Means for cleaning air from industrial dust. Industrial air purification systems: types and basics

Devices for cleaning air and gases from dust

The mixture of air with particles of material not captured in the air separators (aspiration air), as well as the dusty exhaust gases of rotary kilns must be dedusted. Only then can the purified air (gas) be released into the atmosphere.

The aspiration air and gases are purified in two ways - dry or wet.

The captured dust is a valuable material that is usually returned to production or used in other sectors of the economy.

The following methods are used to separate dust from air (gases):
a) mechanical cleaning in centrifugal cyclones ("dry"), in which material particles are separated under the action of centrifugal and gravity forces, as well as in cyclones-washers ("wet") in the presence of water;
b) cleaning using bag (cloth) filters, the fabric of which retains material particles on its surface and passes purified air (gas);
c) electrical cleaning of gases (air) in electrostatic precipitators; material particles are deposited in a high voltage electric field;
d) wet cleaning of gases (in scrubbers).

In the building materials industry, mainly in the cement industry, the dry method of cleaning with the use of aspiration shafts, dust-collecting chambers, cyclones, bag and electric filters is predominantly used.

A centrifugal cyclone is a welded body, consisting of a cylindrical part (Fig. II-16, a), a conical and a dust extraction branch pipe.

Aspiration air (gas) through the inclined inlet pipe enters the cyclone tangentially to its circumference at a speed of up to 20-25 m / s. The angle of inclination of the branch pipe is 15-24 °. The cover 5 is bent along a helical line and has a pitch equal to the height of the inlet pipe. Entering tangentially to the cyclone circumference, the aspiration air rotates along a helical line and goes down.

Due to centrifugal forces, material particles are thrown towards the inner walls of the cyclone. Particles of material (dust) descend along the walls of the cyclone into the conical part of the body and then through a branch pipe and a dust lock (flasher), which prevents air from sucking in from outside, are periodically discharged outside. Dust-free air or gas rises to the upper part of the cyclone and is discharged into the atmosphere through the branch pipe 6 or is sent for further cleaning to bag or electric filters.

It is recommended to select smaller cyclones to ensure a high degree of cleaning. To increase the throughput (and, consequently, productivity), battery cyclones are used, in which cyclonic elements of the same diameter are mounted in a common housing parallel to each other. They have a common air inlet and outlet, as well as a common hopper for collecting dust. In fig. II-16, b shows a cyclonic element of the "Screw" type.

The degree of cleaning of the cyclone depends on its diameter, the size of dust particles, the speed related to the section of the outer casing of the cyclone, which is taken, depending on the design of the cyclone, in the range of 2.4-3.5 m / s. The degree of cleaning of cyclones can be taken equal to 70-90%. The cleaning efficiency of battery cyclones ranges from 78% (for particles less than 10 microns) to 95% (for particles less than 30 microns).

Rice. II-16. Centrifugal cyclone

When using cyclones in the cement industry, the following parameters are taken: the initial dust content of the air is not higher than 400 g / m3, the pressure or vacuum is not higher than 250 mm of water. Art. and the gas temperature is not higher than 400 ° С.

Rice. II-17. Bag filter

The bag filter shown in fig. II-17, a, consists of a body in which fabric sleeves of a cylindrical shape (135-220 mm in diameter) are suspended, grouped (8-12 pieces) in sections. The upper ends of the sleeves are tightly attached to the bar, the lower ends of the sleeves are open for the inlet of aspiration air (gas) entering the bag filter through the pipeline and through the lower chamber.

Passing through the filter cloth of the bags, the air (gas) is purified, and the dust settles on the inner surfaces of the bags. The cleaned air (gas) is collected in the upper part of the filter housing and is transported through the branch pipe 6 to the common air duct.

Bag filters operate under pressure or vacuum.

The filter sleeves are periodically blown out and shaken, since over time they become clogged with dust, and with an increase in the layer, the resistance increases. To avoid condensation of water vapor, the hoses are blown with heated air in the direction opposite to the movement of the aspiration air (gas). The bar is used for shaking and is connected to a shaking mechanism powered by a separate electric motor.

Dust from the bags enters the lower part of the filter housing and is then removed by the screw conveyor to the outside.

The filter fabric of the sleeves is made of cotton, wool, nitron, lavsan and glass fibers. Fiberglass fabrics can withstand temperatures up to 300 ° C.

The degree of purification reaches 99% and depends on the specific load on the filter cloth, which should not exceed 1 m3 / m2-min. When using a fiberglass filter cloth, the specific load is assumed to be no more than 0.5-0.6 m3 / m2-min.

In fig. II-17, b shows the section of the bag filter made of fiberglass. Dust-laden gas is directed through a pipeline to the chambers and sleeves. Dust settles on the inner walls of the hoses, and the cleaned gas is sucked into the atmosphere through the valve box by a smoke exhauster.

To avoid deterioration of the fiberglass cloth, such filters should not be subjected to normal mechanical shaking. In this case, the hoses are cleaned from the settled dust with the help of air directed by a pulsating flow against the movement of the gas. The time relay sends a signal to the actuator, with the help of which one of the two shut-off valves is closed. As a result, one of the chambers is disconnected from the exhauster. At the same time, the valve opens and the purge air flows through the channels (as indicated by the arrows in the figure) into the chamber disconnected from the exhauster. As the valve periodically opens and closes, a pulsating purge air flow is created. Due to this, the fiberglass sleeves are smoothly deformed and the layer of dust deposited on the sleeves is dumped down into the hopper and then discharged outside by a cell feeder. After a set period of time, one chamber is automatically turned on, and the second is blown out with air.

Bag filters are widely used in the cement industry to clean the aspiration air of cement mills, silos, crushers, etc.

Electrostatic precipitator. The electric method of cleaning the aspiration air and waste gases of rotary kilns of the cement industry is the most advanced. The degree of purification reaches 98-99%. Electrostatic precipitators can clean chemically aggressive gases and gases with temperatures up to 425 ° C.

The electric method of cleaning consists in the fact that when aspiration air (gas) moves through an electric field created by two high voltage direct current electrodes, it ionizes, i.e., the process of decay of an electrically neutral molecule into positively and negatively charged ions. Dust particles, having received an electric charge, move towards the electrode, the charge of which has the opposite sign.

Two types of electrodes are used: flat plates and a wire between them, or a hollow cylinder (pipe) and a wire inside it. Depending on the used electrodes, electrostatic precipitators are classified into plate and tubular. In the cement industry, plate electrostatic precipitators (such as UG and UGT) are most widely used.

In fig. II-18, a schematic diagram of the creation of an electric field is presented. A negative direct current is supplied to the wire (corona electrode). The collecting electrode (plate) is connected to the positive sign and grounded.

When an ionic discharge occurs, a bluish glow ("crown") is noticed on the wire. When the aspiration air (gases) moves along the collecting electrodes (as shown by arrow A), dust particles are ionized and deposited on the electrodes. The corona and collecting electrodes are periodically shaken by a system of hammers placed inside the filter, the drives of which are brought out (Fig. 11-18, b).

For uniform gas distribution over the cross-section of the electrostatic precipitator, a gas distribution grid equipped with an electrically driven shaking mechanism is used. The corona and collecting electrodes are installed inside the body of the electrostatic precipitator. Corona electrodes are made of nichrome wire with a diameter of 2.5 mm. They are freely suspended and weighted.

ESP housings can operate under discharges up to 400 li of water. Art. (UGT). The dust settled on the electrodes is discharged into the bunkers, from where it is sent by a system of screw conveyors to the pneumatic pump and further to the warehouse. To avoid dust hanging in the bins, the installation of vibrators is provided.

Rice. II-18. Electrostatic precipitator UG
a - a schematic diagram of the creation of an electric field; b - electrostatic precipitator design

The gases cleaned from dust are directed to the chimney by a smoke exhauster. Depending on the unit behind which the electrostatic precipitator is installed (mill, rotary kiln, etc.), the velocities of gas movement in the electrostatic precipitator are taken from 1 to 1.5 m / s. At these rates, a sufficient residence time of the gas in the electrostatic precipitator is ensured.

To power the electrostatic precipitators with a high voltage current (nominal rectified voltage 80 kV and nominal rectified current 250-400 mA), semiconductor rectifier units APC are used, which provide smooth automatic voltage regulation at the filter electrodes. Start-up of APC units and control over their operation can be carried out remotely.

TO Category: - Machines in the production of building materials

In this article, we will briefly review the methods of air purification that are used in industry, classify and give a brief description.

The history of global pollution

Throughout its industrial history, mankind has polluted the environment to one degree or another. Moreover, one should not think that pollution is an invention of the 19th and 20th centuries. So already in the 13-14 century, the Chinese silver casters of Khan Kublai burned a colossal amount of firewood, thereby polluting the earth with combustion products. Moreover, according to archaeologists, the pollution rate was 3-4 times higher than in modern China, which, as you know, does not put environmental friendliness in the first place.

However, after the industrial revolution with the advent of industrial zoning, the development of heavy industry, the growth of consumption of petroleum products, pollution of nature, and in particular the atmosphere, became global.

Dynamics of carbon emissions into the atmosphere

(source wikipedia.org)

By the end of the 20th century, at least in developed countries, there was an awareness of the need for air purification, and the understanding that the well-being of not only individual countries, but also man as a species, depends on ecology.

A global movement began to legally limit emissions into the atmosphere, which was eventually enshrined in the Kyoto Protocol (adopted in 1997), which obliged the signatory countries to set quotas for harmful emissions into the atmosphere.

In addition to legislation, technologies are also being improved - now, thanks to modern air purification devices, it is possible to capture up to 96-99% of harmful substances.

Legislative justification for the use of air purification systems at industrial enterprises

The main document regulating environmental issues in the Russian Federation is Federal Law No. 7 “On Environmental Protection”. It is he who defines the concept of the rule of nature management, contains the norms for the use of the environment.

The types and measures of punishment for violators of environmental law are contained in the Civil and Labor Code of the Russian Federation.

In the event of air pollution, the following penalties are imposed on offenders:

For the emission of harmful substances into the atmosphere, fines are established: for entrepreneurs from 30 to 50 thousand rubles, for legal entities - from 180 to 250 thousand rubles.

For violation of the conditions of a special permit for the emission of harmful substances, a fine for legal entities is established from 80 to 100 thousand rubles.

Areas of application of air purification systems

Means for purifying the air in one form or another are in every industrial production. But they are especially relevant for:

Metallurgical enterprises that emit into the atmosphere:

ferrous metallurgy - particulate matter (soot), sulfur oxides, carbon monoxide, manganese, phosphorus, mercury vapor, lead, phenol, ammonia, benzene, etc.

non-ferrous metallurgy - solid particles, sulfur oxides, carbon monoxide, and other toxic substances.

Mining and processing plants that pollute the atmosphere with soot, oxides of nitrogen, sulfur and carbon, formaldehydes;

Oil refining complexes - in the course of operation, hydrogen sulfide, oxides of sulfur, nitrogen and carbon are emitted into the atmosphere;

Chemical industries that emit highly toxic waste - sulfur and nitrogen oxides, chlorine, ammonia, fluorine compounds, nitrous gases, etc .;

Energy enterprises (thermal and nuclear power plants) - particulate matter, oxides of carbon, sulfur and nitrogen.

Tasks performed by air cleaning systems

The main tasks of any air purification system at an enterprise are reduced to:

Capture of particles - residues of combustion products, dust, aerosol particles, etc. for their subsequent disposal.

Screening of impurities - steam, gases, radioactive components.

Capture of valuable particles - sifting from the bulk of particles, the preservation of which has an economic justification, for example, oxides of valuable metals.

Classification of the main methods of air purification

It should be noted right away that there is no universal method, therefore, enterprises often use multi-stage air purification methods, when several methods are used to achieve the best effect.

The types of air purification can be classified according to the way of work:

Chemical methods of cleaning polluted air (catalytic and sorption methods of cleaning)

Mechanical air cleaning methods (centrifugal cleaning, water cleaning, wet cleaning)

Physicochemical methods of air purification (condensation, filtration, precipitation)

So for that type of pollution:

Devices for air purification from dust pollution

Devices for cleaning from gas pollution

Now let's look at the methods themselves.

The main methods of air purification from suspended particles

Sedimentation - foreign particles are sifted out from the bulk of the gas due to the action of a certain force:

The forces of gravity in the dust collection chambers.

Inertial forces in cyclone apparatus, in inertial dust collectors in mechanical dry dust collectors.

Electrostatic forces used in electrostatic precipitators.

Examples of dust collection chambers

(Source: intuit.ru)

Filtration- foreign particles are sifted out using special filters that allow the bulk of the air to pass through, but retain suspended particles. The main types of filters:

Bag filters - in the body of such filters there are fabric sleeves (most often an orlon, bike or fiberglass cloth is used), through which a stream of contaminated air passes from the lower branch pipe. Dirt settles on the fabric, and clean air comes out of the nozzle at the top of the filter. As a preventive measure, the sleeves are periodically shaken, dirt from the sleeves falls into a special sump.

Ceramic filters - in such devices, filter elements made of porous ceramics are used.

Oil filters - these filters are a set of individual cassette cells. Inside each cell there are nozzles that are lubricated with a special high-viscosity grease. Passing through such a filter, dirt particles adhere to the attachments.

Bag filter example

(Source: ngpedia.ru)

Electric filters - in such devices, the gas flow passes through an electric field, fine particles receive an electric charge, after which they settle on grounded collecting electrodes.

Example of an electrical filter

(Source: sibac.info)

Wet cleaning - foreign particles in the gas stream are precipitated by mist or foam - water envelops the dust by gravity and flows into the sump.

Most often, scrubbers are used for wet gas cleaning - in these devices, the stream of contaminated gas passes through a stream of finely dispersed water droplets, they envelop the dust under the influence of gravity, settle and drain into a special sump in the form of sludge.

There are about ten types of scrubbers, differing in design and principle of operation, it is worth highlighting separately:

1. Venturi scrubbers - have a characteristic hourglass shape. The operation of such scrubbers is based on the Bernoulli equation - an increase in gas velocity and turbulence due to a decrease in the flow area. At the point of maximum velocity, in the central part of the scrubber, the gas stream mixes with water.

Venturi scrubber

(source: ru.wikipedia.org)

2. Nozzle hollow scrubbers - the design of such a scrubber is a hollow cylindrical container, inside which there are nozzles for spraying water. Water droplets capture dust particles and, under the influence of gravity, flow into the sump.

Scheme of a nozzle hollow scrubber

(Source: studopedia.ru)

3. Foam-bubbling scrubbers - inside such scrubbers there are special bubbling nozzles in the form of a grate or a plate with branches, on which there is liquid. The gas flow, passing through the liquid at high speed (more than 2 m / s), forms a foam, which successfully cleans the gas flow from foreign particles.

Foam bubble scrubbers

(source: ecologylib.ru)

4. Packaged scrubbers, they are also a tower with a packing - inside such scrubbers there are various packing (Berl saddles, Raschig rings, rings with baffles, Berl saddles, etc.), which increase the contact area of polluted air and cleaning liquid. Inside the body, there are also nozzles for spraying the flow of contaminated gas.

Example of a packed scrubber

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Methods for cleaning air from dust

For neutralization of aerosols (dusts 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 apparatuses 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 drops, 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 that use various deposition mechanisms: 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 bunker. 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 that has passed 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> 20 microns.

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. Cyclone devices 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, therefore 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 makes it possible 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 - combining a large number of small cyclones into a group. 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 flow is swirled by a vane swirler and moves upward, 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 gas to be cleaned gradually completely penetrates into it. The annular space around the inlet is equipped with a retaining washer, which ensures the irreversible drainage of dust into the hopper. The vane-type vortex dust collector is distinguished 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 can be battery packs consisting of separate multi-cells with a diameter of 40 mm.

Dynamic dust collectors. 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> 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 are 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 muffled 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 along 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 fibrous 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 cleaning gases 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 between gas and liquid droplets takes place. 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 packing must 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 (bubble, foam). The most common foam machines are those with flop or overflow trays. Overflow trays have holes with a diameter of 3-8 mm. Dust is trapped in 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, in which intensive crushing of the irrigated liquid is ensured 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 the dust particles, and then, under the influence of an electric field, they move and are deposited to the collecting electrodes.

To neutralize waste gases from gaseous and vaporous toxic substances, the following methods are used: 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 recovery; 6) by the type of recovered product; 7) for the organization of the process - periodic and continuous; 8) on constructive 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, and the required degree of cleaning. The choice is made on the basis of 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 a high degree of purification, 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. The gases are cleaned that do not contain dust and catalyst poisons. 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 emitted 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.

Types of dust collectors:

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 general efficiency of dust collection, determined by the ratio of the mass of dust captured 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 various 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 rate lower than the speed of dust hovering, 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 cyclones ranges from 500 ... 1100 Pa. Used for heavy dust: cement, sand, 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 discharge 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. The collecting electrodes are cleaned by tapping or vibration, and sometimes by flushing with water. aerosol filter scrubber

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

Posted on Allbest.ru

...

How to deal with dust in production

There are many types of different kinds of dust collectors, the most common of which are:

cyclones - devices for medium / coarse air cleaning from non-sticking and non-fibrous dust due to centrifugal separation in a rotating air stream;
rotoclones (rotary dust collectors) - a type of centrifugal fans used to clean the air from coarse dust due to inertial forces;
mechanical filters - devices using mesh and porous materials with different characteristic mesh / hole sizes to separate dust particles from the passing through air stream (the range of filters for industrial aspiration systems can be found here - http://ovigo.ru/ochistka-vozduxa- ot-pyili /);
scrubbers - devices that use sprayed liquid to clean the air;
electrostatic precipitators - devices built mainly around the use of the so-called. "corona discharge" in gases and used for the deposition of especially fine dust by giving it an electric charge;
ultrasonic filters are fine cleaning devices that use high-intensity ultrasonic action to coagulate a suspension of particularly fine particles.

Of course, the list above is not exhaustive - and the interested reader should consult the literature for more details.

Specificity of dust collecting devices

It is important to understand that almost any dust is a complex, polydisperse system, the macroscopic properties of which can change very significantly due to external factors. So, a change in air humidity can both increase dust formation and contribute to the agglomeration of particles, and a simple change in the speed of the flow carrying them can affect the value of the accumulated triboelectric volume charge. It would be a big mistake to think that dust collectors for some types of dust / conditions can be easily used under different circumstances with the same efficiency. In practice, the overwhelming majority of dust collectors and aspiration installations first go through the stage of engineering and mathematical calculations and modeling, thus optimizing for a specific consumer and the specifics of his production conditions. It follows that when ordering such devices, it is necessary to communicate with the engineering and technical personnel of a potential supplier, talking about the task at hand in the set of existing conditions. For example, in the case of the planned growth of production activity, the system should be initially designed modularly, i.e. with the possibility of a sectional increase in the productivity of the installation. Of course, only professionals can advise the consumer on the most optimal dust collection methods and efficient types of installations - however, for this they must be provided with accurate technical information in a timely manner.

Emissions of ventilation air at industrial enterprises are different in quantity, various in terms of the harmful substances contained in them and are dispersed throughout the territory of an industrial enterprise. Air pollution in the areas where industrial enterprises are located makes it necessary to clean the outside air before supplying it to the premises by supply ventilation systems and air conditioning systems. Production premises with increased requirements for air purity, for example, need to clean the supply air.

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Introduction ………………………………………………………………… 3
Main part ………………………………………………………… ..4
Conclusion ……………………………………………………….… .22
List of used literature ………………………………… 24

INTRODUCTION

The amount of dust in the outside air depends on the nature of technological processes at industrial enterprises, the degree of urban improvement, traffic intensity, the condition of road surfaces, etc. and can vary widely.

Emissions of ventilation air at industrial enterprises are different in quantity, varied in terms of the harmful substances they contain, and are dispersed over the territory of an industrial enterprise.

Air pollution in the areas where industrial enterprises are located makes it necessary to clean the outside air before supplying it to the premises by supply ventilation systems and air conditioning systems. Cleaning of the supply air is needed in production premises with increased requirements for air purity, for example, separate premises of enterprises of radio electronics, instrument making, precision mechanics, optical and watch factories, etc., as well as premises of medical institutions, research institutes, art galleries, museums, some public buildings (cinemas, theaters, concert halls), etc. Purification of the supply air is also necessary in all cases when the dust content of the outside air exceeds 30% of the permissible dust concentration in the working area of the room. Purification of the supply air allows us to satisfy both sanitary and hygienic and technological requirements for air purity in rooms for various purposes.

The relevance of the topic is that as the air pollution in the world, the cleaning of premises is becoming one of the most global problems that must be solved quickly and efficiently.

The aim is to study dust-free air purification measures.

Based on the goal, we set the following tasks:

study the most popular methods of cleaning ventilation air from dust;
identify the easiest and fastest way to clean;

CLEANING THE VENTILATION AIR FROM DUST: GENERAL INFORMATION ABOUT DUSTED AIR AND METHODS OF ITS CLEANING.

The ambient air, as well as the indoor air, always contains dust.

The nature and amount of it in the outside air depends on the degree of improvement and location of settlements, traffic intensity, technological processes of industrial enterprises and their emissions into the atmosphere, etc.Atmospheric air is considered cleanif the daily averagedust concentration in it (mg / m 3) does not exceed 0.15 slightly polluted - 0.5; heavily polluted - 1, excessively polluted - 3.

Air pollution with dust makes it necessary to clean it in supply ventilation systems. Purification of the supply air is necessary in all cases if the dust content of the outside air exceeds 30% of the maximum permissible concentration of dust established for the premises. Particularly thorough air cleaning is required for enterprises of the radio-electronic industry, precision mechanics and optics, etc. In addition, the supply air must be cleaned to protect ventilation equipment (heat exchangers, irrigation devices, automation, etc.) from dust.

The air in the premises of industrial, municipal and other enterprises is polluted as a result of the release of dust in the process of working on them. This dust, together with the ventilation air, pollutes the air basin. Particularly significant environmental pollution is caused by the release of aerosols and gases through chimneys. There is a need to purify polluted air.

In order to protect the environment, the standards also limit the permissible dust content in the air emitted into the atmosphere by ventilation systems:

when the volume of discharged air is more than 15 thousand m 3 / h

c = 100 * k;

with a volume of discharged air up to 15 thousand m 3 / h

c = (160 - 4 * V),

where c - permissible dust concentration, mg / m 3 ; V is the volume of exhaust air, thousand m 3 / h; k - coefficient depending on the maximum permissible concentration of dust:

Maximum permissible concentration of dust in the air of the working area of the room, mg / m8	and less	More than 2 to 4	More than 4 to 6	and more
Coefficient k

In some cases, exhaust air purification is also provided for capturing dust, which is a raw material or a product of production (flour, sugar, tobacco, etc.).

The choice of a method for air purification depends on the nature, concentration and dispersion of dust (determined by the size of its particles), as well as on the technical characteristics of dedusting devices. The main indicators of the work of dedusting devices include: the degree of cleaning, throughput, dust holding capacity, aerodynamic resistance, energy consumption.

The final result achieved for air purification is determined by the purification factor ε:

ε = (G n - G k) / G n;

where G n and G k - dust concentration in the air, respectively, before and after cleaning, mg / m 3 .

The throughput of the dedusting device is characterized by the permissible specific air load, expressed by the amount of air that can be passed through 1 m during cleaning 2 its working surface or section.

The area of the working surface or cross-section of parallel installed dedusting devices (filters) is determined by the formula

F f = V / V f,

where V is the amount of air to be cleaned, m 3 / h; Vf - permissible specific air load on the dedusting device, m 3 / (h * m 2).

The dust holding capacity is determined by the amount of dust that the device can collect between cleanings.

Coarse, medium and fine cleaning are distinguished according to the degree of dust collection of different dispersion. With coarse cleaning, coarse dust with a particle size of more than 100 microns is captured, with fine cleaning - less than 10 microns.

Depending on the concentration and dispersion of dust, various filters are used to clean the supply air, which retain dust with their porous medium; to clean the exhaust air, dust collectors are used, which deposit dust in their volume due to gravitational, inertial, centrifugal and electric forces. To purify highly polluted air, several dust collectors and filters are installed, the fineness of air purification with which gradually increases in the direction of its movement. This measure protects fine filters from clogging with coarse dust, extends their service life and improves the quality of cleaning.

The air purification factor (1, 2, 3, ..., n) of sequentially installed dedusting devices is expressed by the formula:

ε = 1 - (I - ε 1) * (l - ε 2) * (l - ε 3). ... . (l - ε n).

Filters are divided into three classes according to their effectiveness. Class I filters trap dust particles of all sizes (the cleaning factor is at least 0.99), Class II filters - particles larger than 1 micron (cleaning factor is more than 0.85), Class III filters - particles larger than 10-50 microns (cleaning coefficient not less than 0.60). The characteristics of the air filters are shown in table 1.

Table 1

Air filter range

TYPES OF FILTERS

Dry porous filters. Roll filters FRP are a box-shaped frame with reels in the upper and lower parts of the reel.

In fig. 1 shows a roll filter of the FRU type. A filter material is wound onto the upper reel in the form of a roll, the web of which is fixed on the lower reel. The air passing through the roll panel is cleaned.

As dust accumulates in the filter material, its resistance increases. When the design resistance is reached, the filter material is rewound from the lower drum to the upper one, at the same time it is pneumatically cleaned. FRU filters are used for atmospheric dust content up to 1 mg / m 3 .

Cell filters are a box in which a filtering material with a large surface is placed, the purified air is passed through it. Fiber, thin plates, etc. are used as a filtering material.

So, in dry cellular gear filters FyaP, the filler is a layer of modified polyurethane foam (20-25 mm), treated with an alkali solution.

The unified cell filters FyaR are widely used.

Rice. 1 Roll filter FRU

Wet porous filters.To increase efficiency, the working surface of the filters is wetted with a viscous liquid (industrial, spindle and viscin oil); at low temperatures, transformer oil (at - 35 ° С), instrument MEP (at - 50 ° С) are used. You can also use a water-glycerin solution, perfume oil. In fig. 2 shows an oil filter cell with screens, between which there are metal or porcelain rings soaked in oil.

Rice. 2 Oil filter cell

Rice. 3. FyaR filter

In FYaR cell oil filters, the filtering element is corrugated metal nets with openings of 2.5 mm (five nets), 1.2 mm (four nets) and 0.63 mm (three nets). The meshes are placed in a unified cell (Fig. 3), so that the size of the mesh openings decreases with the flow of air.

Before installation, the filter is immersed in an oil bath. After the excess oil has drained off, it is put in place. Upon reaching a resistance of 1.5 MPa, the filter is removed and cleaned, washing the cells first with a 10% soda solution with a temperature of about 60 ° C, then with hot water.

In FYaV filters, the cells are filled with corrugated vinyl plastic mesh and from the outside with steel mesh. These filters can be used dry and wet. In the FNU filters, an elastic material made of glass fiber of the FSVU brand is used as a filtering layer.

The FRP roll filters are the same in their design and principle of operation as the FRU filters, but the filtering material here is a roll of PV material.

Self-cleaning oil filters KT and KD are widely used in ventilation and air conditioning technology. The diagrams of their device (Fig. 4) are similar to those of roll filters, only instead of roll cloths in the self-cleaning filter there are two endless wire mesh. Each mesh is stretched between two rollers. The upper roller (leading) is driven by an electric motor through a two-stage worm gear and a gear train. There is also an oil bath.

Rice. 4 Self-cleaning oil filter
1 - infinitely movable grids; 2 - oil tank

The air is purified by passing successively through two oil-soaked nets. The screens pass through an oil bath, where dust settles on them and the filter is wetted.

Electric filters. Dust particles from the air stream in them are deposited on the electrodes under the influence of an electric field in which they receive a charge.

Filters with FP material (IV Petryanov's cloth) are designed for ultrafine purification of air and gases from radioactive, toxic, bacterial and other highly dispersed aerosols. Such filters provide almost complete sterility of the purified air.

FP material is a layer of ultra-thin fibers deposited on a perchlorovinyl base. When air passes through, the filter material acquires an electrical charge, which improves its filtering properties.

Rice. 5 Filter design with filtering material FP
1 - box; 2 - vinyl plastic film; 3 - material FP mesh

Rice. 6 Frame filter paper

1 - filter paper; 2 - grid

Filters with FP material are made in the form of a set of U-shaped frames, between which a filtering layer is laid (Fig. 5). In some filters with FP material, for example, in LAIK filters, the frames, bent by the filtering cloth, are placed in the form of a nozzle inside a rectangular box. Before filters made of FP material, a preliminary air filter (oil or other design) must be installed.

Paper frame filters (Fig. 6) are also designed for fine air purification. The filtering material in them is alignin (a mixture of fine asbestos fibers with wood pulp), which is laid in the form of an accordion on a supporting frame. When the filter is filled with six layers of alignin and two layers of silk, the purification factor is 95-96% at an initial dust content of 1-3 mg / m 3 .

The filter material in paper filters and the FP material cannot be regenerated, and after the accumulation of the maximum amount of dust, they are replaced with new ones.

Cleaning the ventilation air from dust: Dust collectors

Dust collectors are designed to capture process dust and clean the exhaust ventilation air. The simplest type of dust collectors are dust settling chambers (Fig. 7). The deposition of dust from dusty air in them occurs due to its own gravity with a decrease in the speed of air movement in the chamber. To increase efficiency and reduce the length of the chamber, it is divided into a number of channels or mazes are arranged (Fig. 8).

Fig. 7 Dust settling chambers
a - simple; b - labyrinth

In the dust settling chambers, coarsely dispersed dust with a size of more than 20 microns is mainly deposited. The cleaning efficiency in them is low (0.55-0.60).

Inertial dust collectors. The most common dust collectors of this type are cyclones (Fig. 8). In the cyclone, the air to be cleaned enters the upper cylindrical part from the side, swirls and is removed through the central pipe. Dust particles under the influence of centrifugal forces are thrown to the walls of the housing, settle into the conical part and fall into the hopper. The cyclones efficiently trap particles larger than 8 microns. They are used in various industries to capture dust from the air, ash from boiler flue gases, soot, talc, shavings, etc.

The efficiency of air purification is significantly increased when using wet dust collectors, scrubbers, cyclone-washers, etc., in which water is used to wash away dust from the walls.
In scrubbers, water is supplied by a special irrigation system with nozzles, as a result of which a constantly flowing down film forms on the walls inside the cylinder. In cyclone washers, water is sprayed into the inlet. One of the varieties of inertial dust collectors is the dust separator shown in Fig. 9.

Fig. 9 Fabric filters

Fig. 10 Cyclone diagram

Fig. 11 Inertial Dust Separator

The dust separator consists of a very large number of cones (rings), the diameter of which gradually decreases with the air flow. There are gaps up to 6 mm wide between the rings. The air supplied to the inside of the device leaves it through the slots between the rings, where its direction changes by about 150 °, and through the small opening of the cone at the end of the device. Due to the fact that dust particles, due to inertia, tend to maintain straightness of motion, then purified air comes out through the slots, and dust, together with 3-7% of the air supplied to the device, comes out through the opening of the last cone. Further, the dust is collected using various devices, for example a cyclone, into which dusty air is fed from the last cone of the inertial dust separator. Such installations are used to purify highly dusty air emitted by ventilation outside of industrial plants.

Cloth dust collectors - filters can clean the air with a fairly high efficiency (0.99 and more). According to the shape of the filtering surface, they are divided into sleeve and frame. Cotton fabrics, cloth, nylon, lavsan, fiberglass, etc. are used as a filtering material in them. The disadvantage of fabric dust collectors is the need for frequent shaking of fabrics to increase dust and the bulkiness of this equipment.

Fabric dust collectors have a fairly high specific air load, but at the same time have high aerodynamic resistance (up to 190 Pa before regeneration).
Effectively cleaning the air from dust using electrostatic precipitators. In them, the air to be cleaned is ionized in a high-voltage electric field (up to 15,000 V). Dust particles that have received a charge are attracted to the electrode with the opposite charge sign. As a result, passing between the two electrodes, the air is cleared of dust. The settled dust flows into the hopper or is removed by shaking. Electrostatic precipitators provide a high degree of purification, but they are expensive to operate.

Features of ventilation of buildings for various purposes: Ventilation of residential buildings

Ventilation of premises of residential buildings is designed to remove excess heat, moisture, carbon dioxide emitted by people, various gases that appear during the cooking process, and other hazards.

The air exchange required for humans is small. So, for the assimilation of carbon dioxide in a room, 46 m3 / h of fresh air per person is required. Taking into account the normalized area for one person, the calculated air exchange in residential premises can be taken equal to 3 m 3 / h per 1 m2 of living space.

The minimum air exchange should be determined based on the need for ventilation of kitchens and bathrooms. The volume of the exhaust from them should be, m 3 / h, not less: in a non-gasified kitchen - 60, in a gasified kitchen of a one-room apartment 60, the same, in a two-room apartment - 75, in a three-room apartment - 90; in the bathroom and in the lavatory - 25 each. In the elevator engine room, electrical control room, garbage collection rooms and other similar utility rooms, an air exhaust should be provided with a volume of exhaust air per hour equal to the volume of the room (the multiplicity is equal to one — 1 / h).

In the premises of residential buildings, as a rule, natural ventilation is provided. Artificial supply and exhaust ventilation is designed in residential buildings located in the northern construction and climatic zone, for heating cold supply air, as well as creating some air pressure in the premises to prevent its infiltration through leaks in building structures.

Artificial ventilation is sometimes also provided in hotels and hostels. In residential buildings in southern regions with a hot climate, it is recommended to install room air conditioners or other cooling devices in order to maintain the internal air temperature not higher than 28 ° C.

Air exchange in residential buildings is organized according to the following scheme: outside air enters directly into the living quarters, and is removed through the exhaust ducts of the kitchens and bathrooms. In apartments with four or more rooms, an additional extractor hood is provided from all rooms, except for the two closest to the kitchen. Such an organization of air exchange ensures the movement of air from residential premises towards household ones. In hostels and hotels, exhaust ventilation is arranged in bedrooms, bathrooms and utility rooms, except for the lobby and storerooms. Isolators should have a separate ventilation system.

FIGHTING DUST IN THE ROLLING PRODUCTION.
TESTING AND ADJUSTMENT OF DUST COLLECTING DEVICES

The test of dust-collecting devices is carried out after adjustment and adjustment of ventilation units equipped with these devices. The performance of each installation must ensure the removal of optimal air volumes from all local suction services it serves.
Before testing, dust collection devices should be in good condition and cleaned. During the test, dusty processing equipment should be operated at normal load. Interruptions in the operation of the equipment, as well as factors affecting the content of dust in the exhaust air, must be noted in the test log. During the test, the following is determined: the speed and flow rate (of the air entering the device; the resistance of the device to the passing air; the cleaning efficiency.
When testing cyclones, centrifugal scrubbers and inertial dust separators, the coefficient of local resistance of the device is additionally determined, referred to the air velocity in the inlet pipe of the dust collector.
Air consumption is determined by measurements before and after the dust collection device. The difference between these costs is the amount of suction or knocking out of air from the device. If this value does not exceed 5% of the total amount of purified air, then in subsequent calculations, the air flow rate is taken as the average of the measurements determined before and after the device.
If there are several cleaning stages in the dust collecting device, the air flow rate is measured before and after the cleaning stage.
For dust-collecting devices with filtering surfaces, the specific air consumption I (air load) per 1 m2 of filtering surface is determined by the formula

where L is the air flow rate, m3 / h;
F - filtering surface, m2.
The amount of dust in the air before and after the dust collecting device is determined by the air flow rate and dust content, mg / m3, in the supply. and outlet ducts. If it is possible to accurately weigh all the dust captured by the dust collecting device for a given period of time, the dust content is determined only from the side of the device inlet.
Air sampling for dust content before and after the dust collecting device is carried out simultaneously. The number of air samples both before and after the device is taken in aspiration units 5-6, and in supply units 3-4.
The efficiency of the dust collecting device is determined by the formula:

where Кн and Кк are respectively the initial and final dust content (before and after the dust collecting device). Comparison and assessment of the same type of dust collecting devices that purify the air from dust of the same composition and dispersion is made by comparing the amount of dust emitted from each device outside and expressed as 1 — e.
Simultaneously with the test of dust-collecting devices, the conditions for the release of cleaned air into the atmosphere are checked. It should not fall into the windows of higher floors and neighboring buildings, as well as into the air intake devices of air supply units.
When evaluating the test results, they are guided by the data in Table. 13.

table 2

The area of rational use and the main indicators of the most common dust collection devices

With insufficient efficiency of dust collecting devices and an increased dust content in the air emitted into the atmosphere after cleaning in comparison with sanitary standards, the operating mode of dust collecting devices is worked out to increase their efficiency.
In cases where the low efficiency is caused by the inadequacy of the dust collection device for the nature of the dust, it should be replaced with a more suitable device. On the basis of the tests carried out, the adjusters develop measures to improve the operation of dust collecting devices.
Cyclones. The test of cyclones, in which the lower cone is used as a dust collector, is allowed only after the installation of separate sealed dust collectors. If the low efficiency of the cyclone is caused by insufficient inlet air velocity in comparison with the data provided for the set cyclone number, it is necessary to replace it with a cyclone of a lower number, and when installing a group of cyclones, reduce their number. In the process of testing a group of cyclones, it is necessary to ensure an even distribution of air between them, for which the resistance of each cyclone must be the same.
Inertial dust separators. Measurements of the full speed and static pressure are made before and after the inertial dust separator, as well as on the dust-removing duct - before and after the cyclone of the dust separator. When working out the operation mode of the dust separator, they ensure that the air flow passing through the dust-removing air duct is 5-7% of the air flow to the dust separator. If the inertial dust separator does not meet the performance requirements significantly, it should be replaced.
Centrifugal scrubbers and wet film cyclones. The water consumption for a certain period of time is determined by measuring the amount of waste water with measuring tanks. The pressure of the supplied water is determined by a pressure gauge, and in the presence of an intermediate tank, by the distance from the water level to the level of the nozzles. Specific water consumption (l / m3 air) must correspond to design data or catalog data. An increase in the amount of water supplied is achieved by opening a valve or increasing the diameter of the water spray nozzles or tubes.

CONCLUSION

Modern civilization exerts unprecedented pressure on nature. Air pollution by industrial emissions has a harmful effect on people, animals, plants, soil, buildings and structures, reduces the transparency of the atmosphere, increases air humidity, increases the number of days with fog, reduces visibility, and causes corrosion of metal products.

Dust from industrial plants, containing mainly metal particles, is a major health hazard. Thus, the dust of copper smelters contains iron oxide, sulfur, quartz, arsenic, antimony, bismuth, lead or their compounds.

In recent years, photochemical fogs have begun to appear, arising from the exposure to intense ultraviolet radiation on the exhaust gases of cars. The study of the atmosphere made it possible to establish that the air at an altitude of 11 km is polluted by emissions from industrial enterprises.

The difficulties of cleaning gases from pollutants include, first of all, the fact that the volumes of industrial gases emitted into the atmosphere are enormous. For example, a large combined heat and power plant is capable of emitting up to 1 billion cubic meters into the atmosphere in one hour. meters of gases. Therefore, even with a very high degree of purification of exhaust gases, the amount of pollutant entering the air basin will be estimated to be significant.

The increase in air pollution requires quick and effective ways to protect it from pollution, as well as ways to prevent the harmful effects of air pollutants. The atmosphere can contain a certain amount of pollutant without causing harmful effects. there is a natural process of its cleaning.

The first step in establishing the harmful effects of air pollution is to develop air quality criteria as well as quality standards.

Typically, industrial plants use gas cleaning and dedusting processes or devices to reduce or prevent emissions. Gas cleaning processes can also destroy or alter its chemical or physical properties so that it becomes less hazardous.

Another approach to improving the state of the atmosphere is the requirement for the use of advanced technological processes, the replacement of harmful materials with harmless ones, the use of wet methods of processing raw materials instead of dry ones.

LIST OF USED LITERATURE

1. Heating and ventilation / ed. V.N. Bogoslovsky. Moscow: Stroyizdat, 1976 .-- 433 p.

2. P.N. Kamenev. Heating and ventilation. Part 2. M .: Stroyizdat,

1964 .-- 472 p.

3. K.V. Tikhomirov, E.S. Sergeenko. Heat engineering, heat and gas supply and ventilation. Moscow: Stroyizdat, 1991 .-- 480 p.

4. Drozdov V.F. Industrial ventilation. M .: 1988 .-- 263 p.

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