Patent GB-347096-A (GB)
Title: Improvements in or relating to the manufacture of paper
IPC: D21C9/12
Filed: 1929-12-07
Abstract: 347,096. Cellulose. MEAD RESEARCH ENGINEERING CO., City National Bank Building, Dayton, Ohio, U.S.A.-(Assignees of Traquair, J. ; of Mead Pulp & Paper Co., Chillicothe, Ohio, U.S.A.)' Dec. 7. 1929, No. 37577. Convention date, Dec. 29, 1928. [Class 96.] In a preparation of paper pulp suitable for the manufacture of high-grade paper from straw, cereal grasses (such as esparto), cane, bamboo, reeds and the like, the material is first subjected to the action of an alkaline solution of dilute concentration, at a temperature below 110 C. and at a low pressure, until the more reactive encrusting substances have been dissolved, and then to a second stage cooking treatment at a much higher temperature and pressure in the presence of the retained chemical cooking liquor substantially less concentrated in active chemical. The treated material is then subjected in accordance with the amount of encrusting sub. stances still remaining to the action of a chlorinating agent in one or two stages. The material may be reduced to a high consistency and treated with chlorine gas, or may be diluted to a low consistency and treated with a chlorinating agent in a manner such as to prevent rise in temperature and then raised to a higher consistency and again treated with a chlorinating agent. The material is fed through a duster mechanism 13, Fig. 1, to a discharge shoot 15 where it is sprayed by a pipe 18 with hot caustic liquor and passed to a steeping tank 30. A mild alkaline liquor is used and the temperature and pressure are controlled to maintain them at comparatively low levels. The material is fed through by a screw 40 at such a speed as to allow approximately half an hour to an hour for the treatment. The treated material is removed by a bucket conveyer 48, surplus liquid drawling back to the tank. Dirt &c. settles through the false bottom 32, is filtered at 70 and the liquor is forced by a pump 73 back through a heater 74 to the tank. The conveyer 48 passes the material to an expeller 55 to remove excess liquor, which passes to the pump 73. The consister.cy of the material having been raised it is passed by a screw 82 to the hopper 86 of a digester 88 where it is cooked at a higher temperature and pressure. When the digestion is completed the slow-out valve 94 is opened and the material is ejected against an impact plate 100 situated in a chamber 101. A discharge valve 104 distributes the pulped mass into a blow-pit 105 whence it is fed to the makedown chest 106. Liquor is supplied to the chest 106 through a pipe 118 and a screw 115 passes the diluted pulp mass to the mixing chest 119, whence it is forced by a pump 120 to a head box 125. Excess stock passes back to the chest 106 through pipe 127. The stock is passed over a weir 130 in the box 125 to a mixing box 132 and thence through a rotary vacuum filter 138 to a shoot 142. The black liquor sucked from the material by the filter 138 is discharged into a second head box 151, the excess black liquor being discharged down the pipe 118 to the make-down chest 106. A second weir 161 in the box 151 enables controlled amounts of the black liquor to be passed through a recovery plant 163, and a heater 165 to the spray 18. The material from the shoot 142 if it contains only about 5 per cent of remaining shives and hard bundles of fibres is dewatered to increase its consistency to 15 per cent or higher by means of a rotor 171, Fig. 2, and rotary screen 175 and is fed bv a shoot 180 to an elevator 182 which discharges it into a hopper 184 whence it is fed by a screw 185 to a chlorinating tower 183. A controlled supply of gas is fed through a pipe 190. Water or other slushing liquid is supplied at the base to dilute the stock and pass it out at the base of the tower either to a storage tank or through a tank 199 where it is mixed with alkali, through a rotary filter 209, bleaching tanks 215, 216, 217 and a further rotary filter 224 to the stock chest 226. If the material from the shoot 142 contains more than about 5 per cent of shives &c. it may be treated to a two-stage chlorinating process. The stock is first diluted and passed through a tant at a controlled rate with a supply of chlorine water, or other agent, it is then washed and, if desired, steeped in alkali, dewatered and passed for further treatment to a chlorinating tower similar to that described above.