GB710691A - Method and apparatus for the preparation and refining of fibres from cellulosic fibrous material - Google Patents

Abstract

<PICT:0710691/IV (a)/1> Fibres suitable for the paper, paper-board, and similar industries, are prepared from cotton, esparto, straw, wood, wood-wool and similar cellulosic material, by subjecting the material in a closed container to a boiling treatment above atmospheric pressure for a few minutes and then to a partial vacuum of not less than 5 ins. of mercury for a few minutes, and repeating these treatments alternately until the digestion of the material is completed. After the material has been placed in the digester, kier boiler, or autoclave, a solution of caustic soda or other reagent of the alkaline or sulphite processes may be added, preferably at about boiling temperature. The air may then be expelled through a relief-valve by introducing steam into the container. Further steam may be introduced to increase the pressure to 20-30 lb. per sq. in. and to effect the boiling treatment for about 3 minutes at this pressure. The pressure is then reduced and the material is subjected to a partial vacuum by condensation of the steam within the vessel, e.g. by means of an internal cold spray or by use of an external condenser, air-pump, or ejector. After treatment with the opening-up chemicals, the fibres may be subjected in a similar manner to treatment with washing and bleaching liquids. The washing water may contain detergents. The apparatus employed comprises a closed vessel, one or more doors in the side of the vessel for loading and unloading the cellulosic material into and from the vessel, a foraminous floor or support for the material in the vessel, a supply valve manifold for at least two chemical reagents, a drain-valve for withdrawing the used reagents, an air-release valve, steam inlet means below the foraminous floor for boiling the contents of the vessel, and means for creating a vacuum in the vessel. Alternatively, a coil or nest of tubes with arrangements for supplying it with steam or cold water as desired constitute the means for boiling the contents of the vessel and for creating a partial vacuum in the vessel. If desired the vessel may be arranged horizontally and may have but a single door for loading and unloading, while the pressure and vacuum conditions are attained by passing steam or cooling water through a coil or tube nest. The material to be treated may be placed in a foraminous cage, and the vessel may be provided with guide and support rails for the cage. As shown, the vessel 1 has a door 2 for the entry of the fibrous material and a foraminous floor 3 for supporting the material during treatment. The material is withdrawn through door 4. A steam inlet pipe 5 has several upwardly directed jets 7. A drain valve 8 is fitted in the lowest part of the vessel. An inlet 9 leading from a supply valve manifold is provided for introducing digesting reagents, bleaching agents, detergents, and water. Valve 10 leads to a condenser or vacuum pump 11, and in the top of the vessel is an air-release valve 12. A group of three treatment vessels may be provided so that while digestion is being effected in one vessel, bleaching of already digested material is being effected in another, and washing is taking place in the third vessel.