Abstract: In a digester, wood chips and white liquor are combined and cooked under pressure to pulp the wood. This produces black liquor which is concentrated and burned in a recovery boiler. The recovery boiler produces ash that contains sodium, sulphur, potassium and chloride. The ash is dissolved and subjected to a process that recovers sodium sulfate and burkeite. The concentration of potassium and chloride is reduced, in part at least, by subjecting the ash to adiabatic cooling in a crystallizer which produces glaserite and a purge stream rich in chloride. By leaching the glaserite, sodium sulfate is removed from the glaserite, leaving potassium sulfate. The recovered sodium sulfate and burkeite can be recycled and used as pulping chemicals. The removed potassium and chloride can be further treated or appropriately discarded.

Abstract: The system and method reduce the liquid/wood ratio at the top of a vapor phase digester in a continuous digester plant. Chips that are to be cooked in the vapor phase digester are fed as a mixture of chips and liquid at a liquid/wood ratio that exceeds 8:1 in a transfer line to an inverted top separator arranged at the top of the vapor phase digester. The top separator feeds the chips upwardly. More than 50% of the liquid content of the mixture of chips and liquid is withdrawn in the top separator and the remaining liquid is fed out from the top separator to the top of the vapor phase digester. A pile of chips and a liquid volume are established at the top, wherein the pile of chips is disposed above the liquid surface of the liquid volume.

Abstract: Systems and methods for purifying wood pulp by caustic-borate extraction. The systems and method include a method for recovering both the caustic and borate compounds from the resultant hemicaustic effluent, so that they may be recycled and re-used. Efficient recovery of these components is enabled by a nanofiltration system that has one or more alkali-resistant nanofiltration membranes.

Abstract: A process for removing silica from nonwood plant materials involving both chemical and mechanical action is described. The silica-rich epidermal cells are liberated mechanically by a pre-pulping and low-consistency refining step and subsequently removed from the pulp via the filtrate of a thickening step. Amorphous silica is liberated chemically by using an alkaline dilution source in the pulper, then removed from the pulp via the filtrate of a thickening step and a dewatering step. The silica is then removed from the filtrate by adjusting the pH, followed by a separation step. The desilicated fibrous material may then be chemically or mechanically pulped and bleached using known processes. The silica removed from the nonwood plant material may then be used as a feedstock for other applications.

Abstract: The process is for continuously cooking chemical pulp in a digester system consisting of at least one vessel for impregnating and cooking comprising an inlet into which a mixture of chips and process liquid is fed. The chips are impregnated at a predetermined impregnation temperature, Timp, and cooked at a predetermined cooking temperature, Tcook, after which dissolved pulp is fed out at the outlet of the digester system. The process liquid which is continually extracted is retained outside the digester system during a dwell time, t, of at least 30 min, without any heating above 140°, and thereafter returned to the digester system to a position which is substantially at the same level as the extraction, or downstream thereof, and thereby constitute part of the process liquid in the subsequent treatment zone. The process results in improved tear strength, beatability, bleachability and reduced color reversion, and increased yield across the digester.

Abstract: The present invention provides a process for preparing polysulfide. More particularly, the process of the present invention allows one to prepare the amount of polysulfide needed using clarified white liquor, and to be used when and where it is needed during the cooking process. The process comprises reacting alkaline digesting liquor after clarification with a catalytic amount of a transition metal oxide catalyst, most preferably manganese dioxide. The reaction is conducted at a temperature of 98° C. or less, and is conducted for a short period of time, e.g., less than five minutes, with no oxygen gas or air being introduced with the catalyst and the main flow of clarified liquor.

Abstract: This invention refers to a method for producing pulp in an alkaline digesting process comprising the following steps: charging lignocellulosic material to a digester system; pre-treating said lignocellulosic material with an impregnation liquor and subsequently with a hotter liquor containing black liquor, simultaneously displacing spent liquor; heating and cooking said lignocellulosic material to produce cooked lignocellulosic material and cooking liquor; displacing a portion of said cooking liquor at cooking temperature from said digester to a first section by supplying a washing liquid; further displacing a second portion of displaced liquor from said digester system to at least a second section by supplying further washing liquid until the temperature of said second portion of displaced liquor drops to a temperature of at least about the boiling point of said cooking liquor at atmospheric pressure, said second portion of displaced liquor having a dry solids content substantially lower than the initial dry

Abstract: The invention relates to a process for treating bleaching liquors from pulping processes based on organic acids. The process is characterized in that inorganic acid such as nitric acid, phosphoric acid and/or sulphuric acid, is added into a bleaching liquor obtained from the bleaching or a stage closely associated with bleaching, whereby organic acids contained in the bleaching liquor are released into the bleaching liquor. The organic acids are then separated from the bleaching liquor and recycled to the cooking stage to be used as cooking chemicals. The nitrogen-, phosphor- and/or sulphur-containing product thereby produced, from which organic acids have been separated, is recovered to be used as a fertilizer or as raw material for a fertilizer.

Abstract: A method of papermaking having zero liquid discharge. A pulp slurry is produced from recycled cellulosic material and the slurry contains suspended cellulosic fiber material, solid contaminants and dissolved water soluble solids. The pulp slurry is subjected to a cleaning operation to produce a first flow stream containing the cellulosic fiber material and dissolved solids and a second flow stream containing dissolved solids along with solid contaminants. The first flow stream is washed with water to remove a substantial portion of the dissolved solids and provide a washed pulp which is used in a papermaking machine to produce a paper sheet. The second flow stream from the cleaning operation is compacted to produce a solid residue that can be landfilled and a liquid residue containing dissolved solids that can be recycled to the pulp cleaning operation.

Abstract: A method and apparatus for treating green liquor from a sulphate pulp mill enhances the clarification of the green liquor and may easily be integrated into existing pulp mills. A first portion of the green liquor from the sulphate pulp mill is clarified in a clarifier to produce a clarified green liquor and a dregs-containing green liquor. The dregs-containing green liquor is filtered in a green liquor filter to produce filtrate and dregs. The filtrate is combined) with the clarified green liquor to produce a first combined stream; and the dregs are filtered in a dregs filter. A second portion of green liquor from the sulphate pulp mill is combined with the dregs-containing green liquor to produce a second combined stream, and the second combined stream is introduced into the green liquor filter. The dregs from step (b) are washed prior to filtering the dregs, the green liquor filter and washer comprising a single structure.

Abstract: A method of papermaking having zero liquid discharge. A cellulosic pulp composed of recycled materials is initially cleaned to remove contaminants and foreign material, and the clean pulp is then washed to remove dissolved solids and pulping chemicals, and the washed pulp is then utilized in the papermaking process. The contaminants are separated from the liquid residue resulting from the pulp cleaning operation, preferably by floatation clarification, and the effluent from the clarification is evaporated to produce steam or water vapor along with an evaporated residue. The evaporated residue is combined with the suspended solids that were removed from the liquid residue and the combined residue is then subjected to a mechanical dewatering operation to reduce the water content so that the dewatered material can then be either landfilled or incinerated. The condensate from the evaporation can be combined with fresh makeup water and used in the papermaking process.

Abstract: In the bleaching of paper pulp without chlorine, such as using an OTZE or OZP bleach sequence, filtrate from subsequent stages is used as a wash liquid in preceding wash stages. The filtrate is treated with a fiber filter, and then passes through a magnesium filter, which has magnesium chips with a maximum dimension of about 3 mm or less. The magnesium removes heavy metal ions, and if any of the magnesium dissolves in the filtrate it provides a beneficial affect on the pulp. The pH of the filtrate is typically maintained in the 2-6 range to facilitate dissolution of Cu, Mn and Fe while the magnesium stays out of solution. Two filters may be provided in parallel so that if one becomes contaminated the other may be quickly put into service, and any explosive gases from the magnesium filter are vented.

Abstract: A process for the comminution, in particular defibrillation, and reaction of fibrous materials having a high dry solids content with the addition of a circulating medium, preferably a carrier gas and/or reaction agent, as well as optionally of chemicals. The invention is mainly characterized in that the circulating medium is recycled after leaving the comminuting device, by changing its temperature, and is then recycled to the comminuting device. Another embodiment of the invention is characterized in that the fibrous materials and liquid reaction agent are separated from the carrier gas and reaction agent vapors, which are then recycled back to comminuting device. A plant for carrying out this process is mainly characterized in that the comminuting device and route for recycling and treatment of the circulating medium form a closed system.

Abstract: A method for regulating the sodium carbonate concentration of a green liquor in the dissolving tank of the Kraft recovery process by measuring the conductivity of the green liquor from the dissolving tank, measuring the conductivity and flow rate of a weak wash solution being added to the green liquor in the dissolving tank, using these measurements to determine the sodium carbonate concentration of the green liquor in the dissolving tank, and adjusting the volume of the weak wash solution being added to the dissolving tank in response to changes in the concentration of sodium carbonate in the green liquor so as to maintain the concentration of sodium carbonate in the green liquor at a predetermined, preferably constant, level.

Abstract: A one-step slaking/causticizing method for producing white liquor from unslaked lime and clarified green liquor comprising introducing a feed slurry of unslaked lime and clarified green liquor into a pressurized slaker/causticizer reaction zone and maintaining the mixture in the zone at a temperature, under sufficient pressure and for a time sufficient, in one step to slake the lime and to convert the slaked lime to a white liquor containing product slurry.

Abstract: A process is provided for the activation and delignification of cellulose pulp, which comprises:(1) subjecting chemical cellulose pulp to activation by reaction with nitrogen dioxide in the presence of water at a temperature within the range from about 20.degree. to 120.degree. C., while(a) separating gas containing at least 1.2 mml nitrogen oxides, including NO, per liter of gas determined at 25.degree. C. and calculated as nitrogen, reacting nitrogen oxides in said withdrawn gas with oxygen gas in an amount within the range from about 10 to about 200 mole percent, calculated on the amount of NO present, and recycling the reacted gas to the activation; and(b) separating gas containing less than 0.4 mml nitrogen oxides, including NO, per liter of gas determined at 25.degree. C. and calculated as nitrogen from the cellulose pulp and removing said gas from the process; and(2) delignifying the activated cellulose pulp.

Abstract: A recovery method for settled black liquor in ponds and lagoons is disclosed so that ponds and lagoons which can no longer be pumped to recovery evaporators and furnaces are reconstituted by augering the settled black liquor and passing the augered material through filters, partical micronization chambers and static mixers.

Abstract: The invention concerns a procedure for recovery of soluble carbohydrates present in wood, in connection with the alkaline cellulose digesting process. According to the invention, recovery of carbohydrates takes place at the initial phase of the cellulose digesting process, where the digesting solution contains dissolved polysaccharides in abundance, while the content of polymeric lignin in the solution is low. A situation like this exists at the stage when the digesting solution has not yet reached the temperature at which the digestion process mainly takes place. As taught by the invention, the carbohydrates are recovered by conducting digesting solution to an ultrafilter, which separates the carbohydrates therefrom, and by returning the filtered solution to the cellulose digestion. The carbohydrates that are obtained may be used e.g. in the manufacturing of sugar alcohols, or as raw materials for biotechnical processes.

Abstract: A process for continuous digestion of wood chips which are passed through a heating zone, a digesting zone and a cooling zone in contact with cooking liquor is disclosed. In this process the wood chips are fed into and the liquid phase removed from the input end of the heating zone in such relative quantities that their heat-capacity flows are of approximately the same order of magnitude.

Abstract: A method for delignifying and/or bleaching cellulose pulp adds to the cellulose pulp a liquid which contains chlorine dioxide, causes the pulp to react with the chlorine dioxide over a selected period of time, and then reduces the amount of available active chlorine, optionally to a negligible amount, either by reducing the amount of liquid accompanying the cellulose pulp and/or by displacing such liquid with a newly supplied liquid containing no active chlorine or at most only a small amount of active chlorine; the displaced liquor can be replenished with chlorine and optionally with chlorine dioxide, and then added mainly to fresh cellulose pulp in the same bleaching stage, and/or to cellulose pulp in another bleaching stage.

Abstract: A method for oxidizing and removing remaining sodium sulfide as well as generated sulfur compounds by introducing oxygen into cooking liquor at high temperature and high pressure in the end stage of kraft cooking.

Abstract: In an apparatus for treating cellulose pulp with oxygen gas by passing the pulp and oxygen gas through a reaction vessel at elevated temperature and pressure, the improvement whereby the exothermic heat of reaction is controlled and the temperature of the pulp being treated is maintained below the point where the pulp would be degraded, the improvement comprising means for withdrawing oxygen gas from the vessel after the gas has been in contact with the pulp, dividing the withdrawn gas into two portions, cooling one of the portions to remove water vapor therefrom, recombining the gas portions whereby the resulting gas has a lower temperature than the gas withdrawn from the vessel and returning the resulting gas to the vessel for further contact with pulp therein, the amount of gas withdrawn from the vessel and the degree of cooling of the cooled portion of withdrawn gas being regulated to maintain the temperature within the vessel below the point where the pulp is degraded.

Abstract: Chemical cellulose is produced by treatment in a digester. In the first step, wood in the form of chips is treated for a period of about from 15 to 90 minutes with a cooking acid of a calculated amount of below 5% by weight and at least 2.5% by weight of SO.sub.2 and a mole ratio of SO.sub.2 to MgO or CaO of from about 2 : 1 to 3.5 : 1 at a temperature of from about 45 to 90.degree. C. The liquid SO.sub.2 is fed into the digester until the total SO.sub.2 content of the cooking acid is from about 6 to 10 percent by weight, and completing the digestion in a second step to obtain a pulp by cooking at a temperature of above 110.degree. C., and working up the pulp in a manner known per se to obtain chemical cellulose.

Abstract: Gaseous reaction apparatus wherein a portion of the supplied gas is discharged from the reaction vessel at a location below the upper level of a therein contained columnar mass of material wherein the gas is discharged into a receiving chamber extending along the outer periphery of the vessel and open to the lower portion of the vessel through an unrestricted opening being free from screens and filters, and such discharged portion of the gas, with or without cooling, is recirculated back into the upper inlet end of the vessel, thereby controlling the temperature in the vessel by removing or redistributing heat therein. Such apparatus is particularly useful in the gas phase treatment of fibrous material such as the bleaching or delignification of lignin-containing cellulose pulp.

Abstract: A process for the comminution, in particular defibrillation, and reaction of fibrous materials having a high dry solids content with the addition of a circulating medium, preferably a carrier gas and/or reaction agent, as well as optionally of chemicals. The invention is mainly characterized in that the circulating medium is recycled after leaving the comminuting device, by changing its temperature, and is then recycled to the comminuting device. Another embodiment of the invention is characterized in that the fibrous materials and liquid reaction agent are separated from the carrier gas and reaction agent vapors, which are then recycled back to comminuting device. A plant for carrying out this process is mainly characterized in that the comminuting device and route for recycling and treatment of the circulating medium form a closed system.