US3414038A - Heat recovery method and apparatus - Google Patents

Heat recovery method and apparatus Download PDF

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Publication number
US3414038A
US3414038A US465635A US46563565A US3414038A US 3414038 A US3414038 A US 3414038A US 465635 A US465635 A US 465635A US 46563565 A US46563565 A US 46563565A US 3414038 A US3414038 A US 3414038A
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United States
Prior art keywords
liquor
evaporator
steam
flash
condensate
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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.)
Expired - Lifetime
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US465635A
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English (en)
Inventor
Laakso Oliver Armas
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Metso Fiber Karlstad AB
Original Assignee
Kamyr AB
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Application filed by Kamyr AB filed Critical Kamyr AB
Priority to US465635A priority Critical patent/US3414038A/en
Priority to SE8220/66A priority patent/SE301413B/xx
Priority to FI01632/66A priority patent/FI48622B/fi
Priority to FR66218A priority patent/FR1484902A/fr
Priority to DE19661692823 priority patent/DE1692823B1/de
Application granted granted Critical
Publication of US3414038A publication Critical patent/US3414038A/en
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    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/06—Flash distillation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/10—Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S159/00—Concentrating evaporators
    • Y10S159/22—Condensate flashing

Definitions

  • a process and apparatus are disclosed for concentrating the black liquor diluent from a cellulose digester.
  • the diluent from the digester is flashed and the residue liquor and flash vapor are passed into indirect heat exchange in an evaporator.
  • the released vapor from the evaporator is passed to a steaming vessel to steam wood chips fed to the digester.
  • the partially concentrated liquor from the evaporator is passed to another flasher and the flash vapor and further concentrated liquor from the second flasher are again passed in indirect heat exchange in a second evaporator.
  • the present invention ⁇ relates to the digestion of cellulose. More particularly, the invention is concerned with a novel process and apparatus for black liquor extraction from the cellulose digester so as to utilize most effectively the heat in the extracted liquor.
  • the black liquor from the digester at elevated temperature and pressure is fed to a first flash tank where the pressure is substantially reduced Because of the pressure reduction, some of the black liquor flashes into steam and this steam is discharged from the flash tank into a steaming vessel for the purpose of preheating wood chips befone they are passed into the digester.
  • the black liquor which remains unvaporized in the first flash tank is then fed to a second flash tank where the pressure is again dropped, usually to about atmospheric pressure.
  • This pressure reduction causes still more of the liquor to flash into steam which is subsequently condensed and then lprocessed for turpentine recovery or the like.
  • the liquor which remains is pumped to storage from which it may also be subsequently processed for re-use, usually after further concentration.
  • the above-described system does not represent the optimum in heat recovery from the hot black liquor discharged from the digester.
  • the solids concentration of the black liquor is obviously increased, it is still quite low and a higher solids concentration is desirable.
  • the solids content of the black liquor discharged from the second flash tank under normal operating conditions may be only around 16.6% solids. This represents an increase of only 1.6% in the solids content of the black liquor and it is usually necessary to further concentrate the liquor if it is to be processed for chemical recovery or re-use.
  • the condensate obtained by condensing the flash from the second flash tank does not readily lend itself to processing for the recovery of turpentine.
  • the principal object of the present invention is to so modify the above described system that there is maximum use of the heat available in the black liquor discharged from the digester.
  • a more specific object of the invention is to improve the utilization of the heat in the black liquor so that the final liquor has a higher solids content and substantially lower temperature than heretofore possible.
  • Another object is to provide certain improvements in the processing of black liquor by means of flash tanks in order that the concentrated black liquor and flash condensate discharged from the system are more readily processible for re-use or the recovery of valuable constituents therein, e.g. turpentine. n
  • the present invention contemplates employing an evaporator after each flash tank and using the steam or vapor formed by flashing to evaporate water from the remaining liquor. More particularly, the present process includes the following steps:
  • the black liquor ultimately discharged from the system is of higher concentration, lower temperature and smaller volume than in the case where the evaporators are omitted.
  • the discharged black liquor is consequently easier and better to handle and process.
  • the hnal condensate is of substantially greater volume and more preferable to handle for turpentine recovery than the corresponding condensate obtained under comparative conditions without using the evaporators as proposed.
  • FIGURE 1 illustrates diagrammatically the system previously employed for processing digestion liquor
  • FIGURE 2 illustrates the present modification of said system.
  • FIGURES 1 and 2 For ease of understanding the systems of FIGURES 1 and 2 are described on the basis of a black liquor supply of 480,430 pounds per hour (at 325 F., 165-200 p.s.i.g. and 15% solids). Other quantities and temperatures recited are determined by calculation based on standard data for heats of vaporization, specific heats for black liquor at indicated temperatures and percent solids, boiling points at percent solids, etc. (e.g. Tappi, lune 1953). For convenience, specific pressures, temperatures, material quantities and other conditions are given but it will be recognized that these can be widely varied provided the present invention concepts are employed.
  • the spent black liquor 1 from the digester is pumped to the first flash tank 2 where the pressure is abruptly reduced to 18 p.s.i.g. This results in the formation of 32,100 pounds per hour of steam (255 F.) which are fed to the steaming vessel 4 for the purpose of steaming wood chips before they are fed into the digester (not shown).
  • Second flash tank 6 is operated at a lower pressure than the first tank, e.g. atmospheric pressure p.s.i.g) as shown. This causes further flashing to occur with the formation of 15,000 pounds of steam per hour (212 F.).
  • This steam is fed to a suitable condenser 8 where it is condensed by cooling water supplied at 10 as shown.
  • the resulting condensate (15,000 pounds per hour) may be pumped by appropriate means 12 through a heat exchanger 14 if desired, to conventional turpentine recovery operations represented by the numeral 16.
  • the liquor remaining after the second flash (amounting to 433,330 pounds per hour on the basis of the present exemplication) is discharged at 16.6% solids and a temperature of 215 F. from tank 6 to the black liquor storage or other processing operations, broadly designated by the numeral 18.
  • FIGURE 2 the main difference over the system of FIGURE 1 is the use of first and second evaporators and 22, respectively.
  • Each of these evaporators receives black liquor from the preceding flash tank and some of the liquor is flashed off therein because of the reduced pressures which are employed. Additionally, however, steam formed in the ash tanks is used to evaporate water from the liquor. This makes possible the increased concentration of the black liquor discharged from the system.
  • spent black liquor 1 from the digester (480,430 pounds per hour at 325 F., 15% solids, 165-200 p.s.i.g.) is fed to the first flash tank 2 where the pressure is reduced to 25 p.s.i.g.
  • the resulting flash amounts to 27,000 pounds of steam per hour and this, optionally with flash from the heat exchanger 24 of the digestion operation (3,100 pounds per hour), is fed at a temperature of 268 F. into the steam chest or heating zone of the first evaporator 20.
  • the liquor which remains after the first ash (453,430 pounds per hour) is discharged (at 270 F. and 15.8% solids) from the bottom of flash tank 2 and pumped by pump 41 into evaporator 20.
  • some flashing occurs, as noted above, due to the fact that the evaporator is operated at a lower pressure (18 p.s.i.g.) than the first ash tank.
  • the liquor is heated by means of the steam from the flash tank 2 and, if used, the flash from the heater condensate 24. Assuming complete condensation of the flash used for heating, this results in the formation of 34,000 pounds per hour of steam (255 F., 18 p.s.i.g.) in the evaporator 20. This steam is fed to the steaming Vessel 4 to steam wood chips as aforesaid.
  • the liquor which remains unevaporated in the first evaporator (419,430 pounds per hour at 258 F. and 17.2% solids) is then fed into the second flash tank 6 which is operated under vacuum. This again results in flashing with the formation of 31,600 pounds per hour of steam at 173 F.
  • This steam is fed directly to the second evaporator 22 where it is used to indirectly heat liquor discharged from flash tank 6.
  • This liquor amounts to 387,830 pounds per hour (18.5% solids) and has a temperature of 176 F. as discharged from flash tank 6.
  • the liquor is pumped into evaporator 22 where, because of the lower pressure in the evaporator (e.g. 20" vacuum) some flashing of the liquor occurs (4,500 pounds per hour).
  • An additional 32,700 pounds per hour of water is evaporated from the liquor by indirectly heating the liquor in evaporator 22 with the flash vapor from flash tank 6 and with the flash vapor from condensate from the first evaporator 20.
  • Cooling water in the amount of 1,580 gallons per minute having an inlet temperature of F. is adequate for this purpose, the outlet temperature of the water being around F.
  • a steam educator 25 may be utilized in association with condenser 8 as shown to ncrease the effectiveness of the condensation.
  • the steam used to effect the evaporation in evaporators 20 and 22 is condensed as a result of the heat exchange with the liquor in the evaporators.
  • the condensate from evaporator 20 is pumped by pump 40 into the bottom of the second evaporator as shown by connecting line 26. With the material amounts :and other conditions used for exemplification herein, this means that 30,100 pounds per hour of condensate are fed from the first evaporator 20 to the bottom of the second evaporator 22.
  • This condensate and the condensate resulting from the condensation of steam (31,600 pounds per hour) fed into evaporator 22 at 20 inches of vacuum as shown at 27 give a total of 61,700 pounds per hour of condensate discharged at the bottom of evaporator 22.
  • This total condensate is pumped or otherwise fed into a condensate ash tank 28 operating at reduced pressure (e.g. 30 p.s.i.g.) with the formation of 800 pounds per hour of steam which is advantageously combined as shown by line 30 with the steam 31 from the second evaporator prior to condensing in condenser 8.
  • the condensate 34 amounts to 38,000 pounds per hour of condensate at 160 F. giving a total quantity of 98,900 pounds per hour when combined with the condensate 32 from tank 28.
  • This total condensate is then fed by pump means 12, optionally but not necessarily, through heat exchange means 14, to the turpentine recovery operation 16. It is to be noted that the amount of condensate fed to the turpentine recovery using the system of FIGURE 2 is much greater than that obtained with the system of FIGURE l. In both cases, the condensate is essentially water but it includes a valuable amount of turpentine which is more readily recoverable from the condensate obtained with the system shown in FIGURE 2.
  • the liquor which remains unevaporated in the second evaporator 22, is discharged from the evaporator and pumped by means 38 to the black liquor storage 18.
  • the liquor pumped to storage 18 amounts to 350,630 pounds per hour and has a temperature of 163 F. and a solids content of 20.2%. It will thus be noted that the solids concentration is substantially increased over that obtainable using the system of FIGURE 1 under comparative conditions (16.6% solids). The ternperature of the liquor is also markedly reduced thus showing more effective heat recovery from the black liquor starting material.
  • heater condensate flash 24 with the ash from the first flash tank 2 is optional although this seems to increase the overall efliciency of the system.
  • the heater condensate liash is obtained as follows: treating liquor (e.g. lye) is withdrawn from the heating zone of the digester, heated in a heat exchanger outside the digester and then fed back into the digester. This maintains a high heat content for the liquor.
  • the heat exchanger is supplied with steam to heat the liquor.
  • a process for the recovery of heat from the black liquor of a cellulose digester which comprises: (1) passing the black liquor at elevated temperature and pressure from the digester into a rst liash tank where the pressure is reduced so that part of the liquor is flashed off as steam; (2) discharging the unflashed liquor from said first liash tank into the vaporizing side of a first evaporator operated at lower pressure than said first flash tank whereby a part of said liquor is flashed off as steam; (3) passing the liquor in said first evaporator in indirect heat exchange relationship with the steam formed by flashing in said first flash tank whereby still more of said liquor is evaporated; (4) discharging the steam formed by flashing and evaporation in steps (2) and (3), respectively, from said first evaporator and utilizing said steam to steam wood chips prior to feeding the latter to said digester; (5) discharging the remaining black liquor from a first evaporator and passing the same into said second ash tank operating at a lower pressure than said first evaporator whereby
  • step (9) is further processed for turpentine recovery.
  • Apparatus for processing black liquor discharged from a cellulose digester which comprises a first flash tank, means for supplying black liquor from said digester to said flash tank whereby a portion of said liquor is vaporized, means for withdrawing vapor from said flash tank and means for discharging unliashed liquor therefrom, a first evaporator receiving residue liquor and liash vapor from said first flash tankV in indirect heat exchange relationship whereby part of said liquor is evaporated and said flash vapors are condensed, a steaming vessel for preheating wood chips prior to feeding the same to said digester, means for withdrawing the released vapor from the liquor side of said evaporator and feeding same to said vessel to heat ⁇ said wood chips, means for withdrawing vunevaporated liquor from said first evaporator; a second flash tank receiving said withdrawn unevaporated liquor to flash the same; a second evaporator for evaporating, by indirect heat exchange, unflashed liquor from said ⁇ second flash tank with the flash ⁇ vapors formed in
  • Apparatus according to claim 5 including a condensate ash tank receiving condensate from said first and second evaporators.

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  • Chemical Kinetics & Catalysis (AREA)
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US465635A 1965-06-21 1965-06-21 Heat recovery method and apparatus Expired - Lifetime US3414038A (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
US465635A US3414038A (en) 1965-06-21 1965-06-21 Heat recovery method and apparatus
SE8220/66A SE301413B (US07122603-20061017-C00187.png) 1965-06-21 1966-06-15
FI01632/66A FI48622B (US07122603-20061017-C00187.png) 1965-06-21 1966-06-20
FR66218A FR1484902A (fr) 1965-06-21 1966-06-21 Procédé et appareil de récupération thermique provenant d'un digesteur de cellulose
DE19661692823 DE1692823B1 (de) 1965-06-21 1966-06-21 Verfahren und Vorrichtung zur Waermerueckgewinnung aus der Schwarzlauge eines Zellstoffkochers durch Entspannungsverdampfung

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US465635A US3414038A (en) 1965-06-21 1965-06-21 Heat recovery method and apparatus

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US3414038A true US3414038A (en) 1968-12-03

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US (1) US3414038A (US07122603-20061017-C00187.png)
FI (1) FI48622B (US07122603-20061017-C00187.png)
SE (1) SE301413B (US07122603-20061017-C00187.png)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3921918A (en) * 1973-09-06 1975-11-25 Sca Development Ab Mechanical refining of fiber material including steam recycle
US4002525A (en) * 1975-03-13 1977-01-11 Flambeau Paper Company Chemical recovery from waste liquors utilizing indirect heat exchangers in multi-stage evaporation plus contact steam stripping
US4239589A (en) * 1978-10-02 1980-12-16 Air Products And Chemicals, Inc. Process for oxidation of black liquor
US4551198A (en) * 1982-03-30 1985-11-05 Kamyr, Inc. Method of flashing black liquor
US4909899A (en) * 1986-09-22 1990-03-20 A. Ahlstrom Corporation Method of concentrating sludges
US5112441A (en) * 1985-04-25 1992-05-12 Oy Tampella Ab Process for the recovery of heat and chemicals from spent liquor
US5174860A (en) * 1988-11-17 1992-12-29 Heiningen Adriaan R P Van Low temperature recovery of kraft black liquor
US5911853A (en) * 1997-09-11 1999-06-15 International Paper Company Method for treating paper mill condensate to reduce the amount of sulfur compounds therein
US6306252B1 (en) 1995-04-10 2001-10-23 Andritz-Ahlstrom Inc. Heat recovery from spent digester cooking liquor
US20030070627A1 (en) * 2001-09-20 2003-04-17 Eugene Sullivan Direct contact evaporator replacement
US20050115691A1 (en) * 2002-01-24 2005-06-02 Lindstroem Mikael Cooking of cellulose pulp in a cooking liquor containing preevaporated black liquor
US9127403B2 (en) 2013-05-28 2015-09-08 Andritz Inc. Flash tank with flared inlet insert and method for introducing flow into a flash tank

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE416969B (sv) * 1978-03-02 1981-02-16 Gloeersen Stig Sett vid overforing av fibermaterial fran en diskontinuerlig behandling till foljande behandlingar
SE463316B (sv) * 1988-01-14 1990-11-05 Ahlstroem Foeretagen Foerfarande och anordning foer indunstning av avlut i samband med kokning av cellulosahaltigt fibermaterial i en kontinuerlig kokare

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2896705A (en) * 1954-11-04 1959-07-28 Ramen Torsten Evaporation of liquids
US2941590A (en) * 1955-03-14 1960-06-21 Rosenblad Curt Fredrik Multiple evaporation methods
US3179159A (en) * 1960-10-19 1965-04-20 Ahlstroem Oy Procedure for evaporating waste lye from pulp
US3183145A (en) * 1962-06-22 1965-05-11 Jr Theron T Collins Odor control and heat recovery in wood pulping process
US3286763A (en) * 1964-10-19 1966-11-22 Jacoby Process Equipment Co In Recovering heat from a blow evaporator for use in a surface evaporator

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2896705A (en) * 1954-11-04 1959-07-28 Ramen Torsten Evaporation of liquids
US2941590A (en) * 1955-03-14 1960-06-21 Rosenblad Curt Fredrik Multiple evaporation methods
US3179159A (en) * 1960-10-19 1965-04-20 Ahlstroem Oy Procedure for evaporating waste lye from pulp
US3183145A (en) * 1962-06-22 1965-05-11 Jr Theron T Collins Odor control and heat recovery in wood pulping process
US3286763A (en) * 1964-10-19 1966-11-22 Jacoby Process Equipment Co In Recovering heat from a blow evaporator for use in a surface evaporator

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3921918A (en) * 1973-09-06 1975-11-25 Sca Development Ab Mechanical refining of fiber material including steam recycle
US4002525A (en) * 1975-03-13 1977-01-11 Flambeau Paper Company Chemical recovery from waste liquors utilizing indirect heat exchangers in multi-stage evaporation plus contact steam stripping
US4239589A (en) * 1978-10-02 1980-12-16 Air Products And Chemicals, Inc. Process for oxidation of black liquor
US4551198A (en) * 1982-03-30 1985-11-05 Kamyr, Inc. Method of flashing black liquor
US5112441A (en) * 1985-04-25 1992-05-12 Oy Tampella Ab Process for the recovery of heat and chemicals from spent liquor
US4909899A (en) * 1986-09-22 1990-03-20 A. Ahlstrom Corporation Method of concentrating sludges
US5174860A (en) * 1988-11-17 1992-12-29 Heiningen Adriaan R P Van Low temperature recovery of kraft black liquor
US6306252B1 (en) 1995-04-10 2001-10-23 Andritz-Ahlstrom Inc. Heat recovery from spent digester cooking liquor
US5911853A (en) * 1997-09-11 1999-06-15 International Paper Company Method for treating paper mill condensate to reduce the amount of sulfur compounds therein
US20030070627A1 (en) * 2001-09-20 2003-04-17 Eugene Sullivan Direct contact evaporator replacement
US20050115691A1 (en) * 2002-01-24 2005-06-02 Lindstroem Mikael Cooking of cellulose pulp in a cooking liquor containing preevaporated black liquor
US7351306B2 (en) * 2002-01-24 2008-04-01 Metso Fiber Karlstad Ab Cooking of cellulose pulp in a cooking liquor containing pre-evaporated black liquor
US9127403B2 (en) 2013-05-28 2015-09-08 Andritz Inc. Flash tank with flared inlet insert and method for introducing flow into a flash tank
US9284684B2 (en) 2013-05-28 2016-03-15 Andritz Inc. Flared inlet insert for introducing flow into a flash tank
RU2634893C2 (ru) * 2013-05-28 2017-11-07 Андритц Инк. Выпарной резервуар с развальцованной впускной вставкой

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FI48622B (US07122603-20061017-C00187.png) 1974-07-31
SE301413B (US07122603-20061017-C00187.png) 1968-06-04

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