FI67412C - FOERFARANDE FOER BEHANDLING AV CELLULOSAHALTIG MASSA - Google Patents

Abstract

In a method for treating cellulose containing pulp, the pulp is fractionated in two or more fractions according to particle size before treating one or more of the fractions with ozone. The fractionation can be carried out in a fractionating device which is included in a complete treatment process, the fractionating device constituting a series of screens. Depending on the quality of the finished paper product, various ozone treated and untreated fractions of the pulp are brought together at various stages in the treatment operation.

Description

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Patent · och registerstyralien AmOksn utlagd och utl ^ kriften pubUcend 30.11.84 (32) (33) (31) Pyrävtty «tuolk.oi-B« ** rtl prlortut 27.04.77 27.04.77 Norway-Norway (NO) 771471, 771472 (71) Myrens Verksted A / S, Bentsebrugaten 20, Oslo 4, Norway-Norge (NO) (72) Bj «Srn H. Fritzvold, Hosle, Nicolai Soteland, Oslo, Norway-Norway (NO) (74) Berggren Oy Ab (54) Method for treating the pulp containing cellulose -Forfarande för behandling av cellulosahaltig pulp

The present invention relates to a process for treating a cellulosic pulp.

The object of the present invention is to provide a process for the treatment of cellulosic pulp which enables efficient utilization of the substances involved in the treatment and by means of which the strength properties of the pre-treated pulp can be optimized with respect to each other according to the pulp application areas.

The problem is solved by a method in which the cellulosic pulp is fractionated according to particle size (fiber length) and in which one fraction is treated with ozone, characterized by changing the concentration of the fractions before ozone treatment so that coarse particles and that the liquid separated from the coarse-containing fractions is passed mainly to the fine-particle fractions, so that the fine-particle fractions are treated with ozone in a well-diluted state, and that the 2 67412 fractions thus treated with ozone are brought together to form a pre-treated mass.

Such a method gives a pre-treated pulp which, in the manufacture of paper, can give the best possible combination of tear strength and breaking strength. With the method according to the invention, ozone can also be utilized more efficiently, because the total consumption of ozone is lower when treating separate fractions than if the entire pulp were treated with ozone simultaneously. This is because fractions of fine particles usually make up a very large part of the total surface area of the pulp, thus using much more ozone than is necessary for quality improvement than is the case when both fine and coarse fractions of the pulp are treated with ozone simultaneously.

Suitably, the fraction or fractions subjected to ozone treatment can be sorted in the sorting steps to separate the specific pulp particles, whereby the effluent is treated with ozone before being subjected to 1 paternal comminution and returned to the sorting steps for further sorting.

When sorting wood pulp with a high chip content, it is intended to separate the large chip particles from the pulp, because the large chip particles do not fit into the pulp which is further processed, e.g. in a paper machine. By performing an ozone treatment on these larger particles before dividing them into smaller particles and returning them to the sorting steps for re-sorting, the effluent can be efficiently utilized while simply adapting the treatment to existing sorting compartments where the pulp-containing pulp is removed.

Ozone-treated twigs can be more easily decomposed, and the method according to the invention thus also contributes to facilitating the decomposition process, e.g. in an existing sorting plant.

The object underlying the present invention is solved in a sorting plant by first applying ozone treatment to the first part of the coarsest effluent 3 6741 2 and then decomposing in the first decomposer before feeding it to a sorting plant different from the sorting stages and feeding the second part of the coarse effluent the part is fed to the sorter so that the input from this sorter is transferred to one or more other sorting stages for further sorting and the effluent is returned to the second digestion device.

The method according to the invention can easily be applied to an already existing sorting compartment by making only relatively minor changes to it.

It is clear that the dewatering and flotation step is also performed in connection with the ozone treatment of the pulp. These steps are carried out before the ozone treatment of the pulp, after which the pulp enters a sludge stage, i.e. a stage in which lye and water are added to the ozone-treated pulp.

The ozone treatment of the coarse pulp is usually carried out with a high degree of concentration, i.e. a dry matter content of about 30-50%. When the aqueous mass is divided into one or more fractions containing coarse particles, it is easier to remove water from these fractions because the coarser the suspended particles (fibers), the easier it is to remove water from the suspended mass.

The present invention can therefore considerably shorten the drying time of high-yield cellulosic pulps for fractions with a low fines content. This directly results in energy savings when the stock is concentrated prior to ozone treatment.

The invention will be explained in more detail below with reference to the drawing showing various embodiments of the present invention.

Figure 1 shows a flow chart of a first embodiment of the method according to the invention.

Fig. 2 shows a flow chart of a modification of the embodiment according to Fig. 1.

Figure 3 shows a flow chart of a further embodiment of the invention.

Figure 4 shows a flow chart of another embodiment of the present invention.

4 6741 2

Figure 5 is a flow chart of an embodiment of the present method used in connection with a sorting plant.

The invention is explained below in connection with the treatment of mechanical pulp. Such a pulp is also called a cellulosic Suur-raan pulp. However, it is clear that the process according to the invention can also generally be used in connection with the treatment of a cellulosic pulp. In addition to mechanical pulp, these pulps include chemimechanical pulp (semi-chemical pulp) and chemical pulp (sulphite or sulphate cellulose).

In Fig. 1, which shows a flow chart of a first embodiment of the method according to the invention, reference numeral 1 denotes an grinding device, i.e. a grinder, which processes the raw material formed by the chips into grind or grit. These pulps may be collectively referred to as mechanical pulp or high yield pulp containing cellulose.

From the device 1, the comminuted mechanical pulp is fed to a fractionator 2, where the pulp is divided into a coarse fraction which is passed to a dewatering / press device 3 and a fine fraction which is partly passed to a first ozonation device 4 and partly to a mixing amraze 5. As shown in the figure. from the device is connected at 3 'to a fine fraction which goes to an ozonation device 4, where the fine fraction is diluted so that its dry matter content is about 0.1-0.5%. A part of the circulating water coming from the dewatering / press device 3 is led directly to the mixing bath 5, as shown by the broken line 6. As shown by the broken line 4 ', part of the untreated fine fraction coming from the fractionation device 2 can be led directly to the mixing bath 5.

When the coarse fraction has a dry matter content of about 35-50%, it is passed from the dewatering / press device 3 to a pulverizer 7, where it has a light and airy composition, after which it is passed to another ozonation device 8, which has approximately the same dry matter content as dewatering. / from the press device 3.

After the ozonation treatment, the coarse fraction treated in the device 8 is fed either directly to the mixing tank 5, as shown by the broken line 9 ', or to a post-grinding device 9, e.g. a refiner, where the internal friction grinds the treated mass. Alternatively, a portion of the ozone-treated coarse fraction may be post-milled in the apparatus 9, while the remainder is fed directly to the mixing bath 5. Such coarse fraction distribution depends on the quality of the final pulp or paper products for which the pulp is to be used.

In the mixing bath 5, the finely divided fines and coarse fractions are combined. The pre-treated and mixed pulp is then passed to the next apparatus, not shown, where it is processed into paper or board products or the like.

In high-yield cellulosic pulps, i.e. mechanical pulp and to some extent also chemimechanical pulp, the improvement in strength is primarily the most significant result of ozone treatment, but these pulp grades also provide higher brightness, i.e. bleaching, especially in birch pulps. Ozone-treated high-yield cellulosic pulps are used primarily in chemical grades instead of chemical pulps. However, it is clear that the described method can also be used for the treatment of chemical pulps, i.e. sulphite and sulphate cellulose.

The strength properties of high-yield cellulosic pulps, especially mechanical pulps, are first known from the proportion of long fibers, the so-called L-factor, and secondly the specific surface area of the middle fraction (total surface area per unit weight), the so-called S-factor. The middle fraction then means the part of the pulp with the average fiber length. The L-factor can be said to determine the fiber length distribution of the pulp, while the S-factor determines the shape of the fibers. The tear strength is primarily dependent on the L-factor and increases with this, i.e. with an increasing proportion of long fibers. In contrast, the so-called tensile properties, such as tensile strength, puncture strength and wet strength, are primarily dependent on the S-factor and partly proportional to it.

Mechanical release of the fibers in grinding or grinding results in some of the fibers being cut, so that both high tear strength and high breaking strength cannot be obtained for the same mass. However, compared to a conventional grinding process, disc grinders, and in particular pressure grinders, provide an advantageous ratio between the tear strength and the breaking strength of wood pulp.

6741 2

In the ozone treatment of high-yield cellulose-containing pulps, the coarser the pulp can be improved the more the coarser the pulp before the ozone treatment, i.e. the tear strength improves. with "fatness" (water-donating property). On the other hand, the coarse pulp gives an uneven surface and is therefore not suitable for the production of newsprint and magazine paper, for example. When pulp is used for such products, it must contain a certain amount of finer particles in order for the paper product to have a smooth surface.

When the present invention is used as described in connection with the embodiment of Figure 1, a very advantageous ratio between the breaking strength and the tear strength of the finished pulp is obtained by dividing the cellulosic pulp into two or more fractions according to the particle size and then performing separate treatment of each part. In addition to the optimal strength ratio, which is known from the combination of high tear strength and high burst strength, the process according to the invention achieves a more efficient ozone recovery because the total ozone consumption is lower than if the whole pulp were treated with ozone to achieve the same properties without pre-fractionation. The higher ozone consumption of conventional ozone treatments is due to the fact that the amount of fines makes up a very large part of the total surface area of the pulp and thus uses much more ozone than if the fine and coarse fractions were treated with ozone separately.

Dividing the ground pulp into two or more fractions according to particle size also has the advantage that the drying / compression treatment of the coarse fraction or fractions is easier to perform because the coarser the suspended particles or fibers, the easier the drying of the pulp. The drying time of the high-yield pulps containing cellulose is thus considerably shortened, i.e. the residence time in the drying / pressing device 3 is shortened to a minimum.

In pulp grades where both coarse and fine fractions have to be treated with ozone, ozone treatment of the fine fraction also results in net energy savings at very low consistency, as the low consistency of the fine fraction is achieved within the water balance of the effluent. The reason why the whole mass is not subjected to ozone treatment at low consistency is that in order to achieve a good reaction, the individual particles must be completely separated in the aqueous phase so that the ozone added to the aqueous phase can enter them freely. In the case of undivided pulp, it is a consistency of about 0.1%, ie a tonne of water / kilo of dry pulp, which is very bulky and involves energy-intensive transport.

The improvement in strength achieved by ozone treatment is due to the surface reaction of the individual fibers, i.e. the change in the surfaces of the particles.

It is therefore desired to make this contact surface as large as possible so that it can be affected as much as possible by ozone.

This is achieved by the addition of expansion chemicals, and in simple lignin types a tripling of the volume has been achieved by the addition of small amounts of lye (NaOH). This chemical is added to the various pulp fractions as they are located in the ozonation devices 4 and 8. In order to allow ozone to affect the surface as well as possible, dispersants can be used so that the particles are distributed as well as possible in the liquid phase. The dispersant is preferably added during the ozone treatment of the fine fraction, as shown in the ozone device 4. A surfactant or solvent may optionally be added to the pulp fractions.

From a process economics point of view, it may be preferable to treat only the coarse fraction with ozone. In the manufacture of various end products such as multi-ply paper, cardboard or paperboard, this can advantageously be done by keeping the different pulp parts or fractions separate, e.g. in three layers, both outer layers preferably consisting of fine fractions giving good optical and printing properties, while the middle layer consists of coarse fraction strength appropriate to the finished paper product.

Figure 2 is a flow chart showing only the rough ozone treatment of the fraction. The ozonation device 4 is omitted here because the fine fraction from the fractionation device 2 is led directly to the mixing tank 5, where it is combined with the ozone-treated and post-ground coarse fraction. From the post-grinding device 9, the pulp can possibly be fed to a sorter and an additional grinder.

Figure 3 shows a flow chart of a further embodiment of the method according to the invention, comprising the same blocks as described in connection with Figure 1. The flow chart according to Fig. 3 is distinguished from the diagram according to Fig. 8 6741 2 1 by the fact that an additional mixture 10 is placed between the ozonation device 4 and the mixing bath 5, into which partly treated and partly untreated fine pulp is fed together with other pulp, e.g. untreated mechanical pulp. as shown by line 11. The mixture of treated and untreated fine fraction from the mixing bath 10 and the untreated cellulosic pulp are passed together with the ozone-treated coarse fractions to the mixing bath 5, whereby the coarse fractions are led either directly from the ozonation device 8 or via the post-grinding device 9.

The reason for the use of the additional mixing bath 10 in the process according to Fig. 3 is that the untreated fines fed according to line 4 'is only slightly neutralizing the tower activator to the well-binding active fibers, of which the coarse fraction mainly consists. In other words, the fine fraction tends to "cure" the binding active fibers. In the flow chart of Figure 3, an attempt has been made to improve this condition by adding cellulosic pulp according to line 11 to a portion of the fine fraction removed via line 4 'from the ozone-treated pulp, which is well mixed in line 10 before being added with ozone-treated particulate matter. to the treated coarse fraction in a mixing bath 5. Such a method achieves a considerably lower concentration of fines, based on the mass into which the coarse fraction is mixed. This thus reduces the curing of the binding active, ozone-treated fibers.

Figure 4 shows another embodiment of the invention in the form of a flow chart containing the same blocks as the flow chart of Figure 1. The diagram of Figure 4 differs from the diagram of Figure 1 in that it lacks the dashed lines 4 ', 6 of Figure 1, while the conveying path 12 between the ozonation devices 8 and 4 for the transfer of organic compounds obtained from the ozone treatment of a very thick coarse pulp in the ozonator 8 is shown. These organic compounds are largely surfactants that promote the reaction rate between ozone and the low consistency fines in device 4.

The properties of ozone-treated pulps can be further improved by adding suitable chemicals to the pulps at appropriate stages before or after ozonation.

In Fig. 5, which shows a flow chart of a preferred embodiment of the method according to the invention when used in connection with a sorting plant, reference numeral 1 'denotes a cellulosic mechanical sorting compound or e.g. a feed path for raw material consisting of chips of different sizes.

The raw material pulp is fed to a coarse sorter 2 ', the function of which is to separate the large particles of the pulp. These large particles are removed from the coarse sorter as an unqualified mass or effluent, and may conveniently be further processed in a grinder or hammer mill, as shown at block 3 '.

Large particles can be passed from a coarse sorter to a grinder or hammer mill in a 3 'gutter, rubber belt or screw conveyor. The grinder may, for example, have a shaft rotating in the body, in which case the perforated plate forms the bottom of the body. Round plates can be attached to the shaft, the circumference of which has teeth approximately like a saw blade. Large particles are rubbed between the rotor and the body before passing the perforated plate.

In a hammer mill, the body rotor may have hammers that break the coarse particles into a homogeneous small chip. This small chip passes through the perforated plate of the hammer mill, after which it is mixed with water and further pumped into the actual reject grinding, which will be explained in more detail below.

The intake from the coarse sorter 2 'is further passed to fine sorting, whereby smaller chips and large fiber bundles are separated from the pulp. In the plant shown in the drawing, fine sorting takes place in a first stage sorter 4 ', a second stage sorter 5' and a resorter 6 '. The first sorter 4 'is fed the intake mass from the coarse sorter 2' and the re-sorter 6 'is fed the intake from the sorter 4'. The effluent of the first sorter 4 'and the re-sorter 6' is fed to the ozone treatment and decomposition stage. The devices included in this step are placed inside the dashed line block 7 'in the drawing.

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The effluent separated from the first stage sorter 4 'is not only chips and fiber bundles, but also contains good fibers which must be used later in the next papermaking.

The pulp qualified from the first stage sorter 4 'is not completely clean, which is why it is once again sorted in the sorter 6'. Although the pulp has been sorted several times, it may contain small chips, sand and bark particles. These unwanted particles are removed from the pulp in the vortex sorting plant 8 'before the pulp leaves the sorting compartment.

Not only the reject of the first stage sorter 4 'and the re-sorter 6' is fed to the block 7 ', but also most, in most cases 100%, of the effluent from the coarse sorter 2', i.e. the effluent pretreated in the hammer mill or grinder 3 '. Any remaining part of this pretreated reject is fed directly to a disintegrator, e.g. a disc grinder 9 ', where the debris is ground into acceptable fibers which improve the strength of the wood pulp. The refiner 9 'is also fed with a pulp passed through the block 7', which, however, has not been accepted by the second sorting step 5 '.

The pulp leaving the disc mill 9 ', i.e. the pulp fed mainly from the block 7' to the second sorting stage 5 ', which has not been validated by this sorting stage, is fed to the second sorting stage 5', and the second stage sorter 5 is fed to the first stage stage 4 '.

The pulp fed to the block 7 ', thus consisting of the main part of the pretreated reject mass from the coarse sorter 2' and the effluent from the first stage sorter 4 'and the re-sorter 6', is first dewatered / compressed 10 ', then passed to a pulverizer 11'. light and airy composition.

From the effervescent 11 ', the pulp is fed to an ozonation device 12', where it is treated with ozone (03) and lye (NaOH) is added. Ozone treatment improves the strength of the pulp. This improvement in strength is due to the surface reaction of the individual fibers, i.e. the change in the surfaces of the particles. It is in this way that the co-operation of the previous sorting methods and the method according to the invention leads to an even more efficient utilization of the entire plant. Thus, a preferred feature of such a plant is that the amount of coarse sorter reject to which the ozone treatment and decomposition is performed is determined by the chip size of the coarse sorter and the total amount of coarse sorter. Thus, when the total amount of coarse sorter is small and / or the chip size is small, only a small amount of coarse sorter is taken for ozone treatment and decomposition, but when the total amount of coarse sorter is large and / or the chip size is large, a large portion of the coarse sorter

It is clear, however, that the decomposing device 13 'can be replaced by a simple, powerful mixing device which vigorously mixes the ozone-treated, diluted mass before it is passed to the second sorting stage 5'. From the sorting step, the large particles, i.e. the effluent, are fed to a refiner 9 ', which performs only the pulp decomposition necessary for the second sorting step of the process and the other sorting steps to validate the coarse mass.

Thus, in already existing plants, the refiner 9 'alone performs the necessary decomposition of the pulp, but the efficiency of the system can still be increased, because the ozone-treated pulp is easier to decompose than the untreated pulp.

With the method according to the invention, the amount of ozone required can be reduced by about a third compared to conventional ozone treatment methods for pulp in the wood processing industry. This lowers both operating costs and means a significant reduction in the cost of capital. The method according to the invention further results in a pulp product with optimal strength properties. At the same time, the individual process steps can be performed even more easily and with the lowest possible energy consumption. This applies not only to the dewatering of pulp fractions containing coarser particles, but also to their possible post-grinding when the ozone treatment is completed, as ozone-treated pulp is much easier to defiber than untreated pulp.

Claims (7)

A method for treating cellulosic pulp, wherein the pulp is fractionated in fractions according to the particle size (fiber length) and wherein one of the fractions is treated with ozone, characterized in that the concentration of the fractions is changed before the ozone treatment, so that fractions with coarse particles is concentrated by separating them from liquid and ozone is treated at a very high solids content and so that liquid which is separated from coarse-particle fractions is supplied mainly with fine particles, so that fractions with fine particles are ozone-treated in very dilute conditions, are combined to form a finished treated pulp. Process according to Claim 1, characterized in that the fine particle fraction after ozone treatment is mixed with a mass fraction of fine particles not treated with ozone, and that this mixture is combined with a mass fraction of coarse particles treated with ozone. Method according to claim 1 or 2, characterized in that the organic compounds which are separated in the ozone treatment of coarse particle fractions are combined with fine particle fractions before or during the treatment thereof with ozone. Process according to any of the preceding claims, characterized in that one or more of the fractions, preferably those with coarse particles and high solids content,