NZ238142A - Manufacturing fibreboard by dry defibration of lignocellulose material - Google Patents

Description

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Class. (• . PA.* 5 ;Patents Form Ho. 5 ;NEW ZEALAND ;PATENTS ACT 1953 COMPLETE SPECIFICATION ;i"* ■ i \ \ ^ MAY J99j x 0 c IV DEFIBERING OF FIBRE MATERIAL WE, SUHDS DBFIBRATOR INDUSTRIES AKTIEBOLAG, a Swedish body corporate of S-851 94 Sundsvall, SWEDEN hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: (followed by page la) la 2 38 1 42 Defibering of fibre material This invention relates to the defibration of lignocellul-ose-containing fibre material, such as wood chips, bagasse or the like, which is intended to be formed to fibreboard by forming and pressing.

At the manufacture of fibreboard according to the dry method, fibre material is fed to an infeed bin, in which a certain preheating with steam of atmospheric pressure takes place. The fibre material can be moist chips, which normally have been washed in a chip washer. A feeding screw, which brings about an air-tight plug, then feeds the chips to a pressurized preheater where the chips are heated with steam of a predetermined pressure for a certain period of time, whereafter the chips are fed further via some type of worm conveyor to a refiner where defibration is carried out between two refiner discs. The def-ibered fibre material normally is mixed with resin during its transport in a blow line and blown by steam to a fibre drier where the fibres are dried to a moisture ratio of ca. 0.1,then are transported to a fibre bin and thereafter formed to a fibre mat, which is pressed in a hot press to a complete board.

The fibres, alternatively, can be mixed with resin in a mixer after the drying. The drying can be carried out in a fibre drier of one- or two-step type. The complete boards can be manufactured as boards of one or several layers. The latter type requires several production lines according to above arranged in parallel.

The preheated material normally is transferred from the preheater to the defibrator by a straight worm conveyor, which advances the material without compressing it.

Modern defibrators are fed laterally, i.e they comprise a worm feeder, which compresses the material slightly and feeds it to a worm belt, which in its turn feeds the chips into the beating zone between the refiner discs. (followed by p«g« 2) A slight compression was chosen, because the steam, which is produced at the refining and flows rearward against the chips via a by-pass pipe connected to the preheater top, is desired to be returned to the preheater for being used in the preheating.

At a method of re-using the produced steam under pressure, as disclosed in the patent SE-8200943-2, a compressing worm feeder of straight-feed design is used.

Further examples of compressing worm feeders of straight--feed design are shown in the patents SE-7603464-4 and 8302014-9.

These patents refer to applications at the manufacture of papermaking pulp, where the pressure in the preheater is kept lower than in the refiner housing in order to achieve a pulp of highest ISO-brightness. At the manufacture of papermaking pulp, defibration and treatment take place in the refiner. This requires high energy input and at the same time produces much steam. As mentioned above, the worm feeder there is intended to prevent the steam from flowing rearward. The compressing worm feeder in these cases, thus, has the object to adjust the pressure difference between preheater and refiner housing. The degree of compression is low. The prerequisite conditions of interest at these applications, therefore, have been different from those at the defibering of fibre material for the manufacture of fibreboard according to the dry method.

At the manufacture of fibreboard according to the dry method, the moist fibres shall be dried to the moisture ratio mentioned above. The moisture ratio of ingoing chips can vary considerably, from 0.2 to 2.0 when no chip washer is used, but after chip washing normally is about 1.3. During the heating of the chips in the feeder bin and preheater, additional moisture is supplied via the steam. Part of this moisture is pressed out in the worm feeder to the preheater, and an additional amount is 238142 allowed to evaporate during the energy-intensive refining, whereafter moisture is added with the size introduced in the blow line. Remaining moisture minus the residue moisture 0.1, however, must be evaporated in the drier. The drier used at the manufacture of fibreboard .is of tubular type, where ingoing air temperature is about 160°C and outgoing air temperature is about 60°C, and where the efficiency degree is correspondingly low. The drying, therefore, requires a relatively high energy input per ton of evaporated moisture.

According to the invention, the energy consumption is reduced due to the fact, that the fibre material at the transfer from the preheater to the defibration is compressed at a compression rate of 1.5-3, preferably 2-3, and dewatered so that the material after defibration has a moisture ratio as low as possible. The energy demand at the subsequent drying can hereby be reduced substantially. The invention implies, that the total energy consumption at fibreboard manufacture can be reduced. The characterizing features of the invention are apparent from the attached claims.

The invention is described in greater detail in the foll- \ ) owing, with reference to the accompanying Figure, which schematically shows an embodiment of a plant for the manufacture of defibered fibre material according to the invention .

Chips are fed from an infeed bin 1 by a worm feeder 2, V which produces an air-tight plug, into a preheater 3, where the chips are heated by steam via a conduit 4 to 140°C - 190°C, preferably 160°C - 180°C. In the worm 2 a certain dewatering takes place. After the preheater 3 a compressing worm 5 is located, which has a compression ratio of 1.5-3, preferably 2-3, i.e. the ratio between the free area of the worm at the inlet and the corresponding area at the outlet. The casing 6 of the worm is provided with a great number of apertures or slits, so that 2 3 8 1 4 an effective dewatering can be achieved. The water pressed out is collected in an air-tight casing 7 and discharged through a conduit 8 to a cleaning plant or returned to the infeed bin 1 for heating the chips. The chips then can be fed from the worm 5 directly to the defibrator 9 or to the refining zone of the defibrator via an angled worm belt, which breaks up the chip plug and ensures uniform infeed to the refining zone of the defibrator. The defibered material is transported in a blow line 10,into which resin is introduced through a conduit 10. Thereafter drying takes place in a tubular drier 12, whereafter the fibres are transferred to a forming station where fibreboard is formed in a manner known per se.

Due to the compression and dewatering of the fibre material in the worm 5, the moisture ratio of the material fed into the defibrator 9 is lowered to 0.7-1.1, suitably 0.7-0.9, preferably about 0.8, and of fibre admixed with resin after the blow line to 0.4-0.5. The heat demand in the drier can hereby be almost halved. For a new plant, therefore, only slightly ■ore than half the drier size is required. This implies for a plant producing 50 000 tons of board per annum a reduction in drying energy at certain prerequisite conditions counted in oil equivalents about 2150 m^ oil/year, in addition to the lower investment costs for the drier. To this°are further to be added reduced costs for almost halved fan energy for the drier as well as almost halved emissions of impurities in the drier exhaust gases, alternatively reduced size of required cleaning equipment. In certain cases the installation of any cleaning equipment can be abandoned.

For an existing plant, the invention implies that the inlet temperature in the drier can be lowered substantially, which results in lower drying costs. Besides, in cases when the drier was limiting the production, the production can be increased. An additional saving probably can 238 142 be made in the amount of resin, because the resin consumption can be expected to decrease due to the lower--drying temperature. All together, even in this case the saving will be substantial.

By increasing the compression ratio and dewatering in the infeed worm 2, the moisture content of the chips fed into the defibrator 9 and drier 12 can be lowered further. An increase in the compression ratio from 1.8 to 2.8 yields a decrease in drying energy by about 10Z.

A drier fibre material also has a lower weight and is thereby easier to transport in the blow line, thereby reducing the demand for additional steam required for the transport.

As mentioned above, the hot water collected from the compressing worm 5 is recovered and returned through the conduit 8 to the infeed bin 1 for heating ingoing cold chips. A considerable saving in steam to the preheater 3 is hereby obtained. Several different designs can be imagined in this respect, depending on whether or not the plant has a chip washer, and whether the chips are pre--steamed in the infeed bin 1. When the plant comprises chip washing, the hot water preferably can be returned via the conduit 8 for use in the chip washer.

At a simple application, the hot water returned through the conduit 8 is mixed with the cold chips in the infeed bin 1, so that temperature equilibrium is obtained. Tests have shown, that such a state can be achieved within a few minutes. By this heating, at certain prerequisite conditions, a saving of 30-35% in the steam demand for the preheater 3 can be made.

Still more energy can be saved when the water pressed out from the worm 2 before the preheater 3 is passed to a chip washer. At an annual production of 50 000 tons of board, about 800 oil, counted in oil equivalents, can be saved. In a new plant, besides, the size of the steam 238142 6 boiler system can be reduced, thereby lowering the investment costs and very probably well compensating for the excess cost of the compressing worm 5 after the preheater 3.

Compared with conventional defibering, at given prerequisite conditions, the waste flow from the worm 2 before the preheater 3 increases from 0.2 to 0.55 m /ton dry ^ substance, which is an amoun-t capable to be handled even when for environmental reasons water purification would be required. It is to be observed that the amount of water--soluble substance in this flow is smaller than that in the hot water from the compressing worm 5 after the preheater 3, because part of the hot water is re-circulated.

Another alternative is to flash off by pressure drop the hot water pressed out and to utilize the steam for pre--steaming the chips in the infeed bin 1 at the same time as the hot water is returned to the chip washer. The invention is not restricted to the embodiments described, but can be varied within the scope of the invention idea. .

Claims (1)

1. 7 12 WHAT JT/WE CLAIM IS: - <»*»;1. A method for manufacturing fibreboard according to;,(as here.in def.ined);the dry method/by defibration of lignocellulose-containing fibre material, comprising: preheating fibre material;.between with steam under pressure at a temperature < 140-190°C in a preheater and subsequently defibering under pressure in a defibrator , admixing resin in the fibre material in a blow line after defibration, drying the fibre material to a moisture ratio cf about 0.1 and forming the fibre material into fibrebcard, wherein ___the fibre material is fed by an airtight worm feeder from an infeed bin to the preheater and simultaneously dewatered with a compression ratio of 2-3, and the transfer cf the fibre material from the preheater _ to the defibrator takes place while the material is simultaneously compressed and dewatered in a compression worm — with a compression ratio cf 1.5-2,;, for lowering the moisture ratio of the fibre material to 0.7-1.1, and further lowering the moisture ratio of the fibre material by defibration so that the moisture ratio after defibration and admixing of resin is 0.4-0.5.;2. A method as defined in claim 1, wherein;the water separated from the compressing worm is re-circulated for heating the fibre material before the preheater;3. A method as defined in claim 2, wherein ——;— — the water is re-circulated to the infeed bin before the preheater;4. A method as defined in claim 2, wherein;. the water is re-circulated to a washer,;from which the fibre material is fed via the infeed bin,;into the preheater;5- A method as claimed in any one of the preceding claims, wherein the water separated from the compressinq worm is allowed to expand, and the steam given off is;15 OCT 1992;-8-;14:2;utilized for pre-steaming the fibre material in the infeed bin before the preheater, and the water is used for washing the fibre material in a washer before the infeed bin.;6. A method as defined in any one of claims 1 to 4;wherein the water separated from the worm feeder is recirculated to be used for washing the fibre material before the infeed bin.;7. A method as claimed in any one of the preceding claims wherein the compression ratio of the compression worm is 2-3.;8. A method as claimed in any one of the preceding claims where the moisture ratio of the fibre material is lowered to 0.7 - 1.1 after passing through the compression worm.;9. A method of manufacturing fibreboard as claimed in claim 1 substantially as hereinbefore described.;10. A method of manufacturing fibreboard substantially as hereinbefore described with reference to the accompanying drawings.;11. Fibreboard formed by the method of any of the preceding claims.;sund ; defibrator industries aktiebolag;By thelir Attorneys;BALDWIf carey r;15 CCT1932*