Patent GB-699232-A (GB)
Title: Improvements in or relating to the digestion and diffusion of paper-making fibres
IPC: D21C7/00
Filed: 1949-09-27
Abstract: <PICT:0699232/IV (a)/1> <PICT:0699232/IV (a)/2> <PICT:0699232/IV (a)/3> <PICT:0699232/IV (a)/4> Paper-making fibres, particularly cereal and grass fibres, are diffused by circulating the leaching liquor so that the same liquor repeatedly passes through a mass of fibres contained in a diffusion vessel, preferably at a rate which is relatively high compared with the rate at which leaching liquor percolates by gravity in the normal type of stationary diffuser, while agitating the mass by causing layers of liquor and fibres to be drawn from the bottom of the mass in an arcuate path towards the top thereof, and filtering the leaching liquor between its exit from and admission to the fibres.  The ratio of the total volume of liquor circulated through the fibres to the volume of the fibres may be small compared with that necessary in the normal type of stationary diffuser.  The process may be carried out under pressure.  The agitation of the mass may be effected by means of a paddle, but is preferably effected by rotation of the whole or part of the diffusion vessel about a horizontal or approximately horizontal axis.  The fibres may be subjected to a digestion process in the same vessel prior to the diffusion process.  As shown in one example digested fibre pulp is fed through the inlet 13 (Fig. 2, which is a sectional view taken on the line II-II of the longitudinal sectional view shown in Fig. 1) of the diffusion vessel 11 (Figs. 1 and 2) and all the inlets and outlets of the vessel are then closed except the leaching liquor inlet and outlets 15a, 16a (Fig. 1).  The leaching liquor is then circulated and the vessel rotated very slowly (by means not shown) about the axis of the trunnions 15a and 16a.  The leaching liquor enters the vessel through the hollow trunnion 15a and the two branch pipes 17, spaced 90 degrees apart, which communicate with two longitudinal chambers, the inner walls of which are constituted by the perforated metal plates 19 (Figs. 1 and 2).  The liquor leaves the vessel through the two branch pipes 18 (spaced 90 degrees apart from pipes 17) and the hollow trunnion 16a, and after passing through a filter (not shown) re-enters the diffusion vessel through the inlet 15a.  The pipes 18 communicate with longitudinal chambers of which the inner wall is constituted by the perforated plates 19, covered by wire mesh 20.  The inner circumference of the vessel 11 is provided with longitudinal ribs or fins 21, which raise the fibres from the lower to the upper part of the vessel when the latter is rotated.  An aperture 14 (Fig. 2) constitutes a steam blow-off.  After the completion of the process the fibres are discharged through the manholes 12 (Fig. 1).  As shown in the other example the digestion and/or diffusion vessel comprises a fixed cylinder 31 (Figs. 3 and 4) having closed ends and mounted therein a rotatable cylindrical agitator provided with longitudinal blades 32, carried at intervals by sets of four arcuate bands 38, attached to the longitudinal chambers 39, which have walls of perforated plates 35.  The leaching liquor enters the axially bored left-hand end of the shaft 34 (Fig. 3) and flows through the lower two pipes 33 into the inlet chambers 39.  It then flows diametrically across the vessel 31 into the outlet chambers 39 (which are covered by the wire screen 40) and thence through the upper two pipes 33 (Figs. 3 and 4) into the right-hand axially-drilled end of the shaft 34.