MANUFACTURE OF MECHANICAL PULP

Abstract: Lignocellulose-containing material in lumps, such as wood chips, is pre-heated and refined in a refiner (8). Steam generated at the refining is utilized for transporting the chips through a blow-line (5) all the way to the refiner (8). During the transport the chips are heated by heat transfer from the transport steam.

Description: Manufacture of mechanical pulp This invention relates to the manufacture of mechanical pulp by refining lignocellulose-containing ' material in lumps, such as wood chips. The chips are pre-heated before refining and possibly also treated with chemicals. The pulps manufactured in this way are called thermomechanical pulp (TMP) and, respectively, chemi-treated thermomechan¬ ical pulp (CTMP). Pulps of this type normally are manufactured by process¬ ing the pre-treated chips in a disc-refiner, in which the material is refined during its passage through a gap between two refiner discs rotatable relative to each other. Both singledisc and doubledisc refiners can be used. The refining of material in this way requires a great amount of energy in the form of electric energy for rotat¬ ing the discs. The energy consumption normally can amount up to 2000 k h/ton pulp. This energy amount supplied conyert.s during the refining process substantially to heat and, as a result thereof, the water following along with the material is evaporated and and goes off from the material processed. The separated steam usually is utilized for pre-heating the material or for other heating purposes. The chips constituting the starting material in the process normally are stored in large storage containers, which are located at a relatively great distance from the refiner or refiners to be used.Belt or screw conveyors transport the chips to the refiners. These conveyors require much space and are expensive. Moreover, a special pre-heater for the chips .is required in connection to the refiner for heating the chips to the correct temperature before refining. According to the present invention, . belt and screw conveyors and separate pre-heater are not required any longer at the manufacture of mechanical pulp from pre-heated chips. At the same time, further advantages over the prior art are obtained. The building, for example, housing the refiners can be designed more economically, due to the simplified chip transport. The energy, furthermore, supplied for the refining process can be utilized more efficiently. The characterizing features of the invention become apparant from the attached claims. The invention is described in greater detail in the foll¬ owing with reference to the accompanying Figure showing an embodiment thereof. In the Figure, a storage container 1 for chips is shown, which is provided with a discharge device 2 connected to a steam-proof plug screw-feeder:3. The outlet of said screw-feeder 3 is coupled to a mixing pipe 4, from which a blow-line 5 extends. The blow-line 5 opens into a steam separator in the form of a first cyclone 6. At the bottom of the cyclone 6 a screw-feeder 7 to a first disc-refiner 8 is mounted, which screw-feeder preferably is of the type, in which the material forms a steam-proof plug. From the inlet end of the refiner 8 a conduit 9 for separ¬ ated steam extends. The embodiment shown also comprises a second refining step, which comprises a second cyclone 10, a second refiner 11 with screw-feeder 12 and a conduit 13 for separated steam. After said second refining step, a third cyclone 14 with a discharge device 15 at its bottom is provided. From said three cyclones 6,10,14 conduits 16,17,18 extend for the steam which is separated. The steam conduits 9 and 13 are coupled together to one conduit 19, which opens into the mixing pipe 4. In order to ensure the chip transport through the blow-line 5, for example when the chips must • __-. transported through a long distance, one or several branch lines 22 can be arranged from the conduit 19, which passes steam to the mixing pipe 4. Said branch lines 22 are connected to add¬ itional nozzles 23 along the blow-line 5. The system operates as follows. The chips are delivered out of the container 1 by means of the discharge device 2 to the plug screw-feeder 3, which produces a steam-proof material plug. From the outlet of the screw-feeder 3 the chips fall down into the mixing pipe 4. The steam generated in the refining process which is led via the conduits 9,13,19 and usually has a temper¬ ature of 100-l4θ°C, themconstitutes transport steam, which takes along chips from the mixing pipe 4 through the blow- -line 5. Possible excess steam can be removed through the conduit 20. Alternatively, as transport steam the steam separated in the second and, respectively, third cyclone 10,14 can be util¬ ized. This steam has a higher pressure and a higher temper¬ ature, due to the increase in pressure arising over the gap of the refiner. The temperature then can exceed 140 C. In this case the steam is passed via the conduits 1 ,18 to the mixing pipe 4. In the blow-line 5 the chips are transported by the steam. The chips normally occupy 4-6% of the space in the cond¬ uit. The steam will have a slightly higher rate than the chips in the conduit. This difference in rate causes turb¬ ulence whereby the chip flow is fluidized. Hereby heat very efficiently is transferred from the steam to the chips, so that the temperature desired for the chip refining can be achieved in the blow-line 5 during the short time used for the transport. Prior to the feed of the chips into the first refiner 8, a separation of chips-steam takes place in the first cyclone 6. This separated steam has a low pressure and a low temperature and can be utilized via the conduit l6 for heating the chips in the store container 1 or for other purposes via a conduit 21. In order to heat the chips sufficiently without causing too much of steam condensation in the blow-line, the chips prior to their entering the blow-line should be heated to at least 70°C. This can be effected preferably by the steam separated from the first cyclone 6 as said above, The number of refining steps, of course, can be varied. It also is possible that more refiners are supplied with chips -from a storage container through blow-lines according to the invention. The separate pre-heaters normally employed have a substantial height. As the invention renders it possible to eliminate these pre-heaters, the building housing the refiners can be designed lower and, thus, more economic. The invention, of course, is not restricted to the embod¬ iments described, but can be varied within the scope of the invention idea.

Claims: Claims 1. A method of manufacturing mechanical pulp by pre- -heating lignocellulose-containing material in lumps, such as wood chips, by steam followed by refining under pressure in a refiner where steam generated at the refin¬ ing is separated from the fibre material and utilized for the pre-heating, c h a r a c t e r i z e d i n, that the chips are transported all the way to the refining through a blow-line (5) by means of transport steam consist¬ ing of the steam separated from the fibre material, where¬ by the chips flow is fluidized and heated during the transport through the blow-line (5) by heat transfer from the transport steam. 2. A method as defined in claim 1, c h a r a c t e r i z e d i n, that the chips prior to the transport through the blow- -line (5) are heated to at least 70 C. 3. A method as defined in claim 1 or 2, c h a r a c t e r i z e d i n, that the transport steam consists of the steam generated at the refining which is separated from the feed-in end of the refiner at a temperature of 100-140 C. 4. A method as defined in claim 1 or 2, c h a r a c t e r i z e d i n, that the transport steam consists of the steam generated at the refining which is separated inasteam separation device located after the refiner at a temperature above 140°C. 5. A method as defined in any one of the preceding claims, c h a r a c t e r i z e d , that the transport steam is separated from the chips after the transport in a cyclone located immediately before the refiner, and said separated transport steam is used for heating the chips prior to the transport.

Inventors: SANDSTROEM NILS ROLAND, WALDENSTEN JAN OTTO, SANDSTROEM, NILS, ROLAND, WALDENSTEN, JAN, OTTO
Applicants: SUNDS DEFIBRATOR, SUNDS DEFIBRATOR AKTIEBOLAG
Application year: 1986
Main classification: D21B1
IPC codes: D21B1