JP2009297655A - Separation method and system of carbon dioxide gas - Google Patents

Separation method and system of carbon dioxide gas Download PDF

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JP2009297655A
JP2009297655A JP2008155305A JP2008155305A JP2009297655A JP 2009297655 A JP2009297655 A JP 2009297655A JP 2008155305 A JP2008155305 A JP 2008155305A JP 2008155305 A JP2008155305 A JP 2008155305A JP 2009297655 A JP2009297655 A JP 2009297655A
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carbon dioxide
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Takashi Asano
浅野　　隆
Yuko Hino
祐子 日野
Kiyomi Funabashi
清美 船橋
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Hitachi Ltd
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a separation method and a system of carbon dioxide gas efficiently separating CO<SB>2</SB>gas in a gaseous state from exhaust gas of an industrial process. <P>SOLUTION: Absorbing liquid containing metal ions constituting hydrogen carbonate or carbonate is impregnated into hollow fiber membranes 5, supply gas containing carbon dioxide gas is supplied into the hollow fiber membranes 5, pressure of surroundings of the hollow fiber membranes 5 is reduced to take in carbon dioxide gas in the supply gas into fine pores of the hollow fiber membranes 5, and to discharge the carbon dioxide gas to surrounding spaces of the hollow fiber membranes 5 of a membrane module 2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

本発明は、火力発電所や製鉄所等の様々な工業プロセスの排出ガスから炭酸ガス（ＣＯ２ガス）を分離する方法とシステムに関する。 The present invention relates to a method and system for separating carbon dioxide (CO 2 gas) from exhaust gases from various industrial processes such as thermal power plants and steelworks.

火力発電所の排ガスは炭化水素化合物を主成分とした化石燃料が燃焼したものであり、ＣＯ２ガスを含んでいる。それに対し、近年、大気中のＣＯ２ガスの温室効果による地球温暖化への懸念から大気中のＣＯ２ガス濃度の増加を抑制することの重要性が叫ばれ、様々な工業プロセスの排出ガスからＣＯ２ガスを分離し、ＣＯ２ガスの大気中への放出を抑制する方法を安価に実現させることが求められている。工業的に実用化されている代表的なＣＯ２ガスの分離方法として、熱炭酸カリウム法やアミン化合物を利用した化学吸収法が知られている。 Exhaust gas from a thermal power plant is obtained by burning fossil fuels mainly composed of hydrocarbon compounds, and contains CO 2 gas. In contrast, in recent years, the importance of suppressing the increase in the CO 2 gas concentration in the atmosphere from the concern about global warming caused by the greenhouse effect of CO 2 gas in the atmosphere is advocated, from the exhaust gas of various industrial processes CO 2 gas was separated, be low cost methods of inhibiting the release of the CO 2 gas in the atmosphere are required. As a typical method for separating CO 2 gas that is put into practical use, a thermal potassium carbonate method and a chemical absorption method using an amine compound are known.

熱炭酸カリウム法では、重量濃度２０〜３０％の炭酸カリウム溶液を吸収液として用い、比較的低温（６０〜１１０℃）・高圧（約０．５ＭＰａ）の吸収塔でＣＯ２ガスを含む供給ガスを吸収液とを接触させてＣＯ２ガスを吸収液に吸収し、次いで吸収液を比較的高温（１００〜１２０℃）・低圧（常圧以下）の再生塔に送って加熱・減圧することで、ＣＯ２を吸収液から回収する（例えば特許文献１参照）。この種の方法では各種の反応促進剤や腐食防止剤を添加する方法も実用化されているが、いずれも単位吸収液当たりのＣＯ２吸収量は２０〜３５Ｎｍ３／ｍ３、供給ガスに残留するＣＯ２濃度は０．０５〜０．２％、ＣＯ２の回収に必要な熱量は１．９〜２．８ＧＪ／ｔｏｎ−ＣＯ２程度である。 In the hot potassium carbonate method, a potassium carbonate solution having a weight concentration of 20 to 30% is used as an absorption liquid, and a supply gas containing CO 2 gas in a relatively low temperature (60 to 110 ° C.) and high pressure (about 0.5 MPa) absorption tower. Is absorbed with the absorbing solution to absorb the CO 2 gas into the absorbing solution, and then the absorbing solution is sent to a relatively high temperature (100 to 120 ° C.) / Low pressure (normal pressure or lower) regeneration tower to be heated and depressurized. CO 2 is recovered from the absorbing solution (see, for example, Patent Document 1). In this type of method, methods of adding various reaction accelerators and corrosion inhibitors have been put into practical use, but all have a CO 2 absorption amount of 20 to 35 Nm 3 / m 3 per unit absorption liquid and remain in the supply gas. The concentration of CO 2 to be produced is 0.05 to 0.2%, and the amount of heat necessary for CO 2 recovery is about 1.9 to 2.8 GJ / ton-CO 2 .

一方、アミン化合物を利用した化学吸収法では、アミン化合物の溶解液を吸収液として用い、熱炭酸カリウム法と同じく、比較的低温・高圧の吸収塔でＣＯ２ガスを含む供給ガスと吸収液とを接触させてＣＯ２を吸収液に吸収させ、その吸収液を比較的高温・低圧の再生塔へ送って吸収液を加熱・減圧することでＣＯ２を吸収液から回収する。使用するアミン化合物の種類によって異なるが、モノエタノールアミン（ＭＥＡ）の例を記すと、単位吸収液当たりのＣＯ２吸収量は１６〜２２Ｎｍ３／ｍ３、供給ガスに残留するＣＯ２濃度は５〜１００ｐｐｍ、ＣＯ２の回収に必要な熱量は４．３〜６．４ＧＪ／ｔｏｎ−ＣＯ２程度である。 On the other hand, in the chemical absorption method using an amine compound, a dissolved solution of the amine compound is used as an absorption liquid, and, similar to the thermal potassium carbonate method, a supply gas containing CO 2 gas and an absorption liquid are absorbed in a relatively low temperature and high pressure absorption tower. To absorb CO 2 in the absorption liquid, and the absorption liquid is sent to a relatively high temperature / low pressure regeneration tower, and the absorption liquid is heated and decompressed to recover CO 2 from the absorption liquid. Although it differs depending on the type of amine compound to be used, when describing an example of monoethanolamine (MEA), the CO 2 absorption amount per unit absorption liquid is 16 to 22 Nm 3 / m 3 , and the CO 2 concentration remaining in the supply gas is 5 to 100 ppm, the amount of heat required for recovery of CO 2 is about 4.3~6.4GJ / ton-CO 2.

しかしながら、工業プロセスの排出ガスからのＣＯ２ガスの分離に適用する場合を考えると、例えば石炭火力発電所の場合、出力１ＭＷ当たりの排ガス発生量は約３×１０３Ｎｍ３／ｈ、排ガス中のＣＯ２濃度は１０数％である。出力１０００ＭＷの発電所を考えると、排ガス発生量は約３×１０６Ｎｍ３／ｈなのでＣＯ２濃度１０％としてもＣＯ２発生量は約６００ｔｏｎ／ｈとなり、上述の熱炭酸カリウム法におけるＣＯ２回収に必要な熱量は約３００ＭＷ、すなわち発電所出力の３０％に相当する熱量となる。これは発電所出力の大幅な低下に繋がり、電力単価を上昇させる。 However, considering the application to separation of CO 2 gas from exhaust gas from industrial processes, for example, in the case of a coal-fired power plant, the amount of exhaust gas generated per 1 MW of output is about 3 × 10 3 Nm 3 / h, The CO 2 concentration is 10 tens%. Given the power plant output 1000 MW, CO in the exhaust gas emissions of about 3 × 10 6 Nm 3 / h, so CO 2 concentration CO 2 emissions as 10% to about 600ton / h, and the thermal potassium carbonate method described above 2 The amount of heat required for recovery is about 300 MW, that is, the amount of heat corresponding to 30% of the power plant output. This leads to a significant decrease in power plant output and increases the unit price of electricity.

そこで、ＣＯ２回収に必要な熱量の少ないアミン化合物の探索やＣＯ２回収に要する熱量又は電力の少なく化学吸収法とは原理の異なるＣＯ２ガス分離方法の開発が進められている。化学吸収法と原理の異なるＣＯ２ガス分離方法の一つに多孔質膜を用いた膜分離法がある。膜分離法は孔の大きさによって決まる分子ふるい効果や拡散速度の違いをＣＯ２分離に利用し、膜の一方の側に供給ガスを流してＣＯ２を膜の他方の側に透過させて回収する。このため、ＣＯ２回収用の熱量が不要となるので、基本的にはガスの流通に必要な動力のみでＣＯ２分離システムを作動させることができ、化学吸収法に比べて安価なＣＯ２分離方法として期待されている。 Therefore, development of a CO 2 gas separation method that is different in principle from the chemical absorption method is being pursued in search of an amine compound that requires a small amount of heat necessary for CO 2 recovery and a small amount of heat or power required for CO 2 recovery. One of the CO 2 gas separation methods having a different principle from the chemical absorption method is a membrane separation method using a porous membrane. The membrane separation method utilizes the molecular sieving effect determined by the size of the pores and the difference in diffusion rate for CO 2 separation, and the supply gas is flowed to one side of the membrane and CO 2 is permeated to the other side of the membrane for recovery. To do. Therefore, since the amount of heat CO 2 for recovery is not required, basically it is possible to operate the CO 2 separation system only by the power required for distribution of the gas, inexpensive CO 2 separation compared to chemical absorption Expected as a method.

膜分離法を工業プロセスの排出ガスからのＣＯ２ガス分離に適用する場合、ＣＯ２ガス分離のコストは、単位時間・単位膜表面積当たりに膜を透過するＣＯ２の量（透過速度）に左右される。透過速度が大きいほど必要な膜表面積は小さくて済み、設備の設置容積や設備の建設費を抑えることができる。また、膜を透過したガスのＣＯ２濃度の要求値は回収したＣＯ２の利用目的によって異なる。例えば回収したＣＯ２を工業利用する場合には、ＣＯ２の工業利用のための精製が不要、若しくは容易となるように高いＣＯ２濃度が望まれる。それに対し、回収したＣＯ２を単に大気から隔離するために地中や海洋に貯蔵したり石油や天然ガスの増進回収のために油田やガス田に注入したりする場合には、工業利用する場合のような高いＣＯ２濃度は求められない。 When the membrane separation method is applied to CO 2 gas separation from industrial process exhaust gas, the cost of CO 2 gas separation depends on the amount of CO 2 permeating the membrane per unit time and unit membrane surface area (permeation rate). Is done. The larger the permeation speed, the smaller the required membrane surface area, and the lower the installation volume of the equipment and the construction cost of the equipment. Further, the required value of the CO 2 concentration of the gas that has passed through the membrane varies depending on the purpose of use of the recovered CO 2 . For example, when the recovered CO 2 is industrially used, a high CO 2 concentration is desired so that purification of the CO 2 for industrial use is unnecessary or easy. On the other hand, when the recovered CO 2 is stored in the ground or the ocean simply to isolate it from the atmosphere, or when it is injected into an oil or gas field for enhanced recovery of oil or natural gas, it is used for industrial use. Such a high CO 2 concentration is not required.

ＣＯ２の透過速度を高める方法として、吸収液を湿潤させた多孔質膜（促進輸送膜）を用いた膜分離法があり、吸収液として炭酸カリウム溶液やアミン化合物の溶解液を利用することが知られている（例えば特許文献２参照)。促進輸送膜の内部では、吸収液に吸収されたＣＯ２が溶液の輸送とともに膜を透過するため、ＣＯ２の透過速度が高まる。 As a method for increasing the permeation rate of CO 2 , there is a membrane separation method using a porous membrane (facilitated transport membrane) in which an absorbing solution is moistened, and a potassium carbonate solution or an amine compound solution can be used as the absorbing solution. It is known (see, for example, Patent Document 2). Inside the facilitated transport membrane, CO 2 absorbed in the absorbing solution permeates the membrane along with the transport of the solution, so that the permeation rate of CO 2 increases.

特開昭５８−２０１８９１号公報JP 58-201891 A 特開２０００−２２９２１９号公報JP 2000-229219 A

膜分離法におけるＣＯ２の透過速度は、同じ膜を用いた場合を考えると、膜の一方側（供給ガスの供給側）と他方側（ＣＯ２ガスが透過した側）の圧力差に比例する。例えば、石炭火力発電所の排ガスの圧力は常圧なので、膜のＣＯ２の透過側を真空ポンプ等で減圧してＣＯ２を回収することができるが、ＣＯ２ガスの透過側の真空度が高いほど（圧力が低いほど）膜の両側の圧力差が大きくなるので、ＣＯ２の透過速度を大きくすることができる。 The permeation rate of CO 2 in the membrane separation method is proportional to the pressure difference between one side of the membrane (supply gas supply side) and the other side (the side through which CO 2 gas has permeated) when the same membrane is used. . For example, the pressure of the exhaust gas coal-fired power plants is a normal pressure, but the permeate side of the CO 2 in the film can be recovered CO 2 under reduced pressure by a vacuum pump or the like, the transmission side of the vacuum degree of the CO 2 gas The higher the pressure (the lower the pressure), the larger the pressure difference on both sides of the membrane, so that the CO 2 permeation rate can be increased.

しかし、アミン化合物の溶解液を利用した促進輸送膜を用いた膜分離法の場合、アミン化合物は有機化合物なので、水分の蒸発に伴ってアミン化合物の一部も蒸発する恐れがある。アミン化合物には配管等を腐食する作用があるので、蒸発したアミン化合物と水蒸気が配管内面に凝縮すると配管が腐食する。さらに、アミン化合物の濃度が低下しないようにアミン化合物の溶解液を膜に供給する必要がある。   However, in the case of a membrane separation method using a facilitated transport membrane using an amine compound solution, since the amine compound is an organic compound, part of the amine compound may evaporate with the evaporation of moisture. Since the amine compound has an action of corroding the pipe and the like, the pipe corrodes when the evaporated amine compound and water vapor are condensed on the inner surface of the pipe. Furthermore, it is necessary to supply a solution of the amine compound to the membrane so that the concentration of the amine compound does not decrease.

また、吸収液として炭酸カリウム溶液を利用した場合には水分の蒸発に伴って減圧側の膜表面が冷却されるので、温度が低いほど炭酸塩の溶解度は低いことから、濃度の高い炭酸カリウム溶液を用いると膜表面に炭酸塩が析出し、ＣＯ２の分離を阻害する恐れがある。 In addition, when a potassium carbonate solution is used as the absorbing solution, the membrane surface on the decompression side is cooled as the moisture evaporates, so the lower the temperature, the lower the solubility of the carbonate. When carbonate is used, carbonate may be deposited on the membrane surface, which may inhibit the separation of CO 2 .

さらに、膜のＣＯ２透過側の真空度を高くすると水分が蒸発するだけでなく、膜から吸収液が滲み出す恐れがある。滲み出した吸収液にはＣＯ２が含まれているため、吸収液からＣＯ２を回収しなければ、膜のＣＯ２透過側を幾ら減圧しても実質的なＣＯ２の透過速度向上には繋がらない恐れがある。 Further, when the degree of vacuum on the CO 2 permeation side of the membrane is increased, not only the water evaporates, but also the absorbing solution may ooze out from the membrane. Since the absorption liquid exuded contains CO 2, unless the CO 2 is recovered from the absorbing liquid, even if much reduced pressure of CO 2 permeate side of the membrane in substantial permeation rate enhancement of CO 2 is There is a risk of not being connected.

本発明は以上に鑑みなされたもので、工業プロセスの排出ガスからＣＯ２ガスを気体の状態で効率的に分離することができる炭酸ガス分離方法及びシステムを提供することを目的とする。 The present invention has been made in view of the above, and an object of the present invention is to provide a carbon dioxide gas separation method and system capable of efficiently separating CO 2 gas from an exhaust gas of an industrial process in a gaseous state.

上記目的を達成するために、本発明は、炭酸ガスを吸収し易く減圧下でも蒸発し難い成分を含有した吸収液を多孔質物質に含浸させ、この多孔質物質の一方側に炭酸ガスを含む供給ガスを供給して他方側を減圧する。   In order to achieve the above object, the present invention impregnates a porous material with an absorbing solution containing a component that easily absorbs carbon dioxide gas and does not evaporate even under reduced pressure, and contains carbon dioxide gas on one side of the porous material. Supply gas is supplied and the other side is depressurized.

本発明によれば、工業プロセスの排出ガスからＣＯ２ガスを気体の状態で効率的に分離することができる。 According to the present invention, CO 2 gas can be efficiently separated from an exhaust gas of an industrial process in a gaseous state.

以下に図面を用いて本発明の実施の形態を説明する。   Embodiments of the present invention will be described below with reference to the drawings.

本実施の形態の炭酸ガス分離方法及びシステムは、ＣＯ２ガスを吸収し易く減圧下で蒸発し難い成分を含有した吸収液を含浸させた多孔質物質を用い、当該多孔質物質の一方側にＣＯ２ガスを含む供給ガスを供給し、多孔質物質の他方側を減圧することで供給ガスからＣＯ２ガスを分離するものである。吸収液には、炭酸水素塩又は炭酸塩を構成するアルカリ金属イオンを含んだ無機アルカリ溶液を用いることができる。この場合、アルカリ金属には各種のものを用いることができるが、多孔質物質の細孔内での流動性を考慮すると原子の小さなカリウムが適しており、炭酸水素塩又は炭酸塩として、ＣＯ２ガス吸収量が大きくＣＯ２を回収し易い水酸化カリウム、炭酸水素カリウム、炭酸カリウムの少なくとも１つを含んでいることが望ましい。この場合、吸収液中のカリウム濃度を炭酸水素カリウム飽和溶液中のカリウム濃度以下とすることで、炭酸水素塩又は炭酸塩の析出を効果的に抑えることができる。 The carbon dioxide gas separation method and system of the present embodiment uses a porous material impregnated with an absorbing liquid containing a component that easily absorbs CO 2 gas and does not easily evaporate under reduced pressure, and is provided on one side of the porous material. A supply gas containing CO 2 gas is supplied, and the CO 2 gas is separated from the supply gas by depressurizing the other side of the porous material. As the absorbing solution, an inorganic alkali solution containing hydrogen carbonate or an alkali metal ion constituting the carbonate can be used. In this case, various alkali metals can be used. However, considering the fluidity in the pores of the porous material, potassium having a small atom is suitable. As the hydrogen carbonate or carbonate, CO 2 is used. It is desirable to contain at least one of potassium hydroxide, potassium hydrogen carbonate, and potassium carbonate, which has a large gas absorption amount and easily collects CO 2 . In this case, precipitation of bicarbonate or carbonate can be effectively suppressed by setting the potassium concentration in the absorbing solution to be equal to or lower than the potassium concentration in the saturated potassium bicarbonate solution.

また、必要に応じて、多孔質物質から滲出又は蒸発した吸収液は、気液分離してＣＯ２ガスを回収した後、供給ガスに混合して多孔質物質に供給することができる。多孔質物質から滲出又は蒸発した吸収液からＣＯ２ガスを回収する際に吸収液を加熱する必要がある場合、供給ガスとの熱交換によって吸収液を加熱することができる。 Further, if necessary, the absorbing liquid that has exuded or evaporated from the porous material can be gas-liquid separated to recover the CO 2 gas, and then mixed with the supply gas to be supplied to the porous material. When it is necessary to heat the absorption liquid when recovering the CO 2 gas from the absorption liquid exuded or evaporated from the porous material, the absorption liquid can be heated by heat exchange with the supply gas.

多孔質物質に吸収液を含浸させるには、多孔質物質の一方側に吸収液を供給して他方側を減圧することで、多孔質物質の細孔を吸収液で満たすことができる。例えば多孔質膜で形成された管（ここでは中空糸膜を例示する）を多孔質物質に用いる場合、まず中空糸膜の中空部分に吸収液を通して膜の一方側（この場合内壁側）を吸収液で満たし、多孔質物質を介した他方側（中空糸膜の外壁側）を真空ポンプで減圧して多孔質膜の細孔内に吸収液を引き込む。この中空糸膜を用いて供給ガスからＣＯ２ガスを分離するには、中空糸膜の中空部に供給ガスを通して中空糸膜の周囲を減圧することで、供給ガス中のＣＯ２ガスを多孔質膜の外側に透過させる。多孔質膜を透過したＣＯ２ガスは、必要に応じて気液分離槽を通して余分な水分と分離して回収する。また、多孔質膜の外部に吸収液が滲み出す場合、滲出した吸収液を液体ポンプで移送し気液分離槽から第二の気液分離槽へ送り、第二の気液分離槽を加熱して吸収液からＣＯ２ガスを回収する構成を追加することもできる。 In order to impregnate the porous material with the absorbent, the pores of the porous material can be filled with the absorbent by supplying the absorbent to one side of the porous material and reducing the pressure on the other side. For example, when a tube formed of a porous membrane (here, a hollow fiber membrane is used as an example) is used as a porous material, first, one side of the membrane (in this case, the inner wall side) is absorbed by passing the absorbent through the hollow portion of the hollow fiber membrane. The other side through the porous material (the outer wall side of the hollow fiber membrane) is decompressed with a vacuum pump, and the absorbing solution is drawn into the pores of the porous membrane. The hollow fiber membrane from a feed gas using a separating CO 2 gas, by reducing the pressure of the surrounding of the hollow fiber membrane through a feed gas to the hollow portion of the hollow fiber membranes, porous CO 2 gas in the feed gas Permeate outside the membrane. The CO 2 gas that has permeated through the porous membrane is separated and recovered from excess water through a gas-liquid separation tank as necessary. Also, when the absorbing liquid oozes out of the porous membrane, the sorbed absorbing liquid is transferred by a liquid pump and sent from the gas-liquid separation tank to the second gas-liquid separation tank, and the second gas-liquid separation tank is heated. It is also possible to add a configuration for recovering CO 2 gas from the absorbent.

この炭酸ガス分離方法によれば、アミン化合物の溶解液を吸収液に用いる場合に比べ、吸収液が低圧下でも蒸発し難く、多孔質物質のＣＯ２ガス透過側の真空度を高くする（低圧にする）ことができる。すなわち、多孔質物質の供給ガス供給側とＣＯ２ガス透過側の圧力差を大きくすることができるので、多孔質物質のＣＯ２ガスの透過速度を大きくすることができる。また、多孔質物質を介して供給ガスからＣＯ２ガスが気体の状態で分離されるので、再生塔に送って大きなエネルギーを費やして吸収液からＣＯ２ガスを気液分離する必要がない。よって、工業プロセスの排出ガスからＣＯ２ガスを気体の状態で効率的に分離することができる。 According to this carbon dioxide separation method, the absorption liquid is less likely to evaporate even under low pressure than when an amine compound solution is used as the absorption liquid, and the degree of vacuum on the CO 2 gas permeation side of the porous material is increased (low pressure). Can). That is, since the pressure difference between the supply gas supply side of the porous material and the CO 2 gas permeation side can be increased, the permeation rate of the CO 2 gas of the porous material can be increased. In addition, since the CO 2 gas is separated from the supply gas in a gaseous state via the porous material, it is not necessary to send the gas to the regeneration tower and spend a large amount of energy to separate the CO 2 gas from the absorbing liquid. Therefore, CO 2 gas can be efficiently separated in a gaseous state from the exhaust gas of the industrial process.

図１は本発明の実施例１に係る炭酸ガス分離システムの概略図である。   FIG. 1 is a schematic view of a carbon dioxide separation system according to Embodiment 1 of the present invention.

図１に示した炭酸ガス分離システムは、火力発電所や製鉄所等の工業プロセスからの排ガスを供給ガスとして送る送風機（ガス供給手段）１と、送風機１から送られる供給ガスからＣＯ２ガスを分離する膜モジュール２と、膜モジュール２の内部空間を減圧する真空ポンプ（減圧手段）３と、膜モジュール２でＣＯ２ガスと分離された供給ガスを大気に放出する排煙塔４とを備えている。 The carbon dioxide gas separation system shown in FIG. 1 has a blower (gas supply means) 1 that sends exhaust gas from an industrial process such as a thermal power plant or a steel mill as a supply gas, and CO 2 gas from the supply gas sent from the blower 1. A membrane module 2 to be separated, a vacuum pump (decompression means) 3 for depressurizing the internal space of the membrane module 2, and a flue gas tower 4 for releasing the supply gas separated from the CO 2 gas by the membrane module 2 to the atmosphere ing.

図１に例示した炭酸ガス分離システムでは、まず送風機１によって排ガスが膜モジュール２へ送り込まれる。膜モジュール２の内部は真空ポンプ３により膜（後述する中空糸膜５）の片側が減圧されており、排ガス中のＣＯ２ガスの一部が減圧された側に分離され、回収タンク（図示せず）等に適宜回収される。回収タンクに回収したＣＯ２は、例えば圧縮と冷却を行って液化ＣＯ２として回収することもできる。減圧側の配管（膜モジュール２と真空ポンプ３とを繋ぐ配管）に圧力計２１、ＣＯ２濃度計２２、流量計２３等を取り付け、分離したＣＯ２ガスを含むガスの真空度、ＣＯ２の量、ＣＯ２濃度をモニターし、これらの値が予め定めた設定値に近付くように、送風機１や真空ポンプ３の動作を制御する構成とすることもできる。一方、膜モジュール２を通過した排ガスは排煙塔４に送られて大気中に放出される。排気ガス側の配管（膜モジュール２と排煙塔４とを繋ぐ配管）にＣＯ２濃度計２４や流量計２５等を取り付け、排ガス中のＣＯ２の量や濃度を計測して排ガスのＣＯ２の含有量を評価できるようにすることもできる。 In the carbon dioxide separation system illustrated in FIG. 1, first, exhaust gas is sent into the membrane module 2 by the blower 1. Inside the membrane module 2, one side of the membrane (hollow fiber membrane 5 described later) is decompressed by the vacuum pump 3, and a part of the CO 2 gas in the exhaust gas is separated to the decompressed side, and a recovery tank (not shown) Etc.) as appropriate. The CO 2 recovered in the recovery tank can be recovered as liquefied CO 2 by performing compression and cooling, for example. Vacuum side of the pipe pressure gauge 21 (membrane module 2 and the pipe connecting the vacuum pump 3), CO 2 concentration meter 22, fitted with a flow meter 23 or the like, the degree of vacuum gas containing the separated CO 2 gas, the CO 2 The amount and CO 2 concentration can be monitored, and the operation of the blower 1 and the vacuum pump 3 can be controlled so that these values approach a predetermined set value. On the other hand, the exhaust gas that has passed through the membrane module 2 is sent to the smoke exhaust tower 4 and released into the atmosphere. The exhaust gas side pipe attached to the CO 2 concentration meter 24 and flow meter 25 or the like (membrane module 2 and Haikemurito 4 and connecting piping), and measuring the amount or concentration of CO 2 in the exhaust gas of the exhaust gas CO 2 The content of can also be evaluated.

図２は膜モジュール２の内部構成を模式的に示した図である。   FIG. 2 is a diagram schematically showing the internal configuration of the membrane module 2.

図２に示した膜モジュール２は、気密性の確保された容器３０と、容器３０内に這い回した中空糸膜５とを備えている。中空糸膜５は吸収液を細孔に含浸させた多孔質物質である。中空糸膜５の両端は容器３０の外部に露出しており、一端が送風機１からの配管に、他端が排煙塔４への配管に接続している。よって、送風機１を作動させることによって、供給ガスが中空糸膜５の中空部を流通し、排煙塔４に導かれる。図２では模式的に１本の中空糸膜５を描いたが、複数の中空糸膜５を膜モジュール２の内部に収めることもでき、この場合には、送風機１からの排ガスを複数に分流させ、それぞれを各中空糸膜５の一端に流入させる。複数の中空糸膜５の他端側は排煙塔４への配管に合流させる。容器３０は配管を介して真空ポンプ３に接続しており、真空ポンプ３を作動させることによって容器３０の内部空間（中空糸膜５の周囲）が減圧され、中空糸膜５の周囲のガスが回収タンク（図示せず）に送られる。容器３０内が減圧されることにより、中空糸膜５（多孔質物質）の内周側（一方側）に対して外周側（他方側）の圧力が低くなり、圧力差が生じる。   The membrane module 2 shown in FIG. 2 includes a container 30 in which airtightness is ensured and a hollow fiber membrane 5 wound around in the container 30. The hollow fiber membrane 5 is a porous material in which pores are impregnated with an absorbing solution. Both ends of the hollow fiber membrane 5 are exposed to the outside of the container 30, one end is connected to the pipe from the blower 1 and the other end is connected to the pipe to the smoke exhaust tower 4. Therefore, by operating the blower 1, the supply gas flows through the hollow portion of the hollow fiber membrane 5 and is guided to the smoke exhaust tower 4. In FIG. 2, one hollow fiber membrane 5 is schematically drawn, but a plurality of hollow fiber membranes 5 can be housed in the membrane module 2, and in this case, the exhaust gas from the blower 1 is divided into a plurality of parts. Each is caused to flow into one end of each hollow fiber membrane 5. The other ends of the plurality of hollow fiber membranes 5 are joined to a pipe to the smoke exhaust tower 4. The container 30 is connected to the vacuum pump 3 through a pipe. By operating the vacuum pump 3, the internal space of the container 30 (around the hollow fiber membrane 5) is depressurized, and the gas around the hollow fiber membrane 5 is reduced. It is sent to a collection tank (not shown). When the inside of the container 30 is depressurized, the pressure on the outer peripheral side (the other side) becomes lower than the inner peripheral side (one side) of the hollow fiber membrane 5 (porous material), and a pressure difference is generated.

特に図示していないが、吸収液を中空糸膜５に含浸させる場合、排ガスからのＣＯ２ガス分離を始める前に、予め吸収液を中空糸膜５の内部に注入する。その際、中空糸膜５の外部を真空ポンプ３により減圧すると、吸収液は多孔質物質の間隙に自発的に浸入し、中空糸膜５を吸収液で湿潤させることができる。 Although not particularly shown, when the hollow fiber membrane 5 is impregnated with the absorbent, the absorbent is injected into the hollow fiber membrane 5 in advance before starting CO 2 gas separation from the exhaust gas. At that time, when the outside of the hollow fiber membrane 5 is depressurized by the vacuum pump 3, the absorbing liquid spontaneously enters the gap between the porous materials, and the hollow fiber membrane 5 can be wetted with the absorbing liquid.

次に中空糸膜５によるＣＯ２ガスの分離動作を説明する。 Next, the separation operation of CO 2 gas by the hollow fiber membrane 5 will be described.

図３は中空糸膜５の一部分を切断して表した模式図である。   FIG. 3 is a schematic view showing a part of the hollow fiber membrane 5 cut.

中空糸膜５は円筒形状をしており、内部を排ガスが通過する。図３の実線矢印はＣＯ２以外の排ガスを表し、点線矢印はＣＯ２ガスを表す。中空糸膜５の材質は多孔質物質であり、その細孔は吸収液で湿潤させている。本実施例では、吸収液として炭酸カリウム溶液を用いている。炭酸カリウム溶液中では、炭酸カリウム（Ｋ２ＣＯ３）はＫ＋イオンとＣＯ３ ２−イオンに解離しており、中空糸膜５の内表面で供給ガス中のＣＯ２が吸収液中のＣＯ３ ２−イオンと反応し、ＣＯ２が吸収液中に取り込まれてＨＣＯ３ −イオンが生成される。即ち、次の（式１）に示した化学反応が左辺から右辺に進行する。 The hollow fiber membrane 5 has a cylindrical shape, and the exhaust gas passes through the inside. The solid line arrow in FIG. 3 represents exhaust gas other than CO 2 , and the dotted line arrow represents CO 2 gas. The material of the hollow fiber membrane 5 is a porous material, and its pores are wetted with an absorbing solution. In this embodiment, a potassium carbonate solution is used as the absorbing solution. In the potassium carbonate solution, potassium carbonate (K 2 CO 3 ) is dissociated into K + ions and CO 3 2− ions, and CO 2 in the supply gas on the inner surface of the hollow fiber membrane 5 becomes CO 2 in the absorbent. It reacts with 3 2− ions, and CO 2 is taken into the absorption liquid to generate HCO 3 − ions. That is, the chemical reaction shown in the following (Formula 1) proceeds from the left side to the right side.

Figure 2009297655
Figure 2009297655

上記反応により供給液中に生じたＨＣＯ３ −イオンは吸収液中を拡散する。このとき、中空糸膜５の周囲空間が減圧されて中空糸膜５の外表面のＣＯ２ガス分圧が低くなっているので、ＨＣＯ３ −イオンは中空糸膜５の外表面に到達すると分解され、これによりＣＯ２ガスが膜モジュール２内の中空糸膜５の周囲空間に放出される。即ち、（式１）に示した化学反応が右辺から左辺に進行する。 HCO 3 − ions generated in the supply liquid by the above reaction diffuse in the absorption liquid. At this time, since the surrounding space of the hollow fiber membrane 5 is decompressed and the CO 2 gas partial pressure on the outer surface of the hollow fiber membrane 5 is lowered, HCO 3 − ions are decomposed when they reach the outer surface of the hollow fiber membrane 5. Thus, CO 2 gas is released into the space around the hollow fiber membrane 5 in the membrane module 2. That is, the chemical reaction shown in (Formula 1) proceeds from the right side to the left side.

吸収液は炭酸カリウム溶液に限定される訳ではなく、炭酸水素カリウム溶液を用いることもできる。この場合には、最初に中空糸膜５の外表面でＨＣＯ３ −イオンが分解してＣＯ２ガスが放出され、その際に生成されたＣＯ３ ２−イオンが中空糸膜５の内表面に至り、排ガス中のＣＯ２ガスが吸収される。炭酸カリウム溶液と炭酸水素カリウム溶液のどちらを用いても定常状態時の吸収液中のＣＯ３ ２−イオンとＨＣＯ３ −イオンの濃度は、排ガスの温度と圧力、排ガス中のＣＯ２ガス濃度、中空糸膜５の外側の真空度、及び吸収液のＫ＋イオン濃度から熱力学的に自律的に定まる。 The absorbing liquid is not limited to the potassium carbonate solution, and a potassium hydrogen carbonate solution can also be used. In this case, first, HCO 3 − ions are decomposed on the outer surface of the hollow fiber membrane 5 to release CO 2 gas, and the CO 3 2− ions generated at that time are formed on the inner surface of the hollow fiber membrane 5. The CO 2 gas in the exhaust gas is absorbed. The concentration of CO 3 2− ions and HCO 3 − ions in the absorption liquid in the steady state, regardless of whether potassium carbonate solution or potassium hydrogen carbonate solution is used, is the temperature and pressure of exhaust gas, the concentration of CO 2 gas in exhaust gas, It is determined thermodynamically autonomously from the degree of vacuum outside the hollow fiber membrane 5 and the K + ion concentration of the absorbing solution.

また、水酸化カリウム溶液を吸収液に用いることもできる。この場合には、次の（式２）に示した化学反応が中空糸膜５の内表面で生じ、以降は炭酸カリウム溶液の場合と同様の化学反応が生じてＣＯ２ガスが中空糸膜５の外表面から放出される。 A potassium hydroxide solution can also be used as the absorbing solution. In this case, the chemical reaction shown in the following (Formula 2) occurs on the inner surface of the hollow fiber membrane 5, and thereafter, the same chemical reaction as in the case of the potassium carbonate solution occurs, so that the CO 2 gas is converted into the hollow fiber membrane 5. Is released from the outer surface.

Figure 2009297655
Figure 2009297655

炭酸カリウム溶液、炭酸水素カリウム溶液、水酸化カリウム溶液は、いずれも単独で吸収液として用いることができるし、他の１種又は２種と混ぜて使用することもできる。但し、上記の何れの吸収液を用いた場合でも、吸収液中のＫ＋イオン濃度が炭酸水素カリウムの飽和溶液中のＫ＋イオン濃度以下であることが望ましい。 Any of the potassium carbonate solution, the potassium hydrogen carbonate solution, and the potassium hydroxide solution can be used alone as an absorbing solution, or can be used by mixing with other one or two kinds. However, even when any of the above absorbents is used, it is desirable that the K + ion concentration in the absorbent is not more than the K + ion concentration in the saturated solution of potassium hydrogen carbonate.

図４に水酸化カリウム、炭酸カリウム及び炭酸水素カリウムについて、それぞれの飽和溶液中のＫ＋イオン濃度を示した図である。 FIG. 4 is a diagram showing the K + ion concentration in each saturated solution for potassium hydroxide, potassium carbonate, and potassium hydrogen carbonate.

図４に示したように、３つの化合物の中では炭酸水素カリウム飽和溶液中のＫ＋イオン濃度が温度０〜１００℃の範囲で一番小さい。このため、Ｋ＋イオン濃度が炭酸水素カリウムの飽和溶液中のＫ＋イオン濃度を超えて存在する場合、ＣＯ２ガスを吸収した際、ＣＯ２ガスの吸収量が多いと炭酸水素カリウムが多孔質物質の間隙中に析出する恐れがある。多孔質物質の間隙の一部が析出した炭酸水素カリウムにより塞がっても直ちに排ガスからのＣＯ２ガスの分離ができなくなる訳ではないが、析出が進行すると多孔質物質が目詰まりを起して分子の流動が阻害される恐れがある。そのため、何れの吸収液を用いた場合でも、吸収液中のＫ＋イオン濃度を炭酸水素カリウムの飽和溶液中のＫ＋イオン濃度以下として、炭酸水素カリウムを析出させ難くしておくことが望ましい。 As shown in FIG. 4, among the three compounds, the K + ion concentration in the saturated potassium hydrogen carbonate solution is the smallest in the temperature range of 0 to 100 ° C. Thus, K + if ion concentration present at greater than K + ion concentration of a saturated solution of potassium hydrogen carbonate, CO 2 upon absorption of the gas, CO 2 gas absorption amount is large, the potassium bicarbonate is porous There is a risk of precipitation in the interstices of the material. Even if a part of the gap of the porous material is blocked by the precipitated potassium hydrogencarbonate, it is not necessarily impossible to separate the CO 2 gas from the exhaust gas. There is a risk that the flow of will be hindered. For this reason, it is desirable to make it difficult to deposit potassium hydrogen carbonate by setting the K + ion concentration in the absorbent liquid to be equal to or lower than the K + ion concentration in the saturated solution of potassium hydrogen carbonate, regardless of which absorption liquid is used.

本実施例においてＣＯ２ガスの分離に用いる化学反応式自体は従来の熱炭酸カリウム法と同じになるが、熱炭酸カリウム法では、吸収塔で先の（式１）で表した化学反応を左辺から右辺に進行させるために、６０〜１１０℃、圧力０．５ＭＰａとするのに対し、本発明では温度と圧力は特に制限されないという特徴がある。また、従来は供給ガスと炭酸カリウム溶液を向流接触させていたので供給ガスと吸収液の接触面積が少なく、化学反応速度を高めるために吸収液を常温、常圧よりも高温、高圧にする必要があったのに対し、本実施例では中空糸膜５の大きさ（太さ）を小さくすることで、多孔質物質の供給ガスが接触する比表面積を任意に大きくすることができるし、中空糸膜５の長さも任意に長くできるので、供給ガスの温度操作は必要なく、常温、常圧で良い。勿論、常温、常圧より高温、高圧に調整した供給ガスを膜モジュール２に供給することもできる。 In this example, the chemical reaction formula itself used for the separation of CO 2 gas is the same as that of the conventional hot potassium carbonate method. However, in the hot potassium carbonate method, the chemical reaction represented by the above (formula 1) in the absorption tower is performed on the left side. In order to make it progress to right side from 60 to 110 degreeC, it is set as the pressure of 0.5 Mpa, but this invention has the characteristics that temperature and a pressure are not restrict | limited in particular. In addition, since the supply gas and potassium carbonate solution have been in countercurrent contact with each other in the past, the contact area between the supply gas and the absorption liquid is small, and the absorption liquid is set to room temperature, higher than normal pressure and high pressure to increase the chemical reaction rate. In contrast to the necessity, in this example, by reducing the size (thickness) of the hollow fiber membrane 5, the specific surface area with which the supply gas of the porous material contacts can be arbitrarily increased, Since the length of the hollow fiber membrane 5 can be arbitrarily increased, the temperature operation of the supply gas is not required, and normal temperature and normal pressure may be used. Of course, the supply gas adjusted to normal temperature, higher temperature than normal pressure, and high pressure can be supplied to the membrane module 2.

一方、炭酸カリウム溶液に吸収されたＣＯ２の回収方法、即ち先の（式１）に示した化学反応を右辺から左辺に進行させる方法についても、熱炭酸カリウム法では再生塔で炭酸カリウム溶液を吸収塔より高い温度にすることで反応速度を高めているのに対し、本実施例では温度が特に制限されない。本実施例では中空糸膜５の大きさ（太さ）を任意に小さくできるし長さも任意に長くできるので、減圧するだけで良い。勿論、ヒーター等を用いて膜モジュール２全体を加熱することもできる。 On the other hand, the method for recovering CO 2 absorbed in the potassium carbonate solution, that is, the method of causing the chemical reaction shown in the above (formula 1) to proceed from the right side to the left side also uses the potassium carbonate solution in the regeneration tower in the hot potassium carbonate method. While the reaction rate is increased by setting the temperature higher than that of the absorption tower, the temperature is not particularly limited in this example. In this embodiment, since the size (thickness) of the hollow fiber membrane 5 can be arbitrarily reduced and the length can be arbitrarily increased, it is only necessary to reduce the pressure. Of course, the whole membrane module 2 can also be heated using a heater or the like.

次に、中空糸膜５の多孔質物質について説明する。吸収液は毛細管現象により多孔質物質の間隙内に留まっている。従って、真空ポンプ３による減圧下で吸収液を多孔質物質の細孔に留まらせるためには、吸収液の表面張力により発現する力が減圧時の中空糸膜５の内表面と外表面の圧力差を上回ることが望ましい。吸収液の表面張力により発現する力は多孔質物質の細孔の寸法に依存するので、多孔質物質の細孔の半径は次の（式３）で制限される。   Next, the porous material of the hollow fiber membrane 5 will be described. The absorbing liquid remains in the gap between the porous materials due to capillary action. Therefore, in order to keep the absorbing solution in the pores of the porous material under reduced pressure by the vacuum pump 3, the force expressed by the surface tension of the absorbing solution is the pressure on the inner surface and outer surface of the hollow fiber membrane 5 at the time of reducing pressure. It is desirable to exceed the difference. Since the force expressed by the surface tension of the absorbing liquid depends on the pore size of the porous material, the radius of the pore of the porous material is limited by the following (Equation 3).

Ｒ≦２・γ・ｃｏｓθ／ΔＰ ・・・（式３）
ここで、Ｒは間隙の半径、γは吸収液の表面張力、θは接触角、ΔＰは内表面と外表面の圧力差である。圧力差は最大で約１気圧なので、γ＝７×１０−２Ｎ／ｍ、ｃｏｓθ＝１、ΔＰ＝１ａｔｍを（式３）に代入するとＲ≦１．４μｍとなるため、間隙の大きさは約３μｍ以下が望ましい。間隙の大きさが約３μｍより大きい場合は、中空糸膜５の周囲の真空度を吸収液が多孔質物質から滲み出さない程度の圧力差となるように真空ポンプ３を制御するか、中空糸膜５から滲み出した吸収液を回収することが望ましい。 R ≦ 2 · γ · cos θ / ΔP (Formula 3)
Here, R is the radius of the gap, γ is the surface tension of the absorbing liquid, θ is the contact angle, and ΔP is the pressure difference between the inner surface and the outer surface. Since the maximum pressure difference is about 1 atm, if γ = 7 × 10 −2 N / m, cos θ = 1, ΔP = 1 atm is substituted into (Equation 3), R ≦ 1.4 μm, so the size of the gap is About 3 μm or less is desirable. When the size of the gap is larger than about 3 μm, the vacuum pump 3 is controlled so that the degree of vacuum around the hollow fiber membrane 5 becomes a pressure difference that does not allow the absorbing liquid to exude from the porous material, or the hollow fiber It is desirable to collect the absorbing liquid that has oozed out of the film 5.

次に、中空糸膜５の内表面と外表面の圧力差と中空糸膜５を透過する単位面積当たりのＣＯ２透過量との関係を説明する。膜分離法における単位面積当たりのガス透過量は内表面と外表面の圧力差に比例することが知られている。判り易く説明するため、図５に圧力差が０．２ａｔｍのときのＣＯ２透過量を１として、圧力差とＣＯ２透過量との関係を示す。本実施例によれば真空度は真空ポンプ３により任意に設定できるので、排ガスが常圧（１ａｔｍ）とすると多孔質物質の前後差圧を１ａｔｍにすることができ、圧力差０．２ａｔｍの場合に比べてＣＯ２透過量を５倍にすることができる。言い換えると、同じ能力を確保するためには、ＣＯ２ガス分離に必要な中空糸膜５の内面積が１／５で済み、それだけ設備容量を小さくする上でも有利である。 Next, the relationship between the pressure difference between the inner surface and the outer surface of the hollow fiber membrane 5 and the CO 2 permeation amount per unit area that passes through the hollow fiber membrane 5 will be described. It is known that the gas permeation amount per unit area in the membrane separation method is proportional to the pressure difference between the inner surface and the outer surface. For easy understanding, FIG. 5 shows the relationship between the pressure difference and the CO 2 permeation amount, where the CO 2 permeation amount is 1 when the pressure difference is 0.2 atm. According to the present embodiment, the degree of vacuum can be arbitrarily set by the vacuum pump 3, so if the exhaust gas is normal pressure (1 atm), the differential pressure across the porous material can be 1 atm, and the pressure difference is 0.2 atm. In comparison with this, the CO 2 permeation amount can be increased five times. In other words, in order to ensure the same capacity, the inner area of the hollow fiber membrane 5 required for CO 2 gas separation is 1/5, which is advantageous in reducing the equipment capacity.

次に、分離したガス中のＣＯ２濃度について説明する。排ガスは石炭火力発電所からの排ガスを想定し、ＣＯ２ガス以外の成分は窒素とし、ＣＯ２濃度は１０モル％と仮定する。このとき、分離したガス中のＣＯ２モル分率は以下の式で表される。 Next, the CO 2 concentration in the separated gas will be described. The exhaust gas is assumed to be exhaust gas from a coal-fired power plant, the components other than CO 2 gas are nitrogen, and the CO 2 concentration is assumed to be 10 mol%. At this time, the CO 2 mole fraction in the separated gas is represented by the following formula.

Ｙ＝［β−｛β２−４α（α−１）ＸＲｐ｝０．５］／｛２（α−１）Ｒｐ｝ ・・・（式４）
但し、β＝（α−１）（Ｘ＋Ｒｐ）+１、Ｒｐ＝Ｐｌ／Ｐｈ
ここで、Ｙは分離したガス中のＣＯ２モル分率、Ｘは排ガス中のＣＯ２モル分率、Ｐｈは中空糸膜５の内側の圧力、Ｐｌは中空糸膜５の外側の真空度、αはＣＯ２の窒素に対する分離係数である。この（式４）から分離係数５０と５００の２通りの場合について求めた分離ガス中のＣＯ２濃度を図６に示す。本実施例によれば真空度は真空ポンプ３により任意に設定できるので、排ガスが常圧（１ａｔｍ）とすると真空度により圧力比Ｒｐ＝Ｐｌ／Ｐｈを任意に小さくでき、中空糸膜５のＣＯ２分離の性能が劣っても分離ガス中のＣＯ２濃度を容易に高めることができる。分離したガスの使い道に応じてＣＯ２分離の性能の良い膜と悪い膜を使い分けることができる。例えば、回収したＣＯ２を単に大気から隔離するために地中や海洋に貯蔵したり、石油や天然ガスの増進回収のために油田やガス田に注入したりする場合には、分離したガス中のＣＯ２濃度は７０〜８０％程度あれば良いので例えば分離係数５０の膜で圧力比０．１以下にし、ＣＯ２を原料として工業利用する場合には、例えば分離係数５００の膜で圧力比０．１以下にするといった使い分けができる。 Y = [β- {β 2 -4α (α-1) XR p } 0.5 ] / {2 (α-1) R p } (Formula 4)
However, β = (α−1) (X + R p ) +1, R p = P 1 / P h
Here, Y is CO 2 molar fraction in the separated gas, X is CO 2 molar fraction in the exhaust gas, P h is the pressure inside the hollow fiber membranes 5, P l is outside the vacuum of the hollow fiber membranes 5 Degree, α is the separation factor of CO 2 for nitrogen. FIG. 6 shows the CO 2 concentration in the separation gas obtained from this (Equation 4) for two cases of separation factors 50 and 500. According to the present embodiment, the degree of vacuum can be arbitrarily set by the vacuum pump 3, so that when the exhaust gas is at normal pressure (1 atm), the pressure ratio R p = P l / P h can be arbitrarily reduced by the degree of vacuum, and the hollow fiber membrane Even if the performance of CO 2 separation of 5 is inferior, the CO 2 concentration in the separation gas can be easily increased. Depending on how the separated gas is used, it is possible to selectively use a membrane having good performance for CO 2 separation and a membrane having poor performance. For example, if the recovered CO 2 is stored in the ground or ocean simply to isolate it from the atmosphere, or injected into an oil or gas field for enhanced recovery of oil or natural gas, when the following pressure ratio 0.1, industrial use of CO 2 as a raw material in the CO 2 concentration may be at about 70-80% of for example film separation factor 50, such as pressure ratios in membrane separation factor 500 It can be used properly such as 0.1 or less.

本実施例によれば、低圧下でも蒸発し難い炭酸水素カリウム溶液、炭酸カリウム溶液、水酸化カリウム溶液等を吸収液に用いることで、中空糸膜５の周囲の真空度を高くする（より低圧にする）ことができ、多孔質物質の前後差圧を大きくすることができるので、中空糸膜５のＣＯ２ガスの透過速度を大きくすることができる。また、中空糸膜５を介して供給ガスからＣＯ２ガスが気体の状態で分離されるので、再生塔に送って大きなエネルギーを費やして吸収液からＣＯ２ガスを気液分離する必要がない。また、中空糸膜５の周囲の真空度を真空ポンプ３によって任意に設定することができる。よって、工業プロセスの排出ガスからＣＯ２ガスを気体の状態で効率的かつ安価に分離することができる。 According to the present embodiment, the degree of vacuum around the hollow fiber membrane 5 is increased by using a potassium hydrogen carbonate solution, a potassium carbonate solution, a potassium hydroxide solution, or the like, which is difficult to evaporate even under a low pressure, as the absorbent (lower pressure). Since the differential pressure across the porous material can be increased, the permeation rate of the CO 2 gas through the hollow fiber membrane 5 can be increased. Further, since the CO 2 gas is separated from the supply gas in a gas state via the hollow fiber membrane 5, it is not necessary to send the gas to the regeneration tower and spend a large amount of energy to separate the CO 2 gas from the absorbent. Further, the degree of vacuum around the hollow fiber membrane 5 can be arbitrarily set by the vacuum pump 3. Therefore, CO 2 gas can be efficiently and inexpensively separated from the exhaust gas of the industrial process in a gaseous state.

また、吸収液の表面張力により発現する、多孔質物質の細孔に吸収液が留まろうとする力が、減圧下における多孔質物質の前後差圧よりも大きく設定することにより吸収液の中空糸膜５からの滲出を抑えることができる。これにより、再生塔等の気液分離のための大規模な加熱設備が後段工程に不要となるため、設備コストを一層安価にすることができる。   In addition, the hollow fiber of the absorbing liquid is set by setting the force that the absorbing liquid stays in the pores of the porous material expressed by the surface tension of the absorbing liquid to be larger than the differential pressure across the porous material under reduced pressure. Exudation from the film 5 can be suppressed. This eliminates the need for a large-scale heating facility for gas-liquid separation, such as a regeneration tower, in the subsequent process, thereby further reducing the equipment cost.

さらには、吸収液のカリウム濃度を炭酸水素カリウム飽和溶液中のカリウム濃度以下とすることで、炭酸水素カリウムの析出による中空糸膜５の目詰まりを生じ難くし、安定したＣＯ２ガスの分離作用を得ることができる。 Furthermore, by making the potassium concentration of the absorbing solution equal to or less than the potassium concentration in the saturated potassium hydrogen carbonate solution, the hollow fiber membrane 5 is not easily clogged due to the precipitation of potassium hydrogen carbonate, and stable CO 2 gas separation action is achieved. Can be obtained.

図７は本発明の実施例２に係る炭酸ガス分離システムの概略図である。図１と同様の部分には図１と同符号を付して説明を省略する。   FIG. 7 is a schematic view of a carbon dioxide gas separation system according to Embodiment 2 of the present invention. Components similar to those in FIG. 1 are denoted by the same reference numerals as those in FIG.

図７に示した本実施例の炭酸ガス分離システムが実施例１のシステムと異なる点は、中空糸膜５を透過したＣＯ２ガスと減圧に伴って膜モジュール２内で蒸発した水分とを気液分離する気液分離槽６を膜モジュール２と真空ポンプ３の間に設けた点にあり、それ以外の構成は実施例１と同様である。 The carbon dioxide gas separation system of the present embodiment shown in FIG. 7 differs from the system of the first embodiment in that CO 2 gas that has permeated through the hollow fiber membrane 5 and moisture evaporated in the membrane module 2 due to decompression are removed. The gas-liquid separation tank 6 for liquid separation is provided between the membrane module 2 and the vacuum pump 3, and other configurations are the same as those in the first embodiment.

この実施例２は、中空糸膜５の周囲の真空度を高くして吸収液が中空糸膜５から滲み出したり、減圧環境で水が蒸発したりする場合に好適な例である。すなわち、膜モジュール２から真空ポンプ３によって吸い出される分離ガスから水分を除去するため、分離ガスを気液分離槽６に導き、気液分離槽６の一部を熱交換器８で冷却し、凝縮水７として分離ガス中の水分を凝縮させる。   This Example 2 is a suitable example when the degree of vacuum around the hollow fiber membrane 5 is increased and the absorbing liquid oozes out of the hollow fiber membrane 5 or when water evaporates in a reduced pressure environment. That is, in order to remove moisture from the separation gas sucked out from the membrane module 2 by the vacuum pump 3, the separation gas is guided to the gas-liquid separation tank 6, and a part of the gas-liquid separation tank 6 is cooled by the heat exchanger 8, The condensed water 7 is used to condense moisture in the separated gas.

本実施例２によれば、実施例１と同等の効果が得られる他、吸収液が多孔質物質から滲み出したり、減圧環境で水が蒸発したりする場合でも、真空度を真空ポンプ３により任意に設定できるので安価にＣＯ２ガスを分離できる。 According to the second embodiment, the same effect as in the first embodiment can be obtained, and even when the absorbing liquid oozes from the porous material or the water evaporates in a reduced pressure environment, the degree of vacuum is adjusted by the vacuum pump 3. Since it can be set arbitrarily, CO 2 gas can be separated at low cost.

図８は本発明の実施例３に係る炭酸ガス分離システムの概略図である。図７と同様の部分には図７と同符号を付して説明を省略する。   FIG. 8 is a schematic view of a carbon dioxide gas separation system according to Embodiment 3 of the present invention. The same parts as those in FIG. 7 are denoted by the same reference numerals as those in FIG.

実施例３の炭酸ガス分離システムが実施例２の炭酸ガス分離システムと異なる点は、気液分離槽６で凝縮した凝縮水７をさらに気液分離し、ＣＯ２ガスを更に回収するとともに分離した液体を膜モジュール２に循環供給する点にあり、それ以外の構成は実施例２と同様である。 The carbon dioxide gas separation system of Example 3 is different from the carbon dioxide gas separation system of Example 2 in that the condensed water 7 condensed in the gas-liquid separation tank 6 is further gas-liquid separated, and the CO 2 gas is further recovered and separated. The liquid is circulated and supplied to the membrane module 2, and the other configuration is the same as that of the second embodiment.

この実施例３は、中空糸膜５の周囲の真空度を高くして吸収液が多孔質物質から滲み出したり減圧環境で水が蒸発したりする場合に好適な例である。排ガスに水分が多少なりとも含まれている場合が多いので、吸収液から失われる水分が排ガスから補充される水分より少ない場合には、中空糸膜５の湿潤状態は維持される。しかし、吸収液から失われる水分が排ガスからの補充量より多い場合には、本実施例のように中空糸膜５の湿潤を維持するために分離ガスから回収した水分を膜モジュール２へ供給することで中空糸膜５の湿潤状態を維持することができる。   This Example 3 is a suitable example when the degree of vacuum around the hollow fiber membrane 5 is increased and the absorbing liquid oozes from the porous material or water evaporates in a reduced pressure environment. Since there are many cases where moisture is contained in the exhaust gas in some cases, the wet state of the hollow fiber membrane 5 is maintained when the amount of water lost from the absorbing liquid is less than the moisture replenished from the exhaust gas. However, when the amount of water lost from the absorption liquid is larger than the replenishment amount from the exhaust gas, the water recovered from the separation gas is supplied to the membrane module 2 in order to maintain the wetness of the hollow fiber membrane 5 as in this embodiment. Thus, the wet state of the hollow fiber membrane 5 can be maintained.

本実施例の炭酸ガス分離システムの具体的な一構成例を説明する。図８に例示した炭酸ガス分離システムは、実施例２の炭酸ガス分離システムの持つ構成要素に加え、気液分離槽６で凝縮した凝縮水７をさらに気液分離する第二の気液分離槽１０と、気液分離槽６から第二の気液分離槽１０に凝縮水７を搬送する液体ポンプ（第一の液体搬送手段）９と、第二の気液分離槽１０に導かれた凝縮水７を供給ガスとの熱交換によって加熱する熱交換器１１と、第二の気液分離槽１０でガスと分離された液体を膜モジュール２に供給する液体ポンプ（第二の液体搬送手段）１２と、第二の気液分離槽１０で分離されたＣＯ２ガスを含むガスを吸引し回収タンク（図示せず）に送り込む真空ポンプ３’とを備えている。 A specific configuration example of the carbon dioxide gas separation system of the present embodiment will be described. The carbon dioxide separation system illustrated in FIG. 8 is a second gas-liquid separation tank that further separates condensed water 7 condensed in the gas-liquid separation tank 6 in addition to the components of the carbon dioxide separation system of the second embodiment. 10, a liquid pump (first liquid transport means) 9 for transporting the condensed water 7 from the gas-liquid separation tank 6 to the second gas-liquid separation tank 10, and the condensation led to the second gas-liquid separation tank 10. A heat exchanger 11 that heats the water 7 by heat exchange with the supply gas, and a liquid pump that supplies the liquid separated from the gas in the second gas-liquid separation tank 10 to the membrane module 2 (second liquid conveying means) 12 and a vacuum pump 3 ′ that sucks the gas containing the CO 2 gas separated in the second gas-liquid separation tank 10 and sends it to a recovery tank (not shown).

本実施例では、気液分離槽６の凝縮水７が液体ポンプ９によって第二の気液分離槽１０へ移送される。第二の気液分離槽１０では、凝縮水７’を第二の熱交換器１１によって加熱し、凝縮水７’からのＣＯ２ガスの放出を促進する。ここで凝縮水７’からのＣＯ２ガスを含む分離ガスは真空ポンプ３’によって回収タンク（図示せず）に回収される。このとき、図８に示したように第二の気液分離槽１０の減圧側の配管（第二の気液分離槽１０と真空ポンプ３’とを繋ぐ配管）に圧力計２６、ＣＯ２濃度計２７、流量計２８等を取り付け、分離したＣＯ２ガスを含むガスの真空度、ＣＯ２の量、ＣＯ２濃度をモニターし、これらの値が予め定めた設定値に近付くように、送風機１や真空ポンプ３，３’の動作を制御する構成とすることもできる。一方、加熱された凝縮水７’は液体ポンプ１２により移送され、排ガスと混合されて膜モジュール２に供給される。 In the present embodiment, the condensed water 7 in the gas-liquid separation tank 6 is transferred to the second gas-liquid separation tank 10 by the liquid pump 9. In the second gas-liquid separation tank 10, the condensed water 7 'is heated by the second heat exchanger 11, condensed water 7' to promote the release of CO 2 gas from. Here, the separation gas containing CO 2 gas from the condensed water 7 ′ is recovered in a recovery tank (not shown) by the vacuum pump 3 ′. At this time, as shown in FIG. 8, the pressure gauge 26 and the CO 2 concentration are connected to the decompression side pipe (the pipe connecting the second gas-liquid separation tank 10 and the vacuum pump 3 ′) of the second gas-liquid separation tank 10. meter 27, fitted with a flow meter 28 or the like, the degree of vacuum gas containing the separated CO 2 gas, the amount of CO 2, to monitor the CO 2 concentration, as close to the set value of these values is predetermined, the blower 1 Alternatively, the operation of the vacuum pumps 3 and 3 ′ may be controlled. On the other hand, the heated condensed water 7 ′ is transferred by the liquid pump 12, mixed with the exhaust gas, and supplied to the membrane module 2.

以上のように、本実施例によれば、実施例１，２と同等の効果が得られることに加え、吸収液が中空糸膜５から滲み出したり減圧環境で水が蒸発したりする場合に、吸収液から失われた水分を回収して膜モジュール２に循環させ、中空糸膜５の湿潤状態を維持することができる。また、例えば排ガスが石炭火力発電所からの排ガスであれば常温より高温なので、本実施例のように第二の熱交換器１１を用いて凝縮水７’を加熱することができ、例えば実施例１，２等に対するエネルギー効率の低下を抑制することができる。   As described above, according to this example, in addition to obtaining the same effects as those of Examples 1 and 2, when the absorbing liquid oozes from the hollow fiber membrane 5 or water evaporates in a reduced pressure environment. The water lost from the absorbent can be collected and circulated through the membrane module 2 to maintain the wet state of the hollow fiber membrane 5. Further, for example, if the exhaust gas is an exhaust gas from a coal-fired power plant, the temperature is higher than normal temperature, so that the condensed water 7 ′ can be heated using the second heat exchanger 11 as in this embodiment. A decrease in energy efficiency with respect to 1, 2, etc. can be suppressed.

本発明の実施例１に係る炭酸ガス分離システムの概略図である。1 is a schematic view of a carbon dioxide gas separation system according to Embodiment 1 of the present invention. 本発明の実施例１に係る炭酸ガス分離システムに用いられる膜モジュールの内部構成を模式的に示した図である。It is the figure which showed typically the internal structure of the membrane module used for the carbon dioxide separation system which concerns on Example 1 of this invention. 本発明の実施例１に係る炭酸ガス分離システムに用いられる中空糸膜の一部分を切断して表した模式図である。It is the schematic diagram which cut and represented a part of hollow fiber membrane used for the carbon dioxide separation system concerning Example 1 of the present invention. 水酸化カリウム、炭酸カリウム及び炭酸水素カリウムについて、それぞれの飽和溶液中のカリウムイオン濃度を示した図である。It is the figure which showed the potassium ion concentration in each saturated solution about potassium hydroxide, potassium carbonate, and potassium hydrogencarbonate. 多孔質物質の前後差圧と炭酸ガス透過量の関係を示す図である。It is a figure which shows the relationship between the differential pressure | voltage of a porous substance, and a carbon dioxide gas permeation | transmission amount. 多孔質物質の両側の圧力比と分離後の炭酸ガス濃度の関係を示す図である。It is a figure which shows the relationship between the pressure ratio of the both sides of a porous material, and the carbon dioxide gas density | concentration after isolation | separation. 本発明の実施例２に係る炭酸ガス分離システムの概略図である。It is the schematic of the carbon dioxide separation system concerning Example 2 of the present invention. 本発明の実施例３に係る炭酸ガス分離システムの概略図である。It is the schematic of the carbon dioxide separation system concerning Example 3 of the present invention.

符号の説明Explanation of symbols

１ 送風機
２ 膜モジュール
３，３’ 真空ポンプ
４ 排気塔
５ 中空糸膜
６ 気液分離槽
７，７’ 凝縮水
８ 熱交換器
９ 液体ポンプ
１０ 第二の気液分離槽
１１ 熱交換器
１２ 液体ポンプ DESCRIPTION OF SYMBOLS 1 Blower 2 Membrane module 3, 3 'Vacuum pump 4 Exhaust tower 5 Hollow fiber membrane 6 Gas-liquid separation tank 7, 7' Condensed water 8 Heat exchanger 9 Liquid pump 10 Second gas-liquid separation tank 11 Heat exchanger 12 Liquid pump

Claims (8)

炭酸水素塩又は炭酸塩を構成する金属イオンを含有した吸収液を多孔質物質に含浸させ、
前記多孔質物質の一方側に炭酸ガスを含む供給ガスを供給して前記多孔質物質の他方側を減圧し、
前記供給ガス中の炭酸ガスを前記多孔質物質の細孔に取り込んで前記多孔質物質の他方側の空間に放出させる
ことを特徴とする炭酸ガス分離方法。 Impregnating a porous material with an absorption liquid containing hydrogen carbonate or metal ions constituting the carbonate,
Supplying a supply gas containing carbon dioxide gas to one side of the porous material to depressurize the other side of the porous material;
Carbon dioxide gas in the supply gas is taken into the pores of the porous material and released into the space on the other side of the porous material. 請求項１の炭酸ガス分離方法において、前記吸収液が無機アルカリ溶液であることを特徴とする炭酸ガス分離方法。   2. The carbon dioxide separation method according to claim 1, wherein the absorbing liquid is an inorganic alkali solution. 請求項２の炭酸ガス分離方法において、前記吸収液は、前記炭酸水素塩又は炭酸塩として、水酸化カリウム、炭酸水素カリウム、炭酸カリウムの少なくとも１種を含むことを特徴とする炭酸ガス分離方法。   3. The carbon dioxide separation method according to claim 2, wherein the absorption liquid contains at least one of potassium hydroxide, potassium bicarbonate, and potassium carbonate as the bicarbonate or carbonate. 請求３の炭酸ガス分離方法において、前記吸収液中のカリウム濃度が、炭酸水素カリウム飽和溶液中のカリウム濃度以下であることを特徴とする炭酸ガス分離方法。   4. The carbon dioxide separation method according to claim 3, wherein the potassium concentration in the absorption liquid is equal to or less than the potassium concentration in the saturated potassium hydrogen carbonate solution. 請求項１〜４のいずれかに記載された吸収液を孔に含浸させた多孔質物質と、
前記多孔質物質の一方側に前記供給ガスを供給するガス供給手段と、
前記多孔質物質の他方側を減圧する減圧手段と
を備えたことを特徴とする炭酸ガス分離システム。 A porous material in which pores are impregnated with the absorption liquid according to claim 1;
Gas supply means for supplying the supply gas to one side of the porous material;
A carbon dioxide gas separation system, comprising: a decompression unit that decompresses the other side of the porous material. 請求項５の炭酸ガス分離システムにおいて、前記多孔質物質を透過した炭酸ガスと減圧に伴って蒸発した水分とを気液分離する気液分離手段を有することを特徴とする炭酸ガス分離システム。   6. The carbon dioxide separation system according to claim 5, further comprising gas-liquid separation means for gas-liquid separation of the carbon dioxide permeated through the porous material and the water evaporated due to the reduced pressure. 請求項６の炭酸ガス分離システムにおいて、
前記気液分離手段で分離された液体を搬送する第一の液体搬送手段と、
前記第一の液体搬送手段により搬送された液体をさらに気液分離する第二の気液分離手段と、
前記第二の気液分離手段で分離された液体を前記多孔質物質に供給する第二の液体搬送手段と
を備えたことを特徴とする炭酸ガス分離システム。 The carbon dioxide gas separation system according to claim 6,
First liquid transporting means for transporting the liquid separated by the gas-liquid separating means;
Second gas-liquid separation means for further gas-liquid separation of the liquid conveyed by the first liquid conveyance means;
A carbon dioxide gas separation system comprising: a second liquid transport unit that supplies the liquid separated by the second gas-liquid separation unit to the porous material. 請求項７の炭酸ガス分離システムにおいて、第二の気液分離手段に導かれた液体を前記供給ガスとの熱交換によって加熱する熱交換器を有することを特徴とする炭酸ガス分離システム。   8. The carbon dioxide separation system according to claim 7, further comprising a heat exchanger that heats the liquid guided to the second gas-liquid separation means by heat exchange with the supply gas.
JP2008155305A 2008-06-13 2008-06-13 Separation method and system of carbon dioxide gas Pending JP2009297655A (en)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2014133219A (en) * 2013-01-11 2014-07-24 Ngk Insulators Ltd Gas removal device and gas removal method using the same
JP2017115891A (en) * 2011-01-20 2017-06-29 サウジ アラビアン オイル カンパニー Film separation process utilizing waste heat for on-vehicle recovery and storage of co2 from exhaust gas of vehicle internal combustion engine
JP2021146318A (en) * 2020-03-23 2021-09-27 トヨタ自動車株式会社 CO2 separation system

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2017115891A (en) * 2011-01-20 2017-06-29 サウジ アラビアン オイル カンパニー Film separation process utilizing waste heat for on-vehicle recovery and storage of co2 from exhaust gas of vehicle internal combustion engine
JP2014133219A (en) * 2013-01-11 2014-07-24 Ngk Insulators Ltd Gas removal device and gas removal method using the same
JP2021146318A (en) * 2020-03-23 2021-09-27 トヨタ自動車株式会社 CO2 separation system
JP7160062B2 (en) 2020-03-23 2022-10-25 トヨタ自動車株式会社 CO2 separation system

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