GB603447A - Method and apparatus for the production of pulp from cellulosic material - Google Patents

Abstract

<PICT:0603447/IV(a)/1> <PICT:0603447/IV(a)/2> Cellulosic fibres are separated from lignocellulosic materials by passing the materials at a controlled rate through a closed chamber containing steam at super normal temperature and pressure and an atomized solution of a soluble chemical, discharging the materials from the chamber while avoiding substantial reduction of the temperature and pressure existing therein and then mechanically defibering the so treated materials. Chemicals of an acidic or alkaline nature may be employed, such as sodium hydroxide, carbonate, sulphite, sulphide or a mixture thereof or sulphur dioxide or the bisulphites of sodium, calcium or magnesium containing excess sulphur dioxide, or ammonium hydroxide, sulphite or bisulphite or sulphuric, nitric or other mineral or organic acid. The pH value of the effluent obtained from the refined material serves to indicate the consumption of the chemical reagent employed and preferably should range between 1 and 12. The amount and concentration of the solution of chemical reagent supplied to the reaction chamber is correlated with the time of transit of the material through the chamber and the type of lignocellulosic material employed in order to prevent degradation of the fibre structure. Referring to Fig. 1, chips or shreds of lignocellulosic material such as wood, straw, flax or bagasse are supplied from hopper 10 and compressed into plugs by screw conveyer 12. The plugs are pressure fed through weighted valve 16 into steam chamber 17. Steam under pressure is supplied to the chamber through pipe 18 and chemical reagent through pipe 19, the reagent being atomized by device A. The casing of chamber 17 is of larger diameter than that of compressor 11 and the plugs of material disintegrate therein. The material then passes into the temperature-pressure treatment zone C which is merely an extension of chamber 17 and comprises chambers 21, 28 (Fig. 2) through which the material is impelled by screw conveyers 32, 35. The material is discharged through neck 31 either to a further extension C1 of the reaction chamber or directly to compartment 39. The speed and pitch of the screw conveyers 32 and 35 control the rate of transit of the material through the chamber. From compartment 39 the material is progressed by screw 40 past the motor-operated duplex alternating valve assembly V which permits emission of material without undue reduction in the temperature and pressure existing in the reaction chamber. The material then passes to cyclone 46 to which wash water and, if desired, steam is supplied before passing in suspension through refiner or grinder R, where it is disintegrated and the fibres separated from one another. If shredded wood is to be supplied to the apparatus, the wood may be previously shredded by a device illustrated in Fig. 6 (not shown). The fibres produced according to the process can be made into various grades of dry felt, paper or paper board. Specification 555,966 is referred to.