US3909344A - Removal of sodium chloride from pulp mill operations - Google Patents

Removal of sodium chloride from pulp mill operations Download PDF

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Publication number
US3909344A
US3909344A US420876A US42087673A US3909344A US 3909344 A US3909344 A US 3909344A US 420876 A US420876 A US 420876A US 42087673 A US42087673 A US 42087673A US 3909344 A US3909344 A US 3909344A
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sodium
sodium chloride
aqueous solution
sodium carbonate
solution
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US420876A
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Jerome A Lukes
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Sterling Canada Inc
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Erco Envirotech Ltd
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Priority to US420876A priority Critical patent/US3909344A/en
Priority to SE7414971A priority patent/SE7414971L/xx
Priority to CA214,505A priority patent/CA1070457A/en
Priority to FI3445/74A priority patent/FI344574A7/fi
Priority to BR10122/74A priority patent/BR7410122A/pt
Priority to JP49137778A priority patent/JPS5088303A/ja
Publication of US3909344A publication Critical patent/US3909344A/en
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Assigned to BANK OF NOVA SCOTIA, THE reassignment BANK OF NOVA SCOTIA, THE SECURITY INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: STERLING CANADA, INC. A DE CORP.
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D7/00—Carbonates of sodium, potassium or alkali metals in general
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D3/00—Halides of sodium, potassium or alkali metals in general
    • C01D3/04—Chlorides
    • C01D3/06—Preparation by working up brines; seawater or spent lyes
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S423/00—Chemistry of inorganic compounds
    • Y10S423/03—Papermaking liquor

Definitions

  • ABSTRACT Sodium chloride is removed from pulp mill systems in which the smelt from the spent pulping liquor recovery operations contains sodium carbonate and sodium chloride, and optionally other components, depending on the pulp mill system.
  • the smelt is made up into a hot aqueous solution thereof, and is evaporatively cooled to crystallize hydrated sodium carbonate, while avoiding deposition of sodium chloride.
  • the mother liquor is evaporated with heating to deposit sodium chloride in a substantially pure form.
  • the sodium carbonate may be converted into an active pulping chemical for recycle, typically into sodium hydroxide by recausticization.
  • the present invention is directed to the removal of sodium chloride, from pulping operations, more particularly from chemical wood pulping operations including bleaching procedures for the pulp, with enhanced efficiency of pulp mill operations.
  • the spent pulping liquor usually is subjected to a series of recovery and regeneration operations to recover pulping chemicals and to provide fresh pulping liquor.
  • the pulping liquor contains alkali metal salts, usually sodium salts, although potassium or lithium salts could be employed.
  • Kraft and soda processes Two well-known pulping processes are the Kraft and soda processes. While the present invention will be described hereinafter with particular reference to Kraft and soda mills, the process is applicable also to other pulp mill operations involving the use of alkali metal salts as pulping chemicals and which utilize spent chemical recovery and pulping chemical regeneration operations. Many such operations involve the use of sulphur-containing chemicals, including the Kraft process, high yield pretreatment Kraft process, alkaline sulfite process, neutral sulfite process, acid sulfite process, bisulfite process, acid bisulfite process, polysulfide process, alkafide process. Other pulping operations which may be employed are the soda-oxygen process and the holopulping process. The present invention also is applicable to cross-recovery operations used in mixed systems.
  • raw cellulosic fibrous material generally wood chips
  • a pulping liquor known as white liquor and containing sodium sulphide and sodium hydroxide as the active pulping chemicals
  • black liquor a pulp and spent pulping liquor, known as black liquor.
  • the black liquor is separated from the pulp by washing in a brown stock washer and the pulp then is passed to the bleach plant for brightening and purification operations.
  • the black liquor then is passed to the recovery and regeneration system in which the black liquor first is concentrated, usually by evaporation, and the concentrated black liquor is burned in a furnace to yield a smelt containing primarily sodium carbonate and sodium sulphide.
  • a sodium-and sulphur-containing compound generally sodium sulphate, is added to the black liquor generally prior to feed of the concentrated black liquor to the furnace, although such sodium-and sulphur-containing compound may be added at any other convenient point, such as to the white liquor prior to the digestion step, to make up sodium and sulphur values lost from the recovery system.
  • the smelt is dissolved in water to yield a raw green liquor which then is clarified to remove undissolved solids.
  • the clarified green liquor is causticized with slaked lime whereby the sodium carbonate is converted to sodium hydroxide.
  • the resulting liquor is white Iiquor which then may be recycled to the digestion step to provide at least part of the pulping liquor.
  • pulping liquor consists predominantly of aqueous sodium hydroxide solution.
  • Spent pulping liquor is subjected to a recovery and regeneration procedure as in the Kraft process.
  • the smelt which results from furnacing in the soda process contains primarily sodium carbonate which, after formation into an aqueous solution, is recausticized to regenerate sodium hydroxide solution for recycle to provide at least part of the pulping liquor.
  • Bleach plant operations generally involve a sequence of brightening and purification steps, together with washing steps.
  • the brightening steps generally involve the use of bleaching agents.
  • At least one of the brightening steps usually involves theuse of at least one chlorine-containing bleaching agent.
  • chlorinecontaining bleaching agents include chlorine, chlorine dioxide, chlorine monoxide and sodium hypochlorite.
  • the purification steps generally involve treatment with sodium hydroxide solution, and usually is known as a caustic extraction step.
  • the bleaching and caustic extraction steps may be combined, for example, using the so-called oxygen bleaching operation.
  • a particular bleaching operation which has been employed involves an initial bleaching of the pulp with an aqueous solution containing chlorine or a mixture of chlorine dioxide and chlorine,'- an intermediate washing, a caustic extraction using aqueous sodium hydroxide solution, a further washing, a bleaching with an aqueous solution of chlorine dioxide, another washing, a further caustic extraction using aqueous sodium hydroxide, an additional washing, a final bleaching with chlorine dioxide solution and a final washing.
  • the present invention will be described with particular reference to this procedure, although other procedures may be employed, such as, the use of an aqueous solution containing approximately percent chlorine dioxide in the first bleaching step. 4
  • CEDED operation may be carried out using the so-called Dynamic Bleaching" process outlined in Canadian Pat. No. 783,483.
  • pulping treating solutions are passed successively through a mat of fibers in which the fibers are maintained relatively stationary with respect to each other. Washing steps, except for a washing after the last step of the bleaching and purification sequence, may be omitted.
  • the spent wash waters from bleach plants generally have been discharged to water: bodies, such as streams, rivers, lakes and oceans, without any attempt to recover chemicals therefrom, although in some instances solid particle recovery operations have been made.
  • bodies such as streams, rivers, lakes and oceans
  • solid particle recovery operations have been made.
  • the bleach plant also produces spent bleaching liquor effluents and spent caustic extraction effluents. These effluents have objectionable colour and are toxic and harmful to aquatic and marine biota and polluting since they contain fibers and materials consuming oxygen present in the water. It is desirable to avoid such environmental pollution, and hence avoid the discharge of these effluents from the mill.
  • the spent wash water contains substantial quantities of sodium chloride.
  • the spent bleaching liquor effluents and the spent caustic extraction liquor effluents are mixed at least part of the residual chlorine and soda values combine to form sodium chloridev
  • the normally discharged effluents, namely. the spent wash water, the spent bleaching chemicals and the spent caustic extraction liquor may be mixed to provide a bleach plant effluent stream, known as BPE.
  • the quantity of the chlorine containing bleaching agents and the quantity of sodium hydroxide used as caustic extraction liquor preferably are balanced to provide about one atom of sodium for each atom of chlorine, whereby these chemicals form sodium chloride.
  • the quantity of sodium hydroxide solution is in a slight stoichiometric excess to ensure the conversion of all the chlorine values to sodium chloride.
  • the equivalence of sodium and chlorine atoms in the bleach plant effluent also is preferred so that the overall sodium inventory of the mill thereby remains unchanged.
  • Sodium chloride present in the bleach plant effluent also may arise from sodium chloride present in the pulp when it is introduced to the bleach plant. Such sodium chloride may be present where the logs are floated in sea water prior to formation of wood chips therefrom. In addition, if brackish water is used to provide the bleach plant wash water, sodium chloride again is present in the bleach plant effluent.
  • Sodium salts may be introduced to the pulp mill system, from other sources, such as from the cellulosic fibrous material itself.
  • the bleach plant effluent preferably is added to the spent pulping liquor recovery and regeneration operation, and in this way this effluent is retained within the mill. It has been proposed previously in Canadian Pat. No. 832,347 and U.S. Pat. No. 3,698,995 to reduce the environmental problems of bleach plant effluent by utilizing the spent wash waters to wash the pulp in the brown stock washer. The use of the spent wash water in this manner reduces the overall water requirement of the mill.
  • the remainder of the mixture is used as wash water to wash the pulp from the intermediate bleaching stage.
  • Spent bleaching chemical from this stage is mixed with the aqueous material resulting from the last mixing, the resulting material, representing the combined effluents from the subsequent steps of the bleach plant, being used partially to wash the pulp from the first caustic extraction stage and partially to wash the pulp from the first bleaching stage.
  • the spent wash water from the washing of the pulp from the first caustic extraction stage is mixed with spent caustic extraction liquor from the first caustic extraction and the mixture is divided into two streams, one of which represents an alkaline effluent and the other is used as wash water for the pulp from the first bleaching stage.
  • the spent wash water from this stage is mixed with spent bleaching chemical from the first bleaching stage to provide an acid liquor, part of which constitutes an acid bleach plant effluent.
  • Another part of the acid liquor may be used to mix with the pulp received from the brown stock washer to provide the water required to bring the pulp to the consistency necessary in the first bleaching stage.
  • a further part of the acid liquor is used as the aqueous medium for dissolving gaseous chlorine used in the first bleaching stage. In this way a portion of the acid liquor, constituted by the latter two parts may be recycled in the first bleaching step.
  • a further part of the acid liquor may be used as wash water to displace into but not through the unbleached pulp on the unbleached decker chest so that it is substantially all discharged to the unbleached decker chest along with the unbleached pulp.
  • Still another part of the acid liquor may be used as wash water to wash the screen on the first bleaching stage washer so that it mixes with spent bleaching chemical from the first bleaching stage and is recycled to become part of the acid liquor.
  • the acid spent bleaching chemical liquor is mixed with the alkaline caustic extraction liquor to provide the bleach plant effluent.
  • the bleach plant effluent may be introduced at other stages of the recovery and regeneration operations. Further, the bleach plant effluent may be split into two or more streams which are introduced at different locations of the recovery and regeneration operations, for example, to wash calcium carbonate mud to provide the weak wash" water or to dilute concentrated white liquor.
  • the quantity of sodium chloride present in the bleach plant effluent varies depending on the bleaching se- 'quence which is' employed.- Ina typical procedure where a mixture of Chlorine dioxide and chlorine are utilized in the first Stage of a CEDEDsequence the quantity of Sodium chloride may vary-between about 120 and sgjlbs/t n of'pulp depending on the propor- "tion of chlorine dioxide used. Typically, when the total available chlorine in the first stage is provided 70 percent by chlorine dioxide and 30 percent by chlorine, t he quantity is about 120 lbs/ton of pulp.
  • sodium chloride rnay r stilldbe present in the mill recovery and regeneration I cycle which is required to be removed to prevent build up.
  • Such sodium chloride may arise from sea-borne ,logs which are pulpedand washed, therebyremoving some sodium chloride, from the pulp and introducing it to the black liquor, prior to passage to the bleach plant. Further, where wash water for washing the pulp prior to passage to the bleach plant is contaminated with sodiurn chloride, at least part of this sodium chloride is introduced to the black liquor.
  • the present invention is concerned broadly, there- I fore, with the, removal. of sodium chloride from pulp mill recovery andlregeneration systems irrespectiveof the source of such sodium, chloride, and is preferably ;concerned ,with the removal of sodium chloride from effluent-free pulpmills, e
  • an alternative sodium chloride separation procedure is provided which, in its preferred embodiments, enables sodium chloride to be removed from the system at a lower cost.
  • a smelt containing sodium carbonate and sodium chloride is dissolved in an aqueous material to form hot aqueous solution thereof, thehot aqueous solution is cooled to crystallize hydrated sodium carbonate therefrom while avoiding precipitation of sodium chloride, the crystallized hydrated sodium carbonate is recovered from the mother liquor,'the mother liquor is evaporated with heating to crystallize sodium chloride therefrom while avoiding substantially the crystallization of sodium carbonate, and the crystallized sodium chloride is removed from the resulting mother liquor.
  • the hot aqueous solution which is cooled bythe procedure of the invention therefore contains dissolved quantities of the material of the smelt, including sodium .carbonate and sodium chloride.
  • the smelt may be substantially sodium chloride-free but the hot aqueous solution nevertheless containsdissolved quantities of sodium chloride as a result of additions of a sodium chloride-containing aqueoussolution, such as bleach plant effluent, to the aqueous solution of the smelt.
  • a sodium chloride-containing aqueoussolution such as bleach plant effluent
  • a hot aqueous solution for treatment in accordance with the present invention from only part of a sodium chloride-containing smelt and such procedures are within the scope of this invention.
  • the hydrated sodium carbonate which is crystallized and recovered in this way then may be recausticized, after making up into an aqueous solution thereof, or otherwise reconverted into pulping chemicals. Since the sodium carbonate crystallization substantially avoids the crystallization of sodium chloride, little or no sodium chloride is recycled with the pulping liquor as a dead load.
  • the mother li'quor remaining after removal of sodium chloride usually still contains dissolved quantities of sodium chloride and sodium carbonate, and this mother liquor may be recycled to the aqueous solution formed from the materials of the smelt.
  • the quantity of sodium chloride recovered by the process of the invention preferably is substantially the same quantity as is originally present in the smelt, and this may be achieved by judicious choice of conditions.
  • the smelt may contain sodium sulfite and small quantities of various sodium and sulfur compounds including sodium sulfate, sodium sulfite, sodium thiosulfate and sodium polysulfide.
  • sodium sulfate is present in the most significant amount.
  • at least the sodium sulfide and sodium sulfate are crystallized along with the sodium carbonate.
  • the cooling of the hot aqueous solution may be carried out in any convenient manner to a temperature which will result in crystallization of hydrated sodium carbonate, optionally together with any other crystallizable salts, with the exception of sodium chloride.
  • the form of the sodium carbonate which is crystallized depends on a number of factors, including the composition of the cooled solution and the temperature to which the hot aqueous solution is cooled to cause crystallization.
  • the sodium carbonate is crystallized in a hydrated form, which may be the septahydrate or decahydrate.
  • the decahydrate is crystallized.
  • the decahydrate form is crystallized at temperatures below about 25C. Crystallization of the sodium carbonate in a hydrated form in the invention removes water from the system, thereby decreasing the quantity of water which must subsequently be evaporated to remove water to deposit sodium chloride.
  • water preferably is evaporated from the aqueous solution to increase the concentration of the dissolved salts and this evaporation may constitute the sole form of cooling the hot aqueous solution.
  • the cooling effect of the evaporation, carried out under vacuum, may be enhanced in any desired manner.
  • the smelt may be fractionated during its formation into the hot aqueous solution to dissolve substantially all the sodium chloride therefrom along with part of the sodium carbonate and part or all of other salts present in the smelt, depending on the conditions of the fractionation.
  • the undissolved portion of the smelt is substantially free from sodium chloride and may be forwarded directly to the recausticization stage. Fractionation of the smelt in this way decreases the energy required to deposit the sodium carbonate from the hot aqueous solution.
  • FIG. 1 is a schematic flow sheet illustrating one embodiment of the invention, as applied to a soda pulp mill.
  • FIG. 2 is a schematic flow sheet illustrating a further embodiment of the invention, as applied to a Kraft pulp mill.
  • wood chips or other raw cellulosic fibrous material, are fed by line to a digester 12 wherein the wood chips are digested with a pulping liquor fed by line 14 and containing sodium hydroxide as the active pulping chemicalin the soda process.
  • the resulting pulp and spent pulping liquor are separated and the pulp is washed in a brown stock washer 16.
  • the pulp is washed, in the embodiment illustrated, with aqueous bleach plant effluent fed by line 18.
  • the pulp may be washed with water or contaminated condensate", and the bleach plant effluent may be utilized elsewhere in the system, as described in more detail below, or discharged as desired.
  • the washed and unbleached pulp is fed by line to a bleach plant 22 wherein the pulp is subjected to a series of bleaching and purification processes involving the use of one or more chlorine-containing bleaching agents.
  • the bleaching and purification processes involve bleaching with chlorine, chlorine dioxide or mixtures thereof fed by line 24 and purification by caustic extraction, using aqueous sodium hydroxide solution fed by line 26, typically in a CEDED sequence as described above.
  • the pulp is washed during the bleach plant operations, typically after each bleaching or caustic extraction operation, by water fed by line 28.
  • the spent wash water from the bleach plant washing operations together with the spent chemicals from the bleaching and caustic extraction steps provide the bleach plant effluent in line 18.
  • the washing operations involve countercurrent flow of pulp and wash water through the bleach plant.
  • the quantity of sodium hydroxide used in the caustic extraction of the pulp is slightly in excess of the stoichiometric requirement of one sodium atom for each chlorine atom in the bleaching chemicals, whereby the bleach plant effluent in line 18 has an alkaline pH.
  • the bleached and purified pulp of required brightness is recovered from the bleach plant 22 by line 30 and is sold as such, or passed to paper making procedures.
  • the bleach plant effluent in line 18 may be added directly to the spent pulping liquor in line 32, although this procedure is less preferred, since the overall water requirement thereby is increased.
  • the bleach plant effluent in line 18 contains considerable quantities of sodium chloride which are transferred to the spent pulping liquor in line 32.
  • the spent pulping liquor is evaporated in an evaporator 34 prior to passage by line 36 to a furnace 38 of any convenient construction.
  • the water recovered from the evaporator 34 by line 40 may be used to provide at least part of the water requirement of the system, for example, as at least part of the water fed to the bleach plant in line 28, after suitable cleaning, if required.
  • the spent pulping liquor forms in the furnace 38 a smelt containing sodium carbonate, and additionally unreacted components, consisting substantially of sodium chloride.
  • a smelt containing sodium carbonaate and sodium chloride is dissolved in a smelt dissolver 42 in water fed by line 44.
  • the water may be constituted by BPE, evaporator condensate or weak wash water, if available after dissolving hydrated sodium carbonate in 54.
  • the water passed by line 44 to the smelt dissolver 42 may be partially bleach plant effluent from line 18, especially in the case where fresh water or contaminated condensate is fed to the brown stock washer 16.
  • the resulting hot aqueous solution in line 46 also contains recycled chemicals as described in more detail below.
  • the smelt need not be dissolved in the aqueous material fed by line 44, but instead the smelt may be leached with the aqueous material fed by line 44 to dissolve substantially all the sodium chloride values and part of the sodium carbonate values of the smelt, leaving substantially pure sodium carbonate. Operation in this manner reduces the quantity of water which requires evaporation.
  • the substantially pure sodium carbonate may be used to form pulping liquor along with the sodium carbonate later separated from the hot aqueous solution resulting from the leaching.
  • the hot aqueous solution is cooled in a crystallizer 48 to crystallize hydrated sodium carbonate, preferably sodium carbonate decahydrate, while avoiding substantially the crystallization of sodium chloride.
  • the cooling preferably is achieved by evaporation of water from the hot solution under vacuum, the evaporated water being removed by line 50.
  • the hot aqueous solution in line 46 which generally has a very high temperature, typically about 180 to 210F, may be subjected to an initial cooling, with or' without evaporation of water, to reduce the cooling load to be borne by the sodium carbonate crystallizer, prior to further evaporative cooling to cause crystallization of the sodium carbonate. More than one such initial cooling steps may be used, if desired. The initial cooling may be omitted, if desired.
  • the hot aqueous solution at an initial temperature of about 200F is cooled to about 120F with some evaporation of water and then the solution is evaporatively cooled to below about 70F, preferably to about 60F, causing crystallization of sodium carbonate decahydrate. Since the sodium carbonate is crystallized in the form of the decahydrate, thereby more water is removed from the solution.
  • the evaporative cooling and crystallization of sodium carbonate preferably are continued until the mother liquor is substantially saturated with respect to sodium chloride.
  • the resulting slurry preferably is diluted with recycled mother liquor to improve the workability thereof and sodium carbonate, substantially free from sodium chloride, is separated from the mother liquor by line 52. While the crystallization of sodium carbonate and its separation from the mother liquor are illustrated as occurring in the same vessel in FIG. 1, this is for ease of illustration and normally separate vessels are used.
  • the sodium carbonate is passed by line 52 to a dissolving tank 54 wherein it is dissolved in water, or any other suitable aqueous medium, preferably weak wash water, fed by line 56 to form an aqueous sodium carbonate solution which is passed to a causticizer 58 by line 60.
  • the sodium carbonate in the aqueous solution is converted substantially completely to sodium hydroxide by the action of lime fed by line 62 from a lime kiln 64.
  • the calcium carbonate mud precipitated in the causticizer 58 after suitable washing to remove entrained alkali values, is returned to the lime kiln 64 by line 66 for reconversion to lime.
  • the weak wash water resulting from the calcium carbonate mud washing may, in part be used as the aqueous material fed by line 44 to dissolve the smelt.
  • the aqueous sodium hydroxide solution resulting from the recausticization process is recycled by line 68 to provide at least part of the pulping liquor fed by line 14 to the digester 12.
  • the evaporation of water in the evaporator 72 is achieved by boiling the solution under a reduced pressure, preferably until the solution is substantially saturated with respect to sodium carbonate.
  • the water evaporated in the evaporator 72 is removed by line 74.
  • the temperature to which the mother liquor is heated to achieve the desired evaporation and crystallization of sodium chloride depends on the temperature at which the sodium carbonate crystallization occurred in the crystallizer 48 and the relative concentrations of sodium carbonate and sodium chloride in the mother liquor.
  • the temperature must be higher than a temperature at which sodium carbonate will crystallize, if substantially pure sodium chloride'is to be recovered, and temperatures as high as 220F may be used. At these temperatures, the temperature to which the hot aqueous solution is cooled to crystallize hydrated sodium carbonate must be quite low, typically about 32 to 50F. Temperatures in the range of about to 140F have proved to be the desirable range.
  • the mother liquor may be heated with boiling to about F to achieve crystallization of sodium chloridel
  • the sodium chloride which is crystallized is removed by line 76 in substantially pure form.
  • the quantity of sodium chloride removed in this manner is substantially the same as the quantity of sodium chloride present in the hot aqueous solution which is subsequently cooled to crystallize hydrated sodium carbonate, less any sodium chloride present in the recycle stream in line 78.
  • the sodium chloride removed by line 76 may be put to a variety of uses.
  • the sodium chloride is utilized to regenerate bleach plant chemicals.
  • the sodium chloride may be used to generate sodium hydroxide by electrolysis of an aqueous solution thereof, the sodium hydroxide being used in the bleach plant in line 26.
  • the sodium chloride may be used to generate chlorine dioxide and chlorine by reaction with sodium chlorate and sulphuric acid, the
  • the sodium chloride may be electrolyzed as an aqueous solution to sodium chlorate for use in a chlorine dioxide producing reaction involving reduction of the sodium chlorate in an acid medium.
  • the evaporation of the mother liquor from the separation of sodium carbonate and the separation of the sodium chloride crystallized therefrom is illustrated as occurring in a single vessel 72.
  • usually two separate vessels are used, the slurry resulting from the evaporation in one vessel being passed to a second vessel for separation of the solid sodium chloride.
  • the mother liquor resulting from the sodium chloride separation usually will still contain quantities of sodium chloride and sodium carbonate and is recycled by line 78 to the smelt dissolver 42 along with the aqueous material in line 44, or, alternatively, is recycled to hot aqueous solution in line 46.
  • the mother liquor in line 78 may contain small quantities of sodium hydroxide, which would not be removed from the system by the illustrated procedure.
  • the sodium hydroxide may arise. from weak wash water from the washing of the calcium carbonate mud where such water is used to provide at least part of the aqueous material fed by line 44 to the smelt dissolver 42.
  • the sodium hydroxide also may arise from small quantities of sodium oxide values in the smelt.
  • the mother liquor in line 78 may be carbonated using carbon dioxide, or in any other convenient manner, to convert such sodium hydroxide values to sodium carbonate, prior to passageof the mother liquor in line 78 to the hot aqueous solution in line 46. In this way, any build up of sodium hydroxide values in the recycled mother liquor in line 78 is avoided.
  • the resulting mother liquor may be cooled again to precipitate further quantities of hydrated sodium carbonate.
  • the sodium carbonate and sodium chloride in the smelt are separated one from another into substantially pure product streams which contain quantities of the hydrated sodium carbonate and sodium chloride which are substantially equal to the quantities of these materials present in the smelt.
  • a smelt consisting predominantly of sodium sulfide, sodium carbonate and sodium chloride, and also containing minor quantities of sodium sulfate and other sodium and sulfur-compounds due to inefficiences of the furnace, is passed by line 110 to a smelt dissolver 112.
  • sodium hydroxide and sodium sulfide are the active pulping chemicals and sodium sulfate, another source of soda and sulfur values, is added to the black liquor to provide make up for soda and sulfur losses.
  • the smelt is dissolved in the smelt dissolver 112 in an aqueous material fed by line 114, which may be water or, in part, weak wash water, to form a hot aqueous solution, commonly known as green liquor, in line 116.
  • the green liquor in line 116 may also contain recycled liquid, as will become more apparent hereinafter.
  • the hot green liquor typically having a temperature of about 200F, is cooled in a precooler 118, with evaporation of some water therefrom, if desired.
  • the water evaporated in the precooler is removed by line 120.
  • the green liquor is cooled to about lOOF in the precooler 118.
  • the precooled green liquor is passed by line 122 to an evaporative cooler 124 wherein the precooled green liquor is subjected to evaporative cooling.
  • Water is evaporated from the precooled green liquor, to cause cooling of the liquor and thereby bring about crystallization of a mixture of sodium carbonate, sodium sulfide and sodium sulfate, together with minor quantities of other precipitated sodium and sulfur salts which may be present while avoiding crystallization of sodium chloride.
  • the water evaporated is removed by line 126.
  • the evaporative cooling is carried out until the mother liquor is substantially saturated with respect to sodium chloride.
  • the hot green liquor is subjected to a two-stage evaporative cooling to achieve crystallization of a mixture of sodium carbonate, sodium sulfide and sodium sulfate in the second stage.
  • the cooling of the green liquor to achieve the desired precipitation may be carried out in a single step, and may be carried out in any convenient manner other than evaporative cooling, if desired. Further, the cooling achieved by evaporation may be enhanced by suitable additional cooling.
  • the slurry resulting from the evaporative cooling is diluted with recycle mother liquor in line 128 and the diluted slurry passes by line 130 to a separator 132 of any convenient construction.
  • the separator 132 the mixture of sodium carbonate, sodium sulfide and sodium sulfate is separated from the mother liquor and is passed by line 134 to a recausticizer wherein the sodium carbonate is converted to sodium hydroxide, the resulting white liquor being subsequently used as pulping liquor.
  • the sodium sulfate passes to the furnace in the subsequently formed black liquor.
  • the quantity of sodium sulfide removed by line 134 is substantially the same as that contained in the smelt in line 110.
  • the quantity of sodium carbonate and sodium sulfate removed in line 134 may be less than the quantity present in the smelt, and, in the case of sodium sulfate, formed in the green liquor and, hence, a further separation of sodium carbonate and sodium sulfate may be necessary. In the illustrated embodiment, this is carried out by passing the mother liquor from the separator 132 by lines 136 and 138 to an evaporator 140, with a portion of the mother liquor being recycled by line 128 as diluent for the slurry formed in the evaporative cooler 124.
  • the mother liquor is heated and evaporated in the evaporator 140 to cause the crystallization of sodium carbonate together with the double salt of sodium carbonate and sodium sulfate known as burkeite water vapor is removed by line 141.
  • the mother liquor may be evaporated at a temperature of about 220F, while avoiding substantially the precipitation of sodium chloride, the evaporation being continued until the solution is substantially saturated with sodium chloride.
  • the slurry of burkeite and aqueous solution is passed by line 142 to a thickener 144 of any convenient construction wherein the sodium carbonate and burkeite is separated from the mother liquor and removed by line 146.
  • the sodium carbonate and burkeite separated in this wax may be passed to the recausticizer along with the solids in line 134.
  • a separator may be employed instead of the thickener 144.
  • the thickener underflow is forwarded to the smelt dissolver 112, to the precooler 118 or to any other convenient location.
  • the mother liquor from the burkeite separation is passed by line 148 to an evaporator 150 wherein water is evaporated to deposit substantially pure sodium chloride, which, after separation from the resulting mother liquor, is removed by line 152.
  • the quantity of sodium chloride removed by line 152 preferably is substantially that contained in the smelt in line 110.
  • the sodium chloride removed in this way may be utilized in ay convenient manner, typically to form bleaching chemicals.
  • the evaporation in evaporator 150 results in water vapor which is removed by line 154 and may be carried out at any convenient temperature. The temperature chosen depends on the initial concentration of the dissolved components of the mother liquor and the quantity of sodium chloriderequired to'be removed.
  • the evaporation of the solution in the evaporator 150 to Y precipitate sodium "chloride generally is carried out until the solution is substantially saturated with respect to sodium carbonate and/or sodium sulfide and/or sodium sulfate, and typically is carried out at a tempera- -ture of about 120F.
  • the mother liquor resulting from the sodium chloride crystallization contains residual quantities of sodium carbonate, sodium sulfide, sodium sulfate and sodium chloride and is recycled by line 156 to carbonator 158.
  • the mother liquor is contacted with carbon dioxide fed by line 160, in order to convert any sodium hydroxide present in the mother liquor in line 156 to sodium carbonate, so that a build up of sodium hydroxide upon repeated recycle is prevented.
  • sodiumhydroxide may arise from weak wash water and- /or from materials in the smelt.
  • the carbonated mother liquor is forwarded by line 162 to the hotgreen liquor in line l-l6. This maybe achieved by feeding the mother liquor in line 162 along with the-aqueous material in line 114 to dissolve the smelt. Alternatively, the mother liquor may be added to the hot greenliquor'in line 116 after formation thereof.
  • the mother liquor resulting after separationof the sodium chloride consists mainly of sodium sulfide solution, which may beevaporated to crystallize therefrom the remaining quantities of sodium carbonate, sodium sulfate, and sodium chloride.
  • the sodium sulfidesolution then may be added to the sodium hydroxide solution resulting fromthe recausticization to provide white liquor for the recycle as pulping liquor.
  • the sodium solution may be recycled as the pulping liquor, while part of the sodium hydroxide solution resulting from the recausticization is for- .Warded to the bleach plant for use therein as caustic ex- ,traction liquor, or in oxygen-bleaching processes.
  • the sodium sulfide solution may be used, in impregnating wood chips. The crystallized solids may be recycled to the hot green liquor.
  • Example 1 A mass balance for the embodiment of FIG. 1 producing 500. tons/day of pulp was calculated from vknown solubility data .for the system Na CO -Na- C1l-l O. 25,209 lbs/hr. of a smelt having a constitution of 87.5% Na CO and 12.5% NaCl is dissolved in 66,774 lbs/hr. of water to provide 91,667 lbs/hr. of green liquor having a temperature of about 200F.
  • the green liquor is mixed with 43,372 lbs/hr. of recycle mother liquor containing sodium carbonate in a concentration of 12.4% and sodium chloride in a concentration of 18.4% and having a temperature of F, to provide a combined liquid stream which is passed to an evaporative precooler wherein 6,034 lbs of water are removed while the temperature is cooled to about 120F, resulting in 129,005 lbs/hr. of precooledliquor.
  • the precooled liquor then is evaporatively cooled to 59F resulting in crystallization of sodium carbonate decahydrate.
  • 11,368 lbs/hr. of stream are evaporated from the precooled liquor in this cooling step, and 52,085 lbs/hr. of recycle mother liquor, containing 9.24% sodium carbonate and 19.10% sodium chloride, is recycled to the evaporative cooler to dilute the slurry of sodium carbonate decahydrate formed therein.
  • 169,722 lbs/hr. of slurry is forwarded to a filter wherein 59,493 lbs/hr. of sodium carbonate decahydrate are recovered, leaving 1 10,229 lbs/hr. of filtrate, which is split into the mother liquor recycle stream to dilute the slurry in the evaporative cooler and into 58,144 lbs/hr. feed stream to an evaporator.
  • the feed stream containing 9.25% sodium carbonate and 19.10% sodium chloride, is heated under a reduced pressure to evaporate 1 1,929 lbs/hr. of water from the solution at 120F, resulting in crystallization of sodium chloride from the solution.
  • Example 2 A mass balance for the embodiment of FIG. 2 producing 500 tons/day of pulp was calculated from experimental solubility data for the system Na SNa CO -NaC1-I-l O. 95,750 lbs/hr of green liquor containing 4.2% sodium sulfide, 17.6% sodium carbonate, 3.3% sodium chloride and 0.65% sodium sulfate and having a temperature of 200F is mixed with 28,408 lbs/hr. of recycled mother liquor from sodium chloride removal containing 10.0% sodium sulfide, 6.2% sodium carbonate, 12.0% sodium chloride and 0.65% sodium sulfate and 7,755 lbs/hr. of burkeite thickener underflow at 225F containing 2.713 lbs/hr.
  • burkeite and 5,043 lbs/hr of liquor containing 7.3% sodium sulfide, 4.6% sodium carbonate, 16.8% sodium chloride and 0.5% sodium sulfate, and the mixture of the three streams is precooled to 120F with evaporation of 6.397 lbs/hr. of water.
  • the resulting 125,516 lbs/hr. of precooled liquor containing 5.8% sodium sulfide, 15.6% sodium carbonate, 5.9% sodium chloride and 2.2% sodium sulfate then is evaporatively cooled to 50F, with evaporation of 12,705 lbs/hr. of water.
  • the resulting slurry containing a solid phase consisting of a mixture of sodium carbonate, sodium sulfide and sodium sulfate is diluted with 56,695 lbs/hr. of recycled filtrate from the solid phase separation containing 6.0% sodium sulfide, 5.3%
  • the 169,506 lbs/hr of slurry is passed to a filter whereon 59,327 lbs/hr. of solid is separated from the liquid phase.
  • the seperated solids consists of 6.8% sodium sulfide, 28.4% sodium carbonate and 1.1% so dium sulfate.
  • the 110,179 lbs/hr. of filtrate from this solid phase separation is divided into two streams, one of which is recycled to dilute the slurry in the evaporative cooler. The other stream, is a quantity of 53,484 lbs/hr.
  • the filtrate stream is recycled to the green liquor.
  • the process of the present invention provides in its preferred embodiments, a salt removal process in which the need for high temperatureresistant equipment is avoided, and the quantity of water requiring evaporation is decreased, and in which a dead load of sodium chloride does not recycle in the white liquor.
  • the present invention represents an improvement on the white liquor evaporation procedures outlined in the aformentioned Canadian Pat. No. 915,361 and its equivalent US. Pat. No. 3,746,612.
  • a pulp mill process which comprises digesting cellulosic fibrous material with a pulping liquor containing at least one active pulping chemical, separating the pulped material from spent pulping liquor and forming a solid mass containing sodium carbonate from said spent pulping liquor, the improvement which comprises dissolving at least part of said solid mass in an aqueous material to form a hot aqueous solution thereof, providing sodium chloride in said hot aqueous solution of said solid mass, cooling said hot aqueous solution to crystallize hydrated sodium carbonate therefrom substantially to the point of saturation of the cooled solution with sodium chloride, whereby said crystallized hydrated sodium carbonate is substantially free from contamination by sodium chloride, separating said crystallized hydrated sodium carbonate from the resulting aqueous solution substantially saturated with sodium chloride, evaporating said sodium chloride solution to deposit sodium chloride therefrom, and separating said deposited sodium chloride from the resulting mother liquor.
  • said active pulping chemical is sodium hydroxide and is formed from said sodium carbonate by forming said separated sodium carbonate into an aqueous solution thereof and causticizing substantially the sodium carbonate values of said aqueous solution to sodium hydroxide.
  • sodium hydroxide and sodium sulfide are the active pulping chemicals in said pulping liquor and said solid mass contains sodium sulfide, and including crystallizing sodium sulfide from said hot aqueous solution of said solid mass together with said hydrated sodium carbonate.
  • said solid mass additionally contains sodium sulfate and including crys-' tallizing at least part of said sodium sulfate from said hot aqueous solution of said solid mass together with said hydrated sodium carbonate and sodium sulfide.
  • sodium hydroxide and sodium sulfide are the active pulping chemicals in said pulping liquor and said solid mass contains sodium sulfide, and including crystallizing hydrated sodium carbonate from said hot aqueous solution of said solid mass while avoiding precipitation of sodium sulfide and sodium chloride, after separation of said crystallized hydrated sodium carbonate, evaporating the resulting sodium sulfide solution to deposit substantially all the sodium chloride and sodium carbonate values therefrom, separating the deposited mixture of sodium chloride and sodium carbonate from the resulting concentrated sodium sulfide solution, recovering substantially pure sodium chloride from said deposited mixture and recycling the remainder of said deposited mixture to said hot aqueous solution.

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CA214,505A CA1070457A (en) 1973-12-03 1974-11-25 Removal of sodium chloride from pulp mill operations
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JP49137778A JPS5088303A (enExample) 1973-12-03 1974-12-03
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Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3945880A (en) * 1974-08-05 1976-03-23 Erco Envirotech Ltd. Sodium chloride removal in pulp mill systems
US3954552A (en) * 1974-08-05 1976-05-04 Erco Envirotech Ltd. Removal of sodium chloride from pulp mill systems
US3986923A (en) * 1973-08-07 1976-10-19 Erco Envirotech Ltd. Removal of dissolved salts from sulphide liquors
US4039372A (en) * 1975-03-11 1977-08-02 Erco Envirotech Ltd. Bleach plant filtrate recovery
US4049490A (en) * 1976-02-23 1977-09-20 Veniamin Petrovich Zaplatin Electrodialysis of bleaching effluent
US4093508A (en) * 1974-03-12 1978-06-06 A. Ahlstrom Osakeyhtio Process for recovering chemicals from the waste liquors of sulfate cellulose digestion and the waste waters of bleaching
US4138312A (en) * 1976-05-19 1979-02-06 Sappi Limited Process of recovering sodium carbonate from spent pulping liquors
US4249990A (en) * 1978-04-19 1981-02-10 Erco Envirotech Ltd. Process for removal of potassium values from pulp mill liquors
US4253911A (en) * 1976-11-15 1981-03-03 Mo Och Domsjo Aktiebolag Process for maintaining a low sodium chloride content in recycled sodium chemicals of sodium-based pulp manufacturing processes
DE3613959A1 (de) * 1985-04-29 1986-10-30 Tampella Oy Ab Zellstoffkoch- und -bleichverfahren
US4981556A (en) * 1986-08-14 1991-01-01 Alby Klorat Ab Process for the preparation of sulfide-free alkali liquor using copperoxide
EP0687766A1 (en) * 1994-06-17 1995-12-20 A. Ahlstrom Corporation Method for the manufacture of cooking liquors by green liquor crystallization
US5507912A (en) * 1991-05-13 1996-04-16 H. A. Simons Ltd. Kraft pulping process wherein sulphide-rich and sulphide-lean white liquors are generated
US5567293A (en) * 1994-12-22 1996-10-22 Pulp And Paper Research Institute Of Canada Electromembrane processes for the treatment of kraft mill electrostatic precipitator catch
WO2013040205A1 (en) * 2011-09-16 2013-03-21 Sabic Innovative Plastics Ip B.V. Method to remove carbonate from a caustic scrubber waste stream

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US1791281A (en) * 1929-04-29 1931-02-03 Morse Harry Wheeler Production of sodium-carbonate liquor
US2642399A (en) * 1949-02-23 1953-06-16 Robert S Aries Process for dissolving ash containing sodium sulfide and sodium carbonate
US2862887A (en) * 1955-10-03 1958-12-02 Western Preciptation Corp Process for production and separation of sodium sulfide and sodium carbonate from spent liquors
US3396076A (en) * 1964-12-10 1968-08-06 Parkinson Crosby & Works Inc Method of recovery of chemical values of a kraft pulping process of cellulosic material
US3560329A (en) * 1968-12-27 1971-02-02 Combustion Eng Process for low sulfide chemical recovery
US3698995A (en) * 1967-01-16 1972-10-17 Electric Reduction Co Digestion and bleaching of wood pulp followed by recovery of chemicals and countercurrent flow of wash water
US3746612A (en) * 1969-12-30 1973-07-17 Erco Envirotech Ltd Removal of sodium chloride from white pulping liquor
US3755068A (en) * 1971-02-23 1973-08-28 Erco Envirotech Ltd Regeneration of chlorine dioxide for pulp treatment

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1791281A (en) * 1929-04-29 1931-02-03 Morse Harry Wheeler Production of sodium-carbonate liquor
US2642399A (en) * 1949-02-23 1953-06-16 Robert S Aries Process for dissolving ash containing sodium sulfide and sodium carbonate
US2862887A (en) * 1955-10-03 1958-12-02 Western Preciptation Corp Process for production and separation of sodium sulfide and sodium carbonate from spent liquors
US3396076A (en) * 1964-12-10 1968-08-06 Parkinson Crosby & Works Inc Method of recovery of chemical values of a kraft pulping process of cellulosic material
US3698995A (en) * 1967-01-16 1972-10-17 Electric Reduction Co Digestion and bleaching of wood pulp followed by recovery of chemicals and countercurrent flow of wash water
US3560329A (en) * 1968-12-27 1971-02-02 Combustion Eng Process for low sulfide chemical recovery
US3746612A (en) * 1969-12-30 1973-07-17 Erco Envirotech Ltd Removal of sodium chloride from white pulping liquor
US3755068A (en) * 1971-02-23 1973-08-28 Erco Envirotech Ltd Regeneration of chlorine dioxide for pulp treatment

Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3986923A (en) * 1973-08-07 1976-10-19 Erco Envirotech Ltd. Removal of dissolved salts from sulphide liquors
US4093508A (en) * 1974-03-12 1978-06-06 A. Ahlstrom Osakeyhtio Process for recovering chemicals from the waste liquors of sulfate cellulose digestion and the waste waters of bleaching
US3945880A (en) * 1974-08-05 1976-03-23 Erco Envirotech Ltd. Sodium chloride removal in pulp mill systems
US3954552A (en) * 1974-08-05 1976-05-04 Erco Envirotech Ltd. Removal of sodium chloride from pulp mill systems
US4039372A (en) * 1975-03-11 1977-08-02 Erco Envirotech Ltd. Bleach plant filtrate recovery
US4049490A (en) * 1976-02-23 1977-09-20 Veniamin Petrovich Zaplatin Electrodialysis of bleaching effluent
US4138312A (en) * 1976-05-19 1979-02-06 Sappi Limited Process of recovering sodium carbonate from spent pulping liquors
US4253911A (en) * 1976-11-15 1981-03-03 Mo Och Domsjo Aktiebolag Process for maintaining a low sodium chloride content in recycled sodium chemicals of sodium-based pulp manufacturing processes
US4249990A (en) * 1978-04-19 1981-02-10 Erco Envirotech Ltd. Process for removal of potassium values from pulp mill liquors
US4799994A (en) * 1985-04-29 1989-01-24 Oy Tampella Ab Process for cooking and bleaching pulp
DE3613959A1 (de) * 1985-04-29 1986-10-30 Tampella Oy Ab Zellstoffkoch- und -bleichverfahren
DE3613959C2 (enExample) * 1985-04-29 1990-03-29 Oy Tampella Ab, Tampere, Fi
US4981556A (en) * 1986-08-14 1991-01-01 Alby Klorat Ab Process for the preparation of sulfide-free alkali liquor using copperoxide
US5507912A (en) * 1991-05-13 1996-04-16 H. A. Simons Ltd. Kraft pulping process wherein sulphide-rich and sulphide-lean white liquors are generated
EP0687766A1 (en) * 1994-06-17 1995-12-20 A. Ahlstrom Corporation Method for the manufacture of cooking liquors by green liquor crystallization
US5607549A (en) * 1994-06-17 1997-03-04 Ahlstrom Machinery Corporation Method for the manufacture of cooking liquors of different sulphidity by green liquor crystallization
US5567293A (en) * 1994-12-22 1996-10-22 Pulp And Paper Research Institute Of Canada Electromembrane processes for the treatment of kraft mill electrostatic precipitator catch
WO2013040205A1 (en) * 2011-09-16 2013-03-21 Sabic Innovative Plastics Ip B.V. Method to remove carbonate from a caustic scrubber waste stream
CN103827037A (zh) * 2011-09-16 2014-05-28 沙特基础创新塑料Ip私人有限责任公司 用于从苛性碱洗涤器废液流中除去碳酸盐的方法
CN103827037B (zh) * 2011-09-16 2016-04-27 沙特基础全球技术有限公司 用于从苛性碱洗涤器废液流中除去碳酸盐的方法
US9364794B2 (en) 2011-09-16 2016-06-14 Sabic Global Technologies B.V. Method to remove carbonate from a caustic scrubber waste stream

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SE7414971L (enExample) 1975-06-04
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CA1070457A (en) 1980-01-29
FI344574A7 (enExample) 1975-06-04

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