Abstract: A method for impregnating chips in a continuous digestion system with an impregnation vessel and a digester. The digestion system has a heat exchanger arranged between a first return line and a black liquor line. The heat exchanger allows a transfer of heat between the two lines. A principal part of the fluid contents of the impregnation vessel is constituted by chips moisture, steam condensate, added white liquor, and the fluid withdrawn from the top separator at the first return line, whereby the impregnation fluid in the impregnation vessel does not contain any substantial amount of black liquor from the digester. An impregnation vessel is established that is hydraulically isolated, in which the flow of fluid and the establishment of its alkali content take place without any influence from the fluid flow in the digester process.

Abstract: One aspect of this invention relates to a method and digester for reducing the deposition of calcium-based scale in a wood chip digester including extraction from the digester of first and second quantities of cooking liquor having respective first and second calcium concentrations, treating the extracted cooking liquors to produce a cooking liquor having a calcium concentration less that the calcium concentration of the either of the first and second extracted cooking liquors, and, reintroducing the treated cooking liquor to the digester. Another aspect of this invention relates to a method and digester in which through put through the digester is increased by the continuous addition of process liquor into the digester preferably at an upper region of the digester.

Abstract: The invention relates to a method for the modification of cellulose fiber with the object of increasing the strength properties of the pulp. Cellulose derivative, preferably in the form of CMC, is added in association with alkali cooking and/or delignification of cellulose chips in a suspension with treatment fluid, in an amount exceeding 2 kg, preferably at least 5–7 kg, per ton of cellulose fibers. The addition of cellulose derivative to the suspension takes place when the suspension has a concentration of calcium released from the cellulose exceeding 20 mg/l. The conditions required for an efficient deposit of cellulose derivative onto the cellulose fibers can be established in this way, where the natural content of calcium in the wood raw material has been released and contributes to a high ionic strength, while an advantageous high temperature is established. No additional process stages are required and operating costs can be kept low.

Abstract: Methods for bleaching chemical pulp are disclosed including dewatering the pulp to a concentration of from 25 to 40%, bleaching in a first chlorine dioxide stage, followed by a second alkaline bleaching stage, followed by a third chlorine dioxide bleaching stage, dewatering the bleached pulp to a concentration of from 10 to 40% and producing a filtrate, and recycling the filtrate to control the pulp concentration of the dewatered chemical pulp to from 8 to 15% in the first bleaching stage.

Abstract: Feeding device for feeding burned lime to a reaction vessel for causticizing a soda liquor to caustic soda. The feeding device, in its upper part, comprises an inlet for a slurry of the burned lime and the soda liquor for formation of said slurry inside said feeding device. The system further comprises a tall and slender feed vessel having a lower part having an outlet defined therein for the slurry. The outlet, via a pump, is operatively connected to the reaction vessel. The process and the feeding system utilize the feeding device, in which process the slurry is created of the burned lime and a first part of the soda liquor, a second part being preheated before addition to the slurry, whereafter slaking and causticizing reactions are completed under elevated temperature and pressure.

Abstract: Compositions and method for improving inhibition of calcium salt scale formation under the conditions found in chemical pulp processes in which an effective amount of selected phosphonates or phosphonate blends is admixed with the aqueous digester composition in a chemical pulping process during the digestion stage. The compositions and method are especially well suited for use in the Kraft pulping process.

Abstract: The invention relates to a coarse dirt collector (7) for removing coarse material from a pulper (1). The coarse dirt collector (7) comprises a support arm (8) with a collecting basket (9). The collecting basket (9) consists of a frame (11) on which tines (Z) are fixed by means of a grid. The coarse dirt collector can be pivoted into and out of the pulper, to which end it moves about an axis of rotation (A) positioned at an angle to the plane that is perpendicular to the longitudinal axis (P) of the pulper. Said angle is between 20° and 40°. The advantage of said device is that the coarse dirt collector (7) has to carry out only one movement between its collecting and unloading position and unloading can take place automatically without need for a special scraping device. Because of the position of the tines (Z) there is no risk of undesirable loss of coarse material prior to unloading.

Abstract: A chip bin for a digester has an upper part through which chips fall freely from an inlet and a lower part within which the chips remain until they are fed to a digester. Steam orifices strike falling chips with steam and disperses the chips over the interior of the chip bin. Further steam heats the chips and drives out non-condensable gas. The lower part of the chip bin is conical. Steam jets aimed down the conical walls propel the chips to an outlet at the bottom and prevent bridging.

Abstract: The present invention relates to the use of urea sulfate or urea hydrochloride, or both, in process streams in the paper and pulping industries to control pH, to bring about flocculation or precipitation of various materials, and to replace all or part of the sulfuric acid, hydrochloric acid, and/or papermaking alum used in the paper and pulping industries.

Abstract: A process and a device for cleaning waste gas from pulp production, especially for cleaning waste gases from a bleaching reactor. Aerosols contained in the waste gas are removed and the gaseous impurities are scrubbed out of the waste gas by a scrubbing liquid.

Abstract: A process for producing microcrystalline cellulose. The process comprising the following steps: a) preparation of a pulp by repulping, b) pressing of the pulp obtained in a), c) decompaction of the pulp obtained in b), d) feeding of the pulp obtained in c) into a pre-heated reactor, e) cooking of the pulp at a temperature, a time and a pressure allowing to obtain a pulp having a desired degree of polymerization, f) cooling and partial controlled depressurization of the reactor by purging the reactor, followed by a water injection into the jacket and directly into the reactor, g) filtering the pulp obtained in f), h) bleaching of the pulp obtained in g), and i) drying the pulp obtained in h). The process allows the application of a controlled depressurization in step f), which in turn allows to keep the natural texture of the fibers and to obtain a cellulose having a low degree of polymerization.

Abstract: Systems and methods by which to subject cellulosic fibers to alkaline treatment are provided. The systems and methods of the invention include equipment, such as nanofiltration units and slurry concentrators, which result in a lowered overall consumption of alkaline solution during alkaline treatment. The systems and methods of the invention further allow the components of hemicaustic streams produced by such alkaline treatments to be utilized in higher value end uses.

Abstract: Compositions and method for improving properties of pulp produced or reducing the digester cycle time in alkaline chemical pulping processes in which an effective amount of at least one selected phosphonate or carboxylate compound or mixtures thereof is admixed with the alkaline aqueous mixture in the digester of the chemical pulping process. The compositions and method are especially well suited for use in the Kraft pulping process.

Abstract: Compositions and method of improving inhibition of calcium salt scale formation under the conditions found in chemical pulp processes in which an effective amount of selected phosphonates or phosphonate blends is admixed with the black liquor composition recovered from the digester in a chemical pulping process. The compositions and method are especially well suited for use in the Kraft pulping process.

Abstract: The method is for controlling the cooking temperature in a continuous vapour phase digester for chip-shaped cellulose material. A high pressure is established in the vapour phase largely by means of steam, without risk of attaining excessively high temperatures in the cooking. A temperature-controlled supply of cooking liquor in close proximity to the surface of the liquor level is introduced to obtain a protective liquor surface with a temperature lower than the vapour phase. A lower initial cooking temperature is obtained in the cooking zone, which ensures that the exothermic cooking process does not lead to the attainment of temperatures detrimental to the pulp quality.

Abstract: The present invention relates to a high surface area product and its production from solid-containing material, such as waste effluent from a paper-treating plant. The high surface area product comprises calcium carbonate, and is useful as a coefficient of friction control filler for newsprint.

Abstract: The invention provides for methods for producing pulp (comprising cellulose) and lignin from lignocellulosic material, such as wood chips. The methods involve acid catalyzed hydrolysis. Lignocellulosic material having a relatively high moisture concentration can be used as the starting material. The lignocellulosic material is impregnated with an acid (preferably nitric acid) and heated. During the heating lignin is depolymerized at relatively low temperatures, and the acid catalyst is distilled off. The acid catalyst can be collected and recycled after impregnation and heating. The lignocellulosic material is then digested in an alkaline solution under heat, dissolving the lignin and allowing the pulp to be removed. Acid is added to the black liquor to precipitate the lignin which is then removed. The resultant amber liquor can be further processed into other ancillary products such as alcohols and/or unicellular proteins.

Abstract: The invention relates to a process for the treatment of fly ash accumulating in the electro-filter of the soda recovery unit in a sulfate cellulose mill, the ash containing primarily Na sulfate, Na chloride, Na carbonate and K sulfate, to produce industrial raw materials, in which process the fly ash is dissolved in water, the carbonate present therein is broken down with hydrochloric acid to Na chloride, a sulfate precipitation chemical in chloride form is added, the sulfate precipitate obtained is separated from the solution, and the chloride-containing solution is recovered.

Abstract: A method of recovery of alkaline sulphite pulping chemicals and for production of steam is disclosed. The method comprises gasification of evaporated spent cooking liquor at conditions resulting in a hydrogen sulphide containing gas and a solid residue. The gas is combusted in a steam boiler, where the hydrogen sulphide is converted into sulphur dioxide and steam is produced. The solid residue is recovered in a leaching process, preferably a two-stage leaching process, where process-foreign substances are removed and the rest of the contents is divided into substantially pure sodium carbonate and a mixture of sodium carbonate, sodium sulphate and sodium sulphide. The substantially pure sodium carbonate is used for absorption of sulphur dioxide from the steam boiler.

Abstract: Pulp, containing black liquor, is separated to produce pulp substantially free of black liquor. An organic solvent forms a layer within a vessel and adding a pulp containing black liquor will establish three layers. From the lower layer, pulp substantially free of black liquor is removed. From the upper layer, black liquor substantially free of pulp is removed, and the layer of organic solvent is retained in place within the vessel. The resulting separation, by dissimilar densities of the organic solvent and pulp containing black liquor produces black liquor devoid of additional dilution by water whereby pulp containing black liquor is separated to create pulp substantially free of black liquor and provides black liquor separated from the organic solvent.

Abstract: Separation of dissolved and colloidal high molecular weight organic by-products from liquors or filtrates in a cellulosic pulping process through a filtration media to improve the overall efficiency of the process.

Abstract: A continuous, alkaline process for the production of pulp from wood chips, wherein the preheated chips are subjected to an extended impregnation step for at least 60 min, preferably longer, at a temperature not exceeding the impregnation liquor boiling point at atmospheric conditions, and a rapid heating and cooking period of less than 65 min, preferably shorter, followed by cooling to below reaction temperature. Fresh alkali is added both during impregnation and the heating/cooking period.

Abstract: An alkaline batch process for the production of pulp from wood chips, wherein the preheated chips are subjected to an extended impregnation step outside the digester for at least 60 min, preferably longer, at a temperature not exceeding the impregnation liquor boiling point at atmos-pheric conditions, and a rapid heating and cooking period in the digester of less than about 90 min, preferably shorter, followed by cooling to below reaction tempera-ture. Fresh alkali is added both during impregnation and the heating/cooking period.

Abstract: A method for obtaining particulate calcium carbonate having an average particle size less than about 12 microns is provided. The method includes the steps of (1) withdrawing from a pulp mill a mixture containing calcium carbonate; (2) treating the mixture to remove contaminants contained in the mixture to produce a treated mixture containing calcium carbonate and further having a chemical composition and/or purity which substantially inhibits the fusing together of calcium carbonate particulates; (3) recovering from the treated mixture particulate calcium carbonate having an average particle size less than about 12 microns. The calcium carbonate produced has a high surface area to volume ratio and is therefore highly reactive and suitable for numerous applications such as in the treatment of soil, filler paper production, paint production, and contaminant containment in coal stack emission assemblies.

Abstract: A process (44) for the production of pulp and paper (28), recycling of cooking chemicals (3, 29), combustion of biomass (30, 37) and generation of heat and electric energy (27, 40) comprising a pulp and paper mill (28), in that the part of the process which is recycling cooking chemicals is adjusted from combustion (29) to gasification (3) to generate synthesis gas (14); and that biomass is added (33, 39) in an amount sufficient for compensating of the decrease in heat and electricity generation as a consequence of the generation of synthesis gas (14).

Abstract: The invention relates to a process for continuous cooking of wood chips at elevated pressure and temperature in a vertical digester (1) for production of chemically dissolved pulp. Fiber material and cooking liquor are introduced at the top of the digester and pulp is discharged from the bottom of the digester (1), via a line (8) in which the pulp is maintained at substantially the same pressure level, to a pressurized wash (7). More than 50% of the used cooking liquor (black liquor) which is extracted from the system in total is extracted from the wash filtrate of the pressurized wash. The pressurized wash is regulated so that a high temperature is maintained in the wash filtrate. The extraction is regulated so that a net co-current flow is established at the bottom of the digester.

Abstract: The invention refers to a method for an integrated treatment of cellulose pulp. The method includes the steps: providing said cellulose pulp (1), providing a determined quantity of white liquor (2) including alkali and sulphur components, providing an oxygen-containing gas, oxidizing (5) the sulphur components of the white liquor by the supply of a part of said gas in such a way that at least a part of the sulphur is present in the form of sulphate, transporting the cellulose pulp having a certain kappa number to at least one mixing device (4), and supplying the oxidized white liquor from the oxidizing step to the cellulose pulp, supplying a part of said gas to the cellulose pulp in said mixing device, mixing the cellulose pulp with the oxidized white liquor and said gas in said mixing device, and transporting the cellulose pulp from said mixing device to a delignification reactor (6) for oxygen delignification of said cellulose pulp, wherein the kappa number is reduced.

Abstract: This invention relates to a process of treating a lignocellulosic material to produce bio-ethanol. The process includes the steps of: (a) exposing the ligno-cellulosic material to conditions including a pH not less than about 8, and steam at a first pressure, to produce a step (a) product; (b) explosively discharging the step (a) product to a second pressure less than the first pressure-to produce a step (b) product; and (c) further processing the step (b) product to produce bio-ethanol and other co-products. In another embodiment, the invention relates to a conical auger fractionation column. The fractionation column includes a column body having an input and an output. A conical filter is positioned inside the column body, the filter having a larger diameter end directed toward the input and a smaller diameter end directed toward the output.

Abstract: The present invention relates to a bacterial strain of accession number MTCC 5098 useful for reducing the Total dissolved solids (TDS) levels from pulp and paper waste water effluents, and a process for the preparation of innoculum of the strain and also, a method of reducing Total dissolved solids (TDS) from pulp and paper waste water effluents using the said strain.

Abstract: The invention relates to a method for avoiding and/or reducing the deposition of volatile and non-volatile wood components in gas-bearing systems, whereby at least one of the volatile wood components, at least partly, condenses in the gas-bearing system and the gas contains at least one compound with a similar condensation profile to the volatile wood component and which at least reduces the deposition of volatile wood components or the reaction products thereof. The invention further relates to a method for reducing and/or avoiding the deposition of wood components on machines and/or equipment components for the production of wood fiber materials from wood chippings, in which the shredding of the wood is achieved in the presence of a compound which forms a film on the surfaces of the above machines and/or equipment components and at least reduces the deposition of volatile wood components and/or the reaction products thereof.

Abstract: A method to produce energy at a pulp mill, including the steps of: combusting pulping process waste liquor in the furnace of a recovery boiler to generate flue gases, recovering the heat from the flue gases by producing saturated and/or partially superheated steam in the recovery boiler, gasifying wood, bark or wood wastes in a gasifier for producing a combustible gas, burning at least part of the combustible gas in a superheating boiler, and superheating the saturated and partially superheated steam in the superheating boiler to produce superheated steam.

Abstract: Polynuclear compounds dissolved and contained within an organic solvent are separated from the organic solvent by rendering the organic compounds insoluble within the organic solvent. Accordingly this invention removes polynuclear compounds from a saturated organic solvent. The polynuclear compounds are derived from black liquor obtained from kraft digestion. Whereby polynuclear compounds, substantially free of an organic solvent, are obtained from the organic solvent.

Abstract: A method of treating solid containing material derived from effluent or sludge from a plant for de-inking paper, the material containing calcium in the form of one or more insoluble calcium compounds, the method including the steps of treating the material with an acid to cause dissolution of the calcium thereby forming a calcium ion-containing solution in which insoluble solids are suspended, separating the solution from the insoluble solids and incinerating the separated solids. The solution containing calcium ions may be treated by adding one or more reagents to form a calcium compound precipitate, eg calcium carbonate. The particulate solids produced following the incineration step and following the precipitate formation may be employed as pigments or fillers in paper making or paper coating.

Abstract: A method is provided for the use of borates in the recausticization of alkali-containing liquors such as those produced in the chemical and semi-chemical pulping of wood and in the oxidation and bleaching of wood pulp. Sodium hydroxide is regenerated from sodium carbonate-containing smelts in such pulp processes by autocausticization through the addition of limited amounts of borate. Autocausticization may be carried out at boron to carbonate molar ratios below 2:1 and at sodium to boron molar ratios exceeding 3:1, resulting in high reaction efficiency. Partial autocausticization using borate may also be combined with conventional lime recausticization for the regeneration of sodium hydroxide from sodium carbonate-containing smelts.

Abstract: A chemical wood pulping process having reduced volatile organic compound emissions includes extracting wood particulates with solvent at a pressure less than 50 psi to reduce naturally-occurring particulate pitch and volatile organic compound content without significant dissolution of lignin and wood cellulosic components. The solvent used is methanol, ethanol, or acetone. This is followed by comingling the extracted wood particulates with a liquor having chemical reactants, not including the solvent used to extract the wood particulates, for solubilizing lignin. Then, allowing the chemical reactants of the liquor to react with lignin contained in the extracted wood particulates under controlled conditions of temperature and pressure for a sufficient time to solubilize and remove lignin. This is followed by producing a wood pulp having individual cellulosic fibers while releasing a reduced amount of VOCs in the wood pulping process.

Abstract: A water soluble, surface active, polymeric agent is mixed with digestion liquor, preferably with an additional surface active defoamer coagulant agent prior to or during acidification of the alkaline digestive liquor. This results in an easily separable, non-gelatinous, non-gummy, coagulated lignin as a solids, particulate fraction that tends to float on a clarified liquid fraction containing recoverable salts. The solids fraction and the liquid frictions are easily separated, one from the other, by a gravity separation step.

Abstract: A method of mixing two or more dissimilar fluids such a gas and a liquid is provided. The method includes the steps of introducing one fluid into the other to form a mixture, inducing cavitation in the mixture to reduce at least one of the fluids to a large number of relatively small units, and distributing the small units uniformly throughout the mixture. In a preferred embodiment, the step of inducing cavitation comprises introducing the mixture into a chamber having a rotating disk formed with a plurality of irregularities such as bores. The irregularities on the rotating disk induce cavitation in the mixture. The cavitation also breaks down van der Waals attractions within the mixture to enhance mixing.

Abstract: A method for the preparation of pulp by means of alkaline cooking, in which method spent liquor is transferred to pressurized tanks, and at least one liquor is expanded corresponding to a temperature difference of 1 to 5° C. The generated steam is led to turpentine recovery. Thus, the removal of turpentine and gases dissolved in said liquor is effective, the amount of recovered turpentine increases, and pulp of better washability and higher quality is obtained.

Abstract: Fiber material and cooking liquor are introduced at the top of the digester and pulp is discharged from the bottom of the digester, via a line in which the pulp is maintained at substantially the same pressure level, to a pressurized wash. More than 50% of the used cooking liquor (black liquor) which is extracted from the system in total is extracted from the wash filtrate of the pressurized wash. At the same time a small portion of the wash filtrate is also to be recirculated to the bottom of the digester as dilution liquid. The pressurized wash is regulated so that a high temperature is maintained in the wash filtrate. The extraction is regulated so that a net co-current flow is established at the bottom of the digester.

Abstract: Described is a process for concentrating weak black liquor to form strong black liquor, said process comprising: a) preconcentrating said weak black liquor; b) heating said preconcentrated weak black liquor in a heating zone under sufficient pressure to prevent said preconcentrated weak black liquor from boiling in said heating zone; c) passing said preconcentrated weak black liquor, having at least one volatile component, into an evaporation zone through one or more orifices; d) applying pressure in said evaporation zone that is lower than the vapor pressure of said preconcentrated weak black liquor as it is passed into said evaporation zone, which allows for flash evaporation of at least a portion of said at least one volatile component of said preconcentrated weak black liquor from said preconcentrated weak black liquor to form strong black liquor; e) adjusting heat in said heating zone.

Abstract: The specification discloses an improved bleaching sequence which provides significant reduction in filtrate volumes and amounts of absorbable organic halide (AOX), color, and chemical oxygen demand (COD) in the effluent. These reductions are achieved without adversely affecting the brightness and viscosity properties of the bleached pulp and without a high capital cost and operating cost penalty or impact on existing mill processes. The bleaching sequence according to the invention for reducing filtrate volumes is an EOD1EOPD2 or EOPD1EOPD2 bleaching sequence wherein substantially all of the filtrates from the later bleaching stages are recycled to earlier bleaching stages and eventually treated in the initial EO or EOP stage prior to discharge from the plant.

Abstract: Compositions and method of improving inhibition of calcium salt scale formation under the conditions found in chemical pulp processes in which an effective amount of selected phosphonates or phosphonate blends is admixed with the black liquor composition recovered from the digester in a chemical pulping process. The compositions and method are especially well suited for use in the Kraft pulping process.

Abstract: An apparatus and method are provided to reduce the size of solid clumps of material and thereby permit reuse of the material. In particular, the apparatus and method allow for reuse of sediment accumulated in a storage area for paper pulping byproducts. The sediment is conveyed from the storage area to an tank. In the tank, the sediment is agitated to produce reduced-size clumps of the sediment. The reduced-size clumps are in a slurry that is capable of being burned at least one of a facility that produces paper pulp and a facility that produces paper products.

Abstract: A method for obtaining particulate calcium carbonate having an average particle size less than about 12 microns is provided. The method includes the steps of (1) withdrawing from a pulp mill a mixture containing calcium carbonate; (2) treating the mixture to remove contaminants contained in the mixture to produce a treated mixture containing calcium carbonate and further having a chemical composition and/or purity which substantially inhibits the fusing together of calcium carbonate particulates; (3) recovering from the treated mixture particulate calcium carbonate having an average particle size less than about 12 microns. The calcium carbonate produced has a high surface area to volume ratio and is therefore highly reactive and suitable for numerous applications such as in the treatment of soil, filler paper production, paint production, and contaminant containment in coal stack emission assemblies.

Abstract: The present invention relates to a process of oxidation, of the wet oxidation or ozonization type, of a liquid contained in a reactor. The gas of the gas headspace is aspirated into the liquid, and the portion which is not dissolved in the liquid is recovered in the gas headspace. The agitation means creates a flow of liquid immediately adjacent to the end of the duct opening into the liquid, and generates a gas/liquid dispersion in the zone, within which the liquid reacts with the gas, then conveys and ejects the said dispersion at its periphery, such that the gas is dissolved in the liquid in the zone extending from the agitation means to the surface of the liquid. The said process is particularly suitable for oxidations which make use of considerable quantities of oxygen or of ozone. It is particularly applied for the oxidation of papermaking liquors.

Abstract: A procedure for arranging water circulations in an integrated paper mill, the paper making process of which having three partly separate process phases concerning the water circulations (I, II, III). In the first phase, the fiber raw material is pretreated, defibered and cleaned for producing mechanical, chemi-mechanical and recycled pulp, in the second phase the pulp is treated further for improving the quality, and in the third phase it is made into paper or board. The circulation waters of the first process phase are concentrated by circulating the filtrates of the concentration and pressing phases counter-current inside the water circulation (I), and the circulation water thus concentrated is conducted into an effluent evaporation plant to be concentrated and then burnt in a combustion boiler. The water quantity discharged from the water circulation (I) of the first process phase is replaced by conducting such circulation waters of the paper mill into the front dilution of the press.

Abstract: Separation of dissolved and colloidal high molecular weight organic by-products from liquors or filtrates in a cellulosic pulping process to improve the overall efficiency of the process.

Abstract: The invention relates to a method of bleaching and/or delignifying cellulose, in which (a) a sodium hydroxide solution and a peroxydisulphate solution are first of all produced by electrolysis of a sulphate, (b) the peroxydisulphate solution is converted by hydrolysis into a Caro's acid/caroate solution, (c) said Caro's acid/caroate solution is left to cool and (d) used immediately as a bleaching solution for bleaching and/or delignifying cellulose, the Caro's acid/caroate solution becoming neutralised upon introduction into the bleaching solution.

Abstract: Compositions and method for improving inhibition of calcium salt scale formation under the conditions found in chemical pulp processes in which an effective amount of selected phosphonates or phosphonate blends is admixed with the aqueous digester composition in a chemical pulping process during the digestion stage. The compositions and method are especially well suited for use in the Kraft pulping process.

Abstract: The invention relates to a process for producing cellulose and a fertilizer by-product by using a closed cycle of cooking chemicals and process waters. In the process of the invention, the pulp is bleached by at least partly using potassium hydroxide as a bleaching chemical. Thus, a bleach concentrate rich in potassium is obtained from the bleach filtrate, which bleach concentrate is combined with ashes obtained from the burning of lignin and other organic matter recovered from pulp production as a by-product, in order to be used as a potash fertilizer. The bleach-concentrate can also be used as a potash fertilizer as such. The invention also relates to a potash fertilizer obtained this way.