| 1. | A method for separating a solid matter from a liquid by filtration, in which method the liquid is led to a filter comprised of an essentially horizontal mineral wool mat having a horizontal prevailing fiber orientation, at least to an essential part of its filtra¬ tion surface, as a volume flow that is lower than the filter permeability, the feed is interrupted when the filter permeability is lower than the volume flow of the feed, the filter is regenerated and the filtration cycle is repeated with a regenerated filter, characterized in that the regeneration is realized by draining the filter and by removing the filtration residue on the filter sur face after the draining step. |
| 2. | A method according to claim 1, characterized in that the draining is performed when the filter is in its es¬ sentially horizontal filtration position. |
| 3. | A method according to claim l, characterized in that the draining is performed by inclining the filter from its filtration position by at least ca. 45° with respect to the horizontal plane. |
| 4. | A method according to claim 3, characterized in that the filter is inclined at the draining step of the regen¬ eration to an essentially vertical plane. |
| 5. | A method according to claim 3 or 4, characterized in that the draining step of the regeneration is performed stepwise in different inclination positions. |
| 6. | A method according to any of the preceding laims 15, characterized in that the filtrate liquic? of the draining step of the regeneration is led during the draining op¬ tionally to the filtrate/feed of the filtration step. |
| 7. | A method according to any of the preceding claims 36, characterized in that the filter is turned for the removal step of the filtration residue of the regeration essentially into an upsidedown position relative to the filtration position. |
| 8. | An equipment for performing the method of claim 3, which equipment comprises a frame, a shaft (2) placed horizontal on the frame and pivoted as rotational, at least one filter element (3) supported by the shaft and tiltable by at least ca. 180° around the shaft from its essentially horizontal filtration position, means (4) for leading the liquid to be filtered to the upper surface of a filtration means (1) of the filter element (3) located in the filtration position, a trough (8) placed below the filtration means (1) for receiving the filtrate, a trough or the like for leading a filtrate (5) away, a trough or the like for receiving a draining filtrate (6) , as well as means (11) for scraping the filtration residue from the filtration surface of the filtration means (1) in the upsidedown position of the filter element (3) . |
| 9. | A device according to claim 8, characterized in that there are several filter elements (3) on the shaft (2) and that they are positioned on a plane going via the shaft. |
| 10. | A device according to claim 8 or 9, characterized in that it has means for observing the liquid layer to be filtered and accumulating on the filter surface. |
The present invention relates to a method and an appar- atus for separating or removing a solid matter from a liquid. The method and the apparatus for realizing it are based on the utilization of a mineral wool mat, having a fiber orientation prevailing in a certain planar direc¬ tion, as a filter element.
It is known to use a filter made of a mineral fiber for several applications, in which constituents have been filtered away from a second medium containing them. A certain solution is described in the US patent publica- tion 4 652 379. In this patent, as a filter element has been used a mat made of a mineral fiber, the fiber orien¬ tation of which mat is prevailingly in one planar direc¬ tion. It is essential in the solution that the medium to be filtered is led into the mat in a direction, which is essentially perpendicular to the prevailing fiber direc¬ tion. The filtrate is in contrast removed in the prevail¬ ing fiber direction. The scope of application proposed is extremely extensive, comprising also the treatment of gases. The publication does not provide information about the regeneration of the filter.
Another known solution is described in the US patent pub¬ lication 4 639 318, which mainly concentrates on a tubu¬ lar filter type. The tube forming the filter insert is made of a two-layer fiber mat, in which the prevailing fiber directions of the layers deviate from each other. The fiber direction v* ~evailing in the outer layer is radial, whereas the fiber direction p mailing in the inner layer is axial. The flow to be filtered is led from the outer periphery of the insert towards the inner por¬ tion, whereby the outer parts of the radial outer layer act as a coarse mesh filter and the inner parts of this layer as a dense mesh filter. One purpose of the axial
layer is to act as a flow distributor uniformly for the insert area. Even this publication does not provide in¬ formation about the regeneration of the filter insert.
The US patent publication 4 388 192 in turn describes the use of mineral fibers as filter material, which is used in the purification of water, including the removal of larger microorganisms. As for the fiber orientation, it has been found preferable to use a fiber structure, in which the prevailing fiber direction is the same as that of the flow to be filtered. On the other hand, it has also been found that a filter structure, in which the prevailing fiber direction is transversal relative to the direction of the filtration flow, is applicable. The lay- ers of the filter may have a different permeability. The regeneration of the filter has not been dealt with in the publication.
In the solutions described in said publications, where the scopes of application have been such that the concen¬ tration of the matter to be separated in the medium is essentially low, the idea has been that when the filter is clogged, it is replaced.
The present invention is in contrast based on an idea, according to which the filter has to be regenerable. It has been realized in accordance with the invention to utilize for the regeneration of the filter a property related to the fiber orientation of the filter, according to which property the liquid content in the filter may be drained from the filter such that the filtrate draining away causes a suction effect to the surface layer of the filter, which effect is sufficient to cause an essential drying of the filtrate residue remaining on the filter. This phenomenon occurs in an emphasized manner, if the filter is turned to a position, in which the plane of the prevailing fiber orientation deviates from the horizontal
plane. The filtrate is then removed from the filter near¬ ly completely. A sufficient drying effect of the surface layer may be achieved according to the basic idea of the invention also when the filter is drained in its essen- tially horizontal filtration position. The fiber struc¬ ture orientated prevailingly horizontally then causes to the filtrate drain ng away also a horizontal flow compo¬ nent, which is sufficient to effectively dry the surface layer of the filter as well as the filtrate residue re- maining thereon in spite of the fact that a considerable filtrate content remains in the filter.
The filtration residue thus made relatively dry may be easily scraped off the filter surface. Along with the medium draining away, an essential part of the substances accumulated in the filter is discharged therefrom, where¬ by the filter may be reused for filtration purposes after the scraping of the filtration residue.
The invention is in the following illustrated with refer¬ ence to the accompanying drawing, in which
Fig. 1 is a schematic view in principle of a device real¬ izing the basic idea of the invention; and
Fig. 2 shows a certain preferred modification of the de¬ vice.
In the device according to Fig. 1, a filter element 3 is comprised of filter made of a mineral wool mat l, which filter is fixed to a suitable frame 10. In the frame, the filter element is supported by a net-like support struc¬ ture 9 11 , in addition to which the frame may have means 9' for keeping the wool board in position in different steps of the operational cycle as well as for supporting the wool board during this operational cycle. The means for keeping the wool board in position do not have to be
very complex, since it is advantageous to provide the board during its preparation with shape permeance to such an extent that it stays in position and retains its shape essentially only when fixed by its edges.
In addition to these means keeping the board in position and supporting it, the frame is formed with an edging, which extends higher than the wool board in the frame. The purpose of this edging is to form for the liquid to be filtered a basin mostly for preventing overflows in a step, in which the filter elemets start to clog. On the other hand, the basin provides a possibility of following the advancement of the filtration, whereby a basin tend¬ ing to be filled is an indication of a filter in need of regeneration.
For leading a filtrate 5 away, under the wool board act¬ ing as a filter is placed a trough 8, which leads the filtrate into a suitable outlet. For bringing a liquid 4 to be filtered may be used various solutions, of which .the figure shows nozzles placed on a transferable beam. The nozzles are preferably placed at such a distance from each other that in a normal filtration situation nonwett- ed intermediate areas remain between the areas wetted by the feed flows of the nozzles. This ensures for the fil¬ trate flow sufficient possibilies of moving laterally in the internal portion of the filter 1 in a manner shown in Fig. 1 by flow arrows, as for the feed flow 4.
If the device is used according to other alternatives of the invention, i.e. the filter element is inclined from its filtration position for enhancing the flowing related to regeneration, the liquid to be filtered may also be led such that it wets the entire surface of the filter. In this case, one possibility is to bring the liquid to be filtered as a larger volume flow essentially to the middle area of the filter, from which the liquid spreads
onto the filter seeking for pearmeable areas. Another possibility of bringing the liquid to be filtered is a pressurized delivering of a liquid, whereby the equipment has to be constructed such that a reasonable pressure may be maintained above the filter, either as a hydrostatic pressure or as a pressure produced by a pump. In some case, it may be advantageous to arrange the feeding of the liquid to be filtered periodically, whereby the fil¬ ter is allowed to permeate the preceding feeding batch just before bringing a new batch.
As a space-saving device construction may be used the realization of Fig. 2, in which the filter elements 3 are placed rotational in different operational positions (a, bl, b, c, d) on a horizontal shaft 2. The shaft 2 supporting the filter elements is step-wise rotational, whereby, when a filter in a filtration position (a) is clogging, a regenerated filter may be turned in place thereof. When a filter clogs, the liquid flow coming thereto is discontinued, and the filter is turned, sup¬ ported by the shaft, into a draining position. In the equipment shown in the figure, the draining position (&) is described as a vertical plane. However, the angle of the draining position may also be more gently sloping (bl) , but an angle of 45° may be regarded as a minimum inclination for making the draining occur within a rea¬ sonable time. A more gently sloping angle than 90° pro¬ vides also a good possibility of placing several filtra¬ tion elements on the shaft, whereby the stepping of the rotations of the shaft has been realized as smaller steps than 90°.
On the other hand, also in the equipment according to the figure, the draining may be realized step-wise in differ- ent inclination steps of the filtration element, whereby e.g. a possibility is obtained for guiding the draining filtrates purposefully out of the equipment. If the fil-
trate predraining is performed e.g. at an inclination angle of 45°, the filtrate has been observed to be pure, whereby it may be led into the actual filtrate. In the final step of the draining in contrast, substances accu- mulated in the filter are discharged therefrom, and it is advisable to lead this draining filtrate to the filtrate feed. In practise however, the quantities of filtrate in the draining step of the regeneration with respect to the total quantity of the filtrate on dilute liquids to be filtered are so low that the selection of the draining filtrate between filtrate/feed is of no essential import¬ ance. If in contrast the concentrations of the liquid to be filtered are high and the filter regeneration has to be performed at short intervals, the guiding of the draining filtrate is relevant from the point of view of the total result.
The regeneration-step draining of the filtrate is relevant in several aspects from the point of view of the efficiency of the regeneration. An extremely important aspect is the suction effect caused by the filtrate draining away in the mineral wool mat acting as a filter, which suction strongly concentrates on the filtration residue on the surface of the filtrate. By the action of this suction, essentially all free liquid leaves the fil¬ tration residue in the same way as free liquid effective¬ ly leaves the structure of the filter itself. This results in a filtration residue having a high solids con¬ tent, which can no longer be wetted in the subsequent treatment steps of the filters. On the other hand, the draining effectively removes constituents travelled into the filter structure.
In the second step of the filtrate regeneration is per- formed the removal of the filtration residue from the filter, for which purpose the filter is preferably turned into an upside-down position (c) according to the figure.
The removal of the filtration residue may be performed by scraping, a rotating brush, an air-jet scraper or in some other purposeful manner known per se. The filtration residue is removed from the equipment either for utiliz- ation or destruction, depending on the liquid to be fil¬ tered by the equipment.
After the removal of the filtration residue, a filter flushing to be connected to the equipment may be considered. This may be realized after the removal step of the filtration residue, when the filter is in its up¬ side-down position. A flushing agent may be led onto the surface of the filter to such an extent that it is suffi¬ cient to impregnate the filter. This liquid can be drained from the filter ir. the next vertical position (d) of the filter, in which it waits for a transfer to the filtration step. For example a pure filtrate may be used for flushing, and the draining filtrate of the washing may be led into the filtration feed.
For achieving an equipment with a larger capacity, the filter el ments may be placed on a suitable support and conveyor apparatus successively, circulating along an endless loop track, whereby the filtration is performed at a straight on-going segment of the lower part of the loop, the draining of the regeneration occurs at a rising segment entering into the loop, the removal of the fil¬ tration residue is performed at a horizontal segment re¬ turning into the loop and a possible flushing draining occurs at a returning vertical segment of the loop.
The mineral wool mat forming the filter itself can have a varying construction. As a fiber diameter in the mat may be used a distribution of the fiber diameter of a conven- tional corresponding mat used for a insulation purpose or substrate purposes, in which distribution a large part of the fibers is in the diameter range 1-20 μm. The mat den-
sity may also be a conventional one used in corresponding boards made for other purposes, i.e. in the range of 20- 80 kg/m 3 . If a higher separation capability is needed, density values up to 150 kg/m 3 may be used. Conventional resin binders are used in the mat. From the point of view of the filter operation, it is advantageous that the mat is treated with a hydrophiliation agent, suitably with similar agents that are used for hydrophiliation of min¬ eral wools made for growing purposes.
The filter material may be rock wool, glass wool or slagg wool.
The functionability of the invention is clarified on the basis of the following embodiment example.
A test was performed by means of the outlet flow of a fish breeding establisment, from which outlet flow most of the solid matter had been removed with conventional purification devices. These conventional purification measures included e.g. a flotation treatment.
The test equipment was a basin, whose bottom had been made as a net structure. On top of the net was placed as a filter a mineral wool mat, whose size was 1200 x 600 mm, i.e. the area of the filter was 0.72 2 . The mat thickness in the tests was 30 mm, but its specific weight was varied between different tests. A value of ca. 30 1/min was used for the feed flow in most tests. The solids specification of the flows was performed according to the standard SFS 3037 with a glass fiber filter Schleicher & Schlill GF/50.
The length of the filtration period was determined such that the feed was discontinued after a liquid layer of ca. 10 cm had accumulated on top of the filter, which was regarded as an indication of the need for filter regener-
ation. The conditions and results of the tests are clar¬ ified by means of the following Table 1.
Table 1
The table lists under the item "Sample code" the idenfication of the test with a letter. The next column first provides information about th * . filter used, i.e. the first two numbers indicate the specific weight of the filter kg/m 3 . The next letter refers to a flow, T = inlet and L = outlet. The next two numbers again relate to a filter mat, i.e. they indicate its thickness in mm. The last number indicates the running number of the test. The
numeral values related to the efficiency of the filtra¬ tion are given in the last column.
A few comments may be given on the tests. As for the samples A and B, the procedure was that a clarifier coming from the flotation basin was run through the fil¬ ter at a flow rate of 30 1/min. The surface load of the filter then becomes 2.5 m/h (2.5 m 3 /m 2 h). Each filtration cycle lasted for about 7 minutes, after which the filter was drained for 7 minutes. The sediment that remained on the filter was then removed by scraping with a knife. The samples A and B were taken after two filter regeneration cycles. On the basis of the solids contents, the purifi¬ cation result may be regarded as excellent.
As for the tests C and D, a denser mat was used, whose specific weight was 80 kg/m 3 . The mat thickness was 30 mm. The first filtration cycle lasted for 7 minutes, after which the regeneration was performed in the manner described above. The samples have been taken from the next filtration cycle. Some by-pass flow was observed in the test because of an unsatisfactory operation of the filtration basin, which by-pass flow has slightly affected the result obtained.
As for the test E, the sample has been taken from the flotation basin. During the second filtration cycle, the filter lasted at a feed load of 30 1/min for about 5 min¬ utes before clogging, after which it was drained in the regeneration step for 7 minutes. The third filtration cycle also lasted for 5 minutes. The sample F was taken during this filtration. After the third filtration step, the draining of the regeneration step lasted for 7 min¬ utes too.
As for the test G (inlet flow E) , the procedure was such that the sample was taken immediately during the filtra-
tion cycle, in which the specific weight of wool was 60 kg/m 3 . The inlet flow was ca. 30 1/min. The filtration step lasted for 6 minutes and the draining period in the regeneration into a surface-dry state for 6 minutes. Fi- nally, the draining step ended after 7 minutes. The sec¬ ond filtration step lasted slightly more than 5 minutes, the draining step into a surface-dry state for 7 minutes, and the filter had emptied in 7.5 minutes. The third fil¬ tration step lasted for 5 minutes, during which step a sample H has been taken. The draining step after the third filtration cycle into a surface-dry state lasted for 7 minutes, and the draining ended after 7.5 minutes. The tests showed a slight filter by-pass flow.
The sample I was taken from the flotation basin. The sample J is comprised of a sedimented cyclone clarifying slurry, in which the solids content is considerably high. The slurry of the test J did not properly penetrate through the wool and a by-pass flow occurred in the test. However, the sample K gives the purification an extremely high value, 99.4%. Nevertheless, the test led to the as¬ sumption that the wool used is not suitable for the fil¬ tration of such a thick slurry.
The sample of the test L also comes from the flotation basin, whereas the sample of the test M is a clear frac¬ tion coming from the cyclone clarifier. After this the result of the filtration is shown in the test N, in which a by-pass flow has however been observed.
In the next tests, a flow corresponding to the sample M was user as a feed such that the feeding mode was varied in comparison to that used previously. In these tests, 0, P and Q were realized such that to the filter was run a fraction to be filtered at a flow rate of ca. 28 1/min in periods of ca. 10 seconds, between which the filter was allowed to dry a little. The results of the test O come
from the filtrate flow after a second 10-second run. The sample P is a parallel determination for the sample M, and the filtrate Q is taken at the start of the fourth filtration cycle. The filter operated well by using this procedure, and ca. 5 minutes were sufficient for the draining drying of the regeneration step. It was observed that the solids content in the filtration residue was ca. 21%.