EP0313730A1 - Vorrichtung und Verfahren zur Herabsetzung der Krustenbildung in Aufschlussverfahren - Google Patents

Vorrichtung und Verfahren zur Herabsetzung der Krustenbildung in Aufschlussverfahren Download PDF

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Publication number
EP0313730A1
EP0313730A1 EP88111367A EP88111367A EP0313730A1 EP 0313730 A1 EP0313730 A1 EP 0313730A1 EP 88111367 A EP88111367 A EP 88111367A EP 88111367 A EP88111367 A EP 88111367A EP 0313730 A1 EP0313730 A1 EP 0313730A1
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EP
European Patent Office
Prior art keywords
liquor
digester
scale
vessel
heat exchanger
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.)
Withdrawn
Application number
EP88111367A
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English (en)
French (fr)
Inventor
Larry A. Wilhelmsen
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.)
Kamyr Inc
Original Assignee
Kamyr Inc
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Kamyr Inc filed Critical Kamyr Inc
Publication of EP0313730A1 publication Critical patent/EP0313730A1/de
Withdrawn legal-status Critical Current

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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
    • D21C3/00—Pulping cellulose-containing materials
    • D21C3/22—Other features of pulping processes
    • D21C3/226—Use of compounds avoiding scale formation
    • 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

Definitions

  • the present invention relates to apparatus and methods for reducing the formation of scale in pulping operations and particularly relates to apparatus and methods associated with the digester of a continuous cooking system for pulp for thermally deactivating a scale-forming constituent, e.g., calcium carbonate, of the liquor whereby a calcium-lean liquor is provided the pulping operation.
  • a scale-forming constituent e.g., calcium carbonate
  • the scale can form in various zones of the digester, for example, in the upper cooking zone and in the heaters. Scale also appears downstream in the cooking, extraction and quench zones, evaporators and in other system parts. Scale buildup in these various zones and parts of the pulping operation have various deleterious effects on its overall operation. For example, scale buildup on screens inhibits liquid flow. As a further example, heater tubes in the heat exchangers are frequently blocked and the rate of heat exchange deteriorates with scale buildup. Thus, the overall efficiency of the process generally diminishes as scale builds up.
  • one or more sacrificial retention vessels are introduced into the pulping system, preferably at a location adjacent or directly downstream of one or more areas of the system at which temperatures above this predetermined temperature are obtained.
  • a slurry temperature in excess of this predetermined temperature occurs immediately after the lower cooking circulation heater. This happens to correspond to the hottest point in a continuous digester system.
  • Other areas in a single-vessel digester where such temperatures occur include the inlet and outlet of the upper heater and the inlet to the lower heater. In a two-vessel digester, such areas would occur adjacent the inlet or outlet of the bottom circulation heaters.
  • the calcium can be made to precipitate as calcium carbonate and either plate out on the walls of the retention vessel or be carried through the pulping system with the cellulosic material.
  • the scale-forming constituent is weaned from the liquor such that when the liquor is returned to the pulping system, the slurry constitutes a mixture lean of scale-forming constituents.
  • This scale-forming constituent deactivating vessel can be readily taken off-line, cleaned and returned to the system without system downtime. This can be accomplished simply by diverting the liquor flow from the heat exchanger directly back into the digester while the retention vessel is being cleaned. (Present continuous digester systems flow the liquor from the heat exchanger directly back into the digester)
  • an additional retention vessel may be used whereby thermal deactivation of the scale-forming constituent may be continued by flowing the liquor to the additional retention vessel while the off-line retention vessel is cleaned.
  • downtime for cleaning the pulping system is greatly reduced or completely eliminated.
  • Chemical addition and its attendant costs are greatly reduced or completely eliminated by the present system. More importantly, the deleterious effects of scaling are minimized or eliminated, thereby reducing or eliminating operational instabilities, mechanical system breakdowns and decreased pulp quality resultant from scaling.
  • the commonly used continuous digester pulping process may be readily adapted to the present scale-forming prevention system.
  • the liquor drawn from the heating zone of the digester, and either before or after passing through the heat exchanger external to the digester, is disposed for a predetermined time period in the retention vessel prior to its return to the digester.
  • retention vessel external to the digester calcium precipitates out of solution and forms as scale on the surfaces of the vessel or forms an insoluble chemical structure which passes through the system without deposition as scale.
  • the liquor which is returned to the digester is thus a liquor lean of the scale-forming constituent, i.e., calcium. Consequently, the major system components of the digester are not contacted with a liquor rich in calcium-originated scale-forming constituents.
  • the precipitated scale-forming constituents may be returned to the slurry in the digester without scaling out on the surfaces of the retention vessel.
  • the slurry with the precipitated calcium would flow through the system without forming scale on its component parts.
  • a method for reducing the formation of scale in an apparatus for treating cellulosic material including a treatment vessel, for example a digester, containing a slurry of cellulosic chip material in a liquor, and a scale-forming constituent dissolved in the slurry, comprising the steps of separating at least part of the liquor together with at least a portion of the dissolved scale-forming constituent from the slurry, heating the separated liquor to a predetermined temperature and retaining the heated liquor at such temperature for a predetermined period of time effective to cause the scale-forming constituent portion to precipitate out of solution and recombining the heated liquor with the slurry in a treatment vessel whereby the precipitated scale-forming constituent portion is not available to form scale in the subsequent treatment of the cellulosic material.
  • apparatus for reducing the formation of scale in the treatment of cellulosic material comprising a treatment vessel for containing a slurry of cellulosic chip material and liquor in a scale-forming constituent dissolved in the slurry.
  • Means are carried by the treatment vessel for separating at least a portion of the liquor and a corresponding portion of the dissolved scale-forming constituent from the cellulosic material.
  • a heat exchanger external of the treatment vessel and in communication with the separating means is used to heat the separated liquor and scale-forming constituent portion to a predetermined temperature to cause the scale-forming constituent to precipitate out of solution.
  • a retention vessel is provided in communication with the heat exchanger for receiving the heated liquor and retaining it for a predetermined time period effective to cause the scale-forming constituent portion to precipitate out of solution.
  • Means are connected between the retention vessel and the treatment vessel for returning the heated liquor to the treatment vessel whereby the scale-forming constituent portion is not available to form scale in subsequent treatment of the cellulosic material in the apparatus.
  • the system may be operated with a single retention vessel.
  • the sacrificial retention vessel has sufficient scale deposits to warrant cleaning
  • the flow of heated liquor is diverted back directly to the digester rather than through the retention vessel.
  • the retention vessel may be cleaned while the digester is maintained in continuous operation until such time as the cleaned retention vessel may be placed back on-line.
  • an additional retention vessel may be provided such that the flow of heated liquor may be diverted from one to the other of the retention vessels.
  • the off-line retention vessel may be cleaned, while the on-line retention vessel continues to serve the function of reducing the scale-forming constituent in the liquor to provide a liquor for flow through the system which is lean in the scale-forming constituent.
  • the sole drawing Figure 1 is a schematic view of a pulping system constructed in accordance with the present invention.
  • a continuous cooking system modified to incorporate the present invention whereby the tendency of the slurry in the system to form scale is eliminated or reduced.
  • a conventional pulp cooking system including a chip hopper 10, a metering device 12, and a low-pressure feeder 14 for feeding cellulosic material, i.e., chips, into a pre-steaming vessel 16.
  • the pre-steamed chips are fed from pre-steamer 16 into a chip chute 18 and a high pressure feeder 20 is used to flow the chips through line 22 to a single-vessel digester, generally designated 24.
  • digester 24 includes a digester impregnation zone 26 for impregnation of the chips, a digester heating zone 28 with liquor circulation for heating the chips to cooking temperature, a digester cooking zone 30 for cooking the chips at the desired temperature, a washing zone 32, in this case, a countercurrent washing zone, and a lowermost cooling zone 34.
  • Cooking liquor and make-up liquor are supplied by a high-pressure pump 38 through a line 36 to the impregnation zone via line 40.
  • high-pressure steam is provided through line 42 to upper and lower heat exchangers 44 and 46 external to digester 24.
  • the steam indirectly heats the liquor withdrawn from the heating zone and the heated liquor is circulated back to the digester to elevate the temperature of the slurry to its cooking temperature.
  • Heat exchangers 44 and 46 communicate with upper and lower portions of the digester via lines 48 and 50, respectively, whereby liquor is pumped from the heating zone 28 into the heat exchangers 44 and 46, respectively, for return to the digester at an elevated temperature.
  • the cooled, cooked chips are discharged from digester 24 by way of line 52.
  • flash tanks 54 and 56 are employed to generate steam for pre-steaming the chips in the pre-steamer 16 and for hot water preparation.
  • drawing Figure 1 refers to a conventional part of a continuous cooking system.
  • scale-forming constituents are dissolved in the liquor and those constituents primarily emanate from the wood chips.
  • the scale-forming constituents are principally calcium, which conventionally scale-out as calcium carbonate on the surfaces of the cooking system.
  • the scale deposits normally occur within the digester and ancillary components, for example, on the screens, not shown, used to withdraw the liquor from the digester for flow to the heat exchangers, an associated piping and also on the heat exchangers themselves.
  • the liquor is weaned of the scale-forming constituent such that a scale-forming constituent lean liquor is returned to the digester 24.
  • a liquor retention vessel 60 for example, disposed between the outlet side of the lower heat exchanger 46 and the return line 66 for returning the heated liquor from heat exchanger 46 to the digester.
  • liquor heated by the upper heat exchanger 44 and returned to the digester is withdrawn by the lower heat exchanger 46 and heated to a still higher temperature at least above the temperature at which the scale-forming constituent precipitates out of solution.
  • the complexes of calcium with dissolved lignin compound are stable up to about 300 to 330°F.
  • the calcium complex is destroyed and calcium forms a scale with carbonate.
  • the liquor is introduced into the retention vessel 60 at such elevated temperature and retained in the retention vessel for a predetermined period of time.
  • the liquor is retained in the retention vessel at a temperature and for a predetermined time effective to precipitate the calcium from solution and enable the calcium carbonate to either plate-out on the walls of the vessel or be carried as an insoluble component of the slurry and chips through the cooking system when the liquor is returned to the digester.
  • the retention vessel 60 is a sacrificial vessel which weans the scale-forming constituent from the heated liquor such that the liquor returned from the retention vessel to the digester is scale-forming constituent lean or calcium deficient. Consequently, the liquor returned to the digester prior to cooking the chips has reduced scale-forming constituents, thus reducing the tendency of scale to form and deposit on various component parts of the digester and subsequent components of the cooking system.
  • any resultant scaling in the digester system when using the present invention appears to be a direct function of time and temperature during retention. For example, recent pilot tests have indicated a liquor retention time of fifteen minutes at 314-320°F reduced scaling by 75%, whereas a retention time of seven minutes at the same temperature range reduced scaling by 50%. These results are based on the location of the retention vessel in a two-vessel digester adjacent the inlet to the bottom circulation heaters. Consequently, it would appear that the temperature must be elevated above about 300°F for a period of time of five minutes or more. Preferably, a treatment time of 10-20 minutes at about 300-320°F is adequate to deactivate most calcium sealing liquors.
  • a second retention vessel 62 may be provided in parallel with the first vessel 60 such that one or the other of the retention vessels may be used on-line, thereby continuously affording a lean liquor, while the off-line retention vessel is cleaned of scale.
  • the liquor from the lower heat exchanger may be returned to the digester directly via line 70, bypassing retention vessel 60, for the limited period of time during which retention vessel 60 is off-line and being cleaned of scale. Once cleaned of scale, the retention vessel 60 would be returned in-line.
  • the retention vessel may be located, in a single-vessel digester system, adjacent the outlet or inlet of the upper heater or the outlet or inlet of the lower heater. In a two-vessel digester system, the retention vessel may be located adjacent the inlet or outlet of the bottom circulation heaters.

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  • Paper (AREA)
EP88111367A 1987-10-26 1988-07-15 Vorrichtung und Verfahren zur Herabsetzung der Krustenbildung in Aufschlussverfahren Withdrawn EP0313730A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US11208187A 1987-10-26 1987-10-26
US112081 1987-10-26

Publications (1)

Publication Number Publication Date
EP0313730A1 true EP0313730A1 (de) 1989-05-03

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP88111367A Withdrawn EP0313730A1 (de) 1987-10-26 1988-07-15 Vorrichtung und Verfahren zur Herabsetzung der Krustenbildung in Aufschlussverfahren

Country Status (6)

Country Link
EP (1) EP0313730A1 (de)
JP (1) JPH01148889A (de)
BR (1) BR8805152A (de)
CA (1) CA1299322C (de)
FI (1) FI883513A (de)
NO (1) NO883329L (de)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999002771A1 (en) * 1997-07-11 1999-01-21 Sunds Defibrator Pori Oy Method for the treatment of spent liquor from kraft pulp production
WO2000011263A1 (en) * 1998-08-21 2000-03-02 Andritz-Ahlstrom Oy Method of preventing scaling
WO2001025531A1 (en) * 1999-10-04 2001-04-12 Metso Chemical Pulping Oy Process for preventing scaling of heat transfer surfaces
WO2003060229A1 (en) * 2001-12-05 2003-07-24 Kvaerner Pulping Ab Process for continuously cooking chemical cellulose pulp
WO2006012286A1 (en) * 2004-06-26 2006-02-02 International Paper Company Methods to decrease scaling in digester systems
WO2013036190A1 (en) 2011-09-05 2013-03-14 Stora Enso Oyj Process for treating hardwood black liquor and hardwood black liquor treated according to the process
US8986504B1 (en) 2013-10-25 2015-03-24 International Paper Company Digester apparatus

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4763917B2 (ja) * 2001-05-29 2011-08-31 シチズンホールディングス株式会社 電子時計

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1945205A (en) * 1929-11-15 1934-01-30 Chemipulp Process Inc Paper manufacture
US2008839A (en) * 1932-09-15 1935-07-23 Samson Torsten Method and means for cleaning sulphite cellulose preheaters
FR2583079A1 (fr) * 1985-06-06 1986-12-12 Ahlstroem Foeretagen Procede et dispositif pour desactiver les lessives epuisees provenant de la fabrication de la pate a papier

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1945205A (en) * 1929-11-15 1934-01-30 Chemipulp Process Inc Paper manufacture
US2008839A (en) * 1932-09-15 1935-07-23 Samson Torsten Method and means for cleaning sulphite cellulose preheaters
FR2583079A1 (fr) * 1985-06-06 1986-12-12 Ahlstroem Foeretagen Procede et dispositif pour desactiver les lessives epuisees provenant de la fabrication de la pate a papier

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
TAPPI, vol. 63, no. 4, April 1980, pages 125-127, Atlanta, US; L.D. MARKHAM et al.: "Formation of calcium carbonate scale in a continuous digester" *

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999002771A1 (en) * 1997-07-11 1999-01-21 Sunds Defibrator Pori Oy Method for the treatment of spent liquor from kraft pulp production
WO2000011263A1 (en) * 1998-08-21 2000-03-02 Andritz-Ahlstrom Oy Method of preventing scaling
WO2001025531A1 (en) * 1999-10-04 2001-04-12 Metso Chemical Pulping Oy Process for preventing scaling of heat transfer surfaces
US6939439B1 (en) 1999-10-04 2005-09-06 Metso Chemical Pulping Oy Batch process for producing chemical pulp by removing and reintroducing calcium-containing spent liquor in the digester
WO2003060229A1 (en) * 2001-12-05 2003-07-24 Kvaerner Pulping Ab Process for continuously cooking chemical cellulose pulp
US7217338B2 (en) * 2001-12-05 2007-05-15 Kvaerner Pulping Ab Process for continuously cooking chemical cellulose pulp
WO2006012286A1 (en) * 2004-06-26 2006-02-02 International Paper Company Methods to decrease scaling in digester systems
US7241363B2 (en) 2004-06-26 2007-07-10 International Paper Company Methods to decrease scaling in digester systems
US7918967B2 (en) 2004-06-26 2011-04-05 International Paper Company Apparatus for decreasing scaling in digester systems
WO2013036190A1 (en) 2011-09-05 2013-03-14 Stora Enso Oyj Process for treating hardwood black liquor and hardwood black liquor treated according to the process
CN107503213A (zh) * 2011-09-05 2017-12-22 斯托拉恩索公司 处理硬木黑液的方法和根据这种方法处理的硬木黑液
US8986504B1 (en) 2013-10-25 2015-03-24 International Paper Company Digester apparatus

Also Published As

Publication number Publication date
NO883329L (no) 1989-04-27
FI883513A0 (fi) 1988-07-26
JPH01148889A (ja) 1989-06-12
BR8805152A (pt) 1989-05-16
CA1299322C (en) 1992-04-28
FI883513A (fi) 1989-04-27
NO883329D0 (no) 1988-07-27

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