Patent GB-536339-A (GB)
Title: An improved process and apparatus for the continuous digestion of fibres
IPC: D21C7/00
Filed: 1939-11-09
Abstract: 536,339. Refining cellulosic materials ; dyeing &c. apparatus. POMILIO CORPORATION, Ltd. Nov. 9, 1939, Nos. 29778 and 29779. Convention dates, Dec. 7, 1938, and Sept. 8, 1939. [Classes 2 (ii) and 15 (i)] Vegetable fibres are subjected to treatment with chemicals at temperatures above 100‹C. by causing them to descend continuously through an upright tower open at the top and containing the chemical solution, heating the solution as locality near the bottom of the tower where the pressure is equal to or greater than the vapour pressure of the solution at the temperature of treatment, and withdrawing the fibres at the bottom of the tower through a pressure balancing device. The solution may be heated, by injecting steam or by means of a heat interchanger. The fibres may be compacted at the bottom of the tower so as to form a partial blockage in the outlet and thereby balance the head of liquid in the tower. The fibres may be passed from the bottom of the tower into the lower end of a second tower open at the top, up which they are caused to ascend, the hydrostatic pressure in the two towers being balanced. As shown, the vertical re-action tower 1 is open at the top. The treatment liquid is.fed into the tower by pipe 8. The wall of the tower near the lower end is provided with openings 9 encircled by a jacket 10 which communicates through pipe 11 with a steam supply. The chemical treatment takes place mainly in the lower part of the tower below the openings 9. One or more laterally-extending chambers 3 each provided with a screw press are provided at the bottom of the tower. The cross-sectional area of chamber 3 increases as it extends away from the tower 1 as does also the cross-section of shaft 5, and the pitch of blades 4 diminishes as the diameter increases. The internal surface of chamber 3 has helical grooves 6 which decrease in pitch as they extend away from the tower. A jacket 13 with perforations 25 surrounds part of the chamber 3 at the bottom of tower 1, and communicates through pump 15 and pipe 16 with the interior of the tower just above openings 9. Another jacket with perforations 17 is provided around the chamber 3 in the region of the end of the screw press. This jacket is connected through pump 20 to pipe 21 which opens into the tower 1 at a short distance from the top. The outlet end of chamber 3 is connected with a second tower 2 and is provided with holes 22 and a jacket 23 communicating with a water-supply pipe 24. The fibres on reaching the base of the tower 1 are forwarded by the screw-press along chamber 3. The diminishing pitch of the screw causes the fibres to be compacted and thus counter-balance the pressure at the bottom of tower 1. When the fibres reach the end of chamber 3 they are washed by water flowing through holes 22 and are forced to the top of the tower 2. If clogging occurs, the pump 15 is operated to draw the material into contact with the conveyer by suction imparted through the holes 25. The liquid expressed as a result of the compacting , effect of the screw-press, is withdrawn through holes 17 and returned to the reaction tower through pipe 16. Instead of heating the fibres by steam, they may be heated by electric resistances within the tower or by fuel burners outside the tower, or by a heat interchanger. In this latter case the re-agent is maintained in continuous circulation by pump 15 and the pipe 16 is connected to jacket 10. The process is applicable to the extraction of purified cellulosic material from vegetable fibres. Alkali solutions may be used for the treatment. Specification 415,224, [Group VIII], is referred to.