FI87996C - FOERFARANDET FOER FILTRERING AV SLAM ELLER DYLIGT AEMNE MED KONTINUERLIGTFUNKTIONERANDE TRYCKFILTER OCH EN FILTER FOER TILLAEMPNING AV FOERFARANDET - Google Patents

Description

87996

METHOD OF FILTERING A SLUDGE OR SIMILAR SUBSTANCE IN A CONTINUOUS PRESSURE FILTER AND A FILTER FOR APPLYING THE METHOD - FÖRFARANDET FÖR FILTRERING FIG

The invention relates to a method for filtering a slurry or the like in a continuous pressure filter having a rotating tank, in which process the slurry and the compressed gas are introduced into the filter, and in which the filtrate and the solid accumulating on the tank are removed from the filter. The invention further relates to a device for applying the method.

Filters are used in the process industry to separate liquid and solid. There are two main types of filters: intermittent and continuous.

In typical intermittent filtrations, the sludge to be filtered is usually pumped into filter elements consisting of filter plates, cartridges or the like. In these elements, the pressurized slurry passes through the filter medium, whereby the solid contained in the slurry remains on the surface of the medium, forming a solid cake as the liquid passes through the medium outside the filter. The cake formed on the filter can; In addition, in many filter models, a further concept is introduced, for example by squeezing and blowing compressed air through the cake to reduce its moisture content. Before the new filtration step, the filter is opened and the solid cakes are removed from the filter. ; either manually or automatically.

The length of the filtration period in such filters is typically 5 to 15 minutes, in some cases several hours. In this type of filter, the sludge is treated with an overpressure (typically 5-15 bar) relative to normal atmospheric pressure. . whereby the formation of the solid cake and its further processing takes place rapidly.

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If the cake is further processed immediately after filtration as a continuous process, a compensating silo is required after the filter, in which the amount of solids entering the silo periodically is converted into a continuous outgoing mass flow.

Continuous filters are generally drum or disc filters in which the surface of a rotating drum or disc coated with a filter medium, most commonly a cloth, is brought into contact with the slurry. There is a vacuum inside the drum or disc, as a result of which the liquid contained in the slurry passes through the fabric to the filtrate outlets and the solid remains on the surface of the fabric. As the cake travels away from the slurry with the rotational movement of the drum or disc, air continues to flow through the cake under the effect of vacuum, which dries the cake. The cake is removed from the surface of the drum or disc before it comes into contact with the slurry again.

.. · The disadvantage of vacuum filters only! is that the maximum theoretical pressure difference between the different sides of the fabric and the cake, which thus directly affects the filtration rate, can be equal to the ambient air pressure. In practice, the pressure difference is almost invariably less than 0.9 bar.

To eliminate this drawback, known structures have been developed in which a normal disc or drum filter is placed inside a pressure vessel. There is typically an overpressure of 1 to 6 bar in the pressure vessel, so that the cake is formed and dried efficiently. All batteries are removed from inside the pressure vessel by means of an 'air lock', e.g. through a shut-off feeder or two successive alternately operated 1 front water 11ii1 so that the pressure inside the tank cannot escape.

Some of the disadvantages of the structure described above are the complexity of the structure and the inconvenience of maintenance.

Disc and drum filters generally need to have efficient sludge mixing because the sludge solids tend to settle to the bottom of the sludge pool and the sludge near the filter cloth at the top tends to clear, thereby reducing the filtration capacity.

The object of the present invention is to provide a continuous drum-type pressure filter in which the above-mentioned disadvantages are eliminated. Characteristic features of the filter according to the invention are set out in the claims.

The filter according to the invention consists of a slowly rotating pressurized container, the inner surface of which is coated with filter elements. Such a filter element can consist, for example, of a fabric-coated grate, in which the grate allows the filtrate to pass through the fabric between the fabric and the wall of the pressure vessel. In this case, a pressure vessel according to the prior art is not required in a continuous pressure filter, but the rotating container according to the invention itself acts as a pressure vessel.

The inner surface of the pressure vessel is most typically divided by grid-height partitions parallel to the axis of the pressure vessel into areas which allow the filtrate to flow only within each area.

- From each e.m. a pipe leaves the area through which the filtrate can leave the outside of the pressure vessel. Each tube ends at a manifold, the tube being closed at a certain point of rotation so that the pressure in the tank cannot escape.

When the filter is operating, a sludge to be filtered is introduced into a pressurized tank rotating about its longitudinal axis, the depth of which is to be kept in the tank at a constant height, for example 1/10 of the diameter of the tank. The overpressure in the tank presses the slurry through the fabric to form a solid cake.

4 87996 The cake formed as the container rotates rises out of the slurry, allowing the pressurized gas in the container to pass through the cake, drying it.

When p.o. as the cake continues to rotate, it is at the top of the cake, typically at the top of the container or in the direction of rotation thereafter, but before the cake is re-slurried, the distribution valve releases a pressurized gas at a pressure slightly higher than the pressure in the container. In this case, e.g. the solid cake formed in the filter element falls on the cake conveyor. The cake conveyor is of the type, for example, a belt or screw conveyor which transports the formed cakes to a place where they are removed from the outside of the container.

The distribution valve closes the filter tube of the filter element past the cake outlet so that the pressure in the tank cannot easily escape outside the tank.

The distribution valve opens the filtration tube when k.o. filter element:, · falls below the sludge surface again and a new filtration stage ‘I’ begins.

The filtration according to the invention thus provides a continuous filter in which multiple pressures can be used as the filtration pressure compared to normal atmospheric pressure. In this case, cake formation, drying, etc. are even more than many times more efficient compared to continuous suction filters.

Compared to a suction filter placed in a pressure vessel, the structure according to the invention achieves a considerably simpler structure, since the tank and the filter are combined here and a 'normal' disc or drum filter is not required. Also cake cake1je11ime 1 ta drip cake pieces and the like.

'' Do not cause problems as they drip into the sludge.

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The structure according to the invention also does not require a slurry mixer. On the contrary, the absence of mixing is only advantageous for the filtration event, because the solids particles of the sludge fed to the filter tend to settle to the bottom of the sludge layer, i.e. the thickest sludge near the surface of the filter element is thus most efficient.

The invention will now be described in more detail by way of example with reference to the accompanying drawings, in which

Figure 1 shows a cross-section of a filter according to the invention,

Fig. 2 shows a cross-section of the filter according to Fig. 1 at a position I-I,

Figure 3 shows a detail A of Figure 2,

Figure 4 shows the steps of a filtering operation in a filter according to the invention.

Referring to Figures 1-3, the most essential part of the pressure filter according to the invention is a horizontal rotatable pressure vessel ..... (1). The rotation can be arranged either according to Figures 1-2 by means of a roller (2) or the pressure vessel can be centrally mounted and rotated. The inner surface of the tank is divided into filter elements (3) parallel to the axis of rotation, which typically consist of a grate (4) and a filter cloth (5) on top of it. The grate (4) consists, for example, of a torn plate (6) which allows the filtrate to flow through the fabric, and support pins (7) which allow the filtrate to flow parallel to the wall of the pressure vessel (1).

The filter elements are separated from each other by partitions (8) parallel to the axis of rotation, which allow the filtrate to flow only in the region of each filter element.

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Each filter element (3) is connected via a filter pipe (9) to a distribution valve (10) which closes and opens each element (3) at the desired point in the filter pipe (9).

Inside the rotating pressure vessel (1) there is a conveyor (11) which is stationary in relation to the environment, for example a belt conveyor according to the figure, which conveys the formed solid cake to the filter outlet. The conveyor (11) can be attached at one end to a support bearing (12) and at the other end to a fixed outlet channel (13), to which the pressure vessel (1) is also connected by a seal (14).

The exhaust duct has an air lock (15) which allows the solids to be removed but does not reduce the overpressure in the pressure vessel (1) to discharge outside the vessel. The air lock (15) can consist, for example, of a shut-off feeder or, according to Fig. 1, two valves (16) which can be opened and closed alternately.

•. The sludge to be filtered is passed to the filter through a sludge pipe (17) and a pressurized gas, most commonly air, through a pipe (18).

• · »* ··· Referring mainly to Figure 4, the operation of the filter can take place · * · * according to the following example: •»

During operation of the filter, there is typically an overpressure of 1-6 bar inside the rotating pressure vessel (1), which is maintained by supplying compressed air to the vessel through a pipe (18). The sludge (19) to be filtered is fed in a continuous stream into the filter via a sludge pipe (17).

; ** 'The divider 11 i i 1 i (10) holds the filter elements in sector A..!. filter tubes open. In this case, the sludge (19) which has settled to the bottom of the tank (1) begins to filter, i.e. the liquid "* * in the slurry passes through the filter cloth (5) into the filter tube (9) and further through the manifold (10) outside the filter 7 due to gravity and overpressure in the tank. 37996 to the filtrate outlet tube (20) while the solid contained in the slurry collects on the surface of the filter cloth (5) to form a solid cake (21).

As the formed solid cake (21) travels away from the slurry as the container (1) rotates, the compressed air in the container is discharged through the cake through the filter tubes (9) and the distribution valve (10) outside the container (1) while drying the formed solid cake (21). In the direction of rotation towards the end of sector A, the distribution valve (10) closes the filter tubes (9).

After the solid cake (21) formed on the filter element (3) has passed to the sector B, a short compressed air blow is blown into the filter element through the release air pipe (22), the distribution valve (10) and the filter pipe (9) at a slightly higher pressure than in the tank (1). In this case, the pressure blow removes the solid cake (21) formed on the surface of the filter element (3), which falls on the conveyor (11). The sides of the conveyor (11) can have, for example, guide plates (22) to prevent the solid cakes (21) from falling back into the slurry:. (19) among.

«; _ When the filter element (3), from which the solid cake (21) has been ·· * · removed, enters sector C, the valve i 1 i (10) closes.

filter tube (9), because the overpressure prevailing in the tank (1) could easily be discharged through the filter cloth (5) alone outside the filter.

When the filter element enters the slurry again as the rotation of the tank (1) proceeds, the distribution valve (10) again opens the filter tube (9) and so on. the filtering step of the element starts again · '* · 1en.

It will be apparent to those skilled in the art that the various embodiments of the invention are not limited to one of the modes of operation described above, but may vary within the scope of the appended claims. Thus, for example, the supply of compressed air, which in the example described above took place via a pipe (1Θ), can take place in whole or in part in sector C via a distribution valve (10) and filtration pipes (9), the pressure tank (1) through a filter cloth (5) the flowing air at the same time cleans the filter fabric of the solid particles adhering to it. Likewise, for example, the point of removal of the solid cakes (sector C) does not have to be at the top of the pressure vessel but closer to the tea area in the direction of rotation, whereby the drying area of the solid cake is made larger. In the filter according to the example described above, it is also possible to wash the filter cloth in sector C, for example by means of pressurized water nozzles.

• * «• · • ·» · • * * «« M »» • · * f «« ♦ * »• · • · *«

Claims (5)

A method for removing sludge or the like Memory in a continuous-running pressure flutter, said filter having a rotating container (1), in which method sludge and compressed gas are fed to the filter and the filtrate and solid which collect the surface of the container are removed. inside the filter, characterized in that the sludge and the pressurized gas are fed into the container (1) in a manner that in the rotating container (1) a substantially uniform overpressure is maintained during the entire filtration process with respect to the outside noxmal air pressure, and that the filtrate and solid collected on the inner surface of the container are removed from inside the container through an air reader (15) or the like, whereby the internal pressure of the container (1) remains substantially uniform. 2. A method according to claim 1, characterized in that solids are formed on the circumference of the inner surface of the rotating container (1), separated from each other by the filtering area (3), and that these solids shake loose from the surface of the filtering area (3). of overpressure pulses directed to these cookies. Method according to claim 1 or 2, characterized in that the sludge is preferably led to the bottom part of the rotating container (1) and that the amount of the conductive sludge in the container (1) is kept substantially unchanged. Method according to any one of the preceding claims, characterized in that the pressure into the container (1) consists of the overpressure of 0.1 - 10 bar, preferably 1-6 bar. 5. Pressure flickers for more continuous operation, consisting of a rotating container, sludge (17, 18) for conducting sludge (7) or the like Sensor and pressure gas for this continuous-pressure pressure filter, devices (9) for conducting the filtrate outside the continuous operating pressure filter, a system for removing the formed solids from the surface of the filtering area (3) to a conveyor (11) for their transport further through air letting (15) outside the filter, characterized in that the devices (17, 18) have been arranged and the devices (9, 11) have been arranged so that the filtrate and the solids can be removed from within the container (1), the internal pressure of the container (1) remaining essential. lie jSmnt.