GB738815A - Improvements in or relating to the manufacture of pulp from fibrous ligno-cellulose-containing materials - Google Patents

Abstract

<PICT:0738815/IV (a)/1> <PICT:0738815/IV (a)/2> Pulp is obtained from fibrous ligno-cellulosic material by subjecting it during continuous feeding to the influence of an atmosphere of steam so as to remove in part air present in the material, thereafter submerging it in a bath of a chemical-containing liquid which is maintained at a temperature considerably lower than that of the steam by circulating the liquid between the bath and a cooler, then subjecting the impregnated material to treatment for a period of at least five minutes in an atmosphere of steam at a temperature exceeding 100 DEG C. and in presence of the chemicals which are selected so as to have a neutralizing effect on organic acids formed during the heating of the material, and then subjecting the material to mechanical defibration. The neutralizing chemical may be caustic soda, lime, sodium hydrosulphite, a mixture of caustic soda and sodium hydrosulphite, or calcium carbonate. As shown in Fig. 1, a hopper 10 feeds wood-chips into shoot 11 which is vibrated so as to cause the chips to travel towards a vertical receiver 13 down which they fall. Steam inlets 17 are provided. The lower parts of the container 13 and conveyer casing 20 are filled with a solution or suspension of the chemicals to be used in the treatment. The liquid is circulated from tank 30 by pump 32, the excess flowing through perforations in casing 20 and through pipe 26 back to tank 30. The impregnated chips are conveyed by screw 22 to discharge shoot 25. The chips pass through a dehydrator 40 which is provided with a conical screw 43 fitting in a correspondingly shaped casing 41. The chip material as it is fed forwards is compressed to form a plug at the pipe 47. The conical part 45 of the screw casing and also pipe 47 are perforated to permit the excess of liquid to be drained off, and for the same purpose, the abutting flanges 46, 48 of the screw casing 45 and the pipe 47 may be provided with grooves. The tube 47 leads to a conduit 50, part of the wall of which is cut away and replaced by a cover 52 hinged about axis 51 and adapted to be pressed against the chip material by means of a hydraulic press 53. The chips upon discharge from conduit 50 enter the hopper 210 (Fig. 2) from whence they are fed by shoot 211 into a screw-feed device 220 and then into a plug-forming pipe 221 and a conduit 223. The material is forced from conduit 223 through door 224 into a first preheater 230 in which a steam pressure exceeding atmospheric pressure is maintained, e.g. a pressure of 8-15 atmospheres. The steam is supplied through pipe 231. The material is fed forward to a mixer 240 where it is disintegrated before it reaches the main preheater 250. In the main preheater it is subjected for at least 5 minutes to an atmosphere of steam at a temperature above 100 DEG C. in the presence of the chemical reagents. The preheater 250 contains a stirring device with stirrers 253, 254. The time of preheating may be regulated by filling the preheater 250 with the material descending through screen 242. The stirrer 253 may co-operate with a feeler adjusting the speed of screw 222 as soon as the material has filled the preheater to the level of the stirrer. The height of the stirrer 253 is adjustable. Screw 255 feeds the material into a defibrator 260. If desired, a double-screw conveyer may be provided instead of the single-screw conveyer 22 shown in Fig. 1.