GB1043460A - Improvements in continuous aqueous prehydrolysis of wood chips - Google Patents

Abstract

1,043,460. Treating wood-pulp. RAYONIER Inc. Dec. 15, 1964 [Aug. 7, 1964 No. 51003/64. Heading D2W. [Also in Division B1] Wood chips are prehydrolysed by effecting an initial mild hydrolysis in steam or water, passing the prehydrolysed chips and hot water concurrently downwards in contact in a vessel, separating part of the water and dissolved substances, cooling the chips by passing them countercurrently to a stream of water to a temperature slightly above the boiling point of water, and discharging them at atmospheric pressure. As shown, wood chips from hopper 1 are fed into vessel 4, which has steam-supply means 7 and 9 and a screw feeder 5 to force the chips to pocket-feeder 6. Some terpenes &c. are volatilized and removed at 8. The chips fall from pocket-feeder 6 to highpressure feeder 12 and are forced by pump 15 in a slurry to screw-feeder 16. The screw 17 squeezes out some water, which is returned through pipe 18. The chips are then forced along pipe 24 and into vessel 27 by water from pump 25. They move downwards through this vessel to the outlet 34. The vessel has four screen sections 36, 37, 38 and 39. At 36 and 37 the chips are charged with hot water from pipes 40 and 43. Water is drawn from the outside of the screen sections 36 and 37 and recirculated through heat-exchangers 60 and 71 by the pumps 41 and 44. The prehydrolysis take place between screens 37 and 38. At 38 a substantial part of the liquor is removed by pump 46. Pipes 50 and 51 introduce cooling water, and pipe 54 introduces dilute liquor containing dissolved chemicals. These pass upwards and are removed at 39 by pump 55 and taken to the dome 30 at the top of vessel 27. The slurry of chips leaving vessel 27 is led through pipe 35 and enlarged chamber 91 to blow-tank 92 and dewatering screen conveyer 95. Part of the water removed at 38 is recirculated through pipe 74. The rest is sent to flash chamber 77, and the concentrated liquor remaining after flashing-off is collected in tank 81 and taken off to a recovery system (not shown). The level of liquid in the flash chamber 77 is controlled by means of float indicator 78 which operates electric impulse valve 80. The condensate from heat exchangers 60 and 71 is passed to another flash chamber 63, with similar means for controlling liquid level. The recovered steam is sent to vessel 4 for use in the presteaming step. The liquid from separator 63 passes to vessel 66, with a similar level control, where more steam is flashed off together with turpentine and other volatile materials which are taken off through pipe 85 to recovery (not shown). The liquid from vessel 66 is passed through pipe 88 to waste or 89 to a powerhouse (not shown).