Abstract: A process for purification treatment of an impure liquid, such as a contaminated condensate, obtained when producing paper or paper pulp. The liquid is introduced intro a stripper device at an admission point (C) and the stripper device is also supplied with an acidifier preferably at a point (D) that is located above the admission point (C) and malodorous gases are driven off from the stripper device.

Abstract: A method for arranging water circulation in a paper mill including a pulp manufacturing plant provided with a water circulation system, such as a TMP plant, and a paper machine provided with a water circulation system. In order to reduce the amount of fresh water supplied to the paper mill, a part of the amount of fresh water supplied to the paper mill is substituted for by water or waters cleaned locally from waters contaminated at the paper mill. The concentrate or concentrates obtained from the stages of water cleaning is/are utilized where applicable by arranging the concentrate(s) to flow upstream in relation to the raw-material flow for reuse at the paper mill. By means of these operations, the amount of contaminants circulating in the paper mill is controlled.

Abstract: This invention is related to a process for producing pulp from a cellulosic starting material, wherein an aqueous process effluent is purified from metal impurity cations. This process comprises that the effluent is purified by an electro-chemical membrane treatment in an electrochemical membrane device comprising a unit cell through which an electric current is passed between an anode side and a cathode side of said cell, said cell comprising at least two ion permeable membranes forming between them at least one compartment, said effluent being fed into an effluent feed compartment in said cell, in which the effluent is purified by removing with the electric current metal impurity cations from the effluent through a cation selective membrane on the cathode side of said compartment, and withdrawing from said compartment the purified effluent. The purified effluent may be recirculated to the pulp mill process, e.g. as washing water.

Abstract: Methods of treating process water containing metal ions is disclosed including contacting the process water with a pulp comprising lignocellulose-containing material at a pH of above about 7 and a temperature of from about 50.degree. to 120.degree. C. whereby at least a portion of the metal ions are removed from the process water. Preferably the process water is produced from initially washing a pulp solution prior to a bleaching step employing hydrogen peroxide or ozone.

Abstract: Improved environmentally acceptable process for retaining chelant-containing effluent within pulp bleach plants, particularly total chloride-free bleaching sequence plants using a chelating agent closed re-cycle process. The process involves treating a pulp liquor in an acidic or near neutral stage with an effective chelating amount of a chelating agent to form a soluble, chelated metal species; removing the pulp to provide a chelated metal species-containing solution; treating this solution in an alkaline stage in the presence of sufficient Ca ions with an effective amount of an alkaline liquor to effect displacement of metals from the chelated metal species and precipitation of the metals as solids in alkaline solution; removing the solids from the alkaline solution to provide a metal-free, chelating agent-containing solution; and recycling the metal-free solution to the pulp liquor.

Abstract: A method for reducing or eliminating the formation of salt scale upon process equipment caused by precipitation of insoluble salts during the bleaching of pulp. The pulp is subjected to a bleaching sequence which includes a plurality of pulp treatment steps, wherein at least one pulp treatment step is conducted under alkaline conditions and at least one pulp treatment step is conducted under acidic conditions. A filtrate stream which contains dissolved insoluble salts therein is thus generated, and at least a portion of the filtrate stream is combined with an alkaline stream and pulp to cause the salts to associate with the pulp, thus removing the salts from the filtrate stream to reduce or eliminate the formation of salt scale upon process equipment during the bleaching of the pulp.

Abstract: The invention described in the specification relates to a process and apparatus for reducing AOX, COD and color bodies from the filtrate streams generated by a kraft pulp bleaching sequence. The method involves vigorously mixing an F.sub.D filtrate with an F.sub.E filtrate to form a filtrate mixture and treating the filtrate mixture with a coagulating compound, a flocculating compound and recycled foam concentrate. After chemically treating the filtrate mixture, the mixture is foamed with air in order to capture floc which formed in the mixture. Concentration of the foam and recycle of the foam to the filtrate mixture has been found to significantly increase the concentration of and reduce the amount of solids generated in the treatment system.

Abstract: A method for reducing or eliminating the formation of salt scale upon process equipment caused by precipitation of salts during the bleaching of pulp. The pulp is subjected to a bleaching sequence which includes a plurality of pulp treatment steps, wherein at least one pulp treatment step is conducted under alkaline conditions and at least one pulp treatment step is conducted under acidic conditions. A filtrate stream which contains dissolved salts therein is thus generated, and at least a portion of the filtrate stream is combined with an alkaline stream and pulp to cause the salts to associate with the pulp, thus removing the salts from the filtrate stream to reduce or eliminate the formation of salt scale upon process equipment during the bleaching of the pulp.

Abstract: Effluents are minimized from a cellulose pulp mill having a recovery boiler by concentrating liquid effluents from the bleach plant and/or liquid spills from process streams, incinerating the concentrated effluents in the recovery boiler, removing particles present in the flue gases from the recovery boiler to produce an ash including salts containing potassium and chloride, and sulfur compounds, and removing the potassium and chloride from the ash while returning the sulfur containing compounds to the recovery loop, so as to balance the sulfur, chloride and potassium levels in the mill. The sulfur is typically returned directly to a stream of black liquor just before entry into the recovery boiler. Green liquor is produced from the melt, which preferably is treated to remove metals from it prior to caustization (e.g. by sedimentation and/or filtration), and prior to green liquor crystallization to produce sodium hydroxide.

Abstract: The invention relates to a process for treating a low-concentrated aqueous feed solution which includes at least one aqueous process stream from a pulp mill. The process includes concentrating the feed solution by evaporation to form an evaporation concentrate, and subjecting at least a part of the concentrate to a first electrodialysis treatment, thereby forming a first electrodialysis concentrate containing salt removed from the evaporation concentrate and at least one diluate depleted in the salt. The invention also relates to a plant for carrying out the above process.

Abstract: Apparatus for a pulp and paper mill, and methods of acting on liquid effluents produced in the mill, which minimizes the discharge of polluting gaseous and liquid effluents to the environment. Liquid effluents from the bleach plant are concentrated (e.g. evaporated), incinerated (e.g. gasified), leached, crystallized (e.g. freeze crystallized) then washed, and then fed to the plant chemical recovery loop. White liquor produced from the recovery boiler melt is fully oxidized and used in place of caustic in the bleach plant. Essentially all sulfuric acid, sulfur dioxide, caustic, and chlorine dioxide necessary for the pulp mill is produced from mill liquid effluents and gas waste streams, on site at the pulp mill. Typical bleaching sequences that can be used are DE.sub.op D.sub.n D, or AZE.sub.o PZP.

Abstract: In minimizing effluents from a cellulose pulp mill, liquid effluents from a bleach plant are concentrated, and then incinerated to produce a residue including sodium, sulfate, and sodium chloride. This residue is distilled with sulfuric acid to produce gaseous hydrogen chloride and remaining residue, the HCl being used in chloride dioxide production for the bleach plant, while the remaining residue is passed to the recovery loop (e.g. recovery boiler). Sulfur containing gases from the non-condensible gas system may be combusted to produce gaseous sulfur dioxide, which is then converted to sulfuric acid, to distill the residue. Where a non-chlorine bleach plant is provided, the liquid effluents may be concentrated in evaporators and then passed directly to the recovery boiler. The liquid streams in the mill are managed by a cascade principle to reserve the cleanest water for only those processes where it is needed while minimizing its use where it is not necessary.

Abstract: Liquid effluent from a pulp mill bleach plant having at least one chlorine chemical bleach stage is evaporated and then used in chlorate manufacture. The bleach plant effluent produced by evaporation may be stored and then transported to an off-site chlorate production location, and/or may be subjected to a sodium chloride removal process (such as evaporative crystallization) and only sodium chloride transported to the off-site location. Chlorates produced off site can be returned to the mill (with acid and caustic that are optionally produced) for chlorine dioxide manufacture on site. The chloride-depleted stream from sodium chloride removal may be burned in the mill recovery boiler.

Abstract: A pulp mill has zero or minimum liquid discharges. The large amounts of liquid that must be processed to achieve this result are handled utilizing a multiple effect evaporator provided with heat from a steam exhaust of a condensing type steam turbine. Super heated steam from the recovery and bark boilers is fed to the turbine to generate electricity for the production of bleaching chemical and other uses in the mill. Three or four steam exhausts having different composite temperature and pressure values are taken from the turbine and used where most suitable in the pulp mill. For evaporation of bleach plant effluent the steam taken from the turbine preferably has a pressure of about 1-3 psia and a temperature of about 120.degree.-140 .degree. F, and has no significant adverse affect on power generation.

Abstract: Apparatus for a pulp and paper mill, and methods of acting on liquid effluents produced in the mill, which minimizes the discharge of polluting gaseous and liquid effluents to the environment. Liquid effluents from the bleach plant are concentrated (e.g. evaporated), incinerated (e.g. gasified), leached, crystallized (e.g. freeze crystallized) then washed, and then fed to the plant chemical recovery loop. White liquor produced from the recovery boiler melt is fully oxidized and used in place of caustic in the bleach plant. Essentially all sulfuric acid, sulfur dioxide, caustic, and chlorine dioxide necessary for the pulp mill is produced from mill liquid effluents and gas waste streams, on site at the pulp mill. Typical bleaching sequences that can be used are DE.sub.op D.sub.n D, or AZE.sub.o PZP.

Abstract: In minimizing effluents from a cellulose pulp mill, liquid effluents from a bleach plant are concentrated, and then incinerated to produce a residue including sodium, sulfate, and sodium chloride. This residue is distilled with sulfuric acid to produce gaseous hydrogen chloride and remaining residue, the HCl being used in chloride dioxide production for the bleach plant, while the remaining residue is passed to the recovery loop (e.g. recovery boiler). Sulfur containing gases from the non-condensible gas system may be combusted to produce gaseous sulfur dioxide, which is then converted to sulfuric acid, to distill the residue. Where a non-chlorine bleach plant is provided, the liquid effluents may be concentrated in evaporators and then passed directly to the recovery boiler. The liquid streams in the mill are managed by a cascade principle to reserve the cleanest water for only those processes where it is needed while minimizing its use where it is not necessary.

Abstract: Chloride dioxide for a cellulose pulp mill bleach plant is produced by concentrating (evaporating) liquid effluents from the bleach plant to a concentration level high enough for incineration, incinerating the concentrated effluents to produce an ash, chemically reacting at least a part of the ash to produce chlorate, and using the chlorate in the manufacture of chlorine dioxide. The ash is purified to produce sodium chloride and the sodium chloride is reacted with oxygen and external energy to produce sodium chlorate. The chlorate is then used in the manufacture of chlorine dioxide. Sulfates produced are used to manufacture acid and/or caustic, and heavy metal hydroxides are disposed of. A part of the ash may be used directly in chlorine dioxide manufacture. At least some of the salt from chlorate manufacture may be fed to the chemical recovery loop, including a recovery boiler, in the pulp mill. Evaporated gases may be returned to the pulp mill and bleach plant.

Abstract: The invention relates to a method of recovering chemicals from chloride-containing green liquor by precarbonating the green liquor by means of flue gases into hydrosulfide and soda, by removing hydrosulfide from the precarbonated solution in the form of hydrogen sulfide, by evaporation crystallizing the chloride- and soda-containing solution in order to separate the chloride salt from the alkaline solution. In order to reduce releases of hydrogen sulfide, the produced hydrogen sulfide is absorbed into a soda solution and/or an alkaline solution in order to produce a solution suitable for the preparation of white liquor, whereas the hydrogen sulfide which remains unabsorbed is returned to the precarbonation stage, in which the hydrogen sulfide is absorbed substantially completely. By means of the invention it is possible to achieve a closed cycle of chemicals without the chloride load of the system increasing, and at the same time the chloride is recovered and returned to the bleaching.

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: The digestion of the cellulose-containing material is performed with a digestion liquor containing sulphur and sodium followed by recovery and regeneration of said digestion liquor and bleaching of the cellulose-containing material with chlorine dioxide. The SO.sub.2 -containing and possibly chloride-containing gas from the recovery boiler (11) of the process and from combustion of evil-smelling gases (20) is absorbed in an absorption liquor containing and alkali metal salt solution free of sulphur or sulphur compounds such as sulphide or thiosulphate, in a scrubber (27). The resulting scrubber liquor is mixed with acid residual solution (26) from the manufacture of chlorine dioxide, whereby sulphur dioxide (32) in gaseous state is returned to the process, whereafter the residual solution (34) free from SO.sub.

Abstract: A cellulosic pulp and bleaching process is described. The process integrates two cycles, one is a digestor liquor cycle and the other is a sulfur cycle.The digestor liquor cycle comprises the steps of digesting a fibrous cellulosic feed to form a pulp, separating the pulp and bleaching it in at least one stage with chlorine dioxide, evaporating and burning the remaining waste liquor to form a smelt, dissolving the smelt to form a green liquor and utilizing the green liquor, after recausticizing, as at least a portion of the feed stock for the digestor step.The sulfur cycle of the present invention utilizes a portion of the green liquor of the digestor liquor cycle. The green liquor is carbonated to form a bicarbonate which is then stripped of H.sub.2 S. The H.sub.2 S is converted into H.sub.2 SO.sub.4 and utilized as a feed stock to a chlorine dioxide generator. The chlorine dioxide generator utilizes H.sub.2 SO.sub.4 as feed stock and produces Na.sub.2 SO.sub.4 as a by-product. The Na.sub.2 SO.sub.

Abstract: A method for cleaning effluents from bleaching plants which use ultrafiltration for cleaning, preferably after the first extraction stage, by dividing the ultrafiltration into two stages, and between them inserting an alkali treatment stage. The high molecular chlorine compounds are thereby split into innocuous sodium chloride in the permeate from the second ultrafiltration stage, which can be returned to the extraction stage so that with the alkali excess after the splitting, it can cover all or part of its alkali requirement.

Abstract: A method is provided for reducing waste stream pollutants by the control and separation of color bodies, COD, BOD and other organics from inorganic chloride pollutants in the aqueous waste effluent of a cellulosic pulp bleaching process containing a sequential chlorination stage (D.sub.c) or mixture (D/C) stage followed by an extraction (E) or oxygen (O) stage, comprising, maintaining the conditions of the D.sub.

Abstract: Sodium sulfate crystals, also known as salt cake, are obtained as a side stream in the manufacture of chlorine dioxide by the reduction of sodium chlorate with chloride ions in an aqueous, acidic medium containing sulfate ions. The sodium sulfate crystals are contained in a mother liquor saturated with sodium sulfate and contaminated with chloride ions. The process provided by the present invention purifies the salt cake crystals by separating the crystals from the mother liquor without evaporation of the mother liquor until a critical dryness level is achieved and then the remaining mother liquor is evaporated to result in purified salt cake crystals having substantially reduced chloride ion content.

Abstract: A process is provided for the separation of sodium chloride in the sodium chemicals recovery stage of sodium-based pulp manufacturing processes so as to maintain a low sodium chloride content in the recycled sodium chemicals, comprising the steps of treating an aqueous sodium chloride-containing solution with carbon dioxide gas, thereby forming a saturated sodium bicarbonate solution; precipitating sodium values of the solution as sodium bicarbonate while retaining sodium chloride in solution; separating such sodium bicarbonate; withdrawing the residual aqueous sodium chloride-containing solution from the process; and recycling the separated sodium bicarbonate.

Abstract: An improved method for purifying dark colored chlorine containing effluents from a chlorine based pulp mill bleaching plant is disclosed, wherein the purification process involves treating the effluent in a bed containing a particulate weakly basic anion exchange and/or absorbent resin which takes up the colored lignin degradation products in the effluent until the resin has been saturated with pollutants to a given degree, whereupon the resin bed is eluted by means of an alkali solution. At least a fraction of the eluate which is released from the resin bed during the elution is acidified to a pH of less than 2, so that the majority of the total solids of the acidified effluent is precipitated, the precipitate is separated from the residual acidic liquor which contains the majority of the inorganic chlorine of the acidified eluate, and the precipitate then may be suitably transferred to a recovery plant of the pulp mill for eventual disposal.

Abstract: A pulp mill bleach plant operation having a low effluent volume, a low consumption of water, energy and chemicals, and yet provides efficient bleaching, caustic extraction and washing is described. Water conservation is practised by controlling the use of wash water in the bleach plant, controlling the design and operation of washers, deckers and other mechanical devices used in the bleach plant and controlling the inflow of water with chemicals. An aqueous polluting effluent-free pulp mill water utilization system is also described.

Abstract: A process for the recovery of chemicals from the waste liquors of sulfate cellulose digestion and from the waste waters of bleaching, wherein a melt from a soda-ash roaster, mainly containing sodium sulfide and sodium carbonate, but also sodium chloride, is dissolved and clarified to produce green liquor containing carbonate, sulfide and chlorides is dissolved. The carbonate is separated from the sulfide and the chlorides, at least part of the sodium chloride is separated from the sulfide in solution, at least part of the carbonate is causticized into hydroxide, and the hydroxide and sulfide in solutions is mixed together in a ratio suitable to form a digestion solution with a desired sulfide content.

Abstract: A cellulose containing vegetable material is bleached by the steps of chlorinating said material, followed by ammonia treatment and post bleaching with washing stages between said steps. Waste waters resulting from the washing stages are purified by subjecting said waste waters to electrodialysis and recovering ammonium chloride from the purified waste waters. The recovered ammonium chloride is used to pre-treat the cellulose material prior to chlorination thereof and the purified waste waters are reused in the washing stages.

Abstract: Environmental regulations tend to restrict the emissions from pulping platns, which increase the amount of sulphur and chlorine in the cooking liquor to undesirable amounts. This is detrimental to the process and increases the risk of corrosion upon the furnace walls. According to the invention certain metals, preferably iron and/or aluminum are burned together with the waste liquor, and will form compounds with the sulphur and the chlorine, respectively, which are easily separated from the chemicals taking part in the normal process cycle.

Abstract: An improved process for the treatment of precipitator catch wherein the catch is slurried with water, sufficient carbon dioxide is added to convert the sodium carbonate present to sodium bicarbonate, and sodium chloride is separated from the sodium sulfate and sodium bicarbonate.

Abstract: An improved process for the treatment, separation, and utilization of precipitator catch wherein treated precipitation catch is separated by countercurrent washing in a column.

Abstract: An improved process for the treatment of precipitator catch wherein the catch is slurried with water, sufficient carbon dioxide is added to convert the sodium carbonate present to sodium bicarbonate, and sodium chloride is separated from the sodium sulfate and sodium bicarbonate.

Abstract: A process for decoloring an aqueous effluent from the bleaching of sulphate pulp with chlorine or chlorine containing compounds, said effluent containing dark colored lignin degradation products, said bleaching including at least one alkali extraction stage, comprisesA. treating the aqueous effluent from at least one alkali extraction stage in the bleaching with at least one acid selected from the group consisting of sulphuric acid, sulphurous acid and hydrochloric acid until a precipitate forms, said precipitate consisting essentially of dark colored lignin degradation products and other organic materialB. separating the treated aqueous effluent from the precipitate andC. contacting the treated aqueous effluent which has been separated from the precipitate with a phenolic resin which is activated by the acidic effluent, said activated resin binding the dark colored lignin degradation products and separating a decolored effluent from the loaded resin.

Abstract: The method of treating a chlorine-based total bleachery effluent in which only a chlorine and sodium salts are used in the bleach sequence comprising the steps of adding aluminum ion to said effluent in an amount sufficient to precipitate substantially all of the organics and suspended solids therein, separating the solids from said effluent, electrodialyzing the treated effluent to provide two effluent streams, one containing 200 to 600 parts per million sodium chloride which can be returned to the bleachery, and a second concentrated stream containing 5 to 10% by weight sodium chloride, evaporating said concentrated stream to a concentration of about 25% sodium chloride by weight, and electrolyzing said concentrated sodium chloride solution to produce chlorine gas, sodium hydroxide, and sodium hypochlorite.

Abstract: Sodium chloride is removed from Kraft mill smelts by fractionating the smelt to separate sodium carbonate and sodium sulphate in solid form from sodium sulphide and sodium chloride which usually is contaminated with residual quantities of sodium carbonate and sodium sulphate and is contained in an aqueous solution thereof. Sodium chloride subsequently is separated from the aqueous solution. Various fractionation procedures are described and various procedures for the removal of the sodium chloride in substantially pure form also are described.

Abstract: Smelts produced in spent pulping liquor recovery operations and containing sodium chloride are treated to remove sodium chloride therefrom in pure form while the loss of usable components is avoided. A solid mixture of sodium chloride, sodium carbonate and sodium sulphate is provided as such in a soda mill, or first is separated from sodium sulphide, by fractionating the smelt where sodium sulphide is present, as in the Kraft mill. The solid mixture is leached at a high temperature to remove all the sodium chloride values therefrom, along with part of the sodium carbonate and sodium sulphate. Pure sodium chloride is deposited by cooling the leach liquor and the mother liquor is recycled to the leaching step.

Abstract: In the recovery and regeneration of spent pulping chemicals from the production of cellulosic fibrous material pulp there is provided a white liquor containing dissolved quantities of sodium chloride and unregenerated pulping chemicals. The white liquor is concentrated by evaporation to deposit therefrom sodium chloride and unregenerated pulping chemicals, unregenerated pulping chemicals substantially free from sodium chloride are recovered from the deposited materials, and sodium chloride is separated and recovered from the deposited materials. The deposition of sodium chloride and unregenerated pulping chemicals is usually carried out in two stages, with unregenerated pulping chemicals substantially free from sodium chloride being deposited in the first stage. The sodium chloride then is deposited in the second stage, possibly in admixture with unregenerated pulping chemicals, in which event substantially pure sodium chloride is separated from the deposited mixture.

Abstract: Smelts produced in Kraft mill and soda mill spent pulping liquor recovery operations and containing sodium chloride are treated to remove sodium chloride therefrom in pure form while the removal of usable components is avoided. A solid mixture of sodium chloride, sodium carbonate and sodium sulphate is provided in the case of the soda mill, or first is separated from the sodium sulphide in the case of the Kraft mill. Thereafter, the solid mixture is leached to remove the sodium carbonate and sodium sulphate while leaving the sodium chloride in a substantially pure form, the resulting leach liquor being refrigerated to deposit sodium carbonate and sodium sulphate. The mother liquor, after removal of the deposited salts is recycled to the solid mixture leaching step.