RU2621662C2 - Method and device for treating liquid flows in pulp mill - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of treating liquid flows in pulp mill, wherein device comprises a wood preparation unit, an unbleached pulp production unit comprising boiling, washing, sorting and oxygen delignification stages, to produce cellulose pulp, a bleaching unit to bleach the obtained cellulose pulp, a chemical regeneration block, a pulp-drying machine, a soda recovery boiler which generates blow-down water of the bolier, an evaporating apparatus which generates condensates, a waste water treatment plant and water production plant, wherein the method comprises transportation from at least one of the following water sources: A) bleaching filtrates (alkali-oxygen-peroxide) from the bleaching unit (30), B) sealing water of Nash pump from the bleaching unit (30), C) condensated from evaporating apparatus (40), D) water from the second settler of the waste water treatment plant (50), E) cooling water of injector condenser from the chemical regeneration block (60), F) sealing water of vacuum pump from the chemical regeneration block (60), and G) blow-down water of the soda recovery bolier (70) to at least one of the following usage centers: H) washing of logs at the wood preparation unit (10), I) chopping at the wood preparation unit (10), J) chip sorting at the wood preparation unit (10), K) conveyor for chip at the wood preparation unit (10), L) washing during oxygen delignification at the unbleached pulp production unit (20), M) thinning water at the unbleached pulp production unit (20), N) plates of drum device for displacement washing of the bleaching unit (30), P) thinning water at the bleaching unit (30), Q) water for sparging dehydrating plant of the pulp-drying machine (80), R) water for sparging gravitation table of the waste water treatment plant (50), S) tank for diluted liquor of the chemical regeneration block (60), T) tank for white liquor condensate of the chemical regeneration block (60), and U) mill water-supply system by connecting water sources to its usage centers according to the following pairs: - from the sourse A or D to the center H, - from the source A or D to the center I, - from the source A or D to the center J, - from the source A or D to the center K, - from the source A, B or D to the center L, - from the source A, B or D to the center M, - from the source B to the center N, O, P or Q, - from the source A, B, C, D, E or F to the center R, - from the source G to the center S or T, or - from the source E or F to the center U. The connection can be carried out according to one or more number of the pairs selected from the abovementioned pairs.

EFFECT: increased efficiency of treatment.

12 cl, 2 dwg, 3 tbl

Description

Technical field

The invention relates to a method and apparatus for processing liquid streams in a pulp mill.

State of the art

Pulp mill wastewater is usually treated in wastewater treatment plants in order to reduce the amount of environmentally hazardous compounds. There are many reasons for reducing the use of water and the volume of wastewater, such as the cost of fresh water supplied, possible water supply restrictions, energy savings and the ability to reduce fiber and chemical losses. Currently, pulp mills are often built in regions and in the vicinity with very strict environmental laws. For example, the amount of water used in a pulp mill can be strictly limited. Thus, it may happen that due to water resources it is impossible to build a pulp mill in a place that in other respects satisfies the requirements. In many areas it is desirable to have a cleaner environment, and therefore pulp mills should produce substances that are less hazardous to the environment. Thus, it is currently important to look for solutions to find processes with a higher degree of water recirculation.

SUMMARY OF THE INVENTION

The invention discloses a method and apparatus for treating liquid streams in a pulp mill. Aspects of the invention are characterized by what is indicated in the independent claims. 1 and 12 of the claims. Various examples of embodiments of the present invention are disclosed in the dependent claims.

The device according to the invention includes:

- at least one block preparation of wood;

- a block for the production of unbleached pulp, including the stages of cooking, washing, sorting and oxygen delignification to obtain pulp;

- a bleaching unit, including the bleaching stage, for bleaching the resulting pulp, the bleaching unit containing the sealing water of the Nash pump (liquid ring pump) and / or filtrates of the bleaching process;

- a chemical recovery unit, which may contain cooling water from a jet condenser and / or sealing water from a vacuum pump;

- soda recovery boiler, which also produces purge water of the boiler; and

- an evaporator that produces condensates.

The device may include presspat. However, it is also possible that the device does not include the indicated presspat.

Advantageously, at least a portion of the process water is recycled to the pulp mill as process water.

Advantageously, a method for treating liquid streams in a pulp mill involves transferring EOR bleach filtrates (alkali-oxygen-peroxide bleach) from the bleach block to reuse at least one process stage of the pulp mill as process water. This use may be wood preparation in a wood preparation unit; water for washing at the stage of oxygen delignification or for dilution in the block for receiving unbleached pulp; or gravity table irrigation water in a sewage treatment plant. Alternatively or in addition, a method of treating liquid streams in a pulp mill involves transporting the sealing water of a Nash pump from the bleach unit for reuse as process water in at least one process step of the pulp mill. This use may be water for washing in the oxygen delignification step or water for dilution in the unbleached pulp production unit; the use on the plates of a drum device for washing by displacement in the bleaching unit; in the washing step (s) or as water for dilution in the bleaching unit; as water for irrigation of the drying unit of the press; or gravity table irrigation water in a sewage treatment plant. Alternatively, or in addition, a method for treating liquid streams in a pulp mill involves dispensing condensates from the evaporator for reuse as process water in at least one process step in the pulp mill. This use may be water for irrigation of a gravity table in a wastewater treatment plant. Alternatively, or in addition, a method for treating liquid streams in a pulp mill involves dispensing water from a second sump of a sewage treatment plant for reuse as process water in at least one process stage of the pulp mill. This use may be preparation of wood in a wood preparation unit, water for washing with oxygen delignification, or water for dilution in an unbleached pulp production unit; or water for irrigation of a gravity table in a sewage treatment plant. Alternatively, or in addition, a method for treating liquid streams in a pulp mill involves sending cooling water to the jet condenser from a chemical recovery unit for reuse as process water in at least one process stage of the pulp mill. This use may be irrigation gravity table water in a sewage treatment plant or a plant water supply system. Alternatively or in addition, a method of treating liquid streams in a pulp mill involves sending the vacuum pump seal water from a chemical recovery unit for reuse as process water in at least one process stage of the pulp mill. This use may be irrigation gravity table water in a sewage treatment plant or a plant water supply system. As an alternative or in addition, a method for treating liquid streams in a pulp mill involves sending purge water to the boiler from the recovery boiler for reuse as process water in at least one process stage of the pulp mill. This use may be a diluted liquor tank or a condensed white liquor tank in a chemical recovery unit.

Preferably, one, two or three of the above waters are used in the present invention, more preferably four or five, and most preferably six or seven of the above waters. However, “water from the second sump of the wastewater treatment plant” is preferably excluded from the above, since their use may not be as advantageous as others.

Advantageously, at least one of the aforementioned waters is directed to use for washing the logs in the wood preparation unit. Alternatively or in addition, at least one of the aforementioned waters is sent for use in a wood preparation unit when chopping wood into wood chips. Alternatively or in addition, at least one of the aforementioned waters is sent for use in sorting chips in a wood preparation unit. Alternatively, or in addition, at least one of the aforementioned waters is sent for use on a wood conveyor in a wood preparation unit. Alternatively or in addition, at least one of the aforementioned waters is sent for use in washing during oxygen delignification in an unbleached pulp production unit. Alternatively or in addition, at least one of the aforementioned waters is sent for use as dilution water in an unbleached pulp production unit. Alternatively or in addition, at least one of the aforementioned waters is sent for use in the plates of a drum washing device by displacing a bleaching unit. Alternatively or in addition, at least one of the aforementioned waters is sent for use in the washing step (s) in the bleaching unit. Alternatively or in addition, at least one of the aforementioned waters is directed to use as dilution water in the bleaching unit. Alternatively or in addition, at least one of the aforementioned waters is diverted for use as irrigation water in a drying press unit. Alternatively or in addition, at least one of the aforementioned waters is directed to use as a water for irrigation of a gravity table in a wastewater treatment site. Alternatively or in addition, at least one of the aforementioned waters is directed to use a chemical recovery unit in a diluted liquor tank. Alternatively or in addition, at least one of the aforementioned waters is directed to use a chemical recovery unit in a white liquor condensate tank.

However, “washing during oxygen delignification in the unbleached pulp production unit” and “dilution water in the unbleached pulp production unit” are preferably excluded from the above list, since these uses may not be as advantageous as others.

Additionally or alternatively, this method mainly includes the direction of at least part of the process water coming from the sealing water of the Nash pump, one, two or three of the following stages:

- at least one step for producing unbleached pulp;

- at least one stage of bleaching, and

- as water for irrigation of the drying unit of the prespat.

Additionally or alternatively, the method mainly includes the direction of at least part of the process water coming from the cooling water of the jet condenser of the causticization stage and / or purge water of the boiler, to one or two of the following applications:

- to the installation of wastewater treatment as water for irrigation of the gravity table, and / or

- for the recovery of chemicals.

Additionally or alternatively, the method advantageously includes at least a portion of the boiler purge water into a white liquor condensate tank of a chemical recovery step. This can increase the stock of liquor and allow the use of a greater amount of secondary condensate during washing after the O ₂ stage. As an alternative or in addition, the method advantageously includes directing at least a portion of the cooling water of the jet condenser and / or water from the sludge filter vacuum pump to the washing step in the sludge treatment area.

Advantageously, a device for processing liquid streams in a pulp mill includes:

- wood preparation unit;

- a block for the production of unbleached pulp, including the stages of cooking (including a digester), washing, sorting and oxygen delignification, to obtain a pulp;

- bleaching unit;

a chemical recovery unit, and

- evaporator.

In addition, the device mainly includes pumping equipment for pumping at least a portion of the process water coming from the evaporator to the wood preparation unit and / or to the unbleached pulp production unit and / or to the bleaching unit and / or to the presspat, and / or to a chemical recovery unit.

In addition, the device mainly includes pumping equipment for pumping at least a portion of the process water coming from the press feed to at least one bleaching stage of the bleaching unit.

In addition, the device advantageously comprises pumping equipment for pumping at least a portion of the process water coming from the soda recovery boiler to at least one stage of the chemical recovery of the chemical recovery unit and / or to the presspat.

In addition, the device preferably comprises a pumping device for pumping at least a portion of the cooling water from the jet condenser of the causticization stage and / or the purge water of the boiler to the wood preparation unit and / or to the unbleached pulp production unit and / or to the bleaching unit, and / or as water for irrigation of the gravity table of the wastewater treatment section, and / or to the stage of chemical recovery of the chemical recovery unit.

In addition, the device advantageously comprises a pumping device for pumping at least a portion of the process water coming from the bleaching unit, for example, the sealing water of the Nash pump to the unbleached pulp production unit and / or to the bleaching unit and / or to the chemical recovery unit.

The transfer devices preferably comprise at least a pipe (s) and a pump (s).

Thus, in accordance with this invention, at least a portion of the fresh water needed in the pulp mill is replaced by the circulation of process water. In other words, part of the process water circulates between the various stages of the process and / or within any stage of the process, most preferably without any treatment at the wastewater treatment site. Thus, thanks to the present invention, the amount of wastewater produced can be significantly reduced.

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

- reduce the burden on the environment created by the pulp mill, and

- reduce the amount of fresh water used by the pulp mill.

In addition, energy and chemicals can also be saved, which can lead to a significant reduction in operating costs.

This invention can be carried out in a pulp mill having a cooking process, at least one stage of bleaching, chemical recovery and various reactors, tanks, pumps, mixers, filters, etc., which are known per se.

Description of drawings

The invention will now be described in more detail with reference to the accompanying drawings, in which:

FIG. 1-2 depict examples of embodiments of the invention in the form of simplified technological schemes.

DETAILED DESCRIPTION OF THE INVENTION

In this application reference is made to FIG. 1-2, in which the following numerical designations are used:

10 wood preparation,

20 obtaining unbleached pulp, including a digester, washing unbleached pulp, oxygen delignification and related washing steps,

30 bleaching, including stages of bleaching and related washing,

40 evaporator

50 wastewater treatment plant including a second sump,

60 chemical recovery, including melt dissolution, green liquor filtration, lime causticization and recycling stages, and

70 soda recovery boiler, and

80 presspat.

The term “water treatment plant” refers to a plant for treating fresh water.

The term "sewage treatment plant" means a sewage treatment plant.

The term "ECF" means "not containing elemental chlorine."

The term "TCF" means "completely free of chlorine."

The term “NPE” means “non-process elements”. NPEs are inorganic substances originating from process devices, some also from wood, untreated water and chemicals that are not involved in the process.

The term "stand" means a metric ton of air-dry pulp with a dry matter content of 90%.

Sealing water is the water used for sealing in vacuum pumps.

The cooling water of a jet condenser is water that is brought into direct contact with steam in a jet condenser, or water that results from such direct contact with steam.

Gravity table is a device used for sludge dewatering during wastewater treatment using a permeable conveyor belt. Gravity table irrigation water is used to wash the tape.

The drum displacement washing device is a rotating drum, where the cellulose layer formed on the outer filter surface of the drum from the pulp is washed to displace the liquid in the sediment layer into the drum.

The purge water of the boiler is the water discharged from the boiler in order to avoid the concentration of impurities during the continuous evaporation of steam.

The white liquor condensate tank of the chemical recovery unit is a tank in the white liquor plant containing secondary condensate from the evaporator. The process water sent to this point can be used in conjunction with condensate for flushing operations in the causticization unit.

The diluted liquor tank is a diluted white liquor tank in a white liquor plant. Secondary condensate from the evaporator is sent to this dilution tank.

The term "runoff" refers to wastewater. Sewage is sent to the wastewater treatment plant for the treatment process. The effluents may contain, for example, effluents from the bleaching process and washings from leaching of the ash residue. In addition, effluents may contain effluent from wood preparation.

The term "bleaching process effluents" refers to effluents from the bleaching unit and the washing stages present therein. The effluents of the bleaching process mainly contain filtrates of the bleaching process. Most preferably, the bleach process effluents are comprised of bleach process filtrates. The bleach process filtrates contain acidic and / or alkaline streams. Advantageously, the bleach process effluents do not contain fibers.

The term "EOR" refers to the alkali extraction stage during bleaching of pulp using oxygen and peroxide as additional chemicals.

The general objective of cooking in the production of bleached pulp is to obtain fibers from the wood chips that are fed to the digester by using chemicals and heat to remove lignin, fiber binder, and in addition to remove wood extractives, which can subsequently cause foam and precipitation in the process. Thus, chemicals that dissolve as much lignin and as little cellulose as possible are usually used in the pulping process. Typically, the manufacturing process for bleached pulp involves the steps of cooking, washing, sorting, bleaching, and cleaning. Currently, the most widely used method for producing cellulose is sulfate cooking, also called kraft cooking, which uses a mixture of sodium hydroxide (NaOH) and sodium sulfide (Na ₂ S). The cooking process can be based on periodic cooking or continuous cooking, including a digester or several digester.

The treatment of unbleached pulp after the cooking process preferably includes a washing process, an oxygen stage and sorting followed by washing. Typically, the last washer in the oxygen stage accepts the cleanest washer fluid to facilitate bleaching of the pulp, and the filtrate obtained from this last washer is used in accordance with the backwash principle as a wash liquid and for dilutions. When the filtrate is obtained from the first apparatus for washing unbleached pulp, it can either be sent directly to the black liquor evaporation unit, or used in the processes occurring in the cooking section for dilution and displacement, after which it is in the black liquor stream. After the last washing step, the pulp can be sent to bleaching.

The bleaching stages are used to improve the brightness, purity and stability of the brightness of the pulp. The main factor affecting the color is residual lignin, so it is usually necessary to remove or lighten it. Typically, the task of bleaching cellulose is to continue delignification and by using bleaching chemicals to remove any amount of lignin, known as residual lignin, which remains in the cellulose after the cooking stage and oxygen stage and which cannot be destroyed and dissolved in the cooking stage and in the oxygen stage, without sacrificing the yield of cellulose or fiber properties. In addition, during bleaching, chromophore compounds are removed and oxidized to colorless compounds. Typically, an important part of bleaching is the washing out of dissolved lignin from cellulose in a washing device following the bleaching step.

To bleach:

- chlorine (Cl ₂ ), ozone (O ₃ ) and / or peroxy acid (Raa (peracetic acid) and Caa (peroxomonosulfuric acid)) can be used to react with aromatic blocks of lignin; and / or

- for the reaction as a whole with lignin structures that have free phenolic hydroxyl groups, chlorine dioxide (ClO ₂ ) and / or oxygen (O ₂ ) can be used; and / or

- for the reaction with certain functional groups, hypochlorite (H) and / or hydrogen peroxide (H ₂ O ₂ ) can be used.

However, in the pulp industry, it is desirable to maintain a technology in which cellulose is bleached with chlorine-containing chemicals in at least one stage, so that chlorine dioxide is the main chemical in the bleaching process in the pulp mill. Thus, for bleaching purposes, at least chlorine dioxide (ClO ₂ ) is preferably used.

The effluent from the bleaching stage is usually a significant source of both biological and chemical oxygen demand. For example, chlorine-containing inorganic compounds and organic chlorine compounds obtained by reactions with chlorine dioxide and / or chlorine may remain in the process. Bleaching separates the various lignin compounds from the fibers, and these compounds remain in the effluent in the form of organic molecules. In addition, at the bleaching stage (s), sulfuric acid can be used to adjust the pH and as the main chemical in the hydrolysis of hexenuronic acids. You can also use sodium hydroxide - to control the pH and extraction of lignin in the alkaline stages. In addition to this, depending on the sequence of the bleaching process, oxygen and / or peroxide can be used in bleaching. However, when conducting an elementary analysis, they turn out to be such substances that their contribution, for example, to the cleaning processes is imperceptible.

In one example, hydrochloric acid is used to adjust the pH, and / or sulfur dioxide, and / or other reducing agents are used to remove chemicals left after bleaching, that is, to remove unreacted chemicals used in bleaching.

The pulp mill has not only wastewater after bleaching, but also process water, such as cooling water, condensation water, waste streams, drainage water, plant wastewater and rainwater, as well as water generated during the preparation of wood. Mentioned process water is usually not in contact with the pulping process, with the exception of water for preparing wood and some drainage water that comes from process flows and, therefore, is in contact with the pulping process. Thus, the emissions accumulated here are mainly leaks and flows, accidental emissions caused by malfunctions of devices, washing water of devices, textile materials (net and cloth) or containers resulting from continuous or periodic washing processes, as well as leaks from the waste system.

As mentioned, the treatment of unbleached pulp involves at least one washing process. Advantageously, the processing of unbleached pulp includes:

- sorting process;

- stage of oxygen delignification; and

- at least one washing step after the oxygen delignification step.

The sorting process can be placed after purging the digester, in the middle or after the washing process, or after oxygen delignification. Typically, these process steps are followed by a bleaching process, preferably based on ECF technology, which includes a pulp bleaching plant with one or more bleaching steps based on the use of chlorine dioxide, in addition to other possible steps using other known bleaching chemicals. Advantageously, the bleaching sequence comprises at least one alkaline step in which at least oxygen and / or peroxide are preferably used. You can also use the stage (s) with ozone, the acid stage (s) and the chelate stage (s) to remove heavy metals.

The method of this invention includes at least an alkaline cooking process to produce cellulose; a bleaching plant using predominantly ECF bleaching, in which chloride-containing effluents are formed; and a wastewater treatment unit (wastewater treatment plant) for treating wastewater of a bleaching plant and / or other wastewater generated in a pulp mill. Alternatively, instead of ECF bleaching, TCF bleaching can be used.

Mostly ECF bleaching is used, wherein said bleaching comprises both an acidic stage and an alkaline one. ECF bleaching encompasses all such bleaching sequences that include at least one chlorine dioxide step and that do not use elemental chlorine in any of the bleaching steps. Modern bleaching ECF used for pulp bleaching usually consists of at least two, more preferably at least three stages of bleaching, including preferably at least three washing devices. If chlorine dioxide is used at one stage of the bleaching, the doses typically range from 5 to 15 kg act. Cl / ris pulp. The dosage of chlorine dioxide for softwood is usually from 25 to 35 kg / stand, and for hardwood - from 20 to 30 kg / stand. If the pulp mill must further reduce the amount of organic chlorine compounds, then the task of the plant is usually to process them within the plant, rather than reduce the use of chlorine dioxide.

A pulp mill typically includes a chemical recovery unit, including an evaporation process, typically with evaporator units connected in series, a recovery boiler, removing chlorides from the process, and a chemical production unit, to produce cooking chemicals.

At least partially closed loop systems for the manufacture of bleached pulp use processes in which at least part of the water and other chemicals are recycled and reused, which minimizes waste disposal. The systems mentioned in particular are intended to minimize water effluents and therefore protect the environment from the effects of the disposal of effluents, without significantly jeopardizing the cost of processing or the value of products intended for sale. Chlorine, potassium, calcium, manganese, silicon, aluminum, phosphorus, iron and barium are some of the elements that are discussed at the plant for the production of bleached pulp.

Advantageously, at least one wastewater treatment line of the wastewater treatment plant is provided with biological treatment. Biological treatment is effective especially when the proportion of hazardous organic substances, which mainly include lignin compounds separated during bleaching, hemicelluloses and components derived from extractive substances, which make up a significant part of effluents from the bleaching plant, is reduced. There are various wood-derived compounds, and some of these compounds are chlorinated, and some of them are low molecular weight carbon and hydrogen compounds. Since microorganisms act so that they use only the organic part of the effluent as nutrients, all inorganic substances, at least inorganic elements, remain in the effluents. Thus, biologically treated water after separation of solid and liquid fractions, for example, by sedimentation, has such an amount of organic substances that makes it clearly cleaner than wastewater treated by other methods, but because of inorganic substances it usually needs to be removed from the process.

In addition to or instead of biological treatment, the purification step can be, for example, chemical, and its task is to remove, for example, metals by precipitation, which also removes some of the organic matter. Alternatively, or in addition to the aforementioned steps, a filtration method, for example ultrafiltration, and / or a method based on membrane technology and / or osmosis can be used. In other words, in addition to or instead of biological treatment, ultrafiltration membranes, ion exchange, chemical deposition, sedimentation, flotation and / or filtration can be used to treat effluents.

FIG. 1 depicts an example of a pulp mill. Typically, in a pulp mill, wood chips and white liquor are fed to a digester for pulping. After cooking, cooked cellulose, the so-called unbleached pulp, is fed to the washing stage and to the oxygen stage. Typically, hot water is used for said washing step (s). The diluted black liquor coming from the cooking step is sent from the cooking step to the evaporation step, in which some water is removed from the diluted black liquor, and thus a concentrated black liquor is obtained. Water removed from diluted black liquor, i.e. condensates from the evaporation step, is preferably sent to the washing step of unbleached pulp. The concentrated black liquor obtained in the evaporation step is treated to obtain green liquor. Green liquor is further processed to obtain white liquor that can be reused for cooking. Cellulose from the washing and oxygen stages for unbleached pulp is sent to the bleaching unit. The bleaching unit typically includes several stages of bleaching for bleaching pulp. The bleach unit typically produces acidic and alkaline effluents during pulp bleaching, and these effluents are typically sent to a wastewater treatment plant. Bleached pulp is usually sent to a paper mill and / or to presspat.

FIG. 2 depicts several examples of the circulation of process water in the form of a simplified flow chart. This can be done, for example, in the pulp mill of FIG. one.

Advantageously, at least a portion of the process water is directed to the preparation of 10 timber. Process water is preferably used to flush logs. Alternatively or in addition, process water is preferably used for chopping wood. Alternatively or in addition, process water is preferably used for sorting chips. Alternatively or in addition, process water is preferably used on a chip conveyor.

Mostly the part of the effluent that should be sent to the preparation of 10 wood includes the filtrate of the second sump of the wastewater treatment plant.

Advantageously, at least a portion of the process water is sent to the unbleached pulp production unit 20. Preferably, the process water is used for washing with oxygen delignification and / or as dilution liquids. Alternatively or in addition, process water is preferably used as a washing liquid for a plate of a drum apparatus for displacing washing.

The process water that is recycled to the unbleached pulp preparation unit 20 preferably contains the seal water of the Nash pump used in the bleaching step.

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

- washing liquid for the plates of the drum device for washing by displacement;

a washing liquid of a pressure washing device, and

- stage washing and dilution of liquids at these stages.

Process water that is recycled to at least one bleaching stage 30 and its associated washing steps preferably includes one, two, three or four of the following:

- water of secondary condensate from the evaporator, and / or

- cooling water jet condenser stage causticization, and / or

- sealing water of the Nash pump bleaching stage, and / or

- purge water of the boiler.

The aforementioned process water is preferably a seal water of a Nash bleaching stage.

Advantageously, at least a portion of the process water is sent to the prespat 80, and is preferably used there as irrigation water. Process water that is recycled to prespat 80 preferably includes one, two, three or four of the following:

- water of secondary condensate from the evaporator,

- purge water of the boiler,

the sealing waters of the Nash pump bleaching stage, and

- cooling water jet condenser stage causticization.

The aforementioned process water is preferably a seal water of a Nash bleaching stage.

Advantageously, at least a portion of the process water is sent to a wastewater treatment plant 50, in which the process water is preferably used as irrigation table water. The process water used as water for irrigation of the gravity table of the wastewater treatment plant preferably includes one, two, three or four of the following:

- sealing water pump Our block 30 bleaching,

- cooling water of the jet condenser from the causticization stage,

- wastewater after the second sump,

- secondary condensates of the evaporator.

Advantageously at least a portion of the process water is recycled to the chemical recovery unit 60 and is preferably used therein in the diluted liquor tank and / or in the white liquor condensate tank therein. The process water used in said chemical recovery unit 60 preferably includes boiler purge water.

Preferably, at least a portion of the process water to be recycled in the pulp mill includes one, two, three, four or five of the following water sources:

a bleaching stage (s) 30, preferably comprising bleach EOR filtrates and / or Nash pump seal waters,

- prespat, preferably containing purified from pulp water,

- evaporator 40, preferably containing condensates,

- soda recovery boiler 70, preferably containing purge water of the boiler, and

- chemical recovery, preferably comprising cooling water of a jet condenser and / or sealing water of a vacuum pump.

Mostly at least a portion of the process water is circulated within the bleaching stage (s) 30. Alternatively or in addition, predominantly at least a portion of the process water is circulated within the chemical recovery stage (s) 60. Thus, at these stages, the total amount of wastewater obtained and the total amount of fresh water needed are reduced. Alternatively or in addition in one example, at least a portion of the process water is recycled within the wastewater treatment stage (s). However, the latter option may not be such an advantageous embodiment, like others.

By circulating at least a portion of the process water, the total amount of effluents that must be treated in a sewage treatment plant can be reduced. In addition, the total amount of necessary untreated water (also called fresh water) is usually reduced.

Advantageously, at least a portion of the water coming from the Nash pumps is used as the wash water for the perforated plate of the displacement flush drum; thus, at this stage, the total amount of effluent formed and the amount of fresh water needed are usually reduced.

A filter device may be provided in the process water circuit. In this case, the filtering device is preferably used for water irrigating the gravity table. Usually no other treatment device is required. Thus, if the irrigation water of the gravity table is not reusable water, then the process water recirculated in accordance with this invention usually does not need any purification step before being used again as process water.

You can also combine waters with different levels of purity, so that they satisfy the level of purity required for this point of use.

Tables 1-3 show several examples of wastewater reduction in accordance with the present invention. “Implemented wastewater reduction [m ³ / t]” refers to the situation in the example of a pulp mill having at the beginning an amount of wastewater of about 22.5 m ³ / t.

One skilled in the art can readily understand that various examples of embodiments of the present invention may find application in areas where it is desirable to optimize liquid flows in a pulp mill. Thus, it is obvious that the invention is not limited only to the examples of embodiment presented above, but it can be modified within the scope of the attached claims.

Claims (112)

1. A method of processing liquid streams in a pulp mill, in which the device includes: - block (10) for the preparation of wood, - a block (20) for obtaining unbleached pulp, including the stages of cooking, washing, sorting and oxygen delignification, to obtain pulp, - bleaching unit (30) for bleaching the resulting pulp, - block (60) for the regeneration of chemicals, - prespat (80), - soda recovery boiler (70) generating a purge water of the boiler, - evaporator (40) generating condensates, - installation (50) of wastewater treatment, and - water treatment plant, where the method includes transporting from at least one of the following water sources: - A) bleach EOP (alkali-oxygen-peroxide) bleach from the block (30) bleach, - B) the sealing waters of the Nash pump from the bleaching unit (30), - C) condensates from the evaporator (40), - D) water from the second sump of the installation (50) wastewater treatment, - E) cooling water of the jet condenser from the chemical recovery unit (60), - F) sealing water of a vacuum pump from a chemical recovery unit (60), and - G) purge water soda recovery boiler (70), at least one of the following points of use: - H) washing the logs in the block (10) preparation of wood, - I) felling in block (10) of wood preparation, - J) sorting chips in the block (10) preparation of wood, - K) a conveyor for wood chips in the block (10) preparation of wood, - L) washing with oxygen delignification in block (20) for the production of unbleached pulp, - M) dilution water in the unbleached pulp block (20), - N) the plate of the drum device for washing by displacement of the bleaching unit (30), O) a washing step (s) in the bleaching unit (30), - P) dilution water in the bleaching unit (30), - Q) water for irrigation of the drying unit of the press prespate (80), - R) water for irrigation of the gravity table of the installation (50) wastewater treatment, - S) a tank for diluted liquor block (60) chemical recovery, - T) a condensate tank for the white liquor of the chemical recovery unit (60), and - U) plant water supply system, by connecting water sources with points of its use in accordance with the following pairs: - from source A or D to point H, - from source A or D to point I, - from source A or D to point J, - from source A or D to point K, - from source A, B or D to point L, - from source A, B or D to point M, - from source B to point N, O, P or Q, - from source A, B, C, D, E or F to point R, - from source G to point S or T, or - from source E or F to point U, however, communication can be carried out in accordance with one or more pairs selected from the above pairs. 2. The method according to p. 1, characterized in that the water sources are associated with points of use in accordance with the following pairs: - from source A or D to point H, - from source A or D to point I, - from source A or D to point J, - from source A or D to point K, - from source A, B or D to point L, - from source A, B or D to point M, - from source B to point N, O, P or Q, - from source A, B, C, D, E or F to point R, or - from source G to point S or T. 3. The method according to p. 1 or 2, characterized in that the sealing water of the Nash pump is sent from the bleaching unit (30) to the presspat (80) and this part is used as water for irrigation of the drying unit (from source B to point Q). 4. The method according to p. 1 or 2, characterized in that at least a portion of the sealing water of the Nash pump coming from the bleaching unit is sent to the alkaline extraction stage, in which oxygen and peroxide are used as additional chemicals (from source B to point O or P). 5. The method according to p. 1 or 2, characterized in that at least part of the sealing water of the Nash pump coming from the bleaching unit is sent to the perforated plate of the drum device for washing by extrusion, upon receipt (20) of unbleached pulp (from source B to paragraph N). 6. The method according to p. 1 or 2, characterized in that the chemical regeneration unit contains a container for diluted white liquor and a vacuum pump filter for lime sludge, and the method includes: - transporting at least a portion of the water from the vacuum pump of the lime sludge filter and / or cooling water of the jet condenser to a container for diluted white liquor (from source E and / or F to point S). 7. The method according to p. 6, characterized in that the water from the vacuum pump of the filter for lime sludge and the cooling water of the jet condenser are combined and sent to a tank for diluted white liquor. 8. The method according to p. 1 or 2, characterized in that the unit for the regeneration of chemicals contains a container for condensation of white liquor, and the method includes: - the direction of at least part of the purge water of the boiler to the condensate tank of white liquor (from source G to point T). 9. The method according to p. 1 or 2, characterized in that the device includes a vacuum filter pump for sludge and a sludge treatment area of a sewage treatment plant; and the method includes: - the direction of at least a portion of the cooling water of the jet condenser and / or water from the sludge filter vacuum pump to the washing stage in the sludge treatment area (from source E and / or F to point R). 10. The method according to p. 1 or 2, characterized in that at least part of the process water is recycled within the bleaching unit. 11. The method according to p. 1 or 2, characterized in that at least part of the process water is recycled within the block (60) of chemical recovery. 12. A device for processing liquid flows in a pulp mill, including: - block (10) for the preparation of wood, - a block (20) for obtaining unbleached pulp, including the stages of cooking, washing, sorting and oxygen delignification, to obtain pulp, - bleaching unit (30) for bleaching the resulting pulp, - block (60) for the regeneration of chemicals, - soda recovery boiler (70), - evaporator (40), - prespat (80), - installation (50) for wastewater treatment, and - water treatment plant, where the specified device further comprises at least one of the following: - A) an apparatus configured to move bleach EOP filtrates from the bleach unit (30), - B) an apparatus configured to transport the sealing waters of the Nash pump from the bleaching unit (30), - C) an apparatus configured to transport condensates from the evaporator (40), - D) an apparatus configured to transport water from a second sump of a sewage treatment plant (50), - E) an apparatus configured to transport cooling water of a jet condenser from a chemical recovery unit (60), - F) an apparatus configured to transport the sealing water of the vacuum pump from the chemical recovery unit (60), and - G) an apparatus configured to transport the purge water of the boiler from the recovery boiler (70), at least one of the following work locations: - H) washing the logs in the block (10) preparation of wood, - I) cutting of wood in block (10) of wood preparation, - J) sorting chips in the block (10) preparation of wood, - K) a conveyor for wood chips in the block (10) preparation of wood, - L) washing with oxygen delignification in block (20) for the production of unbleached pulp, - M) dilution water in the unbleached pulp block (20), - N) the plate of the drum device for washing by displacement of the bleaching unit (30), O) a washing step (s) in the bleaching unit (30), - P) dilution water in the bleaching unit (30), - Q) water for irrigation of the drying unit of the press prespate (80), - R) water for irrigation of the gravity table of the installation (50) wastewater treatment, - S) a tank for diluted liquor block (60) chemical recovery, - T) a condensate tank for the white liquor of the chemical recovery unit (60), and - U) plant water supply system, wherein said device comprises at least one of the following device connections: - from A or D to location H, - from A or D to location I, - from A or D to location J, - from A or D to location K, - from A, B or D to location L, - from A, B or D to location M, - from B to a location of N, O, P or Q, - from A, B, C, D, E or F to location R, - from G to location S or T, or - from E or F to location U, however, the connection can be made in accordance with one or more pairs selected from the above pairs.

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