GB710330A - Device for the treatment of particulate solids with liquids, in particular the production of chemical pulps from wood - Google Patents

Abstract

<PICT:0710330/IV (a)/1> <PICT:0710330/IV (a)/2> <PICT:0710330/IV (a)/3> Apparatus suitable for the production of chemical pulp from wood, e.g. by a treatment with an acid sulphite cooking liquor, comprises a pressure-resistant impregnating vessel provided with means for conveying solid material therethrough, means for feeding discrete quantities of solid material and of liquid into the impregnating vessel against a super-atmospheric pressure without causing any substantial loss of that pressure, a pressure-resistant digesting vessel provided with means for conveying solid material therethrough, means for transferring discrete quantities of solid material from the impregnating vessel to the digesting vessel against a higher super-atmospheric pressure without causing any substantial loss of pressure in either vessel, and means for discharging discrete quantities of solid material and of liquid from the digesting vessel without causing any substantial loss of pressure in that vessel. The impregnating and digesting vessels may be cylindrical and they may be provided with helical screw conveyers. The feeding, transfer, and discharging of the solid material without loss of pressure in the vessels may be effected by means of multi-way rotatable valves. As shown in Fig. 1, a hopper 10 opens into chamber 11 in which screw 12 moves fresh wood chips towards conduit 15. This conduit opens into a charging valve 16 which has a rotatable plug 18 with passage 19 divided by perforated plate 21. Also opening into valve 16 is a conduit 22 with pump 23 connected to a high pressure accumulator 24 (to contain a cooking liquor), and another conduit 25 leading to the impregnating vessel 26. Plug 18 is rotated till passage 19 is in line with conduit 15 so that wood chips drop on to the plate 21 and fill the upper part of passage 19. The plug is then rotated till passage 19 is in line with conduits 22, 25. Cooking liquor is pumped through conduit 22 into passage 19 and through the perforated plate to sweep the chips into conduit 25 and the vessel 26. The plug is then rotated further and the charging cycle is repeated. The vessel 26 has a vertical portion 27 and an inclined portion 28 in which a helical feed-screw 29 operates. An overflow conduit 32 leads liquor back to the accumulator 24. The wood chips are raised by the screw until they are above the level of the cooking liquor and they are then dropped into conduit 33 which opens into transfer valve 34. The vessel 26 is heated by steam which is circulated through jacket 35. Valve 34 has a rotatable plug 41 with a passage 42 divided by a perforated plate 43. The plug is rotated or reciprocated continuously or intermittently so that the passage is first charged with the impregnated chips and then brought to a position where a stream of high pressure steam from conduit 44 sweeps the chips into the digester 46. The digester is provided with a helical feed screw 50 and with a steam jacket 49. Steam, injected through conduit 52, quickly raises the chips to the required digestion temperature. On reaching the end of the digester the digested chips, now in the form of a pulp, drop into conduit 54 which opens into discharge valve 55. This valve has a rotatable plug 57 with passage 58 and perforated plate 59. Low pressure steam from conduit 61 forces the pulp and waste liquor into conduit 62. A modified form of charging valve is shown in p Fig. 2. The conduit 68 is connected to the impregnating vessel 26 at a point below the level of the cooking liquor so that liquor flows into passage 66 of the plug 65. The upper part of passage 66 becomes filled with impregnated chips. When the plug is rotated till passage 66 is in line with conduit 71, the liquor drains away from the chips and may be returned to accumulator 24. The plug may then be rotated till passage 66 is in line with conduit 69, connected to a source of high pressure steam, and conduit 72, which is connected to the digester 46. A modified discharge valve is shown in Fig. 3. Conduit 78 is connected to the digester 46 so that waste liquor flows into passage 76 and the upper part of the passage also becomes filled with wood pulp. When the plug 75 is rotated till the passage 76 is in line with conduit 81, high pressure gases and steam escape from the pulp. Conduit 79 is connected to a source of low pressure steam so that when the passage 76 is in line with conduits 79 and 82, the pulp is swept into and through conduit 82.