Regulating the combustion process (Basic principles of combustion)

For optimal combustion, it is necessary to use more air than the theoretical calculation of the chemical reaction (stoichiometric air).

This is caused by the need to oxidize all available fuel.

The difference between the actual amount of air and the stoichiometric amount of air is called excess air. Typically, excess air ranges from 5% to 50% depending on the type of fuel and burner.

Typically, the more difficult it is to oxidize the fuel, the more excess air is required.

The excess amount of air should not be excessive. Excessive combustion air supply reduces the flue gas temperature and increases the heat loss of the heat generator. In addition, at a certain limiting amount of excess air, the torch cools too much and CO and soot begin to form. Conversely, insufficient air causes incomplete combustion and the same problems noted above. Therefore, to ensure complete combustion of the fuel and high combustion efficiency, the amount of excess air must be very precisely regulated.

The completeness and efficiency of combustion is verified by measuring the concentration of carbon monoxide CO in the flue gases. If there is no carbon monoxide, then combustion has occurred completely.

Indirectly, the excess air level can be calculated by measuring the concentration of free oxygen O 2 and/or carbon dioxide CO 2 in the flue gases.

The amount of air will be approximately 5 times greater than the measured amount of carbon in volume percent.

As for CO 2, its amount in flue gases depends only on the amount of carbon in the fuel, and not on the amount of excess air. Its absolute amount will be constant, but the percentage of volume will vary depending on the amount of excess air in the flue gases. In the absence of excess air, the amount of CO 2 will be maximum; with an increase in the amount of excess air, the volume percentage of CO 2 in the flue gases decreases. Less excess air corresponds to more CO 2 and vice versa, so combustion is more efficient when the amount of CO 2 is close to its maximum value.

The composition of flue gases can be displayed on a simple graph using a "combustion triangle" or Ostwald triangle, which is plotted for each fuel type.

Using this graph, knowing the percentage of CO 2 and O 2, we can determine the CO content and the amount of excess air.

As an example in Fig. Figure 10 shows the combustion triangle for methane.

Figure 10. Combustion triangle for methane

The X-axis indicates the percentage of O2, and the Y-axis indicates the percentage of CO2. The hypotenuse goes from point A, corresponding to the maximum CO 2 content (depending on the fuel) at zero O 2 content, to point B, corresponding to zero CO 2 content and maximum O 2 content (21%). Point A corresponds to the conditions of stoichiometric combustion, point B corresponds to the absence of combustion. The hypotenuse is the set of points corresponding to ideal combustion without CO.

Straight lines parallel to the hypotenuse represent different percentages of CO.

Let's assume that our system runs on methane and flue gas analysis shows that the CO 2 content is 10% and the O 2 content is 3%. From the triangle for methane gas we find that the CO content is 0 and the excess air content is 15%.

Table 5 shows the maximum CO 2 content for different types fuel and the value that corresponds to optimal combustion. This value is recommended and calculated based on experience. It should be noted that when the maximum value is taken from the central column, it is necessary to measure emissions according to the procedure described in Chapter 4.3.

Renovation interior construction

During the life cycle of the building renovation work at a certain period are necessary to update the interior. Modernization is also necessary when interior design or functionality lags behind modern times.

Multi-storey construction

There are more than 100 million housing units in Russia, and most of them are “single-family houses” or cottages. In cities, suburbs and rural areas, own houses are a very common type of housing.
The practice of designing, constructing and operating buildings is most often teamwork various groups of professionals and professions. Depending on the size, complexity and purpose of a particular building project, the project team may include:
1. The real estate developer who provides financing for the project;
One or more financial institutions or other investors that provide financing;
2. Local planning and management bodies;
3. Service that carries out ALTA/ACSM and construction surveys throughout the project;
4. Building managers who coordinate the efforts of various groups of project participants;
5. Licensed architects and engineers who design buildings and prepare construction documents;

Positive traits:

· higher heat transfer to heat exchange surfaces than air (due to the greater emissivity of combustion product particles).

Negative qualities:

Consequences:

· the use of flue gases as a coolant is possible only when using intermediate heat exchange devices to heat the coolant supplied directly to the consumer;

· utilization (saving and use) of the heat of exhaust flue gases is ensured;

· in the presence of substances with high corrosive activity (for example, sulfur compounds), the durability of heat pipes and heat exchange devices is sharply reduced;

· when flue gases are cooled below the dew point, condensation may form and, as a result, dampening of structures and the formation of ice in winter.

Classification of heating stoves:

By heat capacity:

· Non-heat-intensive

I have low thermal inertia. The room is heated only during combustion of fuel. Designed for short-term heating. These ovens include:

1) metal (steel or cast iron)

2) stoves made of a small number of bricks (up to 300 pcs.),

3) fireplaces (brick niches for open burning of fuel).

· Heat-intensive

They have great thermal inertia. The stove material accumulates heat and, after combustion of the fuel, transfers it to the room for a long time (up to 12 hours). Used for continuous heating of rooms.

Heat-intensive furnaces differ in design according to flue gas flow diagram

· Duct . The movement of gases is carried out through internal channels, which can be connected in parallel or in series.

· Channelless (bell-type). The movement of gases is free, and at the end of the fire the furnace does not cool down, since hot flue gases accumulate above the entrance to the chimney. The upper zone is somewhat overheated.

· Combined . Before entering the hood, flue gases pass through channels located below the firebox, which allows the lower zone to be heated and a more uniform temperature distribution in the room to be achieved.

FLUE GASES

FLUE GASES

(Flue gases) - gaseous combustion products.

Samoilov K. I. Marine dictionary. - M.-L.: State Naval Publishing House of the NKVMF of the USSR, 1941

See what “FLUGE GASES” is in other dictionaries:

Flue gases- Gases formed in emission sources during the combustion of organic substances Source: OND 90: Guidelines for the control of sources of air pollution ... Dictionary-reference book of terms of normative and technical documentation

flue gases- Organic fuel combustion products. origin, emanating from the working space of heated metallurgical plants. units. Topics: metallurgy in general EN fume ...

flue gases- fuel combustion products organic origin, emanating from the working space of heated metallurgical units; See also: Gases furnace gases gases in metals waste gases inert gases ...

flue gases- flue gases... Dictionary of chemical synonyms I

wet flue gases- - [A.S. Goldberg. English-Russian energy dictionary. 2006] Energy topics in general EN wet flue gases ... Technical Translator's Guide

recirculating flue gases- - [A.S. Goldberg. English-Russian energy dictionary. 2006] Energy topics in general EN recycled flue gas es ... Technical Translator's Guide

composition-averaged flue gases- - [A.S. Goldberg. English-Russian energy dictionary. 2006] Topics of energy in general EN average flue gases ... Technical Translator's Guide

Gases in technology are used mainly as fuel; raw materials for chemical industry: chemical agents in welding, gas chemical heat treatment metals, creating an inert or special atmosphere, in some... ...

I Gases (French gaz; the name was proposed by the Dutch scientist J. B. Helmont - a state of aggregation of a substance in which its particles are not connected or very weakly connected by interaction forces and move freely, filling the entire ... ... Great Soviet Encyclopedia

chimneys- a structure for creating draft and removing gaseous products of fuel combustion from various metallurgical furnaces and boiler units. In small furnaces, chimneys are designed to create natural draft, under the influence of... ... Encyclopedic Dictionary of Metallurgy

During combustion solid fuel As is known, a residue is formed - ash in the form of small (powdery) particles and large pieces - slag. During layer combustion of fuel various types the bulk of the ash (approximately 75-90%) remains in the furnace and flue ducts of the boiler, and the rest (fine) is carried away by the flue gases into the atmosphere.

When flaring solid fuel (in the form of dust), ash carryover with flue gases will increase significantly and reach 80-90%. The ash and unburnt tiny particles of fuel removed in this way (entrainment) pollute the atmosphere and, therefore, worsen the sanitary and hygienic conditions of the surrounding area. Fly ash emitted into the atmosphere is very fine, it can easily penetrate the eyes and lungs of a person, causing great harm to health. Therefore, before releasing them into the atmosphere, flue gases must be cleaned of ash and entrainment in special devices - ash collectors (for example, ZU ash collectors), which are equipped in almost all modern boiler houses operating on solid fuel.

Boiler installations in large cities are leaders not only in terms of the amount of harmful emissions in environment, but also by their toxic effects. Regular assessments of the environmental impact of highly toxic substances show that air quality in large Russian cities is deteriorating every year. As a result, the number of people with respiratory diseases among the population of these cities is increasing; Residents of megacities have decreased immunity and increased incidence of cancer.

Studies of flue gases from fuel combustion plants show that the main atmospheric pollutants in their composition are carbon oxides (up to 50%), sulfur oxides (up to 20 percent), nitrogen oxides (up to 6-8%), hydrocarbons (up to 5-20%). ), soot, oxides and derivatives of mineral inclusions and hydrocarbon fuel impurities. In turn, exhaust and exhaust gases of thermal engines emit into the air more than 70 percent of carbon oxides and hydrocarbons (benzenes, formaldehydes, benzo(a)pyrene), about 55 percent of nitrogen oxides, up to 5.5 percent of water, as well as soot ( heavy metals), burning, soot, etc.

Flue gases from boiler plants and engines contain tens of thousands of chemicals, compounds and elements, more than two hundred of which are highly toxic and poisonous.

When released into the atmosphere, emissions contain reaction products in solid, liquid and gas phases. Changes in the composition of emissions after their release can manifest themselves in the form of: precipitation of heavy fractions; disintegration into components by mass and size; chemical reactions with air components; interaction with air currents, clouds, precipitation, solar radiation of various frequencies (photochemical reactions), etc.

As a result, the composition of emissions may change significantly, new components may be formed, the behavior and properties of which (in particular, toxicity, activity, ability to perform new reactions) may differ significantly from the original ones. Not all of these processes have currently been studied with sufficient completeness, but for the most important ones there are general ideas relating to gaseous, liquid and solid substances.

The greatest environmental damage to the atmosphere and the natural environment in general is caused by substances such as nitrogen and carbon oxides, aldehydes, formaldehydes, benzo(a)pyrene and other aromatic compounds, which are classified as toxic substances.

In addition, during the operation of any installation and engine, about 1.0-2.0 percent of the fuel consumed is emitted, which settles on surfaces (ground, water, trees, etc.) in the form of unburned hydrocarbons, soot, dust and ash.

Flue gases have an unpleasant odor and have harmful and sometimes fatal effects on the human body, flora and fauna. Gas and thermal air pollution contributes to the formation of acid rain, atmospheric smoke, and changes the nature of cloudiness, which leads to an increase in the greenhouse effect.

The greatest danger to humans and living organisms are the components that cause cancer; these are carcinogenic substances represented in smoke and exhaust gases by polycyclic aromatic hydrocarbons (C X H Y).

Those with greater carcinogenic activity include, first of all, 3,4 benzo(a)pyrene (C 2 0H 12), which is formed when the organization of the combustion process is disrupted. The highest yield of carcinogenic substances, in particular 3,4 benzo(a)pyrene, is observed in non-stationary and transient modes.

Main pollutants

Sulfur dioxide, or sulfur dioxide (sulfur dioxide).

The most widespread sulfur compound is sulfur dioxide (SO 2) - a colorless gas with a pungent odor, approximately twice as heavy as air, formed during the combustion of sulfur-containing fuels (primarily coal and heavy fractions of oil).

Sulfur dioxide is especially harmful to trees, causing chlorosis (yellowing or discoloration of leaves) and dwarfism. In humans, this gas irritates the upper Airways, as it easily dissolves in the mucus of the larynx and trachea. Chronic exposure to sulfur dioxide can cause a respiratory disease similar to bronchitis. This gas itself does not cause significant damage to public health, but in the atmosphere it reacts with water vapor to form a secondary pollutant - sulfuric acid (H 2 SO 4). Drops of acid are transported over considerable distances and, when they enter the lungs, severely destroy them. The most dangerous form of air pollution occurs when sulfur dioxide reacts with suspended particles, accompanied by the formation of sulfuric acid salts, which penetrate into the lungs during breathing and settle there.

Carbon monoxide, or carbon monoxide.

A very poisonous gas without color, smell or taste. It is formed during incomplete combustion of wood, fossil fuels, during the combustion of solid waste and partial anaerobic decomposition of organic matter. IN indoors filled with carbon monoxide, the ability of red blood cell hemoglobin to carry oxygen decreases, which causes a person’s reactions to slow down, perception to weaken, headaches, drowsiness, and nausea to appear. Under influence large quantity carbon monoxide can cause fainting, coma and even death.

Suspended particles.

Suspended particles, including dust, soot, pollen and plant spores, etc., vary greatly in size and composition. They can either be directly contained in the air or be contained in droplets suspended in the air (aerosols). In general, about 100 million tons of aerosols enter the Earth’s atmosphere per year anthropogenic origin. This is approximately 100 times less than the amount of aerosols of natural origin - volcanic ash, windblown dust and splashes sea ​​water. Approximately 50% of anthropogenic particles are released into the air due to incomplete combustion of fuel in transport, factories, factories and thermal power plants. According to the World Health Organization, 70% of the population living in cities in developing countries breathes highly polluted air containing a lot of aerosols.

Aerosols are often the most obvious form of air pollution, as they reduce visibility and leave dirty marks on painted surfaces, fabrics, vegetation and other objects. Larger particles are mainly captured by the hairs and mucous membranes of the nose and larynx and then expelled. It is assumed that particles smaller than 10 microns are most dangerous to human health; They are so small that they penetrate the body's protective barriers into the lungs, damaging the tissues of the respiratory organs and contributing to the development of chronic respiratory diseases and cancer. Other types of aerosol pollution complicate bronchitis and asthma and cause allergic reactions. Accumulation a certain amount small particles in the body make breathing difficult due to blockage of capillaries and constant irritation of the respiratory system.

Volatile organic compounds (VOCs). These are toxic fumes in the atmosphere. They are the source of many problems, including mutations, respiratory disorders and cancer, and also play a major role in the formation of photochemical oxidants.

Anthropogenic sources release many toxic synthetic organic substances into the atmosphere, such as benzene, chloroform, formaldehyde, phenols, toluene, trichloroethane and vinyl chloride. The main part of these compounds enters the air during incomplete combustion of hydrocarbons from automobile fuel, at thermal power plants, chemical and oil refineries.

Nitrogen oxides NO x Nitrogen oxide (NO) and dioxide (NO 2) are formed during the combustion of fuel at very high temperatures (above 650 o C) and excess oxygen. Subsequently, in the atmosphere, nitrogen oxide is oxidized to gaseous dioxide of a red-brown color, which is clearly visible in the atmosphere of most large cities. The main sources of nitrogen dioxide in cities are car exhaust gases and emissions from thermal power plants (which use not only fossil fuels). In addition, nitrogen dioxide is formed during the combustion of solid waste, as this process occurs at high combustion temperatures. NO 2 also plays an important role in the formation of photochemical smog in the surface layer of the atmosphere. In significant concentrations, nitrogen dioxide has a pungent, sweetish odor. Unlike sulfur dioxide, it irritates the lower respiratory system, especially the lung tissue, thereby worsening the condition of people suffering from asthma, chronic bronchitis and emphysema. Nitrogen dioxide increases susceptibility to acute respiratory diseases such as pneumonia.

When nitrogen oxides dissolve in water, acids are formed, which are one of the main causes of so-called “acid” rain, leading to the death of forests. The formation of ozone in the ground layer is also one of the consequences of the presence of nitrogen oxides in it. In the stratosphere, nitrous oxide initiates a chain of reactions that leads to the destruction of the ozone layer, which protects us from the effects of ultraviolet radiation from the Sun.

Ozone O 3. Ozone is formed by the breakdown of either an oxygen molecule (O2) or nitrogen dioxide (NO2) to form atomic oxygen (O), which then combines with another oxygen molecule. This process involves hydrocarbons that bind the nitric oxide molecule to other substances. Although ozone plays an important role in the stratosphere as a protective shield that absorbs short-wave ultraviolet radiation, in the troposphere it destroys plants as a strong oxidant. Construction Materials, rubber and plastic. Ozone has a characteristic odor that is a sign of photochemical smog. Inhalation by humans causes coughing, chest pain, rapid breathing, and irritation of the eyes, nasal cavity, and larynx. Exposure to ozone also leads to a deterioration in the condition of patients with chronic asthma, bronchitis, emphysema and those suffering from cardiovascular diseases.

Carbon dioxide CO 2 Non-toxic gas. But the increase in the concentration of man-made carbon dioxide in the atmosphere is one of the main reasons for the observed climate warming, which is associated with the greenhouse effect of this gas.