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WO2016038247A1 - Procédé de génération de vapeur à une installation de lessiveur d'une usine de pâte chimique - Google Patents

Procédé de génération de vapeur à une installation de lessiveur d'une usine de pâte chimique Download PDF

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Publication number
WO2016038247A1
WO2016038247A1 PCT/FI2015/050581 FI2015050581W WO2016038247A1 WO 2016038247 A1 WO2016038247 A1 WO 2016038247A1 FI 2015050581 W FI2015050581 W FI 2015050581W WO 2016038247 A1 WO2016038247 A1 WO 2016038247A1
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WIPO (PCT)
Prior art keywords
steam
pressure
temperature
black liquor
led
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/FI2015/050581
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English (en)
Inventor
Lasse Hernesniemi
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Andritz Oy
Original Assignee
Andritz Oy
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Filing date
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Application filed by Andritz Oy filed Critical Andritz Oy
Publication of WO2016038247A1 publication Critical patent/WO2016038247A1/fr
Anticipated expiration legal-status Critical
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Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C7/00—Digesters
    • D21C7/10—Heating devices
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C11/00—Regeneration of pulp liquors or effluent waste waters
    • D21C11/06—Treatment of pulp gases; Recovery of the heat content of the gases; Treatment of gases arising from various sources in pulp and paper mills; Regeneration of gaseous SO2, e.g. arising from liquors containing sulfur compounds
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C1/00—Pretreatment of the finely-divided materials before digesting
    • D21C1/02—Pretreatment of the finely-divided materials before digesting with water or steam
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C11/00—Regeneration of pulp liquors or effluent waste waters
    • D21C11/10—Concentrating spent liquor by evaporation
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C7/00—Digesters
    • D21C7/14—Means for circulating the lye

Definitions

  • the present invention relates to a method of generating steam by utilizing the secondary energy of black liquor at a digester plant of a chemical pulp mill.
  • Prior art utilizes a fiberline system with a chip bin, where wood chips or other cellulo- sic material is steamed and liquid is admixed therein for forming a slurry, after which the slurry is pressurized (this section is also referred to as a feed system), fed into a treatment vessel or treatment vessels (which may be an impregnation vessel, a pre- hydrolysis process or other vessels), whereafter follows a digester (this section is also referred to as a cooking system). At present, at least one black liquor flow is discharged from the cooking system (typically at a temperature of 120-170 ⁇ ).
  • Dis- charged black liquor stream or streams can be used as a heat source for "preheating" white liquor, other black liquor flows and/or other liquid flows being led to feed and cooking systems.
  • the discharged black liquor stream (or streams) is then led to a pre-evaporation system, i.e. into one or more flash tanks, where flash steam is formed from the hot black liquor, which flash steam contains steam and other gases.
  • flashing the black liquor is typically cooled to a temperature of approximately 100- ' ⁇ 20 q C. After this the black liquor is cooled in an indirect heat exchanger to a temperature of approximately 80-100 ⁇ and led into an evaporation system of the recovery zone.
  • the thus generated flash steam can be used at another location in the pulping process. Flash steam can e.g. be used for direct preheating of chips in a chip bin prior to cooking.
  • the above described flashing process although being used successfully in conventional continuous digesters, has the disadvantage that the generated flash steam contains in addition to steam volatile compounds, e.g. turpentine, metanol and sulfur compounds, which are not desirable in wood chip pre-steaming.
  • wood chips are steamed at atmospheric or slightly higher pressure, the target temperature of the wood chips typically being approximately 100 At this temperature the volatile compounds entrained in flash steam are not condensed, but they are concentrated to the upper part of the chip bin, wherefrom they are collected and treated.
  • the treatment is typically combustion in a dilute non-condensable gas (NCG) system of the mill. This collection and treatment system becomes especially significant when the used flash steam contains volatile compounds, including sulfur compounds, which have a disadvantageous impact for the environment, including detrimental odor.
  • NCG non-condensable gas
  • US-patent 6,722,130 discloses a system for producing clean steam from black liquor. First the pressure of the black liquor is decreased for producing a second black liquor having a higher concentration and black liquor vapor, which is condensed to condensate. This condensate is heated with the first black liquor and flash- evaporated for producing clean steam to be used in a chip bin.
  • Known solutions offer various systems for producing cleaner steam for the needs of a digester plant and for improving the energy economy of a chemical pulp mill.
  • US-patent application 2010/0236733 discloses a process where two black liquor streams are discharged from the digester.
  • One of the black liquor streams discharged from the digester is flashed, whereby flashed black liquor and flash steam are generated, and the other black liquor stream is evaporated using live steam as heating medium, whereby steam needed in the digester process and evaporated black liquor are generated.
  • Flash steam generated in the flashing of the second black liquor stream discharged from the digester is led into at least one heat exchanger, preferably a reboiler, into an indirect heat exchange contact with clean liq- uor being evaporated for producing clean steam that is used for steaming chips.
  • reboiler solutions comprising for instance a kettle reboiler or a vapor re- boiler.
  • a kettle reboiler is an indirect tube heat exchanger, in which hot black liquor discharged from the digester flows through the reboiler tubes, heating clean liquid. Thereby steam is generated, which can be used in the chip feed system of the digester plant.
  • a disadvantage of a kettle reboiler is that the dry-solids content of black liquor does not increase therein, which increases evaporation of water at the evaporation plant and thus impairs the energy economy of the chemical pulp mill.
  • a vapor reboiler can be a vertical tube heat exchanger, in which the heating flash steam flows inside the tubes and the liquid being boiled flows as a thin film on the outer surface of the tubes.
  • a problem with a vapor reboiler is that in certain cases, especially in winter, it is not always possible to generate an adequate amount of steam required for chip treatment, such as in a chip bin, but low pressure steam from the mill has to be used in addition. This can take place by feeding live steam directly into the chips.
  • Another problem with a vapor reboiler is indirect heat exchange, i.e. a certain ⁇ has to prevail over the heat transfer surface, typically 2 -10 ⁇ .
  • a flash tank such as a flash cyclone, producing flash steam for the vapor reboiler
  • the black liquor exiting the flash cyclone is hotter and it has to be cooled more prior to leading it to further treatment. Thereby an unnecessarily abundant amount of hot water can be generated.
  • a third problem with a vapor reboiler is smaller amount of flash steam generation in a preceding flash cyclone (due to its higher pressure demand). Then the dry-solids content of black liquor exiting the flash cyclone is lower and thus requires more evaporation in further treatment compared to a situation devoid of a vapor reboiler.
  • a fourth problem with a vapor reboiler is increased amount of condensate formed from flash steam compared to a situation devoid of a vapor reboiler. Unless this condensate can be used partially e.g. for pulp washing, it has to be cleaned before letting into the water system.
  • a vapor reboiler heating steam typically flash steam of black liquor
  • "clean" liquid free of volatile compounds for heating the liquid to a temperature higher than its boiling point or to flashing point for producing odorless steam that is substantially free from volatile compounds.
  • the liquid can typically be condensate from a black liquor evaporator, demineralized water, boiler feed water or adequately clean water fraction.
  • the clean steam produced in the reboiler contains a substantially smaller amount of non-condensible gases than vapor produced by direct flashing of black liquor, which is also used as heating steam.
  • a vapor reboiler acts as a distiller, where heating steam is segregated into clean condensate and foul condensate.
  • the flash steam is fed from below to part of the tubes wherein the steam flows upwards, whereby naturally more easily condensed components, such as steam, are condensed.
  • the condensate formed in these tubes is relatively clean water, still containing some methanol. This condensate can be used e.g. in pulp washing in cases when this condensate is considered adequately clean.
  • the steam flowing in these tubes contains a larger percentage of volatile impurities, whereby a so-called foul condensate is formed requiring cleaning.
  • the amount of foul condensate is less than 25% of the total amount of condensate formed in a vapor reboiler.
  • the fouler condensate is led to further treatment and finally cleaned, usually by steam stripping.
  • An object of the present invention is to avoid the above mentioned problems of a vapor reboiler and to provide an improved and alternative method of producing clean steam by means of a vapor reboiler for e.g. steam pretreatment of wood chips by utilizing the secondary heat of black liquor coming from the digester as efficiently as possible and thus decreasing the use of live steam.
  • An object is to intensify the operation of a vapor reboiler so that the use of fresh water of the mill can be decreased and/or the use of clean water available can be intensified.
  • One object is also to improve the overall energy economy of a chemical pulp mill.
  • the present invention provides a method of generating steam at a digester plant of a chemical pulp mill, in which method
  • a. black liquor is discharged from the digester at a first temperature and a first pressure
  • the black liquor is treated in at least one flash tank for producing flashed
  • black liquor and flash steam at a second temperature and a second pressure, which are lower than the first temperature and first pressure;
  • the flash steam is led from stage b. into indirect heat exchange contact with clean liquid in a vapor reboiler for boiling the liquid and producing steam having a third temperature and third pressure, which are lower than the second temperature and second pressure;
  • the steam formed in stage d. is led from the reboiler into an ejector, wherein also a second steam flow is led having a fourth pressure and a fourth temperature, which are higher than said third pressure and third temperature, whereby a third steam flow is formed having a fifth pressure and a fifth temperature, which are higher than said third pressure and third temperature in stage d.;
  • the third steam flow formed in stage e. is led e.g. for pretreatment of comminuted fibrous material, such as wood chips, prior to digester treatment.
  • the method further comprises the steps of:
  • stage g) clean condensate is preferably circulated in such an amount that the fresh water consumption at the mill can be decreased. At least 20%, typically at least 50%, e.g.50-80% or 60-80% of the clean condensate is led back into the vapor re- boiler to the clean liquid side.
  • the pressure and amount of the second steam being led into the ejector in stage e) is adjusted according to the steam requirement for the pretreatement of fibrous material, such as chips. In summer conditions this amount may be zero and correspondingly in winter conditions the limiting maximum amount may be the tem- perature of black liquor exiting stage b), which temperature cannot be decreased under the temperature required for further treatment.
  • the new solution is advantageous especially when, in cold weather conditions, such as in winter, the temperature of the chips is very low, e.g. -15 ⁇ , which means that the chips are even frozen. Then the steam consumption is high in order to heat the chips. Under winter conditions the flash steam is typically not adequate for heating the chips, but live low pressure steam must be added into the chip bin in current process solutions. Decreasing the pressure in the flash tank and increasing the pressure of the steam produced in the reboiler typically allows flashing evaporation of hot liquors such that the temperature of the produced steam is lower and the amount of steam higher than in prior art methods. For instance, the temperature of the steam and liquid in the flash tank can be decreased by means of the invention by at least 5°C compared to prior art (without an ejector). Simultaneously the amount of produced gas (steam) can typically increase by at least 10%, preferably by at least 20% and in some cases by more than 40% compared to prior art.
  • the black liquor discharged from the digester is flashed in two stages.
  • the temperature of the black liquor exiting the first flashing can be below 145 ⁇ .
  • the cooking temperature can b e lo w (the temperature of the black liquor exiting the digester is low, i.e. 120-145 ⁇ ). This is typical for instance when pulp is cooked in the digester to a high Kappa number (typically Kappa number over 50 for soft wood and over 25 for hard wood).
  • the temperature of the black liquor can be lower than usual also when the production is low in view of the volume of the digester. At present, hard wood is typically cooked at low cooking temperatures.
  • a purpose of the invention is to intensify the operation of a vapor reboiler so that the use of fresh water at the mill can be decreased and/or the use of clean water available can be intensified.
  • the present invention also relates to a method of generating steam at a digester plant of a chemical pulp mill, in which method
  • black liquor is discharged from the digester at a first temperature and a first pressure
  • the black liquor is treated in at least one flash tank for producing flashed black liquor and flash steam at a second temperature and a second pressure, which are lower than the first temperature and first pressure;
  • the flash steam is led into indirect heat exchange contact with clean liquid in a vapor reboiler for boiling the liquid and producing steam having a third temperature and third pressure, which are lower than the second temperature and second pressure, and the flash steam is condensed;
  • stage d) the steam flow formed in the reboiler is led from stage d) to further use, such as for pretreament of comminuted cellulosic fiber material prior to treatment in a digester, and
  • foul condensate and clean condensate are formed from the flash steam, and at least a portion of the clean condensate is led into the clean liquid flow to be used in stage d).
  • odorless steam e.g. for steam pretreatment of chips is produced by flashing black liquor discharged from the digester and condensing the flash steam in a reboiler/reboilers, which exchanges heat in the reboiler/s indirectly with "clean" liquid free from volatile compounds for heating the water to a temperature higher than its boiling point or to a flashing point for producing clean and odorless steam free of volatile compounds.
  • the clean steam produced in the reboiler contains a substantially smaller amount of non-condensible gases than steam produced by direct flashing of black liquor.
  • the condensate can be divided based on cleanliness into various fractions, which typically include so-called clean condensate and foul condensate.
  • a tube vapor reboiler the flash steam is fed as heating steam from below to part of the tubes wherein the steam flows upwards, whereby naturally more easily condensed components, such as steam, are condensed.
  • the condensate formed in these tubes is relatively clean water, still containing e.g. some methanol.
  • the steam flowing in these tubes contains by percentage more volatile impurities, whereby a foul condensate is formed, which requires cleaning.
  • the volume of foul condensate may vary within certain limits set by the tube arrangement, depending on the operator's requirements for the cleanliness of the clean condensate. Typically the volume of foul condensate is approximately 10-25%, e.g. 17% of the total amount of condensate in the reboiler. According to the invention, clean condensate is used as feed liquid for a vapor reboiler.
  • the present invention is not limited to the user of a tube-type vapor reboiler. but the heat transfer surface can be formed of something else than a tube, e.g. a plate.
  • a preferred reboiler has a construction where the condensate can be divided into different fractions based on cleanliness.
  • the use of clean condensate in a reboiler decreases the fresh water consumption at the mill and the energy efficiency is improved.
  • the temperature of clean condensate is typically over 100 ⁇ , which is considerably hig her than the temperature of typically used mill water (e.g. 65 ⁇ ).
  • heating of feed water to be reboiled consumes less energy, and more steam to be used in chips treatment can be produced and thus the amount of live steam can be decreased.
  • flash tank is used in this description, the term also used by professionals in the field, a person skilled in the art also knows that the term covers any apparatus, wherein the pressure of hot, pressurized liquid is decreased and liquid is allowed to evaporate, typically very fast, in a closed container for producing a source of steam and liquid at a lower temperature.
  • Figure 1 is a schematic illustration of a preferred embodiment according to the present invention for carrying out the method of the invention.
  • Figure 2 is a schematic illustration of a preferred embodiment according to the pre- sent invention using a tube vapor reboiler.
  • Fig. 1 illustrates a system for generating steam at a digester plant and for treating black liquor such that the heat economy of the cooking process is improved.
  • Figure 1 illustrates a coupling according to an embodiment of the invention.
  • the temperature of the black liquor exiting the digester (not shown) is approximately 165 ⁇ and the solids content 12-17 %.
  • the black liquo r has typically been pressurized in the digester to a pressure of 500 - 1500 kPa (5 - 15 bar) (abs) and its temperature corresponds to the temperature of digester treatment (approximately 1 10° - 180° C).
  • the black liquor is typically flashed in two-stage flashing in two flash tanks.
  • Flash steam from the first stage flows into a steaming vessel (not shown) in the chip feed system, where the chips coming from the chip bin (not shown) are heated to a temperature of approximately 120 ⁇ .
  • the black liquor is cooled in the first flashing stage to a temperature of approximately 143 ⁇ and led via line 1 to a flash tank 2.
  • the black liquor is flashed to a temperature of approximately 106 ⁇ .
  • the generate d flash steam is then at approximately 104 ⁇ , due to the increase in the boil ing point caused by the solids of the black liquor. From the flash tank 2 the black liquor is led via line 3 to further treatment.
  • Flash steam generated in the flash tank 2 is led via line 4 into a vapor reboiler 5.
  • the flash steam is condensed onto the heat surfaces of the vapor reboiler 5.
  • the formed cleaner condensate is led via line 8 into line 9, via which the vaporizable liquid is added into the vapor reboiler to its clean side for generating steam.
  • the formed steam is led via line 10 into an ejector 1 1 , to the side of lower pressure. Via line 12 the ejector 1 1 receives steam at a higher pressure.
  • the construction of the flash tank 5 is substantially convcentional and it has a feed line 1 for hot pressurized black liquor, a discharge line 4 for flash-evaporated vapor, and a discharge line 3 for cooled black liquor at a lower pressure.
  • Flash tanks are usually operated so that the pressure prevailing in them is lower than the pressure of black liquor fed therein. Flash tanks are containers designed for this purpose, which facilitate the pressure decrease of hot, pressurized black liquor, whereby liquid, typically water, is vaporized from the black liquor very quickly, into steam, whereby also the concentration of waste cooking chemical and the products of a cooking reaction (dissolved solids) is increased. In this quick evaporation the formed steam is discharged into the steam discharge line 4 at a pressure prevailing in the tank 2, e.g.
  • the flash steam is led via line 4 into a reboiler 5, wherein the energy contained therein is recovered.
  • the vapor reboiler 5 can be a vertical tube heat exchanger, in which the heating steam flows inside the tubes and the liquid being boiled flows as a film on the outer surface of the tubes, as described in connection with Fig. 2.
  • Clean condensate is accumulated onto the bottom of the reboiler.
  • the clean condensate in line 8 is circulated into the feed water line of the reboiler, into which also mill water can be introduced via line 9. At least a portion, at least 20%, typically over 50%, such as 50-80% or 60-80%, of the clean liquid is formed by the clean condensate of the reboiler from line 8.
  • the foul condensate is led via line 7 to be cleaned e.g. to a stripping plant.
  • the non-condensable gases are introduced to their treatment system via line 6.
  • the flash steam 4 is set in an indirect heat exchange contact with "clean" liquid free of volatile compounds for heating the liquid to a temperature exceeding its boiling point for producing clean steam.
  • the flash steam is condensed inside the tubes as described in the above, while clean liquid boils on the outer surface of the tubes for producing clean steam.
  • the steam is discharged from the reboiler 5 via line 10, which line is provided with an ejector 1 1 .
  • the ejector receives steam from the reboiler, the pressure of which steam is increased in order to provide a pressure and a temperature that are better adquate for heating the chips in the bin (not shown) where the steam is led via line 13.
  • the amount of steam produced in the flash tank can be increased.
  • Steam in line 13 is advantageously used for steaming wood chips. The pressure required for this steam is typically determined based on the pressure requirements of the final object of application in chip steaming.
  • a steam jet ejector is a nozzle device utilizing the venturi-effect, which device utilizes the energy contained in the steam either i) for generating a vacuum, or ii) for increasing the pressure of a gas, or iii) for a combination of points i) and ii).
  • An ejector typi- cally comprises or consists of a substantially cylindrical housing having a high pressure feed opening (feed opening for fluid acting as driving power), a low pressure feed opening (suction feed opening) and a discharge opening (discharge opening for mixed fluid).
  • a flowing substance e.g.
  • the pressure of the flash tank can be decreased so that the black liquor is flash evaporated to a temperature of e.g. approximately 100-108 ⁇ . Thereby, the total amount of available flash steam is increased, and a less amount of valuable live steam is required.
  • the "high pressure" steam used as driving power of the steam jet ejector can be low pressure live steam or high pressure live steam. Additionally, the need for cooling the black liquor being transferred to the evaporation plant is decreased or eliminated and the amount of black liquor to be evaporated is decreased at least to some extent.
  • the clean steam produced in the reboiler contains a substantially smaller amount of non-condensable gases than steam produced by direct flashing of black liquor.
  • Clean steam in line 13 is preferably used for wood chips preheating by means of steam, e.g. in a chip bin.
  • this steam is used for treating chips, a less amount of volatile compounds are generated for collection and treatment by the NCG-system of the mill, since said steam does not bring volatile compounds into the pre-steaming process.
  • Fig. 2 illustrates a vapor reboiler coupling in more detail.
  • Hot black liquor discharged from the digester (not shown) and having a temperature of typically 120-180 ⁇ and a solids content of typically 12-17 % is discharged via digester screens and is led possibly via a first flash tank (not shown) and along line 40 into a flash tank 42.
  • the flashed black liquor is led via line 44 to the evaporation plant of the mill, where the black liquor is concentrated to a high solids content prior to combustion in a recovery boiler.
  • the flash steam is led via line 46 into a reboiler 41 , wherein the energy contained therein is recovered.
  • the vapor reboiler 41 is a vertical tube heat exchanger, in which the heating steam flows inside the tubes and the liquid being reboiled flows as a film on the outer surface of the tubes.
  • the flash steam from line 46 is fed from below to part of the tubes, a first set of tubes 20, wherein the steam flows upwards, whereby naturally more easily condensed components, such as steam, are condensed.
  • the condensate formed in these tubes is relatively clean water, still containing some methanol. Clean condensate is accumulated onto the bottom of the reboil- er 22.
  • the steam flowing in these tubes contains a larger percentage of volatile impurities, whereby a foul condensate is formed, which requires cleaning and is accumulated in chamber 26.
  • the amount is approximately 10-25%, e.g. 17% of the total amount of condensate in the reboiler.
  • the foul condensate is cleaned usually by steam stripping whereto it is led via line 28.
  • the non-condensible gases are introduced to their treatment system via line 36.
  • the flash steam 46 is set in an indirect heat exchange contact with "clean" liquid free of volatile compounds for heating the liquid to a temperature exceeding the boiling point for producing clean steam.
  • the flash steam is condensed inside the tubes as described in the above, while clean liquid boils on the outer surface of the tubes for producing clean steam.
  • the clean liquid is led to the upper part of the tubes onto their outer surface to flow via line 30. At least a portion, e.g. 50-80%, of the clean feed liquid is formed of the clean condensate of the reboiler from line 32. Additionally, if needed, mill water, e.g.
  • boiler water can be introduced
  • the steam is discharged from the reboiler 41 via line 38, which according to a preferred embodiment of the invention can be provided with a pressure increasing device 1 1 , which is an ejector as described in connection with Figure 1 .
  • Steam is introduced into the ejector from the reboiler, the pressure of which steam is increased so that the pressure and the temperature are more adequate for heating the chips in the bin (not shown).
  • the ejector the amount of steam produced in the flash tank can be increased.
  • Example 1 The starting point without an ejector is that the temperature of black liquor entering the flash tank is 143 ⁇ . Then the temperature of I iquor exiting the tank is 1 14 ⁇ and the pressure of the flash steam is 52 kPa (g). Steam at a temperature of 108 ⁇ is generated in the vapor reboiler. In addition, low pressure steam from the mill network is to be introduced into the chip bin when the temperature of the chips is -15 ⁇ .
  • the pressure in the flash tank can be decreased, and the amount of flash steam can be increased.
  • the temperature of the flash steam is 105.6 ⁇ and the pressure 20 kPa (g).
  • the temperatu re of the black liquor exiting the flash tank is 107.9 i.e. more than 6 ⁇ cooler than without an ejector.
  • Steam at a temperature of 102 ⁇ is generated in the reboiler.
  • the pressure of the process steam of the ejector is 260 kPa and the temperature 140 ⁇ .
  • the ejector generates steam at a temperature of 108 ⁇ .
  • the ejector allow s decreasing the need for low pressure steam, but what is most important is that the temperature of the black liquor discharged from the flash tank is clearly lower than without an ejector. Therefore, the cooling requirement for black liquor to be led to the evaporation plant is substantially decreased, and thus the amount of hot water produced in liquor cooling is decreased. Hot water has been generated in excess amounts, which naturally is not sensible in view of the energy economy of the mill.
  • the pressure in the flash tank can be decreased.
  • the temperature of the exiting black liquor is then n 106 ⁇ and the solids content 15.2%.
  • the reboiler generates an adequate amount of steam for the chip bin and there is no need for low pressure steam.
  • the temperature of the black liquor being discharged from the reboiler is 143 ⁇ . It is flashed so that the temperature is decreased to 1 14 ⁇ , and the temperature of the flash steam is 1 12 ⁇ and the pressure 52 kPa.
  • the t emperature of the reboiler feed water containing mainly clean condensate is 103 ⁇ .
  • the temperature of the reboiler discharge steam is 108 ⁇ and the amount greater tha n when using conventional mill water as feed water, so that the use of low pressure steam can be decreased.
  • the energy economy can be further improved by coupling an ejector to the steam discharge line of the reboiler.
  • the overall heat economy of the mill is improved, since the solids content of discharged liquor being led to the evaporation plant is increased.
  • the steam consumption and capacity requirement of the evaporation plant are de- creased.
  • the investment costs of the evaporation plant are decreased due to decreased capacity requirement.

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Abstract

La présente invention concerne un procédé de génération de vapeur à une installation de lessiveur d'une usine de pâte chimique. Dans le procédé, a) une liqueur noire est évacuée du lessiveur à une première température et une première pression ; b) la liqueur noire est traitée dans au moins un réservoir de détente pour générer une liqueur noire détendue et une vapeur de détente, qui sont à une deuxième température et une deuxième pression qui sont inférieures à ladite première température et ladite première pression ; c) la liqueur noire détendue est acheminée du réservoir de détente vers un autre traitement, d) la vapeur de détente de l'étape b) est acheminée en contact d'échange de chaleur indirect dans un rebouilleur avec un liquide propre pour faire bouillir le liquide et produire une vapeur ayant une troisième température et une troisième pression, qui sont inférieures à la deuxième température et la deuxième pression, avec lesquelles la vapeur de détente est condensée, e) le flux de vapeur généré dans le rebouilleur est acheminé de l'étape d) vers une utilisation ultérieure, et f) dans l'étape d), un condensat sali et un condensat propre sont générés, et au moins une partie du condensat propre est acheminée vers l'écoulement de liquide propre à utiliser dans le rebouilleur dans l'étape d).
PCT/FI2015/050581 2014-09-08 2015-09-04 Procédé de génération de vapeur à une installation de lessiveur d'une usine de pâte chimique Ceased WO2016038247A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI20145784A FI20145784A7 (fi) 2014-09-08 2014-09-08 Vesihöyryn kehittäminen sellutehtaan keittämöllä
FI20145784 2014-09-08

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WO2016038247A1 true WO2016038247A1 (fr) 2016-03-17

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WO (1) WO2016038247A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
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