JP4156076B2 - Method for desulfurization of exhaust gas using catalyst - Google Patents
Method for desulfurization of exhaust gas using catalyst Download PDFInfo
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- JP4156076B2 JP4156076B2 JP13950598A JP13950598A JP4156076B2 JP 4156076 B2 JP4156076 B2 JP 4156076B2 JP 13950598 A JP13950598 A JP 13950598A JP 13950598 A JP13950598 A JP 13950598A JP 4156076 B2 JP4156076 B2 JP 4156076B2
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- 239000003054 catalyst Substances 0.000 title claims description 58
- 238000000034 method Methods 0.000 title claims description 15
- 238000006477 desulfuration reaction Methods 0.000 title description 4
- 230000023556 desulfurization Effects 0.000 title description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical class [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 58
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 55
- 239000007789 gas Substances 0.000 claims description 49
- 239000005871 repellent Substances 0.000 claims description 22
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 18
- 230000002940 repellent Effects 0.000 claims description 15
- RAHZWNYVWXNFOC-UHFFFAOYSA-N Sulphur dioxide Chemical compound O=S=O RAHZWNYVWXNFOC-UHFFFAOYSA-N 0.000 claims description 14
- 239000000463 material Substances 0.000 claims description 7
- LSNNMFCWUKXFEE-UHFFFAOYSA-N Sulfurous acid Chemical compound OS(O)=O LSNNMFCWUKXFEE-UHFFFAOYSA-N 0.000 claims description 6
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 4
- 239000001301 oxygen Substances 0.000 claims description 4
- 229910052760 oxygen Inorganic materials 0.000 claims description 4
- 239000012779 reinforcing material Substances 0.000 claims description 4
- 238000007865 diluting Methods 0.000 claims 1
- 239000002245 particle Substances 0.000 description 16
- 238000006243 chemical reaction Methods 0.000 description 9
- 230000003197 catalytic effect Effects 0.000 description 8
- 239000000126 substance Substances 0.000 description 8
- 238000004140 cleaning Methods 0.000 description 7
- 239000006185 dispersion Substances 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 6
- 239000004810 polytetrafluoroethylene Substances 0.000 description 6
- 239000000243 solution Substances 0.000 description 6
- 238000009792 diffusion process Methods 0.000 description 5
- 239000007788 liquid Substances 0.000 description 5
- 239000010419 fine particle Substances 0.000 description 4
- 239000011148 porous material Substances 0.000 description 4
- 238000005670 sulfation reaction Methods 0.000 description 4
- 230000019635 sulfation Effects 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 2
- VUZPPFZMUPKLLV-UHFFFAOYSA-N methane;hydrate Chemical compound C.O VUZPPFZMUPKLLV-UHFFFAOYSA-N 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- -1 polytetrafluoroethylene Polymers 0.000 description 2
- LSNNMFCWUKXFEE-UHFFFAOYSA-L sulfite Chemical compound [O-]S([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-L 0.000 description 2
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical class S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 description 2
- 229910052815 sulfur oxide Inorganic materials 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- 239000013032 Hydrocarbon resin Substances 0.000 description 1
- 230000010718 Oxidation Activity Effects 0.000 description 1
- 239000004743 Polypropylene Substances 0.000 description 1
- 239000004809 Teflon Substances 0.000 description 1
- 229920006362 Teflon® Polymers 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 230000000274 adsorptive effect Effects 0.000 description 1
- 229940043430 calcium compound Drugs 0.000 description 1
- 150000001674 calcium compounds Chemical class 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000010790 dilution Methods 0.000 description 1
- 239000012895 dilution Substances 0.000 description 1
- 238000001125 extrusion Methods 0.000 description 1
- 239000003546 flue gas Substances 0.000 description 1
- 229910052602 gypsum Inorganic materials 0.000 description 1
- 239000010440 gypsum Substances 0.000 description 1
- 229920006270 hydrocarbon resin Polymers 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 238000004898 kneading Methods 0.000 description 1
- 238000010030 laminating Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000011368 organic material Substances 0.000 description 1
- 229920001155 polypropylene Polymers 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 238000009279 wet oxidation reaction Methods 0.000 description 1
Images
Classifications
-
- 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
Description
【０００１】
【発明の属する技術分野】
本発明は排ガスの脱硫方法に関する。より詳しくは、本発明は、亜硫酸ガス、酸素及び水分を含む排ガスを触媒と接触させることにより、亜硫酸ガスを希硫酸にして排ガスから除去する方法に関する。
【０００２】
【従来の技術】
ある種の排煙脱硫プロセス（以下において「接触硫酸化プロセス」と呼ぶ）においては、排ガス中に含まれる亜硫酸ガス等の硫黄酸化物は、共存する酸素により触媒を介して最終的に硫酸にまで酸化される。これはそのまま硫酸（希硫酸）として回収されたり、あるいはカルシウム化合物と反応して石膏の形で回収される。硫黄酸化物の除去には一般に活性炭が有用であるといわれるが、その理由の１つは、活性炭の比表面積が大きく、そのような広い表面積に触媒活性点が多数分布しているからである。
【０００３】
しかしながら、実用的な見地からすると、上記接触硫酸化プロセスにおける活性炭触媒の性能は必ずしも十分であるとはいえず、より高い活性を有する触媒が求められている。この点に関し活性炭触媒について調べてみると、活性炭触媒の性能が十分でない原因は、触媒活性点の量やその活性度が小さいことにあるのではなく、反応分子の粒内拡散が制限されることにあるということがわかってきた。そして、さらに調べてみると、接触硫酸化反応では触媒活性点で生成した無水硫酸が雰囲気中の水蒸気と反応して直ちに希硫酸になって細孔内あるいは触媒表面に留まり、これが反応分子の粒子内部への拡散をブロックするため、内部の触媒活性点が有効に利用されないということもわかってきた。もし生成した硫酸水溶液が触媒内に留まらないようにすることができれば、触媒活性は大きく改善されることが期待できるわけであり、そのためには活性炭触媒表面の撥水性を向上させることが重要であるということになる。
【０００４】
例えば、Chem. Eng. Comm. vol. 60 (1987) p. 253には、平均粒径０．７８ｍｍの粒状活性炭にミクロンサイズのポリテトラフルオロエチレン（ＰＴＦＥ）粒子の分散液を吹きかけることにより、ＰＴＦＥ添加量８〜２０％の領域において亜硫酸ガスの吸着酸化反応の速度定数が３倍に上昇したとの事例が示されている。また、特開昭５９−３６５３１号公報には、亜硫酸ガスを吸収した吸収液中に蓄積した亜硫酸イオンを酸化するため、その吸収液中に粒状活性炭を添加する場合に、当該活性炭に撥水化処理を施すと亜硫酸イオンの吸着酸化活性が上昇することが示されている。具体的には、粒径５〜１０ｍｍの粒状活性炭にＰＴＦＥ分散液を含浸させ、２００℃で２時間加熱処理することにより、活性炭単味の触媒に比べてはるかに高い活性を示すことが示されている。なお、上記事例において撥水化された活性炭は、通常市販されているＰＴＦＥ分散液のＰＴＦＥ粒子サイズが直径０．２〜０．４μｍ程度であり、この粒子サイズは活性炭粒子内部にまで浸透するには大きすぎると考えられることから、活性炭の外表面及びマクロポアの極く一部のみが撥水化された活性炭であったと思われる。
【０００５】
本発明者らは、活性炭表面の撥水性を向上させる、すなわち撥水化処理する目的で、すでに、活性炭粒子に撥水性物質を含浸担持させたもの、活性炭粉末と撥水性物質とを混合して成形したもの、予め撥水化処理した活性炭粉末と撥水性物質とを混合して成形したもの、及び活性炭粉末と撥水性物質とを混合して成形した後に撥水性物質を含浸担持させたものを開発した。ここで、活性炭粒子に撥水性物質を含浸担持させるとは、フッ素樹脂や一部の炭化水素樹脂などの撥水性有機物質の微粒子を含む分散液（ゾル）を含浸させて当該微粒子を活性炭粒子表面に保持させるものであり、活性炭粉末に撥水性物質を混合して成形するとは、そのような撥水性物質の微粒子と活性炭粉末とを混合し、混練、圧縮、造粒等を行って所定形状に成形するものである。また、上記撥水性物質の微粒子分散液や撥水性物質の溶液で当該活性炭粉末を処理する場合もある。こうして表面を撥水化した活性炭触媒は生成した希硫酸を速やかに細孔から排出するので反応分子の粒子内への拡散がブロックされず、活性炭触媒の所期の性能を生かすことができる。
【０００６】
【発明が解決しようとする課題】
しかしながら、上記活性炭触媒上で生成した希硫酸は、撥水化処理を行っても細孔内から完全には排出されないことがしばしばあることがわかった。これは、触媒粒子表面に付着した希硫酸が反応器内から速やかには除去されず、これが細孔内の希硫酸の排出や排ガスと触媒粒子との接触を妨害するためと考えられる。かくして反応器内の希硫酸量が増えるにつれて反応効率が低下し、そのような場合には触媒量を増やさざるを得ず、装置のコンパクト化ができないという結果がもたらされる。すなわち、生成した希硫酸が触媒上にとどまるのを防止し、速やかに反応器から排出させることができれば、排ガスと触媒との接触効率ひいては反応効率が向上し、かくして触媒量の低減につながるわけである。
【０００７】
【課題を解決するための手段】
本発明は、少なくとも亜硫酸ガス、酸素及び水分を含む排ガスを触媒と接触させることにより、亜硫酸ガスを希硫酸にして排ガスから除去する方法であって、該排ガスを触媒層に下向流で流通させることを特徴とする方法を提供し、これにより上記課題を解決するものである。
【０００８】
【発明の実施の形態】
本発明では、触媒層に対して排ガスを下向流で流通させることにより、触媒表面に付着している希硫酸を下方に向かって押し流す。押し流される希硫酸は触媒表面を伝って流下するのであるから、排ガスが触媒表面近傍を表面に対して平行に流れることが好ましく、また触媒表面においてその流速が大きいことが好ましい。一般には触媒を用いる気相酸化反応はガス拡散律速であり、実ガス流速（触媒層内の空間部を通過するガスの流速）が処理対象ガス成分の拡散に影響を与えるガス流速領域（０．０５〜１．０ｍ／ｓ）を超えると除去性能は一定のレベルに落ち着くようになる。しかしながら、亜硫酸ガスを希硫酸に酸化して除去する接触硫酸化プロセスにおいては、上記ガス流速領域を超えても除去性能はさらに向上することがわかった。そのような高ガス流速領域を採用すれば装置はコンパクトになるが、過大なガス流速、具体的には４０ｍ／ｓ以上のガス流速は除去性能の向上に効果がなく、単に圧損の上昇や触媒量の増加を招くだけであるため好ましくない。以上のことを総合的に考慮すれば、触媒表面を接触通過するガス流速は１〜１５ｍ／ｓの範囲にあることが好ましい。
【０００９】
触媒表面におけるガス流速を大きくするということは、反応器内のその他の領域に比べて触媒表面におけるガス流速を相対的に大きくするという意味をも包含するから、必ずしも全体としてのガス流量を大きくすることに直接つながるわけではなく、触媒表面に沿って大きなガス流速が得られるように流れのパターンを形成すればよい。好適には、これは触媒を排ガスの流れ方向に平行な平面のみからなる形状、たとえば流れ方向に延びたハニカム類似形状、四角類似形状、三角類似形状などに成形することにより実現できる。このような成形体は、連続平面を形成しているので希硫酸がスムーズに流下し、また排ガスを高速で流しても抵抗が少ないという利点がある。さらに触媒を撥水化すると、触媒表面の希硫酸が排ガスによって押し流されやすくなるので、好ましいことがわかった。活性炭を前述の方法で撥水化処理すれば、触媒自体としての活性も向上するので好適である。ハニカム類似形状触媒等は、その形状から押し出し、型抜きなどによる成形ができる。なお、活性炭を用いて高活性、小重量かつ高強度のものを製造する好適な方法として、活性炭粉末、撥水性物質及び補強材を用いて構成する方法がある。具体的には、活性炭粉末と撥水性物質を混合混練した後シート状に成形したものを、耐酸性金属材、有機材などからなる板状ないし網状の補強材の片面または両面に、必要により接着性を増加させる材料を用いて張り合わせて板状の触媒を製造し、次いでこれを波状、角状などに折り曲げ加工すればよい。図１は網状の補強材の両面にシート状の触媒を張り合わせた状態を模式的に示すものであり、図２はそれをトライアングル（ａ）または平行板（ｂ）に成形したものを示す。
【００１０】
本発明の方法は、反応器内の（特に触媒表面に付着した状態の）希硫酸を下向流でガスを流すことにより速やかに除去するものであるが、この場合触媒表面をより希薄な硫酸水溶液で洗浄するとさらに脱硫性能が向上することがわかった。この理由は明らかではないが、次のように考えることができる。すなわち、洗浄を行わない場合には触媒表面に濃度２３％程度の希硫酸が生成し、これがガスの下向流により反応器内から除去する対象になるのであるが、より希薄な（たとえば濃度５％程度の）硫酸水溶液で触媒表面を洗浄する場合には、生成硫酸が希釈されることにより粘性が低下してガス流により除去されやすくなるとともに、亜硫酸ガス及び酸素が洗浄液中に溶解して触媒表面に到達する（すなわち一種の湿式酸化が並行して生ずる）のではないかと考えられるのである。上記のように触媒表面を洗浄するには、洗浄液を反応器出口側から反応器入口側に一部戻すことにより循環させればよい。洗浄液の循環量としては、連続洗浄では触媒層１ｍ2当たりの液流量が０．０２〜２ｍ2/ｈとなる範囲が好ましい。間欠洗浄では液流量は連続洗浄の場合より大きくすることができる。洗浄液（硫酸水溶液）の硫酸濃度は２０％以下、特に５％以下であることが好ましい。
【００１１】
【実施例】
実施例
断面３５ｍｍ×４０ｍｍの角形の反応器に、図２に示すように、トライアングル（ａ）または平行板（ｂ）の形状に成形した触媒（高さ９００ｍｍ、平行板ピッチ２ｍｍ）を充填した。この触媒成形体は、活性炭粉末（平均粒径３０μｍの石炭系）とテフロン粉末（平均粒径２０００Åの粒子分散液）とを９：１の比率で混合混練して厚さ０．５ｍｍのシート状に成形し、これを厚さ０．３ｍｍのポリプロピレン製ネットの両側に貼り付けて積層体としたものを加工して製造した。こうして触媒を充填した反応器に下記組成のガス（４５℃）を種々の流速で流し、
Ｏ2 ４％
ＣＯ2 １０％
Ｈ2Ｏ 飽和
ＳＯ2 １０００ｐｐｍ
反応器入口と出口におけるＳＯ2濃度の差から単位時間当たりのＳＯ2除去量として求めた反応速度γ［ｍｏｌ／ｈ］から、下記式
γ＝ｋ×ＣSO2 n
（ＣSO2： ＳＯ2濃度［ｍｏｌ／ｍ3］）
（ｎ： 定数）
により反応速度定数ｋを求めた。結果を図３に示す。図３からわかるように、実ガス流速０．５〜４０ｍ／ｈの範囲で反応速度定数が流速の増加に伴って増加した。
【００１２】
比較例
上記実施例と同じ反応器（トライアングル形）を用い、同じガスを流量３０Ｎｍ3／ｈの上向流で流し、上記実施例と同様にして反応速度定数を求めたところ、ｋの値として３．５×１０-4を得た。これは上記実施例において同じガス流速の下向流で流した場合の７３％に相当する。
【図面の簡単な説明】
【図１】本発明の方法に好適に用いられる板状触媒の例を示す。
【図２】図１の板状触媒をさらに成形した例を示す。
【図３】ガスを下向流で流したときの流速と反応速度定数の関係を示す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas desulfurization method. More specifically, the present invention relates to a method of removing sulfur dioxide gas from exhaust gas by bringing sulfur dioxide gas, oxygen and moisture into contact with a catalyst to make the sulfur dioxide gas dilute sulfuric acid.
[0002]
[Prior art]
In a certain type of flue gas desulfurization process (hereinafter referred to as “catalytic sulfation process”), sulfur oxides such as sulfurous acid gas contained in the exhaust gas are finally converted into sulfuric acid via a catalyst by coexisting oxygen. Oxidized. This is recovered as it is as sulfuric acid (dilute sulfuric acid), or is reacted with a calcium compound and recovered in the form of gypsum. Activated carbon is generally said to be useful for removing sulfur oxides. One of the reasons is that activated carbon has a large specific surface area, and a large number of catalytic active sites are distributed over such a large surface area.
[0003]
However, from a practical standpoint, the performance of the activated carbon catalyst in the catalytic sulfation process is not always sufficient, and a catalyst having higher activity is required. Looking at the activated carbon catalyst in this regard, the reason why the performance of the activated carbon catalyst is not sufficient is not that the amount of the active site of the catalyst and its activity are small, but that the intra-particle diffusion of the reaction molecules is limited. It has been found that there is. And further investigation, in the catalytic sulfation reaction, anhydrous sulfuric acid produced at the catalytic active site reacts with water vapor in the atmosphere and immediately becomes dilute sulfuric acid and remains in the pores or on the catalyst surface. It has also been found that internal catalytic activity sites are not effectively utilized to block diffusion into the interior. If the generated sulfuric acid aqueous solution can be prevented from staying in the catalyst, the catalytic activity can be expected to be greatly improved. For that purpose, it is important to improve the water repellency of the activated carbon catalyst surface. It turns out that.
[0004]
For example, in Chem. Eng. Comm. Vol. 60 (1987) p. 253, PTFE is sprayed by spraying a dispersion of micron-sized polytetrafluoroethylene (PTFE) particles onto granular activated carbon having an average particle size of 0.78 mm. An example is shown in which the rate constant of the adsorptive oxidation reaction of sulfurous acid gas has increased threefold in the region where the addition amount is 8 to 20%. Japanese Patent Application Laid-Open No. 59-36531 discloses that when activated carbon is added to the absorbing solution in order to oxidize sulfite ions accumulated in the absorbing solution that has absorbed sulfurous acid gas, the activated carbon is made water repellent. It has been shown that the adsorption and oxidation activity of sulfite ions increases when the treatment is applied. Specifically, it is shown that a granular activated carbon having a particle size of 5 to 10 mm is impregnated with a PTFE dispersion and heat-treated at 200 ° C. for 2 hours, which shows a much higher activity than a catalyst with a simple activated carbon. ing. In addition, the activated carbon repellent in the above example has a PTFE particle size of a commercially available PTFE dispersion having a diameter of about 0.2 to 0.4 μm, and this particle size penetrates into the activated carbon particles. Is considered to be too large, it seems that only a part of the outer surface of the activated carbon and the macropores were water repellent activated carbon.
[0005]
In order to improve the water repellency of the activated carbon surface, that is, to make the water repellent treatment, the present inventors have already mixed the activated carbon particles impregnated with a water repellent substance, activated carbon powder and a water repellent substance. Molded, pre-water repellent activated carbon powder mixed with water repellent material and molded, mixed with activated carbon powder and water repellent material and then impregnated with water repellent material developed. Here, impregnating and supporting the activated carbon particles with a water-repellent substance means impregnating a dispersion (sol) containing fine particles of a water-repellent organic substance such as a fluororesin or a part of a hydrocarbon resin, and applying the fine particles to the surface of the activated carbon particles. When the activated carbon powder is mixed with a water-repellent substance and molded, the fine particles of the water-repellent substance and the activated carbon powder are mixed, kneaded, compressed, granulated, etc. into a predetermined shape. It is to be molded. In some cases, the activated carbon powder is treated with a fine particle dispersion of the water repellent material or a solution of the water repellent material. The activated carbon catalyst having a water-repellent surface in this manner quickly discharges the produced dilute sulfuric acid from the pores, so that the diffusion of the reaction molecules into the particles is not blocked, and the desired performance of the activated carbon catalyst can be utilized.
[0006]
[Problems to be solved by the invention]
However, it has been found that the dilute sulfuric acid produced on the activated carbon catalyst is often not completely discharged from the pores even after the water repellent treatment. This is presumably because dilute sulfuric acid adhering to the surface of the catalyst particles is not quickly removed from the reactor, and this hinders discharge of dilute sulfuric acid in the pores and contact between the exhaust gas and the catalyst particles. Thus, as the amount of dilute sulfuric acid in the reactor increases, the reaction efficiency decreases. In such a case, the amount of catalyst must be increased, and the result is that the apparatus cannot be made compact. In other words, if the produced dilute sulfuric acid is prevented from staying on the catalyst and can be quickly discharged from the reactor, the contact efficiency between the exhaust gas and the catalyst and thus the reaction efficiency is improved, thus leading to a reduction in the amount of catalyst. is there.
[0007]
[Means for Solving the Problems]
The present invention is a method of removing sulfur dioxide gas from dilute sulfuric acid by contacting exhaust gas containing at least sulfurous acid gas, oxygen and moisture with the catalyst, and flowing the exhaust gas downward through the catalyst layer. A method characterized by this is provided, thereby solving the above-mentioned problems.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the dilute sulfuric acid adhering to the catalyst surface is pushed downward by allowing the exhaust gas to flow through the catalyst layer in a downward flow. Since the dilute sulfuric acid that is pushed down flows down along the catalyst surface, it is preferable that the exhaust gas flows in the vicinity of the catalyst surface in parallel to the surface, and that the flow rate is high on the catalyst surface. In general, the gas phase oxidation reaction using a catalyst is gas diffusion-controlled, and the actual gas flow rate (the flow rate of the gas passing through the space in the catalyst layer) affects the diffusion of the gas component to be treated (0. If it exceeds 05-1.0 m / s), the removal performance comes to a certain level. However, it has been found that in the catalytic sulfation process in which sulfurous acid gas is oxidized and removed to dilute sulfuric acid, the removal performance is further improved even if the gas flow rate region is exceeded. If such a high gas flow rate region is adopted, the apparatus becomes compact. However, an excessive gas flow rate, specifically, a gas flow rate of 40 m / s or more has no effect on the removal performance, and simply increases the pressure loss or the catalyst. This is not preferable because it only increases the amount. Taking the above into consideration, it is preferable that the gas flow rate passing through the catalyst surface in the range of 1 to 15 m / s.
[0009]
Increasing the gas flow rate on the catalyst surface also includes the meaning of relatively increasing the gas flow rate on the catalyst surface as compared to other regions in the reactor, so the overall gas flow rate is necessarily increased. In particular, the flow pattern may be formed so as to obtain a large gas flow rate along the catalyst surface. Preferably, this can be achieved by shaping the catalyst into a shape consisting only of a plane parallel to the flow direction of the exhaust gas, such as a honeycomb-like shape, a square-like shape, a triangle-like shape extending in the flow direction. Since such a molded body forms a continuous plane, dilute sulfuric acid flows smoothly, and there is an advantage that resistance is low even when exhaust gas is flowed at a high speed. Further, it has been found that it is preferable to make the catalyst water repellent because dilute sulfuric acid on the catalyst surface is easily washed away by the exhaust gas. If the activated carbon is subjected to water repellency treatment by the above-mentioned method, the activity as the catalyst itself is improved, which is preferable. A honeycomb-like catalyst or the like can be formed by extrusion or die cutting from its shape. In addition, there exists the method of comprising using activated carbon powder, a water-repellent substance, and a reinforcing material as a suitable method of manufacturing a thing with high activity, small weight, and high intensity | strength using activated carbon. Specifically, the activated carbon powder and water-repellent substance are mixed and kneaded and then formed into a sheet shape, which is bonded to one or both sides of a plate-like or net-like reinforcing material made of acid-resistant metal material, organic material, etc., if necessary. A plate-shaped catalyst may be manufactured by laminating using materials that increase the properties, and then bent into a wave shape or a square shape. FIG. 1 schematically shows a state in which a sheet-like catalyst is bonded to both surfaces of a net-like reinforcing material, and FIG. 2 shows a shape formed into a triangle (a) or a parallel plate (b).
[0010]
In the method of the present invention, dilute sulfuric acid in the reactor (particularly in a state of adhering to the catalyst surface) is quickly removed by flowing a gas in a downward flow. It was found that desulfurization performance was further improved by washing with an aqueous solution. The reason for this is not clear, but can be considered as follows. That is, when washing is not performed, dilute sulfuric acid having a concentration of about 23% is generated on the surface of the catalyst, and this becomes a target to be removed from the reactor by the downward flow of gas. When the surface of the catalyst is washed with an aqueous sulfuric acid solution (about%), the viscosity of the produced sulfuric acid is reduced due to dilution, and it is easy to be removed by the gas flow. It is thought that the surface may be reached (that is, a kind of wet oxidation occurs in parallel). In order to clean the catalyst surface as described above, the cleaning solution may be circulated by partially returning the cleaning liquid from the reactor outlet side to the reactor inlet side. The circulation amount of the cleaning liquid is preferably in a range where the liquid flow rate per 1 m 2 of the catalyst layer is 0.02 to 2 m 2 / h in continuous cleaning. In intermittent cleaning, the liquid flow rate can be made larger than in continuous cleaning. The sulfuric acid concentration of the cleaning liquid (aqueous sulfuric acid solution) is preferably 20% or less, particularly preferably 5% or less.
[0011]
【Example】
Example A catalyst having a cross section of 35 mm × 40 mm was filled with a catalyst (height 900 mm, parallel plate pitch 2 mm) formed in the shape of a triangle (a) or a parallel plate (b) as shown in FIG. This catalyst molded body was prepared by mixing and kneading activated carbon powder (coal system having an average particle size of 30 μm) and Teflon powder (particle dispersion having an average particle size of 2000 mm) in a ratio of 9: 1 to form a sheet having a thickness of 0.5 mm. It was formed into a laminate by pasting it on both sides of a polypropylene net having a thickness of 0.3 mm. In this way, a gas (45 ° C.) having the following composition was allowed to flow at various flow rates into the reactor filled with the catalyst,
O 2 4%
H 2 O saturated SO 2 1000 ppm
From the reaction rate γ [mol / h] obtained as the SO 2 removal amount per unit time from the difference in SO 2 concentration at the reactor inlet and outlet, the following formula γ = k × C SO2 n
(C SO2 : SO 2 concentration [mol / m 3 ])
(N: constant)
To determine the reaction rate constant k. The results are shown in FIG. As can be seen from FIG. 3, the reaction rate constant increased with increasing flow rate in the range of the actual gas flow rate of 0.5 to 40 m / h.
[0012]
Comparative Example Using the same reactor (triangle type) as in the above example, the same gas was allowed to flow in an upward flow of 30 Nm 3 / h, and the reaction rate constant was determined in the same manner as in the above example. 3.5 × 10 −4 was obtained. This corresponds to 73% of the case where the gas flow rate is the downward flow in the above embodiment.
[Brief description of the drawings]
FIG. 1 shows an example of a plate catalyst suitably used in the method of the present invention.
FIG. 2 shows an example in which the plate catalyst of FIG. 1 is further shaped.
FIG. 3 shows the relationship between the flow rate and the reaction rate constant when the gas is flowed downward.
Claims (2)
該触媒が、活性炭粉末、撥水性物質及び補強材からなる成形体であって、排ガスの流通方向と平行な表面をもつ触媒層を構成し、
該排ガスを該触媒層に下向流で流通させ、そのときの該表面における排ガスの流速を１〜１５ｍ／ｓとすることを特徴とする方法。A method for removing sulfur dioxide from dilute sulfuric acid by diluting sulfuric acid gas by contacting exhaust gas containing at least sulfurous acid gas, oxygen and moisture with a catalyst,
The catalyst is a molded body made of activated carbon powder, a water repellent material and a reinforcing material, and constitutes a catalyst layer having a surface parallel to the flow direction of exhaust gas,
Exhaust gas was passed through at a downward flow in the catalyst layer, wherein that you and a flow rate of the 1~15m / s of the exhaust gas at the surface at that time.
Priority Applications (9)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP13950598A JP4156076B2 (en) | 1998-05-21 | 1998-05-21 | Method for desulfurization of exhaust gas using catalyst |
| MYPI99001316A MY121452A (en) | 1998-04-07 | 1999-04-06 | Desulfurization of exhaust gases using activated carbon catalyst. |
| CA002327591A CA2327591C (en) | 1998-04-07 | 1999-04-06 | Desulfurization of exhaust gases using activated carbon catalyst |
| CN99806511.0A CN1117615C (en) | 1998-04-07 | 1999-04-06 | Desulphurization of exhaust gases using activated carbon catalyst |
| AU30564/99A AU3056499A (en) | 1998-04-07 | 1999-04-06 | Desulfurization of exhaust gases using activated carbon catalyst |
| IDW20002276A ID26701A (en) | 1998-04-07 | 1999-04-06 | DESULFURIZATION OF WASTE GAS USING ACTIVE CARBON CATALYST |
| US09/647,680 US6616905B1 (en) | 1998-04-07 | 1999-04-06 | Desulfurization of exhaust gases using activated carbon catalyst |
| PCT/JP1999/001810 WO1999051337A1 (en) | 1998-04-07 | 1999-04-06 | Desulfurization of exhaust gases using activated carbon catalyst |
| TW088105537A TW500623B (en) | 1998-04-07 | 1999-04-07 | Desulfurization of flue gas using active carbon catalyst |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP13950598A JP4156076B2 (en) | 1998-05-21 | 1998-05-21 | Method for desulfurization of exhaust gas using catalyst |
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| Publication Number | Publication Date |
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| JPH11319575A JPH11319575A (en) | 1999-11-24 |
| JP4156076B2 true JP4156076B2 (en) | 2008-09-24 |
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| JP4493813B2 (en) * | 2000-07-21 | 2010-06-30 | 北陸電力株式会社 | Highly water-repellent activated carbon structure for flue gas desulfurization and manufacturing method thereof |
| JP5553966B2 (en) * | 2008-03-19 | 2014-07-23 | 千代田化工建設株式会社 | Mercury adsorbent and smoke treatment method using the adsorbent |
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