Methods and methods for purifying atmospheric air. Effective methods for purifying atmospheric air

Ministry of Education and Science

Federal state budget educational institution HPE

SSTU IM. Gagarina Yu.A.

Engels Institute of Technology (branch)

Department of Ecology and Environmental Protection

COURSE PROJECT

discipline: Environmental protection engineering

Air purification equipment

Completed by: Dolbnya I.V.

Art. group OOS-51

Checked by: professor

Olshanskaya L.N.

Engels - 2013

INTRODUCTION

Atmosphere protection

1 The main pollutants of atmospheric air and the consequences of its pollution

1.2 Atmospheric protection means

2. Methods and equipment for air purification

2.1 Dry dust collectors (cyclones)

2 Wet dust collectors (scrubbers)

3 Filters

2.4 Absorption methods

5 Adsorption methods

6 Catalytic method

2.7 Thermal method

3. Calculation of equipment for atmospheric air purification

1 Initial data

2 Calculation of cyclone TsN-24

3 Bunker calculation

CONCLUSION

LIST OF REFERENCES USED

INTRODUCTION

Currently, the problem of air pollution with various harmful and toxic impurities is acute. This is due, first of all, to the high pace of industrial development, as well as to the enormous scale of the spread of road transport. In various industries, pollution of the atmosphere, hydrosphere and lithosphere occurs. Atmospheric air is daily exposed to emissions of harmful gases and impurities, which mix and enter into chemical reactions with gases included in the constant composition of the atmosphere (N 2, O 2, a mixture of noble gases). As a result, the constant air composition can become variable (CO 2and water vapor) or random, the composition of which depends on local conditions. Such changes in the atmosphere can lead to the formation of acid precipitation, which results from the interaction of SO 2,NO x , CO, CO 2and other oxides with its components. Acid precipitation, in turn, has a detrimental effect on soil, water bodies, vegetation and living organisms. They lead to acidification of water bodies and soil, as a result of which the pH of the environment changes, which contributes to the deterioration of the living conditions of plants, animals and microorganisms, which can lead to their death. In addition, acid precipitation destroys the structure of buildings and structures, as well as natural and architectural monuments. IN pure form Sulfur dioxide, nitrogen and carbon oxides are very harmful and toxic. In addition to these contaminants as a result active work Industrial enterprises release many other harmful substances into the atmosphere, including toxic organic substances, aerosols and dust of various chemical compositions.

Therefore, along with the development of industry, it is necessary to develop and improve methods for protecting and purifying the atmosphere from foreign substances. It is necessary to minimize the amount of emissions of harmful gases. In addition, in air purification processes, many impurities can be recovered and reused in production.

The purpose of this work is to analyze and study scientific literature on methods and means of atmospheric air purification, as well as to calculate the parameters of the TsN-24 cyclone.

1. ATMOSPHERE PROTECTION

Atmosphere - gas envelope celestial body, held near it by gravity. Since there is no sharp boundary between the atmosphere and interplanetary space, the atmosphere is usually considered to be the region around a celestial body in which the gaseous medium rotates with it as a single whole. The depth of the atmosphere of some planets, consisting mainly of gases (gas planets), can be very deep.

The Earth's atmosphere contains oxygen, used by most living organisms for respiration, and carbon dioxide, consumed by plants, algae and cyanobacteria during photosynthesis. The atmosphere is also the planet's protective layer, protecting its inhabitants from the sun's ultraviolet radiation.

.1 Main air pollutants and consequences of air pollution

The main air pollutants generated both during human economic activity and as a result of natural processes are sulfur dioxide SO 2, carbon dioxide CO 2, nitrogen oxides NO x , solid particles - aerosols. Their share is 98% in total volume emissions of harmful substances. In addition to these main pollutants, more than 70 types of harmful substances are observed in the atmosphere: formaldehyde, phenol, benzene, compounds of lead and other heavy metals, ammonia, carbon disulfide, etc.

Towards the most important environmental consequences global pollution atmospheres include:

· possible climate warming (greenhouse effect);

· ozone layer disruption;

· acid rain;

· deterioration of people's health.

The greenhouse effect is an increase in the temperature of the lower layers of the Earth's atmosphere compared to the effective temperature, i.e. the temperature of the planet's thermal radiation observed from space.

In December 1997, at a meeting in Kyoto, Japan, on global climate change, delegates from more than 160 countries adopted a convention obliging developed countries to reduce greenhouse gas emissions. The Kyoto Protocol obliges 38 industrial developed countries reduce by 2008-2012 CO emissions 2by 5% from the 1990 level:

· The European Union must reduce CO emissions 2and other greenhouse gases by 8%,

USA - by 7%,

Japan - by 6%.

In March 2001, the United States, which accounts for 36.1% of global emissions, announced its decision not to participate in the Kyoto Protocol. Canada also left the list of participating countries. Afghanistan<#"justify">The protocol provides for a system of quotas for greenhouse gas emissions. Its essence lies in the fact that each country (so far this applies only to thirty-eight countries that have committed to reducing emissions) receives permission to emit a certain amount of greenhouse gases. It is assumed that some countries or companies will exceed the emission quota. In such cases, these countries or companies will be able to buy the right to additional emissions from those countries or companies whose emissions are less than the allocated quota. Thus, it is assumed that the main goal of reducing greenhouse gas emissions by 5% over the next 15 years will be achieved.

As other reasons causing climate warming, scientists name the variability of solar activity, changes in magnetic field Earth and atmospheric electric field.

.2 Atmospheric protection means

To protect the atmosphere from negative anthropogenic impact The following basic measures are used.

Greening technological processes:

1 creation of closed technological cycles, low-waste technologies that prevent the release of harmful substances into the atmosphere;

2 reduction of pollution from thermal installations: centralized heat supply, preliminary purification of fuel from sulfur compounds, use of alternative energy sources, transition to higher quality fuel (from coal to natural gas);

3 reduction of pollution from motor transport: the use of electric transport, exhaust gas purification, the use of catalytic converters for afterburning fuel, the development of hydrogen transport, the transfer of traffic flows outside the city.

Purification of process gas emissions from harmful impurities.

Dispersion of gas emissions in the atmosphere. Dispersion is carried out using high chimneys (over 300 m high). This is a temporary, forced event, which is carried out due to the fact that existing treatment facilities do not provide complete removal of harmful substances from emissions.

Construction of sanitary protection zones, architectural and planning solutions.

A sanitary protection zone (SPZ) is a strip separating sources of industrial pollution from residential or public buildings to protect the population from the influence of harmful production factors. The width of the sanitary protection zone is established depending on the class of production, the degree of harmfulness and the amount of substances released into the atmosphere (50-1000 m).

Architectural and planning solutions - correct mutual placement of emission sources and populated areas, taking into account the direction of winds, construction of highways bypassing populated areas, etc.

Emission treatment equipment:

· devices for cleaning gas emissions from aerosols (dust, ash, soot);

· devices for purifying emissions from gas and vapor impurities (NO, NO 2,SO 2,SO 3and etc.)

2. METHODS AND EQUIPMENT FOR ATMOSPHERE PURIFICATION

.1 Dry dust collectors (cyclones)

Dry dust collectors are designed for rough mechanical cleaning of large and heavy dust. The principle of operation is the settling of particles under the influence of centrifugal force and gravity. Cyclones have become widespread various types: single, group, battery.

The diagram (Fig. 1) shows a simplified design of a single cyclone. The dust and gas flow is introduced into the cyclone through the inlet pipe 2, twists and performs a rotational and translational movement along the housing 1. Dust particles are thrown under the action of centrifugal forces to the wall of the housing, and then under the influence of gravity they are collected in the dust bin 4, from where they are periodically removed. The gas, freed from dust, turns 180 º and leaves the cyclone through pipe 3.

Rice. 1. Cyclone

.2 Wet dust collectors (scrubbers)

Wet dust collectors are characterized by high cleaning efficiency from fine dust up to 2 microns in size. They work on the principle of deposition of dust particles onto the surface of droplets under the influence of inertial forces or Brownian motion.

The diagram (Fig. 2) shows a scrubber. The dusty gas flow through pipe 1 is directed to the liquid mirror 2, on which the largest dust particles are deposited. The gas then rises towards the flow of liquid droplets supplied through the nozzles, where small dust particles are removed.

Rice. 2. Scrubber

.3 Filters

Designed for fine purification of gases due to the deposition of dust particles (up to 0.05 microns) on the surface of porous filter partitions. Based on the type of filter media, a distinction is made between fabric filters (fabric, felt, sponge rubber) and granular filters. The choice of filter material is determined by the cleaning requirements and operating conditions: degree of purification, temperature, gas aggressiveness, humidity, amount and size of dust, etc. The diagram (Fig. 3) shows the filter device.

Rice. 3. Filter

Electrostatic precipitators - effective method cleaning from suspended dust particles (0.01 microns), from oil mist. The operating principle is based on ionization and deposition of particles in an electric field. At the surface of the corona electrode, ionization of the dust and gas flow occurs. Having acquired a negative charge, dust particles move towards the collecting electrode, which has a sign opposite to the charge of the discharge electrode. As dust particles accumulate on the electrodes, they fall by gravity into a dust collector or are removed by shaking.

In atmospheric air purification processes, two-zone electrostatic precipitators are also used (Fig. 4). A distinctive feature of such filters is the presence of two separate electric fields, in one of which the suspended particles are charged, and in the other they are deposited. In Russia, the most widely used two-zone electric precipitator is the “Rion” type, used mainly for cleaning ventilation air with temperatures up to 40°C with an initial dust content of no more than 10 mg/m ³. The purified air first passes through an ionizer designed to charge dust particles in the field of a corona discharge that occurs between the electrodes of positive and negative polarity. The ionizer is designed in such a way that at a speed of about 2 m/s the captured dust has time to charge, but does not have time to settle. Due to the small diameter of the corona electrodes and the small interelectrode gap, the ionizer operates at a voltage of 14 kV, which is sufficient to obtain a field strength that ensures the occurrence of a corona discharge. The charged dust particles are carried by the air flow into the precipitator, which is a system of plates. The alternation of grounded (negatively charged) plates and plates connected to the positive pole of the rectifier creates a uniform electric deposition field. Charged dust particles settle in the precipitator field on plates of opposite polarity. The small distance between the plates (6-7 mm) makes it possible, at a low voltage between the plates (7 kV), to obtain a field strength of 8-10 kV/cm, i.e. approximately twice as high as in single-zone electrostatic precipitators, which is sufficient to deposit the smallest particles (submicron size). The high field strength and small distance between the plates cause a high rate of dust deposition. To capture 85-95% of dust, staying in the precipitator for 0.2-0.4 s is sufficient. Electrostatic precipitators of the "Rion" type are designed for the following flow rates of the purified air - 20,000 m ³/ h (Rion-2.7); 10000 m ³/ h (Rion-1.4); 4000 m ³/ h (Rion-0.55) and 1000 m ³/ h (Rion-0.17). The degree of purification in all types of electric precipitators is 85-95%.

Rice. 4. Schematic diagram of a two-zone electrostatic precipitator: a - ionizer; b - precipitant. 1,2 - positive and negative electrodes of the ionizer; 3.4 - positive and negative electrode precipitators

Electric precipitators are powered by rectified high voltage current (60-80 kV). To convert alternating current of normal frequency (50 Hz) and low voltage (380 V), relatively low power electrical units (20-150 kW) are used. Each electrical unit consists of a step-up transformer, rectifier, voltage regulator and control panel.

2.4 Absorption methods

The essence of absorption is the absorption of the removed components by the liquid. Depending on the characteristics of the interaction between the absorber and the component extracted from the gas mixture, absorption methods are divided into methods of physical absorption and chemical absorption (chemisorption), accompanied by a chemical reaction in the liquid phase. For physical absorption, absorbers are used - water, organic solvents that do not react with the extracted gas. During chemisorption purification, the components released from gases enter into chemical reactions with chemisorbents, which are solutions of mineral and organic substances, suspensions and organic liquids. Absorption methods are used to purify gases from CO, N x O y ,SO 2, H 2S, HCl, CO 2 .

Depending on the method of creating the contact surface of the phases, surface, bubbling and spraying absorption devices are distinguished.

In the first group of devices, the contact surface between the phases is a liquid mirror or the surface of a flowing liquid film. This also includes packed absorbents, in which liquid flows over the surface of a packed packing made from bodies of various shapes.

In the second group of absorbents, the contact surface increases due to the distribution of gas flows into the liquid in the form of bubbles and jets. Sparging is carried out by passing gas through a liquid-filled apparatus or in column-type apparatuses with plates of various shapes.

In the third group, the contact surface is created by spraying a liquid into a mass of gas. The contact surface and the efficiency of the process as a whole are determined by the dispersion of the sprayed liquid.

The most widespread are packed (surface) and bubbling plate absorbers. For the effective use of aqueous absorption media, the component to be removed must be well dissolved in the absorption medium and often chemically interact with water, as, for example, when purifying gases from HCl, HF, NH 3,NO 2. Common disadvantages absorption methods is the formation of liquid waste and the cumbersomeness of the equipment.

Among surface absorbers, film absorbers attract attention and are widely used. A design feature of film contact devices with a fixed phase contact surface are channels of round, rectangular, triangular and other sections, along the inner surface of which a thin liquid film moves, interacting with the gas flow. The interaction of phases at the contact stage can be either co-current or counter-current. Usually they use the principle of direct-flow interaction of phases at each stage, ensuring countercurrent in the apparatus as a whole.

In order to intensify the absorption process and improve phase separation, swirlers (swirlers) are installed in circular channels. Additional rotational movement, imparted to a two-phase flow, increases the efficiency of mass transfer by 1.5-2 times and makes it possible to use the resulting centrifugal force to separate phases after leaving the contact zone. In the contact zone, the liquid under the influence of this force forms a helical film moving upward on the inner surface of the channel. This was the impetus for the use of swirling motion in the contact zone in the development of high-speed absorption devices (Fig. 5).

Rice. 5. High-speed absorber with direct-flow interaction of gas and liquid in an ascending swirling flow

atmospheric pollution dust collector filter

Each stage consists of parallel-operating tubular elements AE with multi-blade helical axial swirlers CD. The gas flow rising through the apparatus enters the contact zone BE and captures the liquid flowing from the sprayer B. The gas flow carrying liquid droplets passes through the spray zone BC and enters the axial swirler CD. The presence of a spray zone with a developed interfacial surface in front of the swirler increases the efficiency of mass transfer. After the swirler, the swirling flow passes through the film zone DE, from which the liquid through the separation gap EA is ejected onto the wall of the separation pipe and flows down, and the gas flow rises to the next stage. The liquid enters the lower stage atomizer through the inter-element space, radial transfer pipes and central transfer pipe. Mass transfer between gas and liquid occurs in three zones: atomization, swirling and film.

The most representative group in terms of design is bubble absorbers (Fig. 6). As a result of the interaction of phases (the liquid is a continuous phase, and the gas is a dispersed phase), a gas-liquid layer is formed on the plates, consisting of a relatively pure liquid and a foamed liquid. The total height of the layer on the plate and its components depend on the design of the plate, on the ratio of material flows and the physical and chemical properties of the system.

Among bubbling contact devices, a special place is occupied by sieve and cap plates, which are widely used in industry. One of the new designs of bubble absorbers is a column with sieve trays and a stack of tortuous plates located between the trays. A package of tortuous plates helps create an additional mass transfer zone, trap liquid splashes resulting from bubbling on a sieve plate, and return them to the liquid layer on the same plate. The overflow device ensures the flow of liquid from plate to plate along the height of the column. The overflow can be carried out in the absence or presence of a receiving pocket in the overflow device. Overflow devices without a receiving pocket allow you to increase the working area of ​​the plate and, therefore, increase the productivity of the column. In cases where the range of operation of the overflow device limits the operation of the plate as a whole, it is advisable to install regulating overflow devices, for example, with annular slots that alternately enter into operation, or with rotary valves that regulate the flow area of ​​the overflow device. Sink plates do not have overflow devices, which makes it possible to more fully utilize the area of ​​the plates and significantly simplifies them in terms of design. Gas and liquid move in countercurrent. One of the disadvantages of such trays is their relatively narrow operating range with respect to gas loads.

The intensification of the absorption process in devices with failed plates has recently been carried out along the path of creating plates with an ordered flow of liquid and a constant free cross-section, with enlarged perforation and with a self-regulating free cross-section of the plates.

Rice. 6. Absorber with sieve plates: 1-plate; 2 - overflow device; 3 - separation zone

2.5 Adsorption methods

Adsorption methods of gas purification are based on the absorption of gaseous and vaporous impurities by solids with a developed surface - adsorbents. Absorbed gas molecules are held on the surface of a solid by van der Waals forces (physical adsorption) or chemical forces(chemisorption).

The adsorption process is carried out in several stages: transfer of gas molecules to the outer surface of the solid; penetration of gas molecules into the pores of a solid; adsorption itself. The slowest stage limits the process as a whole.

Adsorption is recommended for purifying gases with low concentrations of harmful components. Adsorbed substances are removed from adsorbents by desorption with an inert gas or steam. In some cases, thermal regeneration is carried out. The process is carried out in adsorbers with a stationary, moving and fluidized layer of sorbent, in batch and continuous action.

Materials with a highly developed internal surface are used as adsorbents. Adsorbents can be of either natural or synthetic origin. The main types of industrial adsorbents include activated carbons, silica gels (SiO 2?nН 2O), aluminum gels (active aluminum oxide A1 2ABOUT 3?nН 2O), zeolites and ion exchangers.

The following main methods for carrying out adsorption purification processes can be distinguished:

) After adsorption, desorption is carried out and the captured components are recovered for reuse.

) After adsorption, the impurities are not disposed of, but are subjected to thermal or catalytic afterburning. This variety adsorption purification is economically justified at low concentrations of pollutants and (or) multicomponent pollutants.

) After cleaning, the adsorbent is not regenerated, but is subjected, for example, to burial or combustion together with a strongly chemisorbed pollutant. This method is suitable when using cheap adsorbents.

A variety of equipment has been developed to carry out adsorption processes. The most common adsorbers are those with a fixed layer of granular or honeycomb adsorbent (Fig. 7). The continuity of the processes of adsorption and regeneration of the adsorbent is ensured by the use of fluidized bed apparatus.

Adsorption methods are one of the most common gas purification methods in industry. Their use makes it possible to return a number of valuable compounds to production. At concentrations of impurities in gases of more than 2-5 mg/m ³, cleaning even turns out to be cost-effective. The main disadvantage of the adsorption method is the high energy intensity of the desorption and subsequent separation stages, which significantly complicates its use for multicomponent mixtures.

Rice. 7. Shelf multi-section type adsorber with fixed layers of adsorbent: 1 - apparatus body; 2 - adsorbent layer

.6 Catalytic method

This method transforms toxic components industrial emissions into substances that are harmless or less harmful to the environment by introducing them into the system additional substances called catalysts. Catalytic methods are based on the interaction of the substances being removed with one of the components present in the gas being purified, or with a substance specially added to the mixture on solid catalysts. The action of catalysts is manifested in the intermediate (surface) chemical interaction of the catalyst with the reacting compounds, as a result of which intermediate substances and a regenerated catalyst are formed.

Methods for selecting catalysts are very diverse, but they are all based mainly on empirical or semi-empirical methods. The activity of catalysts is judged by the amount of product obtained per unit volume of catalyst, or by the rate of catalytic processes that provide the required degree of conversion.

In most cases, catalysts can be metals or their compounds (platinum and platinum series metals, oxides of copper and manganese, etc.). To carry out the catalytic process, small amounts of catalyst are required, positioned in such a way as to provide maximum contact surface with the gas stream. Catalysts are usually made in the form of balls, rings or wire twisted into a spiral. The catalyst may consist of a mixture of base metals with the addition of platinum and palladium (hundredths of a percent by weight of the catalyst), deposited in the form of an active film on a nichrome wire twisted into a spiral.

The volume of the catalyst mass is determined based on the maximum rate of gas neutralization, which in turn depends on the nature and concentration of harmful substances in the exhaust gas, the temperature and pressure of the catalytic process and the activity of the catalyst. The permissible rate of neutralization is in the range of 2000-60000 volumes of gas per volume of catalytic mass per hour. On catalysts developed at the Dzerzhinsky branch of NIIOGAZ, at a neutralization rate of 30,000-60,000 volumes of neutralized gas per volume of catalyst mass per hour and a temperature of 350-420°C, impurities of ethylene, propylene, butane, propane, acetaldehyde, alcohols (methyl, ethyl) are almost completely oxidized , propyl, allylic, etc.), acetone, ethyl acetone, benzene, toluene, xylene, carbon monoxide, etc.

The gas temperature has a significant influence on the speed and efficiency of the catalytic process. Each reaction occurring in a gas flow is characterized by a so-called minimum temperature for the start of the reaction, below which the catalyst does not show activity. The temperature at which the reaction begins depends on the nature and concentration of the trapped pollutants, the flow rate and the type of catalyst. As the temperature increases, the efficiency of the catalytic process increases. For example, methane begins to oxidize on the surface of a catalyst consisting of 60% manganese dioxide and 40% copper oxide only at a temperature of 320°C, and a 97% reaction is observed at t=450°C. However, it should be borne in mind that for each catalyst there is a temperature limit. An increase in this level leads to a decrease in activity and then to the destruction of the catalyst.

To maintain the required gas temperature, combustion products from an auxiliary burner operating on some high-calorie fuel are sometimes mixed into it (especially during the startup period). In Fig. Figure 8 shows a catalytic reactor designed for the oxidation of toluene contained in gas-air emissions from paint shops. Air containing toluene impurities is heated in the inter-tube space of the heat exchanger - recuperator 1, from where it enters the heater 4 through transition channels. The combustion products of natural gas burned in burners 5 are mixed with the air, increasing its temperature to 250-350 ° C, t i.e. to a level that ensures the optimal rate of toluene oxidation on the catalyst surface. The chemical transformation process occurs on the surface of the catalyst 3, located in the contact device 2. Natural manganese ore (pyromsite) in the form of granules 2-5 mm in size, promoted with palladium nitrate, is used as a catalyst. As a result of the oxidation of toluene, non-toxic products are formed: carbon monoxide and water vapor. A mixture of air and reaction products at a temperature of 350-450°C is sent to recuperator 1, where it transfers heat to the gas-air flow for cleaning, and is then released into the atmosphere through the outlet pipe. The cleaning efficiency of such a reactor is 95-98% with an auxiliary fuel (natural gas) consumption of 3.5-4.0 m 3at 1000 m 3purified air. Hydraulic resistance of the reactor at rated load (800-900 m 3/h) does not exceed 150-180 Pa. The process speed is in the range from 8000 to 10000 volumes per volume of catalyst mass per 1 hour.

Rice. 8. Catalytic reactor

.7 Thermal method

High-temperature afterburning (thermal neutralization) has developed quite significantly in the practice of neutralizing harmful impurities contained in ventilation and other emissions. To carry out afterburning (oxidation reactions), it is necessary to maintain high temperatures of the gas being purified and the presence of a sufficient amount of oxygen. The choice of afterburning scheme depends on the temperature and amount of emissions, as well as on the content of harmful impurities, oxygen and other components in them. If the exhaust gases have a high temperature, the afterburning process occurs in a chamber with the addition of fresh air. For example, afterburning of carbon monoxide occurs in gases removed by the ventilation system from electric arc melting furnaces, afterburning of products of incomplete combustion (CO and C x N y ) car engine directly at the outlet of the cylinders under conditions of the addition of excess air.

If the temperature of the emissions is insufficient for oxidation processes to occur, then natural or some other high-calorie gas is burned in the exhaust gas stream. One of the simplest devices used for fire neutralization of process and ventilation emissions is a burner designed to burn natural gas (Fig. 9). In this case, the neutralized emissions are fed into channel 1, where they wash the burner 2. From the collector 3, the gas serving as fuel enters the nozzles, at the end of which primary air from the environment is injected. The combustion of a mixture of gas and primary air takes place in the V-shaped cavity of the collector. The afterburning process occurs at the exit from the cavity, where the tail part of the torch contacts the neutralized emissions as they flow out of the annular gap between the burner body and the collector.

Rice. 9. Installation for fire neutralization of process and ventilation emissions

3. CALCULATION OF EQUIPMENT FOR CLEANING ATMOSPHERIC AIR

.1 Initial data

Cyclone type: TsN-24 G =65000 m 3/h - amount of purified gas under operating conditions;

µg=25?10-6 Pa?s - dynamic viscosity of gas at operating temperature; m=30 µm - medial diameter at which the mass of all dust particles smaller or larger dm is 50%;

H=0.35 - standard deviation of the value;

H=2400kg/m3 - particle density;

G=0.68 kg/m3 - gas density under operating conditions; in=70?103 kg/m3 - gas dust content;

Required gas purification efficiency.

.2 Calculation of cyclone TsN-24

We calculate the cyclone design using the method of successive approximations in the following order.

Selecting the type of cyclone according to table 4.3. determine the optimal gas speed in the apparatus? opt, m/s

Opt(CN-24) = 4.5 m/s

We determine the required cross-sectional area of ​​the cyclone (in m2):

F = (65000/3600)/4.5 = 4.01 (m2)

We determine the diameter of the cyclone, given the number of cyclones N=1 (in m):

(m)

The diameter of the cyclone is rounded to 2400 mm = 2.4 m.

We calculate the actual gas speed in the cyclone:

?= V g/0.785ND 2,

? = 18,06/0,785?1?(2,4)2= 3.99 (m/s)

The gas speed in the cyclone does not deviate by more than 15% from the optimal speed.

665 > 3,99 > 3,315

We determine the coefficient of hydraulic resistance of a cyclone or group of cyclones:

?ts = K 1TO 2? ? joint venture ts500 + K 3,

Where ? joint venture ts500 - coefficient of hydraulic resistance of a single cyclone with a diameter of 500 mm (Table 4.4.), ?joint venture ts500 =80; TO 1- correction factor depending on the diameter of the cyclone (Table 4.5.), K 1=1; TO 2- correction factor taking into account dust content of gas (Table 4.6.), K 2=0.905; TO 3- coefficient taking into account additional pressure losses associated with the arrangement of cyclones in a group (for single cyclones K3 =0).

C = 1?0,905?80 = 72,4

We determine the pressure loss in the cyclone (in Pa):

P= ?ts ?? ?2/2,

P = 72.4?(0.68?(3.99)2 /2) = 391.9 (Pa)

We determine the diameter of particles captured by 50%:

where the index “t” means the standard operating conditions of the cyclone.

8.5 µm;

0.6 m;

1930 kg/m 3;

22,2 ? 10-6Pass;

3.5 m/s

(µm)

We determine the parameter x using the formula:

x = log(d m /d 50)/lg 2??+lg2 ?h ,

lg? ? = 0,308;

lg? h = 0,35

x = log(30/15.2)/log0.308+log0.35 = 1.43

We determine the distribution function Ф(х) (Table 4.7.) and the total gas purification coefficient using the formula (in%):

R =50?,

Ф(х) = 0.9234,

?p = 50? = 96.17%

IndicatorTsN-24TsN-24 calc., mm Cyclone diameter Exhaust pipe inner diameter d Dust outlet d 1Width of the inlet pipe in the cyclone (internal dimension) b at the inlet (internal dimension) b 1 Length of the inlet pipe l Diameter of the average length of the cyclone D Wed Flange installation height h fl Angle of inclination of the cover and inlet pipe of the cyclone ?,deg Height of the inlet pipe a of the exhaust pipe h T cylindrical part H ts conical part H To external part of the exhaust pipe h V Total height of the cyclone H 0.59 0.3-0.4 0.2 0.26 0.6 0.8 0.1 24 1.11 2.11 2.11 1.75 0.4 4.26 2400 1420 720-960 480 620 1400 1900 240 24 2660 5060 5060 4200 960 10220

3.3 Bunker calculation

Hopper diameter:

Db = 1.5D,

D b = 1.5?2400 = 3600 mm

Height of the cylindrical part of the hopper:

8D = 0.8?2400 = 1920 mm

CONCLUSION

With the enormous growth of industry comes significant impacts on the environment. Negative factors Atmospheric air, water in large volumes, as well as vast areas of soil are exposed by enterprises and road transport. The atmosphere is under pressure from harmful, toxic substances entering it, both inorganic and organic. Many of the gaseous emissions are capable of forming acid precipitation by interacting with air components. This leads to acidification of soils and water bodies, which can result in the death of living organisms. In addition, acid precipitation has a detrimental effect on the design of buildings, natural and cultural monuments. When in the air, some gases cause the formation of the greenhouse effect, which, in turn, leads to climate change on the planet. In addition, these harmful components lead to deterioration in people's health. No less dangerous air pollutants are aerosols and dust. They also change the composition of the air and have a detrimental effect on people’s livelihoods and health.

In this regard, many methods and means of protecting the atmosphere from harmful effects. The equipment differs in purpose, principle of operation, design features, as well as cleaning efficiency. When choosing the appropriate equipment, it is necessary to initially establish the type and composition of harmful components, after which great attention must be paid to the cleaning efficiency of the selected device.

Cyclones are used for mechanical cleaning of dust emissions. The principle of their operation is based on centrifugal force and gravity. When passing through the apparatus, the flow of the purified gas swirls, and dust particles, under the influence of appropriate forces, fall out as sediment into the hopper. The cleaning efficiency of such equipment is 50-90% and even higher, and its value depends on the design of the cyclone and the diameter of the settling particles. Calculation of the parameters of the TsN-24 cyclone showed that it purifies the atmospheric air from dust pollution by 96.17%. This gives grounds to use it as cleaning equipment to protect the atmosphere from dust.

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Ziganshin, M.G. Design of dust and gas cleaning devices / M.G. Ziganshin, A.A. Kolesnik, V.N. Posokhin. - M.: Ecopress - 3M, 1998. - 505 p.

Kasatkin, A.G. Basic processes and apparatuses of chemical technology. - M.: Chemistry, 1993. - 753 p.

Environmental protection / ed. S.V. Belova. - M.: graduate School, 2007. - 616 p.

12. Ecologylib, ru. (2001-2013). Ecologylib. Web

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Plan

Introduction

1. Atmospheric purification methods

2. Bioremediation of the atmosphere

Conclusion

Bibliography

Introduction

The problem of cleaning the air in the area of ​​human life from various pollutants introduced by industry, from aerosols and bacteria is one of the most pressing problems. Treatises on the issue are becoming more and more frequent

sound like a cry of impending disaster. This question has gained special meaning after the invention of atomic and hydrogen bombs, because the atmospheric air began to become more and more saturated with fragments of nuclear decay. These fragments, in the form of highly dispersed suspended substances, rise into the atmosphere to a great height during an explosion, then within a short time they spread throughout the entire atmospheric ocean and gradually fall to the surface of the earth in the form of fine radioactive dust, or are carried away by precipitation - rain and snow. And they are a threat to humans anywhere on the surface of our planet.

1. Atmospheric purification methods

All cleaning methods are divided into regenerative and destructive. The former allow the components of emissions to be returned to production, the latter transform these components into less harmful ones.

Methods for cleaning gas emissions can be divided according to the type of component being processed (cleaning from aerosols - from dust and fog, cleaning from acidic and neutral gases, and so on).

· Electrical cleaning methods.

With this cleaning method, the gas flow is directed to an electric precipitator, where it passes in the space between two electrodes - corona and precipitation. Dust particles are charged, move towards the collecting electrode, and are discharged on it. This method can be used to clean dust with a resistivity of 100 to 100 million Ohm*m. Dusts with a lower resistivity are immediately discharged and fly away, while those with a higher resistivity form a dense insulating layer on the collecting electrode, sharply reducing the degree of purification. The electrical cleaning method can remove not only dust, but also mists. Cleaning of electric precipitators is carried out by washing off dust with water, vibration or using a hammer-impact mechanism.

· Various wet methods.

Use of foam apparatus, scrubbers.

The following methods are used to remove gases:

· Adsorption.

That is, the absorption of a gas (in our case) component by a solid substance. Activated carbons of various brands, zeolites, silica gel and other substances are used as adsorbents (absorbers). Adsorption is a reliable method that allows you to achieve high degrees of purification; In addition, this is a regenerative method, meaning that the captured valuable component can be returned back to production. Batch and continuous adsorption are used. In the first case, upon reaching the full adsorption capacity of the adsorbent, the gas flow is directed to another adsorber, and the adsorbent is regenerated - for this purpose, blowing with live steam or hot gas is used. Then the valuable component can be obtained from the condensate (if live steam was used for regeneration); For this purpose, rectification, extraction or sedimentation is used (the latter is possible in the case of mutual insolubility of water and the valuable component). With continuous adsorption, the adsorbent layer is constantly moving: part of it works for absorption, part of it is regenerated. This, of course, contributes to the abrasion of the adsorbent. If the cost of the regenerated component is sufficient, the use of adsorption can be advantageous. For example, recently (in the spring of 2001) a calculation of the xylene recovery section carried out for one of the cable plants showed that the payback period would be less than a year. At the same time, 600 tons of xylene that were released into the atmosphere annually will be returned to production.

· Absorption.

That is, the absorption of gases by liquid. This method is based either on the process of dissolving gas components in a liquid (physical adsorption), or on dissolution together with a chemical reaction - chemical adsorption (for example, the absorption of an acid gas by a solution with alkaline reaction). This method is also regenerative; a valuable component can be isolated from the resulting solution (this is not always possible when using chemical adsorption). In any case, the water is purified and at least partially returned to the circulating water supply system.

· Thermal methods.

They are destructive. If the calorific value of the exhaust gas is sufficient, it can be burned directly (everyone has seen flares on which associated gas burns), catalytic oxidation can be used, or (if the calorific value of the gas is low) it can be used as a blast gas in furnaces. The resulting thermal decomposition components must be less hazardous to the environment than the original component (for example, organic compounds can be oxidized to carbon dioxide and water - if there are no other elements except oxygen, carbon and hydrogen). This method achieves a high degree of purification, but can be expensive, especially if additional fuel is used.

· Various chemical cleaning methods.

Typically associated with the use of catalysts. Such, for example, is the catalytic reduction of nitrogen oxides from vehicle exhaust gases (in general, the mechanism of this reaction is described by the following scheme:

CnHm + NOx + CO----->CO2 + H2O +N2,

where platinum, palladium, ruthenium or other substances are used as the kt catalyst). Methods may require the use of reagents and expensive catalysts.

· Biological treatment.

Specially selected cultures of microorganisms are used to decompose pollutants. The method is characterized by low costs (few reagents are used and they are cheap, the main thing is that the microorganisms are alive and reproduce themselves, using contaminants as food), a fairly high degree of purification, but in our country, unlike the West, it is, unfortunately, not yet widely used .

· Aeroions - tiny liquid or solid particles that are positively or negatively charged. The effect of negative (light air ions) is especially beneficial. They are rightly called air vitamins.

The mechanism of action of negative air ions on particles suspended in the air is as follows. Negative air ions charge (or recharge) dust and microflora in the air to a certain potential, proportional to their radius. Charged dust particles or microorganisms begin to move along the electric field lines towards the opposite (positively) charged pole, i.e. to the ground, to the walls and ceiling. If we express the gravitational and electrical forces acting on fine dust in lengths, we can easily see that electrical forces exceed the forces of gravity thousands of times. This makes it possible, at will, to strictly direct the movement of a cloud of fine dust and thus purify the air in this place. In the absence of an electric field and the diffuse movement of negative air ions, lines of force arise between each moving air ion and the positively charged ground (floor), along which this air ion moves along with a particle of dust or bacteria. Microorganisms settled on the surface of the floor, ceiling and walls can be periodically removed.

Atmospheric air pollution should be understood as any change in its composition and properties, which has a negative impact on human and animal health, the condition of plants and ecosystems.

Atmospheric pollution can be natural (natural) and anthropogenic).

Natural pollution air caused by natural processes. These include volcanic activity, weathering of rocks, wind erosion, massive flowering of plants, smoke from forest fires, etc.

Anthropogenic pollution associated with the release of various pollutants during human activities. In scale, it significantly exceeds natural air pollution.

By state of aggregation emissions of harmful substances into the atmosphere are classified into:

1) gaseous (sulfur dioxide, nitrogen oxide, carbon monoxide, hydrocarbons, etc.);

2) liquid acids, alkalis, salt solutions, etc.;

3) solid (carcinogenic substances, lead and its compounds, organic and inorganic dust, soot, resinous substances and others).

Main pollutants (pollutants) of atmospheric air, formed during industrial and other human activities - sulfur dioxide (SO 2), nitrogen oxide (NO x), carbon monoxide (CO) and particulate matter. They account for about 98% of the total emissions of harmful substances. In addition to the main pollutants, more than 70 types of harmful substances are observed in the atmosphere of cities and towns, including formaldehyde, hydrogen fluoride, lead compounds, ammonia, phenol, benzene, carbon disulfide, etc. However, it is the concentrations of the main pollutants (sulfur dioxide, etc.) that are most often exceed permissible levels in many Russian cities.

The total global emission into the atmosphere of the four main atmospheric pollutants (pollutants) was 401 million tons in 1990, and in Russia in 1991 it was 26.2 million tons. In addition to these main pollutants, many other very dangerous pollutants enter the atmosphere. toxic substances: lead, mercury, cadmium and others heavy metals(emission sources: cars, smelters, etc.); hydrocarbons (C x H x), among them the most dangerous is benzo(a)pyrene, which has a carcinogenic effect (exhaust gases, boiler fires, etc.), aldehydes, and primarily formaldehyde, hydrogen sulfide, toxic volatile solvents (gasolines, alcohols, ethers), etc.

Most dangerous pollution atmosphere - radioactive. Currently, it is caused mainly by globally distributed long-lived radioactive isotopes– test products nuclear weapons carried out in the atmosphere and underground. The surface layer of the atmosphere is also polluted by emissions of radioactive substances into the atmosphere from operating nuclear power plants during their normal operation and other sources.

Atmospheric protection.

1. Dust collector (dry).

It is necessary that the bunker is sealed, otherwise dust will be blown out. Efficiency 80-95%, particles with size d h > 10 microns. As well as cyclones and dust settling chambers.

Cyclone operation diagram:

1. frame
2. pipe branch
3. pipe
4. bunker

Dry dust collectors (cyclones, dust settling chambers) are designed for rough mechanical cleaning of emissions from large and heavy dust. The principle of operation is the settling of particles under the influence of centrifugal forces and gravity. The dust and gas flow is introduced into the cyclone through a pipe, then it performs a rotational and translational movement along the body; Dust particles are thrown towards the walls of the cyclone and then fall down into the dust collector (hopper), from where they are periodically removed. To increase operating efficiency, group (battery) cyclones are used.

Venturi scrubber.

η = 99% d > 2 µm.

It works on the principle of deposition of dust particles onto the surface of droplets under the influence of inertial forces and Brownian motion. Indispensable for removing dust from explosive and flammable gases.

Rice. Venturi scrubber

1. Irrigation nozzle

2. Venturi tube

3. Drop eliminator

Filters.

The filter element may be granular layer(fixed), with flexible partitions(fabrics, felt, sponge rubber, polyurethane foam), with semi-rigid partitions(knitted mesh, shavings), with rigid partitions(porous ceramics, porous metals). Handheld filters clean the air from dust with a size d h > 10 microns, the degree of purification is 97-99%. d to< 0,05 мкм.

Filter circuit

2. filter element

3. layer of impurity particles

4. Wet dust collectors (bubbling-foam).

High efficiency of particle purification d h ≥ 0.3 µm. Gas moves through the grate, a layer of water and foam passes through - they are sensitive to uneven gas supply, the grate is prone to clogging. Purification efficiency is 0.95-0.96%, as well as scrubbers, turbulent, gas scrubbers.

Rice. Bubbler-foam dust collector

2. Foam layer

3. Overflow grate

Mist eliminators.

Deposition of droplets on the surface of the pores with subsequent flow of liquid along the fibers into bottom part mist eliminator. Cleaning efficiency 0.999 particles 3 microns.

Rice. Low-velocity mist eliminator filter element diagram

2. Mounting flange

3. Mesh cylinders

4. Fiber filter element

5. Bottom flange

6. Water seal tube

Absorption method.

Purification of gases from gases and vapors is based on the absorption of the latter by liquid. The decisive condition for the application of the method is the solubility of vapors and gases in the absorbent (liquid). So, to remove ammonia, chlorine and hydrogen fluoride, water is used, alkalis, water, ammonia, and ferrous sulfate are used. h = 85%.

Chemosorbers - absorb gases and vapors with liquid and solid absorbers with the formation of slightly soluble or low-volatile compounds. The cleaning is effective against nitrogen oxide and acid vapors. Efficiency from nitric oxide is from 0.17-0.86, from acids – 0.95.

Adsorption method.

Adsorbents are absorbers, solids that absorb components from a gas mixture. Activated carbon, activated alumina, activated alumina, synthetic zeolites. Effective against solvents (vapors), acetone, hydrocarbons. Used in respirators and gas masks. (97-99%).

Thermal neutralization.

Combustion of gases to form less toxic substances. Neutralizers are used for this: direct combustion, thermal oxidation, catalytic afterburning. Oxidation or combustion reaches carbon dioxide and water (at an oxidation temperature of 950-1300 °C, catalytic combustion 250-450 °C). Efficiency 99.9%.

Rice. Installation diagram for thermal oxidation

2. Inlet pipe

3. Heat exchanger

4. Burner

6. Outlet pipe

Electrostatic precipitators.

The most advanced method of purifying gases from suspended dust particles up to 0.01 microns in size (d< 0,01), η = 99-99,5%. Принцип действия: ионизация пыле-газового потока у поверхности коронирующих электродов. Приобрела отрицательный заряд, пылинки движутся к осадительному электроду, имеющим положительный заряд. При встряхивании электродов осажденные частички пыли под действием силы тяжести падают вниз в сборник пыли. Электроды требуют большого расхода электроэнергии – это их основной недостаток.

One of the most advanced methods for removing dust and fog particles. It is based on impact ionization of gas, transfer of ion charge to impurity particles and deposition of the latter on electrodes.

Cleaning efficiency ranges from 0.95 to 0.99. Depends on We - the speed of movement of particles in an electric field and Fsp - the specific surface of the collecting electrodes.

The best cleaning is combined methods. For example, gas purification in cyclones - Venturi strubbers - electric precipitators.

Enterprises everywhere use various methods for purifying exhaust gases from aerosols (dust, ash, soot) and toxic gas and vapor impurities (NO, NO 2, SO 2, SO 3, etc.), however, from the point of view of the future, dust and gas purification devices the above reasons have no prospects.

Currently used to purify emissions from aerosols. Various types devices depending on the degree of dust in the air, the size of solid particles and the required level of cleaning.

Hydrosphere pollution.

It has been established that 400 types of substances can cause water pollution. Distinguish chemical, biological and physical pollutants (Bertox, 1980)

Chemical pollutants – oil, surfactants, pesticides, heavy metals, dioxins.

Biological – viruses, microbes.

Physical – radioactive substances, heat.

The main sources of pollution include:

1. discharge of untreated wastewater into water bodies;

2. washing away pesticides with rainfall;

3. gas and smoke emissions;

4. leaks of oil and petroleum products.

Oil refinery- discharge petroleum products, surfactants, phenols, ammonium salts, sulfides.

Pulp and paper mill, forest industry– sulfates, lignins, nitrogen, organic substances.

Mechanical engineering, metallurgy– heavy metals, fluorides, ammonium nitrogen, phenols, resins, cyanides.

Light, textile, food industries– Surfactants, organic dyes, petroleum products.

Environmental consequences pollution of freshwater ecosystems leads to eutrophication of water bodies. “Blooming” of water – proliferation of blue-green algae, loss of the gene pool, deterioration of self-regulation. Pollution of water bodies is a decrease in biosphere functions and environmental significance as a result of the entry of harmful substances into them.

Protection of the hydrosphere.

1. Mechanical cleaning– straining, settling, filtering (up to 90%) – sand, clay, scale. Grates, sand traps, sand filters, settling tanks, and grease traps are used. Substances floating on the surface of wastewater (oil, resins, oils, fats, polymers, etc.) are retained by oil-oil traps and other types of traps or burned off.

Septic tanks can be horizontal, radial, combined.

Hydrocyclone(combined).

Rice. Scheme of a combined hydrocyclone

1. Inlet pipeline

2. Chamber for purified waste water

3. Receiving chamber

4. Pipeline with adjustable flow area

5. Oil products removal pipeline

6. Water drainage pipeline for further cleaning

7. Sludge collector

Wastewater containing oil products moves upward. The density of impurities is less and they are concentrated in the core of the swirling flow and enter the chamber (3), through the pipeline (5) the oil products are removed from the hydrocyclone. Waste water, cleared of solid particles and oil, accumulates in chamber (2) from where it is discharged through pipeline (6) for further purification. Air from the core of the swirling flow goes into the pipe (4).

Used to remove fine solid impurities - granular filters, separators. Cleaning efficiency 0.97-0.99 (polyurethane foam).

Grain filter.

Waste water through a pipe (4) enters the housing (1) through a filter layer (3) of marble chips. Purified waste water is discharged from the filter through a pipe (8). Particulate matter in the filtered material. The pressure drop in the filter increases and when the limit value is reached, the inlet pipeline (4) is closed. Static air is supplied through pipe (9). It displaces water and particles from the filtered layer into a trough (6) and is discharged through a pipe (7). It is better if the filter is polyurethane foam. η = 97-99%.

Rice. Grain filter circuit

1. Filter housing

2. Porous partition 3. Filter media

3. Waste water inlet pipe

4. Porous partition 6. Gutter

5. Solids removal pipeline

6. Purified water discharge pipeline

7. Compressed air supply pipeline.

Separator filter

.

Rice. Filter-separator circuit

2. Rotor with filter media

3. Pockets for draining oil products

4. Lower and upper support grids

5. Waste water supply pipeline

6. Receiving ring pocket for removing purified water

7. Electric motor

Waste water in the pipe (5) is supplied to the support grid (4). Water passes through the filter load in the rotor (2), the upper grid (4) and the water, cleared of impurities, is poured into the receiving ring pocket (6) and removed from the housing (1). η = 92-90%

t filter -16-24 hours.

When the electric motor (7) is turned on, the rotor (2) with the filter rotates. loading. As a result, polyurethane foam particles, under the influence of centrifugal force, are thrown towards the inner walls of the rotor, squeezing out oil products from it, which enter pockets (3) and go for regeneration.

Physico-chemical methods.

Coagulation– introduction of coagulants (ammonium salts, Fe, copper, sludge) to form flocculent sediments.

Flotation– to wash out oil products when they are enveloped in gas bubbles supplied to wastewater. Adhesion of oil particles and bubbles flotation: steam, pneumatic, foam, chemical, vibration, biological, electroflotation. Hydrogen, a coagulant, is used as the supplied gas. Clustering of particles and gas bubbles.

Extraction– redistribution of impurities in the wastewater in a mixture of mutually insoluble liquids (wastewater and extractant). To remove phenol, benzene and butyl acetate are used as extractants.

Neutralization– for the separation of acids, alkalis, and metal salts from wastewater. This is the combination of hydrogen ions and a hydroxyl group into water molecules. As a result, wastewater has a pH value of 6.7 (neutral environment). Alkali neutralizers: caustic soda, caustic potassium, lime, dolomite. Marble, chalk, soda, magnesite. For alkalis: salt, nitrogen.

Sorption– cleaning from soluble impurities (ash, toror, sawdust, slag, clay, activated carbon).

Ion exchange purification– using resins (0.2-2 mm granules), ion exchangers are made from water-insoluble substances and cations and anions are placed on their surface. They react with ions of the same sign. Cations H +, Na +, anions OH -

Hyperfiltration– treatment by osmosis, through membranes. Low energy.

Biological treatment.

Cleaning in irrigation fields, biological ponds, filtration fields. And in artificial methods (aeration tanks, biofilters). After clarification of wastewater, a sludge is formed, which is discharged in reinforced concrete tanks (digesters), and then removed to sludge beds for drying and then used as fertilizer. Now heavy metals are found in the sediment, so we can’t go into the fields.

The clarified part of the wastewater is treated in aeration tanks– closed, where the water is enriched with oxygen and mixed with activated sludge (mold, yeast, aquatic fungi, rotifers) (carbon-oxidizing bacteria, carbon-oxidizing nitrate bacteria, nitrifying bacteria). Oxygen 5 mg/m2. BOD. After secondary settling, the wastewater is disinfected (chlorine against bacteria and viruses.

Scheme of biological water purification.

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Sources of pollution

The main factor in indoor air pollution is dust. It contains microscopic textile fibers, fungal and mold spores, skin particles, bacteria, plant pollen, street soot, small mites and their waste products. Half of it consists of strong allergens that can cause allergic rhinitis, eye inflammation, cough, skin irritation and even asthma.

In addition to dust, air pollution occurs through kitchen fumes, consisting of tiny droplets of fat and creating an unpleasant specific odor in the apartment.

• Smoking, or more precisely, tobacco smoke, which may not disappear for several weeks, is another important factor in air toxicity.
• The cleanliness of the air in your home also depends on the area in which you live. The sources of its contamination are often the finishing materials used to improve the apartment, as well as substances released from the walls of houses and low-quality furniture, building materials from chipboard.
• Mercury vapor is also a common phenomenon that can be observed in apartments. Usually the cause is a broken thermometer.
• The effect of toxins on the body occurs gradually. Poisoning occurs as a result of their constant exposure. Toxins enter our body through the mouth, but mainly through inhaled air.

The list of toxins and harmful substances contained in the air can be continued for a long time. But the main point should be clear to everyone: the air in the apartment needs constant cleaning. How it's done? We'll talk about this further.

In practice, the purification of gaseous emissions from dust or fog is carried out in devices of various designs, which can be divided into four main groups:

1. mechanical dust collectors (dust settling or dust settling chambers, inertial dust and splash collectors, cyclones and multicyclones). Devices of this group are usually used for preliminary purification of gases;
2. wet dust collectors (hollow, packed or bubbling scrubbers, foam apparatus, Venturi pipes, etc.). These devices are more efficient than dry dust collectors;
3. filters (fibrous, cell, with bulk layers of granular material, oil, etc.). Bag filters are the most common;
4. electrostatic precipitators - devices for fine gas purification - collect particles with a size of 0.01 microns. The efficiency of the electrostatic precipitator can reach 99.9%.

Typically, the required degree of purification can only be achieved by a combined installation, including several devices of the same or different types.

Cleaning methods

One of the pressing problems today is air purification from various types of pollutants. It is their physical and chemical properties that must be taken into account when choosing one or another cleaning method. Let's consider the main modern methods of removing pollutants from the air.

Mechanical cleaning

The essence of this method is the mechanical filtration of particles when air passes through special materials, the pores of which are able to pass air flow, but at the same time retain the pollutant. The speed and efficiency of filtration depends on the size of the pores and cells of the filter material. The larger the size, the faster the cleaning process occurs, but its efficiency is lower. Therefore, before choosing this cleaning method, it is necessary to study the dispersion of pollutants in the environment in which it will be used. This will allow cleaning to be carried out within the required degree of efficiency and in a minimum period of time.

Absorption method

Absorption is the process of dissolving a gaseous component in a liquid solvent. Absorption systems are divided into aqueous and non-aqueous. In the second case, low-volatile organic liquids are usually used. The liquid is used for absorption only once or it is regenerated, releasing the pollutant in its pure form. Schemes with a single use of an absorber are used in cases where absorption leads directly to the production of a finished product or intermediate product.

Examples include:

• receiving mineral acids(SO3 absorption in the production of sulfuric acid, absorption of nitrogen oxides in the production of nitric acid);
• obtaining salts (absorption of nitrogen oxides alkaline solutions with the production of nitrite-nitrate liquors, absorption aqueous solutions lime or limestone to produce calcium sulfate);
• other substances (absorption of NH3 by water to produce ammonia water, etc.).

Schemes with repeated use of the absorber (cyclic processes) are more widespread. They are used to capture hydrocarbons, purify flue gases from thermal power plants from SO2, purify ventilation gases from hydrogen sulfide using the iron-soda method to produce elemental sulfur, and monoethanolamine gas purification from CO2 in the nitrogen industry.

Depending on the method of creating the contact surface of the phases, surface, bubbling and spraying absorption devices are distinguished.

• In the first group of devices, the contact surface between the phases is a liquid mirror or the surface of a flowing liquid film. This also includes packed absorbents, in which liquid flows over the surface of a packed packing from bodies of various shapes.
• In the second group of absorbents, the contact surface increases due to the distribution of gas flows into the liquid in the form of bubbles and jets. Sparging is carried out by passing gas through a liquid-filled apparatus or in column-type apparatuses with plates of various shapes.
• In the third group, the contact surface is created by spraying a liquid into a mass of gas. The contact surface and the efficiency of the process as a whole are determined by the dispersion of the sprayed liquid.

The most widespread are packed (surface) and bubbling plate absorbers. For the effective use of aqueous absorption media, the component to be removed must be well dissolved in the absorption medium and often chemically interact with water, as, for example, when purifying gases from HCl, HF, NH3, NO2. To absorb gases with less solubility (SO2, Cl2, H2S), alkaline solutions based on NaOH or Ca(OH)2 are used. Additions of chemical reagents in many cases increase the absorption efficiency due to the occurrence of chemical reactions in the film. To purify gases from hydrocarbons, this method is used much less frequently in practice, which is primarily due to the high cost of absorbents. Common disadvantages of absorption methods are the formation of liquid waste and the cumbersomeness of the equipment.

Electrical cleaning method

This method is applicable for fine particles. In electric filters, an electric field is created, upon passing through which the particle is charged and deposited on the electrode. The main advantages of this method are its high efficiency, simplicity of design, ease of operation - there is no need to periodically replace cleaning elements.

Adsorption method

Based on chemical purification from gaseous pollutants. The air comes into contact with the surface of the activated carbon, during which contaminants are deposited on it. This method is mainly applicable for removing unpleasant odors and harmful substances. The downside is the need to systematically replace the filter element.

The following main methods for carrying out adsorption purification processes can be distinguished:

• After adsorption, desorption is carried out and the captured components are recovered for reuse. In this way, various solvents, carbon disulfide in the production of artificial fibers and a number of other impurities are captured.
• After adsorption, the impurities are not disposed of, but are subjected to thermal or catalytic afterburning. This method is used to purify waste gases from chemical, pharmaceutical and paint factories, Food Industry and a number of other industries. This type of adsorption purification is economically justified at low concentrations of pollutants and (or) multicomponent pollutants.
• After cleaning, the adsorbent is not regenerated, but is subjected, for example, to burial or combustion together with a strongly chemisorbed pollutant. This method is suitable when using cheap adsorbents.

Photocatalytic purification

It is one of the most promising and effective cleaning methods today. Its main advantage is the decomposition of dangerous and harmful substances into harmless water, carbon dioxide and oxygen. The interaction of the catalyst and the ultraviolet lamp leads to interaction on molecular level contaminants and catalyst surfaces. Photocatalytic filters are absolutely harmless and do not require replacement of cleaning elements, which makes their use safe and very profitable.

Thermal afterburning

Afterburning is a method of neutralizing gases by thermal oxidation of various harmful substances, mainly organic, into practically harmless or less harmful, mainly CO2 and H2O. Typical afterburning temperatures for most compounds are in the range of 750-1200 °C. The use of thermal afterburning methods makes it possible to achieve 99% gas purification.

When considering the possibility and feasibility of thermal neutralization, it is necessary to take into account the nature of the resulting combustion products. Combustion products of gases containing compounds of sulfur, halogens, and phosphorus can be more toxic than the original gas emissions. In this case, additional cleaning is necessary. Thermal afterburning is very effective in neutralizing gases containing toxic substances in the form of solid inclusions of organic origin (soot, carbon particles, wood dust, etc.).

The most important factors determining the feasibility of thermal neutralization are the energy (fuel) costs to ensure high temperatures in the reaction zone, the caloric content of the impurities being neutralized, and the possibility of preheating the purified gases. An increase in the concentration of afterburning impurities leads to a significant reduction in fuel consumption. In some cases, the process can proceed in autothermal mode, i.e. the operating mode is maintained only due to the heat of the reaction of deep oxidation of harmful impurities and preheating of the initial mixture with waste neutralized gases.

The fundamental difficulty when using thermal afterburning is the formation of secondary pollutants, such as nitrogen oxides, chlorine, SO2, etc.

Thermal methods are widely used to purify exhaust gases from toxic flammable compounds. Designed in last years Afterburning units are compact and have low energy consumption. The use of thermal methods is effective for afterburning dust of multicomponent and dust-laden exhaust gases.

Flushing method

It is carried out by flushing a gas (air) stream with liquid (water). Operating principle: liquid (water) introduced into the gas (air) flow moves at high speed, crushes into small drops (fine suspension) envelops suspended particles (liquid fraction and suspension merge) as a result, the enlarged suspensions are guaranteed to be captured by the washing dust collector. Design: washing dust collectors are structurally represented by scrubbers, wet dust collectors, high-speed dust collectors, in which liquid moves at high speed, and foam dust collectors, in which gas in the form of small bubbles passes through a layer of liquid (water).

Plasmachemical methods

The plasma-chemical method is based on passing an air mixture with harmful impurities through a high-voltage discharge. As a rule, ozonizers are used based on barrier, corona or sliding discharges, or pulsed high-frequency discharges on electric precipitators. Air with impurities passing through the low-temperature plasma is bombarded with electrons and ions. As a result, atomic oxygen, ozone, hydroxyl groups, excited molecules and atoms are formed in the gas environment, which participate in plasma-chemical reactions with harmful impurities. The main areas of application of this method are the removal of SO2, NOx and organic compounds. The use of ammonia, when neutralizing SO2 and NOx, produces powdered fertilizers (NH4)2SO4 and NH4NH3 at the reactor outlet, which are filtered.

The disadvantages of this method are:

• insufficiently complete decomposition of harmful substances to water and carbon dioxide, in case of oxidation organic components, at acceptable discharge energies
• the presence of residual ozone, which must be decomposed thermally or catalytically
• significant dependence on dust concentration when using ozonizers using barrier discharge.

Gravity method

Based on gravitational deposition of moisture and (or) suspended particles. Operating principle: the gas (air) flow enters the expanding settling chamber (tank) of the gravity dust collector, in which the flow speed slows down and, under the influence of gravity, droplet moisture and (or) suspended particles settle.

Design: Structurally, the settling chambers of gravity dust collectors can be of the direct-flow type, labyrinth type, or shelf type. Efficiency: the gravitational method of gas purification allows you to capture large suspended particles.

Plasma catalytic method

This is a fairly new cleaning method that uses two well-known methods - plasma-chemical and catalytic. Installations operating on the basis of this method consist of two stages. The first is a plasma-chemical reactor (ozonizer), the second is a catalytic reactor. Gaseous pollutants, passing through the high-voltage discharge zone in gas-discharge cells and interacting with electrosynthesis products, are destroyed and converted into harmless compounds, up to CO2 and H2O. The depth of conversion (purification) depends on the amount of specific energy released in the reaction zone. After the plasma-chemical reactor, the air undergoes final fine cleaning in a catalytic reactor. Ozone synthesized in the gas discharge of a plasma-chemical reactor reaches the catalyst, where it immediately decomposes into active atomic and molecular oxygen. Remains of pollutants (active radicals, excited atoms and molecules), not destroyed in the plasma-chemical reactor, are destroyed on the catalyst due to deep oxidation with oxygen.

The advantage of this method is the use of catalytic reactions at temperatures lower (40-100 °C) than with the thermocatalytic method, which leads to an increase in the service life of the catalysts, as well as lower energy consumption (at concentrations of harmful substances up to 0.5 g/m³ .).

The disadvantages of this method are:

• high dependence on dust concentration, the need for preliminary cleaning to a concentration of 3-5 mg/m³,
• at high concentrations of harmful substances (over 1 g/m³), the cost of equipment and operating costs exceed the corresponding costs in comparison with the thermocatalytic method

Centrifugal method

It is based on the inertial deposition of moisture and (or) suspended particles due to the creation of centrifugal force in the field of gas flow and suspension. The centrifugal method of gas purification refers to inertial methods of gas (air) purification. Operating principle: the gas (air) flow is directed to a centrifugal dust collector in which, by changing the direction of movement of gas (air) with moisture and suspended particles, usually in a spiral, gas purification occurs. The density of the suspension is several times greater than the density of the gas (air) and it continues to move by inertia in the same direction and is separated from the gas (air). Due to the movement of gas in a spiral, a centrifugal force is created, which is many times greater than the force of gravity. Design: Structurally, centrifugal dust collectors are represented by cyclones. Efficiency: relatively fine dust is deposited, with a particle size of 10 - 20 microns.

Don't forget about elementary methods cleaning the air from dust, such as wet cleaning, regular ventilation, maintaining optimal humidity levels and temperature conditions. At the same time, periodically get rid of accumulations in the room of a large amount of trash and unnecessary items that are “dust collectors” and do not carry any useful functions.

IN Currently, there are a large number of different methods for purifying air from various harmful pollutants. The main methods include:

• Absorption method.
• Adsorption method.
• Thermal afterburning.
• Thermocatalytic methods.
• Ozone methods.
• Plasmachemical methods.
• Plasma catalytic method.
• Photocatalytic method.

Absorption method

A absorption is the process of dissolving a gaseous component in a liquid solvent. Absorption systems are divided into aqueous and non-aqueous. In the second case, low-volatile organic liquids are usually used. The liquid is used for absorption only once or it is regenerated, releasing the pollutant in its pure form. Schemes with a single use of an absorber are used in cases where absorption leads directly to the production of a finished product or intermediate product. Examples include:

• production of mineral acids (SO 3 absorption in the production of sulfuric acid, absorption of nitrogen oxides in the production of nitric acid);
• obtaining salts (absorption of nitrogen oxides by alkaline solutions to produce nitrite-nitrate liquors, absorption by aqueous solutions of lime or limestone to produce calcium sulfate);
• other substances (absorption of NH 3 by water to produce ammonia water, etc.).

A adsorption method

A The adsorption method is one of the most common means of protecting the air from pollution. In the USA alone, tens of thousands of adsorption systems have been introduced and are successfully operating. The main industrial adsorbents are activated carbons, complex oxides and impregnated sorbents. Activated carbon (AC) is neutral towards polar and non-polar molecules of adsorbed compounds. It is less selective than many other sorbents and is one of the few suitable for use in wet conditions. gas flows. Activated carbon is used, in particular, for gas purification from foul-smelling substances, solvent recovery, etc.

ABOUT oxide adsorbents (OA) have higher selectivity towards polar molecules due to their own non-uniform distribution of electrical potential. Their disadvantage is a decrease in efficiency in the presence of moisture. The OA class includes silica gels, synthetic zeolites, and aluminum oxide.

M The following main methods of carrying out adsorption purification processes can be distinguished:

• After adsorption, desorption is carried out and the captured components are recovered for reuse. In this way, various solvents, carbon disulfide in the production of artificial fibers and a number of other impurities are captured.
• After adsorption, the impurities are not disposed of, but are subjected to thermal or catalytic afterburning. This method is used to purify waste gases from chemical-pharmaceutical and paint-and-varnish enterprises, the food industry and a number of other industries. This type of adsorption purification is economically justified at low concentrations of pollutants and (or) multicomponent pollutants.
• After cleaning, the adsorbent is not regenerated, but is subjected, for example, to burial or combustion together with a strongly chemisorbed pollutant. This method is suitable when using cheap adsorbents.

Thermal afterburning

D combustion is a method of neutralizing gases by thermal oxidation of various harmful substances, mainly organic, into practically harmless or less harmful substances, mainly CO 2 and H 2 O. Typical after-combustion temperatures for most compounds are in the range of 750-1200 ° C. The use of thermal afterburning methods makes it possible to achieve 99% gas purification.

P When considering the possibility and feasibility of thermal neutralization, it is necessary to take into account the nature of the resulting combustion products. Combustion products of gases containing compounds of sulfur, halogens, and phosphorus can be more toxic than the original gas emissions. In this case, additional cleaning is necessary. Thermal afterburning is very effective in neutralizing gases containing toxic substances in the form of solid inclusions of organic origin (soot, carbon particles, wood dust, etc.).

IN The most important factors determining the feasibility of thermal neutralization are the energy (fuel) costs to ensure high temperatures in the reaction zone, the caloric content of the impurities being neutralized, and the possibility of preheating the purified gases. An increase in the concentration of afterburning impurities leads to a significant reduction in fuel consumption. In some cases, the process can proceed in autothermal mode, i.e. the operating mode is maintained only due to the heat of the reaction of deep oxidation of harmful impurities and preheating of the initial mixture with waste neutralized gases.

P A fundamental difficulty when using thermal afterburning is the formation of secondary pollutants, such as nitrogen oxides, chlorine, SO 2, etc.

T Thermal methods are widely used to purify exhaust gases from toxic flammable compounds. Afterburning units developed in recent years are compact and have low energy consumption. The use of thermal methods is effective for afterburning dust of multicomponent and dust-laden exhaust gases.

Thermocatalytic methods

TO alytic methods of gas purification are distinguished by their versatility. With their help, it is possible to free gases from sulfur and nitrogen oxides, various organic compounds, carbon monoxide and other toxic impurities. Catalytic methods make it possible to convert harmful impurities into harmless, less harmful and even useful ones. They make it possible to process multicomponent gases with low initial concentrations of harmful impurities, achieve high degrees of purification, conduct the process continuously, and avoid the formation of secondary pollutants. The use of catalytic methods is most often limited by the difficulty of finding and manufacturing catalysts suitable for long-term operation and sufficiently cheap. Heterogeneous catalytic transformation gaseous impurities carried out in a reactor loaded with a solid catalyst in the form of porous granules, rings, balls or blocks with a structure close to a honeycomb. The chemical transformation occurs on the developed internal surface of the catalysts, reaching 1000 m²/g.

IN A variety of substances serve as effective catalysts that are used in practice - from minerals, which are used almost without any pre-treatment, and simple massive metals to complex compounds of a given composition and structure. Typically, solids with ionic or metal bonds, possessing strong interatomic fields. One of the main requirements for a catalyst is the stability of its structure under reaction conditions. For example, metals should not be converted into inactive compounds during the reaction.

WITH Modern neutralization catalysts are characterized by high activity and selectivity, mechanical strength and resistance to poisons and temperatures. Industrial catalysts, manufactured in the form of rings and blocks of a honeycomb structure, have low hydrodynamic resistance and a high external specific surface area.

N The most widespread are catalytic methods for neutralizing waste gases in a fixed catalyst bed. We can distinguish two fundamentally various methods implementation of the gas purification process - in stationary and artificially created non-stationary modes.

1. Stationary method.

P rates of chemical reactions acceptable for practice are achieved at most cheap industrial catalysts at a temperature of 200-600 °C. After preliminary purification from dust (up to 20 mg/m³) and various catalytic poisons (As, Cl 2, etc.), the gases usually have a significantly lower temperature.

P Heating of gases to the required temperatures can be carried out by introducing hot flue gases or using an electric heater. After passing through the catalyst layer, the purified gases are released into the atmosphere, which requires significant energy consumption. Energy consumption can be reduced if the heat from the exhaust gases is used to heat the gases entering the treatment. Recuperative tubular heat exchangers are usually used for heating.

P Under certain conditions, when the concentration of flammable impurities in the exhaust gases exceeds 4-5 g/m³, implementing the process using a heat exchanger scheme allows you to do without additional costs.

T Such devices can operate effectively only at constant concentrations (flow rates) or when using advanced automatic process control systems.

E These difficulties can be overcome by carrying out gas cleaning in a non-stationary mode.

2. Non-stationary method (reverse process).

R The reverse process involves periodically changing the direction of filtration of the gas mixture in the catalyst layer using special valves. The process proceeds as follows. The catalyst bed is preheated to a temperature at which the catalytic process occurs at high speed. After this, purified gas is supplied to the apparatus at a low temperature, at which the rate of chemical transformation is negligible. From direct contact with a solid material, the gas heats up, and a catalytic reaction begins to occur in the catalyst layer at a noticeable speed. The layer of solid material (catalyst), giving off heat to the gas, is gradually cooled to a temperature equal temperature gas at the inlet. Since heat is released during the reaction, the temperature in the bed may exceed the initial heating temperature. A heat wave is formed in the reactor, which moves in the direction of filtration of the reaction mixture, i.e. in the direction of exit from the layer. Periodically switching the direction of gas supply to the opposite allows you to keep the heat wave within the layer for as long as desired.

P The advantage of this method is the stability of operation with fluctuations in the concentrations of flammable mixtures and the absence of heat exchangers.

ABOUT The main direction of development of thermocatalytic methods is the creation of cheap catalysts that operate efficiently at low temperatures and are resistant to various poisons, as well as the development of energy-saving technological processes with low capital costs for equipment. Most mass application Thermocatalytic methods are found in the purification of gases from nitrogen oxides, the neutralization and utilization of various sulfur compounds, the neutralization of organic compounds and CO.

D For concentrations below 1 g/m³ and large volumes of purified gases, the use of the thermocatalytic method requires high energy consumption, as well as a large amount of catalyst.

Ozone methods

ABOUT zone methods are used to neutralize flue gases from SO 2 (NOx) and deodorize gas emissions from industrial enterprises. The introduction of ozone accelerates the oxidation reactions of NO to NO 2 and SO 2 to SO 3 . After the formation of NO 2 and SO 3, ammonia is introduced into the flue gases and a mixture of the resulting complex fertilizers (ammonium sulfate and ammonium nitrate) is released. The contact time of gas with ozone required to remove SO 2 (80-90%) and NOx (70-80%) is 0.4 - 0.9 seconds. Energy consumption for gas purification using the ozone method is estimated at 4-4.5% of the equivalent power of the power unit, which is apparently the main reason limiting industrial application of this method.

P The use of ozone for deodorization of gas emissions is based on the oxidative decomposition of foul-smelling substances. In one group of methods, ozone is introduced directly into the gases to be purified; in another, the gases are washed with pre-ozonated water. Subsequent passing of ozonated gas through a layer of activated carbon or supply to the catalyst is also used. When ozone is introduced and the gas is subsequently passed through the catalyst, the transformation temperature of substances such as amines, acetaldehyde, hydrogen sulfide, etc. is reduced to 60-80 °C. Both Pt/Al 2 O 3 and oxides of copper, cobalt, and iron on a carrier are used as a catalyst. The main application of ozone deodorization methods is in the purification of gases that are released during the processing of raw materials of animal origin in meat (fat) plants and in everyday life.

P laser-chemical method

P The laser-chemical method is based on passing an air mixture with harmful impurities through a high-voltage discharge. As a rule, ozonizers based on barrier, corona or sliding discharges, or pulsed high-frequency discharges on electric precipitators are used. Air with impurities passing through the low-temperature plasma is bombarded with electrons and ions. As a result, atomic oxygen, ozone, hydroxyl groups, excited molecules and atoms are formed in the gas environment, which participate in plasma-chemical reactions with harmful impurities. The main directions for the application of this method are the removal of SO 2, NOx and organic compounds. The use of ammonia, when neutralizing SO 2 and NOx, produces powdered fertilizers (NH 4) 2 SO 4 and NH 4 NH 3 at the reactor outlet, which are filtered.

N The disadvantages of this method are:

• insufficiently complete decomposition of harmful substances to water and carbon dioxide, in the case of oxidation of organic components, at acceptable discharge energies
• the presence of residual ozone, which must be decomposed thermally or catalytically
• significant dependence on dust concentration when using ozonizers using barrier discharge.

P Lasmocatalytic method

E This is a fairly new cleaning method that uses two well-known methods - plasma-chemical and catalytic. Installations operating on the basis of this method consist of two stages. The first is a plasma-chemical reactor (ozonizer), the second is a catalytic reactor. Gaseous pollutants, passing through the high-voltage discharge zone in gas-discharge cells and interacting with electrosynthesis products, are destroyed and converted into harmless compounds, up to CO 2 and H 2 O. The depth of conversion (purification) depends on the amount of specific energy released in the reaction zone. After the plasma-chemical reactor, the air undergoes final fine cleaning in a catalytic reactor. Ozone synthesized in the gas discharge of a plasma-chemical reactor reaches the catalyst, where it immediately decomposes into active atomic and molecular oxygen. Remains of pollutants (active radicals, excited atoms and molecules), not destroyed in the plasma-chemical reactor, are destroyed on the catalyst due to deep oxidation with oxygen.

P The advantage of this method is the use of catalytic reactions at temperatures lower (40-100 °C) than with the thermocatalytic method, which leads to an increase in the service life of the catalysts, as well as lower energy consumption (at concentrations of harmful substances up to 0.5 g/m³ .).

N The disadvantages of this method are:

• high dependence on dust concentration, the need for preliminary cleaning to a concentration of 3-5 mg/m³,
• at high concentrations of harmful substances (over 1 g/m³), the cost of equipment and operating costs exceed the corresponding costs in comparison with the thermocatalytic method

F otocatalytic method

WITH Nowadays, the photocatalytic method for the oxidation of organic compounds is being widely studied and developed. Basically, catalysts based on TiO 2 are used, which are irradiated with ultraviolet light. There are household air purifiers from the Japanese company Daikin that use this method. The disadvantage of this method is that the catalyst becomes clogged with reaction products. To solve this problem, they use the introduction of ozone into the mixture to be purified, however, this technology is applicable for a limited composition of organic compounds and at low concentrations.