WO2003027384A1 - Procede de recuperation des produits chimiques de trituration dans un traitement de trituration au sulfite alcalin et de production de vapeur - Google Patents

Procede de recuperation des produits chimiques de trituration dans un traitement de trituration au sulfite alcalin et de production de vapeur Download PDF

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Publication number
WO2003027384A1
WO2003027384A1 PCT/SE2002/001556 SE0201556W WO03027384A1 WO 2003027384 A1 WO2003027384 A1 WO 2003027384A1 SE 0201556 W SE0201556 W SE 0201556W WO 03027384 A1 WO03027384 A1 WO 03027384A1
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WO
WIPO (PCT)
Prior art keywords
sodium
leaching
stage
liquor
sodium carbonate
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Application number
PCT/SE2002/001556
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English (en)
Inventor
Lennart Delin
Original Assignee
Stfi, Skogsindustrins Tekniska Forskningsinstitut 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 Stfi, Skogsindustrins Tekniska Forskningsinstitut Ab filed Critical Stfi, Skogsindustrins Tekniska Forskningsinstitut Ab
Priority to US10/487,071 priority Critical patent/US20040194900A1/en
Publication of WO2003027384A1 publication Critical patent/WO2003027384A1/fr
Priority to SE0400395A priority patent/SE526435C2/sv

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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
    • D21C11/12—Combustion of pulp liquors
    • D21C11/125—Decomposition of the pulp liquors in reducing atmosphere or in the absence of oxidants, i.e. gasification or pyrolysis
    • 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
    • D21C11/02—Regeneration of pulp liquors or effluent waste waters of acid, neutral or alkaline sulfite lye

Definitions

  • the present invention relates to a method for recovery of alkaline sulphite pulping chemicals and for production of steam.
  • the sulphate pulping process has hitherto been dominating in the production of chemical pulps as well as semi-chemical pulps due to both its ability of disclosing a wide variety of lignocellulosic raw materials to a pulp of good quality and to its well-developed chemical recovery system, which is tested in large scale and has a high energy efficiency. Since the sixties, different alkaline sulphite processes have been proposed for production of pulps having the same or even superior strength qualities as compared to corresponding sulphate pulps. Increased process flexibility has also been noted concerning the adaptation to different technical paper qualities and to the pulp yield. It has also been noted that a proper choice of cooking conditions will result in substantially improved bleaching properties of the unbleached pulp.
  • each amount of anthraquinone charged to the process has a corresponding optimal sulphide charge (at a higher anthraquinone charge the optimal amount of sulphide is lower).
  • the positive effect of the sulphide is relatively soon is lost at smaller or larger than optimal sulphide charges.
  • alkaline sulphite processes have been to, in addition to a so-called redox-catalyst such as anthraquinone, to add a low boiling point organic solvent, such as methanol (R. Patt och O. Kordsachia, EP-A1 -205778, Sulfitauf gleichtechnisch Kunststoff Kunststoff aus lignozellulose restroomn Materialen mit R ⁇ ck,ung der Auf gleichchemikalien).
  • ASAM Alkaline Sulphite Anthraquinone Methanol
  • ASAM Alkaline Sulphite Anthraquinone Methanol
  • a chemical recovery system for the ASAM process has also been developed (M. Bobik, D. Chybin, A. Glasner och K. Taferner, WO-A 1-9423124, Process for converting sodium sulphate).
  • This system involves combustion in a conventional recovery boiler and a multi-stage carbonization using a part of the purified flue gas to drive off the sulphide as hydrogen sulfide, leaving sodium carbonate in the solution.
  • the hydrogen sulphide is combusted to sulphur dioxide (SO 2 ) and used for production of sodium sulphite (Na 2 SO 3 ) from the more or less pure sodium carbonate.
  • gasification technology for sulphite pulping processes has been impeded by the weak position of the traditional sulphite industry and the doubts regarding commercial development of new sulphite pulping techniques.
  • the gasification technology development has therefore been directed to chemical recovery in sulphate pulping processes. Gasification technology has thus been of use in smaller reactors, working in parallel to soda recovery boilers, to give a slight increase in the chemical recovery capacity in sulphate processes having inadequate capacity in the recovery boiler.
  • Document SE-B-462106 (A. Andersson and B. Warnqvist) discloses a process for recovery of energy and process chemicals, primarily intended for sulphate processes.
  • spent liquor is thermally decomposed under an elevated pressure (10-50 bar) and an oxygen supply that is insufficient for complete combustion.
  • the decompositio temperature is below the temperature that gives a melt (i.e. 700-850°C).
  • the gas formed during the thermal decomposition is led to a first scrubber where hydrogen sulphide and other sulphur containing compounds are absorbed in a sodium hydroxide solution. Thereafter the gas is led to a second scrubber for washing the gas with water.
  • Document SE-C2-503455 discloses a method for preparation of a sulphite containing cookingliquor comprising chemical recovery of a sulphite process spent liquor wherein the spent liquor is decomposed into a hot gas and a melt, in a reactor working at a high temperature.
  • the aim of this method is mainly to concentrate hydrogen sulphide by a sorption/desorption operation. Chemical recovery of sulphite process spent liquor according to this process has turned out to be complicated and expensive.
  • the existing gasification processes have suffered from the problem of achieving a good energy balance due to the reduction heat required for the pyrolysis of sulphite to sulphide, the take out of hot pyrolysis residue (solid or as a melt) for subsequent dissolution in water and/or extensive dust-cleaning of the pyrolysis gases in a scrubber before final combustion.
  • the existing gasification processes have so far also lacked a settled removal of process-foreign substances, soluble as well as non-soluble. It would thus be desirable to develop a chemical recovery process, which involves a good energy balance and means for handling the presence of sulphide in the solid phase of a gasification reactor.
  • the method of the present invention provides a simple, energy effective and flexible method of recovery of alkaline sulphite pulping chemicals, which method will render alkaline sulphite processes competitive in production of high quality pulps also in comparison to a modern sulphate pulping process.
  • the method comprises gasification of the evaporated spent cooking liquor, resulting in a hydrogen sulphide containing gas and a solid residue.
  • the gas is combusted in a steam boiler, where the hydrogen sulphide is converted into sulphur dioxide and steam is produced.
  • the solid residue is recovered in a leaching process, where process- foreign substances are removed and the rest of the contents is divided into substantially pure sodium carbonate and a mixture of sodium carbonate, sodium sulphate and sodium sulphide.
  • the substantially pure sodium carbonate is used for absorption of sulphur dioxide from the steam boiler and the mixture of sodium carbonate, sodium sulphate and sodium sulphide is causticized and the resulting sodium hydroxide containing solution can optionally be mixed with the substantially pure sodium carbonate after the absorption of sulphur dioxide in order to produce a fresh cooking liquor.
  • Figure 1 shows the alkaline sulphite chemical recovery process schematically in a block diagram.
  • the reference letters a)-k) in the diagram represent the process steps of the present method and correspond to the process steps as described in the claims.
  • the process steps are: a) gasification, b) leaching, c) dissolving, d) filtration and oxidation, e) causticizing, f) dust cleaning and combustion in steam boiler,-g) SO 2 -absorption, h) CO 2 -desorption, i) preparation of fresh cooking liquor, j) production of H 2 SO 4 and k) separate causticizing
  • Figure 1 also includes the Total Dry Substance (TS) of evaporated spent liquor that is fed into the gasification stage and the amounts of certain chemicals in the different stages of the process expressed in kg/ADt (Air Dry tonne) chips charged in the cook.
  • the steam boiler effect is given in GJ/ADt.
  • the present invention thus provides a method for recovery of pulping chemicals in an alkaline sulphite pulping process and for production of steam.
  • the method will here be described in detail with reference to Figure 1, which illustrates an example of the process adapted to a standard ASAM-process, with the exception that sulphide is accepted and desired in the fresh cooking liquor.
  • the recovery process of the present invention can of course also be adapted to other alkaline sulphite processes.
  • evaporated spent cooking liquor is fed into a gasification reactor (step a), in which the evaporated liquor is decomposed into a hydrogen sulphide (H 2 S)-containing gas and a solid residue.
  • step a gasification reactor
  • the application of gasification technology provides for a simple regeneration of cooking liquor from spent liquor in one stage.
  • the choice of gasification technology is a response to the need of achieving a simple and robust system that can be scaled to the very large capacities, as required by the pulp mills of today.
  • the equilibrium of sulphur gives that most of the sulphur will turn into the gas phase.
  • the amount of sulphur transferred to the gas phase is in the region of 50-75%.
  • the spent liquor has an initial sulphur content about twice as high as for kraft black liquor, which in the least should lead to an amount of sulphur transferred to the gas phase of at least the same size.
  • the energy balance of the gasification stage is crucial to the competitive strength of the process.
  • the solid residue contains sodium carbonate (Na CO 3 ) and a controlled concentration of sodium sulphide (Na 2 S).
  • the evaporated spent liquor fed into a gasification reactor has a dry content of 60-85 %.
  • the gasification is carried out at a temperature of 650-750 °C, preferably 700-750 °C and at a pressure of at most 5 bar, preferably at most 2 bar.
  • Air is added to the gasification reaction in an amount of 25-75 %, preferably 30-50 % of the total amount required for complete combustion of the evaporated spent liquor. Since each reactor is individual and requires different conditions, these parameters have to be experimentally determined in each case.
  • the gasification reaction is advantageously carried out in a fluidized bed reactor, but other types of gasification equipment could also be appropriate. . - • • - •
  • This solid residue is transferred via an optional heat exchanger to a series of treatment stages (steps b-d) where non-process elements are separated and the remaining quantity of sodium salts is divided into two separate cooking liquor lines, one of which is a substantially pure sodium carbonate (Na CO 3 ) stream and the other a mixture of sodium sulphide (Na 2 S), sodium sulphate (Na 2 SO ) and sodium carbonate (Na 2 CO 3 ).
  • the pure sodium carbonate (Na CO 3 ) stream is used for absorption of SO 2 and the mixed stream containing alLsodium salts is led to causticizing.
  • This measure gives a possibility to allow sulphide in the solid phase after gasification, since the sulphide is bypassed from the absorption of SO 2 .
  • SO 2 in not absorbed in NaOH but in Na 2 CO 3 , the causticizing need will be much lower than in a conventional process. Division into two cooking liquor lines also gives the opportunity to both conventional cooking where all chemicals are simultaneously charged, and specialized cooking processes where chemicals are charged in two or more steps.
  • the solid residue is led into to a leaching stage (step b), where any soluble process- foreign substances (such as K and Cl) and sodium sulphate (Na 2 SO 4 ) and a portion of the sodium carbonate (Na CO 3 ) present and the sodium sulphide (Na 2 S) are dissolved and separated.
  • the solid residue mainly consisting of sodium carbonate (Na 2 CO 3 ), remaining after the leaching process is then led to a dissolving stage (step c), where it is dissolved in water, after which it is filtered and oxidized step d).
  • a counter-current leaching process involves a transport direction of the leaching liquor that is opposite to that of the solid residue.
  • Each leaching stage is carried out in a separate vessel. In some cases, e g when a higher purity of the fractions is desired, it may be advantageous to involve more than two leaching stages.
  • soluble process-foreign substances such as K and Cl are dissolved and separated.
  • a second leaching stage b" sodium sulphide (Na 2 S), sodium sulphate (Na 2 SO 4 ) and a portion of the sodium carbonate (Na 2 CO 3 ) present are dissolved and separated. This separated stream will be further treated in a causticizing stage e).
  • the solid residue remaining after the leaching process in step b) consists mainly of sodium carbonate (Na 2 CO 3 ) and is now substantially free from Na 2 S, but any non-soluble process-foreign substances are still present.
  • the residue is dissolved in water in a dissolving stage (step.c), and the resulting solution is filtered (step d) to remove non-soluble process- . foreign substances and any possible remaining carbon.
  • the solution is then treated in an oxidizing stage (step d) to remove even small amounts of disturbing Na 2 S remnants in order to give a substantially pure sodium carbonate (Na 2 CO 3 ) solution. If desired the filtration can be carried out after the oxidizing stage.
  • the resulting pure Na 2 CO 3 solution will subsequently be used for absorption of SO 2 from the steam boiler flue gas and for production of sulphite as required.
  • the leaching liquor used in the leaching process is preferably a portion of the substantially pure sodium carbonate (Na 2 CO 3 ) stream, taken from the filtrate stream after the filter of step d). Water is fed into the dissolving tank c) and is led through the dissolving stage of step c) and the filtration stage of step d). After the filter, the stream is divided and one part is led to the oxidizing stage of step d) and the other is led to the leaching stages b") and b'). The leaching liquor taken out after the filtration stage of step d), is first fed into the second leaching stage b"). After having passed the second leaching stage b"), the leaching liquor is divided into two streams.
  • Na 2 CO 3 substantially pure sodium carbonate
  • the stream that is led to the first leaching stage b') amounts to less than 5 %, preferably 1-2 % of the total amount of the leaching liquor taken out from the second leaching stage b").
  • the solid residue that is transferred to the first leaching stage b') is thus leached with a solution, which represents a portion of the saturated liquid phase of leaching stage b").
  • the remains of the solid residue are then transferred to the second leaching stage b"), where sodium sulphide (Na 2 S) and sodium sulphate (Na 2 SO 4 ) are dissolved in the filtrate from step d).
  • the saturated leaching liquor taken out from the second leaching stage b") contains 20-60 %, preferably 40-59 % of the total amount of the sodium salts that were fed into the second leaching stage.
  • Both leaching stages are carried out at a temperature of 20- 100 °C, preferably 50-70 °C.
  • the conditions of the leaching process should advantageously be adjusted so that the amount of pure Na 2 CO 3 resulting from the filtration/oxidation stage (step d) will be sufficient for the absorption of SO 2 from the steam boiler.
  • a portion of the pure Na 2 CO -solution can optionally be utilized in a separate causticizing stage for production of additional NaOH, for use e.g. in a bleaching plant.
  • the amount of pure Na CO 3 -solution resulting from the filtration/oxidation stage must.be increased in relation to the amount of NaOH desired.
  • step e The solution that was separated in the second leaching stage of step b), which contains the sodium sulphide (Na 2 S), sodium sulphate (Na 2 SO 4 ) and the portion of sodium carbonate (Na 2 CO 3 ) that is not required for absorption of SO 2 , is led to a causticizing stage (step e), where it is causticized.
  • the resulting sodium hydroxide (NaOH)-containing solution may be use for preparation of fresh cooking liquor. Since the absorption of SO 2 utilizes the pure sodium carbonate resulting from the filtration/oxidation stage, no NaOH will be required for that purpose and it will thus be sufficient if the causticizing stage produces the amount of NaOH required for production of fresh cooking liquor.
  • the causticized liquor containing mainly Na 2 S, Na 2 CO 3 and NaOH, is then optionally mixed with the Na 2 SO 3 solution that has passed through the SO 2 -absorption stage, so as to form the required fresh cooking liquor.
  • the causticized liquor or a part of it may also be charged into the cooking process in a later stage if that would be desired.
  • the hydrogen sulphide (H 2 S)-containing gas from the gasification reactor in step a) is led to a dust cleaning stage (step f). In the dust cleaning stage all possible particles are separated e g in a cyclone or a ceramic filter.
  • the resulting clean gas is then combusted in a steam boiler (step f), for production of steam.
  • the gas does not contain any substantial amount of chemicals it would be possible to choose steam conditions considerably higher, than in a conventional recovery boiler.
  • the gas has preferably not been subjected to any cooling before it is led to final combustion, but if desired the gasification air may be heated by heat exchange with the gas before combustion.
  • the hydrogen sulphide (H 2 S) is converted to sulphur dioxide (SO 2 ).
  • the steam boiler of step f) has a working pressure of 60-120 bar and a super-heating temperature of 450-560 °C.
  • the thus generated sulphur dioxide (SO 2 ) is led to an absorption stage (step g) where it is absorbed in the substantially pure sodium carbonate (Na 2 CO 3 ) solution that results from the oxidizing stage of step d).
  • the resulting solution is then led through an additional carbon dioxide-desorption stage (step h), where carbon dioxide corresponding to the bicarbonate formed, is removed.
  • the result will be a substantially pure sodium sulphite (Na 2 SO 3 ) solution, which may be mixed with a desired portion of NaOH.
  • the chemical recovery plant can easily be supplemented with a separate plant for production of H 2 SO 4 from SO 2 -rich flue gas from the combustion in the steam boiler, in order to support the bleaching plant with H 2 SO .
  • a separate plant for production of H 2 SO 4 from SO 2 -rich flue gas from the combustion in the steam boiler in order to support the bleaching plant with H 2 SO .
  • the recovery process can, as mentioned above, optionally be completed by mixing (step i) the resulting substantially pure sodium sulphite (Na 2 SO 3 ) solution with a predetermined amount of the sodium hydroxide (NaOH)-containing solution resulting from the causticizing stage (step d) thus giving a fresh sulphite cooking liquor containing a controlled amount of sodium sulphide (Na 2 S).
  • the predetermined amount is adjusted in relation to the desired amount of sodium sulphite in the fresh cooking liquor.
  • the recovery method of the present invention achieves a number of savings.
  • the gasification and combustion of the gas in a separate boiler gives two large energy savings. Firstly, the need for soot blowing steam will vanish since the combusted gas is clean. Conventional recovery boilers use 5-10% of the steam produced for soot blowing. Secondly, the energy loss related to the smelt in a conventional recovery boiler of a sulphate process is omitted. This is due to that the non- gaseous chemicals taken out of the gasification reactor are not in the form of a smelt, but in the form of a solid residue, and thus contain less heat.
  • the gas boiler of the present recovery method will give about 7 % or 1.2 GJ/ADt more useful energy than can be obtained from a conventional recovery boiler. Due to the higher steam data that can be used for the gas boiler, in comparison to a conventional recovery boiler, the electricity production will increase even more.

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Abstract

La présente invention concerne un procédé, d'une part de récupération des produits de trituration au sulfite alcalin, et d'autre part de production de vapeur. Ce procédé implique une gazéification de la lessive de cuisson usée évaporée dans des conditions donnant un gaz chargé d'hydrogène sulfuré et un résidu solide. Le gaz est brûlé dans une chaudière à vapeur où l'hydrogène sulfuré est converti en anhydride sulfureux avec production de vapeur. Les résidus solides sont récupérés par lixivation, de préférence en deux temps, les substances étrangères au traitement étant éliminées, le reste se divisant en carbonate de sodium sensiblement pur et en un mélange de carbonate de sodium, de sulfate de sodium et de sulfate de sodium. Le carbonate de sodium sensiblement pur sert à l'absorption de l'anhydride sulfureux provenant de la chaudière à vapeur. Le mélange de carbonate de sodium, de sulfate de sodium et de sulfate de sodium est caustifié, la solution de soude caustique résultante pouvant éventuellement être mélangée avec le carbonate de sodium sensiblement pur après absorption de l'anhydride sulfureux de façon à produire une lessive de cuisson fraîche.
PCT/SE2002/001556 2001-09-28 2002-09-02 Procede de recuperation des produits chimiques de trituration dans un traitement de trituration au sulfite alcalin et de production de vapeur WO2003027384A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US10/487,071 US20040194900A1 (en) 2001-09-28 2002-09-02 Method for recovery of pulping chemicals in an alkaline sulphite pulping process and for production of steam
SE0400395A SE526435C2 (sv) 2001-09-28 2004-02-20 Metod för återvinnande av massakemikalier i ett alkaliskt sulfitmassaförfarande och för framställning av ånga

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE0103241-6 2001-09-28
SE0103241A SE0103241D0 (sv) 2001-09-28 2001-09-28 Method for recovery of pulping chemicals in an alkaline sulphite pulping process and for production of steam

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WO2003027384A1 true WO2003027384A1 (fr) 2003-04-03

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WO (1) WO2003027384A1 (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN100371527C (zh) * 2005-03-09 2008-02-27 宁夏紫金花纸业有限公司 以沙柳为原料制浆抄造生活用纸的方法
DE102007036380A1 (de) * 2007-07-31 2009-02-05 Voith Patent Gmbh Verfahren und Anlage zur Aufbereitung der Ablauge eines Sulfitverfahrens
EP3124501A1 (fr) * 2009-03-09 2017-02-01 TreeToTextile AB Procédé de fabrication de cellulose façonnée

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE175928C1 (fr) * 1961-01-01
WO1995009269A1 (fr) * 1993-09-27 1995-04-06 Kvaerner Pulping Technologies Ab Preparation d'une liqueur de cuisson contenant du sulfite

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA868884A (en) * 1968-08-21 1971-04-20 Pulp And Paper Research Institute Of Canada Method for the production of activated carbon
US3676064A (en) * 1970-04-16 1972-07-11 Owens Illinois Inc Methods for the treatment of spent sulfite pulping liquors and the recovery of chemical pulping values therefrom
US3954552A (en) * 1974-08-05 1976-05-04 Erco Envirotech Ltd. Removal of sodium chloride from pulp mill systems
US4148684A (en) * 1976-11-08 1979-04-10 Mei Systems Inc. Methods for recovery and recycling of chemicals from sodium sulfite and sodium bisulfite pulping operations
US5302246A (en) * 1992-07-30 1994-04-12 Kamyr, Inc. Method of managing liquid steams in a pulp mill

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE175928C1 (fr) * 1961-01-01
WO1995009269A1 (fr) * 1993-09-27 1995-04-06 Kvaerner Pulping Technologies Ab Preparation d'une liqueur de cuisson contenant du sulfite

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US20040194900A1 (en) 2004-10-07
SE0103241D0 (sv) 2001-09-28

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