US3448003A - On-stream cleaning of wood chip digesters using chelating agents - Google Patents

On-stream cleaning of wood chip digesters using chelating agents Download PDF

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Publication number
US3448003A
US3448003A US517983A US3448003DA US3448003A US 3448003 A US3448003 A US 3448003A US 517983 A US517983 A US 517983A US 3448003D A US3448003D A US 3448003DA US 3448003 A US3448003 A US 3448003A
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United States
Prior art keywords
chelating agent
digester
liquor
per minute
gallons per
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Expired - Lifetime
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US517983A
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English (en)
Inventor
Wayne R Merriman
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Dow Chemical Co
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Dow Chemical Co
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Classifications

    • DTEXTILES; PAPER
    • D21PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21CPRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C3/00Pulping cellulose-containing materials
    • D21C3/22Other features of pulping processes
    • D21C3/226Use of compounds avoiding scale formation

Definitions

  • a continuous pulp digester such as a Kamyr digester, using hot, highly alkaline aqueous pulping liquor under pressure and having one or more heating-mixing cycles carried out continuously in the upper half of the digester, which has accumulated substantial deposits of hardness in the heating-mixing cycle equipment substantially restricting the flow of liquor through such equipment, is restored to proper operation by continuously feeding an aqueous solution of chelating agent into the digester along with the white liquor in suflicient concentration and for a long enough time to substantially remove the hardness deposits from the heating-mixing section.
  • Such treatment is carried out while the digester remains on-stream although it is generally preferred to reduce the throughput of the digester to about one-half during the treatment period, thus increasing the residence time of the chelating agent.
  • the invention relates to the cleaning of wood chip digesters and more particularly relates to the cleaning of continuous wood chip digesters, such as the Kamyr digesters, without taking such digesters out of service.
  • wood chips are often digested in a continuous process employing a highly alkaline aqueous liquor.
  • the process may be the soda process, employing caustic soda solution and a little sodium sulfide, or it may be the kraft process using an aqueous solution made up mainly from sodium sulfate, caustic, and water.
  • the modern digester is generally a vertical, substantially cylindrical pressurized reactor, e.g., feet in diameter and 100 feet high. Such digesters are mainly of the Kamyr or the Impco designs.
  • Cooking liquor called white liquor in the trade, is introduced near the top of the reactor against an operating pressure of about 110 to 120 pounds per square inch gauge.
  • Wood chips are also introduced at the top, or if a countercurrent system is employed, the wood chips are introduced near the bottom.
  • a mixture of pulp and liquor is drawn otf near the bottom of the reactor.
  • Heating and mixing is effected by withdrawing pulping mixture through a screen at one or more levels in the reactor, heating the sieved mixture, hereinafter referred to as pulp liquor, and returning the heated pulp liquor to the reactor through a downcomer to about the level of the point of withdrawal and spaced apart therefrom.
  • pulp liquor heating the sieved mixture
  • two such heating-mixing cycles are operated, each at a different vertical level of the reactor.
  • the volume of pulping liquor circulated through the heating-mixing cycle is from five to seven times the volume of cooking liquor being introduced into the digester.
  • Kraft cooking, continuous alkaline pulping, and digesters are further discussed in: Preparation and Treatment of Wood Pulps, J. S. Stephenson, editor, vol. I, McGraw- Hill Book Company (1950), pp. 364402, 453-57; Pulp and Paper Science and Technology, vol. I Pulp, C. E. Libby, editor, McGraw-Hill Book Company (1962), pp. 181-83; Studies in Continuous Alkaline Pulping, W. I. Nolan et al., TAPPI 34 No. 12:529-38 (1951); Experimental Development of High-Speed Continuous Alkaline Pulping, W. J. Nolan et al., Pulp and Paper Magazine of Canada 53 August: 98110 (1952); Studies in Continuous Alkaline Pulping, W. I. Nolan et al., TAPPI 35 No. 1l:5( 55 10 (1952); and Studies in Continuous Alkaline Pulping, W. J. Nolan, TAPPI 36 No. 9:406- 417 (1953).
  • a principal object of the invention is to provide a method of on-stream cleaning of a continuous process wood chip digester of the type which is subject to clogging or fouling by flow restricting mineral deposits.
  • Another object of the invention is to provide a method of periodic on-stream cleaning of a continuous wood chip digester subject to clogging or fouling by flow restricting mineral deposits whereby the digester can readily be cleaned frequently enough that the throughput does not fall materially below design capacity.
  • the method of the invention is based on the discovery that upon injecting a stable, high capacity chelating agent for polyvalent metal ions, which form flow restricting mineral deposits, into the heating-mixing cycle of an onstream continuous wood chip digester at a concentration greater than that required to chelate all such polyvalent metal ions in solution in the cooking mixture being cycled, at least part of the added chelating agent remains in the recirculatnig heatingmixing cycle for a substantial period of time and flow restricting mineral or hardness deposits on the heaters, downcomers, and intake screens of the cycle are substantially reduced or eliminated.
  • Any chelating agent for polyvalent metal ions will do providing that it is highly soluble in the hot (about 350 C.) aqueous alkaline pulping liquor, that it is stable in such solutions having an alkalinity of about pH 14 and that it has a high chelating capacity for mineral depositforming polyvalent metal ions such as calcium and magnesium ions.
  • High capacity chelating agents for polyvalent metal ions are those capable of chelating about 0.2 to 0.4 gram of calcium (expressed as CaCO per gram of chelating agent.
  • alkaline stable high-capacity chelating agents for polyvalent metal ions are: ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, and nitrilotriacetic acid. These compounds in the form of free acids are soluble in the hot alkaline pulping liquor and may be used in that form if facilities are available for injecting dry or slurried compound into the pulping liquor. Generally it is much more convenient to inject an aqueous solution of chelating agent into the pressurized system of the digester. To that end, the more suitable chelating agents should have a water solubility of at least about 10 percent by weight.
  • the chelating agent is dis solved in water to make at least a 10 percent by weight aqueous solution and more preferably about a 30 to 45 percent by weight solution. Less concentrated solutions may be used if desired, but the less concentrated solutions tend to unduly dilute the pulping mixture and cause greater interference with the pulping operation during the on-stream cleaning process.
  • the aqueous solution of chelating agent is injected into the apparatus of the heating-mixing cycle, generally by means of a T-connection to a line running from the screencovered intake inside the reactor to the heat exchangers used to heat the pulping liquor, though injection can be made at other points such as to the downcomers leading down into the reactor on the return side of the heatingmixing cycle. Usually injection is made into the cycle located in the upper cooking zone of the digester.
  • the flow of white liquor into the reactor and withdrawal of digested pulp mixture i.e., the throughput of the digester
  • the throughput of the digester are preferably cut down substantially so as to decrease the ratio of throughput to cycled pulp liquor.
  • higher concentrations of chelating agent can be built up in the heating-mixing cycle while reducing loss of chelating agent into the output of the digester.
  • the throughput is reduced to about 70 to 100 gallons per minute, achieving a compromise between high chelating agent concentration and substantially complete loss in production.
  • a 10 to 45 percent by weight aqueous solution of high capacity chelating agent is injected into the heating-mixing cycle at the rate of about 3 to 15 gallons per minute, and preferably at the rate of about 6 to 10 gallons per minute until from about 1,000 to 2,500 gallons have been used.
  • the injection rate is from about 1 to about gallons per minute per 500 gallons per minute recirculation flow rate, the latter being taken as design capacity.
  • the total quantity of chelating agent injected must be capable of chelating the entire quantity of deposit to be removed.
  • the quantity of chelating agent may be gauged by its effect and the addition may be stopped when design capacity of liquid flow of circulating pulp liquor in the heating-mixing cycle has been substantially restored, e.g., 90 percent of design capacity, as where rather thorough cleaning is being carried out.
  • design capacity of liquid flow of circulating pulp liquor in the heating-mixing cycle e.g. 90 percent of design capacity
  • EXAMPLE 2 A 430 ton per day Kamyr wood chip digester having a design throughput of 150 gallons per minute and a recirculation capacity in the heating-mixing cycle located in the upper cooking zone of 1,500 gallons per minute was clogged to the extent that recirculation capacity was only 600 gallons per minute. The flow rate of incoming white liquor was cut to 70-75 gallons per minute while maintaining production of pulp at a reduced rate. Then a 38 percent by weight aqueous solution of the tetrasodium salt of ethylenediaminetetraacetic acid was injected into the heating-mixing cycle at the level of the upper cooking zone in the line leading from the intake screen to the heater.
  • Injection was made at a rate varying from 9.5 to 12.5 gallons per minute. After about to gallons of the aqueous chelant solution had been injected, the recirculation flow rate in the upper zone heating-mixing cycle jumped from 600 to 1,150 gallons per minute. The balance of 2,000 gallons of aqueous chelant solution was added over about a 4 hour period. At the end of the injection period, the recirculation rate was 1,380 gallons per minute. The throughput of the digester was then brought back to 150 gallons per minute as normal operations were resumed. Five hours after the injection was completed the recirculation flow rate had risen still further to 1,400 gallons per minute.
  • the chelating agent employed may be injected in dry form into the stream of pulp liquor in the heating-mixing cycle. This may be accomplished by (1) placing the chelating agent in dry particulate form in an enclosed compartment which is provided with a communicating passage to the stream of pulp liquor and appropriate valving, (2) pressurizing the compartment and (3) screw extruding the particulate material directly into the stream of circulating pulp liquor.
  • While the present method of removing flow restricting deposits may be carried out on each of the recirculation means, i.e., heating-mixing cycles, of a digester, it is generally sufficient to carry out the process on the upper most recirculation means.
  • the lower recirculation means are less subject to fouling and are generally cleared by the chelating agent which gets into the pulping mixture during cleaning of the upper recirculation means.
  • an alkaline-stable high capacity chelating agent for polyvalent metal ion into the withdrawn pulping liquor in the recirculation means in sufficient amount and for a sufiicient time to substantially remove flow restricting mineral deposits from the recirculation means, said chelating agent being further characterized as being stable in hot aqueous alkaline pulping liquor having a pH of about 14, in having the capacity to chelate about 0.2 to 0.4 gram of calcium, expressed as CaCO per gram of chelating agent, and in having a water solubility of at least about percent by weight.
  • the chelating agent is employed as an aqueous solution having a concentration of at least 10 percent by weight and the aqueous solution is injected at a rate of from about 1 to 5 gallons per minute per 500 gallons per minute of withdrawn pulping liquor being recirculated for a sufficient time to substantially remove flow restricting mineral deposits from the recirculation means.
  • the chelating agent is a compound selected from the group consisting of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediamine triacetic acid and nitrilotriacetic acid and the ammonium and alkali metal salts thereof.

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  • Shaping Metal By Deep-Drawing, Or The Like (AREA)
US517983A 1966-01-03 1966-01-03 On-stream cleaning of wood chip digesters using chelating agents Expired - Lifetime US3448003A (en)

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US51798366A 1966-01-03 1966-01-03

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DE (1) DE1692845B2 (enrdf_load_html_response)
FI (1) FI48484C (enrdf_load_html_response)
GB (1) GB1125656A (enrdf_load_html_response)
NO (1) NO118527B (enrdf_load_html_response)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999020830A1 (fr) * 1997-10-17 1999-04-29 Solvay (Societe Anonyme) Fabrication de pate a papier chimique
US20030010458A1 (en) * 2001-06-06 2003-01-16 Jacob Owen Thompson Method for inhibiting calcium salt scale
WO2002099184A3 (en) * 2001-06-06 2003-02-20 Solutia Inc Method and aqueous composition for the production of improved pulp
US20030075290A1 (en) * 2001-06-06 2003-04-24 Thompson Jacob Owen Method for inhibiting calcium salt scale

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2851355A (en) * 1951-02-28 1958-09-09 Waldhof Zellstoff Fab Process for the preparation of semi-cellulose
US2920010A (en) * 1956-11-05 1960-01-05 Voiret Eugene Gilbert Manufacture of wood pulp
US2947657A (en) * 1956-02-18 1960-08-02 Saint Gobain Extraction of cellulose from vegetable matter
US3071504A (en) * 1958-05-12 1963-01-01 Us Movidyn Corp Paper mill boil out methods and compositions
US3143458A (en) * 1961-10-24 1964-08-04 Stevens Paper Mills Inc Method of making electrical paper

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2851355A (en) * 1951-02-28 1958-09-09 Waldhof Zellstoff Fab Process for the preparation of semi-cellulose
US2947657A (en) * 1956-02-18 1960-08-02 Saint Gobain Extraction of cellulose from vegetable matter
US2920010A (en) * 1956-11-05 1960-01-05 Voiret Eugene Gilbert Manufacture of wood pulp
US3071504A (en) * 1958-05-12 1963-01-01 Us Movidyn Corp Paper mill boil out methods and compositions
US3143458A (en) * 1961-10-24 1964-08-04 Stevens Paper Mills Inc Method of making electrical paper

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999020830A1 (fr) * 1997-10-17 1999-04-29 Solvay (Societe Anonyme) Fabrication de pate a papier chimique
BE1011503A3 (fr) * 1997-10-17 1999-10-05 Solvay Interox Fabrication de pate a papier chimique.
US20030010458A1 (en) * 2001-06-06 2003-01-16 Jacob Owen Thompson Method for inhibiting calcium salt scale
WO2002099184A3 (en) * 2001-06-06 2003-02-20 Solutia Inc Method and aqueous composition for the production of improved pulp
US20030075290A1 (en) * 2001-06-06 2003-04-24 Thompson Jacob Owen Method for inhibiting calcium salt scale
US20030221805A1 (en) * 2001-06-06 2003-12-04 Thompson Jacob Owen Method for the production of improved pulp
US20040256070A1 (en) * 2001-06-06 2004-12-23 Thompson Jacob Owen Method for inhibiting calcium salt scale
US6869503B2 (en) 2001-06-06 2005-03-22 Solutia, Inc. Composition for inhibiting calcium salt scale
US6890404B2 (en) 2001-06-06 2005-05-10 Solutia, Inc. Composition for the production of improved pulp
US20050115692A1 (en) * 2001-06-06 2005-06-02 Thompson Jacob O. Method for the production of improved pulp
US20050126727A1 (en) * 2001-06-06 2005-06-16 Thompson Jacob O. Method for inhibiting calcium salt scale
US20060144533A1 (en) * 2001-06-06 2006-07-06 Thompson Jacob O Method for the production of improved pulp
US7097739B2 (en) 2001-06-06 2006-08-29 Solutia Inc. Method for the production of improved pulp
US7172677B2 (en) 2001-06-06 2007-02-06 Solutia Inc. Method for inhibiting calcium salt scale
US7300542B2 (en) 2001-06-06 2007-11-27 Thermophos Trading Gmbh Method for inhibiting calcium salt scale
USRE41552E1 (en) 2001-06-06 2010-08-24 Thermphos Trading Gmbh Composition for the production of improved pulp

Also Published As

Publication number Publication date
NO118527B (enrdf_load_html_response) 1970-01-05
FI48484C (fi) 1974-10-10
FI48484B (enrdf_load_html_response) 1974-07-01
GB1125656A (en) 1968-08-28
DE1692845A1 (de) 1971-10-21
DE1692845B2 (de) 1977-06-02

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