US3650888A - Pollution controlled polysulfide recovery process - Google Patents

Pollution controlled polysulfide recovery process Download PDF

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US3650888A
US3650888A US45455A US3650888DA US3650888A US 3650888 A US3650888 A US 3650888A US 45455 A US45455 A US 45455A US 3650888D A US3650888D A US 3650888DA US 3650888 A US3650888 A US 3650888A
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liquor
nahco3
spent
recycle stream
spent liquor
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Carl Bertil Fogman
Hugh Wharton Nelson
Utah Tsao
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Combustion Engineering Inc
Lummus Technology LLC
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/06—Investigating concentration of particle suspensions
    • G01N15/0656—Investigating concentration of particle suspensions using electric, e.g. electrostatic methods or magnetic methods
    • 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
    • D21C11/04—Regeneration of pulp liquors or effluent waste waters of alkali lye
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P40/00—Technologies relating to the processing of minerals
    • Y02P40/40—Production or processing of lime, e.g. limestone regeneration of lime in pulp and sugar mills
    • 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

  • the spent liquor is [22] June 1 1970 pre-evaporated and mixed with a recycle stream of liquor con- 2 1 APPL 45,455 taining Na CO and NaHCO
  • the mixture is next carbonated with a gas stream rich in CO which has been generated from lime kiln flue gas.
  • the carbonated spent liquor is then vacuum [52] US. Cl ..162/30, 23/48, 162/60 stripped to release 5 which is converted to lf
  • the sulfur [51] Int.
  • V 7 etc. are included to reduce air and water pollution.
  • Kraft pulping is done with an aqueous solution containing NaOH and Na S.
  • sulfur is added to the same type of cooking liquor under conditions permitting the formation of sodium polysulfide, Na s."
  • the improvement in pulp yield over the conventional process is on the order of to 14 percent and since raw wood is the major cost item in pulp production, the economic incentives to develop the process are obvious.
  • the initial sulfur charge in polysulfide pulping may be more than three times higher than that of kraft and the spent liquor cannot undergo normal kraft evaporation and combustion without serious consequences.
  • there would be an intolerable level of H S release in the mill operation causing an air and water pollution problem and there would also be increased corrosion and decreased capacity in the multiple-effect evaporators.
  • the present invention is therefore directed to a practical chemical recovery system for use with polysulfide pulping.
  • An object of the invention is to remove sulfur from the spent liquor prior to combustion in a chemical recovery furnace and to use this sulfur for producing fresh polysulfide cooking liquor.
  • a further object is to prevent as much sulfur loss as possible thus preventing air and water pollution.
  • the pulp washing after digestion is carried out so as to minimize the oxidation of NaSH which minimization is necessary to maximize sulfur recovery.
  • the spent liquor is then preevaporated and mixed with a recycle stream containing NaH- CO and Na CO- so as to bring up the bicarbonate concentration to lower the pH for soap skimming and to bring up the carbonate concentration for the carbonation and H 8 stripping steps.
  • Carbonation of the "spent liquor to form the bicarbonate results in some H S release.
  • the bulk of the H S release takes place in the subsequent vacuum stripping step to produce a concentrated H 5 stream for conversion to elemental sulfur for the production of polysulfide cooking liquor.
  • Other features of the invention include controlling the concentration and pH so as to minimize or avoid process difficulties and recovering sulfur-containing gas or liquid streams which otherwise might cause pollution.
  • FIG. 1 is an overall process flow diagram.
  • FIG. 2 is a flow diagram of the pulp washing portion of the system.
  • FIG. 3 is a flow diagram of the multiple-effect evaporator system.
  • FIG. 4 is a flow diagram of an alternate liquor recycle arrangement.
  • Wood chips such as loblolly pine ships, polysulfide liquor and white liquor are fed to the digester 12 along with any recycled spent back liquor necessary for fill.
  • the preferred amount of polysulfide sulfur in the cooking liquor mixture amounts to about 4 percent by weight (dry basis) of the wood.
  • the maximum practical amount of polysulfide sulfur is about 7 percent and the invention is operable to any amount of polysulfide up to this maximum.
  • the polysulfide digestion process may be carried out either in a batch or continuous type operation. The digestion products are fed to a blow or flash tank 14 in which vapors are released.
  • Pulp Washing In conventional kraft processes, the pulp undergoes a countercurrent washing operation to obtain a clean pulp product and a spent liquor at a relatively high concentration of dissolved nonpulp wood fractions and used chemicals. This washing is generally done in a threeor four-filter drum system having an open. exhaust hood for vapor outlet which permits air entry.
  • the liquor in a pulp washer contains a considerable amount of NaSH.
  • a substantial amount of this NaSH is oxidized to Na S O This is desirable in a kraft process since it fixes part of the sulfur in a nonvolatile form which does not produce H 5 in the evaporators downstream.
  • the liquor coming from a polysulfide pulp process contains two to three times more NaSH than in the case of the kraft process.
  • the present invention employs a pulp washing system 20 as illustrated in detail in FIG. 2.
  • This system includes a pulp washer 22 which is illustrated as having three filter drums. This pulp washer is totally enclosed by the hood 24 to essentially avoid any air infiltration.
  • the filtrate from the drum washers is fed to individual filtrate tanks 26 in a countercurrent operation and the spent liquor discharged to the next operation as will be described hereinafter.
  • the vapors from the filtrate tanks are fed to a foam tank 28 and then recycled by means of the blower 30 through vapor surge tank 32.
  • the vapor surge tank 32 is connected by means of the surge line 34 with the polysulfide liquor tank 36. This is for the purpose of blanketing the polysulfide liquor in its storage tank with nitrogen and water vapor to prevent oxidation of polysulfide to inactive thiosulfate.
  • This totally enclosed pulp washing system would have to operate for an initial short period (1 2 hours) to exhaust the oxygen inventory of the washing system.
  • the oxygen would be exhausted by reacting with some of the NaSH present during this initial period. After this period, the vapor would be essentially nitrogen and water vapor thus preventing further oxidation.
  • a secondary beneficial effect of enclosing the pulp washer is a reduced heat consumption.
  • hot water at 5560 C. is fed to the last filter drum as wash water.
  • flash evaporation of water from the liquor occurs which keeps the temperature of the filtrate liquor leaving the first filter drum at about C.
  • the barometric leg suction principle applied to this type of washing operation would not function.
  • the wash water temperature must be reduced to about 3540 C.
  • a further advantage of the enclosed washing system is the elimination of H 8 discharge to the atmosphere such as occurs in an open system.
  • Pre-evaporation The spent liquor from the pulp washing operation 20, after any necessary portion has been recycled to the digester 12, is fed to the pre-evaporators 38 which may consist, for example, of the last four stages of a six-stage multiple-effect evaporator system.
  • the purpose of evaporation in a pulp mill chemical recovery system is to concentrate the organic and inorganic constituents so that the liquor may be burned in the chemical recovery furnace.
  • the purpose of the pre-evaporation step at this point in the present invention is to create optimum conditions for two subsequent steps in the polysulfide sulfur recovery process, namely CO absorption and H 8 stripping. This pre-evaporation concentrates the NaSH and Na CO which increases the kinetics of the subsequent processing steps and reduces the size of the necessary equipment.
  • soaps can be effectively separated from the spent liquor after it has been pre-evaporated to 25-30 percent dry solids.
  • This soap separation facilitates the following processing steps because of lessened foaming tendencies.
  • the pre-evaporation also gives a relatively high liquor specific gravity, 1.12-1.15, and reasonably low viscosity, about 2 centipoise. The higher specific gravity results in the easier collapse of any foam that is generated and the viscosity of low enough for obtaining good chemical mass transfer in the CO absorption and H 5 stripping operations.
  • Stages lll through VI of the multiple effect evaporators are employed in the pre-evaporation section.
  • the liquor flows from Stage VI to Stage V to Stage IV to Stage III and then out of the evaporator system to the soap skimmer 44 at a concentration of -30 percent dry solids.
  • the vapors in the preevaporation section flow from Stage lll to IV to V and then to Stage Vl. Minor continuous vapor purge from the steam chests ofStages IV, V, and V! are made to release H S through the lower part of the steam chests of the evaporator bodies.
  • the effluent from these steam chests is conducted to condenser with the condensate being fed to the above-mentioned condensate treating system and with the H S-containing vented vapors being fed to compressor 42 along with the vapors from Stage VI.
  • the compressor 42 is used for receiving the vented vapors from the condenser 40.
  • lmproved Soap Skimming and Recycle The effluent from Stage III of the pre-evaporation section is fed to a conventional soap skimmer 44 which provides approximately one hour dwell time as in normal skimming operation. The 25-30 percent dry solids concentration of this feed to the soap skimmer is most favorable to such a skimming operation.
  • FIG. 4 An alternate recycle scheme is illustrated in FIG. 4.
  • the recycle is H 8 stripped liquor taken from the vacuum stripper rather than carbonated liquor from the carbonating tower.
  • This recycle is passed through a recarbonator 49 in which Na CO is converted to NaHCO
  • the CO supply to the recarbonator 49 may be a 100 percent CO stream (dry basis) such as from a hot carbonate system, which will be described hereinafter, or it may be a flue gas stream such as from a lime kiln.
  • This recarbonation step provides the NaH- CO in the recycle stream necessary for effective soap skimming as described above.
  • the soap skimming operation in the present invention has several advantages. IN passing spent liquor containing soaps through a packed column, there is a tendency for the soaps to coat the packing material. This soap coating forms a sticky surface to which the precipitated lignin readily adheres. This can very rapidly cause the packed column to plug. Effective soap removal can essentially eliminate this problem. Another problem which occurs when soaps are present in spent liquor is foaming in various operations such as gas-spent liquor contact steps including carbonation, stripping, and oxidation. This foaming problem can also be reduced by means of the improved soap skimming operation. A third benefit of the improved soap skimming is that the soap yield and consequently the tall oil yield if significantly increased.
  • this recycle may be anywhere from 0 100 percent of the quantity of liquor coming from the preevaporation section.
  • NaHCO available to permit the subsequent stripping of H 8 and CO according to reactions (2) and (3) above.
  • the CO gas stream fed to the carbonating tower 50 is preferably 100 percent CO (dry basis) at about the tower operating pressure and temperature.
  • This pure CO gas stream is obtained from a hot carbonate system which will be described hereinafter and it is passed countercurrent to the downcoming liquor stream. It is desirable that only enough CO be passed through the carbonating tower 50 to produce the desired amount of NaHCO.
  • the fact that the CO stream is concentrated and thus small, in terms of gas flow, means that the amount of H 8 released in the carbonating tower will be small because of its partial pressure/vapor pressure relabonating tower would be much higher.
  • the discharge would be a gas stream lean in H S. But the purpose of this invention is to create a mixture of gases from the carbonating tower, the H 8 stripping tower and other sources so rich in H 8 as to permit an efficient operation of the Clause reactor 84.
  • the amount of CO fed to the carbonating tower should be as follows:
  • the carbonating tower 50 may operate, for example, at a pressure anywhere from atmospheric to 100 p.s.i.a.- and at a temperature from 25-l00 C., a more practical range is atmospheric pressure to 30 p.s.i.a. and 5080 C.
  • a pressure anywhere from atmospheric to 100 p.s.i.a.- and at a temperature from 25-l00 C.
  • a more practical range is atmospheric pressure to 30 p.s.i.a. and 5080 C.
  • the overhead vapor stream from the carbonating tower 50 containing excess CO and some H S is combined with the vent from condenser 54, the discharge from compressor 42, and the vapor sphere discharge stream as part of the feed to the Claus reactor 84.
  • H S Stripping A portion of the carbonated liquor stream discharged from the carbonating tower 50 is recycled to the soap skimmer 44 as discussed hereinbefore.
  • the remaining carbonated liquor stream is fed to the vacuum stripping tower 51 together with a bleed stream from the hot carbonate system which will be explained hereinafter.
  • This bleed stream contains sodium carbonate and bicarbonate (approximately 12 to 15 percent) and a small amount of Na SO (approximately 5 to 6 percent).
  • the bleed stream can also be introduced before the carbonating tower 50.
  • 'l'hc stripping tower 51 is a packed column in which the hicarbonatcd liquor undergoes vacuum steam stripping whereby H 8 and some CO are released. Any other type of equipment conventionally used for gas stripping may be used in place of the packed column.
  • the stream for carrying out this stripping operation is obtained, for example, from Stage I of the multiple effect evaporator system as indicated in FIG. 3 or from stages II or III.
  • the primary reaction that occurs is:
  • the liquor temperature in the stripping tower will be at or below the boiling point of the liquor at the tower pressure.
  • the vacuum stripping tower may operate, for example, at a pressure anywhere from about 5 in. Hg absolute up to atmospheric pressure. A more practical range is 8-17 in. Hg absolute with the preferred pressure being about 10 in. Hg absolute.
  • the overhead vapor stream from the stripping tower is condensed to overhead condenser 52, compressed by vacuum pump 53 to atmospheric pressure, fed to condenser 54 and then fed to the sulfur recovery system along with other vented vapor streams.
  • Themakeup chemical in a kraft mill is generally Na SO, in which the ratio of sodium and sulfur losses (Na,:S) is equal to one.
  • Na SO sodium and sulfur losses
  • the sulfide sulfur contained in all liquor streams is substantially higher than in the case of kraft.
  • elemental sulfur recovered for reuse in the process resulting in a chemical loss ratio (Na,:S) of about 1.4.
  • sodium hydroxide is used as a makeup for sodium losses and is added to the main liquor stream after the H 8 stripping step.
  • the liquor coming from the stripping tower 51 has a pH of about l0.0-10.5 and the addition of NaOH will increase the pH.
  • the amount of NaOH added for sodium makeup reasons may not be sufiicient to increase the pH to a range in which the precipitated lignin will be dissolved and kept in solution through the subsequent evaporation steps. Otherwise, lignin precipitate would foul the surfaces of the evaporators. Therefore, in order to increase the pH to the desired range of 12-13, a quantity of white liquor is recycled as shown in FIG. 1. This increased pH will also prevent the release of H 5 in the following direct contact evaporation step.
  • the amount of white liquor recycled and the exact pH desired will depend primarily upon the type of direct contact evaporator which is used. If the evaporating gas stream is hot flue gas, which contains CO that lowers the liquor pH, it will be necessaryv to add more white liquor to give a higher initial pH. If hot air is used in the direct contact evaporator, in which case the pH will not be lowered, less white liquor can be recycled and perhaps the recycle can even be eliminated. Oxidation The recycle of white liquor as described above will introduce some Na S into the black liquor stream in addition to whatever residual Na s might be present. This Na S may be partially converted to H 8 in a flue gas direct contact evaporator and as such would be released to the atmosphere as a pollutant.
  • the black liquor after the white liquor addition is subjected to a low level oxidation step in which the Na S is oxidized to the stable Na S O
  • This step is carried out with air or oxygen in the oxidizing tower 56 which may be a packed tower or any other suitable form of liquid gas contactor.
  • Black liquor oxidizers have been used in the past but with soap-containing liquors they have failed due to foaming. In the present invention, however, the soaps have been removed and foaming is no longer a serios problem.
  • air from the oxidizing tower 56 which may contain some sulfur compounds, is incinerated in the recovery boiler as shown in FIG. 1.
  • the H 3 stripped liquor after mixing with the makeup NaOH and any necessary white liquor recycle and after oxidizing tower 56 is then fed to Stage II of the multiple-effect evaporator system as shown in FIG. 3.
  • the final evaporators 57 increase the concentration of the liquor up to 50-55 percent dry solids.
  • the vapors from Stage II of the final evaporation section are used to heat Stage III of the pre-evaporator section while the vapors from Stage I of the final evaporation section are used both to heat Stage II and to feed the vacuum stripping tower 51 as previously mentioned.
  • the liquor discharged from Stage I of the final evaporation system is fed to a direct contact evaporator such as a conventional cascade evaporator in which water is evaporated from the liquor by direct contact with the flue gases from the recovery boiler.
  • a direct contact evaporator such as a conventional cascade evaporator in which water is evaporated from the liquor by direct contact with the flue gases from the recovery boiler.
  • Another type of direct contact evaporator which can be used is the air cascade evaporator in which air, which has been heated by heat exchange with the flue gases, is used for the evaporation instead of flue gases. In this case, the liquor would not be contacted with the flue gas CO and its pH would not be lowered. Therefore, as described above, it might be possible to reduce or eliminate the white liquor recycle. With the air cascade evaporator, the oxidizing tower 56 can also be eliminated.
  • the liquor is concentrated in this evaporator from 50-55 percent to about 70 percent dry solids concentration producing a liquor suitable for burning. Due to the low content of NaSH and Na s in the liquor at this point and the high pH, the emission of H 8 from the direct contact evaporator by reaction with CO will be close to nil. Under certain conditions H S discharged from the recovery furnace could be partially absorbed in this evaporator contributing to the reduction in air pollution by H S.
  • the liquor from the direct contact evaporator is next fed to a conventional chemical recovery furnace 60 with steam boiler discharging a smelt consisting mainly of Na S and Na CO and a flue has which generates steam in the boiler section of the furnace.
  • the sulfidity of the smelt is about 25 percent, which is normal as compared to conventional kraft units.
  • High sulfur-to-sodium ratio in the feed liquor to a chemical recovery furnace causes corrosion problems and greatly increases the chances of dangerous smelt-water explosions.
  • a sulfidity of about 25 percent is significantly below the danger level.
  • the flue gases from the chemical recovery furnace are used either directly or indirectly to carry out the evaporation in the direct contact evaporator as indicated above and in FIG. 1.
  • the smelt from the chemical recovery furnace is handled in much the same manner as in the conventional kraft process.
  • the smelt is dissolved in an aqueous solution in tank 62 producing what is commonly called the green liquor.
  • the green liquor from the smelt dissolving tank together with cal- Cium oxide from the lime kiln is then reacted in the causticizer 64 to form conventional white liquor which is then clarified at 66.
  • the white liquor from the clarifier is drained off into the white liquor storage tank 67 and a portion recycled to the H 8 stripped black liquor stream as needed and discussed above.
  • the solid precipitate from the clarifier 66 containing mostly CaCO is conducted to the washer 68 in which the CaCO is washed.
  • the wash water is then used to dissolve the smelt in tank 62.
  • the CaCO from the washer is next fed to the lime kiln 70 in which the CaCO is converted to CaO and C
  • the CaO from the lime kiln 70 is then recycled to the causticizer 64.
  • the gases from the lime kiln 70 containing primarily CO and N are passed to a wet scrubber 72 for the removal of particular matter and the major part of any SO present and then passed by means of the blower 74 into the hot carbonate systemv
  • the hot carbonate system comprises a C0 absorption tower 76 and a C0 desorption tower 78.
  • the absorbing liquor in the hot carbonate system is a mixture of NaHCO and Na CO
  • the gases as discharged from the absorption tower 76 to atmosphere do not contain any H 8 or SO thus eliminating this pollution problem.
  • the liquor from the absorption tower 76 is then sent via a heater 80 to the CO desorption tower 78 in which CO is stripped off the bicarbonate/carbonate mixture at a temperature of about 220230 F.
  • This desorption tower has a reboiler at the bottom to furnish the necessary heat for the stripping operation.
  • the liquor from the desorption tower, which is then cooled, is recycled to the absorption tower 76.
  • the overhead vapor from the desorption tower 78 contains 100 percent CO (dry basis) and is used to feed the carbonating tower 50. Since there will be a tendency to build up Na SO and other matter in the hot carbonate system, a portion of the circulating liquor in this system is bled and fed to the carbonation tower 50 or the stripping tower 51 as previously discussed. Pure NaOH is used as makeup for the circulating liquor in the hot carbonate system as a replacement for the bleed stream.
  • the vapors from the vacuum stripping tower 51, the carbonation tower 50, the pre-evaporators 38 and the vapor sphere 18 are mixed as shown in FIG. 1.
  • the mixture containing about 50 percent H S and 50 percent CO by volume is further compressed at 82.
  • the gas from the compressor 82 is passed to a reactor 84 in which the hydrogen sulfide is converted to elemental sulfur.
  • This conversion may be accomplished by any one of the many processes available.
  • One such process is the well-known Claus reaction, a gas phase, catalytic reaction, which takes place at relatively high temperature.
  • the gas from the compressor 82 at a pressure of about 9 p.s.i.g. is combined with air also at 9 p.s.i.g. in the exact stoichiometric ratio and reacted in the Claus reactor as follows:
  • the tail-end gases from the Claus reactor contain primarily CO and N but may contain some unreacted H 5 and 80,. These gases are therefore sent as part of the air feed to the chemical recovery furnace for complete incineration of the H S and S0
  • volatilized Na O will combine with S0 to form Na SO
  • This Na SO is removed from the flue gases by the conventional electrostatic precipitator.
  • the elemental sulfur from the Claus reactor is discharged to the sulfur storage 85.
  • the exothermix heat from the Claus reactions can be utilized for steam generation.
  • n normally 1-4, preferably 1.0-2.5.
  • the amount of polysulfide produced in this conventional reaction will depend upon the various proportions of sulfur to white liquor and various operating conditions in the digester 12.
  • the polysulfide liquor is then fed to tank 36 for storage under oxygen-free blanket in preparation for use in pulping.
  • Sulfur compounds are generated in a polysulflde pulpproducing mill at a rate five to six times larger than in a kraft mill. This requires that measures be taken to prevent air and water pollution. This is accomplished according to the present invention by collecting all such streams and recovering the sulfur compounds.
  • the gases from the digester 12, the blow tank 14, the pre-evaporators 38, and the carbonating tower 50 after removing the condensibles are sent to the Claus reactor 84 for the conversion of sulfur compounds into elemental sulfur.
  • the condensates C" from condenser 16, 40, 48, 52 and 54 are sent to a condensate recovery system which includes an H 5 stripping tower 90. The combined condensate is heated and stripped at 212 F.
  • a method of processing the NaSH- and Na CO -containing spent liquor from a polysulfide pulping process comprising the steps of:
  • step (b) is a recycle stream of carbonated spent liquor from step (c).
  • step (b) is a recycle stream of vacuum stripped spent liquor from step (d) and further including the step of recarbonating said recycle stream to convert at least a portion of the Na CO in said recycle stream to NaHCO 6.
  • step (d) is a recycle stream of vacuum stripped spent liquor from step (d) and further including the step of recarbonating said recycle stream to convert at least a portion of the Na CO in said recycle stream to NaHCO 6.
  • step (d) is a recycle stream of vacuum stripped spent liquor from step (d) and further including the step of recarbonating said recycle stream to convert at least a portion of the Na CO in said recycle stream to NaHCO 6.
  • said spent liquor is pre-evaporated to a dry solids content of 25-30 percent.
  • step (c) takes place'at a temperature of from about 25 to 100 C. and at a pressure of between about atmospheric pressure and I00 p.s.i.a.
  • stripping pressure is between about 8 17 in. Hg absolute.
  • step (e) of increasing the pH of said stripped spent liquor further includes the step of recycling a quantity of white liquor to increase the pH of said stripped spent liquor above the point attained by said NaOH addition.
  • a method according to claim 13 wherein said carbonating step (c) comprises contacting said spent liquor with a gas stream which is substantially pure CO on the dry basis.
  • processing step (f) comprises concentrating said spent liquor by evaporation, burning said spent liquor to produce a smelt containing Na CO and Na s and processing said smelt to produce said white liquor and additionally to produce a C0 containing gas stream and further including the step of processing said Co -containing gas stream to produce said substantially pure CO for step (c).
  • a method of processing the spent liquor from a polysulfide pulping process wherein said liquor contains NaSH and Na CO comprising the steps of:
  • step (c) is a recycle stream of vacuum stripped liquor from step (f) and further including the step of recarbonating said recycle stream to convert at least a portion of the Na CO in said recycle stream to NaHCO 18.
  • step (1) further includes collecting the gaseous effluents containing sulfur compounds from other of said processing steps and converting said sulfur compounds to elemental sulfur.

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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3884751A (en) * 1972-04-25 1975-05-20 Texaco Inc Coking of spent pulping liquors used in the alkaline sulfite process
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
US5246542A (en) * 1991-09-18 1993-09-21 Fosberg Theodore M Evaporation and recovery process for bleached chemical thermo-mechanical pulp (BCTMP) effluent
US5277759A (en) * 1990-07-09 1994-01-11 A. Ahlstrom Corporation Method of controlling sulfidity of a sulfate cellulose mill
WO1995021291A1 (en) * 1994-02-07 1995-08-10 Kvaerner Pulping Technologies Ab Process for separating off chloride from sulphide-containing alkaline liquor
WO1999014423A1 (en) * 1997-09-18 1999-03-25 Kvaerner Pulping Ab Polysulfide pulping process
US5911853A (en) * 1997-09-11 1999-06-15 International Paper Company Method for treating paper mill condensate to reduce the amount of sulfur compounds therein
US6143130A (en) * 1997-09-09 2000-11-07 Kvaerner Pulping Ab Polysulfide pulping process
WO2005033404A1 (en) 2003-10-03 2005-04-14 Oy Metsä-Botnia Ab Desulphurization of odorous gases of a pulp mill
WO2006037857A1 (en) * 2004-10-04 2006-04-13 Metso Paper, Inc. A method and a device for preparing cellulose pulp

Families Citing this family (1)

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CH632340A5 (fr) 1979-11-16 1982-09-30 Charmilles Sa Ateliers Procede et dispositif pour controler la concentration de particules solides en suspension dans un liquide.

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US3448002A (en) * 1964-06-20 1969-06-03 Domtar Ltd Pulping process
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US2574193A (en) * 1947-12-06 1951-11-06 Remington Rand Inc Chemical recovery and control in the kraft pulp process
US2999044A (en) * 1955-08-02 1961-09-05 Jr Theron Tilford Collins Production of paper pulp
US3331732A (en) * 1962-12-17 1967-07-18 Mo Och Domsjoe Ab Method of removing hydrogen sulfide from an aqueous solution of alkali sulfide
US3448002A (en) * 1964-06-20 1969-06-03 Domtar Ltd Pulping process
US3514371A (en) * 1966-03-01 1970-05-26 Katsuo Watanabe Preparation of kraft process liquor from waste soda liquor from petroleum industries

Cited By (12)

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Publication number Priority date Publication date Assignee Title
US3884751A (en) * 1972-04-25 1975-05-20 Texaco Inc Coking of spent pulping liquors used in the alkaline sulfite process
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
US5277759A (en) * 1990-07-09 1994-01-11 A. Ahlstrom Corporation Method of controlling sulfidity of a sulfate cellulose mill
US5246542A (en) * 1991-09-18 1993-09-21 Fosberg Theodore M Evaporation and recovery process for bleached chemical thermo-mechanical pulp (BCTMP) effluent
WO1995021291A1 (en) * 1994-02-07 1995-08-10 Kvaerner Pulping Technologies Ab Process for separating off chloride from sulphide-containing alkaline liquor
US6143130A (en) * 1997-09-09 2000-11-07 Kvaerner Pulping Ab Polysulfide pulping process
US5911853A (en) * 1997-09-11 1999-06-15 International Paper Company Method for treating paper mill condensate to reduce the amount of sulfur compounds therein
WO1999014423A1 (en) * 1997-09-18 1999-03-25 Kvaerner Pulping Ab Polysulfide pulping process
WO2005033404A1 (en) 2003-10-03 2005-04-14 Oy Metsä-Botnia Ab Desulphurization of odorous gases of a pulp mill
US20070034344A1 (en) * 2003-10-03 2007-02-15 Oy Metsa-Botnia Ab Desulphurization of odorous gases of a pulp mill
RU2349693C2 (ru) * 2003-10-03 2009-03-20 Ой Мется-Ботния Аб Способ и система для десульфуризации газов целлюлозного завода, обладающих неприятным запахом
WO2006037857A1 (en) * 2004-10-04 2006-04-13 Metso Paper, Inc. A method and a device for preparing cellulose pulp

Also Published As

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FR2096202A5 (enrdf_load_stackoverflow) 1972-02-11
NO133554C (enrdf_load_stackoverflow) 1976-05-19
JPS5013361B1 (enrdf_load_stackoverflow) 1975-05-19
CA941106A (en) 1974-02-05
ES392100A1 (es) 1973-11-01
GB1336899A (en) 1973-11-14
SE391546B (sv) 1977-02-21
ZA713733B (en) 1972-01-26
NO133554B (enrdf_load_stackoverflow) 1976-02-09

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