Abstract: The bleaching of fluff cellulosic pulp with a gaseous ozone bleaching agent at an acidic pH is often followed by an alkaline treatment, usually an alkaline extraction or an alkaline hydrogen peroxide bleaching treatment, at a much higher water content than the gaseous ozone treatment of the fluff pulp. Such a bleaching sequence of gaseous ozone bleaching followed by an alkaline treatment is improved by the present invention based upon two discoveries, first, the discovery of peroxygen bleaching values in the water associated with the fluff pulp leaving the ozone bleaching treatment, and second, the peroxygen values are destroyed at the alkaline pH used for the alkaline treatment that follows the gaseous ozone bleaching treatment. In accordance with the discoveries, a Low Consistency Acidic Retention Treatment is interposed between the gaseous ozone bleaching treatment and the alkaline treatment.

Abstract: The invention relates to a process for bleaching preoxidized paper pulp enabling a pulp having a very high degree of whiteness to be obtained with a limited number of treatment steps and enabling pollution to be reduced without degrading the qualities of the pulp; such a process essentially comprises the combination of the three successive treatment steps, namely:(a) a first step of hot chlorination with gaseous chlorine at a temperature of between about 30.degree. and 80.degree. C., and preferably between 35.degree. and 50.degree. C., in the presence of urea used at a rate of 0.5 to 5% by weight of the chlorine used, and preferably from 1 to 3%, with a concentration of pulp of between 3 and 30%, and a duration of retention of the chlorine of 30 seconds to 45 minutes;(b) a second step of alkaline extraction in the presence of an oxidizing agent of the hypochlorite or peroxide type, at a temperature of between about 30.degree. and 70.degree. C., and at a pH of between about 8 and 12, and preferably between 10.

Abstract: A process and apparatus for washing high consistency fibre stock in the de-inking of paper. Grey stock is passed along a passage from a grey stock inlet to an outlet for cleaned stock. The passage is defined by a filter screen preferably of wire gauze. Within the passage is disposed a stirring member. Washing liquid such as water is introduced into the passage preferably by means of apertures in a central portion of the stirring member. Effluent liquid passes through the screen for extraction through a suitable outlet, or for recirculation. The arrangement is such that relative rotation of the screen and member results in clusters of stock fibres, which move around the passage as they pass therealong. The stirring member preferably includes a plurality of longitudinally extending, axis parallel bars radially spaced from the central portion.

Abstract: A method and apparatus for screenless treatment of cellulose fiber material without channeling of treatment liquid through a fiber material column being treated. An inner vertical vessel extends into an outer vertical vessel which has a larger diameter than the inner vessel, and an annular space in the outer vessel is defined by a portion of the inner vessel extending into the outer vessel. At least three baffles extend through the annular space into the area of the outer vessel below the inner vessel to define at least three distinct flow areas, and an outlet nozzle is provided in each of the flow areas. Liquid is withdrawn from the annular space through at least two of the flow areas, while liquid is backflushed into one of the flow areas.

Abstract: Gaseous reaction apparatus wherein a portion of the supplied gas is discharged from the reaction vessel at a location below the upper level of a therein contained columnar mass of material wherein the gas is discharged into a receiving chamber extending along the outer periphery of the vessel and open to the lower portion of the vessel through an unrestricted opening being free from screens and filters, and such discharged portion of the gas, with or without cooling, is recirculated back into the upper inlet end of the vessel, thereby controlling the temperature in the vessel by removing or redistributing heat therein. Such apparatus is particularly useful in the gas phase treatment of fibrous material such as the bleaching or delignification of lignin-containing cellulose pulp.