Abstract: The invention relates to a closed air circulation system for an apparatus used for sorting wood chips, containing chips in a variety of sizes and/or fines particles, in a wood chips processing chamber, in separate fractions by means of a gas flow, which is delivered from one or more nozzle chambers by way of a nozzle slit into the wood chips processing chamber and which applies an impulse action to the processing-bound wood chips sliding along an inclined support surface. Air is circulated from the wood chips processing chamber by way of a dedusting cyclone into said one or more nozzle chambers. The wood chips processing chamber is maintained at a negative pressure by regulating the volume of air removed from the chamber. A conduit extending between the wood chips processing chamber and the one or more nozzle chambers is open to the ambient atmosphere.

Abstract: A spent liquor recovery boiler in the pulp and paper industry including a water/steam circulation system having superheaters, the circulation system connected to a steam turbine comprising a high-pressure part, and a furnace for burning spent liquor to produce flue gases, and including an upper portion through which the flue gases flow, wherein the steam/water circulation system of the recovery boiler is provided with a reheater for reheating steam from the high-pressure part of the turbine.

Abstract: The present invention relates to a method in connection with smelt removal form a recovery boiler, whereby the smelt is removed from the boiler via a smelt spout surrounded outside the boiler by a hood and a dispersion medium, preferably steam, is fed into the smelt flow falling from the smelt spout for shattering the smelt flow. An essential characteristic is that at least one wall of the hood is washed with liquid so that the liquid first flows downwards on the outer surface of the hood wall and is led into the interior of the hood via at least one trough-like member arranged on the outer surface of the wall and openings in the wall so that the liquid further flows downwards on the inner surface of the wall. The invention also relates to an arrangement for washing the hood and the feeding device for the dispersion medium.

Abstract: The present invention relates to a method of and apparatus for treating pulp with filler. The method and apparatus according to the invention are especially well suitable for treating pulp with filler, the mixing of which to the pulp requires simultaneous treatment of the pulp with gas. The treatment of cellulose pulp suspension of the paper making industry and calcium hydroxide with carbon dioxide is presented as one preferred embodiment of the invention.

Abstract: An apparatus for sorting wood chips includes a feeder for supplying wood chips onto a sloping support surface to slide along the support surface over a slit extending thereacross. The slit is configured to provide an impulse action by means of a continuous gas flow on the chips or the fines particles presently in line with the slit. The bottom end of the support surface upstream of the slit is provided with a section (a) diverging from the rest of the support surface in terms of its gradient, over which section an angle of inclination (?) relative to the horizontal plane is smaller than an angle of inclination (?) of the support surface upstream of the same in the advancing direction of the wood chips.

Abstract: A spent liquor recovery boiler system including a boiler having a water/steam circulation system with superheaters and a furnace for recovering energy and chemicals from spent liquor combusted therein, the walls of the boiler are formed of a plurality of water-cooled tubes connected to the water/steam circulation system. The system is provided with at least one cavity having walls formed of water-cooled tubes connected to the water/steam circulation system, means for combusting a fuel and at least one outlet for discharging combustion gases to the boiler, the interior of the at least one cavity being provided with heat exchanger means for final superheating of the steam generated in the boiler, said heat exchanger means being connected to the superheaters of the boiler.

Abstract: The present invention relates to a method of treating condensates containing compounds, which are more volatile than water, in an evaporation plant, where liquid, such as effluent liquid from a pulp or paper mill is evaporated in multiple effects and where condensates generated in the evaporation are flashed and purified in a steam stripping column. In the method, the condensates from at least two evaporation effects are combined and flashed together, and the vapor obtained from the flashing is made to contact with a condensate stream to be purified in the stripping column, wherefrom the impurities-containing vapor and the purified condensate stream are discharged.

Abstract: Chemical cellulose pulp produced by alkaline delignification and having a kappa number of under 24 (e.g. 14 or below) having hexenuronic acid is treated to remove at least 50% of the hexenuronic acid (e.g. 90-97%) such as by treating the pulp at a temperature over 85° C. (e.g. about 90-180° C., preferably about 90-110° C.) at a pH between about 2-5 (e.g. about 2.5-4), which also results in a reduction of kappa number by at least two units (e.g. about 2-9 units, preferably about 3-6 units). The treatment time t, in minutes, is at least 0.5 exp(10517/(T+273)−24), where T is the treatment temperature in degrees C. The chemical cellulose pulp is bleached in at least one bleaching stage; where the bleaching stage is a chlorine dioxide, ozone, or peracid, treatment takes place before bleaching. Under some other circumstances treatment can take place simultaneous with bleaching or after bleaching.

Abstract: An arrangement is disclosed for supplying an air jet form to the furnace of a recovery boiler, where the furnace has a front wall, a rear wall and side walls. Black liquor spraying devices are disposed on the furnace walls at one or several levels of the furnace. A plurality of air ports are located at several horizontal levels for introducing air into the furnace from an air supply. In the arrangement for the secondary air flows, two horizontal air levels at different elevations are arranged above the lower primary levels and below the black liquor sprayer. Secondary air is supplied from two opposite walls and the air ports from each of the two levels are located so that the air jets are introduced in an interlaced pattern having an even number of jets on one opposite wall and an uneven number of jets on the other opposite wall. The air jets of said at least two air levels are located substantially one above each other in substantially vertical rows.

Abstract: The present invention relates to the thickening of pulp suspensions. A low consistency pulp suspension is fed to a pre-thickener (10) through an inlet conduit (18). A layer of thickened pulp, formed on a filter surface (22), is pushed along the filter surface by a cleaning member to the discharge end of the pre-thickener and is discharged through the outlet (20). The cleaning member comprises a rotating shaft (30) on which shaft at least one screw thread (32) is fixed so as to leave a free space between the shaft and the screw thread. Essentially non-thickened pulp is allowed to flow through the apparatus via this space.

Abstract: The present invention relates to a method and an arrangement for use in connection with the combustion of black liquor. In the method the black liquor is concentrated in a multi-effect evaporation plant in order to obtain black liquor at a suitable dry-solids content for combustion and to generate vapor. The concentrated black liquor is taken to be combusted in a recovery boiler, into which combustion air is fed at several levels for the combustion process. It is a characteristic feature of the invention that the air fed to at least one air level is preheated by using vapor generated in the concentration of the black liquor as heat source.

Abstract: An arrangement is disclosed for supplying an air jet form to the furnace of a recovery boiler, where the furnace has a front wall, a rear wall and side walls. Black liquor spraying devices are disposed on the furnace walls at one or several levels of the furnace. A plurality of air ports are located at several horizontal levels for introducing air into the furnace from an air supply. In the arrangement for the secondary air flows, two horizontal air levels at different elevations are arranged above the lower primary levels and below the black liquor sprayer. Secondary air is supplied from two opposite walls and the air ports from each of the two levels are located so that the air jets are introduced in an interlaced pattern having an even number of jets on one opposite wall and an uneven number of jets on the other opposite wall. The air jets of said at least two air levels are located substantially one above each other in substantially vertical rows.

Abstract: The present invention relates to a method of pretreating, by acidification and chelation, of pulp to be bleached with peroxide. Especially, the invention relates to intensifying, and at the same time simplifying the pretreatment required by peroxide bleaching. It is characteristic of the invention to introduce pulp into an acid tower (14, 112) where the pressure is 0 to 20 bar, preferably 1 to 10 bar, and the temperature 75 to 130° C. preferably 80 to 110° C., to treat the pulp in acid tower (14, 112) at a pH of 2 to 6, preferably 3 to 4, for 20 to 240 minutes, for decreasing the kappa number by 1-9, preferably 2-6 kappa units, to transfer the pulp from acid tower (14, 112) to a tower (24) of a second treatment stage, to treat the pulp with either a complexing agent at a pH of 4 to 9, preferably 5 to 6, or with an oxidizing chemical such as chlorine dioxide, Caro's acid, peracids or equivalent, and to wash and/or press the pulp.

Abstract: The present invention relates to a method of and an apparatus for controlling the operation of the short circulation of a paper, paper board or the like production machine. The method and apparatus according to the invention are especially preferably suitable for use in the approach system, i.e. so-called short circulation, of said production machines for regulating the headbox feed pressure. A characteristic feature of the method and apparatus according to the invention is that at a suitable location in the approach system of said production machine there is arranged a controllable parallel flow, by means of which at least one flow in the approach system is regulated so that the pressure in the headbox remains essentially constant.

Abstract: The present invention relates to a method and apparatus for controlling the operation of an approach system of a paper machine or the like web formation apparatus. Especially preferably the method of controlling the operation of an approach system according to the invention is applicable to be used in connection with paper and paperboard machines as well as in connection with various apparatuses performing non-woven webformating.

Abstract: The present invention relates to a method of treating chemical pulp in order to optimize the consumption of bleaching chemicals and to improve the quality of the pulp. Especially the invention relates to a method according to which filtrate obtained from a suitable stage of the washing of brown stock preferably cooked by an alkaline cooking method is treated with an oxidizing chemical prior to the oxygen stage following the brown stock washing.

Abstract: The present invention relates to the thickening of pulp suspensions. A low consistency pulp suspension is fed to a pre-thickener (10) through an inlet conduit (18). A layer of thickened pulp, formed on a filter surface (22), is pushed along the filter surface by a cleaning member to the discharge end of the pre-thickener and is discharged through the outlet (20). The cleaning member comprises a rotating shaft (30), on which shaft at least one screw thread (32) is fixed so as to leave a free space between the shaft and the screw thread. Essentially non-thickened pulp is allowed to flow through the apparatus via this space.

Abstract: The present invention relates to a wire pit. A characteristic feature of the wire pit (50) according to the invention is that its wall/walls (52′, 52″, 54′, 62) converge downwards so that the average flow direction of the liquid along the most part of the wire pit's (50) height deviates from vertical.

Abstract: An arrangement and a rotor for screening of pulp is disclosed that is suitable for the screening of chemical and mechanical pulps, i.e. fiber suspensions of the wood processing industry. A feature of the arrangement and rotor is that inside the rotor (16) there is arranged at least one dilution liquid chamber (24′, 24″, 24′″) restricted by a surface of the rotor (16), which surface is provided with means for connecting said at least one chamber (24′, 24″, 24′″) with the screening space defined between the rotor and the screen drum in such a way that dilution liquid from said at least one chamber (24′, 24″, 24′″) is brought into the screening space at a distance of at least 20 mm from the inner surface of the screen drum (14).

Abstract: A method to produce energy at a pulp mill, including the steps of: combusting pulping process waste liquor in the furnace of a recovery boiler to generate flue gases, recovering the heat from the flue gases by producing saturated and/or partially superheated steam in the recovery boiler, gasifying wood, bark or wood wastes in a gasifier for producing a combustible gas, burning at least part of the combustible gas in a superheating boiler, and superheating the saturated and partially superheated steam in the superheating boiler to produce superheated steam.