GB480170A - Improvements in or relating to processes and apparatus for the extraction of cellulosic fibres from vegetable material - Google Patents

Abstract

<PICT:0480170/IV/1> <PICT:0480170/IV/2> A process for the extraction of cellulosic fibres suitable for paper or cardboard from vegetable material such as cereal stalks, flax, maize, hemp, sisal, bagasse, grasses, or residues from the manufacture of textile material consists in treating the material with alkali, e.g. 1-2 per cent caustic soda solution at a temperature between 80 and 100 DEG C., then treating it with chlorine at a temperature not exceeding 65 DEG C., and immersing it in cold water immediately after the chlorination treatment. The reactions are controlled as to concentration of solution and time of treatment to ensure that the above temperatures are not exceeded and thus prevent damage to the fibres. The alkali is employed in quantities just sufficient to react with the encrusting substances in the raw material. The alkali reaction lasts for 1-4 hours. Moist or even moisture saturated chlorine diluted with air, e.g. prepared electrolytically, is used for the second step of the process. After the chlorination treatment the material may be treated with ,1-10 per cent alkali solution at temperatures up to 100 DEG C. The material cut to suitable size is loaded into hoppers 10 and delivered to a trough 14, supplied with alkali solution at 23 to a fixed level, and having a double screw conveyer which mixes the material with the alkali and feeds it to the tops of two reaction towers 12. A controllable deflector 16 permits variation in the relative amounts of material fed to each tower. The mixing device effects a mixture of 1 part vegetable material to 4 parts of solution. The mixture descends the tower by gravity, steam being introduced by a number of pipes in the top portion of the tower. The material becomes compacted as it descends and forms a seal at the bottom preventing too rapid an escape of liquid. The time of treatment is controlled by the rate of removal from the bottom by an adjustable extractor 27 comprising two parallel oppositely rotating shafts each carrying a number of interlacing starshaped members. The distance apart of the shafts may be regulated. The material is fed by a conveyer 32 through screening devices 31 where spent liquor and washings are separated and led to a tank 37 while the fibre passes to a screw press 39 for removal of spent liquor residue and to an opener 42 where it is converted to the floccular state. Air blowers 44 then raise it through conduits 45 to a chamber 46 where a plate 48 deflects it into the chlorination tower 47. The material descends these towers by gravity, moist chlorine diluted with air being introduced by pipes 49, 51 about 1/3 of the distance from the top of the tower. The material is removed at controlled rate by an extractor at the foot of the tower and led straight into a cold water tank 60, thence by a trough 62 to sieve 63 where it is freed from dilute hydrochloric acid formed during the chlorination, and into screw presses 65. Treatment with soda solution of ,5 per cent strength or less follows in vat 66, and the fibres thereafter pass to the usual washing and sorting apparatus.