Harmful gases and vapors - Theoretical basis of environmental protection

2.4. Harmful gases and vapors

Many technological processes at the enterprises of the metallurgical, chemical, petrochemical industry, in a number of shops of machine-building plants, in many other industries are accompanied by the release of harmful gases and vapors into the atmospheric air. Manufacture and use of polymeric materials and resins is accompanied by the release of toxic substances. For this reason, the use in the construction of phenol-formaldehyde polyester resins is limited. Distant gases of diphenylpropane, epoxy resins, etc., are harmful to living organisms. Polystyrene and polyvinyl chloride films contaminate the atmosphere with styrene, dibutyl phthalate. The active pollutant of atmospheric air is transport, first of all automobile.

The approximate composition of products in industrial gaseous emissions is given in Table. 2.3.

Table 2.3. Composition of waste gases by industry

Production type

Chemical composition of gaseous wastes

Oil refining

Mercaptans, hydrogen sulphide, ammonia, organic nitrogen compounds, carbon monoxide

Production of gas from coal

Sulfur compounds (hydrogen sulphide, carbon disulfide, thiophene, thiols, carbon sulphide)

Natural Gas Processing

Hydrogen sulphide, mercaptans

Production of acids and alkalis

Oxygen compounds of nitrogen and sulfur

Production of mineral and organic fertilizers

Ammonia, sulfur compounds, hydrogen fluoride, mercaptans, trimethylamine, etc.

Chemical plants (production of resins, varnishes, plastics, fats, oils, etc.)

Formaldehyde, amines, amides, solvents, sulfur compounds, acetylene, phenol, etc.

Pharmaceutical factories, breweries, fermentation processes

Amines, reduced sulfur compounds, furfural, methanol

Textile and paper mills

Urea, starch decomposition products, dimethyl sulphide

The main gas pollutants of atmospheric air are the following substances.

Carbon monoxide (carbon monoxide CO) is a colorless gas, odorless. Highly toxic substance. The density with respect to air is 0.967. It is formed as a result of incomplete combustion of carbon (combustion of carbon in conditions of lack of oxygen). Release of CO occurs in foundry, thermal, smithy shops, in boiler houses, especially those working on coal fuel; CO is contained in the exhaust gases of cars, tractors, etc.

Hydrogen sulphide (H 2 S) - a colorless gas smelling of rotten eggs. The boiling point is 60.9 ° C, the density with respect to air is 1.19. Lit by a blue flame to form water and sulfur dioxide. It occurs when processing, obtaining or using sulfur barium, sodium sulfide, antimony, in the leather industry, in beet-sugar production, in silk factories, in the extraction of oil and its processing and other industries. Has a high toxicity.

Sulfur dioxide (sulfur dioxide SO 2 ) is a colorless gas with an acute odor. Density relative to air 2,213. It occurs when burning fuel containing sulfur in boiler houses, smithies, foundries, sulfuric acid production, copper smelters, leather production and a number of others. A very common harmful substance.

Nitrogen oxides are a mixture of nitrogen compounds at different ratios. Very common harmful substances are released during the production of nitric acid, fertilizers, blasting, etc.

Gas pollution, like aerosol, significantly impairs the quality of atmospheric air, and in some cases makes it unsuitable for people to be in it.

In order to avoid these serious consequences and maintain air quality at a level that meets sanitary requirements, air emissions must be cleared not only from aerosol contaminants, but also from harmful fumes and gases by technological measures.

Gaseous air pollutants (harmful gases and vapors) are essentially gas solutions (gas mixtures). The most important characteristic of any solution is its composition. It also reflects the qualitative (from which components the solution consists), and the quantitative (in what concentrations the component is contained in the solution) of the solution side. There are several ways of expressing the concentration of the solution.

The homogeneous gas mixture is represented as a mixture of ideal gases, considering it possible to apply to it and to each of its components the laws of ideal gases. There are several generally accepted ways of expressing the composition of such a mixture.

For the calculation of the processes associated with the change in pressure in the system, the composition of the mixture is usually given in units of pressure. According to Dalton's law, the pressure of the gas mixture P can be calculated by adding the partial pressures p i of its components:


Specifying the composition of an ideal gas mixture with a set of partial pressures of its components is equivalent to specifying the amount (number of moles) of each component in fractions of the total number (number of moles) of the mixture.

According to the Amaga law, analogous to Dalton's law, the additivity of the partial volumes V i is assumed:


Based on this, the composition of the mixture can be specified by the partial volumes of the components in volume units.

Often the compositions of mixtures are given relative values, using volume, molar and mass fractions or percentages for this purpose.

The volume fraction of the i component of v i , is expressed by the ratio of its partial volume to the volume of the mixture, the molar fraction n i - the amount of matter moles) of the i-th component, referred to the amount of substance (moles) of the mixture, the mass fraction g i is the ratio of the mass of the i-th component to the mass of the mixture:


The numerical values ​​of the volume and molar fractions of the components of an ideal gas mixture are the same (v i = n i ), since in equal volumes of ideal gases, at equal temperatures and pressures, the same amount of substance (moles). Mass fractions are related to bulk and molar fractions by the ratio


where M is the average (apparent) molar mass of the mixture, which is calculated according to the additivity rule:




Along with the fractions, the content of the mixture components is expressed in bulk, molar and mass percentages, as well as in relative molar or mass concentrations.

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