Machine for micro-filtering solid particles suspended in a liquid stream

Abstract: The invention relates to a machine for micro-filtering solid particles suspended in a liquid stream comprising: a couple of coaxial filtering discs (5, 6, 20, 21, 91, 92, 93, 94) rotating around its own axis (71) arranged horizontal and normal to direction of the flow to be treated and at least a partially cylindrical wall (7) defining together with the rims of said couple of discs a hydraulic sealing coupling so as to enclose the liquid treating space comprising at least the rotation axis. Each disc of said couples of discs is provided with one or more washing ramps (14, 15) arranged outside said treating chambers and provided with nozzles throwing water against said discs at the portions emerging (51, 61) from the treating chamber. The washing water is collected by at least a liquid conveyance channel (8) feeding the liquid back to the purification plant arranged upstream said machines.

Description: The present invention relates to a machine for micro-filtering solid particles suspended in a liquid stream, more particularly water discharged from civil or industrial drainage. It is known that drainage of civil or industrial waste water is governed by increasingly stricter laws. The European regulations presently provide that the micro-particles present in waste water should not exceed 35 mg per liter. It is to be noted that the previous regulations, at least in force for industrial plants, allowed a concentration of micro-particles up to 80 mg per liter. Therefore there is now the need to lower the level of micro-particles from 80 mg per liter up to now allowed, to 35 mg per liter as now ruled. In order to reach said results according to the prior art there are purification plants with sand filters, but these filters however have very big dimensions. Moreover the sand filters are limited because filtration is not continuous since said filters must be regenerated after a predetermined number of operation hours. Another solution of the problem consists in using machines with a drum provided with filtering surfaces: the waste water to be treated is fed inside the drum and passes through the drum filtering surface. These filtering surfaces are periodically washed to avoid clogging. One of the problems related to this filtering technique is that the machines are very big and cumbersome and their operation is expensive. Another simpler and more efficient method to carry out filtering mainly of fibrous solids suspended in water, consists in using machines provided with filters comprising opposed rotary discs, in which water is introduced centrally in a direction almost tangent to the surface of the filtering discs and the combined action of disc rotation with water flow with a direction almost tangent to said disc, generates a force in a direction tangent to the disc and a direction normal to it. The normal component causes water to travel through the filter and carries out filtration while the tangential component is ineffective. During this filtering process a layer of fibers is formed and deposited adhering to the filtering surface, so that the fibers partially occlude the holes to which water is being filtered. The bulk of fibers gradually formed in the filtration chamber carries out a sliding action on the surface of the filters causing the filtering holes to be self-cleaned. Obviously this self-cleaning action does not reach a perfect level. In other words these kinds of machines can operate in the above mentioned way only if they have sufficiently or relatively big holes so that the filtered water cannot have a contents of micro-particles with size less than 50 or 40 µ, that is not admitted with the present regulations. Such a filtering machine is known from EP-A 388 709 which is the basis of the preamble of claim 1. US-A 5 116 400 and FR-A 602 884 disclose filtering machines having a single filtering disc the rotary axis of which is parallel to the flow direction of the liquid to be treated. With these machines it is not possible to retain very small and fine impurities. A similar filtering device is known from GB-A 1 002 819. Here, the axially arriving liquid is drawn through the filtering disc by a suction pump with the effect that even relatively large particles are passing through the filter apertures . The object of the present invention is to overcome the limits of the above described known technique. More particularly the object is to make a machine carrying out a continuous micro-filtration with considerable water flow so as to result in a filtered water having a contents of micro-particles equal or less than 20 mg per liter. Another intended object is to provide a machine adapted to process considerable volumes of water without requiring too big dimensions. Another object to be obtained is to provide a machine which is relatively inexpensive and highly reliable in operation. The above mentioned objects and others that will be better indicated hereinafter are attained by the machine of the invention according to claim 1. Advantageously the micro-filtration machine of the invention keeps the advantages of the known machines with couples of filtering discs allowing that the flow of water with suspended particles having a direction almost tangent to the discs, to intercept the disc holes according to a force component normal to the disc surface. The result of such combined action is that the disc hole is operatively smaller than the actual hole made in the disc. The machine of the invention carries out its best performance when used downstream a water purification plant and more particularly downstream a conventional machine with filtering discs for instance of the kind disclose in European Patent 0388709 in the name of the same applicant. The substantial difference between the machine disclosed in European Patent EP 0388709 and the machine of the present invention consists in that in the machine of the present invention the self-cleaning action of the filter on the disc surface cannot be kept because filtering surfaces must be adopted with still smaller holes to obtain the micro-filtration required for lowering the contents of solids in the filtered liquid to at least 20 µm or 20 mg per liter or even less. Therefore it is clear that the filtering disc must be constantly cleaned from the filtered material so as to avoid clogging of the filtering holes. Another advantage of the machine of the invention consists in the possibility of treating high rates of flow to be treated without needing a proportional increase of size and overall dimensions of the machine. This result is due to the effect created in the treating chamber by the hydrostatic head of the liquid to be treated. More particularly the increase of the diameter of the filtering discs and the consequent increase of the hydrostatic head generates a greater pressure on the surface of the filtering discs that in this way succeed to treat rates of liquid flow higher than the simple proportional increase of the filtering surface due to the increase of the diameter. Further characteristics and features of the invention will be better understood from the detailed description of the machine with reference to the figures of the accompanying drawings in which: Fig. 1 is a perspective view of the machine of the invention in which the motion of the discs is obtained through an axial reduction gear; Fig. 2 shows the machine of the invention in which the motion of the discs is obtained through a circumferential arrangement of pinion and wheel gear; Fig. 3 is a sectional view of the machine of Fig. 1; Fig. 4 is a sectional view of a version of the machine of Fig. 1 with conical discs; and Fig. 5 is a sectional view of another version of the machine of the invention provided with two couples of discs. With reference now to the drawings it is to be noted that the machine of the invention has a substantially box like shape in which there is a feeding chamber 2 for the flow of liquid to be treated, delivering through the feeding duct 3 the liquid to be treated to the treating chamber 4. Said treating chamber as shown in Fig. 1 and Fig. 3, is defined by two opposed discs 5 and 6 and the semi-cylindrical wall 7 extending between the discs 5 and 6 to the upper limit formed by the bottom 8' of the a collecting channel 8 that will be described hereinafter. The treated water passes through the filtering discs 5 and 6 and reaches the conveying chambers 10 and 11 each provided with at least one bottom outlet 101 and 110 conveying the treated water to the collection chamber 12 which is provided with a discharge pipe 121 for the final discharge of the treated liquid according to the regulations presently in force, that is with a concentration of solids lower than 20 mg per liter. As shown in Fig. 3, above the treating chamber 4 there is a washing chamber 13 defined by the collecting channel 8 arranged on the bottom of said chamber and the portions of the filtering discs 5 and 6 emerging from the treating chamber and indicated by reference numerals 51 and 61. The portions 51 and 61 of the discs emerging from the treating chamber are hit by strong jets coming from washing ramps 14 and 15 so as to remove the filtered impurities from all the holes of the filtering surface of the discs. In this way the washed disc portion is circulated to the new filtering operation during the rotation of the discs without undergoing a decrease of the filtering action. The cleaning water and the particles detached from the portions 51 and 61 of discs 5 and 6, are collected in the channel 8 provided with a discharge pipe 82 feeding again the so recycled water to purification plants arranged upstream the machine of the invention. In the embodiment shown in Figs. 1, 2 and 3 the machine of the invention has discs 5 and 6 with flat surface. The operation of the machine does not change if the discs are not flat but are discs with frustum conical surface as those disclosed in European Patent EP 0388709. Fig. 4 indeed shows a sectional view of a constructional version of the machine of Fig. 1 in which the discs 20 and 21 are conical instead of being flat. In this case the line of contact of collecting channel 8 with discs 20 and 21 will be an arc indicated at 201 and 211 instead of a straight line. For the rest the operation of the machine is not altered. The embodiment of the machine illustrated in Figss. 1 to 4 shows a machine with a couple of discs in which the means transmitting the motion are provided by a geared motor 70 whose slow shaft not shown in the drawing is coaxial to the axis of the filtering discs so that the rotation torque is transmitted to the shaft 71 supporting the discs 5 and 6 of Figs. 1 and 3 and the discs 20 and 21 of Fig. 4. It is also to be noted that the machines of Figs. 1 to 3 and the version of Fig. 4 have discs provided on their circumference with gaskets 52 and 62 for the discs 5 and 6 and 202 and 212 for the discs 20 and 21, respectively. These gaskets work on the cylindrical curved bottom plate 7 so that there is a sealing action between said bottom plate and the discs and all the water is filtered without loss of hydraulic seal between the discs and the bottom plate 7. In a constructional version shown in Fig. 2 the transmission of the motion to the couple of opposed discs of the machine is carried out by a pinion and wheel gear group where the pinion 80 is engaged with the wheel gear 81 mounted on the inner circumference of disc 82. This construction is particularly suitable for machines having filtering discs with a big diameter where the torque at the axis would be very high and therefore it is advisable to use a geared motor having a sufficiently high rotation speed at the pinion so as to use geared motors with low torque. According to a further constructional version shown in the sectional view of Fig. 5, the micro-filtration machine of the invention is provided with two couples of discs indicated with 91, 92 and 93, 94 respectively. In this case said couples of discs will define two treating chambers 95 and 96 and three conveyance chambers 97, 98 and 99 conveying the filtered water to a collection chamber indicated with 100. The collecting channel 8 will anyway be provided between the couple of discs 91 and 92 and also between the couple of discs 93 and 94. Obviously each couple of discs will be provided with the washing ramps indicated with 14 and 15. As to the filtering surface of the discs, such surface may be carried out with micro-perforated metal sheet, for instance of stainless steel, or resistant plastic textile fabric also provided with micro-holes or equivalent means. It is apparent that by cleaning continuously the filters at their upper portion outside the treating chamber, the filtering discs can steadily carry out at best their operation and filtration may take place in the best way without machine stops and ensuring a constant filtration quality.

Claims: A machine for micro-filtering solid particles suspended in a liquid stream, comprising: a feeding chamber (2) for collecting the liquid to be treated; a duct (3) defining a flow direction; at least one treating chamber (4, 95, 96) communicating with said feeding chamber (2) though said duct (3), said treating chamber being defined by at least one pair of filtering discs (5, 6, 20, 21, 91, 92, 93, 94) mounted coaxially on a shaft (71) having a rotation axis extending substantial horizontal and normal to said flow direction, each treating chamber (4, 95, 96) defining a treating space including at least said rotation axis; at least one partially cylindrical wall (7) adapted to co-operate with the peripheral rims of said filtering discs (5, 6, 20, 21, 91, 92, 93, 94) to enclose said treating space; conveyance chambers (10, 11, 97, 98, 99) positioned at the opposite outer sides of said treating chamber for conveying the treated liquid, said conveyance chambers (10, 11, 97, 98, 99) having bottom outlets (101, 110); at least one collection chamber (12, 100) connected to said conveyance chamber (10, 11, 97, 98, 99) through said bottom outlets (101, 110) and having liquid discharge pipes (121); means for transmitting a rotation motion to said shaft (71) to rotate said at least one pair of filtering discs; means for cleaning said filtering discs (5, 6, 20, 21, 91, 92, 93, 94), said cleaning means including one or more washing ramps (14, 15) arranged outside of said treating chamber and each provided with nozzles for continuously ejecting cleaning water against said filtering discs at the portion thereof emerging from said treating chamber; characterised in that a collecting channel (8) is provided between said at least one pair of filtering discs for collecting said cleaning water and the solid particles dispersed therein, said collecting channel (8) having a bottom wall (8') defining the upper limit of said at least one treatment chamber (4, 95, 96), said filtering discs (5, 6, 20, 21, 91, 92, 93, 94) having filtering surfaces comprising sheets or textile fabric with micro-perforations or micro-holes, sealing means (52, 62; 202, 212) being provided between the peripheral rims of said discs (5, 6, 20, 21, 91, 92, 93, 94) and said partially cylindrical wall (7). The machine according to claim 1, characterised in that said sealing means (52, 62; 202, 212) comprise gaskets located on the peripheral rims of said filtering discs (5, 6, 20, 21, 91, 92, 93, 94) for acting against said partially cylindrical wall (7). The machine according to claim 1, characterised in that said sealing means (52, 62; 202, 212) comprise gaskets located on said partially cylindrical wall (7) for acting against the peripheral rims of said filtering discs (5, 6, 20, 21, 91, 92, 93, 94). The machine according to claim 1, characterised in that said collecting channel (8) has side edges defining contact lines with said filtering discs (5, 6, 20, 21, 91, 92, 93, 94). The machine according to claim 1, characterised in that said filtering discs (5, 6) have a generally flat surface. The machine according to claim 1, characterised in that said filtering discs (5, 6) have a generally frustum conical surface. The machine according to any preceding claims, characterised in that said transmission means comprise a geared motor (70) connected to said horizontal shaft (71). The machine according to any preceding claims, characterised in that said transmission means comprise a gear motor having a slow shaft integral with a pinion (81) meshing with a wheel gear (82) arranged on the periphery of one of said filtering discs. The machine according to any preceding claims, characterised in that said micro-filtering surfaces of said filtering discs (5, 6, 20, 21, 91, 92, 93, 94) comprise micro-perforated metal or plastic sheets provided with micro-holes suitable to obtain a concentration of solids in the filtered liquid equal to or less than 20 mg per liter.

Inventors: MASSIGNANI DONATO, MASSIGNANI, DONATO
Applicants: MASSIGNANI DONATO, MASSIGNANI, DONATO
Application year: 2001
Main classification: B01D33
IPC codes: B01D33