JPS631090B2 - - Google Patents
Info
- Publication number
- JPS631090B2 JPS631090B2 JP55076606A JP7660680A JPS631090B2 JP S631090 B2 JPS631090 B2 JP S631090B2 JP 55076606 A JP55076606 A JP 55076606A JP 7660680 A JP7660680 A JP 7660680A JP S631090 B2 JPS631090 B2 JP S631090B2
- Authority
- JP
- Japan
- Prior art keywords
- magnesium
- sulfite
- exhaust gas
- desulfurization
- cleaning
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000004140 cleaning Methods 0.000 claims description 76
- 239000007788 liquid Substances 0.000 claims description 61
- 238000006477 desulfuration reaction Methods 0.000 claims description 41
- 230000023556 desulfurization Effects 0.000 claims description 41
- 238000000034 method Methods 0.000 claims description 24
- 230000003647 oxidation Effects 0.000 claims description 24
- 238000007254 oxidation reaction Methods 0.000 claims description 24
- 239000003795 chemical substances by application Substances 0.000 claims description 13
- 229910052815 sulfur oxide Inorganic materials 0.000 claims description 13
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical class S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 claims description 12
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims description 10
- 239000011777 magnesium Substances 0.000 claims description 10
- 229910052749 magnesium Inorganic materials 0.000 claims description 10
- 150000002681 magnesium compounds Chemical class 0.000 claims description 9
- 239000012535 impurity Substances 0.000 claims description 8
- LSNNMFCWUKXFEE-UHFFFAOYSA-N Sulfurous acid Chemical compound OS(O)=O LSNNMFCWUKXFEE-UHFFFAOYSA-N 0.000 claims description 7
- 230000003009 desulfurizing effect Effects 0.000 claims description 6
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims description 5
- 229940043430 calcium compound Drugs 0.000 claims description 5
- 150000001674 calcium compounds Chemical class 0.000 claims description 5
- 238000006243 chemical reaction Methods 0.000 claims description 3
- 239000007789 gas Substances 0.000 description 36
- CSNNHWWHGAXBCP-UHFFFAOYSA-L Magnesium sulfate Chemical compound [Mg+2].[O-][S+2]([O-])([O-])[O-] CSNNHWWHGAXBCP-UHFFFAOYSA-L 0.000 description 16
- GBAOBIBJACZTNA-UHFFFAOYSA-L calcium sulfite Chemical compound [Ca+2].[O-]S([O-])=O GBAOBIBJACZTNA-UHFFFAOYSA-L 0.000 description 15
- 235000010261 calcium sulphite Nutrition 0.000 description 15
- JESHZQPNPCJVNG-UHFFFAOYSA-L magnesium;sulfite Chemical compound [Mg+2].[O-]S([O-])=O JESHZQPNPCJVNG-UHFFFAOYSA-L 0.000 description 14
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 description 12
- LSNNMFCWUKXFEE-UHFFFAOYSA-L sulfite Chemical class [O-]S([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-L 0.000 description 11
- VTHJTEIRLNZDEV-UHFFFAOYSA-L magnesium dihydroxide Chemical compound [OH-].[OH-].[Mg+2] VTHJTEIRLNZDEV-UHFFFAOYSA-L 0.000 description 10
- 239000000347 magnesium hydroxide Substances 0.000 description 10
- 229910001862 magnesium hydroxide Inorganic materials 0.000 description 10
- 238000001556 precipitation Methods 0.000 description 10
- RAHZWNYVWXNFOC-UHFFFAOYSA-N Sulphur dioxide Chemical compound O=S=O RAHZWNYVWXNFOC-UHFFFAOYSA-N 0.000 description 8
- 229910052943 magnesium sulfate Inorganic materials 0.000 description 8
- 235000019341 magnesium sulphate Nutrition 0.000 description 8
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 7
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 7
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 7
- 229910052791 calcium Inorganic materials 0.000 description 7
- 239000011575 calcium Substances 0.000 description 7
- 229910052760 oxygen Inorganic materials 0.000 description 7
- 239000001301 oxygen Substances 0.000 description 7
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 6
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 5
- 239000002002 slurry Substances 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- -1 and if necessary Substances 0.000 description 4
- 239000000395 magnesium oxide Substances 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 230000003472 neutralizing effect Effects 0.000 description 4
- 229910000019 calcium carbonate Inorganic materials 0.000 description 3
- 239000001569 carbon dioxide Substances 0.000 description 3
- 229910002092 carbon dioxide Inorganic materials 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 description 3
- 230000001590 oxidative effect Effects 0.000 description 3
- 239000002912 waste gas Substances 0.000 description 3
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000012530 fluid Substances 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- 239000002351 wastewater Substances 0.000 description 2
- LSNNMFCWUKXFEE-UHFFFAOYSA-M Bisulfite Chemical compound OS([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-M 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- LVGQIQHJMRUCRM-UHFFFAOYSA-L calcium bisulfite Chemical compound [Ca+2].OS([O-])=O.OS([O-])=O LVGQIQHJMRUCRM-UHFFFAOYSA-L 0.000 description 1
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 description 1
- 235000010260 calcium hydrogen sulphite Nutrition 0.000 description 1
- 239000000920 calcium hydroxide Substances 0.000 description 1
- 229910001861 calcium hydroxide Inorganic materials 0.000 description 1
- 235000019402 calcium peroxide Nutrition 0.000 description 1
- 235000011132 calcium sulphate Nutrition 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- LPHFLPKXBKBHRW-UHFFFAOYSA-L magnesium;hydrogen sulfite Chemical compound [Mg+2].OS([O-])=O.OS([O-])=O LPHFLPKXBKBHRW-UHFFFAOYSA-L 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 230000003134 recirculating effect Effects 0.000 description 1
- 238000005201 scrubbing Methods 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
Description
本発明は排ガス脱硫方法に係り、更に詳しく
は、ボイラー排ガス、金属加熱炉排ガス、都市ゴ
ミ焼却炉排ガスなどの硫黄酸化物（SOx）を含む
排ガスを、洗浄塔において、水酸化マグネシウ
ム、酸化マグネシウムなどのマグネシウム化合物
を脱硫剤として含むマグネシウム系循環洗浄液と
気液接触せしめて排ガス中に含まれる硫黄酸化物
を脱硫する方法に関する。
上記したようなマグネシウム化合物を脱硫剤と
して排ガス中の硫黄酸化物を除去する方法は既に
知られている。しかしながら、かかるマグネシウ
ム系循環洗浄液を用いて排ガス中の硫黄酸化物を
除去する場合には、循環洗浄液中に主として水に
難溶性の亜硫酸マグネシウムが生成し、洗浄塔内
部にスケーリングが発生したり、配管、バルブそ
の他の洗浄装置系で詰りを生じたりして、脱硫運
転を長期間安定に実施することが困難であつた。
更に、水酸化マグネシウムなどの市販のマグネシ
ウム化合物中には不純物として１〜２％程度のカ
ルシウム化合物を含んでいるため、前記マグネシ
ウム系循環洗浄液中にはカルシウム化合物が不純
物として含まれ、これが脱硫反応によつて主とし
て亜硫酸カルシウムが系内に生成することにな
る。周知の通り亜硫酸カルシウムの水に対する溶
解度は亜硫酸マグネシウムに比較して遥かに小さ
いので（50℃で約0.05ｇ／）、実際には亜硫酸
マグネシウムより亜硫酸カルシウムの析出の問題
の方が大きい。
亜硫酸マグネシウムあるいは亜硫酸カルシウム
の析出を防止するためには、(i)循環洗浄液のPHを
低くして液中の亜硫酸マグネシウムあるいは亜硫
酸カルシウムを、溶解度の大きな重亜硫酸マグネ
シウムあるいは重亜硫酸カルシウムに変換せしむ
るか、(ii)洗浄液中のマグネシウム化合物の濃度
（従つて不純物としてマグネシウム化合物に随伴
するカルシウム化合物の濃度）をあらかじめ析出
濃度以下に希薄にしておくか、又は(iii)洗浄液中の
亜硫酸マグネシウムあるいは亜硫酸カルシウムの
溶解量以上を、より溶解度の高い硫酸マグネシウ
ムあるいは硫酸カルシウムに変換することによつ
てなす事が出来る。しかるに上記(i)の方法におい
てほとんどの亜硫酸を重亜硫酸にするためにはPH
をかなり酸性にしなければならず、SO2の分圧の
関係からも脱硫率が低下して実用的でなく、上記
(ii)の方法において洗浄液中のマグネシウム化合物
の濃度を希薄にすれば脱硫率を確保するために処
理設備からの排水量が増大してしまい、そして上
記(iii)の洗浄液中の亜硫酸マグネシウムあるいは亜
硫酸カルシウムの過剰分を硫酸マグネシウムある
いは硫酸カルシウムに酸化する方法は、酸化しす
ぎると脱硫に必要な亜硫酸根がなくなり、脱硫率
が低下してしまう等コントロール上の欠点があつ
た。
そこでまず考えられたのは上記(iii)の酸化量をコ
ントロールする手段として酸化槽を別に設け、溶
解量以上の亜硫酸根を常に酸化しながら硫酸根と
する方法である。この方法であればPHを中性以上
で行う事が出来るため確かに不純物としてカルシ
ウムを含まない中和剤を用いる場合は脱硫効率が
高く、亜硫酸マグネシウムの析出をコントロール
出来るため中和剤濃度を高く出来、排水量を少な
く出来る等の効果がある。しかるに、前述したよ
うに、工業的に使用する市販品の水酸化マグネシ
ウム等にはどうしても不純物としてカルシウムが
含まれ実用上はカルシウムによるスケーリングの
防止を考慮しなくてはならない。特にボイラー排
ガス等排ガス中に炭酸ガスが存在する場合はさら
に排ガス中に含まれる炭酸ガスを吸収してしま
い、亜硫酸カルシウムより溶解度の低い炭酸カル
シウムを生じ結局この析出防止のためマグネシウ
ム濃度を低くおさえる（すなわち排水量を多くせ
ざるを得ない）欠点がのこされた。
他の方法として上記(i)と(iii)の方法を組み合わせ
た方法が提案されている。すなわちPHを4.5以下
にし亜硫酸根をほとんどない状態にしかつ過剰の
重亜硫酸根を常に酸化処理してしまうことによつ
て、不純物としてカルシウムを含む中和剤を用い
ても、もちろん炭酸は吸収されないから炭酸カル
シウムの析出は考えなくてよいし又亜硫酸にとも
なうスケールトラブルもない方法である。しかし
この方法では析出問題はないが、基本的にPHを低
くする事によつて亜硫酸濃度を抑えるため、脱硫
効率がどうしても悪くなる事、又一部取出して酸
化する際も触媒等を添加しないと酸化効率が低い
という欠点が残された。
本発明者等は前記した実設備における従来のマ
グネシウム系洗浄液を用いた脱硫方法の欠点を解
決するため検討した結果、溶解度の低い亜硫酸カ
ルシウムが大過剰の硫酸マグネシウムを添加する
事によつてその溶解度が高くなるという現象をみ
いだし、これを利用すれば従来法の欠点を解決す
る事が出来るものと判断し循環水のPHを炭酸カル
シウムが存在出来る値を上限とし、脱硫率が落ち
ない点（95％以上の脱硫が可能な点）を下限とす
る領域においてさらに検討を重ねた結果、脱硫系
におけるスケーリングトラブルを生ずることなく
廃ガス中の硫黄負荷変動に対する運転制御が容易
であり、しかも高脱硫率で廃ガス脱硫出来るとと
もに系外への排液量を最小にしたマグネシウム脱
硫方式を開発するに到つた。
即ち、本発明に係る排ガス脱硫方法は、洗浄塔
において不純物としてカルシウム化合物を１％以
上含有するマグネシウム化合物を脱硫剤として含
むマグネシウム系洗浄液を循環せしめつつ硫黄酸
化物を含む排ガスと前記洗浄液とを気液接触せし
めて排ガスを脱硫するにあたり、洗浄塔へ供給す
る洗浄液のPHを4.6〜5.9、好ましくは4.8〜5.8の
範囲に保持し、かつ、循環洗浄液の一部を酸化槽
に導びいて脱硫反応により生成した亜硫酸塩を硫
酸塩に酸化せしめ酸化後の液の一部を再び洗浄液
中に循環せしめる事によつて溶解度の低い亜硫酸
カルシウムを、過剰の硫酸マグネシウムによつて
溶解度の高い亜硫酸マグネシウム及び硫酸カルシ
ウムとなすことによつてスケールの発生を防止す
ることを特徴とする。
以下図面を参照し乍ら本発明を詳細に説明す
る。
第１図は本発明の脱硫方法を実施するための装
置の一例を示すフローチヤートである。
本発明方法に従えば、硫黄酸化物を含む排ガス
１１は適当な洗浄塔（例えば、堰及び溢流部のな
い多孔板又は格子棚を備えた段塔）１２の底部に
導入され、塔１２の頂部から導入される循環洗浄
液１３と塔内で気液接触して排ガス中の硫黄酸化
物は主として亜硫酸マグネシウム（他に亜硫酸カ
ルシウム、硫酸マグネシウム、硫酸カルシウムな
ども生成）として循環洗浄液１４中に捕捉され、
脱硫された排ガス１５は大気中に放出される。
一方、亜硫酸マグネシウム等を含んだ洗浄液１
４は洗浄液循環槽１６に入り、その一部１７は循
環槽１６から酸化槽１８に送られる。酸化槽１８
には酸素、空気などの酸素含有ガス１９を導入し
て液１７中の亜硫酸マグネシウム及び亜硫酸カル
シウムをそれぞれ硫酸マグネシウム及び硫酸カル
シウムに酸化する。酸化槽１８において酸化され
た液の一部２０は排液として系外に排出され、必
要あれば硫酸マグネシウムを回収した後廃棄す
る。
洗浄液循環槽１６および酸化槽１８には脱硫剤
補給槽２１から例えば適当な濃度の水酸化マグネ
シウムスラリー２２を添加して循環洗浄液１３の
PHが前記した4.6〜5.9のPH範囲になるよう制御す
る。かかる制御はPHメーター（図示せず）を用い
て容易に実施することができる。なお、水酸化マ
グネシウムスラリーに代えて、酸化マグネシウム
などを用いることもできる。このようにしてPH制
御された洗浄液循環槽１６の液２３と、酸化槽１
８の液２４とは合流して循環洗浄液１３として洗
浄塔１２へ導入される。なお、水酸化マグネシウ
ムスラリー２２を洗浄液循環槽１６のみに補給し
て循環洗浄液１３のPHを所定の範囲内に制御する
こともできることはいうまでもない。
このように本発明方法に従えば、洗浄塔へ供給
される循環洗浄液のPHを4.6〜5.9、好ましくは4.8
〜5.8の範囲に制御し、しかも洗浄塔からの循環
洗浄液の一部を酸化槽において酸化し（亜硫酸塩
→硫酸塩）、その一部を系外に排出すると共に残
部を循環洗浄液として再循環するので、
(i) 洗浄塔その他の装置内においてスケーリング
トラブルが発生せず、脱硫運転を長期間安定に
実施することができる、
(ii) 95％以上の高脱硫率で排ガス中の硫黄酸化物
を安定に除去することができる、
(iii) 例えばボイラーの油焚量の変動等に伴なう排
ガス中の硫黄酸化物の負荷変動に対して容易に
対処し得る、
(iv) 系外へ排出する排液量を最小にすることがで
きる、
という実用上極めて卓越した効果が得られる。
これらの点について更に詳しく説明すると、前
述の如く、市販の水酸化マグネシウムは、通常
MgO65重量％程度及びCaO1.5重量％程度の組成
であり、これを脱硫剤として用いた場合には循環
洗浄液中にMgSO3及びCaSO3などの水に難溶性
の亜硫酸塩が生成し、スケーリングの原因となる
ことは前述の通りである。ところで、硫黄酸化
物、主として亜硫酸ガスを排ガスから除去するた
めには洗浄液中に水酸イオン又は亜硫酸イオンが
存在することが必要であるが、水酸イオンが存在
するような領域では系内に水酸化マグネシウムの
沈澱が析出して好ましくなく、亜硫酸イオンの存
在するような領域では亜硫酸カルシウムの沈澱の
析出が問題となる。本発明者の知見によれば、脱
硫に必要な亜硫酸イオンを循環洗浄液中に確保し
かつ亜硫酸カルシウムの析出を防止し、しかも系
外への排出液の量を最小にするためには、循環洗
浄液中の亜硫酸イオンの一部を酸化して硫酸イオ
ンにすると共に洗浄液のPHを低目に押えて亜硫酸
ガスを吸収するのに必要な亜硫酸イオンを洗浄液
中に確保する必要があり、このPHの上限が約5.9、
好ましくは5.8である。一方、洗浄液のPHを下げ
過ぎると洗浄液中の亜硫酸イオンが重亜硫酸イオ
ンとなり、亜硫酸カルシウムなどの沈澱の析出の
問題は起らないが、脱硫に必要な亜硫酸イオンが
確保できなくなり、脱硫は単純な水吸収と同様に
なり脱硫効率が悪化して実用的でなくなる。かか
る現象を回避するために必要な洗浄液PHの下限は
約4.6、好ましくは4.8である。従つて、循環洗浄
液のPHは少なくとも4.6〜5.9の範囲内に制御しな
ければならず、このPH範囲内において循環洗浄液
の一部を酸化して亜硫酸イオンを硫酸イオンと
し、その一部を系外に排出すると共に残部を循環
洗浄液中に再循環することによつて、スケーリン
グトラブルを惹起することなく長期間にわたり安
定かつ高脱硫率で排ガスを脱硫することができ、
しかも排ガス中の硫黄酸化物の変動に対する運転
操作の制御が容易になり系外への排出液量を少な
くすることができる。
前述の如く、本発明方法においては洗浄液循環
層と酸化槽とをそれぞれ独立せしめて循環洗浄液
の一部を酸化層に導びき、そこで洗浄液中の亜硫
酸イオンを酸素又は酸素含有ガスを用いて完全に
酸化せしめる。酸素又は酸素含有ガスの供給量は
例えばDOメーター（図示せず）と連動させるこ
とによつて液中の亜硫酸イオンの負荷変動に合せ
て容易に制御することができる。なお酸化槽を洗
浄液循環槽と独立に設けることによつて、酸化槽
における液PHを酸化に最も好適なPH（例えば、
4.5〜７）にしたり、或いはそのまま系外へ放流
出来るPH（例えば5.8〜8.6）にしたりすることが
出来るという利点もある。この場合には両槽から
の洗浄液の合流後の洗浄液PHが前記所定範囲にな
るよう洗浄液循環槽の液PHを制御しなければなら
ないことはいうまでもない。
酸化槽としては従来マグネシウム脱硫法におい
て或いはカルシウム脱硫法において一般に使用さ
れている任意の酸化装置、例えばパプリング方
式、多孔板式等を使用することができる。
以下に本発明の具体的な実施例を、比較例と共
にあげて説明するが、本発明の範囲を以下の実施
例に限定するものでないことはいうまでもない。
実施例 １
亜硫酸ガス含量1300〜1500ppm、酸素３〜４
％、炭酸ガス12〜15％および水分９〜10％を含む
温度200℃のボイラー排ガスを塔径４ｍ及び塔高
８ｍで堰及び溢流部のない多孔板（開孔率35％）
３段を備えた洗浄塔においてマグネシウム系循環
洗浄液と気液接触させて１ケ月間連続的に脱硫し
た。この間のボイラー排ガス流量の変動は18000
〜67000Nm2／Ｈであつたが、循環洗浄液の流量
を400m3／Ｈ（うち40m3／Ｈは酸化槽からのくみ上
げ液量）に一定に保ち、洗浄液PHを5.4〜5.6に制
御し乍ら脱硫したところ、塔出口の亜硫酸ガス濃
度は70ppm以下で約95％以上の脱硫率が得られ、
しかも１ケ月間スケールを生じることなく安定に
運転することができた。
なお補給脱硫剤（中和剤）としては市販の水酸
化マグネシウム（組成：MgO65重量％及びCaO2
重量％）をスラリー濃度3.7重量％で使用した。
また酸化槽から系外へ排出した排液量（液中の硫
酸マグネシウム濃度7.7重量％、硫酸カルシウム
濃度0.18重量％）は平均５m3／Ｈであつた。循環
洗浄液の組成は、水酸化マグネシウム0.05重量
％、亜硫酸マグネシウム5.3重量％、硫酸マグネ
シウム1.5重量％、水酸化カルシウム0.0007重量
％、亜硫酸カルシウム0.13重量％、及び硫酸カル
シウム0.03重量％であつた。
実施例 ２
実施例１において酸化槽から循環洗浄液ライン
に再循環せしめた液くみあげ量を下記第１表に示
した量にした以外は実施例１と同様にして（全循
環洗浄液量は400m3／Ｈのまま）ボイラー排ガス
の脱硫運転を行なつたところ、第１表に示すよう
な結果を得た。
The present invention relates to an exhaust gas desulfurization method, and more specifically, exhaust gas containing sulfur oxides (SOx) such as boiler exhaust gas, metal heating furnace exhaust gas, municipal waste incinerator exhaust gas, etc., is treated in a cleaning tower with magnesium hydroxide, magnesium oxide, etc. The present invention relates to a method for desulfurizing sulfur oxides contained in exhaust gas by bringing the magnesium compound into gas-liquid contact with a magnesium-based circulating cleaning solution containing a magnesium compound as a desulfurizing agent. A method of removing sulfur oxides from exhaust gas using the above-mentioned magnesium compound as a desulfurization agent is already known. However, when such a magnesium-based circulating cleaning liquid is used to remove sulfur oxides from exhaust gas, magnesium sulfite, which is sparingly soluble in water, is mainly produced in the circulating cleaning liquid, causing scaling inside the cleaning tower and piping. It has been difficult to carry out desulfurization operation stably for a long period of time due to clogging of valves and other cleaning equipment systems.
Furthermore, since commercially available magnesium compounds such as magnesium hydroxide contain about 1 to 2% of calcium compounds as impurities, the magnesium-based circulating cleaning solution contains calcium compounds as impurities, which are harmful to the desulfurization reaction. Therefore, mainly calcium sulfite is produced in the system. As is well known, the solubility of calcium sulfite in water is much lower than that of magnesium sulfite (approximately 0.05 g/at 50°C), so the problem of precipitation of calcium sulfite is actually greater than that of magnesium sulfite. In order to prevent the precipitation of magnesium sulfite or calcium sulfite, (i) lower the pH of the circulating cleaning solution to convert the magnesium sulfite or calcium sulfite in the solution into magnesium bisulfite or calcium bisulfite, which has high solubility. or (ii) the concentration of the magnesium compound in the cleaning solution (therefore, the concentration of the calcium compound that accompanies the magnesium compound as an impurity) is diluted in advance to below the precipitation concentration, or (iii) the concentration of magnesium sulfite or sulfite in the cleaning solution is diluted in advance. This can be achieved by converting more than the dissolved amount of calcium into magnesium sulfate or calcium sulfate, which have higher solubility. However, in the method (i) above, in order to convert most of the sulfite into bisulfite, the PH
must be made quite acidic, and the desulfurization rate decreases due to the partial pressure of SO 2 , making it impractical.
In method (ii), if the concentration of magnesium compounds in the cleaning solution is diluted, the amount of waste water from the treatment equipment will increase in order to ensure the desulfurization rate, and the amount of magnesium sulfite or calcium sulfite in the cleaning solution in (iii) above will increase. The method of oxidizing the excess to magnesium sulfate or calcium sulfate has drawbacks in terms of control, such as excessive oxidation, which eliminates the sulfite radicals necessary for desulfurization, resulting in a decrease in the desulfurization rate. Therefore, the first idea was to provide a separate oxidation tank as a means of controlling the amount of oxidation in (iii) above, and constantly oxidize the sulfite radicals in excess of the dissolved amount to convert them to sulfate radicals. With this method, the pH can be maintained above neutral, so if a neutralizing agent that does not contain calcium as an impurity is used, the desulfurization efficiency is high, and the precipitation of magnesium sulfite can be controlled, so the concentration of the neutralizing agent can be increased. This has the effect of reducing the amount of waste water. However, as mentioned above, commercially available magnesium hydroxide and the like that are used industrially inevitably contain calcium as an impurity, and in practice, prevention of scaling due to calcium must be taken into consideration. In particular, when carbon dioxide gas is present in exhaust gas such as boiler exhaust gas, the carbon dioxide gas contained in the exhaust gas is further absorbed, producing calcium carbonate which has a lower solubility than calcium sulfite.In order to prevent this precipitation, the magnesium concentration is kept low ( In other words, the amount of water discharged had to be increased). As another method, a method combining the above methods (i) and (iii) has been proposed. In other words, by lowering the pH to 4.5 or less, leaving almost no sulfite radicals, and constantly oxidizing excess bisulfite radicals, even if you use a neutralizing agent that contains calcium as an impurity, carbonic acid will of course not be absorbed. There is no need to consider the precipitation of calcium carbonate, and this method does not cause scale problems associated with sulfite. However, although there is no problem with precipitation with this method, the desulfurization efficiency is inevitably reduced because the sulfite concentration is basically suppressed by lowering the pH, and also when a portion is taken out and oxidized, a catalyst etc. must be added. The disadvantage of low oxidation efficiency remained. The present inventors investigated in order to solve the drawbacks of the conventional desulfurization method using a magnesium-based cleaning solution in actual equipment, and found that by adding a large excess of magnesium sulfite, the solubility of calcium sulfite, which has low solubility, can be improved. We discovered that the phenomenon of increased carbonation and determined that this could be used to solve the drawbacks of the conventional method.We decided to set the pH of the circulating water to a value that allows the presence of calcium carbonate as the upper limit, and ensure that the desulfurization rate does not decrease ( As a result of further studies in the area where the lower limit is 95% or more desulfurization (the point at which desulfurization is possible), we found that it is easy to control operation in response to fluctuations in the sulfur load in waste gas without causing scaling problems in the desulfurization system, and that it is possible to achieve high desulfurization. We have developed a magnesium desulfurization method that can desulfurize waste gas at a high rate and minimize the amount of liquid discharged outside the system. That is, the exhaust gas desulfurization method according to the present invention circulates a magnesium-based cleaning solution containing a magnesium compound containing 1% or more of calcium compounds as an impurity as a desulfurizing agent in a cleaning tower, while purifying the exhaust gas containing sulfur oxides and the cleaning solution. When desulfurizing exhaust gas through liquid contact, the pH of the cleaning liquid supplied to the cleaning tower is maintained in the range of 4.6 to 5.9, preferably 4.8 to 5.8, and a portion of the circulating cleaning liquid is led to an oxidation tank to perform the desulfurization reaction. By oxidizing the generated sulfite to sulfate and circulating a portion of the oxidized solution into the cleaning solution, calcium sulfite with low solubility is converted into magnesium sulfite and sulfuric acid with high solubility due to excess magnesium sulfate. It is characterized by preventing scale formation by forming it with calcium. The present invention will be described in detail below with reference to the drawings. FIG. 1 is a flowchart showing an example of an apparatus for carrying out the desulfurization method of the present invention. According to the method of the invention, the exhaust gas 11 containing sulfur oxides is introduced into the bottom of a suitable scrubbing column 12 (e.g. a tray column with perforated plates or grate shelves without weirs and overflows). Sulfur oxides in the exhaust gas are captured in the circulating cleaning liquid 14 mainly as magnesium sulfite (calcium sulfite, magnesium sulfate, calcium sulfate, etc. are also produced) through gas-liquid contact within the tower with the circulating cleaning liquid 13 introduced from the top. ,
The desulfurized exhaust gas 15 is released into the atmosphere. On the other hand, cleaning solution 1 containing magnesium sulfite etc.
4 enters the cleaning liquid circulation tank 16, and a portion 17 of it is sent from the circulation tank 16 to the oxidation tank 18. Oxidation tank 18
An oxygen-containing gas 19 such as oxygen or air is introduced to oxidize magnesium sulfite and calcium sulfite in the liquid 17 to magnesium sulfate and calcium sulfate, respectively. A portion 20 of the liquid oxidized in the oxidation tank 18 is discharged outside the system as waste liquid, and if necessary, magnesium sulfate is recovered and then disposed of. For example, magnesium hydroxide slurry 22 of an appropriate concentration is added to the cleaning liquid circulation tank 16 and the oxidation tank 18 from the desulfurization agent supply tank 21 to make the circulating cleaning liquid 13.
The PH is controlled to be within the PH range of 4.6 to 5.9 as described above. Such control can be easily performed using a PH meter (not shown). Note that magnesium oxide or the like can also be used instead of the magnesium hydroxide slurry. The liquid 23 in the cleaning liquid circulation tank 16 whose pH is controlled in this way and the oxidation tank 1
8 and the liquid 24 are combined and introduced into the cleaning tower 12 as the circulating cleaning liquid 13. It goes without saying that the pH of the circulating cleaning liquid 13 can be controlled within a predetermined range by replenishing the magnesium hydroxide slurry 22 only into the cleaning liquid circulation tank 16. According to the method of the present invention, the pH of the circulating cleaning liquid supplied to the cleaning tower is 4.6 to 5.9, preferably 4.8.
~5.8, and part of the circulating cleaning liquid from the cleaning tower is oxidized in the oxidation tank (sulfite → sulfate), part of it is discharged outside the system, and the remainder is recirculated as circulating cleaning liquid. Therefore, (i) desulfurization operation can be carried out stably for a long period of time without causing scaling troubles in the cleaning tower or other equipment; (ii) sulfur oxides in exhaust gas can be removed with a high desulfurization rate of 95% or more. (iii) It is possible to easily cope with changes in the load of sulfur oxides in the exhaust gas due to fluctuations in the amount of oil fired in the boiler, etc. (iv) It can be discharged outside the system. An extremely outstanding practical effect can be obtained in that the amount of liquid discharged can be minimized. To explain these points in more detail, as mentioned above, commercially available magnesium hydroxide is usually
It has a composition of approximately 65% by weight of MgO and 1.5% by weight of CaO, and when this is used as a desulfurization agent, water-insoluble sulfites such as MgSO 3 and CaSO 3 are generated in the circulating cleaning solution, resulting in scaling. The cause is as described above. By the way, in order to remove sulfur oxides, mainly sulfur dioxide gas, from exhaust gas, it is necessary that hydroxide ions or sulfite ions exist in the cleaning solution. Precipitation of magnesium oxide is undesirable, and in areas where sulfite ions are present, precipitation of calcium sulfite becomes a problem. According to the findings of the present inventors, in order to secure sulfite ions necessary for desulfurization in the circulating cleaning solution, prevent precipitation of calcium sulfite, and minimize the amount of liquid discharged to the outside of the system, it is necessary to It is necessary to oxidize some of the sulfite ions in the solution to sulfate ions and to keep the pH of the cleaning solution low to ensure that the cleaning solution has enough sulfite ions to absorb sulfur dioxide gas. is about 5.9,
Preferably it is 5.8. On the other hand, if the pH of the cleaning solution is lowered too much, the sulfite ions in the cleaning solution become bisulfite ions, and although the problem of precipitates such as calcium sulfite does not occur, it becomes impossible to secure the sulfite ions necessary for desulfurization, and desulfurization becomes simple. This is similar to water absorption, and the desulfurization efficiency deteriorates, making it impractical. The lower limit of the cleaning liquid pH required to avoid such a phenomenon is about 4.6, preferably 4.8. Therefore, the pH of the circulating cleaning fluid must be controlled within the range of at least 4.6 to 5.9, and within this pH range, a portion of the circulating cleaning fluid is oxidized to convert sulfite ions to sulfate ions, and a portion of this is removed from the system. By discharging the waste gas and recirculating the remainder into the circulating cleaning solution, it is possible to desulfurize the exhaust gas stably and at a high desulfurization rate over a long period of time without causing scaling problems.
Moreover, it is easy to control the operating operation with respect to fluctuations in sulfur oxides in the exhaust gas, and the amount of liquid discharged outside the system can be reduced. As mentioned above, in the method of the present invention, the cleaning liquid circulation layer and the oxidation tank are made independent, and a part of the circulating cleaning liquid is guided to the oxidation layer, where the sulfite ions in the cleaning liquid are completely removed using oxygen or an oxygen-containing gas. Oxidize. The amount of oxygen or oxygen-containing gas supplied can be easily controlled in accordance with changes in the load of sulfite ions in the liquid, for example, by interlocking with a DO meter (not shown). By providing the oxidation tank independently of the cleaning liquid circulation tank, the pH of the liquid in the oxidation tank can be adjusted to the most suitable pH for oxidation (for example,
It also has the advantage that it can be adjusted to a pH of 4.5 to 7) or to a pH (for example, 5.8 to 8.6) that can be discharged out of the system as it is. In this case, it goes without saying that the liquid PH in the cleaning liquid circulation tank must be controlled so that the cleaning liquid PH after the cleaning liquids from both tanks are combined falls within the predetermined range. As the oxidation tank, any oxidation device commonly used in the conventional magnesium desulfurization method or calcium desulfurization method, such as a pupling type, perforated plate type, etc., can be used. Specific examples of the present invention will be described below along with comparative examples, but it goes without saying that the scope of the present invention is not limited to the following examples. Example 1 Sulfur dioxide gas content 1300-1500 ppm, oxygen 3-4
%, carbon dioxide gas 12-15% and moisture 9-10%, at a temperature of 200℃, using a perforated plate with a column diameter of 4 m and tower height of 8 m, without weirs or overflow parts (porosity: 35%).
Desulfurization was carried out continuously for one month by bringing the mixture into gas-liquid contact with a magnesium-based circulating cleaning solution in a cleaning tower equipped with three stages. The fluctuation in boiler exhaust gas flow rate during this period was 18,000
However, the flow rate of the circulating cleaning liquid was kept constant at 400m 3 / H (of which 40m 3 /H is the amount of liquid pumped from the oxidation tank), and the pH of the cleaning liquid was controlled at 5.4 to 5.6. When desulfurized, the sulfur dioxide concentration at the tower outlet was less than 70 ppm, and a desulfurization rate of more than 95% was obtained.
Furthermore, it was possible to operate stably for one month without any scale formation. As a supplementary desulfurization agent (neutralizing agent), commercially available magnesium hydroxide (composition: MgO65% by weight and CaO2
% by weight) was used at a slurry concentration of 3.7% by weight.
The amount of liquid discharged from the oxidation tank to the outside of the system (concentration of magnesium sulfate in the liquid was 7.7% by weight, concentration of calcium sulfate in the liquid was 0.18% by weight) was 5 m 3 /H on average. The composition of the circulating cleaning liquid was 0.05% by weight of magnesium hydroxide, 5.3% by weight of magnesium sulfite, 1.5% by weight of magnesium sulfate, 0.0007% by weight of calcium hydroxide, 0.13% by weight of calcium sulfite, and 0.03% by weight of calcium sulfate. Example 2 The procedure was the same as in Example 1, except that the amount of liquid pumped up from the oxidation tank to the circulating cleaning liquid line was changed to the amount shown in Table 1 below (the total amount of circulating cleaning liquid was 400 m 3 / When desulfurization of the boiler exhaust gas was carried out, the results shown in Table 1 were obtained.
【表】
比較例 １
実施例１で用いたボイラー排ガスを循環洗浄液
のPHを3.9〜4.1および6.0〜6.2に制御し乍ら循環
洗浄液への酸化槽からの液くみ上げ量を第２表に
示すように変化させて（循環洗浄液量の合計量は
いずれの場合も400m3／Ｈとした）、実施例１と同
様にして連続脱硫運転を実施した。結果は第２表
に示す通りであつた。[Table] Comparative Example 1 While controlling the pH of the circulating cleaning liquid using the boiler exhaust gas used in Example 1 to be 3.9 to 4.1 and 6.0 to 6.2, the amount of liquid pumped from the oxidation tank to the circulating cleaning liquid was as shown in Table 2. (The total amount of circulating cleaning liquid was 400 m 3 /H in both cases), and continuous desulfurization operation was carried out in the same manner as in Example 1. The results were as shown in Table 2.
第１図は本発明の脱硫剤方法を実施するための
装置の一例を示すフローチヤートである。
１１……排ガス、１２……洗浄塔、１３……供
給循環洗浄液、１４……吐出循環洗浄液、１５…
…脱硫後の吐出排ガス、１６……洗浄液循環槽、
１８……酸化槽、２０……排液、２１……脱硫剤
補給槽、２２……補給水酸化マグネシウムスラリ
ー。
FIG. 1 is a flowchart showing an example of an apparatus for carrying out the desulfurization agent method of the present invention. 11... Exhaust gas, 12... Cleaning tower, 13... Supply circulating cleaning liquid, 14... Discharge circulating cleaning liquid, 15...
...Discharged exhaust gas after desulfurization, 16...Cleaning liquid circulation tank,
18... Oxidation tank, 20... Drainage liquid, 21... Desulfurization agent supply tank, 22... Supply magnesium hydroxide slurry.
Claims (1)
物を１％以上含有するマグネシウム化合物を脱硫
剤として含むマグネシウム系洗浄液を循環せしめ
つつ硫黄酸化物を含む排ガスと前記洗浄液とを気
液接触せしめて排ガスを脱硫するにあたり、洗浄
塔へ供給する洗浄液のPHを4.6〜5.9の範囲に保持
し、かつ、循環洗浄液の一部を酸化槽に導びいて
脱硫反応により生成した亜硫酸塩を硫酸塩に酸化
せしめ酸化後の液の一部を再び洗浄液中に循環せ
しめることを特徴とする排ガス脱硫方法。1. In desulfurizing the exhaust gas by circulating a magnesium-based cleaning solution containing a magnesium compound containing 1% or more of calcium compounds as impurities as a desulfurizing agent in the cleaning tower and bringing the cleaning solution into gas-liquid contact with the exhaust gas containing sulfur oxides, The pH of the cleaning liquid supplied to the cleaning tower is maintained in the range of 4.6 to 5.9, and a part of the circulating cleaning liquid is led to the oxidation tank to oxidize the sulfite produced by the desulfurization reaction to sulfate. An exhaust gas desulfurization method characterized by circulating a portion of the exhaust gas back into the cleaning solution.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP7660680A JPS574213A (en) | 1980-06-09 | 1980-06-09 | Desulfurizing method of waste gas |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP7660680A JPS574213A (en) | 1980-06-09 | 1980-06-09 | Desulfurizing method of waste gas |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS574213A JPS574213A (en) | 1982-01-09 |
| JPS631090B2 true JPS631090B2 (en) | 1988-01-11 |
Family
ID=13609985
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP7660680A Granted JPS574213A (en) | 1980-06-09 | 1980-06-09 | Desulfurizing method of waste gas |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS574213A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01138985U (en) * | 1988-03-07 | 1989-09-22 | ||
| WO2020261422A1 (en) * | 2019-06-26 | 2020-12-30 | 日本電信電話株式会社 | Method for evaluating risk of hydrogen embrittlement fracture of reinforcing bar |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100697840B1 (en) | 2006-01-03 | 2007-03-20 | 박정봉 | SOx, VOx and NOx reduction system at furnace |
| JP7233914B2 (en) * | 2018-12-19 | 2023-03-07 | クボタ環境エンジニアリング株式会社 | Exhaust gas desulfurization method |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS4976798A (en) * | 1972-11-25 | 1974-07-24 | ||
| JPS5213797A (en) * | 1975-07-22 | 1977-02-02 | Jidosha Denki Kogyo Co Ltd | Burn-out alarm unit for electric lamp used for automobile |
| JPS5232894A (en) * | 1975-09-09 | 1977-03-12 | Mitsui Miike Mach Co Ltd | Process for removing sulfur oxide in waste gas and by-producting magne sium sulfate |
| JPS5364674A (en) * | 1976-11-22 | 1978-06-09 | Kurashiki Boseki Kk | Method of removing sulfur oxides from exhaust gas |
-
1980
- 1980-06-09 JP JP7660680A patent/JPS574213A/en active Granted
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS4976798A (en) * | 1972-11-25 | 1974-07-24 | ||
| JPS5213797A (en) * | 1975-07-22 | 1977-02-02 | Jidosha Denki Kogyo Co Ltd | Burn-out alarm unit for electric lamp used for automobile |
| JPS5232894A (en) * | 1975-09-09 | 1977-03-12 | Mitsui Miike Mach Co Ltd | Process for removing sulfur oxide in waste gas and by-producting magne sium sulfate |
| JPS5364674A (en) * | 1976-11-22 | 1978-06-09 | Kurashiki Boseki Kk | Method of removing sulfur oxides from exhaust gas |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01138985U (en) * | 1988-03-07 | 1989-09-22 | ||
| WO2020261422A1 (en) * | 2019-06-26 | 2020-12-30 | 日本電信電話株式会社 | Method for evaluating risk of hydrogen embrittlement fracture of reinforcing bar |
| JPWO2020261422A1 (en) * | 2019-06-26 | 2020-12-30 |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS574213A (en) | 1982-01-09 |
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