WO2003016616A1 - Procede de lixiviation des cendres de filtres electriques dans une chaudiere de recuperation - Google Patents

Procede de lixiviation des cendres de filtres electriques dans une chaudiere de recuperation Download PDF

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Publication number
WO2003016616A1
WO2003016616A1 PCT/SE2002/001405 SE0201405W WO03016616A1 WO 2003016616 A1 WO2003016616 A1 WO 2003016616A1 SE 0201405 W SE0201405 W SE 0201405W WO 03016616 A1 WO03016616 A1 WO 03016616A1
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WO
WIPO (PCT)
Prior art keywords
electrical filter
leaching
filter ash
leaching tank
slurried
Prior art date
Application number
PCT/SE2002/001405
Other languages
English (en)
Inventor
Martin Wimby
Lars Olausson
Mikael Eriksson
Original Assignee
Kvaerner Power Ab
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 Kvaerner Power Ab filed Critical Kvaerner Power Ab
Priority to EP02751936A priority Critical patent/EP1444395B1/fr
Priority to DE60237629T priority patent/DE60237629D1/de
Priority to AT02751936T priority patent/ATE480662T1/de
Publication of WO2003016616A1 publication Critical patent/WO2003016616A1/fr

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Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C11/00—Regeneration of pulp liquors or effluent waste waters
    • D21C11/06—Treatment of pulp gases; Recovery of the heat content of the gases; Treatment of gases arising from various sources in pulp and paper mills; Regeneration of gaseous SO2, e.g. arising from liquors containing sulfur compounds
    • D21C11/063—Treatment of gas streams comprising solid matter, e.g. the ashes resulting from the combustion of black liquor
    • D21C11/066—Separation of solid compounds from these gases; further treatment of recovered products

Definitions

  • the invention relates to a process for leaching electrical filter ash from a recovery boiler in accordance with the preamble of Patent Claim 1.
  • Chlorides are also supplied to the pulp process by way of make-up chemicals and water.
  • the wood also has a content of chloride, even if this content is normally low.
  • Potassium is another non-process element which is principally supplied by way of the wood. Even low contents of the non-process elements such as potassium and chlorides in the flows entering the pulp process contribute to high contents in the pulp process since the process is becoming increasingly closed. Heavy metals are also supplied to some degree.
  • Potassium and chlorides contribute to clogging of the recovery boiler and to corrosion of heating surfaces. High contents of potassium and chlorides in the dust which is separated off from the flue gases from the recovery boiler have a detrimental effect on the efficiency of electrical filters.
  • the electrical filter ash which is separated off from the flue gases from the recovery boiler principally contains Na 2 S0 4 , it also contains, due to the process being closed, the highest concentrations of potassium and chlorides within the pulp mill.
  • One way of decreasing the content of potassium and chloride in the liquor stock in the pulp mill is to separate off part of the electrical filter ash from the chemical cycle in the mill. The separation can take place by the ash being dumped or by the ash being dissolved in water and then conducted to the water purification in the mill. These types of separation result in the heavy metals which are present in the electrical filter ash polluting the effluent.
  • the loss of sodium sulphate which occurs when electrical filter ash is separated off from the chemical cycle must be compensated for by supplying make-up chemicals.
  • SE,C, 504374 discloses a process in which the electrical filter ash is treated in a pressurized filter, in which process filtration and washing of the filter cake, and any possible leaching, take place in one and the same vessel. This process affords a good result as long as the filter can be kept free from clogging. Methods for cleaning the filter, with the cleaning taking place either during operation or in association with occasional interruptions in the filtration process, are required.
  • US,A, 3833462 discloses another process in which leaching takes place at pH 3-6 and 40-80°C, followed by filtration in a filter.
  • a proposed remedial measure was that of using a larger filter; while such a filter should, per se, extend the period of operation, the filter would have to be cleaned sooner or later. It was stated that it was possible to leach out, from the electrical filter ash, a good 89% of the sodium chloride that was present in the ash.
  • SE,A, 9504281 discloses another method which includes cooling.
  • the leaching is to take place at a pH of less than 10 and at a temperature greater than 20°C, typically at 30°C, after which the total quantity of slurried material undergoes cooling down to a temperature of less than 20 °C.
  • This process involves a need for cooling, with an attendant consumption of energy.
  • SE,A, 9603972 also discloses another method for leaching the electrical filter ash in which the latter firstly undergoes a leaching at at least 32°C, preferably in the vicinity of the boiling point of the aqueous solution, and in which a first substance which has crystallized out is returned, after separation, to the black liquor.
  • the leachate which is obtained from the process then also undergoes cooling down to approx. 10-15°C, after which a second substance which has crystallized out is likewise returned to the black liquor. While this system affords good leaching, it demands a high requirement of energy for the cooling even if the cooling is only required for the relatively small quantities constituted by the leachate.
  • the object of the invention is to obtain an improved process for recovering the useful chemicals, principally Na 2 S0 4 , in the electrical filter ash, which process does not suffer from the disadvantages of the prior art. While the improvement is first and foremost aimed at a lower energy consumption, it is also aimed at an improved degree of recovery of these useful chemicals without these chemicals being accompanied by a high proportion of chlorides, in particular, but also potassium. Another object is to obtain a continuous process which does not include filtrations, which filtration processes give rise to clogging problems and the need to regenerate the filter medium. An optimized process, which ensures favourable particle formation, should not require any filtration apparatus.
  • Fig. 1 shows an apparatus set-up which can be used for applying the process according to the invention when leaching electrical filter ash and subsequently separating off the solid phase.
  • Figure 1 shows an apparatus set-up which can be used in accordance with the process according to the invention.
  • Electrical filter ash, and liquid for leaching, and liquid phase which has been returned from a subsequent separation stage, and any chemicals which may be required so as to ensure that a suitable mixture is obtained are supplied to a first leaching tank 1.
  • the liquid for leaching can expediently be fabrication water from the bleaching department or the pulp drying machine, evaporation condensate or scrubber condensate. Water can also be used.
  • H 2 S0 can be supplied when the electrical filter ash contains high contents of Na 2 C0 3 .
  • the amount supplied is typically around 0.1 kg per 1.0 kg of electrical filter ash, i.e. in proportions of approx. 5-15% by weight.
  • the electrical filter ash can typically have a composition corresponding to the following;
  • the ash which is supplied to the leaching tank contains chloride ions and potassium ions.
  • the chloride content in the slurry is 2.0-7.0% by weight.
  • a pH in the interval pH 8-13, preferably 11-12, and consequently a strongly alkaline environment, is established in the leaching tank.
  • the mixture in the leaching tank should not exceed 1600 kg/m 3 , which thus sets an upper limit to the leaching process. If the consistency becomes too high, something which already begins to become apparent at 1570 kg/m 3 , the mixture then becomes increasingly difficult to pump and agitate with the stirrers. In particular, the initial admixing with the electrical filter ash using the first stirrer 11 is rendered more difficult at these concentrations.
  • a suitable lower concentration level corresponds to a mixture at 1450-1550 kg/m 3 .
  • the temperature should be kept within the interval 65-105°C, with a relatively high temperature within the interval 85-105°C being most favourable for the leaching process.
  • An optimum temperature both from the point of view of the process and the point of view of the apparatus is around 95°C.
  • leaching takes place under these process conditions (pH, concentration and temperature) for a relatively long time, within the interval 1-5 hours, preferably 2 hours, and while agitating gently, favourable process conditions are created for crystal growth of, in particular, a solid phase of Na 2 S0. It has been found that the crystals which are formed are distributed normally around a particle size of about 200 ⁇ m, which is a surprisingly good result which should be compared with what can be obtained using the energy-intensive cooling technique, where a crystal formation with particles normally distributed around 300 ⁇ m can be achieved under optimum conditions.
  • the leaching tank is shaped such that repeated gentle agitation is obtained over the whole volume. An initial agitation preferably takes place using a first stirrer 11 in connection with the electrical filter ash being supplied.
  • the mixture passes through at least one additional agitation zone and preferably two agitation zones.
  • This can be achieved by installing at least one double bottom 13 in the middle of the leaching tank.
  • An intermediate-stage stirrer 12a is arranged in an outlet from this double bottom 13, and a final-stage stirrer 12b is arranged in connection with the outlet from the leaching tank.
  • the dwell time in the leaching tank, between agitations, when the mixture is not subjected to direct agitation, should amount to at least 30% of the total dwell time in the leaching tank.
  • the intermediate-stage stirrer consequently acts on the slurried electrical filter ash when the latter has had a dwell time in the region of 30-70% of the total dwell time in the leaching tank, and the slurried electrical filter ash is subjected to a final-stage stirrer in a lower part of the leaching tank in connection with the outlet from the leaching tank.
  • the agitation should be gentle in order to ensure that particles which have already crystallized out are not broken, and a mechanical blade-equipped stirrer of the propeller type can expediently be used, in each respective position, for the intermediate-stage and final-stage stirrers, with both the stirrers being driven by the same shaft, which latter is driven at a moderate rotational speed in the region of 50-200 rpm, preferably around 80 rpm.
  • the slurry which is obtained in this way is pumped onwards, via the pump 4, to a centrifugation stage, in this present case a decanter centrifuge 2, where particles which have been formed, i.e. solid phase containing Na 2 S0 4 , are separated out as a dry fraction.
  • a decanter centrifuge affords a continuous process which does not require to be interrupted for regenerating the equipment (due to clogging, etc.).
  • the decanter centrifuge comprises, in a known manner, a rotating screw body 20, on which a worm 21 has been formed.
  • a casing 22, which also rotates, is arranged around the screw body 20.
  • the slurry is fed into the decanter centrifuge via the inlet 23 and, due to the rotation of the casing 22, the leached liquid is flung against the inside of the casing, where the heavier solid-particle fraction forms the outer layer 28, due to the centrifugal effect, and the liquid fraction forms the inner layer 29.
  • the liquid fraction leaves the decanter centrifuge via the spillway 25, while the screw feeds the solid fraction out towards the outlet 24. Due to the spillway 25 for the liquid fraction being located at a shorter distance from the axis of rotation than the outlet 24, it will be mainly the solid fraction which is transported by the worm 21 towards the outlet 24 via the conformed outlet of the casing.
  • the solid fraction which is obtained in this way, and which chiefly consists of Na 2 S0 4 , is given, by the decanter centrifuge, a dry substance content, in the dry substance fraction, which is in the interval 58-97%, and is then fed to a slurrying vessel 3, where it is admixed with black liquor/BL, for example, for forwarding to recovery, either via evaporation (not shown) or directly to the recovery boiler 18.
  • the solid phase also contains the greater part of the heavy metals present in the electrical filter ash, such as Ba, Pb, Cd, Co and Mn. The heavy metals are returned to the liquor cycle of the pulp process and are separated off in that section of the process which is most favourable.
  • the liquid fraction with its content of chloride ions and potassium ions, can in part be returned to the leaching tank 1 or in part, 26, forwarded to the effluent for external purification or further working- up.
  • a washing zone can be arranged in the decanter centrifuge. This is shown in the figure by means of a distribution ring 27 for washing liquid, which ring opens up radially inwards towards the layer 28 of the solid fraction which is passing by.
  • the washing liquid which is preferably pressurized, can expediently be the condensate (cond.) which is otherwise added to the top of the leaching tank in connection with the initial slurrying of the electrical filter ash.
  • the washing liquid is advantageously added at a position in the decanter centrifuge at which a separating effect is exerted on the liquid even after the position at which the washing liquid is added.
  • the chlorides are bled out via the liquid fraction from the decanter centrifuge, with 0.77 ton of liquid fraction per ton of electrical filter ash being forwarded to effluent or further working-up.
  • the liquid fraction which is separated off from the decanter centrifuge can typically have a content of 7% by weight of chlorides and 3.5% by weight of potassium, with the possibility of these levels building up in a closed process being avoided.

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  • Processing Of Solid Wastes (AREA)
  • Incineration Of Waste (AREA)
  • Electrostatic Separation (AREA)
  • Manufacture And Refinement Of Metals (AREA)

Abstract

L'invention concerne un procédé permettant d'éliminer les chlorures dans les cendres de filtres électriques. Ce procédé comprend en particulier une lixiviation suivie d'une séparation du composant cristallisé, ce dernier étant recyclé dans le circuit de traitement pour la production de lessive noire. Pour réaliser une séparation adéquate de la phase solide sous forme de Na2SO4 cristallin on soumet les cendres de filtres électriques en suspension dans un réservoir de lixiviation à une agitation douce répétée pendant un temps de séjour allant de 1 à 5 heures, cette étape étant directement suivie d'une centrifugation des cendres de filtres électriques lixiviées. La phase solide est transférée dans la lessive noire avant que celle-ci ne soit soumise à une phase d'évaporation finale et/ou récupérée dans la chaudière de récupération. Ce procédé permet une lixiviation efficace de 70 % du contenu en chlorures et 70 % du contenu en potassium des cendres de filtres électrique, assurant ainsi une utilisation améliorée des produits chimiques de traitement.
PCT/SE2002/001405 2001-08-14 2002-07-23 Procede de lixiviation des cendres de filtres electriques dans une chaudiere de recuperation WO2003016616A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
EP02751936A EP1444395B1 (fr) 2001-08-14 2002-07-23 Procede de lixiviation des cendres de filtres electriques dans une chaudiere de recuperation
DE60237629T DE60237629D1 (de) 2001-08-14 2002-07-23 Verfahren zum auslaugen von elektrofilter-asche aus einem rückgewinnungskessel
AT02751936T ATE480662T1 (de) 2001-08-14 2002-07-23 Verfahren zum auslaugen von elektrofilter-asche aus einem rückgewinnungskessel

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE0102717A SE0102717L (sv) 2001-08-14 2001-08-14 Förfarande för lakning av elfilteraska från en sodapanna
SE0102717-6 2001-08-14

Publications (1)

Publication Number Publication Date
WO2003016616A1 true WO2003016616A1 (fr) 2003-02-27

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE2002/001405 WO2003016616A1 (fr) 2001-08-14 2002-07-23 Procede de lixiviation des cendres de filtres electriques dans une chaudiere de recuperation

Country Status (5)

Country Link
EP (1) EP1444395B1 (fr)
AT (1) ATE480662T1 (fr)
DE (1) DE60237629D1 (fr)
SE (1) SE0102717L (fr)
WO (1) WO2003016616A1 (fr)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007035169A1 (fr) * 2005-09-21 2007-03-29 Metso Power Ab Procédé de nettoyage de gaz de carneau et de traitement de cendre provenant de la combustion de déchets
EP1798297A1 (fr) * 2005-12-16 2007-06-20 CTU - Conzepte Technik Umwelt AG Procédé pour le traitement de poussières contenant des métaux lourds
WO2008063123A1 (fr) * 2006-11-22 2008-05-29 Metso Power Ab Lixiviation de chlorure et de potassium à partir de cendres de filtre électrique
WO2011002354A1 (fr) * 2009-05-06 2011-01-06 Metso Power Ab Procédé de lixiviation améliorée de cendres de filtre électrostatique en provenance d'une chaudière de récupération
US11725341B2 (en) 2017-04-28 2023-08-15 Andritz Oy Method of treating fly ash of a recovery boiler
SE2230392A1 (en) * 2022-11-30 2024-05-31 Valmet Oy A method for removing non-process elements in a kraft pulping process

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9333468B2 (en) 2012-09-24 2016-05-10 Abengoa Bioenergy New Technologies, Llc Soak vessels and methods for impregnating biomass with liquid

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0745799A1 (fr) 1995-05-29 1996-12-04 Siemens Aktiengesellschaft Valve manuelle
EP0754799A2 (fr) * 1995-07-12 1997-01-22 Eka Chemicals AB Procédé de lixivation
US5840085A (en) * 1994-12-15 1998-11-24 Mitsubishi Jukogyo Kabushiki Kaisha Process for removing sodium chloride and potassium salts from ash collected from a soda recovery boiler
SE512504C2 (sv) 1999-04-23 2000-03-27 Kemira Kemi Ab Sätt att behandla aska
US6162408A (en) * 1996-10-31 2000-12-19 Kvaerner Pulping Ab Process for purifying ash which principally consists of sodium sulphate from a recovery boiler

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5840085A (en) * 1994-12-15 1998-11-24 Mitsubishi Jukogyo Kabushiki Kaisha Process for removing sodium chloride and potassium salts from ash collected from a soda recovery boiler
EP0745799A1 (fr) 1995-05-29 1996-12-04 Siemens Aktiengesellschaft Valve manuelle
EP0754799A2 (fr) * 1995-07-12 1997-01-22 Eka Chemicals AB Procédé de lixivation
US6162408A (en) * 1996-10-31 2000-12-19 Kvaerner Pulping Ab Process for purifying ash which principally consists of sodium sulphate from a recovery boiler
SE512504C2 (sv) 1999-04-23 2000-03-27 Kemira Kemi Ab Sätt att behandla aska

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007035169A1 (fr) * 2005-09-21 2007-03-29 Metso Power Ab Procédé de nettoyage de gaz de carneau et de traitement de cendre provenant de la combustion de déchets
EP1798297A1 (fr) * 2005-12-16 2007-06-20 CTU - Conzepte Technik Umwelt AG Procédé pour le traitement de poussières contenant des métaux lourds
WO2008063123A1 (fr) * 2006-11-22 2008-05-29 Metso Power Ab Lixiviation de chlorure et de potassium à partir de cendres de filtre électrique
WO2011002354A1 (fr) * 2009-05-06 2011-01-06 Metso Power Ab Procédé de lixiviation améliorée de cendres de filtre électrostatique en provenance d'une chaudière de récupération
EP2427598A1 (fr) * 2009-05-06 2012-03-14 Metso Power AB Procédé de lixiviation améliorée de cendres de filtre électrostatique en provenance d'une chaudière de récupération
CN102421961A (zh) * 2009-05-06 2012-04-18 美卓电力有限公司 改进的从回收锅炉中浸提静电除尘器灰的工艺
EP2427598A4 (fr) * 2009-05-06 2014-04-02 Metso Power Ab Procédé de lixiviation améliorée de cendres de filtre électrostatique en provenance d'une chaudière de récupération
US11725341B2 (en) 2017-04-28 2023-08-15 Andritz Oy Method of treating fly ash of a recovery boiler
SE546320C2 (en) * 2017-04-28 2024-10-01 Andritz Oy Method of treating fly ash of a recovery boiler
SE2230392A1 (en) * 2022-11-30 2024-05-31 Valmet Oy A method for removing non-process elements in a kraft pulping process

Also Published As

Publication number Publication date
ATE480662T1 (de) 2010-09-15
SE517587C2 (sv) 2002-06-25
SE0102717D0 (sv) 2001-08-14
EP1444395A1 (fr) 2004-08-11
SE0102717L (sv) 2002-06-25
EP1444395B1 (fr) 2010-09-08
DE60237629D1 (de) 2010-10-21

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