. The manufacture of pulp and paper : a textbook of modern pulp and paper mill practice. complete, becausethe stock is of high consist-ency. The temperature of thestock before circulation beginsis low; hence, little or nobleaching occurs up to thispoint; this gives the stock achance to absorb the bleachthoroughly, so the action canbe uniform throughout thefibers when the bleachingtakes place. As soon as thechamber is filled and circula-tion started, the temperatureis raised from about 60°-75° 95°-102°F., depending onthe speed of bleaching desired and the condition of the steam is
. The manufacture of pulp and paper : a textbook of modern pulp and paper mill practice. complete, becausethe stock is of high consist-ency. The temperature of thestock before circulation beginsis low; hence, little or nobleaching occurs up to thispoint; this gives the stock achance to absorb the bleachthoroughly, so the action canbe uniform throughout thefibers when the bleachingtakes place. As soon as thechamber is filled and circula-tion started, the temperatureis raised from about 60°-75° 95°-102°F., depending onthe speed of bleaching desired and the condition of the steam is then shut off, and the temperature is allowed tofall slowly. The heating should be complete after 4 to 5 hours, and thebleaching after 8 to 12 hours. After the bleaching is finished,the stock is dumped to drainers through pipes E\ and A\>, andthe bleach water is washed out. No excess bleach should bleach may be tested for by adding to a handful of stocka few drops of a solution of starch that contains a little sodium or Section XXFig. 5. 22 BLEACHING OF PULP §9. §9 BLEACHING THE STOCK 23 potassium iodide; if a blue color appears, an excess of bleach ispresent. The conveyor runs at 350 ; it requires 30 operate it for a tub holding 10,000 pounds of air-dry where very large digesters arc used, it is advisable tohave the bleachers of such capacity that the stock from eachdigester may be bleached separately; this allows proper variationof the bleaching process, to provide for differences in cooking. 35. New Type of Bleaching Tub.—In Fig. 6 is shown a recentdesign of bleaching tub. It consists of two vats, or channels,Ai and A2, separated by the partition B. In the bottom of eachchannel, is a pair of screw conveyors Ci and C2, C3 and C4, andthe channel bottom (bottom on drawing) is shaped to form twosemi-circular depressions, which correspond to the shape of thepropellers. At each end, near the bottom of the dividing wall,are other (
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpaperma, bookyear1921
