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 number of different, efficient treatments of slurries and liquid with gas can be provided. A slurry or liquid is introduced into a first end of a vortex. A gas--such as a chemically reactive gas--is introduced from exteriorly of the vortex into contact with the slurry or liquid in the vortex, so that a desired reaction between the slurry or liquid and the gas takes place. The treated slurry or liquid is removed from the second end of the vortex while any residual or carrier gas is removed from the first end of the vortex. Gas introduction is preferably accomplished through a porous surface of revolution (e.g. cylindrical or conical) wall surrounding the vortex, the gas being in minute bubble form when it enters the slurry or liquid.

Abstract: The invention relates to a method of bleaching waste paper pulp. The pulp is first treated to a reductive chemical followed by acidification and washing or dewatering. The pulp is then subjected to ozone and then to hydrogen peroxide. The reductive chemical used is either formamidine sulphinic acid or sodium hydrosulfite.

Abstract: A process for bleaching pulp, in which, after fiber liberation, a first filtrate containing metals, principally in ionic form, is separated off from the pulp, and supplied downstream to the pulp flow after a bleaching stage.

Abstract: An oxygen delignification method and apparatus in which a charge of heated wood pulp is reacted with oxygen in the presence of a charge of caustic soda in a plurality of reaction stages located between mixing stages in which caustic is mixed with the wood pulp. The use of the plurality of mixing stages reduces peak pH exposure of the wood pulp that would otherwise occur if the charges of caustic and wood pulp were mixed all at once. Moreover, the caustic mixed in such manner replenishes neutralized caustic and ensures that the average pH level is increased above that in conventional oxygen delignification. The increase in average pH level favors an increase in the delignification. Filtrate from a washing stage is introduced into the mixing stages to prevent wood pulp degradation.

Abstract: The method solves the problem of delignifying technical cellulose pulp in a selective manner which will result in very low residual contents of lignin in the pulp and a correspondingly high quantity of lignin dissolved in spent liquors, which are recovered in the chemical recovery system of the pulp mill. The method comprises activating liquid-containing lignocellulosic material in the presence of nitrate with a gas that contains nitrogen dioxide, followed by the alkaline delignification of the lignocellulosic material, and measuring the acidity of the liquid accompanying the material on at least one occasion during the activation. The method is characterized in that the acidity of the liquid is measured subsequent to bringing the time derivative of the nitrate concentration of the liquid, expressed as millimols per liter of liquid per minute, to a level beneath +0.

Abstract: A two stage ozone-pulp bleaching method and apparatus are disclosed. In the first stage, high consistency pulp particles are turbulently mixed and contacted with a gaseous mixture containing ozone to mix and contact substantially all of the pulp particles with ozone to react at least a portion of the pulp particles with the ozone. Pulp particles and gaseous bleaching mixture are then directed to a second stage including a quiescent pulp bed. Pulp particles may complete their reaction in the bed, which also serves to strip ozone which was not contacted with pulp particles in the first stage from the gaseous bleaching mixture.

Abstract: A process for delignifying and bleaching a lignocellulosic pulp without the use of elemental chlorine by partially delignifying the pulp to a K No. of about 10 or less and a viscosity of greater than about 13 cps; and further delignifying the partially delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10, and a GE brightness of at least about 50%. The substantially delignified pulp may be brightened by the addition of a bleaching agent such as chlorine dioxide or a peroxide to obtain a final product having a GE brightness of at least about 65%, preferably above 70% to as high as 90%. Because of the absence of elemental chlorine in this sequence, filtrate from all stages but the chlorine dioxide stage (if used) can be recovered without sewering. Major environmental improvements are thus achieved.

Abstract: A process is disclosed for bleaching pulp without chlorine containing chemicals and for greatly reducing total washing filtrate discharge, comprising the steps of: 1) sending pulp that has been subjected to continuous digestion, oxygen-delignification and then washing, through a washing press; 2) treating, with agitation, the delignified washed pulp with sulfuric acid and a chelating agent; 3) washing the pulp in a washing apparatus; 4) bleaching with hydrogen peroxide in a reaction vessel; 5) washing the hydrogen peroxide bleached pulp; 6) adding sulfuric acid and ozone with mixing of the pulp; 7) reacting the pulp with ozone in a reaction vessel; and 8) washing the ozone reacted pulp, wherein the majority of liquid filtrate from the bleaching process that is waste not to be recycled is drawn off from the washing apparatus of step 3, the washings in step 3 and 5 have at least 85% efficiency, filtrate from washing step 5 is recirculated to the washing apparatus of step 3, and filtrate from the washing apparat

Abstract: In a method of bleaching medium consistency pulp with ozone using a mixer, ozone containing gas and about 6-15% consistency pulp are fed to the mixer, and then discharged in a first, preferably vertical, path. The mixture of pulp and ozone moves in a first part of the vertical path a time period of about 1-5 seconds at a velocity of about 1-5 m/s so that the gas and pulp do not separate during movement in this first part, and the vast majority of the pulp brightening reaction between the ozone and pulp takes place. This is preferably accomplished by passing the mixture upwardly in a small diameter conduit having a height of about 3-20 meters. Then the velocity of the pulp is slowed while still moving in the first path, preferably by feeding it directly to a much larger diameter (e. g. 1.5-10 times) conduit, so the height of the unit may be kept under 100 feet. The pulp flows in the large diameter conduit for about 0.5-5 minutes so that residual reactions take place.

Abstract: A process for delignifying a lignocellulosic material comprising exposing the material to a mixture of peracid and ozone. Preferred peracids include Caro's acid and peracetic acid. Also disclosed is a kraft pulp delignification mixture comprising in combination: (a) water; (b) a kraft pulp at 1-40% consistency; (c) a peracid; and (d) from 0.1 to 5.0% ozone on pulp.

Abstract: Medium consistency (e.g. about 6-15%) paper pulp is effectively bleached with ozone in a carrier gas (typically oxygen) by effecting efficient separation of carrier gas from the pulp after reaction with the ozone, and introducing the ozone into the pulp at a pressure of about 10-13 bar. Ozone in oxygen and medium consistency paper pulp are fed to a fluidizing mixer; the intimate uniform mixture produced is then passed upwardly in a reaction vessel until about 99% of the ozone has been consumed, and then separation of gas from the pulp is initiated by moving the pulp mixture into a generally horizontal tube leading to a gas zone in a large diameter retention vessel. A pressurized gas pad is maintained at and above the introduction of the pulp into the retention vessel, while the level of pulp in the retention vessel is maintained below the point of introduction.

Abstract: A process for delignifying and bleaching a lignocellulosic pulp without the use of elemental chlorine or chlorine-containing compounds by oxygen delignifying the pulp to a K No. of about 14 or less and a viscosity of greater than about 10 cps and thereafter further delignifying the partially delignified pulp by lifting, displacing and tossing the pulp in a radial direction while advancing it in an axial direction in a plug flow-like manner with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 6 or less, a viscosity of at least about 7 cps and a GE brightness of at least about 35. The substantially delignified pulp may then be brightened to a final product having a GE brightness of at least about 75, or alternately up to about 83 or more by contacting the ozonated pulp with chlorine dioxide or a peroxide compound.

Abstract: A method for controlling the gas recycle loop of an ozone bleaching process wherein an ozone generator produces an ozone containing gas from an oxygen containing feed gas and delivers the ozone containing gas to an ozone reactor at a variable flow rate responsive to reactor ozone demand. Pulp is bleached with the ozone containing gas, thereby producing an exhaust gas having a flow rate that varies in response to the flow rate of the ozone containing gas delivered to the ozone reactor. The exhaust gas is then recovered and its flow rate is modified within the recycle loop so that an amount equivalent to reactor ozone demand is returned to the ozone generators. The oxygen content of the oxygen containing feed gas is monitored at or near the inlet of the ozone generator and an amount of fresh oxygen is supplied to the oxygen containing feed gas to obtain a predetermined level of oxygen therein.

Abstract: Transition metals are removed from cellulose pulp and treatment fluids in a pulp mill. Medium consistency digested pulp is treated in an acidic stage, and then washed to produce a filtrate. The pH of at least a substantial part of the filtrate is adjusted so that it is greater than 9 (preferably greater than 10.5), while a sufficient carbonate content is provided to keep the calcium content low. Adjusting the pH causes dissolved transition metals in the filtrate to precipitate as solids, and the solids can then be filtered out, e.g. by precoat filtering, or clarification followed by polishing filtering. The greatly reduced transition metal content filtrate is then used elsewhere in the pulp mill, as in a washer following an oxygen delignification stage. The acidic stage may be an EDTA stage, an ozone stage, an acid only stage, etc., and the pulp is preferably treated so that it is bleached in at least one Z stage and one P stage, and preferably also an E (e.g. E.sub.op) stage.

Abstract: Method for the treatment of cellulosic pulp in which pulp is distributed upward through a vertical reactor using a unique conical distributor and is discharged using a unique dilution method to eliminate plugging. The system is particularly useful for delignifying virgin wood pulps or decolorizing pulps made from waste paper materials.

Abstract: In a multi-stage bleaching sequence for kraft pulps employing a chlorine-containing bleaching agent in the first and final stages thereof and an intermediate alkaline extraction stage, the improvement for enhancing the brightness of the pulp and reducing the quantity of dioxin or chlorinated organics comprising contacting the pulp, in a mixer, at an acidic pH and a temperature of below about 60.degree. C. with a mixture of ozone and oxygen at a pressure of between about 60 and 80 psig wherein the quantity of ozone introduced to the pulp is between about 0.2% and about 0.4%, based on pulp.

Abstract: A method for delignification and bleaching of cellulosic pulp which comprises reacting a cellulosic pulp with peracetic acid, ozone and oxygen under conditions of acidic pH. The ozone substantially completely reacts with the pulp and, thereafter, the oxygen reacts with the pulp under under an acidic pH.

Abstract: In a three-stage process for the delignification of cellulose-containing raw materials, pulping is initially performed with a solution of concentrated aqueous acetic acid at an elevated temperature and under an elevated pressure. The resultant acetic acid-moist pulp is treated in a second stage with the aforementioned pulping solution with the addition of nitric acid and is then washed or extracted with water or with the pulping solution. In a third treatment stage, the thus-obtained acetic acid-moist pulp is treated with an ozone-containing gas.

Abstract: Laboratory equipment for practicing experiments and mixing ozone with medium consistency cellulosic pulp allows precise control of the timing and amount of ozone injected into the mixer, providing a method of testing that is more accurate than prior methods. An injection cylinder and fluidizing laboratory mixer are utilized. Pulp is fed into the mixer, the cylinder is charged with a known predetermined amount of ozone containing gas, the ozone containing gas is injected from the cylinder into the mixer, the mixer is operated to effect mixing of the ozone containing gas with the pulp for a predetermined period of time, and then gas containing residual ozone (which has not reacted with the pulp) from the mixer is vented from the mixer, including by utilizing a purge gas such as nitrogen. The ozone is created by an ozone generator which continuously operates. A three-way valve directs the output of the ozone generator to an ozone destruction device when the ozone is not being charged into the cylinder.

Abstract: A method for bleaching pulp with ozone and, more specifically, to a method for bleaching pulp without deterioration of pulp quality. The starting material is a medium consistency pulp with easy handling during transfer and dewatering, namely, pulp of a consistency of about 10% by weight to 20% by weight. During the initial stage of the ozone bleaching process, the reaction velocity is maintained higher, while during the latter stage of the bleaching process, cellulose attack is prevented. Specifically, pulp bleaching is done with ozone, while the pulp consistency during the bleaching process is lowered in a stepwise manner within the range for a medium consistency pulp.

Abstract: A method and apparatus supply ozone containing gas under superatmospheric pressure to an ozone delignification device. The speed of a water ring compressor is controlled so that it compresses as much ozone gas per unit time at desired superatmospheric pressure as the ozone delignification unit utilizes, with essentially no excess. The ozone containing gas is fed from the water ring compressor through a separator buffer tank which levels out pressure pulses and separates cooling water from compressed ozone gas prior to the gas entering the ozone delignification unit. The gas passes through a control valve controlled by a mass flowmeter which senses the amount of cellulose pulp fed to the ozone delignification unit. The speed control of the compressor may be provided by a differential pressure controller connected across the control valve.

Abstract: A method of bleaching a chemical pulp by adjusting the pH of the pulp to 1.5-3.5, chelating the pulp and then treating the pulp in an N stage with nitric oxide (NO) in the amount of at least 1.5% by weight of the oven dried pulp at a consistency of between 30 and 55% and further treating the pulp in a Z stage with ozone to produce a bleach pulp having a higher viscosity for a given permanganate number compared with a similar pulp bleached without using the N stage.

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 method of bleaching a chemical pulp with a gaseous bleaching agent by uniformly impregnating the pulp with a solvent for lignin and that is fully miscible with water but does not significantly swell cellulose so that the availability, of lignin to the bleaching agent is significantly improved, then subjecting the impregnated pulp to the action of the bleaching agent to preferentially attack the lignin for its subsequent solubilization and separation from the pulp.

Abstract: A process for bleaching wood pulp is provided comprising subjecting the wood pulp, after brown stock washing, to an oxygen delignification stage, a washing sequence, a first chlorine dioxide bleaching stage, an oxidative extraction stage, at least one final chlorine dioxide bleaching stage and then recycling the filtrate from the oxidative extraction stage countercurrently through the bleaching plant and brown stock washing. Additionally, and quite beneficially, the filtrate from the first chlorine dioxide bleaching stage is also recycled countercurrently through the brown stock washing thereby significantly reducing the environmental impact associated with the manufacture of bleach wood pulp.

Abstract: Waste cellulosic paper products, for example, old corrugated container are recycled employing oxygen delignification in the presence of an alkaline material to produce a recycled pulp of lower kappa number, while maintaining adequate strength in the pulp. The recycling process preferably employs an acid pretreatment in combination with the oxygen delignification, and exposure of the waste product to the alkaline material is preferably controlled so that at any point in the delignification the waste product is exposed to not more than 50%, by dry weight, of the alkaline material based on the weight of residual lignin in the waste paper product.

Abstract: A process for the chlorine-free bleaching of pulps in an aqueous suspension which comprises forming the suspension with a consistency of 3 to 20 mass percent; introducing into the suspension an ozone-containing gas having an ozone content of 20 to 300 g/m.sup.3 in an amount corresponding to at most 2 mass percent ozone calculated on dry pulp of the suspension during vigorous agitation of the suspension to form a reaction mixture; maintaining a pressure of the ozone-containing gas at a pressure of 1 to 15 bar during introduction into the suspension; and controlling reaction conditions during contact of the ozone-containing gas with the suspension to maintain a reaction temperature of 15.degree. to 80.degree. and a pH value of 1 to 8.

Abstract: Kraft pulp is bleached to a brightness of about 90 CPPA or greater, without the use of chlorinated organic compounds that has commercially acceptable strength properties. During production of the kraft pulp it is subjected to extended delignification, by adding kraft white liquor to a first recirculation loop in the digester, and/or a second, wash, recirculation loop in the digester; or by conventional pulping followed by two oxygen stages, with washing between the stages. The extended delignification pulp is then subjected to ozone bleaching, with an ozone dosage of less than 1.0% (preferably less than about 0.5%). The ozone bleaching sequence may be a (ZE)P(ZE)P sequence.

Abstract: In a process for chlorine-free bleaching of cellulose with an .alpha.-cellulose content of more than 90%, preferably from boiled cotton linters, more than 75% whiteness is achieved in a single-stage process using oxygen. The bleaching is conducted using the oxygen obtained by disproportionation of peroxo compounds in the pH range from 6 to 13 and with the bleaching time, depending on the bleaching temperature of 35.degree. C. to 15.degree. C., being between 15 and 150 minutes.

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: The invention relates to a process for bleaching chemically delignified lignocellulose-containing pulp, to render more efficient a peroxide-containing treatment stage, by treating the pulp with a complexing agent before the peroxide step, so that the trace metal profile of the pulp is altered by the treatment with the complexing agent, in the absence of sulphite, at a pH in the range from 3.1 up to 9.0 and at a temperature in the range from 10.degree. C. up to 100.degree. C., whereupon, in a subsequent step, the treatment with a peroxide-containing substance is carried out at a pH in the range from 7 up to 13, said two-step treatment being carried out at an optional position in the bleaching sequence applied to the pulp.

Abstract: Waste cellulosic paper products, for example, old corrugated containers are recycled employing oxygen delignification in the presence of an alkaline material to produce a recycled pulp of lower kappa number, while maintaining adequate strength in the pulp. The recycling process preferably employs an acid pretreatment in combination with the oxygen delignification, and exposure of the waste product to the alkaline material is preferably controlled so that at any point in the delignification the waste product is exposed to not more than 50%, by dry weight, of the alkaline material based on the weight of residual lignin in the waste paper product.

Abstract: A process for delignifying and bleaching a lignocellulosic pulp without the use of elemental chlorine by partially delignifying the pulp to a K No. of about 10 or less and a viscosity of greater than about 13 cps; and further delignifying the partially delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10, and a GE brightness of at least about 50%. The substantially delignified pulp may be brightened by the addition of a bleaching agent such as chlorine dioxide or a peroxide to obtain a final product having a GE brightness of at least about 65%, preferably above 70% to as high as 90%. Because of the absence of elemental chlorine in this sequence, filtrate from all stages but the chlorine dioxide stage (if used) can be recovered without sewering. Major environmental improvements are thus achieved.

Abstract: A process for conditioning an ozone gas recycle stream in an ozone pulp bleaching process, wherein the level of carbon dioxide in the recycle stream is controlled to allow full capacity operation of the ozone generator. Carbon dioxide concentration is identified over the relevant operational ranges and maximum concentration is identified for full capacity/optimum efficiency operation. Specific methods are described for controlling carbon dioxide concentration including purging a portion of the recycle stream, counter-current scrubbing of the recycle stream with an alkaline solution and passing the recycle stream through an adsorbent material. Contaminants entering the system also may be reduced by directing the purged recycle stream, which is relatively oxygen rich, into the dewatering press where pulp consistency is increased. In this manner nitrogen surrounding the pulp is displaced by oxygen and thus, does not enter the bleaching/ozone system with the pulp.

Abstract: Process for producing pulp suitable as raw material for paper, board or fiberboards and similar products. A pumpable alkaline slurry of fibrous raw material is conducted through a pressurized tube system by the use of pulp pumps, the pressure increasing in steps from the beginning of the process to the end of the process. On its way the slurry is repeatedly dewatered and rediluted with process liquid. An apparatus suitable for being used in carrying out the process comprises a dewatering tube (64) and a dewatering and venting tube (67) arranged centrally and axially within the tube (64) which may be provided with a perforated part (66). The tube (67) is provided with perforations (68) through which gas and liquid from fiber-containing slurry introduced into the outer tube (64) can escape. At the opposite end from the inlet end of the outer tube (64) there is an outlet (72, 65) for thickened fiber-containing slurry.

Abstract: A high-efficiency wood pulp bleaching process to produce wood pulps with higher brightness at equal chlorine dioxide usage or of equal brightness at significantly reduced chlorine dioxide usage. The process comprises reacting the chlorine dioxide with wood pulp at a pH of about 5-10 for about 5-40 minutes and then acidifying the mixture to a pH of about 1.9-4.2. The mixture is then allowed to react for about 2 or more hours to complete the two-step high/low pH bleaching process.

Abstract: Delignification and bleaching of lignocellulosic material is enhanced after the pulp has been treated with peroxomonosulfuric acid.

Abstract: Secondary pulp is deinked and bleached by contacting the pulp simultaneously with oxygen, alkali, and a surfactant in a reaction zone followed by washing to recover a secondary fiber product. Simultaneous contacting with oxygen and surfactant yields higher pulp brightness than sequential contacting in oxygen bleaching and washing stages, and enhances bleachability in further bleaching stages.

Abstract: Unbleached pulp is combined with an aqueous alkaline solution while in a state of low consistency to distribute a first amount of alkaline material substantially uniformly throughout the pulp. The consistency of the pulp is then increased to above about 18%, and the high consistency alkali containing pulp is then treated with oxygen to effect delignification. The total amount of alkaline material applied to the pulp is between 0.8 and 7% by weight of oven dry pulp. High strength, low lignin pulps are subsequently formed which may be further bleached to high brightness with reduced amounts of chemicals.

Abstract: A process for oxygen bleaching fibrous cellulose pulp is described in which the pulp passes a first delignification zone with a predetermined low temperature and a second delignification zone with a predetermined high temperature which is higher than that in the first delignification zone. The pulp is fed through a first vertical reactor containing said first delignification zone with low temperature, and thereafter through a second vertical reactor containing said second delignification zone with high temperature. The temperature in the first delignification zone is either maintained at the temperature that the pulp entering for bleaching has acquired during a previous treatment before the oxygen bleaching, or as required is adjusted by the controlled supply of steam to a mixer disposed in the pipe before the first reactor. The temperature in the second delignification zone is adjusted by the controlled supply of steam to a mixer disposed in the pipe between the two reactors.

Abstract: A process for delignifying and bleaching a lignocellulosic pulp without the use of elemental chlorine by partially delignifying the pulp to a K No. of about 10 or less and a viscosity of greater than about 13 cps; and further delignifying the partially delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10, and a GE brightness of at least about 50%. The substantially delignified pulp may be brightened by the addition of a bleaching agent such as chlorine dioxide or a peroxide to obtain a final product having a GE brightness of at least about 65%, preferably above 70% to as high as 90%. Because of the absence of elemental chlorine in this sequence, filtrate from all stages but the chlorine dioxide stage (if used) can be recovered without sewering. Major environmental improvements are thus achieved.

Abstract: A process for delignifying and bleaching a lignocellulosic pulp without the use of elemental chlorine by partially delignifying the pulp to a K No. of about 10 or less and a viscosity of greater than about 13 cps; and further delignifying the partially delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10, and a GE brightness of at least about 50%. The substantially delignified pulp may be brightened by the addition of a bleaching agent such as chlorine dioxide or a peroxide to obtain a final product having a GE brightness of at least about 65%, preferably above 70% to as high as 90%. Because of the absence of elemental chlorine in this sequence, filtrate from all stages but the chlorine dioxide stage (if used) can be recovered without sewering. Major environmental improvements are thus achieved.

Abstract: An apparatus for delignifying and bleaching a lignocellulosic pulp without the use of elemental chlorine. The bleaching reactor is a horizontal vessel having a central rotatable shaft which preferably contains paddles, cut and folded screw flights or a ribbon flight, to disperse and advance the pulp particles in a plug flow manner while contacting and mixing the pulp particles with a gaseous bleaching agent such as ozone for substantially uniform bleaching thereof.

Abstract: Process for bleaching lignocellulosic material comprising an oxygen bleaching treatment and an enzymatic treatment with a substantially cellulase-free xylanase, which process is compatible with, and can be incorporated into, conventional bleaching sequences. The process provides a delignified and bleached pulp using lower amounts of chlorine-containing compounds, and the opportunity of eliminating the use of elemental chlorine, thereby reducing the polluting effluent from a pulp mill employing the process. Also, a greater extent of delignification can be achieved while retaining acceptable pulp strength properties. The oxygen bleaching treatment and the enzynmatic treatment are done in series.

Abstract: A method for delignifying and bleaching a lignocellulosic pulp with a gaseous bleaching agent in a reactor without the use of elemental chlorine. The bleaching reactor is a horizontal vessel having a central rotatable shaft which preferably contains paddles, cut and folded screw flights or a ribbon flight, to disperse and advance the pulp particles in a plug flow manner while contacting and mixing the pulp particles with a gaseous bleaching agent such as ozone for substantially uniform bleaching thereof.

Abstract: Unbleached pulp is combined with an aqueous alkaline solution while in a state of low consistency to distribute a first amount of alkaline material substantially uniformly throughout the pulp. The consistency of the pulp is then increased to above about 20%. Additional alkali is applied onto the high consistency pulp to provide a total amount of between 0.8 and 7% by weight of oven dry pulp. The high consistency alkali containing pulp is then treated with oxygen to effect delignification. High strength, low lignin pulps are formed which may be further bleached to high brightness with reduced amounts of chemicals by following the methods of the invention.

Abstract: A process for delignifying and bleaching a lignocellulosic pulp without the use of elemental chlorine by partially delignifying the pulp to a K No. of about 10 or less and a viscosity of greater than about 13 cps; and further delignifying the partially delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10, and a GE brightness of at least about 50%. The substantially delignified pulp may be brightened by the addition of a bleaching agent such as chlorine dioxide or a peroxide to obtain a final product having a GE brightness of at least about 65%, preferably above 70% to as high as 90%. Because of the absence of elemental chlorine in this sequence, filtrate from all stages but the chlorine dioxide stage ( if used) can be recovered without sewering. Major environmental improvements are thus achieved.

Abstract: A process for delignifying and bleaching a lignocellulosic pulp without the use of elemental chlorine by partially delignifying the pulp to a K No. of about 10 or less and a viscosity of greater than about 13 cps; and further delignifying the partially delignified pulp with an effective amount of ozone for a sufficient time to obtain a substantially delignified pulp having a K No. of about 5 or less, a viscosity of greater than about 10, and a GE brightness of at least about 50%. The substantially delignified pulp may be brightened by the addition of a bleaching agent such as chlorine dioxide or a peroxide to obtain a final product having a GE brightness of at least about 65%, preferably above 70% to as high as 90%. Because of the absence of elemental chlorine in this sequence, filtrate from all stages but the chlorine dioxide stage (if used) can be recovered without sewering. Major environmental improvements are thus achieved.

Abstract: A fluid is continously processed by being fed to the top of a hydraulic downdraft tube (15) which forms a downdraft column which is of a height such that the pressure at the bottom thereof will approximately be at the pressure necessary to dissolve sufficient oxygen in water to control the surgical oxidation of lignite in paper pulp in concert with proper retention time and predetermined temperature high and low limits. The fluid is conducted to the bottom of the tube (15) and treated in a variable depth reaction zone (25) in which turbulence is introduced with an injected mixture of reactant and non-reactant gases. The result is that lignite in the pulp will be bleached releasing a controlled proportion of heat to the fluid which enhances the reaction. The treated fluid is fed into an updraft annulus (26) wherein the reaction is selectively restrained by variable depth cooling device (21) and the non-reacting gas is allowed to expand inducing controlled updraft velocities.