowed to flow through the cooling medium to be condensed or solidified and separated, a refrigerant having a boiling point equal to or lower than the condensation or solidification temperature of the steam is used, and the dew point of the exhaust gas is used. To about −50 ° C. or less.
The water vapor is cooled in a low-temperature cooling medium, and the excess is condensed to a saturated vapor pressure and separated from the gas phase. For example, when the dew point is −50 ° C., the moisture concentration in the gas phase is 38.0 ppm. To cool the exhaust gas to this dew point, a cooling medium having a coagulation temperature equal to or lower than the dew point, for example, dimethyl ether (coagulation temperature −141.5 ° C, boiling point -24.9 ° C) and methanol (coagulation temperature-97.8 ° C, boiling point 64.7 ° C). However, in order to separate the cooling medium from the condensed moisture, it is advantageous to have a larger difference in boiling point between the cooling medium and the moisture.
[0020]
In consideration of these points, for example, dimethyl ether is preferably used as an available cooling medium. Hereinafter, description will be given based on FIG.
FIG. 1 shows an example of a process flow for separating and recovering CO ₂ in exhaust gas.
[0021]
The high-temperature exhaust gas generated in the boiler 1 is guided to a condenser 3 via a line 2. Here, it is cooled to about room temperature by seawater, industrial water, tap water or the like, and a part of the steam in the exhaust gas is condensed and separated. The cooled exhaust gas is further guided to the dehumidifier 5 through the heat exchanger 4. The dehumidifier 5 contains a low-temperature cooling medium, and the exhaust gas is cooled to about −50 ° C. or less, and the water vapor in the exhaust gas is condensed and separated. The dehumidified exhaust gas is cooled by the heat exchanger 6 and then guided to a carbon dioxide (CO ₂ ) solidification device 7. Here, the CO ₂ in the exhaust gas is cooled to a temperature at which it solidifies, and the solidified CO is separated from the exhaust gas through the line 9 as dry ice. The heat exchangers 4 and 6 are cooled by a cold heat source 8 (cooling medium A, low-temperature liquefied natural gas LNG, or the like) supplied from a refrigerator or the like.
On the other hand, the cooling medium B circulates in the dehumidifier 5, and the cooling medium B containing water condensed from the exhaust gas is discharged to the refrigerant / water separator 11 via the line 10, where the cooling medium B and the water are separated. Then, the cooling medium B is cooled again and returned to the dehumidifier 5 via the line 12. The water separated by the refrigerant / water separator 11 is mixed with the water in the line 13 via the line 14 and then discharged from the line 15.
Examples of the cooling medium include aqueous solutions of inorganic salts (such as sodium chloride and potassium chloride), aqueous solutions of bromine compounds (such as lithium bromide and bromide), ethers (such as dimethyl ether and methyl ether), alcohols (such as methanol and ethanol), A solution containing at least one kind of silicon oil, paraffinic hydrocarbon (propane, normal butane, or the like), or olefinic hydrocarbon is used. In the steam separation step, these cooling media are cooled below the solidification temperature of steam. In order to separate the cooling medium and the condensed water, it is advantageous that the difference in boiling point between the cooling medium and the water is large. The refrigerant to be used is determined in consideration of these points. Among the above cooling media, for example, ethers (dimethyl ether, methyl ether, etc.) and alcohols (methanol, ethanol, etc.) are preferably used, and dimethyl ether, normal butane silicone oil, etc. are particularly preferable.
Among the above-mentioned cooling media, dimethyl ether is mentioned as an example suitable for the dehumidification process of the present invention. Dimethyl ether has a coagulation temperature of -141.5 ° C and a boiling point of 24.8 ° C. Hereinafter, examples of operating conditions when applied to the method of the present invention will be described.
[0022]
The exhaust gas cooled to about 5 ° C. in the heat exchanger 4 is cooled in the dehumidifier 5 to about −50 ° C. or less. The cooled steam solidifies below the freezing point and forms a sorbet state with dimethyl ether (cooling medium B).
[0023]
Next, the mixture in the sherbet state is discharged from the line 10 and supplied to the refrigerant / water separator 11. Here, when the temperature in the apparatus is heated to -24.8 ° C. or higher, dimethyl ether boils and evaporates, and ice remains. The ice is melted and converted into liquid water, and the generated water is discharged through a line 14. The vaporized dimethyl ether is cooled again in the heat exchanger 16, becomes a liquid state, and is circulated to the dehumidifier 5 through the line 12.
In the present embodiment, the cooling medium B maintains a liquid state at a temperature at which water solidifies and becomes ice. Therefore, it has the function of transmitting the cold heat held by the cooling medium B to the exhaust gas to cool the steam below the freezing temperature. In the dehumidifier 5, the steam is once cooled to a solidification temperature or lower and solidified and separated from the exhaust gas as ice. Then, it is necessary to separate the cooling medium B and ice. Therefore, the cooling medium B and the ice can be separated by the difference in the melting points.
FIG. 3 shows another example of the process flow for separating and recovering CO ₂ in exhaust gas according to the present invention.
[0024]
The high-temperature exhaust gas generated in the boiler 1 is led to the heat exchanger 38 via the line 2. Here, it is cooled to about room temperature by seawater, industrial water, tap water or the like, and a part of the steam in the exhaust gas is condensed and separated. The cooled exhaust gas is led to the dehumidifier 5. A low-temperature cooling medium is sent to the dehumidifier 5 from the line 34, the exhaust gas is cooled to about −50 ° C. or lower, and the water vapor in the exhaust gas is condensed and separated. The dehumidified exhaust gas is cooled by the heat exchanger 6 and then guided to a carbon dioxide (CO ₂ ) solidification device 7. Here, the CO ₂ in the exhaust gas is cooled to a temperature at which it solidifies, and the solidified CO is separated from the exhaust gas through the line 9 as dry ice. The heat exchanger 38, the dehumidifier 5 and the CO ₂ solidifier 7 are cooled by the action of the lines 33, 34, 35, 36 of the cooling medium A sent from the cold heat source 8.
[0025]
On the other hand, similarly to the system of FIG. 1, a cooling medium B is circulated in the dehumidifier 5, and the cooling medium B containing water condensed from the exhaust gas is discharged to a refrigerant / water separator 11 through a line 10, where it is discharged. Then, the cooling medium B is cooled again, and is returned to the dehumidifier 5 through the line 12.
[0026]
Further, in the system of FIG. 3, the cool air discharged from the carbon dioxide (CO ₂ ) solidification device 7 is sent to the heat exchanger 6 by the line 30 and then sent to the heat exchanger 38 by the line 31. The gas warmed by the heat exchange in each device is exhausted from the chimney 37 via the line 32.
Hereinafter, the effects of the cooling medium used in the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples. Further, even in a system in which carbon dioxide is not solidified and separated at a low temperature, it can be dehumidified to a low-temperature dew point.
[0027]
【Example】
Example 1
The separation (dehumidification) of water vapor in the exhaust gas was performed using a small dehumidification test device as shown in FIG. 2, and the dew point was evaluated.
(1) Device specifications 1) Dehumidifier 5
Model: Bubbling tower (bubbling from exhaust gas supply pipe 20)
Dimensions: inner diameter 100 x length 1, 210 mm
Material: transparent acrylic resin 2) Cooling medium circulation pump 22
Average circulation flow rate = 15 (m ³ / h)
(2) Cooling medium dimethyl ether, ethanol, methanol, normal butane (3) Exhaust gas property water = 5-10, CO ₂ = 3-10, N ₂ = 80-90 (vol%)
(4) Operation results The operation results are shown in Tables 1 and 2.
[0028]
Dimethyl ether was found to be easily separated from the solidified water, and was very suitable as a cooling medium used in the system of the present invention. Further, it was found that it was necessary to apply a distillation method or a membrane separation method to the separation of water with respect to methanol.
[0029]
[Table 1]

[0030]
[Table 2]

[0031]
Example 2
The bubbling system according to the present invention and the conventional adsorbent system (PSA) were used as the dehumidifying system to perform the operation of solidifying and separating CO _{2 in} boiler exhaust gas. Table 3 shows a comparison of the CO ₂ separation ratio in the exhaust gas at the outlet of the CO ₂ solidification device in this operation. As a result, the CO ₂ separation rate is increased by lowering the water vapor dew point in the exhaust gas at the inlet of the CO ₂ solidifying device 7. It is clear that the effect of the bubbling type dehumidifier according to the present invention is great.
(Operating conditions)
1) Boiler exhaust gas exhaust gas amount = 60 (Nm ³ / h)
Exhaust gas composition CO ₂ concentration = 3.9 (%), H ₂ O concentration = 7.6 (%)
N ₂ concentration = 75.6 (%), _{O 2} concentration = 12.9 (%)
2) Dehumidifier bubbling method: Temperature = -70 ° C
[0032]
[Table 3]

[0033]
【The invention's effect】
According to the method of the present invention, water vapor in exhaust gas can be separated and removed up to a dew point that cannot be treated by the conventional dehumidifying method. As a result, even when the exhaust gas is cooled to a temperature equal to or lower than the solidification temperature of steam in order to solidify CO ₂ , it is possible to prevent troubles caused by condensation on the wall surface of the apparatus, the pipe surface, and the like. Further, it is possible to prevent a decrease in heat transfer performance due to solidification of steam on the heat transfer tube surface of the CO ₂ solidification device. Therefore, the method and system for recovering carbon dioxide of the present invention are extremely useful industrially.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing an example of a system suitable for carrying out a carbon dioxide recovery method of the present invention.
FIG. 2 is a diagram showing a configuration of a dehumidification test device used in Example 1.
FIG. 3 is a diagram schematically showing another example of a system suitable for carrying out the carbon dioxide recovery method of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Boiler 3 Condenser 5 Dehumidifier 7 Carbon dioxide solidification device 8 Cold heat source (refrigerator etc.)
11 Refrigerant / water separator 4, 6, 16, 38 Heat exchanger

Claims (8)

A method for dehumidifying exhaust gas, comprising flowing exhaust gas through a cooling medium and condensing or solidifying and separating water vapor contained in the exhaust gas. The cooling medium is a solution containing at least one selected from the group consisting of inorganic salts, bromine compounds, ethers, alcohols, silicone oil, paraffinic hydrocarbons and olefinic hydrocarbons, and the cooling medium 2. The method for dehumidifying exhaust gas according to claim 1, wherein the water is cooled to a temperature equal to or lower than the solidification temperature of steam. 2. The method for dehumidifying exhaust gas according to claim 1, wherein the cooling medium is a solution containing dimethyl ether, and the dimethyl ether is used in a low temperature state having a boiling point or lower and a freezing point or higher. An exhaust gas dehumidifying system comprising a dehumidifying device that circulates exhaust gas through a cooling medium and condenses or solidifies and separates water vapor contained in the exhaust gas. The cooling medium is a solution containing at least one selected from the group consisting of inorganic salts, bromine compounds, ethers, alcohols, silicone oil, paraffinic hydrocarbons and olefinic hydrocarbons, and the cooling medium 5. The exhaust gas dehumidification system according to claim 4, wherein the gas is cooled to a temperature equal to or lower than the solidification temperature of steam. The exhaust gas dehumidification system according to claim 4, wherein the cooling medium is a solution containing dimethyl ether, and the dimethyl ether is used in a low temperature state having a boiling point or lower and a freezing point or higher. A carbon dioxide gas solidifying device that cools exhaust gas directly or indirectly and separates and collects carbon dioxide gas in the exhaust gas in a liquid or solid state at a subsequent stage of the dehumidifier. 7. The exhaust gas dehumidification system according to any one of the above items 6. The exhaust gas dehumidifying system according to any one of claims 4 to 7, wherein a refrigerant / water separator that circulates a cooling medium and separates and recovers water is connected to the dehumidifying device.

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