Use of the heat of the exhaust flue gases. Decrease in flue gas temperature. Brick chimneys and modern boilers

Flue gas and air temperature entering the smoke collector should not be higher than 500 ° C. The volume of the smoke collector must not be overestimated (it is difficult to create the required heat voltage in a large smoke collector), but it is also impossible to underestimate its size - it is difficult to create the required vacuum in a small smoke collector: it will not cope with a large amount flue gases and air. Each fireplace has its own smoke collector according to its size. The internal surfaces of the smoke collector must be smooth. "At the level of the pass, on either side, a hermetically closing cleaning door must be installed.

As noted above, fuel combustion in fireplaces occurs with a multiple excess of air. The fireplace does not have an entrance door, the path of smoke from the firebox to the room is blocked by a constant air flow directed from the room to the hearth and then through the chimney into the atmosphere.To pass all this volume of flue gases and air, the chimney must have a sufficient cross-section with an extremely smooth inner surface. The section of the chimney must correspond to the section of the fireplace inlet. It is known that the higher the chimney, the more thrust is created in it. This should be taken into account, but based on this, the section of the chimney should not be underestimated.

According to Swedish researchers, the ratio of the cross-sectional area of ​​a rectangular chimney to the area of ​​the fireplace inlet with a chimney height of 5 m should be 12 percent; with a chimney height of 10 m - 10 percent.

What should be the chimney for gas and diesel boilers?

Chimneys are an important part of heat generators. No boiler can work without a chimney. The function of the chimney is to remove combustion products or flue gases from the combustion chamber of the boiler. In individual houses, chimneys are internal - passing through the ceilings and roof of the building, external - mounted vertically along the outer surface of the wall and horizontal - exhaust gases through the outer wall of the building. The latter type of chimney is used for boilers with forced removal of flue gases and is usually a "pipe in pipe" design. (The combustion products are removed through the inner pipe, air is supplied to the boiler combustion chamber through the outer pipe.) Chimneys are individual - one per boiler or group, for several boilers, as, for example, in apartment buildings with apartment heating. Chimneys must be designed and selected by a specialist. An incorrectly installed chimney can lead to unstable boiler operation; installed without taking into account the roof configuration can be “blown out” by the wind and extinguish the boiler. It is important for you to know that the internal diameter of the chimney should be no less than the diameter of the boiler neck, that there should be as few bends and bends in the path of the flue gases as possible, and that measures should be taken to prevent the formation of condensation when installing the chimney.

What is condensation and how is it formed?

A feature of modern boilers operating on gas and liquid fuel is the low temperature of flue gases at the outlet of the boiler - from 100 ° C. In the process of combustion of hydrocarbon fuel - natural gas or diesel fuel, water vapor, carbon dioxide, sulfur dioxide and many other chemical compounds are formed. Going up the chimney, this gas mixture cools down. When its temperature drops to + 55 ° C (dew point temperature), the water vapor present in the gas mixture cools and turns into water - condenses. This water dissolves compounds of sulfur and other chemicals in the flue gases. They form a very aggressive mixture of acids, which, when flowing down, quickly corrodes the material of the chimneys. The flue gases are usually cooled down to the dew point temperature at a height of 4 - 5 m from the boiler outlet. Therefore, chimneys, the height of which is greater, are made of stainless steel and insulated. A condensate trap is always installed at the bottom of the chimney. For outdoor chimneys, there is a sandwich-type design - the chimney pipe is placed in a pipe of a larger diameter, and the space between them is filled with a heat insulator. The thickness of the thermal insulation layer is selected depending on the value of the minimum outside air temperatures.

Stainless steel chimneys are very expensive. Can a brick chimney be used for the chimney like in a wood stove?

This should never be done. First, the acid mixture is so aggressive that brickwork, if not made of special acid-resistant bricks, can be destroyed in one heating season. Secondly, flue gases through inconspicuous cracks in the masonry can penetrate into living quarters and cause harm to human health. If the house has a channel made of brickwork, then it can serve as a chimney only if an inset stainless steel chimney with thermal insulation is placed in it.

Are there - are there chimney systems that do not use metal?

Yes. Recently, a chimney system of an original design has appeared on the Russian market, which is called an "insulated chimney system with ventilation." It consists of individual modules with a height of 0.33 m. Each module is a rectangular block of lightweight concrete, inside which a ceramic pipe is fixed. There is a channel between the inner wall of the block and the outer wall of the ceramic pipe, which plays the role of a ventilation channel, which is not the case with other types of chimneys. The blocks are installed one on top of the other, sealed with a special sealant and mounted in a chimney of any configuration and height. The complete set of the chimney system contains a full set of necessary elements for connecting boiler chimneys, for leading the chimney through the roof and for decorative completion of the pipe. Four types of modules allow the construction of one-way and two-way chimneys or chimneys with separate ventilation ducts. This makes the design of the chimney system versatile and versatile. The inner ceramic tube is resistant to high temperatures and temperature fluctuations; acid-resistant (protected from condensation), hermetically sealed and durable. The system is easy to install and does not require highly qualified specialists. The cost of an insulated chimney system is commensurate with the cost of high-end stainless steel chimneys.

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3.1.1. Decrease in flue gas temperature

Improving the energy efficiency (efficiency) of a combustion plant achieves a reduction in CO2 emissions, provided that this improvement leads to a reduction in fuel consumption. In this case, CO2 emissions are reduced in proportion to the reduction in fuel consumption. However, the result of an increase in efficiency can also be an increase in the production of useful energy at a constant fuel consumption (an increase in Hp at a constant Hf in Equation 3.2). This can lead to an increase in the productivity or capacity of the production unit while improving energy efficiency. In this case, there is a reduction in specific CO2 emissions (per unit of production), but the absolute volume of emissions remains unchanged (see section 1.4.1).

Guidelines for energy efficiency (KPIs) and related calculations for various combustion processes are provided in industry Briefing Papers and other sources. In particular, the document EN 12952-15 contains recommendations for calculating the efficiency of water-tube boilers and related auxiliary equipment, and document EN12953-11 - fire-tube boilers.

general characteristics

One of the options for reducing thermal energy losses during combustion is to reduce the temperature of flue gases emitted into the atmosphere. This can be achieved through:

Selection of the optimal dimensions and other characteristics of the equipment based on the required maximum power, taking into account the estimated safety margin;

Intensification of heat transfer to the technological process by increasing the specific heat flux (in particular, using swirlers-turbulators that increase the turbulence of the working fluid flows), increasing the area or improving the heat exchange surfaces;

Recovery of heat from flue gases using an additional technological process (for example, steam production using an economizer, see section 3.2.5);

Installing an air or water heater, or organizing preheating of fuel using the heat of flue gases (see 3.1.1). It should be noted that air heating may be necessary if the process requires a high flame temperature (for example, in glass or cement production). The heated water can be used to power the boiler or in hot water supply systems (including centralized heating);

Cleaning of heat exchange surfaces from accumulating ash and carbon particles in order to maintain high thermal conductivity. In particular, soot blowers can be used periodically in the convection zone. Cleaning of heat exchange surfaces in the combustion zone, as a rule, is carried out during equipment shutdown for inspection and maintenance, however, in some cases, non-stop cleaning is used (for example, in heaters at a refinery);

Ensuring a level of heat production that meets existing needs (does not exceed them). The heat output of the boiler can be adjusted, for example, by selecting the optimum throughput of the injectors for liquid fuel or the optimum pressure under which the gaseous fuel is supplied.

Environmental benefits

Energy saving.

Impact on various components of the environment

Reducing the flue gas temperature under certain conditions can conflict with air quality objectives, for example:

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Page 3

The flue gas temperature at the outlet of the furnace must be at least 150 C higher than the initial temperature of the heated raw material in order to prevent intensive corrosive wear of the pipe surfaces in the convection chamber.

The flue gas temperature at the boiler outlet, the heated air temperature at the furnace inlet, the consumption and thermodynamic parameters of the superheated and intermediate steam, feed water for a given load factor are considered unchanged.

The flue gas temperature above the pass wall is especially important. The high temperature of the gases at the pass corresponds to the high heat density of the surface of the radiant tubes, the temperature of their walls, and a high probability of coke formation. Deposing on the inner surface of the pipes, coke impedes heat transfer, which leads to a further increase in the temperature of the walls and to their burnout.

The flue gas temperature in front of the recuperator in heating furnaces reaches 1400 C.

The temperature of the flue gases entering the chimney must be maintained no higher than 500 C by adjusting the flow rate of the cooling air supplied to the flue gas duct by the fan.

The flue gas temperature at the inlet to the heat exchanger of the starting heater should not exceed 630 - 650 C. Exceeding this temperature may lead to its premature failure. It is even more important that during the operation of the starting heater, air or gas is always supplied to the shell side of the heat exchanger. When the air or gas is turned off, the temperature of the tube plates and pipes rises sharply and the heat exchanger may fail. In this case, it is necessary to immediately reduce the temperature of the flue gases to 450 C.

The temperature of the flue gases at the entrance to the second chamber is maintained at 850 C. The gases leaving this chamber with a temperature of 200 - 250 C enter the first (along the acid path) chamber, where their temperature drops to 90 - 135 C.

The temperature of the flue gases leaving the convection chamber and going into the chimney depends on the temperature of the raw material entering the furnace and exceeds it by 100 - 150 C. However, when the temperature of the raw material is high for technological reasons (furnaces for heating fuel oil, catalytic reforming furnaces, etc.) ), the flue gases are cooled using their heat in a steamer, air heater, or for underfloor condensate water and obtaining water vapor.

The flue gas temperature above the pass wall is one of the most important indicators. The high temperature of the flue gases above the pass wall corresponds to the high heat density of the radiant tubes, the high temperature of their walls and the likelihood of coke deposition in the furnace tubes, and, consequently, the possibility of their burnout. The high speed of the heated flow of raw materials allows for greater heat removal, lowering the temperature of the pipe walls and, thus, working with a higher temperature of gases over the pass and heat intensity of radiant pipes. An increase in the surface of the radiant tubes also contributes to a decrease in their heat density and a decrease in the temperature of the flue gases above the pass. The cleanliness of the inner surface of the coil pipes is also the most important factor affecting the temperature of the gases above the pass wall. The temperature of the gases over the pass is carefully controlled and usually does not exceed 850 - 900 C.

The flue gas temperature at the entrance to the radiation zone is 1100 - 1200 С, at the entrance to the convective zone 800 - 850 С.

The flue gas temperature at the outlet of the tube furnace is 900 C.

The flue gas temperature in front of the recuperator will be approximately 1100 C.

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And only by shielding the combustion chamber and increasing its volume, normal conditions were created for the operation of the coil. Radiant tube furnaces were created. In early designs of such furnaces, the ceiling screen tubes were protected from the strong effects of the flame by cuffs of fire retardant material. Corrugated cast iron collars on convection pipes raised the heating surface in the convection chamber of the oven. As a result of the shielding of the furnace ceiling, the heat transfer by radiation increased, the temperature of the flue gases over the pass decreased and the need for protective cuffs and recirculation of flue gases disappeared. For maximum heat utilization

Flue gas temperature after the boiler - 210 210 -

The technological design standards provide for a decrease in the temperature of flue gases before entering the chimney with natural draft to 250 ° C. In the presence of special smoke exhausters, the temperature can be reduced to 180-200 ° C. The heat of flue gases with a temperature of 200-450 ° C (average figure) can be used for heating air, water, oil and for the production of water vapor in the installation. Below are the data on the thermal resources of flue gases at the ELOU-AVT unit with secondary distillation of gasoline with a capacity of 3 million tons / year of sulphurous oil.

Average temperature of flue gases in 293 305 310 -

The temperature regime of raw heat exchangers is also limited. The maximum allowable temperature at a regeneration pressure of 3.0-4.0 MPa should not exceed 425 ° C, in connection with which the temperature of flue gases leaving the reactors before entering the raw heat exchanger should be reduced by mixing with a cold coolant.

Heat density of pipes, kcal / (m2-h) radiant convection pipes Temperature of flue gases,

Heater surface, Air heating temperature in air heaters, ° С Flue gas temperature, ° С

Usually, the temperature of the flue gases at the pass is automatically controlled with a correction for the temperature of the product at the outlet of the furnace. To control and regulate tube furnaces, the following elements are provided in their piping.

Liquid fuel consumption, kg / h Flue gas temperature at the outlet from the furnace, ° С. ... ... ... Flue gas volume at gas outlet temperature 4000 3130 2200

Flue gas temperature in front of boilers, ° С 375 400 410 -

In drying plants, the processed material is not located in the immediate vicinity of the furnace, as is the case in furnaces for various types of cooking, distillation and other similar boilers. Therefore, the temperature in the combustion chamber of a drying installation can be significantly higher than the temperature in the furnaces, in devices that consume heat are placed. However, in this case, the temperature is determined by the properties of the material to be dried and the requirements dictated by the quality of the product.

By the amount of heat given off by a given amount of flue gases in the radiation system, the temperature of the flue gases entering the convective system is determined.

During the operation of the regenerator, the flue gas temperature can exceed normal due to the afterburning of carbon monoxide. With timely detection of this phenomenon, it is necessary to redistribute the air over the sections, reducing the supply era to those sections where there is an excess of oxygen in the flue gases leaving the section, and increasing its input into the sections where there is not enough oxygen. In the event of a sharp increase in the temperature of the flue gases, the air supply to some or all of the sections is temporarily interrupted.

The primary reforming of natural gas with water vapor is carried out in vertically arranged pipes heated by flue gases, the lower ends of which are introduced directly into the secondary methane reformer. A portion of the flue gas is fed through a perforated plate to the secondary reforming catalyst bed, which produces a nitrogen-rich gas. Flue gas temperature - 815 ° С

Convection ovens replaced the campfire stoves, in which the pipe coil is separated from the combustion chamber by a pass wall. During the operation of such furnaces, significant drawbacks were established: high temperature of flue gases above the pass wall, melting and deformation of brickwork, burnout of pipes in the upper rows of the coil. To reduce the temperature in the combustion chamber, flue gas recirculation was used and fuel was burned with an increased excess air ratio. However, the increased air consumption reduced the efficiency of the furnaces and did not reduce the burnout of the pipes.

Superheater temperature. In some cases, a coil is mounted in the convection section of the furnace for superheating the water vapor supplied to the distillation columns for stripping low-boiling fractions. The superheater is placed where the flue gas temperature is 450-550 ° C, i.e. in the middle or lower section of the convection chamber. The superheated steam temperature is 350-400 ° C.

The flue gas temperature above the pass wall is especially important. The high temperature of the gases at the pass corresponds to the high heat density of the surface of the radiant tubes, the temperature of their walls, and a high probability of coke formation. Deposing on the inner surface of the pipes, coke impedes heat transfer, which leads to a further increase in the temperature of the walls and to their burnout.

An increase in the speed of movement of heated raw materials in the furnace tubes increases the efficiency of heat removal, lowers the temperature of the walls of the tubes and thus makes it possible to work with higher heat intensity of the radiant tubes and the temperature of the flue gases at the pass.

On a typical unit ELOU - AVT (A-12/9) with a capacity of 3 million tons / year with secondary distillation of gasoline, five furnaces with a total thermal capacity of 81 Gkcal / h are installed. All furnaces burn 11 130 kg of fuel in 1 hour. The flue gas temperature at the outlet of the convection chambers of the ovens is 375-410 ° C. To use the thermal energy of flue gases before entering them into the chimney, remote heat recovery boilers of the KU-40 type are installed in the furnaces.

The lower the temperature of the flue gases leaving the convection chamber, the more heat is absorbed by the heated oil product. Usually, the temperature of the flue gases at the exit from the convection chamber is taken to be 100-150 ° C higher than the temperature of the raw material entering the furnace. But since the temperature of the raw material entering the furnace is quite high, about 160-200 ° C, and for some processes it reaches 250-300 ° C, an air heater (recuperator) is installed to utilize the heat of the flue gases, in which the air going to the furnace is heated ovens. In the presence of an air heater and a smoke exhauster, it is possible to cool the flue gases before releasing them into the chimney to a temperature of 150 ° C. With natural draft, this temperature is at least 250 ° C.

Convection pipes receive heat due to convection of flue gases, radiation from masonry walls and radiation from triatomic gases. As noted at the beginning of this chapter, heat transfer in the convection chamber depends on the speed and temperature of the flue gases, as well as the temperature of the feedstock, the diameter of the pipes and their layout. The speed of flue gases in a convection shaft usually fluctuates within 3-4 m / s, and in a chimney 4-6 m / s.

Solution. Let us determine the efficiency of the furnace if the temperature of the flue gases at the outlet of the convection chamber is

The temperature of the flue gases at the outlet of the furnace is 500 C. The heat of the flue gases is utilized in a tubular three-way (by air) air heater with a heating surface of 875 m. After the air heater, flue gases at 250 C are removed into the atmosphere through the chimney without the use of forced draft.

Let us set the temperature of the flue gases after the heating section of the radiation chamber r, c = 850 ° C, and after the reaction section ip. c = 750 ° C. Heat content of flue gases but fig. 6.1 at a = 1.1

A distinctive feature of waste-heat boilers, as equipment for steam generation, is the need to ensure the passage of a large amount of heating flue gases per unit of generated steam (E1 / d.g / C). This ratio is a direct function of the initial temperature of the flue gases at the inlet to the apparatus and their flow rate. Due to the relatively low temperature of flue gases for generating steam, their specific consumption in waste heat boilers is much higher (8-10 times) than in conventional furnaces. The increased specific consumption of heating gases per unit of generated steam predetermines the design features of waste heat boilers. They have large dimensions, high metal consumption. To overcome the additional gas-dynamic resistance and create the required vacuum in the furnace furnace (for draft), 10-15% of the equivalent electric power of the waste heat boiler is spent.

After filling the hopper with the dried catalyst, open the valve under the hopper and pour the catalyst into the calcining column. The volume of the hopper corresponds to the useful volume of the calcining column, i.e. one load. After filling the column with catalyst, the furnace is ignited under pressure (on liquid fuel), directing the flue gases into the atmosphere. Then, having adjusted the combustion in the furnace, the flue gases are introduced into the casing of the calcining column. After warming up the casing and making sure that the fuel is burning normally, the flue gases are directed to the bottom of the calcining column in the minimum amount necessary only to overcome the resistance of the catalyst bed. Then a slow rise in the temperature of the flue gases at the outlet of the furnace and the heating of the catalyst begin. The heating of the system is continued for about 10-12 hours during this time, such an amount of flue gases is introduced so that there is no carryover of the catalyst from above. Reaching the temperature at the bottom of the column of 600-650 ° C is considered the beginning of the catalyst calcination. The duration of calcination at this temperature is 10 hours.

Then the temperature of the flue gases at the outlet from the furnace is gradually reduced and the fuel supply is stopped at 250-300 ° C, but

The temperature of the gases at the pass, the thermal intensity of the heating surface of the radiant tubes and the direct return coefficient of the furnace are mutually related. The greater the direct return coefficient, the lower the temperature of the flue gases at n (ripening), and the lower the thermal intensity of the heating surface of the radiant tubes, all other things being equal, and vice versa.

Tubular coil reactors. The vertical tube coil reactor was designed for continuous bitumen production at domestic refineries. Temperature regime of reactors. (Kremenchug and Novogorkovsky refineries) is supported by the heat of flue gases coming from the pre-chamber furnace. However, with such a solution, the specificity of the exothermic oxidation process is poorly taken into account. Indeed, to accelerate the heating of the reaction mixture in the first upstream reactor tubes, it is necessary to increase the temperature of the flue gases, but as a result, the oxidizable material in the subsequent tubes overheats, where the oxidation reaction and heat release proceed at high rates. Thus, it is necessary to maintain some intermediate temperature of the flue gases, neo [tpmal y, both to heat the reaction mixture to the reaction temperature and to subsequently maintain the temperature at the desired level. For the units of the Angarsk, Kirish, Polotsk, Novoyaroslavl and Syzran refineries, a more successful solution was found, the feedstock is preheated in a tube furnace, and the excess heat of reaction, if necessary, is removed by blowing air into the reactor tubes placed in a common casing (according to the project of the Omsk branch of VNIPIneft, each reactor tube housed in a separate casing).

If the temperature of the flue gases at the outlet from the common collectors of the regenerator exceeds 650 °, this indicates the beginning of the afterburning of carbon monoxide. To stop it, it is necessary to sharply decrease the air supply to the upper part of the regenerator.

In order to reduce the temperature of the flue gases above the pass wall in radiant-convection furnaces of the old design, especially thermal cracking furnaces, recirculation of flue gases is used. The colder flue gases from the hog furnace are returned to the combustion chamber, which leads to a redistribution of heat between the chambers. In the convection chamber, the thermal stress of the upper pipes decreases, but due to an increase in the volume of flue gases, their speed increases, while heat transfer throughout the convection chamber improves. The recirculation ratio in tube furnaces ranges from 1-3.

The imperfection of the design of the burners of furnaces and boilers for burning fuel and the insufficient tightness of the furnaces do not allow for the time being to work with small excess air. Therefore, it is believed that the temperature of the air heater tubes should be higher than the dew point temperature of aggressive flue gases, i.e. not lower than 130 ° C. For this, preliminary or intermediate heating of cold air or special layouts of the heating surface are used. There are devices that are structurally designed so that the heat exchange surface on the side of the flue gases is much larger than on the side of the atmospheric air, therefore, the sections of air heaters are assembled from pipes with different finning coefficients increasing towards the cold end (to the place where cold air enters), and thus the temperature the pipe walls are approaching the flue gas temperature. According to this principle, Bashorgener-goneft air heaters are designed from cast iron ribbed and ribbed-toothed pipes with good performance.

Heating and calcination of the catalyst is carried out by direct contact with flue gases coming from the furnace, in which gaseous or liquid fuel is burned. The flue gas temperature is automatically maintained at the level of 630-650 ° C, while the temperature in the calcination zone is 600-630 ° C. The calcined catalyst enters the cooling chon through the flow tubes of the lower gate lattice, where it moves between the rows of air-cooled tubes and he cools himself to the desired temperature. A movable metal cup is put on the end of the overflow tube, the position of which regulates the height of the catalyst bed on the conveyor located below and, consequently, the rate of product discharge. The unloaded catalyst is fed by a belt conveyor to a screen for screening out fines. Then it is poured into metal drums and delivered to the finished product warehouse.

The higher the temperature of the heated raw material in the radiant tubes and the greater its tendency to coke formation, the lower the heat intensity should be, and, consequently, the lower the temperature of the flue gases above the pass. For a given furnace, an increase in the surface of the radiant tubes leads to a decrease in the temperature of the flue gases above the pass and the heat congestion of the radiant tubes. Contamination of the inner surface of the pipes with coke or other deposits can lead to an increase in the temperature of the flue gases over the pass and to burnout of the first rows of pipes in the convection chamber of the furnace. The temperature over the pass is carefully controlled and usually does not exceed 850-900 ° C.

The temperature of the flue gases above the pass wall is usually maintained at 700-850 ° C, that is, high enough to transfer part of the heat by radiation to the upper rows of pipes in the convection chamber. But the main amount of heat in the convection chamber is transferred due to the priming convection of flue gases (created by a chimney or smoke exhauster).

The fraction of the distillate at the exit from the furnace is e = 0.4, the vapor density of the distillate is 0.86. residue density = 0.910. The diameter of the tubes in the radiation chamber is 152 X 6 mm, in the convection chamber is 127 X 6 mm, the useful length of the tubes is 11.5 m, the number of tubes is 90 and 120, respectively. Fuel composition and theoretical air consumption are the same as in examples 6.1 and 6. 2, the heat content of flue gases with an excess of air a = 1.4 is found in Fig. 6. 1. Temperature of flue gases at the pass

The total duration of the hydrothermal treatment, including heating, is approximately one day. After the start of the pressure drop in the apparatus, the temperature of the flue gases at the outlet from the furnace is gradually reduced and, finally, the nozzle is extinguished. The apparatus is cooled with cold air from the firebox through the casing. The dried balls are unloaded and sent to the bunker of the calcining column.

Suction pyrometers. In the practice of measuring high temperatures of flue gases, suction pyrometers are used. The main elements of suction pyrometers are a thermocouple placed in a cooled housing, a system of screens and a device for suction of gases. Thermal electrodes are insulated from one another and from a protective cover with rigid elements (straws, beads, one- and two-channel) made of quartz (up to 1100 ° C), from porcelain (up to 1200 ° C), from porcelain with a high alumina content (up to 1350 ° C) ) ceramic materials and glass enamels applied by broaching methods.

When the nyrozmeeviki coke, there is a gradual increase in the temperature of the pipe wall, the pressure drop increases, and white spots can be observed in the places of overheating of the pipes. The formation of coke deposits in pyrosmeeviks is also judged by the increase in the temperature of the flue gases at the pass of the furnace. Coking of the ZIA is characterized by an increase in the hydraulic resistance of the system with an increase in the temperature of the pyrolysis products after the PIA. An increase in the hydraulic resistance in the pyroskeeches and ZIA is accompanied by an increase in pressure in the furnace unit and, as a consequence, the contact time increases, and the yield of lower olefins decreases.

Outside the window is a chilly autumn evening, and a fire is burning brightly in the fireplace, and a very special warmth fills the room ... For this suburban idyll to become a reality, you need a well-designed and installed chimney, which, unfortunately, is often remembered last.

The degree of reliability and efficiency of the chimney operation largely depends on the heating devices connected to them, and vice versa. Therefore, for each type of fireplace, there is an optimal chimney option.

Very different fireplaces

And finally, the last type is the fireplace stove. The main distinguishing feature of such devices, which makes them resemble a real stove, is the presence of a built-in smoke channel, passing through which the flue gases are cooled to a rather low temperature. In this regard, there is a need for a massive masonry or well-insulated modular chimney.

Make way for smoke!

Ethnographic touches

The houses of Korean settlers in the Ussuri region were equipped with very exotic chimneys. Here is how VK Arseniev described them: “Inside ... there is a clay canal. It takes up more than half of the room. Chimneys run under the canal, warming the floors in the rooms and spreading heat throughout the house. The chimneys are led out into a large hollow tree that replaces the chimney. "

Some peoples of the Volga region and Siberia before the 30s. XX century Chuval was widespread - a wall open hearth with a straight chimney hanging over it. The hearth was built of stones or logs covered with a layer of clay, and the chimney was made of hollow wood and thin poles coated with clay. In winter, the chuval was stoked all day, the pipe was plugged at night.

Brick chimneys until recently, both in urban and rural construction were practically uncontested. Being a versatile construction material, brick allows you to vary the number of chimney channels and wall thickness (you can make the necessary thickenings in the places where floors, roofs, as well as when building the street part of the chimney). Subject to construction technologies, a brick chimney is very durable. However, it also has disadvantages. Due to the significant mass (pipe with a cross section of 260

For the construction of a brick chimney, a very high qualification of builders is required. What are the most common mistakes when building it? This is a choice of low-quality or unsuitable bricks (poorly fired partition or wall); thickness of masonry joints more than 5 mm; masonry on the edge; the use of stepped ("jagged") masonry in inclined areas; improper preparation of the solution (for example, if the ratio of parts of clay and sand is chosen without taking into account the fat content of the clay), sloppy splitting or cutting of bricks; inattentive filling and bandaging of masonry seams (the presence of voids and double vertical seams); laying the pipe close to structures made of combustible materials.

The condition of the brick pipe requires constant monitoring. Before, it was certainly whitewashed, since it is easier to notice soot on a white surface, indicating the presence of cracks.

Expert opinion

The brick chimney has served man faithfully for centuries. The laying of stoves and fireplaces from this material is almost an art. The paradox is that during the period of mass dacha construction in our country, this skill suffered serious damage. The consequences of the "work" of numerous would-be stove-makers were sad, and most importantly, they gave rise to distrust of brick furnaces and chimneys. Therefore, favorable conditions have arisen and remain for the promotion of prefabricated chimney systems on the domestic market.

Alexander Zhilyakov,
head of the wholesale department of the company "Saunas and Fireplaces"

Stainless steel pipes can be safely attributed to the most widely used type of chimneys today. Steel modular systems have a number of undeniable advantages. The main ones are low weight, ease of installation, a wide selection of pipes of different diameters and lengths, as well as fittings. Steel chimneys are manufactured in two versions - one- and two-circuit (the latter is in the form of a "sandwich" of two coaxial pipes with a layer of non-combustible thermal insulation). The first ones are designed for installation in heated rooms, connecting the fireplace to an existing chimney, as well as rehabilitating old brick pipes. The latter are a ready-made constructive solution, equally suitable for the installation of a chimney both inside the building and outside. A special type of stainless steel smoke ducts - flexible single- and double-walled (without thermal insulation) corrugated hoses.

For the production of single-circuit chimneys and inner pipes of "sandwich" type chimneys, heat- and acid-resistant alloy steel sheet (usually 0.5-0.6 mm thick) is used. Single-circuit chimneys made of carbon steel, coated on the outside and inside with special black enamel (such as, for example, in the assortment of Bofill, Spain), even surpass stainless steel pipes in heat resistance; they are also not afraid of condensate, but only under the condition of the integrity of the coating, which is easy to damage (say, when cleaning the chimney). The service life of pipes without coating made of "black" steel with a thickness of 1 mm does not exceed 5 years.

The casing (shell) of "sandwich" pipes, as a rule, is made of ordinary (non-heat-resistant) stainless steel, which is electrochemically polished to a mirror finish, and some manufacturers, such as Jeremias (Germany), offer enamel painting in any color on the scale RAL. The use of a galvanized steel casing is justified only when installing a chimney inside a building. Outside, such a pipe, if you actively operate the chimney, will not last long: due to periodic heating, corrosion intensifies.

Expert opinion

Stainless steels used for the production of chimneys are divided into two categories: magnetic ferrite (in the American standardization system ASTM - these are AISI 409, 430, 439, etc.) and non-magnetic austenitic (AISI 304, 316, 321, etc.). ). According to our tests of AISI 409 steel (composition: 0.08% C, 1% Mn, 1% Si, 10.5-11.75% Cr, 0.75% Ti), the critical temperature value in the inner pipe of the insulated chimney fragment , at which the effect of intercrystalline corrosion became noticeable, was equal to 800-900

Alexey Matveev,
head of the commercial department of the company "NII KM"

The thermal insulation layer in the "sandwich" pipes solves three problems at once: it prevents the overcooling of flue gases that negatively affects the draft, does not allow the temperature of the inner walls of the chimney to drop to the dew point, and, finally, ensures the fire-safe temperature of the outer walls. The choice of insulating materials is small: usually it is cotton wool - basalt (Rockwool, Denmark; Paroc, Finland) or organosilicon (Supersil, Elits, both - Russia), pearlite sand (but it can be filled up only during the installation of the chimney).

Such a very important characteristic of the chimney as gas tightness depends on the design of the pipe joints, therefore each manufacturer seeks to bring it to perfection. So, the sealing of the chimney Hild (France) is provided by centering couplings; the double annular protrusion formed at the joint is clamped by the clamps supplied with each module. Raab chimneys are provided with a tapered connection in combination with a collar. In Selkirk systems (Great Britain), high gas tightness can be achieved due to the special design of the clamp. The vast majority of stainless steel chimneys are mounted in the traditional way, and here a lot depends on the quality of the parts. Usually, the upper module is put on the lower one, however, single-circuit ones, and with an external gasket, double-circuit modules should be joined by inserting the upper one into the lower one, which will avoid condensate leaks through the joints.

Chimneys for fireplaces with different characteristics

* - when using hardwoods, coal as fuel, as well as with excessive draft, the temperature may exceed the specified value;
** - for fireplace stoves made of talcomagnesite; for metal - up to 400

Ceramic chimneys- these are the same "sandwiches", but "cooked" according to a completely different recipe. The inner pipe is a pottery made of chamotte mass, the middle layer is unchanged basalt wool, the outer one is a section of lightweight concrete or mirror stainless steel. Such systems are presented on the domestic market by Schiedel (Germany).

Chimneys made of ceramics are resistant to high temperatures (up to 1000

Ceramic systems also have their drawbacks. Chimneys with a concrete casing have a significant mass (1 running meter weighs from 80 kg), can be used only as main (free-standing) ones, do not allow to bypass obstacles. The "weak link" of such chimneys is the connection unit. Manufacturers provide for the use of a metal module (s), which has a shorter service life and therefore will require replacement in the future, which must be foreseen during the construction of the fireplace.

Chimneys Raab with stainless steel inner pipe and concrete casing:
with ventilation duct (a)
or without it (b)

And finally, metal does not combine very well with ceramics, since it has a high coefficient of thermal expansion: along the perimeter of the steel pipe, where it enters the ceramic, it is necessary to leave a rather large (about 10 mm) gap, which is filled with asbestos cord or heat-resistant sealant.

However, the high reliability and durability of ceramic chimneys (the factory warranty is 30 years, and the actual service life, according to the manufacturers, is more than 100 years) allows you to close your eyes to the listed disadvantages. Moreover, the price of Schiedel products is quite comparable to the cost of imported stainless steel systems - only a set of the first three meters of the chimney is relatively expensive, including a condensate trap, an audit, a connection unit and a gate. For example, a 10 m high chimney of the Uni system with ceramic pipes 200 mm in diameter without a ventilation duct costs about 43 thousand rubles.

Comparative cost of a double-circuit stainless steel module 1000 mm long, rub.

How many pipes are right?

The question of the possibility of connecting two fireplaces to one chimney is a controversial one. According to the requirements of SNiP 41-01-2003, "for each stove, as a rule, a separate chimney or channel should be provided ... It is allowed to connect two stoves to one chimney, located in the same apartment on the same floor. When connecting chimneys in them cuts should be provided (middle walls dividing the chimney into two channels. - Ed.) with a height of at least 1 m from the bottom of the pipe connection. "As for the cut, it can only be done in a brick chimney. the smaller one is cut into the larger one), after which it is necessary to increase the channel section. the common pipe will warm up better and the draft will increase, but this only applies to chimneys with a height of more than 6 m.

When connecting two stoves located on different floors to one chimney, everything is much more complicated. Practice shows that such systems work, but only with careful calculation and numerous additional conditions (increase in the height of the chimney, installation of dampers after the lower firebox and on the inlet pipe of the upper one, observance of the sequence of ignition or complete exclusion of simultaneous operation, etc.).

We draw your attention to the fact that everything said in this section applies only to fireplaces with a closed hearth. An open firebox is more fire hazardous and demanding for draft, therefore it does not allow any "liberties" and requires the construction of a separate chimney.

On the street with a pillar, in a hut with a tablecloth

Poor draft, as a rule, occurs due to errors in the design of the chimney. The desire to explain it by unfavorable weather conditions (changes in atmospheric pressure and air temperature) is unreasonable, since these factors are also taken into account with a competent decision. Let's list the reasons for poor traction and its periodic overturning (that is, the occurrence of reverse thrust):

It is much more difficult to determine the cause in each specific case, since several factors often act at once, none of which plays an independent role. To improve draft, it is necessary to change the design of the chimney, sometimes not too much (for example, to increase the thickness of the thermal insulation on the last one and a half to two meters of the pipe). There is also such a problem as excessive thrust. You can deal with it with a gate. It is only necessary to provide for its installation before starting the installation of the chimney.

No smoke without ... water

The main combustion gases of carbonaceous fuels are carbon dioxide and water vapor. In addition, during combustion, the moisture present in the fuel itself (wood) evaporates. As a result of the interaction of water vapor with sulfur and nitrogen oxides, acid vapors of weak concentration are formed, which condense on the inner surface of the chimney when they are cooled to a temperature below the critical temperature (when burning wood - about 50

If you heat a fireplace with an external non-insulated metal chimney in the cold season, the amount of condensate can be measured in liters per day. A brick pipe is capable of accumulating heat, therefore it behaves differently: condensate is formed only at the stage of heating the pipe (although this is a rather long period of time). In addition, the material partially absorbs condensate, so the latter is not too noticeable, which, however, does not prevent it from having a destructive effect on the masonry. If the intensity of combustion is low and the ambient temperature is low, the brick may cool down and condensation will start to form again. If the thickness of the insulation is insufficient and the temperature of the exhaust gases is low (the firebox is adjusted for long-term combustion), condensate can also appear in the sandwich-type modular chimney. One way or another, it is impossible to completely get rid of condensate, you just need to reduce its amount to a minimum (the main means for this is the use of more effective thermal insulation) and prevent leaks.

We have touched on only a small part of the problems associated with the coexistence of chimney and smoke. Trying to answer all the questions that the owners of fireplaces have in one article is an impossible task. An individual approach is often required, and, as experts say, sometimes only experience and professional intuition can prompt the right decision.

The editors would like to thank Raab, Rosinox, Schiedel, Tulikivi, Maestro, NII KM, Saunas and Fireplaces, EcoKamin for their help in preparing the material.

A beautiful enamelled stove implies a beautiful enameled chimney.
Is it possible to put a stainless steel?

New Product

These enamelled flues are coated with a special compound of high temperature resistance and acid resistance. The enamel can withstand very high flue gas temperatures.

For example, modular chimney systems LOKKI production facilities of the Novosibirsk plant "SibUniversal" have the following data:

• The operating temperature of the chimney is 450 ° С, a short-term temperature rise up to 900 ° С is allowed.
• Able to withstand the temperature of the "furnace fire" 1160 ° C for 31 minutes. Although the standard is 15 minutes.

Flue gas temperature

In the table, we have collected the temperature readings of the flue gases of various heating devices.

After comparison, it becomes clear to us that working temperature of enameled chimneys 450 ° С not suitable for Russian wood-fired stoves and fireplaces, wood-fired sauna stoves and coal boilers, but for all other types of heating devices this chimney is quite suitable.

In the descriptions of the chimneys of the system "Locke" it is so bluntly said that they are intended for connection to any type of heating devices with an operating temperature of exhaust gases from 80 ° C to 450 ° C.

Note. We love to turn the sauna stove red hot to its fullest. And even for a long time. That is why the temperature of the flue gases is so high, and that is why fires occur so often in the baths.
In these cases, especially in sauna stoves, a thick-walled steel or cast iron pipe can be used as the first element after the stove. The fact is that most of the hot gases are cooled to an acceptable temperature (less than 450 ° C) already at the first pipe element.

What is heat resistant enamel?

Steel is a durable material, but it has a significant drawback - a tendency to corrosion. In order for metal pipes to withstand adverse conditions, they are covered with protective compounds. One of the options for the protective composition is enamel, and since we are talking about chimneys, the enamel must be heat-resistant.

Please note: the enameled chimneys have a two-layer coating, the metal pipe is first covered with soil, and then with a cover enamel.

To give the enamel the necessary properties, during its preparation, special additives are introduced into the molten mixture. The basis of the ground and cover enamel is the same; for the manufacture of the charge, a melt is used from:

• Quartz sand;
• Kaolin;
• Potash and a number of other minerals.

But the additives for cover and ground enamel are used differently. Metal oxides (nickel, cobalt, etc.) are introduced into the soil composition. Thanks to these substances, reliable adhesion of the metal to the enamel layer is ensured.

Titanium and zirconium oxides, as well as fluorides of some alkali metals are added to the cover enamel. These substances provide not only increased heat resistance, but also the strength of the coating. And to give the coating decorative properties during the preparation of the cover enamel, colored pigments are introduced into the molten composition

Pipe material

Attention. The low weight of thin-walled metal and mineral wool makes it possible to do without a special foundation for the chimney system. The pipes are mounted on brackets on any wall.

Equipment

In the double-walled version, the space between the pipes is filled with mineral (basalt) wool, which is a non-combustible material with a melting point of more than 1000 degrees.

Manufacturers and suppliers of enamelled chimney systems offer a wide range of accessories:

• Double-circuit and single-circuit pipes.
• Double-circuit and single-circuit taps.
• Tees.
• (gate valves) rotary with fixation.
• Roof cuts - nodes for roof passage.
• Ceiling gaps - nodes for the passage of the ceiling.
• Umbrellas.
• Heads.
• Plugs.
• Flanges, including decorative flanges.
• Protective screens.
• Fasteners: clamps, brackets, cleaning windows.

Mounting

In any case, we begin to mount the chimney "from the stove", from the heater, that is, from the bottom up.

1. The inner pipe of each next element enters the inside of the previous element. This prevents condensation or precipitation from entering the basalt insulation. And the outer pipe, which is often called the shell, is put on the previous pipe.
2. According to the requirements of fire safety standards, the pipe fit (nozzle depth) must be at least half the diameter of the outer pipe.
3. The joints are sealed with clamps or fitted on a cone. This is determined by the manufacturer of the structure. For a reliable seal, there are sealants with an operating temperature of 1000 ° C.
4. Pipe joints with tees or bends must be fastened with clamps.
5. Wall mounting brackets are installed at least every 2 meters.
6. Each tee is attached to a separate support bracket.
7. The chimney route should not have horizontal sections of more than one meter.
8. In places where walls, ceilings and roofs go through, elements that meet fire safety requirements must be used.
9. Chimney routes should not come into contact with gas, electricity and other pipelines.

Reasonable care must be taken during installation work. It is recommended to use only rubberized tools, this will avoid violating the integrity of the pipe coating (chips, cracks). This is very important, since a corrosive process begins to develop at the place of damage to the enamel, which destroys the pipe.

In general, we can say that such chimneys have undoubted aesthetic advantages over stainless steel. But there are no technical, operational and installation advantages.