EP0852272A1 - Rückgewinnungsverfahren in einer Zellstoffabrik - Google Patents

Rückgewinnungsverfahren in einer Zellstoffabrik Download PDF

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Publication number
EP0852272A1
EP0852272A1 EP97203861A EP97203861A EP0852272A1 EP 0852272 A1 EP0852272 A1 EP 0852272A1 EP 97203861 A EP97203861 A EP 97203861A EP 97203861 A EP97203861 A EP 97203861A EP 0852272 A1 EP0852272 A1 EP 0852272A1
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EP
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Prior art keywords
potassium
solution
ion exchange
precipitator dust
zeolite
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EP97203861A
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English (en)
French (fr)
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EP0852272B1 (de
Inventor
Roland Pudas
Magnus Linsten
Björn Svedin
Ingrid Velander
Roy Hammer-Olsen
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Nouryon Pulp and Performance Chemicals AB
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Eka Chemicals AB
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    • 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
    • D21C11/0042—Fractionating or concentration of spent liquors by special methods
    • D21C11/005—Treatment of liquors with ion-exchangers
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C11/00—Regeneration of pulp liquors or effluent waste waters
    • D21C11/06—Treatment of pulp gases; Recovery of the heat content of the gases; Treatment of gases arising from various sources in pulp and paper mills; Regeneration of gaseous SO2, e.g. arising from liquors containing sulfur compounds
    • D21C11/063—Treatment of gas streams comprising solid matter, e.g. the ashes resulting from the combustion of black liquor
    • D21C11/066—Separation of solid compounds from these gases; further treatment of recovered products

Definitions

  • the present invention relates to an environmental-friendly process for reducing the content of potassium ions in a liquid inventory of a chemical pulp mill.
  • chips of lignocellulose-containing material are cooked in an alkaline or acid aqueous solution.
  • This cooking liquid contains inorganic pulping chemicals to improve the dissolution of lignin.
  • the cooking is normally carried out at a temperature above 100°C to reduce the residence time for the pulp produced. Therefore, the cooking is carried out in a pressure vessel known as a digester.
  • An essential part of the recovery system is the recovery boiler, where the spent liquor is burned. Normally, make-up chemicals are added to the spent liquor before the recovery boiler to make up for the chemicals lost during cooking and recovery.
  • the spent liquor is sprayed into the lower part of the boiler, previously at a relatively low temperature to remove free water.
  • Modern recovery boilers operate at a high temperature to reduce the content of sulphur in the flow gases leaving the boiler. Higher up in the boiler, gases and vapours of light hydrocarbons and decomposition products are volatilized. This is known as pyrolysis. Then, the pyrolysis products are burned after mixing with air or oxygen.
  • the solid carbon-based residue which remains after complete pyrolysis of the organics is then heterogeneously burned.
  • the solid particles formed are collected as a dust in precipitators at the top of the recovery boiler, to reduce the release of solid material to the surrounding atmosphere.
  • chloride and potassium in the spent liquor entering the recovery boiler. These elements tend to reduce the capacity of the recovery boiler to produce useful chemicals. Thus, chloride and potassium increase the stickiness of carryover deposits and dust particles to the recovery boiler tubes, which accelerate fouling and plugging in the upper part of the recovery boiler. Chloride also tend to increase the corrosion rate of superheater tubes.
  • Chloride and potassium are concentrated in the dust formed during the combustion of spent liquor in the recovery boiler.
  • the dust is collected in dry-bottom or wet-bottom electrostatic precipitators.
  • the dust mainly consists of sodium and potassium salts, where sulphate, carbonate and chloride are the dominant anions.
  • the amount of dust corresponds to from about 5 up to about 15% by weight of the sodium entering the recovery boiler, which corresponds to from about 50 up to about 150 kg dust per tonne pulp, if the dust is calculated as sodium sulphate.
  • the largest source of potassium is the wood, and the intake will depend on the wood source generally varying from about 0,5 to 5 kg per tonne pulp.
  • the hardwood species usually contains larger amounts of potassium than softwood species.
  • the content of chloride in the spent liquor can be very high for coastal mills, if the raw material consists of logs floated in seawater. As the environmental legislation becomes more stringent regarding pulp mill discharges to air and water, the degree of system closure increases. This means that even a small input of chloride and potassium becomes a severe problem, unless the content can be controlled by purging the system in some environmentally acceptable way.
  • Chloride and potassium removal are preferably carried out in a common waste water treatment. Chloride can be removed efficiently by e.g. electrodialysis, while potassium still is difficult to remove efficiently electrochemically.
  • WO-A1-9404747 discloses a process, in which the content of chloride in a recovery system for pulping chemicals can be reduced.
  • the process comprises collecting precipitator dust, dissolving the dust in water to produce an aqueous solution of precipitator dust, whereupon said aqueous solution is electrolysed in a cell for production of chlorine or hydrochloric acid in the anolyte.
  • Use of ion exchange is suggested as a pretreatment before the electrolyses, chiefly to remove divalent ions such as Ca 2+ and Mg 2+ .
  • the present invention relates to a process by which the content of potassium ions in a recovery system for pulping chemicals can be reduced.
  • the process comprises bringing spent liquor to a recovery boiler, burning said spent liquor, collecting precipitator dust formed, forming a solution by dissolving the precipitator dust in a liquid, where the solution of precipitator dust is subjected to a treatment with an inorganic ion exchange material in order to remove at least a part of the potassium therein.
  • An advantage of the present process is the possibility to reduce the content of potassium in the liquid inventory and more particularly in the spent liquor entering the recovery boiler.
  • the problem of sticky deposits in the recovery boiler can be substantially reduced. This means an improved energy efficiency as well as a higher degree of recovery of the pulping chemicals.
  • the present invention can be used in the production of a chemical pulp and especially for production of a sulphate pulp, soda pulp or sulphite pulp with an alkali metal as base.
  • a kraft pulp is a special type of sulphate pulp, where the pulp is under-cooked to produce a dark-coloured pulp of exceptional strength.
  • the present invention can also be used in the production of sulphate, soda or sulphite pulps with an alkali metal as base, where the cooking processes have been modified, combined or extended compared to the normal pulping techniques.
  • the present process is applied where the recovery system for pulping chemicals is a kraft recovery system.
  • a liquid inventory is the total quantity of various liquids in a mill, with varying contents of active or activatable cooking liquid components.
  • the liquid inventory of a sulphate mill mainly consists of white liquor, black liquor, green liquor and spent liquor entering the recovery boiler.
  • the spent liquor to be burned in the present process is a used cooking liquid withdrawn from a digester, optionally with added make-up chemicals. Potassium and sodium are alkali metals present in the spent liquors.
  • the amount of precipitator dust formed depends mainly on the temperature in the boiler, the ratio between sodium and sulphur in the spent liquor and the raw material and sulphidity of the cooking process. A high temperature in the lower part of the boiler to reduce the sulphur content in the flow gases, increases the amount of dust formed.
  • composition of precipitator dust formed in recovery boilers vary considerably depending on type and origin of wood, cooking process, purity of make-up chemicals, temperature in the boiler, type of precipitator etc. However, irrespective of these factors the dust mainly consists of sodium and potassium salts, where sulphate, carbonate and chloride are the dominant anions.
  • a typical composition of precipitator dust from a kraft recovery system is Na 2 SO 4 80-85% by weight, Na 2 CO 3 2-8% by weight, NaCl 2-8% by weight, NaHSO 4 + Na 2 S 2 O 7 ⁇ 2% by weight, K 2 SO 4 5-10% by weight, K 2 CO 3 0.5-1% by weight, KCl ⁇ 1% by weight, metal ions such as Ca, Fe, Mg, P, Si, Mn, Zn, Mo ⁇ 1% by weight and organic material ⁇ 1% by weight.
  • Natural as well as synthetic inorganic ion exchange material can be used.
  • Suitable inorganic ion exchange materials are aluminosilicates, hydrous oxides, acid salts of polyvalent metals or salts of heteropolyacids.
  • Zeolites are inorganic crystalline compounds mainly consisting of SiO 2 and Al 2 O 3 in tetrahedral co-ordination.
  • zeolites also relate to other crystalline compounds of zeolite structure, such as aluminium phosphates.
  • Such crystalline compounds of zeolite structure which can be used in the present invention are defined in W.M. Meier et al, Atlas of zeolite structure types, sec. ed., Butterworths, London, 1987, which is hereby incorporated by reference in the present application. Many zeolites occur naturally, but most commercially used zeolites are synthetically produced.
  • zeolites function as adsorbents or molecular sieves and may, depending on the size of the cavities and the nature of the zeolite surface, be used to increase or decrease the taking-up of specific chemical compounds.
  • a very essential property of the zeolites is their selectivity towards potassium relative to sodium.
  • a suitable zeolite can be selected from the group consisting of mordenite, chabazite, clinoptilolite, zeolite A and zeolite Y. Preferably use is made of mordenite.
  • mordenite a wide variety of zeolites are available on the market. For instance, Wessalith P is a A-zeolite manufactured by Degussa. Zeolite Y EY250, Zeolite Y N3S, Zeolite BMH and Zeolite Sodium Mordenite EM120 is manufactured by Eka Chemicals AB.
  • hydrous oxides which can be used are hydrous titanium oxide, iron hydroxide, hydrous stannic oxide, hydrous zirconium oxide, silica gel etc.
  • Crystalline antimonic acid is known to exhibit the following selectivity series Li>K>Rb>Na.
  • Suitable acid salts of polyvalent metals used as ion exchange material may be zirconium phosphate crystal or titanium phosphate crystals.
  • the amount of inorganic ion exchange material used may vary within wide limits.
  • the amount of inorganic ion exchange material used may be up to 1 tonne/tonne of dry precipitator dust and e.g. lie in the range of from about 1 kg/tonne up to about 1000 kg/tonne of dry precipitator dust, suitably in the range of from about 10 kg/tonne up to about 1000 kg/tonne of dry precipitator dust and preferably in the range of from about 100 kg/tonne up to about 500 kg/tonne of dry precipitator dust.
  • the amount of inorganic ion exchange material used is based upon the ion exchange capacity of the actual inorganic material and the amount of potassium in the precipitator dust.
  • the inorganic ion exchange material is preferably used in excess of the stoicheometric amount of potassium.
  • the potassium and chloride containing solution is treated with an inorganic ion exchange material.
  • the ion exchanged material, enriched on potassium is then preferably filtered and washed with water, whereafter the spent ion exchanger material can be deposited in a land fill.
  • the solution depleted on potassium and chloride can be recycled in the pulp mill or forwarded to another step in the treatment of precipitator dust for mixing or dilution.
  • the separation and washing can preferably take place in a centrifuge, a filter press or a vacuum filter.
  • a sodium rich aqueous solution This could for example be a solution of the Na 2 SO 4 salt cake obtained from a chlorine dioxide generator (or from a crystallisator, or a chloride concentrate from an electrochemical cell). Separation, washing, regeneration and dewatering then may take place in the same piece of equipment operating in a continuos mode. Even the ion exchange may take place in the separation equipment. This can be done batchwise in a filter press or continuos eg. in a centrifuge or a rotating filter of vacuum or pressure type.
  • the inorganic ion exchange material is made in the form of granules or pellets and are placed as a fixed bed in a column, thus forming an ion exchanger.
  • the precipitator dust solution, rich on potassium is forced to flow through the bed of ion exchange material to which the potassium is adsorbed.
  • the reaction zone proceeds down the column as the upper layers of ion exchange material reaches equilibrium with the solution.
  • the ion exchange material is backwashed (regenerated) with a sodium electrolyte.
  • the flow of potassium rich solution is simultaneously switched to another column.
  • a number of columns can be arranged in parallel so that the continuos operation is ensured.
  • the advantage with this embodiment, columns arranged in parallel, over the previously described is that the operation is continuous and that a more efficient ion exchange can be achieved as multiple equilibrium stages are obtained (cf. McKabe-Thiele diagram).
  • the amount potassium removed in a precipitator dust solution subjected to a treatment with an inorganic ion exchange material can be above about 40 %, suitably above about 50 %, preferably above about 60 % and most preferred above about 70 %.
  • a potassium free or potassium depleted stream which has undergone the inorganic ion exchange, is preferably recycled to the weak black liquor or may, in the cases where the water balance allows, be mixed with the strong black liquor and fed directly into the recovery boiler in the recovery system.
  • a solution of precipitator dust will also commonly have a pH between about 7 and about 11, within which range most ion exchange material are stable and thus preferred.
  • the pH is not critical since many ion exchange material work satisfactory outside the pH range 7-11.
  • the ion exchange is suitably performed in the range from above 0°C up to about 100°C and preferably from about 20°C up to about 60°C.
  • the residence time for the suitable batchwise ion exchange is preferably at least about 1 minute.
  • the residence time is at least about 1 hour, preferably at least about 2 hours and most preferred at least about 5 hours.
  • the upper residence time is not critical, but have to be set by process-technical reasons.
  • the flow rate for the suitable continuous operation of the ion exchange is suitably at least from about 0.1 up to 20 BV/h (Bed Volume per hour), preferably from about 1 up to 10 BV/h and most preferred from about 2 up to 6 BV/h.
  • the ion exchange is preferably carried out by a continuous operation.
  • the potassium concentration of the solution is increased by leaching the precipitator dust with a liquor.
  • the added liquid may comprise of water, or water solutions of sulphate or carbonate.
  • Added sulphate may be alkali metal, preferably sodium sulphate, suitably at least a part derives from a recirculated solution, depleted of chloride and potassium, for instance from a suitable electrochemical treatment or recrystallisation. If water is added, it can be either fresh water or purified process water.
  • the potassium enriched leach solution is separated from the solid phase of the leached precipitator dust, by e.g. filtration, centrifugation, sedimentation etc..
  • the concentrate in the slurry obtained from the leaching step may comprise from about 1 g/l up to about 60 g/l potassium, and will be saturated with sulphate.
  • the solution depleted of potassium obtained from the ion exchange may comprise from 0 g/l up to about 60 g/l potassium (counted as e.g. K + , K 2 SO 4 , KCl).
  • the inorganic ion exchange according to the present invention is preferably combined with another process. This could for example be a process for leaching and electrodialysis of precipitator dust.
  • the ion exchange can also be combined with processes where precipitator dust is split in electrolysis cell or a electrodialysis cell with bipolar membranes. The advantage is, especially when removing the potassium prior to electrolysis, that NaOH with little or no potassium impurities can be prepared.
  • the inorganic ion exchange according to the present invention can also be combined with a process where sodium sulphate is re-crystallised from the precipitator dust.
  • the inorganic ion exchange according to the present invention can be advantageously combined with a process where chloride ions are ion exchanged from the precipitator dust (for instance the Precipitator Dust Purification System, PDPTM).
  • Another possible application is to use the inorganic ion exchange according to the present invention on bleach filtrates recovered back to the chemical recovery.
  • Figure 1 shows a schematic description of the use of an inorganic ion exchanger in a process for treatment of precipitator dust applying a combination of leaching and electrodialysis treatments.
  • Figure 2 shows the application of an inorganic ion exchanger in yet another embodiment in combination with a recrystallisation of sodium sulphate from precipitator dust.
  • precipitator dust (1) can be mixed with a near saturated solution of sodium sulphate (2) in a leach tank (3) where the mixed solution can be subjected to a leaching treatment.
  • the chloride and potassium compounds in the precipitator dust are leached out and the potassium and chloride enriched solution (31) is brought to an ion exchange column (8).
  • a slurry (4) is separated on a filter (5), a centrifuge (not shown) or the similar.
  • the filter cake (6) virtually free of chloride and potassium, is recovered to the strong black liquor.
  • the filtrate (7) is recycled (71) to the leach tank (3) or forwarded (72) to the ion exchange column (8) where potassium ions are removed (9), and the potassium depleted filtrate, still containing a high concentration of chloride ions (10), can be further brought to the diluate chamber(s) (13) of an electrodialysis stack (11) holding mono-anion selective membranes (12).
  • an electric field is applied to the electrodialysis stack the chloride ions are removed by migration through the anion selective membranes to the concentrate (brine) chamber(s) (14).
  • the remaining chloride and potassium depleted sodium sulphate solution (2) can be recycled for use as leachant in the first step (3).
  • the electrodialysis stack (11) may also comprise cation selective membranes through which cations such as sodium and potassium are removed by migration.
  • the concentrated sodium chloride solution prepared in the electrodialysis step (15) can be recirculated back to the concentrate chamber(s) of the cell, but a part may be purged and used for regenerating (16) the ion exchange material.
  • water can be added to dilute the concentrated chloride solution (17).
  • Precipitator dust (21) can be mixed with water (22) (preferably condensate from the crystallisator (28)) in a dissolving tank (23).
  • the dissolved solution (24) is forwarded to an ion exchange column (25), where potassium, are removed (26) and the potassium depleted filtrate (27), may further be brought to a crystallisator (28) where sodium sulphate is re-crystallised from the precipitator dust.
  • the solution (29) containing mother liquor and sodium sulphate crystals is brought to a separation step with conventional technique, for instance a vacuum drum filter (30) and an addition of water (31), where the sodium sulphate crystals (32) (Na 2 SO 4 ) is separated from the mother liquor (33).
  • Condensed water (22) from the re-crystallisation (28) may be recycled to the dissolving step (23).
  • the sodium sulphate crystals can be recycled to the strong black liquor, alternatively can a small portion of the crystals be dissolved in water and used for regeneration of the ion exchanger.
  • the mother liquor is preferably discharged.
  • the process shown in fig.2 purges a stream of the mother liquor to control the potassium and chloride levels.
  • the limiting factor is the solubility of Organic (NaK 3 (SO 4 ) 2 ).
  • the concentration of potassium in the precipitator dust solution may vary between 0 and about 35 g/l. After ion exchange, the solution fed to the crystallizator may have a potassium concentration down to 0 g/l.
  • a 20 wt% ash solution was prepared from a kraft mill precipitator dust, with a content in the ash of 32 wt% Na, 42 wt% SO 4 , 3.0 wt% K, 3.4 wt% Cl, 16 wt% CO 3 and impurities ⁇ 4 wt%.
  • the pH of the solution was adjusted by 50% H 2 SO 4 to pH 7 or 9 and filtered through an OOH filter paper. After that the solution contained about 7.5 g/l potassium.
  • the ash solution was mixed with the zeolite and left for stirring for at least 10 minutes. The samples that were run at 50°C the solution was heated and stirred at the same time. When the samples reached 50°C they were stirred for 5 minutes more.
  • the zeolites used in the examples were of two different types.
  • the Wessalith P is a zeolite manufactured by Degussa.
  • the tested zeolites were powder form. Analyses of potassium content were done on the ash, the start solution and on the filtrate. The experiments were run at pH 7, and at room temperature with different amounts of zeolites. In tables I and II below the results of the removal of potassium in % for each are shown.
  • Table I shows the results from the experiments with Wessalith P. Test: 1 2 3 4 5 Amount zeolite [g]/100 ml solution 3,9 5,8 7,8 31 38,8 K in start solution, [g/l] 7,2 7,2 7,2 7,4 7,4 K after treatment, [g/l] 6,5 6,1 5,9 3,9 3,7 Removal of K + [%] 10% 15% 18% 47% 50%
  • Table II shows the results from the experiments with Zeolite Sodium Mordenite EM120. test: 1 2 3 4 5 6 Amount zeolite [g]/100 ml solution 3,9 7,8 15,5 23,3 31 38,8 K in start solution, [g/l] 7,7 7,7 7,7 7,2 7,2 7,2 K after treatment, [g/l] 6,2 6,0 4,3 3,3 2,8 2,4 Removal of K + [%] 19% 22% 44% 54% 61% 67%
  • a 20 wt% ash solution was prepared from the precipitator dust used in example 1.
  • the pH of the solution was adjusted by 50% H 2 SO 4 to pH 8. After that the solution contained about 7.7 g/l potassium.
  • the ash solution was mixed with the zeolite and left for stirring for 5 hours at a temperature of 80°C.
  • the zeolite used was Sodium Mordenite EM120 manufactured by Eka Chemicals in Bohus, Sweden.
  • the zeolite was in powder form. 100ml solution/20g zeolite was used in this test.
  • the start concentration of potassium is 7,7g/l.
  • Analyses of potassium content and the calculation of amount potassium removed were done in accordance with example 1. Samples were taken once every hour from the solution with the zeolite.
  • Amberlite IRC-718 (a cationic exchange resin) manufactured by Rohm and Haas was used in an experiment. Before start the resin was regenerated as follows:
  • a 20 wt% ash solution was prepared from the precipitator dust used in example 1.
  • the pH of the solution was adjusted by 50% H 2 SO 4 to pH 10.
  • the solution contained after that about 7,5 g/l potassium.
  • the ash solution was mixed with the wet ion exchanger and stirred for 30min at 40 °C. After that the solution was filtered.
  • Analyses of potassium content and the calculation of amount potassium removed were done in accordance with example 1. In table IV below the results of the removal of potassium in % for each are shown.
  • the amount of zeolite/100 ml ash solution has been recalculated as dry zeolite.
  • Test 1 2 3 Amount zeolite g / 100 ml solution 25 37,5 50 K in start solution [g/l] 7,5 7,5 7,5 K after treatment [g/l] 6,0 5,5 5,1 Removal of K [%] 20 26 32

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  • Treatment Of Water By Ion Exchange (AREA)
  • Manufacture And Refinement Of Metals (AREA)
EP97203861A 1997-01-03 1997-12-10 Rückgewinnungsverfahren in einer Zellstoffabrik Expired - Lifetime EP0852272B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9700012 1997-01-03
SE9700012A SE9700012D0 (sv) 1997-01-03 1997-01-03 Recovery process in a pulp mill

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EP0852272A1 true EP0852272A1 (de) 1998-07-08
EP0852272B1 EP0852272B1 (de) 2002-03-27

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EP (1) EP0852272B1 (de)
AT (1) ATE215143T1 (de)
CA (1) CA2225927C (de)
DE (1) DE69711355T2 (de)
ES (1) ES2171832T3 (de)
PT (1) PT852272E (de)
SE (1) SE9700012D0 (de)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2016099392A1 (en) * 2014-12-17 2016-06-23 Aprotech Engineering Ab Process for production of a fertilizer comprising potassium sulfate
US11725341B2 (en) 2017-04-28 2023-08-15 Andritz Oy Method of treating fly ash of a recovery boiler

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015010179A1 (en) * 2013-07-25 2015-01-29 Noram Engineering And Constructors Ltd. Method of reducing chloride and potassium ion concentrations in a pulp mill chemical recovery system

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3684672A (en) * 1969-08-07 1972-08-15 Mitsubishi Heavy Ind Ltd Process for paper manufacture
WO1994004747A1 (en) * 1992-08-24 1994-03-03 Eka Nobel Ab Reduction of chloride in pulping chemical recovery systems
US5352332A (en) * 1991-01-28 1994-10-04 Maples Gerald E Process for recycling bleach plant filtrate
EP0754799A2 (de) * 1995-07-12 1997-01-22 Eka Chemicals AB Auslaugungsverfahren

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3684672A (en) * 1969-08-07 1972-08-15 Mitsubishi Heavy Ind Ltd Process for paper manufacture
US5352332A (en) * 1991-01-28 1994-10-04 Maples Gerald E Process for recycling bleach plant filtrate
WO1994004747A1 (en) * 1992-08-24 1994-03-03 Eka Nobel Ab Reduction of chloride in pulping chemical recovery systems
EP0754799A2 (de) * 1995-07-12 1997-01-22 Eka Chemicals AB Auslaugungsverfahren

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2016099392A1 (en) * 2014-12-17 2016-06-23 Aprotech Engineering Ab Process for production of a fertilizer comprising potassium sulfate
US11725341B2 (en) 2017-04-28 2023-08-15 Andritz Oy Method of treating fly ash of a recovery boiler
SE546320C2 (en) * 2017-04-28 2024-10-01 Andritz Oy Method of treating fly ash of a recovery boiler

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CA2225927A1 (en) 1998-07-03
ATE215143T1 (de) 2002-04-15
SE9700012D0 (sv) 1997-01-03
ES2171832T3 (es) 2002-09-16
CA2225927C (en) 2002-04-09
PT852272E (pt) 2002-08-30
DE69711355T2 (de) 2002-10-31
EP0852272B1 (de) 2002-03-27
DE69711355D1 (de) 2002-05-02

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