GB753377A - Improvements in or relating to method for the digestion of cellulose-bearing material - Google Patents

Abstract

<PICT:0753377/IV(a)/1> <PICT:0753377/IV(a)/2> In the continuous treatment of cellulosebearing material under pressure, the material is fed into the pressurized treating apparatus by continuously forming the material into a pressure-resistant plug which is continuously extruded into the apparatus and disintegrated therein. Disintegration is preferably effected by a compressive force, e.g. a ram acting on the end of the extruded plug, in a direction opposite to the movement of the plug. The end of the ram can be so shaped that, in the event of the extruded plug disintegrating or breaking off short, the ram closes the point of entry of the plug into the pressurized chamber, to prevent blow-back. The material may be subjected to a preliminary wetting or chemical treatment and, upon being compressed to form the extruded plug, entrained liquid is removed. After digestion, the material may again be extruded as a plug and disintegrated. The material under treatment may be cotton linters, comminuted wood, wheat straw, bagasse, pulp requiring further refinement, or the like. In Fig. 1, linters and caustic soda solution are passed through lines 1 and 2 into a mixer 4 and fed by screw-conveyer to apparatus 10 wherein it is compressed to remove entrained liquor and is formed into a plug and extruded into chamber 43 and disintegrated therein by ram 14 (details below). The disintegrated material is treated under pressure in digesters 19, being progressed therethrough by screw conveyers, and is again extruded as a plug in apparatus 26, disintegrated by ram 29, still under pressure, and thence to a blow tank 34 wherein blow valve 36 is actuated at ten-second intervals, and into tank 35 at atmospheric pressure. One form of plug forming and disintegrating apparatus is shown in Fig. 10. Material enters at 1, is compressed by screw 20, entrained liquid being removed at 6, the material passing through a forming tube 5 and being extruded as an annular plug surrounding the screw shaft 21. The extruded plug is broken up by ram 23, the disintegration being assisted by the sharpened ends 20a of the two screw flights. The rotating shaft 21 passes through the ram and the ram is suitably splined to prevent rotation thereof. Should the plug disintegrate within the forming tube 5, the ram closes the end of tube 5 to prevent blow-back. This may be effected automatically by controlling the ram according to the power requirements of the motor driving the screw, a sudden drop in power following failure of the plug causing the ram to be actuated. In a modification, the shaft 21 is hollow and pressure steam passes therethrough and emerges through perforations within the plug, to assist disintegration thereof. Alternatively, the extension 21 of the screw-shaft may be omitted.