RU1200449C - Method of hydraulic discharging of grain filtering material - Google Patents

Description

 The invention relates to methods for hydraulically unloading granular filter material on bulk filters with a flat drainage grate and can be used in filters for treating water from thermal and nuclear power plants, as well as in chemical and other industries.

The aim of the invention is the complete cleaning of the drainage lattice from granular material with a density of 1100-4300 kg / m ³ .

 In FIG. 1 shows a filter for implementing the method; figure 2 section aa in figure 1.

 The filter contains a vertical cylindrical housing 1, in the lower part of which a flat drainage grill 2 is installed, equipped with filter elements 3. Above the central part of the grill 2 there is a hydraulic discharge pipe 4, which is a curved pipe mounted on the wall of the housing. Directly above the drainage grid 2 there is installed a device for tangential water inlet into the housing, which is, for example, pipes 6 connected by a common collector 5. Since the pipes 6 are located radially to the housing 1, guide walls 7 of the grooved type are provided on its inner wall, overlapping the outlet openings of the pipes 6. To prevent the filter material 8 from getting into the water supply pipe for additional discharge, safety devices 9 are installed on each pipe 6, made, for example, in de ball check valve. In addition, the design of the apparatus provides nozzles 10 and 11, respectively, designed to supply water under the drainage grid 2 and enter water into the collector 5 to reload material.

 PRI me R. Transporting water was supplied under a drainage grate with a diameter of 1 m at a speed of 10 m / h, the anionite layer AB-17 was weighed, and, together with water, it was removed from the filter through a hydraulic discharge pipe installed above the center of the grate. After unloading, a part of the material remains on the drainage grate. For its additional discharge, a layer of water rotating relative to the axis of the filter was created in the filter housing (rotation can be provided by any method, for example, using pipes to supply a jet of water and into the filter housing tangentially to its wall or using a mixer).

 Under certain conditions of rotation, the material distributed along the grate was collected towards its center and, with a water flow through a centrally located hydraulic discharge pipe, it was removed from the filter, for example, under the influence of the vacuum created in the transport line, as a result of which the filter material was completely unloaded.

 As you know, in a rotating system, particles of a heavier filter material should be discarded to the periphery under the action of centrifugal force, and not collected to the center.

 The reverse picture is explained by the following.

 When the fluid rotates, a centrifugal force appears, dropping the fluid to the periphery and exerting pressure on the walls of the housing. Since the outflow of fluid occurs from the center, a region of reduced pressure appears here. The value of centrifugal pressure is the same along the wall with the exception of the bottom layer, where the fluid is inhibited by friction. In this near-bottom boundary layer, the rotational speed, and hence the centrifugal force, is zero or much less than in the main volume.

 As a result of this, fluid circulation occurs in the bottom layer, and the latter, under the action of increased centrifugal pressure, falls along the walls to the bottom, and then moves radially to the area of reduced pressure to the center, where it rises from the bottom and is again discarded to the periphery. The occurring circulation leads to the fact that in the bottom layer there is a centripetal force acting on the particles towards the center. At a certain speed, or rather in a certain range of speeds, the boundary layer has a sufficiently large height and affects the particles placed on the drainage grid, inhibiting them. As a result of inhibition, the centrifugal force acting on the particles decreases and becomes less centripetal. Under the influence of the difference of these forces, the particles move to the center and together with water are removed from the filter.

 However, with an increase in the rotation speed, the height of the boundary layer decreases and it affects the particles less, which leads to an increase in the centrifugal force acting on them. As the rotation speed increases, the centrifugal force increases and finally there comes a moment when it becomes more centripetal and the collection of material to the center does not occur. The value characterizing the centrifugal force is the separation factor, or without taking into account the constant value of the gravitational acceleration, centrifugal acceleration.

With an increase in centrifugal acceleration over a certain critical value, which depends on the density of the material and the higher, the higher its density, the collection of particles to the center stops, and the collected material begins to erode. During the experiment, it was determined that for one of the lightest filter materials having a density higher than the water density of anion exchange resin AB-17 with a density of 1100 kg / m ^{3, the} critical value of centrifugal acceleration is 2.2 m / s ² , and for the heaviest brand sorbent GDT-M with a density of 4300 kg / m ³ 9.8 m / s ² . For other filtering materials having an intermediate density, the critical value of centrifugal acceleration was in the range of 2.2–9.9 m / s ² , and the specific value of acceleration was determined by the density of the material, provided that the grain size of these materials lies in the usual range: 0 , 4-1.5 mm. It follows from the foregoing that a necessary condition for the implementation of the proposed method is to ensure such rotation of the liquid layer in the apparatus so that the value of centrifugal acceleration during its rotation does not exceed the critical value for this material.

In this case, the specific acceleration values for various granular filtering materials with a density of 1100-4300 kg / m ³ are in the range of 2.2-9.8 m / s ² . In addition, the best conditions for collecting particles to the center are created, ceteris paribus, with a layer height of a rotating stream of water equal to 0.6-1 diameter of the filter.

 Tables 1 and 2 show the experimental results.

 As can be seen from the data presented, for a device with a diameter of 0.3 m, the best results were obtained with a height of a water layer of 180-300 mm, for a device with a diameter of 0.4 at a height of 240-400 m, and for a device with a diameter of 0.5 m at a height of 300- 500 mm.

 Therefore, we can conclude that the best conditions for moving particles of the filter material are indeed created at a height of a rotating layer of water equal to 0.6-1.0 of the diameter of the apparatus.

Claims (2)

1. METHOD FOR HYDRAULIC GRAIN LOADING OF A GRAIN FILTERING MATERIAL from a flat filter drainage grate, including weighing the granular filter material by feeding a stream of water under the drainage grate from the bottom up, discharging the resulting suspension, subsequent additional flow of water over the drainage grate and discharging the resulting suspension, which that, in order to completely clean the drainage grate from granular material with a density of 1100 4300 kg / m ³ , rotational motion is imparted to the additional flow of water with centrifugal acceleration not exceeding 2.2 9.8 m / s ² , respectively, and the resulting suspension is discharged from the central part of the lattice.  2. The method of hydraulic discharge according to claim 1, characterized in that the height of the rotating layer of water is maintained within 0.6 to 1.0 of the diameter of the filter.

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