Patent GB-910002-A (GB)
Title: Improvements in or relating to the production of pulp from lignocellulose-containingmaterial
IPC: D21C1/10
Filed: 1959-09-15
Abstract: A method for the continuous production of pulp from lignocellulose containing material comprises an impregnating step effected under increased pressure in a chemical-containing <PICT:0910002/IV(a)/1> <PICT:0910002/IV(a)/2> liquid, the material being caused to undergo a mechanical compression, followed by an expansion while immersed below the level of the liquid, and at least one cooking step with or without a subsequent mechanical disintegration step, the increased pressure for the impregnating step being produced by means of the same steam atmosphere as that used for the cooking step and the mechanical compression pressure being many times higher than said impregnating step pressure.  The impregnating and cooking steps may be effected in separate containers interconnected at their upper ends, the material after the mechanical compression being conveyed upwardly through the container for the impregnation step while during the major part thereof being immersed in the liquid, and downwardly through the container for the cooking step, which container also contains a chemical-containing liquid. Impregnation may be effected at a lower liquid temperature than that maintained in the subsequent cooking step, the impregnating liquid and the cooking liquid preferably having mutually different compositions.  The material may be contacted with steam during the later part of its upwardly directed movement in the first container and the early part of its downwardly directed movement in the second container, and the material, after cooking in the liquid zone of the second container may be subjected to further cooking in a steam atmosphere.  Prior to the mechanical compression step, the material may be subjected to the action of a steam atmosphere having a pressure and temperature the same as or lower than the steam utilized in the cooking step.  Said first steam treatment may be effected in a closed space.  Apparatus comprises a first container having at its base means for high mechanical compression of the lignocellulose-containing material prior to its introduction into and expansion below the level of a first chemical containing liquid in the lower portion of the container, the first container having a steam zone in its upper portion and communicating at its upper end with the upper portion of a second container also containing in its lower portion a chemical containing liquid so that both containers form a closed system within which a superatmospheric pressure of steam is maintained to effect a preliminary impregnation of the material with the first chemical containing liquid and a subsequent cooking of the material in vapour and liquid phases.  As shown (Fig. 1) lignocellulose containing material, e.g. wood chips, is supplied by conveyer 18 and discharge tube 20 to vertical container 10 via the rotating cell feeder 22, which is vented by pipe 24.  Steam enters 10 from pipe 26 and flows upwardly through the container, preheating the chips and expelling air therefrom.  Level regulators 30 actuate the driving motor of the cell feeder and control the level of the chips.  The softened chips are fed via screw feeder 34 driven by motor 33 to a conveyer or container 36 while being mechanically compressed under a very high pressure, e.g. 20-50 Kg./cm2, owing to the action of screw feeder 34, plug forming tube 38 and flap 40, which is loaded via arm 42 by a servomotor 44.  Air and free water are thus expelled from the pores of the chips.  Conveyer 36 houses screw 48 driven by motor 46, and is supplied via pipe 54 with a solution of chemicals from tank 58.  Pipe 54 may be surrounded by a heating coil 60.  Liquid rises in 36 to a level determined by regulators 62, which actuate pump 56.  The top of conveyer 36 is linked by a horizontal conveyer 64 to a cooker 66, the level of chips in which is controlled by regulators 67 which govern the screw feeder 34.  A chemical-containing solution is fed to cooker 66 from a vessel 68 (Fig. 2) via pipe 70, the feed being regulated by valve 76 controlled by servo-mechanism 74, which is actuated by level regulator 78.  Thus cooker 66 comprises a lower liquid zone and a higher vapour zone which latter communicates via conveyer 64 with the top portion of conveyer 36.  Steam at, e.g. 8-10 Kg./cm2, is supplied to 66 via conduit 82, the same steam pressure prevailing in the conveyer 36.  Air can be vented via 86. Thus when the compressed chips expand at the base of 36 chemical-containing solution is sucked into the pores of the material, which at the same time is subjected to an elevated pressure due partly to the liquid column in 36 but mainly to the steam pressure in the top part of the column, which may be ten times the liquid pressure.  Hence air still present in the pores of the chips is compressed and replaced by the chemical-containing solution, which may be at temperatures of from 80 DEG -100 DEG C., depending on circumstances.  An atmosphere of water vapour is formed in the portion of 36 above the level of regulators 62, and in the portion of 66 above regulator 78.  Thus the impregnated chips are cooked first in the vapour phase and subsequently in the liquid phase.  The base portion of 66 communicates via conveyers 90, 96, driven by motor 92 which is controlled by regulator 67, with a further conveyer 98 housing conveyer screws 100 driven by motor 102.  Hence liquid phase cooking is continued in the lower part of 98 and vapour phase cooking in the upper part, which communicates with the vapour zone of 66 through a pressure equalizing tube 103.  All the reaction vessels 10, 36, 66 and 98 may be interconnected to equalize the pressures therebetween, by means of tubes 128, 130, leading off 103.  Water vapour may be supplied or discharged via pipe 142.  The treated pulp may be blown out directly into a centricleaner 104 (Fig. 2).  As shown, a mechanical disintegrator 106, e.g. a disc refiner, is interposed ahead of said cleaner, the discharge side of 106 communicating with 104 by means of conduit 108.  Conveyer 110 transports material discharged from 104 to hopper 112, forming part of a de-watering device 114, in which cooking liquid expelled by compression of the chips is drawn off through pipe 116, pulp being discharged by conveyer 118.  The product may be diluted with water in vessel 120 and refined in a second disc refiner 122 from which it is fed to storage vessel 124.  Conventional chemicals are used in the process, suitably of differing compositions for the impregnating and cooking steps.  The impregnating liquid in conveyer 36 may consist of sodium sulphite and sodium carbonate, and the cooking liquid made in 68 may contain sodium sulphite and sodium hydroxide or sodium sulphide. Specification 910,001 is referred to.