Deep cleaning of humid air with organic dust. Improvement of the air environment. Cleaning the air from dust. Methods for cleaning dust and gas emissions

Dust collectors and filters are used to clean the air from dust. Filters include devices in which the separation of dust particles from air is performed by filtration through porous materials. Devices based on different principles of dust separation are called dust collectors.

Depending on the nature of the forces acting on the dust particles suspended in the gas, the following types of dust collecting devices are used to separate them from the gas flow:

dry mechanical dust collectors (suspended particles are separated from the gas using external mechanical force);

wet dust collectors (suspended particles are separated from the gas by flushing it with a liquid that captures these particles);

electric dust collectors (dust particles are separated from the gas stream by electric forces);

filters (porous partitions or layers of material that trap dust particles when dusty air is passed through them);

combined dust collectors (different cleaning principles are used simultaneously).

According to their functional purpose, dust-collecting equipment is divided into two types: 1) for cleaning the supply air in ventilation and air conditioning systems; 2) for purification of air and gases emitted into the atmosphere by industrial ventilation systems.

The main technical and economic indicators characterizing the industrial operation of dust collectors and filters are:

performance (or the throughput of the apparatus), determined by the volume of air that can be cleaned of dust per unit of time (m 3 / h, m 3 / s);

aerodynamic resistance of the apparatus the passage of purified air through it (Pa). It is determined by the difference in total pressures at the inlet and outlet of the apparatus, i.e. p \u003d p in - p out;

total cleaning factor or total dust collection efficiency, determined by the ratio of the mass of dust captured by the device G st , to the mass of dust entering it with GBX polluted air and expressed in relative units or in%:

η = ( G st/G in)100;

fractional cleaning factor, i.e. the efficiency of dust collection of the apparatus in relation to fractions of various sizes (in fractions of a unit or in%)

η \u003d [Ф in - Ф out (1 - η)]/F in

where F in, F out - content of the dust fraction in the air, respectively, at the inlet and outlet of the dust collector,%.

Air purification cost(RUB per 1000 m 3 of purified air).

The most simple devices in terms of design and operation are dust-collecting chambers, in which the separation of dust particles from air occurs under the action of gravity when air passes through the chambers. These devices are used for rough cleaning, their dust collection efficiency is 50 ... 60%. The speed of air movement in the chamber is selected from the condition of ensuring laminar movement and is usually 0.2 ... 0.8 m / s. The aerodynamic resistance of the chambers is low and equal to 80 ... 100 Pa. In order to increase the efficiency of dust collection, the chambers are sometimes divided in height by shelves, which can be periodically shaken to clean the settling dust. For the same purpose, labyrinth-type dust-collecting chambers are used.

Centrifugal dust separators - cyclones - are more widely used, since with a relatively simple design they provide a high degree of air dedusting (80 ... 90%). The most famous types of domestic cyclones are shown in Fig. 7.1.

The cyclone consists of a cylindrical body, to which an inlet pipe is tangentially connected; the lower conical part and the exhaust pipe located inside the housing coaxially with it. Entering the cyclone at a speed of 1 & ... 20 m / s, the dusty air acquires a rotational motion and goes down. In this case, dust particles under the action of inertial forces are thrown to the walls of the apparatus and, sliding down them, fall into the bunker. The cleaned air flow turns upwards and exits the cyclone through the exhaust pipe.

The efficiency of dust collection increases with an increase in the speed of air entering the cyclone, however, if the speed is too high, turbulization of the air medium increases and the efficiency of the cyclone decreases. The maximum air speed is usually taken no more than 20 m / s. The efficiency of these devices is also influenced by their diameter: with its increase, the efficiency decreases, therefore the diameter of the cyclones is taken to be no more than 1 m.

The hydraulic resistance of the cyclones ranges from 500 to 1100 Pa. It depends on the design of the apparatus and the speed of the air entering it.

Figure: 7.1. Schemes of cyclones of the main types:

and - NIIOGAZ TsN-15; b - SIOT; at - VTSNIIOT; r - Giprodrev;

1 - inlet pipe; 2-exhaust pipe; 3-cylindrical body; 4-tapered part; 5-bunker; 6-snail at the exit; 7-hole exhaust pipe; 8 conical insert; 9-partitions

The designs of modern cyclones are quite diverse, which is explained by the variety of conditions for their rational use. The most widespread are cyclones of the NIIOGAZ type (several modifications), SIOT, VTSNIIOT, LIOT, Giprodreva (see Fig. 7.1). They differ in design, dust retention efficiency and hydraulic resistance. Each cyclone has its own rational area of \u200b\u200bapplication.

Cyclone NIIOGAZ has an elongated conical part and has a low hydraulic resistance. It is used to trap non-sticking and non-fibrous dusts.

The SIOT cyclone has a cone-shaped body without a cylindrical part with an inlet pipe of triangular cross-section. It is used in cases where there are limitations in height dimensions.

The cyclone VTSNIIOT is recommended to be used for trapping abrasive dust, since it differs in low wear of the walls due to the presence of a cone located at the bottom of the apparatus. Its hydraulic resistance is slightly higher than that of other types of cyclones. The cyclone VTSNIIOT can be used to trap fibrous dusts (the lower inner cone is removed in this case).

The LIOT cyclone has a developed cylindrical part and is used to trap dry non-sticking dust.

Cyclone Giprodreva is distinguished by a barrel-shaped form, has a low hydraulic resistance and is used mainly for catching woodworking waste.

The final choice of one or another type of cyclone should be determined according to technical and economic indicators. In cases where it is required to clean large volumes of air, group cyclones are used. In them, the devices are connected in parallel with the inlet pipes to a common pipeline and are installed on one large hopper. A necessary condition effective work cyclones in this case is the exclusion of the possibility of air flow from one cyclone to another.

Bag filters for capturing dry non-sticking dusts are widely used in industry (Fig. 7.2). The main working elements of these devices are cloth sleeves suspended from a shaking device and placed in a sealed metal case. The lower open ends of the sleeves are connected to the hopper. Air passing through the fabric of the bags leaves dust on their surface and is removed from the filter housing by a fan. As a layer accumulates on the surface of the fabric, dust itself becomes a filter medium and increases the efficiency of dust retention of the filter. The cleaning of the fabric of the hoses from the settled dust is carried out by shaking them, for which an automatically acting shaking mechanism is installed. In many types of filters, the shaking of the bags is combined with backflushing them in order to better clean the dust. Filters are multisectional. When one of the sections for cleaning the sleeves is turned off, the rest continue to work. Filters are of suction and pressure type.

Figure: 7.2. Bag filter diagram:

1 - inlet pipe; 2- sleeve; 3- suspension of sleeves; 4- shaking mechanism;

5- outlet branch pipe; 6 - bunker

The dust retention efficiency of bag filters is 90 ... 99%. The air load on the fabric is taken in the range of 50 ... 80 m 3 / (m 2 h). The hydraulic resistance of the filter, depending on the degree of dustiness of the bags, ranges from 1 ... 2.5 kPa.

In recent years, filters have been developed in which sleeves are made of fiberglass or porous ceramic materials. The filter elements in them are cleaned with compressed air. Such filters can be used to purify high-temperature gases sucked from technological equipment. Of the bag filters produced by the industry, filters of the FVK, FVV, FRM, FTNS, etc. types are most widely used.

Electric filters (Fig. 7.3) are widely used in the construction industry for cleaning air and industrial gases from dust. In these devices, the separation of dust particles from the air is carried out under the influence of a high-intensity static electric field. In a metal case, the walls of which are grounded and are collecting electrodes, there are corona electrodes connected to a direct current source. The rectified voltage is 30 ... 100 kV.

An electric field is generated around the negatively charged electrodes. The dusty gas passing through the electrostatic precipitator is ionized, as a result of which they acquire negative charges and dust particles. The latter begin to move to the filter walls, and, settling on them, form a dense layer. Cleaning of the collecting electrodes is done by tapping or vibration, and sometimes by flushing with water.

Figure: 7.3. Electrofilter circuit:

1 - inlet pipe; 2- electrostatic precipitator housing (collecting electrode); 3-corona electrode;

4- insulators; 5- outlet branch pipe; 6- high voltage rectifier; 7- bunker

The efficiency of dust collection of electrostatic precipitators is high, it reaches 99.9%. Moreover, particles of any size are captured, including submicron ones at their high concentrations in gases, reaching 50 g / m 3. The advantages of these devices are low hydraulic resistance 100 ... 150 Pa, economic operation, the ability to purify gases at high temperatures (up to 450 ° C).

For various conditions of use, the industry produces different types electrostatic precipitators: UG, EGA, UTT, OGP, UB, UVV, PG, DM, etc.

Wet-type dust collectors are deep cleaning devices and are distinguished by high dust collection efficiency. Their use is advisable in the case when the captured dust is well wetted with water, does not cement and does not form hard, difficult to destroy deposits.

Of this class of devices, a cyclone with a water film of LIOT is most often used (Fig. 7.4). It has a vertical cylindrical body, in the lower part of which the cleaned air is fed tangentially. The latter is twisted and, rotating, rises to the upper part of the apparatus, from where it is discharged into the atmosphere through the exhaust pipe.

Figure: 7.4. Cyclone with water film:

1 - inlet pipe; 2 - case; 3 - outlet branch pipe; 4 - water supply device

When the flow rotates, dust particles are released from it under the action of centrifugal forces, which are removed from the walls of the apparatus by water flowing down from above. The latter is fed to the walls of the apparatus through a water supply ring and several tangentially located tubes and flows down the walls of the apparatus in the form of a continuous water film. The resulting sludge is collected in a hopper.

The efficiency of dust collection for cyclones with a water film is 99.0 ... 99.5%, the pressure loss in the apparatus is 400 ... 800 Pa. When cleaning aggressive gases from dust that destroy the metal walls of the apparatus, the latter are reinforced with acid-resistant coatings from the inside.

Foam dust collectors are also distinguished by high performance indicators (Fig. 7.5). Devices of this type have a cylindrical metal body, inside which a grating is placed horizontally. Water is supplied to the grate through which the cleaned air is passed from below. In this case, a layer of foam forms on the grate, the height of which depends on the height of the overflow partition (threshold). Usually it is 80 ... 100 mm. In order to reduce drip entrainment of moisture, a droplet separator is placed in the upper part of the apparatus, made in the form of a lattice with labyrinth channels.

Figure: 7.5. Foam dust collector:

1 - receiving box; 2- building; 3- lattice; 4- drain baffle (threshold); 5-drain box

1. Name the main sources and properties of dust emitted at construction sites. 2. What are the methods for controlling dustiness in the air? 3. List the general and personal protective equipment for workers from dust. 4. Name the main types of dust collectors and filters used for air purification. 5. What are the technical and economic indicators used in the assessment of dust collectors and filters? 6. Explain the principle of operation and indicate the areas of application of dust collection chambers and cyclones. 7. How do bag filters work and work? 8. Explain the principle of operation of electrical filters. 9. How are wet-type dust collectors arranged and when are they used? 10. Explain the principle of operation of the foam dust collectors.

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Methods for cleaning air from dust

For neutralization of aerosols (dust and mists), dry, wet and electrical methods are used. In addition, the devices differ from each other both in design and in the principle of sedimentation of suspended particles. The operation of dry apparatus is based on gravitational, inertial and centrifugal sedimentation mechanisms or filtration mechanisms. In wet dust collectors, dusty gases come into contact with liquid. In this case, deposition occurs on droplets, on the surface of gas bubbles or on a liquid film. In electrostatic precipitators, the separation of charged aerosol particles occurs at the collecting electrodes.

Dry mechanical dust collectors include devices in which various deposition mechanisms are used: gravitational, inertial and centrifugal.

Inertial dust collectors. With a sharp change in the direction of movement of the gas flow, dust particles under the influence of the inertial force will tend to move in the same direction and, after turning the gas flow, fall into the hopper. The effectiveness of these devices is small.

Venetian blinds. These devices have a louvred grille consisting of rows of plates or rings. The gas to be cleaned, passing through the grate, makes sharp turns. Due to inertia, dust particles tend to maintain their original direction, which leads to the separation of large particles from the gas flow, and their impacts on the inclined planes of the lattice, from which they are reflected and bounced away from the slots between the blades of the louvers, as a result, the gases are divided into two flows. The dust is mainly contained in the stream, which is sucked off and sent to the cyclone, where it is cleaned of dust and again discharged with the main part of the stream passing through the grate. The gas velocity in front of the louver must be high enough to achieve the effect of inertial dust separation.

Typically, louver dust collectors are used to collect dust with a particle size\u003e 20 μm.

The efficiency of collecting particles depends on the efficiency of the grid and the efficiency of the cyclone, as well as on the proportion of gas that is sucked out in it.

Cyclones. Cyclones are the most common in industry.

According to the method of supplying gases to the apparatus, they are subdivided into cyclones with spiral, tangential and screw-like, as well as axial supply. Cyclones with axial gas supply operate both with and without gas return to the upper part of the apparatus.

The gas rotates inside the cyclone, moving from top to bottom, and then moving up. Dust particles are thrown by centrifugal force against the wall. Typically, in cyclones, the centrifugal acceleration is several hundred, or even a thousand times greater than the acceleration of gravity, so even very small dust particles are not able to follow the gas, but under the influence of centrifugal force they move towards the wall.

In industry, cyclones are divided into high-efficiency and high-performance.

At high flow rates of the gases to be cleaned, a group arrangement of devices is used. This allows not to increase the diameter of the cyclone, which has a positive effect on the cleaning efficiency. Dust-laden gas enters through a common manifold and then is distributed among the cyclones.

Battery cyclones - grouping a large number of small cyclones. Reducing the diameter of the cyclone element aims to increase the cleaning efficiency.

Vortex dust collectors. The difference between vortex dust collectors and cyclones is the presence of an auxiliary swirling gas flow.

In a nozzle-type apparatus, a dust-laden gas stream is swirled by a vane swirler and moves upward, while being exposed to the action of three jets of secondary gas flowing out of tangentially located nozzles. Under the action of centrifugal forces, the particles are thrown to the periphery, and from there into the spiral flow of the secondary gas excited by the jets, directing them down into the annular annular space. The secondary gas in the course of the spiral flow around the stream of the purified gas gradually completely penetrates into it. The annular space around the inlet pipe is equipped with a retaining washer that ensures the irreversible drainage of dust into the hopper. The vane-type vortex dust collector is characterized by the fact that the secondary gas is taken from the periphery of the cleaned gas and supplied by an annular guide vanes with inclined blades.

Fresh atmospheric air, part of the cleaned gas or dusty gases can be used as secondary gas in vortex dust collectors. The most economically advantageous is the use of dusty gases as a secondary gas.

As with cyclones, the efficiency of vortex devices decreases with increasing diameter. There may be battery installations consisting of separate multi-cells with a diameter of 40 mm.

Dynamic dust collectors. The cleaning of gases from dust is carried out due to centrifugal forces and Coriolis forces arising from the rotation of the impeller of the draft device.

The most widespread is the smoke exhauster-dust collector. It is designed to capture dust particles\u003e 15 μm. Due to the pressure difference created by the impeller, the dusty flow enters the "snail" and acquires a curvilinear motion. Dust particles are thrown to the periphery under the action of centrifugal forces and together with 8-10% of the gas are discharged into a cyclone connected to the volute. The cleaned gas flow from the cyclone returns to the central part of the volute. The cleaned gases through the guide vane enter the impeller of the smoke exhauster-dust collector, and then through the emission casing into the chimney.

Filters. All filters are based on the process of gas filtration through a partition, during which solid particles are retained, and the gas completely passes through it.

Depending on the purpose and value of the input and output concentration, filters are conventionally divided into three classes: fine filters, air filters and industrial filters.

Bag filters represent a metal cabinet, divided by vertical partitions into sections, each of which contains a group of filter bags. The upper ends of the sleeves are plugged and suspended from a frame connected to a shaking mechanism. At the bottom there is a dust bin with an auger for unloading it. Shaking the sleeves in each of the sections is done alternately. (Figure 6)

Fiber filters. The filter element of these filters consists of one or more layers in which the fibers are uniformly distributed. These are volumetric filters, since they are designed to capture and accumulate particles predominantly over the entire depth of the layer. A continuous layer of dust forms only on the surface of the most dense materials. Such filters are used at a dispersed solid phase concentration of 0.5-5 mg / m 3 and only some coarse-fiber filters are used at a concentration of 5-50 mg / m 3. At such concentrations, the bulk of the particles are less than 5-10 microns in size.

There are the following types of industrial fiber filters:

Dry - fine-fiber, electrostatic, deep, pre-filters (pre-filters);

Wet - mesh, self-cleaning, with periodic or continuous irrigation.

The filtration process in fiber filters consists of two stages. At the first stage, the trapped particles practically do not change the structure of the filter over time; at the second stage of the process, continuous structural changes occur in the filter due to the accumulation of trapped particles in significant quantities.

Grain filters. They are used for gas cleaning less often than fibrous filters. Distinguish between packed and rigid granular filters.

Hollow scrubbers. The most common are hollow nozzle scrubbers. They represent a column of circular or rectangular cross-section, in which contact is made between gas and liquid droplets. In the direction of gas and liquid movement, hollow scrubbers are divided into counter-flow, direct-flow and with a transverse liquid supply.

Packed scrubbers are columns with bulk or regular packing. They are used to trap well-wetted dust, but at a low concentration.

Gas scrubbers with a movable nozzle are widely used in dust collection. Balls made of polymeric materials, glass or porous rubber are used as nozzles. The attachment can be rings, seats, etc. The density of the balls of the nozzle should not exceed the density of the liquid.

Scrubbers with a movable conical ball nozzle (KSSh). To ensure the stability of operation in a wide range of gas velocities, improve the distribution of liquid and reduce the entrainment of splashes, devices with a movable conical ball nozzle are proposed. Two types of devices have been developed: nozzle and ejection

In an ejection scrubber, the balls are irrigated with a liquid that is sucked in from a vessel with a constant level of gases to be cleaned.

Disc-type scrubbers (bubbler, foam). The most common foam machines are with flop or overflow trays. Overflow trays have holes with a diameter of 3-8 mm. Dust is captured by a foam layer that forms when gas and liquid interact.

The efficiency of the dust collection process depends on the size of the interface.

Foam machine with foam layer stabilizer. A stabilizer is installed on the failure grid, which is a honeycomb grid of vertically arranged plates dividing the section of the apparatus and the foam layer into small cells. Thanks to the stabilizer, there is a significant accumulation of liquid on the tray, an increase in the foam height compared to a failed tray without a stabilizer. The use of a stabilizer can significantly reduce water consumption for irrigation of the apparatus.

Shock-inertial gas scrubbers. In these devices, the contact of gases with a liquid is carried out due to the impact of the gas flow on the surface of the liquid, followed by passing the gas-liquid suspension through holes of various configurations or by direct discharge of the gas-liquid suspension into the liquid phase separator. As a result of this interaction, droplets with a diameter of 300-400 microns are formed.

G gas washers of centrifugal action. The most widespread are centrifugal scrubbers, which can be divided into two types by design: 1) devices in which the gas flow is swirled using a central blade swirling device; 2) devices with lateral tangential or coiled gas supply.

High-speed scrubbers (Venturi scrubbers). The main part of the apparatus is a spray pipe, which provides intensive crushing of the irrigated liquid by a gas flow moving at a speed of 40-150 m / s. A drop eliminator is also available.

Electrostatic precipitators. Gas cleaning from dust in electrostatic precipitators occurs under the action of electrical forces. In the process of ionization of gas molecules by an electric discharge, the particles contained in them are charged. Ions are absorbed on the surface of dust particles, and then, under the influence of an electric field, they move and are deposited to the collecting electrodes.

The following methods are used to neutralize waste gases from gaseous and vaporous toxic substances: absorption (physical and chemisorption), adsorption, catalytic, thermal, condensation and compression.

Absorption methods for cleaning waste gases are subdivided according to the following criteria: 1) according to the absorbed component; 2) by the type of absorbent used; 3) by the nature of the process - with and without gas circulation; 4) on the use of the absorbent - with regeneration and its return to the cycle (cyclic) and without regeneration (not cyclic); 5) on the use of captured components - with and without recuperation; 6) by the type of recovered product; 7) for the organization of the process - periodic and continuous; 8) on the design types of absorption equipment.

For physical absorption, in practice, water, organic solvents that do not react with the extracted gas, and aqueous solutions of these substances are used. In chemisorption, aqueous solutions of salts and alkalis, organic substances and aqueous suspensions of various substances are used as absorbents.

The choice of the cleaning method depends on many factors: the concentration of the recovered component in the exhaust gases, the volume and temperature of the gas, the content of impurities, the presence of chemisorbents, the possibility of using recovered products, the required degree of cleaning. The choice is made based on the results of technical and economic calculations.

Adsorption methods for cleaning gases are used to remove gaseous and vaporous impurities from them. The methods are based on the absorption of impurities by porous adsorbent bodies. Purification processes are carried out in batch or continuous adsorbers. The advantage of the methods is high degree cleaning, and the disadvantage is the impossibility of cleaning dusty gases.

Catalytic cleaning methods are based on the chemical transformation of toxic components into non-toxic solid catalysts on the surface. Gases that do not contain dust and catalyst poisons are cleaned. The methods are used to purify gases from nitrogen oxides, sulfur, carbon and organic impurities. They are carried out in reactors of various designs. Thermal methods are used to neutralize gases from easily oxidized toxic impurities.

Methods for cleaning air from dust when released into the atmosphere

To clean the air from dust, dust collectors and filters are used:

Filters are devices in which dust particles are separated from air by filtration through porous materials.

Dust collector types:

The main indicators are:

productivity (or throughput of the apparatus), determined by the volume of air that can be cleaned of dust per unit of time (m 3 / hour);

aerodynamic resistance of the apparatus to the passage of purified air through it (Pa). It is determined by the pressure difference between the inlet and outlet.

the general cleaning factor or the overall efficiency of dust collection, determined by the ratio of the mass of dust caught by the apparatus C y to the mass of dust that entered it with polluted air C in: C y / C in x 100 (%);

fractional cleaning factor, i.e. the efficiency of dust collection of the apparatus in relation to fractions of different sizes (in fractions of a unit or in%)

Dust collection chambers, dust collection efficiency - 50 ... 60%. The principle of cleaning is the outflow of dusty air from the chamber at a speed lower than the dust hovering speed, i.e. dust has time to settle (see Fig. 1).

Cyclones - dust collection efficiency - 80 ... 90%. The principle of cleaning is the throwing of heavy dust particles onto the cyclone walls by swirling the dusty air flow (see Fig. 2). The hydraulic resistance of the cyclones ranges from 500 to 1100 Pa. They are used for heavy dust: cement, sandy, wood ...

Bag filters (for capturing dry non-sticking dust) dust collection efficiency - 90 ... 99%. The principle of cleaning is the trapping of dust particles on the filter elements (see Fig. 3). The main working elements are cotton sleeves suspended from a shaking device. They are used for heavy dusts: wood, flour, ...

The hydraulic resistance of the filter, depending on the degree of dustiness of the bags, ranges from 1 ... 2.5 kPa.

Filter cyclones are a combination of a cyclone (separation of heavy particles) and a bag filter (separation of light particles). See fig. 3.

Electric filters - the separation of dust particles from the air is carried out under the influence of a high intensity electrostatic field. In a metal case, the walls of which are grounded and are collecting electrodes, there are corona electrodes connected to a direct current source. Voltage - 30 ... 100 kV.

An electric field is generated around the negatively charged electrodes. The dusty gas passing through the electrostatic precipitator is ionized and the dust particles acquire negative charges. The latter begin to move towards the filter walls. Cleaning of the collecting electrodes is done by tapping or vibration, and sometimes by flushing with water. aerosol filter scrubber

Dust collection efficiency - 99.9%. Low hydraulic resistance 100 ... 150 Pa,

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Acquaintance with the most common and effective methods of air purification. Characteristics of the Cyclone-TsN15U apparatus: analysis of areas of use, consideration of functions. Features of the development and industrial production of cheap filter fabrics.

Air purification from dust can be carried out both by supplying outside air to the room and by removing dusty air from it. In the first case, the protection of workers in industrial premises is ensured, and in the second - the protection of the surrounding atmosphere.

There is no one-size-fits-all dust collection device suitable for all types of dust and for any initial concentration. Each of these devices is suitable for a specific type of dust, initial concentration and required degree of cleaning.

An important indicator of the operation of dedusting equipment is the air purification factor, which is determined by the formula

Kf \u003d ((q1-q2) / q1) 100%,

where q1 and q2 are the content before and after cleaning, mg / m3.

Air purification from dust can be rough, medium and fine. During coarse air cleaning, coarse dust (particle size\u003e 100 μm) is retained. Such cleaning can be used, for example, as a preliminary for highly dusty air in multi-stage cleaning. With medium cleaning, dust with a particle size of up to 100 microns is retained, and its final content should not exceed 100 mg / m3. Fine cleaning is such a cleaning, in which very fine dust (up to 10 microns) is retained with a final content of up to 1 mg / m3 in the air of supply and recirculation systems.

Dedusting equipment is subdivided into dust collectors and filters.

Dust collectors. Dust collectors are devices whose operation is based on the use of gravity or inertial forces for the deposition of dust particles, which separate dust from the air flow when the speed (in dust settling chambers) and the direction of its movement (single and battery cyclones, inertial and rotary dust collectors) changes.

Dust collectors are used when the dust content in the removed air is more than 150 mg / m3.

Dust settling chambers. These chambers are used to sediment coarse and heavy dust with a particle size of more than 100 microns (Fig. 11, a). The speed of dusty air in the cross section of the chamber is taken to be small - about 0.5 m / s so that the dust can settle in the chamber before it leaves it. Therefore, the dimensions of the chambers are quite large, which limits their use, despite the obvious advantages - low hydraulic resistance, cheap operation and ease of maintenance.

The cleaning efficiency can be increased (up to 80-95%) if the chamber is made of a labyrinth type (Fig. I, b), although this entails an increase in hydraulic resistance.

Inertial dust collectors. Such a dust collector (Fig. 11, c) is a set of truncated cones 1, installed in series in such a way that gaps are formed between them 2. Dusty air enters through hole 5. Dust separation is based on changing the direction of movement of dusty air, while suspended dust particles , having a significantly greater force of inertia than clean air, continue to move in the same axial direction to the narrow hole 4, and clean air exits through the slots 2.

Cyclones. They are used for coarse and medium cleaning from dry, non-fibrous and non-sticking dust. Dust separation in cyclones is based on the principle of centrifugal separation. Getting into the cyclone tangentially through the inlet pipe 1 (Fig. 11, d), the air flow acquires a rotational motion in a spiral and, having dropped to the bottom of the conical part 2, goes out through the central pipe 3. Under the action of centrifugal forces, dust particles are thrown towards the cyclone wall and, entrained by the air flow, they descend to the bottom of the cyclone, and from there they are removed into the dust collector. The cleaning efficiency increases (up to 90%) with decreasing cyclone size, since the magnitude of the centrifugal force is inversely proportional to the distance of dust particles from the cyclone axis. Therefore, instead of one cyclone big size put in parallel two or more smaller cyclones - the so-called battery cyclones.

Due to the possible ignition and dust explosions in cyclones, they are installed outside production facilities.

To clean air with a high dust content, cyclones with a water film created on its inner surface are used.

Rotary dust collectors (rotoclones). These dust collectors are a centrifugal fan (Fig. 11, e), which, simultaneously with the movement of air, cleans it from large dust particles (\u003e 10 microns) due to the inertia forces arising from the rotation of the impeller.

Dusty air enters the suction port 1. When the wheel 2 rotates, the dust-air mixture moves along the interscapular channels of the wheel, while the dust particles under the action of centrifugal forces and Coriolis forces are pressed against the surface of the wheel disc and against the oncoming sides of the wheel blades. Dust with a very small amount of air (3-5%) enters through the gap 8 between the wheel 2 and the wheel disk into the ring-shaped receiver 5, and the purified air enters the volute 4 and the outlet pipe 9. The mixture enriched with dust enters the hopper b through the pipe 5, in which the dust settles, and the air freed from it through the opening 7 returns to the dust receptacle 3. In the bunker 6 the dust is moistened.

Rotoklones are used in dusty industries such as foundries. They provide a relatively high cleaning efficiency: for dust particles from 8 to 20 microns - 83%, and for larger ones - up to 97%.

Figure: 11. Dust separators: a, b - dust settling chambers; в - louvered dust separator; d - cyclone; d - rotoclone

Filters. Filters are devices in which dusty air is passed through porous, mesh materials, as well as through structures that can trap or deposit dust.

Glass wool, gravel, coke, metal shavings, porous paper or cloth, thin metal mesh, porcelain or metal hollow rings are used as filter materials. Depending on the material used, the filters have a corresponding name - cloth, paper, etc.

Paper filters. The filtering material in them is corrugated, porous paper (cellulose wool) or the so-called silk forging (silky porous paper), folded in 4-10 sheets and placed in special cassettes. Such cassettes are installed in the cells of the metal frame. The cleaning efficiency of paper filters is very high - up to 98-99%. These filters are used to clean the air supplied to the room.

In order for the cassettes to be periodically freed from part of the deposited dust, the filter is shaken.

Cloth filters. In fig. 12, a shows a self-shaking bag filter of the FV type with backwash. It consists of several sections, each of which contains 18 hoses with a diameter of 135 mm.

The filter works as follows: the dusty air through the nozzle 1 enters the housing 2, which is common to all the sleeves, from where it enters the sleeves 3, and, passing through the fabric of the latter, leaves dust on its surface. The cleaned air through the valve boxes 4 leaves the filter.

Periodic shaking of the filter sleeves is performed by mechanism 7, and backflushing is performed by variable valve position 8. Dust is removed into dust collector 5 with exhaust valve 6 by means of a screw 9. For fine and almost complete air purification (99.9%), in a number of industries filters from FPP fabrics.

Oil filters. Such filters are used to clean the air supplied to the room at low dust concentrations (up to 20 mg / m3).

A number of constructions represent a cassette covered with mesh and filled with porcelain or copper rings, corrugated mesh (Fig. 12, b). This cassette is dipped into spindle or liquid paraffin before being installed in the network.

Dust particles, passing with air through a labyrinth of holes formed by rings or nets, are retained on their wetted surface. The cleaning efficiency reaches 95-98%.

Figure: 12. Filters:

a - self-shaking cloth sleeve; b - cassette oil; c - self-cleaning oil

Currently, self-cleaning oil filters (Fig. 12, c), in which filtration is carried out by two continuously moving sheets 2 made of a metal mesh, are widely used. The lower part of the blade is 150 mm immersed in oil in bath 1.

If the oil filters are dirty, the rings and nets are washed in a soda solution.

Electric filters. Filters are used to clean air and gas from fine dust. The operation of electrostatic precipitators is based on the creation of a strong electric field using a rectified high-voltage current (50-100 kV) supplied to the corona electrodes (Fig. 13, a). When dusty gas or air passes through the filter, the dust particles are ionized, that is, positive and negative ions are formed. Dust, charged from the negative corona electrode, tends to settle on the positive electrode, which are the grounded filter walls and special collecting electrodes. These electrodes are periodically shaken using a special mechanism, and the settled dust is collected in a hopper, from where it is removed.

Ultrasonic filter. In such filters (Fig. 13, b), used for fine cleaning, under the influence of high-intensity ultrasound, the coagulation of the smallest dust particles occurs. The resulting coarse particles are then deposited in conventional dust collectors such as cyclones.

Figure: 13. Filters:

a - electric; b - ultrasonic; 1 - insulator; 2 - filter walls; 3 - corona electrode; 4 - grounding; 5 - ultrasound generator; 6 - cyclone

The cleaning efficiency is 90% with the action of ultrasound for 3-5 s.

If the required cleaning efficiency is achieved in one dust collector or filter, then such cleaning is called one-stage. With a large initial dust content of the air, two-stage cleaning is used to obtain the required purity. For example, if the first stage of air purification is a cyclone, then a cloth filter, etc. can serve as the second.

Correct operation of filters (timely cleaning, rinsing, etc.) is of great importance for efficient ventilation.

Cleaning your computer from dust is an important operation that every computer user should carry out. Many users have never cleaned their computer, and some have never even opened the computer case and have no idea what state the system unit is in now.

Why clean your computer from dust

Dust that builds up inside system unit, causes overheating of various components of the system unit. Due to an increase in the temperature of the components of the system unit, the computer begins to make a lot of noise, the wear of the components increases and, in the end, this can lead to the failure of one or more components of the system unit.

Agree, not the best prospect. But this can be avoided by spending 30 minutes every six months to clean the computer from dust.

How to clean your computer from dust

To clean the computer from dust, you can use one of two basic principles: blow dust from the system unit or suck in dust, in addition, you can combine these two methods.

Dust can be blown out using a can of compressed air, a vacuum cleaner (which can blow out air), a hair dryer (but not hot air), and any device that can produce a jet of air under pressure.

We will suck in the dust with a vacuum cleaner. In addition, you will need a brush or brush (with which we will remove dust from hard-to-reach places and suck it up with a vacuum cleaner).

Preparatory stage

Before you start cleaning your computer from dust, you need to decide on the cleaning tools.

To clean the computer we need:

• Vacuum cleaner
• Long hair brush
• Toothbrush
• Compressed air can
• Screwdriver

Of course, not all of these tools will be necessary for you when working (for example, if you are going to suck out dust with a vacuum cleaner, then you may not use a hairdryer or a can of compressed air). I have given only the basic tools that you can use when cleaning your computer from dust.

Precautionary measures

When cleaning the system unit from dust, observe the following rules:

• Be sure to disconnect the system unit from the outlet;
• Do not touch the components of the system unit with a vacuum cleaner. The boards can only be touched with a brush;
• Do not get into the system unit with wet or sticky hands;
• Do not try to blow dust out of your mouth. By blowing off dust in this way, it will enter the eyes and respiratory tract;
• If you are blowing out dust with a hair dryer, then the air should be cold, but by no means hot.

Step 1. Open the system unit

We disconnect the system unit from all peripheral devices, network, power, etc. By disconnecting all devices, we can move the system unit wherever we want. For the convenience of work, I would advise you to put the system unit on a table or any flat surface above the floor. It will be more convenient to work this way than to crawl on the floor.

Now you need to remove the side wall (cover) from the system unit. We need to remove the side wall, which is on the left side of the system unit, when looking at it from the front (where the power button and the drive are located). If you are going to blow out dust, it is better to remove both side walls (there will be more holes through which you can blow dust out of the system unit).

To remove the cover, you must first unscrew the bolts that secure the side walls from the back. On new models of the case of the system unit, the side walls can be attached not to the bolts at the back, but to special mechanisms (latches) that can be located on the walls themselves.

Having opened the crumb, we examine the system unit and assess the dustiness of the system unit.

Step 2. General cleaning

When we opened the hull and appreciated the scope of work, we need to start cleaning. It is necessary to remove dust from the case and from all devices as thoroughly as possible. Go through all the places: the bottom and sides of the case, all the boards, fans, do not forget about the power supply and fans on the case.

If you are blowing dust out of the case, then you need to remove the system unit from the room (for example, a balcony or take it out of the apartment into the corridor). When you blow out dust, it will fly in all directions and settle on your furniture and enter your respiratory tract. Therefore, you need to do it outside the apartment. Blow dust from all corners and crevices, boards, devices, fans.

If you are sucking in dust, remove the tube from the vacuum cleaner and start vacuuming up dust from all devices, fans and corners. Use a long-haired brush to shake off hard-to-reach places or fan blades and vacuum up the dust.

Advanced users can also remove the front housing cover and clean it from dust. In many system units, a fan is also installed on the front side of the case, which eventually gets clogged. If you are not sure that you can remove and replace the front cover, it is best not to.

Step 3. Cleaning individual compotes

Now you need to detach some of the components from the motherboard and case. You need to disconnect the video card, RAM modules and other devices (for example, a TV tuner, sound card) that are connected to the motherboard. By disconnecting the devices, we can clean them of dust more thoroughly than with general cleaning. In addition to the devices themselves, you need to remove dust from the connectors where they were attached.

It is not necessary to remove the drive from the housing and hard drives... In most cases, dust can be removed from them without removing them from the body (vacuum cleaner, brush). But still assess the situation, in some cases, the drive or hDD can be installed not very conveniently and it is extremely difficult to clean them from dust. In this case, you will have to detach them from the case for cleaning.

Please note that the devices need to be disconnected only after general cleaning of the case (step 2), otherwise dust may clog into the connectors where the disconnected devices (video card, RAM, etc.) are installed.

Step 4. Finish cleaning

Having cleaned all the components and devices, install them in place, close the case and check the performance of the computer.

Conclusion

Cleaning your computer from dust helps prevent damage to computer components and reduce the operating noise. Carry out this operation at least once every six months, and it is better to periodically open the lid of your system unit and see its condition.