Patent GB-190823947-A (GB)
Title: Improved Method of, and Apparatus for, the Bleaching of Pulp used in the Manufacture of Paper.
Inventor: GUNN GILBERT
Filed: 1908-11-09
Granted: 1909-04-01
Abstract: 23,947. Gunn, G. Nov. 9. Bleaching paper-pulp. In bleaching paper-pulp, (1) apparatus is employed which enables the concentrated liquor to be separated from the pulp, as far as possible, when it has done its work, and (2) either just sufficient bleaching-liquor is employed, (that is less than is customary) in treating the pulp once only, or the pulp is treated more than once, using less each time than the necessary quantity to bleach completely, but more in the aggregate. In the case of easily bleached material (wood pulp and short fibre) the pulp is filled through a pipe S' into a vertical cylindrical vessel A, Fig. 1, with a false perforated conical or disk-shaped annular bottom PB. The excess of water is removed and run to waste by a drum-pump DP, and bleaching-liquor is introduced containing a quantity of bleaching. material equal to, or preferably less than, that required by theory; the drum pump DP and a circulating-pump, connected to a discharge pipe SO at the bottom of the vessel A, are then started. The latter pump circulates the stuff through a heater and delivers it into the top of the vessel A again ; while the former pump abstracts a portion of the liquor through the perforated bottom PB and a pipe ELP, and redelivers it to the top of the vessel through an annular sieve S forming the inner side of a trough T which surrounds the upper edge of the vessel A. When the bleaching-solution has done its work, it is abstracted by the drumpump DP and run to waste. Water is then run into the top of the vessel A through a pipe WP, so that adherent liquor is washed out by downward displacement, and run to waste. If the pulp is difficult to bleach, a further quantity of bleaching- liqu r is next added, and the whole treatment is repeated with the exception that the liquor is not run to waste but used again, either as it is or mixed with more bleaching-material, in subsequent operations. If rags and long-fibred pulp are being treated, the stuff is preferably treated with acid and then with alkali between the application of the first and second lot of bleach liquor. Instead of using one vessel A, a number may be used and the stuff transferred from one vessel to another in the known way. To dilute the pulp for such transference, water may be run in at the top and bottom of the vessel A simultaneously. An agitator CA is provided. For bleaching rags and long-fibred pulp, it is preferable to use another apparatus, Fig. 4, having an agitator CA consisting of helical arms. In this case the first lot of bleaching-liquor is added in the hollander, and the stuff is then transferred to the vessel A, where it is subjected first to acid and then to alkaline treatment with constant agitation and abstraction of the liquor after each operation, and so on as before. After sufficient agitation the mass is pumped into a drainer &c. and allowed to bleach up. In either case liquor may be withdrawn by means of a vacuum or compressed air instead of by a pump. The vessel A may have an air-tight lid. C.