AT Currently, there are a large number of different methods of air purification from various harmful contaminants. The main methods include:

• absorption method.
• adsorption method.
• Thermal afterburning.
• thermocatalytic methods.
• ozone methods.
• Plasma chemical methods.
• Plasma catalytic method.
• photocatalytic method.

absorption method

BUT 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, usually low-volatile organic liquids are used. The liquid is used for absorption only once, or it is regenerated, releasing the contaminant in its pure form. Schemes with a single use of the absorber are used in cases where absorption leads directly to the receipt of the finished product or intermediate. Examples include:

• obtaining mineral acids (absorption of SO 3 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 obtain nitrite-nitrate liquors, absorption by aqueous solutions of lime or limestone to obtain calcium sulfate);
• other substances (absorption of NH 3 by water to obtain ammonia water, etc.).

BUT adsorption method

BUT The adsorption method is one of the most common means of protecting the air basin from pollution. In the United States alone, tens of thousands of adsorption systems have been introduced and successfully operated. The main industrial adsorbents are activated carbons, complex oxides and impregnated sorbents. Activated carbon (AC) is neutral with respect to polar and nonpolar molecules of adsorbed compounds. It is less selective than many other sorbents and is one of the few suitable for use in wet gas streams. Activated carbon is used, in particular, to purify gases from foul-smelling substances, recover solvents, etc.

O oxide adsorbents (OA) have a higher selectivity with respect to polar molecules due to their own inhomogeneous distribution of the electric potential. Their disadvantage is the decrease in efficiency in the presence of moisture. The OA class includes silica gels, synthetic zeolites, aluminum oxide.

M It is possible to single out the following main methods for implementing adsorption purification processes:

• After adsorption, desorption is carried out and the trapped 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, impurities are not disposed of, but are subjected to thermal or catalytic afterburning. This method is used to clean off gases of chemical-pharmaceutical and paint-and-lacquer enterprises, the food industry and a number of other industries. This type of adsorption treatment is economically justified at low concentrations of pollutants and (or) multicomponent pollutants.
• After cleaning, the adsorbent is not regenerated, but subjected, for example, to burial or incineration together with the strongly chemisorbed pollutant. This method is suitable when using cheap adsorbents.

Thermal afterburning

D burning is a method of neutralizing gases by thermal oxidation of various harmful substances, mainly organic, into practically harmless or less harmful, mainly CO 2 and H 2 O. The usual afterburning temperatures for most compounds lie 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 expediency of thermal neutralization, it is necessary to take into account the nature of the resulting combustion products. Combustion products of gases containing sulfur, halogen, and phosphorus compounds can exceed the initial gas emission in terms of toxicity. In this case, additional cleaning is required. 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.).

AT The most important factors determining the expediency of thermal neutralization are the energy (fuel) costs for providing high temperatures in the reaction zone, the calorific value of the neutralized impurities, and the possibility of preheating the gases to be purified. Increasing the concentration of afterburning impurities leads to a significant reduction in fuel consumption. In some cases, the process can proceed in an autothermal mode, i.e., the operating mode is maintained only due to the heat of reaction of deep oxidation of harmful impurities and preliminary heating of the initial mixture with neutralized exhaust gases.

P The fundamental difficulty in 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 combustible compounds. Afterburning plants developed in recent years are characterized by compactness and low energy consumption. The use of thermal methods is effective for afterburning dust of multicomponent and dusty exhaust gases.

Thermal catalytic methods

To Catalytic gas cleaning methods are versatile. With their help, it is possible to release gases from oxides of sulfur and nitrogen, various organic compounds, carbon monoxide and other toxic impurities. Catalytic methods make it possible to convert harmful impurities into harmless, less harmful and even beneficial ones. They make it possible to process multicomponent gases with low initial concentrations of harmful impurities, to achieve high degrees of purification, to conduct the process continuously, and to avoid the formation of secondary pollutants. The use of catalytic methods is most often limited by the difficulty of finding and fabricating catalysts suitable for long-term operation and sufficiently cheap. Heterogeneous catalytic conversion of gaseous impurities is 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 honeycomb. The chemical transformation takes place on the developed internal surface of the catalysts, reaching 1000 m²/g.

AT A wide variety of substances serve as effective catalysts that are used in practice - from minerals, which are used almost without any pretreatment, and simple massive metals to complex compounds of a given composition and structure. Typically, catalytic activity is exhibited by solids with ionic or metallic bonds, which have strong interatomic fields. One of the main requirements for a catalyst is the stability of its structure under the 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 made in the form of rings and honeycomb blocks have low hydrodynamic resistance and high external specific surface.

H The most widespread are catalytic methods for the neutralization of exhaust gases in a fixed catalyst bed. Two fundamentally different methods of carrying out the gas cleaning process can be distinguished - in stationary and in artificially created non-stationary modes.

1. Stationary method.

P practical rates of chemical reactions are achieved on 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.), gases usually have a much lower temperature.

P heating 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. It is possible to achieve a reduction in energy consumption if the heat of the exhaust gases is used to heat the gases entering the treatment. For heating, recuperative tubular heat exchangers are usually used.

P Under certain conditions, when the concentration of combustible impurities in the exhaust gases exceeds 4-5 g / m³, the implementation of the process according to the scheme with a heat exchanger makes it possible to do without additional costs.

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

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

2. Non-stationary method (reverse process).

R the evers process provides for a periodic change in the direction of filtration of the gas mixture in the catalyst bed using special valves. The process proceeds as follows. The catalyst bed is preheated to a temperature at which the catalytic process proceeds at a high rate. After that, purified gas is fed into 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 proceed at a noticeable rate in the catalyst layer. The layer of solid material (catalyst), giving off heat to the gas, is gradually cooled to a temperature equal to the temperature of the gas at the inlet. Since heat is released during the reaction, the temperature in the layer may exceed the temperature of the initial heating. A thermal 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. Periodic switching of the direction of gas supply to the opposite one makes it possible to keep the thermal 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 combustible mixtures and the absence of heat exchangers.

O The main direction in the development of thermal catalytic 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. Thermal catalytic methods are most widely used 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 thermal catalytic method requires high energy consumption, as well as a large amount of catalyst.

Ozone methods

O 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 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 formed complex fertilizers (ammonium sulfate and nitrate) is isolated. The contact time of the gas with ozone required for purification from SO 2 (80-90%) and NOx (70-80%) is 0.4 - 0.9 sec. Energy consumption for gas purification by the ozone method is estimated at 4-4.5% of the equivalent capacity of the power unit, which is, apparently, the main reason that hinders the industrial application of this method.

P The use of ozone for the deodorization of gaseous emissions is based on the oxidative decomposition of foul-smelling substances. In one group of methods, ozone is injected directly into the gases to be purified, in the other, the gases are washed with pre-ozonized water. The subsequent passage of the ozonized gas through a layer of activated carbon or its supply to the catalyst is also used. With the introduction of ozone and the subsequent passage of gas through the catalyst, the temperature of transformation of such substances as amines, acetaldehyde, hydrogen sulfide, etc. decreases to 60-80 °C. As a catalyst, both Pt/Al 2 O 3 and oxides of copper, cobalt, and iron on a support are used. The main application of ozone deodorization methods is found 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 lasmochemical method

P The lasma-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 electrostatic precipitators are used. Air with impurities passing through the low-temperature plasma is bombarded by electrons and ions. As a result, atomic oxygen, ozone, hydroxyl groups, excited molecules and atoms are formed in the gaseous medium, which participate in plasma-chemical reactions with harmful impurities. The main directions for the application of this method are to remove SO 2 , NOx and organic compounds. The use of ammonia, when neutralizing SO 2 and NOx, gives powdered fertilizers (NH 4) 2 SO 4 and NH 4 NH 3 at the outlet after the reactor, which are filtered.

H 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 ozone generators with the use of a barrier discharge.

P catalytic method

E This is a fairly new purification method that uses two well-known methods - plasma-chemical and catalytic. Installations based on this method consist of two stages. The first is a plasma-chemical reactor (ozonator), 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 conversion (purification) depth depends on the specific energy released in the reaction zone. After the plasma-chemical reactor, the air is subjected to final fine purification in a catalytic reactor. The ozone synthesized in the gas discharge of the plasma-chemical reactor enters the catalyst, where it immediately decomposes into active atomic and molecular oxygen. Remains of pollutants (active radicals, excited atoms and molecules) that are 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 thermal catalytic method, which leads to an increase in the service life of catalysts, as well as to lower energy costs (at concentrations of harmful substances up to 0.5 g/m³ .).

H The disadvantages of this method are:

• high dependence on dust concentration, the need for pre-treatment 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 thermal catalytic method

F catalytic method

With The photocatalytic method for the oxidation of organic compounds is currently being widely studied and developed. Basically, catalysts based on TiO 2 are used, which are irradiated with ultraviolet light. Known household air purifiers of the Japanese company "Daikin" using this method. The disadvantage of this method is the clogging of the catalyst with the reaction products. To solve this problem, the introduction of ozone into the mixture to be purified is used; however, this technology is applicable to a limited composition of organic compounds and at low concentrations.

Mechanical Methods

1.Inertial dust collectors— the mechanism of gravitational settling of particles from a horizontally directed gas flow is used. Coarsely dispersed particles with a size of 50 microns and more are captured. They are used as gas pre-treatment devices, for example, for separating large particles and unloading devices of subsequent stages.

2. Cyclones(Fig.), The principle of operation is based on the use of centrifugal force arising from the rotational-translational movement of the gas flow. Centrifugal force throws dust particles to the walls of the cyclone body, then the dust particles, flowing down the walls, fall into the bunker, and the purified gas through the exhaust pipe located along the axis of the cyclone is emitted into the atmosphere or supplied to the consumer. They are used to remove ash from flue gases and dry (wood, asbestos-cement, metal) dust with a particle size of 25-30 microns from the air. Cyclones make up the largest group of environmental equipment - more than 90% of the total number of dust collectors used in industry. They capture more than 80% of the total mass of dust captured by all devices

1 - polluted stream;

2 - suspended matter

3. Filters When using fabric dust collectors, the degree of air purification can be 99% or more. When passing dusty air through the fabric, the dust contained in it is retained in the pores of the filter material or on a layer of dust accumulating on its surface.

Fabric dust collectors according to the shape of the filtering surface are sleeve and frame. As a filtering material, cotton fabrics, filter cloth, nylon, wool, nitron, lavsan, fiberglass and various nets are used.

1 - polluted flow; 2 - sleeves made of fleecy fabric; 3 - cleaned stream

Physical Methods

1. Electrostatic precipitators- one- or two-section rectangular apparatus, a device in which the purification of gases from aerosol, solid or liquid particles occurs under the action of an electric. forces (Fig.). The active zone of electrostatic precipitators consists of collecting electrodes (flat sheets made of plate elements of a special profile) and corona electrodes (tubular frames in which corona elements are stretched). E., in which the trapped solid particles are removed from the electrodes by shaking, called. dry, and those in k-rykh osazh. particles are washed off the electrodes with a liquid or liquid particles (fog, splashes) are captured - wet. Dry electrostatic precipitators are used to remove dry dust, and wet ones are used to purify gases from acid vapors: sulfuric, hydrochloric, nitric. The cleaning effect is 97-99%.

Rice. Single zone electrostatic precipitator with transverse gas flow

1 - precipitation electrodes; 2 – corona electrodes

Physical and chemical methods

Physico-chemical methods are based on the physico-chemical interactions of pollutants with cleaning agents. These methods include: absorption, chemisorption, adsorption, catalytic method, thermal method .

1. Absorption is based on the separation of the gas-air mixture into its constituent parts by absorbing the gas components of this mixture with a liquid absorbent (absorbent). Water is used to remove ammonia, hydrogen chloride and hydrogen fluoride from emissions. Sulfuric acid is used to remove aromatic hydrocarbons. Currently, scrubber-absorbers are the most widely used as absorbers (Fig.).

Rice. . Irrigated scrubber-absorber with nozzle: 1 - nozzle; 2 - sprinkler

2.Adsorption I is based on the extraction of mixtures of harmful impurities from gases with the help of solid adsorbents. The most widely used adsorbent is activated carbon; in addition, there are sorbents such as activated alumina, silica gel, activated alumina, and synthetic zeolites. Some adsorbents are impregnated with reagents that increase the efficiency of adsorption and turn a harmful impurity into a harmless one due to chemisorption occurring on the surface of the adsorbent. The main treatment equipment are vertical, horizontal, scrubbers - adsorbers. 1 - grid; 2 - adsorbent; 3 - purified stream; 4 - polluted flow

3. Chemisorption is based on the absorption of gases and vapors by liquid and solid absorbers with the formation of chemical compounds. This method is used to remove hydrogen sulfide and nitrogen oxides from emissions. Scrubbers are used as treatment equipment, and arsenic-oxalic and ethanolamine solutions are chemical absorbers.

4. Catalytic method purification consists in the selective acceleration of a chemical reaction and the transformation of a pollutant into a harmless substance (Fig.). To reduce the toxicity of exhaust gases, catalytic converters are used, in which polluted air is passed over a catalyst, most often aluminum oxide. With the help of such purification equipment, it is possible to purify the air from carbon monoxide, hydrocarbons, nitrogen oxides. Used in liquid neutralizers to reduce the content of aldehydes and nitrogen oxides
10% aqueous solutions of Na2SO3 or NaHSO4 with the addition of 0.5% basic reagent to prevent premature oxidation. This method can achieve complete purification of gases from aldehydes, and the content of nitrogen oxides is reduced by 70%.

Fig. Catalytic converter: 1 - frame; 2 – reactor;
3 - net; 4 – thermal insulation; 5 – catalyst; 6 - flange

5. Thermal method is based on afterburning and thermal destruction of harmful substances in emissions. It is used when harmful impurities in emissions are combustible. This method is used to clean emissions from paint and impregnation areas. Thermal and fire neutralization systems provide cleaning efficiency up to 99%.

If we talk about the purity of drinking water, then this can be achieved with the help of various filters, which today are offered in a wide range. It’s a little more difficult with air purity, since in the modern world of technological progress, the development of industrial enterprises gradually leads to an environmental disaster.

If the possibility of cleaning the air in the environment is reduced to zero, then making the air in your home is a top priority. How to clean the air from dust?

Dust enters the room with the help of external (pollen, smoke and small particles of soil brought from the street on clothes or through the ventilation system) and internal sources (textiles, walls and ceilings, animal hair, human hair and dander).

Air purification problems

Getting rid of dust that has settled on furniture, floors and various interior items is much easier than removing dust from indoor air. The dustiness of the air in the house has a detrimental effect on health, since harmful microorganisms and various small particles that are part of the dust most often cause the development of allergic diseases of the upper respiratory tract. To date There are several effective systems for cleaning the air from dust., which help get rid of dust mites, therefore, will be useful to every housewife in the fight against dust.

The most common way to remove dust from the air is to use a household air purifier., which can be divided into several categories depending on the filtering principle:

• Ionizing (electrostatic precipitators) - produce the strongest oxidizing agent ozone, perfectly clean the air from dust, but do not free the air from toxic pollutants.

  In addition, excessive ozone content in indoor air can lead to poisoning, so the use of these filters should not be prolonged;

• Photocatalytic - organic substances that fall on the catalyst are oxidized under the action of ultraviolet radiation to clean air components that have a beneficial effect on humans;
• Adsorption (coal) - attract toxic impurities and keep them inside the device.

  If the filter cassettes are not changed in a timely manner, they can become a source of harmful substances;

• Dust - the most simple, since the basis of the device uses a fabric with various fibers, which retains dust.

It should be noted that photocatalytic air purification is the most effective method of filtering dust mites and all kinds of toxic impurities.

The principle of operation is a bit like natural processes in nature, due to which these filters are used everywhere and are the most efficient and economical.

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

How to clean the air?

Rapidly developing technological progress brings not only more benefits, but also more and more problems. Perhaps the most important problem is environmental pollution, which undermines our health. Scientists have found that already now our immune system spends 80% of its resources on neutralizing harmful environmental factors.

And this percentage will only increase.

What to do?

Air purification methods

We have been trying for a long time to eat organic food, purify or buy clean water. More difficult with clean air. We always need him. We can live a few days without food, but less without water.

How long can we not breathe?
Therefore, air purification is of great importance, especially in rooms where we spend most of our lives, and where the air is much more polluted than outside.

And now a person who has matured to recognize the vital need to purchase an air purifier comes to a specialized store. But here his eyes just run wide.

Most of all, air ionizers are represented, which are also considered purifiers. But they only attract dust. And gas molecules ionize. But, if ionized oxygen becomes more useful, then harmful gases are even more harmful.

It is necessary to ionize already purified air.

There are many other types of air purifiers, such as those that pass it through water or wet spinning discs, but they all collect only dust. Gases are collected by activated carbon. But charcoal air purifiers also have disadvantages. First, coal begins to collect gases with a molecular weight greater than 40. And the most common exhaust gases in the city consist of carbon and oxygen molecules with masses of 12 and 16, i.e.

in total less than 40. So, even a gas mask does not save from exhaust gases. Secondly, coal collects pollution in the amount of 7-10 percent of its mass and stops working.

Filters need to be changed, but they are expensive, especially imported ones.

But how does nature itself purify the air? She, unlike us, does not accumulate and does not bury pollution, but simply breaks them down.

There is a process called photocatalysis. On some chemical compounds, harmful gases, odors, even bacteria and viruses decompose under the action of sunlight. It is known that all organic compounds are 95 percent composed of carbon, oxygen and hydrogen. These atoms break down air pollution, and the elements immediately combine into carbon dioxide and water. Thus, photocatalysis is a natural phenomenon, as a result of which complex and harmful organic molecules turn into simple and harmless ones.

Only nature itself can no longer cope with the increasing amount of pollution.

Photocatalysis, like photosynthesis, was studied by scientists more than 100 years ago, but so far it has not been possible to create a device that works on this principle. About 20 years ago, this problem was solved by the Novosibirsk chemist Evgeny Savinov. He dealt with the fundamental problems of solar energy and natural photocatalysis.

His daughter suffered from allergies. He tried all the filters available at that time, including HEPA brought from America. Nothing helped. Then Evgeny Nikolaevich took the photocatalyst powder, since he worked at the Institute of Catalysis of the Siberian Branch of the Russian Academy of Sciences, a sun lamp and a fan. Made a device and placed it in my daughter's room.

This device turned out to be quite noisy and cumbersome, but the girl stopped coughing and began to sleep well.

This device became the prototype of unique photocatalytic air purifiers-disinfectors developed by Russian scientists.

Since they use a natural phenomenon, they:

Firstly, they are completely safe and can even be placed above the baby's bed.

Secondly, the spectrum of their action is extremely wide - from exhaust gases, any odors and chemical compounds to bacteria and viruses.

Thirdly, they are economical.

Household appliances consume only 40 watts and are designed for continuous operation.

Fourthly, they do not require any replaceable elements, since they do not accumulate anything, but decompose to carbon dioxide and water.

We have been using photocatalytic air purifiers for a long time in our Moscow apartment. I can talk about existing models, how to choose them, how to use them effectively, where to buy and how much they cost.

Remember this word - photocatalysis. Let's help nature fight pollution, starting with our own apartment.

And we will be healthy.

Measures to prevent air pollution

4 groups of measures: federal and municipal laws and regulations; technological, planning, sanitary measures. Main value technological measures. This is the creation of closed processes and the reduction of emissions into the atmosphere, the introduction of the principles of environmental management in training, the proper use of waste.

The following measures should be implemented: harmful substances in production are harmless; purification of raw materials from harmful impurities; Replacement of dry cleaning methods of dusty materials with a wet method; replacing a fire extinguisher with electric current; process seal; The replacement of intermittent processes is continuous to avoid reflecting pollutant emissions.

Event planning: registration of the "wind rose", the area of ​​urban areas, the organization of sanitary zones, landscaping of settlements, planning of residential areas. Determining the area of ​​the city, we pay great attention to the "garden of the wind" and the field.

The industrial areas are located in well-ventilated areas downstream depending on the residential areas. Also consider seasonal wind speed.

METHODS FOR CLEANING ATMOSPHERIC AIR

In addition, green plants play an important role in cleaning up urban dust from dust. The presence of green zones allows to reduce the concentration of harmful substances three times.

For horticultural hygiene and inside the square, gas-resistant wood and clay are used.

Proper block development planning is required. The area closest to the highway is built with general buildings, then low-rise buildings, tall buildings, and then kindergartens, medical facilities (buildings requiring air quality). The closed building is used only in cities where high-speed winds help clean the air. Sanitary measures– installation of dust collection systems (mechanical dust collectors, filtering devices, electrostatic filters, wet cleaners, dust collection chambers).

This also includes exhaust pumps - ash collectors in which dust is deposited when the gas passes through porous bulkheads. Electrostatic precipitators are state-of-the-art gas cleaning devices used to collect solid and liquid aerosols. By their nature, gases can be dry and wet in the direction of gases - horizontal and vertical. cleaners— common wet gas cleaning system, different in design.

Methods for cleaning the atmosphere are determined by the nature of the pollutants. A number of modern technological processes are associated with the grinding of substances. At the same time, some of the materials turn into dust, which is harmful to health and causes significant material damage due to the loss of valuable products.

The dust settled in industrial cities mainly contains 20% iron oxide, 15% silicon oxide and 5% soot. Industrial dust also includes oxides of various metals and non-metals, many of which are toxic. These are oxides of manganese, lead, molybdenum, vanadium, antimony, arsenic, tellurium. Dust and aerosols not only make it difficult to breathe, but also lead to climate change, as they reflect solar radiation and make it difficult to remove heat from the Earth.

The principles of operation of dust collectors are based on the use of various particle settling mechanisms: gravitational settling, centrifugal force settling, diffusion settling, electric (ionization) settling, and some others. According to the method of dust collection, the devices are dry, wet and electric cleaning.

The main criterion for choosing the type of equipment: the physical and chemical properties of dust, the degree of purification, the parameters of the gas flow (inflow rate). For gases containing combustible and toxic impurities, it is better to use wet scrubbers.

The main direction of protecting the atmosphere from pollution is the creation of low-waste technologies with closed production cycles and the integrated use of raw materials.

cleaning - removal (separation, trapping) of impurities from various media.

Existing purification methods can be divided into two groups: non-catalytic (absorption and adsorption) and catalytic.

Neutralization - treatment of impurities to a state harmless to humans, animals, plants and the environment in general.

Disinfection - inactivation (deactivation) of various types of microorganisms in gas-air emissions, liquid and solid media.

Deodorization - treatment of odorants (substances with an odor) contained in air, water or solid media in order to eliminate or reduce the intensity of odors.

Purification of gases from carbon dioxide:

1. Water absorption. The method is simple and cheap, but the cleaning efficiency is low, since the maximum absorption capacity of water is 8 kg of CO2 per 100 kg of water.

2. Absorption with ethanolamine solutions: Monoethanolamine is usually used as an absorbent, although triethanolamine is more reactive.

3. Cold methanol is a good CO2 absorber at 35°C.

4. Cleaning with zeolites. CO2 molecules are very small: 3.1A, so molecular sieves are used to extract CO2 from natural gas and remove waste products (moisture and CO2) in modern environmentally isolated systems (spaceships, submarines, etc.).

Purification of gases from carbon monoxide:

• Afterburning on a Pt/Pd catalyst.
• Conversion (adsorption method).

Purification of gases from nitrogen oxides .

In the chemical industry, 80% of the removal of nitrogen oxides is carried out due to transformations on a catalyst:

1. Oxidative methods are based on the oxidation reaction of nitrogen oxides followed by absorption by water:

• Oxidation by ozone in liquid phase.
• Oxidation with oxygen at high temperature.

2. Recovery methods are based on the reduction of nitrogen oxides to neutral products in the presence of catalysts or under the action of high temperatures in the presence of reducing agents.

3. Sorption methods:

• Adsorption of nitrogen oxides by aqueous solutions of alkalis and CaCO3.
• Adsorption of nitrogen oxides by solid sorbents (brown coal, peat, silica gels).

Purification of gases from sulfur dioxide SO2:

1. Ammonia cleaning methods. They are based on the interaction of SO2 with an aqueous solution of ammonium sulfite.

The resulting bisulfite is easily decomposed by acid.

2. SO2 neutralization method, provides a high degree of gas purification.

3. Catalytic methods. Based on the chemical transformations of toxic components into non-toxic ones on the surface of catalysts:

• pyrolusite method - oxidation of SO2 with oxygen in the liquid phase in the presence of a catalyst - pyrolusite (MnO2); the method can be used to produce sulfuric acid.
• The ozone catalytic method is a variation of the pyrolusite method and differs from it in that the oxidation of Mn2+ to Mn3+ is carried out in an ozone-air mixture.

The cleaning efficiency depends on many factors: partial pressures of SO2 and O2 in the gas mixture being cleaned; flue gas temperature; presence and properties of solid and gaseous components; the volume of gases to be purified; availability and availability of components; the required degree of gas purification.

After the purification, the gas enters the atmosphere and dissipates, while air pollution in the surface layer should not exceed the MPC.

Industrial cleaning - this is gas purification for the purpose of subsequent disposal or return to production of the product separated from the gas or turned into a harmless state. This type of cleaning is a necessary stage of the technological process, while the technological equipment is connected to each other by material flows with the appropriate piping of the apparatus. Unloading cyclones, dust settling chambers, filters, adsorbers, scrubbers, etc. can be used as dust and gas collecting equipment.

Sanitary cleaning - this is gas purification from the residual content of a pollutant in the gas, which ensures compliance with the MPC established for the latter in the air of populated areas or industrial premises. Sanitary cleaning of gas-air emissions is carried out before the exhaust gases enter the atmospheric air, and it is at this stage that it is necessary to provide for the possibility of sampling gases in order to control them for the content of harmful impurities.

The choice of an off-gas purification method depends on the specific production conditions and is determined by a number of key factors:

The volume and temperature of the exhaust gases;

Aggregate state and physicochemical properties of impurities;

The concentration and composition of impurities;

The need to recuperate or return them to the technological process;

Capital and operating costs;

ecological situation in the region.

Dust collection equipment. Dust collection equipment depending on the method of separating dust from the gas-air flow is divided into dry, when dust particles are deposited on a dry surface, and wet, when the separation of dust particles is carried out using liquids.

The choice of the type of dust collector is determined by the degree of dustiness of the gas, the dispersion of particles and the requirements for the degree of its purification.

Devices for gravity cleaning are simple in design, but are mainly suitable for coarse pre-treatment of gases. The simplest are dust chambers. They are mainly used for pre-treatment of gases from coarse dust (with a particle size of 100 microns or more) and at the same time for gas cooling. The chamber is a hollow or with shelves box of rectangular section with a hopper at the bottom to collect dust. The cross-sectional area of ​​the chamber is much larger than the area of ​​the supply gas ducts, as a result of which the gas flow moves slowly in the chamber - about 0.5 m/s, and the dust settles (Fig. 1).

Fig 1. Dust settling chamber: a - hollow; b - with partitions

Advantages of the dust collector:

1. has low aerodynamic drag;

2. easy and profitable to operate.

Disadvantages - bulkiness, low degree of purification.

The efficiency of the chamber can be increased to 80 - 85% if partitions are made inside the chamber, increasing the time the gas stays in it. Typically, dust collection chambers are built into gas ducts; they are made of metal, brick, concrete, etc.

Inertial dust collectors. In these devices, due to a sharp change in the direction of the gas flow, dust particles by inertia hit the reflective surface and fall onto the conical bottom of the dust collector, from where they are continuously or periodically removed from the device by an unloading device. The simplest of the dust collectors of this type are dust collectors(bags) shown in fig. 2. They also retain only large fractions of dust, the degree of purification is 50 - 70%.

Rice. 2. Inertial dust collectors (dust collectors): a - with a partition; b - with a central pipe

In more complex louvered devices capture particles with a size of 50 microns or more. They are designed to clean large volumes of gas-air emissions. The louvres consist of overlapping rows of plates or rings with gaps of 2-3 mm, and the entire grille is given some taper to maintain a constant gas flow rate. The gas flow, passing through the grate at a speed of 15 m/s, abruptly changes direction. Large dust particles, hitting the inclined planes of the grating, are reflected by inertia from the latter to the axis of the cone and are deposited. The gas freed from coarse dust passes through the grate and is removed from the apparatus. Part of the gas flow in the amount of 5-10% of the total flow sucked from the space in front of the louvre contains the main amount of dust and is sent to the cyclone, where it is freed from dust and then joins the main dust-laden gas flow. The degree of gas purification from dust larger than 25 µm is approximately 60% (Fig. 3). The main disadvantages of louvered dust collectors are the complex arrangement of the apparatus and the abrasive wear of the louvered elements.

Rice. 3. Inertial louvered dust collector: 1 - inertial apparatus; 2 - cyclone; 3 - louvre

Commonly used dust collectors are cyclones , the action of which is based on the use of centrifugal force. The dust-gas mixture tangentially enters the device through the fitting and acquires a directed movement down the spiral. In this case, dust particles are thrown by centrifugal force to the wall of the cyclone, fall down and are collected in the receiving hopper. The dust is periodically discharged from the hopper through the shutter. The purified air is expelled through the central pipe from the device.

The efficiency of dust collection in a cyclone is directly proportional to the mass of particles and inversely proportional to the diameter of the device. Therefore, instead of one large cyclone, it is advisable to install several smaller cyclones in parallel. Such devices are called group battery cyclones .

For purification of large volumes of gases with non-coalescing solid particles of medium dispersion, it is possible to use multicyclones (Fig. 4) . In these devices, the rotational movement of the dust and gas flow is organized using a special guiding device (socket or screw) located in each cyclone element. Multicyclones, consisting of elements with a diameter of 40 - 250 mm, provide a high (up to 85-90%) degree of gas purification from fine particles with a diameter of less than 5 microns.

Rice. 4 Multicyclone and its element

Cyclones are effective dust collectors, the degree of purification of which depends on the particle size and can reach 95% (with a particle size of more than 20 microns) and 85% (with a particle size of more than 5 microns).

The disadvantages of cyclones of all designs include a relatively high aerodynamic resistance (400 - 700 Pa), significant abrasive wear of the walls of the apparatus, the likelihood of re-entrainment of dust settled in the dust collector due to gas overload and leaks. In addition, cyclones do not effectively capture polydisperse dusts with a particle diameter of less than 10 μm and a low density of the material.

To eliminate the shortcomings of cyclones developed vortex dust collectors (VPU), which also belong to direct-flow devices of centrifugal action. There are two types of WPU - nozzle and bladed (5, a, b).

Rice. 5 Vortex dust collectors

In devices of this type, dusty gas enters chamber 1 through an inlet pipe with a paddle swirler 5 of the "socket" type and a fairing 4. The annular space around the inlet pipe is formed by a retaining washer 2, the position and dimensions of which ensure the irreversible deposition of dust into the dust bin. The fairing directs the flow of dusty gas to the walls of the apparatus and upwards, and the jet of secondary air coming out of the nozzle 3 due to their tangentially inclined arrangement, they convert the flow movement into rotational. The centrifugal forces arising in the air flow throw dust particles to the walls of the apparatus, and from there they, together with the spiral air flow, are directed downwards.

In those cases where humidification of the gas to be purified is acceptable, apply hydro dust collectors. In these devices, the dusty flow comes into contact with the liquid or the surfaces irrigated by it. Wet dust collectors differ from dry ones in higher efficiency at a relatively low cost. They are especially effective for cleaning gas-air emissions containing flammable and explosive, as well as sticky substances.

Wet cleaning devices can be used to purify gases from fine dusts with a particle size of 0.1 microns, as well as from gas and vaporous harmful substances.

Wet dust collectors are divided into five groups:

1 - scrubbers;

2 - wet centrifugal dust collectors;

3 - turbulent dust collectors;

4 - foam apparatus;

5 - fan dust collectors.

The simplest and most common devices for cleaning and cooling gases are hollow and packed scrubbers .

Rice. 6 Scrubbers: a- hollow; 6 – packed

They are vertical cylindrical columns, in the lower part of which dusty gas is introduced, and atomized liquid is supplied from above through nozzles. The purified gas is removed from the upper part of the apparatus, and the water with the trapped dust in the form of sludge is collected at the bottom of the scrubber. The degree of purification from dust with a particle size of more than 5 microns can be more than 90%.

The highest cleaning results are achieved when using coarse spray nozzles that form drops with a diameter of 0.5 - 1.0 mm. To reduce spray entrainment, the speed of the cleaned gas in the scrubber should not exceed 1.0 - 1.2 m/s.

Packed scrubbers are filled with various packed bodies (Raschig rings, Berle saddles, mesh, fiberglass, etc.) laid on a support grid. Simultaneously with the capture of dust on the complex surface of the packed bodies, the absorption of individual components of the gas mixture can also occur. The hydraulic resistance of a packed scrubber depends on the gas velocity (usually it is 0.8 - 1.25 m/s), irrigation density, packing height, and some other parameters, and it is in the range of 300 - 800 Pa.

Centrifugal wet dust collectors are the largest group of separating devices for various purposes.

Rice. 7. Water film cyclone (CWP)

The inner wall of the apparatus case 3 irrigated with water supplied from collector 5 through a nozzle 4, which is installed at an angle of 300 downwards tangent to the inner surface of the housing. To prevent splashing, the spray of water coincides with the direction of rotation of the dusty gas flow. At the bottom of the device is a water seal 6.

From turbulent dust collectors In recent years, Venturi scrubbers (Fig. 8) have gained wide popularity, the high efficiency of which makes it possible to provide gas purification for almost any concentration of captured dust. These devices are easy to manufacture, install and operate, are characterized by small dimensions.

Rice. 8. Venturi scrubber

AT Venturi scrubber dusty gas through a confuser 3 is fed into the neck 2, where, due to a decrease in the free section of the apparatus, the flow velocity increases to 30 - 200 m/s. Water is supplied to the confuser zone. When mixed with a gas stream, it disperses into small droplets. In neck 2 and diffuser 1 dust particles contained in dusty air combine with water droplets, moisten, coagulate and are released in the separator in the form of sludge 4 (drip catcher). Water can be supplied to the scrubber in various ways, however, the most common way is to supply liquid to the confuser.

Almost all known types of hydromechanical devices for separating inhomogeneous systems (separators, cyclones, foam devices, electrostatic precipitators, etc.) are used as drop eliminators. Most often, cyclones of various types are used.

In the industry of the republic are widely used foam machines :

Rice. 9. Foam machines

In these dust collectors, a dusty air flow passes through a layer of liquid at a speed of 2-3 m/s (exceeds the speed of free floating of air bubbles during bubbling), as a result of which conditions are created for the formation of a layer of highly turbulent foam. Foam machines are supplied in two types: with failed gratings (Fig. 9, a) and overflow grate (Fig. 9, b). In devices with a failed grate, all the liquid for the formation of the foam layer comes from the irrigation device 3 on gratings 4, falls through its holes onto the lower grate, and then, together with the sludge, is removed from the apparatus. The dusty air flow enters the body of the apparatus 1 from below, forming a layer of foam on the gratings when interacting with water. To catch water splashes, a drop catcher 2 is installed in the upper part of the apparatus.

The main disadvantage of foam apparatuses is sensitivity to fluctuations in the flow rate of the gas to be purified. In this case, it turns out to be impossible to maintain a layer of foam over the entire area of ​​the grate: at gas flow rates that are less than optimal, foam cannot form uniformly over the entire surface of the grate, and at high flow rates, the foam layer is also uneven and even blown away in some places. This leads to a breakthrough of raw gases, increased spray entrainment and, as a result, a sharp decrease in the efficiency of the apparatus.

To fan dust collectors include dry and wet rotoclones (Fig. 10), which are widely used abroad.

Rice. 10. Rotoclone

In essence, they are combined dust collectors, the principle of operation of which is based on the deposition of dust by irrigated surfaces, the action of inertial and centrifugal forces, water spraying, etc. For example, dusty air is sucked in through the central pipe 3 into the body 2 of a wet rotoclone, while dust particles are thrown onto the blades 1 of a special profile, moistened with water supplied from the spray nozzles 4. Dust particles are moistened, coagulated and come in the form of sludge to the lower part of the apparatus, from where they are removed through pipe 5 to the sump.

The efficiency of wet dust collectors depends to a large extent on the wettability of the dust. When capturing poorly wetted dust, a surfactant is introduced into the irrigation water.

The disadvantages of wet dust collection include: high water consumption, the difficulty of separating the trapped dust from the sludge, the possibility of equipment corrosion during the processing of aggressive gases, a significant deterioration in the conditions for dispersion through the factory pipes of exhaust gases due to a decrease in their temperature. In addition, wet dust collectors require a significant amount of electricity to supply and spray water.

Filtration- represents the most radical solution to the problem of gas purification from solid impurities, provides a degree of purification of 99-99.9% at moderate capital and operating costs. In connection with the increased requirements for the degree of gas purification in recent years, there is a clear trend towards an increase in the proportion of filters used in comparison with wet scrubbers and electrostatic precipitators.

filters called devices in which dusty air is passed through porous materials that can trap or precipitate dust. Cleaning of coarse dust is carried out in filters filled with coke, sand, gravel, nozzles of various shapes and nature. For cleaning from fine dust, filter materials such as paper, mesh, non-woven materials, felt or fabrics of various densities are used. Paper is used to purify atmospheric air or gas with a low dust content.

Used in industrial environments fabric, or sleeve, filters. They are in the form of a drum, fabric bags or pockets, working in parallel. Dust particles, settling on the filter material, create a layer with pores smaller than that of the filter material, so the trapping ability of the dust layer increases, but at the same time, its aerostatic resistance also increases.

Of the filter-type devices for dust removal, the most widely used are fabric (bag) filters(Fig. 11).

Rice. 11. Bag filter

Fabric sleeves are made from cotton, wool, dacron, nylon, polypropylene, teflon, fiberglass and other materials. Often, silicone coatings are applied to fabrics to improve flex resistance, heat resistance, shrink resistance, abrasion resistance, or improve tissue regeneration. The choice of filter material depends on the operating conditions. The degree of purification of gases from dust with proper operation of filters can reach 99.9%.

The disadvantages of bag filters are the complexity of caring for the fabric of the bags and the high metal consumption of the devices, since the tension of the bags is carried out with the help of weights.

In industry, a large number of filter designs made of porous materials are widely used for fine purification of gases from dust and toxic impurities. These include filters with semi-rigid filtering baffles made of ultra-thin polymeric materials (Petryanov filters) with heat resistance, mechanical strength and chemical resistance. Among the many filter designs of this type, the most widely used frame filters(Fig. 12).

Rice. 12 Frame filter with FP fabric

The filter is assembled from three-sided frames 1 in such a way that the end side is alternately on the right, then on the left. The filter partition 2 is laid as shown in the diagram (Fig. 12 ). The air passes through the gaps between the frames, is filtered through the filter partition and exits cleaned from the other side. The package of frames is placed in the case 4. To prevent the webs from connecting to each other under the pressure of the air flow, corrugated separators are placed between them 3 (Fig. 12, a, b, c, d, e). On the side of the inlet of the dusty flow, there is a flange on the body 5 with a glued rubber gasket 6. The filter housing is made of plywood, plastics, metal.

Many structures are known landing filter box-type with a nozzle made of fiberglass, slag wool and other fibrous materials. The packing thickness is 100 mm with a packing density of 100 kg/m3 and a filtration rate of 0.1 - 0.3 m/s. The aerodynamic resistance of such filters is 450 - 900 Pa. box-shaped, or cassette, filters are usually used for purification of ventilation gases at low temperatures (30-40 °C) and low initial dust content of the order of 0.1 g/m3.

Electrostatic precipitators are used to clean dusty gases from the smallest dust particles, fogs up to 0.01 microns in size. Industrial electrostatic precipitators are divided into two groups: single-stage (single-zone), in which ionization and air purification occur simultaneously, and two-stage (two-zone), in which ionization and air purification are carried out in different parts of the apparatus.

By design, electrostatic precipitators are divided into lamellar and tubular, horizontal and vertical, two-field and multi-field, one- and multi-section, dry and wet.

On fig. 13 shows the diagrams of the tubular (a) and lamellar (b) electrostatic precipitators.

Rice. thirteen.Schemes of electrostatic precipitators

In the body 1 of the tubular electrostatic precipitator there are collecting electrodes 2 3-6 m high, made of pipes with a diameter of 150-300 mm. Corona electrodes are stretched along the axis of the pipes 3 with a diameter of 1.5-2 mm, which are fixed between the frames 4. Upper frame 4 connected to the bushing insulator 5. There is a distribution grid 6.

In a plate electrostatic precipitator (Fig. 13, b) corona electrodes 3 stretched between the parallel surfaces of the collecting electrodes 2. The distances are 250 - 350 mm. The walls of the metal case serve as two extreme electrodes. If the voltage of the electric field between the electrodes exceeds the critical one, which at atmospheric pressure and a temperature of 15 ° C is 15 kV / cm, then the air molecules in the apparatus are ionized and acquire positive and negative charges. Ions move towards the oppositely charged electrode, meet dust particles on their way, transfer their charge to them, and they, in turn, go to the electrode. Having reached it, dust particles form a layer, which is removed from the electrode surface by impact, vibration, washing, etc.

A high-voltage direct current (50 - 100 kV) is fed into the electrostatic precipitator to the corona (usually negative) and collecting electrodes. Electrostatic precipitators provide a high degree of purification. At gas velocities in tubular electrostatic precipitators from 0.7 to 1.5 m/s, and in lamellar ones from 0.5 to 1.0 m/s, it is possible to achieve a degree of gas purification close to 100%. These filters have a high throughput. The disadvantages of electrostatic precipitators are their high cost and complexity in operation.

Ultrasonic devices are used to improve the efficiency of cyclones or bag filters. Ultrasound with a strictly defined frequency leads to coagulation and coarsening of dust particles. The most common sources of ultrasound are different types of sirens. Ultrasonic dust collectors give a relatively good effect at a high concentration of dust in the gas being cleaned. To increase the efficiency of the apparatus, water is supplied to it. Ultrasonic installations in combination with a cyclone are used to capture soot, mist of various acids.

Absorption- is the process of absorption of gases or vapors from gas or vapor mixtures by liquid absorbers - absorbents. Distinguish between physical and chemical absorption. At physical absorption the molecules of the absorbed substance (absorptive) do not enter into a chemical reaction with the molecules of the absorbent. In this case, a certain equilibrium pressure of the component exists above the solution. The absorption process takes place until the partial pressure of the target component in the gas phase is higher than the equilibrium pressure over the solution.

At chemical absorption Absorptive molecules enter into chemical interaction with the active components of the absorbent, forming a new chemical compound. In this case, the equilibrium pressure of the component over the solution is negligible compared to physical absorption, and its complete extraction from the gaseous medium is possible.

The absorption process is selective and reversible.

Selectivity- this is the absorption of a specific target component (absorbent) from a mixture using an absorbent of a certain type. The process is reversible, since the absorbed substance can be again extracted from the absorbent (desorption) and the absorbent can be used again in the process.

On fig. 14 shows a schematic diagram of an absorption plant for capturing a target component from a gas mixture.

Rice. 14. Schematic diagram of the absorption-desorption process

The gas mixture enters the absorber 1, where it contacts with the cooled absorbent, which selectively absorbs the extractable component (absorbent). The gas purified from the component is removed, and the solution in the exchanger 4, is heated in it and fed by pump 5 to the desorber 3, where the absorbed component is extracted from it by heating the absorber with water vapor. The absorber freed from the target component by the pump 6 goes first to the heat exchanger 4, where it is cooled, giving off heat to the saturated absorbent, then through the refrigerator 2 it again enters the absorber for irrigation.

The absorbents used must dissolve the extracted gas well, have a minimum vapor pressure in order to pollute the purified gas with absorber vapors as little as possible, be cheap, and not cause equipment corrosion.

To clean gases from carbon dioxide, water, ethanolamine solutions, and methanol are used as absorbents.

Purification from hydrogen sulfide is carried out with solutions of ethanolamines, aqueous solutions of Na2CO3, K2CO3, NH3 (with subsequent oxidation of the absorbed H2S with air oxygen to obtain elemental sulfur).

To clean gases from sulfur dioxide, ammonia methods, lime method, manganese method are used.

To remove carbon monoxide, it is absorbed with copper-ammonia solutions.

The absorption process takes place at the interface, so the absorber should have the most developed contact surface between liquid and gas. According to the method of formation of this surface, absorbers can be divided into surface, packed and bubbling absorbers. Surface absorbers are inefficient and are used to absorb only highly soluble gases. The most common universal types are packed absorbers. They have a more developed contact surface, are simple in design, and reliable. They are widely used to purify gases from nitrogen oxides, SO2, CO2, CO, C12 and some other substances.

More compact, but also more complex in design, are bubbling absorbers, in which gas is bubbling through a layer of absorbent placed in a column on trays.

Even more perfect are foam absorbers. In these devices, the liquid interacting with the gas is brought to the state of foam, which provides a large contact surface between the absorbent and the gas, and, consequently, high cleaning efficiency.

In general, any mass transfer apparatus used in the chemical industry can be used as absorbers.

Adsorption - based on the selective extraction of impurities from the gas with the help of adsorbents - solids with a developed surface. Adsorbents must have a high absorption capacity, selectivity, thermal and mechanical stability, low resistance to gas flow, and easy release of the adsorbed substance. Active carbons, silica gels, synthetic and natural zeolites are mainly used as adsorbents.

active carbons are granular or powdered carbon adsorbents made using a special technology from coal, peat, polymers, coconut pits, wood and other raw materials. Gas and recuperative coals are used to clean gas-air emissions.

Gas coals are used to capture relatively poorly sorbed substances with a small concentration. If the concentration of the target component in the gas flow is significant, then in this case it is necessary to use recuperative coals.

silica gels are mineral adsorbents with a regular pore structure. They are produced in two types: lumpy (grains of irregular shape) and granular (grains of spherical or oval shape). Silica gels are solid vitreous or opaque grains 0.2 - 7.0 mm in size, bulk density 400 - 900 kg/m3. Silica gels are mainly used for drying air, gases and absorbing vapors of polar substances, such as methanol.

Close in properties to silica gels are alumogels (active alumina), which are produced by the industry in the form of cylindrical granules (2.5-5.0 mm in diameter and 3.0-7.0 mm high) and in the form of balls (with an average diameter of 3-4 mm).

Zeolites (molecular sieves) are synthetic aluminosilicate crystalline substances that have a high absorption capacity and high selectivity even at a very low content of a certain substance (adsorbent) in the gas.

By origin, zeolites are divided into natural and synthetic. Natural zeolites include such minerals as clinoptilolite, mordenite, erionite, chabazite, etc. Synthetic zeolites are characterized by an almost perfectly homogeneous microporous structure and the ability to selectively adsorb small molecules at low concentrations of the adsorbed component.

Adsorption is carried out mainly in batch adsorbers. The gas to be purified passes from top to bottom through the adsorbent bed. The process of absorption of the adsorbent begins with the upper layer of the sorbent, then the absorption front gradually moves down, capturing all its layers, and after the absorption capacity of all layers is exhausted, a "breakthrough" of the absorbed component occurs, indicating that the apparatus should be switched to the desorption process.

Desorption is usually carried out with live steam supplied from below, which removes the product absorbed by it (adsorbate) from the sorbent and enters the condenser, where the product is separated from water.

Batch adsorbers are simple and reliable. Their disadvantages are the periodicity of the process, low productivity and relatively low efficiency.

Continuous processes of adsorption purification of gases are carried out in a fluidized bed of adsorbent.

On fig. 15 shows a schematic diagram of adsorption gas purification with a circulating fluidized adsorbent.

Rice. 15. Schematic diagram of adsorption gas purification with a circulating fluidized adsorbent

The gas to be purified is fed into the adsorber 1 at such a rate that a fluidized bed of adsorbent 3 is formed and maintained in it, in which the target components are absorbed. Some part of the adsorbent is constantly lowered into the desorber 2 for regeneration, which is carried out by the displacing agent supplied to the bottom of the desorber. A fluidized bed of adsorbent is also maintained in the desorber, the adsorbate is extracted from it and removed from the system. The regenerated adsorbent is returned to the adsorber 1.

Fluidized bed adsorbers are complex in design and require precise process control.

Plan

Introduction

1. Methods for cleaning the atmosphere

2. Atmospheric bioremediation

Conclusion

Bibliography

Introduction

The problem of air purification in the area of ​​human life from a variety of pollution introduced by industry, from aerosols and bacteria is one of the most urgent problems. Treatises on the subject appear more and more often as a cry of impending catastrophe. This question acquired special significance after the invention of atomic and hydrogen bombs, because the atmospheric air became 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 spread over the entire atmospheric ocean for a short time and gradually fall to the earth's surface 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. Methods for cleaning the atmosphere

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

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

• Various wet methods.

Use of foam apparatus, scrubbers.

The following methods are used for gas purification:

• Adsorption.

That is, the absorption of a gas (in our case) component by a solid substance. Active carbons of various grades, zeolites, silica gel and other substances are used as adsorbents (absorbers). Adsorption is a reliable method that allows achieving high degrees of purification; moreover, it is a regenerative method, that is, the captured valuable component can be returned back to production. Applied periodic and continuous adsorption. In the first case, upon reaching the full adsorption capacity of the adsorbent, the gas flow is sent to another adsorber, and the adsorbent is regenerated - for this, stripping with live steam or hot gas is used. Then a valuable component can be obtained from the condensate (if live steam was used for regeneration); for this purpose, rectification, extraction or settling is used (the latter is possible in the case of mutual insolubility of water and a valuable component). With continuous adsorption, the adsorbent layer is constantly moving: part of it works for absorption, part is regenerated. This, of course, contributes to the attrition of the adsorbent. In the case of a sufficient cost of the regenerated component, the use of adsorption can be beneficial. For example, recently (in the spring of 2001), a calculation of the xylene recovery section 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, which annually fell into the atmosphere, will be returned to production.

• Absorption.

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

• thermal methods.

They are destructive. With sufficient calorific value of the exhaust gas, 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 blast gas in furnaces. The components resulting from thermal decomposition should 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 than 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 scheme:

C n H m + NO x + CO -----> CO 2 + H 2 O + N 2,

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

• Biological cleaning.

For the decomposition of pollutants, specially selected cultures of microorganisms are used. The method is characterized by low costs (few reagents are used and they are cheap, the main thing is that microorganisms are alive and reproduce themselves, using pollution as food), a sufficiently high degree of purification, but in our country, unlike the West, unfortunately, it has not yet received wide distribution. .

• Air ions - tiny liquid or solid particles, positively or negatively charged. The effect of negative (light air ions) is especially favorable. They are rightly called the vitamins of the air.

The mechanism of action of negative air ions on particles suspended in the air is as follows. Negative air ions charge (or recharge) the dust and microflora in the air to a certain potential, in proportion 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 in lengths the gravitational forces and the electric forces acting on fine dust, then one can easily see that the electric forces exceed the gravitational forces by 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 a given place. In the absence of an electric field and the diffuse movement of negative air ions between each moving air ion and the positively charged ground (floor), lines of force arise along which this air ion moves along with a particle of dust or a bacterium. Microorganisms that have settled on the surface of the floor, ceiling and walls can be periodically removed.

2. Atmospheric bioremediation

Bioremediation of the atmosphere- a set of methods for cleaning the atmosphere with the help of microorganisms.

• Cyanobacteria:

Researchers from the School of Engineering and Applied Sciences. Henry Samueli at the University of California at Los Angeles was genetically modified cyanobacteria (blue-green algae), which are now able to absorb CO2 and produce liquid fuel isobutane, which has great potential as an alternative to gasoline. The reaction takes place under the action of solar energy through photosynthesis. The new method has two advantages. First, the volume of greenhouse gases is reduced due to the utilization of CO2. Secondly, the resulting liquid fuel can be used in the current energy infrastructure, including in most cars. Using cyanobacteria Synechoccus elongatus, the researchers genetically increased the amount of the carbon dioxide-capturing enzyme. Then, genes from other microorganisms were introduced that allowed them to absorb CO2 and sunlight. As a result, the bacteria produce isobuteraldehyde gas.

• Biofiltration:

Biofiltration is the most economically advantageous and the most mature technology for cleaning exhaust gases. It can be successfully used to protect the atmosphere in food, tobacco, oil refining industries, wastewater treatment plants, as well as in agriculture.

Institute of Biochemistry. A.N. Bach RAS (INBI) - the leader of the Russian market in the field of biological methods for cleaning industrial ventilation emissions from vapors of volatile organic compounds (VOCs). It has developed a unique microbiological technology BIOREACTOR, which compares favorably with existing methods in terms of its technical parameters, capital and operating costs. The basis of BIOREACTOR technology is a consortium of natural immobilized microorganisms, specially selected and adapted for highly efficient (80-99%) degradation of various VOCs, for example, aromatic hydrocarbons, carbonyl, C1-, organochlorine and many other compounds. The BIOREACTOR is also effective in removing unpleasant odors. The method is based on the microbiological utilization of harmful organic substances with the formation of carbon dioxide and water by specially selected non-toxic strains of microorganisms (contaminant destructors), tested and registered in the prescribed manner. The method is implemented in a new highly efficient biofiltration plant that provides efficient continuous purification of exhaust gas-air emissions from various organic contaminants: phenol, xylene, toluene, formaldehyde, cyclohexane, white spirit, ethyl acetate, gasoline, butanol, etc. .

The installation includes:

Bioabsorber, - auxiliary equipment - circulation pump, valve,

Tank (100l) for brine, instrumentation, heat exchanger, tail fan.

The unit in working condition (with liquid) weighs approx. 6.0 t, has dimensions of 4 * 3.5 * 3 m (indoors) and an installed power of 4 kW.

Development Benefits. The biofiltration plant has the following main advantages:

High efficiency of cleaning gas-air emissions (from 92 to 99%),

Low operating energy costs up to 0.3 kW*h/m3,

High productivity in terms of the gas flow to be cleaned (10-20 thousand/m3*h),

Low aerodynamic resistance to gas flow (100-200 Pa),

Easy maintenance, long, reliable and safe operation.

The scientific and technical development has been worked out in an industrial version.

• Biological products MICROZYM(TM) ODOR TRIT:

Biological product - odor neutralizer, acting on the principle of neutralization of volatile compounds. The biological product is a complex of biological extracts of plant origin that enter into biochemical reactions with a wide range of volatile compounds from chemical ones: acetone, phenols, to organic ones: mercaptans, hydrogen sulfide, ammonia, and as a result of the reaction destroy volatile compounds and neutralize odors caused by these volatile compounds. The biological product does not mask the odor with the help of fragrances or fragrances, but destroys the odor by naturally cleaning the air from volatile compounds. The result of the action of the drug Odor Treat is an acceptable level of odor (intensity of 1-2 points) without foreign odors (flavors, fragrances).

Conclusion

At present, the problem of cleaning the atmosphere has become acute for mankind, due to various pollution by man, industry, and agriculture. For several decades, scientists have been coming up with more and more inventions and purification facilities, trying to come up with more economical ways to purify the atmosphere. One such method is bioremediation.

List of used literature

1. Neutralization of odors, purification of air from volatile compounds, deodorization of waste. [electronic resource], access mode: http://www.microzym.ru/odorcontrol

2. Industrial air ionization. [electronic resource], access mode: http://www.tehnoinfa.ru/ionizacija/21.html

3. Bacteria will cleanse the atmosphere of CO2. [electronic resource], access mode: http://gizmod.ru/2009/12/16/bakterii_ochistjat_atmosferu_ot_co2/

4. TECHNOLOGY FOR PROTECTION OF THE AIR BASIN (ATMOSPHERE) FROM POLLUTION. [electronic resource], access mode: http://zelenyshluz.narod.ru/articles/atmosfer.htm

2 Physical criteria and principles for setting standards (rationing)

3 Optimal and permissible values ​​of microclimate indicators at workplaces of industrial premises, depending on the category of work

4 Ionizing radiation. The nature of the impact, evaluation criteria.

5. Harmful substances, their classification and biological effects

1 Types of environmental pollution forecasts. Features of building short-term and long-term forecasts.

2. Principles of organization of the air pollution monitoring system. Types of control posts.

3. Organization of a monitoring system for surface water pollution. Principles of placement of observation points.

4. Principles of organizing a system for monitoring soil pollution in agricultural areas and urban areas

5. Methods and means of environmental control (contact, remote, biological).

1. The impact of economic sectors on the state of the environment

2. The impact of negative factors on humans and the technosphere

4. Characteristics of the main pollutants and the mechanism of their formation.

5. Characteristics of industrial technogenesis in one of the industries

2. Structure, governing bodies and modes of operation of the Russian emergency system (RSChS).

3. Engineering protection of the population.

4. General concepts of the sustainability of the functioning of economic objects in peacetime and wartime.

6. Psychological preparation of the population for actions in emergency situations.

1. Classification of the VPF.

3. Measures for the prevention of occupational diseases, poisoning.

4. Basic principles of hygienic classification of working conditions according to the degree of harmfulness, severity and intensity of the labor process.

5. Hygienic requirements for the organization of workplaces for PC users.

6. Industrial ventilation. Classification. Purification of air from dust and harmful substances.

1. Legal and regulatory framework for the state examination of working conditions in the Russian Federation

2. Bodies of supervision and control in the field of conditions and labor protection, industrial safety. Tasks and functions

3. The system of certification of work on labor protection in organizations (ssot) The main goal, objectives, functions.

4. Objects of certification in the System of certification of work on labor protection in organizations (ssot). Organizational structure of ssot. Functions of Certification Bodies (CB) and Testing Laboratories (IL).

5. The procedure for certification of work on labor protection in organizations.

6.Rules for accreditation of certification bodies and testing laboratories

1. Physical and chemical bases of combustion.

2. Theory of combustion: thermal, diffusion, chain.

3. Conditions for the emergence and development of combustion processes.

1. Basic concepts in the field of labor safety (hazard, safety, labor safety, risk, acceptable risk, ergonomics).

4. Explosions: types of explosions, classification.

3. Structure, main functions and rights of Rostekhnadzor.

4. General safety requirements when performing work of increased danger.

5. Ensuring electrical safety at the enterprise.

6. Organization of fire safety at the enterprise.

7. Certification of work on labor protection in the organization (certification procedure, safety sign).

8. Ensuring safety when working at height and climbing.

9. Safety requirements when performing loading and unloading operations.

10. General safety requirements for the operation of steam and hot water boilers, vessels under pressure.

1. Diagrams of cause-and-effect relationships as models of processes in the system

2. The main stages of system analysis

1.Goals, objectives and principles of environmental expertise.

2. Ecological requirements for placement, design, construction, reconstruction, commissioning of enterprises, structures and other facilities.

1. Legislation and regulatory and technical foundations of life safety

2. State requirements in the field of labor protection.

3. Federal law "on technical regulation".

4. The order of investigation and accounting of accidents at work.

5. Order of investigation of occupational diseases.

6. Insurance against accidents at work and occupational diseases.

7. The procedure for compensation for harm caused to the health of an employee at work.

8. Control system from the enterprise.

9. Instructions for from within the organization.

10. State supervision and control in the field from.

11. State system of management of labor protection and activities in emergency situations

12. Instruction and training of employees of the organization from.

13. Certification of workplaces for working conditions, Benefits and compensation for special working conditions.

1. Classification of accidents and disasters. Statistics of arias and catastrophes

2. Forecasting accidents and catastrophes

3. Fundamentals of risk theory. Risk analysis. risk management.

1. Principles and methods of management. Socio-psychological foundations of management.

2. State environmental management system

3.Economic evaluation of the effectiveness of environmental protection measures. The essence and process of environmental decision-making

4. Evaluation of the economic efficiency of the introduction of security tools

1. Classification and main applications of eco-bioprotective equipment and technologies

2. Chemical methods of air purification

3. Wastewater treatment systems

4. Principles and methods of noise protection of residential buildings, territories of residential buildings

2. Chemical methods of air purification

The main physical characteristic of atmospheric impurities is concentration - the mass of the substance in a unit of air volume at n.o. The concentration of impurities (mg / m3) determines the physical, chemical and other effects of substances on the environment and humans and serves as the main parameter in standardizing the content of impurities in the atmosphere. Methods for cleaning industrial emissions from gaseous and vaporous pollutants according to the nature of the flow of physical and chemical. processes are divided into five groups: absorption, chemisorption, adsorption, thermal neutralization, catalytic method.

Method absorption provides purification of gas emissions by separating the gas-air mixture into its constituent parts due to the absorption of one or more harmful impurities (absorbates) contained in this mixture by a liquid absorbent (absorbent) with the formation of a solution. Water is used as a liquid absorbent to remove gases such as ammonia, hydrogen chloride or hydrogen fluoride from process emissions. The purified gas is usually discharged into the atmosphere, and the liquid containing harmful soluble impurities is subjected to regeneration to separate harmful substances, after which it is returned to the apparatus or discharged as waste. Method chemisorption consists in the absorption of harmful gas and vapor impurities contained in gas emissions by solid or liquid absorbers with the formation of low-volatile or slightly soluble chemical compounds. This method is used at low concentrations of harmful impurities in the waste gases. It is widely used to clean gases from nitrogen oxides formed during fuel combustion, released from pickling baths. Purification is carried out using lime mortar as a chemisorbent. Adsorption the method is based on the absorption of harmful impurities contained in gases by the surface of solid porous bodies with an ultramicroscopic structure, called adsorbents. The greater the adsorbent porosity and the higher the impurity concentration, the more intense the adsorption process. Activated carbon, as well as activated alumina and silica gel are widely used as adsorbents. Chemical neutralization ensures the oxidation of toxic impurities in gas emissions to less toxic ones in the presence of free oxygen and high gas temperatures. This method is used for large volumes of gas emissions and high concentrations of impurities. catalytic method is designed to convert harmful impurities into substances that are harmless or less harmful to the environment using special substances - catalysts. Catalysts change the speed and direction of a chemical reaction. Platinum, palladium and other noble metals or their compounds are used as catalysts. Catalytic methods are widely used to remove harmful impurities contained in gas-air emissions from paint shops, as well as to neutralize vehicle exhaust gases.

3. Wastewater treatment systems

Wastewater treatment system. Water supply and sanitation systems in agglomerations are joint for residential and industrial. Zones. As a rule, large enterprises have their own water management system with a full technological cycle from water intake to its purification, neutralization and disposal of the solid phase. Water intake facilities take natural water from a surface water source. The pumping station of the first rise delivers e to the treatment plant through pressure pipelines. Here, the water is purified to drinking quality and from the reservoirs the pumping station of the second lift is supplied to the settlement, which usually has a ring water supply network. Water is used for drinking, household needs, watering streets and plantings, at local industry enterprises. The used water is diverted outside the city through a closed sewer network and is supplied by the main sewer pumping station to the city's wastewater treatment plant. Here, wastewater undergoes mechanical and biological treatment, disinfected and fed to biological ponds, where it is purified in natural conditions. After the ponds, the water in its qualities slightly differs from the water of a natural reservoir, it can be discharged into a river, lake, etc. The industrial enterprise consumes drinking and industrial water. Industrial water is most often used in water circulation cycles. Wastewater from industrial enterprises containing specific pollution, as well as rain and melt water from the territories of industrial sites, can be discharged into the sewerage system of a settlement and be subjected to biological treatment together with city wastewater after passing through local treatment facilities.

Wastewater treatment involves:

Purification from suspended and emulsified impurities (coarsely dispersed impurities: settling, filtering and filtration (hydrocyclones), flotation, clarification in suspended sediment, centrifugal filtration and settling; fine impurities: coagulation, flocculation, electrocoag-I, electrofloc-I);

Purification of dissolved impurities (mineral impurities - distillation, reverse osmosis freezing; organic impurities - extraction, adsorption, oxidation; gases - stripping, heating, reagent methods; undissolved and dissolved impurities - elimination, injection into wells, burial, injection into the depths of the seas, thermal destruction).

Sumps; aerotent(k) (water bubbling - air is supplied and impurities are oxidized); hydrocyclone.

Cleaning water is provided by the introduction of a trace. Technical solutions and events.

Mechanical cleaning - improvement of the hydrodynamic regimes of existing settling facilities; the use of mesh installations instead of settling tanks; pre-treatment of wastewater before clarification with coagulants.

Chemical cleaning - the use of more active coagulants; reuse of slags and chemical sludges. Water purification; isolation and utilization in the primary or secondary production of reaction products

Physico-chemical purification - expansion and improvement of the processes of hyper-, ultrafiltration, extraction, adsorption, ion exchange, which make it possible to isolate and return products to the main production, and use purified water after adjusting the composition to standard values ​​in circulating water supply; development of methods of preliminary physical. And chem. Impacts on treated waters; physical Processing (magnetization, ultrasonic, high-frequency), leading to a change in the physico-chemical characteristics and, accordingly, to a deeper degree of pollution from the water.

Biological treatment - application of the method of preliminary anaerobic preparation of sewage. Waters; the use of higher aquatic vegetation (eichornia water or water hyacinth, pistia, calamus) as an independent phytoreactor for the treatment of wastewater from agricultural complexes .; widespread use of biosorption methods. At present, the greatest technological and environmental difficulty is not wastewater treatment, but the problem of processing and recycling their solid phase.