| WO1989002951A1 | 1989-04-06 | |||
| WO1989005374A1 | 1989-06-15 |
| 1. | A method at the manufacture of groundwood pulp to paper etc. for the impregnation of wood pieces with a length of at least 300 mm in the fiber direction by compression followed by expansion, and after possible further treatment grinding into pulp in a wood grinder, c h a r a c t e r i z e d b y that a batch of wood pieces oriented with the fibers in one and the same direction is introduced into a closed press chamber, that the wood batch is pressed together across the fiber direction by means of a press stamp under such a high pressure that the pores of the wood substance are substantially compressed, that squeezed out liquid and gas are removed from the chamber, whereupon liquor containing chemicals, and/or gas, conceivably under superatmospheric pressure, is introduced into the chamber and the stamp pressure is released, at which the wood expands back and the liquor/gas is absorbed by the pores of the wood, and that the wood batch is discharged out of the press chamber and conveyed further to a conceivable further treatment and subsequently to grinding. |
| 2. | A method according to claim 1, c h a r a c t e r i z e d b y that the wood batch is charged into the chamber through an inlet gate, which can be closed, at one side of the chamber, and at the same time expels the preceding batch through a gate, which can be closed, at the opposite side of the chamber. |
| 3. | A method according to any of the foregoing claims, c h a r a c t e r i z e d b y that before the pressing, steam, liquor and/or gas is added to the wood. |
| 4. | A method according to any of the foregoing claims, c h a r a c t e r i z e d b y that before the wood is introduced into the press chamber, the wood is precompacted so that the cavities between the wood pieces are substantially filled, and the wood is then expanded under absorption of liquid and/or gas, which may be at superatmospheric pressure. |
| 5. | A method according to any of the foregoing claims, c h a r a c t e r i z e d b y that before the treatment, thick wood pieces have been split in the fiber direction to a thickness of maximum 50, preferably maximum 25 mm. |
| 6. | A method according to any of the foregoing claims, c h a r a c t e r i z e d b y that the impregnated wood batch is further treated and ground in the shape of a compact bale. |
| 7. | A method according to any of the foregoing claims, c h a r a c t e r i z e d b y that before grinding, the impregnated wood is heated to a temperature exceeding 100°C. |
| 8. | A method according to any of the foregoing claims, c h a r a c t e r i z e d b y that a number of impregnated wood batches is stored during a certain time, and possibly at a controlled temperature. |
| 9. | A method according to any of the foregoing claims, c h a r a c t e r i z e d b y that the impregnated wood batch is compressed again for the removal of spent liquor and expanded again in the presence of another impregnation liquor, possibly under superatmospheric pressure. |
| 10. | An apparatus at the manufacture of groundwood pulp to paper etc. for impregnating wood pieces with a length of atleast 300 mm in the fiber direction by compression followed by expansion, and after possible further treatment grinding to pulp in a wood grinder, c h a r a c t e r i z e d b y organ (6) for introducing a batch of wood pieces oriented with the fibers in one and the same direction into a closed press chamber (15), which is equipped with a press stamp (22) for pressing the wood together across the fiber direction at such a high pressure that the pores of the wood substance are substantially compressed, organs (25,26) for removing liquid and gases through openings (24) in the case of the chamber, organs (27,28) for introducing liquor containing chemicals, and/or gas, through the openings (24), conceivably under superatmospheric pressure, while the stamp pressure is relieved, and organs (30,32) for discharging and conveying the wood batch out of the press chamber. |
| 11. | An apparatus according to the foregoing claim, c h a r a c t e r i z e d b y that the organ (6) is shaped to push the wood batch into the press chamber (15) through an inlet gate (16) in one side of the chamber and at the same time push an impregnated wood batch out through a gate (17) in the opposing side, and doors (18,19) for closing the gates. |
| 12. | An apparatus according to any of the foregoing claims, c h a r a c t e r i z e d b y a compaction throat (8) , located in the feed direction before the press chamber, through which the wood batch is pushed in by the organ (6), with a section, diminishing in the feed direction, and openings (9) for discharging liquid and gas, followed by an expansion duct (12) with a section, increasing in the feed direction, and openings (13) for introducing liquor and/or gas, which may be at superatmospheric pressure. |
| 13. | An apparatus according to any of the foregoing claims, c h a r a c t e r i z e d b y a treatment chamber (34) adjacent to the outlet gate (17), in which chamber a number of impregnated wood batches in a row is stored, and which may be equipped with organs (35,36) for controlling the temperature in the chamber. |
| 14. | An apparatus according to any of the foregoing claims, c h a r a c t e r i z e d b y a movable retaining device (30), which is pressed against the impregnated wood batch, prevents it from falling down and indicates and possibly controls the wood feed. |
The invention concerns a method and an apparatus according the preamble of patent claims 1 and 10 respectively.
When grinding untreated wood in the shape of cut off logs, a pulp is obtained which is above all used for the manufacture of newsprint etc. The paper gets a smooth and good printing surface. When torn out of the wood, however, many fibers are cut off, so that the pulp is shortfibred and produces a weak paper. It must therefore be reinforced by longfibred chemical pulp, which is expensive and impairs the printability and optical characteristics of the paper. The method is mainly limited to longfibred softwood, spruce in particular. Fast-growing hardwoods such as aspen, poplar and some eucalypt species are being ground to some extent but yield still weaker pulps. Dense hardwoods such as birch and beech cannot be used at all.
To improve the fiber length and strength of the groundwood, the grinding can take place at superatmospheric pressure, so that a temperature exceeding 100°C is obtained, whereby the surface layer of the wood in the grinding zone is softened. This, however, makes the grinder complicated and expensive. The temperature increase is limited by the darkening of the pulp. To obtain a decisive quality improvement and an increased use of hardwoods, a treatment of the wood is necessary before grinding with chemicals which accomplish softening, swelling and conversion or dissolution of some unwanted constituents. The great difficulty of this is the introduction of the chemicals into the log. According to US patent No. 2,713,540, the logs are put under vacuum, impregnated with a chemical solution under superatmospheric pressure and digested for a long time in big digesters. This is, of course, expensive, complicated and time consuming. The heart of the log is still unimpregnated, so that the pulp is dark colored during the digestion. With another method according to US patent No, 2,075,023, the wood, particularly thinnings, is impregnated with a chemical solution at super¬ atmospheric pressure and digested. The logs are then made up
into bundles and ground to pulp.
All similar methods for impregnation by means of a hydraulic pressure suffer from the drawback that the air and liquid in the pores of the wood are blocked and prevent the introduction of the chemical solution. See e.g. Rydholm: Pulping Processes, Interscience Publishers 1965, page 301: "It was also shown that when penetration is allowed to occur from both sides of the blocks, the back-pressure of entrapped air, which becomes compressed by capillary forces from both sides, soon checks the penetration."
Lately, it has also been suggested to split the wood in the fiber direction before impregnation in order to improve the same, according to Swedish patent No. 458 690, and to compress the split wood across the fiber direction between two rolls, followed by expansion in the liquor, Swedish patent No. 461 796. As the fiber direction is not straight, the split pieces are curved, twisted and of various dimensions. The piecewise handling and feeding are troublesome and an efficient, controlled and uniform compression in the roll nip is difficult to achieve.
These difficulties have caused that all industrially applied methods for pulp manufacture by means of chemical impregnation of the wood use chips as raw material. Their smaller dimensions make it easier to expel the air, e.g. by steam, and for the chemical solution to penetrate. There are also various methods for compressing the chips and then gettin them expanded in the liquor, which is then absorbed by the cavities of the wood. The compression is usually achieved by a screw press, e.g. according to Swedish patent No. 160 636. It has also been tried to press the chips between rolls as per Canadian patent No. 677 418. This is, however, difficult in practice and is not being made.
To grind chips is inconvenient, so they are instead refined in disk refiners and the like. The drawback of this is mainly that the power consumption is very high.
The purpose of the invention is to devise a method and means for efficient impregnation of wood for grinding without the above-mentioned drawbacks in accordance with the characterizing parts of the two principal claims.
An implementation of the invention is shown at the following drawings. Fig. 1 shows a vertical section of the app ratus and fig. 2 a horizontal section. A wood bin 1 with a steam inlet 2 has a bottom that can be opened by a gate valve 3, operated by a pneumatic or hydraulic cylinder 4. Under it a rectangular box 5 -is located. The left gable of the box constitutes a wood feeding device 6 in the shape of a plate, which is moved back and forth by a cylinder 7. The box passes into a compaction throat 8 with a rectangular section and diminishing height in the feeding direction, stepwise with reversed steps according to fig. 1. The throat is equipped with wall openings 9 into a casing with an outlet 10. The compaction throat passes into a right angled plug throat 11 and this in turn into an expansion duct 12 with increasing height. The walls of the expansion duct are equipped with openings 13 to a closed casing, which has an inlet with a valve 14. The duct passes into a press chamber 15 with two side walls, two gables, a bottom and top side. The gables are shaped as gates 16 and 17, which can be opened and closed by means of doors 18 and 19, powered by cylinders 20 and 21. The top side consists of a movable press stamp 22, powered by a hydraulic cylinder 23. The bottom is equipped with openings 24, which are connected to an outlet pipe 25 with a valve 26 and an inlet pipe 27 with a valve 28. The right gate 17 of the chamber is connected to an outlet box 29 with the same length in the feeding direction as the chamber. The box is equipped with a retaining plate 30, which is pressed onto the gate by a cylinder 31, and a discharger 32 at right angle to the retaining plate and powered by a cylinder 33.
The starting material of the method is normally logs of soft- or hardwoods. Thinnings can conveniently be used and also sawmill waste as slabs and edgings. The wood is cut into uniform lengths of at least 300, suitably at least 500 mm. Thick pieces are conveniently split leng-ftiwi-se to a thickness
of maximum 50, suitably maximum 25 mm.
The apparatus functions in the following way. It is presumed that it has been filled up from the bin 1 up to the press chamber 15 with a continuous string of wood pieces, which have their fiber direction horizontal and perpendicular to the section I-I, with one or two, possibly more, pieces after another in the fiber direction. The wood feeder 6 shall be located at its left rear position, the piston 22 at its top position, according to the figures, the doors 18 and 19 open and the discharger 32 at its rear position according to fig. 2.
The wood in the bin 1 is steamed through the steam inlet 2. The gate valve 3 is closed by means of the cylinder 4. The inlet valve 14 is opened. The wood feeder 6 is moved forwards to the right by the cylinder 7 and pushes the whole string of wood pieces in front of it. A wood batch in the box 5 is then pushed into the compaction throat 8. The wood becomes compacted, so that the voids between the wood pieces are filled up. Air, condensate etc. are squeezed out through the openings 9 to the outlet 10. The previously compacted wood batch in the compaction throat is via the plug pipe 11 pushed into the expansion pipe 12, where it expands again. A first impregnation liquor and/or gas from the inlet valve 14 under superatmospheric pressure flows through the openings 13 into the reopened voids between the wood pieces and fills them up. The liquor and /or gas are sealed off backwards by the compacted wood in the plug throat 11. From the expansion pipe the previously preimpregnated wood batch is pushed into the press chamber 15, and from there the wood batch is pushed further out into the outlet box 29. The retaining plate 30 is pushed forwards by the wood, and at the same time it keeps the wood string together and prevents the wood from falling down. When the wood has filled up the outlet box, so that the retaining plate has been pushed up to the front wall to the right of the outlet box, the retaining plate is locked in this position and gives a signal to the cylinder 7.
The wood feeder is then locked in its actual position. The doors 18 and 19 are closed, and the wood in the outlet box is pushed out by the discharger 32. This is then reversed, and the retaining plate 30 is released and returns to the gate 17. The wood feeder 6 is returned to its rear position, and the steps of the compaction throat 8 prevent the wood from falling back into the box 5. The gate valve 3 is opened, and a new batch of wood falls down into the box 5. The press stamp 22 is moved down and presses the wood together in the press chamber under such a high pressure that the pores of the wood are compressed. The pressure at the wood ought to be at least 5 MPa. Through the openings 24 squeezed out liquid and gas are discharged via the outlet valve 26 to the outlet 25. Then the outlet valve is closed and through the inlet pipe 27 with the inlet valve 28 a second impregnation liquor under super¬ atmospheric pressure is introduced through the openings 24 into the chamber. As chemicals can be used e.g. sodium hydroxide, sodium bisulphite, hydrogen peroxide or a mixture of some of these. Gas such as oxygen, ozone, sulphur dioxide or a mixture of some of these can also be added, either alone or together with liquor. The pressure is released by reversing the press stamp. The wood expands then and the solution is absorbed into its pores. The inlet valve 28 is closed and the outlet valve 26 is opened, and after that the doors 18 and 19 are opened. The gate valve 3 is closed, the wood feeder 6 is moved forwards, pushes a new batch ahead and the process is repeated. The treated wood is ground to pulp as usual by pressing the wood pieces against a rotating grinding tool while adding water.
After compression, chemical impregnation and expansion, the wood batch constitutes a compact bale. Its final dimensions are adjusted to the grinder, so that the bale can be directly fed into it. All handling of single wood pieces is consequently finished after they have fallen down
into the bin 1. The whole process is carried out in an industrially rational way with bales of fixed dimensions, independent of the irregularities of the individual wood pieces. The compaction of the wood into bales reduces also the tendency of thin wood pieces to be torn out of the grinding zone and unground get into the pulp.
The impregnated wood can be introduced into a second press chamber (not shown) where the spent chemical solution is squeezed out and another solution is injected. The impregnated wood can also be digested under superatmospheric pressure in a digester.
Between the press chamber 15 and the outlet box 29, a treatment chamber 34 can be located, as shown on fig. 3. The impregnated wood batches are pushed out of the press chamber into the treatment chamber, which allows for as many batches in a row, that are required for the desired treatment time. The chamber may be heated by steam through a steam inlet 35, controlled by a TIC (temperature indicatio and control) equipment 36. At the outlet of the treatment chamber, the string of wood batches is pushed against the retaining plate 30, pushed out into the outlet box 29, discharged batch-wise by the discharger 32, and the feed is controlled, as previously described.
The invention can be varied within the scope of the idea of the invention. For example, other devices than those described can be used to handle and convey the wood batch and charge it into and discharge it out of the press chamber.