RU2440170C2 - Sand filter - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to sand filter for water treatment. Said filter comprises cylindrical container housing the plate to divide it into top and bottom zones. Top zone contains filtration medium comprising single layer of sand with height H defined by formula H=a·e^b-v, where a varies from 500 to 800, b varies from 0.020 to 0.045 and filtration rate v makes 40-70 m/h. Back flushing of sand filter consists in draining filtered water contained in container top section to the level of filtration medium top surface. Air back flow is forced therein to break the crown and create air bubbles in filtration medium. Said back air-water flow is forced therein to remove dirt released in water change in sand volume and force water backflow to precipitate filtration medium. Now final flushing is performed in parallel flow to prepare said medium for filtration and eliminate dirt not removed in back flushing.

EFFECT: higher efficiency of filtration, longer life.

12 cl, 5 dwg

Description

FIELD OF THE INVENTION

The present invention relates to a sand filter device used in water treatment plants or WTP installations, and in particular, primary, secondary water treatment plants and cooling water treatment plants.

State of the art

Various sand filtering devices used in water treatment systems are known.

However, such devices exhibit various disadvantages, such as:

- formation of surface crusts with frequent filter clogging phenomena and subsequent frequent backwashing operations;

- they do not allow to achieve high filtration rates, and, therefore, systems require a large number of filters;

- they require a layer of anthracite over a layer of sand in order to retain oils and greases contained in contaminated water;

- they imply high capital costs and operating costs.

Thus, there is a need for a sand filter system that overcomes the aforementioned disadvantages.

Disclosure of invention

The main objective of the present invention is to create a sand filter device for primary, secondary water treatment and cooling water treatment plants, containing a single-layer filter medium or just a filter that allows you to get completely clean water and a long service life at high filtration rates.

Another objective of the device according to the invention is to obtain a very effective backwash operation of the filter, able to timely ensure the throughput of the filter.

Accordingly, the present invention proposes to solve the above problems by creating a sand filtering device for water purification, which in accordance with paragraph 1 of the claims contains a substantially cylindrical tank defining a longitudinal axis, equipped with a plate located inside it so as to separate this tank itself to the upper the zone and the lower zone, in which the upper zone contains a filter medium containing a single layer of sand having a height H, determined by the formula:

H = a · e ^bv ,

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 filtering speed "v" has a value in the range of 40-70 m / h.

Another aspect of the invention relates to a backwash method of the aforementioned filter device, which, in accordance with paragraph 10 of the claims, contains the following steps, in which:

- drain the filtered water contained in the upper zone of the tank until the water level is established near the upper surface of the filter medium;

- introduce a reverse air flow in order to destroy the tip and form air bubbles in the filter medium, for a period of time of approximately 1 minute;

- introducing a reverse flow of air - water in order to remove the released dirt, during the period of time required to change the water contained in the volume of sand at least 10 times,

- a reverse flow of water alone is introduced over a period of time ranging from 2 to 5 minutes in order to precipitate the filter medium in a uniform, uniform manner;

- carry out the final washing in parallel flow, in order to prepare the filter medium for the filtering operation and eliminate dirt that is not removed at the stage of backwashing.

It is useful that the aforementioned relationship between the height of the filter layer, the grain size of the sand used and the filtering speed allows you to set the size of the filtering medium in such a way as to guarantee optimal filtering conditions at high speeds.

The subject of the present invention, which is a filter device, being suitable for efficient operation at filtering speeds, which can also reach 70 m / h, provides the following advantages:

- it allows you to offer filter systems that use approximately half of the traditional filters;

- It allows you to create more compact and more rational layouts with a significant reduction in capital costs and operating costs.

It is useful that the device according to the invention uses a large height of a single layer of filter medium, which increases the filtration path, and a relatively large grain size of sand, which allows you to use a larger filtration volume and distribute the dirt contained in the water to be purified over said volume to avoid the formation of surface crusts and therefore frequent filter plugging.

Due to this feature, the device according to the invention does not require a layer of anthracite over a layer of sand, as is the case with known filters in order to trap oils and greases contained in contaminated water, with significant savings in capital costs and operating costs.

The dependent claims describe preferred embodiments of the invention.

Brief Description of the Drawings

Additional features and advantages of the invention will be more apparent from a detailed description of a preferred, but not exclusive, embodiment of a filter device, illustrated as a non-limiting example using the accompanying drawings.

Figure 1 shows a schematic sectional view of a filter device according to the invention;

on figa and 2b shows views in section along mutually perpendicular planes of a component of the device shown in figure 1;

figure 3 shows a top view of part of the second component of the device according to the invention;

figure 4 shows a side view of a variant of the third component of the device according to the invention;

figure 5 shows an enlarged image of the element shown in figure 1.

The implementation of the invention

The drawings show a filter device, indicated generally by reference numeral 1, contained in a substantially cylindrical steel tank or tank (2) provided with vertical walls (3), a bottom (4) and a cover (5). The tank (2) is divided internally into two zones by a plate (7). The upper zone is equipped with a filter medium (6) containing a single layer of appropriately selected sand. Typically, the filter medium (6) rests on a thin layer of rather large gravel (30), which does not have a filtering effect, which in turn rests on the plate (7).

The purified water is supplied to the filter medium (6) through a central pipe (8) located along the longitudinal axis of the tank (2). Such a pipe (8) is equipped with a filtered water inlet section (10) near the bottom of the tank (4) and a said water outlet section near the lid (5).

The fact that a single layer of filter sand is provided allows a more uniform use of the filter medium. The grain size of the sand, relatively large and uniform, allows to achieve high filtration rates, operate the filter layer to the full depth and, thus, distribute the dirt throughout the layer, avoiding the formation of surface crusts and, thus, the phenomenon of early clogging of the filter.

An additional advantage is represented by the fact that the filter medium (6) has a predetermined height so as to determine a larger filtration volume and a filtration path longer in relation to this path in conventional filters; it also allows you to extend the time you use the filter before you need to perform a backwash, since the filter does not clog.

To correctly determine the dimensions of the filter medium or a single filter layer (6), taking into account the grain size used, the following preferred mathematical ratio was determined, which gives the optimal layer height:

H _OPTIMAL = a · e ^bv ,

where "a" and "b" are parameters that depend on the grain size of the sand, and "v" is the filtration rate. Such an equation shows the logarithmic dependence of the layer height on the filtration rate. Parameter a has a value from 500 to 800, and parameter b has a value from 0.020 to 0.045.

The grain size was found to be the best in terms of performance, ranging from 1.0-2.0 mm, which corresponds to an “a” value of approximately 580, and a “b” value of approximately 0.029, which allows one to obtain a filtration rate of at least 50 m / h, with a height of the filter medium (6) of approximately 2.5 meters. Under such conditions, starting with a concentration of particles suspended in the feed sludge equal to 80 parts per million, it is thus possible to obtain a maximum concentration at the output of only 10 parts per million.

It was found that a smaller grain size of 0.7-1.0 mm requires a thinner filter layer, but is too small to allow dirt to precipitate throughout the filter medium, a preferred condition for ensuring long service life before how to flush back.

In addition, it was found that larger grain sizes greater than 2 mm would instead require filter layers that are too thick to be used in filters of acceptable sizes at higher filtration speeds equal to or higher than 50 m / h.

The filter medium (6) is supported by a plate (7) over which nozzles (9) are uniformly distributed, of the type described, for example, in patent application DE 202004006883. The mentioned nozzles, preferably made of polypropylene or fiberglass reinforced polypropylene, are inserted in the holes made in the plate (7), and attached to it by means of a lock nut. The nozzle heads (13) are immersed in a small layer of coarse gravel (3), which forms the base for the filter medium (6). The function of the nozzles (9) is both to drain the water during the filtration step and to distribute the backflow of air and / or water during the backwash step.

During the filtering operation, each nozzle (9) allows filtered water to enter through very narrow slots (12) obtained on the surface of its head (13), and then drains it from the bottom through a tubular stem (14) having a cross-section in the shape of a round rim , to the lower zone of the tank (2). The slots (12) of the nozzles (9) are designed so as to minimize the risk of contamination of the head. The lower zone of the tank (2), suitable for collecting filtered filtered water from tubular stems (14), is equipped on the bottom (4) with a pipe or pipe (8 '), which are used to pump out the filtered water, but also in order to drain the filter and introduce backwash water.

Preferably, two vertical slots (15), (15 ') are provided at the bottom of each of the stems (14), the exact function of which is to let air through during the backwash phase of the filter; it is preferred that the backwash water enters the nozzles through an opening at the lower end of the stem (14).

Air and water are already mixed inside the stem and then will be mixed more closely when passing through the slots (12) of the head (13). Preferably, the air-water interface, also called the meniscus, in the lower zone of the tank (2) is maintained at the height contained in the interval between the slots (15), (15 ') and the lower end of the stem (14), for in order to always leave a gap for introducing air through at least one of said slots.

Preferably, the meniscus is flat and stable throughout the entire backwash phase, thereby ensuring that there are no jumps in the air and water flow rates to the nozzles and, therefore, the uniformity of the backwash.

The backwash air is introduced by means of a jacket (16), external and coaxial with respect to the central water inlet pipe (8). Air enters the shirt (16) through the pipe (22). Said shirt (16) is connected to a plurality of air diffusers (17) arranged preferably in the form of a dial, preferably in the amount of six, under the plate (7) as shown in FIG. 3. Preferably, the nozzles (9) are distributed over said plate in circular sectors defined by the dial of the valves (17).

It is preferable that each distributor (17) has a rectangular section and is equipped with slots (18) with a vertical longitudinal axis located on two lateral sides and located closer to each other on the outside, with respect to the longitudinal axis of the tank, of the distributor, because the surface here is larger. The air is evenly distributed under the nozzle plate (holder) (7), thus forming an air pocket. This backwash air distribution configuration is particularly convenient, increasing the efficiency of the backwash itself.

In contrast, the backwash water is introduced by means of a pipe connected to the tank nozzle (8 ').

The backwash water, which during its passage through the sand granules pulled with it substances that were retained by the filter medium (6), is then transferred for discharge to the central pipe (8), which was previously used to introduce the water to be cleaned into the filter. To this end, an upwardly funnel-shaped funnel (11) is provided at the end of said pipe (8), which has the sign that it is relatively large and flattened. The special shape of the funnel (11), equipped with an edge (31), which has a substantially conical shape and expands in the downward direction, makes possible an optimal overflow and promotes the necessary separation of air from the backwash water: this effect is facilitated by a decrease in speed and the formation of a thin films in the funnel, which contributes to the release of less dense air. Air that has been freed of water is discharged through an appropriate safety valve (20) located on the top of the tank (2).

The funnel (11) also allows you to properly supply water during the introduction of it for filtering.

The filtering process and the subsequent backwash processes that are periodically necessary to clean the filter medium are described below.

The filtering process allows you to remove from the purified water all suspended substances that cause turbidity of the water itself, and simply allows the passage of the purified water or simply sludge through a single filter layer of the selected sand. Water passes through the filter medium (6) from the top to the bottom and filtering occurs after the gradual deceleration of solid particles due to the loss of kinetic energy during their bounce / collisions with sand particles. Preferably, the filtration rate is in the range of 40-70 m / h.

After some working cycle of the filter, the filter medium needs to be cleaned or restored. The recovery is carried out by means of a backwash operation, which consists in the flow of water and / or air in the opposite direction to the filtration direction, i.e. from the bottom upwards, so as to perform backwash, which allows you to remove the dirt accumulated in the filter medium, then drain the dirty water the aforementioned central pipe.

Such an operation should be very effective because the filter medium (6), having a large thickness, preferably from 2 to 4 m, and grain size preferably from 1 to 2 mm, implies that the dirt settles very deep in this filter medium.

Preferably, the backwash operation comprises the following steps:

- drain;

- the introduction of air backwash alone in order to destroy the tip;

- the introduction of air - water backwash for effective backwash;

- the introduction of only backwash water;

- final flushing in parallel flow.

During the draining operation, the water contained in the tank (2) is drained through the pipe (8 ') in order to reduce the weight of the water column that presses on the plate (7). Draining is performed in order to bring the water level closer to the upper surface of the filter medium, approximately a few centimeters from it. This operation is performed in order to make possible a faster and, among other things, smoother start of the subsequent bubbling of air in the filter medium.

The stage of introducing backwash air alone leads to the formation of air bubbles in the sand layer and to subsequent bubbling of air in the filter medium, which rises and expands. This operation lasts approximately 1 minute and allows you to effectively separate the dirt from the granules of sand.

Preferably, the next step is the introduction of a mixture of air and water backwash. This step takes place immediately after the previous step in order to quickly remove the dirt that has been released, thus preventing it from penetrating deeper into this layer. Therefore, the backwash operation itself is carried out using air and water, while the air serves again to separate the dirt from the sand granules, while the water serves to carry the dirt away. This stage is the most important and, which is significant, lasts for the period of time necessary in order to change the water contained in the expanded volume of sand at least 10 times. The turbulence generated by the air-water mixture within the granular material allows a very effective flushing.

The next step involves the introduction of only backwash water. This stage lasts for 2-5 minutes and allows the filter medium to settle uniformly and evenly, without leaving any free spaces that could reduce the filtering efficiency.

The backwashing operation ends with a washing step in a parallel flow, which serves to prepare the filter for the filtering operation, further compacting the deposited layer and allowing the removal of dirt not removed during the backwashing step, thus providing completely clean water immediately after restart the filter. This washing step lasts for approximately 5 minutes.

Preferably, during the backwash, the air and water velocity parameters are respectively 60 to 110 m / h and 11 to 14 m / h.

Claims (12)

1. Sand filtering device for water purification, containing a substantially cylindrical tank (2) defining a longitudinal axis, provided with a plate (7) located inside it so as to separate this tank itself into the upper zone and the lower zone, in which the upper the zone contains a filter medium (6) containing a single layer of sand having a height H, determined by the formula:
H = a · e ^bv
where parameter a has a value from 500 to 800, parameter b has a value from 0.020 to 0.045, and the filtering speed v has a value in the range of 40-70 m / h. 2. The filter device according to claim 1, in which 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 claim 1, in which nozzles (9) are evenly distributed on the surface of the plate (7), fixed in the corresponding holes. 4. The filter device according to claim 3, in which the lower zone is provided on the bottom (4) with a pipe or pipe (8 ') for pumping out filtered water, draining the filter medium and introducing backwash water. 5. The filter device according to claim 4, in which the nozzles (9) are equipped with stems (14) having two vertical slots (15), (15 ') in order to pass air and / or backwash water into the nozzles (9) . 6. The filter device according to claim 5, in which a jacket (16) is provided, external and coaxial with respect to the central water inlet pipe (8), for introducing backwash air connected through the pipe (22). 7. The filter device according to claim 6, in which said shirt (16) is connected to a plurality of air diffusers (17) arranged in the form of a dial. 8. The filter device according to claim 7, in which the said distributors (17) have a rectangular cross section and are provided on two sides with slots (18) with a vertical longitudinal axis. 9. The filtering device according to claim 6, wherein an upwardly extending funnel (11) having a wide and flattened shape and having an edge (31) of substantially conical shape and expanding along the upper end portion of said central pipe (8) is provided downward direction. 10. A method for backwashing a sand filter device, comprising the following steps, in which:
- drain the filtered water contained in the upper zone of the tank (2) until the water level is established near the upper surface of the filter medium (6);
- introduce a reverse air flow in order to destroy the tip and form air bubbles in the filter medium for a period of time of approximately 1 min;
- introducing a reverse flow of air - water in order to remove the dirt that has been released during the period of time required to change the water contained in the volume of sand at least 10 times,
- a reverse flow of water alone is introduced over a period of time ranging from 2 to 5 minutes, in order to precipitate the filter medium in a uniform uniform manner;
- carry out the final washing in a parallel flow in order to prepare the filter medium for the filtering operation and eliminate dirt not removed at the backwash stage. 11. The backwash method according to claim 10, in which the parameters of air and water velocity are respectively from 60 to 110 m / h and from 11 to 14 m / h. 12. The backwash method according to claim 10, in which the air-water interface is kept flat and stable throughout the entire backwash, so that there are no jumps in the air and water flow rates to the nozzles (9) and so that the uniformity of the backwash is maintained flushing.

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