GB418133A - Improvements in continuous bleaching processes and apparatus - Google Patents

Abstract

<PICT:0418133/III/1> Fibrous cellulosic material in a substantially dry, sub-divided form is bleached by advancing the mass through a reaction chamber, the manner of introduction and withdrawal of the material being such as to maintain a substantially air-tight seal at the inlet and outlet of the chamber, and treating the material with gaseous bleaching agent under abnormal pressure conditions within the chamber. The material may be first subjected to a vacuum in one portion of the chamber and then reacted with a gaseous bleaching agent in another portion of the chamber. A suitable apparatus comprises a reaction chamber 10 suitably lined with rubber, glass, phenolic condensation products or the like 11. The top of the chamber is provided with a tapered neck 12 in which turns a feed screw 14 driven by a motor 18. The pulp obtained from a screw-press 21, from which water drains by way of the discharge pipe 25, is fed into a pulper, disintegrator, or breaker 27 from which it is discharged into the tapered neck 12. The lower portion of the chamber converges towards a narrow discharge neck 29 fitted with a screw 30 driven by a motor 32. For removing the air from the material a vacuum pump 34 is provided which may have a plurality of connections 35. At a point further down a suitable bleaching agent such as chlorine is introduced from a vessel 36, and may be present either at, below, or above atmospheric pressure. In order to remove residual chlorine, one or more byepass connections 38 are provided. In other forms of apparatus (not shown) the screws 14 and 30 may be replaced by reciprocating pistons, and a series of chambers may be provided having means for washing and pressing the pulp between treatments in successive chambers.ALSO:<PICT:0418133/IV/1> Fibrous cellulosic material in a substantially dry subdivided form is bleached by advancing the mass through a reaction chamber, the manner of introduction and withdrawal of the material being such as to maintain a substantially air-tight seal at the inlet and outlet of the chamber, and treating the material with gaseous bleaching agent under abnormal pressure conditions within the chamber. The material may be first subjected to a vacuum in one portion of the chamber and then reacted with a gaseous bleaching agent in another portion of the chamber. If required, the material may have an alkaline substance distributed through it before it enters the chamber, and according to a modification, the material may be subjected to successive bleaching treatments in separate chambers and prior, to introducing the material into each chamber, an alkaline solution is added thereto and partly expressed. A suitable apparatus comprises a reaction chamber 10 suitably lined with rubber, glass, phenolic condensation products or the like 11. The top of the chamber is provided with a tapered neck 12 in which turns a feed screw 14 driven by a motor 18. The pulp obtained from a screwpress 21, from which water drains by way of the discharge pipe 25, is fed into a pulper, disintegrator, or breaker 27 from which it is discharged into the tapered neck 12. The lower portion of the chamber converges towards a narrow discharge neck 29 fitted with a screw 30 driven by a motor 32. For removing the air from the material a vacuum pump 34 is provided which may have a plurality of connections 35. At a point further down a suitable bleaching agent such as chlorine is introduced from a vessel 36, and may be present either at, below, or above atmospheric pressure. In order to remove residual chlorine, one or more byepass connections 38 are provided. Preferably, only a partial bleach is effected during each treatment and the material is passed through the chamber several times, the discharged material being washed and advantageously admixed with alkali such as caustic soda before being returned to the screwpress 21. In other forms of apparatus (not shown) the screws 14 and 30 may be replaced by reciprocating pistons, and a series of chambers may be provided having means for washing and pressing the pulp between treatments in successive chambers.