RU2134139C1 - Method of flushing pressure clarifying filter - Google Patents

Abstract

FIELD: preparation of water at water preparation plants; flushing mechanical filters. SUBSTANCE: flushing the pressure clarifying filter is effected by draining the water cushion, loosening the media with air, drying the filter, feeding water-and-air mixture under filter media, discontinuing air supply before transfer of water to discharge device and replacement of volume of water in above-medium space due to opening inlet gate of filter. EFFECT: reduced consumption of water required for flushing the filter; ease of removal of dirt from filter medium. 6 dwg

Description

 The method relates to a technology for the preparation of water in water treatment plants, namely to flushing pressure clarifying filters.

In water treatment plants of power plants, fast pressure filters with a filter loading height of 1.0 m are most widely used. The recommended intensity of washing the filter with water is 12 l / s • m ² . In terms of a filter with a diameter of 3.4 m, the performance of the pump by flushing water will be:
Q = 3.6 F • W = 3.6 • 9.1 • 12 = 393 m ³ / h = ~ 400 m ³ / h
where F is the filter area (m ² );
W is the washing intensity (l / s • m ² ).

 Such a flow rate of washing water requires powerful pumps, a tank farm, and large-diameter supply lines. When trying to raise the filtration rate to 10 - 12 m / h with an equivalent grain diameter of the filter layer of 1.1 - 1.2 mm, the loading height should be ~ 2000 mm (V.A. Klyachko, I.E. Apeltsin. Purification of natural waters. - M .: Publishing house of literature on construction, 1971, p. 248-253).

Recommended water flushing rate is 18 l / s • m ² . In terms of a filter of the same diameter, the performance of the wash water pump will be:
Q = 3.6 • 1.9 • 18 = 589 m ³ / h = ~ 600 m ³ / h.

 Such a flow of water is practically impractical.

 Patent N 20006251 protects a method that allows, regardless of the type of loading, to carry out the filtered suspension into the supercharging space by means of intensive air-water washing. The action of the washing effect of water-air washing begins when the water mirror rises from a certain level above the loading surface and ends before it overflows into the discharge funnel. This distance is about 500 - 700 mm.

 The free volume of the supercharge space determined by this height is small for filling it with the overflow of wash water from the pore space of a two-meter load. Substitution of water in the pore space should be at least once, and this condition determines the duration of the operation of the water-air washing. With such a limited movement of the water column level, complete removal of contaminants from the two-meter thickness of the load is not possible.

 A method for washing the filter load with a height of 2000 mm is proposed; its implementation is illustrated by the example of a single-chamber filter (Fig. 1).

 The descent of the water cushion is carried out from the low level sensor (NU) located above the load at a height of ~ 1.2 H, where H is the height of the load, which provides 20% expansion when it is loosened by air.

 The operation of loosening the air is carried out with the open valve 6 with air exhaust through the open valve 4 (figure 2). This operation, carried out in a limited water volume, allows you to wipe away any contaminants from the surface of the grains. Its time is 5-10 minutes, depending on the nature of the pollution. When air bubbles move through the pore space, the load of pollution is not only rubbed off from the grains, but also dispersed (see USSR Author's Certificate N 936963, class B 01 D 23/24, 06.23.82). After loosening, the filter is completely drained with open valves 4 and 5. As the water escapes, the pore loading space is filled with air (Fig. 3).

The next operation is water-air flushing. To do this, the valve 5 closes and the valves 3 and 6 open. Water and air are supplied under the load. Air is supplied at a flow rate of ~ 12 l / s • m ² . The criterion for the intensity of the air supply is its sufficiency for distribution over the entire filter area. The intensity of the water supply during the air purge can vary within wide limits, but should not fall below 1.4 l / s per m ² . Moreover, the higher the rinsing water consumption, the faster and more efficient rinsing occurs (see Degremon. Technical Notes on Water Problems, T.1, p. 273).

When testing the proposed method, the water flow rate was 2.5 l / s per 1 m ² .

 In the newly wetted charge, apparently, the proppant pressure of a thin layer of liquid begins to act between the grain surfaces and the mass of suspension particles settled on them. Dispersed contaminants with a weakened attachment strength to the grain surface of the filter material are pushed into the free pore space at the interface with the dense medium of a boiling water-air front (figure 4).

 Unlike the flushing method of A.M. Fominykh (see Flushing fast filters. Overview, N 70 USSR Ministry of Land Reclamation and Water Resources, TsBNTI, Moscow, 1981, p. 16.28), air-flushing continues almost to the level of overflow , after which the air turns off. All that, for some reason, did not fall into the coverage area of the rising front front, is crushed by the water-air flow during the ascent of the mirror from the loading surface to the level of the VU (Fig. 5). After the air supply stops, water continues to flow under the load for some time. This is necessary to displace the remaining air from the load and to deposit grains of filter material raised into the loading space. Then the water supply stops. By this time, most of the contaminants have been removed from the filter load and collected in a layer of water between its surface and the upper drainage.

 In the event that the contaminants are heavy or difficult to remove, these operations can be repeated.

 Subsequent removal of the raised dirt is carried out by replacing water in the loading space. To do this, the inlet valve 1 opens and water flows through the scrubbing device into the loading space, preventing dispersed contaminants from settling onto the loading surface (Fig. 6). Draining through an open 4th valve ensures water exchange in the loading space.

In this way:
1. Using the operation of loosening the air before draining the filter allows you to extend the time for dispersion of the detained contaminants. This facilitates their subsequent removal from the load with a time-limited water-air washing, which makes it more efficient.

 2. The relatively small flow rate of water supplied to the load during water-air washing, and the use of an inlet valve 1 for exchanging it in the loading space, eliminates the need for powerful pumps, an expensive tank farm, saves electric energy for own needs and eliminates wiring from large-diameter pipes .

Claims (1)

 A method of washing a pressure-clarifying filter, including operations of lowering a water cushion, loosening the load with air, water-air washing, characterized in that after loosening the load with air, the filter is drained, and then the water-air mixture is fed under the load, and the air supply is stopped before the water overflows into the discharge device and replaced the volume of water in the charging space, opening the inlet valve of the filter.

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