UA95987C2 - Sand filtering device - Google Patents

Abstract

A sand filtering device comprising a single layer filtering bed, or simply a filter, which allows to obtain perfectly clean water and a high operative working life at high filtering speeds. Advantageously, an appropriate, experimentally obtained correlation between the height of the filtering layer, the grain size of the used sand and the filtering speed allows a dimensioning of the filtering bed such as to ensure optimal filtering conditions. The device of the invention further allows to obtain a very effective filter back washing operation which restores the efficiency of the filter.

Description

Field of application of the invention

The invention relates to a sand filter device, which is used in water treatment plants, in particular, in natural, circulating and cooling water treatment plants.

Technical level

A variety of sand filter devices are known, which are used in water purification systems.

However, such devices have numerous disadvantages, such as: - the formation of surface crusts with the frequent occurrence of the phenomenon of filter clogging, as a result of which there is a need for frequent backwashing; - the impossibility of achieving high filtering speeds, as a result of which the systems require an increase in the number of filters; - the need for a layer of anthracite above a layer of sand to filter out oils and fats that are in polluted water; - high capital and operating costs.

Based on this, there is a need to create a sand filtration system that makes it possible to overcome the above-mentioned shortcomings.

The essence of the invention

The main purpose of the invention is to create a sand filter device for water treatment in natural, circulating and cooling water treatment plants, which includes a single filter layer, or simply a filter, which enables obtaining perfectly purified water and has a high operational durability with high filtration rates. An additional goal of the present invention is to create a highly efficient method of backwashing the filter device capable of ensuring the efficiency of filtration for a long time.

Thus, according to this invention, it is proposed to achieve the above-mentioned goals by using a sand filter device for water treatment, which according to clause 17 of the claims of the invention includes an essentially cylindrical container with a longitudinal axis, which has a plate inside that divides the container into an upper zone and a lower a zone in which a filter layer is located inside the upper zone, which consists of a single layer of sand with a height H determined by the equation

Naaest, where the parameter "a" has a value from 500 to 800, the parameter "p" has a value from 0.020 to 0.045, and the filtering speed "Y" is 40-70 m/h.

Another aspect of the invention is related to the method of backwashing the above-mentioned filter device, which according to clause 10 of the claims of the invention includes the following operations: - draining the water intended for filtering, which is contained in the upper zone of the container, until the water level approaches the upper surface of the filter layer; - providing a reverse flow of air to clean the head and create air bubbles in the filter layer for about 1 minute; - providing a return flow of the air-water mixture to remove the separated dirt from the filter device during the time required to change the water in the volume of the pipe, at least 10 times; - return flow of water only for 2-5 minutes. to obtain a uniformly and homogeneously deposited layer; - final backwash with a flow in the direction of filtration to prepare the filter device for filtration and to remove dirt not removed during the backwash operation.

In a preferred embodiment, said relationship between the height of the filter bed, the size of the sand grain used, and the filtration speed ensures that the filter bed is sized to provide optimal filtration conditions at high speeds.

The filter device, which is the subject of the present invention and is suitable for efficient operation with filtering speeds that can also reach 70 m/h, provides the following advantages: - it enables the creation of filter systems that use approximately half the number of filter elements compared to conventional filters ; - it enables the production of more compact and more rational equipment with a significant reduction in capital and operating costs.

In a preferred embodiment, the device of the present invention has a large height of the single filter layer to increase the filter path and a relatively coarse-grained sand, which enables the use of a larger filter volume and a more uniform distribution of the dirt contained in the treated water over said volume and avoiding the formation of surface crusts, and therefore frequent clogging of the filter device.

Due to these features, the device according to the invention does not require a layer of anthracite above the layer of sand, which occurs in known filters, to filter out the oils and greases that are present in the polluted water, which gives a significant saving in capital and operating costs.

The dependent claims correspond to preferred embodiments of the invention.

Detailed description of figures

Additional differences and advantages of the present invention will become clearer from the further detailed description of the variant of its implementation, which is preferred, but which is not exclusive and the only possible one, illustrated only in the form of an example, which does not limit the essence of the invention, by the accompanying figures, in which:

Fig. 1 is a schematic cross-section of the filter device according to the present invention;

Fig. 2a and Fig. 25 are sections along mutually perpendicular planes of one of the nodes of the device shown in Fig. 1;

Fig. C is a top view of the second node of the device according to the present invention;

Fig. 4 is a side view of the third unit of the device according to the present invention;

Fig. 5 is an enlarged local view of the filter device shown in FIG. 1.

Detailed description of the preferred embodiment of the invention

The figures show a filtering device, generally indicated by the position 1, located inside a substantially cylindrical steel tank or container 2, which has vertical walls 3, a bottom part 4 and a cover 5. The tank 2 is internally divided into two zones by a plate 7. In the upper zone there is filter layer b, which includes a single layer of appropriately selected sand. Usually, the filter layer would be located on a thin layer of relatively coarse gravel ZO, which in turn is located on plate 7 and does not perform a filtering function.

The water to be purified is supplied to the filter layer 6 through a central pipe 8 located along the longitudinal axis of the tank 2. Such a pipe 8 has an inlet section 10 for the water to be filtered, located near the bottom part 4 of the tank, and an outlet section for said water near cover 5.

According to the preferred option, the use of a single layer of filter sand allows for increased uniformity of the use of the filter layer. The size of the grain of sand, which is relatively large and homogeneous, makes it possible to achieve high filtration speeds in order to use the filter layer in its depth, and therefore to distribute dirt throughout the layer, which allows you to avoid the formation of surface crusts and, accordingly, the phenomenon of early clogging of the filter device.

An additional advantage is that the filter layer 6 has such a defined height that provides a larger filter volume and a longer filter path compared to conventional filters; it also makes it possible to extend the time of use of the filter before the need for backwashing occurs due to the reduction of the rate of its clogging.

In order to correctly determine the size of the filter layer or single-layer filter 6 according to the size of the applied grain according to the preferred option, a mathematical relationship was determined that determines the optimal height of the layer:

Nortma: - ageh, where "a" and "p" are parameters depending on the size of the sand grain, and "m" is the filtering speed. This equation shows the logarithmic dependence of bed height and filtration rate. The parameter "a" has a value from 500 to 800, and the parameter "p" has a value from 0.020 to 0.045.

It turned out that the grain size that provides the best characteristics is 1.0-2.0 mm, for which the value of "a" is approximately equal to 580, and the value of "p" is approximately equal to 0.029, which makes it possible to obtain a filtration speed of at least 50 m/h for the height of the filter layer 6, which is approximately 2.5 m. Under such conditions, if the input concentration of particles suspended in the input sludge is equal to 80 million", it is possible to obtain a maximum output concentration of only 10 million".

A smaller grain size of 0.7-1.0 mm has been found to require a thinner filter bed, but is too fine to allow the dirt to be distributed throughout the filter bed, which is the preferred option for extended time work until the need for backwashing occurs.

Additionally, larger grain sizes greater than 2 mm have been found to require the use of excessively thick filter layers in filters of acceptable size with higher filtration velocities equal to or greater than 50 m/hr.

The filter layer 6 supports the plate 7, on which the nozzles 9 of the type, for example, described in the patent application OE2O2004006883, are evenly located. According to the preferred option, said nozzles are made of polypropylene or polypropylene reinforced with glass fiber, installed in the holes in the plate 7 and attached to it by means of a locking nut. The heads 13 of the nozzles are embedded in a thin layer of coarse gravel 30, which forms the basis for the filter layer 6. The purpose of the nozzles 9 is to ensure both the output of water during filtering and the distribution of the return flow of air and/or water during backwashing.

During filtering, each of the nozzles 9 enables the passage of filtered water through very narrow slots 12 made in the surface of its head 13, after which it exits from below through the tubular element 14, which has a circular cross-section near the end, into the lower zone of the tank 2. Slots 12 nozzles 9 are designed to minimize the risk of contamination of the head. The lower zone of the tank 2, made with the possibility of collecting filtered water from the tubular elements 14, is located in the bottom part 4 with a drain or pipe 8, designed for the removal of filtered water, as well as for draining the remaining water from the filter device and supplying water for backwashing.

Two vertical slots 15" and 15", preferably located axially, have the distinct purpose of passing air through during backwashing, and preferably located at the bottom of each of the tubular elements 14; the supply of backwash water to the nozzles in the preferred embodiment is through an opening in the lower end of the tubular element 14.

The air and water are mixed already inside the tubular element and are then mixed more actively when passing through the slots 12 of the head 13. In a preferred embodiment, the air-water contact surface in the lower zone of the tank 2, also called a mirror or "meniscus", supported at a height between the slits 15, 15" and the lower end of the tubular member 14, so as to always leave a gap for air to enter through at least one of said slits. In a preferred embodiment, this meniscus is flat and constant throughout the backwash, such that thus ensuring no sudden changes in air and water flow rates at the nozzles in order to maintain the uniformity of the backwash.

Air supply for backwashing occurs through the casing 16, coaxially located outside the central water supply pipe 8. Air enters the casing 16 through a pipe 22. The said casing 16 is connected to a plurality of distributors 17 of air ducts, which, according to the preferred variant, are arranged in a star like a dial disk under the plate 7, and according to the preferred variant, their number is six, as shown in Fig. 3. The nozzles 9 according to the preferred option are located on the mentioned plate in the sectors of the circle formed by the disc with the star of the distributor located 17.

In a preferred variant, each distributor 17 has a rectangular cross-section and has openings 18 in the form of slits with a vertical longitudinal axis, made on two sides and located on the part of the distributor remote from the longitudinal axis of the tank relative to each other at a smaller distance, since the surface which should be covered by them, much larger. The air is evenly distributed under plate 7 of the nozzle holder, forming an air cushion. This backwash air distribution system design is particularly preferred. This design increases the efficiency of backwashing as such.

The supply of water for backwashing in this case occurs through a pipe connected to the outlet 8' of the tank.

Water for backwashing, which during its passage through the grains of sand took away the substances retained by the filter layer 6, is then fed to drain into the central pipe 8, which was previously used to supply the water intended for cleaning to the filter device. For this, in the end part of the mentioned pipe 8, a funnel 11 with a bell, which increases and expands upwards, is provided. The specific shape of the funnel 11, which has a bent edge 31 of an essentially conical shape, which expands downwards, enables optimal pouring of the flow and contributes to the necessary separation of air from water for backwashing: this effect is facilitated by the simultaneous reduction of the speed and the formation of a thin film in the funnel, which contributes to the separation air that has a lower density. The air separated from the water is released through the corresponding bypass valve 20, located in the upper part of the tank 2.

The funnel 11 also ensures proper distribution of water when feeding for filtering.

The filtration process and subsequent backwashing processes, which are periodically required to clean the filter bed, are described below.

The filtration process makes it possible to remove from the water intended for purification all suspended substances that cause pollution of the water itself, and also allows you to limit yourself to simply passing the water intended for purification, or simply sludge, through a single filter layer of selected sand.

Water passes through the filter layer 6 from top to bottom, and filtration occurs due to the gradual inhibition of solid particles due to the loss of kinetic energy during contact/collision with sand particles. In the preferred embodiment, the filtration speed is 40-70 m/h.

After a certain cycle of operation of the filter device, its filter layer must be cleaned or regenerated. Recovery is carried out with the help of backwashing, which consists in passing water and/or air in the direction opposite to the direction of filtration, that is, from the bottom up, so as to carry out backwashing, which enables the removal of dirt accumulated in the filter layer, after which the contaminated water is drained into the aforementioned central pipe.

Such an operation should be very efficient because the filter layer 6 has a large thickness, which in the preferred embodiment is between 2 m and 4 m, and the grain size in the preferred embodiment is between 1 mm and 2 mm, due to which dirt penetrates very deeply into the filter layer.

According to the preferred option, backwashing involves the following operations: - draining; - supply of only air for reverse blowing to perform cleaning of the head; - supplying an air-water mixture for effective backwashing; - supplying only water for backwashing; - final washing with a stream in the direction of filtration.

During the draining operation, the water contained in tank 2 is drained through outlet 8' to reduce the weight of the water column acting on plate 7. Draining is carried out to bring the water level near the upper surface of the filter layer to about a few centimeters above it. This operation is carried out to enable a faster, and above all, uniform start of further formation of air bubbles in the filter layer.

The air-only back-purge operation causes air bubbles to form in the sand bed and the subsequent rise and spread of air bubbles in the filter bed. This operation takes about 1 minute. and enables effective separation of dirt from sand particles.

According to the preferred option, after this, the operation of supplying a mixture of air and water for backwashing is carried out. This operation is carried out immediately after the previous one in order to quickly remove the separated dirt, to prevent its penetration even deeper into the filter layer. Thus, the backwashing operation as such is carried out using air and water. The air is also intended to separate the dirt from the sand granules, and the water is intended to transport the removed dirt to the outside. This operation is the most important and quantitatively lasts for the time required to change the water that is in the swollen volume of sand, at least 10 times. The turbulence created by the air-water mixture inside the granular material enables very effective washing.

The next operation involves supplying only water for backwashing. This operation lasts 2-5 minutes. It enables uniform and uniform deposition of the layer without the formation of empty spaces, which can reduce the efficiency of filtering.

The final operation of the backwash is backwashing with a stream in the direction of filtration, which is intended to prepare the filter device for filtration by further compacting the sedimented layer, and also to enable the removal of dirt not removed during the backwash operation, thus ensuring that perfectly purified water is obtained immediately after resumption of operation of the filtering device. This washing operation lasts about 5 minutes.

In a preferred embodiment, during backwashing, the air and water velocities are between 60 m/h and 110 m/h and between 11 m/h and 14 m/h, respectively. ! Cook Vol a

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Claims (12)

1. A sand filter device for water treatment, which includes a substantially cylindrical container (2) with a longitudinal axis, which has a plate (7) inside, which divides the container into an upper zone and a lower zone, in which a filter layer is located inside the upper zone (b), which consists of a single layer of sand with a height H determined by the equation H-aet, where the parameter "a" has a value from 500 to 800, the parameter "B" has a value from 0.020 to 0.045, and the filtration rate "y" is 40-70 m/h. 2. The filtering device according to item I, characterized in that the parameter "a" is approximately 580, the parameter "B" is approximately 0.029, and the filtering speed is approximately 50 m/h. 3. The filtering device according to item I, which is characterized by the fact that the nozzles (9) are installed in the corresponding holes, which are evenly located on the surface of the plate (7). 4. The filter device according to claim 3, which is characterized by the fact that the lower zone has a drain or pipe (8) in the bottom part (4) for removing the filtered water, draining the remaining water from the filter layer and supplying water for backwashing. 5. The filter device according to claim 4, which is characterized in that the nozzles (9) have tubular elements (14) in which two vertical longitudinal slots (15, 1U) are made for the passage of air and/or water for backwashing through the nozzles (9 ). 6. The filter device according to claim 5, which is characterized by the fact that a casing (16) is provided for air supply for backwashing, coaxially located outside the central water supply pipe (8) and connected by means of a pipe (22). 7. The filtering device according to point b, which is characterized by the fact that the said casing (16) is connected to a plurality of channels (17) of air ducts, which are arranged in a star like a dial disk. 8. Filtering device according to claim 7, which is characterized by the fact that said channels (17) have a rectangular section and on two sides have openings (18) in the form of slits with a vertical longitudinal axis. 9. Filtering device according to claim 6, which is characterized by the fact that on top of the end part of the mentioned central pipe (8) there is a funnel (11) with a bell that increases and expands upwards and has a bent edge (31) of an essentially conical shape that expands down. 10. The method of backwashing the sand filter device according to claim 1, which includes the following operations: draining the water intended for filtering, which is contained in the upper zone of the container (2), until the water level approaches the upper surface of the filter layer (b); reverse flow of air to clean the head and create air bubbles in the filter layer for about 1 min; providing a reverse flow of the air-water mixture to remove the separated dirt during the time required to change the water in the volume of sand at least 10 times; reverse flow of only water for 2-5 minutes to obtain a uniformly and homogeneously deposited layer; a final backwash to prepare the filter bed for filtration and to remove dirt not removed during the backwash operation. 11. The method of backwashing according to claim 10, which is characterized by the fact that the speed of air and water, respectively, is from 60 m/h. up to 110 m/h. and from 11 m/h. up to 14 m/h. 12. The method of backwashing according to claim 10, which is characterized by the fact that the contact surface of air with water is kept flat and unchanged during the entire backwashing, and thus ensures the absence of sudden changes in the flow rate of air and water at the nozzles (9) in order to preserve uniformity of backwash.