JP4097573B2 - Waste gas treatment furnace waste gas treatment method and treatment system - Google Patents

Waste gas treatment furnace waste gas treatment method and treatment system Download PDF

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JP4097573B2
JP4097573B2 JP2003188715A JP2003188715A JP4097573B2 JP 4097573 B2 JP4097573 B2 JP 4097573B2 JP 2003188715 A JP2003188715 A JP 2003188715A JP 2003188715 A JP2003188715 A JP 2003188715A JP 4097573 B2 JP4097573 B2 JP 4097573B2
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exhaust gas
solid
waste
slurry
solid content
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JP2005021774A (en
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務 鈴木
宜久 田中
崇幸 鈴木
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Taiheiyo Cement Corp
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Taiheiyo Cement Corp
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Description

【0001】
【発明の属する技術分野】
本発明は、ごみ焼却炉、溶融炉等の廃棄物処理用加熱炉から排出される排ガスに含まれている塩化水素および硫黄酸化物(SO)を除去するための処理方法および処理システムに関する。
【0002】
【従来の技術】
従来より、ごみ焼却炉等から排出される塩化水素等の酸性ガスを含む排ガスに対して、消石灰を添加して、塩化カルシウム等を生成させ、この生成物および未反応の消石灰を、バグフィルター等の集塵手段を用いて捕集し、酸性ガスが除去された排ガスを得る技術が、知られている。
そして、この技術に対して更に改良を加えた技術も、種々提案されている。
例えば、ケイ酸カルシウム水和物粒子、水酸化カルシウム粒子及び活性炭粒子を含む排ガス処理剤を用いて、HCl、SO等の酸性ガスとダイオキシン類の除去を同時に行なう排ガス処理方法が提案されている(特許文献1)。
【0003】
【特許文献1】
特開2002−58963(第2頁の請求項1、請求項8)
【0004】
【発明が解決しようとする課題】
従来、ごみ焼却炉等の排ガスに消石灰を添加して得られる塩化カルシウム等を含む固体分は、ごみ焼却炉等に戻すか、あるいは、重金属等を除去する処理を行なった後、埋め立て処分されていた。
しかし、塩化カルシウム等を含む固体分を、ごみ焼却炉等に戻した場合、排ガスの処理系内において塩素分や硫黄分が循環することになり、排ガス中の塩化水素や硫黄酸化物の濃度が次第に増大していくという問題がある。
また、塩化カルシウム等を含む固体分を埋め立て処分することは、廃棄物の埋立地の確保が困難になりつつある現状下において、望ましいことではない。
そこで、本発明は、ごみ焼却炉の如き廃棄物処理用加熱炉の排ガスに含まれる塩化水素および硫黄酸化物を除去することができると共に、除去処理の過程で得られる固体分を、廃棄物として系外に搬出することなく、有用物として再資源化することのできる処理方法および処理システムを提供することを目的とする。
【0005】
【課題を解決するための手段】
本発明者は、上記課題を解決するために鋭意検討した結果、ごみ焼却炉の如き廃棄物処理用加熱炉から排出される排ガスに対して、消石灰の如きCaO源を添加した後、反応生成物であるカルシウム塩(具体的には、塩化カルシウム、硫酸カルシウム等)を含む固体分を捕集し、次いで、この固体分と、アルカリ化剤を含む水溶液とを混合して、固体分に含まれているカルシウム塩を水酸化カルシウムに変化させた後、このスラリーを固液分離すれば、セメント原料等として使用可能な固形分が得られる一方、廃棄物として系外に搬出すべき固体分が生じず、固液分離後の濾液に対して排水処理のみを行なえばよいこと等を見出し、本発明を完成した。
【0006】
すなわち、本発明(請求項1)の廃棄物処理用加熱炉の排ガスの処理方法は、(A)ごみ焼却炉の如き廃棄物処理用加熱炉から排出される塩化水素および硫黄酸化物を含む排ガスに対して、消石灰の如きCaO源を添加した後、バグフィルターの如き集塵手段を用いて固気分離して、塩化カルシウム、硫酸カルシウム等を含む固体分と、浄化された排ガスを得る排ガス浄化工程と、(B)工程(A)で得られた塩化カルシウム、硫酸カルシウム等を含む固体分と、水酸化ナトリウムの如きアルカリ化剤を含む水溶液とを混合して、pH13.0以上のスラリーを得た後、該スラリーを、濾過装置等を用いて固液分離して、水酸化カルシウムを含む固形分と、塩素分(塩化物イオン)および硫酸分(硫酸イオン)を含む液分を得るカルシウム分回収工程とを含むことを特徴としている。
【0007】
本発明の処理方法によれば、排ガス浄化工程(A)で得られる塩化カルシウム、硫酸カルシウム等を含む固体分は、アルカリ化剤を含む水溶液と混合されて、水酸化カルシウムを含む固体分となるので、セメント原料や骨材の原料等として利用することができる。
したがって、排ガス浄化工程(A)で得られる塩化カルシウム、硫酸カルシウム等を含む固体分を、ごみ焼却炉の如き廃棄物処理用加熱炉に戻す場合に見られる排ガス中の塩化水素や硫黄酸化物の濃度の増大という問題は、生じることがない。また、排ガス浄化工程(A)で得られる塩化カルシウム等を含む固体分を、廃棄物として埋め立て処分する必要がないので、廃棄物の量の削減、および廃棄物の再資源化の促進という社会的要請にも合致する。
なお、カルシウム分回収工程(B)で得られる固形分に含まれる重金属等は、セメント焼成炉内で揮発成分となるので、排ガスの煙道に設けた集塵手段を用いて捕集して、別途、処理すればよい。
【0008】
本発明(請求項2)の廃棄物処理用加熱炉の排ガスの処理システムは、ごみ焼却炉の如き廃棄物処理用加熱炉と、該廃棄物処理用加熱炉に一端が接続された、該廃棄物処理用加熱炉内で発生する排ガスを流通させるための排ガス流通路と、該排ガス流通路における所定の地点にて該排ガス流通路内に消石灰の如きCaO源を供給するためのCaO源供給手段と、前記排ガス流通路の他端に接続されたバグフィルターの如き固気分離手段と、該固気分離手段で捕集された固体分、アルカリ化剤および水を混合して、pH13.0以上のスラリーを得るための混合槽と、該混合槽で得られたスラリーを固液分離して、水酸化カルシウムを含む固形分を得るための、濾過装置の如き固液分離手段とを含むことを特徴としている。
【0009】
【発明の実施の形態】
以下、本発明を詳細に説明する。
本発明の廃棄物処理用加熱炉の排ガスの処理方法は、(A)廃棄物処理用加熱炉から排出される塩化水素および硫黄酸化物を含む排ガスに対して、CaO源を添加した後、固気分離して、固体分と、浄化された排ガスを得る排ガス浄化工程と、(B)工程(A)で得られた固体分と、アルカリ化剤を含む水溶液とを混合した後、固液分離して、水酸化カルシウムを含む固形分と、塩素分および硫酸分を含む液分を得るカルシウム分回収工程とからなるものである。
【0010】
[(A)排ガス浄化工程]
本発明で処理対象となる排ガスは、廃棄物処理用加熱炉から排出される排ガスである。
ここで、廃棄物処理用加熱炉としては、例えば、ごみ焼却炉や、溶融炉等が挙げられる。なお、溶融炉とは、ごみ焼却炉等で生じる煤塵や焼却残渣を高温で溶融した後、冷却して固化させ、有害な重金属が溶出せずかつ減容化された埋め立て処分に適するスラグを得るための加熱炉をいう。
廃棄物処理用加熱炉から排出される排ガスには、酸性ガスである塩化水素(HCl)および硫黄酸化物(SO)が含まれている。例えば、ごみ焼却炉において、ごみに含まれている可燃性硫黄分は、燃焼してSO等になる。また、ごみに含まれているポリ塩化ビニル等の廃プラスチックは、燃焼して塩化水素ガスを発生する。
排ガス中には、通常、塩化水素等の酸性ガスの他、飛灰、重金属、ダイオキシン等が含まれている。
【0011】
本工程では、まず、処理対象物である排ガスに対して、CaO源が添加される。
ここで、CaO源としては、例えば、消石灰(Ca(OH))、生石灰(CaO)、炭酸カルシウム(CaCO)等が挙げられる。
中でも、消石灰は、反応効率が高く、かつ取り扱いも容易であることから、本発明において好ましく用いられる。
CaO源は、排ガス中の塩化水素や硫黄酸化物と反応して、塩化カルシウム、硫酸カルシウム等を生成する。例えば、CaO源である消石灰は、排ガス中の塩化水素および二酸化硫黄と次のように反応する。
Ca(OH)+2HCl → CaCl+2H
Ca(OH)+SO → CaSO+H
CaSO+1/2O → CaSO
【0012】
本発明において、CaO源の添加方法としては、通常、全乾式または半乾式の方法が採用される。
全乾式とは、消石灰の如きCaO源を乾燥固体の形態で添加する方法である。全乾式は、添加設備が簡易であり、設備費を低減できると共に、添加設備の取り扱いや維持(メンテナンス)が容易であるという利点がある。
半乾式とは、消石灰の如きCaO源をスラリーの形態で添加する方法である。半乾式は、CaO源のスラリー中の水分が、排ガスの熱によって突沸して蒸発するため、多孔質の粒子が生じ、排ガス中の塩化水素等との反応の効率が高いという利点がある。
【0013】
CaO源の添加量は、排ガス中の塩化水素および硫黄酸化物の量に応じて適宜定めればよく、具体的には、塩化水素および硫黄酸化物の合計の当量に対して、好ましくは0.5〜10倍、より好ましくは2〜5倍の当量とすればよい。該値が0.5倍未満では、CaO源の添加後に排ガス中に残る未反応の塩化水素および硫黄酸化物の量が多くなり、排ガスの浄化を十分に達成することができなくなる。該値が10倍を超えると、反応せずに残るCaO源の量が多くなり、不経済となる。
廃棄物処理用加熱炉からの排ガスにCaO源を添加して、このCaO源と排ガス中の塩化水素および硫黄酸化物との反応を生じさせた後、排ガスを固気分離して、固体分と、浄化された排ガスを得る。
ここで、固気分離は、例えば、バグフィルターや電気集塵機等の集塵手段を用いて行なわれる。特に、バグフィルターは、固気分離後の排ガス中に含まれる塩化水素等の濃度が、電気集塵機等と比べて小さくなる傾向があるので、本発明において好ましく用いられる。
【0014】
固気分離して得られる固体分は、塩化カルシウム、硫酸カルシウム、重金属の塩化物、煤塵(例えば、ごみ焼却炉で発生する焼却飛灰や、溶融炉で発生する溶融飛灰等)等を含むものである。
一方、固気分離して得られる浄化された排ガスは、わずかに残る有害物質(具体的には、未反応の塩化水素および硫黄酸化物の他、ダイオキシン類、重金属、揮発性有機物質等)を含むものである。
この排ガスは、例えば、吸着材を用いた浄化処理等を行なった後、大気中に排出される。ここで、吸着材としては、例えば、活性コークスが挙げられる。活性コークスとは、石炭を原料とする成型活性炭の一種であり、脱硫・脱硝性能及び重金属やダイオキシンの吸着性能を有する吸着材である。活性コークスを充填した活性コークス塔内に、排ガスを通過させると、排ガス中に残存する重金属やダイオキシン類等の有害物質が除去される。
【0015】
廃棄物処理用加熱炉からの排ガスにCaO源を添加する前に、排ガスの温度をダイオキシン類の再合成を抑制し得る温度にまで低下させる排ガス冷却工程を設けてもよい。
ダイオキシン類は、高温下において分解されるが、300〜400℃で再合成されることが知られている。この温度範囲内に排ガスが長時間保持されて、ダイオキシンの生成が促進されるのを回避するために、ダイオキシン類が再合成される温度よりも低い温度(例えば、200℃以下)まで、排ガスの温度を急激に低下させる工程を設けることができる。
【0016】
[(B)カルシウム分回収工程]
本工程では、まず、排ガス浄化工程(A)で得られた塩化カルシウム、硫酸カルシウム等を含む固体分と、アルカリ化剤を含む水溶液とを混合して、スラリーを得る。
ここで、アルカリ化剤としては、水中で溶解して水酸化物イオンを生成し、pHを上昇させるものであればよく、例えば、水酸化ナトリウム等のアルカリ金属の水酸化物や、アンモニア等が挙げられる。
固体分と、アルカリ化剤を含む水溶液の配合割合は、特に限定されないが、水酸化カルシウムを効率的に生成させるために、アルカリ化剤を含む水溶液1リットル当たりの固体分の質量が400g以下となるように定めることが好ましい。
【0017】
アルカリ化剤の添加量は、スラリーのpHが13.0以上になる量であり、好ましくは、スラリーのpHが13.5以上になる量である。
固体分と、アルカリ化剤を含む水溶液とを混合する方法としては、例えば、工程(A)で得られた固体分と、アルカリ化剤と、水とを別々に混合槽内に投入して、撹拌混合する方法や、工程(A)で得られた固体分と、予め調製済みのアルカリ化剤を含む水溶液とを混合槽内に投入して、撹拌混合する方法等が挙げられる。
【0018】
次に、得られたスラリーを固液分離して、水酸化カルシウムを含む固形分(ケーキ)と、塩素分および硫酸分を含む液分を得る。
ここで、固液分離の方法としては、例えば、ベルトフィルターやフィルタープレス等の濾過装置を用いて濾過する方法や、遠心分離する方法等が挙げられる。
固液分離して得られる固形分は、水酸化カルシウムを含み、かつ、塩素分等が除去されているので、セメントや骨材等の原料として、再資源化することができる。この固形分を、固形分100質量部当たり50質量部以上の量の水で洗浄することは、当該固形分に付着している塩素分や硫酸分等の量を低減させるので、好ましい。
なお、固形分に含まれている重金属は、セメント焼成炉等において高温の雰囲気下で揮発し、煙道に設けたバグフィルター等の集塵手段によって捕集され、処理される。
一方、固液分離して得られる液分は、水溶性の塩素分(塩化物イオン)、硫酸分(硫酸イオン)、アルカリ性領域下で溶出する重金属等を含むものであり、必要に応じて中和処理や重金属除去処理等を行なった後、系外に排出される。
【0019】
次に、本発明の排ガスの処理システムについて、図面を参照しつつ説明する。図1は、本発明の排ガスの処理システムの一例を示す図である。
図1中、ごみ焼却炉(廃棄物処理用加熱炉)1内におけるごみの燃焼によって発生した排ガスは、排ガス流通路2内に流入した後、排ガス流通路2の途中の所定の地点にて、消石灰供給装置4から粉状の消石灰(CaO源)が供給される。排ガス中の塩化水素および硫黄酸化物は、各々、この消石灰と反応して、固体分である塩化カルシウムおよび硫酸カルシウムとなる。
なお、ごみ焼却炉1と消石灰供給装置4の間に、ダイオキシン類の再合成を抑制するためのガス冷却装置(図示せず)を設けてもよい。
【0020】
その後、排ガスは、バグフィルター(固気分離手段)3にて、固体分が除去される。この固体分は、塩化カルシウム、硫酸カルシウム、重金属の塩化物、飛灰等を含むものである。バグフィルター3を通過した後の排ガスは、排ガス流通路5および必要に応じて活性コークス塔等の浄化装置(図示せず)を通過した後、煙突6から大気中に排出される。
一方、バグフィルター3で捕集された固体分は、混合槽7に導かれる。混合槽7には、バグフィルター3からの固体分と共に、アルカリ化剤貯留槽8からの水酸化ナトリウム、および水貯留槽9からの水が供給される。そして、混合槽7内にて、撹拌翼によって、固体分、水酸化ナトリウムおよび水が撹拌混合されて、所定のpH値(例えば、13.5)に調整されたスラリーとなる。
【0021】
なお、混合槽7は、バッチ式と連続式のいずれの形式でもよいが、処理の効率性の観点からは、連続式とすることが望ましい。この場合、バグフィルター3で捕集された固体分は、管路等の供給路を介して混合槽7に供給される。また、水および水酸化ナトリウムは、混合槽7内のスラリーが所定の液量およびpHとなるように、各々、アルカリ化剤貯留槽8、水貯留槽9から供給量調整弁等を介して連続的または断続的に混合槽7内に供給される。混合槽7には、pH測定装置が取り付けてあり、このpH測定装置によって、水酸化ナトリウムの供給量が調整される。
混合槽7内のスラリーは、濾過装置(固液分離手段)10に導かれて濾過され、水酸化カルシウム等を含む固形分(ケーキ)と、塩化物イオン、硫酸イオン等を含む液分とに分離される。
このうち、固形分は、水洗した後、セメント原料等として用いられる。液分は、中和処理槽11に導かれ、酸貯留槽12から供給される塩酸等の酸によってpHを中性領域に調整され、さらに必要に応じて重金属除去処理装置等を経た後、系外に排水される。
【0022】
【発明の効果】
本発明の処理方法および処理システムにおいて、ごみ焼却炉等の廃棄物処理用加熱炉から排出される排ガス中の塩化水素および硫黄酸化物は、消石灰の如きCaO源が添加されて、固体分である塩化カルシウムおよび硫酸カルシウムとなった後、水酸化ナトリウムの如きアルカリ化剤を含む水溶液と混合されて、水酸化カルシウムを含む固体分と、塩化物イオン、硫酸イオン等を含む液分とになる。このように、排ガスの浄化のために添加される消石灰等のCaO源は、最終的に、廃棄物として埋め立て処分の必要な固体分を発生させず、セメントや骨材の原料として再資源化される。
本発明は、処理過程で得られる固体分が、廃棄物とはならず再資源化されるので、廃棄物の量の削減や、廃棄物の再資源化という社会的要請に合致し、極めて有用性の高いものである。
【図面の簡単な説明】
【図1】本発明の排ガスの処理システムの一例を示す図である。
【符号の説明】
1 ごみ焼却炉
2 排ガス流通路
3 バグフィルター(固気分離手段)
4 消石灰貯留槽(CaO源供給手段)
5 排ガス流通路
6 煙突
7 混合槽
8 アルカリ化剤貯留槽
9 水貯留槽
10 濾過装置(固液分離手段)
11 中和処理槽
12 酸貯留槽
[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a treatment method and a treatment system for removing hydrogen chloride and sulfur oxide (SO x ) contained in exhaust gas discharged from a waste treatment heating furnace such as a waste incinerator and a melting furnace.
[0002]
[Prior art]
Conventionally, slaked lime is added to exhaust gas containing acidic gas such as hydrogen chloride discharged from a garbage incinerator, etc. to produce calcium chloride, etc., and this product and unreacted slaked lime are converted into bag filters, etc. There is known a technique for obtaining an exhaust gas from which acid gas is removed by collecting using a dust collecting means.
Various techniques with further improvements to this technique have been proposed.
For example, an exhaust gas treatment method that simultaneously removes acidic gases such as HCl and SO 2 and dioxins using an exhaust gas treatment agent containing calcium silicate hydrate particles, calcium hydroxide particles, and activated carbon particles has been proposed. (Patent Document 1).
[0003]
[Patent Document 1]
JP 2002-58963 (Claim 1, Claim 8 on page 2)
[0004]
[Problems to be solved by the invention]
Conventionally, solids containing calcium chloride, etc., obtained by adding slaked lime to exhaust gas from a waste incinerator, etc., are returned to the waste incinerator, etc., or have been disposed of in landfills after processing to remove heavy metals, etc. It was.
However, if the solid content including calcium chloride is returned to a waste incinerator, etc., chlorine and sulfur will circulate in the exhaust gas treatment system, and the concentration of hydrogen chloride and sulfur oxides in the exhaust gas will be reduced. There is a problem of increasing gradually.
In addition, it is not desirable to dispose of a solid content containing calcium chloride or the like under the present circumstances where it is becoming difficult to secure a landfill for waste.
Therefore, the present invention can remove hydrogen chloride and sulfur oxide contained in the exhaust gas of a waste treatment heating furnace such as a waste incinerator, and the solid content obtained in the removal treatment process as waste. It is an object of the present invention to provide a processing method and a processing system that can be recycled as useful materials without being carried out of the system.
[0005]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventor has added a CaO source such as slaked lime to exhaust gas discharged from a waste treatment heating furnace such as a waste incinerator, and then a reaction product. The solid content containing calcium salt (specifically, calcium chloride, calcium sulfate, etc.) is collected, and then this solid content is mixed with an aqueous solution containing an alkalizing agent to be contained in the solid content. After changing the calcium salt to calcium hydroxide, if this slurry is solid-liquid separated, solids that can be used as a cement raw material can be obtained, while solids that should be carried out as waste are generated. First, the present invention was completed by finding out that only the drainage treatment should be performed on the filtrate after the solid-liquid separation.
[0006]
That is, the exhaust gas treatment method for a waste treatment furnace of the present invention (Claim 1) is (A) an exhaust gas containing hydrogen chloride and sulfur oxide discharged from a waste treatment furnace such as a waste incinerator. On the other hand, after adding a CaO source such as slaked lime, solid-gas separation is performed using a dust collecting means such as a bag filter to obtain a solid component containing calcium chloride, calcium sulfate, etc., and a purified exhaust gas purification process And (B) mixing the solid content containing calcium chloride, calcium sulfate and the like obtained in step (A) with an aqueous solution containing an alkalizing agent such as sodium hydroxide to obtain a slurry having a pH of 13.0 or more. and then, the slurry was solid-liquid separation using a filter device or the like, and solid matter containing calcium hydroxide, chlorine (chloride ions) and sulfuric acid content of calcium content to obtain a liquid fraction containing the (sulfate ion) It is characterized in that it comprises a yield process.
[0007]
According to the treatment method of the present invention, the solid content containing calcium chloride, calcium sulfate and the like obtained in the exhaust gas purification step (A) is mixed with an aqueous solution containing an alkalinizing agent to become a solid content containing calcium hydroxide. Therefore, it can be used as a raw material for cement or an aggregate.
Therefore, the solid content containing calcium chloride, calcium sulfate, etc. obtained in the exhaust gas purification step (A) is returned to the waste treatment furnace such as a waste incinerator, and the hydrogen chloride and sulfur oxides in the exhaust gas are found. The problem of increased concentration never occurs. In addition, since there is no need to landfill the solids containing calcium chloride, etc., obtained in the exhaust gas purification process (A) as waste, it is a social matter that reduces the amount of waste and promotes recycling of waste. It matches the request.
In addition, since the heavy metal contained in the solid content obtained in the calcium content recovery step (B) becomes a volatile component in the cement firing furnace, it is collected using a dust collecting means provided in the flue of the exhaust gas, What is necessary is just to process separately.
[0008]
An exhaust gas treatment system for a waste treatment furnace according to the present invention (Claim 2) includes a waste treatment heating furnace such as a waste incinerator, and one end connected to the waste treatment heating furnace. Exhaust gas flow passage for circulating exhaust gas generated in a material processing heating furnace, and CaO source supply means for supplying a CaO source such as slaked lime into the exhaust gas flow passage at a predetermined point in the exhaust gas flow passage When the solid-gas separation means such as a bag filter connected to the other end of the exhaust gas flow path, the solids were collected by solid gas separator, a mixture of alkaline agent and water, pH 13.0 or more And a solid-liquid separation means such as a filtration device for solid-liquid separation of the slurry obtained in the mixing tank to obtain a solid content containing calcium hydroxide. It is a feature.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The waste gas treatment furnace waste gas treatment method according to the present invention includes: (A) after adding a CaO source to an exhaust gas containing hydrogen chloride and sulfur oxides discharged from a waste treatment furnace; Gas separation is performed to mix the solid content, the exhaust gas purification step for obtaining the purified exhaust gas, (B) the solid content obtained in the step (A), and the aqueous solution containing the alkalizing agent, followed by solid-liquid separation. Thus, a solid content containing calcium hydroxide and a calcium content recovery step for obtaining a liquid content containing chlorine content and sulfuric acid content are included.
[0010]
[(A) Exhaust gas purification process]
The exhaust gas to be treated in the present invention is exhaust gas discharged from a waste treatment heating furnace.
Here, examples of the waste treatment heating furnace include a waste incinerator and a melting furnace. The melting furnace means that dust and incineration residue generated in a waste incinerator, etc. are melted at a high temperature and then cooled and solidified to obtain a slag suitable for landfill disposal that does not elute harmful heavy metals and is reduced in volume. Refers to a heating furnace.
The exhaust gas discharged from the waste treatment furnace contains hydrogen chloride (HCl) and sulfur oxide (SO X ), which are acidic gases. For example, in a waste incinerator, combustible sulfur contained in the waste is burned to become SO 2 or the like. In addition, waste plastic such as polyvinyl chloride contained in the garbage burns to generate hydrogen chloride gas.
The exhaust gas usually contains fly ash, heavy metal, dioxin and the like in addition to acidic gas such as hydrogen chloride.
[0011]
In this step, first, a CaO source is added to the exhaust gas that is the object to be treated.
Here, examples of the CaO source include slaked lime (Ca (OH) 2 ), quick lime (CaO), calcium carbonate (CaCO 3 ), and the like.
Among them, slaked lime is preferably used in the present invention because of its high reaction efficiency and easy handling.
The CaO source reacts with hydrogen chloride and sulfur oxide in the exhaust gas to generate calcium chloride, calcium sulfate, and the like. For example, slaked lime as a CaO source reacts with hydrogen chloride and sulfur dioxide in exhaust gas as follows.
Ca (OH) 2 + 2HCl → CaCl 2 + 2H 2 O
Ca (OH) 2 + SO 2 → CaSO 3 + H 2 O
CaSO 3 + 1 / 2O 2 → CaSO 4
[0012]
In the present invention, as a method for adding the CaO source, a completely dry or semi-dry method is usually employed.
The all-dry method is a method of adding a CaO source such as slaked lime in the form of a dry solid. The all-dry type has the advantage that the addition equipment is simple, equipment costs can be reduced, and the handling and maintenance (maintenance) of the addition equipment is easy.
The semi-dry method is a method of adding a CaO source such as slaked lime in the form of a slurry. The semi-dry method has an advantage that the water in the slurry of the CaO source bumps and evaporates due to the heat of the exhaust gas, so that porous particles are generated and the reaction efficiency with hydrogen chloride or the like in the exhaust gas is high.
[0013]
The addition amount of the CaO source may be determined as appropriate according to the amounts of hydrogen chloride and sulfur oxide in the exhaust gas. Specifically, the amount of CaO source is preferably 0.8 with respect to the total equivalent of hydrogen chloride and sulfur oxide. The equivalent may be 5 to 10 times, more preferably 2 to 5 times. If the value is less than 0.5 times, the amount of unreacted hydrogen chloride and sulfur oxide remaining in the exhaust gas after the addition of the CaO source is increased, and the exhaust gas cannot be sufficiently purified. When the value exceeds 10 times, the amount of the CaO source remaining without reacting increases, which is uneconomical.
After adding a CaO source to the exhaust gas from the waste treatment furnace and causing this CaO source to react with hydrogen chloride and sulfur oxide in the exhaust gas, the exhaust gas is separated into solid and gas, A purified exhaust gas is obtained.
Here, solid-gas separation is performed using dust collecting means such as a bag filter or an electric dust collector. In particular, the bag filter is preferably used in the present invention because the concentration of hydrogen chloride or the like contained in the exhaust gas after solid-gas separation tends to be lower than that of an electric dust collector or the like.
[0014]
The solid content obtained by solid-gas separation includes calcium chloride, calcium sulfate, heavy metal chlorides, dust (for example, incineration fly ash generated in refuse incinerators, molten fly ash generated in melting furnaces, etc.), etc. .
On the other hand, the purified exhaust gas obtained by solid-gas separation contains slightly remaining harmful substances (specifically, unreacted hydrogen chloride and sulfur oxides, dioxins, heavy metals, volatile organic substances, etc.). It is a waste.
This exhaust gas is discharged into the atmosphere after, for example, a purification process using an adsorbent. Here, examples of the adsorbent include activated coke. Active coke is a type of molded activated carbon made from coal, and is an adsorbent having desulfurization / denitration performance and heavy metal or dioxin adsorption performance. When exhaust gas is allowed to pass through an active coke tower filled with active coke, harmful substances such as heavy metals and dioxins remaining in the exhaust gas are removed.
[0015]
Before adding the CaO source to the exhaust gas from the waste treatment furnace, an exhaust gas cooling step for reducing the temperature of the exhaust gas to a temperature at which resynthesis of dioxins can be suppressed may be provided.
Dioxins are decomposed at high temperatures, but are known to be re-synthesized at 300 to 400 ° C. In order to avoid that the exhaust gas is kept in this temperature range for a long time and the generation of dioxins is promoted, the exhaust gas is reduced to a temperature lower than the temperature at which dioxins are re-synthesized (eg, 200 ° C. or less) A step of rapidly decreasing the temperature can be provided.
[0016]
[(B) Calcium content recovery step]
In this step, first, the solid content obtained in the exhaust gas purification step (A) including the calcium chloride, calcium sulfate, and the like is mixed with the aqueous solution containing the alkalizing agent to obtain a slurry.
Here, the alkalizing agent is not particularly limited as long as it dissolves in water to generate hydroxide ions and raise the pH. For example, alkali metal hydroxides such as sodium hydroxide, ammonia, etc. Can be mentioned.
The blending ratio of the solid content and the aqueous solution containing the alkalizing agent is not particularly limited, but in order to efficiently generate calcium hydroxide, the mass of the solid content per liter of the aqueous solution containing the alkalizing agent is 400 g or less. It is preferable to determine so that
[0017]
The addition amount of the alkalizing agent is an amount that makes the pH of the slurry 13.0 or higher, and preferably an amount that makes the pH of the slurry 13.5 or higher.
As a method of mixing the solid content and the aqueous solution containing the alkalizing agent, for example, the solid content obtained in the step (A), the alkalizing agent, and water are separately charged into a mixing tank, Examples thereof include a method of stirring and mixing, a method in which the solid content obtained in step (A) and an aqueous solution containing a preliminarily prepared alkalizing agent are introduced into a mixing tank, and stirring and mixing.
[0018]
Next, the obtained slurry is subjected to solid-liquid separation to obtain a solid (cake) containing calcium hydroxide and a liquid containing chlorine and sulfuric acid.
Here, examples of the solid-liquid separation method include a filtration method using a filtration device such as a belt filter and a filter press, and a centrifugation method.
Since the solid content obtained by solid-liquid separation contains calcium hydroxide and the chlorine content and the like are removed, it can be recycled as a raw material for cement and aggregates. It is preferable to wash the solid content with water in an amount of 50 parts by mass or more per 100 parts by mass of the solid content because the amount of chlorine, sulfuric acid, and the like attached to the solid content is reduced.
The heavy metal contained in the solid content is volatilized in a high-temperature atmosphere in a cement firing furnace or the like, and is collected and processed by dust collecting means such as a bag filter provided in the flue.
On the other hand, the liquid obtained by solid-liquid separation contains water-soluble chlorine (chloride ions), sulfuric acid (sulfate ions), heavy metals that elute under alkaline conditions, etc. After performing sum treatment and heavy metal removal treatment, it is discharged out of the system.
[0019]
Next, the exhaust gas treatment system of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an example of an exhaust gas treatment system of the present invention.
In FIG. 1, exhaust gas generated by combustion of waste in a waste incinerator (waste treatment heating furnace) 1 flows into the exhaust gas flow passage 2 and then at a predetermined point in the middle of the exhaust gas flow passage 2. Powdered slaked lime (CaO source) is supplied from the slaked lime supply device 4. Hydrogen chloride and sulfur oxide in the exhaust gas react with the slaked lime to form calcium chloride and calcium sulfate, which are solid components.
A gas cooling device (not shown) for suppressing the resynthesis of dioxins may be provided between the waste incinerator 1 and the slaked lime supply device 4.
[0020]
Thereafter, the solid content of the exhaust gas is removed by a bag filter (solid-gas separation means) 3. This solid content contains calcium chloride, calcium sulfate, heavy metal chloride, fly ash and the like. The exhaust gas after passing through the bag filter 3 passes through the exhaust gas flow passage 5 and, if necessary, a purification device (not shown) such as an activated coke tower, and is then discharged from the chimney 6 into the atmosphere.
On the other hand, the solid content collected by the bag filter 3 is guided to the mixing tank 7. Along with the solid content from the bag filter 3, sodium hydroxide from the alkalizing agent storage tank 8 and water from the water storage tank 9 are supplied to the mixing tank 7. Then, in the mixing tank 7, the solid content, sodium hydroxide, and water are stirred and mixed by the stirring blade, and the slurry is adjusted to a predetermined pH value (for example, 13.5).
[0021]
The mixing tank 7 may be either a batch type or a continuous type, but it is desirable that the mixing tank 7 be a continuous type from the viewpoint of processing efficiency. In this case, the solid content collected by the bag filter 3 is supplied to the mixing tank 7 through a supply path such as a pipe line. Further, water and sodium hydroxide are continuously supplied from the alkalizing agent storage tank 8 and the water storage tank 9 through a supply amount adjusting valve or the like so that the slurry in the mixing tank 7 has a predetermined liquid amount and pH. It is fed into the mixing tank 7 periodically or intermittently. A pH measuring device is attached to the mixing tank 7, and the supply amount of sodium hydroxide is adjusted by the pH measuring device.
The slurry in the mixing tank 7 is guided to a filtration device (solid-liquid separation means) 10 and filtered to be a solid content (cake) containing calcium hydroxide and the like and a liquid content containing chloride ions and sulfate ions. To be separated.
Among these, solid content is used as a cement raw material etc. after washing with water. The liquid component is guided to the neutralization tank 11 and adjusted to a neutral region by an acid such as hydrochloric acid supplied from the acid storage tank 12, and further passed through a heavy metal removal treatment apparatus or the like as necessary. Drained outside.
[0022]
【The invention's effect】
In the treatment method and treatment system of the present invention, hydrogen chloride and sulfur oxides in the exhaust gas discharged from a waste treatment heating furnace such as a waste incinerator is a solid content by adding a CaO source such as slaked lime. After becoming calcium chloride and calcium sulfate, it is mixed with an aqueous solution containing an alkalizing agent such as sodium hydroxide to form a solid containing calcium hydroxide and a liquid containing chloride ions, sulfate ions and the like. In this way, CaO sources such as slaked lime added for purification of exhaust gas are finally recycled as raw materials for cement and aggregates without generating solids that require landfill disposal as waste. The
Since the solid content obtained in the treatment process is not recycled but is recycled, the present invention meets the social demands of reducing the amount of waste and recycling waste, and is extremely useful. It is highly probable.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of an exhaust gas treatment system of the present invention.
[Explanation of symbols]
1 Waste incinerator 2 Exhaust gas passage 3 Bag filter (solid-gas separation means)
4 Slaked lime storage tank (CaO source supply means)
5 exhaust gas flow passage 6 chimney 7 mixing tank 8 alkalizing agent storage tank 9 water storage tank 10 filtration device (solid-liquid separation means)
11 Neutralization tank 12 Acid storage tank

Claims (2)

(A)廃棄物処理用加熱炉から排出される塩化水素および硫黄酸化物を含む排ガスに対して、CaO源を添加した後、固気分離して、固体分と浄化された排ガスを得る排ガス浄化工程と、
(B)前記工程(A)で得られた固体分と、アルカリ化剤を含む水溶液とを混合して、pH13.0以上のスラリーを得た後、該スラリーを固液分離して、水酸化カルシウムを含む固形分と、塩素分および硫酸分を含む液分を得るカルシウム分回収工程と、
を含むことを特徴とする廃棄物処理用加熱炉の排ガスの処理方法。
(A) Exhaust gas purification process for obtaining solid gas and purified exhaust gas after adding CaO source to exhaust gas containing hydrogen chloride and sulfur oxide discharged from a waste treatment furnace When,
(B) The solid content obtained in the step (A) and an aqueous solution containing an alkalinizing agent are mixed to obtain a slurry having a pH of 13.0 or higher, and then the slurry is subjected to solid-liquid separation , followed by hydroxylation. A calcium content recovery step for obtaining a solid content containing calcium and a liquid content containing chlorine and sulfuric acid;
An exhaust gas treatment method for a waste treatment heating furnace, comprising:
廃棄物処理用加熱炉と、該廃棄物処理用加熱炉に一端が接続された、該廃棄物処理用加熱炉内で発生する排ガスを流通させるための排ガス流通路と、該排ガス流通路における所定の地点にて該排ガス流通路内にCaO源を供給するためのCaO源供給手段と、前記排ガス流通路の他端に接続された固気分離手段と、該固気分離手段で捕集された固体分、アルカリ化剤および水を混合して、pH13.0以上のスラリーを得るための混合槽と、該混合槽で得られるスラリーを固液分離して、水酸化カルシウムを含む固形分を得るための固液分離手段とを含むことを特徴とする廃棄物処理用加熱炉の排ガスの処理システム。A waste treatment heating furnace, an exhaust gas flow passage having one end connected to the waste treatment heating furnace for circulating exhaust gas generated in the waste treatment heating furnace, and a predetermined in the exhaust gas flow passage The CaO source supply means for supplying the CaO source into the exhaust gas flow passage at the point, the solid gas separation means connected to the other end of the exhaust gas flow passage, and the solid gas separation means A solid tank containing calcium hydroxide is obtained by solid-liquid separation of a mixing tank for obtaining a slurry having a pH of 13.0 or higher by mixing a solid, an alkalizing agent and water, and a slurry obtained in the mixing tank. And a solid-liquid separation means for the waste gas treatment furnace exhaust gas treatment system.
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