JP4382770B2 - Carbon dioxide purification method - Google Patents
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- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 title claims description 90
- 229910002092 carbon dioxide Inorganic materials 0.000 title claims description 45
- 239000001569 carbon dioxide Substances 0.000 title claims description 45
- 238000000034 method Methods 0.000 title claims description 28
- 238000000746 purification Methods 0.000 title description 10
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 claims description 81
- 238000006243 chemical reaction Methods 0.000 claims description 57
- 239000007789 gas Substances 0.000 claims description 53
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 52
- 239000001301 oxygen Substances 0.000 claims description 52
- 229910052760 oxygen Inorganic materials 0.000 claims description 52
- 229910052739 hydrogen Inorganic materials 0.000 claims description 37
- 239000001257 hydrogen Substances 0.000 claims description 37
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 31
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims description 28
- 229910002091 carbon monoxide Inorganic materials 0.000 claims description 26
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 16
- 238000007254 oxidation reaction Methods 0.000 claims description 11
- 230000003647 oxidation Effects 0.000 claims description 3
- 238000006722 reduction reaction Methods 0.000 description 31
- 239000003054 catalyst Substances 0.000 description 15
- 239000002994 raw material Substances 0.000 description 15
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 10
- 239000012535 impurity Substances 0.000 description 8
- 150000002431 hydrogen Chemical class 0.000 description 6
- 238000002485 combustion reaction Methods 0.000 description 5
- 229910052757 nitrogen Inorganic materials 0.000 description 5
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 4
- 238000004821 distillation Methods 0.000 description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 4
- 239000002574 poison Substances 0.000 description 4
- 231100000614 poison Toxicity 0.000 description 4
- 238000001179 sorption measurement Methods 0.000 description 4
- 238000005260 corrosion Methods 0.000 description 3
- 230000007797 corrosion Effects 0.000 description 3
- 230000001877 deodorizing effect Effects 0.000 description 3
- 239000003949 liquefied natural gas Substances 0.000 description 3
- 239000003209 petroleum derivative Substances 0.000 description 3
- 238000010926 purge Methods 0.000 description 3
- 150000003464 sulfur compounds Chemical class 0.000 description 3
- MGWGWNFMUOTEHG-UHFFFAOYSA-N 4-(3,5-dimethylphenyl)-1,3-thiazol-2-amine Chemical compound CC1=CC(C)=CC(C=2N=C(N)SC=2)=C1 MGWGWNFMUOTEHG-UHFFFAOYSA-N 0.000 description 2
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 2
- 229910021529 ammonia Inorganic materials 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 238000005984 hydrogenation reaction Methods 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- JCXJVPUVTGWSNB-UHFFFAOYSA-N nitrogen dioxide Inorganic materials O=[N]=O JCXJVPUVTGWSNB-UHFFFAOYSA-N 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 1
- 229910021536 Zeolite Inorganic materials 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 229910002090 carbon oxide Inorganic materials 0.000 description 1
- 238000004517 catalytic hydrocracking Methods 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 239000000567 combustion gas Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000007791 dehumidification Methods 0.000 description 1
- 238000006477 desulfuration reaction Methods 0.000 description 1
- 230000023556 desulfurization Effects 0.000 description 1
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- TXKMVPPZCYKFAC-UHFFFAOYSA-N disulfur monoxide Inorganic materials O=S=S TXKMVPPZCYKFAC-UHFFFAOYSA-N 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000003546 flue gas Substances 0.000 description 1
- 239000002778 food additive Substances 0.000 description 1
- 235000013373 food additive Nutrition 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 238000006479 redox reaction Methods 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical compound S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 description 1
- 229910052815 sulfur oxide Inorganic materials 0.000 description 1
- 230000009897 systematic effect Effects 0.000 description 1
- 239000010457 zeolite Substances 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/50—Carbon dioxide
-
- 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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
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- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Inorganic Chemistry (AREA)
- Carbon And Carbon Compounds (AREA)
- Separation By Low-Temperature Treatments (AREA)
Description
本発明は、二酸化炭素の精製方法に関し、詳しくは、石油、液化天然ガス(LNG)等の燃焼排ガスを回収し、その主成分である二酸化炭素中に微量に含まれている不純物を除去して二酸化炭素を精製する方法、特に、二酸化炭素を精製する工程中の予備精製工程に関する。 The present invention relates to a method for purifying carbon dioxide. Specifically, it recovers combustion exhaust gas such as petroleum and liquefied natural gas (LNG), and removes impurities contained in trace amounts in carbon dioxide, which is the main component. The present invention relates to a method for purifying carbon dioxide, and more particularly to a preliminary purification step in the step for purifying carbon dioxide.
二酸化炭素を得るための方法として、石油、天然ガス等の燃焼排ガスを回収し、その排ガスから各種不純物を除去して二酸化炭素を精製する方法が知られている。回収した燃焼排ガスに含まれる不純物は、燃料の種類、燃焼条件等によって大きく異なるが、主に、窒素、酸素、一酸化炭素、窒素酸化物(NO、NO2等)、硫黄化合物(SOx、H2S等)である。製品二酸化炭素とするためには、これらの不純物を除去する必要があり、特に、食品添加用とするためには、許容される不純物の濃度は厳しく制限されている。 As a method for obtaining carbon dioxide, a method is known in which combustion exhaust gas such as petroleum and natural gas is recovered, and various impurities are removed from the exhaust gas to purify carbon dioxide. Impurities contained in the recovered flue gas vary greatly depending on the type of fuel, combustion conditions, etc., but are mainly nitrogen, oxygen, carbon monoxide, nitrogen oxides (NO, NO 2 etc.), sulfur compounds (SOx, H 2 S etc.). In order to obtain product carbon dioxide, it is necessary to remove these impurities. In particular, for use as a food additive, the allowable impurity concentration is severely limited.
二酸化炭素の精製は、吸着、吸収、還元反応や酸化反応による分解といった各工程の組合せで予備精製を行った後、液化工程、蒸留工程を行うのが一般的である。予備精製における各工程の組合せは種々あり、原料となる燃焼排ガスの温度、圧力等の条件や、含まれる不純物の組成に応じて最適な組合せが選択される。 In general, carbon dioxide is purified by preliminarily purifying it by a combination of steps such as adsorption, absorption, reduction reaction and decomposition by oxidation reaction, followed by liquefaction step and distillation step. There are various combinations of the steps in the pre-purification, and an optimal combination is selected according to conditions such as temperature and pressure of the combustion exhaust gas as a raw material and the composition of impurities contained therein.
前記各種不純物のうち、露点が二酸化炭素と大きく異なる成分は、液化工程や蒸留工程によって比較的容易に分離除去することが可能である。しかし、二酸化窒素(NO2)は、二酸化炭素を液化する際に液中に混入する性質があり、蒸留工程の前に完全に除去する必要がある。具体的には、吸着、あるいは、次式のような水素添加による還元反応によってNO2を除去するのが一般的である。 Among the various impurities, a component having a dew point greatly different from that of carbon dioxide can be separated and removed relatively easily by a liquefaction process or a distillation process. However, nitrogen dioxide (NO 2 ) has the property of being mixed into the liquid when carbon dioxide is liquefied, and needs to be completely removed before the distillation step. Specifically, NO 2 is generally removed by adsorption or a reduction reaction by hydrogenation as shown in the following formula.
2NO2 + 4H2 → N2 + 4H2O 2NO 2 + 4H 2 → N 2 + 4H 2 O
また、一酸化炭素は、液化工程で分離可能であるが、上述の還元反応において触媒毒となるため、例えば、次式で示す酸化反応によって予め除去することが望ましい。 Although carbon monoxide can be separated in the liquefaction step, it becomes a catalyst poison in the above-described reduction reaction. Therefore, it is desirable to remove in advance by an oxidation reaction represented by the following formula, for example.
2CO + O2 → 2CO2 2CO + O 2 → 2CO 2
例えば、転炉ガスボイラーからの燃焼ガスを原料とする二酸化炭素の精製方法として、圧力変動吸着法で二酸化炭素を濃縮し、所定圧力まで昇圧して脱硫塔で硫黄化合物を除去した後、温度60〜100℃、圧力約300〜500kPa(ゲージ圧)の条件で水素化分解塔に導入して酸素及び窒素酸化物を窒素と水とに分解し、その後、更に昇圧してから脱湿器で水分を除去し、脱臭塔で残存する微量のSO2、H2S、NO2等を除去し、最後に液化蒸留装置で高純度の二酸化炭素を得る方法が提案されている(例えば、特許文献1参照。)。 For example, as a method for purifying carbon dioxide using combustion gas from a converter gas boiler as a raw material, the carbon dioxide is concentrated by a pressure fluctuation adsorption method, the pressure is increased to a predetermined pressure, and a sulfur compound is removed by a desulfurization tower. It is introduced into a hydrocracking tower under conditions of -100 ° C. and a pressure of about 300-500 kPa (gauge pressure) to decompose oxygen and nitrogen oxides into nitrogen and water. A method is proposed in which trace amounts of SO 2 , H 2 S, NO 2 and the like remaining in a deodorizing tower are removed, and finally high-purity carbon dioxide is obtained with a liquefied distillation apparatus (for example, Patent Document 1). reference.).
また、二酸化炭素中の不純物除去に水素添加による還元反応を利用する場合、含まれる一酸化炭素による触媒毒の影響を回避するためには、一酸化炭素のみを予め除去するか、あるいは、過剰の酸素によって同時に酸化除去する方法がある。例えば、一酸化炭素による触媒毒の影響を回避するため、初めに酸素存在下で一酸化炭素を酸化除去した後、水素存在下で窒素酸化物を還元除去する方法が提案されている(例えば、特許文献2参照。)。このときの一酸化炭素の酸化反応条件は、触媒に白金あるいはパラジウムを用いて反応温度を100〜200℃としており、その後の水素存在下での窒素酸化物の還元反応は40〜100℃としている。 In addition, when a reduction reaction by hydrogenation is used for removing impurities in carbon dioxide, in order to avoid the influence of the catalyst poison due to the contained carbon monoxide, only carbon monoxide is removed in advance or an excessive amount of carbon monoxide is removed. There is a method of oxidizing and removing simultaneously with oxygen. For example, in order to avoid the influence of the catalyst poison due to carbon monoxide, a method of reducing and removing nitrogen oxide in the presence of hydrogen after first oxidizing and removing carbon monoxide in the presence of oxygen has been proposed (for example, (See Patent Document 2). At this time, the oxidation reaction conditions of carbon monoxide are platinum or palladium as a catalyst, the reaction temperature is 100 to 200 ° C., and the subsequent reduction reaction of nitrogen oxides in the presence of hydrogen is 40 to 100 ° C. .
一般に、酸素と還元ガスとの反応速度は、他の反応速度より大きいことが知られており、酸素が還元されてから、窒素酸化物が還元されると考えられている(例えば、特許文献3参照。)。したがって、窒素酸化物と一酸化炭素とを同時に除去する方法において、従来は、窒素酸化物還元用の水素の他に、一酸化炭素酸化用として過剰に添加した酸素を全量還元するための水素を供給する必要があった。例えば、原料二酸化炭素に酸素が200ppm、一酸化窒素(NO)が100ppm含まれる場合、温度100〜120℃において同時に還元すると、それぞれの還元のために、400ppm、100ppmの水素がそれぞれ消費される(例えば、特許文献4参照。)。すなわち、原料二酸化炭素の組成によっては、除去の対象である窒素酸化物の還元に必要な水素よりも、過剰に存在する酸素の還元に必要な水素の方が多くなる場合もある。
一酸化炭素をあらかじめ除去する方法は、酸化反応、還元反応のそれぞれの最適条件を選ぶことが可能だが、反応塔が増えることは、イニシャルコスト、設置面積が増えるだけでなく、メンテナンスも増加することになる。これを考慮すると、構成機器は少ない方がよく、窒素酸化物と一酸化炭素とを同時に除去できる方法が望ましい。 In the method of removing carbon monoxide in advance, it is possible to select the optimum conditions for each of the oxidation reaction and reduction reaction. become. Considering this, it is better that the number of components is small, and a method capable of simultaneously removing nitrogen oxides and carbon monoxide is desirable.
しかし、同時に除去する方法では、上述のように窒素酸化物の還元に必要な水素よりも、過剰に存在する酸素の還元に必要な水素の方が多くなる場合もあり、ランニングコストが上昇するといった問題があった。 However, in the method of removing at the same time, as described above, the hydrogen necessary for the reduction of excess oxygen may be larger than the hydrogen necessary for the reduction of nitrogen oxides, which increases the running cost. There was a problem.
ここで、窒素酸化物の還元反応は高温で行われるため、熱効率を考えると、反応塔の前後に熱交換器を設置し、エネルギー回収を行うのが好ましい。しかし、窒素酸化物、酸素の還元反応では、水蒸気が生成されるため、過剰な酸素を還元した結果、大量に水蒸気が発生すると、熱交換器内で凝縮し、腐食しやすくなるという問題が考えられる。とりわけ、アルミニウム製のプレートフィン熱交換器を用いた場合、腐食によって流路に孔が開いたりするなどの問題が予想される。 Here, since the reduction reaction of nitrogen oxides is performed at a high temperature, it is preferable to perform energy recovery by installing heat exchangers before and after the reaction tower in view of thermal efficiency. However, in the reduction reaction of nitrogen oxides and oxygen, water vapor is generated. As a result of excessive oxygen reduction, if a large amount of water vapor is generated, it may condense in the heat exchanger and become susceptible to corrosion. It is done. In particular, when an aluminum plate fin heat exchanger is used, problems such as a hole being formed in the flow path due to corrosion are expected.
そこで本発明は、反応塔において一酸化炭素の酸化反応と窒素酸化物の還元反応とを同時に行った場合でも、過剰酸素の還元による水蒸気の発生を極力抑えるとともに、効率よく、二酸化炭素の予備精製を行うことができる二酸化炭素の精製方法を提供することを目的としている。 Therefore, the present invention suppresses the generation of water vapor due to the reduction of excess oxygen as much as possible even when the oxidation reaction of carbon monoxide and the reduction reaction of nitrogen oxide are simultaneously performed in the reaction tower, and efficiently preliminarily purifies carbon dioxide. It aims at providing the purification method of the carbon dioxide which can be performed.
上記目的を達成するため、本発明の二酸化炭素の精製方法は、二酸化炭素を主成分とする混合ガスを反応塔に導入し、該混合ガス中の窒素酸化物を水素との還元反応で、一酸化炭素を酸素との酸化反応で、それぞれ同時に除去する二酸化炭素の精製方法であって、前記反応塔内での反応条件を、反応塔出口から導出される反応塔出口ガス中に未反応の酸素が残存する条件に設定することを特徴としている。 In order to achieve the above object, the carbon dioxide purification method of the present invention introduces a mixed gas containing carbon dioxide as a main component into a reaction tower, and the nitrogen oxide in the mixed gas is reduced by a reduction reaction with hydrogen. A method for purifying carbon dioxide in which carbon oxides are simultaneously removed by oxidation reaction with oxygen, wherein the reaction conditions in the reaction column are determined as unreacted oxygen in the reaction column outlet gas derived from the reaction column outlet. It is characterized in that it is set to a condition that remains.
さらに、本発明の二酸化炭素の精製方法は、前記反応塔での反応温度を110℃以下に設定すること、前記反応塔入口における混合ガス中の水素量は、該混合ガス中の酸素を還元するのに必要な当量より少ない量に設定すること、また、前記反応塔入口における混合ガス中の水素量は、該反応塔に導入する前記混合ガスと前記反応塔出口ガスとを熱交換させて前記混合ガスを昇温するとともに前記反応塔出口ガスを降温する熱交換器から導出した降温後の反応塔出口ガス中の水蒸気圧力が飽和水蒸気圧力未満となる量に設定することを特徴とし、前記酸素が系外から前記混合ガスに添加されることを特徴としている。 Furthermore, in the method for purifying carbon dioxide of the present invention, the reaction temperature in the reaction tower is set to 110 ° C. or lower, and the amount of hydrogen in the mixed gas at the inlet of the reaction tower reduces oxygen in the mixed gas. The amount of hydrogen in the mixed gas at the inlet of the reaction tower is obtained by exchanging heat between the mixed gas introduced into the reaction tower and the outlet gas of the reaction tower. The oxygen pressure is set to an amount such that the water vapor pressure in the reaction tower outlet gas after the temperature lowering derived from the heat exchanger for raising the temperature of the mixed gas and lowering the reaction tower outlet gas is less than the saturated water vapor pressure. Is added to the mixed gas from outside the system.
本発明の二酸化炭素の精製方法では、原料二酸化炭素中に含まれる窒素酸化物を還元反応によって除去する必要があり、対象となる二酸化炭素中に一酸化炭素が存在し、その触媒毒としての影響を最小限とするために過剰の酸素が必要な場合であっても、一部の酸素を未反応のまま反応塔から排出させることで、二酸化炭素の精製に必要な水素供給量を少なくできる。 In the carbon dioxide purification method of the present invention, it is necessary to remove nitrogen oxides contained in the raw carbon dioxide by a reduction reaction, and carbon monoxide is present in the target carbon dioxide, and its influence as a catalyst poison. Even when excessive oxygen is required to minimize the amount of hydrogen, the amount of hydrogen supply required for the purification of carbon dioxide can be reduced by discharging some oxygen from the reaction tower while remaining unreacted.
これは、酸素の還元反応に対して当量より少ない水素を供給すること、及び、反応温度を一般的な触媒反応としては低い110℃以下とすることで、酸素の還元が抑制されることによる効果である。しかも、一つの反応塔で一酸化炭素、窒素酸化物の同時除去が可能であり、特に原料二酸化炭素中に含まれる一酸化炭素及び酸素の濃度が比較的高い場合に本発明の効果が顕著となる。 This is because the reduction of oxygen is suppressed by supplying less than an equivalent amount of hydrogen to the reduction reaction of oxygen, and by setting the reaction temperature to 110 ° C. or lower, which is low as a general catalytic reaction. It is. In addition, carbon monoxide and nitrogen oxide can be removed simultaneously in one reaction tower, and the effect of the present invention is particularly remarkable when the concentration of carbon monoxide and oxygen contained in the raw carbon dioxide is relatively high. Become.
さらに、還元される酸素量が少ないことにより、生成される水蒸気量が少なく、後工程における装置腐食の懸念が少なくなり、水分吸着器に必要な吸着容量の低減が可能となる。 Furthermore, since the amount of oxygen to be reduced is small, the amount of water vapor produced is small, and there is less concern about device corrosion in the subsequent process, and the adsorption capacity required for the moisture adsorber can be reduced.
図1は本発明の二酸化炭素の精製方法を適用した精製装置の一例を示す系統図である。 FIG. 1 is a system diagram showing an example of a purification apparatus to which the carbon dioxide purification method of the present invention is applied.
まず、石油、LNGを原料とした発電設備等からの高温の燃焼排ガスは、冷却後、除塵等の処理が施され、原料ガスとして圧縮機11で所定の圧力まで昇圧される。この原料ガスの主成分は二酸化炭素であり、微量の一酸化炭素、一酸化窒素、二酸化窒素、酸素、水素、硫化水素、硫黄酸化物、水蒸気等を含んでいる。 First, a high-temperature combustion exhaust gas from a power generation facility or the like that uses petroleum or LNG as a raw material is cooled and then subjected to processing such as dust removal, and is pressurized to a predetermined pressure by the compressor 11 as a raw material gas. The main component of the raw material gas is carbon dioxide, which contains a small amount of carbon monoxide, nitrogen monoxide, nitrogen dioxide, oxygen, hydrogen, hydrogen sulfide, sulfur oxide, water vapor and the like.
なお、原料ガスに酸素、水素が含まれない場合には、系外から配管50、51を通して酸素、水素を適宜添加すればよい。酸素を供給する場合、代わりに空気を供給してもよい。また、配管50から水素を添加する場合は、その濃度を、混在する酸素を全て還元するのに必要な当量の水素濃度よりも少なくする。
In the case where oxygen and hydrogen are not included in the source gas, oxygen and hydrogen may be appropriately added from outside the system through the
昇圧された原料ガスは、脱臭塔12、乾燥塔13に導入され、原料ガスに含まれる硫黄化合物、水蒸気等が除去される。その後、原料ガスは、熱交換器14、加熱器15で所定の温度まで昇温される。昇温された排ガスは反応塔16に導入される。
The pressurized source gas is introduced into the deodorizing
反応塔16は、一酸化炭素と窒素酸化物とを同時に除去する触媒層を含んでいる。反応塔16における触媒層は、図2(A)に示すように、触媒層A,Bに異なる触媒を充填したものであってもよく、図2(B)に示すように、同じ触媒層Aが二段に充填されていてもよい。さらに、図2(C)に示すように、反応塔を二塔16a、16bに分割することも可能である。異なる触媒が充填されている場合でも、一つの触媒層において、二酸化炭素中の一酸化炭素と窒素酸化物との同時除去を行うことができるようにしている。
The
反応塔16では、原料ガス中の窒素酸化物を水素との還元反応で、一酸化炭素を酸素との酸化反応で、それぞれ同時に除去するにあたり、反応塔16内での反応条件を、反応塔出口から導出される反応塔出口ガス中に未反応の酸素が残存するように設定され、内部に充填した触媒により一酸化炭素、一酸化窒素がそれぞれ酸化反応、還元反応により除去される。このとき、1つの触媒層で酸化反応と還元反応とを同時に行い、反応温度は110℃以下、好ましくは90〜100℃とするのがよい。
In the
混在する酸素を全て還元するのに必要な当量の水素濃度よりも少なくすることと、反応温度を110℃以下とすることにより、酸素の還元反応(O2+2H2→2H2O)を抑制し、酸素の還元に消費される水素を低減することが可能となる。酸素の還元反応が抑制されることで、反応しなかった酸素は、反応塔16から導出される。
The oxygen reduction reaction (O 2 + 2H 2 → 2H 2 O) is suppressed by reducing the hydrogen concentration equivalent to that necessary for reducing all the mixed oxygen and by setting the reaction temperature to 110 ° C. or lower. It is possible to reduce hydrogen consumed for oxygen reduction. Oxygen that has not reacted is led out from the
窒素、酸素、水素、水蒸気等を含む原料ガス(反応塔出口ガス)は、熱交換器14で熱エネルギーを回収される。このとき、前記反応塔16の入口における原料ガス中の水素量を、該原料ガス中の酸素を還元するのに必要な当量より少ない量に設定し、酸素の還元反応を抑制しているので、反応塔16から導出された原料ガスにおける水蒸気の含有量も少なくなっている。したがって、熱交換器14内で原料ガスの温度が下がっても、水蒸気が凝縮することはほとんどない。
The source gas (reaction tower outlet gas) containing nitrogen, oxygen, hydrogen, water vapor and the like recovers thermal energy by the
熱交換器14を出た原料ガスは、切替使用される脱湿塔17に導入され、水蒸気等が吸着除去される。脱湿塔17から導出され、窒素、酸素、水素を含む原料ガスは、二酸化炭素液化装置18に導入され、液化蒸留されることにより、配管19から製品液化二酸化炭素LCOが得られる。脱湿塔17は、通常用いられている脱湿装置でよく、例えばゼオライト等が充填された吸着器を用いればよい。
The raw material gas exiting the
微量の窒素、酸素、水素は、二酸化炭素液化装置18から配管52のパージガス中に排出される。条件によっては、パージガスを回収して原料ガスに導入することにより、パージガス中の酸素、水素の再利用が可能である。
Trace amounts of nitrogen, oxygen, and hydrogen are discharged from the
微量の一酸化炭素、一酸化窒素を含む原料二酸化炭素ガスを、白金系の触媒を充填した1つの反応塔を用い、一酸化炭素、一酸化窒素を同時に除去する実験を行った。原料二酸化炭素中の酸素濃度は約150〜300ppmとした。酸素の還元に必要な水素濃度は約300〜600ppmとなるが、酸素の還元反応を抑制するために、反応塔入口での水素濃度を50〜100ppmとした。実験は、温度90〜110℃、圧力600〜900kPa(絶対圧)の範囲で行った。その結果を表1に示す。
従来の方法では、前述のように、窒素酸化物の還元を目的とする反応では40〜120℃の反応温度が、また、一酸化炭素と一酸化窒素の同時除去では、100〜200℃の反応温度が用いられている。 In the conventional method, as described above, a reaction temperature of 40 to 120 ° C. is used for the reaction aiming at reduction of nitrogen oxides, and a reaction temperature of 100 to 200 ° C. is used for simultaneous removal of carbon monoxide and nitrogen monoxide. Temperature is used.
一般的には、温度が高い程、反応が促進されるが、反応温度が120℃を超えると、アンモニア(NH3)が発生する可能性もある。いずれの場合にも、一酸化炭素、一酸化窒素が同時に除去できること、及び、110℃以下においては、アンモニアが発生しないことを確認した。原料二酸化炭素に含まれる酸素の約10〜20%は、水素により還元されたと考えられるが、残り約80〜90%が反応することなく、反応塔出口で確認できた。つまり、反応塔入口の水素濃度を、酸素の還元に必要な当量の水素濃度以下とすることにより、酸素の還元が抑制されたこと、換言すると添加が必要な水素量の低減が確認できた。また、約80〜90%の酸素が未反応であるということは、水蒸気の発生量も抑制される。 In general, the higher the temperature, the more the reaction is promoted. However, when the reaction temperature exceeds 120 ° C., ammonia (NH 3 ) may be generated. In any case, it was confirmed that carbon monoxide and nitric oxide can be removed simultaneously, and that ammonia is not generated at 110 ° C. or lower. About 10 to 20% of the oxygen contained in the raw carbon dioxide was considered to have been reduced by hydrogen, but the remaining about 80 to 90% could be confirmed at the outlet of the reaction tower without reacting. That is, by reducing the hydrogen concentration at the inlet of the reaction column to be equal to or less than the equivalent hydrogen concentration necessary for the reduction of oxygen, it was confirmed that the reduction of oxygen was suppressed, in other words, the reduction of the amount of hydrogen required to be added. Moreover, the fact that about 80 to 90% of oxygen is unreacted also suppresses the amount of water vapor generated.
11…圧縮機、12…脱臭塔、13…乾燥塔、14…熱交換器、15…加熱器、16…反応塔、17…脱湿塔、18…二酸化炭素液化装置 DESCRIPTION OF SYMBOLS 11 ... Compressor, 12 ... Deodorizing tower, 13 ... Drying tower, 14 ... Heat exchanger, 15 ... Heater, 16 ... Reaction tower, 17 ... Dehumidification tower, 18 ... Carbon dioxide liquefying apparatus
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