CN104160088A - A method and a system for treating liquid flows at a chemical pulp mill - Google Patents

Abstract

The invention relates to a method for treating liquid flows at a chemical pulp mill. The method comprises conveying at least one predetermined water flow to at least one predetermined place at the system. In addition, the invention relates to a system for treating liquid flows. EOP bleaching filtrates from the bleaching unit (30) and/or waters from a second clarifier of the waste water treatment plant (50) are conveyed to wood handling in the wood handling unit (10) and/or to gravity table shower water of the waste water treatment plant (50).

Description

A method and system for treating liquid streams in a chemical pulp mill

field of invention

The present invention relates to a method and system for treating liquid streams in a chemical pulp mill.

Background technique

Chemical pulp mill effluents are often treated in wastewater treatment facilities to reduce the amount of environmentally harmful chemicals. There are many motivating factors to reduce water usage and effluent volumes, such as the cost of supplying raw water, potentially limited water supplies, energy savings, and the potential for reduced fiber and chemical losses. Currently, pulp mills are usually built in areas and environments with very strict environmental protection requirements. For example, there may be severe restrictions on the amount of water used in chemical pulp mills. Therefore, it may be impossible to establish a pulp mill in an otherwise satisfactory location due to water resources. In many cases, the need for a cleaner environment requires pulp mills to produce materials that are less harmful to the environment. Therefore, it is now important to look for a solution to discover a more closed method of the water cycle.

Contents of the invention

The present invention discloses a method and system for treating liquid streams in a chemical pulp mill. Some aspects of the invention are characterized in the independent claims 1 and 10 . Various embodiments of the invention are disclosed in the dependent claims.

The system according to the invention includes:

- at least one wood treatment unit,

- a brown stock preparation plant comprising cooking, washing, screening and oxygen delignification stages for the production of pulp,

- a bleaching plant comprising a bleaching stage to bleach the produced pulp, the bleaching plant comprising Nash pump seal water and/or bleach filtrate,

- chemical recovery unit, which may include jet condenser cooling water and/or vacuum pump seal water,

- recovery boiler, which also produces boiler drainage, and

- An evaporator, which produces condensate.

The system may include a pulp dryer. However, the system may also not include said pulp dryer.

Preferably, at least a part of the process water is sent to be reused as process water in the pulp mill.

Preferably, the method of treating liquor streams in a chemical pulp mill comprises conveying EOP bleach filtrate from a bleaching plant to be reused as process water in at least one of the following pulp mill treatment stages: 1) wood treatment and 2) wastewater treatment facilities The gravity sorting table is sprayed with water. Alternatively or additionally, the method of treating liquid streams in a chemical pulp mill comprises conveying water from a second clarifier of a wastewater treatment facility to be reused as process water in at least one of the following pulp mill treatment stages: 1) wood treatment and 2 ) Gravity sorting table spray water of wastewater treatment facility.

The method for treating liquid streams in chemical pulp mills may also include the use of other water. The method for treating liquid streams in a chemical pulp mill may further comprise conveying Nash pump seal water from a bleaching plant to be reused as process water for at least one pulp mill treatment stage. Accordingly, the method for treating liquid streams in a chemical pulp mill may also comprise conveying white water from a pulp dryer to be reused as process water for at least one pulp mill treatment stage. The method for treating liquid streams in a chemical pulp mill may further comprise conveying condensate from the evaporator to be reused as process water for at least one pulp mill treatment stage.

The method for treating liquid streams in a chemical pulp mill may further comprise conveying jet condenser cooling water from a chemical recovery unit to be reused as process water for at least one pulp mill treatment stage. The method for treating liquid streams in a chemical pulp mill may further comprise conveying vacuum pump seal water from a chemical recovery unit to be reused as process water for at least one pulp mill treatment stage. The method for treating liquid streams in a chemical pulp mill may further comprise conveying boiler effluent from the recovery boiler to be reused as process water for at least one pulp mill treatment stage.

Preferably, one or two of the above-mentioned other waters, more preferably three or four of the above-mentioned other waters, most preferably five or six of the above-mentioned other waters are used in the present invention.

EOP bleach filtrate from the bleach plant and/or water from the second clarifier of the wastewater treatment facility is directed for wood treatment. They can be used for log washing in wood handling units. As an alternative or in addition, they can be used in chipping operations in wood treatment plants. As an alternative or in addition, they can be used for chip screening in wood treatment plants. As an alternative or in addition, they can be used in chip conveyors in wood handling plants.

It is also possible to direct at least one of the aforementioned waters to oxygen delignification washing for the brown stock preparation unit. It is also possible to direct at least one of the aforementioned waters to the dilution water for the brown stock preparation unit. It is also possible to direct at least one of the above waters to drum displacement scrubber (DD scrubber) pans for the bleach plant. It is also possible to direct at least one of the aforementioned waters to a washing step for the bleaching apparatus. It is also possible to direct at least one of the aforementioned waters to the dilution water for the bleaching plant. It is also possible to direct at least one of the aforementioned waters to dryer spray water for the pulp dryer. It is also possible to direct at least one of the above waters to gravity table spray water for use in wastewater treatment facilities. It is also possible to direct at least one of the aforementioned waters to a weak liquor tank for a chemical recovery unit. It is also possible to direct at least one of the aforementioned waters to a white liquor condensation tank for a chemical recovery unit.

However, "Oxygen delignification washing of the brown stock preparation unit" and "Dilution water in the brown stock preparation unit" are preferably excluded because they are less preferred than the others.

The method preferably comprises conveying at least a portion of the process water from the Nessler pump seal water to one, two or three of the following stages:

- at least one brown stock preparation stage,

- at least one bleaching stage, and

- At least one chemical recovery stage.

The method preferably includes conveying at least a portion of the process water from the causticizing jet condenser cooling water and/or boiler blowdown to one, two, three, four or five of the following stages:

- wood treatment,

- brown stock preparation,

- bleach, and/or

- waste water treatment facility for gravity sorting table spray water, and/or

- Chemical recycling.

In one example, "wastewater treatment facility for gravity table spray water" is excluded from the above listing.

The method preferably includes conveying at least a portion of the lime mud filter vacuum pump water and/or jet condenser cooling water to the chemical recovery thin white liquor tank. This allows for higher liquid inventory and the use of more secondary condensate in post- _O2 treatment washes. The method preferably includes conveying at least a portion of the boiler effluent to a chemical recovery white liquor condensate tank. This allows for higher liquid inventory and the use of more secondary condensate in post- _O2 treatment washes. The method preferably includes a washing step of conveying at least a portion of the jet condenser cooling water and/or the refuse filter vacuum pump water to the sludge treatment area.

Preferred systems for treating liquid streams in chemical pulp mills include:

- wood handling units,

- a brown stock preparation plant comprising cooking (including digester), washing, screening and oxygen delignification stages for the production of pulp,

- bleaching device,

- chemical recovery unit, and

-Evaporator.

The system includes delivery equipment for delivering at least a portion of the process water from the bleach plant, the equipment being adapted to deliver the EOP bleach filtrate to the gravity table showers of the wood treatment and/or wastewater treatment facility. Additionally or alternatively, the system also includes delivery means adapted to deliver water from the second clarifier of the wastewater treatment facility to the gravity table showers of the wood treatment and/or wastewater treatment facility.

Water sent to the wood treatment unit is sent to at least one of the operations listed below:

- log washing in wood handling units,

- chipping operations in wood handling plants,

- debris screening in wood handling plants,

- Chip conveyors for wood handling plants.

Furthermore, the system preferably comprises a conveying device for conveying at least a part of the process water from the evaporator to a wood treatment unit and/or a brown stock preparation unit and/or a bleaching unit and/or a pulp dryer and/or a chemical recovery unit.

In addition, the system preferably comprises conveying means for conveying at least a portion of the process water from the recovery boiler to at least one chemical recovery stage of the chemical recovery plant and/or to the pulp dryer.

In addition, the system preferably includes a gravity separator for conveying at least a portion of cooling water from the causticizing jet condenser and/or boiler effluent to a wood treatment unit and/or a brown stock preparation unit and/or a bleaching unit and/or a waste water treatment unit. Optional spray water and/or conveying equipment for the chemical recovery stage of the chemical recovery unit.

In addition, the system preferably comprises conveying means for conveying at least a part of the process water from the bleaching plant as Nessler pump seal water to the brown stock preparation plant and/or the bleaching plant and/or the chemical recovery plant.

The delivery device preferably comprises at least one or more pipelines and a pump.

Thus, according to the invention at least a part of the raw water required by the pulp mill is replaced by recycled process water. In other words, a part of the process water is recycled between and/or within the different treatment stages, most preferably without any treatment in the wastewater treatment facility. Thus, thanks to the present invention, the amount of waste water produced can be significantly reduced.

EOP filtrate sent to wood treatment can be used for round wood and chip washing to form wet chips for transportation (to prevent dusting). The alkaline filtrate from the EOP bleaching stage neutralizes the organic acids from the treated wood, especially where the wood is eucalyptus, thereby preventing acid corrosion of the conveying equipment. In addition, the water from the second clarifier of the wastewater treatment facility has a purity suitable for wood treatment. Short piping systems can be used when water from a second clarifier at a wastewater treatment facility is used for gravity table spray water at the same facility.

Thus, thanks to the present invention, it is possible to provide a system capable of:

- can reduce the environmental impact of chemical pulp mills, and

- Can reduce raw water consumption in chemical pulp mills.

Furthermore, energy and chemical reagents are saved, thereby significantly reducing operating costs.

The invention can be implemented in a chemical pulp mill with the following processes or devices: digestion process, at least one bleaching stage, chemical recovery, and various reactors, vessels, pumps, mixers, filters, etc. known to those skilled in the art .

Description of drawings

Hereinafter, the present invention is described in more detail with reference to the accompanying drawings, in which:

1-2 show some exemplary embodiments in simplified schematic diagrams.

Detailed description of the invention

In this application, reference is made to the accompanying drawings 1-2, wherein the following reference numerals are used:

10 wood treatment,

20 Brown stock preparation, which includes digester, brown stock washing, oxygen delignification and washing stages,

30 Bleaching, which includes a bleaching stage and washing,

40 evaporator,

50 Wastewater treatment facilities, including second clarifier,

60 Chemical recovery, including smelt dissolution, green liquor filtration, causticizing and lime recycling stages,

70 recovery boiler, and

80 Dryer.

The term "raw water treatment facility" refers to a fresh water treatment facility.

The term "effluent treatment facility" refers to a wastewater treatment facility.

The term "ECF" means elemental chlorine free.

The term "TCF" means completely free of chlorine.

The term "NPE" refers to non-process elements. NPE are inorganic substances from process equipment and sometimes wood, raw water and chemicals that do not require treatment.

The term "Adt" means the air-dried metric ton of 90% dry chemical pulp.

Sealing water is water used for sealing in vacuum pumps.

Jet condenser cooling water is water directed into direct contact with steam in the jet condenser or water resulting from direct contact with steam.

A gravity sorting table is a device used to dewater sludge through a permeable belt in wastewater treatment. Gravity sorting table spray water is used to wash the belt.

Drum displacement washers are rotating drums in which a pulp mat formed from pulp on the outer filter surface of the drum is washed to displace the liquid in the mat to the interior of the drum.

Boiler drain is the water drained from the boiler to avoid the concentration of impurities during continuous steam evaporation.

The white liquor condensate tank of a chemical recovery unit is the tank in a white liquor facility that contains secondary condensate from the evaporator. The process water sent there can be used along with the condensate for a scrubbing operation in the causticizing plant.

The weak liquor tank is the weak white liquor tank in the white liquor facility. Secondary condensate from the evaporator is sent to this tank for dilution.

The term "effluent" means waste water. The effluent is sent to a wastewater treatment facility for the purification process. Effluents may include, for example, bleaching effluents and ash leaching purges. Additionally, effluents may contain wood treatment effluents.

The term "bleach effluent" refers to the effluent from the bleaching plant and washing steps described herein. Preferably, the bleach effluent contains bleach filtrate. More preferably, the bleach effluent consists of bleach filtrate. The bleach filtrate contains acidic and/or alkaline streams. Preferably, the bleach effluent is free of fibres.

The term "EOP" refers to the alkaline extraction stage in pulp bleaching using oxygen and peroxides as additional chemicals.

The general purpose of the cooking operation in the production of bleached chemical pulp is to recover fibers from the chips fed to the digester, specifically the use of chemicals and heat to remove the lignin which binds the fibers and which after removal will result in Wood extract that foams and settles. Therefore, chemicals that dissolve as much lignin as possible and as little cellulose as possible are often used in the pulping process. Generally, the process of manufacturing bleached chemical pulp includes pulping, washing, screening, bleaching and cleaning stages. Currently, kraft cooking is the most commonly used method of pulp production, also known as kraft cooking or pulping, which uses a mixture of sodium hydroxide (NaOH) and sodium sulfide (Na2S). The cooking method can be based on batch cooking or continuous cooking involving one digester or several digesters.

Brown stock treatment after the cooking process preferably includes a washing process, an oxygen stage, and screening followed by washing. Usually, the last washing equipment in the oxygen stage receives the wash liquor with the highest purity to facilitate bleaching of the pulp, and the filtrate obtained from this final washing equipment is used as washing liquor and diluted for use according to the countercurrent washing principle. When filtrate is recovered from the first brownstock washing plant, it can be sent onwards directly to the black liquor evaporation plant, or it can be used in the digester plant process for dilution and stripping before ending with the black liquor stream. After the final washing stage, the pulp can be directed to a bleaching process.

A bleaching step is used to improve the brightness, cleanliness and brightness stability of the pulp. Residual lignin is a major contributor to color and must be removed or lightened. Typically, the purpose of bleaching pulp is to continue delignification, and with bleaching chemicals, to remove any woody matter remaining in the pulp after the cooking and oxygen stages, ie residual lignin, which does not decompose and dissolves in cooking and oxygen stages without sacrificing pulp yield or fiber properties. Also, during bleaching, chromogenic compounds are removed and oxidized to colorless compounds. Usually, an important part of bleaching is washing the dissolved lignin out of the pulp on the scrubber after the bleaching stage.

For bleaching purposes,

- Chlorine (Cl ₂ ), ozone (O ₃ ) and/or peroxyacids (Paa and Caa) can be used to react the aromatic lignin units, and/or

- typically chlorine dioxide ( _ClO2 ) and/or oxygen ( _O2 ) can be used to react lignin structures with free phenolic hydroxyl groups, and/or

- Some functional groups can be reacted with hypochlorite (H) and/or hydrogen peroxide (H ₂ O ₂ ).

However, the chemical pulp industry needs to maintain a technique in which the pulp is bleached with chlorine-containing chemicals in at least one stage such that chlorine dioxide is the main chemical in the pulp mill bleaching process. Therefore, it is advantageous to use at least chlorine dioxide (ClO2) for bleaching purposes.

Bleaching effluents are often an important source of biological and chemical oxygen consumption. For example, chlorine-containing inorganic compounds and organic chlorine compounds from the reaction of chlorine dioxide and/or chlorine may remain during the process. The bleaching process separates various lignin compounds from the fibers, which remain in the effluent as organic molecules. Additionally, sulfuric acid can be used in the bleaching stage for pH adjustment and as the main chemical for the hydrolysis of hexenuronic acids. In the alkaline stage, sodium hydroxide can also be used for pH adjustment and lignin extraction. Besides, oxygen and/or peroxide may be used in the bleaching treatment, depending on the bleaching sequence. However, in elemental analysis they should be such substances that they have a negligible effect on e.g. purification processes.

In one example, hydrochloric acid is used for pH adjustment and/or sulfur dioxide and/or other reducing agents are used to remove chemical residues from the bleaching process, ie to remove unreacted bleaching chemicals.

Pulp mills have not only bleaching effluents, but also process waters such as cooling water, sealing water, reject flows, channel water, washing water for equipment, rainwater and wood processing water. The process waters generally do not come into contact with the pulping process, with the exception of wood processing water and some channel water from process overflows, which come into contact with the pulping process. The discharges accumulated therein are therefore mainly spills and overflows, temporary discharges from equipment breaks, washing water for equipment, from continuous or intermittent washing of fabrics (screens and felts) or containers, from waste systems of the spill.

As mentioned above, brown stock treatment includes at least one washing process. Advantageously, brown stock treatment includes:

- sieving process,

- Oxygen delignification stage, and

- at least one washing stage following the oxygen delignification stage.

The screening process can be located after the digester purge, during or after the washing process, or after the oxygen delignification stage. Typically, these process stages are followed by a bleaching process, preferably based on ECF technology, comprising a pulp bleaching plant with one or more bleaching stages based on the use of chlorine dioxide and possibly stages using other known bleaching chemicals. Advantageously, the bleaching process comprises at least one alkaline stage, wherein preferably at least oxygen and/or peroxide are used. Ozone stages, acid stages and chelate stages for removal of heavy metals can also be used.

The method according to the invention comprises at least an alkaline cooking process for producing pulp, preferably a bleaching plant using ECF bleaching, in which a chlorine-containing effluent is formed, and for treating the bleaching plant effluent and/or producing at the pulp mill Effluent purification facilities for other effluents (wastewater treatment facilities). Alternatively, TCF bleaching can be used instead of ECF bleaching.

It is advantageous to use ECF bleaching, wherein the bleaching comprises both an acidic and an alkaline phase. ECF bleaching includes all bleaching sequences that include at least one chlorine dioxide stage and that do not use elemental chlorine in any bleaching stage. Modern ECF bleaching processes currently used for bleaching pulp generally consist of at least two, more advantageously at least three bleaching stages, preferably comprising at least three washing units. If chlorine dioxide is used in a bleaching stage, the most common dosage is 5-15 kg act.Cl/adt pulp. Chlorine dioxide dosages are typically 25-35 kg/adt for softwoods and 20-30 kg/adt for hardwoods. If a pulp mill wants to further reduce the amount of organochlorine compounds, the policy of the pulp mill is usually to treat them in the pulp mill instead of reducing the use of chlorine dioxide.

A pulp mill typically includes a chemical recovery facility, which includes an evaporation process, usually with evaporation plants connected in series, a chemical recovery boiler, to remove chlorides from the process, and a chemical production facility for the production of cooking chemicals.

An at least partially closed circulation system for the production of bleached chemical pulp is suitable for a process in which at least part of the water and other chemicals are recycled and reused, thereby minimizing waste disposal. The system is particularly suited for minimizing aqueous effluents, thus protecting the environment from effluent disposal, without significantly compromising process costs or the value of the salable product. Chlorine, potassium, calcium, manganese, silicon, aluminum, phosphorus, iron and barium are some of the elements involved in bleached chemical pulp mills.

Preferably, biological treatment is provided to at least one effluent treatment line of the wastewater treatment facility. Biological treatment is particularly effective when the proportion of hazardous organic matter comprising mainly lignin compounds separated in bleaching, hemicellulose and components derived from extraction, which constitute the major part of the effluent of a bleaching plant, is reduced . There are many compounds derived from wood, some of these compounds are chlorinated and some are low molecular weight hydrocarbons. Since the microorganisms only use the organic portion of the effluent as nutrients, all inorganic matter, at least inorganic elements, remain in the effluent. Thus, biologically treated water, after separation of solid and liquid fractions, e.g. It must be discharged from the process.

In addition or as an alternative to the biological treatment, the purification stage can be, for example, a chemical treatment, the purpose of which is to remove, for example, metals by precipitation, whereby part of the organic matter is also removed. As an alternative or in addition to the above-mentioned stages, filtration techniques such as ultrafiltration and/or methods based on membrane technology and/or osmosis can be used. In other words, in addition to or instead of biological treatment, the effluent can be treated using, for example, ultrafiltration membranes, ion exchange, chemical precipitation, sedimentation, flotation and/or filtration.

Figure 1 shows an example of a pulp mill. Typically, at a pulp mill, chips and white liquor are supplied to a digester for pulp cooking. After cooking, the cooked pulp (so-called brown stock) is conveyed to a washing and oxygen treatment stage. Typically, hot water is used for the washing stage. The darkish liquid from the brewing operation is conveyed from the brewing operation to an evaporation stage where some water is removed from the light black liquid, thus producing a dark black liquid. Water recovered from the darkish liquid, ie condensate from evaporation, is preferably sent to the washing stage or brown stock. The dark black liquid produced during the evaporation stage is processed to obtain a green liquid. The green liquor is further processed to obtain white liquor that can be reused for brewing. After emerging from the brown stock washing and oxygen treatment stages, the pulp is conveyed to the bleaching unit. A bleaching plant usually comprises several bleaching stages for bleaching the pulp. Bleaching units typically produce acidic and alkaline effluents while bleaching pulp, which are usually sent to wastewater treatment facilities. Bleached pulp is usually sent to a paper mill or pulp dryer.

Figure 2 shows some examples of process water cycles in a simplified schematic. These examples can be implemented, for example, in a pulp mill according to FIG. 1 .

At least part of the process water is sent to wood treatment 10 . Process water is preferably used for log washing. As an alternative or in addition, process water is preferably used for the shredding operation. As an alternative or in addition, process water is preferably used for chip sieving. As an alternative or in addition, process water is preferably used for chip conveying. Process water sent to wood treatment consists of EOP bleach filtrate (thick line 1 in Figure 2).

Furthermore, preferably, at least a portion of the process water delivered to the wood treatment 10 comprises secondary condensate from the evaporator 40 . Alternatively or additionally, at least a part of the process water fed to the wood treatment 10 comprises bleached 30 Nessler pump seal water. Alternatively or additionally, at least a portion of the process water delivered to the wood treatment 10 comprises causticizing jet condenser cooling water. Alternatively or additionally, at least a part of the process water fed to the wood treatment 10 comprises boiler discharge water.

A portion of the effluent that will be sent to wood treatment 10 comprises the second clarifier filtrate of the wastewater treatment plant (thick line 2 in Figure 2).

Preferably, at least a portion of the process water is sent to the brown stock preparation unit 20 . Preferably, process water is used for oxygen delignification washing and/or diluting the liquor. As an alternative or in addition, process water is preferably used for the washing liquid of drum displacement (DD) scrubber pans.

The process water recycled to the brown stock preparation unit 20 preferably comprises causticizing jet condenser cooling water and/or boiler discharge water. Alternatively or additionally, the process water recycled to the brown stock preparation unit 20 preferably comprises bleach Nessler pump seal water and/or evaporator condensate water.

Preferably, at least a portion of the process water is recycled to at least one bleaching stage 30, preferably for one, two or three of the following:

- washing liquid for DD scrubber pans (drum displacement scrubbers),

- washing liquid for pressurized washing units,

- The washing phase and the dilution of the liquid therein.

The process water recycled to at least one bleaching stage 30 and the washing steps therein preferably comprises one, two, three or four of the following listed:

- secondary condensate from the evaporator, and/or

- causticizing jet condenser cooling water, and/or

- Bleach Nessler pump seal water, and/or

- Boiler drain.

Preferably, at least a portion of the process water is conveyed to the dryer 80, and preferably used as spray water therein. Process water recycled to dryer 80 preferably contains one, two, three or four of the following:

- secondary condensate from the evaporator,

- boiler drainage,

- bleach Nessler pump seal water, and

- Causticizing jet condenser cooling water.

Preferably, at least a portion of the process water is sent to a waste water treatment facility 50 where the process water is preferably used as spray water for gravity sorting tables. The water used for the spray water was the waste water after the second clarifier (thick line 3 in Fig. 2). Process water used as gravity classifier spray water for wastewater treatment facilities may also contain one, two, three or four of the following:

- Nessler pump seal water for bleach plant 30,

- jet condenser cooling water from causticisation,

- boiler drainage, and

- Evaporation of secondary condensate.

Preferably, at least a portion of the process water is recycled to the chemical recovery unit 60, preferably for the weak liquor tank and/or white liquor condensate tank therein. The process water used for the chemical recovery 60 preferably comprises the secondary condensate water of the evaporator and/or the cooling water of the spray condenser and/or the boiler drainage and/or the seal water of the bleach Nessler pump.

Preferably, at least a part of the process water to be circulated in the chemical pulp mill comprises one, two, three, four or five of the following water sources:

- a bleaching stage 30, preferably comprising EOP bleach filtrate and/or Nessler pump seal water,

- a dryer, preferably containing white water,

- evaporator 40, preferably containing condensate,

- recovery boiler 70, preferably containing boiler drainage, and

- Chemical recovery, preferably comprising jet condenser cooling water and/or vacuum pump seal water.

Preferably, at least a portion of the process water is circulated within the bleaching stage 30 . Alternatively or additionally, preferably at least a portion of the process water is recycled within the chemical recovery stage 60 . Thus, the total amount of effluent produced and the total amount of raw water required is reduced. Alternatively or additionally, in one example at least a portion of the process water is recycled within the wastewater treatment stage. However, the latter is not a preferred embodiment like the others.

The bold line 4 in FIG. 2 shows the EOP bleach filtrate from the gravity table spray water of the bleach plant 30 for the wastewater treatment facility 50 .

Due to the recirculation of at least a portion of the process water, the total amount of effluent to be purified in the wastewater treatment facility can be reduced. In addition, the total amount of raw water (also referred to as fresh water) required is generally reduced.

Preferably, at least a portion of the water from the Nessler pump is used as wash water for the DD scrubber screen pans; thus, both the total amount of effluent produced and the amount of raw water required is reduced.

Filters may be present in the process water circuit. In this case, the filter unit is preferably used for the spray water of the gravity sorting table. Usually, no other purification means are required. Therefore, if the gravity table spray water is not reused water, the process waters recycled according to the invention generally do not require any purification steps before they can be reused as process water.

Waters of different purity levels can also be combined such that they match the required purity level at the point of use.

Tables 1-3 show some examples of waste water reduction according to the present invention. "Achieved waste water [m ³ /t] reduction" refers to the following situation: In one example, the initial waste water volume of the pulp mill was about 22.5 m ³ /t.

Table 1. Wastewater Reduction in Fiberlines

Table 2. Wastewater Reduction in Chemical Recycling and Raw Water Treatment Facilities

Table 3. Wastewater Reduction in Wood Treatment

Those skilled in the art will readily understand that different embodiments of the present invention may be applied in contexts where optimization of liquid flow in a pulp mill is required. It is therefore evident that the invention is not limited to the embodiments described above, but it can be modified within the scope of the appended claims.

Claims (12)

1. in a method for chemical pulp mills treatment fluid stream, this system comprises:

-wood treatment device (10),

-slightly starch preparation facilities (20), it comprises the boiling for the production of paper pulp, washing, screening and oxygen go the wooden stage,

-bleaching system (30), bleaches for the paper pulp that bleaching is produced,

-chemical recovery device (60),

-pulp dryer (80),

-recovery boiler (70), it produces discharging of boiler,

-evaporimeter (40), it produces condensate,

-waste water disposal facility (50), and

-former water processing establishment,

Wherein, described method comprises at least one in following water source:

-bleach filter liquor from the EOP of bleaching system (30),

-from the water of the second clarifier of waste water disposal facility (50),

Be transported to following at least one in listed:

Wood treatment in-wood treatment device (10),

The gravity table shower water of-waste water disposal facility (50).

2. the method for claim 1, it is characterized in that, EOP bleaching filter liquor from bleaching system (30) and/or the gravity table shower water of waste water disposal facility (50) are transported to wood treatment device, at least one of the following stated:

The round log washing of-wood treatment device (10),

The chopping operation of-wood treatment device (10),

The fragment screening of-wood treatment device (10),

The fragment of-wood treatment device (10) is carried.

3. method as claimed in claim 1 or 2, is characterized in that, at least a portion process water is transported to pulp dryer (80), the shower water by this part process water as drying machine.

4. the method according to any one of the preceding claims, is characterized in that, at least a portion is transported to the alkaline extraction stage from the Nash pump sealing water of bleaching system, uses oxygen and peroxide as extra chemical reagent in this stage.

5. the method according to any one of the preceding claims, is characterized in that, at least a portion is transported to the screening dish of the drum-type displacement washing device in thick slurry preparation (20) from the Nash pump sealing water of bleaching system.

6. the method according to any one of the preceding claims, is characterized in that, described chemical recovery device comprises weak white liquor storage and lime mud filter device vavuum pump, and described method comprises:

-at least a portion lime mud filter device vavuum pump water and/or ejector condenser cooling water are transported in weak white liquor storage.

7. the method according to any one of the preceding claims, is characterized in that, described chemical recovery device comprises rare white liquid condensing groove, and described method comprises:

-at least a portion discharging of boiler is transported in described white liquid condensing groove.

8. the method according to any one of the preceding claims, is characterized in that, described system comprises dregs filter vavuum pump and the Treatment of Sludge region of waste water disposal facility, and described method comprises:

-at least a portion ejector condenser cooling water and/or dregs filter vavuum pump water are transported to the washing step in Treatment of Sludge region.

9. the method according to any one of the preceding claims, is characterized in that, the process water of at least a portion circulates in bleaching system.

10. the method according to any one of the preceding claims, is characterized in that, the process water of at least a portion circulates in chemical recovery device (60).

11. 1 kinds of systems at chemical pulp mills treatment fluid stream, this system comprises:

-wood treatment device (10),

-slightly starch preparation facilities (20), it comprises the boiling for the production of paper pulp, washing, screening and oxygen go the wooden stage,

-bleaching system (30), for the paper pulp of producing is bleached,

-chemical recovery device (60),

-recovery boiler (70),

-evaporimeter (40),

-pulp dryer (80),

-waste water disposal facility (50), and

-former water processing establishment,

Wherein said system also comprises following at least one in listed:

-be applicable to transport the equipment from the EOP of bleaching system (30) bleaching filter liquor,

-be applicable to transport the equipment from the water of the second clarifier of waste water disposal facility (50),

The destination of described conveying is following at least one in listed:

-wood treatment device (10),

The gravity table shower water of-waste water disposal facility (50).

12. systems as claimed in claim 11, it is characterized in that, be applicable to transport from the equipment of the EOP of bleaching system (30) bleaching filter liquor and/or be applicable to transport from the equipment of the water of waste water disposal facility (50) second clarifiers and be connected with wood treatment device (10), at least one of the following stated:

The round log washing of-wood treatment device (10),

The chopping operation of-wood treatment device (10),

The fragment screening of-wood treatment device (10),

The fragment of wood treatment device (10) is carried.