FI91171C - Method and apparatus for precipitating fiber suspension - Google Patents

Description

91171 i

Method and apparatus for precipitating a fiber suspension

The present invention relates to a method and an apparatus for more efficiently separating a liquid from a liquid / fiber suspension by dividing the suspension into two parts, one containing mainly liquid and the other both fibers and liquid. The method and apparatus according to the invention are particularly well suited for thickening fiber suspensions in the low (0.5 to 5%) range of consistency of the paper and pulp industry.

There are processes in the pulp and paper industry that have to be carried out at a low consistency, even below 1%. Such processes include, for example, normal and covered 15 wheel cleaning. The pulp suspension of the PyiSrr cleaning fraction is passed to the next process step, which may be a precipitator or a paper or dryer batch machine. In any case, the next step after hydrotreating is almost always precipitation, in which case a low-consistency precipitator 20 is required, which must be able to handle large Maari fiber suspensions and remove myds large Maari liquid from the suspension, although the increase in consistency is not very high. ).

25 Even the trend in paper machines today is to use ever higher consistency densities (1 to 3%) to improve the cost structure and quality level of the paper machine itself and the finished product, so that the consistency of the pulp from the hydrotreaters is too low for the paper machine.

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Precipitation is carried out according to the prior art with different types of silicone disc or drum precipitators and arc screens. With conventional drum or disc precipitators, dewatering or precipitation is based on gravity (so-called Gravity Deckers), suction-35 precipitation (so-called vacuum filters) or pressure precipitation (so-called pressure filters).

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In gravity precipitators, the precipitation takes place with a drum made of wire-punched perforated sheet metal. The difference in bale required for precipitation arises from the silent surface difference between the inlet of the pulp and the filtrate space. The pulp can be filtered either from the inside of the rune to the outside from the outside, which is the most common. In use, the diameter of the poem can be 4 m, of which 60% is, for example, submerged. The sisal content of the runes is 10-15%. The maximum pressure difference is thus about 20 kPa. At the bottom dead center of the rune 10, the paln difference is zero, from which it also increases when the head of the inlet basin is depressed to said maximum value. It follows from T3 that little precipitation occurs on either side of the lower dead center. However, the same situation prevails in the part of the poetry Silia, which is not submerged. The rune surfaces of the gravity precipitator are significantly affected by inefficient use. The operating power of the drum part in the effective operating socket varies depending on the pressure difference with respect to the filtrate surface. The specific precipitation capacity of gravity-force filters varies depending on the mass 20 and the driving conditions, but is typically 400 to 700 1 / m2 / min. Precipitates of this type are used to pre-precipitate a dilute mass, e.g. from 0.5% to 1.5-5%.

25 The filterable surface of the drum is kept clean or open to flow by moving it against the filtrate or using air to clean it. For example, in a mill producing 500 tons of 90% pulp, a filter with a diameter of 4 m and a length of 7 m with an area of about 30 88 m2 of wire surface is needed to precipitate the pulp from 0.5% to 1.5%.

In suction drum precipitators and disc precipitators, the pressure difference required for filtration is provided by the suction foot. Precipitators of this type differ from gravity precipitators in that a mass layer is formed on them. This means that the consistency of the precipitator fraction is 8 to 14%. Suction or disc

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91171 The settling of the 3 precipitator is of the same order as in the gravity filter. The difference is that on the surface to be filtered, when it is immersed in the pulp suspension, an attempt is made to form a pulp path by means of Suction. From the web formed on the part of the drum 5 which rises above the surface of the suspension, the filtrate is sucked in so that the consistency of said removal is 8 to 14%. It is clear that when forming a mass layer on the surface to be filtered, the dewatering of the layer through the layer is substantially slowed down.

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It is not advantageous to use precipitators of this type when aiming for pre-precipitation, but applications where the removal consistency requirement is high are suitable. The specific precipitation capacity varies from 50 to 300 l / min / m 2 depending on the pulp quality and conditions. Compared to the previous example, 2 suction filters of said size would be required in order to achieve a consistency of 10%. The advantage of the disc filter over the suction filter is that the filter surface can be made to the same volume considerably.

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The pressure filter differs from the suction drum filter in that the pressure difference to be filtered is provided by compressed air. The filtration rate does not differ significantly from the suction drum filter.

25 Arc screen type precipitation is based on gravity filtration. The suspension to be precipitated is pumped onto an oblique filterable surface. The precipitation capacity in use is 3-5% and the specific dewatering capacity is of the same order as with drum filters. The advantage is that the device has no mechanically moving parts. The disadvantage is the high susceptibility of the device to clogging, because it is difficult to arrange efficient cleaning. Arc screen type precipitators are used in the pulp industry when it comes to waxy precipitation and pulp capacity.

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Conventional precipitators of the type described above are characterized in that the precipitation is carried out with a very small pressure difference in more or less open equipment and a part of the hydraulics on the surface to be filtered. The small difference in pressure-5 and the partial use of the filtration surface result in a low fluid combustion capacity. The open structure and the principle of dusting, in turn, mean that the pulp and the filtrate may contain air. The air in the pulp weakens the known pulp leaching property 10 Alva decisively.

In recent years, A. AHLSTROM 0Y has entered the market in accordance with Finnish patent applications 873020 and 874854, where the dusting pad treads from a large number of the remaining 15 conventional clones. In Malnltul applications, kgsltellggn e.g. a precipitation method in which the pulp is plucked from the outside air into a closed device consisting of a sealing surface and a surface passing relative thereto, in which pressure / suction pulses are applied to the screening surface 20 due to a difference in speed of the surfaces to break and mix the pulp layer. Most commonly, the screen surface is a drum arranged in an upright position, and the sliding surface relative thereto is a substantially cylindrical rotor 25 arranged on the surface of the screen surface, on the surface of which either cap-like protrusions are arranged to cause wage differences. In all cases, however, the screen surface has been a sileg, perforated sheet material.

30 This type of device has a specific precipitation capacity of about 4500 to 5500 1 / m2 / min. However, it has been found in the tests that a thin, but still non-precipitating, non-woven mat is formed in the vicinity of the screen surface, the liquid leaving the lg of the suspension having to be compressed to leave the filtrate space. In order for that nonwoven mat to be effective

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91171 5 dispersed rotor pressure differentials, said eliminators had to be added More turbulent energy to the suspension, for example either by reshaping the bodies to increase the speed, which would cause the gold mat to disintegrate but at the same time increase energy consumption strongly.

In the present invention, the above problem is solved by arranging 10 high-intensity microturbulence members on the screen surface, and by reducing the size of the apertures in the screen surface so that the diameter of the apertures (holes) is about 0.15 to 0.2 nun. The slag of the suspension in the direction of the sieve surface caused by the members causing the pressure differences of the tail rotor is disturbed by the surface of the sieve-15, only if the gold mat sticking along the surface of the sieve surface breaks and mixes with the rest of the suspension, smoothing the consistency. However, this is not a complete fluidization of the suspension in the precipitation state, as there is no need due to the fact that it is possible to remove the desired amount of liquid without having to break all the smaller fiber flocs in the suspension. In addition, the microturbulence in the vicinity of the screen surface keeps the floc size of the circulating mass as small as possible, making it easier for the "free" liquid between the fibers and the small flocs to escape and exit the filtrate tank. Of particular importance to the members causing the turbulence of the screen surface is that they do not substantially affect the main flow direction of the fiber suspension, which still remains parallel to the circumferential surface of the screen. It is thus characteristic of our invention that an attempt is made to cause turbulence of high intensity exactly where it is needed, i.e. to the proximity of the screen surface. Thus, it is already possible to divide the tasks of the precipitating device correctly with the rotor and the screen surface 35, i.e. so that the rotor simply rotates the mass along the screen surface 6 surface, it has been possible to reduce the specific energy consumption of the device and increase its capacity.

Of course, a device is known in the prior art in which means are arranged on the sieve surface to prevent the formation of non-fibrous on the sieve surface. This device is described in detail in FI patent-10 application 771541, which focuses on the handling of pulps in the consistency range of 5 to 25%. For example, in Figures 5-8 of said application, the apparatus is applied to pulp precipitation. The screen surface according to the present application is provided with sparsely arranged rib-like protrusions, which are said to be preferably about 3 to 18 mm high. As can be seen from the height of the fins, it is by no means a matter of generating a light microturbulence on the sieve surface, but of fluidizing the suspension between the rotor and the sieve surface in the entire precipitation space, as shown in the said application myOs kSy. The reason is that the precipitation of a mass in a consistency range of more than 5% (so-called medium-thick range) requires completely different conditions and measures than operating in a range of 1% consistency due to e.g. that the liquid in the suspension is separable from the fibers at a low consistency in a completely different way than at a consistency of more than 5%. The mass of more than 5% forms, especially when precipitating, and as the tail of the consistency rises, large masses of pulp with strong silky bonds, which can be broken for the sole reason that the mass 30 could overflow in the precipitator. On the other hand, the pulp must be timed to fluidize completely throughout the precipitation space, because otherwise the liquid could not be effectively separated from the medium-density or high-density pulp. However, fluidization throughout the space requires large 35 ma & rat energy, so it must be avoided whenever possible. A sieve plate and a rotor with relatively high protrusions of the type described above cause a strong turbulence extending over the entire suspension area, but the average intensity of the suspension is low throughout the treatment area.

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It should be noted that in the solution according to the FI application in question, the number of ribs or protrusions of the screen surface is relatively small, i.e. they are placed on a very sparse screen surface. For example, in the solution 10 of Figure 6, the screen surface has only six ribs. This arrangement created a strong but intense low turbulence that damped rapidly. The attenuation of the turbulence is greatly facilitated by the infiltration of the liquid through the sieve surface, since most of the pyrofoil is present with the filtrate.

The deposition method according to the invention is characterized in that microturbulence is induced on the screen surface by means of the screen surface, with which the non-fibrous mat deposited on the surface is decomposed or its formation on the screen surface is prevented.

The precipitating apparatus according to the present invention is characterized in that epitho uniformities are arranged on the screen surface, which, together with the speed of movement of the fiber suspension 25, results in a high microturbulence

The method and device according to the invention will now be described in more detail with reference to the accompanying figures, in which Figure 1 shows the specific structure of a precipitating device using the device according to the invention, Fig. 2a and ... c shows a preferred embodiment of the device according to the invention. of the embodiment of Fig. 2, and Fig. 4 shows the test arrangement used in testing the device according to the invention.

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According to Fig. 1, the precipitating device comprising the device according to the invention consists of a body 1, a lid 2, a base 3 and drive devices 4. The body 1 has a pulp core 5, a filtrate outlet 6, a precipitated outlet 7 and a possible scrap or reject 8. screen cylinder 9. Inside the screen cylinder 9 there is a rotatably mounted rotor 10 on the surface of which there are members 11 which release the pulp layer. If desired, a device for removing light contaminants such as plastic or the like 12 can also be connected to the device.

Figures 2a to ...c show a screen cylinder solution 9 according to a preferred embodiment, made of a substantially planar smooth metal or similar plate 20 with small holes 22 throughout, preferably 0.1 to 0.25 mm in diameter, having a size corresponding to its deposition properties. other openings. In some cases, at most ✓ if the particle density of the suspension to be precipitated is higher, a somewhat larger hole / hole size may be used. Irrespective of the location of said holes / openings 22 in the plate 21, irregularities 24, preferably shallow grooves, have been machined on the surface 23 facing the suspension side of the plate 22, the shape of which may differ greatly from that shown in the figure. However, it is most important to note that the machined grooves 24 need only be about 0.2 to 1.0 mm deep. Such surface roughness results in a sufficiently high intensity microturbulence specifically for the silence of the screen surface, whereby the relatively thin nonwoven mat formed on the screen surface due to its low consistency is broken or prevented from forming. Experiments have shown, among other things, that the thickness of the turbulent layer with a high intensity above 0.5 nun can be prevented from felting on the screen surface. If the thickness 5 of the turbulent layer in question significantly exceeds 2 nun, the amount of myds turbulence increases so that the possibility of the fibers getting into the filtrate increases.

Fig. 3 shows, as another preferred alternative for manufacturing a screen plate 9 according to the invention, a plate 26, 10 in which slit holes 27 corresponding to the plate of Fig. 2 are made, but on the surface 28 of which irregularities such as strips 29 or the like are attached. It is conceivable to use myds, for example terds yarns or the like, which are easy to choose so that they have a higher wear resistance than the base material because they come into contact with the consuming flow. Of course, it is possible that said strips 29 or wires are attached to the plate before machining the screen openings 27, whereby it is possible to obtain 20 screen surfaces at the myds strips 29.

The apparatus described above in connection with various embodiments operates by injecting a low consistency fiber suspension into the apparatus by pressure, flowing from the hardened direction of the apparatus 25, preferably to the silent precipitation state of the rotor 10 and screen cylinder 9, and preferably tangential to the rapidly rotating rotor 10. the fiber suspension acquires a swirling motion in the precipitation space in the silence of the screen cylinder 9 and the rotor 10 30. The small-hole sieve plate 9 fastens through the filtrate, but not the fibers. A layer of precipitated mass tends to form on the surface of the screen sieve plate 9, which is disintegrated by the circulating motion of the precipitated suspension and the microturbo-35 lens generated by the surface irregularities 24,29 of the surface of the screen plate 9. The members on the rotor 10 or arranged on the surface of the rotor 10 cause low frequency 10 pressure / suction pulses in the suspension in the precipitation state, mixing with the fresh suspension already precipitated and decomposed by microturbulence, thus keeping the consistency of the suspension uniform throughout the precipitation state. In the solution of our invention, the rotation of the rotor 10 initiates the crude turbulence of the intensity in the entire precipitation state, which also contributes to the mixing of the suspension described above. It should be noted in culture that the consistency of the suspension increases steadily with the passage of the precipitated mass 10, correspondingly decreasing the mggrg of the liquid infiltrating the target surface.

The experimental set-up according to Figure 4 has been studied methodically and in the laboratory. Reference numeral 30 denotes a circulation circuit 15 from which the pulp is pumped by a feed pump 31 to a test screen device 32 via a feed valve 33. If necessary, the pulp can be redirected back to the recirculation tank 30 directly from the valve 34 of the outlet 32. A portion of the non-precipitated pulp 35 was taken and a total of 36 of the precipitated pulp was taken from the thick pulp 36. A sample of the filtrate was taken from a total of 38 filtration valves after 39. Venttlllelllg 37 and 39 apply the desired pressure situation to the screen device 32.

25 The area of the screen cylinder of the test device was 0.4 m2, of which the open area was 10% with a hole size of 0.2 mm. The sliding surface according to the invention was made in such a way that substantially axial grooves with a depth of about 0.5 mm were machined on the surface of the smooth perforated plate. The dimension parallel to the bottom plane of the groove was about 1.5 mm, one of the side walls of the groove was perpendicular to the screen surface and the other formed an angle of 30 ° with the screen surface. The radial dimension of the drum between the grooves of the jg & v & n ridge was about 0.35 mm. Thus, the vM of the ridges is just over three milli-35 meters. It is essential for the screen plate according to our invention, and in particular for its non-uniformity, that the height of the screen

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91171 11 divide into stacks 0.2 to 2.0 mm, preferably into stems 0.2 to 1.5 mm And that the stack distance of these is 1.0 to 10 mm, preferably 1.0 to 6.0 mm.

5 In the test runs, it has first been shown that when using a sieve cylinder with an uneven surface, the power consumption per tonne of precipitated pulp has been lower, i.e. the specific power consumption has been lower than when using a single cylinder. The explanation for the tempered unexpected phenomenon 10 is that there is a continuously thin deposited nonwoven mat on the screen surface of the silea, which makes it difficult for the liquid to seep through the screen surface. The surface irregularities, in turn, give rise to high-intensity microturbulence, breaking the precipitated nonwoven and mixing the mytts with some 15 masses, whereby the liquid content of the surface layer is higher. The corresponding Kay explains myOs that in tests the specific precipitation capacity has been found to be more than 80% higher when using an uneven plate. The silent 'free liquid' of the fibers makes it easier to come into contact with the screen surface 20, and thus the mytts more easily seep through the surface.

Comparing the computational turbulence level in the vicinity of a smooth and uneven screen surface, the following table is obtained as a function of flow rates: 25

Flow rate Turbulence level m / s Smooth surface Uneven surface 5 1.0 2.5 10 1.7 3.5 30 20 2.7 7.6

It is noted that a flow / rotation velocity of about four times the surface is required to achieve a certain level of turbulence. On the other hand, it is contemplated that on a non-uniform surface 35 the level of turbulence at the same rotational speed is 2-3 times that of a smooth surface.

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In the actual precipitation tests, the following result was obtained: 5 si plate uneven plate - input consistency to the bed 0.5% 0.5% - consistency of the precipitated mass 1.5% 1.5% - consistency of the filtrate approx. 0.03% approx. 0.06% - dewatering capacity. 1 / m2 / rain approx. 5500 approx. 10000 10 - pressure difference during test run 20 - 40 kPa 20 - 40 kPa

The experiments carried out show that, firstly, with a pressure precipitation method and apparatus, it is possible to achieve a multiple capacity with respect to conventional precipitators. From the above result, it is found that, as already discussed above, the specific precipitation capacity is 80% higher when using an unbalanced slate plate when using a slurry plate. When comparing power consumption, it is found that the power required when using an uneven board is zero 80% of the value of 20 smooth boards. Thus, the use of a mucosal precipitation plate of the invention can be considered to be almost 130% more efficient if the power used to precipitate the amount of pulp used is used as a reference. The invention of our invention has the advantages of lime pulp handling on its 25 sides. Both the filtrate and the precipitated pulp are pressurized from the bottom of the palletized dusting pad, so that there is a great deal of freedom and space-saving potential in the placement under factory conditions. It is impossible for llsaksl to get into the pulp.

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In the test run, it is clear that the consistency of the fiber suspension increases rapidly from the feed to the discharge bed, whereby it is possible to intensify the precipitation event by changing the size of the surface unevenness. This is due to the fact that the flocs formed from the gold are, as the consistency increases, the harder the single cult. The loose the strip is so easily detached, so that the irregularities are the same size along the entire length / height of the screen surface. Thus, a screen plate with one or more erl sizes with 5 irregularities is used in the bed. The most practical arrangement has been completed. ni in that the inlet stream has the smallest irregularities, the middle is slightly larger and the precipitated pulp outlet is the largest.

10 As can be seen from the above, a new type of Alva precipitation method and process has been developed which is able to eliminate the disadvantages of the prior art devices with new mucus problem areas. It is clear that only a few preferred device alternatives and applications have been described above, which are not intended to limit the invention to what is set forth in the appended claims, which alone define the subject matter of the invention and the scope thereof. Thus, it is clear that both the surface and the moving surface may be different in shape from the cylinder, the essential to the molded member being only that they are substantially rotationally sinusoidal, the cylindrical, conical and spherical surface, or some combination thereof . MyOs exemplified grooved screen surface can be used in either direction, i.e., the perpendicular side surface of the groove vol can be either the end surface of the selected ridge of the grooves or the discontinuous surface.

Claims (15)

A process for dewatering the paper and cellulose industry's fiber suspensions through the low consistency range (1 to 5%), in which process a fiber suspension is fed into a drainage space provided with at least one side surface and saturated in proportion to a screen surface, whereby liquid is separated from the suspension by the screen surface with the help of pressure, characterized in that by means of irregularities on the screen the micro-turbulence is produced by the screen surface, whereby the fiber mat deposited on the surface is degraded or its appearance on the screen surface is prevented. 2. Dilution method according to claim 1, characterized in that in a fiber suspension low intensity turbulence is generated, the movement of the fiber suspension is maintained in the drainage space and with the help of inequalities on the screen surface high intensity micro turbulence is achieved. 20 3. Dilution method according to claim 1, characterized in that with the help of organs belonging to the actual screen surfaces in conjunction with the rate of movement of the fiber suspension, high intensity microturbulence rising from the screen surface is generated, whereby the fiber mat deposited on the screen the screen surfaces are prevented. 4. Device for dewatering the paper and cellulose industry's fiber suspensions within the low consistency range (1 - 5%), which device consists of a stand (1), a lid (2), inlet and outlet pipes (5, 6 and 7) for the respective mass input, the filtrate and the deposited mass, and of at least one screen surface (9; 23, 28) provided with openings and arranged inside the frame (1) and of a surface area relative to this screen surface or a means (10) in proximity, characterized therein, that recesses 18 and / or projections (24, 29) are arranged on the screen surface (23, 28) which, in conjunction with the rate of movement of the fiber suspension, generate high intensity microturbulence, whereby the fiber mat which is prone to formed in the immediate vicinity of the silicate (9; 23, 28) is degraded to optimize the dewatering process. Drainage device according to claim 4, characterized in that the screen surface (9; 23, 28) consists essentially of a screen plate (9) which has one or more openings (22, 27. of different sizes). Drainage device according to claim 4, characterized in that the diameter of the sieve surface (9; 23, 28) hole (22, 27) or slit on the feed duct is at most 0.2 mm. 7. Dilution device according to claim 4, characterized in that grooves (24) are machined on the screen surface (23), depths or the like to generate micro-turbulence. Dilution device according to claim 4, characterized in that fixed band-like, wire-like or nodular projections (29) are provided on the screen surface (23) to generate 2. microturbulence. Drainage device according to claim 4, characterized in that the openings (22, 27) in the screen surface (23, 28) are arranged independently of the position 30 of the bumps (24, 29) on the surface or their future position. Dilution plate performing the process according to claim 1 or 2 and used in the drainage device according to claim 4, characterized in that it consists of a slab plate (21, 26), filter openings (22, 27) therein and irregularities (24, 29). arranged on that side of the surface (23, 28) of the plate (21, 26), the mass to be dewatered is fed. II 19 91171 11. Dilution plate according to claim 10, characterized in that the elements (29) on the screen surface (27) are provided with strip-like, wire-like or nodular projections. 5 Dilution plate according to claim 10, characterized in that the irregularities (24) on the screen surface (22) are formed by machined grooves, depressions or the like. Dilution plate according to claim 10, characterized in that the height of the irregularities (24, 29) is between 0.2 - 2.0 mm. Dilution plate according to claim 10, characterized in that when the filter openings (22, 27) are made of holes, their diameter is between 0.1 - 0.25 mm. Dilution plate according to claim 11 or 12, characterized in that the distance between the projections 20 (29), the depths (24) or the corresponding on the screen surface (23, 28) is between 1.0 - 10 mm.