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: A method of diagnosing a malfunction of a process control system which includes at least one closed loop control loop comprising measuring a histogram of tracking error of the control loop, determining distortion of the tracking error relative to a Gaussian distribution, and indicating a malfunction in the process in the event a deviation from the Gaussian distribution of the tracking error exceeds predetermined limits.

Abstract: A process employing a fixed-resin bed Acid Retardation Unit (ARU) to separate spent acid from chlorine dioxide generators into a de-acidified sodium sulfate component and a purified sulfuric acid component. The de-acidified sodium sulfate produced is returned to the chemical recovery cycle of the kraft mill in place of acidic chlorine dioxide generator effluent thereby avoiding the destruction of alkalinity in pulp mill liquors. In addition, sulfuric acid is purified providing an opportunity for reuse in various mill applications, and/or concentrated and recycled to the generator. Alternatively, to avoid high evaporation costs, the purified acid can be used to regenerate a cation-exchange unit (CEU) used in the conversion of sodium chlorate to a sodium chlorate/chloric acid mixture which is fed to the generator in place of sodium chlorate and sulfuric acid. Using this approach, the sulfuric acid requirement of chlorine dioxide generators and, in turn, the amount of acidic generator effluent can be reduced.

Abstract: A process of delignifying and bleaching a chemical wood pulp with hydrogen peroxide and dicyandiamide as an activator provides a higher degree of delignification and brightness of the pulp and overcomes problems of fibre degradation. The process comprises adding hydrogen peroxide and dicyandiamide as a bleaching activator to a chemical wood pulp slurry under alkaline conditions.

Abstract: The invention relates to an apparatus for detecting plugged sites and holes and for measuring of the water permeability properties of pervious machine fabrics. Plugged sites in a permeable fabric are detected by sensing water pressure pulses occurring in the nozzle at the moment when a stream of water flowing through the nozzle contacts a plugged site on a fast running fabric. The apparatus can be used on-line to simultaneously detect plugged sites and holes on a moving pervious fabric while monitoring its water permeability properties.

Abstract: A process for the bleaching of kraft pulps with non-chlorine chemicals, employing a sequential reaction of oxidative enzymes and hydrogen peroxide. The kraft pulp can be from conventional or extended pulping, or from an oxygen delignification step. The enzyme reaction is monitored by methanol release which results from the demethylation of lignin. The process essentially comprises three steps. The first step is the oxidation of kraft pulp either with manganese peroxidase enzyme in the presence of Mn(II) salts, hydrogen peroxide and chelator, or with laccase enzyme preferably in the presence of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS), or a combination of both enzymes in a crude mixture as typically produced by certain fungi. The Mn(II) salts and chelator may already be present in sufficient amount in the pulp. This first step is performed at an acidic pH, and moderate temperatures for a period of time between 30 and 240 minutes.

Abstract: The invention overcomes the problem of paper edge overdrying during the paper drying process on paper machine drying cylinders. It comprises applying a thin ceramic coating onto the circumferential exterior surface of the cylinder near the cylinder edges, thereby forming a thermal barrier coating which decreases paper drying rate at said edges and reduces or eliminates paper edge overdrying.

Abstract: Solid films with novel optical properties are produced from colloidal suspensions of cellulose crystallites; the colloidal suspensions are prepared by acid hydrolysis of crystalline cellulose under carefully controlled conditions; the solid materials possess a helicoidal arrangement of the constituent crystallites; by appropriate selection of conditions for preparation and treatment of the colloidal suspensions, solid films are produced that reflect circularly polarized visible light; the wavelength of the reflected light can be controlled to give colours across the visible spectrum from red to violet, and if necessary to infrared and ultraviolet wavelengths.

Abstract: A rapid method is provided for the on-line determination of sodium sulfide concentration and/or percent sulfidity in green liquors or smelt solutions used for the production of either kraft or sulfite pulp. The method eliminates manual sampling, and the need for frequent equipment maintenance.

Abstract: A process for bleaching high-yield (mechanical or chemi-mechanical) pulps to high brightnesses and low yellownesses (b*) in a single treatment employs di-oxygen gas (O.sub.2), alkaline agent and a borohydride. The combined treatment gives brightnesses comparable with those achieved with stabilized alkaline hydrogen peroxide. By comparison the reaction of di-oxygen and alkali alone darkens high-yield pulps; and treatment with alkaline borohydride in the absence of added di-oxygen bleaches to give only about half the brightness gained if di-oxygen is added. The bleaching may possibly occur through the conversion of di-oxygen molecules (O.sub.2) to hydroperoxide ions (HOO-) utilizing ionized phenolic groups or hydroquinones in the lignin. The hydroperoxide ions are thus generated in situ in the lignin and can destroy colored lignin chromophores. Without the addition of borohydride the lignin phenolic groups would be irreversibly oxidized.

Abstract: A process for the recovery of alkali metal hydroxide and acid from the alkali metal salts of monovalent anions which are mixed with the alkali metal salts of multivalent anions employs a water-splitting system composed of bipolar membranes in conjunction with ion-selective membranes; a two-compartment cell employs monovalent anion-selective membranes to define salt/base and acid compartments with the bipolar membranes, and a three-compartment cell employs, monovalent anion-selective and cation-selective membranes to define with the bipolar membranes, acid, salt and base compartments; the process has particular applicability to the conversion of the sodium/potassium chloride portion of the Electrostatic Precipitator (ESP) Catch of the recovery boiler of coastal and/or closed-cycle kraft pulp mills, a mixture of mostly sodium/potassium sulphate and chloride, into sodium/potassium hydroxide and hydrochloric acid; the remaining sodium/potassium sulphate solution, depleted in chloride, can thus be used as sodium/s

Abstract: A method and apparatus are described for continuously sampling a process stream, or reservoir of aqueous cellulosic pulp and detecting oversize contaminants in the sampled stream. This serves the overall objective of estimating the level of contamination in the process stream or reservoir during a given period of production; the method may include the following stages: 1) a continuous sample stream is drawn from the process or main stream, 2) the stream is passed through a centrifugal device which divides the sampled stream according to density, 3) the stream with the higher level of contaminants from the centrifugal device is passed to a screen which isolates the contaminants, and 4) the contaminants are flushed from the screen so that they can be quantified; these measurements are used to assess the purity of the material being produced. One useful application of this invention is to assess the presence of trace amounts of plastic contaminants in the production of the cellulosic pulp.

Abstract: A process using an electrodialysis system employing cation-selective membranes and anion-selective membranes, particularly monovalent anion-selective membranes is used to separate kraft pulping liquors into two streams; one that is rich in sulphides (to be used in the initial stage of pulping), and another that is poor in sulphides (to be used in the final stage of pulping). By separating pulping liquors in this way, the sulphur balance in the kraft process can be maintained while obtaining the benefits of modified pulping. The same electrodialytic system can be used to separate green and polysulphide liquors into sulphide-rich and sulphide-poor components.

Abstract: A method for the production of kraft pulps in a digester, by modifying the cooking chemical concentration, and lignin concentration profiles during the cook, has provided extended delignification and improved selectivity in a simpler way than has previously been possible. The cooking is performed at an elevated temperature in two stages. The first stage liquor is a mixture of 1) the spent liquor of the second stage and 2) a portion of the conventional charge of fresh cooking chemicals needed for the complete cook. The second stage liquor is made up by adding an aqueous diluent, for example, fresh water or washing filtrate to the remaining portion of the fresh cooking chemicals.

Abstract: A method and apparatus for monitoring the fiber surface development of pulps due to the refining or beating of mechanical or chemical pulps; an optical cell, fabricated with light-transparent windows, permits an incident collimated beam of light to pass through pulp stock flowing through the cell. The beam is transmitted through a polarizing filter prior to entering the cell, and through a second, crossed, polarizing filter, on exiting from the cell. The exit beam converges onto a photodetector. A gradual variation in the mass of fibers of the pulp stock is established over a predetermined range and this produces a change in the intensity of the transmitted light. As the light intensity changes, it passes through a maximum value; this is accompanied by a similar change in the photodetector electrical output signal.

Abstract: A process for the removal of dispersed contaminants less dense than water from pulp and paper mill process liquids, comprises passing the liquid through a centrifuge and collecting the contaminants as a less dense fraction. The application of this invention to paper industry process liquids provides a means of removing a significant fraction of the wood resin and wood resin soaps from the process stream, thus enabling (1) a greater extent of reuse of filtrates and, hence, less effluents from mills, and (2) fewer problems from wood resin, such as deposit formation, loss of strength of product, and contamination of product with dirt particles.

Abstract: A latex comprises a colloidal suspension in water of essentially non-crystalline particles of a polymer or copolymer or .beta.-hydroxyalkanoates, for example .beta.-hydroxybutyrate and .beta.-hydroxyvalerate; the latex may be employed to produce self-supporting filfms or papers which are biodegradable and also readily recyclable.

Abstract: Acidic papers, books, and other sheets of cellulosic material may be deacidified and so given a prolonged life by bringing the papers, books, or other sheets of cellulosic material to be treated in intimate contact with a source of solid alkali such as calcium carbonate filled paper, at an elevated humidity and under mechanical pressure for a period long enough to produce deacidification; the process differs from other processes in that it is carried out in the solid state without the use of liquid or gaseous reactants.

Abstract: The two-dimensional medium-pass filter principle is used to acquire a sharpened image initially In practice the sharpened image is obtained from the difference of a linear array signal of a partially out-of-focus image from another linear array signal of the same image but in focus. Integrated intensity of dirt specks higher than a user selected threshold are measured and accumulated. Each integrated intensity value is converted into its corresponding speck size with the use of a predefined fined look-up table. The counter generates a dirt speck histogram and statistical data within a preselected time interval or area coverage.

Abstract: A direct monitoring and control method is provided for on-line measurement of effective alkali, carbonate, sulfate and thiosulfate concentrations in process liquors for the production of kraft pulp. The control method eliminates frequent sampling, and the need for frequent equipment maintenance. The method includes the steps of withdrawing samples of a liquor from the kraft manufacturing process, subjecting the samples to infrared spectrophotometry at predetermined wave numbers to produce peak-absorbance measurements relative to a background spectrum of water, determining peak absorbance for different alkali concentrations, correlating relationships between the peak-absorbance measurements of samples with the peak absorbance for different alkali concentrations to determine optimum effective alkali in the samples, and controlling at least one process parameter to obtain effective alkali of the liquor.