Separate smoke exhaust system of a gas boiler. Separate smoke exhaust system

What is the difference between a coaxial smoke exhaust system and a separate one. Features of types of smoke removal systems.

When installing a heating boiler in a house, of course, you need to take care of the removal of combustion products. This task is rather difficult, but thanks to the use of modern equipment, it is easily solved, and without any special financial costs.

Installation modern look smoke extraction systems are convenient and by the fact that at the same time it allows solving the problem of providing the heating boiler with oxygen. The fact is that during the operation of the boiler, a significant amount of oxygen is consumed.

If you take it from the inner space of the room, then drafts are created, and the microclimate is significantly deteriorating. In addition, the room temperature will drop all the time.

After all, the outside air will be constantly drawn into the room. The energy of the boiler will be consumed to warm it up. Thus, it will be practically impossible to protect yourself from the cold.

Therefore, it is best of all that the air is supplied from the street directly to the heating boiler. This will avoid any interaction with the indoor air, which means your cold protection system will work as efficiently as possible.

Coaxial view of the smoke extraction system

The coaxial fume extraction system consists of an outer pipe and an inner pipe. Combustion products (smoke, water vapor, carbon dioxide), due to the traction force of the heating boiler itself, are led out. And, through the space between the pipes, air is supplied necessary to maintain the combustion process in the boiler.

The diameter of the smaller pipe is usually 6 cm, and the larger one is 10 cm. For the operation of small gas boilers, a pipe diameter of 6 cm is quite sufficient. Therefore, the coaxial smoke extraction system is recommended for use in private houses and for small commercial (public) areas.

But still, such equipment is not some kind of universal solution because it has a certain ratio of pros and cons.

The advantage of the coaxial smoke extraction system is its low fire hazard. Indeed, the temperature of the outer pipe is quite low, and the interaction of combustible objects and substances with the inner pipe is practically impossible.

The disadvantages of this smoke removal system include its high cost. In the case of a long chimney length, it is more advantageous to use a separate smoke extraction system.

Split view of the smoke extraction system

The split fume extraction system also uses two pipes. Through one pipe, the combustion products are removed outside, and through the other, air enters the boiler. This fume extraction system is ideal for powerful boilers. Indeed, the larger the heating boiler, the more combustion products are formed during its operation.

Advantages of a separate smoke extraction system:

1. This system can be used for boilers operating on in different ways fuel ( natural gas, fuel oil, coal, firewood).
2. Inexpensive installation.

As a rule, a special room is allocated for powerful boilers, into which oxygen can easily enter both through a special pipe and through a ventilation system.

What is the peculiarity of assembling and installing types of smoke removal systems

For the installation of both smoke extraction systems, use: straight sections (pipes) and adapters. The straight sections of the system are first connected to each other. Then, with the help of special fastening parts, they are installed on the walls of the building. If the section is difficult, then adapters are used to connect the straight sections.

The time of stoves and coal stoves is gradually coming to an end. And even the most modern industrial boiler houses are forced to make room for individual heating stations and the ever-increasing demand for wall-mounted gas boilers. One of the reasons for such a surge in popularitygas wall-hung boilers - the ability to install them in almost any room, combined with an amazing ease of installation and adaptability to any needs and conditions.

To a large extent, the scope of application of boiler equipment is expanded by the proposed chimney system. In addition to the usual atmospheric chimney, which we all have known since childhood, coaxial chimneys have appeared, as well as various separate systems.

The smoke exhaust and combustion air supply system is an important part of heating and water heating technology. From correct selection and installation of a smoke exhaust system largely depends on the service life of your boiler equipment. There is no need to talk about such a factor as safety - carbon monoxide must be withdrawn in a timely manner in compliance with all fire-prevention measures. Design errors can affect both the economy of the heating system and its performance.

Coaxial and separate smoke exhaust systems are used to remove flue gases from domestic gas boilers with closed chamber combustion. They can be used in both individual and multi-family residential buildings.

Both of these systems consist of two parts - a chimney and an air duct. The chimney must ensure complete removal of flue gases from the boiler into the atmosphere, and the air duct must provide the required volume of air for gas combustion. Air intake can be carried out both directly outside the building and inside the building, if it meets the necessary requirements and provides sufficient supply ventilation.

1. COAXIAL FLUE SYSTEMS OF WALL-MOUNTED BOILERS

The coaxial smoke exhaust system is used to remove flue gases from domestic gas boilers with a closed combustion chamber, where the flue gas temperature does not exceed 200 C. The installation is allowed underpressure or overpressure up to 200 Pa.

Coaxial chimneys usually made with a thickness of 1.0, 1.5 and 2.0 mm., round section. The inner tube is made of aluminum, the outer tube is made of steel or aluminum. Diameter options are usually 60/100 or 80/125. Moreover, the standard size 60/100 is the most common, and 80/125 is used with wall-mounted condensing boilers, or in cases where the chimney system exceeds 4-5 meters.

Almost all elements of the coaxial system are universal - they are suitable for any thermoblocks, regardless of the brand. For example, extensions towall-mounted boilers Vaillant, Buderus, Viessmann, Bosch boilers etc. are completely interchangeable.

An exception is the element that is attached directly to the boiler - this is an angled elbow or a vertical adapter for connecting to the boiler. The angle adapter is used for horizontal passage through the wall, and the vertical adapter for passage through the roof, or in cases where it is necessary to mount the horizontal passage slightly higher.

Therefore, if you purchase a set of passage through the wall (or roof), then you also need to choose it, like the boiler adapter, depending on the manufacturer of your boiler equipment.

WITH outside chimney elements are paintedI'm in White color... Elements of a coaxial system can also be used in conjunction with elementsseparate chimney system 80/80 .

Any additional insulation is not required during installation - the minimum distance from combustible materials is 0 mm.

1.1 Calculation of the smoke exhaust system

The calculation of the coaxial smoke exhaust system must be carried out taking into account the installation site, the characteristics of the boiler and the geometry of the chimney.

When calculating, it is necessary to check the resistance of the chimney, and make sure that under all possible weather conditions and operating modes of the thermoblock, the vacuum at the inlet to the chimney is sufficient to overcome the resistance of the boiler and the chimney itself, and also provides a sufficient flow of air for combustion.

It should be borne in mind that usually for a diameter of 60/100, the total length of the chimney should not exceed 4.5 meters, and each 90 degree bend reduces it by another 0.5 meters. If a large length of the structure is required, then you should switch to a separate system, or to a coaxial chimney with a diameter of 80/125.

The temperature of the inner surface of the chimney must be at least 0 C. Failure to fulfill this condition, during the period of negative temperatures, will lead to freezing of condensate inside the chimney, narrowing of the working section and possible emergency shutdown of the boiler. It is also necessary to make sure that the temperature of the inner surface of the chimney in all modes exceeds the dew point temperature in the combustion products.

1.2 Diagrams of coaxial smoke extraction

1.2.1 Horizontal outlet via outer wall

This is the most common scheme for building a chimney for a wall-mounted boiler. Due to its simplicity and low cost, it is used in the overwhelming majority of cases.

| The coaxial flue gas vent is discharged horizontally through the outer wall. During installation, it is necessary to ensure a slope of 2-3 degrees from the boiler in order to exclude the ingress of condensate into the device.

For mounting, standard basic wall penetration kits are usually used. The kits are selected according to the type (manufacturer) of the wall-mounted boiler. For examplebasic wall pass VAILLANT(art. 303807) or horizontal set BUDERUS (art. 7 747 380 027 3) differ in the angle adapter for connection to the boiler. The rest of the parts are the same and interchangeable. And of course, you can use any extension elements for them, for exampleextension of coaxial pipe 60/100 1 meter, or coaxial knee 60/100 angle 90 .

1.2.2 Vertical roof passage

In this case, the chimney is led out from the top of the boiler through the roof of the building. In this case, a vertical adapter is used (it is put on directly on the boiler and each manufacturer has its own, see for exampleCoaxial vertical adapter Ø60 / 100 BOSCH, Buderus). Further mounted required amount extension pieces, for exampleCoaxial pipe 60/100 2.0 m ... Completes the design from the topTerminal vertical Ø60 / 100 for passage through the roof - it provides a tight connection to the roof.

This scheme is usually used in private houses and cottages.

1.2.3 Connection to a collective chimney

The coaxial chimney is led into the collective chimney shaft. Combustion air is supplied from the free space between the outer wall of the shaft and the liner of the common chimney.

In this case, a careful calculation of both the entire shaft and the chimney sleeve (cross-sectional area, maximum length, distance between devices, etc.) is necessary in order to avoid the draft from overturning from one thermoblock to another.

If such a calculation is difficult, then it is preferable to design a multichannel collective chimney - when air is taken in through a common space, and combustion products are removed through an individual channel.

Such chimney systems are commonly used for apartment heating in apartment buildings.

1.3 Installation rules for coaxial flues

1.3.1 Vertical section

When designing and installing a vertical roof passage, it is necessary to be guided by the diagram below.

Chimney height for houses with flat roof should be more than 2.0 m, and if the roof is adjacent to the chimney - at least 0.5 above the adjacent roof.

To prevent condensate from getting into the boiler at the beginning of the section, aCondensate trap coaxial Ø60 / 100 for straight-through pipes.

1.3.2 Horizontal section

When installing a horizontal wall passage, the following diagram must be observed:

When designing a chimney, it is important to reduce its length and the number of turns as much as possible. It is advisable to use no more than 3 90 ° turns, since each of them reduces the permissible chimney length by an average of 0.5 meters.

For condensate drainage, condensate traps are provided, and the chimney itself is mounted with a slope of 2-3 degrees from the boiler.

We will talk about a separate 80/80 chimney system in part 2 of this article.

Efficient and safe operation of boiler heating units depends on the competent installation of systems air supply and removal of combustion products. When choosing smoke exhaust systems for a heat-generating unit, the calculation is made taking into account technical characteristics boiler plant. There are several ways to organize the supply of air to the combustion chamber and the removal of combustion products from it:

• for equipment with an open combustion chamber, this is a traditional chimney (natural draft);
• for installations with a closed chamber, coaxial or separate chimneys are used.

Selection of a smoke exhaust system for a heating boiler with an open combustion chamber

The area and shape of the chimney section, its height determine the amount of vacuum - the draft that occurs in the pipe due to the temperature and pressure difference. The higher the chimney, the higher the draft will be. And, in turn, a deterioration in traction can occur due to:

• insufficient height of the chimney;
• poor thermal insulation of the chimney;
• lack of air in the combustion chamber, etc.

The main requirements for the chimney are:

• tightness;
• fire resistance;
• corrosion resistance;
• the ability to withstand multiple temperature drops;
• ease of installation.

The most popular option for organizing chimneys for heating equipment private households are stainless steel structures.

Selection of a chimney system for boilers with a closed combustion chamber

Depending on the design heating system with closed type combustion chambers use one of following options air supply and exhaust of combustion products:

• coaxial pipelines, in which air is supplied through the outer pipe, and the removal of smoke and gas through the inner pipe.
• separate pipelines: air supply and combustion products are removed through different pipes.

Selection of a smoke exhaust system for a gas condensing heating boiler

When organizing chimneys for condensing boilers (construction), chimneys are made of resistant plastic.

Regulatory requirements for the design of chimneys

When organizing a heating system, in particular, a device for air supply and removal of combustion products, these measures are carried out taking into account the requirements of a number of regulatory documents:

• DBN V.2.5-20-2001 "Gas supply";
• SNiP ("Boiler plants. Design standards", "Heating, ventilation, air conditioning");
• DSTU ("Chimneys. Methods of heat engineering and aerodynamic calculations", "Heat supply of residential buildings with gas-fired heat generators with a closed combustion chamber")

Chimney systems classification

According to international classification There are several types of chimney systems, designated B22-23, C12-82, etc. In smoke exhaust systems "B", combustion air is taken from the boiler room, and the combustion products are discharged outside. In "C" smoke systems, air is taken in from the outside and the smoke is discharged to the outside. The numbers indicate the type of camera.

For the correct choice of the flue gas system, take into account:

• type of heating unit;
• technical characteristics of the thermal installation;
• type of air supply and combustion products removal system and other parameters.

Boilers are distinguished by the following features:

By appointment:

Energetically e- generating steam for steam turbines; they are distinguished by high productivity, increased steam parameters.

Industrial - generating steam both for steam turbines and for the technological needs of the enterprise.

Heating - producing steam for heating industrial, residential and public buildings. These include hot water boilers. A hot water boiler is a device designed to produce hot water with a pressure above atmospheric.

Waste heat boilers - designed to generate steam or hot water by using the heat of secondary energy resources (RES) in the processing of chemical waste, household waste etc.

Energy technology - are designed to generate steam by means of secondary energy resources and are an integral part of the technological process (for example, soda recovery units).

By the design of the combustion device (fig. 7):

Rice. 7. General classification of combustion devices

Distinguish between furnaces layered - for burning lump fuel and chamber - for burning gas and liquid fuels, as well as solid fuels in a pulverized (or finely crushed) state.

Layer furnaces are subdivided into dense and fluidized bed furnaces, and chamber furnaces - into direct-flow flare and cyclonic (vortex) ones.

Chamber furnaces for pulverized fuel are divided into furnaces with solid and liquid ash removal. In addition, by design they can be single-chamber and multi-chamber, and by aerodynamic regime - under vacuum and supercharged.

Basically, a vacuum circuit is used, when a pressure is created in the boiler gas ducts by a smoke exhauster, which is less than atmospheric pressure, that is, a vacuum. But in some cases, when burning gas and fuel oil or solid fuel with liquid bottom ash removal, a pressurized scheme can be used.

Boiler diagram under pressure. In these boilers, a high-pressure blowing unit provides an overpressure in the combustion chamber of 4 - 5 kPa, which makes it possible to overcome the aerodynamic resistance of the gas path (Fig. 8). Therefore, there is no smoke exhauster in this scheme. The gas-tightness of the gas path is ensured by the installation of membrane screens in the combustion chamber and on the walls of the boiler gas ducts.

The advantages of this scheme:

Relatively low capital costs for lining;

Lower than a boiler operating under

discharge, electricity consumption for own needs;

Higher efficiency due to the reduction of losses with flue gases due to the absence of air suction into the gas path of the boiler.

Flaw- the complexity of the design and manufacturing technology of membrane heating surfaces.

By type of coolant generated by the boiler: steam and hot water.

On the movement of gases and water (steam):

gas-tube (fire-tube and with smoke tubes);

water tube;

combined.

Fire tube boiler diagram. The boilers are designed for closed heating, ventilation and hot water supply systems and are manufactured to operate at an admissible operating pressure of 6 bar and permissible temperature water up to 115 ° C. The boilers are designed to operate on gaseous and liquid fuels, including fuel oil and crude oil, and provide efficiency when operating on gas - 92% and on fuel oil - 87%.

Steel hot water boilers have a horizontal reversible combustion chamber with a concentric arrangement of smoke tubes (Fig. 9). To optimize heat load, combustion chamber pressure and flue gas temperature, the flue pipes are equipped with stainless steel turbulators.

Rice. 8. Boiler diagram under "pressurization":

1 - air intake shaft; 2 - high-pressure fan;

3 - air heater of the 1st stage; 4 - water economizer

1st stage; 5 - 2nd stage air heater; 6 - air ducts

hot air; 7 - burner device; 8 - gas-tight

screens made of membrane pipes; 9 - gas duct

Rice. 9. Diagram of the combustion chamber of fire-tube boilers:

1 - front cover;

2 - boiler furnace;

3 - smoke tubes;

4 - tube sheets;

5– boiler fireplace part;

6 - mantel hatch;

7 - burner device

By the way of water circulation all the variety of designs of steam boilers for the entire range of operating pressures can be reduced to three types:

- with natural circulation - rice. 10a;

- with multiple forced circulation - rice. 10b;

- straight-through - rice. 10c.

Rice. 10. Methods of water circulation

In boilers with natural circulation, the movement of the working fluid along the evaporative circuit is carried out due to the difference in the densities of the columns of the working medium: water in the drop feed system and steam-water mixture
in the lifting evaporator part of the circulation circuit (Fig.10a). Circulation driving head
in the contour can be expressed by the formula

, Pa,

where h is the height of the contour, g is the acceleration of gravity, ,
- density of water and steam-water mixture.

At critical pressure working environment is single-phase and its density depends only on temperature, and since the latter are close to each other in the lowering and lifting systems, the driving head of the circulation will be very small. Therefore, in practice, natural circulation is used for boilers only up to high pressures, usually not higher than 14 MPa.

The movement of the working fluid along the evaporation circuit is characterized by the circulation rate K, which is the ratio of the hourly mass flow rate of the working fluid through evaporation system boiler to its hourly steam production. For modern ultra-high pressure boilers, K = 5-10, for low and medium pressure boilers, K is from 10 to 25.

A feature of boilers with natural circulation is the way of arranging heating surfaces, which consists in the following:

In boilers with multiple forced circulation, the movement of the working fluid along the evaporation circuit is carried out due to the operation of the circulation pump included in the downstream flow of the working fluid (Fig.10b). The circulation rate is maintained low (K = 4-8), since the circulating pump guarantees its preservation under all load fluctuations. Boilers with multiple forced circulation allow saving metal for heating surfaces, since higher speeds of water and working mixture are allowed, thus partially improving the cooling of the pipe wall. At the same time, the dimensions of the unit are somewhat reduced, since the diameter of the pipes can be chosen smaller than for boilers with natural circulation. These boilers can be used up to critical pressures of 22.5 MPa, the presence of a drum makes it possible to drain steam well and blow out contaminated boiler water.

In once-through boilers (Fig.10c), the circulation rate is equal to one and the movement of the working fluid from the inlet to the economizer and to the outlet of the superheated steam unit is forced by a feed pump. The drum (a rather expensive element) is absent, which gives a certain advantage to direct-flow units at ultra-high pressure; however, this circumstance causes a rise in the cost of station water treatment at supercritical pressure, since the requirements for the purity of the feed water, which in this case should contain no more impurities than the steam produced by the boiler, increase. Direct-flow boilers are universal in terms of operating pressure, and at supercritical pressure they are generally the only steam generators and are widely used in modern power engineering.

There is a type of water circulation in once-through steam generators - combined circulation, carried out by a special pump or an additional parallel circulation circuit of natural circulation in the evaporator part of a once-through boiler, which allows to improve cooling screen tubes at low boiler loads due to an increase of 20–30% in the mass of the working medium circulated through them.

Boiler diagram with multiple forced circulation the subcritical pressure is shown in Fig. eleven.

Rice. 11. Structural diagram of a boiler with multiple forced circulation:

1 - economizer; 2 - drum;

3 - downstream feed pipe; 4 - circulation pump; 5 - distribution of water through the circulation circuits;

6 - evaporative radiation heating surfaces;

7 - scallop; 8 - superheater;

9 - air heater

The circulation pump 4 operates with a pressure drop of 0.3 MPa and allows the use of small-diameter pipes, which saves metal. The small diameter of the pipes and the low circulation rate (4 - 8) cause a relative decrease in the water volume of the unit, therefore, a decrease in the dimensions of the drum, a decrease in drilling in it, and hence a general decrease in the cost of the boiler.

The small volume and independence of the effective circulation head from the load allow you to quickly melt and stop the unit, i.e. work in an adjustment and starting mode. The area of ​​application of boilers with multiple forced circulation is limited by relatively low pressures, at which the greatest economic effect can be obtained due to the reduction in the cost of developed convective evaporative heating surfaces. Boilers with multiple forced circulation are widely used in heat recovery and steam-gas installations.

Direct-flow boilers. Direct-flow boilers do not have a fixed boundary between the economizer and the evaporative part, between the evaporative heating surface and the superheater. When the temperature of the feed water, the operating pressure in the unit, the air mode of the furnace, the moisture content of the fuel and other factors change, the ratio between the heating surfaces of the economizer, the evaporating part and the superheater changes. So, when the pressure in the boiler decreases, the heat of the liquid decreases, the heat of evaporation rises and the heat of superheat decreases, therefore the zone occupied by the economizer (heating zone) decreases, the zone of evaporation grows and the zone of overheating decreases.

In direct-flow units, all impurities entering with the feed water cannot be removed with blowing like drum boilers and are deposited on the walls of the heating surfaces or are carried away with steam into the turbine. Therefore, once-through boilers place high demands on the quality of the feed water.

To reduce the risk of pipe burnout due to the deposition of salts in them, the zone in which the last drops of moisture evaporate and steam overheating begins, at subcritical pressures is taken out of the furnace into a convective gas duct (the so-called extended transition zone).

In the transition zone, there is a vigorous precipitation and deposition of impurities, and since the temperature of the pipe metal wall in the transition zone is lower than in the furnace, the danger of pipe burnout is significantly reduced and the thickness of the deposits can be allowed to be greater. Correspondingly, the inter-flushing working campaign of the boiler is lengthened.

For aggregates of supercritical pressures, the transition zone, i.e. a zone of increased salt deposition is also present, but it is strongly stretched. So, if for high pressures its enthalpy is measured in the value of 200-250 kJ / kg, then for supercritical pressures it increases to 800 kJ / kg, and then the implementation of the removed transition zone becomes impractical, especially since the salt content in the feed water is so small here, which is practically equal to their solubility in steam. Therefore, if a boiler designed for supercritical pressure has a remote transition zone, then this is done only for reasons of conventional cooling of flue gases.

Due to the small storage volume of water in direct-flow boilers important role the synchronization of the supply of water, fuel and air plays. If this correspondence is violated, wet or overheated steam can be supplied to the turbine, and therefore, for direct-flow units, the automation of the regulation of all processes is simply mandatory.

Direct-flow boilers designed by Professor L.K. Ramzin. A specific feature of the boiler is the arrangement of the radiation heating surfaces in the form of horizontally lifting winding of tubes along the walls of the furnace with a minimum of collectors (Fig. 12).

Rice. 12. Structural diagram of Ramzin's direct-flow boiler:

1 - economizer; 2 - bypass unheated pipes;

3 - lower water distribution manifold; 4 - screen

pipes; 5 - the upper collecting collector of the mixture; 6 - taken out

transition zone; 7 - wall part of the superheater;

8 - convective part of the superheater; 9 - air heater;

10 - burner

As practice later showed, such screening has both positive and negative sides. Uniform heating of individual pipes included in the tape is a positive feature, since the pipes pass all temperature zones along the height of the furnace under the same conditions. Negative - the impossibility of performing radiation surfaces with large factory blocks, as well as an increased tendency to thermohydraulic sweeps(uneven distribution of temperature and pressure in pipes along the width of the gas duct) at ultrahigh and supercritical pressures due to a large increase in enthalpy in a long coil.

For all systems of direct-flow units, certain General requirements... So, in a convective economizer, the feed water is not heated to boiling by about 30 ° C before entering the furnace screens, which eliminates the formation of a steam-water mixture and its uneven distribution along the parallel tubes of the screens. Further, in the zone of active fuel combustion in the screens, a sufficiently high mass velocity ρω ≥ 1500 kg / (m 2 About 70 - 80% of the water turns into steam in the furnace screens, and the remaining moisture evaporates in the transition zone and all the steam is overheated by 10-15 ° C to avoid salt deposition in the upper radiation part of the superheater.

In addition, steam boilers are classified according to steam pressure and steam output.

Steam pressure:

low - up to 1 MPa;

medium from 1 to 10 MPa;

high - 14 MPa;

ultra-high - 18-20 MPa;

supercritical - 22.5 MPa and above.

By performance:

small - up to 50 t / h;

medium - 50-240 t / h;

large (energy) - over 400 t / h.

Boiler marking

The following indices are set for marking boilers:

fuel type a: TO – coal; B- brown coal; WITH- shale; M- fuel oil; G- gas (when burning fuel oil and gas in a chamber furnace, the furnace type index is not indicated); O- waste, garbage; D- other types of fuel;

furnace type : T- chamber furnace with solid ash removal; F- chamber furnace with liquid slag removal; R- a layered furnace (the index of the type of fuel burned in a layered furnace is not indicated in the designation); V- vortex furnace; C- cyclone furnace; F- fluidized bed firebox; the index is entered into the designation of boilers with pressurization N; with seismically resistant design - index WITH.

way of circulation : E- natural; NS- multiple forced;

PP- once-through boilers.

Figures indicate:

for steam boilers- steam capacity (t / h), superheated steam pressure (bar), superheated steam temperature (° С);

for hot water- heating capacity (MW).

For example: Pp1600-255-570 Zh... Direct-flow boiler with a steam capacity of 1600 t / h, superheated steam pressure - 255 bar, steam temperature - 570 ° С, furnace with liquid slag removal.

Boiler layout

The boiler layout means the relative position of the gas ducts and heating surfaces (Fig. 13).

Rice. 13. Boiler layout diagrams:

a - U-shaped layout; b - two-way layout; c - layout with two convection shafts (T-shaped); d - arrangement with U-shaped convective shafts; d - layout with an inverter furnace; e - tower layout

Most common U-shaped layout (fig. 13a - one-way, 13b - two-way). Its advantages are the supply of fuel to lower part furnaces and removal of combustion products from the lower part of the convection shaft. The disadvantages of this arrangement are the uneven filling of the combustion chamber with gases and the uneven washing of the heating surfaces by the combustion products located in the upper part of the unit, as well as the uneven concentration of ash over the section of the convection shaft.

T-shaped the arrangement with two convection shafts located on both sides of the furnace with the lifting movement of gases in the furnace (Fig.13c), allows to reduce the depth of the convection shaft and the height of the horizontal gas duct, but the presence of two convection shafts complicates the evacuation of gases.

Three-way the arrangement of the unit with two convection shafts (Fig. 13d) is sometimes used with the upper location of the smoke exhausters.

Four-way the layout (T-shaped two-way) with two vertical transitional gas ducts filled with discharged heating surfaces is used when the unit operates on ash fuel with low-melting ash.

Tower the layout (Fig. 13f) is used for peak steam generators operating on gas and fuel oil in order to use the gravity of gas ducts. In this case, difficulties arise associated with the fastening of convective heating surfaces.

U- figurative the configuration with an inverter furnace with a descending flow of combustion products in it and their lifting movement in a convection shaft (Fig.13e) ensures good filling of the furnace with a torch, a low location of superheaters and a minimum resistance of the air path due to the short length of the air ducts. The disadvantage of this arrangement is the deteriorated aerodynamics of the transitional flue, due to the location of burners, smoke exhausters and fans at a high altitude. This arrangement may be useful when the boiler is running on gas and fuel oil.

Mounting gas boiler- a complex process, in which every stage, every component is important. Therefore, when there is a conversation about the smoke removal of a gas boiler, it must be understood that it comes about the correct approach to the selection and installation of a chimney. It is on this pipe that the quality of work and the safety of operation of the heating equipment itself depend.

What is a smoke exhaust system

If we talk specifically about gas boilers, then the smoke exhaust system is actually a pipe made of non-combustible materials. The section shape can be round or rectangular. It is installed on a gas boiler, or rather, on its outlet pipe, which connects the chimney with the firebox, where fuel is burned. And they lead the other end out onto the street.

The main requirement for a boiler smoke exhaust system is complete tightness of the structure and as few deviations as possible from the straightness of the circuit. In this case, a calculation is made for the cross-section of the pipe, which depends on the power of the gas equipment.

What is better to make a chimney for a gas boiler

As mentioned above, the chimney must be made of non-combustible materials. Therefore, manufacturers offer a fairly wide range of this product from different materials.

1. Brick. He has a large mechanical strength, the brick keeps warm for a long time. Among the disadvantages: only a rectangular shape can be assembled, which is not ideal for gas streams. In addition, the surface of the chimney is porous, not smooth, which affects the speed of the exhaust gases. This means that there is a decrease in traction. To this we must add the complexity of the installation, a large specific gravity and big problems with service.
2. Steel. it modular system smoke exhaust of gas boilers, that is, the chimney is assembled from several parts. Manufacturing material - acid-resistant stainless steel with a thickness of 0.6-1 mm. This variety has many advantages: low specific weight, low price, ease of installation and maintenance, smooth inner surface, high corrosion resistance. The only negative is that such a smoke exhaust system must be insulated. This variety includes corrugated pipes and sandwich modification.
3. Ceramic. In fact, this is a combination of several materials: the chimney itself, made of heat-resistant ceramics, insulation in the form of a mat made of non-combustible material and a protective channel from aerated concrete... This option is not inferior to metal.
4. Asbestos-cement. In principle, not bad cheap option, but it has two rather serious drawbacks: low mechanical strength and the impossibility of creating outlet circuits.
5. Polymeric. They are most often used when it is necessary to remove flue gases at low temperatures. They are not used in other smoke extraction systems.

Summing up, it can be noted that the best option today there is a stainless steel chimney and a ceramic model.

Coaxial and split system

All smoke extraction systems are divided into two groups: natural draft and forced. The first is when flue gases are discharged through a vertically installed chimney, and air is supplied to the gas boiler firebox for fuel combustion through a blower. Such a boiler is called an open-hearth boiler.

There are boilers with a closed firebox, into the combustion chamber of which air enters through the chimney itself. The latter is called coaxial. The second system is called separate. How do they differ from each other?

Coaxial smoke exhaust system

A coaxial duct is two pipes that are inserted into each other. Across inner tube flue gases are removed, air enters the furnace through the gap between the pipes. Perfect design with excellent characteristics. Today, it has become often used in private housing construction, where small capacity boilers are installed.

The coaxial flue gas system is fire safe because the flue gases do not heat up the outer pipe. The latter is usually taken out through the wall, near which the gas boiler is placed.

Separate smoke exhaust system

A separate smoke exhaust system consists of two separately located pipes. Through one, flue gases are discharged, through the other into the furnace Fresh air... That is, there are two branch pipes in the construction of a gas boiler. This type of chimney is most often used in high-power boilers, in which a large amount of fuel is burned, and this requires a large chimney diameter.

It should be noted that any ready-made chimneys made of different materials can be used for separate smoke exhaust systems. The main requirement for them is no different from chimneys with natural draft. But conditions come first fire safety.

Chimney arrangement for atmospheric gas boilers

Atmospheric gas boilers belong to the open-hearth category. Their distinctive feature is gas-burner, in which air is mixed with gas, and then ignites at the outlet of the nozzle. Hence and high efficiency combustion of fuel.

As for the chimney, natural smoke exhaust is most often used here with the installation of a round pipe. True, the location of the pipes can be different.

1. Vertically up through the floors of the house.
2. Horizontally across the room with an outlet to the street, and then vertically outside the roof of the building.

The chimney device for atmospheric boilers is not cast in anything from ordinary ones. The only thing you need to pay attention to is the cross-sectional area of ​​the pipe. It should be bigger.

Fire safety requirements

Fire safety rules are the main requirement to which the selection and installation of the smoke exhaust system pipe are tied. What are these requirements.

1. The flue gas duct must ensure complete removal of flue gases.
2. It must be resistant to high temperatures(+ 400C).
3. The joints between the connected parts of the chimney must be tight.
4. A vertical chimney can have a deviation from the vertical by no more than 30 °.
5. Do not install a pipe with big amount turns. Their maximum number is 3.
6. The chimney must not touch materials that could catch fire from the temperature of the flue gases.
7. The pipe is brought out of the roof 0.5 m above the ridge (this is the minimum).
8. If the roofing material is a flammable coating, for example, bituminous shingles, then a spark arrestor is installed on the upper edge of the chimney.
9. On the street and in non-burned rooms, it is necessary to ensure the insulation of the smoke exhaust system.
10. The joints of the two sections should not be located inside the floors of the house.
11. In the attic, you cannot construct horizontal sections and turns, you cannot make revisions here for cleaning.

Calculations

Manufacturers of gas boilers in the instructions for use indicate exactly which section of the chimney must be installed on the purchased unit. Therefore, in this regard, no calculations are needed. But if it becomes necessary to carry out such calculations, then there are several ratios that are taken as a basis.

1. For 1 kW of thermal energy, at least 8 cm² of pipe cross-section is needed. In such a chimney, the speed of movement of flue gases should be 0.15-0.6 m / s.
2. The ratio is 1:10, where the first indicator is the chimney area, the second is the furnace.

How to check chimney draft

The chimney draft is the speed of the flue gases. There is a special table where this indicator is shown depending on the temperature of the gases and the air temperature outside, because these two values ​​determine the natural removal of the gas mixture.

The table shows that the maximum thrust is 0.818 m / s. This means that devices such as an anemometer cannot determine the amount of thrust. Because it has a limit of 1 m / s.

The easiest option is to bring a flame of fire to the door of the firebox. It could be a lighted match, a lighter, or a piece of paper. Flame deflection indicates the presence or absence of draft.

Errors are common. Unfortunately, the craftsmen do not attach importance to trifles, and there are no such in boiler smoke exhaust systems. Here are just common mistakes, as well as recommendations from experts:

• the parameters of the chimney are incorrectly selected;
• the number of turns is more than three;
• there are long horizontal sections;
• no insulation was carried out in areas that pass along the street or in unheated rooms;
• the length of the chimney is significant, which creates a reverse draft due to a strong gust of wind;
• deviation of the upper part of the chimney from the vertical;
• large cross-section of the chimney, due to which the flue gases cool down quickly, hence the decrease in draft;
• fan connection in gas boilers with forced smoke removal should be strictly carried out according to the manufacturer's recommendations, taking into account the parameters of the system itself;
• strictly adhere to fire safety requirements.

And one more question that worries the owners of private houses, how to properly bring the system outside the building. In principle, this question was answered in the section on chimney arrangement. Of course, everything will depend on what kind of pipe design is used. If this is a coaxial chimney, then the installation is carried out horizontally, all others are vertical.