WO1999014423A1 - Procede de reduction en pate faisant appel a du polysulfure - Google Patents

Procede de reduction en pate faisant appel a du polysulfure Download PDF

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Publication number
WO1999014423A1
WO1999014423A1 PCT/SE1998/001665 SE9801665W WO9914423A1 WO 1999014423 A1 WO1999014423 A1 WO 1999014423A1 SE 9801665 W SE9801665 W SE 9801665W WO 9914423 A1 WO9914423 A1 WO 9914423A1
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WO
WIPO (PCT)
Prior art keywords
liquor
cooking
polysulfide
process according
spent
Prior art date
Application number
PCT/SE1998/001665
Other languages
English (en)
Inventor
Lars Stigsson
Mikael Lindström
Original Assignee
Kvaerner Pulping 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
Priority claimed from SE9703365A external-priority patent/SE9703365D0/xx
Application filed by Kvaerner Pulping Ab filed Critical Kvaerner Pulping Ab
Priority to JP2000511951A priority Critical patent/JP4205855B2/ja
Priority to AU91955/98A priority patent/AU9195598A/en
Publication of WO1999014423A1 publication Critical patent/WO1999014423A1/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
    • D21C11/12—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
    • D21C1/00—Pretreatment of the finely-divided materials before digesting
    • D21C1/06—Pretreatment of the finely-divided materials before digesting with alkaline reacting compounds
    • 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
    • D21C11/0064—Aspects concerning the production and the treatment of green and white liquors, e.g. causticizing green liquor
    • D21C11/0078—Treatment of green or white liquors with other means or other compounds than gases, e.g. in order to separate solid compounds such as sodium chloride and carbonate from these liquors; Further treatment of these compounds
    • 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
    • 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
    • D21C3/02—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
    • D21C3/022—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes in presence of S-containing compounds

Definitions

  • the present invention relates to a process for cooking a cellulosic fiber material in the presence of polysulfide and regenerating polysulfide from spent cooking liquors .
  • Extended delignification may have a negative impact on the quality of the delignified pulp and can also undesirably decrease the pulp yield.
  • a major portion of the yield loss in the Kraft process results from the well known alkaline peeling or unzipping reactions of the carbohydrates, such as hemicellulose and cellulose. Cellulose value is also lost through alkaline extraction and splitting of glycoside linkages, thus reopening sites for secondary peeling. /Alkaline extraction can take place, even at room temperature, but is enhanced by increased temperatures and high alkalinity.
  • the peeling reactions are automatically halted during bulk delignification for still unknown reasons, and the cellulose chain is stabilized towards further degradation by alkali .
  • the terminal reducing aldehyde group of the hemicellulose and cellulose responsible for the initiation of peeling reactions can be eliminated by means of either reducing or oxidizing reactions .
  • the gluconic acid end groups stabilize the polysaccharide during pulping.
  • the reduction in polysaccharide degradation results in a higher yield when pulping is performed to a given kappa number or results in a lower kappa number when pulping is performed to a fixed yield.
  • the increased pulp yield in polysulfide Kraft processes is mainly a result of glucomannan stabilization in softwoods and xylan stabilization in hardwoods.
  • Anthraquinone addition to polysulfide pulping processes has been shown to further increase pulp yield.
  • U.S. patent no. 3,874,991 describes a process where external sulfur, in a molten state, is added to a combined spent polysulfide solution-hydroxyl ion depleted white liquor extracted after impregnation for preparation of a polysulfide cooking liquor. This liquor is used for impregnation of the wood chips at a temperature below digestion temperatures , from 90 to 140 °C, preferably from 100 to 130 °C. This process suffers from an intolerable imbalance between sodium and sul ur in the mill .
  • U.S. patent no. 3,331,732 discloses treating green liquor in a scrubber with flue gas. The carbonated green liquor is then treated in a stripper to evolve hydrogen sulfide gas, which is then further treated in a Claus type reactor to produce elemental sulfur.
  • U.S. patent no. 3,650,888 describes a polysulfide recovery process based on vacuum stripping a carbonated spent liquor to evolve hydrogen sulfide for further conversion to sulfur.
  • U.S. patent no. 4,024,229 describes a partial white liquor oxidation process based on air oxidation using a wet proofed activated carbon bed to promote formation of polysulfides.
  • a similar process based on polysulfide preparation by partial oxidation in a packed bed reactor with small porous active carbon granules is described in U.S. patent no. 4,855,123. More recently partial white or green liquor oxidation processes have been suggested based on manganese additions to the liquors to enhance partial oxidation selectivity towards polysulfide.
  • the elemental sulfur then reacts with sodium sulfide to form polysulfide in the white liquor in accordance with reaction 2.
  • a typical polysulfide cooking liquor from a partial white liquor oxidation process contains at the most 6 to 10 grams/liter of active polysulfide sulfur and a significant quantity of inert thiosulfate.
  • the active sulfide content is lowered substantially with a negative impact on pulping performance and product pulp strength properties .
  • substantially all white (or green) liquor must be partially oxidized and consequently all effective alkali has to be charged to the digester in combination with the polysulfide.
  • the present invention provides a novel process for polysulfide regeneration comprising the steps of:
  • step (d) gasifying at least a portion of the spent cooking liquor from step (c) in a gasification reactor to form a first gas stream comprising hydrogen sulfide;
  • the present invention also provides a novel process for polysulfide cooking in combination with polysulfide regeneration comprising the steps of:
  • step (d) gasifying at least a portion of the spent cooking liquor extracted from step (c) or at least a portion of a spent liquor extracted after the impregnation step (a) in a gasification reactor to form a first gas stream comprising hydrogen sulfide;
  • step (i) adding at least a portion of the alkaline polysulfide liquor from step (g) to the second cooking liquor or directly to the one or more cooking stages in step (b) ;
  • step (j) adding a portion of the polysulfide liquor to the first cooking liquor or directly to the impregnation step (a) to provide a desired polysulfide concentration in the impregnation stage when the amount of polysulfide supplied by the spent cooking liquor in step (h) is below an amount sufficient to provide the desired polysulfide concentration in the impregnation stage.
  • Fig. 1 illustrates the different unit operations in a Kraft mill utilizing polysulfide cooking and polysulfide regeneration in accordance with the present invention .
  • Fig. 2 shows a continuous two vessel steam/liquid-phase digester arrangement according to a preferred embodiment of the present invention.
  • Fig. 3 is a graph of the difference in the delignification rate with (M) and without (0) polysulfide present during the first 240 minutes of Kraft cooking at 147°C.
  • Fig. 4 is a graph of the thermal decomposition of polysulfide over a period of 120 minutes at 140°C.
  • the improved polysulfide regeneration process according to the present invention comprises the steps of:
  • step (d) gasifying at least a portion of the spent cooking liquor from step (c) in a gasification reactor to form a first gas stream comprising hydrogen sulfide;
  • the cellulosic fiber material is contacted with - li ⁇
  • the first cooking liquor in a separate impregnation zone which may be a top portion of a continuous digester or a separate impregnation vessel .
  • the polysulfide liquor can be added directly to the impregnation vessel .
  • the cellulosic fiber material should be contacted with the polysulfide under conditions such that the cellulosic fiber material is stabilized against undesirable peeling reactions by oxidation of the cellulose aldehyde end groups to more stable carboxylic groups. Based on the disclosure provided herein, one skilled in the art can easily determine the conditions required to provide this carbohydrate stabilization. This carbohydrate stabilization provides a higher content of hemicellulose in the pulp product and a higher overall pulp yield.
  • the first cooking liquor should comprise about 60% or less of the total effective alkali utilized in the overall delignification process to form delignified pulp.
  • the second cooking liquor introduced after the impregnation zone comprises an alkaline solution, such as a low sulfidity white liquor. Cooking is performed in accordance with well known practices to the desired kappa level. Suitable cooking temperatures are from about 120 to about 175EC.
  • the second cooking liquor should comprise at least about 40%, preferably at least about 60%, of the total effective alkali utilized in the overall delignification process to provide delignified pulp.
  • the second cooking liquor can be added at various locations during bulk and final delignification, and it can be diluted with wash liquor to provide the desired alkalinity and liquor-to-wood ratio.
  • the design of the cooking stages are not critical and the overall process described in the present invention may be practiced in all modern cooking systems including single and dual vessel steam liquor phase and hydraulic continuous digesters, as well as modified batch systems.
  • a steam vapor phase zone can be provided after impregnation to further stabilize the carbohydrates before injection of the second cooking liquor to the digester.
  • the cellulosic fiber material can be treated with steam at a temperature of from about 130 to about 175 °C, for a period of from about 5 to about 30 minutes after the impregnatio .
  • the residual alkali content in conventional Kraft cooking and modified Kraft cooking spent liquor transferred to the recovery stage should be from about six to about twelve grams per liter.
  • At least a portion of the spent cooking liquors extracted and withdrawn from the impregnation and/or cooking stages are gasified in a gasification reactor to extract the valuable sulfur compounds, which can be used to regenerate polysulfide.
  • the spent cooking liquor Prior to gasification, the spent cooking liquor is normally concentrated using a multi-effect evaporator system to a dryness of from about 65 to about 85%, preferably from about 70 to about 85%.
  • An example of a suitable gasification reactor and auxiliary system for partial oxidation of spent pulping liquors is described in U.S. patent No. 4,808,264, the complete disclosure of which is incorporated herein by reference.
  • a major task for the recovery process is an efficient conversion of the calories present in the spent cooking liquor to steam and/or power.
  • the combustible fuel gas generated in the spent cooking liquor gasification process can advantageously be used to fuel a gas turbine power plant.
  • the sodium and sulfur compounds present in the spent cooking liquor can be split as desired into two separate process streams.
  • One stream comprising reduced sulfur in the form of an aqueous solution of sodium sulfide and sodium hydrosulfide can be produced by quenching the melt in an aqueous liquid.
  • Another stream, comprising reduced sulfur can be discharged from the gasification reactor in the form of a combustible gas comprising hydrogen sulfide.
  • the proportion of reduced sulfur in the two streams can be controlled, for example, by varying the reaction temperature in the reactor and the operating pressure in the reactor.
  • At least about 20%, more preferably, from about 30 to about 60% of the sulfur compounds supplied to the gasification reactor are recovered as sodium sulfide.
  • at least about 20% of the sulfur compounds supplied to the gasification reactor are recovered as hydrogen sulfide.
  • sulfur compounds may be added to the gasification reactor to displace the sulfur equilibrium in the gasification reactor towards the formation of sodium sulfide. Further control of the degree of sodium-to-sulfur split in the reactor could be achieved by adjusting the steam partial pressure in the reactor, for example, by atomizing steam, moderator steam, water content of the spent cooking liquor, and the like.
  • the aqueous sulfide containing stream discharged from the reactor can be subjected to conventional causticizing to form a low sulfidity white liquor.
  • the combustible gas comprising hydrogen sulfide
  • the acidic gas stream is transferred to a Claus plant for recovery of hot liquid elemental sulfur.
  • the conversion of acidic gases comprising hydrogen sulfide and carbon dioxide to hot liquid elemental sulfur via the Claus reaction is a well known established practice in the chemical industry. Although there are a number of reactions in the conversion of hydrogen sulfide to sulfur, the overall conversion can be represented by:
  • a hot elemental sulfur stream advantageously can be mixed with sulfide containing liquors, such as green liquor and white liquor, to form a polysulfide liquor.
  • the polysulfide containing liquor is formed from a white liquor. It has been found that substantially no thiosulfate is formed during preparation of polysulfide liquors in accordance with the present invention, even at high concentrations of polysulfides , such as greater than about 10 grams/liter.
  • the polysulfide liquor can be used as at least a portion of the first cooking liquor containing polysulfides as necessary to maintain the level of polysulfide in the impregnation stage and to provide the desired level of carbohydrate stabilization.
  • the polysulfide liquor can be added directly to the impregnation stage to maintain the level of polysulfide therein.
  • the desired level of polysulfide will vary depending upon the particular type of digesting to be conducted. Based on the disclosure provided herein, one skilled in the art will be able to provide and maintain the desired level of polysulfide in the impregnation stage.
  • the polysulfide recovery process according to the present invention provides the advantage that the polysulfide liquor can be prepared at a high concentration and consequently it can be applied as desired at effective alkali concentrations optimal for carbohydrate stabilization.
  • the hot liquid elemental sulfur is admixed with a hot, preferably at least about 80 °C, sulfide containing liquor. It has been found that polysulfide liquors having a concentration of from about 10 up to about 100 grams per liter can be prepared for use in the present invention. Preferred ranges are however from about 15 to about 40 grams per liter.
  • the polysulfide liquor is utilized in the digester to provide polysulfide cooking in combination with polysulfide regeneration.
  • the polysulfide cooking and polysulfide regeneration process according to the present invention includes the steps of:
  • step (d) gasifying at least a portion of the spent cooking liquor extracted from step (c) or at least a portion of a spent liquor extracted after the impregnation step (a) in a gasification reactor to form a first gas stream comprising hydrogen sulfide; (e) treating the first gas stream to form an acidic gas stream comprising hydrogen sulfide and carbon dioxide;
  • step (i) adding at least a portion of the alkaline polysulfide liquor from step (g) to the second cooking liquor or directly to the one or more cooking stages in step (b) ;
  • step (j) adding a portion of the polysulfide liquor to the first cooking liquor or directly to the impregnation step (a) to provide a desired polysulfide concentration in the impregnation stage when the amount of polysulfide supplied by the spent cooking liquor in step (h) is below an amount sufficient to provide the desired polysulfide concentration in the impregnation stage.
  • the amount of intact polysulfide is about 30% or more, preferably about 40% or more, of the initial amount of polysulfide supplied to the cooking stage.
  • this black liquor containing a significant amount of polysulfide is recycled to the initial impregnation zone to make up at least a portion of the first cooking liquor, wherein the polysulfide can be used to stabilize the cellulose.
  • the amount of polysulfide liquor required in the impregnation stage can be substantially reduced.
  • polysulfide liquor may only have to be periodically added to the recycled black liquor to maintain a desired polysulfide concentration in the impregnation stage.
  • a major portion of the polysulfide liquor is added to the cooking stage (b) directly or as at least a part of the second cooking liquor.
  • the polysulfide liquor is added periodically to the impregnation stage when the level of polysulfide in the impregnation stage falls below a desired amount.
  • One skilled in the art will be able to select the desired amounts of polysulfide liquor to be added to each of the impregnation and cooking stages, based on the desired amount of polysulfide to be present during impregnation and cooking.
  • a lower steam temperature should be utilized, such as from about 130 to about 150EC.
  • the lower steam temperatures will help retain polysulfide present in the cellulosic fiber material exiting the impregnation stage. In this manner, the amount of polysulfide present during digestion will be further enhanced.
  • Thiosulfate is inert in Kraft cooking systems and besides the dead load can cause corrosion in digesters and impregnation vessels.
  • Prior experiences with sulfur additions to pulping liquors in mills and in laboratories are based on addition of powdered sulfur, with causes undesirable mixing complications and side reactions with oxygen in the powder bulk.
  • the hot liquid elemental sulfur can be discharged directly into the sulfide containing liquor in a closed vessel with a minimum of contact with air or oxygen, such that undesirable sulfur oxidation reactions are substantially avoided.
  • Polysulfide liquors prepared in accordance with the present invention can be utilized as the first cooking liquor added to the impregnation zone alone or in combination with other liquors to establish the desired liquor-to-wood ratio and level of effective alkali charge.
  • the polysulfide liquor comprises a white liquor which has been treated with the hot liquid elemental sulfur stream to form polysulfides and the polysulfide liquor is utilized as at least a portion of the first cooking liquor.
  • the first cooking liquor comprises a spent cooking liquor from the cooking stage to which polysulfide liquor formed from white liquor is added in an amount necessary to establish optimum sulfur and alkali profiles in the impregnation stage.
  • the quantities of fresh and spent liquors should be selected so as to provide sufficient effective alkali to sustain polysulfide and neutralization reactions during impregnation and initial delignification.
  • the ratio of pulping liquor to cellulosic fiber material is at least about 3.5:1.
  • a preferred embodiment of the invention is based on the surprising discovery that the delignification rate can be increased by polysulfide cooking at relatively low temperatures.
  • a delignification rate increase in the digester is combined with a carbohydrate stabilizing effect in the pre-impregnation vessel .
  • the polysulfide liquor is primary added to the impregnation stage.
  • Wood chips or other comminuted cellulosic fiber material are transported to a chip bin and steaming vessel (1) , where the material is subjected to steaming at a temperature of from about 100 to about 140 °C in order to remove air from the chip matrix.
  • the steamed chips are discharged from the steaming vessel to a high pressure feeder system which pressurizes and transports the chip slurry from the low pressure feed system to the high pressure impregnation vessel (2) .
  • the impregnated chips are then passed to the upper section of a steam/liquor phase digester (7) where the chips are exposed to steam, raising the temperature to full cooking temperature, for example, a temperature of from about 120 to about 175 EC , preferably from about 130 to about 150 EC.
  • Low sulfidity white liquor comprising at least about 40% of the effective alkali to be used during impregnation and cooking is added through one or several conduits to the cooking circulations or directly into the digester.
  • the cooking and delignification reactions are allowed to proceed to a predetermined kappa number, whereafter the digested chips are discharged from the digester and passed to the brownstock washers (8) .
  • Hot spent cooking liquor (4) is extracted from the digester through extraction screens for recycle to impregnation and /or recovery of fresh cooking chemicals.
  • the pulp After brownstock washing, the pulp is further treated in an oxygen delignification reactor (9) and is transferred to a downstream bleach plant (10) to prepare a bleached pulp product with the desired physical properties.
  • the filtrates (11) from the brownstock washers and oxygen delignification stage are recycled to the digester to provide the desired ratio of liquor-to-wood in the digester.
  • At least a portion of the spent cooking liquor extracted after impregnation and/or from the digester is withdrawn to a multi-effect evaporation system (12) and concentrated to a dry solids content of from about 70 to about 85%.
  • the concentrated spent cooking liquor (black liquor) is thereafter directed to an integrated black liquor gasification combined cycle plant (IGCC) for recovery of cooking chemicals and energy.
  • This plant comprises a gasification reactor (13) , a gas cooling system (14) , a gas cleaning (15) system and a power generation block (16) .
  • Concentrated black liquor is injected into the gasification reactor (18) with an oxidant (26) , preferably cryogenic quality oxygen from an adjacent oxygen plant (17) .
  • the oxygen sustains the partial oxidation reactions taking place in the gasification reactor, which usually operates at a temperature of from about 850 to about 1200 °C and at a pressure of from about 0.5 to about 10 MPa.
  • the sulf rous chemicals charged to the gasification reactors are decomposed in the reactor and split into one stream of hydrogen sulfide gas following the fuel gas stream from the gasification reactor (18) and into another stream as a melt of sodium sulfide which is dissolved into an aqueous medium and discharged from the reactor vessel as a low sulfidity green liquor (19) .
  • the latter stream is directed to a causticizing plant (20) to convert the low alkalinity green liquor into high alkalinity white liquor.
  • At least about 20 %, preferably from about 30 to about 60 %, of the sulfur charged into the gasification reactor is recovered as sodium sulfide.
  • the fuel gas stream comprising the balance of sulfur as hydrogen sulfide is cooled to a temperature below about 100 °C and directed to a regenerative gas cleaning system (15) comprising an absorber and a stripper.
  • the fuel gas is separated from the sulfur compounds and these sulfur compounds are recovered in an acidic gas stream (21) comprising hydrogen sulfide and carbon dioxide.
  • the cleaned fuel gas exiting the absorber is directed to the gas-turbine power plant for recovery of power and steam.
  • the acidic gas is transferred to an oxygen blown Claus plant (22) for recovery of hot liquid elemental sulfur.
  • the tailgas stream (23) from the Claus plant is discharged to an onsite sulfuric acid plant or to the odor gas handling system of the pulp mill .
  • the temperature of the hot product liquid sulfur stream (25) is kept higher than about 120 °C and charged directly into a mixing vessel (22) filled with hot white liquor.
  • the charge of white liquor and elemental sulfur is controlled so as to bring the concentration of polysulfide liquor produced in the mixing vessel to about 10 grams/liter or greater.
  • the strong polysulfide liquor is supplied to the impregnation vessel as the first cooking liquor to complete the circle (3) .
  • Fig. 2 shows a continuous two vessel steam/liquid-phase digester arrangement according to a preferred embodiment of the invention.
  • the delignification rate is significantly increased at low temperatures by polysulfide cooking, in accordance with the following.
  • a cellulosic fiber material, such as wood chips, (90) is introduced into the top of the impregnation vessel (100) .
  • the top of the impregnation vessel includes a screw feeder which makes the chips move slowly downwards in a plug flow trough the impregnation vessel (100) in a liquor-to-wood ratio of from about 2:1 to about 10:1, preferably from about 3:1 to about 8:1, and more preferably from about 4:1 to about 7:1.
  • Hot black liquor which is extracted from the digester, through screen (101) , is added, via conduit (102), together with less than about 20%, or possibly none, of the polysulfide liquor (92) , which has been prepared according the previous description, via conduit (103) , to the top of the impregnation vessel (100) .
  • the polysulfide concentration in the black liquor is sufficient, no fresh polysulfide liquor is required. In this manner, the polysulfide liquor can be added as necessary to maintain a desired polysulfide level in the first cooking liquor.
  • the concentration of polysulfide in the total liquor added through the conduits (102) and (103) , at the top of the impregnation vessel should be about 2.5 grams/liter or greater, and the effective alkali concentration (calculated as NaOH) should be about 15 grams/liter or greater.
  • Extra alkali can be added through conduit (112) , such as white liquor.
  • the temperature during the impregnation step should be from about 80 to about 140°C for a period of about 20 to about 120 minutes.
  • the chips which have been thoroughly impregnated and partially delignified in the impregnation vessel , are fed to the top of the digester (104) and conveyed into the top separator.
  • at least a portion of black liquor is withdrawn from the top of the digester and led to evaporation through conduit (105) .
  • More than about 80% of the polysulfide liquor used in the process shown in Fig. 2 is added to the top of the digester (104) , via conduit (107) .
  • the polysulfide liquor is preferably heated by means of a heat exchanger (108) .
  • the concentration of polysulfide should be about 5 grams/liter or greater and the effective alkali concentration (calculated as NaOH) should be about 20 grams/liter or greater. Extra alkali, if required, can be added through conduit (112) .
  • the chips then move down in zone (B) at a relatively low cooking temperature, for example, from about 120 to about 150 °C, preferably from about 135 to about 148 EC, and more preferably from about 140 to about 145 °C.
  • the retention time in this first cooking zone should be at least about 50 minutes , preferably at least about 60, and more preferably at least about 70 minutes .
  • Laboratory tests have shown that the delignification rate is increased when polysulfide is present, see Fig 3.
  • the polysulfide is, however rapidly decomposed at high temperatures generally practiced in conventional Kraft cooking system, such as from about 160 to aboutl70 °C. At a temperature of about 140°C, however, as much as 50% of the charged polysulfide remains after 120 minutes, see Fig 4.
  • the hot black liquor from the digester will, therefore contain a large concentration of polysulfides.
  • This black liquor, with released lignin, a relatively high content of effective alkali, and remaining polysulfide is withdrawn through the screen (101) and is introduced at the top of the impregnation vessel via conduit (102) as described above.
  • the alkaline content of this withdrawn black liquor (102) usually exceeds about 15 grams/liter.
  • low sulfidity white liquor is added in two recirculation lines (110, 111).
  • the alkali concentration demand in the cooking zone (C) is dependent on the desired lignin content of the produced pulp.
  • the produced pulp is washed using a washing liquid supplied by conduit (94) and the washed pulp exits the digester through conduit (96) .

Abstract

Cette invention a trait à un procédé de production de pâte à partir de fibres cellulosiques avec régénération de polysulfure seul ou en association avec un lessivage au polysulfure. On imprègne les fibres cellulosiques de polysulfure avant lessivage et l'on extrait la liqueur de lessivage épuisée. On gazéifie une partie de cette liqueur épuisée pour donner de l'hydrogène sulfuré et on la traite de manière à obtenir un gaz acide comportant de l'hydrogène sulfuré et du dioxyde de carbone. On fait réagir le gaz acide dans des conditions permettant d'obtenir un courant chaud de soufre élémentaire, ce courant étant mélangé à une liqueur alcaline contenant du sulfure. On obtient, de la sorte, une liqueur alcaline de polysulfure que l'on ajoute lors du lessivage ou de l'imprégnation. Durant le lessivage, on recycle une partie de la liqueur de lessivage épuisée extraite aux fins de l'opération d'imprégnation et on maintient la teneur en polysulfure à un taux souhaité lors de l'opération d'imprégnation en ajoutant de la liqueur de polysulfure.
PCT/SE1998/001665 1997-09-18 1998-09-17 Procede de reduction en pate faisant appel a du polysulfure WO1999014423A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
JP2000511951A JP4205855B2 (ja) 1997-09-18 1998-09-17 ポリサルファイドパルプ化プロセス
AU91955/98A AU9195598A (en) 1997-09-18 1998-09-17 Polysulfide pulping process

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
SE9703365A SE9703365D0 (sv) 1997-09-18 1997-09-18 Method in connection with impregnation and digestion of lignocelulosic material
SE9703365-8 1997-09-18
US08/992,114 US6143130A (en) 1997-09-09 1997-12-17 Polysulfide pulping process
US08/992,114 1997-12-17

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005064075A1 (fr) * 2003-12-31 2005-07-14 Metso Paper, Inc. Procede discontinu de preparation de pate
WO2009067231A1 (fr) * 2007-11-20 2009-05-28 International Paper Company Utilisation de polysulfure dans une cuisson modifiée
EP2537979A1 (fr) * 2011-06-23 2012-12-26 Metsä Fibre Oy Procédé de production de pulpe de cellulose
WO2013032377A1 (fr) 2011-08-30 2013-03-07 Metso Paper Sweden Ab Procédé de cuisson kraft utilisant une liqueur de cuisson au polysulfure
US9580864B2 (en) 2011-08-30 2017-02-28 Valmet Ab Kraft cooking method using polysulfide cooking liquor
EP3186439A4 (fr) * 2014-08-26 2018-03-07 Valmet AB Procédé rentable de cuisson de kraft à l'aide d'une liqueur de cuisson au polysulfure

Citations (5)

* Cited by examiner, † Cited by third party
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US5660685A (en) * 1991-12-16 1997-08-26 Chemrec Aktiebolag Gasifying black liquor with recycling of generated hydrogen sulphide gas to the gasifier
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WO2005064075A1 (fr) * 2003-12-31 2005-07-14 Metso Paper, Inc. Procede discontinu de preparation de pate
WO2009067231A1 (fr) * 2007-11-20 2009-05-28 International Paper Company Utilisation de polysulfure dans une cuisson modifiée
US7828930B2 (en) 2007-11-20 2010-11-09 International Paper Company Use of polysulfide in modified cooking
EP2537979A1 (fr) * 2011-06-23 2012-12-26 Metsä Fibre Oy Procédé de production de pulpe de cellulose
RU2606867C2 (ru) * 2011-06-23 2017-01-10 Андритц Ои Способ изготовления целлюлозной массы
WO2013032377A1 (fr) 2011-08-30 2013-03-07 Metso Paper Sweden Ab Procédé de cuisson kraft utilisant une liqueur de cuisson au polysulfure
US9580864B2 (en) 2011-08-30 2017-02-28 Valmet Ab Kraft cooking method using polysulfide cooking liquor
EP3186439A4 (fr) * 2014-08-26 2018-03-07 Valmet AB Procédé rentable de cuisson de kraft à l'aide d'une liqueur de cuisson au polysulfure

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