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    • 专利摘要:
    SUMMARY The present invention relates to a method for treating and utilizing liquid streams in a chemical pulp mill. The method comprises at least the following steps: a) chemical pulp is prepared in an alkaline cooking process, b) the brown stock formed during the cooking is treated, the treatment comprising washing the stock and preferably white oxygen delignification and subsequent washing of the stock, c) a bleaching process for the brown stock, wherein the bleaching sequence uses chlorine dioxide and in addition at least one oxidizing bleaching step and has at least two washing steps for treatment liquefied and for the preparation of filtrates, and d) filtrates from step c) are purified at an effluent treatment plant at the chemical pulp mill which comprises at least biological treatment, to obtain purified effluent. The process further comprises a step e), wherein the purified effluent having a color of 200 mg / l (R color) or more and a COD value above 150 mg / l is used as a pulp treatment liquid in step c).
    公开号:SE1250617A1
    申请号:SE1250617
    申请日:2010-11-22
    公开日:2012-06-13
    发明作者:Janne Vehmaa；Olavi Pikka；Pekka Tervola
    申请人:Andritz Oy；
    IPC主号:
    专利说明:

    bleached with chlorine-containing chemicals so that chlorine dioxide is the main chemical in the mill's bleaching process. Several years of pressure to reduce the amount of organic chlorine compounds in bleaching effluents has led to the point that first the use of chlorine and hypochlorite was abandoned and further the kappa mass after boiling was reduced from level 30 to level 10-15 for softwood and from level 16-20 to level 10 -13 for Iövved using an oxygen step. In the 1990s, the goal was to abandon the use of chlorine dioxide as well, and many mills switched to the use of completely chlorine-free bleaching technology (TCF, "total chlorine free"), in which the use of chlorine dioxide was also replaced by completely chlorine-free bleaching chemicals, such as ozone and peroxide. With this technology, all chlorine-containing chemicals could be avoided, but on the other hand, many paper manufacturers were not satisfied with the properties of pulp produced without chlorine chemicals.The marginal condition for all end-of-life solutions is that chlorine dioxide is still used as a bleaching chemical.
    The dominant position for chlorine dioxide as a bleaching chemical has thus increased in recent years and not even the latest research or recent industrial experience has been able to destabilize its position, but the whole pulp industry has generally, with only a few exceptions, approved the use of chlorine dioxide as the main chemical in bleaching. If a mill is to further reduce the amount of organic chlorine compounds, the mill's goal will thus be, first and foremost, to eliminate them and to treat them within the mill, rather than to reduce the use of chlorine dioxide.
    Modern ECF bleaching used for pulp bleaching typically consists of at least three bleaching steps and three washing machines. As a special case, there may be only two washing machines, but such applications are rare.
    ECF bleaching includes all those bleaching sequences that have at least one chlorine dioxide step and that do not use elemental chlorine in any bleaching step. Since the use of hypochlorite for pulp quality reasons is limited to the production of only a few special pulps, such as dissolving pulps, it is also not considered that hypochlorite is used in the production of ECF pulp, but it is not completely excluded. The bleaching sequence further comprises an alkaline step, in which the additional chemicals used today are typically either oxygen, peroxide or both. Modern bleaches can further utilize ozone, various types of acidic steps and a chelate step for removing heavy metals. The literature describes the bleaching steps in letters: O = oxygen delignification D = chlorine dioxide step H = hypochlorite step C = chlorination step E = alkaline extraction step EO = alkaline extraction step which uses oxygen as an additional chemical EP = alkaline extraction step which uses peroxide (extra chemical) using oxygen and peroxide as additional chemical P = alkaline peroxide step A = acid hydrolysis step, hexenuronic acid removal step a = mass acidification step Z = ozone step PAA = peracetic acid step, acid peroxide step This patent application lists the chemical amounts and other amounts of pulp , ie air dry metric ton of 90% dry chemical pulp).
    When bleaching is called ECF bleaching, the amount of chlorine dioxide used in the bleaching sequence is more than 5 kg act.C | / adt mass. If chlorine dioxide is used in a bleaching step, the doses are most typically between 5 and 15 kg act. Cl / adt. The doses refer to active chlorine, whereby when converted to chlorine dioxide the dose must be divided by the ratio 2.63.
    If the use of peroxide in bleaching is limited to doses less than 6 kg and if chlorine dioxide is the main bleaching chemical, the chlorine dioxide dose in bleaching increases from a level of 25 kg / adt depending on the bleaching properties of the pulp and the amount of kappa mass. has been reduced before starting the bleaching with chlorine-containing chemicals.
    Thus, in view of the process, the bleaching technique can be adjusted quite freely to different levels of chlorine dioxide consumption so that the amount of chlorine-containing chemicals leaving the bleaching corresponds to the capacity of the chemical cycle to receive chlorides.
    In the context of the present invention, in view of the practice, it is most preferable to select as the reference sequence for hardwood a bleaching sequence AID-EOP-D-P which is carried out with four bleaching steps and omitting ozone. The corresponding sequence for softwood is D-EOP-D-P. The quality of the pulp can then be considered to correspond to the qualities required for ECF pulp and the pulp exchange remains reasonable. The chlorine dioxide doses for softwood are then typically 25-35 kg / adt mass and for hardwood 20-30 kg / adt. These values can be considered as dimensioning values and there is no need to invent any new specific techniques for bleaching. The theory of bleaching and different connection alternatives create the possibility of countless different bleaching sequences, starting from connecting two washing machines up to bleaching sequences with six steps. At the same time, the number of chlorine dioxide steps can vary from one to four and in between alkaline steps are suitable.
    When the amount of active chlorine is calculated as described above in the form of the amount of chlorine, it is noted that even coniferous wood, to obtain a good bleaching result, the bleaching line produces about 10 kg of chlorides per tonne of pulp and a bleaching line for hardwood even less. If the plant is closed so that less and less fresh water is led to bleaching, there may be a need to prepare for up to 50% larger chlorine dioxide doses and on the other hand the amount of chlorides in bleaching effluents increases to a level of about 15 kg, which means that in practice, the largest doses of active chlorine are 60-70 kg / adt. Values higher than this cannot be considered economically reasonable, but the basic bleaching solution follows these starting points. On the other hand, the object of the present invention is to introduce an alternative by which closure of the bleaching does not substantially increase the chemical consumption. 10 15 20 25 30 A proposed technique for reducing the environmental impact of chlorine-containing chemicals is the closure of the liquid cycles at bleaching plants and modern bleaching plants have reached a level of 10-15 m3 effluent / adt pulp without lowering the pulp quality. Nevertheless, even when the amount of bleach effluent is reduced from a level of 15 m3 / adt mass to a level of 10 mB / adt, an increase in chemical consumption is seen, which thus leads to an ever-increasing amount of organic chlorine compounds from bleaching. Thus, it can be concluded that closure of the bleaching water cycles as such does not directly affect the amount of organic chlorine compounds, while on the other hand a smaller amount and a greater concentration of effluent enables simpler and more economical purification thereof.
    Chloride-containing chemicals are used in bleaching so that the total chloride dose to the bleaching plant is 5-10 kg chlorides per one tonne of chemical pulp.
    Since this amount must be adjusted so that the amount of liquid to be evaporated in the process remains reasonable, the challenge is to find such a process arrangement where a chloride-containing liquid replaces any other liquid used in a process at the mill. Thus, there is no need for separate treatment steps, new non-productive sub-processes at the mill, but the treatment can be performed using existing process steps.
    In order to be able to optimize the treatment of chloride-containing liquid and in practice the treatment of bleach effluent, it is inevitable to first know the properties of the effluent. In bleaching, chlorine-containing inorganic compounds and organic chlorine compounds from the reactions of chlorine dioxide or chlorine remain in the process. Bleaching separates from the fibers various lignin compounds, which remain in effect in the form of organic molecules. In addition, sulfuric acid is used in bleaching for pH regulation and as the main chemical in the hydrolysis of hexenuronic acids. Sodium hydroxide is also used for pH regulation and lignin extraction in alkaline steps. In addition to these, depending on the bleaching sequence, oxygen and peroxide are used in bleaching, which, however, in elemental analysis are such substances that their contribution in, for example, purification processes is not noted. In some special cases, hydrochloric acid can also be used in pH regulation and sulfur dioxide or other reducing agents in the elimination of chemical residues from bleaching, ie. in the elimination of unreacted ink chemicals.
    Closure of the bleaching is based on recycling of filtrates from washing machines from later bleaching steps to the previous step. The bleaching is planned only for circulating filtrate between bleaching steps and pulp from one step to another for reaction with different bleaching chemicals. Closure of the entire bleaching is thus an idea based on the fact that all substances separated during the bleaching end up in filtrates. Optimization of the end of the bleaching is largely based on the way in which the bleaching reaction products disrupt the bleaching process. Although it has been stated in many different contexts that different degrees of closure are possible, practical experience has shown that such wash water arrangements for bleaching in which the filtrates are connected so that the amount of wastewater is less than 12-13 m3 / adt increase the consumption of bleach. chemicals. The pulp quality and construction of the bleaching plant naturally dictate the amount of additional chemicals used in the bleaching when the amount of effluent in the plant decreases below the level indicated above.
    US 5,470,480 presents a method by which e.g. an effluent stream in a chemical pulp mill is treated so that hydrogen peroxide is added and the stream is exposed to ultraviolet radiation to form hydroxyl radicals from the peroxide. The hydroxyl radicals oxidize organic pollutants in the effluent stream to achieve a desired level of purity, e.g. in the form of chemical oxygen demand, COD ("chemical oxygen demand"), or expressed as color.
    The treated effluent can be recycled back to the chemical pulp mill, e.g. for mass washing in bleaching. The color of the effluent is remarkably reduced by the method, as measured by Color Method EPA 111.2, to below 500, preferably to below 20. According to one embodiment, crude acidic effluent is added to the thus purified water, after which the mixture is treated in an oxidizing pond, after which part of it can EP 863 113 discloses a method in which the alkaline filtrate from bleaching in a chemical pulp mill is treated (e.g. by ultrafiltration) to form an alkaline concentrate which contains abundant organic compounds. with high molecular weight, and a stream from which the organic compounds have been removed.
    Said fractions can be used in brown melt washing. Recycling of these fractions enables the reduction of the amount of AOX removed from the bleaching plant to an effluent treatment plant or to a surrounding water system. The acidic effluent is treated with biological effluent treatment to obtain the desired AOX, COD and color values for the effluent from the mill to the environment.
    The publication Fontanier, V., et al. ("Simulation of Pulp Mill Wastewater Recycling after Tertiary Treatment", Environ. Technology, 2005, vol. 26, pp. 1335-1344) has studied the circulation in a chemical pulp mill of ef fl uent treated at a biological treatment plant and ef fl uent which is not It was stated in the study that the af fl uent should be treated further in a tertiary step to prevent the increase in the consumption of bleaching chemicals and the decrease in pulp lightness.The most effective tertiary treatment was catalytic ozonation.The effluents were recycled to EO step, to purification and after t2 step.The tertiary treated effluent produced almost the same COD content as the use of pure water.Use of untreated effluent from the biological treatment plant, in turn, led to high amounts of COD, which can cause additional consumption of bleaching chemicals (t. eg NaOH in the EO stage) and loss of pulp brightness.Treated biological effluent has high COD and color levels, while the corresponding values for ef fl uent treated by catalytic ozonation are low. The use of untreated effluent is said to possibly cause damage at several stages in the process due to the high COD levels. That is, also according to this publication, liquids used in pulp treatment should be liquids with a purity level close to that of pure water. The brown color of effluents is mainly of organic origin, in particular from lignin decomposition products formed in various stages of pulp boiling and bleaching. Other substances that produce paint are both wood extract substances and tannins and resins. Decolorization of effluents before being led to a surrounding water system is considered important, as they are considered to have a detrimental effect on the aquatic organisms' living organisms and plants. According to the aforementioned publications, the effluents must also be decolorized before reuse in a pulp production process to obtain good quality pulp.
    WO 2008/152185 (F1 application 20080144) discloses a method by which purified effluent in an amount of at least 1 mß / adt pulp is introduced into dilution after a press or washing press, which is effected from the dilution to the first process step of bleaching. The effluent has preferably been biologically purified to reduce the lignin content.
    WO 2008/152186 (F1 application 20080298) describes a method by which more than one treatment line is arranged at the effluent training plant for the mill effluents and effluents with different chemical composition are purified in separate treatment lines so that the quality and amount of purified water from each treatment line is suitable. for use in one or more steps in the production process, to which purified ef fl uent is returned. With this method, one or more filtrates from a bleaching sequence can be taken to a purification treatment and typically returned as washing or diluting water for bleaching and / or brown mill washing. The purpose of using purified effluent is a purpose for which this purified effluent is most suitable in view of its composition, such as chemical composition. Also in this method, the effluent has been biologically purified to reduce the lignin content. The lignin content of the effluent decreased without dilution by at least 30%, preferably above 40%, more preferably above 60%.
    The standard defined by the Technical Association of Pulp and Paper Industry, Tappi, in which e.g. the limit pre-paint is very low, is still considered the quality requirement for raw water used in a bleaching plant. The quality of the water has been considered a critical factor and there has therefore been no desire to deviate from the standard, except in those exceptional cases where it is impossible to meet the quality requirements due to the poor quality of the mill's raw water. Even in these cases, attempts have been made to make the quality of the water as close to the requirements of the standard as possible.
    The most important component that causes light loss is lignin. During secondary treatment of effluent, the color does not change, even if the lignin content decreases.
    This has led to a misinterpretation of the importance of the color of the waters and filtrates in a mass bleaching process.
    An object of the present invention is to provide a method for further improving the conditions for closing water circulations at a chemical pulp mill and thus for reducing the amount of pure water required, in particular at the bleaching plant at a chemical pulp mill. The brightness and quality of the pulp must remain at the same level as in known methods.
    Partial closure of bleaching and external purification of the generated filtrates (with a volume of 10-15 ms / adt) using e.g. filtration, various known forms of biological treatment, various techniques for chemical treatment and clarification have been considered the so-called best available technology for bleach effluents. The treated water is then returned to the water system to the same channel from where the liquid was taken to the process in the mill or to another channel. This is used for both TCF and ECF pulp mills. Biological treatment is effective specifically when the proportion of harmful organic substances is reduced, which mainly includes lignin compounds separated by bleaching, hemicelluloses and components derived from extractives, which form a significant part of the effluent coming from the bleaching plant.
    There are a wide variety of compounds derived from wood and some of the compounds are chlorinated and some of them are low molecular weight compounds of carbon and hydrogen. Since microbes behave in such a way that their nutrients mainly comprise the organic part of the effluent, all inorganic substances, at least inorganic elements, remain in the effluent in one form or another, regardless of whether the microbes have needed them as nutrients or not. Biologically treated water thus has an organic load that makes it clearly cleaner than other treated effluent, but due to the inorganic substances, especially chlorine, the only choice has been to remove it from the process. In addition, after secondary purification, the color of the effluent remains largely unchanged compared to incoming water; the effluent may even be darker in color than the water entering the treatment. The color of the effluent is a clear visual disadvantage, but very little information is available regarding the chemical properties of the color of the effluent. Since the color at some plants can be, for example, a key figure for emissions and on the other hand because only a little studied information exists, the color is incorrectly associated with lignin content. When the properties of the effluent are estimated, the color as such has been considered as such a significant disadvantage that color-containing effluent falls short in almost all evaluations regarding use as raw water in pulp processes.
    The basis of this invention is that the color of the effluent has no significant significance with respect to bleaching, but that color-containing water in the conditions for ECF bleaching and definitely also in TCF bleaching is a fully functioning raw water and produces similar bleaching results as bleaches performed with pure water .
    Furthermore, the literature has repeatedly indicated that chlorides increase the development of brightness in the chlorine dioxide step and it has been used as a basis for many filtrate solutions which have led to the closure of bleaching. The present invention removes harmful lignin from the raw water of bleaching without affecting the color of the water, but due to its chemical nature returns a remarkable amount of chloride back to the bleaching. A new raw water source for bleaching has thus been defined based on the previously lacking understanding of the color of purified effluent, especially in this case affecting the bleaching result.
    Here, emphasis is placed on a limitation that is essential to the invention, ie. here, reference is made to the color only of such a biological treatment plant which is essentially derived from the production of chemical pulp or other treatment of lignocellulosic fibers and the purification of effluent generated therein. Thus, an invention is created which aims at treatment, purification and recycling back to the original process of a filtrate or of filtrates from a bleach line.
    The present invention relates to a method for treating and utilizing liquid streams in a chemical pulp mill, which method comprises at least the following steps: a) chemical pulp is produced in an alkaline cooking process, b) the brown stock formed during the cooking is treated, the treatment comprising washing the pulp and preferably oxygen delignification and subsequent washing of the pulp, c) a bleaching process for the treated brown stock, the bleaching sequence comprising at least one step utilizing chlorine dioxide and at least one oxidizing bleaching step and having at least two washing steps for treating the pulp with liquids and for production of filtrates, d) filtrates from step c) are purified at an effluent plant at the chemical pulp mill, the plant comprising at least biological purification, to obtain purified effluent. The method is characterized in that it comprises a further step: e) the purified effluent with a color of over 200 mg / l (Pt color) and a COD value above 150 mg / l is used as pulp treatment liquid in step c).
    According to a preferred embodiment of the invention, purified effluent is used after the first bleaching step of the bleaching sequence and before the last oxidizing bleaching step.
    Oxidizing bleaching chemicals typically include oxygen, ozone and peroxide compounds, such as hydrogen peroxide and peracids, chlorine dioxide and hypochlorite.
    Typical oxidizing bleaching steps are thus EO, EOP, P and Z steps. In general, all bleaching steps are based on oxidation, excluding acidic A-steps which are hydrolysis. Purified effluent is thus not used for washing after the last oxidizing bleaching step and not for pulp purification (screening) or pulp drying after bleaching. When the liquid used to treat pulp after the last oxidizing bleaching step is a liquid that is substantially purer than purified effluent, the bleaching can be performed using "dirtier" liquid than recommended, without compromising the brightness or quality of the pulp. Here, "dirt" refers to such parameters as are used to describe dirt, but does not substantially describe how harmful the water is with respect to the bleaching step.
    In connection with the invention, the biological effluent treatment plant comprises at least aeration and final clarification, typically also explanation.
    The effluent is neutralized before aeration. The method according to the invention does not require tertiary treatment of the effluent.
    Purified effluent is used in the flow direction of the pulp during the washing of the first bleaching stage or thereafter when a bleaching sequence requires dilution or washing water, but before the last oxidizing bleaching step in the sequence. Purified effluent from step d) is not used in the last washing machine before storing the pulp, such as before a dryer.
    Pulp washing steps are typically present between the bleaching steps. Purified ef fl uent can be used for bleaching as a diluent or as a washing liquid in a press, a washing press or a pressurized drum cleaner, such as a Drum DisplacerTM wash (DD wash) from Andritz Oy, or another suitable pulp washer.
    It has been noted in connection with the present invention that although the color of the effluent after purification is above 200 mg / l (Pt color), up to a level of 1000-2000 mg / I, typically 200-2000 mg / I (Pt color), it has no effect on the bleaching result. The brightness or quality of the pulp does not deteriorate compared to a pulp bleached using a cleaner liquid. The COD level for purified effluent is above 150 mg / I, even 200-400 mg / I, which also does not impair the bleaching result. COD for purified ef fl uent can thus correspond to e.g. condensate from an evaporation plant, in which the chemical oxygen consumption is generated from chemical compounds that do not substantially react with bleaching chemicals.
    The most important component that causes light loss is lignin. In secondary treatment, however, the color does not change in the same proportion as lignin is removed. The above-mentioned WO patent applications 2008/152185 and 10 15 20 25 30 13 2008/152186 state that when the effluent content of the effluent is reduced in biological treatment, the effluent can be used e.g. for brown flour washing. The lignin content must be reduced during treatment by more than 50% to make the recycling of purified effluent profitable. In biological treatment, the color of the effluent does not decrease by more than 20%.
    Biological treatment of effluent includes explanation of the effluent, whereby a primary sludge is generated, and an activated sludge plant, in whose aeration basin the effluent is treated with activated sludge which breaks down impurities present in the effluent, such as lignin. The aeration basin is followed by final clarification, where activated sludge is separated from purified water. The present method utilizes precisely this type of effluent training, which has been found to be adequate for purifying effluent for reuse.
    It is common knowledge that in bleaching plants with closed liquid cycles and a production rate of effluent below 20 ms / adt, preferably below 15 m3 / adt, the COD level of the effluent increases in acid effluent to above 1300 mg / l and in alkaline to above 1800 mg / l . If the amount of effluent decreases to remarkably below 15 m3 / adt, close to 10 m3 / adt, an increase in chemical consumption can be noted.
    In our opinion, the use of purified effluent will be profitable especially when the COD level of the bleaching effluent increases to over 1500 mg / l, preferably to over 1800 mg / l, thereby reducing the amount of effluent obtained by internal closure of processes has reached a level at which the accumulation of impurities in the effluent leads to additional consumption of chemicals. This COD level has since been formed from a bleaching process, washing losses from a washing apparatus after the oxygen step and from condensate and chemicals used. In practice, the COD of a bleaching plant effluent does not exceed 5000 mg / l with a normal bleaching process.
    The present method is preferably used in a bleaching sequence with at least one step utilizing chlorine dioxide. As a result, chlorine compound-containing filtrates are formed, which are purified in biological effluent treatment, whereby the lignin content is reduced by at least 50%, but the purification has no significant effect on the amount of chlorine compounds. According to the present method, purified effluent is used only in the bleaching plant, whereby the chlorine compounds do not end up e.g. via brown flour washing in black liquor and on to chemical recycling. Thus, this method does not require a separate procedure or plant for the removal of chlorine compounds, when the effluent to be purified is not used in the last washing apparatus of the oxygen stage. The recycled chloride reacts with bleaching and thus even reduces the amount of necessary bleaching chemicals to a small extent.
    The chloride in the purified effluent thus actually promotes a better bleaching result. In effluent treatment, it is preferable to obtain as large a reduction in the equation content as possible, while the chloride content may remain unchanged. With the help of effluent treatment, the ratio of lignin to chloride (total Cl / Cl ') can be changed in a favorable direction. In effluent circulation, it has been considered important to remove paint and metals, the ratio of lignin to chloride has not been mentioned. Since chlorine / chloride is an inorganic substance that does not substantially evaporate, precipitate or form separable particles or compounds under the conditions prevailing in treatment plants, in practice the entire amount of total chlorine added leaves the plant together with liquid.
    Control of metals has also been considered important in connection with the closure of water circulation. However, it has been stated that the effect of metals is not of such importance and that during biological treatment the amount of metals removed is adequate at least in terms of ECF bleaching. This is because the mass is neutralized during the purification and the solubility of many metals is thereby changed. If the solubility of a metal decreases, the delay in the purification process and the environment are adequate for precipitating a particle containing the metal so that it is not returned to the purified effluent.
    In the present method, in which biologically purified effluent is used within a bleaching plant, the consumption of bleaching chemicals remains essentially the same as when using pure water, when the target is a certain brightness level for the pulp. The strength properties of the pulp do not change in relation to the use of clean water.
    The examples are based on a simplified model, where biological purification would treat only ef fl uent that comes from bleaching and thus create the illustrated savings. A necessary condition is that other effluents from the mill are treated at another treatment line, where e.g. however, the amount of organic chlorine compounds is very low. However, if all effluents are treated in one plant, the total reduction of effluent resulting from bleaching can be calculated as follows: (amount of effluent resulting from bleaching / total amount of effluent) * amount of eff fl uent recycled to the process = reduction of the amount of eff fl uent as derives from bleaching.
    The smaller the amount of different leaking water or other water that is led to the treatment plant, the greater the reduction in the amount of effluent resulting from bleaching. Thus, when the goal is to stop the bleaching plant, separate treatment of different effluent fractions becomes increasingly appropriate.
    The presented connections illustrate a few different modes where purified effluent can be used. However, it is clear that purified effluent can be used in any washing machine, from where the pulp is introduced into a bleaching step, thus excluding the bleaching last washing machine upstream of drying or a paper machine, where paint causes real disadvantage. The bleach's last washing apparatus can preferably use circulating water from a pulp dryer, hot water or condensate.
    The present invention is described in greater detail with reference to the accompanying figures.
    Figure 1 illustrates a bleaching coupling utilizing the present invention.
    Figure 2 illustrates another bleach plant coupling utilizing the present invention. Figure 1 illustrates a bleaching plant utilizing chlorine dioxide, the plant being preceded by a press 2. The bleaching sequence is D0-EOP-D1-D2.
    The figure shows bleaching steps D0, EOP, D1 and D2 and the washing apparatus following each bleaching step, which appliances in this example are washing presses. In the direction of mass flow, the last D2 wash 10 receives wash water 12 which is circulating water from a dryer or hot water or alternatively condensate (7-11 ms / adt). The filtrate 14 from the D2 wash 10 is led to the D1 wash 8 in countercurrent with respect to the pulp and also to dilution downstream of the wash. Half of the D1 filtrate is passed through line 16 after the EOP wash 6 to dilute the pulp stream to the D1 stage. Half of the D1 filtrate is led via line 18 to dilute the pulp stream which is led to the DO wash 4. The filtrate 24 from the DO wash 4 and a part of the filtrate from the EOP wash 6 are led to the mill's effluent treatment plant 32 for biological treatment. A portion of the EOP filtrate is taken via line 22 to the pulp stream downstream of the DO wash 4.
    Purified effluent can be introduced from line 26 for dilution of pulp coming from the press 2 before the DO step via line 30. Purified effluent is introduced via line 34 for dilution of pulp before the DO wash 4 and for dilution of the pulp stream before the EOP wash 6 via line 28.
    In the solution of this embodiment, the amount of the DO wash filtrate typically taken for effluent purification is 10 mB / adt and the amount of EOP filtrate is 5 mB / adt. The amount of effluent returned to the bleaching process is 10 ms / adt.
    The amount of effluent from bleaching that leaves the plant in line 37 is then approximately 4-5 mß / Abt.
    Figure 1 illustrates in broken lines 36, 38 and 39 alternative applications for purified effluent: Dilution after DO step before DO wash, dilution after EOP wash, dilution after D1 step before D1 wash or dilution after D1 wash . By using effluent also for these purposes, it is possible to even reach a zero level for the amount of bleaching effluent leaving the mill. If necessary, filtrate from the D1 wash can be directed to eff fl purification 32.
    Figure 2 illustrates bleaching that uses chlorine dioxide and has a sequence D0 - EOP- D1 - D2. The oxygen step washing upstream is performed with a Drum Displacer type washing machine.
    Figure 2 illustrates bleaching steps D0, EOP, D1 and D2 and the downstream washers for each bleaching stage, which in this example are Drum Displacer-type drum washers which enable multi-stage washing. The D2 wash 46 receives wash water 48 which is circulating water from a pulp dryer, hot water or condensate in an amount of 7-9 m3 / ADt. The filtrate 50 of the D2 wash 46 is passed to the D1 wash 44 in countercurrent with respect to the pulp. Half of the Df filtrate 52 is passed to the EOP wash 42. Half of the D1 filtrate 52 is passed to the D0 wash 40.
    The filtrate 66 from the D0 wash 40 and a portion of the filtrate 56 from the EOP wash 42 are passed to the mill effluent treatment plant 60 for biological treatment. A portion of the EOP filtrate 58 is taken to the D0 wash 40.
    Purified effluent is introduced as wash water to the EOP wash 42 via line 62.
    In the solution according to this embodiment, the amount of the D0 wash filtrate typically taken for effluent treatment is 10 m 3 / adt and the amount of EOP filtrate is 5 ms / adt.
    The amount of effluent returned to the bleaching process is 5 ms / adt. The amount of effluent leaving the plant is approximately 11 m3 / ADt. This leaving purified effluent 54 can alternatively be taken to the DO wash 40 and / or the D1 stage wash 44, as illustrated by lines 68 and 64. Example: The pulp was treated in bleach sequences, using purified effluent as wash water and clean water being used as reference.
    Example 1: Sequence: A-EP-DP initial mass Coat 10.9 Brightness 63.3 A-step and D1-A-step with step with efflu- Pure A-step effluent *) ent **) A-step 240 min, 90 ° C H2SO4,% 0.52 0.55 0.55 Final pH 3.2 3.4 3.4 EP step 90 min, 85 ° C NaOH,% 0.88 0.88 0.88 H2O2,% 0.55 0.55 0.55 Brightness,% 67 69 67 D-step 120 min, 70 ° C CIO2,% 2 2 2 Brightness,% 83.8 83.8 84.5 P-step 90 min, 85 ° C H2O2,% 0.44 0.44 0.44 H2Û2, o / o fÖF- used 0.33 0.29 0.29 NaOH,% 0.72 0.72 0.72 Brightness,% 90.2 90, 5 90.7 Total CIO2, kg / adt 18 18 18 HzOz, kg / adt 9 9 9 *) Effluent test: purified effluent 6.5 ms / adt set to A-step **) Effluen test: purified effluent 6.5 ms / adt set to A-step and 4 ma / adt to D-step Purified effluent. AOX 0.28 mg / l, COD 140 mg / l, color 400 mg / l Pt Example 2: Sequence: A / D-EP-DP initial mass Coat 11.3 Brightness 57.8 Pure A- A / D step with step effluent 240 + 10 min, 90 + 85 A / D step ° C H 2 SO 4,% 0.52 0.55 Final pH 3.2 3.4 ClOg,% 0.45 0.45 EP step 90 min, 85 ° C NaOH,% 0.88 0.88 H 2 O 2, ° / o 0.56 0.56 Brightness,% 76.3 76 D-step 90 min, 70 ° C ClOg,% 1.33 1.33 Brightness,% 87, 87.2 P step 90 min, 85 ° C H 2 O 2,% 0.18 0.18 H 2 O 2, ° / o follow-up 0.18 0.12 NaOH,% 0.7 0.7 Brightness,% 89.8 90.7 Total ClOg, kg / adt 17 17 H2Û2, Kg / adt 7 7 Effluent test: 4.5 m3 / adt effluent set to A / D step Purified ef fl uent. AOX 1.6 mg / I, COD 180 mg / I, color 380 mg / I Pt The examples show that the use of purified ef fl uent in connection with bleaching does not impair the pulp qualities. The brightness of the pulp is even better when using purified effluent compared to pure water.
    权利要求:
    Claims (10)
    [1]
    A method of treating and utilizing liquid streams in a chemical pulp mill, comprising at least the following steps: a) chemical pulp is prepared in an alkaline cooking process, b) the brown stock formed during the cooking is treated, the treatment comprising washing the pulp and preferably oxygen delignification and subsequent washing of the pulp, c) a bleaching process for the treated brown stock with a bleaching sequence comprising at least one step using chlorine dioxide and in addition at least one oxidizing bleaching step and with at least two washing steps for treating the pulp with liquids and for producing filtrate, d ) filtrate from step c) is purified at an effluent plant at the chemical pulp mill which comprises at least biological treatment, to obtain purified effluent, characterized in that the method comprises a further step e) the purified effluent with a color of 200 mg / l (Pt ) or more and a COD value above 150 mg / l is used as e n pulp treatment liquid in step c) between the first bleaching sequence of the bleaching sequence and the last oxidizing bleaching step.
    [2]
    Method according to claim 1, characterized in that purified effluent is used in the direction of the pulp stream during the washing of the first bleaching step or downstream thereof as dilution or washing water, but before the last oxidizing bleaching step of the sequence.
    [3]
    Method according to Claim 1 or 2, characterized in that the color of the purified effluent is 200-2000 mg / l (Pt).
    [4]
    Method according to one of the preceding claims, characterized in that the COD of the filtrate stream which is led to purification in step d) is above 1500 mg / l, preferably above 1800 mg / l. 10 15 20 21
    [5]
    Method according to one of the preceding claims, characterized in that in step d) the lignin content of the filtrates decreases by more than 50%.
    [6]
    Method according to one of the preceding claims, characterized in that the purified effluent is used as washing liquid in a pulp washing device during bleaching.
    [7]
    Method according to one of the preceding claims, characterized in that the purified effluent is used as diluent for the pulp washing device during bleaching.
    [8]
    Method according to one of the preceding claims, characterized in that the effluent recycled in step e) is heated in step d) with heat obtained from the effluent which is led to purification and the heated effluent is used in bleaching.
    [9]
    Method according to one of the preceding claims, characterized in that the purified effluent from step d) is not used in the last washing device before storing the pulp, such as before a dryer.
    [10]
    Method according to one of the preceding claims, characterized in that in step d) the biological treatment comprises an effluent explanation of the effluent and an activated sludge plant, the aeration basin of which is followed by final clarification, from which the purified effluent is discharged and used in step e).
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    同族专利:
    公开号 | 公开日
    AU2010323001B2|2014-09-11|
    US20120279669A1|2012-11-08|
    FI20096243A|2011-05-26|
    CN102666976A|2012-09-12|
    FI20096243A0|2009-11-25|
    CN102666976B|2015-09-02|
    WO2011064447A1|2011-06-03|
    FI126551B|2017-02-15|
    ZA201203463B|2013-01-31|
    BR112012012493A2|2016-04-12|
    AU2010323001A1|2012-05-24|
    US8815053B2|2014-08-26|
    SE537408C2|2015-04-21|
    BR112012012493A8|2016-10-04|
    CL2012001343A1|2012-08-31|
    BR112012012493B1|2020-10-20|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    SE395920B|1975-12-19|1977-08-29|Uddeholms Ab|WHEN BLANKING AND WASHING THE CELLULOSA PULP|
    FI893844A|1988-08-23|1990-02-24|Sappi Ltd|ELIMINERING AV BLEKNINGSAVLOPPSVAETSKOR.|
    FI85293C|1990-05-04|1992-03-25|Poeyry Jaakko & Co Oy|FOERFARANDE FOER RENING OCH AOTERFOERING AV CELLULOSAFABRIKERS BLEKERIAVATTEN.|
    US5380402A|1992-07-30|1995-01-10|Kamyr, Inc.|Reducing pulp mill liquid discharge|
    AUPM452794A0|1994-03-17|1994-04-14|Amcor Limited|Waste water recovery system|
    SE9604802L|1996-12-27|1998-06-28|Aga Ab|Process for treating cellulose fibers|
    FI117391B|2000-05-16|2006-09-29|Andritz Oy|Method and apparatus for pulping|
    FI122812B|2007-06-15|2012-07-13|Andritz Oy|A method for treating fluid flows at a pulp mill|
    FI122241B|2007-06-15|2011-10-31|Andritz Oy|Procedure in connection with pulp washing at a pulp mill|
    FI20080298A|2007-06-15|2009-10-22|Andritz Oy|A method for treating and operating fluid streams at a pulp mill|RU2526013C2|2010-03-23|2014-08-20|Интернэшнл Пэйпа Кампани|Advanced system and method of recycling filtrate of chemi-thermomechanical pulp|
    FI128111B|2012-11-09|2019-10-15|Upm Kymmene Corp|A method and a system for treating liquid flows at a chemical pulp mill|
    CN103266520B|2013-05-14|2016-02-10|昆明理工大学|A kind of preparation method of bleaching straw pulp|
    法律状态:
    2020-07-28| CANC| Patent cancelled, revoked after opposition|
    优先权:
    申请号 | 申请日 | 专利标题
    FI20096243A|FI126551B|2009-11-25|2009-11-25|A method for treating fluid flows at a pulp mill|
    PCT/FI2010/050943|WO2011064447A1|2009-11-25|2010-11-22|Method of treating liquid flows at a chemical pulp mill|
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