JPS6353142B2 - - Google Patents
Info
- Publication number
- JPS6353142B2 JPS6353142B2 JP7039279A JP7039279A JPS6353142B2 JP S6353142 B2 JPS6353142 B2 JP S6353142B2 JP 7039279 A JP7039279 A JP 7039279A JP 7039279 A JP7039279 A JP 7039279A JP S6353142 B2 JPS6353142 B2 JP S6353142B2
- Authority
- JP
- Japan
- Prior art keywords
- gypsum
- type hemihydrate
- hemihydrate gypsum
- converter
- slurry
- 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
- ZOMBKNNSYQHRCA-UHFFFAOYSA-J calcium sulfate hemihydrate Chemical compound O.[Ca+2].[Ca+2].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O ZOMBKNNSYQHRCA-UHFFFAOYSA-J 0.000 claims description 88
- 239000013078 crystal Substances 0.000 claims description 68
- 239000010440 gypsum Substances 0.000 claims description 68
- 229910052602 gypsum Inorganic materials 0.000 claims description 68
- CSNNHWWHGAXBCP-UHFFFAOYSA-L Magnesium sulfate Chemical compound [Mg+2].[O-][S+2]([O-])([O-])[O-] CSNNHWWHGAXBCP-UHFFFAOYSA-L 0.000 claims description 44
- 239000002002 slurry Substances 0.000 claims description 41
- 150000004683 dihydrates Chemical class 0.000 claims description 33
- 229910052943 magnesium sulfate Inorganic materials 0.000 claims description 22
- 235000019341 magnesium sulphate Nutrition 0.000 claims description 22
- 238000004519 manufacturing process Methods 0.000 claims description 21
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims description 8
- 238000006477 desulfuration reaction Methods 0.000 claims description 8
- 230000023556 desulfurization Effects 0.000 claims description 8
- 239000003546 flue gas Substances 0.000 claims description 8
- 230000007704 transition Effects 0.000 claims description 8
- 230000009466 transformation Effects 0.000 claims description 6
- 238000001035 drying Methods 0.000 claims description 5
- 239000012452 mother liquor Substances 0.000 claims description 4
- 230000003647 oxidation Effects 0.000 claims description 2
- 238000007254 oxidation reaction Methods 0.000 claims description 2
- 238000010298 pulverizing process Methods 0.000 claims 1
- 238000000034 method Methods 0.000 description 20
- 239000003607 modifier Substances 0.000 description 18
- 239000007788 liquid Substances 0.000 description 14
- 239000000047 product Substances 0.000 description 10
- 230000000694 effects Effects 0.000 description 8
- 239000007864 aqueous solution Substances 0.000 description 7
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 description 7
- 238000006243 chemical reaction Methods 0.000 description 6
- 238000012546 transfer Methods 0.000 description 5
- 238000010438 heat treatment Methods 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 239000006227 byproduct Substances 0.000 description 3
- 239000003795 chemical substances by application Substances 0.000 description 3
- 238000010335 hydrothermal treatment Methods 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 230000002195 synergetic effect Effects 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 150000001990 dicarboxylic acid derivatives Chemical class 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 230000005484 gravity Effects 0.000 description 2
- 230000036571 hydration Effects 0.000 description 2
- 238000006703 hydration reaction Methods 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 150000003464 sulfur compounds Chemical class 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 238000005979 thermal decomposition reaction Methods 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- 238000004065 wastewater treatment Methods 0.000 description 2
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000003915 air pollution Methods 0.000 description 1
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 description 1
- 229910052921 ammonium sulfate Inorganic materials 0.000 description 1
- 235000011130 ammonium sulphate Nutrition 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 238000007664 blowing Methods 0.000 description 1
- GBAOBIBJACZTNA-UHFFFAOYSA-L calcium sulfite Chemical compound [Ca+2].[O-]S([O-])=O GBAOBIBJACZTNA-UHFFFAOYSA-L 0.000 description 1
- 235000010261 calcium sulphite Nutrition 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 238000010924 continuous production Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 239000013505 freshwater Substances 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000009499 grossing Methods 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 238000007562 laser obscuration time method Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 230000000737 periodic effect Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 239000000779 smoke Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical class S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 description 1
- 229910052815 sulfur oxide Inorganic materials 0.000 description 1
Description
〔産業上の利用分野〕
本発明は、天然石こうまたは化学石こうなどの
２水石こうのスラリーに硫酸マグネシウムを存在
させ、該スラリーを加圧下で水熱処理することに
より、良好な柱状結晶形を持つα型半水石こうを
製造する方法に関するものである。
〔従来の技術〕
最近の大気汚染の規制の強化に伴い、燃料中の
硫黄化合物の燃焼により発生する排ガス中の硫黄
化合物を除去する排煙脱硫プロセスはきわめて多
くの方式が開発されており、脱硫副生物として硫
酸、硫黄、硫安、石こうなどが回収されている。
このうち、石こうは化学的に安定で二次公害のお
それがなくまた建築・土木材料等として利用価値
が高いので副生品として最も望ましいと考えられ
ており、石こうを副生品として回収する排煙脱硫
装置が最も多く普及している。
石こう回収排煙脱硫プロセスにおいては、排ガ
ス中の硫黄酸化物の吸収により一次副生物として
生成する亜硫酸カルシウムスラリーを酸素含有ガ
ス（一般には空気）の吹込みにより酸化する方法
が一般的であり、この場合、通常の条件下では２
水石こうが得られる。
一方、２水石こうに水熱処理を施しα型半水石
こうを製造する方法は、加圧水溶液法、加圧水蒸
気法、および常圧水溶液法等が代表的であるが、
従来の技術では生産コストが高いとか生産能率が
良くない等の欠点がある。このため、α型半水石
こうは２水石こうを焼成して生成されるβ型半水
石こう（焼石こうとも称せられる）に比して良質
できわめて高強度を呈する水和硬化体を形成する
にもかかわらず、生産量もわずかであり特殊な用
途にしか使用されていない。
最近の大型排煙脱硫装置の普及に伴い排煙脱硫
石こう（通常は２水石こう）が多量に生成される
ようになつたため、排煙脱硫石こうをより高品質
にして利用範囲を広げる努力が払われるようにな
つた。この結果、２水石こうを効率よくかつ安価
にα型半水石こうに転化させることが注目され始
めた。２水石こうのα型半水石こうの転移方法
は、すでにのべた如く加圧水溶液、加圧水蒸気法
および常圧水溶液法が代表的であるが、大量生産
を指向する工業的α型半水石こう製造法として
は、加圧水溶液法が一般的である。加圧水溶液法
は２水石こう粉末に加えてスラリーとし、オート
クレーブ等の圧力容器内で撹拌しながら加圧水熱
処理を施す方法であり、生成されるα型半水石こ
うの結晶形を板状または短柱状とするために、ジ
カルボン酸塩等の有機質媒晶剤が添加されてい
た。これは一般にα型半水石こうは高強度を呈す
る水和硬化体を得るために、板状または短柱状に
よく成長した立方体に近い形状を持つことが要求
されるためである。
通常、２水石こうスラリーの転移処理時に、ジ
カルボン酸塩等の有機媒晶剤を添加する方法が一
般的である。
〔発明が解決しようとする問題点〕
しかしながら、２水石こうのα型半水石こうへ
の転移を工業的大規模に実施する際には、媒晶剤
としてジカルボン酸塩等の有機物を使用すること
は次に示す種々の問題点がある。
まず第１に、通常媒晶剤の種類によつて最適濃
度条件領域が存在するが、有機媒晶剤濃度の計
測・監視と適正濃度の保持がきわめて困難なこと
である。２水石こうからα型半水石こうへの転移
は、通常105℃以上の高温でかつ加圧下のもとに
実施されており、添加した媒晶剤はこのような条
件下では熱分解を起こしやすい。また転移により
生成したα型半水石こうおよびα型半水石こうの
含液中に媒晶剤が含まれ、転化器外に持ち去られ
ることもある。したがつて、短柱状または板状の
α型半水石こうを円滑に生成させるためには、媒
晶剤濃度を常時正確に測定しかつ常に適正濃度に
制御することが不可欠である。しかしながら、実
際の工業的規模のプロセスでは、有機媒晶剤濃度
の検出方法の困難さより考慮すれば、媒晶剤の濃
度を適正に制御することはきわめて難しい。
第２に、媒晶剤を２水石こうスラリーに添加し
加熱処理を施すと、型無水石こうが生成しやす
くなる。型無水石こうの形状および大きさは、
媒晶剤濃度および転移時の温度などの生成条件に
よつて異なるが、通常は微細な粒状、針状および
扁平な短冊状などであり、水和硬化体の強度が小
さくなり、α型半水石こうの品質の低下の原因と
なる。
第３に、排液の処理の問題がある。有機媒晶剤
を使用するα型半水石こうの製造プロセスでは媒
晶剤の熱分解生成物が濃縮または蓄積された液お
よび定期点検時の滞留液等の廃液が発生するが、
この廃液中の媒晶剤または媒晶剤の分解生成物は
BODおよびCODを有するため充分な廃水処理を
施さなければ放流できない。
このように、大型の工業的規模のα型半水石こ
うの製造プロセスにおいて、有機媒晶剤を使用す
る方式はきわめて多くの問題がある。したがつ
て、有機物である媒晶剤を添加しないで、かつ密
度が大きくかつ結晶形が良好なα型半水石こうを
多量にかつ安価に生成する大型の工業的プロセス
が要望されている。
本発明者らは、上記の従来の問題点を解消し、
媒晶剤を添加せずに結晶形が良好で、かつ嵩比重
の大きいα型半水石こうを製造する方法について
鋭意研究を重ねた結果、２水石こうスラリーを加
圧下で水熱処理をしα型半水石こうを製造する際
に、硫酸マグネシウムの存在下で操作条件を適当
に選ぶことにより、２水石こうの転移によるα型
半水石こうの生成速度を、すでに転化器内に存在
するα型半水石こう結晶における結晶生成速度に
等しくするか、または結晶成長速度より小さくす
るように調節することにより、該α型半水石こう
結晶を単結晶的に遂次大きく成長させ、該α型半
水石こう結晶の長軸方向の長さが約150〜1500μ、
結晶の直径が約30〜100μで、Ｌ／Ｄ（結晶の長
さ／結晶の径）が５〜15である大きなα型半水石
こうの柱状結晶を生成させることができることを
知見した。また該α型半水石こう結晶では、機械
的に粉砕することにより短柱状の嵩比重が大き
く、かつ結晶形の良好なα型半水石こうを容易に
製造することができた。なお上記で「すでに転化
器内に存在するα型半水石こう結晶」と述べた結
晶成長の核となるα型半水石こうとしては、必ら
ずしも転移開始前に予め柱状結晶のα型半水石こ
うを種晶して添加する必要はなく、２水石こうス
ラリーの加熱処理の初期に生成されるα型半水石
こうを種晶とすることができた。
一般に、α型半水石こう製造においては、結晶
の形と大きさをコントロールすることが重要であ
る。結晶の大きさを決める可能性のあるフアクタ
ーとしては、温度、溶液組成など数多くのものが
考えられる。
本発明者らは実験の結果、そのなかでも転移速
度、すなわち一定時間に生成する石こうの量が大
きな支配力を持つことを見出した。
連続法の場合、転移速度は原料供給速度、すな
わち平均滞留時間で直接支配できる。そこで連続
法のテスト装置により、平均滞留時間を種々に変
化させて実験を繰り返し、３〜７時間の平均滞留
時間、言いかえればそれに相当する転移速度が望
ましい結晶の大きさを与えることを見出した。
本発明は上記の知見に基づきなされたもので、
２水石こうスラリーを加圧下で水熱処理してα型
半水石こうを製造するに際し、石こうスラリー中
の硫酸マグネシウムの濃度、石こうスラリーの温
度、石こうスラリー中の原料石こうとα型半水石
こうとの合計濃度および転化器内の平均滞留時間
を適切な数値内に入れることにより、連続的に転
移速度を制御して柱状結晶形のα型半水石こうを
製造することにより、有機媒晶剤を添加すること
なく、乾燥した後、機械的に粉砕することによ
り、容易に高強度の水和硬化体を得ることができ
る、肥大した柱状結晶形を有するα型半水石こう
の製造方法を提供することを目的とするものであ
る。
〔問題点を解決するための手段および作用〕
上記の目的を達成するために、本願における第
１の発明のα型半水石こうの製造方法は、２水石
こうを転化器内で加圧下で水熱処理してα型半水
石こうを製造するに際し、転化器内における石こ
うスラリー濃度を15〜50wt％、硫酸マグネシウ
ム濃度を１〜10wt％、石こうスラリー温度を110
〜150℃に調節するとともに、転化器内における
石こうスラリーの平均滞留時間を３〜７時間に調
節することにより、連続的に転移速度を制御して
柱状結晶形のα型半水石こうを製造した後、乾
燥・粉砕することを特徴としている。
また本願における第２の発明のα型半水石こう
の製造方法は、２水石こうを転化器内で加圧下で
水熱処理してα型半水石こうを製造するに際し、
硫酸マグネシウム濃度が３〜10wt％である母液
を有する排煙脱硫装置の酸化塔から排出される２
水石こうスラリーを15〜40wt％の濃度に濃縮し
た後、母液とともにスラリーの状態で転化器に連
続的に導入し、転化器内における石こうスラリー
温度を110〜150℃に調節するとともに、転化器内
における石こうスラリーの平均滞留時間を３〜７
時間に調節することにより、連続的に転移速度を
制御して柱状結晶形のα型半水石こうを製造した
後、乾燥・粉砕することを特徴としている。
すなわち本発明の方法は、転化器内における石
こうスラリー濃度、硫酸マグネシウム濃度、石こ
うスラリー温度、平均滞留時間（転移速度）を所
定値に限定した相乗効果により、柱状結晶形の高
強度のα型半水石こうが製造できることを見出し
たことに基づいてなされたものであり、石こうス
ラリー濃度15〜50wt％、硫酸マグネシウム濃度
１〜10wt％、石こうスラリー温度110〜150℃、
平均滞留時間３〜７時間の４つの条件が揃つては
じめてこれらの相乗効果により優れた品質のα型
半水石こうが製造できるものであり、これらの条
件が１つでも欠けるとその効果は失われるもので
ある。
なお２水石こうスラリーを連続的に転化器に供
給する代りに、天然石こうまたは化学石こうの細
粉末原料を、硫酸マグネシウム濃度約１〜10wt
％、温度約110〜150℃の熱水を満たした完全混合
型転化器に連続的に供給し、熱水中の原料石こう
とα型半水石こうとの合計濃度が15〜50wt％、
転化器内の平均滞留時間が３〜７時間の操作条件
で連続的に転移速度を制御するようにする場合も
ある。
以下、本発明を詳細に説明する。２水石こうス
ラリーと硫酸マグネシウムを共存させた状態の適
当な操作条件の下で、水熱処理を施すと硫酸マグ
ネシウムの作用により、Ｌ／Ｄが約５〜15となる
肥大したα型半水石こうの柱状結晶が生成され
る。
α型半水石こうの柱状結晶の成長速度に適合す
るように、２水石こうの転移によるα型半水石こ
うの生成速度を調節する（平均滞留時間で調節す
る）ことにより、生成されたα型半水石こうはす
でに転化器に存在しているα型半水石こうの柱状
結晶の成長にあずかり、該α型半水結晶は単結晶
状に成長し大きくなる。
α型半水石こうの生成速度がすでに転化器内に
存在するα型半水石こう結晶の結晶成長速度より
大きくなると、該α型半水石こうの結晶の成長に
あずからない。α型半水石こうは新しい結晶核と
なり微細柱状結晶が新たに発生し、粉砕しても水
和硬化体の強度は低くなりα型半水石こう本来の
特性は得られない。
硫酸マグネシウムが存在しない系において、２
水石こうスラリーのみを加圧下、加熱処理を施す
際に、結晶を大きく成長させることは技術的にき
わめて難かしく、通常は微細結晶が多く発生す
る。また硫酸マグネシウムが存在しない系におい
て２水石こうスラリーを加圧下で加熱処理させる
際に、転化器に予めα型半水石こうの柱状結晶を
存在させると、該α型半水石こう柱状結晶上に針
状または束柱状の結晶が多結晶状に成長し、粉砕
しても嵩密度は大きくならない。
本発明において、硫酸マグネシウムは２水石こ
うの転移により生成されるα型半水石こうの結晶
のＬ／Ｄを約５〜15とする媒晶効果を呈するとと
もに、操作条件を適当に選ぶことにより、α型半
水石こうの柱状結晶上に２水石こうの転移により
新たに生成するα型半水石こうの結晶を、単結晶
状に成長させることを容易にするものである。α
型半水石こうの生成速度調節には種々の要因が複
雑に影響しているが、これについて本発明者らが
研究した結果、前述のように転化器内の硫酸マグ
ネシウム濃度、スラリー温度、スラリー濃度およ
び滞留時間が最も重要であり、これについて最適
な状態が存在することを見出した。
すなわち、本発明において転化器内における液
中の硫酸マグネシウムの濃度は１〜10wt％、好
ましくは３〜10wt％、また転化器内のスラリー
濃度は15〜50wt％の範囲としなければならない。
ここで、液中の硫酸マグネシウム濃度が1wt％
未満になると、生成されるα型半水石こうは柱状
とならずに針状となる。また円滑なる液中の硫酸
マグネシウム濃度が10wt％を越えると、型無
水石こうが生成しやすくなり柱状α型半水石こう
の生成が困難となる。
転化器内のスラリー濃度については、15wt％
未満ではα型半水石こうの結晶の粒径が小さく、
よく成長した肥大な結晶形状を呈さない。スラリ
ー濃度が50wt％を越えると、配管部ならびにバ
ルブ部にて閉塞が生じ操作上著しく不具合とな
る。
２水石こうのα型半水石こうへの転化率を実用
上差支えない程度にし、また型無水石こうへの
移行を防ぐために、液温は110〜150℃りすること
が必要である。液温が110℃未満の場合は、２水
石こうからα型半水石こうへの転化率が低すぎ
て、製品として取り出されるα型半水石こう中に
未反応の２水石こうが混在することになる。液温
が150℃を越える場合は、型無水石こうが発生
することになる。２水石こう、型無水石こうと
もα型半水石こうのような水和硬化性は持たず、
またα型半水石こう中に少量混じるだけでも、嵩
密度を低下させるなどの悪影響を及ぼすので、こ
れらの混在は極力避けなければならない。
また２水石こうのα型半水石こうへの転化率お
よびα型半水石こうの結晶成長の点から、転化器
内での平均滞留時間は３〜７時間の範囲としなけ
ればならない。すなわち、平均滞留時間３〜７時
間に相当する転移速度に制御しなければならな
い。平均滞留時間が３時間未満の場合は、α型半
水石こうの生成速度が、すでに転化器内に存在す
るα型半水石こうの結晶成長速度より大きくな
り、該α型半水石こう結晶の成長にあずからな
い。α型半水石こうは新しい結晶核となり、微細
柱状結晶が新たに発生する。その結果、製品とし
て得られるα型半水石こうは嵩密度の低い低品位
のものとなる。平均滞留時間を長くして行くと、
それに伴つて平均的な結晶径が大きくなつて行く
が、その傾向は次第に飽和に達し、平均滞留時間
を７時間以上にしても、もはや顕著な効果は見ら
れなくなる。一般に滞留時間を長くすることは、
装置の生産性を低下させ、また時定数が大きくな
ることにより、制御性を悪化させる。したがつて
７時間以上に滞留時間を取ることは無益である。
またテストの経験上、滞留時間を長くとると、
型無水石こうが発生する場合が散見されたが、滞
留時間が７時間以内であれば、そうした現象は生
じなかつた。
本発明においては、液中の硫酸マグネシウム濃
度１〜10wt％、液温110〜150℃、液中の原料石
こうとα型半水石こうとの合計濃度15〜50wt％、
転化器内の平均滞留時間３〜７時間のすべての条
件を満足する必要があり、これらの条件の相乗的
効果により優れた効果を奏するもので、これらの
条件のうち１つが欠けても本発明の効果を期待す
ることができない。
上記の条件下で得られたα型半水石こうは良く
成長し、肥大した結晶形状を有しており、乾燥し
た後、通常の市販の粉砕機により粉砕することに
よつて、容易に高強度の水和硬化体を得ることが
できる。
〔実施例〕
以下、本発明の実施例および比較例について説
明する。
実施例
スラリー中の濃度が２水石こう20wt％、硫酸
マグネシウム5wt％および清水75wt％であるスラ
リーを完全混合方式の転化器（内容積1000）に
250／Hrの割合で連続的に供給し、液温120℃、
平均滞留時間４時間の条件下で転化処理を施し柱
状結晶形のα型半水石こうを生成させ、連続的に
排出させた。ついでこのα型半水石こうを脱水乾
燥した後、ボールミルで粉砕した。
このようにして得たα型半水石こうの形状を第
１表に示す。また該α型半水石こうの水和硬化体
は第２表に示すような特性を示した。
[Industrial Application Field] The present invention provides a method for producing α with a good columnar crystal shape by adding magnesium sulfate to a slurry of dihydrate gypsum such as natural gypsum or chemical gypsum, and hydrothermally treating the slurry under pressure. The present invention relates to a method for manufacturing molded hemihydrate gypsum. [Prior art] With the recent tightening of air pollution regulations, a large number of flue gas desulfurization processes have been developed to remove sulfur compounds from exhaust gas generated by the combustion of sulfur compounds in fuel. Sulfuric acid, sulfur, ammonium sulfate, and gypsum are recovered as byproducts.
Of these, gypsum is considered the most desirable as a by-product because it is chemically stable, has no risk of secondary pollution, and has high utility value as a building and civil engineering material. Smoke desulfurization equipment is the most widely used. In the gypsum recovery flue gas desulfurization process, a common method is to oxidize calcium sulfite slurry, which is produced as a primary by-product by absorbing sulfur oxides in flue gas, by blowing oxygen-containing gas (generally air) into the slurry. If, under normal conditions, 2
Water gypsum is obtained. On the other hand, typical methods for producing α-type hemihydrate gypsum by subjecting dihydrate gypsum to hydrothermal treatment include pressurized aqueous solution method, pressurized steam method, and normal pressure aqueous solution method.
Conventional techniques have drawbacks such as high production costs and poor production efficiency. For this reason, α-type hemihydrate gypsum forms a hydration-hardened product of better quality and extremely high strength than β-type hemihydrate gypsum (also called calcined gypsum), which is produced by firing dihydrate gypsum. However, the amount produced is small and it is only used for special purposes. With the recent spread of large-scale flue gas desulfurization equipment, large amounts of flue gas desulfurization gypsum (usually dihydrate gypsum) are being produced, so efforts are being made to improve the quality of flue gas desulfurization gypsum and expand its range of use. I started to get angry. As a result, attention has begun to be paid to the efficient and inexpensive conversion of dihydrate gypsum to α-type hemihydrate gypsum. Typical methods for converting dihydrate gypsum into α-type hemihydrate are the pressurized aqueous solution, pressurized steam, and normal pressure aqueous solution methods, as mentioned above, but the industrial α-type hemihydrate production method is aimed at mass production. A pressurized aqueous solution method is commonly used. The pressurized aqueous solution method is a method in which dihydrate gypsum powder is added to form a slurry and subjected to pressurized hydrothermal treatment while stirring in a pressure vessel such as an autoclave. To achieve this, organic modifiers such as dicarboxylic acid salts have been added. This is because α-type hemihydrate gypsum is generally required to have a well-grown plate-like or short column-like shape close to a cube in order to obtain a hydration-hardened product exhibiting high strength. Usually, during the transfer treatment of dihydrate gypsum slurry, an organic modifier such as a dicarboxylic acid salt is added. [Problems to be solved by the invention] However, when carrying out the transformation of dihydrate gypsum to α-type hemihydrate gypsum on an industrial scale, it is necessary to use an organic substance such as a dicarboxylate as a crystal modifier. has various problems as shown below. First of all, although there is usually an optimal concentration condition range depending on the type of crystal modifier, it is extremely difficult to measure and monitor the organic crystal modifier concentration and maintain an appropriate concentration. The transformation from dihydrate gypsum to α-type hemihydrate gypsum is usually carried out at a high temperature of 105°C or higher and under pressure, and the added crystal modifier is likely to undergo thermal decomposition under these conditions. . In addition, a crystal modifier may be contained in the liquid of α-type hemihydrate gypsum and α-type hemihydrate gypsum produced by the transition, and may be carried out of the converter. Therefore, in order to smoothly generate α-type hemihydrate gypsum in the form of short columns or plates, it is essential to always accurately measure the crystallizing agent concentration and to always control it to an appropriate concentration. However, in actual industrial-scale processes, it is extremely difficult to appropriately control the concentration of the organic crystal modifier, considering the difficulty in detecting the concentration of the organic crystal modifier. Second, adding a crystal modifier to the dihydrate gypsum slurry and subjecting it to heat treatment facilitates the formation of type anhydrous gypsum. The shape and size of type anhydrous gypsum are
Although it varies depending on the formation conditions such as the concentration of the crystallizing agent and the temperature at the time of transition, it is usually in the form of fine particles, needles, or flat strips, and the strength of the hydrated hardened product is small, resulting in an α-type hemihydrate. It causes deterioration of the quality of gypsum. Thirdly, there is the problem of wastewater treatment. In the production process of α-type hemihydrate gypsum that uses organic modifiers, waste liquids such as concentrated or accumulated thermal decomposition products of modifiers and stagnant liquid during periodic inspections are generated.
The modifier or decomposition products of the modifier in this waste liquid are
Because it contains BOD and COD, it cannot be discharged without thorough wastewater treatment. As described above, there are many problems in the method of using organic modifiers in the manufacturing process of α-type hemihydrate gypsum on a large-scale industrial scale. Therefore, there is a need for a large-scale industrial process that can produce large amounts of α-type hemihydrate gypsum with a high density and good crystalline shape at low cost without adding an organic crystal modifier. The present inventors have solved the above conventional problems,
As a result of extensive research into a method for producing α-type hemihydrate gypsum with good crystal shape and high bulk specific gravity without adding crystallizing agents, we found that dihydrate gypsum slurry was hydrothermally treated under pressure to produce α-type hemihydrate gypsum. When producing hemihydrate gypsum, by appropriately selecting the operating conditions in the presence of magnesium sulfate, the production rate of α-type hemihydrate gypsum due to the transformation of dihydrate gypsum can be increased compared to the α-type hemihydrate already present in the converter. By adjusting the crystal formation rate to be equal to or lower than the crystal growth rate in hydrogypsum crystals, the α-type hemihydrate gypsum crystals are successively grown larger as a single crystal, and the α-type hemihydrate gypsum crystals are The length of the crystal in the long axis direction is approximately 150 to 1500μ,
It has been found that large columnar crystals of α-type hemihydrate gypsum with a crystal diameter of approximately 30 to 100 μ and a L/D (crystal length/crystal diameter) of 5 to 15 can be produced. In addition, by mechanically crushing the α-type hemihydrate gypsum crystals, it was possible to easily produce α-type hemihydrate gypsum having a short columnar shape and a high bulk specific gravity and a good crystal shape. It should be noted that the α-type hemihydrate gypsum that forms the core of crystal growth mentioned above as ``α-type hemihydrate gypsum crystals that already exist in the converter'' does not necessarily have to be formed from the α-type columnar crystals before the start of the transition. There was no need to add hemihydrate gypsum as a seed crystal, and α-type hemihydrate gypsum produced at the initial stage of heat treatment of dihydrate gypsum slurry could be used as a seed crystal. Generally, in the production of α-type hemihydrate gypsum, it is important to control the shape and size of crystals. There are many factors that can determine crystal size, including temperature and solution composition. As a result of experiments, the present inventors have found that among these, the transfer rate, that is, the amount of gypsum produced in a certain period of time, has a great influence. In the case of continuous processes, the rate of transfer can be directly controlled by the feed rate, ie the average residence time. Using a continuous test device, they repeated the experiment by varying the average residence time, and found that an average residence time of 3 to 7 hours, or in other words, an equivalent transition rate, gave the desired crystal size. . The present invention was made based on the above findings,
When producing α-type hemihydrate gypsum by hydrothermally treating dihydrate gypsum slurry under pressure, the concentration of magnesium sulfate in the gypsum slurry, the temperature of the gypsum slurry, and the relationship between the raw gypsum and the α-type hemihydrate gypsum in the gypsum slurry are determined. Addition of organic modifiers by continuously controlling the transition rate to produce α-type hemihydrate gypsum in columnar crystal form by keeping the total concentration and average residence time in the converter within appropriate values. To provide a method for producing α-type hemihydrate gypsum having an enlarged columnar crystal shape, by which a high-strength hydrated hardened product can be easily obtained by drying and mechanically crushing without drying. The purpose is to [Means and effects for solving the problem] In order to achieve the above object, the method for producing α-type hemihydrate gypsum of the first invention of the present application is to convert dihydrate gypsum into water under pressure in a converter. When producing α-type hemihydrate gypsum by heat treatment, the gypsum slurry concentration in the converter is set at 15 to 50 wt%, the magnesium sulfate concentration is 1 to 10 wt%, and the gypsum slurry temperature is set at 110%.
By adjusting the temperature to ~150°C and the average residence time of the gypsum slurry in the converter to 3 to 7 hours, the transformation rate was continuously controlled to produce α-type hemihydrate gypsum in the form of columnar crystals. After that, it is dried and crushed. In addition, the method for producing α-type hemihydrate gypsum of the second invention of the present application includes hydrothermally treating dihydrate gypsum under pressure in a converter to produce α-type hemihydrate gypsum.
2 discharged from the oxidation tower of a flue gas desulfurization equipment having a mother liquor with a magnesium sulfate concentration of 3 to 10 wt%
After concentrating the water-gypsum slurry to a concentration of 15 to 40 wt%, it is continuously introduced into the converter as a slurry together with the mother liquor, and the temperature of the gypsum slurry in the converter is adjusted to 110 to 150℃, and The average residence time of gypsum slurry in
The method is characterized in that α-type hemihydrate gypsum in the form of columnar crystals is produced by continuously controlling the transition rate by adjusting the time, and then dried and pulverized. In other words, the method of the present invention produces high-strength α-type half-forms with columnar crystals by the synergistic effect of limiting the gypsum slurry concentration, magnesium sulfate concentration, gypsum slurry temperature, and average residence time (transition rate) to predetermined values in the converter. This was done based on the discovery that hydrogypsum can be produced, with a gypsum slurry concentration of 15 to 50 wt%, a magnesium sulfate concentration of 1 to 10 wt%, a gypsum slurry temperature of 110 to 150°C,
Only when the four conditions of an average residence time of 3 to 7 hours are met can the synergistic effect of these conditions produce superior quality α-type hemihydrate gypsum, and if even one of these conditions is missing, the effect will be lost. It is something. In addition, instead of continuously feeding dihydrate gypsum slurry to the converter, fine powder raw material of natural gypsum or chemical gypsum is used at a magnesium sulfate concentration of about 1 to 10 wt.
%, the total concentration of raw gypsum and α-type hemihydrate gypsum in the hot water is 15-50wt%,
In some cases, the transfer rate may be continuously controlled under operating conditions with an average residence time in the converter of 3 to 7 hours. The present invention will be explained in detail below. When hydrothermal treatment is performed under appropriate operating conditions in which dihydrate gypsum slurry and magnesium sulfate coexist, enlarged α-type hemihydrate gypsum with an L/D of about 5 to 15 is produced by the action of magnesium sulfate. Columnar crystals are produced. By adjusting the production rate of α-type hemihydrate gypsum through the transition of dihydrate gypsum (adjusting the average residence time) to match the growth rate of columnar crystals of α-type hemihydrate gypsum, the α-type produced The hemihydrate gypsum participates in the growth of columnar crystals of α-type hemihydrate gypsum already present in the converter, and the α-type hemihydrate crystal grows into a single crystal and becomes larger. If the production rate of α-type hemihydrate gypsum is higher than the crystal growth rate of α-type hemihydrate gypsum crystals already present in the converter, the α-type hemihydrate gypsum crystals will not be able to grow. α-type hemihydrate gypsum becomes a new crystal nucleus and new fine columnar crystals are generated, and even if crushed, the strength of the hydrated hardened product becomes low and the original characteristics of α-type hemihydrate gypsum cannot be obtained. In a system without magnesium sulfate, 2
When only water-gypsum slurry is subjected to heat treatment under pressure, it is technically extremely difficult to grow large crystals, and usually many fine crystals are generated. Furthermore, when heat treating dihydrate gypsum slurry under pressure in a system where magnesium sulfate does not exist, if columnar crystals of α-type hemihydrate gypsum are pre-existing in the converter, needles will form on the α-type hemihydrate gypsum columnar crystals. Polycrystalline or bundle-columnar crystals grow in a polycrystalline manner, and the bulk density does not increase even when crushed. In the present invention, magnesium sulfate exhibits a medic effect that makes the L/D of α-type hemihydrate gypsum crystals produced by the transformation of dihydrate gypsum about 5 to 15, and by appropriately selecting operating conditions, This makes it easy to grow α-type hemihydrate gypsum crystals, which are newly generated on columnar crystals of α-type hemihydrate gypsum by dislocation of dihydrate gypsum, into a single crystal. α
Various factors affect the production rate of hemihydrate gypsum in a complex manner, and as a result of research by the present inventors, we found that the concentration of magnesium sulfate in the converter, the slurry temperature, the slurry concentration, etc. It has been found that residence time and residence time are most important and that an optimum condition exists for this. That is, in the present invention, the concentration of magnesium sulfate in the liquid in the converter must be in the range of 1 to 10 wt%, preferably 3 to 10 wt%, and the slurry concentration in the converter must be in the range of 15 to 50 wt%. Here, the concentration of magnesium sulfate in the liquid is 1wt%
When the amount is less than 1, the α-type hemihydrate gypsum produced becomes needle-like instead of columnar. Furthermore, if the magnesium sulfate concentration in the smoothing liquid exceeds 10 wt%, type anhydrous gypsum is likely to be formed, making it difficult to form columnar α-type hemihydrate gypsum. Regarding the slurry concentration in the converter, 15wt%
If it is below, the grain size of α-type hemihydrate gypsum crystals is small
It does not exhibit a well-grown, enlarged crystal shape. If the slurry concentration exceeds 50wt%, the pipes and valves will become clogged, resulting in significant operational problems. In order to maintain the conversion rate of dihydrate gypsum to α-type hemihydrate gypsum to a level that is acceptable for practical use and to prevent the conversion to type anhydrous gypsum, the liquid temperature must be 110 to 150°C. If the liquid temperature is less than 110℃, the conversion rate from dihydrate gypsum to α-type hemihydrate gypsum will be too low, and unreacted dihydrate gypsum will be mixed in the α-type hemihydrate gypsum extracted as a product. Become. If the liquid temperature exceeds 150℃, mold anhydrous gypsum will occur. Both dihydrate gypsum and type anhydrous gypsum do not have hydration hardening properties like α-type hemihydrate gypsum.
In addition, even a small amount mixed in α-type hemihydrate gypsum will have an adverse effect such as lowering the bulk density, so their mixing must be avoided as much as possible. In addition, in view of the conversion rate of dihydrate gypsum to α-type hemihydrate gypsum and the crystal growth of α-type hemihydrate gypsum, the average residence time in the converter must be in the range of 3 to 7 hours. That is, the transfer rate must be controlled to correspond to an average residence time of 3 to 7 hours. If the average residence time is less than 3 hours, the production rate of α-type hemihydrate gypsum will be higher than the crystal growth rate of α-type hemihydrate gypsum already present in the converter, and the growth of the α-type hemihydrate gypsum crystals will increase. I don't share in it. The α-type hemihydrate gypsum becomes a new crystal nucleus, and new fine columnar crystals are generated. As a result, the α-type hemihydrate gypsum obtained as a product is of low quality and has a low bulk density. As the average residence time increases,
Correspondingly, the average crystal diameter increases, but this tendency gradually reaches saturation, and even if the average residence time is increased to 7 hours or more, no significant effect can be seen anymore. In general, increasing the residence time is
This reduces the productivity of the device, and increases the time constant, thereby worsening controllability. A residence time of more than 7 hours is therefore futile.
Also, based on our test experience, if the residence time is long,
Although there were some cases where anhydrous gypsum was generated, such a phenomenon did not occur if the residence time was within 7 hours. In the present invention, the concentration of magnesium sulfate in the liquid is 1 to 10 wt%, the liquid temperature is 110 to 150°C, the total concentration of raw gypsum and α-type hemihydrate gypsum in the liquid is 15 to 50 wt%,
It is necessary to satisfy all the conditions of average residence time in the converter of 3 to 7 hours, and the synergistic effect of these conditions produces an excellent effect, and even if one of these conditions is missing, the present invention cannot expect the effect of The α-type hemihydrate gypsum obtained under the above conditions grows well and has an enlarged crystal shape, and after drying, it can be easily ground with a commercially available grinder to achieve high strength. A hydrated and cured product can be obtained. [Examples] Examples and comparative examples of the present invention will be described below. Example: A slurry with a concentration of 20wt% dihydrate gypsum, 5wt% magnesium sulfate, and 75wt% fresh water was transferred to a complete mixing converter (inner volume 1000).
Continuously supplied at a rate of 250/Hr, liquid temperature 120℃,
Conversion treatment was carried out under conditions of an average residence time of 4 hours to produce α-type hemihydrate gypsum in the form of columnar crystals, which was continuously discharged. Next, this α-type hemihydrate gypsum was dehydrated and dried, and then ground in a ball mill. Table 1 shows the shape of the α-type hemihydrate gypsum thus obtained. The hydrated and hardened α-type hemihydrate gypsum exhibited the properties shown in Table 2.
【表】
比較例 １
回分式加圧水蒸気法により製造した通常のα型
半水石こうの特性を測定した。結果は第２表に示
す如くであつた。[Table] Comparative Example 1 The properties of normal α-type hemihydrate gypsum produced by a batch pressurized steam method were measured. The results were as shown in Table 2.
以上に示したように、加圧水溶液法を用いて２
水石こうよりα型半水石こうを製造する際に、硫
酸マグネシウムの存在下で、適切な操作条件を選
択して２水石こうをα型半水石こうに転化させる
ことにより、有機媒晶剤を使用せずに水和硬化時
の機械的強度の良好なるα型半水石こうを生成す
ることができるので、本発明はα型半水石こうを
多量にかつ長時間の運転に対して安定に生成する
プロセスを可能とするものである。
As shown above, using the pressurized aqueous solution method, 2
When producing α-type hemihydrate gypsum from hydrogypsum, organic modifiers are used in the presence of magnesium sulfate by selecting appropriate operating conditions to convert dihydrate gypsum to α-type hemihydrate gypsum. Since it is possible to produce α-type hemihydrate gypsum that has good mechanical strength during hydration and hardening without drying, the present invention can produce α-type hemihydrate gypsum in large quantities and stably for long periods of operation. It is what makes the process possible.
Claims (1)
てα型半水石こうを製造するに際し、転化器内に
おける石こうスラリー濃度を15〜50wt％、硫酸
マグネシウム濃度を１〜10wt％、石こうスラリ
ー温度を110〜150℃に調節するとともに、転化器
内における石こうスラリーの平均滞留時間を３〜
７時間に調節することにより、連続的に転移速度
を制御して柱状結晶形のα型半水石こうを製造し
た後、乾燥・粉砕することを特徴とするα型半水
石こうの製造方法。 ２ ２水石こうを転化器内で加圧下で水熱処理し
てα型半水石こうを製造するに際し、硫酸マグネ
シウム濃度が３〜10wt％である母液を有する排
煙脱硫装置の酸化塔から排出される２水石こうス
ラリーを15〜40wt％の濃度に濃縮した後、母液
とともにスラリーの状態で転化器に連続的に導入
し、転化器内における石こうスラリー温度を110
〜150℃に調節するとともに、転化器内における
石こうスラリーの平均滞留時間を３〜７時間に調
節することにより、連続的に転移速度を制御して
柱状結晶形のα型半水石こうを製造した後、乾
燥・粉砕することを特徴とするα型半水石こうの
製造方法。[Claims] 1. When producing α-type hemihydrate gypsum by hydrothermally treating dihydrate gypsum under pressure in a converter, the gypsum slurry concentration in the converter is 15 to 50 wt%, and the magnesium sulfate concentration is 1. ~10wt%, adjust the gypsum slurry temperature to 110~150℃, and adjust the average residence time of the gypsum slurry in the converter to 3~10wt%.
A method for producing α-type hemihydrate gypsum, which comprises producing α-type hemihydrate gypsum in the form of columnar crystals by continuously controlling the transition rate for 7 hours, followed by drying and pulverizing. 2 When producing α-type hemihydrate gypsum by hydrothermally treating dihydrate gypsum under pressure in a converter, it is discharged from the oxidation tower of the flue gas desulfurization equipment, which has a mother liquor with a magnesium sulfate concentration of 3 to 10 wt%. After concentrating the dihydrate gypsum slurry to a concentration of 15 to 40 wt%, it is continuously introduced into the converter in the form of a slurry together with the mother liquor, and the temperature of the gypsum slurry in the converter is raised to 110%.
By adjusting the temperature to ~150°C and the average residence time of the gypsum slurry in the converter to 3 to 7 hours, the transformation rate was continuously controlled to produce α-type hemihydrate gypsum in the form of columnar crystals. A method for producing α-type hemihydrate gypsum, which is characterized in that it is then dried and crushed.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP7039279A JPS55162426A (en) | 1979-06-05 | 1979-06-05 | Manufacture of alpha-type hemihydrate gypsum |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP7039279A JPS55162426A (en) | 1979-06-05 | 1979-06-05 | Manufacture of alpha-type hemihydrate gypsum |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS55162426A JPS55162426A (en) | 1980-12-17 |
| JPS6353142B2 true JPS6353142B2 (en) | 1988-10-21 |
Family
ID=13430118
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP7039279A Granted JPS55162426A (en) | 1979-06-05 | 1979-06-05 | Manufacture of alpha-type hemihydrate gypsum |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS55162426A (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0742107B2 (en) * | 1987-05-06 | 1995-05-10 | 三菱重工業株式会社 | Method for producing α-type hemihydrate gypsum |
| US5639298A (en) * | 1995-11-27 | 1997-06-17 | Air Products And Chemicals, Inc. | Modified gypsum compositions |
| CN104262850B (en) * | 2014-09-30 | 2016-05-11 | 华中师范大学 | Alpha-semi water plaster stone/polyvinyl chloride ordered composite material and preparation method thereof |
-
1979
- 1979-06-05 JP JP7039279A patent/JPS55162426A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS55162426A (en) | 1980-12-17 |
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