JP3835082B2

JP3835082B2 - Sulfuric acid production system

Info

Publication number: JP3835082B2
Application number: JP31091799A
Authority: JP
Inventors: 孝司坂本; 靖志一色
Original assignee: Sumitomo Metal Mining Co Ltd
Current assignee: Sumitomo Metal Mining Co Ltd
Priority date: 1999-11-01
Filing date: 1999-11-01
Publication date: 2006-10-18
Anticipated expiration: 2019-11-01
Also published as: JP2001130902A

Description

【０００１】
【発明の属する技術分野】
本発明は、硫酸製造システムに関し、具体的には、硫酸プラントにおける熱回収に関し、特に、濃硫酸に三酸化流黄を吸収させるとき生じる発熱の回収に関する。
【０００２】
【従来の技術】
硫酸製造システムでは、金属製錬廃ガス等の二酸化硫黄を含むガスより硫酸を製造する。
【０００３】
硫化精鉱を用いる製錬方法に、自熔炉等の熔錬炉と転炉とを用いて粗銅を得るプロセスがある。このような製錬方法では、熔錬炉で硫化精鉱を熔錬してマットとスラグとを得るときに、二酸化硫黄を含む熔錬炉廃ガスが生じる。そして、転炉でマットを熔錬し、マット中の不純物を含むスラグと、銅分を含む粗銅と、硫黄分を二酸化硫黄の形で含む転炉廃ガスを得ている。そして、熔錬炉廃ガスと転炉廃ガスとを合わせて硫酸工場で処理して、これらの廃ガス中の二酸化硫黄を硫酸として回収している。
【０００４】
硫酸工場に導入された廃ガスは温度２５０〜３５０℃の高温であるため、まず増湿塔で冷却される。その後、洗浄塔で更に冷却洗浄され、清浄化される。廃ガスは、その後湿式電気集塵機でミストを除去したのち、乾燥塔で９５％の濃硫酸と接触されて乾燥される。こうして乾燥された廃ガスは、二酸化硫黄を４〜２０体積％、酸素を８〜２０体積％の範囲で含む。
【０００５】
五酸化バナジウムを活性物質とする触媒層を設けた転化器に前記廃ガスが導入され、二酸化硫黄は三酸化硫黄に転化される。生成した三酸化硫黄は吸収塔で９８％濃硫酸と接触され、濃硫酸中に吸収される。こうして、二酸化硫黄の少なくとも９５％が硫酸として回収される。
【０００６】
近年、この転換・吸収工程は２段に分けられ、第一段で転換・吸収された後に、第二段で、残りの二酸化硫黄を更に転化・吸収する。これによって、９９．５％以上の高い二酸化硫黄の回収率が達成されている。
【０００７】
この際、吸収塔での三酸化硫黄の吸収反応は発熱反応で、多量の熱が発生する。このため、循環している硫酸を冷却水で冷却して熱を除去している。従来、吸収塔の各設備を硫酸による腐食から護るため、循環している硫酸の温度を１００℃以下に保つので、冷却水は、比較的低い温度で排水されるように制御され、廃棄されていた。
【０００８】
近年、特開昭６０−３６３１０号公報、特開昭６１−１１７１０５号公報に記載されているように、吸収塔の廃熱を回収するシステムが開発され、硫黄炊きの硫酸工場や、連続炉による非鉄金属精錬工場で実際に稼働している。
【０００９】
図６〜図８は、特開昭６０−３６３１０号公報、特開昭６１−１１７１０５号公報で開示された硫酸製造システムにおける吸収塔からの熱回収に関するものである。図６は、熱回収装置を備えた硫酸工場の例を示すフロ−図である。図７は、熱回収設備を備えた吸収塔の例を示すシステム図である。図８は、熱回収の操作サイクルと、代表的な中間吸収塔の操作サイクルとの関係の例を示すグラフで、腐食線はＳＵＳ３０４Ｌのものである。
【００１０】
図６〜図８から判るように、この硫酸製造システムは、濃度９９％以上、温度２００℃以上という濃熱硫酸を使用するため、その濃度の管理が大変重要になる。
【００１１】
この硫酸製造システムでは、吸収塔内を循環している濃硫酸の温度を２００℃付近まで上昇させ、ボイラ−を通して冷却水を蒸発させて蒸気を得るので、高温の濃熱硫酸の使用により、非常に厳しい操業条件が要求される。
【００１２】
【発明が解決しようとする課題】
上記硫酸製造システムは、操業条件が非常に厳しいので、連続的に安定した操業のできる硫黄炊きの硫酸工場や、連続炉による非鉄金属精錬工場の硫酸プラントには前記熱回収システムを適用できるが、ＰＳ転炉のようなバッチ炉をもつ一般の非鉄金属精錬工場の硫酸プラントでは操業の変動が大きく、前記熱回収システムの導入は困難であった。
【００１３】
三酸化硫黄用吸収塔の操業に影響を与える因子は、導入ガス量、導入ガスの二酸化硫黄濃度である。更に、廃ガスの乾燥工程では、大量の廃ガスを乾燥させるため、乾燥塔を循環する濃硫酸が水分を吸収し濃度の低下が生じる。この濃度を維持するために乾燥塔と吸収塔との間で交酸を行う必要があり、この交酸の量の変動も熱回収システムに大きな影響を与える。
【００１４】
図４に従来の硫酸製造システムの吸収工程に熱回収設備を設置した場合のフロ−を示す。製錬からの廃ガスは、ガス精製工程で、冷却、洗浄され、ミストコットレルでミストを除去され、その後硫酸製造工程へ送られる。硫酸製造工程では、まず乾燥塔でガス中の水分を硫酸に吸収させて除去した後、転化器でガス中のＳＯ₂をＳＯ₃に転化し吸収塔に送られる。吸収塔では、ガス中のＳＯ₃を硫酸中に吸収させて、工業用水を補給して硫酸濃度を調整し、製品硫酸を得る。この時、乾燥塔の硫酸濃度を維持するためと、乾燥塔で吸収した水分を吸収塔の補給水として使用するために、乾燥塔と吸収塔の間で交酸を行っている。また、吸収塔で熱回収を行う。
【００１５】
図４に示すような一系列の硫酸製造工程からなる従来例の吸収塔からの蒸気の発生パタ−ンを図５（縦目盛：５ｔ／ｈ、横目盛：０．５ｈ）に示す。ここに、熱回収の大きな変動が見られる。
【００１６】
吸収塔の配管には、通常は耐酸鋳鉄管を使用している。また、塔類は鉄鋼板（ＳＳ）にレンガライニングを行っている。このため、通常の操作範囲（ＥＤＦ）では、耐酸鋳鉄の腐食はほとんど０であり、塔類のレンガの腐食もない。しかし、これらの材料は濃熱硫酸には耐性がないため、ある程度の耐腐食範囲をもつステンレスを使用することになるが、熱回収設備の操作範囲は非常に重要で、この範囲を外れると、設備を猛烈な腐食環境にさらすことになる。また、注水の応答精度や濃度計の信頼性も、負荷変動が大きい場合には、大きな問題になってくる。
【００１７】
ＰＳ転炉の場合の製錬廃ガスは、ガス量及び二酸化硫黄濃度がどちらも変動するため、吸収塔の酸濃度の制御が難しくなる。また、二酸化硫黄濃度が比較的低いため、大量の廃ガスが乾燥塔へ導入されることにより、交酸量が増大し、吸収塔の酸濃度の制御が困難になる。更に、交酸により吸収塔から大量の濃熱硫酸が乾燥塔に払い出されるため、吸収塔における熱回収効率が悪く、二酸化硫黄濃度が低下すると、吸収塔で蒸気が発生しなくなる。
【００１８】
上述のように、この熱回収システムの導入には、操業の変動を小さくすることが要求されるため、ＰＳ転炉を用いた非鉄金属精錬工場においては、大変困難であった。
【００１９】
【課題を解決するための手段】
本発明の目的は、三酸化硫黄の転化・吸収工程を２系列で各々行い、１系列でのみ熱回収を行い、もう１つの系列では、熱回収を行わないで操業の負荷変動を吸収させ、熱回収設備内で乾燥塔と熱回収吸収塔の交酸を行わず、熱回収設備の乾燥塔は、通常の熱回収を行わない系列の吸収塔と交酸することにより、熱回収系の負荷変動を導入ガスの二酸化硫黄濃度のみとすることにより、効率よく安定した熱回収を行えるようにすることである。
【００２０】
すなわち、本発明の硫酸製造システムは、廃ガスから得られる三酸化硫黄を硫酸に吸収させると共に、このとき発生する吸収熱を熱交換で回収するために、三酸化硫黄の吸収を第１系列と第２系列からなる２系列で各々行い、第１系列においてのみ熱回収を行い、主として第２系列で負荷変動を吸収する。
【００２１】
第一系列の熱回収設備内で乾燥塔と熱回収吸収塔の交酸を行わず、第１系列の乾燥塔は、通常の熱回収を行わない第２系列の吸収塔と交酸することにより、第一系列の熱回収系への交酸の影響を排除し、負荷変動を導入ガスの二酸化硫黄濃度のみとする。
【００２２】
第１系列は、熱回収用吸収塔と最終吸収塔を有し、第２系列は、第１吸収塔と最終吸収塔を有し、前記第１吸収塔と各系列の乾燥塔の間で交酸を行い、硫酸の製造に必要な水の大部分を第１系列における熱回収に供給し、第１，２系列の最終吸収塔には、乾燥塔の硫酸を補給することで硫酸濃度を制御することが好ましい。
【００２３】
熱回収を行う第１系列への廃ガスの流量を一定に維持し、第２系列への廃ガスの流量を制御することが好ましい。
【００２４】
廃ガスの二酸化硫黄濃度を最終吸収塔を出たガスで希釈することが好ましい。
【００２５】
【発明の実施の形態】
本発明者らは、第１系列と第２系列の２系列で三酸化硫黄を各々転化・吸収する設備を用意し、第１系列の設備では上記熱回収を行い、かつ、第２系列では熱回収を行わないで負荷変動を吸収するようにして、上記課題を解決できることを発見した。
【００２６】
熱回収する第１系列内では、乾燥塔と吸収塔とで硫酸の交酸を行わない。そして、熱回収する第１系列の乾燥塔と、熱回収を行わない第２系列の吸収塔とで交酸することにより、熱回収する第１系列の負荷変動を導入ガスの二酸化硫黄濃度のみとする。これにより安定した熱回収を行えることが見出された。
【００２７】
また、ＰＳ転炉で吹錬を行っていない場合は、ガス量が非常に少なく、かつ二酸化硫黄濃度が高いため、転化器触媒の温度が上がりすぎるので、一般には希釈空気を導入して二酸化硫黄の濃度を下げている。この場合には、大量の希釈空気が必要となり、二酸化硫黄の量に比べて大量の水分が入ってくるため、交酸の量が増大し、かつ、水バランスがとれなくなるおそれがある。これについては、希釈空気の代わりに、最終吸収塔から出た水分のないガスを使用することで解決できることを見いだした。更に、従来、最終吸収塔の硫酸の濃度制御は水を補加して行っていたが、この代りに乾燥塔から出た硫酸を利用し、この硫酸を制御することで、熱回収側の吸収塔で最大限の熱を回収することが可能になった。
【００２８】
図１に本発明を適用した場合の硫酸製造システムのフロ−を示す。硫酸製造工程が二つの系列からなり、ガスは分配され、かつ熱回収する第１系列では、吸収塔と乾燥塔との間で交酸を行わず、熱回収する第１系列の乾燥塔は、熱回収を行わない第２系列の吸収塔との間で交酸する。なお、この図の実施例では第１系列と第２系列の両方に乾燥塔（ガス乾燥）を設けているが、乾燥塔を１基にして、乾燥塔までを１系列にしてそれ以降を２系列にしてもよい。また、この図での実施例ではテ−ルガス処理工程を第１系列と第２系列に各々設けているが、１系列にまとめてもよい。
【００２９】
図２に本発明による硫酸製造工程のダイヤグラムを示す。第１系列では、熱回収を行う吸収塔（ＨＲＴ）および熱回収を行わない吸収塔（２ＡＴ）を導入し、第２系列は熱回収を行わない吸収塔（１ＡＴ、２ＡＴ）を設ける。第２系列にて発生した熱はクーラーで冷却水によって冷却されて廃棄される。ここでは、＃１ブロワ−がガス量を一定になるように制御されるため、第１系列には常に一定のガス量が送り込まれる。一方、第２系列は＃２ブロワ−をガス流量で制御せず、硫酸工場入り口の圧力で制御するためガス量が常に変動する。
【００３０】
第１系列における交酸は、第１系列の乾燥塔（１ＤＴ）と第２系列の吸収塔（１ＡＴ）とで行い、第１系列の熱回収用吸収塔（ＨＲＴ）では行わない。更に、乾燥塔の水分を最大限利用して系内水のバランスをとるために、最終吸収塔（２ＡＴ）は、従来では工業用水で硫酸濃度を調整していたが、本発明では第１系列、第２系列ともに乾燥塔（２ＤＴ）の硫酸で調整する。これにより、第１系列に分配されるガスの量を最大にすることができる。
【００３１】
ガス量を一定にすることによって転化器での反応が安定するため、ＳＯ₂濃度を高く保つことができ、かつ熱回収用吸収塔（ＨＲＴ）で交酸を行わないことによって、従来では熱回収される吸収塔と乾燥塔との間の交酸のために乾燥塔に払い出されていた高温硫酸がなくなる。このため、熱回収用吸収塔（ＨＲＴ）での熱回収効率が向上し、硫酸工程が２系列であり、１系列だけにしか熱回収用吸収塔（ＨＲＴ）を設定しないにもかかわらず、従来の１系列硫酸製造システムと、ほぼ同じ熱回収を行うことができる。
【００３２】
ＰＳ転炉を使用した非鉄金属精錬では、ＰＳ転炉を操業せずに自熔炉だけ操業している時間が出現するが、この時ガス量が少なくＳＯ₂濃度の濃いガスが硫酸工場に導入される。この際、転化器の触媒温度が上昇してしまうために、大量の希釈空気をいれてＳＯ₂濃度を下げなければならない。しかし、この場合には、ガス量が少なくＳＯ₂濃度が低いため、第２系列だけでは第１系列の乾燥塔（１ＤＴ）の水分を吸収しきれなくなり、水バランスがくずれてしまう。そこで、このような自熔炉のみの操業時には、希釈用の空気の代わりに第２系列の最終吸収塔（２ＡＴ）を出たテ−ルガスを使用することで、余分な水分が系列内に入らなくなり、水バランスを維持することができる。
【００３３】
【実施例】
図２の硫酸製造システムにおいて、第１系列の排ガス量を一定値１００ｋＮｍ³／Ｈに維持し、第２系列の排ガス量を９０〜１７０ｋＮｍ³／Ｈで変動させた。全ガス量は２５０ｋＮｍ³／Ｈであった（ＳＯ₂１３体積％）。交酸量は、１ＤＴ、２ＤＴから１ＡＴへ３．４ｔ／ｍｉｎ、各２ＡＴへ各々０．３ｔ／ｍｉｎであった。注水量は、ＨＲＴへ０．１７ｔ／ｍｉｎ、１ＡＴへ０．０７ｔ／ｍｉｎであった。
【００３４】
図３に本発明の実施例による熱回収吸収塔からの蒸気の発生パタ−ン（縦目盛：５ｔ／ｈ、横目盛：０．５ｈ）を示す。図５の発生パターンに比較して、本発明の方法により、安定した蒸気回収が行われることがわかる。このことは、熱回収設備への負荷変動が少なく、より安定した硫酸の濃度管理が行えることを示している。更に、熱回収用吸収塔へのガス量が固定され、乾燥塔との交酸も無くなったことにより、熱回収用吸収塔の硫酸の濃度はＳＯ₂濃度のみに依存することになるため、必要な注水量をＳＯ₂濃度から計算するこができる。これによって、常時硫酸濃度計の監視が可能となる。更に、注水量をＳＯ₂濃度によりフィ−ドフォワ−ド制御することも可能であり、常に安定した濃度制御を実現できる。
【００３５】
【発明の効果】
本発明により、熱回収システムの変動が少なく安定した操業が可能になるため、ＰＳ転炉を有する製錬所に熱回収用吸収塔を導入することが可能になる。
【図面の簡単な説明】
【図１】本発明を適用した場合の硫酸製造システムのフロ−を示す。
【図２】本発明による硫酸製造工程のダイヤグラムを示す。
【図３】本発明の実施例による熱回収吸収塔からの蒸気の発生パタ−ンを示す。
【図４】従来の硫酸製造システムの吸収工程に熱回収設備を設置した場合のフロ−を示す。
【図５】図４に示す一系列の硫酸製造工程からなる従来例の熱回収用吸収塔からの蒸気の発生パタ−ン図である。
【図６】熱回収装置を備えた硫酸工場の例を示すフロ−図である。
【図７】熱回収設備を備えた吸収塔の例を示すシステム図である。
【図８】熱回収の操作サイクルと、代表的な中間吸収塔の操作サイクルとの関係の例を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sulfuric acid production system, and more particularly to heat recovery in a sulfuric acid plant, and more particularly, to recovery of heat generated when concentrated trisulfate absorbs yellow trioxide.
[0002]
[Prior art]
In the sulfuric acid production system, sulfuric acid is produced from a gas containing sulfur dioxide such as metal smelting waste gas.
[0003]
As a smelting method using sulfide concentrate, there is a process of obtaining crude copper using a smelting furnace such as a self-smelting furnace and a converter. In such a smelting method, when a sulfide concentrate is smelted in a smelting furnace to obtain mats and slag, smelter waste gas containing sulfur dioxide is generated. Then, the mat is smelted by a converter, and a converter waste gas containing slag containing impurities in the mat, crude copper containing copper, and sulfur in the form of sulfur dioxide is obtained. Then, the smelter waste gas and the converter waste gas are combined and processed in a sulfuric acid factory, and sulfur dioxide in these waste gases is recovered as sulfuric acid.
[0004]
Since the waste gas introduced into the sulfuric acid factory has a high temperature of 250 to 350 ° C., it is first cooled in a humidification tower. Thereafter, it is further cooled and washed in a washing tower to be cleaned. The waste gas is then dried by contacting with 95% concentrated sulfuric acid in a drying tower after removing mist with a wet electrostatic precipitator. The waste gas thus dried contains 4 to 20% by volume of sulfur dioxide and 8 to 20% by volume of oxygen.
[0005]
The waste gas is introduced into a converter provided with a catalyst layer containing vanadium pentoxide as an active substance, and sulfur dioxide is converted into sulfur trioxide. The produced sulfur trioxide is contacted with 98% concentrated sulfuric acid in the absorption tower and absorbed in concentrated sulfuric acid. Thus, at least 95% of the sulfur dioxide is recovered as sulfuric acid.
[0006]
In recent years, this conversion / absorption process is divided into two stages. After the conversion / absorption in the first stage, the remaining sulfur dioxide is further converted / absorbed in the second stage. As a result, a high sulfur dioxide recovery rate of 99.5% or more has been achieved.
[0007]
At this time, the absorption reaction of sulfur trioxide in the absorption tower is an exothermic reaction, and a large amount of heat is generated. For this reason, the circulating sulfuric acid is cooled with cooling water to remove heat. Conventionally, in order to protect each facility of the absorption tower from corrosion by sulfuric acid, the temperature of the circulating sulfuric acid is kept at 100 ° C. or lower, so the cooling water is controlled to be drained at a relatively low temperature and discarded. It was.
[0008]
In recent years, as described in JP-A-60-36310 and JP-A-61-117105, a system for recovering waste heat from an absorption tower has been developed. It is actually operating at a non-ferrous metal refining plant.
[0009]
6 to 8 relate to heat recovery from an absorption tower in a sulfuric acid production system disclosed in Japanese Patent Application Laid-Open Nos. 60-36310 and 61-117105. FIG. 6 is a flowchart showing an example of a sulfuric acid factory equipped with a heat recovery device. FIG. 7 is a system diagram showing an example of an absorption tower equipped with a heat recovery facility. FIG. 8 is a graph showing an example of the relationship between the operation cycle of heat recovery and the operation cycle of a typical intermediate absorption tower, and the corrosion line is that of SUS304L.
[0010]
As can be seen from FIGS. 6 to 8, since this sulfuric acid production system uses concentrated hot sulfuric acid having a concentration of 99% or more and a temperature of 200 ° C. or more, the management of the concentration is very important.
[0011]
In this sulfuric acid production system, the temperature of concentrated sulfuric acid circulating in the absorption tower is raised to around 200 ° C. and the cooling water is evaporated through a boiler to obtain steam. Severe operating conditions are required.
[0012]
[Problems to be solved by the invention]
Since the sulfuric acid production system has very severe operating conditions, the heat recovery system can be applied to a sulfuric acid factory for sulfur cooking that can be operated stably and a sulfuric acid plant for a non-ferrous metal refining factory using a continuous furnace, In a sulfuric acid plant of a general non-ferrous metal refining plant having a batch furnace such as a PS converter, operation fluctuations are large, and it is difficult to introduce the heat recovery system.
[0013]
Factors affecting the operation of the sulfur trioxide absorber are the amount of introduced gas and the sulfur dioxide concentration of the introduced gas. Further, in the waste gas drying step, a large amount of waste gas is dried, so that concentrated sulfuric acid circulating in the drying tower absorbs moisture and lowers the concentration. In order to maintain this concentration, it is necessary to perform acidification between the drying tower and the absorption tower, and fluctuations in the amount of this acid also greatly affect the heat recovery system.
[0014]
FIG. 4 shows a flow when heat recovery equipment is installed in the absorption process of a conventional sulfuric acid production system. Waste gas from smelting is cooled and washed in a gas purification process, mist is removed by a mist cot rel, and then sent to a sulfuric acid production process. In the sulfuric acid production process, first, moisture in the gas is absorbed and removed by sulfuric acid in the drying tower, and then SO ₂ in the gas is converted to SO ₃ by a converter and sent to the absorption tower. In the absorption tower, SO ₃ in the gas is absorbed in sulfuric acid, industrial water is supplied to adjust the sulfuric acid concentration, and product sulfuric acid is obtained. At this time, in order to maintain the sulfuric acid concentration in the drying tower and to use the water absorbed in the drying tower as make-up water for the absorption tower, the cross acid is performed between the drying tower and the absorption tower. In addition, heat recovery is performed in an absorption tower.
[0015]
FIG. 5 (vertical scale: 5 t / h, horizontal scale: 0.5 h) shows the steam generation pattern from the conventional absorption tower comprising a series of sulfuric acid production processes as shown in FIG. Here, a large variation in heat recovery is seen.
[0016]
Usually, acid-resistant cast iron pipe is used for the piping of the absorption tower. In addition, towers perform brick lining on steel sheets (SS). For this reason, in the normal operating range (EDF), the corrosion resistance of acid-resistant cast iron is almost zero and there is no corrosion of tower bricks. However, because these materials are not resistant to concentrated hot sulfuric acid, stainless steel with a certain corrosion resistance range will be used, but the operating range of the heat recovery equipment is very important. The equipment will be exposed to a severe corrosive environment. In addition, the response accuracy of water injection and the reliability of the densitometer are also serious problems when the load fluctuation is large.
[0017]
Since the smelting waste gas in the case of the PS converter varies in both gas amount and sulfur dioxide concentration, it becomes difficult to control the acid concentration of the absorption tower. Further, since the sulfur dioxide concentration is relatively low, a large amount of waste gas is introduced into the drying tower, so that the amount of acid is increased and it becomes difficult to control the acid concentration of the absorption tower. Furthermore, since a large amount of concentrated sulfuric acid is discharged from the absorption tower to the drying tower by the acid, the heat recovery efficiency in the absorption tower is poor, and when the sulfur dioxide concentration is reduced, no steam is generated in the absorption tower.
[0018]
As described above, since the introduction of this heat recovery system is required to reduce fluctuations in operation, it has been very difficult in a nonferrous metal smelting plant using a PS converter.
[0019]
[Means for Solving the Problems]
The object of the present invention is to perform the sulfur trioxide conversion / absorption process in two series , respectively , to perform heat recovery only in one series, and in the other series, to absorb fluctuations in operation load without performing heat recovery, In the heat recovery facility, the drying tower and the heat recovery absorption tower are not subjected to acid exchange, and the heat recovery equipment drying tower is subjected to acid exchange with a series of absorption towers that do not perform normal heat recovery. By making the fluctuation only the sulfur dioxide concentration of the introduced gas, it is possible to perform efficient and stable heat recovery.
[0020]
That is, in the sulfuric acid production system of the present invention, sulfur trioxide obtained from waste gas is absorbed into sulfuric acid, and in order to recover the absorbed heat generated at this time by heat exchange, the absorption of sulfur trioxide is the first series. Each of the two series is performed in the second series, heat recovery is performed only in the first series, and load fluctuation is mainly absorbed in the second series.
[0021]
In the first series of heat recovery equipment, the drying tower and the heat recovery absorption tower are not acidified, and the first series of drying towers is acidified with the second series of absorption towers that do not perform normal heat recovery. In this case, the influence of acetic acid on the first heat recovery system is eliminated, and the load fluctuation is limited to the sulfur dioxide concentration of the introduced gas.
[0022]
The first series has a heat recovery absorption tower and a final absorption tower, and the second series has a first absorption tower and a final absorption tower, which are exchanged between the first absorption tower and the drying tower of each series. Acid is supplied and most of the water required for sulfuric acid production is supplied to heat recovery in the first series, and the sulfuric acid concentration is controlled by supplying sulfuric acid from the drying tower to the first and second series of final absorption towers. It is preferable to do.
[0023]
It is preferable to maintain a constant flow rate of the waste gas to the first series that performs heat recovery and control the flow rate of the waste gas to the second series.
[0024]
It is preferable to dilute the sulfur dioxide concentration of the waste gas with the gas leaving the final absorption tower.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
The present inventors prepare facilities for converting and absorbing sulfur trioxide in two systems of the first system and the second system, respectively, recovering the heat in the first system, and heat in the second system. It was discovered that the above problem can be solved by absorbing load fluctuations without performing recovery.
[0026]
In the first series in which heat is recovered, sulfuric acid is not acidified between the drying tower and the absorption tower. Then, the first series of drying towers for heat recovery and the second series of absorption towers that do not perform heat recovery are cross-acidified, so that the first series of load fluctuations for heat recovery are changed to only the sulfur dioxide concentration of the introduced gas. To do. It has been found that this enables stable heat recovery.
[0027]
In addition, when blowing is not performed in a PS converter, the amount of gas is very small and the concentration of sulfur dioxide is high, so the temperature of the converter catalyst is too high. In general, diluted air is introduced to introduce sulfur dioxide. The concentration of is lowered. In this case, a large amount of diluted air is required, and a large amount of water enters as compared with the amount of sulfur dioxide. Therefore, the amount of acid is increased and the water balance may not be achieved. It has been found that this can be solved by using a moisture-free gas from the final absorption tower instead of dilution air. Furthermore, conventionally, the concentration of sulfuric acid in the final absorption tower was controlled by adding water, but instead of using sulfuric acid from the drying tower and controlling this sulfuric acid, absorption on the heat recovery side was performed. It was possible to recover the maximum heat in the tower.
[0028]
FIG. 1 shows a flow of a sulfuric acid production system when the present invention is applied. In the first series in which the sulfuric acid production process consists of two series , the gas is distributed , and heat is recovered, no acid is exchanged between the absorption tower and the drying tower. Acidification is performed with a second series of absorption towers that do not perform heat recovery. In the embodiment of this figure, drying towers (gas drying) are provided in both the first line and the second line. However, one drying tower and one line from the drying tower to one line are used. It may be a series. Further, in the embodiment shown in this figure, the tail gas processing steps are provided in the first series and the second series, respectively, but may be combined into one series.
[0029]
FIG. 2 shows a diagram of the sulfuric acid production process according to the present invention. In the first series, an absorption tower (HRT) that performs heat recovery and an absorption tower (2AT) that does not perform heat recovery are introduced, and in the second series, absorption towers (1AT and 2AT) that do not perform heat recovery are provided. The heat generated in the second series is cooled by cooling water with a cooler and discarded. Here, since the # 1 blower is controlled so that the gas amount becomes constant, a constant gas amount is always fed into the first series. On the other hand, in the second series, the # 2 blower is not controlled by the gas flow rate, but is controlled by the pressure at the sulfuric acid factory entrance, so that the gas amount always fluctuates.
[0030]
The cross acid in the first series is performed in the first series drying tower (1DT) and the second series absorption tower (1AT), and not in the first series heat recovery absorption tower (HRT). Furthermore, in order to balance the water in the system by maximally using the moisture of the drying tower, the final absorption tower (2AT) has conventionally adjusted the sulfuric acid concentration with industrial water. The second series is adjusted with sulfuric acid in the drying tower (2DT). As a result, the amount of gas distributed to the first series can be maximized.
[0031]
Since the reaction in the converter is stabilized by keeping the gas amount constant, the SO ₂ concentration can be kept high, and heat recovery has conventionally been achieved by not performing the acid exchange in the heat recovery absorption tower (HRT). high temperature sulfuric acid which has been paid out to a drying tower for交酸between the absorption tower and the drying tower is eliminated by. For this reason, the heat recovery efficiency in the heat recovery absorption tower (HRT) is improved, the sulfuric acid process has two lines, and the heat recovery absorption tower (HRT) is set only in one line. The heat recovery can be performed in substantially the same manner as the one-series sulfuric acid production system.
[0032]
In non-ferrous metal refining using a PS converter, there is a time when only the auto-smelting furnace is operated without operating the PS converter. At this time, a gas with a small amount of gas and a _high concentration of SO ₂ is introduced into the sulfuric acid factory. The At this time, since the catalyst temperature of the converter increases, a large amount of diluted air must be introduced to lower the SO ₂ concentration. However, in this case, since the amount of gas is small and the SO ₂ concentration is low, the water in the first series drying tower (1DT) cannot be absorbed by the second series alone, and the water balance is lost. Therefore, at the time of operation of only such a flash furnace, the use of tail gas that has exited the second absorption tower (2AT) in place of dilution air prevents excess moisture from entering the system. Can maintain water balance.
[0033]
【Example】
In the sulfuric acid production system of FIG. 2, the first series exhaust gas amount was maintained at a constant value of 100 kNm ³ / H, and the second series exhaust gas amount was varied from 90 to 170 kNm ³ / H. The total gas amount was 250 kNm ³ / H (SO ₂ 13% by volume). The acidity was 3.4 t / min from 1DT, 2DT to 1AT, and 0.3 t / min to each 2AT. The amount of water injection was 0.17 t / min for HRT and 0.07 t / min for 1AT.
[0034]
FIG. 3 shows steam generation patterns (vertical scale: 5 t / h, horizontal scale: 0.5 h) from the heat recovery absorption tower according to the embodiment of the present invention. Compared with the generation pattern of FIG. 5, it can be seen that stable vapor recovery is performed by the method of the present invention. This indicates that there is little fluctuation in the load on the heat recovery equipment, and the sulfuric acid concentration can be controlled more stably. In addition, the amount of gas to the heat recovery absorption tower is fixed, and there is no cross acid with the drying tower, so the concentration of sulfuric acid in the heat recovery absorption tower depends only on the SO ₂ concentration. The amount of water injection can be calculated from the SO ₂ concentration. This makes it possible to constantly monitor the sulfuric acid concentration meter. Furthermore, it is also possible to feed forward control the amount of water injected by the SO ₂ concentration, so that stable concentration control can always be realized.
[0035]
【The invention's effect】
According to the present invention, since the heat recovery system can be stably operated with less fluctuation, it is possible to introduce a heat recovery absorption tower into a smelter having a PS converter.
[Brief description of the drawings]
FIG. 1 shows the flow of a sulfuric acid production system when the present invention is applied.
FIG. 2 shows a diagram of a sulfuric acid production process according to the present invention.
FIG. 3 shows a steam generation pattern from a heat recovery absorption tower according to an embodiment of the present invention.
FIG. 4 shows a flow when heat recovery equipment is installed in an absorption process of a conventional sulfuric acid production system.
FIG. 5 is a steam generation pattern diagram of a conventional heat recovery absorption tower comprising a series of sulfuric acid production steps shown in FIG. 4;
FIG. 6 is a flow diagram showing an example of a sulfuric acid factory equipped with a heat recovery device.
FIG. 7 is a system diagram showing an example of an absorption tower equipped with heat recovery equipment.
FIG. 8 is a graph showing an example of a relationship between a heat recovery operation cycle and a typical intermediate absorption tower operation cycle.

Claims

It has a waste gas drying tower and a sulfur trioxide absorption tower, and sulfur trioxide obtained from the waste gas discharged from the drying tower is absorbed by sulfuric acid in the absorption tower, and the heat generated at this time is recovered by heat exchange. in sulfuric acid production system, perform each conversion and absorption of sulfur trioxide in the first stream and second stream, performs a heat recovery only in the first series, sulfuric acid, characterized in that to absorb the load variation in the second sequence Manufacturing system.

The first series has an absorption tower for heat recovery and a final absorption tower, and the second series has a first absorption tower and a final absorption tower, which are exchanged between the first absorption tower and the drying tower of each series. Acid is supplied and most of the water required for sulfuric acid production is supplied to heat recovery in the first series, and the final absorption towers in the first and second series are replenished with sulfuric acid from the drying tower to control the sulfuric acid concentration. The sulfuric acid production system according to claim 1.

2. The sulfuric acid production system according to claim 1, wherein the flow rate of the waste gas to the first series for heat recovery is kept constant, and the flow rate of the waste gas to the second series is controlled.

The sulfuric acid production system according to claim 1, wherein the sulfur dioxide concentration of the waste gas is diluted with the gas exiting the final absorption tower.

Sulfur trioxide obtained from smelting exhaust gas is absorbed into sulfuric acid, and this heat is transferred to other fluids with a heat exchanger. It has an absorption facility, and one of the sulfur trioxide conversion / absorption facilities is equipped with the above heat recovery facility, and the other series of sulfur trioxide conversion / absorption facilities does not perform normal heat recovery. introducing facilities, in the heat recovery equipment without交酸drying tower sulfate and the heat recovery absorption tower sulfate, drying tower sulfate heat recovery equipment is交酸the absorption tower of the sequence is not performed ordinary heat recovery Thus, the sulfuric acid production system is characterized in that stable heat recovery is performed by limiting the load fluctuation of the heat recovery system to only the sulfur dioxide concentration of the introduced gas.