RU2192914C2 - Aerosol sorbing filter and method of its manufacture - Google Patents

Abstract

FIELD: aerosol sorbing filters. SUBSTANCE: aerosol sorbing filter has casing accommodating filter medium arranged in zigzag with separators of corrugated aluminum sheet installed in filter medium folds. Filter medium is made of coarse-fibrous material containing highly dispersed sorbent with highly porous particles 1-100 mcm in diameter and packed in layers. The layer last in said layers in direction of air flow is made of fine-fibrous material and contains no sorbent. Use of said filter provides for simplification of process of complex air cleaning due to the fact that it possesses highly efficient dust-capacitive aerosol filter absorbing iodides, highly efficient with respect to aerosols and highly capacitive relative to molecular iodine and its organic compounds. EFFECT: higher efficiency. 8 cl, 2 dwg, 1 tbl

Description

 The invention relates to techniques for gas purification by filtering, including from radioactive and highly toxic chemicals, and more specifically, to devices for separating aerosol particles and sorption of molecular compounds by filter material intended for highly efficient air purification from radioactive and other and other harmful substances in aerosol and molecular form, and can be used in gas purification systems of nuclear reactors and other objects, the operation of which leads to pollution of the gaseous medium radio active substances.

 The operation of nuclear reactors, plants for the processing and disposal of nuclear fuel and other facilities whose work is associated with the use of radioactive substances, poses many problems due to the need to protect personnel, the public and the environment as a whole from radioactive contamination.

 The entry of radionuclides into the indoor air and into the process gas environment occurs both under normal technological processes and in emergency situations when radionuclide emissions can be especially significant.

 In this case, radionuclides enter the air both in the form of aerosols, i.e., solid and liquid particles containing radionuclides, and in the form of gaseous and vaporous molecular compounds, which are then partially deposited on aerosol particles.

The sizes of aerosol particles contained in the air of atomic and other enterprises to be cleaned, as well as in the supply air, lie in a wide range from thousandths of a micrometer to several tens of micrometers, while the bulk of the particles have sizes from fractions of a micrometer to 3-5 micrometers . The mass concentration of aerosol particles, as a rule, is 0.05-0.5 mg / m ³ , but can reach values of several g / m ³ . The radioactivity of individual particles is usually 1-100 Bq, but individual particles can carry tens or hundreds of Becquerels.

Radionuclides in gaseous and (or) vaporous form are radioactive noble gases and vapors of iodine, rhenium and some other radionuclides and vapors of their volatile compounds, for example CH ₃ J - methyl iodide.

 The main danger is represented by pairs of elementary radioiodines and pairs of their organic compounds - methyl iodides.

 Thus, in order to reduce the content of radionuclides in the air of nuclear facilities and to reduce their emission into the atmosphere, especially in case of accidents, nuclear plants should have highly efficient reliable exhaust and flow recirculation air purification systems operating both in normal operating conditions of the enterprise and in conditions accidents, and providing cleaning from radioactive aerosols and radioiodines.

 At nuclear plants, as a rule, two-stage cleaning systems are used, consisting of a high-performance aerosol filter and an iodine adsorber filter.

 Filter adsorbers as a stage of iodine purification are, as a rule, devices in which the sorbent is placed in a box-type chamber, divided into sections filled with sorbent granules. As a sorbent, in most cases, granules of activated carbons of about 1-2 mm in size are used, impregnated with various chemical compounds that provide chemisorption of molecular iodine and (or) methyl iodide [German Patent 3129384, cl. B 01 D 46/30, 53/00, application. 07/25/1981, publ. 02.24.1983; German patent 2149604, class G 21 F 9/00, B 01 D 46/34, application. 04/19/1964, publ. 10/30/1975].

 Granular sorbent adsorber filters have a number of significant disadvantages.

Firstly, with granule sizes of 1-2 mm, the ratio of the geometric surface area of the granules to their mass is small, as a result, to ensure high adsorber efficiency, a large sorbent mass is required, which leads to a high aerodynamic drag of the adsorber and, as a result, to a high cost of operating the adsorber . So, for example, the AUI-1500 iodine adsorber used in Russia [AUI-1500-1 carbon adsorber, passport I 18192B, Birch, 1995] contains about 250 kg of carbon sorbent, has a capacity of 1500 m ³ / h and at the same time its aerodynamic drag reaches 2500 Pa.

 Secondly, the abrasion of the granular sorbent, especially based on activated carbons, inevitably caused by the movement of air, leads to the formation of dust, which is partially carried away and partially remains in the adsorber, clogs the channels between the granules and thereby sharply increases the aerodynamic drag, making it at the end ends inoperative. Removal of dust from the adsorber, i.e. small particles of sorbent containing radionuclides, requires the installation of another aerosol filter, which further increases the cost of manufacture and the cost of operation of the cleaning system.

 Thirdly, the disposal of the exhausted filter-adsorber with a large amount of granular sorbent is very expensive. Its cost is ten times higher than the cost of disposal of an aerosol filter of the same performance.

 Known filter unit for air purification of nuclear installations from radioactive substances [French Patent 2473348, cl. G 21 F 9/02, B 01 D 46/42, application. 01/09/81, publ. 07.17.81], which consists of two standard containers connected in series, in one of which a granular or powdery filter layer is placed, and in the other, a solid filter material, both containers are connected to the air channel.

 In addition to the disadvantages inherent in adsorber filters, this installation is inconvenient to use, since it is bulky and difficult to replace.

 Known aerosol sorbent filter containing a housing in which the filter element is placed, made of a zigzag folded multilayer filter material containing finely ground carbon particles, and with separators-separators located between the folds [Yu. N. Filatov. "Electroforming of fibrous materials (EPI process)", M. 1997, pp. 254-259, 198-203].

 However, the dust capacity of such a filter is small and with a high dust content of the cleaned air containing molecular iodine and especially its organic compounds, it is not effective enough. The filter is quickly filled with iodides, and other aerosol particles with sizes less than 1 μm containing radioiodine can pass through the pores of the filter material. The objective of the present invention is to increase the efficiency of air purification from aerosols containing molecular iodine and its organic compounds by increasing the dust absorption of the filter adsorbing iodides, as well as simplifying the process of comprehensive air purification and filter design.

The problem is solved in that in an aerosol sorbent filter containing a housing in which a filter element is placed containing a sorbent made of a zigzag folded multilayer filter material with separator-separators located between the folds, all layers of coarse-fibered filter material, except for the last one in the direction of the stream to be cleaned air, contain particles of finely ground sorbent with a diameter of 1-100 microns in an amount of 10-500 g / m ² , and the last layer along the surface of the cleaned air stream Ha is made of fine fiber material that does not contain a sorbent with a packing density of not more than 0.06.

 To ensure the heat resistance of the filter, fiberglass was used as a filter material, and impregnated activated carbon particles were used as a finely ground sorbent.

 For the rational organization of the flow into the filter, separators-separators installed between the folds of the zigzag folded filter material are made of corrugated aluminum sheet.

The problem is solved in that the filter is made by a method that consists in placing a zigzag folded, pre-packed in layers of fibrous filter material in the housing, and separating separators in folds, all layers except the last along the stream being cleaned, made of filter material, into which the sorbent particles are finely divided diameter of 1-100 microns in an amount of 10-500 g / m ^2, and the latter in the course of cleaning air flow layer is made of soda not zhaschego sorbent particles of the filter material at a packing density of not more than 0.06.

 Sorbent particles can be introduced into the filter material by an air stream at a speed of 0.5-1.0 m / s directed directly to the filter, with simultaneous vibration of the filter housing with a frequency of 100-1000 Hz.

A comparative analysis with the prototype showed that the inventive filter differs from the known one in that all layers of coarse fiber filter material, except the last, contain particles of finely ground sorbent with a diameter of 1-100 μm in an amount of 10-500 g / m ^{2 of} highly porous material, and the last layer is the cleaned air stream is made of a thin fiber material that does not contain sorbent, a material with a packing density of not more than 0.06, which allows us to judge whether the criterion of "novelty" is met.

 The invention consists in the following.

 In order for the filter to function simultaneously as an aerosol high-performance filter and as an adsorber of vapors of molecular radioiodine and vapors of organic compounds of a radioiodine, it is proposed to use highly dispersed particles with highly porous particles of 1-100 μm in diameter, which were previously introduced or introduced into the finished filter into one or several layers of highly porous highly dust-sensitive material. Since the obtained sorbent-containing material cannot have high efficiency of filtering aerosol particles with sizes less than 0.5 μm, it is proposed to supplement the material with the sorbent with a layer of highly efficient filtering material that provides high filtering efficiency of the most penetrating particles with sizes of 0.2-0.4 μm.

 From a multilayer sorption-filtering material, it is possible to create a separator-type filter adsorber in which the material is placed in a rigid case with folds separated by aluminum corrugated plates, which allows a relatively large material surface to be developed in a relatively small volume of the filter. This leads to the fact that at a fairly high air flow through the filter, the flow rate through the filter surface is insignificant - of the order of several centimeters per second, which simultaneously means high efficiency of aerosol filtration, high efficiency of sorption of vapors of organic compounds of radioiodines and low aerodynamic drag of the filter as a whole . The use of highly porous highly dusty material in the first layers allows you to have a filter with a fairly significant dust absorption.

 The invention is illustrated by drawings, in which Fig. 1 shows a general diagram of a device, and in Fig. 2 a fragment of a filter element. The filter contains a housing 1, in which a zigzag folded filter material 2 is placed, in the folds of which separators 3 of a corrugated aluminum sheet are inserted. The filter material is made of coarse fiber material 4 containing a highly dispersed sorbent with highly porous particles with a diameter of 1-100 μm, packed in layers. Last in the course of the cleaned air stream, layer 5 in this material is made of a material not containing sorbent with a packing density of fibers of 0.06.

 Such a filter can be made as follows. Material 4 containing sorbent particles is packed into layers, the last layer 5 of material not containing sorbent with a packing density of fibers of 0.06 is attached to the multilayer material, this material is folded in a zigzag fashion, corrugated aluminum sheets and the filter element assembled in this way are inserted placed in the housing 1. The folded side edges of the material 2 and the side ribs of the corrugated separator plates are rigidly attached (for example, glued) to the two inner surfaces of the housing 1. The outer surfaces and the first and last folds are also glued to the remaining two inner surfaces of the filter. The untreated air enters the filter through the grooves-troughs of the corrugations of the input separator separators and, after passing through the material covering the separator on both sides, leaves the filter through the hollows of the corrugation of the output separator-separators.

 As a coarse-grained material with sorbent particles, it is possible to use a prefabricated material, for example, by blowing air containing finely divided sorbent through a fibrous material superimposed on a material or vibration stream [RF Patent 2114681, cl. B 01 D 39/00, application. July 17, 1996, publ. 07/10/98, 19].

 However, the use of the material obtained by this method can sometimes lead to a decrease in the filtration efficiency as a whole, since with a change in the speed of the gas stream being cleaned, it is possible to blow out sorbent particles from the material.

 Such a filter can be manufactured in another way, which consists in the fact that a multilayer material without a sorbent is placed in the housing, and the sorbent itself is introduced directly into the filter with an air flow at a speed of 0.5-1.0 m / s. In this case, all the particles of the sorbent are in the first few layers of coarse fiber material.

 In the last layer of fine-fibrous material with a packing density of not more than 0.06, at which the pore sizes are comparable with the diameter of the fibers, the sorbent particles with sizes of no more than 1 μm do not penetrate. For a more uniform distribution of sorbent particles in the layers of the material, in addition to the latter, the filter is subjected to vibrations with a frequency of 100-1000 Hz while blowing it with air with sorbent particles.

 The characteristics of the aerosol sorbent filter and iodine filter sorbers are shown in the table.

 The inventive aerosol sorbent filter can be used in high-performance multi-stage cleaning systems as an iodine stage. At the same time, its high efficiency of aerosol filtration and high dust absorption allow using it also as coarse and fine cleaning steps and excluding the last aerosol step as unnecessary. In this case, the resulting cleaning system may consist of a step for separating drop moisture and two or even three aerosol-sorbing filters.

 The filtration efficiency of such a system and the efficiency of sorption of vapors and organic compounds of the radioiodine turn out to be very high, and its aerodynamic drag is reduced. The dust-collecting capacity of such a system is ensured by the dust-collecting capacity of the first aerosol-sorbing filter. The capacity of the system for iodine, and thus the serviceability resource, which is entirely determined by the serviceability resource of the iodine stage, increases with an increase in the number of aerosol sorbent filters in it.

 A significant advantage of the created aerosol sorbent filter is also the possibility of using it (with appropriate dimensions) instead of the aerosol filter currently widely used in air purification systems from radioactive aerosols, without the need to redo the filter installation units on existing speakers.

 In addition, in such a filter there is no problem of abrasion of the sorbent. The entrainment of sorbent particles is excluded, since the last layer is highly effective for aerosol particles of any size.

 The problem of disposing of a filter that has worked out its useful life is exactly the same as the problem of disposing of conventional aerosol filters, which is solved by compacting them into a small volume and burial. The cost of manufacturing and operating the created filter is comparable, although somewhat higher, with similar values for aerosol filters of about the same class (by aerosols) and the same performance.

Claims (8)

1. An aerosol sorbent filter containing a housing in which a filter element is placed, made of a zigzag folded multilayer filter material with separating separators located between the folds, characterized in that all layers of coarse-fiber filter material, except for the last along the cleaned air stream, contain fine particles crushed highly porous sorbent with a diameter of 1-100 μm in an amount of 10-500 g / m ² and the last layer along the cleaned air stream is made of a fibrous material that does not contain a sorbent with a packing density of not more than 0.06.  2. The aerosol sorbent filter according to claim 1, characterized in that glass fiber is used as a filter material.  3. An aerosol sorbent filter according to claim 1, characterized in that particles of impregnated activated carbon are used as finely divided sorbent.  4. The aerosol sorbent filter according to claim 1, characterized in that the separator separators are made in the form of a corrugated metal sheet.  5. The aerosol sorbent filter according to claim 1, characterized in that the separator separators are made of corrugated aluminum sheet. 6. A method of manufacturing an aerosol sorbent filter according to paragraphs. 1-5, including the placement in the housing of a zigzag folded and packaged in layers of filter material, installation between the folds of separators, separators, characterized in that all layers, except the last along the cleaned stream, are made of filter material into which particles of finely ground sorbent are introduced with a diameter of 1-100 μm in an amount of 10-500 g / m ² , and the last layer along the stream of cleaned air is made of a particle filter-free sorbent particle with a packing density of not more than 0.06.  7. A method of manufacturing an aerosol sorbent filter according to claim 6, characterized in that all layers of the filter material, except the last along the cleaned air stream, are injected with an air stream at a speed of 0.5-1.0 m / s directed directly to the filter , particles of ground sorbent with simultaneous vibration of the filter housing.  8. A method of manufacturing an aerosol sorbent filter according to claim 7, characterized in that the filter is subjected to vibration with a frequency of 100-1000 Hz.

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