Abstract: White liquor produced from black liquor is partially or completed oxidized. The white liquor contains dregs that are utilized as a carbon based catalyst. Dregs are produced by separating the dregs from green liquor an intermediate product between the black liquor and the oxidized white liquor. After formation of the oxidized white liquor, the dregs are separated therefrom to form a waste dreg stream which can be recycled so that part of the dregs present within the dregs containing white liquor stream to be oxidized is contributed by the waste dreg stream.

Abstract: A method for reusing spent gas from an ozone bleaching reactor includes steps for removing lint from the spent gas, compressing it, passing it through a reactor in which hydrocarbons and carbon monoxide are destroyed by oxidation, and cooling the gas. Injecting the gas together with compressed air into a mist separator for removal of any mist from the gas and then passing the gas through a pressure swing adsorption device in which nitrogen, carbon dioxide, trace water vapor, and other trace elements may be removed by adsorption on a molecular sieve material. The recycled gas is fed to an ozone generator and from there to an ozone/pulp bleaching reactor. By appropriate selection and layering of molecular sieve materials in the pressure swing adsorption device, it is possible to provide selective removal of a variety of gaseous elements from a gas stream.

Abstract: Sodium chloride is removed from pulping chemicals used in a Kraft pulping process by the use of a snake-cage polyelectrolyte ion exchange resin, coupled with removal of sulfide prior to treatment, or treatment of chemicals which are already low in sulfide. In one aspect of the invention, dust is collected from exhaust gases produced in the black liquor recovery cycle and is dissolved in water to produce a solution containing sodium chloride and sodium sulfate. The solution is filtered to yield a solid product and a filtrate solution. The filtrate solution is fed to an ion exchange unit which removes chloride and produces a purified sodium sulfate product. The sodium chloride is removed from the ion exchange resin by water elution, and useful recovered chemicals are recycled to the recovery cycle of the Kraft process.

Abstract: The invention described in the specification is a method for removing hydrogen sulfide, volatile mercaptans and methyl sulfides from a paper mill condensate stream. In the method, carbon dioxide is injected into the condensate stream under pressure and the pressure of the resulting CO.sub.2 -enriched condensate is reduced rapidly to a pressure sufficient to cause hydrogen sulfide and volatile mercaptans to pass from the CO.sub.2 -enriched condensate to a gas phase. The gas phase containing hydrogen sulfide and mercaptans may then be recycled or burned and the treated condensate may be recycled for pulp washing. The method is very cost effective and can be easily retrofitted into existing paper mill systems without significant capital expenditures or production down time.

Abstract: The invention relates to a process for purifying electric precipitator ash of chlorides and potassium by means of leaching, filtering and washing a filter cake, with the leaching being carried out using water and recirculated filtrate from a previous washing. The process is characterized in that the filtration and the washing of the filter cake, and, where appropriate, the leaching, take place in a pressure filter in one and the same vessel.

Abstract: A method for destroying chlorine dioxide includes irradiating the chlorine dioxide to effect conversion to chlorine and then reacting at least part of the resulting chlorine to form chloride.

Abstract: Method of reducing corrosion in a power boiler of a pulp mill using biofuel and suspended matter obtained from the waste water treatment of the mill. In the method flue gases obtained from a waste heat boiler are fed into the power boiler, causing the sulfur dioxide contained in them to react with the alkali chlorides in the boiler and the chlorine to form hydrogen chloride.

Abstract: A paper mill and method of producing paper from waste paper in which no liquid effluent is produced, and wherein the spent treatment liquors are subjected to an oxidative treatment, microfiltration, and reverse osmosis.

Abstract: A method is described for the treatment of a solid containing material obtained from effluent from an industrial plant or process, eg. a plant for the de-inking of waste paper. Such effluent comprises an aqueous suspension of solids comprising organic material and inorganic particulate material. The inorganic particulate material contains a substantial amount of calcium carbonate and is likely also to contain kaolin or metakaolin. The solids may also contain carbon particles. The method includes subjecting the solid containing material to a heat treatment process such that the temperature is controlled to be maintained in the range 600.degree. C. to 800.degree. C. preferably 600.degree. C. to 750.degree. C., to cause burning of the organic material without decomposition of more than about 50% by weight, preferably not more than about 10% by weight, of the calcium carbonate present to produce a particulate calcium carbonate-containing inorganic material substantially free of organic material.

Abstract: A method for recovery and use of a particulate waste material, i.e. inorganic and/or organic solid fines, present in an aqueous suspension, comprising the steps of:a) treating the aqueous suspension so as to precipitate, in the presence of the solid fines, crystals of an alkaline earth metal carbonate whereby the solid fines become entrained by and bonded to the crystals, thereby forming in the aqueous suspension a mixed aggregated particulate solid comprising the crystals and the fines; andb) recovering the mixed aggregated particulate solid and supplying such solid for use as a filler or pigment in a filler- or pigment-containing composition.

Abstract: The present invention relates to a method for continuously producing pulp in which finely divided fiber material, preferably wood chips, is impregnated in an impregnation vessel (10), preferably by being fed in at the top (14) and fed out from the bottom (16) of the said vessel (10), in which cooking pressure essentially prevails in the said first vessel (10). The impregnation vessel, preferably, does not have a screen. The chips are heated and impregnated with the aid of black liquor that is concurrently flowing with a flow of the wood chips which have been thoroughly impregnated with boiling hot black liquor are transferred to the top (28) of a steam-phase digester (12). The pulp is permitted to flow passed at least one screen girdle (32) for drawing off spent liquor. The drawn off spent liquor has a high amount of effective alkali.

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: 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: Chemical (typically kraft) pulp having enhanced intrinsic fiber strength and bleachability compared to pulp produced using conventional or modified kraft cooking is produced by using high alkali and/or pH cooking, preferably by adding the vast majority of cooking liquor (such as kraft white liquor) after the first removal of liquid from the digester so that the effective alkali concentration is high near the end of the cook. That is during at least the last minute (preferably at least the last 15 minutes and most preferably at least the last 30 minutes) before the cook is terminated the effective alkali concentration is between 15-50 g/l, more preferably between about 18-40 g/l, and most preferably between about 20-35 g/l.

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: The invention is directed to a paper machine including a headbox having an inlet and an outlet. A fluid conduit is connected to the inlet of the headbox. A sensor is disposed in communication with an interior of the headbox. The sensor senses a pressure of the fiber suspension within the headbox and provides a signal corresponding thereto. A first pump is connected to the fluid conduit and supplies a fiber suspension to the headbox through the fluid conduit. A second pump is connected to the fluid conduit between the first pump and the headbox, and further is connected to the sensor. The second pump is a substantially pulseless pump, and transports the fiber suspension away from the fluid conduit, dependent upon the sensed signal.

Abstract: Low temperature steaming and slurrying of wood chips results in significant improvement in treatment, the chips being maintained at a temperature below 110.degree. C. (more desirably at about 105.degree. C. or less, and most desirably at about 100.degree. C. or less) until actually heated to cooking temperature. Steaming may be accomplished utilizing a vertical chip bin with one dimensional convergence and side relief or a horizontal steaming vessel, the steaming device connected to a high pressure feeder. A pump having an NPSHR less than the NPSHA may be used for drawing slurry into the high pressure feeder from the steaming device, or a pump may be disposed between the steaming device and the high pressure feeder for forcing slurry into the high pressure feeder through a conduit including a radiused elbow. The steaming is practiced at a pressure of 5 psig or less, preferably substantially atmospheric steaming is practiced.

Abstract: A process is disclosed for extracting pure, coarse-grain silicic acid crystals from silicic acid-containing spent lye in cellulose production, comprising adding coarse-grain silicic acid to alkalized spent lye, lowering the pH of the alkalized spent lye to about 9 such that a sediment is formed, separating the sediment formed into coarse grain and fine grain silicic acid with little lignin and lignin-containing spent lye free from silicic acid, and separating the coarse grain and fine grain silicic acid with little lignin into course grain silicic acid and lignin. At least part of the course grain silicic acid separated is fed back to the alkalinized spent lye to be desilicified.

Abstract: A novel method and device for the production of pulp by a continuous cooking process is provided wherein hot impregnated chips are fed into the top of a countercurrent steam digester which has a bottom outlet and at least one draw off screen girdle for removing black liquor. At least 50%, preferably 70%, of the cooking liquor is fed to the top of the digester as finely divided droplets.

Abstract: Black liquor is subjected to high shear to cause a breakdown of macromolecules contained therein and provide a reduction in viscosity, thereby improving the processability of the black liquor and enabling the solids content to be increased.

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: 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: The invention relates to a method of adjusting the sulphur balance of a sulphate cellulose plant, in which method black liquor is concentrated and heat treated by keeping it at a temperature higher than the cooking temperature for a certain time period to separate the sulphur compounds contained in the black liquor as gaseous sulphur compounds therefrom in the last evaporation stage of a series of evaporation stages.

Abstract: A defoamer composition made from the reaction product of an epoxide containing composition selected from epoxide fatty acids, epoxide vegetable oils and mixtures thereof and at least one secondary compound selected from the group consisting of fatty acids and alkoxylated derivatives thereof, alkoxylated polyols, alcohols, alkoxylated alcohols, alkylphenols, alkoxylated alkylphenols, alkylamides, alkoxylated alkylamides, acetylenic glycols, alkoxylated acetylenic glycols, polybasic acids, alkylene oxides, organo silicones and polymers thereof, and methods of using the same especially for defoaming black liquor produced in the pulp and paper industry.

Abstract: A method and apparatus facilitate removal of metals from acidic liquids containing dissolved metals (such as pulp mill bleach plant washer filtrate) by oxidizing the liquid with ozone, hydrogen peroxide, oxygen, and/or air to increase the valence of the metals (like Mn and Fe) so that they become easier to precipitate. Oxidation may be practiced using any suitable reactor, such as a gas-contact reactor, or a plunger type reactor where the oxidizing agent is primarily gaseous, or a static mixer or stirred tank where the oxidizing agent is primarily liquid. After oxidation the pH of the liquid is adjusted (e.g. to over 6, preferably about 8-11) to precipitate the metals. The precipitated metals are then removed by filtration, sedimentation or flotation, and the metals-depleted liquid used elsewhere in the pulp mill.

Abstract: Resonant tubes of a pulse combustor are immersed in a bed of solid particles in a reaction zone to provide indirect heat from the pulsating combustion gases to the solid particles of the bed. The bed is maintained in an agitated state by a gas or vapor flowing through the bed. Reactant materials are introduced into the agitated bed and undergo reaction at enhanced rates resulting from heat transfer coefficients at least about twice as high as those of steady flow combustors and an intense acoustic pressure level propagated from the pulsating combustor into the reaction zone. The apparatus is useful, for example, to steam reform heavy hydrocarbons and to gasify carbonaceous material, including biomass and black liquor to produce combustible gas at relatively low temperatures, with steam being utilized as the bed fluidizing medium. Black liquor gasification, utilizing sodium carbonate as bed solids, results in liquor energy and chemical content recovery without smelt production.

Abstract: Chemical (typically kraft) pulp having enhanced intrinsic fiber strength and bleachability compared to pulp produced using conventional or modified kraft cooking is produced by using high alkali and/or pH cooking. After being impregnated with a first cooking liquor (e.g. white liquor) having low effective alkali, the first liquor is extracted from the pulp, and it is impregnated with a second cooking liquor having an effective alkali concentration of at least 25 g/l and cooked at cooking temperature (e.g. 140.degree.-190.degree. C.) to produce a spent second cooking liquor having a residual effective alkali concentration of at least about 15 g/l, which is then extracted from the pulp. The spent second liquor may be used to preheat incoming white liquor, and then flashed and used as the first liquor. The pH of the first liquor is typically less than about 13.0, and the residual pH of the spent second liquor is about 13.0 or more.

Abstract: Digestion liquor is used in the paper pulping process to dissolve lignins and free the cellulose fiber from raw wood chips. After pulping, spent digestion liquor is laden with lignins. Heretofore, it was known that lignins could be coagulated by acidification of the digestion liquor, but such method coagulated the lignins in a slimy gelatinous mass that was difficult to separate from the liquor. It has been discovered that the addition of water soluble, surface active, polymeric agents to the digestion liquor prior to acidification, results in an easily separable lignin coagulant after acidification.

Abstract: The process for producing hydrogen peroxide, used in the bleaching of pulp, uses the hydrogen generated wholly or partly by the gasification or partial combustion of cellulose spent liquors used in digesting cellulose material to produce the hydrogen peroxide.

Abstract: Cooking liquors of significantly different sulphidity (e.g. one having a sulphidity about 30-40% and the other a sulphidity of above 40%, e.g. about 60-70%) may be produced in a simple energy-efficient manner. Black liquor is treated to recover chemicals, and the chemicals are dissolved to produce green liquor, which is clarified, as is conventional. The temperature of a first portion of the green liquor is decreased to effect crystallization of sodium carbonate in the green liquor by expanding the green liquor in at least two (and typically more than three) stages with vapor being produced during expansion. The sodium carbonate crystals produced are separated from the first portion of green liquor to produce a green liquor with high sulphidity (greater than about 40%) and this high sulphidity liquor may be heated by bringing it into direct heat exchange relationship with at least part of the expansion vapor (in a number of different stages).

Abstract: A method for recovering sodium from a spent cooking liquor used in a kraft pulping process employing sodium hydroxide as a cooking agent resulting in the presence of sodium and sulfur combined with various elements in the spent cooking liquor. Black liquor is converted to green liquor, and the green liquor is reacted with lime in a causticizer to produce caustic and calcium carbonate. The caustic is recovered for use as a cooking liquor and the calcium carbonate is heated in a lime kiln to provide a source of lime. Flue gases containing free lime evolved from the lime kiln are contacted with a sodium carbonate solution in a scrubber to convert lime to caustic.

Abstract: A process for the production of cellulose from wood and annual plants is provided where the digesting liquor contains free caustic soda, sodium salts of alkyl benzenesulfonic acids, and of aromatic or aliphatic carboxylic acids. By the addition of anthraquinone or its derivatives to the digesting liquor, the delignification is improved. Anthraquinone is resistant to wet oxidation and can be reintroduced into the digesting process. The solubility and, therefore, the effectiveness of anthraquinone is improved by the use of sulfonic acid salts. For the recovery of the digesting chemicals contained in the black liquor, solubilized liquor is precipitated with mineral acid or carbon dioxide and the hemicelluloses are separated by ultra filtration. The resins are separated by extraction with the residual organic compounds, except for the sulfonates and carboxylics, being burned in an aqueous phase with air and/or oxygen.

Abstract: Processes for preparing pulp from lignin-containing cellulosic material are disclosed including a prehydrolysis step followed by neutralizing hydrolysate and the prehydrolyzed cellulosic material in the reactor with alkaline neutralizing liquor, removing the neutralized hydrolysate from the reactor and delignifying the neutralized prehydrolyzed cellulosic material with alkaline cooking liquor containing sodium sulfide and sodium hydroxide.

Abstract: There is disclosed a process for separating fine solids from water in the used water recovery system of a sheet forming mill, wherein the used water recovery system includes at least one stage in which an alkaline earth metal carbonate is precipitated in the aqueous suspension constituting the used water whereby the particulate material present in the used water becomes entrained in the alkaline earth metal carbonate precipitate. By the invention it is possible to recover the water and the fine solid materials which pass through the wire mesh belt of a paper or board forming machine, and optionally recycle those recovered materials.

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: A method of integrating bleaching and recovery in connection with the production of chemical pulp that has been digested and preferably delignified with oxygen gas using processes that retain the viscosity and strength, to kappa number less than 16 without the use of chemicals containing chlorine, and using a bleaching sequence including at least one step with sequestering agent and/or acid, and a peroxide step.

Abstract: A high solids black liquor which has solids content of at least 65% by weight of liquor is mixed with a viscosity reducing additive prior to firing in a chemical recovery furnace. The additive is an admixed compound consisting of monoethylene glycol, diethylene glycol and triethylene glycol.

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: In a chemicals recovery plant in a sulphate pulp mill, in order to provide green liquor with improved sedimentation and filtration properties, there is passed, from a flow (10) of slaked lime and green liquor between a lime slaker (9) and a causticizing tank (1 1), a partial flow (32, 35) to a soda dissolver (2) or to a container (26) for unclarified green liquor provided after the soda dissolver. For this purpose there is provided, in a line (10) between the lime slaker (9) and the causticizing tank (11), a branch line (32, 35) which passes to the soda dissolver (2) or to a container (26) for unclarified green liquor provided after the soda dissolver.

Abstract: The removal of bleaching chemical-consuming metals from treatment fluids in a cellulose pulp mill is facilitated by treating the pulp in an acidic or neutral stage to dissolve metals, washing or thickening the pulp to produce a filtrate containing dissolved metals, and then using an alkali liquid to adjust the pH of the filtrate to cause dissolved metals to precipitate. The alkali liquid is pretreated with carbon dioxide to reduce the sulfide content and increase the carbonate content thereof, preferred alkali liquids being green liquor and white liquor. The reduced-metal content filtrate is used in the bleach plant of the pulp mill, to make bleaching chemicals, as a wash liquid, etc. Treatment of the alkali liquid with carbon dioxide is typically practiced by scrubbing the liquor with carbon dioxide gas, for example, using a plate column scrubber or a stationary packing scrubber.

Abstract: Waste lignocellulosic material, for example brown kraft grocery bag and corrugated paperboard, is treated in a multi-step process to produce a recycle brownstock pulp having a sufficiently low kappa number that it may be bleached according to conventional means such that its final optical and strength properties are comparable to that of virgin pulps bleached according to similar means; biological enzymes are used in conjunction with medium consistency pulping to separate fibers and loosen contaminants, such as wax and adhesives; low temperature soaking of waste lignocellulosic material in an alkaline peroxide liquid using long reaction times is used to minimize energy consumption, degrade contaminants, and to selectively remove lignin; loosened contaminants and poorly bonding lignocellulose debris are removed by screening and cleaning methods; high consistency peroxygen cooking is used to substantially delignify the pulp and to destroy contaminants in an energy efficient manner; liquid streams are treated an

Abstract: A method for white liquor oxidation in a kraft mill utilizes a two-stage selective oxidation system in which the first stage is operated to remove sulfide while the second stage is operated to oxidize a significant fraction of the remaining oxidizable sulfur compounds to sulfate. The resulting selectively oxidized white liquor products are used as alkali sources for various process steps in the mill. Optionally, white liquor can be oxidized in a single stage to convert a significant fraction of the oxidizable sulfur compounds to sulfate. Methods for controlling the selective oxidation process are disclosed.

Abstract: Kraft pulp of increased strength (e.g. at least about 15% greater tear strength at a specified tensile for fully refined pulp, and as much as about 27%) is produced by keeping the dissolved organic material (DOM) concentration below about 100 g/l (e.g. <50 g/l) throughout substantially the entire kraft cook. This may be done by extracting liquor containing a level of DOM substantial enough to adversely affect pulp strength, and replacing some or all of the extracted liquor with liquor containing a substantially lower effective DOM level than the extracted liquor, so as to positively affect pulp strength. The replacement liquor may be water, white liquor, pressure heat treated black liquor, washer filtrate, cold blow filtrate, or combinations, or the extracted liquor can be treated to remove or passivate the DOM (e.g. by precipitation, ultrafiltration, or absorption).

Abstract: A method and reactor for thermally decomposing a carbonaceous raw material (6) to recover gas and, if applicable, solid or liquid chemicals, the raw material being fed into a chamber (2) for gasification under under-stoichiometric conditions, the gasification is carried out in a gasification zone (15) at a pressure from atmospheric pressure up to about 150 bar and at a temperature within the range 500.degree.-1600.degree. C. According to the invention a part of the thermal energy required to maintain the endothermic reactions in the gasification zone (15) is produced by combustion of a fuel (8) in a combustion zone (16) located close to and in gaseous contact with the gasification zone, the raw material and fuel being supplied through different nozzle channels (12 and 13, respectively). An oxygen-containing gas (17) is supplied in an amount sufficient to oxidize substantially all the fuel.

Abstract: The invention relates to a method and apparatus for use in the pulp industry for improving the safety of a spent liquor recovery boiler, such as a soda recovery boiler. The boiler comprises, for recovering chemical and energy, a furnace cooled by water tubes and connected to the water/steam circulation system of the boiler, the cooling of the bottom of the furnace being provided by a separate cooling circulation. The separately cooled lower section of the furnace is provided by separating the bottom or the bottom and part of the furnace walls from the boiler water circulation system. This separated section is supplied with a cooling fluid of its own which may be a gas (e.g. air or inert gas) or a liquid (e.g. molten zinc) which does not cause an explosion of it contacts the melt of the furnace.

Abstract: An improved method of chemical recovery from kraft black liquor is disclosed in which the heat generated by controlled oxidation of the liquor is utilized to reduce the viscosity and net heating value of the liquor which allows the firing of a more concentrated liquor in the recovery boiler. Net steam recovery is increased for a given black liquor feed rate. Alternatively, the firing of liquor having a higher solids concentration is possible, which increases the throughput of the recovery boiler.

Abstract: A method and apparatus for recovering wash water from effluent generated by a pulp and paper mill. The method includes filtering at least a portion of the effluent to form a filtrate stream and an organic solids feed stream. The organic solids feed stream is exposed to a temperature and a pressure which are supercritical for water to cause a substantial portion of the organic component to oxidize and form a product stream that, when cooled, includes a gaseous component, an inorganic solids component, and a liquid wash water component. The wash water component is separated from the gaseous and inorganic solids components, thereby recovering wash water.

Abstract: This invention relates to an alkaline scrubber for condensate stripper off-gases. In particular, this invention relates a process for selectively removing hydrogen sulfide and methyl mercaptan from a gas stream containing these compounds and methanol. Such gas streams are commonly generated during pulp and paper production.

Abstract: A method of producing oxidized white liquor from white liquor in which sodium sulfide is oxidized to sodium sulfate. In accordance with the method, an oxygen containing gas is contacted with the white liquor at a temperature of at least 110.degree. C. and such that the total pressure of oxygen and water vapor is no less than 9.2 atmospheres during the contacting.