JP3859413B2

JP3859413B2 - Slurry or solution material drying method, slurry or solution material drying apparatus, and ceramic sintered body manufacturing method

Info

Publication number: JP3859413B2
Application number: JP33401499A
Authority: JP
Inventors: 政一上村
Original assignee: NGK Spark Plug Co Ltd
Current assignee: NGK Spark Plug Co Ltd
Priority date: 1999-11-25
Filing date: 1999-11-25
Publication date: 2006-12-20
Anticipated expiration: 2019-11-25
Also published as: JP2001153560A

Description

【０００１】
【発明の属する技術分野】
本発明は、スラリー状又は溶液状材料の乾燥方法、スラリー状又は溶液状材料の乾燥装置及びセラミック焼結体の製造方法に関する。
【０００２】
【従来の技術】
スラリー状又は溶液状材料の乾燥装置の一例として、噴霧乾燥装置（スプレードライヤ）を図１２に示す。この装置では、スラリー状又は溶液状の材料Ｍが乾燥室３０上方の投入口１０から供給されるとともに、外気が加熱器２３で加熱され、給気Ｉとして乾燥室３０の上面又は周面の給気口２０から乾燥室３０に導入される。そして、乾燥室３０内を上部の投入口１０側から下部の取出口４０側に向け自然落下する材料Ｍに対して、加熱された給気Ｉを接触させることにより、材料Ｍの水分が熱風（給気）Ｉ中を浮遊する間に給気Ｉに移行（吸収）され、材料Ｍの乾燥が行われる。乾燥後の乾燥粉末Ｇは乾燥室３０下部の取出口４０から、一方給気Ｉは排気Ｏとして乾燥室３０中間部の排気口５０から、それぞれ乾燥室３０の外部へ取り出される。
【０００３】
ところで、このような乾燥装置では、得られる乾燥粉末Ｇに含まれる水分量（含水量）を一定の値となるように制御する必要があり、従来から種々の乾燥制御（乾燥システム）を考慮して乾燥粉末Ｇの水分量制御がなされている。この乾燥制御の代表的なものとして、次のような乾燥システムが知られている。すなわち、赤外線等を利用した水分量測定計６ａを試料採取部６Ａに設置して乾燥粉末Ｇの水分量を直接測定し、測定された検出水分量と乾燥粉末Ｇの規定水分量との比較に基づいて、材料Ｍの投入量を制御部８及び流量調整弁１２、流量計１ｂ等によりコントロールしながら、乾燥粉末Ｇの水分量制御を行う方法である。なお、試料採取部６Ａは、例えば図１２のように乾燥粉末Ｇの取出流路４１等から分岐させて設けられる。
【０００４】
【発明が解決しようとする課題】
上記の方法では、完成した乾燥粉末Ｇの水分量のみが検知対象（具体的な検知手段は水分量測定計６ａ）であり、一方システム先頭の乾燥室３０内への材料Ｍの投入量が制御対象（具体的な制御手段は流量調整弁１２等）であることから、両者間で必然的に応答の遅れが発生して、乾燥粉末Ｇの水分量制御にハンチングが生じ易い傾向にある。したがって、乾燥粉末Ｇの水分量を安定させるために、得られた異なる水分量の乾燥粉末Ｇを収集して、ブレンダ等で撹拌混合して乾燥粉末Ｇの水分量を均一化させることが必要になる。しかしながら、乾燥後に撹拌混合といった再加工を施すことからコストアップの要因となり、また再加工に伴い乾燥粉末Ｇの品質の低下を引き起こすおそれもある。
【０００５】
さらに上記方法では、水分量測定計６ａの試料採取部６Ａは乾燥粉末Ｇの流量を一定にし水分量の測定を安定させるため、狭い通路で形成されていることから、乾燥粉末Ｇの詰まりＧ’を生じたり、あるいは水分量測定計６ａに過水分乾燥粉末が付着したりすることがある。そのために乾燥粉末Ｇの水分量制御が不能になるのみならず乾燥システムにて乾燥条件を作る上での制御に暴走が発生する可能性がある。また、乾燥装置の起動時（運転開始時）や材料投入一時停止後の再起動時（運転再開時）等には取出口４０に乾燥粉末Ｇが存在しない場合があり、かかる場合にも乾燥条件を作る上での制御に暴走が発生する可能性がある。
【０００６】
本発明の課題は、乾燥粉末の水分量制御を行うにあたり、応答性がよくハンチングを起こしにくく、また試料採取部に詰まりが発生した場合とか、乾燥装置の起動時や材料投入一時停止後の再起動時等のように取出口に乾燥粉末が存在しない場合にも、乾燥条件を作る上での制御に暴走が発生する恐れが少なく、生産性を阻害しないスラリー状又は溶液状材料の乾燥方法及びスラリー状又は溶液状材料の乾燥装置を提供することにある。また、そのようにして製造される乾燥粉末を成形・焼結して品質のよいセラミック焼結体を得るセラミック焼結体の製造方法を提供することにある。
【０００７】
【課題を解決するための手段及び作用・効果】
上記課題を解決するために、第一番目の発明にかかるスラリー状又は溶液状材料の乾燥方法は、
セラミック原料を含有するスラリー状又は溶液状材料を乾燥部に設けられた投入口から乾燥室に供給するとともに、加熱器を通じて加熱された外気を給気として前記乾燥部に設けられた給気口から前記乾燥室に導入し、
前記投入口から供給された前記材料に対して前記給気を接触させることにより当該材料の乾燥を行い、
乾燥後の前記材料を前記乾燥部に設けられた取出口から乾燥粉末として取り出す一方、前記給気を前記乾燥部に設けられた排気口から排気として前記乾燥室の外部に排出し、
前記排気口の近傍にて前記排気の絶対湿度を特定するのに必要な情報を検出し、該排気絶対湿度の検出値Ｈ_Ｏ'に基づいて、規定水分量を有する前記乾燥粉末が得られるように前記給気の有する給気熱量を調整するとともに、
前記投入口への供給に先立つ前記材料の温度と投入量とによって、前記材料を介しての投入熱量を検出し、該材料投入熱量の検出値に基づいて前記給気熱量を補助的に調整することを特徴とする。
【０００８】
また、第一番目の発明にかかるスラリー状又は溶液状材料の乾燥装置は、
セラミック原料を含有するスラリー状又は溶液状材料を供給する投入口と、
外気を加熱器で加熱し給気として導入する給気口と、
前記投入口から供給された前記材料に対して前記給気を接触させることにより当該材料の乾燥を行う乾燥室と、
乾燥後の前記材料を乾燥粉末として外部へ取り出す取出口と、
前記給気を排気として外部へ排出する排気口とを備え、
前記排気口の近傍にて前記排気の絶対湿度を特定するのに必要な情報を検出する検出器が設けられ、その検出器により検出された排気絶対湿度の検出値Ｈ_Ｏ'に基づいて、規定水分量を有する前記乾燥粉末が得られるように前記給気の有する給気熱量を調整する制御部が設けられるとともに、
前記投入口への供給に先立つ前記材料の温度を測定する温度計とその投入量を測定する流量計とが設けられ、前記制御部は、それら温度計と流量計とによって検出された材料投入熱量の検出値に基づいて、前記給気熱量を補助的に調整することを特徴とする。
【０００９】
これらの発明によれば、排気絶対湿度の検出値Ｈ_Ｏ'に基づいて、規定水分量を有する乾燥粉末が得られるように給気の有する給気熱量を調整することで、完成した乾燥粉末の水分量を直接的に測定しなくてもよい。すなわち乾燥中の情報を利用して粉末水分量の制御を行うことから応答性の遅れが少なく、ハンチングを起こしにくい安定した粉末水分量の制御が期待できる。また、水分量測定計の試料採取部に詰まりが発生した場合とか、乾燥装置の起動時や材料投入一時停止後の再起動時等のように取出口に乾燥粉末が存在しない場合にも、乾燥条件を作る上での制御に暴走が発生する恐れが少なく、生産性を阻害しないスラリー状又は溶液状材料の乾燥方法及びスラリー状又は溶液状材料の乾燥装置が得られる。
【００１０】
なお、排気絶対湿度の目標値Ｈ_Ｏに関して、目標値Ｈ_Ｏを所定の値一点に定めておいても、ハンチングを起こしにくい安定した粉末水分量の制御が期待できるが、所定の値に対する上下のうち少なくとも一方に不感帯を設定した目標値Ｈ_Ｏとしておけば、より一層のハンチング防止が図れる。また、本明細書において「水分量」というときは、湿量基準（例えば「水分率」）の場合と乾量基準（例えば「含水率」）の場合とを含んでいる。
【００１１】
また、本発明の給気熱量の調整は、材料からの単位時間当たりの除去水分量を略一定に又は規定範囲内に維持するように行われる場合がある。ここで、材料からの単位時間当たりの除去水分量とは、言い換えれば材料の乾燥速度を表しており、乾燥粉末の生産性を上げるためには大きいほどよい。しかし一方では、乾燥装置の性能は勿論、材料の変質（例えば物理的又は化学的性質の変化等）防止の観点からも自ずと制限されることになる。本発明によれば、材料に対して最適な乾燥速度のもとでの安定した連続運転が可能になる。なお、材料からの単位時間当たりの除去水分量に関しても、排気絶対湿度の目標値Ｈ_Ｏと同様に、所定の値に対する上下のうち少なくとも一方に不感帯を設定しておけば、ハンチング防止に効果的である。
【００１２】
ここで本発明の給気熱量の調整は、より具体的には、排気絶対湿度の検出値Ｈ_Ｏ'と、材料の保有水分量と乾燥粉末の規定水分量とから定まる排気絶対湿度の目標値Ｈ_Ｏとの比較において、Ｈ_Ｏ'＜Ｈ_Ｏのとき給気熱量を大きくし、Ｈ_Ｏ'＞Ｈ_Ｏのとき給気熱量を小さくすればよい。この場合には、比較的簡便な加熱器の温度調節によって、乾燥粉末の水分量の制御が応答性よく行える。
【００１３】
したがって、比較的低水分量の、例えば水分率３％以下の乾燥粉末を製造する場合でも、乾燥粉末の詰まりや変質等が少ない状態で取り出すことができる。なお、本明細書では「水分率」を湿量基準で用いている。
【００１４】
さらに本発明では、材料の供給に先立つ所定時間にわたって、材料の保有する水分が乾燥室にて単位時間当たりに蒸発するに要する蒸発熱量に略等しい熱量となる所定量の冷媒を、投入口から供給することができる。例えば乾燥装置の起動時（運転開始時）や材料投入一時停止後の再起動時（運転再開時）のような、取出口に乾燥粉末が存在しない場合にも、乾燥粉末の水分量の制御が不能になったり、乾燥条件を作る上での制御に暴走が発生する恐れが少なく、安定した制御が行える。
【００１５】
さらに本発明では、乾燥粉末の水分量を検出し、乾燥粉末の検出水分量Ａ'と規定水分量Ａとの比較において、Ａ'＜Ａのとき給気熱量を小さくし、Ａ'＞Ａのとき給気熱量を大きくする制御を補助的に行ってもよい。ここでも給気熱量を制御対象とすることで、応答性のよい粉末水分量の制御が可能となる。なお、規定水分量Ａに対する上下のうち少なくとも一方に不感帯を設定しておけば、ハンチング防止に効果的である。
【００１６】
さらに本発明では、加熱器を通じて加熱される前の外気の温度、湿度又は風量のうち少なくとも一つの特性値を検出し、特性値に基づいて給気熱量を補助的に調整してもよい。この場合には、規定水分量を有する乾燥粉末を得るために外気状況の変化に応じたより精密な粉末水分量の制御ができる。なお、この場合の湿度は絶対湿度、相対湿度のいずれでもよい。
【００１７】
さらに本発明では、乾燥室からの放熱量を特定するのに必要な情報を検出し、乾燥室放熱量の検出値に基づいて給気熱量を補助的に調整してもよい。また、乾燥粉末の残存熱量を特定するのに必要な情報を検出し、粉末残存熱量の検出値に基づいて給気熱量を補助的に調整してもよい。あるいは、投入口への供給に先立つ材料の温度と投入量とによって、材料を介しての投入熱量を検出し、材料投入熱量の検出値に基づいて給気熱量を補助的に調整してもよい。これらの場合には、規定水分量を有する乾燥粉末を得るために材料や雰囲気等の状況変化に応じたより精密な粉末水分量の制御が可能となる。
【００１８】
さらに本発明では、乾燥粉末の水分量を検出し、乾燥粉末の検出水分量が規定水分量を満たしていないとき、この規定外の乾燥粉末は規定水分量の乾燥粉末とは分離して回収することができる。例えば乾燥装置の起動時（運転開始時）や材料投入一時停止後の再起動時（運転再開時）に乾燥粉末の検出水分量が規定水分量を外れたときでも、乾燥粉末の水分量の制御が不能になったり、乾燥条件を作る上での制御に暴走が発生する恐れが少なく安定した制御が行える。
【００１９】
なお、上記分離回収された規定外の乾燥粉末は、水分量検出前の乾燥粉末と再混合される場合がある。このときは、乾燥粉末の生産効率と歩留まりをさらに向上させることができる。
【００２０】
また、第二番目の発明にかかるスラリー状又は溶液状材料の乾燥方法は、
セラミック原料を含有するスラリー状又は溶液状材料を乾燥部に設けられた投入口から乾燥室に供給するとともに、加熱器を通じて加熱された外気を給気として前記乾燥部に設けられた給気口から前記乾燥室に導入し、
前記投入口から供給された前記材料に対して前記給気を接触させることにより当該材料の乾燥を行い、
乾燥後の前記材料を前記乾燥部に設けられた取出口から乾燥粉末として取り出す一方、前記給気を前記乾燥部に設けられた排気口から排気として前記乾燥室の外部に排出するとともに、
前記材料の供給に先立つ所定時間にわたって、前記材料の保有する水分が前記乾燥室にて単位時間当たりに蒸発するに要する蒸発熱量に略等しい熱量となる所定量の冷媒を、前記投入口から供給することを特徴とする。
【００２１】
一方、第二番目の発明にかかるスラリー状又は溶液状材料の乾燥装置は、
セラミック原料を含有するスラリー状又は溶液状材料を供給する投入口と、
外気を加熱器で加熱し給気として導入する給気口と、
前記投入口から供給された前記材料に対して前記給気を接触させることにより、当該材料の乾燥を行う乾燥室と、
乾燥後の前記材料を乾燥粉末として外部へ取り出す取出口と、
前記給気を排気として外部へ排出する排気口とを備え、
前記材料の供給に先立つ所定時間にわたって、前記材料の保有する水分が前記乾燥室にて単位時間当たりに蒸発するに要する蒸発熱量に略等しい熱量となる所定量の冷媒を、前記投入口から供給するための冷媒供給部を配設したことを特徴とする。
【００２２】
これらの発明によれば、例えば乾燥装置の起動時（運転開始時）や材料投入一時停止後の再起動時（運転再開時）のような、取出口に乾燥粉末が存在しない場合にも、乾燥室の状況を急変させることなく、乾燥粉末の水分量の制御が不能になったり、乾燥条件を作る上での制御に暴走が発生する恐れが少なく安定した制御が行え、生産性を阻害しないスラリー状又は溶液状材料の乾燥方法及びスラリー状又は溶液状材料の乾燥装置が得られる。
【００２３】
ところで、上記第一番目又は第二番目の発明の方法により、セラミック原料を含有するスラリー状又は溶液状のセラミック材料を乾燥して得られた乾燥粉末は、平均粒径が略一定で、規定水分量を略安定的に含有する状態で、スラリー状又は溶液状材料の供給開始から供給終了まで連続的に歩留まりよく生産される。したがって、その乾燥粉末を用いて所定形状の成形体を成形し、その成形体を焼結することにより得られる、本発明にかかるセラミック焼結体は、品質のよい製品として安価に生産することができる。
【００２４】
【発明の実施の形態】
以下、本発明の実施の形態を図面に示す実施例を参照して説明する。図１は、本発明の一例たるスプレードライヤ（噴霧乾燥装置）の全体正面図を示す。このスプレードライヤは、アルミナ、窒化アルミニウム等のセラミック粉末粒子を懸濁したスラリー状材料の乾燥装置として利用される。スラリー状材料（原液）Ｍは、材料供給部１のタンク１１からパイプ路を通って乾燥部３に形成される乾燥室３０へ送られる（パイプ路内を自然落下させてもよいし、ポンプ等によって圧送させてもよい）。具体的にはスラリー状材料Ｍは、流量調整弁１２を介して、乾燥室３０の天井部の投入口１０に配置された微粒化装置（アトマイザ）１３に供給される。アトマイザ１３は、乾燥スピードのアップ、粉末の球状化、粉末径の均一化等を目的として微粒化した原液Ｍを乾燥室３０全体に噴霧状に吐出する。原液Ｍは、通常の場合水分率２０〜５０％のスラリー状で、例えば水分率３３％のアルミナスラリーがアトマイザ１３に供給され、乾燥室３０全体に吐出される。なお、セラミックの材質によっては、セラミック原料成分を溶解させた溶液状材料Ｍを使用できる場合もある。一方、給気部２のフィルタ２４及びダンパ２１を介して送風機２２で取り込まれた外気が加熱器２３へ送られ、加熱されたのち給気Ｉとして、乾燥室３０の上面又は上部周面に設けられた給気口２０から乾燥室３０に向けて導入される。
【００２５】
そして、乾燥室３０において、アトマイザ１３から噴霧状に吐出され、乾燥室３０内を上部の投入口１０側から下部の取出口４０側に向け自然落下するスラリー状材料Ｍに対して、加熱された給気Ｉを接触させる。これにより、スラリー状材料Ｍは熱風（給気）Ｉ中を浮遊する間にその水分が給気Ｉに移行され、スラリー状材料Ｍの乾燥が行われる。次いで、乾燥されたスラリー状材料Ｍは、乾燥室３０下部の取出部４に形成された取出口４０から取出流路４１を経て乾燥粉末Ｇとして取り出される。一方給気Ｉは乾燥室３０の中間部周壁の排気口５０から、乾燥室３０中間部に浮遊する一部の乾燥粉末Ｇとともに排気部５に設けられた排風機５６で吸引され、排気口５０に接続された排気流路５１へ排気Ｏとして取り出される。
【００２６】
ここで、図１の実施例では、乾燥粉末Ｇの生産効率と歩留まりを向上させるために、取出流路４１に次のような機構を備えている。取出口４０下方の取出流路４１には篩４２が設けられ、取出口４０から出た乾燥粉末Ｇはまず篩４２にかけられる。篩４２の加振により粒子径が細かく揃えられた乾燥粉末Ｇは、篩４２を流下した後、分離・回収部６に設けられた排風機６９の吸引力によって捕集サイクロン６０内に投入される。一方篩４２を透過できなかった大径粉末やゴミ等の異物は回収箱４４に回収される。
【００２７】
そして、捕集サイクロン６０内に導入された乾燥粉末Ｇは、捕集サイクロン６０の内壁に沿う旋回流によって撹拌されるとともに、比重差で塵等の異物と選別・分離される。つまり、相対的に重い乾燥粉末Ｇは捕集サイクロン６０下部より回収流路６１に取り出され、保管サイロ６６に収容される。一方、相対的に軽い塵等の異物は、フィルタ６７及びダンパ６８を経て排風機６９で系外に排出される。
【００２８】
さて、捕集サイクロン６０出口に接続された回収流路６１には以下のようなフィードバック機構が設けられている。捕集サイクロン６０下部より回収流路６１に取り出された乾燥粉末Ｇの一部は、試料採取部６Ａに分岐し、赤外線等を利用した水分量測定計６ａで水分量を直接測定され、その後戻り流路６１’を介して取出流路４１（図１では篩４２の下流側）に循環されている。試料採取部６Ａよりも下流側の回収流路６１には４ポート３位置型の電磁切換弁６２が設置されている。回収流路６１の乾燥粉末Ｇを複数（図１では２槽）の保管サイロ６６に収容するとき、各サイロ６６のレベル計６ｂからの制御信号によって電磁切換弁６２がｂ又はｃの位置に切り換えられる。また、水分量測定計６ａで測定された乾燥粉末の水分率Ｍ_Ｇ'が規定水分率Ｍ_Ｇを満たしていないとき、水分量測定計６ａからの制御信号によって、電磁切換弁６２はａ位置に切り換えられる。その結果、この規定外の乾燥粉末Ｇは規定水分率の乾燥粉末Ｇとは分離して分離流路６３の一時貯留タンク６４に回収される。一時貯留タンク６４の出口と取出流路４１とは還元流路６５によって接続されており、回収された規定外の乾燥粉末Ｇは還元流路６５を通じて取出流路４１（図１では取出口４０と篩４２との間）に戻され、乾燥部３から取り出され水分率測定前の乾燥粉末Ｇと再度混合される。そして、混合された乾燥粉末Ｇは排風機６９の吸引力によって捕集サイクロン６０に投入され、試料採取部６Ａに至ると水分量測定計６ａで再び水分率Ｍ_Ｇ'が測定される。
【００２９】
例えば乾燥装置の起動時（運転開始時）や材料投入一時停止後の再起動時（運転再開時）に乾燥粉末Ｇの検出水分率Ｍ_Ｇ'が規定水分率Ｍ_Ｇを外れたときでも、この規定外の乾燥粉末Ｇを規定水分率の乾燥粉末Ｇとは分離して回収する分離流路６３が設けられているので、乾燥粉末Ｇの水分量の制御が不能になったり、乾燥条件を作る上での制御に暴走が発生する恐れが少なく安定した制御が行える。しかも分離回収された規定外の乾燥粉末Ｇは、還元流路６５により還元されて水分率検出前の後続の乾燥粉末Ｇと混合されるので、乾燥粉末Ｇの生産効率と歩留まりを向上させることができる。このとき、規定外の乾燥粉末Ｇと後続の乾燥粉末Ｇとが捕集サイクロン６０によって混合・撹拌されるので、水分率を均一化する上で有効である。
【００３０】
一方、乾燥粉末Ｇを含む排気Ｏは、排気流路５１を経て排気用サイクロン５２内に導入され、排気用サイクロン５２の内壁に沿う旋回流によって撹拌されるとともに、比重差で乾燥粉末Ｇと選別・分離される。つまり、相対的に重い乾燥粉末Ｇは排気用サイクロン５２下部より合流流路５３に取り出され、回収流路６１に合流される。一方、相対的に軽い排気Ｏは、フィルタ５４及びダンパ５５を経て排風機５６で系外に排出される。
【００３１】
なお、電磁切換弁６２は複数の切換ダンパ等に置き換えて使用してもよい。また、戻り流路６１’及び還元流路６５は、水分量測定計６ａよりも上流側であれば捕集サイクロン６０や回収流路６１に戻してもよい。ただし、戻り流路６１’又は還元流路６５を通じてフィードバックされる乾燥粉末Ｇと取出口４０から流下する後続の乾燥粉末Ｇとは水分率が異なる場合があるので、両乾燥粉末Ｇが充分混合・撹拌されてから水分量測定計６ａによる水分率測定が行われることが望ましい。特に、規定水分率Ｍ_Ｇを外れる乾燥粉末Ｇが継続的かつ大量にフィードバックされる可能性がある還元流路６５は、できるだけ上流側で取出流路４１に接続することが望ましい。これによって還元流路６５を通じてフィードバックされる乾燥粉末Ｇが、取出口４０から流下する後続の乾燥粉末Ｇと合流してから、水分量測定計６ａで再度水分率測定されるまでの時間と距離を長くとれる。よって両乾燥粉末Ｇが充分に混合・撹拌されるので、水分量測定計６ａによる水分率測定値のバラツキが抑えられる。さらに、還元流路６５に絞り弁（図示せず）等を設けて、規定水分率Ｍ_Ｇを外れる乾燥粉末Ｇが一時貯留タンク６４から取出流路４１に戻るときに少しずつ後続の乾燥粉末Ｇと混合するようにすれば、早く規定水分率Ｍ_Ｇに復帰できるようになる。ところで、合流流路５３の還元位置についても、回収流路６１以外に、取出流路４１、捕集サイクロン６０等を選択することができる。
【００３２】
保管サイロ６６に収容される乾燥粉末Ｇは、例えば規定水分率Ｍ_Ｇが３％以下、平均粒径が３０〜２００μｍ（より好ましくは５０〜１５０μｍ）として得られる。このような乾燥粉末Ｇがアルミナ、窒化アルミニウム等の場合は、例えばスパークプラグ用絶縁体の製造に使用される。
【００３３】
７は冷媒供給部を示し、スラリー状材料Ｍの供給に先立つ所定時間にわたって、スラリー状材料Ｍ中の水分が乾燥室３０において単位時間当たりに蒸発するに要する熱量に等しいか又は略等しい熱量を有する冷媒（例えば水）Ｃを、タンク７１から流量調整弁７２を経て投入口１０に供給する（後述の式（２０）参照）。これによって、乾燥装置の起動時（運転開始時）や材料投入一時停止後の再起動時（運転再開時）等のように取出口４０に乾燥粉末Ｇが存在しない場合にも、乾燥室３０内の状況を急変させることがなく、乾燥条件を作る上での制御に暴走が発生する恐れが少なくなり、生産性を阻害する恐れも少なくなる。さらに、本実施例のスプレードライヤでは、各部に設けられた検出器１ａ，１ｂ，２ａ，２ｂ，４ａ，５ａ，６ａ，６ｂ，７ａ等（各検出器については後述する）からの入力信号に基づき、加熱器２３、流量調整弁１２，７２、電磁切換弁６２等に対する制御信号を出力して、スプレードライヤの作動をコントロールするための制御部８が搭載されている。
【００３４】
このような噴霧乾燥装置を熱−水分系としてみたときの熱収支及び水分収支について図２を参照して考察する。まず、水分収支について、以下の関係が成り立つと考えられる。なお、ここでは水分量を湿量基準の「水分率」で管理する場合について記載するが、換算式等を用いれば乾量基準の「含水率」でも同様に管理することができる。
投入口１０から乾燥室３０に供給されるスラリー状材料Ｍにおいて、材料投入量をＱ_Ｍ［ｍ^３／ｈ］、材料比重をρ_Ｍ［ｇ／ｍ^３］、原料成分量をＷ［ｇ／ｈ］、材料保有水分率をＭ_Ｍ［％］としたとき、材料投入重量Ｗ_Ｍ［ｇ／ｈ］及び材料水分量ｗ_Ｍ［ｇ／ｈ］は、次式（１）及び（２）で表される。
Ｗ_Ｍ＝Ｗ＋ｗ_Ｍ＝Ｑ_Ｍ・ρ_Ｍ（１）
ｗ_Ｍ＝Ｑ_Ｍ・ρ_Ｍ・Ｍ_Ｍ／１００（２）
このとき材料保有水分率Ｍ_Ｍは、次式（３）で表される。
Ｍ_Ｍ＝（ｗ_Ｍ／（Ｗ＋ｗ_Ｍ））×１００（３）
一方、取出口４０から得られる乾燥粉末Ｇにおいて、粉末規定水分率をＭ_Ｇ［％］としたとき、粉末生成重量Ｗ_Ｇ［ｇ／ｈ］及び粉末水分量ｗ_Ｇ［ｇ／ｈ］は、次式（４）及び（５）で表される。
Ｗ_Ｇ＝Ｗ＋ｗ_Ｇ＝１００ｗ_Ｇ／Ｍ_Ｇ（４）
ｗ_Ｇ＝Ｗ_Ｇ・Ｍ_Ｇ／１００（５）
このとき粉末規定水分率Ｍ_Ｇは、次式（６）で表される。
Ｍ_Ｇ＝（ｗ_Ｇ／（Ｗ＋ｗ_Ｇ））×１００（６）
【００３５】
次いで、水蒸気比重をρ_Ｖ［ｇ／ｍ^３］、密度増加量をαとしたとき、スラリー状材料Ｍからの単位時間当たりの除去水分量に該当する水蒸気排出水分量ｗ_Ｖ［ｇ／ｈ］及び水蒸気容積Ｑ_Ｖ［ｍ^３／ｈ］が、次式（７）及び（８）で表される。
ｗ_Ｖ＝ｗ_Ｍ−ｗ_Ｇ（７）
Ｑ_Ｖ＝ｗ_Ｖ・α／ρ_Ｖ（８）
なお本明細書では、ｗ_Ｖを除去水分量とも呼ぶことにする。この除去水分量ｗ_Ｖは、言い換えればスラリー状材料Ｍの乾燥を行う乾燥速度を表しており、乾燥粉末Ｇの生産性を上げるためには大きいほどよいが、一方で乾燥装置の性能やスラリー状材料Ｍの変質（例えば物理的又は化学的性質の変化等）防止の点から制限される。
【００３６】
そして、排気口５０から排出される排気Ｏの排気風量をＱ_Ｏ［ｍ^３／ｈ］、給気絶対湿度をＨ_Ｉ［ｇ-H_２O／ｍ^３-dry air］としたとき、給気口２０から導入される給気Ｉの給気風量Ｑ_Ｉ［ｍ^３／ｈ］及び給気水分量ｗ_Ｉ［ｇ／ｈ］、さらには排気水分量ｗ_Ｏ［ｇ／ｈ］が、次式（９）、（１０）および（１１）で表される。
Ｑ_Ｉ＝Ｑ_Ｏ−Ｑ_Ｖ（９）
ｗ_Ｉ＝Ｑ_Ｉ・Ｈ_Ｉ（１０）
ｗ_Ｏ＝ｗ_Ｖ＋ｗ_Ｉ（１１）
よって、目標となる排気絶対湿度Ｈ_Ｏ［ｇ-H_２O／ｍ^３-dry air］は、次式（１２）で与えられる。
Ｈ_Ｏ＝ｗ_Ｏ／Ｑ_Ｏ（１２）
【００３７】
次に、熱収支に関しては、以下の関係が成り立つと考えられる。
給気風量をＱ_Ｉ［ｍ^３／ｈ］、給気比重をρ_Ｉ［ｇ／ｍ^３］、給気温度をＴ_Ｉ［Ｋ］、給気比熱をＣ_Ｉ［Ｊ／ｇ］としたとき、給気口２０から導入される給気Ｉの給気熱量ｑ_Ｉ［Ｊ／ｈ］は、次式（１３）で表される。
ｑ_Ｉ＝Ｑ_Ｉ・ρ_Ｉ・Ｔ_Ｉ・Ｃ_Ｉ（１３）
なお、加熱器２３に導入される外気風量をＱ_Ｉ'［ｍ^３／ｈ］、外気比重をρ_Ｉ'［ｇ／ｍ^３］、外気温度をＴ_Ｉ'［Ｋ］、外気比熱をＣ_Ｉ'［Ｊ／ｇ］としたとき、加熱器２３に導入される外気Ｉ’の外気熱量ｑ_Ｉ'［Ｊ／ｈ］は、次式（１３）’で表される。
ｑ_Ｉ'＝Ｑ_Ｉ'・ρ_Ｉ'・Ｔ_Ｉ'・Ｃ_Ｉ' （１３）’
よって、加熱器２３により外気Ｉ’に付与される付加熱量をｑ_２３［Ｊ／ｈ］とすると、給気熱量ｑ_Ｉ，外気熱量ｑ_Ｉ'及び付加熱量ｑ_２３の間には次式（１３）”の関係が成り立つ。
ｑ_Ｉ＝ｑ_Ｉ'＋ｑ_２３（１３）”
式（１３）”から明らかなように、給気熱量ｑ_Ｉは付加熱量ｑ_２３の変化（加熱器２３のボリューム等）によって調整可能であり、また周囲環境（外部状況）の変化によって外気熱量ｑ_Ｉ'も変動する。
一方、水の沸点をＴ_Ｖ［Ｋ］、材料温度をＴ_Ｍ［Ｋ］、水の比熱をＣ_Ｖ［Ｊ／ｇ］、水の気化熱をＲ_Ｖ［Ｊ／ｇ］としたとき、スラリー状材料Ｍに含有される水分の蒸発熱量ｑ_Ｖ［Ｊ／ｈ］は、次式（１４）で表される。
ｑ_Ｖ＝ｗ_Ｖ（（Ｔ_Ｖ−Ｔ_Ｍ）Ｃ_Ｖ＋Ｒ_Ｖ）（１４）
排気比重をρ_Ｏ［ｇ／ｍ^３］、排気温度をＴ_Ｏ［Ｋ］、排気比熱をＣ_Ｏ［Ｊ／ｇ］としたとき、排気口５０から排出される排気Ｏの排気熱量ｑ_Ｏ［Ｊ／ｈ］は、次式（１５）で表される。
ｑ_Ｏ＝Ｑ_Ｏ・ρ_Ｏ・Ｔ_Ｏ・Ｃ_Ｏ（１５）
粉末比熱をＣ_Ｇ［Ｊ／ｇ］、粉末温度をＴ_Ｇ［Ｋ］としたとき、乾燥粉末Ｇにおける残存熱量ｑ_Ｇ［Ｊ／ｈ］は、次式（１６）で表される。
ｑ_Ｇ＝Ｗ_Ｇ・Ｃ_Ｇ（Ｔ_Ｇ−Ｔ_Ｍ）（１６）
なお、材料比熱をＣ_Ｍ［Ｊ／ｇ］としたとき、材料Ｍを介しての投入熱量ｑ_Ｍ［Ｊ／ｈ］は、次式（１６）’で表される。
ｑ_Ｍ＝Ｗ_Ｍ・Ｔ_Ｍ・Ｃ_Ｍ＝Ｑ_Ｍ・ρ_Ｍ・Ｔ_Ｍ・Ｃ_Ｍ（１６）’
周囲温度をＴ_Ａ［Ｋ］、乾燥室表面積をＡ［ｍ^２］、伝熱係数をＫ［Ｊ／ｈ／ｍ^２］としたとき、乾燥室放熱量ｑ_Ｌ［Ｊ／ｈ］は、次式（１７）で表される。
ｑ_Ｌ＝Ｔ_Ａ・Ａ・Ｋ（１７）
したがって、乾燥室３０に対する熱収支を考慮すると、上記給気熱量ｑ_Ｉは次式（１８）で表される。
ｑ_Ｉ＝ｑ_Ｖ＋ｑ_Ｏ＋ｑ_Ｇ＋ｑ_Ｌ（１８）
【００３８】
図３に本発明を適用したスプレードライヤを模式的に示す。図３において、スプレードライヤは、次のような乾燥条件を作る上での制御機能を有している。
▲１▼排気口５０の近傍にて排気Ｏの絶対湿度Ｈ_Ｏ'を検出し、この排気絶対湿度の検出値Ｈ_Ｏ'と、スラリー状材料Ｍの保有水分率Ｍ_Ｍと乾燥粉末Ｇの規定水分率Ｍ_Ｇとから定まる排気絶対湿度の目標値Ｈ_Ｏとの比較において、Ｈ_Ｏ'＜Ｈ_Ｏのとき給気Ｉの有する給気熱量ｑ_Ｉを大きくし、Ｈ_Ｏ'＞Ｈ_Ｏのとき給気熱量ｑ_Ｉを小さくすることで、スラリー状材料Ｍからの単位時間当たりの除去水分量ｗ_Ｖを略一定に維持して、規定水分率Ｍ_Ｇを有する乾燥粉末Ｇを得ること。（図４参照）
▲２▼乾燥装置の起動時（運転開始時）や材料投入一時停止後の再起動時（運転再開時）等に、スラリー状材料Ｍの供給に先立つ所定時間にわたって、スラリー状材料Ｍの保有水分量が乾燥室３０にて単位時間当たりに蒸発するに要する蒸発熱量ｑ_Ｖに略等しい熱量となる所定量の冷媒Ｃを、投入口１０に供給すること。（図５参照）
▲３▼乾燥粉末Ｇの水分率Ｍ_Ｇ'を検出し、乾燥粉末Ｇの検出水分率Ｍ_Ｇ'と規定水分率Ｍ_Ｇとの比較において、Ｍ_Ｇ'＜Ｍ_Ｇのとき給気Ｉの有する給気熱量ｑ_Ｉを小さくし、Ｍ_Ｇ'＞Ｍ_Ｇのとき給気熱量ｑ_Ｉを大きくすることで、スラリー状材料Ｍからの単位時間当たりの除去水分量ｗ_Ｖを略一定に維持して、規定水分率Ｍ_Ｇを有する乾燥粉末Ｇを得ること。（図６参照）
▲４▼加熱器２３を通じて加熱される前の外気Ｉ’の温度、湿度又は風量のうち少なくとも一つの特性値を検出し、得られた特性値に基づいて（得られた特性値により求められる外気熱量ｑ_Ｉ'に基づいて）給気Ｉの有する給気熱量ｑ_Ｉを調整して、規定水分率Ｍ_Ｇを有する乾燥粉末Ｇを得ること。（図７参照）
▲５▼乾燥室３０からの放熱量ｑ_Ｌを検出し、乾燥室放熱量ｑ_Ｌの検出値に基づいて給気Ｉの有する給気熱量ｑ_Ｉを調整して、規定水分率Ｍ_Ｇを有する乾燥粉末Ｇを得ること。（図８参照）
▲６▼乾燥粉末Ｇの残存熱量ｑ_Ｇを検出し、粉末残存熱量ｑ_Ｇの検出値に基づいて給気Ｉの有する給気熱量ｑ_Ｉを調整して、規定水分率Ｍ_Ｇを有する乾燥粉末Ｇを得ること。（図９参照）
▲７▼投入口１０への供給に先立つスラリー状材料Ｍの温度Ｔ_Ｍと投入量Ｑ_Ｍとによって、スラリー状材料Ｍを介しての投入熱量ｑ_Ｍを検出し、材料投入熱量ｑ_Ｍの検出値に基づいて給気Ｉの有する給気熱量ｑ_Ｉを調整して、規定水分率Ｍ_Ｇを有する乾燥粉末Ｇを得ること。（図１０参照）
【００３９】
上記の制御機能を果たすため、図３のスプレードライヤには、その作動をコントロールするための制御部８を設けている。制御部８は、Ｉ／Ｏポート８１とこれに接続されたＣＰＵ８２，ＲＯＭ８３，ＲＡＭ８４等からなるマイクロプロセッサにより構成されており、ＲＯＭ８３には制御プログラムが格納されている。
【００４０】
Ｉ／Ｏポート８１の入力側には、次のような検出器（センサ）等が接続されている。
・温度計１ａ：スラリー状材料Ｍの投入経路に設けられ、スラリー状材料Ｍの温度Ｔ_Ｍを測定する。
・流量計１ｂ：スラリー状材料Ｍの投入経路に設けられ、スラリー状材料Ｍの流量（投入量）Ｑ_Ｍを測定する。
・温度計２ａ：給気Ｉの給気経路に設けられ、給気Ｉの温度Ｔ_Ｉを測定する。
・温度計、湿度計又は流量計のうち少なくとも一種２ｂ：加熱器２３により加熱される前の外気Ｉ’の給気経路に設けられ、外気Ｉ’の温度、湿度又は風量のうち少なくとも一つの特性値を測定する。なお、ここで使用する湿度（計）は、絶対湿度（計）、相対湿度（計）のいずれであってもよい。
・温度計４ａ：乾燥粉末Ｇの取出流路４１に設けられ、乾燥粉末Ｇの粉末温度Ｔ_Ｇを測定する。
・重量流量計４ｂ：温度計４ａに隣接して乾燥粉末Ｇの取出流路４１に設けられ、乾燥粉末Ｇの重量流量（粉末生成重量）Ｗ_Ｇを測定する。
・絶対湿度測定装置（温度計、相対湿度計）５ａ：排気Ｏの排気流路５１（排気口５０の近傍）に設けられ、排気Ｏの温度Ｔ_Ｏと相対湿度を測定し、既知の換算式により、排気絶対湿度の検出値Ｈ_Ｏ'を得る。ここに、絶対湿度とは、標準状態での気体中の絶対水分量を特定するパラメータ（重量％、分圧、モル分率等）を総称するものである。具体的には測定温度Ｔ_Ｏでの飽和水蒸気量νの値に相対湿度値ｈ_Ｒを乗ずることにより、標準状態の気体の単位体積当たりの水蒸気量として絶対湿度を算出することができる。なお、露点計等を用いてもよい。
・赤外線等を利用した水分量測定計６ａ：乾燥粉末Ｇの取出口４０に続く取出流路４１（取出口４０の近傍）又は捕集サイクロン６０の出口に続く回収流路６１、若しくはそれらから分岐させた試料採取部６Ａに設置され（図９又は図１参照）、乾燥粉末Ｇの水分量として水分率Ｍ_Ｇ（湿量基準）を測定する。なお、乾燥粉末Ｇの水分量として含水率（乾量基準）を測定してもよい。
・温度計７ａ：冷媒Ｃの投入経路に設けられ、冷媒Ｃの温度Ｔ_Ｃを測定する。
【００４１】
一方Ｉ／Ｏポート８１の出力側には、次のような作動部材（アクチュエータ）等が接続されている。
・加熱器２３の温度設定器２３ａ：制御信号に基づき、加熱器２３の設定温度を調節して、給気温度Ｔ_Ｉや給気熱量ｑ_Ｉを変更する。
・冷媒Ｃ側流量調整弁７２の供給量設定器７２ａ：制御信号に基づき、流量調整弁７２の開度を調節（弁閉を含む）して、冷媒供給量ｗ_Ｃを変更する。
・材料Ｍ側流量調整弁１２の供給量設定器１２ａ：制御信号に基づき、流量調整弁１２の開度を調節（弁閉を含む）して、材料投入量Ｑ_Ｍを変更する。
【００４２】
なお、上記した以外にＩ／Ｏポート８１の入力側には、保管サイロ６６に設けられ、乾燥粉末Ｇの収容量を測定するレベル計６ｂも接続されている（図１参照）。また、Ｉ／Ｏポート８１の出力側には、水分量測定計６ａ又はレベル計６ｂの出力に起因する制御信号に基づき、電磁ソレノイドを作動して回収流路６１と分離流路６３とを切り換える電磁切換弁６２も接続されている（図１参照）。しかし、既述の通りその制御機能は、乾燥粉末Ｇの水分量制御には直接的には関与していない。そこで、レベル計６ｂと電磁切換弁６２とは図３の制御系から割愛した（図４以降において同じ）。
【００４３】
次に、水分量測定計６ａを設ける位置について、捕集サイクロン６０の出口に続く回収流路６１から分岐させた試料採取部６Ａに設ける場合（図１参照）と、乾燥室３０の取出口４０に続く取出流路４１から分岐させた試料採取部６Ａに設ける場合（図１２参照）とで、乾燥粉末Ｇの水分量制御に関して作用・効果上の差異は見られない。そこで、取出流路４１から回収流路６１に至る経路は図３の制御系において中間省略した（図４以降において同じ）。したがって、水分量測定計６ａは取出流路４１から回収流路６１に至る経路の任意の位置に取り付け可能である。
【００４４】
スプレードライヤにおける乾燥条件を作る上での各制御機能について機能毎に分けて解説する。図４において、絶対湿度測定装置５ａによって排気Ｏの絶対湿度Ｈ_Ｏ'を検出し、この検出値Ｈ_Ｏ'と、材料Ｍの保有水分Ｍ_Ｍと乾燥粉末Ｇの規定水分Ｍ_Ｇとから定まる排気絶対湿度の目標値Ｈ_Ｏとを比較する。ところで、式（７）（１０）（１１）（１２）及び（１３）より、次式（１９）が導かれる。Ｈ_Ｏ＝（ｗ_Ｖ＋ｑ_Ｉ・Ｈ_Ｉ／（ρ_Ｉ・Ｔ_Ｉ・Ｃ_Ｉ））／Ｑ_Ｏ（１９）（ａ）いま、排気絶対湿度の検出値Ｈ_Ｏ'が目標値Ｈ_Ｏと等しいときは式（１９）が成立しており、またこのとき単位時間当たりの除去水分量ｗ_Ｖ（乾燥速度）は、
ｗ_Ｖ＝ｗ_Ｍ−ｗ_Ｇ＝ｃｏｎｓｔ．（７）’
が維持されている。
（ｂ）ここで、恒率乾燥期間から減率乾燥期間への移行又は外乱要因等によって乾燥速度ｗ_Ｖが低下したとき、式（１９）より排気絶対湿度の検出値Ｈ_Ｏ'は目標値Ｈ_Ｏを下回ることになる。このとき乾燥粉末Ｇの粉末水分量ｗ_Ｇが大きくなるので、上記式（６）により検出水分率Ｍ_Ｇ'が規定水分率Ｍ_Ｇよりも大きくなっている。そこで、式（１９）において給気熱量ｑ_Ｉに着目し、加熱器２３の温度設定器２３ａの設定温度を高め給気熱量ｑ_Ｉを大きくすれば、簡単かつ効果的に元の状態に戻すことができる。つまり給気熱量ｑ_Ｉが大きくなると、式（１９）により排気絶対湿度の検出値Ｈ_Ｏ'が大きくなって目標値Ｈ_Ｏと等しくなる。排気絶対湿度の検出値Ｈ_Ｏ'が大きくなるにつれて粉末水分量ｗ_Ｇが低下し、式（６）により検出水分率Ｍ_Ｇ'も低下する。よって排気絶対湿度の検出値Ｈ_Ｏ'が目標値Ｈ_Ｏと等しくなれば、乾燥速度ｗ_Ｖも元の状態に維持されることになる。（ｃ）一方、乾燥速度ｗ_Ｖが増大したとき、排気絶対湿度の検出値Ｈ_Ｏ'は目標値Ｈ_Ｏを上回り、このとき乾燥粉末Ｇの粉末水分量ｗ_Ｇは小さくなるので、検出水分率Ｍ_Ｇ'が規定水分率Ｍ_Ｇよりも小さくなっている。そこで、加熱器２３の温度設定器２３ａの設定温度を低め給気熱量ｑ_Ｉを小さくすると、排気絶対湿度の検出値Ｈ_Ｏ'が小さくなり目標値Ｈ_Ｏと等しくなる。排気絶対湿度の検出値Ｈ_Ｏ'が小さくなるにつれて粉末水分量ｗ_Ｇが増大し、検出水分率Ｍ_Ｇ'も増大する。よって排気絶対湿度の検出値Ｈ_Ｏ'が目標値Ｈ_Ｏと等しくなれば、乾燥速度ｗ_Ｖも元の状態に維持されることになる。
【００４５】
上記排気絶対湿度の目標値Ｈ_Ｏ又は／及び除去水分量ｗ_Ｖに関して、目標値Ｈ_Ｏ又は／及び除去水分量ｗ_Ｖを所定の値一点に定めておいても、ハンチングを起こしにくい安定した乾燥粉末Ｇの水分量制御が期待できる。しかし、上記所定の値に対する上下のうち少なくとも一方に不感帯を設定した目標値Ｈ_Ｏ又は／及び除去水分量ｗ_Ｖとしておけば、より一層のハンチング防止が図れる。なお、排気の絶対湿度Ｈ_Ｏ'は直接的に測定しても勿論よいが、排気の温度と相対湿度とを測定し、既知の換算式から絶対湿度を算出する方法が実用的である。
【００４６】
図５において、乾燥装置の起動時（運転開始時）や材料投入一時停止後の再起動時（運転再開時）等に、スラリー状材料Ｍの供給に先立つ所定時間にわたって、スラリー状材料Ｍの保有する水分が乾燥室３０にて単位時間当たりに蒸発するに要する蒸発熱量ｑ_Ｖに略等しい熱量となる所定量の冷媒Ｃ（例えば水）を、投入口１０に供給する。式（１４）において、冷媒の沸点をＴ_Ｖ'［Ｋ］、冷媒の温度をＴ_Ｃ［Ｋ］、冷媒の比熱をＣ_Ｃ［ｃａｌ／ｇ］、冷媒の気化熱をＲ_Ｃ［ｃａｌ／ｇ］としたとき、必要とされる冷媒供給量ｗ_Ｃ［ｇ／ｈ］は、次式（２０）で表される。

冷媒が水の場合には、冷媒温度Ｔ_Ｃ＝材料温度Ｔ_Ｍであれば式（２０）は、
ｗ_Ｃ＝ｗ_Ｖ（２０）’となり、冷媒供給量ｗ_Ｃは除去水分量（水蒸気排出水分量）ｗ_Ｖに等しくなる。
【００４７】
具体的には、材料投入開始ボタンが押された直後（図示せず）においては、制御部８にて所定時間にわたって流量調整弁１２を閉じてスラリー状材料Ｍの供給を中止する。そしてその間は流量調整弁７２を開いて式（２０）又は（２０）’で表される冷媒供給量ｗ_Ｃ［ｇ／ｈ］の冷媒Ｃ（例えば水）を供給する制御信号が、両流量調整弁１２，７２の供給量設定機構１２ａ，７２ａに対して発せられる。このとき乾燥室３０では、乾燥粉末Ｇは生じないものの、その他の水分収支及び熱収支についてはスラリー状材料Ｍを供給した場合と略同等の運転状態、いわば模擬運転状態にある。したがって、乾燥装置の起動時（運転開始時）や材料投入一時停止後の再起動時（運転再開時）等のように取出口４０に乾燥粉末Ｇが存在しない場合（このとき水分量測定計６ａは粉末水分率Ｍ_Ｇ'＝０％と検出する）にも、乾燥室３０の状況を急変させることがない。つまり、かかる場合にも乾燥条件を作る上での制御の暴走が発生する恐れが少なくなり、生産性を阻害する恐れも少なくなる。なお、スラリー状材料Ｍに代わって冷媒Ｃを供給する時間は、基本的に乾燥室３０の状況が安定するまでの間でよい。ただし、スラリー状材料Ｍを供給する状態での通常運転に切り替えたときに、取出口４０から乾燥粉末Ｇが取り出されるまでの時間を含む場合には乾燥室３０の状況がより安定する。
【００４８】
図６では、水分量測定計６ａにより乾燥粉末Ｇの水分率Ｍ_Ｇ'を検出し、乾燥粉末Ｇの規定水分率Ｍ_Ｇと検出水分率Ｍ_Ｇ'との比較を行う。
（ａ）いま、検出水分率Ｍ_Ｇ'が規定水分率Ｍ_Ｇと等しいときは、
Ｍ_Ｇ＝（ｗ_Ｇ／（Ｗ＋ｗ_Ｇ））×１００（６）
が成立しており、またこのとき単位時間当たりの除去水分量ｗ_Ｖ（乾燥速度）は、
ｗ_Ｖ＝ｗ_Ｍ−ｗ_Ｇ＝ｃｏｎｓｔ．（７）’
が維持されている。
（ｂ）ここで、検出水分率Ｍ_Ｇ'が規定水分率Ｍ_Ｇよりも大きくなったとすると、このとき乾燥粉末Ｇの粉末水分量ｗ_Ｇが増大して乾燥速度ｗ_Ｖが低下しており、上記の排気絶対湿度の検出値Ｈ_Ｏ'が目標値Ｈ_Ｏを下回るケースと同様の状態になっている。そこで、上記のケースと同様に加熱器２３の温度設定器２３ａの設定温度を高め給気熱量ｑ_Ｉを大きくすれば、粉末水分量ｗ_Ｇが低下し、検出水分率Ｍ_Ｇ'も低下する。よって検出水分率Ｍ_Ｇ'が規定水分率Ｍ_Ｇと等しくなれば、乾燥速度ｗ_Ｖも元の状態に維持されることになる。
（ｃ）一方、検出水分率Ｍ_Ｇ'が規定水分率Ｍ_Ｇよりも小さくなったときは、乾燥粉末Ｇの粉末水分量ｗ_Ｇが低下して乾燥速度ｗ_Ｖが増大している。そこで、加熱器２３の温度設定器２３ａの設定温度を低め給気熱量ｑ_Ｉを小さくすると、粉末水分量ｗ_Ｇが増大し、検出水分率Ｍ_Ｇ'も増大する。よって検出水分率Ｍ_Ｇ'が規定水分率Ｍ_Ｇと等しくなれば、乾燥速度ｗ_Ｖも元の状態に維持されることになる。なお、図６の制御は図４の制御に対して補助的に行われる。
【００４９】
図７において、加熱器２３を通じて加熱される前の外気Ｉ’の温度、湿度又は風量のうち少なくとも一つの特性値を測定して外部状況の変化を検出し、得られた特性値に基づいて給気Ｉの有する給気熱量ｑ_Ｉを調整する。具体的には、例えば外気の温度Ｔ_Ｉ'と風量Ｑ_Ｉ'とを測定し、その測定値から式（１３）’より外気熱量ｑ_Ｉ'を求め、この外気熱量ｑ_Ｉ'の変化を感知すると加熱器２３の温度設定器２３ａの設定温度を変更し、給気熱量ｑ_Ｉを調整する。すなわち、図７の制御は外気熱量ｑ_Ｉ'の変動感知による予測制御（フィードフォーワード）である。なお、図７の制御も図４の制御に対して補助的に行われる。
【００５０】
図８において、乾燥室３０からの放熱量ｑ_Ｌを検出し、乾燥室放熱量ｑ_Ｌの検出値に基づいて給気Ｉの有する給気熱量ｑ_Ｉを調整する。前述の式（１７）において、周囲温度Ｔ_Ａを外気温度Ｔ_Ｉ'で近似すると乾燥室放熱量ｑ_Ｌは、次式（１７）’で表される。
ｑ_Ｌ＝Ｔ_Ａ・Ａ・Ｋ≒Ｔ_Ｉ'・Ａ・Ｋ（１７）’
そこで外気温度Ｔ_Ｉ'を測定し、その測定値から式（１７）’より乾燥室放熱量ｑ_Ｌを求め、この乾燥室放熱量ｑ_Ｌの変化を感知すると加熱器２３の温度設定器２３ａの設定温度を変更し、給気熱量ｑ_Ｉを調整する。このとき、前述の式（１８）において乾燥室放熱量ｑ_Ｌの変動量を補うように給気熱量ｑ_Ｉを調節するとよい。なお、図８の制御も図４の制御に対して補助的に行われる。
【００５１】
図９において、乾燥粉末Ｇの残存熱量ｑ_Ｇを検出し、粉末残存熱量ｑ_Ｇの検出値に基づいて給気Ｉの有する給気熱量ｑ_Ｉを調整する。具体的には、例えば粉末生成重量Ｗ_Ｇ、粉末温度Ｔ_Ｇ及び材料温度Ｔ_Ｍを測定し、その測定値から式（１６）より粉末残存熱量ｑ_Ｇを求め、この粉末残存熱量ｑ_Ｇの変化を感知すると加熱器２３の温度設定器２３ａの設定温度を変更し、給気熱量ｑ_Ｉを調整する。このとき、前述の式（１８）において粉末残存熱量ｑ_Ｇの変動量を補うように給気熱量ｑ_Ｉを調節するとよい。なお、図９の制御も図４の制御に対して補助的に行われる。
【００５２】
図１０において、投入口１０への供給に先立つスラリー状材料Ｍの温度Ｔ_Ｍと投入量Ｑ_Ｍとを測定して、式（１６）’によりスラリー状材料Ｍを介しての投入熱量ｑ_Ｍを検出し、この材料投入熱量ｑ_Ｍの検出値に基づいて給気Ｉの有する給気熱量ｑ_Ｉを調整する。すなわち、図１０の制御は材料投入熱量ｑ_Ｍの変動感知による予測制御（フィードフォーワード）である。なお、図１０の制御も図４の制御に対して補助的に行われる。
【００５３】
このようにして、アルミナ等のセラミック原料を含有するスラリー状のセラミック材料を乾燥して得られた乾燥粉末は、平均粒径が略一定で規定水分量を略安定的に含有し、スラリー状材料の供給開始から供給終了まで連続的に歩留まりよく生産される。したがって、その乾燥粉末を焼結することにより得られるセラミック焼結体、例えばスパークプラグ用絶縁体は、品質のよい製品として安価に生産することができる。
【００５４】
図１１にセラミック焼結体としてのスパークプラグ用絶縁体の製造方法の一例を、スパークプラグの主要構造とともに示す。まず、図１１（ａ）に示すように、スパークプラグ用絶縁体はラバープレス法によって成形されるのが一般的である。成形機２００に設けられる上下方向の凹部に沿って環状のキャビティ２１０を張設し、このキャビティ２１０の内側に環状のゴム型２２０を挿入固定する。ゴム型２２０の下方開口部には底蓋２３０を嵌合させ、下方側ホルダ２４０により底蓋２３０を押圧保持する。スパークプラグ用絶縁体１０２を形成するセラミック原料として、図１の乾燥装置で得られたアルミナを主体とする乾燥粉末Ｇを、底蓋２３０で下方を閉鎖されたゴム型２２０の内部空間に充填する。このとき、プレスピン２５０がこの内部空間の中心に位置するように上方側ホルダ２６０で押圧保持されており、このプレスピン２５０は絶縁体１０２において中心電極１０３等を挿通するための中心孔１０２ａに対応する形状を有している。そして、成形機２００の管路２７０を通って水圧、油圧等の液圧ＦＰがキャビティ２１０の外側からゴム型２２０の径方向内側に作用し、絶縁体成形体１０２Ａが形成される。
【００５５】
次に、図１１（ｂ）に示すように、液圧ＦＰを解除しゴム型２２０から絶縁体成形体１０２Ａを取り出す。絶縁体成形体１０２Ａからプレスピン２５０と上方側ホルダ２６０とを取り外した後、グラインダ研削等によって外形を仕上げる。
【００５６】
このようにして得られた絶縁体成形体１０２Ａは、トンネル窯において１６００℃前後の温度で焼成される。これに釉薬をかけ９００℃前後で再び焼成すると、図１１（ｃ）に示すようなセラミック焼結体としての絶縁体焼結体１０２Ｂが得られる。
【００５７】
そして、図１１（ｄ）では、絶縁体焼結体１０２Ｂに寸法調整等が施された絶縁体１０２が筒状の主体金具１０１の内側に嵌め込まれ、絶縁体１０２の中心孔１０２ａには中心電極１０３が配置される。一端が主体金具１０１に固定された接地電極１０４の他端が中心電極１０３の先端部と対向するように曲げられ、接地電極１０４と中心電極１０３との間に火花放電ギャップｇが形成されて、スパークプラグ１００が構成されている。
【００５８】
本発明に係る乾燥装置の適用例として、噴霧乾燥装置について説明してきたが、この他にも内部撹拌式や流動層式の乾燥装置等、スラリー状又は溶液状材料に使用可能な乾燥装置であれば適用可能である。
【図面の簡単な説明】
【図１】本発明の乾燥装置の一実施例たる噴霧乾燥装置を示す全体説明図。
【図２】図１の噴霧乾燥装置の水分収支及び熱収支を表す模式図。
【図３】図１の噴霧乾燥装置の主要制御機能を示すブロック図。
【図４】図３の制御機能のうちの一部を示すブロック図。
【図５】図３の制御機能のうちの他の一部を示すブロック図。
【図６】図３の制御機能のうちのさらに他の一部を示すブロック図。
【図７】図３の制御機能のうちのさらに他の一部を示すブロック図。
【図８】図３の制御機能のうちのさらに他の一部を示すブロック図。
【図９】図３の制御機能のうちのさらに他の一部を示すブロック図。
【図１０】図３の制御機能のうちのさらに他の一部を示すブロック図。
【図１１】セラミック焼結体としてのスパークプラグ用絶縁体の製造方法の一例を、スパークプラグの主要構造とともに示す説明図。
【図１２】従来の噴霧乾燥装置を示す説明図。
【符号の説明】
１０投入口
２０給気口
２３加熱器
３乾燥部
３０乾燥室
４０取出口
５ａ絶対湿度測定装置（検出器）
５０排気口
７冷媒供給部
８制御部
Ｃ水（冷媒）
Ｇ乾燥粉末
Ｉ給気
Ｉ’ 外気
Ｍスラリー状材料（材料）
Ｏ排気
Ｈ_Ｏ排気絶対湿度
Ｍ_Ｇ粉末規定水分率（粉末規定水分量）
Ｍ_Ｍ材料保有水分率（材料保有水分量）
ｑ_Ｉ給気熱量
ｑ_Ｇ粉末残存熱量
ｑ_Ｌ乾燥室放熱量
ｑ_Ｍ材料投入熱量
ｑ_Ｖ蒸発熱量
ｗ_Ｃ冷媒供給量
ｗ_Ｖ水蒸気排出水分量（除去水分量）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for drying a slurry or solution material, a drying apparatus for the slurry or solution material, and a method for producing a ceramic sintered body.
[0002]
[Prior art]
As an example of a slurry or solution material drying apparatus, a spray drying apparatus (spray dryer) is shown in FIG. In this apparatus, slurry-like or solution-like material M is supplied from the inlet 10 above the drying chamber 30, and the outside air is heated by the heater 23 to supply the upper surface or peripheral surface of the drying chamber 30 as the supply air I. The air is introduced into the drying chamber 30 from the mouth 20. Then, by bringing the heated air supply I into contact with the material M that naturally falls in the drying chamber 30 from the upper inlet 10 side toward the lower outlet 40 side, the moisture of the material M is heated by hot air ( Supply air) While floating in I, the air is transferred (absorbed) to supply air I, and the material M is dried. The dried powder G after drying is taken out from the outlet 40 at the lower part of the drying chamber 30, while the supply air I is taken out from the drying chamber 30 as exhaust O through an outlet 50 in the middle of the drying chamber 30.
[0003]
By the way, in such a drying apparatus, it is necessary to control the moisture content (moisture content) contained in the obtained dry powder G so as to be a constant value. Conventionally, various drying controls (drying systems) are considered. Thus, the moisture content of the dry powder G is controlled. The following drying systems are known as typical drying controls. That is, a moisture meter 6a using infrared rays or the like is installed in the sampling unit 6A to directly measure the moisture content of the dry powder G, and to compare the measured moisture content with the specified moisture content of the dry powder G. Based on this, the moisture content of the dry powder G is controlled while controlling the input amount of the material M by the control unit 8, the flow rate adjusting valve 12, the flow meter 1b and the like. Note that the sample collection unit 6A is provided, for example, as branched from the extraction flow channel 41 of the dry powder G as shown in FIG.
[0004]
[Problems to be solved by the invention]
In the above method, only the moisture content of the finished dry powder G is a detection target (specific detection means is a moisture meter 6a), while the input amount of the material M into the drying chamber 30 at the head of the system is controlled. Since the target (the specific control means is the flow rate adjusting valve 12 or the like), a delay in response inevitably occurs between the two, and hunting tends to occur in the moisture content control of the dry powder G. Therefore, in order to stabilize the moisture content of the dry powder G, it is necessary to collect the obtained dry powder G having different moisture content, and stir and mix with a blender or the like to make the moisture content of the dry powder G uniform. Become. However, since reprocessing such as stirring and mixing is performed after drying, the cost increases, and the quality of the dry powder G may be reduced due to reprocessing.
[0005]
Furthermore, in the above method, the sampling unit 6A of the moisture meter 6a is formed with a narrow passage in order to stabilize the measurement of the moisture content while keeping the flow rate of the dried powder G constant. Or the excessive moisture dry powder may adhere to the moisture meter 6a. Therefore, the moisture content of the dry powder G cannot be controlled, and there is a possibility that runaway may occur in the control in creating the drying conditions in the drying system. In addition, the dry powder G may not be present at the outlet 40 when the drying apparatus is started (when the operation is started) or when the material is temporarily stopped after the material is temporarily stopped (when the operation is restarted). There is a possibility that runaway may occur in the control in making the
[0006]
The object of the present invention is to control the moisture content of the dry powder, because it has good responsiveness and is unlikely to cause hunting, and when the sampling part is clogged, or when the drying apparatus is started up or after the material input is paused. Even when there is no dry powder at the outlet, such as when starting up, there is little risk of runaway control in creating drying conditions, and a slurry or solution material drying method that does not hinder productivity and An object of the present invention is to provide a drying apparatus for slurry-like or solution-like materials. It is another object of the present invention to provide a method for producing a ceramic sintered body that obtains a high-quality ceramic sintered body by molding and sintering the dry powder thus produced.
[0007]
[Means for solving the problems and actions / effects]
  In order to solve the above-mentioned problem, a method for drying a slurry-like or solution-like material according to the first invention is as follows:
  The slurry-like or solution-like material containing the ceramic raw material is supplied to the drying chamber from the input port provided in the drying unit, and from the air supply port provided in the drying unit with the outside air heated through the heater as supply air Introduced into the drying chamber,
  Drying the material by bringing the supply air into contact with the material supplied from the inlet,
  The material after drying is taken out as a dry powder from an outlet provided in the drying unit, while the supply air is discharged from the exhaust port provided in the drying unit to the outside of the drying chamber,
  Information necessary for specifying the absolute humidity of the exhaust gas is detected in the vicinity of the exhaust port, and a detected value H of the exhaust absolute humidity is detected._OBased on ', adjust the amount of heat supplied by the supply air so that the dry powder having a specified moisture content is obtainedWith
  The input heat amount through the material is detected based on the temperature and input amount of the material prior to supply to the input port, and the supply air heat amount is supplementarily adjusted based on the detected value of the material input heat amount.It is characterized by that.
[0008]
  Moreover, the slurry-like or solution-like material drying apparatus according to the first invention is:
  An inlet for supplying a slurry-like or solution-like material containing a ceramic raw material;
  An air inlet that heats the outside air with a heater and introduces it as air supply;
  A drying chamber for drying the material by bringing the supply air into contact with the material supplied from the input port;
  An outlet for taking out the dried material as a dry powder,
  An exhaust port for exhausting the supply air to the outside as exhaust;
  Near the exhaust portBeforeA detector that detects the information necessary to determine the absolute humidity of the exhaustWas detected by its detectorExhaust humidity detection value H_OIs provided with a control unit that adjusts the amount of heat supplied by the air supply so that the dry powder having a specified amount of water is obtained.And
  A thermometer for measuring the temperature of the material prior to supply to the input port and a flow meter for measuring the input amount are provided, and the control unit detects the amount of heat input to the material detected by the thermometer and the flow meter. Based on the detected value, the heat supply heat amount is supplementarily adjustedIt is characterized by that.
[0009]
According to these inventions, the exhaust absolute humidity detection value H_OBy adjusting the heat supply heat quantity of the supply air so that a dry powder having a prescribed water content is obtained based on ', the water content of the finished dry powder may not be directly measured. In other words, since the moisture content of the powder is controlled by using the information during drying, a stable control of the moisture content of the powder that is less likely to cause hunting with little delay in responsiveness can be expected. Also, when the sample collection part of the moisture meter is clogged, or when there is no dry powder at the outlet, such as when the drying device is started or when restarting after temporarily stopping the material charging, There is little risk of runaway in control in creating conditions, and a slurry-like or solution-like material drying method and a slurry-like or solution-like material drying apparatus that do not hinder productivity can be obtained.
[0010]
Note that the exhaust absolute humidity target value H_OTarget value H_OCan be expected to stably control the amount of powder moisture that is unlikely to cause hunting, but a target value H in which a dead zone is set on at least one of the upper and lower sides of the predetermined value._OAs a result, it is possible to further prevent hunting. Further, in the present specification, the term “water content” includes the case of a moisture content standard (for example, “moisture content”) and the case of a dry content standard (for example, “water content”).
[0011]
In addition, the adjustment of the heat supply amount of heat according to the present invention may be performed so that the amount of water removed from the material per unit time is maintained substantially constant or within a specified range. Here, the amount of water removed per unit time from the material represents the drying speed of the material, and is preferably as large as possible to increase the productivity of the dry powder. However, on the other hand, the performance of the drying apparatus is naturally limited from the viewpoint of preventing the quality of the material (for example, change in physical or chemical properties). According to the present invention, stable continuous operation can be performed under an optimum drying speed for the material. Note that the exhaust absolute humidity target value H is also related to the amount of water removed from the material per unit time._OSimilarly to the above, if a dead zone is set at least one of the upper and lower sides with respect to a predetermined value, it is effective for preventing hunting.
[0012]
Here, the adjustment of the heat supply heat quantity of the present invention is more specifically performed by detecting the exhaust absolute humidity detected value H._O'And the target absolute value H of exhaust humidity determined by the amount of moisture contained in the material and the specified amount of moisture in the dry powder_OIn comparison with H_O'<H_OIncrease the amount of heat supplied, and H_O'＞ H_OIn this case, the amount of heat supplied may be reduced. In this case, the moisture content of the dry powder can be controlled with high responsiveness by relatively simply adjusting the temperature of the heater.
[0013]
Accordingly, even when a dry powder having a relatively low water content, for example, a moisture content of 3% or less, is produced, the dry powder can be taken out with little clogging or alteration. In the present specification, “moisture ratio” is used on a moisture basis.
[0014]
Further, according to the present invention, a predetermined amount of refrigerant having a heat amount substantially equal to the heat of evaporation required for the water content of the material to evaporate per unit time in the drying chamber is supplied from the input port for a predetermined time prior to the material supply. can do. For example, the moisture content of the dry powder can be controlled even when the dry powder does not exist at the outlet, such as when the drying device is started (when the operation is started) or when the material is temporarily restarted (when operation is resumed). Stable control can be performed with little risk of running out of control in making drying conditions impossible.
[0015]
Furthermore, in the present invention, the moisture content of the dry powder is detected, and in comparison between the detected moisture content A ′ of the dry powder and the specified moisture content A, when A ′ <A, the amount of heat supplied is reduced, and A ′> A Sometimes, control for increasing the amount of heat supplied may be supplementarily performed. In this case as well, by controlling the amount of heat supplied, it is possible to control the amount of powder moisture with good responsiveness. In addition, if a dead zone is set in at least one of the upper and lower sides with respect to the specified moisture amount A, it is effective for preventing hunting.
[0016]
Furthermore, in the present invention, at least one characteristic value of the temperature, humidity, or air volume of the outside air before being heated through the heater may be detected, and the amount of heat supplied may be supplementarily adjusted based on the characteristic value. In this case, in order to obtain a dry powder having a prescribed moisture content, it is possible to control the powder moisture content more precisely according to changes in the outside air condition. In this case, the humidity may be either absolute humidity or relative humidity.
[0017]
Furthermore, in the present invention, information necessary for specifying the amount of heat released from the drying chamber may be detected, and the amount of heat supplied may be supplementarily adjusted based on the detected value of the amount of heat released from the drying chamber. Further, information necessary for specifying the residual heat quantity of the dry powder may be detected, and the heat supply heat quantity may be supplementarily adjusted based on the detected value of the powder residual heat quantity. Alternatively, the heat input through the material may be detected based on the temperature and input amount of the material prior to the supply to the input port, and the supply air heat amount may be supplementarily adjusted based on the detected value of the material input heat amount. . In these cases, in order to obtain a dry powder having a specified moisture content, it becomes possible to control the moisture content of the powder more precisely in accordance with changes in conditions such as materials and atmosphere.
[0018]
Furthermore, in the present invention, the moisture content of the dry powder is detected, and when the detected moisture content of the dry powder does not satisfy the specified moisture content, the dry powder outside the regulation is separated and collected from the dry powder having the prescribed moisture content. be able to. For example, control of the moisture content of the dry powder even when the detected moisture content of the dry powder deviates from the specified moisture content at the start-up of the drying device (at the start of operation) or at the restart after the material input is temporarily stopped (when the operation is resumed). Stable control can be performed with a low risk of running out of control in making drying conditions.
[0019]
Note that the non-regulated dry powder separated and collected may be remixed with the dry powder before the moisture content is detected. At this time, the production efficiency and yield of the dry powder can be further improved.
[0020]
Moreover, the drying method of the slurry-like or solution-like material according to the second invention is as follows:
The slurry-like or solution-like material containing the ceramic raw material is supplied to the drying chamber from the input port provided in the drying unit, and from the air supply port provided in the drying unit with the outside air heated through the heater as supply air Introduced into the drying chamber,
Drying the material by bringing the supply air into contact with the material supplied from the inlet,
While taking out the dried material as a dry powder from the outlet provided in the drying unit, while discharging the air supply to the outside of the drying chamber as exhaust from an exhaust port provided in the drying unit,
Over a predetermined time prior to the supply of the material, a predetermined amount of refrigerant is supplied from the input port so as to have a heat amount substantially equal to the heat of evaporation required for the water content of the material to evaporate per unit time in the drying chamber. It is characterized by that.
[0021]
On the other hand, the slurry-like or solution-like material drying apparatus according to the second invention is
An inlet for supplying a slurry-like or solution-like material containing a ceramic raw material;
An air inlet that heats the outside air with a heater and introduces it as air supply;
A drying chamber for drying the material by bringing the supply air into contact with the material supplied from the inlet;
An outlet for taking out the dried material as a dry powder,
An exhaust port for exhausting the supply air to the outside as exhaust;
Over a predetermined time prior to the supply of the material, a predetermined amount of refrigerant is supplied from the input port so as to have a heat amount substantially equal to the heat of evaporation required for the water content of the material to evaporate per unit time in the drying chamber. For this purpose, a refrigerant supply unit is provided.
[0022]
According to these inventions, for example, when there is no dry powder at the outlet, such as at the time of starting the drying apparatus (at the start of operation) or at the time of restarting after stopping the material charging (when restarting the operation) Slurry that does not impede productivity and can control the moisture content of the dry powder without making a sudden change in the room, making it possible to perform stable control with little risk of runaway control during the creation of drying conditions. And a drying method for slurry-like or solution-like material and a drying apparatus for slurry-like or solution-like material are obtained.
[0023]
By the way, the dry powder obtained by drying the slurry-like or solution-like ceramic material containing the ceramic raw material by the method of the first or second invention has an average particle diameter of substantially constant, and has a specified moisture content. It is produced with a high yield continuously from the start of supply of slurry-like or solution-like material to the end of supply in a state of containing the amount substantially stably. Therefore, the ceramic sintered body according to the present invention, which is obtained by forming a molded body of a predetermined shape using the dry powder and sintering the molded body, can be produced at low cost as a high-quality product. it can.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to examples shown in the drawings. FIG. 1 shows an overall front view of a spray dryer (spray drying apparatus) as an example of the present invention. This spray dryer is used as a drying device for slurry-like materials in which ceramic powder particles such as alumina and aluminum nitride are suspended. The slurry-like material (stock solution) M is sent from the tank 11 of the material supply unit 1 through the pipe path to the drying chamber 30 formed in the drying unit 3 (the pipe path may be naturally dropped, a pump or the like May be pumped by). Specifically, the slurry-like material M is supplied to the atomization device (atomizer) 13 disposed at the inlet 10 in the ceiling portion of the drying chamber 30 via the flow rate adjustment valve 12. The atomizer 13 sprays the stock solution M atomized for the purpose of increasing the drying speed, spheroidizing the powder, homogenizing the powder diameter and the like into the entire drying chamber 30 in a spray form. The stock solution M is normally in the form of a slurry having a moisture content of 20 to 50%. For example, an alumina slurry having a moisture content of 33% is supplied to the atomizer 13 and discharged to the entire drying chamber 30. Depending on the material of the ceramic, there may be a case where a solution material M in which a ceramic raw material component is dissolved can be used. On the other hand, outside air taken in by the blower 22 through the filter 24 and the damper 21 of the air supply unit 2 is sent to the heater 23 and heated, and then provided as an air supply I on the upper surface or the upper peripheral surface of the drying chamber 30. The air supply port 20 is introduced toward the drying chamber 30.
[0025]
Then, in the drying chamber 30, the slurry-like material M discharged from the atomizer 13 in a spray form and spontaneously falls in the drying chamber 30 from the upper inlet 10 side toward the lower outlet 40 side was heated. The supply air I is brought into contact. Thereby, while the slurry-like material M floats in the hot air (supply air) I, the moisture is transferred to the supply air I, and the slurry-like material M is dried. Subsequently, the dried slurry-like material M is taken out as a dry powder G from the take-out port 40 formed in the take-out part 4 at the lower part of the drying chamber 30 through the take-out channel 41. On the other hand, the supply air I is sucked from the exhaust port 50 on the peripheral wall of the intermediate part of the drying chamber 30 together with a part of the dry powder G floating in the intermediate part of the drying chamber 30 by the exhaust fan 56 provided in the exhaust unit 5. Is taken out as exhaust O to the exhaust flow path 51 connected to the.
[0026]
Here, in the embodiment of FIG. 1, in order to improve the production efficiency and yield of the dry powder G, the take-out flow path 41 is provided with the following mechanism. A sieve 42 is provided in the extraction flow path 41 below the outlet 40, and the dry powder G discharged from the outlet 40 is first passed through the sieve 42. The dry powder G whose particle diameters are finely aligned by the vibration of the sieve 42 flows down the sieve 42 and is then introduced into the collection cyclone 60 by the suction force of the exhaust fan 69 provided in the separation / recovery unit 6. . On the other hand, foreign substances such as large-diameter powder and dust that could not pass through the sieve 42 are collected in the collection box 44.
[0027]
The dry powder G introduced into the collection cyclone 60 is agitated by a swirling flow along the inner wall of the collection cyclone 60, and is separated and separated from foreign substances such as dust by a specific gravity difference. That is, the relatively heavy dry powder G is taken out from the lower part of the collection cyclone 60 to the recovery flow path 61 and stored in the storage silo 66. On the other hand, foreign matters such as relatively light dust are discharged out of the system by the exhaust fan 69 through the filter 67 and the damper 68.
[0028]
Now, the following feedback mechanism is provided in the recovery flow path 61 connected to the outlet of the collection cyclone 60. A part of the dry powder G taken out from the lower part of the collection cyclone 60 to the recovery flow path 61 branches to the sample collection unit 6A, where the moisture content is directly measured by the moisture meter 6a using infrared rays or the like, and then returned. It is circulated through the extraction channel 41 (on the downstream side of the sieve 42 in FIG. 1) via the channel 61 ′. A four-port, three-position electromagnetic switching valve 62 is installed in the recovery flow path 61 on the downstream side of the sample collection unit 6A. When the dry powder G in the recovery channel 61 is stored in a plurality (two tanks in FIG. 1) of storage silos 66, the electromagnetic switching valve 62 is switched to the position b or c by a control signal from the level meter 6b of each silo 66. It is done. Further, the moisture content M of the dry powder measured by the moisture meter 6a_G'Is the specified moisture content M_GIs not satisfied, the electromagnetic switching valve 62 is switched to the position a by a control signal from the moisture meter 6a. As a result, the non-regulated dry powder G is separated from the dry powder G having a specified moisture content and collected in the temporary storage tank 64 of the separation channel 63. The outlet of the temporary storage tank 64 and the extraction channel 41 are connected by a reduction channel 65, and the collected unspecified dry powder G passes through the reduction channel 65 through the extraction channel 41 (in FIG. 1, the extraction channel 40. (Between the sieve 42), taken out from the drying unit 3, and mixed again with the dry powder G before moisture content measurement. Then, the mixed dry powder G is put into the collection cyclone 60 by the suction force of the exhaust fan 69 and reaches the sample collection unit 6A._G'Is measured.
[0029]
For example, the detected moisture content M of the dry powder G at the time of starting the drying apparatus (at the start of operation) or at the time of restarting after the material input is temporarily stopped (at the time of restarting the operation)_G'Is the specified moisture content M_GEven when the dry powder G is removed, the separation flow path 63 for separating and recovering the dry powder G outside the specified range from the dry powder G having the specified moisture content is provided, so that the water content of the dry powder G cannot be controlled. And stable control can be performed with little risk of runaway in the control of making drying conditions. Moreover, the non-regulated dry powder G separated and recovered is reduced by the reduction flow path 65 and mixed with the subsequent dry powder G before the moisture content detection, so that the production efficiency and yield of the dry powder G can be improved. it can. At this time, the non-standard dry powder G and the subsequent dry powder G are mixed and stirred by the collecting cyclone 60, which is effective in making the moisture content uniform.
[0030]
On the other hand, the exhaust O containing the dry powder G is introduced into the exhaust cyclone 52 through the exhaust flow path 51 and stirred by the swirling flow along the inner wall of the exhaust cyclone 52 and is separated from the dry powder G by the difference in specific gravity.・ Separated. That is, the relatively heavy dry powder G is taken out from the lower part of the exhaust cyclone 52 to the merge channel 53 and merged into the recovery channel 61. On the other hand, the relatively light exhaust O is discharged out of the system by the exhaust fan 56 through the filter 54 and the damper 55.
[0031]
The electromagnetic switching valve 62 may be used in place of a plurality of switching dampers. Further, the return flow path 61 ′ and the reduction flow path 65 may be returned to the collection cyclone 60 and the recovery flow path 61 as long as they are upstream of the moisture content meter 6 a. However, since the dry powder G fed back through the return flow path 61 ′ or the reduction flow path 65 and the subsequent dry powder G flowing down from the outlet 40 may have different moisture contents, the dry powder G is sufficiently mixed. It is desirable that the moisture content is measured by the moisture meter 6a after stirring. In particular, the specified moisture content M_GIt is desirable to connect the reducing flow path 65 from which the dry powder G that deviates from the above may be fed back continuously and in a large amount as much as possible to the extraction flow path 41 on the upstream side. Thus, the time and distance from when the dry powder G fed back through the reduction channel 65 joins the subsequent dry powder G flowing down from the outlet 40 until the moisture content is measured again by the moisture meter 6a. Take long. Therefore, since both dry powders G are sufficiently mixed and stirred, variation in the moisture content measured by the moisture meter 6a can be suppressed. Further, a throttle valve (not shown) or the like is provided in the reduction channel 65 so that the specified moisture content M_GIf the dry powder G that deviates from the temporary storage tank 64 returns to the take-out flow path 41 and is gradually mixed with the subsequent dry powder G, the specified moisture content M can be quickly increased._GWill be able to return. By the way, also about the reduction | restoration position of the confluence | merging flow path 53, the extraction flow path 41, the collection cyclone 60, etc. can be selected besides the collection | recovery flow path 61. FIG.
[0032]
The dry powder G accommodated in the storage silo 66 is, for example, a specified moisture content M._GIs 3% or less and the average particle size is 30 to 200 μm (more preferably 50 to 150 μm). When such dry powder G is alumina, aluminum nitride, or the like, it is used, for example, in the manufacture of an insulator for a spark plug.
[0033]
Reference numeral 7 denotes a refrigerant supply unit, which has a heat amount equal to or substantially equal to the amount of heat required for the water in the slurry-like material M to evaporate per unit time in the drying chamber 30 over a predetermined time prior to the supply of the slurry-like material M. Refrigerant (for example, water) C is supplied from the tank 71 through the flow rate adjusting valve 72 to the inlet 10 (see formula (20) described later). Thus, even when the dry powder G does not exist in the outlet 40, such as when the drying apparatus is started (when the operation is started) or when the material is temporarily stopped after the material is temporarily stopped (when the operation is restarted), In this case, there is less risk of runaway control in making drying conditions, and there is less risk of impeding productivity. Further, in the spray dryer of this embodiment, based on input signals from

detectors

1a, 1b, 2a, 2b, 4a, 5a, 6a, 6b, 7a, etc. (each detector will be described later) provided in each part. A control unit 8 is mounted for controlling the operation of the spray dryer by outputting control signals for the heater 23, the flow

rate adjusting valves

12, 72, the electromagnetic switching valve 62, and the like.
[0034]
The heat balance and moisture balance when such a spray dryer is viewed as a heat-water system will be discussed with reference to FIG. First, regarding the moisture balance, the following relationship is considered to hold. Although the case where the moisture content is managed by the “moisture content” based on the moisture content is described here, the “moisture content” based on the dry content can be similarly managed by using a conversion formula or the like.
In the slurry-like material M supplied from the inlet 10 to the drying chamber 30, the material input amount is set to Q._M[M³/ H], the material specific gravity is ρ_M[G / m³], The raw material component amount is W [g / h], and the material moisture content is M_MMaterial input weight W when [%]_M[G / h] and material water content w_M[G / h] is represented by the following formulas (1) and (2).
W_M= W + w_M= Q_M・ Ρ_M                      (1)
w_M= Q_M・ Ρ_M・ M_M/ 100 (2)
At this time, moisture content M_MIs represented by the following equation (3).
M_M= (W_M/ (W + w_M)) X 100 (3)
On the other hand, in the dry powder G obtained from the outlet 40, the specified moisture content of the powder is M_G[%], Powder production weight W_G[G / h] and powder moisture content w_G[G / h] is represented by the following formulas (4) and (5).
W_G= W + w_G= 100w_G/ M_G                (4)
w_G= W_G・ M_G/ 100 (5)
At this time, the specified moisture content of the powder M_GIs represented by the following equation (6).
M_G= (W_G/ (W + w_G)) X 100 (6)
[0035]
Next, the specific gravity of water vapor is ρ_V[G / m³] When the density increase amount is α, the water vapor discharge water amount w corresponding to the water content removed from the slurry material M per unit time_V[G / h] and water vapor volume Q_V[M³/ H] is expressed by the following equations (7) and (8).
w_V= W_M-W_G                               (7)
Q_V= W_V・ Α / ρ_V                           (8)
In this specification, w_VIs also referred to as the amount of water removed. This removed water amount w_VIn other words, it represents the drying speed at which the slurry-like material M is dried, and it is better to increase the productivity of the dry powder G. It is limited in terms of prevention (change in physical or chemical properties, etc.).
[0036]
The exhaust air volume of the exhaust O discharged from the exhaust port 50 is set to_O[M³/ H], the absolute humidity of the air supply is H_I[G-H₂O / m³-dry air], the supply air amount Q of the supply air I introduced from the supply port 20_I[M³/ H] and supply water amount w_I[G / h], and further, exhaust water amount w_O[G / h] is represented by the following formulas (9), (10), and (11).
Q_I= Q_O-Q_V                               (9)
w_I= Q_I・ H_I                              (10)
w_O= W_V+ W_I                              (11)
Therefore, the target exhaust absolute humidity H_O[G-H₂O / m³-dry air] is given by the following equation (12).
H_O= W_O/ Q_O                              (12)
[0037]
Next, regarding the heat balance, the following relationship is considered to hold.
Q_I[M³/ H], the specific gravity of the air supply is ρ_I[G / m³], T_I[K], the specific heat supply is C_IWhen [J / g], the amount of heat supplied q of the air supply I introduced from the air supply port 20_I[J / h] is represented by the following formula (13).
q_I= Q_I・ Ρ_I・ T_I・ C_I                    (13)
Note that the amount of outside air introduced into the heater 23 is Q_I'[M³/ H], the outside air specific gravity is ρ_I'[G / m³], T_I'[K], the outside specific heat is C_I'[J / g], the amount of outside air q of outside air I' introduced into the heater 23_I'[J / h]' is expressed by the following equation (13) '.
q_I'= Q_I'・ Ρ_I'・ T_I'・ C_I'(13)'
Therefore, the amount of additional heat given to the outside air I ′ by the heater 23 is q₂₃Assuming [J / h], the charge heat quantity q_I, Outside air q_I'And additional heat q₂₃The following equation (13) "holds.
q_I= Q_I'+ Q₂₃                            (13) "
As is clear from the equation (13) ", the charge heat quantity q_IIs the added heat q₂₃Can be adjusted by the change in the volume of the heater 23 (volume of the heater 23, etc.), and the outside heat q_I'Also fluctuates.
On the other hand, the boiling point of water is T_V[K], the material temperature is T_M[K], the specific heat of water is C_V[J / g], the heat of vaporization of water is R_VWhen [J / g], the heat of evaporation q of water contained in the slurry material M_V[J / h] is represented by the following formula (14).
q_V= W_V((T_V-T_M) C_V+ R_V(14)
Exhaust specific gravity is ρ_O[G / m³], Exhaust temperature T_O[K], exhaust specific heat is C_OWhen [J / g], the exhaust heat quantity q of the exhaust O discharged from the exhaust port 50_O[J / h] is represented by the following formula (15).
q_O= Q_O・ Ρ_O・ T_O・ C_O                    (15)
Powder specific heat is C_G[J / g], powder temperature T_GWhen [K] is assumed, the residual heat quantity q in the dry powder G_G[J / h] is represented by the following formula (16).
q_G= W_G・ C_G(T_G-T_M(16)
The material specific heat is C_MWhen [J / g], the input heat quantity q through the material M_M[J / h] is represented by the following equation (16) ′.
q_M= W_M・ T_M・ C_M= Q_M・ Ρ_M・ T_M・ C_M     (16) ’
Ambient temperature is T_A[K], the drying chamber surface area is A [m²], The heat transfer coefficient is K [J / h / m²], The drying chamber heat dissipation q_L[J / h] is expressed by the following equation (17).
q_L= T_A・ AK (17)
Therefore, when the heat balance with respect to the drying chamber 30 is taken into consideration, the amount of heat supplied q_IIs represented by the following equation (18).
q_I= Q_V+ Q_O+ Q_G+ Q_L                    (18)
[0038]
FIG. 3 schematically shows a spray dryer to which the present invention is applied. In FIG. 3, the spray dryer has a control function for creating the following drying conditions.
(1) Absolute humidity H of the exhaust O in the vicinity of the exhaust port 50_O'Is detected, and this exhaust absolute humidity detection value H_O'And the moisture content M of the slurry material M_MAnd moisture content M of dry powder G_GExhaust absolute humidity target value H determined from_OIn comparison with H_O'<H_OThe charge heat quantity q of the supply air I_IIncreases, H_O'＞ H_OThe amount of heat supplied q_IThe amount of water removed from the slurry material M per unit time w_VIs maintained substantially constant, and the specified moisture content M_GTo obtain a dry powder G having (See Figure 4)
(2) Moisture retained in the slurry-like material M for a predetermined time prior to the supply of the slurry-like material M at the time of starting the drying apparatus (at the start of operation) or at the time of restarting after the material charging is temporarily stopped (when restarting the operation). The amount of heat of evaporation q required for the amount to evaporate per unit time in the drying chamber 30_VA predetermined amount of the refrigerant C, which has a heat quantity substantially equal to (See Figure 5)
(3) Moisture content M of dry powder G_G'And detect the moisture content M of the dry powder G_G'And specified moisture content M_GIn comparison with M_G'<M_GThe charge heat quantity q of the supply air I_I, M_G'> M_GThe amount of heat supplied q_IThe amount of water removed from the slurry material M per unit time w is increased by increasing_VIs maintained substantially constant, and the specified moisture content M_GTo obtain a dry powder G having (See Figure 6)
(4) At least one characteristic value is detected from the temperature, humidity, or air volume of the outside air I ′ before being heated through the heater 23, and based on the obtained characteristic value (outside air obtained from the obtained characteristic value) Calorie q_IThe charge heat quantity q of the supply air I (based on ')_ITo adjust the specified moisture content M_GTo obtain a dry powder G having (See Figure 7)
(5) Heat dissipation q from the drying chamber 30_L, And drying chamber heat dissipation q_LSupply air quantity q of supply air I based on the detected value of_ITo adjust the specified moisture content M_GTo obtain a dry powder G having (See Figure 8)
(6) Residual heat quantity q of dry powder G_GAnd the amount of heat remaining in the powder q_GSupply air quantity q of supply air I based on the detected value of_ITo adjust the specified moisture content M_GTo obtain a dry powder G having (See Figure 9)
(7) Temperature T of slurry-like material M prior to supply to charging port 10_MAnd input Q_MThe input heat quantity q through the slurry material M_MThe amount of heat input q_MSupply air quantity q of supply air I based on the detected value of_ITo adjust the specified moisture content M_GTo obtain a dry powder G having (See Figure 10)
[0039]
In order to fulfill the above control function, the spray dryer of FIG. 3 is provided with a control unit 8 for controlling its operation. The control unit 8 includes a microprocessor including an I / O port 81 and a CPU 82, ROM 83, RAM 84, and the like connected to the I / O port 81. The ROM 83 stores a control program.
[0040]
The following detectors (sensors) and the like are connected to the input side of the I / O port 81.
Thermometer 1a: A temperature meter T of the slurry material M provided in the slurry material M charging path._MMeasure.
Flow meter 1b: A flow rate (input amount) Q of the slurry material M provided in the input path of the slurry material M_MMeasure.
Thermometer 2a: provided in the supply path of the supply air I, the temperature T of the supply air I_IMeasure.
At least one of a thermometer, a hygrometer, and a flow meter 2b: provided in the supply path of the outside air I ′ before being heated by the heater 23, and at least one characteristic of the temperature, humidity, or air volume of the outside air I ′ Measure the value. The humidity (meter) used here may be either absolute humidity (meter) or relative humidity (meter).
Thermometer 4a: provided in the take-out channel 41 of the dry powder G, and the powder temperature T of the dry powder G_GMeasure.
Weight flow meter 4b: a weight flow rate (powder generation weight) W of the dry powder G provided in the take-out flow path 41 of the dry powder G adjacent to the thermometer 4a_GMeasure.
Absolute humidity measuring device (thermometer, relative hygrometer) 5a: provided in the exhaust flow path 51 (in the vicinity of the exhaust port 50) of the exhaust O, and the temperature T of the exhaust O_OAnd the relative humidity is measured, and the exhaust gas absolute humidity detection value H is calculated using a known conversion formula._O'Get. Here, the absolute humidity is a general term for parameters (weight%, partial pressure, molar fraction, etc.) that specify the absolute water content in the gas in the standard state. Specifically, measured temperature T_ORelative humidity value h_RThe absolute humidity can be calculated as the amount of water vapor per unit volume of the gas in the standard state. A dew point meter or the like may be used.
-Moisture meter 6a using infrared rays or the like: the extraction channel 41 (in the vicinity of the extraction port 40) following the extraction port 40 of the dry powder G or the recovery channel 61 following the outlet of the collection cyclone 60, or branched from them Installed in the sample collection unit 6A (see FIG. 9 or FIG. 1), and the moisture content M as the moisture content of the dry powder G_G(Moisture standard) is measured. The moisture content (dry basis) may be measured as the moisture content of the dry powder G.
Thermometer 7a: provided in the charging path of the refrigerant C, the temperature T of the refrigerant C_CMeasure.
[0041]
On the other hand, the following operation member (actuator) or the like is connected to the output side of the I / O port 81.
-Temperature setting device 23a of the heater 23: Based on the control signal, the set temperature of the heater 23 is adjusted, and the supply air temperature T_IHeat supply q_ITo change.
Supply amount setting device 72a for the refrigerant C side flow rate adjustment valve 72: Adjusting the opening of the flow rate adjustment valve 72 (including valve closing) based on the control signal, and supplying the refrigerant supply amount w_CTo change.
Supply amount setting device 12a for the material M-side flow rate adjustment valve 12: Adjusting the opening of the flow rate adjustment valve 12 (including valve closing) based on the control signal, the material input amount Q_MTo change.
[0042]
In addition to the above, on the input side of the I / O port 81, a level meter 6b that is provided in the storage silo 66 and measures the amount of the dry powder G is also connected (see FIG. 1). Further, on the output side of the I / O port 81, based on a control signal resulting from the output of the water content meter 6a or the level meter 6b, an electromagnetic solenoid is operated to switch between the recovery channel 61 and the separation channel 63. An electromagnetic switching valve 62 is also connected (see FIG. 1). However, as described above, the control function is not directly involved in the moisture content control of the dry powder G. Therefore, the level meter 6b and the electromagnetic switching valve 62 are omitted from the control system of FIG. 3 (the same applies to FIG. 4 and subsequent figures).
[0043]
Next, the position at which the moisture meter 6a is provided is provided in the sample collection section 6A branched from the collection flow path 61 following the collection cyclone 60 outlet (see FIG. 1), and the outlet 40 of the drying chamber 30. In the case where it is provided in the sample collection part 6A branched from the extraction flow path 41 following (see FIG. 12), there is no difference in action and effect regarding the moisture content control of the dry powder G. Therefore, the route from the take-out flow path 41 to the recovery flow path 61 is omitted in the control system of FIG. 3 (the same applies to FIG. 4 and subsequent figures). Therefore, the moisture content meter 6 a can be attached to any position on the path from the take-out flow path 41 to the recovery flow path 61.
[0044]
Each control function for creating drying conditions in a spray dryer is explained separately for each function. In FIG. 4, the absolute humidity H of the exhaust O is measured by the absolute humidity measuring device 5a._O'And detect this value H_O'And water content M of material M_MAnd moisture content M of dry powder G_GExhaust absolute humidity target value H determined from_OAnd compare. By the way, the following equation (19) is derived from the equations (7), (10), (11), (12), and (13). H_O= (W_V+ Q_I・ H_I/ (Ρ_I・ T_I・ C_I)) / Q_O      (19) (a) Exhaust absolute humidity detection value H_O'Is the target value H_OIs equal to Eq. (19), and at this time, the amount of water removed per unit time w_V(Drying speed) is
w_V= W_M-W_G= Const. (7) ’
Is maintained.
(B) Here, the drying speed w due to the transition from the constant rate drying period to the decreasing rate drying period or due to disturbance factors, etc._VWhen the value of the exhaust gas has decreased, the exhaust gas absolute humidity detection value H_O'Is the target value H_OWill be below. At this time, the amount of powder water w of the dry powder G_GTherefore, the detected moisture content M is calculated by the above equation (6)._G'Is the specified moisture content M_GIs bigger than. Therefore, the charge heat quantity q in equation (19)_IFocusing on the above, the set temperature of the temperature setter 23a of the heater 23 is increased and the amount of heat supplied q_IIf is increased, the original state can be easily and effectively restored. In other words, heat supply q_IIncreases, the exhaust gas absolute humidity detection value H is obtained by the equation (19)._O'Becomes larger and the target value H_OIs equal to Exhaust humidity detection value H_OAs the value of 'increases, the powder moisture content w_G, And the detected moisture content M is calculated by the equation (6)._G'Also falls. Therefore, the detection value H of exhaust absolute humidity_O'Is the target value H_OIs equal to the drying speed w_VWill be maintained in their original state. (C) On the other hand, the drying speed w_VWhen the exhaust gas increases, the detection value H of exhaust absolute humidity_O'Is the target value H_OAt this time, the powder moisture content w of the dry powder G_GIs smaller, so the detected moisture content M_G'Is the specified moisture content M_GIs smaller than Therefore, the set temperature of the temperature setter 23a of the heater 23 is lowered and the amount of heat supplied q_IIf the value is made smaller, the exhaust gas absolute humidity detection value H_O'Becomes smaller and the target value H_OIs equal to Exhaust humidity detection value H_OPowder moisture content w as'_GIncreases and the detected moisture content M_G'Also increases. Therefore, the detection value H of exhaust absolute humidity_O'Is the target value H_OIs equal to the drying speed w_VWill be maintained in their original state.
[0045]
Target value H of exhaust absolute humidity_OOr / and removed water amount w_VTarget value H_OOr / and removed water amount w_VEven if the value is set to a predetermined value, stable moisture content control of the dry powder G that hardly causes hunting can be expected. However, the target value H in which a dead zone is set in at least one of the upper and lower sides with respect to the predetermined value._OOr / and removed water amount w_VAs a result, it is possible to further prevent hunting. The absolute humidity H of the exhaust_OOf course, 'may be directly measured, but it is practical to measure the exhaust temperature and relative humidity and calculate the absolute humidity from a known conversion formula.
[0046]
In FIG. 5, the slurry-like material M is retained for a predetermined time prior to the supply of the slurry-like material M at the time of starting the drying device (at the start of operation) or at the time of restarting after the material input is temporarily stopped (when the operation is resumed) Heat of evaporation q required for water to evaporate per unit time in the drying chamber 30_VA predetermined amount of the refrigerant C (for example, water) having a heat quantity substantially equal to is supplied to the charging port 10. In equation (14), the boiling point of the refrigerant is expressed as T_V'[K], the refrigerant temperature is T_C[K], the specific heat of the refrigerant is C_C[Cal / g], the heat of vaporization of the refrigerant is R_CRequired refrigerant supply amount w when [cal / g]_C[G / h] is represented by the following formula (20).

When the refrigerant is water, the refrigerant temperature T_C= Material temperature T_MThen, equation (20) becomes
w_C= W_V (20) 'and refrigerant supply amount w_CIs the amount of water removed (water vapor discharged water) w_VIs equal to
[0047]
Specifically, immediately after the material input start button is pushed (not shown), the control unit 8 closes the flow rate adjusting valve 12 for a predetermined time and stops the supply of the slurry material M. In the meantime, the flow rate adjustment valve 72 is opened and the refrigerant supply amount w expressed by the equation (20) or (20) 'is established._CA control signal for supplying [g / h] refrigerant C (for example, water) is issued to the supply

amount setting mechanisms

12 a and 72 a of both flow

rate adjusting valves

12 and 72. At this time, in the drying chamber 30, although the dry powder G is not generated, the other moisture balance and heat balance are in an operation state substantially equivalent to the case where the slurry-like material M is supplied, that is, a simulated operation state. Accordingly, when the dry powder G is not present at the outlet 40, such as at the time of starting the drying apparatus (at the time of starting operation) or at the time of restarting after temporarily stopping the material charging (when restarting the operation) (at this time, the moisture content meter 6a Is the moisture content of powder M_G'= 0% is detected), and the situation of the drying chamber 30 is not suddenly changed. That is, even in such a case, there is less risk of runaway control in creating drying conditions, and there is less risk of impeding productivity. The time for supplying the refrigerant C instead of the slurry material M may be basically until the condition of the drying chamber 30 is stabilized. However, when switching to the normal operation in a state where the slurry-like material M is supplied, the situation of the drying chamber 30 is more stable when the time until the dry powder G is taken out from the outlet 40 is included.
[0048]
In FIG. 6, the moisture content M of the dry powder G is measured by the moisture meter 6a._G”And the specified moisture content M of the dry powder G_GAnd detected moisture content M_GCompare with '.
(A) Now, the detected moisture content M_G'Is the specified moisture content M_GIs equal to
M_G= (W_G/ (W + w_G)) X 100 (6)
In this case, the amount of water removed per unit time w_V(Drying speed) is
w_V= W_M-W_G= Const. (7) ’
Is maintained.
(B) Here, the detected moisture content M_G'Is the specified moisture content M_GIf it becomes larger than this, the powder water content w of the dry powder G at this time_GIncreases the drying speed w_VThe exhaust absolute humidity detected value H_O'Is the target value H_OIt is in the same state as the case below. Therefore, similarly to the above case, the set temperature of the temperature setter 23a of the heater 23 is increased to increase the amount of heat supplied q._IIncreases the powder moisture content w_GDecreases and the detected moisture content M_G'Also falls. Therefore, the detected moisture content M_G'Is the specified moisture content M_GIs equal to the drying speed w_VWill be maintained in their original state.
(C) On the other hand, the detected moisture content M_G'Is the specified moisture content M_GWhen it becomes smaller than this, the powder moisture content w of the dry powder G_GDecreases and drying speed w_VHas increased. Therefore, the set temperature of the temperature setter 23a of the heater 23 is lowered and the amount of heat supplied q_IIs reduced, the powder water content w_GIncreases and the detected moisture content M_G'Also increases. Therefore, the detected moisture content M_G'Is the specified moisture content M_GIs equal to the drying speed w_VWill be maintained in their original state. Note that the control in FIG. 6 is performed in an auxiliary manner to the control in FIG.
[0049]
In FIG. 7, at least one characteristic value of the temperature, humidity, or air volume of the outside air I ′ before being heated through the heater 23 is measured to detect a change in the external situation, and the supply is performed based on the obtained characteristic value. Supply air quantity q of qi_IAdjust. Specifically, for example, the temperature T of the outside air_I'And air volume Q_I', And from the measured value, the outside air calorific value q according to the equation (13)'_I'And calculate the amount of outside air q_IWhen the change of 'is detected, the set temperature of the temperature setter 23a of the heater 23 is changed, and the amount of heat supplied q_IAdjust. That is, the control in FIG._IThis is predictive control (feed forward) based on 'change detection'. Note that the control in FIG. 7 is also performed in an auxiliary manner to the control in FIG.
[0050]
In FIG. 8, the heat dissipation q from the drying chamber 30_L, And drying chamber heat dissipation q_LSupply air quantity q of supply air I based on the detected value of_IAdjust. In the above equation (17), the ambient temperature T_AOutside air temperature T_IApproximate by 'drying room heat dissipation q_LIs represented by the following equation (17) ′.
q_L= T_A・ A ・ K ≒ T_I'・ A ・ K (17)'
So outside temperature T_I'Is measured, and from the measured value, the heat radiation amount q in the drying chamber is calculated from the equation (17)'._LThis drying room heat dissipation q_LIs detected, the set temperature of the temperature setter 23a of the heater 23 is changed, and the amount of heat supplied q_IAdjust. At this time, in the above-described equation (18), the drying chamber heat dissipation q_LHeat charge q so as to compensate for the fluctuation amount of_IIt is good to adjust. Note that the control of FIG. 8 is also performed in an auxiliary manner to the control of FIG.
[0051]
In FIG. 9, the residual heat quantity q of the dry powder G_GAnd the amount of heat remaining in the powder q_GSupply air quantity q of supply air I based on the detected value of_IAdjust. Specifically, for example, the powder production weight W_G, Powder temperature T_GAnd material temperature T_MFrom the measured value, the residual powder heat q from the formula (16)_GThis powder residual heat quantity q_GIs detected, the set temperature of the temperature setter 23a of the heater 23 is changed, and the amount of heat supplied q_IAdjust. At this time, the residual amount of heat q in the equation (18) described above_GHeat charge q so as to compensate for the fluctuation amount of_IIt is good to adjust. Note that the control of FIG. 9 is also performed in an auxiliary manner to the control of FIG.
[0052]
In FIG. 10, the temperature T of the slurry-like material M prior to the supply to the charging port 10._MAnd input Q_MAnd the input heat quantity q through the slurry material M according to the equation (16) '_MThis material input heat quantity q_MSupply air quantity q of supply air I based on the detected value of_IAdjust. That is, the control of FIG._MThis is predictive control (feed forward) based on perception of fluctuations. Note that the control of FIG. 10 is also performed in an auxiliary manner to the control of FIG.
[0053]
In this way, the dry powder obtained by drying the slurry-like ceramic material containing the ceramic raw material such as alumina, the average particle diameter is substantially constant, and the specified moisture content is contained almost stably. From the start of supply to the end of supply, it is continuously produced with good yield. Therefore, a ceramic sintered body obtained by sintering the dry powder, for example, an insulator for a spark plug, can be produced as a high-quality product at a low cost.
[0054]
FIG. 11 shows an example of a method for manufacturing an insulator for a spark plug as a ceramic sintered body, together with the main structure of the spark plug. First, as shown in FIG. 11A, the spark plug insulator is generally formed by a rubber press method. An annular cavity 210 is stretched along a vertical recess provided in the molding machine 200, and an annular rubber mold 220 is inserted and fixed inside the cavity 210. The bottom lid 230 is fitted into the lower opening of the rubber mold 220, and the bottom lid 230 is pressed and held by the lower holder 240. As the ceramic raw material for forming the spark plug insulator 102, the dry powder G mainly composed of alumina obtained by the drying apparatus of FIG. 1 is filled in the internal space of the rubber mold 220 closed at the bottom by the bottom lid 230. . At this time, the press pin 250 is pressed and held by the upper holder 260 so as to be positioned at the center of the internal space, and the press pin 250 is inserted into the center hole 102a through which the center electrode 103 and the like are inserted in the insulator 102. It has a corresponding shape. Then, a hydraulic pressure FP such as water pressure or hydraulic pressure is applied from the outside of the cavity 210 to the inside in the radial direction of the rubber mold 220 through the pipe line 270 of the molding machine 200, so that the insulator molded body 102A is formed.
[0055]
Next, as shown in FIG. 11B, the hydraulic pressure FP is released and the insulator molded body 102 </ b> A is taken out from the rubber mold 220. After the press pin 250 and the upper holder 260 are removed from the insulator molded body 102A, the outer shape is finished by grinder grinding or the like.
[0056]
The insulator molded body 102A thus obtained is fired at a temperature of about 1600 ° C. in a tunnel kiln. When this is coated with glaze and fired again at around 900 ° C., an insulator sintered body 102B as a ceramic sintered body as shown in FIG. 11C is obtained.
[0057]
In FIG. 11 (d), the insulator 102, whose dimensions are adjusted to the insulator sintered body 102B, is fitted inside the cylindrical metal shell 101, and a center electrode is placed in the center hole 102a of the insulator 102. 103 is arranged. The other end of the ground electrode 104 having one end fixed to the metal shell 101 is bent so as to face the tip of the center electrode 103, and a spark discharge gap g is formed between the ground electrode 104 and the center electrode 103. A spark plug 100 is configured.
[0058]
As an application example of the drying apparatus according to the present invention, a spray drying apparatus has been described. However, other drying apparatuses that can be used for slurry-like or solution-like materials, such as an internal stirring type or a fluidized bed type drying apparatus. If applicable.
[Brief description of the drawings]
FIG. 1 is an overall explanatory view showing a spray drying apparatus as an embodiment of a drying apparatus of the present invention.
FIG. 2 is a schematic diagram showing a moisture balance and a heat balance of the spray drying apparatus of FIG.
FIG. 3 is a block diagram showing main control functions of the spray drying apparatus of FIG. 1;
4 is a block diagram showing a part of the control functions in FIG. 3;
FIG. 5 is a block diagram showing another part of the control function of FIG. 3;
6 is a block diagram showing still another part of the control functions of FIG. 3. FIG.
7 is a block diagram showing still another part of the control functions of FIG. 3;
FIG. 8 is a block diagram showing still another part of the control function of FIG. 3;
FIG. 9 is a block diagram showing still another part of the control functions of FIG. 3;
10 is a block diagram showing still another part of the control functions of FIG. 3;
FIG. 11 is an explanatory view showing an example of a method for producing an insulator for a spark plug as a ceramic sintered body together with the main structure of the spark plug.
FIG. 12 is an explanatory view showing a conventional spray drying apparatus.
[Explanation of symbols]
10 slot
20 Air supply port
23 Heater
3 Drying section
30 Drying room
40 outlet
5a Absolute humidity measuring device (detector)
50 Exhaust vent
7 Refrigerant supply section
8 Control unit
C Water (refrigerant)
G Dry powder
I air supply
I ’open air
M Slurry material (material)
O exhaust
H_O     Exhaust absolute humidity
M_G     Powder specified moisture content (powder specified moisture content)
M_M     Material moisture content (Material moisture content)
q_I     Supply heat quantity
q_G     Powder residual heat quantity
q_L     Drying room heat dissipation
q_M     Material heat input
q_V     Heat of evaporation
w_C     Refrigerant supply amount
w_V     Water vapor discharged (removed water)

Claims

The slurry-like or solution-like material containing the ceramic raw material is supplied to the drying chamber from the input port provided in the drying unit, and from the air supply port provided in the drying unit with the outside air heated through the heater as supply air Introduced into the drying chamber,
Drying the material by bringing the supply air into contact with the material supplied from the inlet,
The material after drying is taken out as a dry powder from the outlet provided in the drying unit, while the supply air is discharged from the exhaust port provided in the drying unit as exhaust to the outside of the drying chamber,
Information necessary to specify the absolute humidity of the exhaust gas is detected in the vicinity of the exhaust port, and the dry powder having a specified moisture content can be obtained based on the detected value H _O ′ of the exhaust absolute humidity. Adjusting the amount of heat supplied by the air supply ,
The input heat amount through the material is detected based on the temperature and input amount of the material prior to supply to the input port, and the supply air heat amount is supplementarily adjusted based on the detected value of the material input heat amount. A method for drying a slurry-like or solution-like material.

The adjustment of the heat supply heat amount is made by comparing the detected value H _O ′ of the exhaust absolute humidity with the target value H _O of the exhaust absolute humidity determined from the moisture content of the material and the specified moisture content of the dry powder. The method for drying a slurry-like or solution-like material according to claim 1, wherein the amount of heat supplied is increased when H 2 _O ′ <H 2 _{O, and} the amount of heat supplied is reduced when H 2 _O ′> H 2 _O.

The method for drying a slurry-like or solution-like material according to claim 1 or 2, wherein the specified moisture content of the dry powder is 3% or less.

Over a predetermined time prior to the supply of the material, a predetermined amount of refrigerant is supplied from the input port so as to have a heat amount substantially equal to the heat of evaporation required for the water content of the material to evaporate per unit time in the drying chamber. drying methods slurry or solution-like material according to any one of claims 1 to 3.

When the moisture content of the dry powder is detected, and the detected moisture content A ′ of the dry powder is compared with the specified moisture content A, when A ′ <A, the amount of heat supplied is reduced, and when A ′> A drying methods slurry or solution-like material according to any one of claims 1 to 4 to increase the air supply amount of heat.

The ambient air temperature before being heated through the heater, detects at least one characteristic value of the humidity or the air volume, claims 1 to adjust the air supply amount of heat on the basis of the characteristic value any one of 5 4. A method for drying a slurry-like or solution-like material according to 1.

7. The information according to claim 1, wherein information necessary for specifying a heat release amount from the drying chamber is detected, and the heat supply heat amount is adjusted based on a detection value of the drying chamber heat release amount. A method for drying a slurry or solution material.

The residual heat of the dry powder to detect the information needed to identify, slurry according to any one of claims 1 to 7 for adjusting the air supply quantity of heat based on the detected value of the powder remaining heat Or the drying method of a solution-like material.

When the moisture content of the dry powder is detected, and the detected moisture content of the dry powder does not satisfy the specified moisture content, the dry powder outside this regulation is collected separately from the dry powder with the prescribed moisture content. drying methods slurry or solution-like material according to any one of claims 1 to 8.

The slurry-like or solution-like material containing the ceramic raw material is supplied to the drying chamber from the input port provided in the drying unit, and from the air supply port provided in the drying unit with the outside air heated through the heater as supply air Introduced into the drying chamber,
Drying the material by bringing the supply air into contact with the material supplied from the inlet,
While taking out the dried material as a dry powder from the outlet provided in the drying unit, while discharging the air supply to the outside of the drying chamber as exhaust from an exhaust port provided in the drying unit,
For a predetermined time prior to supply of said material, a predetermined amount of refrigerant is substantially equal amount of heat to evaporate heat water held in the material required to evaporate per unit time Te in the drying chamber is supplied from the inlet A method for drying a slurry-like or solution-like material.

A slurry-like or solution-like material containing a ceramic raw material is dried by the method according to any one of claims 1 to 10 to form a dry powder, and a molded body having a predetermined shape is formed using the dry powder. A method for producing a ceramic sintered body, comprising obtaining a ceramic sintered body by sintering the formed body.

An inlet for supplying a slurry-like or solution-like material containing a ceramic raw material;
An air inlet that heats the outside air with a heater and introduces it as air supply;
A drying chamber for drying the material by bringing the supply air into contact with the material supplied from the input port;
An outlet for taking out the dried material as a dry powder,
An exhaust port for exhausting the supply air to the outside as exhaust;
A detector for detecting information necessary to specify the absolute humidity of the exhaust gas is provided in the vicinity of the exhaust port, and a detected value H of the exhaust absolute humidity detected by the detector. _ＯO ' And a control unit that adjusts the amount of heat supplied by the supply air so as to obtain the dry powder having a specified amount of moisture.
A thermometer for measuring the temperature of the material prior to supply to the input port and a flow meter for measuring the input amount are provided, and the control unit detects the amount of heat input to the material detected by the thermometer and the flow meter. The apparatus for drying slurry-like or solution-like material, wherein the amount of heat supplied is supplementarily adjusted based on the detected value.

The controller controls the exhaust absolute humidity detected value H _O ′ detected by the detector, the exhaust absolute humidity target value H _O determined from the moisture content of the material and the specified moisture content of the dry powder, and in comparison, according to claim 12 for emitting a control signal H _O '<emits a control signal for increasing the air supply quantity of heat possessed by the air supply when the H _{_O,} H _O'> to reduce the air supply heat when the H _O The slurry-like or solution-like material drying apparatus described.

Over a predetermined time prior to the supply of the material, a predetermined amount of refrigerant is supplied from the input port so as to have a heat amount substantially equal to the heat of evaporation required for the water content of the material to evaporate per unit time in the drying chamber. 14. The slurry-like or solution-like material drying apparatus according to claim 12 or 13 , wherein a refrigerant supply unit is provided .

Separation in which the moisture content of the dry powder is detected, and when the detected moisture content of the dry powder does not satisfy the specified moisture content, the non-specified dry powder is separated from the dry powder having the prescribed moisture content and recovered. The slurry-like or solution-like material drying apparatus according to any one of claims 12 to 14, wherein a flow path is provided .

An inlet for supplying a slurry-like or solution-like material containing a ceramic raw material;
An air inlet that heats the outside air with a heater and introduces it as air supply;
A drying chamber for drying the material by bringing the supply air into contact with the material supplied from the inlet;
An outlet for taking out the dried material as a dry powder,
An exhaust port for exhausting the supply air to the outside as exhaust;
Over a predetermined time prior to the supply of the material, a predetermined amount of refrigerant is supplied from the input port so as to have a heat amount substantially equal to the heat of evaporation required for the water content of the material to evaporate per unit time in the drying chamber. A slurry- or solution-like material drying apparatus , characterized in that a refrigerant supply unit is provided .