• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    13 ABSTRACT A method and a system for generating steam in a digester plant of a chemical pulpmill, wherein black liquor is produced in the digester system. Afirst stream of blackliquor is extracted from the digester and evaporated using fresh steam as a heatingmedium to generate vapor required in the digester process and evaporated blackliquor having an increased dry solids content. The vapor from the evaporation isused for heating fibrous material in the digester. A second stream of black liquor ex-tracted from the digester is flashed to generate flashed black liquor and flash vapor,which is introduced to at least one heat exchanger into an indirect heat exchangecontact with a clean evaporable liquid to produce clean steam. The clean steam is used for steaming chips, and the flashed black liquor is led to further evaporation.
    公开号:SE1050126A1
    申请号:SE1050126
    申请日:2010-02-08
    公开日:2010-08-10
    发明作者:Petri Tikka；Jarmo Kaila
    申请人:Andritz Inc；
    IPC主号:
    专利说明:

    i.a. are not desired when spraying wood chips. compounds, sulfur compounds, such as wood chips typically based on atmospheric pressure, or slightly above it, so that the residual gases not absorbed by the wood chips are collected and treated. The treatment is typically performed by combustion in the factory's non-condensable (NCG) system. This collection and gas treatment system becomes particularly significant when the steam used contains volatile e.g. incl. compounds, sulfur compounds, which have an undesirable environmental impact, harmful odor. It is therefore preferred to use a steam source that minimizes or eliminates the supply of volatile compounds to the basing process. Steam is also needed to heat the fibrous material to boiling temperature in the steam phase of the boiler. In the known systems, medium pressure steam from the factory's turbine plant is typically used for this purpose. Due to energy costs, further improvement of the energy efficiency of the chemical pulp mill is needed.
    U.S. Pat. No. 4,944,440 discloses a process in which effluent drawn by a boiler is evaporated in a plurality of evaporation steps. Vapors generated in the evaporation steps are fed directly to the impregnation and boiling zones of a digester to heat the fibrous material.
    SE patent 453673 discloses a process in which fibrous material is boiled with boiling liquid, while steam is led to the boiling point, where the fibrous material and the liquid flow in a continuous stream and are separated and the boiling liquid is recirculated.
    According to the process, some cooking liquid is drawn from the digester and led to a steam converter for the production of steam. The steam is supplied to the digester to heat the fed fibrous material to the desired temperature.
    Document US 6722130 discloses a system for generating pure steam of black liquor. The pressure of the black liquor is first lowered in order to produce a second black liquor at a higher concentration and black liquor vapor which is condensed to form a condensate.
    The condensate is heated with the first black liquor and evaporated to expand in order to produce pure steam which is used in a chip silo.
    Document US 6176971 discloses a system for generating clean steam to be used in chip silos. Substantially clean usable steam is produced from hot residual liquor (eg black liquor) by passing the residual liquor to a reboiler, and then pressurizing (eg with an ejector, fan or compressor) the pure steam leaving the reboiler. The amount of clean steam produced is increased by subjecting the pure steam side of the steam converter to negative pressure in the steam converter with a steam driven ejector. The submerged pressure on the side of the clean steam ensures that more heat can be drawn off the black liquor, which in itself gives a larger amount of steam, whereby the input of steam into the ejector also contributes to the production of larger amounts of steam. In this case, however, the steam formed consists of a mixture of pure steam which has been expelled from the process liquid and of steam which has been taken from the factory steam network to drive the ejector.
    Document US 6306252 discloses a further process for generating pure steam for use in chip silos, where the black liquor from the digester is passed through a heat exchanger, in which pure process water is heated, after which the pressure of the heated process water is lowered so that pure steam is generated.
    Document US 20070131363 discloses a process involving the generation of black liquor in a digester system, where the black liquor is fed to an evaporator system without using a pre-evaporator system, the black liquor is relaxed in the evaporator system to generate steam, and at least some of the steam is used to base chips and / or to be fed to indirect heat exchangers in the boiler system for the purpose of preheating white liquor and / or filtrates for use in the boiler system. Document WO 2007073333 discloses a system and method a cooking plant for the purpose of hot, for generating steam in producing chemical cellulose pulp. The pressure of pressurized black liquor from a digester is lowered in a first step to form black liquor steam which is used for pre-treatment of the chips with steam in a second preheating step. Pure steam for pretreatment of the chips with steam in a first is generated by preheating steps by reheating the black liquor, whose pressure has been lowered before a final subsequent pressure drop, where the increased amount of black liquor steam is led to a steam converter to generate clean steam.
    Document WO 2008/057040 relates to a method which comprises an impregnation vessel, in which the chips are to be impregnated, which chip is then fed in a transfer medium to a boiler vessel thereon. One is taken from the following black liquor deduction boiler, which deduction is led to the bottom in order to heat the chips there before it is fed out of the impregnation vessel. A deduction to one of the transfer medium is taken from the top of the cooker and led to the position, where it acts as an impregnating liquid in the impregnation vessel. At least a part of the transfer medium drawn by the kettle top passes through an indirect heat exchanger, in which the transfer medium subtracted from the kettle top at a given temperature indirectly heat exchanges with a first medium for producing steam of the first medium. The produced steam is then led to a position for pre-treatment with steam, upstream of the impregnation process in order to heat the chips in said position for pre-treatment with steam.
    The known solutions have different systems for producing cleaner steam for heating needs in the cooking plant and for improving the pulp mill's energy economy.
    SUMMARY OF THE INVENTION An object of the present invention is to provide an improved alternative process for producing pure steam for pretreating wood chips with steam using the heat of the black liquor and for producing steam from black liquor to heat fibrous material. j_ a cook. A further purpose is to generate steam from black liquor so that the treated black liquor has better properties with regard to the further treatment at the pulp mill also to improve the entire recycling area. One purpose is the pulp mill's energy economy.
    A first aspect of the present invention relates to a process for generating steam in a boiling plant of a chemical pulp mill, in which process a) black liquor is produced in the boiler system, b) a first stream of black liquor is drawn from the digester and evaporated using fresh steam as a heating medium to generate steam and evaporated black liquor having an increased dry matter content, c) the steam from the evaporation in step b) is used to heat fibrous material in the digester, d) a second, black liquor extracted from the digester is depressurized to produce relaxed black liquor and relaxation steam fed into at least one heat exchanger, preferably a reboiler, indirect heat exchange contact with a clean, evaporable liquid to produce pure steam, used to base chips, and e) the pure steam is passed from step d) f) the relax the black liquor from step d) until further evaporation.
    According to a preferred embodiment, step d) is performed so that the evaporated black liquor from step b) and the second flow of black liquor drawn off from the digester are combined before or during the relaxation.
    According to a preferred embodiment, the evaporated black liquor from step a) has a higher dry matter content than the relaxed black liquor from step d). The pure evaporable liquid in step d) may consist of evaporator condensate, desalinated water, the boiling water of the boiler or of a sufficiently pure water fraction.
    In a preferred embodiment, the fresh steam is condensed at step b) to the factory evaporation in and fresh steam condensate as. thereby producing a recycling boiler plant, where it is used as feed water.
    Preferably, step f) is performed so that it. relaxed black liquor from step d) is conducted together with. the evaporated black liquor from step b) to further evaporation.
    The basic ideas of the present invention are as follows: - Steam needed in the kettle top is produced by evaporating stripped black liquor in one / several single or multi-stage evaporators using fresh steam as a heating medium, and - Odorless steam for pre-treatment of chips with steam is generated by defrosting extracted liquor and condense the relaxation steam in a heat exchanger, preferably in one / several reboilers, which exchange heat indirectly with the condensate or sufficiently clean water to produce odorless steam. The produced steam is then led to a position for pre-treatment with steam in a retention and / or basing vessel.
    Another aspect of the present invention relates to a fiber line system. to produce chemical cellulose pulp, comprising a chip silo (10), in which evaporation of cellulosic material takes place by using pure steam from a (2): the cellulosic material to form a slurry, steam line a feed system, in which liquid is added after which the slurry in which ( 5a) pressurized; optionally one or more treatment vessels, the slurry is treated before boiling; and a continuous boiler for boiling the slurry, which boiler is connected to a first line (4, 5) for drawing at least one black liquor stream (5a) in which evaporator (6) from the boiler and for at least one ( 6), to generate secondary steam and evaporated black liquor, input thereof into the black liquor is evaporated before and to an evaporator second line (14, 13) for drawing at least one black liquor flow from the digester (5a) and feeding it into a relaxation vessel (15), in which the pressure vessel of the liquor is lowered to produce the steam vapor and the relaxed black liquor; which evaporator (6) is further connected to a steam extraction line (II) to the inlet of the boiler, for conducting secondary steam son1 generated in the evaporator (6) where said steam is used as heat steam to heat fibrous material in the slurry, and to a line for the evaporator ( 6) and (15), in stripping evaporated black liquor from feeding it into a stripping vessel which produces (15) for stripping relaxed stripping vessel the pressure of the liquor is lowered to steam steam and relaxed black liquor; which shut-off vessel (18) black liquor and feed thereof into the plant's evaporation plant, is further connected to a line and to a steam line (16) for directing steam steam to a heat exchanger (17), preferably a reboiler, where the steam generates indirect heat-evaporating exchange with an evaporator (17) pure steam by pure, liquid; which heat exchanger is further connected to a steam line (2) for extracting pure steam and line thereof to the chip silo (10).
    In a preferred embodiment, said line for drawing evaporated black liquor from the evaporator (6) and either said first for drawing both or both, line (4) or said second line (14, 13) is at least one black liquor flow from the digester (5a), combined to feed these liquids into said relaxation vessel (15), or controlled individually to said relaxation vessel (15).
    In a preferred embodiment, the evaporator is further connected to a steam introduction line (8) for introducing fresh steam into the evaporator (6) for the purpose of heating the slurry, and to a condensate line 10 (20) (6), a line for stripping condensed fresh steam from the evaporator which condensate line (12) directs the evaporator condensate to (21) for feeding clean, evaporable liquid to the heat exchange system (17).
    In a preferred embodiment, the evaporator (6) and the relaxation vessel (15) are arranged so as to produce evaporated black liquor which has a higher dry matter content than the relaxed black liquor.
    In a preferred embodiment, the evaporator is connected to a steam introduction line (8) for introducing fresh steam into the evaporator (6) and to a condensate line (12) (6), the steam condensate for heating the slurry, for which to evaporate condensed fresh steam from the evaporator (12) the factory's recycling boiler as feed water. condensate line controls fresh In a preferred embodiment, a pressurized fiber filter (7) is arranged in the first line (5) between the digester (5a) and the evaporator (6) to allow fiber removal from the black liquor flow.
    In a preferred embodiment, the evaporator (6) is a falling film evaporator provided. with a plurality of heat exchange elements (9) consisting of plates or tubes, along the outer surfaces of which the black liquor removed from the digester is arranged to flow.
    In a preferred embodiment, said at least one evaporator (6) consists of two or more evaporators or of a multi-stage evaporator which generates steam with different temperatures, steam lines directing said steam to the digester (5a) to heat the fibrous material. Description of the drawing Figure 1 schematically shows a system according to the invention.
    Detailed Description of Preferred Embodiments Figure 1 shows a system for generating steam in a cooking plant and treating black liquor so that the heating efficiency of the cooking process is improved.
    The fiber line system comprises a chip silo 10, in which basing of wood chips or other cellulosic material with steam from a line 2 takes place, liquid is added to form a slurry, after which the slurry is pressurized (this section is also called a feed system), after which a continuous digester 5a (this section is also referred to as a cooking system) is provided.
    Before the boiler 5a, the slurry may optionally be fed to and treated in one or more treatment vessels (may be an impregnation vessel, a prehydrolysis process vessel or some other vessels, not shown).
    The slurry of chips and cooking liquid is fed through. a line '3 to the top of the cooker 5a. Only the components that. are important for the invention are shown in the drawing, and other types of chip base or feed or boiler circulations may of course be provided in the boiler system. At least one black liquor flow (typically at a temperature of 120 - 160 ° C and at a dry matter content of 12 - 17%), is drawn from the digester 5a through a line 4 and fed further through a line 5 into an evaporator 6. Optionally, a pressurized fiber filter 7 may be provided in the conduit 5 between the digester 5a and the evaporator 6 to allow fiber removal from the black liquor flow to a level of about 40 ppm upon departure from the filter. The fibrous material removed from the filter would be in the form of a slurry to be returned to the digester 5a or to the feed system.
    According to the invention, the black liquor is evaporated in the evaporator 6. Fresh steam (the steam pressure is typically 6 - 17 bar (g) and the steam can be extract steam from a turbine) is fed through a line 8 to heat exchange element 9. The evaporator is typically a 10 15 20 25 30 35 10 case film evaporators such as. is provided with a plurality of heat exchange elements consisting of plates or tubes. The black liquor which is evaporated, in other words the black liquor which is removed from the digester 5a, is caused to flow along the outer surfaces of the heat exchange elements 9. The secondary steam generated in the evaporator 6 is led through a line 11 to the top of the boiler 5a to be used as heat steam. The steam typically has a temperature that exceeds the boiling temperature so that the fibrous material is heated to the boiling temperature with the steam passed through the steam inlet opening of the boiler 5a which communicates with the steam space of the evaporator 6. The black liquor can also be evaporated in two or more and vapors with different evaporators or in a multi-stage evaporator, temperatures are generated and can be used to heat the fibrous material in the digester 5a. The solids content of the black liquor is increased in accordance with the total evaporation in the evaporator (s). The fresh steam is condensed in the evaporator, and the fresh steam condensate produced is clean and it can be led through a line 12 to the factory's recovery boiler plant, where it can be used as feed water without any purification process.
    The amount of black liquor to be evaporated depends on the steam flow required in the digester 5a. It is not advantageous to generate excess black liquor vapor during evaporation by using fresh steam, as it would impair the factory's heat economy.
    By using the steam from the black liquor evaporator 6 in the digester 5a for heating fibrous material, better heat economy is achieved, since the black liquor is not diluted by adding fresh steam in the digester 5a.
    Hot black liquor drawn by the digester 5a typically at a temperature of 120 - 160 ° C and at a dry matter content of 12 - 17% is also passed through genius lines 14, 13 to a relaxation vessel 15, where the lye is used to produce relaxation steam, 100 - 130 ° C , pressure is typically reduced by. a temperature of and relaxed black liquor, the dry matter content of which can be increased by 2 - 4% during relaxation. Preferably, one or more black liquor flows are combined, which. drawn from the digester 5a through an outlet or several outlets and through the conduits 4, 14, with the evaporated black liquor from the evaporator 6. The flow rate of (kg / s) of the evaporated black liquor is typically less than the black liquor coming directly from the digester 5a to it is possible to direct the evaporated black liquor directly to the factory's evaporation plant, but it is preferable to mix it with non-evaporated black liquor in order to be able to utilize all available heat at a reasonable temperature level.
    The relaxed black liquor is passed through a line 18 to the factory's evaporation plant, where the black liquor is concentrated to a high dry matter content before incineration in a recycling boiler takes place.
    The energy in the relaxation steam in line 16 is recovered in a reboiler 17, in which. the steam passes in an indirect heat exchange relationship with "pure" liquid free of volatile compounds to heat the water above its boiling point or relaxation point in order to produce pure, odorless steam free of volatile compounds. The pure liquid. fed through a line 21. It may typically be evaporator condensate, desalinated water, the boiler feed water or a sufficiently pure water fraction. The pure steam produced in the reboiler has a substantially lower amount of non-condensable gases than the steam produced by direct relaxation of black liquor. The pure steam in line 2 is preferably used for pre-treatment of wood chips with steam, for example in chip silo 10. When the steam is used for treatment of chips, the load of volatile compounds that need to be collected and treated with the factory NCG system is reduced, as the steam does not cause volatile compounds to the process of astonishment.
    The relaxation vapor from the black liquor relaxation vessel contains volatile compounds, such as sulfur compounds. These compounds are fed to a crude condensate and to a stream of concentrated uncondensable gases (CNCG) generated in the reboiler. The crude condensate is passed from the reboiler through a line 19 to the evaporator, where it is treated in a manner to which the CNCG flow itself is directed. through a line 20 to a capacitor, for example to the boiler auxiliary capacitor (not shown).
    The present invention has at least the following advantages: - The overall heat economy of the factory will be improved, as the dry matter content in the deductions led to the factory's evaporation plant will increase. Increased dry matter content is a consequence of the relaxation of the fume hoods and the fact that steam is not used directly in the boiler. Steam consumption and capacity requirements are reduced in the evaporation plant.
    - The investment costs of the evaporation plant are reduced due to the lower capacity requirement. - Recirculation of fresh steam condensate increases and thus reduces the factory's total steam consumption.
    - Methanol recovery from the factory's total system is improved, as the first evaporated fractions from the black liquor are to be heat exchangers (evaporate and condense in specialized reboilers).
    权利要求:
    Claims (14)
    [1] 1. A method for generating steam in a digester plant of a chemical pulp mill, in which methoda) black liquor is produced in the digester system,b) a first stream of black liquor is extracted from the digester and evaporated us-ing fresh steam as a heating medium to generate vapor required in the digesterprocess and evaporated black liquor having an increased dry solids content,c) the vapor from the evaporation in step b) is used for heating fibrous material inthe digester,d) a second stream of black liquor extracted from the digester is flashed to gen-erate flashed black liquor and flash vapor, which is introduced to at least oneheat exchanger, preferably a reboiler, into an indirect heat exchange contact witha clean evaporable liquid to produce clean steam,e) the clean steam from step d) is used for steaming chips, and f) the flashed black liquor from step d) is led to further evaporation.
    [2] 2. A method according to claim 1, characterized in that in step d) is practiced so thatthe evaporated black liquor from step b) and the second stream of black liquor ex- tracted from the digester are combined before or during the flashing.
    [3] 3. A method according to claim 1 or 2,, characterized in that the evaporated blackliquor from step a) has a higher dry solids content than the flashed black liquor from step d).
    [4] 4. A method according to any one of the preceding claims, characterized in that the clean evaporable liquid in step d) is evaporator condensate.
    [5] 5. A method according to any one of the preceding claims, characterized in that thefresh steam is condensed in the evaporation in step b) and fresh steam condensate thus produced is led to the mill's recovery boiler plant where it is used as feed water.
    [6] 6. A method according to any one of the preceding claims, characterized in that stepf) is practiced so that the flashed black liquor from step d) is led together with the evaporated black liquor from step b) to further evaporation. 11
    [7] 7. Afiberline system for production of chemical cellulose pulp, comprising a chip bin(10) where steaming of a cellulose material occurs using clean steam from a steamline (2); a feed system where liquid is added to the cellulose material to form a slurry,followed by pressurization of the slurry; optionally one or more treatment vesselswhere the slurry is treated prior to cooking; and a continuous digester (5a) for cook-ing the slurry, said digester being connected to a first line (4,5) for withdrawing atleast one black liquor stream from the digester (5a) and feeding it into at least oneevaporator (6), in which evaporator (6) the black liquor is evaporated to generatesecondary vapor and evaporated black liquor, and to a second line (14, 13) for with-drawing at least one black liquor stream from the digester (5a) and feeding it to aflash tank (15), in which flash tank the pressure of the liquor is decreased to produceflash vapor and flashed black liquor; said evaporator (6) further being connected to asteam Withdrawal line (1 1) for directing secondary vapor generated in the evaporator(6) to the digester inlet, where said steam is used as heating steam for heating fibrousmaterial in the slurry, and to a line for withdrawing evaporated black liquor from theevaporator (6) and feeding it to a flash tank (15), in which flash tank the pressure of theliquor is decreased to produce flash vapor and flashed black liquor; said flash tank (15)further being connected to a line (18) for withdrawing flashed black liquor and feeding itto the evaporation plant of the mill, and to a vapor line (16) for directing flash vapor to aheat exchanger (17), preferably a reboiler, where the vapor produces clean steam byindirect heat exchange with a clean, evaporable liquid; said heat exchanger (17) furtherbeing connected to a steam line (2) for withdrawing clean steam and directing it to thechip bin (10).
    [8] 8. A system according to claim 7, characterized in that said line for withdrawing eva-porated black liquor from the evaporator (6) and either said first line (4) or said secondline (14, 13) for withdrawing at least one black liquor stream from the digester (5a), orboth, are combined for feeding these liquids to said flash tank (15), or are individuallydirected to said flash tank (15).
    [9] 9. A system according to any one of claims 7-8, characterized in that the evaporatoris further connected to a steam supply line (8) for supplying fresh steam to the eva-porator (6) to heat the slurry, and to a condensate line (12) for withdrawing conden-sated fresh steam from the evaporator (6), which condensate line (12) is directing theevaporator condensate to a line (21 ) for supplying clean, evaporable liquid to the heat exchange system (17). 12
    [10] 10. A system according to any one of claims 7-9, characterized in that the evapora-tor (6) and the flash tank (15) are arranged so as to provide evaporated black liquor having a higher dry so|ids content than the flashed black liquor.
    [11] 11. A system according to any one of claims 7-10, characterized in that the evapora-tor is connected to a steam supply line (8) for supplying fresh steam to the evapora-tor (6) to heat the slurry, and to a condensate line (12) for withdrawing condensatedfresh steam from the evaporator (6), which condensate line (12) is directing the fresh steam condensate to the mill's recovery boiler plant as feed water.
    [12] 12. A system according to any one of claims 7-11, characterized in that a pressu-rized fiber filter (7) is located in the first line (5) betvveen the digester (5a) and the evaporator (6) to allow the removal of fiber from the black liquor stream.
    [13] 13. A system according to any one of claims 7-12, characterized in that the evapora-tor (6) is a falling film evaporator which has a plurality of plate or tube heat exchangeelements (9), along the outer surfaces of which the black liquor discharged from the digester is arranged to flow.
    [14] 14. A system according to any one of claims 7-13, characterized in that said at leastone evaporator (6) is constituted by two or more evaporators or a multistage evaporatorgenerating vapors having different temperatures, wherein vapor lines are directing said vapors to the digester (5a) for heating the fibrous material.
    类似技术:
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    同族专利:
    公开号 | 公开日
    CN101798771A|2010-08-11|
    US20100236733A1|2010-09-23|
    FI122983B|2012-09-28|
    JP5734572B2|2015-06-17|
    RU2519939C2|2014-06-20|
    CL2010000106A1|2010-12-31|
    BRPI1000226A2|2011-03-29|
    US8512514B2|2013-08-20|
    JP2010180523A|2010-08-19|
    SE534546C2|2011-09-27|
    CA2692090A1|2010-08-09|
    FI20090039A0|2009-02-09|
    CA2692090C|2017-07-25|
    CN101798771B|2014-06-04|
    RU2010104385A|2011-09-20|
    BRPI1000226B1|2020-04-28|
    FI20090039A|2010-08-10|
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    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    FI20090039A|FI122983B|2009-02-09|2009-02-09|A process for steam generation at a pulp mill digester|
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