1
Content
I. Structure and composition of the atmosphere
II. Air pollution:
- The quality of the atmosphere and the characteristics of its pollution;
The main chemical impurities that pollute the atmosphere.
- Basic methods of protecting the atmosphere from chemical impurities;
Classification of air purification systems and their parameters.
I. Structure and composition of the atmosphere
Atmosphere - This is the gaseous shell of the Earth, consisting of a mixture of various gases and extending to a height of more than 100 km. It has a layered structure, which includes a number of spheres and pauses located between them. The mass of the atmosphere is 5.91015 tons, the volume–
13.2-1020 m3. The atmosphere plays a huge role in all natural processes and, first of all, regulates the thermal regime and general climatic conditions, and also protects humanity from harmful cosmic radiation.
The main gas components of the atmosphere are nitrogen (78%), oxygen (21%), argon (0.9%) and carbon dioxide (0.03%). The gas composition of the atmosphere changes with altitude. In the ground layer, due to anthropogenic impacts, the amount of carbon dioxide increases and oxygen decreases. In some regions, as a result of economic activities in the atmosphere, the amount of methane, nitrogen oxides and other gases increases, causing such adverse phenomena as the greenhouse effect, destruction of the ozone layer, acid rain, and smog.
Atmospheric circulation affects the regime of rivers, soil and vegetation cover, as well as exogenous processes of relief formation. And finally the air–
a necessary condition for life on Earth.
The densest layer of air adjacent to the earth's surface is called the troposphere. Its thickness is: at middle latitudes 10-12 km, above sea level and at the poles 1-10 km, and at the equator 16-18 km.
Due to the uneven heating by solar energy, powerful vertical air currents are formed in the atmosphere, and in the ground layer there is instability in its temperature, relative humidity, pressure, etc. But at the same time, the temperature in the troposphere is stable in altitude and decreases by 0.6°C for every 100 m in the range from +40 to -50°C. The troposphere contains up to 80% of all moisture present in the atmosphere; clouds form in it and all types of precipitation are formed, which in essence are air purifiers of impurities.
Above the troposphere is the stratosphere, and between them is the tropopause. The thickness of the stratosphere is about 40 km, the air in it is charged, its humidity is low, while the air temperature from the boundary of the troposphere to an altitude of 30 km above sea level is constant (about -50°C), and then it gradually rises to +10°C at altitude 50 km. Under the influence of cosmic radiation and short-wave ultraviolet radiation from the Sun, gas molecules in the stratosphere are ionized, resulting in the formation of ozone. The ozone layer, located up to 40 km, plays a very important role, protecting all life on Earth from ultraviolet rays.
The stratopause separates the stratosphere from the overlying mesosphere, in which the amount of ozone decreases and the temperature at an altitude of about 80 km above sea level is -70 ° C. The sharp temperature difference between the stratosphere and mesosphere is explained by the presence of the ozone layer.
II. Air pollution
1) Quality of the atmosphere and features of its pollution
The quality of the atmosphere is understood as the totality of its properties that determine the degree of impact of physical, chemical and biological factors on people, flora and fauna, as well as on materials, structures and the environment as a whole. The quality of the atmosphere depends on its pollution, and the pollution itself can enter it from natural and anthropogenic sources. With the development of civilization, anthropogenic sources are increasingly predominant in atmospheric pollution.
Depending on the form of matter, pollution is divided into material (ingredient), energy (parametric) and material-energy. The first includes mechanical, chemical and biological contaminants, which are usually combined under the general concept of “impurities”, the second includes thermal, acoustic, electromagnetic and ionizing radiation, as well as radiation in the optical range; the third - radionuclides.
On a global scale, the greatest danger is posed by atmospheric pollution by impurities, since air acts as a mediator of pollution of all other natural objects, contributing to the spread of large masses of pollution over considerable distances. Industrial emissions carried through the air pollute the oceans, acidify soil and water, change the climate and destroy the ozone layer.
Atmospheric pollution is understood as the introduction of impurities into it that are not found in natural air or that change the ratio between the ingredients of the natural composition of air.
The size of the Earth's population and the rate of its growth are predetermining factors in increasing the intensity of pollution of all geospheres of the Earth, including the atmosphere, since with their increase the volumes and rates of everything that is mined, produced, consumed and sent to waste increase. The greatest air pollution is observed in cities where the usual pollutants are dust, sulfur dioxide, carbon monoxide, nitrogen dioxide, hydrogen sulfide, etc. In some cities, due to the characteristics of industrial production, the air contains specific harmful substances, such as sulfuric and hydrochloric acid , styrene, benzo(a)pyrene, carbon black, manganese, chromium, lead, methyl methacrylate. There are several hundred different air pollutants in cities.
Air pollution caused by newly created substances and compounds is of particular concern. WHO notes that out of 105 known elements of the periodic table, 90 are used in industrial practice, and on their basis over 500 new ones have been obtained chemical compounds, almost 10% of which are harmful or particularly harmful.
2) Basic chemical impurities,
air pollutants
There are natural impurities, i.e. caused by natural processes, and anthropogenic, i.e. arising as a result of human economic activity (Fig. 1). The level of atmospheric pollution with impurities from natural sources is background and has small deviations from the average level over time.
Rice. 1. Scheme of the processes of emissions of substances into the atmosphere and transformation
starting substances into products with subsequent precipitation
Anthropogenic pollution is distinguished by the variety of types of impurities and the numerous sources of their release. The most stable zones with high concentrations of pollutants occur in places of active human activity. It has been established that every 10-12 years the volume of global industrial production doubles, and this is accompanied by approximately the same increase in the volume of pollutants released into the environment. For a number of pollutants, the growth rates of their emissions are significantly higher than average. These include aerosols of heavy and rare metals, synthetic compounds that do not exist or form in nature, radioactive, bacteriological and other contaminants.
Impurities enter the atmosphere in the form of gases, vapors, liquid and solid particles. Gases and vapors form mixtures with air, and liquid and solid particles form aerosols (dispersed systems), which are divided into dust (particle sizes greater than 1 micron), smoke (solid particle sizes less than 1 micron) and fog (liquid particle size less than 10 microns ). Dust, in turn, can be coarse (particle size more than 50 microns), medium (50-10 microns) and fine (less than 10 microns). Depending on their size, liquid particles are divided into superfine fog (up to 0.5 microns), fine fog (0.5-3.0 microns), coarse fog (3-10 microns) and splashes (over 10 microns). Aerosols are often polydisperse, i.e. contain particles of different sizes.
The main chemical impurities that pollute the atmosphere are the following: carbon monoxide (CO), carbon dioxide (CO 2), sulfur dioxide (SO 2), nitrogen oxides, ozone, hydrocarbons, lead compounds, freons, industrial dusts.
The main sources of anthropogenic aerosol air pollution are thermal power plants (TPPs) consuming high-ash coal, enrichment plants, metallurgical, cement, magnesite and other plants. Aerosol particles from these sources are highly chemically diverse. Most often, compounds of silicon, calcium and carbon are found in their composition, less often–
metal oxides: iron, magnesium, manganese, zinc, copper, nickel, lead, antimony, bismuth, selenium, arsenic, beryllium, cadmium, chromium, cobalt, molybdenum, as well as asbestos. An even greater variety is characteristic of organic dust, including aliphatic and aromatic hydrocarbons and acid salts. It is formed during the combustion of residual petroleum products, during the pyrolysis process at oil refineries, petrochemical and other similar enterprises.
Constant sources of aerosol pollution include industrial dumps–
artificial embankments made of redeposited material, mainly overburden rocks formed during mining or from waste from processing industry enterprises, thermal power plants. The production of cement and other building materials is also a source of dust pollution.
Coal combustion, cement production and iron smelting produce a total dust emission into the atmosphere equal to 170 million tons/year.
A significant portion of aerosols are formed in the atmosphere through the interaction of solid and liquid particles with each other or with water vapor. Dangerous anthropogenic factors that contribute to a serious deterioration in the quality of the atmosphere include its contamination with radioactive dust. The residence time of small particles in the lower layer of the troposphere is on average several days, and in the upper–
20-40 days. As for particles that enter the stratosphere, they can stay there for up to a year, and sometimes more.
III. Methods and means of protecting the atmosphere
1) Basic methods of protecting the atmosphere
from chemical impurities
All known methods and means of protecting the atmosphere from chemical impurities can be combined into three groups.
The first group includes measures aimed at reducing emission power, i.e. reduction in the amount of emitted substance per unit time. The second group includes measures aimed at protecting the atmosphere by processing and neutralizing harmful emissions with special cleaning systems. The third group includes measures to regulate emissions both at individual enterprises and devices, and in the region as a whole.
To reduce the power of emissions of chemical impurities into the atmosphere, the following are most widely used:
- replacing less environmentally friendly fuels with environmentally friendly ones;
fuel combustion by special technology;
creation of closed production cycles.
Fuel combustion using a special technology (Fig. 2) is carried out either in a fluidized (fluidized) bed or by preliminary gasification.
Rice. 2. Scheme of a thermal power plant using afterburning
flue gases and sorbent injection: 1 - steam turbine; 2 - burner;
3 - boiler; 4 - electric precipitator; 5 - generator
To reduce the power of sulfur emissions, solid, powdered or liquid fuels are burned in a fluidized bed, which is formed from solid particles of ash, sand or other substances (inert or reactive). Solid particles are blown into passing gases, where they swirl, mix intensively and form a forced equilibrium flow, which generally has the properties of a liquid.
Coal and oil fuels undergo preliminary gasification, but in practice coal gasification is most often used. Since the produced and exhaust gases in power plants can be effectively purified, the concentrations of sulfur dioxide and particulate matter in their emissions will be minimal.
One of the promising ways to protect the atmosphere from chemical impurities is the introduction of closed production processes that minimize waste emitted into the atmosphere by reusing and consuming them, i.e., turning them into new products.
2) Classification of air purification systems and their parameters
Based on their state of aggregation, air pollutants are divided into dusts, mists and gaseous vapor impurities. Industrial emissions containing suspended solid or liquid particles are two-phase systems. The continuous phase in the system is gases, and the dispersed phase–
solid particles or liquid droplets.
etc.............
Emissions from industrial enterprises are characterized by a wide variety of dispersed composition and other physicochemical properties. In this regard, various methods for their purification and types of gas and dust collectors - devices designed to purify emissions from pollutants - have been developed.
Methods for cleaning industrial emissions from dust can be divided into two groups: dust collection methods "dry" method and dust collection methods "wet" method. Gas dust removal devices include: dust settling chambers, cyclones, porous filters, electric precipitators, scrubbers, etc.
The most common dry dust collection installations are cyclones various types.
They are used to capture flour and tobacco dust, ash formed when burning fuel in boiler units. The gas flow enters the cyclone through pipe 2 tangentially to the inner surface of housing 1 and performs a rotational-translational motion along the housing. Under the influence of centrifugal force, dust particles are thrown to the wall of the cyclone and, under the influence of gravity, fall into the dust collection hopper 4, and the purified gas exits through the outlet pipe 3. For normal operation of the cyclone, its tightness is necessary; if the cyclone is not sealed, then due to suction outside air, dust is carried out with a flow through the outlet pipe.
The tasks of cleaning gases from dust can be successfully solved by cylindrical (TsN-11, TsN-15, TsN-24, TsP-2) and conical (SK-TsN-34, SK-TsN-34M, SKD-TsN-33) cyclones, developed by the Research Institute for Industrial and Sanitary Gas Purification (NIIOGAZ). For normal operation, the excess pressure of gases entering the cyclones should not exceed 2500 Pa. In this case, in order to avoid condensation of liquid vapors, the temperature of the gas is selected to be 30 - 50 o C above the t dew point, and according to the conditions of structural strength - no higher than 400 o C. The productivity of the cyclone depends on its diameter, increasing with the growth of the latter. The cleaning efficiency of cyclones of the TsN series decreases with increasing angle of entry into the cyclone. As the particle size increases and the cyclone diameter decreases, the cleaning efficiency increases. Cylindrical cyclones are designed to collect dry dust from aspiration systems and are recommended for use for pre-cleaning of gases at the inlet of filters and electric precipitators. Cyclones TsN-15 are made of carbon or low-alloy steel. Canonical cyclones of the SK series, designed for cleaning gases from soot, have increased efficiency compared to cyclones of the CN type due to greater hydraulic resistance.
For purification of large masses of gases they are used battery cyclones, consisting of a larger number of parallel installed cyclone elements. Structurally, they are combined into one housing and have a common gas supply and outlet. Experience in operating battery cyclones has shown that the cleaning efficiency of such cyclones is somewhat lower than the efficiency of individual elements due to the flow of gases between the cyclone elements. The domestic industry produces battery cyclones such as BC-2, BTsR-150u, etc.
Rotary Dust collectors are centrifugal devices that, while moving air, clean it from dust fractions larger than 5 microns. They are very compact, because... the fan and dust collector are usually combined in one unit. As a result, during the installation and operation of such machines, no additional space is required to accommodate special dust collection devices when moving a dusty flow with an ordinary fan.
The design diagram of the simplest rotary type dust collector is shown in the figure. When the fan wheel 1 operates, dust particles, due to centrifugal forces, are thrown towards the wall of the spiral casing 2 and move along it in the direction of the exhaust hole 3. The dust-enriched gas is discharged through a special dust receiving hole 3 into the dust bin, and the purified gas enters the exhaust pipe 4 .
To increase the efficiency of dust collectors of this design, it is necessary to increase the portable speed of the purified flow in the spiral casing, but this leads to a sharp increase in the hydraulic resistance of the device, or to reduce the radius of curvature of the casing spiral, but this reduces its productivity. Such machines provide a fairly high efficiency of air purification while capturing relatively large dust particles - over 20 - 40 microns.
More promising rotary dust separators, designed to clean air from particles > 5 µm in size, are counter-flow rotary dust separators (RPD). The dust separator consists of a hollow rotor 2 with a perforated surface built into the casing 1 and a fan wheel 3. The rotor and fan wheel are mounted on a common shaft. When the dust separator operates, dusty air enters the housing, where it swirls around the rotor. As a result of the rotation of the dust flow, centrifugal forces arise, under the influence of which suspended dust particles tend to separate from it in the radial direction. However, aerodynamic drag forces act on these particles in the opposite direction. Particles whose centrifugal force is greater than the aerodynamic drag force are thrown towards the walls of the casing and enter hopper 4. Purified air is thrown out through the perforation of the rotor using a fan.
The efficiency of PRP cleaning depends on the selected ratio of centrifugal and aerodynamic forces and theoretically can reach 1.
A comparison of PDPs with cyclones demonstrates the advantages of rotary dust collectors. So, overall dimensions cyclone by 3 - 4 times, and the specific energy consumption for purifying 1000 m 3 of gas is 20 - 40% higher than that of the PRP, all other things being equal. However widespread Rotary dust collectors were not used due to the relative complexity of the design and operating process compared to other devices for dry gas purification from mechanical contaminants.
To separate the gas flow into purified gas and dust-enriched gas, use louvered dust separator On the louvre grille 1, the gas flow with flow rate Q is divided into two flow paths with flow rates Q 1 and Q 2. Usually Q 1 = (0.8-0.9)Q, and Q 2 = (0.1-0.2)Q. The separation of dust particles from the main gas flow on the louvre grille occurs under the influence of inertial forces that arise when the gas flow turns at the entrance to the louvre grille, as well as due to the effect of reflection of particles from the surface of the grille upon impact. The dust-enriched gas flow after the louvered grille is directed to a cyclone, where it is cleaned of particles, and is reintroduced into the pipeline behind the louvered grille. Louvre dust separators are simple in design and are well arranged in gas ducts, providing a cleaning efficiency of 0.8 or more for particles larger than 20 microns. They are used to clean flue gases from coarse dust at temperatures up to 450 – 600 o C.
Electric precipitator. Electrical cleaning is one of the most advanced types of gas purification from suspended particles of dust and fog. This process is based on impact ionization of gas in the corona discharge zone, transfer of ion charge to impurity particles and deposition of the latter on collecting and corona electrodes. Precipitation electrodes 2 are connected to the positive pole of the rectifier 4 and grounded, and the corona electrodes are connected to the negative pole. The particles entering the electrostatic precipitator are connected to the positive pole of the rectifier 4 and are grounded, and the corona electrodes are charged with ana impurity ions. Usually they already have a small charge obtained due to friction against the walls of pipelines and equipment. Thus, negatively charged particles move towards the collection electrode, and positively charged particles settle on the negative discharge electrode.
Filters widely used for fine purification of gas emissions from impurities. The filtration process consists of retaining impurity particles on porous partitions as they move through them. The filter consists of housing 1, separated by a porous partition (filter-
element) 2 into two cavities. Contaminated gases enter the filter and are cleaned as they pass through the filter element. Impurity particles settle on the inlet part of the porous partition and are retained in the pores, forming layer 3 on the surface of the partition.
According to the type of partitions, filters are: - with granular layers (stationary, loosely poured granular materials) consisting of grains of various shapes, used to purify gases from large impurities. To purify gases from dust of mechanical origin (from crushers, dryers, mills, etc.), gravel filters are often used. Such filters are cheap, easy to operate and provide high cleaning efficiency (up to 0.99) of gases from coarse dust.
With flexible porous partitions (fabrics, felts, sponge rubber, polyurethane foam, etc.);
With semi-rigid porous partitions (knitted and woven mesh, pressed spirals and shavings, etc.);
With rigid porous partitions (porous ceramics, porous metals, etc.).
The most widely used in industry for dry purification of gas emissions from impurities are bag filters. The required number of hoses 1 is installed in the filter housing 2, into the internal cavity of which dusty gas is supplied from the incoming pipe 5. Due to sieve and other effects, particles of contaminants settle in the pile and form a dust layer on the inner surface of the hoses. Purified air leaves the filter through pipe 3. When the maximum permissible pressure drop across the filter is reached, it is disconnected from the system and regeneration is carried out by shaking the hoses and blowing them with compressed gas. Regeneration is carried out by a special device 4.
Dust collectors of various types, including electric precipitators, are used at elevated concentrations of impurities in the air. Filters are used for fine air purification with impurity concentrations of no more than 50 mg/m 3; if the required fine air purification occurs at high initial concentrations of impurities, then the purification is carried out in a system of series-connected dust collectors and filters.
Devices wet cleaning gases are widespread, because are characterized by high cleaning efficiency from fine dust with d h ≥ (0.3-1.0) microns, as well as the ability to clean hot and explosive gases from dust. However, wet dust collectors have a number of disadvantages that limit their scope of application: formations during the cleaning process sludge, which requires special systems for its processing; removal of moisture into the atmosphere and formation of deposits in exhaust flues when gases are cooled to the dew point temperature; the need to create circulating systems for supplying water to the dust collector.
Wet cleaning devices operate on the principle of deposition of dust particles onto the surface of either liquid droplets or a liquid film. The deposition of dust particles onto the liquid occurs under the influence of inertial forces and Brownian motion.
Among wet cleaning devices with the deposition of dust particles on the surface of droplets, in practice they are more applicable Venturi scrubbers. The main part of the scrubber is Venturi nozzle 2, into the confuser part of which a dusty gas flow is supplied and liquid is supplied through centrifugal nozzles 1 for irrigation. In the confuser part of the nozzle, the gas accelerates from an input speed of 15-20 m/s to a speed in the narrow section of the nozzle of 30-200 m/s, and in the diffuser part of the nozzle the flow is decelerated to a speed of 15-20 m/s and fed into the droplet eliminator 3. The droplet eliminator is usually made in the form of a direct-flow cyclone. Venturi scrubbers provide high efficiency in cleaning aerosols with an average particle size of 1-2 microns with an initial impurity concentration of up to 100 g/m 3 .
Wet dust collectors include bubbling foam dust collectors with failure and overflow grilles. In such devices, the gas for cleaning enters under the grid 3, passes through the holes in the grid and, passing through a layer of liquid or foam 2, under pressure, is cleaned of part of the dust due to the deposition of particles on the inner surface of gas bubbles. The operating mode of the devices depends on the speed of air supply under the grille. At speeds up to 1 m/s, a bubbling mode of operation of the apparatus is observed. A further increase in gas velocity in the apparatus body from 1 to 2-2.5 m/s is accompanied by the appearance of a foam layer above the liquid, which leads to an increase in the efficiency of gas purification and splash removal from the apparatus. Modern bubbling-foam devices provide an efficiency of gas purification from fine dust of ≈ 0.95-0.96 at a specific water consumption of 0.4-0.5 l/m 3 . But these devices are very sensitive to uneven gas supply under the failure grates, which leads to local blowing off of the liquid film from the grate. Grates are prone to clogging.
Methods for purifying industrial emissions from gaseous pollutants, based on the nature of the physical and chemical processes, are divided into five main groups: washing emissions with solvents of impurities (absorption); washing emissions with solutions of reagents that bind impurities chemically (chemisorption); absorption of gaseous impurities by solid active substances (adsorption); thermal neutralization of waste gases and the use of catalytic conversion.
Absorption method. In gas emissions purification technology, the absorption process is often called scrubber process. Purification of gas emissions by the absorption method involves separating a gas-air mixture into its component parts by absorbing one or more gas components (absorbates) of this mixture with a liquid absorber (absorbent) to form a solution.
The driving force here is the concentration gradient at the gas-liquid phase boundary. The component of the gas-air mixture (absorbate) dissolved in the liquid penetrates into the internal layers of the absorbent due to diffusion. The process proceeds faster, the larger the phase interface, flow turbulence and diffusion coefficients, i.e. in the process of designing absorbers special attention attention should be paid to organizing the contact of the gas flow with the liquid solvent and selecting the absorbing liquid (absorbent).
The decisive condition when choosing an absorbent is the solubility of the extracted component in it and its dependence on temperature and pressure. If the solubility of gases at 0°C and a partial pressure of 101.3 kPa is hundreds of grams per 1 kg of solvent, then such gases are called highly soluble.
The organization of contact of the gas flow with the liquid solvent is carried out either by passing the gas through a packed column, or by spraying the liquid, or by bubbling the gas through a layer of absorbent liquid. Depending on the implemented method of gas-liquid contact, the following are distinguished: packed towers: nozzle and centrifugal scrubbers, Venturi scrubbers; bubbling foam and other scrubbers.
General device counterflow packed tower is shown in the figure. Contaminated gas enters bottom part tower, and the cleaned leaves it through the top, where with the help of one or more sprinklers 2
A clean absorbent is introduced, and the waste solution is taken from the bottom. The purified gas is usually released into the atmosphere. 
The liquid leaving the absorber is regenerated, desorbing the contaminant, and returned to the process or removed as a waste (by-product). The chemically inert nozzle 1, filling the internal cavity of the column, is designed to increase the surface of the liquid spreading over it in the form of a film. As a nozzle, bodies of different geometric shapes are used, each of which is characterized by its own specific surface area and resistance to the movement of the gas flow.
The choice of purification method is determined by technical and economic calculations and depends on: the concentration of the pollutant in the gas being purified and the required degree of purification, depending on the background air pollution in a given region; volumes of purified gases and their temperatures; the presence of accompanying gaseous impurities and dust; the need for certain recycling products and the availability of the required sorbent; the size of the areas available for the construction of a gas treatment plant; availability of the necessary catalyst, natural gas, etc.
When choosing equipment for new technological processes, as well as when reconstructing existing gas purification installations, it is necessary to be guided by the following requirements: maximum efficiency of the purification process in a wide range of load characteristics at low energy costs; simplicity of design and maintenance; compactness and the possibility of manufacturing devices or individual units from polymer materials; possibility of working with circulation irrigation or self-irrigation. The main principle that should be the basis for the design of treatment facilities is the maximum possible retention harmful substances, heat and their return to the technological process.
Task No. 2: At the grain processing enterprise, equipment is installed that is a source of grain dust. To remove it from working area, the equipment is equipped with an aspiration system. In order to clean the air before releasing it into the atmosphere, a dust collection unit consisting of a single or battery cyclone is used.
Determine: 1. Maximum permissible emission of grain dust.
2. Select the design of a dust collection installation consisting of cyclones from the Research Institute for Industrial and Sanitary Gas Purification (NII OGAZ), determine its efficiency according to the schedule and calculate the dust concentration at the inlet and outlet of the cyclone.
Emission source height H = 15 m,
The speed of release of the gas-air mixture from the source w o = 6 m/s,
Source mouth diameter D = 0.5 m,
Release temperature Тg = 25 о С,
Ambient air temperature Тв = _ -14 о С,
Average dust particle size d h = 4 µm,
MPC of grain dust = 0.5 mg/m 3,
Background concentration of grain dust C f = 0.1 mg/m 3,
The company is located in Moscow region,
The terrain is calm.
Solution.1. Determine the maximum permissible value of grain dust:
M pdv = 
, mg/m 3
from the definition of the maximum permissible value we have: C m = C maximum permissible concentration – C f = 0.5-0.1 = 0.4 mg/m 3 ,
Gas-air mixture flow rate V 1 = 
,
DT = Тg – Тв = 25 – (-14) = 39 о С,
determine the emission parameters: f =1000 
, Then
m = 1/(0.67+0.1 + 0.34) = 1/(0.67 + 0.1 +0.34) = 0.8.
V m = 0.65 
, Then
n = 0.532V m 2 – 2.13V m + 3.13= 0.532×0.94 2 – 2.13×0.94 + 3.13 = 1.59, and
M pdv = 
g/s.
2. Selection of a treatment plant and determination of its parameters.
a) The selection of a dust collection unit is made according to catalogs and tables (“Ventilation, air conditioning and air purification at food industry enterprises” E.A. Shtokman, V.A. Shilov, E.E. Novgorodsky et al., M., 1997). The selection criterion is the performance of the cyclone, i.e. the flow rate of the gas-air mixture at which the cyclone has maximum efficiency. To solve the problem, we will use the table:
The first line provides data for a single cyclone, the second - for a battery cyclone.
If the calculated productivity is in the range between the table values, then choose the design of the dust collection installation with the next higher productivity.
We determine the hourly productivity of the treatment plant:
V h = V 1 × 3600 = 1.18 × 3600 = 4250 m 3 / h
According to the table, according to the nearest larger value V h = 4500 m 3 / h, we select a dust collection unit in the form of a single cyclone TsN-11 with a diameter of 800 mm.
b) According to the graph in Fig. 1 of the appendix, the efficiency of the dust collection installation with an average diameter of dust particles of 4 microns is hp = 70%.
c) Determine the dust concentration at the exit from the cyclone (at the mouth of the source):
From out = 
The maximum concentration of dust in the purified air Cin is determined:
C in = 
.
If the actual value of Cin is more than 1695 mg/m 3, then the dust collection installation will not give the desired effect. In this case, more advanced cleaning methods must be used.
3. Determine the pollution indicator
P = 
,
where M is the mass of pollutant emission, g/s,
The pollution indicator shows how much clean air is needed to “dissolve” the pollutant emitted by the source per unit of time to the maximum permissible concentration, taking into account the background concentration.
P = 
.
The annual pollution indicator is the total pollution indicator. To determine it, we find the mass of grain dust emissions per year:
M year = 3.6 × M MPE × T × d ×10 -3 = 3.6 × 0.6 × 8 × 250 × 10 -3 = 4.32 t/year, then
åР = 
.
The pollution indicator is necessary for comparative assessment various sources emissions.
For comparison, let’s calculate åP for sulfur dioxide from the previous problem for the same period of time:
M year = 3.6 × M MPE × T × d × 10 -3 = 3.6 × 0.71 × 8 × 250 × 10 -3 = 5.11 t/year, then
åР = 
And in conclusion, it is necessary to draw a sketch of the selected cyclone according to the dimensions given in the appendix, on an arbitrary scale.
Pollution control environment. Payment for environmental damage.
When calculating the amount of pollutant, i.e. ejection mass is determined by two values: gross emissions (t/year) and maximum single emissions (g/s). The gross emission value is used for a general assessment of air pollution by a given source or group of sources, and is also the basis for calculating payments for environmental pollution.
The maximum single emission allows us to assess the state of atmospheric air pollution in at the moment time and is the initial value for calculating the maximum surface concentration of a pollutant and its dispersion in the atmosphere.
When developing measures to reduce emissions of pollutants into the atmosphere, it is necessary to know what contribution each source makes to the overall picture of air pollution in the area where the enterprise is located.
TSV – temporarily coordinated release. If at a given enterprise or group of enterprises located in the same area (Normal Physics is large), the MPE value for objective reasons cannot be achieved at the present time, then, in agreement with the body exercising state control over the protection of the atmosphere from pollution, the user of natural resources is assigned an ELV with adoption of a gradual reduction of emissions to MPE values and the development of specific measures for this.
Fees are charged for the following types harmful effects on the natural environment: - release of pollutants into the atmosphere from stationary and mobile sources;
Discharge of pollutants into surface and underground water bodies;
Waste disposal;
Dr. types of harmful effects (noise, vibration, electromagnetic and radiation effects, etc.).
Two types of basic payment standards have been established:
a) for emissions, discharges of pollutants and waste disposal within acceptable standards
b) for emissions, discharges of pollutants and waste disposal within established limits (temporarily agreed standards).
Basic payment standards are established for each pollutant ingredient (waste), taking into account their degree of danger to the environment and public health.
The rates of payment for pollution of hazardous pollutants are indicated in the Decree of the Government of the Russian Federation of June 12, 2003. No. 344 “On payment standards for emissions of pollutants into the atmospheric air from stationary and mobile sources, discharges of pollutants into surface and underground water bodies, disposal of industrial and consumer waste” for 1 ton in rubles:
Payment for emissions of pollutants that do not exceed the standards established for the user of natural resources:
П = С Н × М Ф, with М Ф £ М Н,
where М Ф – actual emission of pollutant, t/year;
МН – maximum permissible standard for this pollutant;
С Н – rate of payment for the emission of 1 ton of a given pollutant within the limits of permissible emission standards, rubles/t.
Payment for emissions of pollutants within established emission limits:
P = S L (M F – M N) + S N M N, with M N< М Ф < М Л, где
S L – rate of payment for the emission of 1 ton of pollutant within the established emission limits, rub/t;
M L – established emission limit for a given pollutant, t/year.
Payment for excess emissions of pollutants:
P = 5× S L (M F – M L) + S L (M L – M N) + S N × M N, with M F > M L.
Payment for the emission of pollutants when the user of natural resources has not established standards for the emission of pollutants or a fine:
P = 5 × S L × M F
Payments for maximum permissible emissions, pollutant discharges, waste disposal are made at the expense of the cost of products (works, services), and for exceeding them - at the expense of the profit remaining at the disposal of the natural resource user.
Payments for environmental pollution are received:
19% to the Federal Budget,
81% to the budget of the subject of the Federation.
Task No. 3. “Calculation of technological emissions and payment for environmental pollution natural environment using the example of a bakery"
The bulk of pollutants, such as ethyl alcohol, acetic acid, acetaldehyde, are formed in baking chambers, from where they are removed through exhaust ducts due to natural draft or released into the atmosphere through metal pipes or shafts with a height of at least 10 - 15 m. Emissions of flour dust mainly occur in flour warehouses. Oxides of nitrogen and carbon are formed when natural gas is burned in baking chambers.
Initial data:
1. Annual production of the Moscow bakery is 20,000 tons/year of bakery products, incl. bakery products from wheat flour– 8,000 t/year, bakery products from rye flour – 5,000 t/year, bakery products from mixed rolls – 7,000 t/year.
2. Roll recipe: 30% - wheat flour and 70% - rye flour
3. The storage condition for flour is bulk.
4. Fuel in furnaces and boilers is natural gas.
I. Technological emissions from the bakery.
II. Payment for air pollution, if the maximum permissible limit is:
Ethyl alcohol – 21t/year,
Acetic acid – 1.5 t/year (VSV – 2.6 t/year),
Acetaldehyde – 1 t/year,
Flour dust – 0.5 t/year,
Nitrogen oxides – 6.2 t/year,
Carbon oxides – 6 t/year.
1. In accordance with the methodology of the All-Russian Research Institute of HP, technological emissions when baking bakery products are determined by the method of specific indicators:
M = B × m, where
M – amount of pollutant emissions in kg per unit of time,
B – production output in tons for the same period of time,
m – specific indicator of pollutant emissions per unit of output, kg/t.
Specific emissions of pollutants in kg/t of finished products.
1. Ethyl alcohol: bakery products made from wheat flour – 1.1 kg/t,
bakery products made from rye flour – 0.98 kg/t.
2. Acetic acid: bakery products made from wheat flour – 0.1 kg/t,
bakery products made from rye flour – 0.2 kg/t.
3. Acetaldehyde – 0.04 kg/t.
4. Flour dust – 0.024 kg/t (for bulk storage of flour), 0.043 kg/t (for containerized storage of flour).
5. Nitrogen oxides - 0.31 kg/t.
6. Carbon oxides – 0.3 kg/t.
I. Calculation of process emissions:
1. Ethyl alcohol:
M 1 = 8000 × 1.1 = 8800 kg/year;
M 2 = 5000 × 0.98 = 4900 kg/year;
M 3 = 7000(1.1×0.3+0.98×0.7) = 7133 kg/year;
total emission M = M 1 + M 2 + M 3 = 8800 + 4900 + 7133 = 20913 kg/year.
2. Acetic acid:
Bakery products made from wheat flour
M 1 = 8000 × 0.1 = 800 kg/year;
Bakery products made from rye flour
M 2 = 5000 × 0.2 = 1000 kg/year;
Mixed roll baked goods
M 3 = 7000(0.1×0.3+0.2×0.7) = 1190 kg/year,
total emission M = M 1 + M 2 + M 3 = 800 + 1000 + 1190 = 2990 kg/year.
3. Acetaldehyde M = 20000 × 0.04 = 800 kg/year.
4. Flour dust M = 20000 × 0.024 = 480 kg/year.
5. Nitrogen oxides M = 20000 × 0.31 = 6200 kg/year.
6. Carbon oxides M = 20000 × 0.3 = 6000 kg/year.
II. Calculation of fees for pollution of hazardous pollutants.
1. Ethyl alcohol: M H = 21 t/year, M F = 20.913 t/year Þ P = S H × M f = 0.4 × 20.913 = 8.365 rub.
2. Acetic acid: M H = 1.5 t/year, M L = 2.6 t/year, M F = 2.99 t/year Þ P = 5 S L (M F – M L) + S L ( M L – M N)+S N × M N =
5 × 175 × (2.99-2.6) + 175 × (2.6 – 1.5) + 35 × 1.5 = 586.25 rub.
3. Acetic aldehyde: M H = 1 t/year, M F = 0.8 t/year Þ P = S H × M F = 68 × 0.8 = 54.4 rub.
4. Flour dust: M N = 0.5 t/year, M F = 0.48 t/year Þ P = S N × M F = 13.7 × 0.48 = 6.576 rubles.
5. Nitrogen oxide: МН = 6.2 t/year, МФ = 6.2 t/year Þ P = СН × МФ = 35 × 6.2 = 217 rub.
6. Carbon oxide: M H = 6 t/year, M F = 6 t/year Þ
P = S N × M F = 0.6 × 6 = 3.6 rub.
Coefficient taking into account environmental factors, for the Central region of the Russian Federation = 1.9 for atmospheric air, for the city the coefficient is 1.2.
åП = 876.191 · 1.9 · 1.2 = 1997.72 rubles
CONTROL TASKS.
Task 1
| Option No. | Boiler room productivity Q about, MJ/hour | Source height H, m | Mouth diameter D, m | Background concentration of SO 2 C f, mg/m 3 |
| 0,59 | 0,004 | |||
| 0,59 | 0,005 | |||
| 0,6 | 0,006 | |||
| 0,61 | 0,007 | |||
| 0,62 | 0,008 | |||
| 0,63 | 0,004 | |||
| 0,64 | 0,005 | |||
| 0,65 | 0,006 | |||
| 0,66 | 0,007 | |||
| 0,67 | 0,008 | |||
| 0,68 | 0,004 | |||
| 0,69 | 0,005 | |||
| 0,7 | 0,006 | |||
| 0,71 | 0,007 | |||
| 0,72 | 0,008 | |||
| 0,73 | 0,004 | |||
| 0,74 | 0,005 | |||
| 0,75 | 0,006 | |||
| 0,76 | 0,007 | |||
| 0,77 | 0,008 | |||
| 0,78 | 0,004 | |||
| 0,79 | 0,005 | |||
| 0,8 | 0,006 | |||
| 0,81 | 0,007 | |||
| 0,82 | 0,008 | |||
| 0,83 | 0,004 | |||
| 0,84 | 0,005 | |||
| 0,85 | 0,006 | |||
| 0,86 | 0,007 | |||
| 0,87 | 0,004 | |||
| 0,88 | 0,005 | |||
| 0,89 | 0,006 |
Lecture 11. Collective means of human protection at work
Surrounding a person atmospheric air is constantly exposed to pollution. The air of the production premises is polluted by emissions from technological equipment or during technological processes without localization of waste substances. Ventilation air removed from the premises can cause air pollution in industrial sites and populated areas. In addition, the air of industrial sites and populated areas is polluted by technological emissions from workshops, emissions from thermal power plants, and vehicles.
The air in residential premises is polluted by combustion products of natural gas and other types of fuel, solvent fumes, detergents, wood-shaving structures, etc., as well as toxic substances entering residential premises with the supply of ventilation air. In the summer, at an average outside temperature of 20 0 C, about 90% of outdoor air impurities penetrate into residential premises, during the transition period at t = 25 0 C - 40%, in winter time– up to 30%.
Sources of air pollution in industrial premises are:
1. In foundries, these are dust and gas emissions from cupola furnaces, electric arc and induction furnaces, areas for storing and processing charge (casting components) and molding materials, areas for knocking out and cleaning castings.
2. In forging and pressing shops - dust, carbon monoxide, sulfur oxide and other harmful substances.
3. In galvanic shops, these are harmful substances in the form of fine mist, vapors and gases. The most intensively harmful substances are released in the processes of acid and alkaline etching. When applying galvanic coatings, it is hydrogen fluoride, etc.
4. When machining metals on machines - dust, fog, oils and emulsions.
5. In areas of welding and cutting metals - dust, gases (hydrogen fluoride, etc.).
6. In soldering and tinning areas there are toxic gases (carbon monoxide, hydrogen fluoride), aerosols (lead and its compounds).
7. In paint shops - toxic substances during degreasing and aerosols from varnish and paints.
8. From the operation of various power plants (ICE, etc.)
They are used to remove and purify air in industrial premises. various systems purification and localization of harmful substances.
1. Removal of toxic substances from premises by general ventilation;
2. Localization of toxic substances in the area of their formation local ventilation with the purification of contaminated air in special devices and its return to the production or domestic premises, if the air after cleaning in the device corresponds regulatory requirements to the supply air;
3. Localization of toxic substances in the area of their formation by local ventilation, purification of polluted air in special devices, release and dispersion in the atmosphere.
Figure 3.
1 – sources of toxic substances;
2 – devices for localizing toxic substances (local suction);
3 – cleaning apparatus.
4. Purification of technological gas emissions in special devices; in some cases, the exhaust gases are diluted with atmospheric air before being released;
5. Purification of exhaust gases from power plants (for example, internal combustion engines) in special units, and release into the atmosphere or production area (mines, quarries, warehouses, etc.).
In cases where actual emissions exceed the maximum permissible emissions (MPE), taking into account existing atmospheric pollution or, more precisely, its components already existing in the atmosphere, it is necessary to use devices for purifying gases and impurities in the emission system.
Figure 4.
1–source of toxic substances and process gases;
2 – cleaning apparatus;
3 – pipe for dispersing emissions;
4 – device (blower for supplying air to dilute emissions).
Devices for cleaning ventilation and process emissions into the atmosphere are divided into:
Dust collectors (dry, electric, wet filters);
Mist eliminators (low-speed and high-speed);
Devices for collecting vapors and gases (absorption, chemisorption, absorption and neutrolyzers);
Multi-stage cleaning devices (dust and gas collectors, mists and solid impurities collectors, multi-stage dust collectors).
Dry dust collectors – cyclones – are widely used for purifying gases from particles.
The most advanced way to purify gases from dust and mists suspended in them are electric precipitators.
Various filters are used for fine purification of gases from particles and droplets.
Wet gas cleaning devices are widely used and are used for cleaning fine dust with d 2 ≥ 0.3 µm, as well as for cleaning heated and explosive gases from dust.
To clean the air from mists of acids, alkalis, oils and other liquids, fiber filters and mist eliminators are used.
The absorption method - purification of gas emissions from gases and vapors - is based on the absorption of the latter by liquid. The decisive condition for the application of this method is the solubility of gases and vapors in water. This could be, for example, technological emissions of ammonia, chlorine or hydrogen fluoride.
The operation of chemosorbers is based on the absorption of gases and vapors by liquid or solid absorbers with the formation of poorly soluble and low-volatile chemical compounds (gases from nitrogen oxides and acid vapors).
The absorption method is based on the ability of some finely dispersed solids as an absorbent (activated alumina, silica gel, activated aluminum oxide, etc.) to extract and concentrate individual components of the gas mixture emissions on their surface. They are used to clean the air from vapors of solvents, ether, acetone, various hydrocarbons, etc. Absorbents are widely used in respirators and gas masks.
Thermal neutralization is based on the ability of flammable gases and vapors included in ventilation and process emissions to burn to form less toxic substances.
The atmosphere is one of necessary conditions the origin and existence of life on Earth. It participates in shaping the climate on the planet, regulates its thermal regime, and contributes to the redistribution of heat near the surface. Part of the radiant energy of the Sun is absorbed by the atmosphere, and the rest of the energy, reaching the surface of the Earth, partly goes into the soil, water bodies, and partly is reflected into the atmosphere.
In its current state, the atmosphere has existed for hundreds of millions of years; all living things are adapted to its strictly defined composition. The gas shell protects living organisms from harmful ultraviolet, x-rays and cosmic rays. The atmosphere protects the Earth from falling meteorites. The sun's rays are distributed and scattered in the atmosphere, which creates uniform illumination. It is the medium where sound travels. Due to the action of gravitational forces, the atmosphere does not dissipate in outer space, but surrounds the Earth and rotates with it.
The main (by mass) component of air is nitrogen. In the lower layers of the atmosphere its content is 78.09%. The most active atmospheric gas in biosphere processes is oxygen. Its content in the atmosphere is about 20.94%. An important component of the atmosphere is carbon dioxide (CO 2), which makes up 0.03% of its volume. It significantly influences the weather and climate on Earth. The carbon dioxide content in the atmosphere is not constant. It enters the atmosphere from volcanoes, hot springs, through the respiration of humans and animals, during forest fires, is consumed by plants, and is highly soluble in water. The amount of dissolved carbon dioxide in the ocean is 1.3 10 14 tons.
The atmosphere contains carbon monoxide (CO) in small quantities. There are also few inert gases such as argon, gel krypton, and xenon. Of these, the most is argon - 0.934%. The atmosphere also contains hydrogen and methane. Inert gases enter the atmosphere during the continuous natural radioactive decay of uranium, thorium, and radon.
Ozone is found in low concentrations in the upper layers of the stratosphere. Therefore, this part of the atmosphere is called the ozone shield. The total ozone content in the atmosphere is small - 2.10%, but it reflects up to 5% of ultraviolet rays, which protects living organisms from their destructive effects. Delaying up to 20% infrared radiation reaching the Earth, ozone increases the warming effect of the atmosphere. The formation of the ozone screen is influenced by the presence in the stratosphere of chlorine, nitrogen oxides, hydrogen, fluorine, bromine, and methane, which provide photochemical reactions of ozone destruction.
In addition to gases, the atmosphere contains water and aerosols. In the atmosphere, water exists in solid (ice, snow), liquid (drops) and gaseous (steam) states. When water vapor condenses, clouds form. Complete renewal of water vapor in the atmosphere occurs in 9-10 days.
Substances in the ionic state are also found in the atmosphere - up to several tens of thousands per 1 cm 3 of air.
An air pollutant can be any physical agent, chemical substance or biological species (mainly microorganisms) that enters the environment or is formed in it in quantities higher than natural ones.
Atmospheric pollution refers to the presence in the air of gases, vapors, particles, solid and liquid substances, heat, vibrations, radiation that adversely affects humans, animals, plants, climate, materials, buildings and structures.
Based on their origin, pollution is divided into natural, caused by natural, often anomalous processes in nature, and anthropogenic, associated with human activity.
Atmospheric pollutants are divided into mechanical, physical and biological.
Mechanical pollution - dust, ash, phosphates, lead, mercury. Their sources are volcanic eruptions, dust storms, forest fires, They are formed during the combustion of fossil fuels and during the production process building materials, which produces up to 10% of all pollution. A large amount of pollution enters the atmosphere during the operation of the cement industry, during the extraction and processing of asbestos, the operation of metallurgical plants, etc.
Physical pollution includes thermal (the entry of heated gases into the atmosphere); light (deterioration of natural illumination of the area under the influence of artificial light sources); noise (as a result of anthropogenic noise); electromagnetic (from power lines, radio and television, work of industrial installations); radioactive, associated with an increase in the level of radioactive substances entering the atmosphere.
Biological pollution is mainly a consequence of the proliferation of microorganisms and anthropogenic activities (thermal power engineering, industry, transport, actions of the armed forces).
The most common toxic air pollutants are carbon monoxide CO, sulfur dioxide SO2, nitrogen oxide N02, carbon dioxide CO2, hydrocarbons CH and dust.
The main atmospheric pollutant with carbon monoxide is the transport and road complex. Of the 35 million tons of harmful emissions from the complex, 89% comes from emissions from road transport and the road construction complex. Cars account for 25% of fuel burned; one car emits up to 10 tons of CO during its existence; (there are about 700 million cars in the world). Exhaust gases contain more than 200 harmful compounds, including carcinogenic ones.
Petroleum products, wear products of tires and brake linings, bulk and dusty cargo, chlorides used as road surface deicers pollute roadside strips and water bodies.
Air pollution from asphalt concrete plants is of significant importance, since the emissions from these enterprises contain carcinogenic substances. Asphalt mixing plants of various capacities currently operating in Russia emit from 70 to 300 thousand tons of suspended substances per year into the atmosphere. A random survey showed that the treatment equipment does not work effectively in any of them due to design imperfections, unsatisfactory technical condition and incomplete routine maintenance. Mobile road facilities providing construction, repair and maintenance of public roads annually emit 450 thousand tons of dust, soot and other harmful substances.
A significant supplier of carbon monoxide, dust, soot is the metallurgical industry (carbon monoxide about 2.2 million tons), energy complexes (dust about 2 million tons), non-ferrous metallurgy more than 300 thousand tons of CO and almost the same amount of dust, oil industry (600 thousand tons of CO)
Carbon monoxide interferes with the transfer of oxygen, causing oxygen starvation in the body. Prolonged inhalation of carbon monoxide can be fatal to humans.
Dust. Pollutants enter the body through the respiratory system. The daily volume of inhaled air for one person is 6-12 m3. During normal breathing, with each breath, the human body receives from 0.5 to 2 liters of air.
The harmful effects of various dusty industrial emissions on humans are determined by the amount of pollutants entering the body, their condition, composition and time of exposure.
Presence of dust in the atmosphere, in addition to the above negative consequences, reduces the flow of ultraviolet rays to the Earth's surface. The strongest impact of pollution on human health occurs during smog periods. At this time, people’s well-being worsens, the number of pulmonary and cardiovascular diseases increases sharply, and influenza epidemics occur.
Sulfur dioxide, sulfuric anhydride and other sulfur compounds affect the respiratory tract. Their main suppliers are ferrous (300 thousand tons) and non-ferrous metallurgy (more than 1 million tons), gas industry and oil refining industry, energy (up to 2.4 million tons).
The dissolution of sulfur dioxide in atmospheric moisture leads to acid rain, which affects forests, soils, and human health. Acid rain is especially common in areas of Southern Canada, Northern Europe, the Urals, primarily in the Norilsk region.
Atmospheric pollution by industrial emissions significantly enhances the corrosion effect. Acidic gases contribute to the corrosion of steel structures and materials. Sulfur dioxide, nitrogen oxides, hydrochloride, when combined with water, form acids, increasing chemical and electrochemical corrosion, destroying organic materials(rubber, plastics, dyes). Ozone and chlorine have a negative effect on steel structures. Even small amounts of nitrates in the atmosphere cause corrosion of copper and brass.
Acid rain acts similarly: it reduces soil fertility, negatively affects flora and fauna, shortens the service life of electrochemical coatings, especially chromium-nickel paints, reduces the reliability of machines and mechanisms, and more than 100 thousand types of colored glass used are at risk.
The destructive effects of industrial pollution depend on the type of substance. Chlorine damages the eyes and respiratory system. Fluorides, entering the human body through the digestive tract, wash calcium from the bones and reduce its content in the blood. Dangerous for inhalation of vapors or heavy metal compounds. Beryllium compounds are harmful to health.
Aldehydes are dangerous even in small concentrations in the atmosphere. Aldehydes irritate the organs of vision and smell and are drugs that destroy the nervous system.
Atmospheric pollution may have little effect on human health, but can lead to complete intoxication of the body.
One of the serious problems associated with air pollution is possible climate change from the influence of anthropogenic factors, which cause a direct impact on the state of the atmosphere associated with an increase or decrease in air temperature and humidity.
Environmentalists warn that if it is not possible to reduce carbon dioxide emissions into the atmosphere, then our planet will face a catastrophe associated with rising temperatures due to the so-called greenhouse effect. The essence of this phenomenon is that ultraviolet solar radiation passes quite freely through the atmosphere with a high content of CO 2 and methane CH 4. Infrared rays reflected from the surface are delayed by an atmosphere with a high CO 2 content, which leads to an increase in temperature and, consequently, to climate change. An analysis of observations over the past 100 years shows that the heaviest years were 1980, 1981, 1983, 1987 and 1988.
In the Northern Hemisphere, surface temperatures are currently 0.4 0C higher than in 1950-1980. In the future, a further increase in temperature is expected, for example by 2-4 0 C by 2050.
Therefore, due to the melting of glaciers and polar ice In the next 25 years, sea levels are expected to rise by 10 cm.
Already at the beginning of the 21st century. scientists predict widespread tsunamis, typhoons, and floods. And in the XXII century. warming will be 5...10°C and will become irreversible, possibly causing the last great flood. Thus, those climate changes that were barely noticeable in the 20th century can become disastrous for humanity in the 22nd century.
Climate fluctuations affect the condition and life of a person. When air temperature and precipitation change, the distribution of water resources and development conditions change human body.
Anthropogenic processes also include the destruction of the Earth's ozone layer. The ozone layer, whose maximum concentration is located at an altitude of 10...25 km in the troposphere, protects life on Earth from deadly ultraviolet radiation. It is destroyed by nitrogen oxides, especially chlorofluorocarbons, which are practically absent in natural systems, but humans are actively adding them to the atmosphere:
Operation of refrigerators using freon and aerosol units;
The release of NO as a result of the decomposition of mineral fertilizers;
Airplane flights at high altitudes and satellite launches (emission of nitrogen oxides and water vapor);
Nuclear explosions (formation of nitrogen oxides);
Processes that contribute to the penetration of chlorine compounds of anthropogenic origin into the stratosphere.
A change in the thickness of the ozone layer by just 1% increases the intensity of ultraviolet radiation by 2%, and the risk of skin cancer by 3...6%. Ultraviolet radiation particularly affects phytoplankton located in the surface layer of the World Ocean, as well as cultivated plants. The scale of destruction of the ozone layer is such that ozone holes have formed over some regions, such as Australia, Antarctica, etc.; a tendency towards a decrease in the ozone layer is recorded for all geographical regions of the Earth.
Air pollution also has a harmful effect on plants. Different gases have different effects on plants, and plants are not equally susceptible to the same gases. The most harmful to them are sulfur dioxide, hydrogen fluoride, ozone, chlorine, nitrogen dioxide, and hydrochloric acid.
From all of the above, we can conclude that even if we do not take into account other factors, such as water and soil pollution, there are enough harmful substances in the atmosphere, the concentration of which must be controlled.
The greatest pollution is observed in industrial regions: about 90% of emissions of harmful substances (HS) occur on 10% of the land area ( North America, Europe, East Asia), especially in large cities, where the maximum permissible concentrations are exceeded for many explosives. Approximately 20% of humanity breathes air in which the concentration of explosives exceeds the maximum permissible concentrations.
Chemical load per resident of Russia over a lifetime (60 years)
Chemical load - total quantity harmful and toxic substances that enter the human body during his life.
In our country, for the first time in 1939, standards for maximum permissible concentrations of harmful substances in the air were developed and introduced into environmental practice. settlements, based on hygienic requirements. The current standards include more than 2,500 different substances that may be contained in food, air, soil, and water. They are revised periodically and we currently use sanitary standards CH 245-71.
MPC is the maximum concentration of an impurity in the atmosphere, related to a certain averaging time, which, with periodic exposure or throughout a person’s entire life, does not have a harmful effect, including long-term consequences, and also does not have a harmful effect on the environment. This value is of a legislative nature. In the Russian Federation, the MPC corresponds to the lowest values recommended by WHO. Two values are set: the maximum one-time value within 20 - 30 minutes and the average daily MPC value.
Maximum single dose The maximum permissible concentration should not lead to unpleasant reflex reactions of the human body (runny nose, unpleasant odor), and the average daily concentration should not lead to toxic, carcinogenic and mutagenic effects.
To regulate emissions of explosives into the biosphere, maximum permissible emission standards (MPE) are used, individual for each substance and enterprise, which take into account the number of sources, the height of their location, the distribution of emissions in time and space and other factors (GOST 17.2.3.02-78)
MPE - the maximum amount of a harmful substance allowed to be released from a given source, which does not create a concentration near the Earth that is dangerous for people, flora and fauna
The MPE value (g/s) for combustion products is calculated using the following formula
For heated discharge:
MPE = maximum permissible concentration (/A F m n.
For cold exhaust:
MDV = 8 MPC.
If there are multiple emission sources:
where V c is the total volumetric solution of the gas mixture
Vc =V1+ V2 + V3…
V 1 is the volume of gas emitted by each source. (m 3 /s);
H - height of the emission source above the surface (m);
DT - temperature difference between the emitted gas and air (degree C)
A is a coefficient that depends on the temperature gradient of the atmosphere and determines the conditions for the vertical and horizontal dispersion of harmful substances;
F is the rate coefficient for the deposition of harmful substances in the air;
m,n - coefficients taking into account the conditions for the exit of the gas mixture from the mouth of the source;
D is the diameter of the source mouth.
The methodology for calculating the maximum permissible limit is set out in SN 369 -74. The calculation takes into account the background concentrations of harmful substances in the air C f and the concentration from pollution sources C, the sum of which must be less than or equal to the MPC:
MPC?С +С f
When several substances with different MPCs and different concentrations are present in the air together, the total concentration must satisfy the following relationship:
In accordance with GOST 17.2.3.02-78 for each industrial enterprise the maximum permissible limit for harmful substances into the atmosphere is established, provided that emissions of explosives from a given source in combination with other sources do not create a concentration exceeding the maximum permissible concentration.
Compliance with these requirements is achieved by localizing harmful substances at the point of their formation, removing them from the premises or equipment, as well as dispersing them into the atmosphere. If the concentration of emissions of harmful substances in the atmosphere exceeds the maximum permissible concentration, then the emissions are purified from harmful substances in cleaning devices installed in the exhaust system. The most common are ventilation, technological and transport exhaust systems.
2 .2.1 Atmospheric protection means
All known methods and means of protecting the atmosphere from chemical impurities can be combined into three groups.
The first group includes measures aimed at reducing emission power, i.e. reduction in the amount of emitted substance per unit time. The second group includes measures aimed at protecting the atmosphere by processing and neutralizing harmful emissions with special cleaning systems. The third group includes measures to regulate emissions both at individual enterprises and devices, and in the region as a whole.
To reduce the power of emissions of chemical impurities into the atmosphere, the following are most widely used:
Replacing less environmentally friendly fuels with environmentally friendly ones. In this case, fuel with a lower air pollution rating is used.
Fuel combustion using special technology. It is carried out either in a fluidized (fluidized) bed or by preliminary gasification.
Creation of closed production cycles. One of the promising ways to protect the atmosphere from chemical impurities is the introduction of closed production processes that minimize waste emitted into the atmosphere by reusing and consuming them, i.e., turning them into new products.
Classification of air purification systems and their parameters. Based on their state of aggregation, air pollutants are divided into dusts, mists and gaseous vapor impurities. Industrial emissions containing suspended solid or liquid particles are two-phase systems.
Air purification systems from dust are divided into 4 main groups: dry and wet dust collectors, electrostatic precipitators and filters. If the dust content is high, dust collectors and electrostatic precipitators are used. Filters are used for fine air purification with impurity concentrations of less than 100 mg/m 3 .
The choice of one or another dust collection device, which represents a system of elements including a dust collector, an unloading unit, control equipment and a fan, is determined by the dispersed composition of the captured industrial dust particles.
The following methods are used to purify air from gaseous impurities.
The absorption method involves separating a gas-air mixture into its component parts by absorbing one or more gas components with an absorber (absorbent) to form a solution.
The composition of the absorbent is selected from the condition of dissolution of the absorbed gas in it. For example, to remove gases such as ammonia and hydrogen chloride from process emissions, water is used as an absorbent. To capture water vapor, sulfuric acid is used, and aromatic hydrocarbons (from coke oven gas) are viscous oils.
The chemisorption method is based on the absorption of gases and vapors by solid or liquid absorbers with the formation of chemical compounds. Chemisorption reactions are exothermic.
The adsorption method is based on the physical properties of some porous materials to selectively extract individual components from a gas-air mixture. A well-known example of an adsorbent with an ultramicroscopic structure is activated carbon.
With the catalytic method, toxic components of the gas-air mixture, interacting with a special substance - a catalyst, are converted into harmless substances. Metals or their compounds (platinum, oxides of copper and manganese, etc.) are used as catalysts. The catalyst, made in the form of balls, rings or spiral wire, plays the role of an accelerator of the chemical process.
The thermal method or high-temperature afterburning, sometimes called thermal neutralization, requires maintaining high temperatures the gas being purified and the presence of a sufficient amount of oxygen. Thermal catalysts burn gases such as hydrocarbons, carbon monoxide, and paint production emissions.
6.5. ATMOSPHERE PROTECTION MEANS.
The air of industrial premises is polluted by emissions from technological equipment or during technological processes without localization of waste substances. Ventilation air removed from the premises can cause air pollution in industrial sites and populated areas. Moreover, the air
polluted by technological emissions from workshops, such as forging and pressing shops, shops for thermal and mechanical processing of metals, foundries and others, on the basis of which modern mechanical engineering is developed. In the production process of machinery and equipment, welding operations, mechanical processing of metals, processing of non-metallic materials, paint and varnish operations, etc. are widely used. Therefore, the atmosphere needs protection.
Atmospheric protection means must limit the presence of harmful substances in the air of the human environment at a level not exceeding the maximum permissible concentration. This is achieved by localizing harmful substances at the point of their formation, removing them from the premises or from equipment and dispersing them into the atmosphere. If the concentrations of harmful substances in the atmosphere exceed the maximum permissible concentration, then the emissions are purified from harmful substances in cleaning devices installed in the exhaust system. The most common are ventilation, technological and transport exhaust systems.
In practice, the following options for protecting atmospheric air are implemented:
removal of toxic substances from the premises by general ventilation;
ventilation, purification of contaminated air in special devices and
its return to the production or domestic premises if the air
after cleaning in the device, it complies with regulatory requirements for
supply air,
localization of toxic substances in the zone of their formation local
ventilation, purification of contaminated air in special devices,
release and dispersion into the atmosphere,
purification of process gas emissions in special devices,
release and dispersion into the atmosphere; in some cases before release
the exhaust gases are diluted with atmospheric air.
To comply with the maximum permissible concentrations of harmful substances in the atmospheric air of populated areas, maximum permissible emissions (MAE) of harmful substances from exhaust ventilation systems, various technological and energy installations are established.
In accordance with the requirements of GOST 17.2.02, for each designed and operating industrial enterprise, a maximum permissible limit for harmful substances into the atmosphere is established, provided that emissions of harmful substances from a given source in combination with other sources (taking into account the prospects for their development) do not create a ground concentration exceeding the maximum permissible concentration .
Devices for cleaning ventilation and process emissions into the atmosphere are divided into:
dust collectors (dry, electric filters, wet filters);
mist eliminators (low-speed and high-speed);
apparatus for collecting vapors and gases (absorption,
chemisorption, adsorption and neutralizers);
multi-stage cleaning devices (dust and gas collectors,
mists and solids traps, multi-stage
dust collectors).
Electrical cleaning (electric precipitators) is one of the most advanced types of gas purification from suspended dust and fog particles. This process is based on impact ionization of gas in the corona discharge zone, transfer of ion charge to impurity particles and deposition of the latter on collecting corona electrodes. For this purpose, electric precipitators are used.
Electrostatic precipitator circuit.
1-corona electrode
2-precipitating electrode
Aerosol particles entering the zone between the corona 1 and precipitation 2 electrodes adsorb ions on their surface, acquiring an electrical charge, and thereby receive acceleration directed towards the electrode with a charge of the opposite sign. Considering that the mobility of negative ions in air and flue gases is higher than that of positive ones, electrostatic precipitators are usually made with a corona of negative polarity. The charging time of aerosol particles is short and measured in fractions of seconds. The movement of charged particles towards the collecting electrode occurs under the influence of aerodynamic forces and the force of interaction between the electric field and the particle charge.
The filter is a housing 1, divided by a porous partition (filter element) 2 into two strips. Contaminated gases enter the filter and are cleaned as they pass through the filter element. Impurity particles settle on the inlet part of the porous partition and are retained in the pores, forming layer 3 on the surface of the partition. For newly arriving particles, this layer becomes part of the filter partition, which increases the cleaning efficiency
filter and pressure drop across the filter element. The precipitation of particles on the surface of the pores of the filter element occurs as a result of the combined action of the touch effect, as well as diffusion, inertial and gravitational effects.
Wet dust collectors include bubbling-foam dust collectors with failure and overflow grids.
Scheme of bubbling-foam dust collectors with failure (a) and (b)
overflow grates.
3-lattice
In such devices, the gas for cleaning enters under the grate 3, passes through the holes in the grate and, bubbling through a layer of liquid and foam 2, is cleaned of dust by depositing particles on the inner surface of the gas bubbles. The operating mode of the devices depends on the speed of air supply under the grille. At speeds up to 1 m/s, a bubbling mode of operation of the apparatus is observed. A further increase in gas velocity in the body 1 of the apparatus to 2...2.5 m/s is accompanied by the appearance of a foam layer above the liquid, which leads to an increase in the efficiency of gas purification and splash removal from the apparatus. Modern bubbling-foam devices provide an efficiency of gas purification from fine dust of -0.95...0.96 at a specific water consumption of 0.4...0.5 l/m. The practice of operating these devices shows that they are very sensitive to uneven gas supply under the failure gratings. An uneven supply of gas leads to local blowing off of the liquid film from the grate. In addition, the grilles of the devices are prone to clogging.
To clean the air from mists of acids, alkalis, oils and other liquids, fiber filters - mist eliminators - are used. The principle of their operation is based on the deposition of droplets on the surface of the pores, followed by the flow of liquid along the fibers into the lower part of the mist eliminator. The deposition of liquid droplets occurs under the influence of Brownian diffusion or an inertial mechanism for separating pollutant particles from the gas phase on filter elements depending on the filtration speed W. Mist eliminators are divided into low-speed (W< 0,15 м/с), в которых преобладает механизм диффузного осаждения капель, и высокоскоростные (W=2...2,5 м/с), где осаждение происходит главным образом под воздействием инерционных сил.
Felts made of polypropylene fibers are used as filter packing in such mist eliminators, which work successfully in an environment of dilute and concentrated acids and alkalis.
In cases where the diameters of fog droplets are 0.6...0.7 µm or less, to achieve acceptable cleaning efficiency it is necessary to increase the filtration speed to 4.5...5 m/s, which leads to noticeable spray removal from the outlet side of the filter element (spray entrainment usually occurs at speeds of 1.7...2.5 m/s), splash entrainment can be significantly reduced by using splash eliminators in the mist eliminator design. To capture liquid particles larger than 5 microns, splash traps made from mesh packages are used, where the capture of liquid particles occurs due to the effects of touch and inertial forces. The filtration speed in splash traps should not exceed 6 m/s.
Diagram of a high-speed mist eliminator.
1 - splash trap
3-filter element
High-speed mist eliminator with a cylindrical filter element 3, which is a perforated drum with a blind lid. Coarse fiber felt 2 with a thickness of 3...5 mm is installed in the drum. Around the drum on its outer side there is a splash trap 1, which is a set of perforated flat and corrugated layers of vinyl plastic tapes. The splash trap and filter element are installed with the lower part into the liquid layer.
Low-velocity mist eliminator filter element diagram
3-cylinders
4-fiber filter element
5-bottom flange
6-tube water seal
In the space between 3 cylinders made of meshes,
place a fibrous filter element 4, which is secured using
flange 2 to the mist eliminator body 1. Liquid deposited on
filter element; flows onto the lower flange 5 and through the tube
water seal 6 and glass 7 are drained from the filter. Fibrous
low-velocity mist eliminators provide high
gas purification efficiency (up to 0.999) from particles smaller than 3 microns and completely captures large particles. Fibrous layers are formed from glass fiber with a diameter of 7...40 microns. The layer thickness is 5... 15 cm, the hydraulic resistance of dry filter elements is 200... 1000 Pa.
High-speed mist eliminators are smaller in size and provide cleaning efficiency equal to 0.9...0.98 at Ap=1500...2000 Pa, from fog with particles less than 3 microns.
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INTRODUCTION
The revival of Russian industry is the primary task of strengthening the country's economy. Without a strong, competitive industry, it is impossible to ensure the normal life of the country and people. Market relations, the independence of factories, and the departure from a planned economy dictate that manufacturers produce products that are in global demand and at minimal cost. The engineering and technical personnel of the factories are entrusted with the task of producing these products at minimal cost in the shortest possible time, with guaranteed quality.
This can be achieved by using modern technologies for processing parts, equipment, materials, production automation systems and product quality control. The reliability of the manufactured machines, as well as the economics of their operation, largely depend on the adopted production technology.
The urgent task is to improve the technological support for the quality of manufactured machines, and first of all their accuracy. Precision in mechanical engineering is of great importance for improving the operational quality of machines and for their production technology. Increasing the accuracy of manufacturing workpieces reduces the labor intensity of machining, and increasing the accuracy of machining reduces the labor intensity of assembly as a result of eliminating fitting work and ensuring the interchangeability of product parts.
Compared to other methods for producing machine parts, cutting provides the greatest accuracy and the greatest flexibility of the production process, creating the possibility of the fastest transition from processing workpieces of one size to processing workpieces of a different size.
The quality and durability of the tool largely determine the productivity and efficiency of the processing process, and in some cases, the general ability to obtain parts of the required shape, quality and accuracy. Improving the quality and reliability of cutting tools contributes to increasing the productivity of metal cutting.
A reamer is a cutting tool that allows you to obtain high precision of machined parts. It is an inexpensive tool, and labor productivity when working with a reamer is high. Therefore, it is widely used in the finishing of various holes of machine parts. With the modern development of the mechanical engineering industry, the range of parts produced is enormous and the variety of holes requiring processing with reamers is very large. Therefore, designers are often faced with the task of developing a new development. They can be helped in this by a package of application programs on a computer, which calculates the geometry of the cutting tool and displays the working drawing of the development on the plotter.
The design sequence and calculation methods for cutting tools are based both on the general principles of the design process and on the specific features characteristic of the cutting tool. Each type of tool has design features that must be taken into account during design.
Specialists who will work in the metalworking industries must be able to competently design various designs of cutting tools for modern metalworking systems, effectively using computer technology (computers) and advances in the field of tool production.
To reduce time and increase the efficiency of cutting tool design, automated computer calculations are used, the basis of which is software and mathematics.
Creating application software packages for calculating the geometric parameters of complex and particularly complex cutting tools on a computer can dramatically reduce the cost of design labor and improve the quality of cutting tool design.
Places, %; Totd - time for rest and personal needs, %; K - coefficient taking into account the type of production; Kz - coefficient taking into account assembly conditions. For the general assembly of the hydraulic lock, the standard time is: = 1.308 min. Calculation of the required number of assembly stands and its load factors Let's find the estimated number of assembly stands, pcs. =0.06 pcs. Round up CP=1. ...