SE428813B - SET FOR MANUFACTURING FIBER DISCS BY THE WATER METHOD - Google Patents

Description

aloeaaees 10 15 20 25 30 35 This means that in a tightly closed backwater system the fiber discs become hot-colored during hot pressing and can also become dark-stained and have a tendency to stick to the press plates. D To avoid the above problems, it is necessary that the amount of released, organic material is low in the backwater system and thus in the fibreboards. In order to obtain a low content of soluble substance in the backwater, so far some of the backwater has usually been deducted and replaced with fresh water.

Deducted backwater must expect to neutralize, which can happen e.g. by evaporation in combination with combustion of the thick liquor or by various biological treatment methods. However, the known methods all have the disadvantage of making the process more expensive and thus the end product.

The main object of the invention is to provide a new way of reducing the content of released, organic substance in the backwater in the production of pulp for fibreboards and this object is achieved in that the method is characterized by * dewatering the fibrous mass obtained during defibration and that the resulting aqueous solution of defibrillator The organic material released in the process is returned to the process by impregnating the chips before defibrating with it.

According to the invention, it has been found that if the incoming chip is impregnated with an aqueous solution of substance released during defibration and then defibrated at 17D ° C, the solute binds practically completely in the pulp and cannot be removed by washing with water. The conversion of the solute into an insoluble form probably takes place through the interaction of several processes of a chemical as well as a physical nature. The released substance consists essentially of polysaccharides, which can undergo both polymerization and condensation processes and form substances that are difficult to dissolve in water. It is also possible that the polysaccharides are absorbed so strongly in and on the fiber walls that they cannot be dissolved by water.

Knowing that when impregnating fish with water it is possible to obtain one tonne of dry coniferous wood of coniferous wood with 50% dry content to absorb one m3 of water, in a hard-boiled process water system a substantial amount of the released substance can be returned to the fish and According to the invention, the invention is neutralized in the defibration process. The impregnation is then carried out in such a way that the film is first softened by steam treatment at! 00 ° C and then compressed and freed from excess water and in a compressed state the impregnation solution is applied, in which case the film then expands and absorbs solution. This is put in certain fails at the same time under pressure to facilitate the absorption of liquid11.

How much waste material must be undamaged depends on how much waste material can be allowed to remain in the fibreboard and is determined by the concentration of waste substance in the backwater. As long as the concentration in the rear water can be considered to be as high as 5.0%, the problem can often be solved by directly dewatering the finished mass to 50-60% dry heat mechanically and using extruded aqueous solution for impregnation, provided that the solution can be completely limited. ti11 what the fish can absorb.

If the backwater concentration has to be lowered to 3.0% or less, extra water must usually be added and the dewatering done in one or more steps with the adjoining water content. In order to lower the heat of the substance in the backwater to the said value, it may be necessary to add so much water during the dewatering of the mass that the amount of extruded solution is greater than that which can be absorbed during the impregnation and in such a case the solution must be evaporated. to an amount suitable for impregnation. 8106369-5 10 l5 20 025 30 In some cases it may also be desirable to neutralize contaminated water coming from other parts of the system, e.g. extruded wood water after the chip has been steamed, and this can be done by using the contaminated water to dilute the finished defibrated fibrous material before its mechanical dewatering to remove the released substance. In such cases, so much extruded solution is usually obtained that evaporation becomes necessary to the volume that can be absorbed by the chips.

Evaporation of the extruded solution can take place in all known ways. The pre-evaporation should suitably take place under vacuum in order to avoid inconvenience with crust formation or also by evaporation of heated aqueous solution with air, the water escaping as an air-vapor mixture.

The invention will be described in more detail in the following in an exemplary embodiment of a plant for carrying out the method. The figure schematically shows a flow chart for the plant for carrying out the method.

The incoming chip is transported by means of a conveyor 10 to the basing vessel 12 where it is based with steam which is supplied via a line 14 from a cyclone 16 in a later part of the plant. The moist chips are discharged into a screw press 18 where water is mechanically drained and discharged via the line 20 to the underlying vessel 22.

The chip plug compressed in the screw press 18 is pressed into an impregnation vessel 24 where it is allowed to expand and absorb aqueous solution with released substance of polysaccharides etc., which aqueous solution is obtained by mechanical HV watering of the fibrous mass in a later stage in the plant and fed to the impregnation vessel 24 via a line. 26.

Via a feed screw 28, the chips are fed into a preheater 30 which is under steam pressure and to which steam is supplied from a line 32, from which a branch line 32a also opens into the basing vessel 12. The steam-heated chips are fed via a screw feeder 34 to a defibrillator 36 with motor 38 and defibrated into fibrous pulp. The finished fibrous mass, in which the organic substance supplied during the impregnation in the vessel 24 has turned into insoluble form, is blown through a blowing line 40 to the cyclone 16.

The fibrous mass is fed from the cyclone 16 with a screw feeder 46 to the container 48, which is provided with a stirring device. To the container 48 leads a conduit 42 from the vessel 22 through which conduit wood water from the vessel 22 is supplied to the container by means of a pump 44. From the container 48 the fibrous mass is fed via a chute 50 into a high-pressure screw press 52 where the fibrous mass is mechanically dewatered.

The aqueous solution thus obtained of organic material released during the defibration process drains from the screw press 52 via a line 54 to the vessel 56, from where it is pumped by means of a pump 58 via the line 60 through a heat exchanger 62 to a cooling tower 64 where a part of the water is evaporated. The heating in the preheater 62 takes place with steam which is drained from the cyclone 16 via a line 14a and which leaves the preheater via a line 66. Some of the water is thus evaporated in the tower 64, as a steam-air mixture, the air being supplied by means of a fan 68 The evaporated solution is pumped by means of a pump 70 through the line 26 to the impregnation vessel 24 for impregnation of newly added chips in the process, as previously described.

From the high-pressure screw press 52 the fibrous mass flows down into a pulp bin 72, to which simultaneous backwater is supplied from a tank 74 by means of a pump 76 and the line 78. The finished pulp suspension is pumped by means of the pump 80 via the line 82 to the forming machine 84. from which run-off effluent is collected via line 86 in the tank 74. The wet sheet is fed to the hot press 88 where it is mechanically dewatered and finally dried under heat and pressure to a finished product in the usual manner.

To further illustrate the invention, it will be described in the following in an exemplary embodiment, indicating the various conditions which may prevail in the process. It should be clear, however, that this is only an example of the invention and that this is not limited to the stated values.

Example: 0 The incoming softwood chips, which per hour are assumed to be 8000 kg ts + 8000 kg water, are supplied to the basing vessel l2 and at the same time 1925 kg of steam is supplied through the line l4, after which the moist l00% chip is lowered into the screw press 18 where it is dewatered to 55% ts, whereby 3380 kg of H 2 O of 100 ° C drains to the vessel 22 and the compressed chip plug is pressed into the impregnation vessel 24 and is allowed to expand and absorb aqueous solution with released substance of polysaccharides to be fed via preheater 28 into preheater 30, which is under steam pressure at 170 ° C and steam is supplied through line 32. The chip heated to 170 ° C with its content of water and organic substance absorbed by the chip is fed to the defibrillator 36 via the screw feeder 34. The finished fibrous mass, in which now the the impregnated organic substance has passed into an insoluble form, is blown through the line 40 to the cyclone 16.0 Ü Mass from the cyclone is fed with the screw 46 to the container 48, to which at the same time 3380 kg of wood water is led from the vessel 22 by means of the pump 44 and the line 42. From the container 48, provided with a device for good stirring, the massani high-pressure screw press 52 is drained and dewatered to 55% dry matter. In this case, 1,0400 kg of water with 400 kg of soluble substance of a total of 640 kg released from the chips drains to the vessel 56. 245 kg of solute remains in the pulp. This amount of solute must be allowed to remain in the fibreboard in order for all released material to be rendered harmless. When the fibreboards during hot pressing after mechanical pressing of backwater to 60% dry content hold about 5200 kg of water, which must be evaporated and removed, the backwater can be allowed to hold 245 kg of solids per 5200 kg of water or 4.5%. Since the solution flowing to the vessel 56 constitutes 10,400 kg of water + 400 kg of released substance, this is more than the chips can normally absorb and which usually does not exceed 8000 kg of water on 8000 kg of dry-fired chips. 2400 kg of water must therefore be evaporated in the tower 64, which is done by preheating the solution.

The preheating takes place with steam coming from the cyclone 16 through the line 14a. In tower 64, 2400 kg of water is evaporated as a vapor-air mixture. The air is supplied with the fan 68. Evaporated solution, 8000 kg of water + 400 kg of soluble substance, is pumped to the impregnation vessel 24 through the line 26.

Any amount of wood released can be neutralized in such a way that 400 kg is bound in the pulp during defibration and 245 kg is bound in the fibreboards. In the hot press evaporated 5200 kg of water is replaced by adding water to the rear water cycle. No discharge of backwater needs to take place and the content of 4.5% dissolved organic matter in the backwater is kept at a sufficiently low level to avoid discoloration of the fibreboards during hot pressing. In addition, all blackened firewood has been rendered harmless.

Claims (5)

8106369-5 PATENT REQUIREMENTS 1. A method of producing fibrous sheets according to the wet method with a purified backwater system, in the case of freezing of igneous material containing preheated material in an atmosphere of saturated steam at elevated temperature and elevated pressure and then atmospherically defibrating or at elevated pressure, backwater so that a pulp suspension is obtained for forming wet sheets which are released from water by pressing under heat supply, the extruded water being returned to the storage step, characterized in that the fibrous mass obtained during defibration is mechanically dewatered and the water obtained in this process is materiai is used for impregnation of the fish before preheating. 2. A method according to claim 1, characterized in that the impregnation of the freeze takes place by the freeze being based and compressed, mechanically dewatered and then fed under compression pressure into an impregnating solution containing during the defibration free of organic substance and allowed to expand therein. thereby absorbing solution. 3. A claim according to any one of claims 1-2, characterized in that the defibrated pulp is provided with so much water that the pulp, after dewatering, has an amount of organic substance which is suitable for the further process. ~ g 4. In accordance with claim 3, it is claimed that the water leaving during the compression of the base fish is fed to the backwater cyclone. 5. A method according to any one of claims 1-4, characterized in that the solution squeezed for the impregnation of the chips is caused by evaporation to have an adequate amount of water for the impregnation.