Chimneys for solid fuel boilers: device, circuit and types

An important attribute for the effective operation of a solid fuel boiler and the creation of the required conditions for fuel combustion in it is a properly installed chimney, otherwise the thrust will not occur in the unit, which is needed to remove combustion products.

A key criterion for the quality work of the boiler flue is an excellent draft. It is estimated based on the speed of flue gas advancement through the chimney. The draft depends on the roughness of the surface, the height of the chimney, the internal section and the difference in the temperatures of the ambient air and combustion products. It is necessary that the chimney be fire resistant, resistant to high temperatures and equipped in accordance with fire safety rules. Since the cross-section for different boilers is not the same, the diameter of the chimney for a solid fuel boiler should be selected in accordance with the technical passport (instruction) provided by the equipment manufacturer.

Thrust

So, what is the pull? Thrust - a characteristic of the chimney, reflecting the speed of movement of flue gases in it. It appears because of the difference in temperatures (heat tends upward) and the pressure between the street (atmosphere) and the room in which the boiler is installed. It should also be clarified that in addition to the qualitative characteristics of traction and quantitative - this parameter is more influenced by the diameter of the chimney for a solid fuel boiler. At the same time, draft directly depends more on the design (height, fresh air intake, turns, corners).

In absolutely all systems of chimneys, the thrust is determined by several constant factors: the temperature of the wind, flue gases; Temperature difference inside and outside the room.

Than the room is warmer, and the street is colder, the better traction will have chimneys for solid fuel boilers. This can be explained by the fact that the density of cold air is greater than that of warm air, which means that warm air has a lower pressure of the gas column. This factor ensures the appearance of pressure difference outside and inside the pipe. If the building is not tight, then at the foot of the structure due to the difference in pressure there is a flow of air, which is directed inwards. Warm air is forced out and out through the opening at the top of the structure, and cold air is inside thanks to the holes inside the structure. There is a natural air ventilation.

It should be borne in mind that the properties of smoke are not constant, since combustion in solid fuel boilers is uneven, respectively, the temperature of flue gases varies in quite a considerable range (in coal-fired boilers - 400-600 ˚С, and in wood boilers 70-300 ˚С). The smoke temperature increases sharply when the boiler is ignited and decreases after the work is started in the standard operating mode. This all also has an effect on cravings.

The length of the chimney also plays a significant role for traction. In other words, warm flue gases, when rising on straight sections, gain a certain speed, and this provides an increase in flue gas flow through the chimney. There is also a definite formula that proves the dependence of thrust on the smoothness of the walls, the section and length of the chimney, the temperature both on the street and in the room.

Chimney design

The next important nuance is the device of the chimney. The less amount of zaugments, horizontal sections, turns, so the draft will be better. This is due to the fact that the gases from the boiler rise upward along the chimney, while in each of the bends the change in the course of movement of the flue gases is effected, and their mixing is ordinary. At the same time, the chimney, which has a roughness of the walls, protrusions or bends, creates resistance to the smoke gas vortices that form in it.

Drawing the conclusion from the above, we can say that the best option for the chimney will be a round, cross-section, having smooth walls. If it is not possible to mount such a structure, it can be made rectangular, square or oval, corresponding to the section. By the way, in the corners of the chimney, which has a rectangular shape, vortices are formed, and this worsens the draft and promotes the accumulation of soot in the chimney.

In the draft there are exceptions. For example, temporary weakening of traction, reverse traction often occur in the summer, when temperatures and temperatures change on the street and in the house. There is also a rollover or blowout. An important role in these problems is played by the device of the chimney.

The anemometer is a special device for measuring thrust. It can be digital and analog. It is usually used by inspectors of appropriate instances. In everyday life, a method with a deflection of a sheet of paper is often used, but it does not provide accurate results, but merely indicates the presence or absence of traction per se.

Thrust quality factors

It is possible to separate several important facts that attest to the level of quality of thrust:

• Humming and noise in the chimney - unnecessary traction: you should adjust the thrust, using the gate;
• Smoke is collected in the room after exiting the fires of the furnace - an improper level of thrust: it is necessary to open the gate, to increase the air flow to the room where the boiler is installed.

If during operation of the boiler the draft is too weak and the flame turns red, the smoke is bubbling, the damper is useless, we should focus on these nuances:

• Height of the chimney: the check is carried out using an anemometer, best before the activation of the boiler;
• Section of the chimney: verification is performed by comparing the section of the chimney and the section of the exit from the solid fuel boiler;
• The flow of air into the room with heating equipment: it is necessary to check whether the douchebags are blocked, whether the grilles are clogged with dust;

Soot: the question of its availability is ambiguous, it all depends on the design of the boiler and the type of fuel, but in any case before the start of the season, check the inspection holes.

Types of smoke channels

Chimneys should only be made of high-quality and fire-safe materials.

The following types of chimneys are distinguished:

• brick;
• metal;
• ceramic;
• glass.

Chimneys made of bricks

This material for the laying of the smoke channel has been used for a very long time. Brick chimneys for solid fuel boilers can be connected to boilers at a given altitude and allow to skirt small obstacles. However, there is one drawback: the classical scheme of a chimney from this material suggests that it will have too much mass and size, and this will require a lot of effort. It should also be taken into account that the brick can not withstand a temperature of more than 500 ° C.

The complete arrangement of a brick chimney, having a length of 10 m and a width of 140 mm, with an asbestos-cement insert is from 23,300 rubles.

Metal chimneys

Such chimneys for solid fuel boilers are made of stainless and black steel. Structures made of black steel are unstable to aggressive environments, so they are undesirable to use. With continuous operation of the boiler, a similar chimney pipe, the price of which is relatively low, will quickly become unusable and fire hazardous for your home.

The cost of pipes depends on the grade of steel used for their manufacture. So, 1 m of the most inexpensive corrosion-resistant steel pipe with a diameter of 115 mm has a price of 400 rubles. A similar pipe made of steel AISI 439 with the addition of titanium costs from 800 rubles per meter.

Ceramic chimneys for solid fuel boilers

A great choice for a solid fuel boiler. Chimneys made of ceramics have the following properties:

• Are not afraid of condensate;
• Have a high refractoriness (maximum permissible temperature of flue gases is 1200 ° C);
• Resistant to mechanical stress;
• Are resistant to the influence of atmospheric phenomena.

Chimneys made of glass

Such chimneys are quite rare, they are characterized by low thermal inertia, rather extravagant appearance and complete absence of corrosion. A similar chimney pipe, the price of which is quite high, is not available to everyone. It should be taken into account not only the high cost of material, but also the high cost of installation of this chimney.