Abstract: The present invention relates to a method and a device for mixing a second medium into a first medium. The method and the device according to the invention are particularly advantageous when used for mixing different chemicals, both liquid and gaseous, or steam into pulp suspension in the wood processing industry. In the method and device according to the invention, the first medium is fed into the mixer housing (10), mixed therein and removed from said housing (10), a freely rotatable rotor (20) being placed in said housing (10) and turned by means of the incoming medium flow into the housing (10).

Abstract: An improved double acting deaeration vessel is most desirably used in the pulp and paper industry. The deaeration vessel removes gas from a fiber suspension without requiring fine adjustment of the final consistency of the suspension fed to the deaeration vessel. In the same gas volume where the fiber suspension is treated in the deaeration vessel a second partition wall forming a second weir is provided, and the vessel jacket is provided with one or more inlets for a second fluid medium to be introduced into the vessel, with an outlet for the substantially gas free second fluid medium. A common outlet is provided in the common gas volume for gas separated from both the fiber suspension in the second fluid medium, as well as an outlet for the fraction of the second fluid medium separated by the weir.

Abstract: A method of inhibiting calcium carbonate scaling in a multi-stage evaporation plant of black liquor by heat-treating calcium-containing liquor includes a first stage wherein the calcium-containing liquor is heated to about 110-145.degree. C. with direct contact with the heating medium; a second stage wherein the liquor is maintained at this temperature in a retention tank for 1-20 minutes to reduce the amount of calcium in the liquor by precipitating calcium carbonate; and a third stage wherein the heat-treated liquor is evaporated for combustion.

Abstract: A method is provided by which it possible to intensify a cellulose pulp wash without requiring the purchase of additional equipment. In a washing system having a plurality of stages with a filtrate from each stage, the stages in sequence being N, N+1, etc., and each stage including filtrates F.sub.N and F.sub.N+1, etc., part of the filtrate F.sub.N (e.g. about 5-30 %) is combined with all or part of the filtrate for F.sub.N+1 to produce a combined filtrate, and the combined filtrate is fed in washing stage N as wash liquid. The part of the filtrate F.sub.N that is taken for use as wash liquid in stage N is typically from the end of the washing stage N. The process may be repeated for most of the stages of the washing system.

Abstract: A method of separating impurities from lime or the calcium carbonate or the lime sludge produced in the chemical recovery system of a pulp mill so that lime sludge or lime is dissolved in a solution containing carbonate or hydrocarbonate in order to dissolve impurities. Subsequently the lime sludge or lime is separated from the solution containing dissolved impurities. A method of causticizing green liquor containing impurities, such as silicon, in two stages. In the first stage green liquor is causticized with such an amount of lime that impurities substantially remain in the liquor. The lime produced in this stage is removed from the liquor and the rest of the lime required in the causticizing is added to this liquor, so that impurities precipitate with the lime sludge produced in the second stage and at least a portion of the lime sludge rich in impurities is discharged from the process.

Abstract: A method is provided for reducing emissions of harmful nitrogen compounds from a pulp mill (e.g. kraft mill) having malodorous gases which include ammonia and reduced sulphur compounds therein. The method is practiced by (a) treating the pulp mill malodorous gases to lower the ammonia content thereof (e.g. by washing them with a bisulfite solution, such as one produced from washing flue gases with sodium sulphite), and then (b) burning the malodorous gases (e.g. in a dedicated incinerator, recovery boiler, power boiler, or lime kiln) under conditions which effect oxidation of reduced sulfur compounds therein (e.g. with an air excess of at least about 3% and a temperature of over 800 degrees C) so as to reduce odor emissions and emissions of harmful nitrogen compounds from the pulp mill.

Abstract: A method and apparatus for extending the life of air ports and nozzles in furnaces, particularly recovery boilers for burning black liquor to produce heat and a chemical melt. Apparatus is provided for feeding combustion air into a furnace having a tube wall, the apparatus comprising: an air port disposed in the tube wall, and connected to an air duct through which air flows into and then through the air port, and into the furnace; and a protective insert of heat conductive and heat and corrosion resistant material mounted in the air port and positioned so that it is cooled by the air flowing through the air port. The protective insert has sufficient thermal mass (e.g. a volume of between 40,000-4,000,000 cubic mm) so as to effectively even out temperature peaks caused by melt splashes from the furnace impacting the vicinity of the air port, e. g. the protective insert is made out of highly corrosion resistant steel such as stainless steel.

Abstract: A method and apparatus for treatment of recycled fiber material and/or of the reject fraction discharged from paper mill screening systems of the short circulation of a paper machine, recover fillers as completely as possible and return the fillers back to the process as efficiently and economically as possible. The loss of fiber/mineral discharge as mill rejects from vortex cleaning and filler manufacture is decreased by treating a concentrated mineral fraction of the rejects to disperse the filler-mineral fraction and return the filler back to the paper making process.

Abstract: A method and apparatus for supplying lime sludge to a rotary kiln guides the flow of the lime sludge into the kiln, and the flow of flue gases out of the kiln, in distinct paths so that contact between the lime sludge entering the kiln and flue gases exiting the kiln is substantially prevented. This is typically accomplished by providing a general horizontal tubular duct interiorly of the kiln first end and extending into a substantially vertical flue gas conduit with an annular chamber defined between an outer surface of the tubular duct and an inner surface of an inlet to the first end of the rotary kiln. The lime sludge is introduced into the annular chamber. Spiral feeding blades are preferably provided on the outer surface of the tubular duct and the duct rotates with the rotary kiln so that the spiral feeding blades engage the lime sludge and move it toward the kiln. The lime sludge is preferably dried before it is fed into the annular chamber.

Abstract: The intensity of explosions as a result of hot (750-820 degrees C.) smelt from a pulp mill recovery boiler impacting cool (70-100 degrees C.) liquid in a dissolving tank is minimized by more effectively disrupting the flow of smelt from a spout free end tip into the tank. First and second nozzles which issue jets of disrupting fluid (such as steam or green liquor) are positioned on opposite sides of the center line of the spout, and are positioned and spaced from the spout tip and each other so that the jet emanating from at least one of the nozzles always intersects the flow of smelt from the spout even though the smelt flow path varies during normal operation of the recovery boiler.

Abstract: A pressure screen comprises an outer housing with a pulp inlet, and accepts and rejects outlets and an advantageous mount of a stationary screen drum (screen cylinder) in the housing. The screen drum is secured at an upper end flange with bolts to an intermediate ring and supported via the intermediate ring by the housing. A rotating rotor is disposed inside the screen drum. The bottom end of the screen drum is provided with at least one groove with at least one primarily flexible material ring disposed in the groove. Cooperating substantially conical surfaces are provided in the bottom of the screen drum and a bottom intermediate ring, in which the groove is formed.

Abstract: A method and apparatus to clean a filter drum used for thickening lime mud. The drum is rotated about a horizontal axis in a first direction so that the circumferential surface of the drum moves into contact with lime mud in a vat and a precoat layer formed on the drum, as well as an external layer of lime mud which forms a thickened lime mud cake when a vacuum is applied to the drum withdrawing liquid from the lime mud. The thickened external layer of lime mud cake is scraped from the drum at a second side of the vat, and at a first opposite side of the vat a first jet of liquid is directed onto the drum surface (e.g. at a pressure of about 30-100 bar) to remove a strip of the precoat layer, a third jet of liquid cleans the drum after removal of the precoat layer, and a second jet of liquid is directed onto the drum with sufficient intensity (e.g. a pressure of about 2-20 bar) to remove, by spreading and partially detaching, a strip from the thickened lime mud cake.

Abstract: The present invention relates to a method of improving the operation of a boiler plant in a chemical pulp mill. At least part of the black liquor flow of the chemical pulp mill is divided into several batches being substantially in a solid form, which are mechanically turned into substantially equal-sized pieces for deeding into the recovery boiler and for combustion taking place therein. Waste liquor batches may be stored prior to the combustion. The invention also relates to a system for carrying out the method.

Abstract: A falling film evaporator includes a shell with a number of heat transfer elements within the shell. Each heat transfer element has two opposed essentially rectangular plates joined together along upright sides and along seams substantially parallel to the upright sides. The seams form with each other, and the upright sides, a number of vertical flow channels through which steam (heating fluid) flows in the interior of the heat transfer elements to evaporate evaporable liquid flowing downwardly in a film over the outer surfaces of the heat transfer plates.

Abstract: A method and apparatus for improving a batch cooking process, e.g. providing about 7% increase in discharge time, are provided. The invention is especially suitable for improving modern displacement batch cooking processes. A dedicated pump is mounted directly to each digester and discharges to a common superatmospheric pressure discharge tank.

Abstract: An otherwise conventional recovery boiler for burning black liquor (e.g. with a consistency of between about 70-90%) requires less capital investment and takes up less space by constructing the economizers in a particular manner. At least first and second economizers are provided for preheating feed water utilizing flue gas from combustion of the black liquor. The economizers are positioned substantially adjacent each other and connected in such a way that flue gas leaving the first economizer passes substantially directly (i.e. without going through a conventional accessory passage) into the second economizer. The economizer inlets and outlets are substantially at the same level as the adjacent economizer outlets and inlets, or vertically spaced less than about one-third the length of the previous economizer. A boiler bank may be connected between the superheater section of the recovery boiler and the first economizer, and any number of economizers can be utilized.

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: Recycled fiber pulp from a vortex cleaning plant (e.g. connected to the short circulation of a paper machine) effects the recovery and return of fillers in the recycled fiber pulp discharged from the vortex cleaning plant, in an efficient and economical manner. The loss of filler in the recycled fiber pulp discharged from the vortex cleaning plant is decreased by treating a concentrated fraction of the rejects from the vortex cleaning plant with a mixer/disperser for dispersing the filler in the recycled fiber pulp, and returning as much usable filler as possible back to the process.

Abstract: An otherwise conventional recovery boiler for burning black liquor requires less capital investment and takes up less space by constructing the economizers in a particular manner. At least first and second economizers are provided for preheating feed water utilizing flue gas from combustion of the black liquor. The economizers are positioned substantially side-by-side, in the width dimension of the recovery boiler furnace, and connected in such a way that flue gas leaving the first economizer passes in a substantially transverse horizontal direction and then through a substantially vertical intra-economizer flow channel into the second economizer. A boiler bank may be connected between the superheater section of the recovery boiler and the first economizer, and any number of economizers may be utilized.

Abstract: Bleaching of cellulose pulp with peroxide is accomplished and has the advantages of conventional pressurized peroxide bleaching without the need for a large pressurized vessel. Pulp at a consistency of between about 8-20% is mixed with peroxide and introduced into a first relatively-small treatment vessel where it is held at a pressure of between about 3-20 bar, and is treated for between 10-60 minutes. Pulp reacts with the peroxide so that there is less than 5 kg of hydrogen peroxide per ton of pulp remaining, and then between about 40-90% of the gas is separated from the pulp at or adjacent discharge of the pulp from the first vessel. The pulp is then passed to a second substantially-unpressurized bleaching tower having an interior volume at least about twice as great as the first vessel. The pulp is introduced into the bottom of the second vessel and flows upwardly in it and is discharged from adjacent the top of the second vessel.