FI57483B - OVER ANCHORING FOR TORKNING AV CELLULOSA - Google Patents

Description

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Patent · and the National Board of Registration (44) Date of publication -, n

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Sweden-Sweden (SE) UU58 / 7I

(71) MoDo-Chemetics Aktiebolag, Fack, 891 01 Örnsköldsvik, Sweden-Sweden (SE) (72) Bengt Olof Arvid Hedström, Gothenburg, Sweden-Sweden (SE) ("Jk") Leitzinger Oy (5U) Method and apparatus for drying cellulose The present invention relates to a process for drying cellulose which, in the form of flakes together with a gas, is passed through a drying apparatus comprising a plurality of drying units constructed in substantially the same manner and connected in series, each consisting of a drying section and a final drying section. , wherein the mixture of gas and cellulose flakes entering the beginning of the dryer is passed in repeated heating-heating equalization cycles in such a way that heat is continuously applied to the gas and the flowing cellulose flakes in each heating section and that the gas and cellulose are smoothed by the heat transfer between them.

The invention further means a drying device for carrying out the above-mentioned method, which device comprises a number of drying units constructed in substantially the same way and connected in series with each other. each of which consists of a heating part and a temperature equalizing part connected to its end end, the drying units being connected in series by transport fans in such a way that the end of the heat equalizing part of the previous drying unit is connected to the suction side of the transport fan that in each drying unit the heating part comprises a first conveying pipe surrounding the steam pipes running along it and that the temperature equalizing part comprises a second conveyor pipe arranged substantially parallel to and connected at its end to the first conveying pipe.

For the so-called flake drying of cellulose, the fibrous web is usually prepared by removing water from the fiber suspension and compressing it very tightly in a press suitably formed for the purpose, e.g. a roll press. The fibrous web thus obtained is torn into flakes by a tearing device, which is dried by allowing them to flow together with the warm gas for some time.

Known flake drying methods and equipment have many drawbacks. Heat recovery is poor when large amounts of gas are required to transfer heat to the goods to be dried. These disadvantages are particularly great in pulp mills with a high hot water demand, as is the case for pulp mills. Excessive gas temperatures during drying can in some cases easily compromise the quality of the cellulosic pulp. Variations in mass transport through dryers with congestion and consequent clogging of the ducts of the apparatus are common.

Swedish patent publication 216 788 discloses a method for drying a cellulose pulp flake. The drying takes place in a mill with a fan effect and takes place in such a way that the pulp in particulate form is fed to the mill in an air flow with an outlet temperature of 300-550 ° C. In the mill, an efficient mixing of air and pulp is achieved, whereby the pulp is simultaneously disintegrated. The mixture is subjected to a turbulence treatment in which the amounts of air and pulp and the turbulence are such that the water evaporates rapidly from the pulp and thus the air cools rapidly so that the pulp does not heat above 120 ° C, the pulp and air mixture is then blown into the cyclone. where the mass is separated from the air. Drying takes place over a short period of time, usually less than 5 seconds.

The material loading in this method is similar to the present invention. However, the use of high air temperatures and short drying times can be detrimental to pulp quality, in addition to which the implementation of the process may be economically disadvantageous due to the high energy consumption and low potential for energy recovery for reuse.

The object of the present invention is to eliminate as far as possible the drawbacks described above which have hitherto been associated with the methods and devices known hitherto.

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The invention solves the problems caused by heat transfer conditions between gas and pulp particles by presenting a method and an apparatus in which heat exchange takes place sequentially along a pulp particle transport distance with a suitable mixing ratio of pulp particles and gas, whereby good they are transported. Steam with a low saturation pressure from 2-3 aty to 12 aty or more can be used for heating, depending on local conditions. According to the invention, it becomes possible that the drying of the pulp can take place at a suitable temperature while the spent gas can be used for the production of hot water.

The method according to the invention is essentially characterized in that the amount of cellulose flakes and gas are each adjusted in their own known manner so that the material load in the heating parts is kept below 0.35 kg of dry cellulose per kilogram of entrained gas and at the same time heat input and temperature equalization are adjusted the gas leaving the imaging device maintains a humid temperature not below 60 ° C and a dry temperature not exceeding 120 ° C. The device according to the invention is characterized essentially in that the dimensions of the steam pipes in each heating part are such that they are arranged substantially evenly in the cross-sectional area of the inner part of the transport pipe so that the hydraulic diameter of the heating part does not exceed 200 mm.

When the material load exceeds 0.35 kg of dry cellulose per kilogram of flowing gas, a fiber network is formed in the transport system, because then no fibers can move but come into contact with other fibers. If all the fibers in the ideal position were straight, a fiber network would already form at loads of 0.05 and 0.10 kg of dry cellulose per kilogram of entrained gas, but since virtually the cellulose pulp is not completely decomposed and the fibers twisted together, a material load can be allowed without great risk. in the heating parts of the dryer up to 0.35 kg of dry cellulose per kg of gas. At current material loads, the hydraulic diameter of the heating part must be limited so that the velocity profile in its transport pipes does not receive any non-stable (straight) part of the same order of magnitude as the accumulations formed by the material. If such unstable parts are present, a slight deformation of the velocity profile is easily formed, which may cause variations in transport with consequent clogging. The device size for the fluffed mass has been experimentally proven to be 50 to 100 mm, which corresponds to the "standard part" of the speed profile in a power line with a hydraulic diameter of 200 mm. The hydraulic diameter of the heating element should therefore preferably not exceed 200 mm. In order for the heat of the gas leaving the dryer to be economically utilized for the production of hot water, the humid temperature of the gas must be at least 60 ° C. Practical experiments have also shown that during drying times which are actual in the drying device according to the invention, the temperature of the outgoing gas must not exceed 120 ° C, so that the quality of the pulp is not exposed to the risk of damage.

The installation costs of the device according to the invention are lower than in previously known devices for pulp drying, although low pressure steam is used for heating, depending largely on the heating in a number of drying units by temperature equalization between the cellulose flakes and the transport gas after each drying unit. Due to the fact that the drying heat is passed successively during the transport of the fly particles through the device, the amounts of gas to be treated become small and, as a result, the transport fans and cyclones, etc. are relatively small, which helps to reduce costs.

The device according to the invention requires a particularly small space due to the fact that the conveyor can advantageously be arranged vertically. The entire drying plant can be located outdoors, in which case only weather protection is required for motors and instrumentation, which means minimal construction costs.

The apparatus readily allows the use of a gas other than air (e.g., a chemically inert gas such as deoxygenated air) for drying, as well as the easy recovery of the liquid removed during drying (e.g., acetone-extract drying). Thus, particularly advantageous drying conditions can be achieved.

The device will be described in more detail below with reference to the figures of the accompanying drawings.

Fig. 1 is a schematic side view of two conveying fans with their abbreviated conveying conveyor devices arranged above them, which together form two drying units of the device.

Fig. 2 is a sectional side view of Fig. 1 taken along line I-I.

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Figures 3-5 show details of a steam pipe system inside heated transport pipes.

Fig. 6 schematically shows a shortened side view of a built-in drying device according to the invention.

Fig. 7 shows a plan view taken along the line III-III in Fig. 6.

Figure 1 shows the conveying fans 1 with their drive motors 3 directly connected and the conical pipes 5 connected to the suction side of the fans. with heated steam pipes and positioned so that their center lines coincide with the center lines of the outlets of the transport fan 1. The transport pipes 7 are provided at their upper end with 180-degree bend pipe wedges 13, the transport pipes being connected via conical bodies 15 to a second transport pipe 17, the cross-section of which is substantially square and which is tightly fitted next to the transport pipe 7. The conveying pipe 17 becomes round at its lower end when it joins the conical pipe 5, which in turn is connected to the suction side of the next conveying fan. The bend pipe 13 is formed in such a way that its outlet diameter is reduced by the most suitable 30-40% reduction in the total surface area localized to the inner circumference of the bend pipe when moving to the conical body 15. Figure 2 shows inlet pipes 19, shut-off valve 21 and steam distribution pipes 23. , shut-off valve 27 and condensate outlet pipes 29. Figures 3 and 4 show parts of a vertical section through the transport pipe 7 with internal steam pipes 11. Figure 3 shows the upper part of the transport pipe 7 and how the steam pipes 11 are welded to the distribution pipes 23. how the steam pipes 11 at their lower end are provided with a conical body which is welded to the collector pipes 25. Fig. 5 shows a horizontal section of the transport pipe 7 along the line II-II in Fig. 4.

Fig. 6 shows an abbreviated side view of a built-in drying device with an inlet pipe 3 3 and an outlet pipe vj,. Fig. 35 is a plan view taken along line III-III of Fig. 6, showing how the nine drying units are combined into a drying device.

The drying device is provided with the required control devices known per se, which are not shown in the figures, for controlling the supply of cellulose flakes, gas and heat and the transport speed and thus for adjusting the durations in different parts of the drying device.

The drying device operates in such a way that the mixture of cellulose flakes and gas (usually air) is introduced into the device under overpressure through an inlet pipe 33 extending to the suction side of the first conveying fan 1 conveying the mixture vertically through the cone body 9 and conveying pipe 7. fitted to the steam pipes through the distribution pipes 23. Due to temperature differences between the mixture and the outside of the steam tubes, heat transfer occurs from the steam tubes to the mixture of air and cellulose flakes. As a result of said heat transfer, they cool to a steam pipe temperature below the saturation temperature of the steam, as a result of which condensation of steam takes place on the inside of the steam pipes, the heat of condensation being transferred to the walls of the steam pipes. The formed seal drains down and collects in the collecting pipes 25, from where it is led from the device through the outlet pipe 29. The heat given off by the steam is transferred to the mixture and first to its air, which quickly absorbs the heat. There is a continuous transfer of heat from the heated air to the cellulose flakes. These are not able to absorb heat as fast as air, which creates a temperature difference between the air and the cellulose flakes on the way through the transport tube 7. In order to reduce the risk of cellulose flakes sticking to the distribution tube 23, these are arranged at different levels inside the transport tube 7. The same applies to the collector tubes 25, the different positioning of which in the height direction facilitates the passage of the mixture so that the risk of clogging is reduced. The purpose of the plow-shaped covers 31 welded to the distribution pipes 23 between the steam pipes 11 is also to prevent the transport pipe 7 from clogging. After passing through the conveying tube 7, the mixture first enters the bend tube 13, where its upward flow is folded down 180 degrees through the temperature compensating part of the drying unit, which is formed not only by the bend tube 13, the conical pieces 15, 5,

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7 57483 jet tube 17 and conveying fan 1. In this part of the drying unit, there are no heating devices, so that the cellulose flakes during their passage have time to absorb most of the heat of the surrounding air, whereby the temperature differences between the cellulose flakes and the air are considerably reduced. A particularly favorable temperature-smoothing effect is obtained in the transport fan 1 and immediately thereafter due to the high relative velocities of the cellulose flakes and air. The treatment of the mixture described above is then repeated in series drying units, after which the mixture exits the apparatus through an outlet pipe 35 from which it is passed to a cyclone (not shown) to separate the pre-dried cellulose flakes from moist air.

Due to the fact that the bend tube 13 is provided with a flow area constriction placed on its inner circumference and that a suitably shaped cone piece 15 is fitted immediately after the bend tube, the emission normally occurring at the end of a conventional bend tube and immediately thereafter at its inner edge is reduced, eddy currents in the discharge area also decrease, which may otherwise cause cellulose flakes to accumulate in the area following the inner edge of the bend. Such agglomerates pose a risk of jerky transport, leading to clogging of the dryer.

The above description in connection with the accompanying drawings gives only an example of the use of the invention, and many different alternatives are possible within the scope of the claims set out below. > *: · -: · f *;

Claims (2)

57483 A method for drying cellulose which, in the form of flakes, together with a gas, is passed through a drying device comprising a plurality of drying units constructed in substantially the same manner and connected in series, each consisting of a heating core and a thermally equalizing part is carried out in repeated heating-heat equalization cycles in such a way that heat is continuously applied to the gas and the flowing cellulose flakes in each heating part and that in each temperature equalization part the temperature differences between the gas and the cellulose flakes is regulated in such a way that the material load in the heating components is kept below 0.35 kg of dry cellulose per kilogram of flowing gas; ua and at the same time the heat input and the temperature equalization are each adjusted in a known manner so that the gas leaving the dryer maintains a humid temperature which does not fall below 60 ° C and a dry temperature which does not exceed 120 ° C. A drying device for carrying out the process according to claim 1 for cellulose drying, which in the form of flakes together with the gas is made to flow through a drying device comprising a plurality of drying units constructed in substantially the same way and connected in series, each consisting of a heating part (9, 7, 11) and an end the drying units (13, 15, 17, 5) with the drying units connected in series by means of transport fans (1) in such a way that the end (5) of the temperature equalizing part of the previous drying unit is connected to the suction side of the transport fan (1) to the next initial end (9) of the drying unit Ijfcnating part and that in each drying unit it comprises a first conveying pipe (7) surrounding the steam pipes (11) running along it and that the temperature equalizing part comprises a second conveyor pipe (17) arranged substantially parallel i with the first transport pipe (7) and is connected at its end to the fact that in each heating part (9, 7, 11) the dimensions of the steam pipes (11) are such that they are in the transport pipe (7) arranged substantially evenly over the cross-sectional area of the inner part at such distances from each other that the hydraulic diameter of the heating part does not exceed 200 mm. t.'Sk '.L s AU 57483