【発明の詳細な説明】[Detailed description of the invention]
本発明はクラフトパルプ製造工程において発生
する希黒液を膜分離装置を用いて処理して得られ
た濃縮液を通常の濃縮・燃焼工程に送り一方、透
過液は緑液の苛性化工程におけるライムマツド洗
浄用水として使用するクラフトパルプ廃液の処理
法に関するものであり、特に膜分離装置として膜
を介して水、無機イオン、或いは低分子物を透過
させて高分子物を排除する限外過（UF）装置
を用いるクラフトパルプ廃液の処理法に係るもの
である。
第１図に示した様に従来法のクラフトパルプ製
造工程のフローシートから判る様に苛性ソーダ
（NaOH）及び硫化ソーダ（Na2S）の混合液で
ある白液１０を用いて蒸解し、蒸解後の廃液は蒸
解釜からの抽出黒液１１及び引続いて行なわれる
洗浄工程２からの洗浄黒液１３として回収され
る。通常之等を合わせた液１４は希黒液と称され
ている。この希黒液１４は濃縮工程３のエパボレ
ータで濃縮された後、燃焼工程４のボイラで還元
燃焼され、有機物は熱エネルギーとして回収さ
れ、一方ナトリウム塩は炭酸ソーダ（Na2CO3）
及び硫化ソーダ（Na2S）から成るスメルト１８
として回収される。この様にして回収されたスメ
ルト１８は水２１或いはライムマツドの洗浄水で
ある弱液２０で溶解され、緑液１９となり、更に
苛性化工程５において白液１０に転換再生された
後、蒸解用薬液として再使用される。
さて通常のクラフトパルプ製造工程において
は、希黒液が12t／ｔパルプ程度の量を発生する
ので濃縮工程３において2t／ｔパルプ以上の濃縮
用蒸気を必要とし、現在パルプ工場での主要エネ
ルギー消費部所となつている。之に対し昨今のエ
ネルギーコスト高騰に伴なつて濃縮工程３での使
用蒸気の節減に関して種々の検討が行なわれてい
るのであるが、その中の一方法として洗浄工程２
で使用するパルプ洗浄用水１２を節減して希黒液
１４の濃度を高くすることが考えられる。しか
し、この方法では製品パルプ９の洗浄不良が起こ
りナトリウム損失の増大、或いは後に晒工程が続
く場合においては、この工程での薬品使用量増
加、更には晒工程から系外へ排出される汚濁物質
量の増加が起こるため、その実用化は殆んど期待
出来ない。また他の一方法としては苛性化工程５
で使用される用水２１の代わりに希黒液１４を使
用することが考えられる。この方法は濃縮工程３
での濃縮用蒸気が節減出来るだけでなく蒸解工程
１で消費し切れず希黒液１４中にその侭残存する
有効な無機薬品も現行の様に不要な濃縮工程３、
燃焼工程４を経由することなく、苛性化工程５を
経由するのみで効率良く再使用出来るためにメリ
ツトとしては非常に大きいものがある。しかしな
がら、この方法の最大の欠点は希黒液１４の回収
先である苛性化工程５において、この工程内の循
環液である弱液２０及び緑液１９が極度に濁り、
その結果、白液１０が濁る様になり遂には蒸解工
程１と洗浄工程２とに重大な影響を及ぼすことで
ある。
この濁りの状況を更に詳しく説明するために示
す第２図は苛性化工程への廃液混入率を弱液中の
SS濃度との関係を示すグラフであり、苛性化工
程５への希黒液１４の混入率と工程内循環液の一
つである弱液２０中のSSとの関係について示し
たものである。なお図中●は希黒液を、○・はUF
透過液を、点線はS.S.の許容レベルを示す。茲で
廃液混入率は次式で示された数値である。
廃液混入率（％）＝
新規補給総水量中の廃液使用量／苛性化工程で新規補
給された総水量
第２図から判る様に希黒液１４をその侭回収す
る場合、弱液２０中のS.S.は僅か５％の廃液混入
率でも3000mg／以上、10％の混入率では10000
mg／以上となり、現行の希黒液１４を全く回収
しない場合の200mg／というレベルと比較する
と、極めて僅かの希黒液１４の混入によつて弱液
２０中の濁りの状況が大幅に悪化する。この希黒
液１４の回収率と液の濁りとの関係は緑液１９及
び白液１０についても全く同様の結果が得られ
る。
そこで本発明者等はこの希黒液１４を苛性化工
程５へ回収する方法を見出すために先ずこの濁り
の状況及び原因について種々研究の結果、濁りと
なつて現われる物質即ちS.S.の主成分は苛性化工
程５内に大量に存在するライムマツド〔炭酸カル
シウム（CaCO3）〕であり、またこの濁りを惹き
起こしている原因が希黒液１４中に存在している
木材チツプ７に由来する高分子リグニンの有して
いる非常に強い分散能にあることを究明した。そ
して更にこの結果を基にして濁りを惹き起こす主
原因物質である高分子リグニンを除去する方法に
ついても種々研究した結果、希黒液１４を限外
過（UF）装置を用いて処理することにより効率
良く高分子リグニンを除去出来ることを見出し
た。この状況を更に詳細に説明するために次表に
希黒液１４のUF処理例とのデータを示す。
In the present invention, the concentrated liquid obtained by treating the dilute black liquor generated in the kraft pulp manufacturing process using a membrane separator is sent to the normal concentration and combustion process, while the permeated liquid is used as a lime ash in the green liquor causticizing process. This relates to a method for treating kraft pulp waste liquid used as cleaning water, and in particular ultrafiltration (UF), which is used as a membrane separation device to pass water, inorganic ions, or low molecular weight substances through a membrane and eliminate high molecular weight substances. The present invention relates to a method for treating kraft pulp waste liquid using a device. As shown in the flow sheet of the conventional kraft pulp manufacturing process as shown in Figure 1, white liquor 10, which is a mixture of caustic soda (NaOH) and sodium sulfide (Na 2 S), is used for cooking, and after cooking, The waste liquor is recovered as extracted black liquor 11 from the digester and washed black liquor 13 from the subsequent washing step 2. The liquid 14, which is a mixture of ordinary liquids, is called dilute black liquor. This diluted black liquor 14 is concentrated in the evaporator in the concentration step 3 and then reductively burned in the boiler in the combustion step 4, and the organic matter is recovered as thermal energy, while the sodium salt is converted into sodium carbonate (Na 2 CO 3 ).
and smelt 18 consisting of sodium sulfide (Na 2 S)
will be collected as. The smelt 18 recovered in this way is dissolved in water 21 or a weak liquor 20 which is lime mud washing water to become a green liquor 19, which is further converted into a white liquor 10 in a causticizing process 5 and regenerated, and then converted into a cooking chemical solution. reused as Now, in the normal kraft pulp manufacturing process, dilute black liquor is generated in an amount of about 12t/t pulp, so in the concentration step 3, more than 2t/t pulp is required, which is the main energy consumption in pulp mills. It has become a club. In response to the recent rise in energy costs, various studies are being conducted to reduce the amount of steam used in the concentration process 3, and one of the methods is to reduce the amount of steam used in the cleaning process 2.
It is conceivable to reduce the amount of pulp washing water 12 used and increase the concentration of the diluted black liquor 14. However, with this method, the product pulp 9 may be washed improperly, resulting in increased sodium loss, or if the bleaching process is followed, the amount of chemicals used in this process will increase, and furthermore, the pollutants discharged from the bleaching process may increase. Since the amount will increase, its practical application can hardly be expected. Another method is causticization step 5.
It is conceivable to use diluted black liquor 14 instead of the water 21 used in . This method is the concentration step 3.
Not only can the steam for concentration in the cooking process 1 be saved, but the effective inorganic chemicals that are not consumed in the cooking process 1 and remain in the diluted black liquor 14 are also unnecessary as in the current concentration process 3.
It has a very large merit because it can be reused efficiently by only passing through the causticizing process 5 without going through the combustion process 4. However, the biggest drawback of this method is that in the causticizing process 5, where the dilute black liquor 14 is recovered, the weak liquor 20 and green liquor 19, which are circulating fluids in this process, become extremely cloudy.
As a result, the white liquor 10 becomes cloudy, which ultimately has a serious effect on the cooking process 1 and the washing process 2. To explain this turbidity situation in more detail, Figure 2 shows the percentage of waste liquid mixed into the causticizing process.
It is a graph showing the relationship with the SS concentration, and shows the relationship between the mixing rate of the dilute black liquor 14 into the causticizing process 5 and the SS in the weak liquid 20, which is one of the circulating liquids in the process. In the figure, ● indicates dilute black liquor, and ○ indicates UF.
The dotted line indicates the permeate and the acceptable level of SS. The waste liquid contamination rate is the value shown by the following formula. Waste liquid mixing rate (%) = Amount of waste liquid used in the total amount of newly replenished water / Total amount of newly replenished water in the causticizing process As can be seen from Figure 2, when the dilute black liquor 14 is recovered while it is, SS is 3000mg/or more even at a waste liquid contamination rate of only 5%, and 10000mg/at a 10% contamination rate.
mg/ or more, and compared to the current level of 200 mg/ when no dilute black liquor 14 is recovered, the turbidity in the weak liquid 20 will be significantly worsened due to the very small amount of dilute black liquor 14 mixed in. . The relationship between the recovery rate of the diluted black liquor 14 and the turbidity of the liquid is exactly the same for the green liquor 19 and the white liquor 10. Therefore, in order to find a method for recovering this dilute black liquor 14 to the causticizing process 5, the present inventors first conducted various studies on the conditions and causes of this turbidity, and found that the main component of the substance that appears as turbidity, that is, SS Lime mat [calcium carbonate (CaCO 3 )] present in large quantities in the black liquor 14 is present in large quantities, and the cause of this turbidity is the polymer lignin derived from the wood chips 7 present in the diluted black liquor 14. It was discovered that the reason lies in the extremely strong dispersion ability possessed by Furthermore, based on this result, we conducted various studies on methods for removing polymeric lignin, which is the main cause of turbidity, and found that by treating dilute black liquor 14 using an ultrafiltration (UF) device, We have discovered that polymer lignin can be removed efficiently. In order to explain this situation in more detail, the following table shows data for an example of UF treatment of diluted black liquor 14.
【表】
茲では原料即ち希黒液１４をUF装置を用いて
何れも等量の濃縮液、透過液を得る条件、所謂２
倍濃縮の条件で処理を行なつた場合を示している
が、この結果を見ても判る様に高分子リグニンに
ついてはUF処理の場合はその殆んどが、濃縮液
側に濃縮される。その一方、透過液中には濁りの
主原因物質である高分子リグニンは殆んど、含ま
れていないため之を苛性化工程用水２１として使
用しても工程内での濁りのトラプルは大幅に改善
される。この様にして希黒液１４をUF処理して
得られた夫々の透過液を苛性化工程５へ回収した
場合の弱液２０の濁りの状況を示したのが先きに
示した第２図である。前に示した表のUF処理条
件で得た夫々の透過液を苛性化工程５へ回収する
際の弱液２０中のS.S.の許容レベルを200mg／
とした場合、UF透過液は50％混入することが出
来る。
なお、UF装置を用いる場合に関しては、リグ
ニン除去率のより高い膜を用いたり、或いは濃縮
倍率などの処理条件を選定することにより更に廃
液混入率を増大させることが出来る。
以上説明した如く本発明者等が次に示す第３図
はクラフトパルプ製造工程へUFを適用する本発
明方法のフローシートであり、茲に示す様に希黒
液１４をUF処理した後、濃縮液１４′は現行法の
濃縮工程３、燃焼工程４へ送る一方、透過液２２
を苛性化工程用水２１の一部ないし全部として使
用することによつてクラフトパルプ製造における
希黒液濃縮工程３での蒸発負荷の大幅低減と同時
に苛性化工程５における新水２１使用量の大幅低
減を効果的に実施出来ることを見出し本発明を完
成させたものである。なお本発明方法適用の際に
は前述した様にUF装置６において使用する膜に
ついては透過液２２の回収計画に合わせた適切な
性能の膜、或いは処理条件を選定することと同時
に膜材料についても充分考慮することが肝要であ
る。
第４図は苛性化工程におけるライムマツド洗浄
装置の説明用断面図であり、図中２３はライムマ
ツドスラリー（洗浄前）を、２１′はライムマツ
ド洗浄用水を、２４はライムマツドスラリーとラ
イムマツド洗浄用水の混合液を２０′は弱液を、
２５はライムマツドスラリー（洗浄後）を示す。
本発明方法の対象となるクラフトパルプの希黒
液は高温・高PHであることから膜材料としては、
それに充分耐え得るもの、例えば芳香族ナイロ
ン、芳香族スルホン、ポリアミド−ヒドラジド系
などをベースとしたものを使用する必要がある。
以上の様に本発明方法を適用することにより大
幅なエネルギー節減効果が得られることが明らか
になつたが、その効果を更に説明するため以下に
実施例を示す。
実施例 １
第３図に示す希黒液１４を、UF装置６を用い
て10Kg／cm2の操作圧で1.3倍濃縮して得られた透
過液（リグニン濃度2000ppm）を苛性化用水２１
の一部として用いた。苛性化工程５での具体的な
使用場所は、第４図に示すライムマツドウオツシ
ヤであり、ライムマツド洗浄用水として使用され
る3.5t／ｔパルプの新水の約70％に相当する
2.5t／ｔパルプをこのUF透過液で代替したが、
弱液２０中のS.S.は150mg／にしかならず、100
％新水を用いた場合（この時の弱液２０中のS.S.
は100mg／）と同様、苛性化工程でのトラプル
は全く認められなかつた。
そしてこの場合、濃縮工程３へ送られるUF濃
縮液１４′の量は2.5t／ｔパルプ減少し、その結
果濃縮用蒸気の量が通常に比べ0.7t／ｔパルプ減
少した。また苛性化用水２１としての新水使用量
も、通常に比べ2.5t／ｔパルプ減少した。
比較例
実施例１と同様第４図に示すライムマツドウオ
ツシヤにて使用される苛性化用水２１′の一部と
して、希黒液１４（リグニン濃度63000ppm）を
用いた。この場合、通常使用される3.5t／ｔパル
プの５％に相当する0.18t／ｔパルプを希黒液１
４で代替した時の弱液２０′中のS.S.は3500mg／
となり、苛性化工程５および蒸解工程１・洗浄
工程２でのトラブルが大きく、この種の排液は殆
んど回収出来なかつた。[Table] In the case of the raw material, dilute black liquor 14, the conditions for obtaining equal amounts of concentrated liquid and permeated liquid using a UF device, so-called 2
This shows the case where the treatment was carried out under conditions of double concentration, but as can be seen from the results, most of the polymeric lignin is concentrated in the concentrate side in the case of the UF treatment. On the other hand, the permeate contains almost no polymer lignin, which is the main cause of turbidity, so even if it is used as water 21 for the causticizing process, problems with turbidity during the process will be greatly reduced. Improved. Figure 2 shown earlier shows the turbidity of the weak liquid 20 when each permeate obtained by subjecting the dilute black liquor 14 to the UF treatment in this manner is recovered to the causticizing step 5. It is. The allowable level of SS in the weak liquid 20 when each permeate obtained under the UF treatment conditions shown in the table above is recovered to the causticizing process 5 is set at 200mg/
In this case, 50% of the UF permeate can be mixed. Note that when using a UF device, the rate of waste liquid contamination can be further increased by using a membrane with a higher lignin removal rate or by selecting processing conditions such as concentration ratio. As explained above, Fig. 3 shown below by the present inventors is a flow sheet of the method of the present invention in which UF is applied to the kraft pulp manufacturing process. The liquid 14' is sent to the concentration step 3 and the combustion step 4 of the current method, while the permeate 22
By using this as part or all of the water 21 for the causticizing process, the evaporation load in the dilute black liquor concentration process 3 in kraft pulp production is significantly reduced, and at the same time, the amount of fresh water 21 used in the causticizing process 5 is significantly reduced. The present invention was completed by discovering that it is possible to effectively carry out the following steps. In addition, when applying the method of the present invention, as mentioned above, the membrane used in the UF device 6 should have an appropriate performance according to the recovery plan of the permeated liquid 22, or the processing conditions should be selected, and at the same time, the membrane material should also be selected. It is important to give sufficient consideration. FIG. 4 is an explanatory cross-sectional view of the lime mud cleaning equipment in the causticizing process, in which 23 is lime mud slurry (before cleaning), 21' is lime mud cleaning water, and 24 is lime mud slurry and lime mud cleaning water. 20' of mixed liquid is weak liquid,
25 indicates lime pine slurry (after washing). Since the dilute black liquor of kraft pulp, which is the target of the method of the present invention, has a high temperature and high pH, it can be used as a membrane material.
It is necessary to use a material that can sufficiently withstand this, for example, a material based on aromatic nylon, aromatic sulfone, polyamide-hydrazide, etc. As described above, it has become clear that a significant energy saving effect can be obtained by applying the method of the present invention, and examples are shown below to further explain the effect. Example 1 The diluted black liquor 14 shown in FIG. 3 was concentrated 1.3 times using the UF device 6 at an operating pressure of 10 kg/cm 2 and the obtained permeate (lignin concentration 2000 ppm) was added to the causticizing water 21.
It was used as part of the The specific place of use in causticizing process 5 is the lime mud washer shown in Figure 4, which corresponds to approximately 70% of the fresh water of 3.5t/t pulp used as lime mud washing water.
2.5t/t pulp was replaced with this UF permeate, but
SS in weak liquid 20 is only 150 mg/100
When using % fresh water (SS in weak liquid 20 at this time)
(100mg/), no trouble was observed in the causticizing process. In this case, the amount of UF concentrate 14' sent to the concentration step 3 was reduced by 2.5 t/t pulp, and as a result, the amount of concentrating steam was reduced by 0.7 t/t pulp compared to normal. The amount of fresh water used as causticizing water 21 was also reduced by 2.5t/t pulp compared to normal. Comparative Example As in Example 1, dilute black liquor 14 (lignin concentration 63,000 ppm) was used as part of the causticizing water 21' used in the lime and pine washer shown in FIG. In this case, 0.18t/t pulp, which is equivalent to 5% of the normally used 3.5t/t pulp, is mixed with 1 diluted black liquor.
SS in weak liquid 20' when replaced with 4 is 3500mg/
This caused major troubles in the causticizing process 5, cooking process 1, and cleaning process 2, and almost no waste liquid of this type could be recovered.
【図面の簡単な説明】[Brief explanation of the drawing]
第１図は現行のクラフトパルプ製造工程のフロ
ーシート、第２図は、苛性化工程への廃液混入率
と弱液中のSS濃度の関係のグラフ、第３図は、
本発明によるクラフトパルプ製造工程へのUF適
用プロセスのフローシート、第４図は、苛性化工
程におけるライムマツド洗浄装置の説明用断面図
を夫々示す。
図中、１……蒸解工程、２……洗浄工程、３…
…濃縮工程、４……燃焼工程、５……苛性化工
程、６……膜処理工程、７……木材チツプ、８…
…未洗浄パルプ、９……洗浄パルプ、１０……白
液、１１……抽出黒液、１２……パルプ洗浄用
水、１３……洗浄黒液、１４……希黒液、１４′
……膜処理濃縮液、１５……濃縮工程における蒸
発水、１６……濃黒液、１７……燃焼工程におけ
る蒸発水、１８……スメルト、１９……緑液、２
０……弱液、２０′……弱液、２１……苛性化用
水（ライムマツド洗浄用水）、２１′……ライムマ
ツド洗浄用水、２２……膜処理透過液、２３……
ライムマツドスラリー（洗浄前）、２４……混合
液、２５……ライムマツドスラリー（洗浄後）、
●印……希黒液、○・印……UF透過液、点線……
S.S.の許容レベル。
Figure 1 is a flow sheet of the current kraft pulp manufacturing process, Figure 2 is a graph of the relationship between waste liquid contamination rate in the causticizing process and SS concentration in the weak liquid, and Figure 3 is:
FIG. 4, a flow sheet of the process of applying UF to the kraft pulp manufacturing process according to the present invention, each shows an explanatory cross-sectional view of the lime mud cleaning device in the causticizing process. In the figure, 1...cooking process, 2...cleaning process, 3...
...Concentration process, 4...Combustion process, 5...Caussizing process, 6...Membrane treatment process, 7...Wood chips, 8...
...unwashed pulp, 9 ... washed pulp, 10 ... white liquor, 11 ... extracted black liquor, 12 ... water for pulp washing, 13 ... washed black liquor, 14 ... diluted black liquor, 14'
... Membrane treatment concentrate, 15 ... Evaporated water in the concentration process, 16 ... Concentrated black liquor, 17 ... Evaporated water in the combustion process, 18 ... Smelt, 19 ... Green liquor, 2
0...Weak liquid, 20'...Weak liquid, 21...Water for causticizing (water for washing lime mud), 21'...Water for washing lime mud, 22...Membrane treatment permeate, 23...
Lime pine slurry (before washing), 24... Mixed liquid, 25... Lime pine slurry (after washing),
● mark...dilute black liquor, ○ mark...UF permeate liquid, dotted line...
Tolerance level of SS.