An important attribute for the efficient 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 draft will not arise in the unit, which is needed to remove combustion products.
The key criterion for the quality performance of the boiler chimney is excellent draft. It is estimated based on the speed of flue gases moving through the chimney. The draft depends on the roughness of the surface, the height of the chimney, the internal cross-section and the temperature difference between the air and the combustion products. It is necessary that the chimney is fireproof, 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), which is provided by the equipment manufacturer.
Thrust
So what is traction? A draft is a characteristic of a chimney reflecting the speed of movement of flue gases in it. It appears due to the difference in temperatures (heat rises up) and 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 characteristic, the draft also has a quantitative one - this parameter is more influenced by the diameter of the chimney for a solid fuel boiler. However, the thrust itself is more dependent on the design (height, fresh air flow, turns, angles).
In absolutely all chimney systems, draft is determined by several constant factors: temperature of the wind, flue gases; temperature difference inside and outside the room.
The warmer the room and the colder it is, the better the draft will have chimneys for solid fuel boilers. This can be explained by the fact that the density of cold air is higher than that of warm air, which means that warm air has a lower gas column pressure. This factor provides the occurrence of pressure differences outside and inside the pipe. If the building is leaky, then at the foot of the structure, due to the pressure difference, a stream of air appears, which is directed inward. In this case, warm air is forced out and exits through the hole at the top of the building, and cold air is inside thanks to the holes inside the structure. Natural air ventilation occurs.
It is necessary to take into account that the properties of smoke are not constant, since combustion in solid fuel boilers is not uniform, therefore, the temperature of flue gases varies in a rather considerable range (in coal-fired boilers - 400-600 ° C, and in wood-fired boilers 70-300 ° C). The temperature of the smoke increases sharply when the boiler is ignited and decreases after the work begins to be carried out in standard operating mode. This all also affects traction.
The length of the chimney also plays a significant role in the draft. In other words, warm chimney gases, when rising in straight sections, gain a certain speed, and this ensures an increase in the flow of flue gases through the chimney. There is also a certain formula proving the dependence of the draft on the smoothness of the walls, the cross section and length of the chimney, the temperature both on the street and in the room.
Chimney construction
The next important nuance is the installation of the chimney. The smaller the number of narrowings, horizontal sections, turns, the traction will be better. This is due to the fact that the gases from the boiler rise along the chimney in a spiral upward, while at each of the bends the course of movement of the flue gases is changed, their ordinary mixing occurs. At the same time, a chimney, which has a roughness of the walls, protrusions or bends, creates resistance for the flue gas turbulence formed in it.
Drawing a conclusion from the foregoing, we can say that the best option for the chimney is a round, cross-section with smooth walls. If it is not possible to mount such a structure, it can be made rectangular, square or oval in shape, corresponding section. By the way, in the corners of the chimney, which has a rectangular shape, turbulences form, and this worsens the draft and contributes to the accumulation of soot in the chimney.
There are exceptions to traction. For example, temporary weakening of traction, reverse traction often happen in the summer, when temperature indicators change on the street and in the house. Tipping or blowing traction also occurs. An important role in these problems is played by the chimney device.
Anemometer is a special device for measuring traction. It is digital and analog. It is usually used by inspectors of the relevant authorities. In everyday life, a method with a deviation of a sheet of paper is often used, however, it does not provide accurate results, but simply indicates the presence or absence of traction as such.
Traction Quality Factors
There are several important facts that indicate the level of traction quality:
- buzz and noise in the chimney - excessive draft: you should adjust the draft using a gate;
- smoke is collected in the room after exiting the firebox cracks - inadequate draft level: it is necessary to open the gate, increase the air flow into the room where the boiler is installed.
If during the operation of the boiler the draft is too weak, and the flame turns red, smoke swirls, the gate is not useful in any way, you should pay attention to such nuances:
- chimney height: the check is carried out using an anemometer, it is best before activating the boiler;
- chimney section: the check is performed by comparing the chimney section and the exit section of the solid fuel boiler;
- air flow into the room with heating equipment: it is necessary to check whether the stranglers are clogged or the grates are clogged with dust;
soot: the question regarding its availability is ambiguous, it all depends on the design of the boiler and the type of fuel, but in any case, check the inspection holes before starting the season.
Types of smoke ducts
Chimneys must be made only of high-quality and fireproof materials.
The following types of chimneys are distinguished:
- brick;
- metal;
- ceramic;
- glass.
Brick Chimneys
This material for laying 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 height and allow you to bend around small obstacles. However, there is one drawback: the classical scheme of the chimney made of this material suggests that it will have too much mass and dimensions, and this will require a lot of effort. It should also be borne in mind that a brick cannot withstand temperatures 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 tab is from 23,300 rubles.
Metal chimneys
Such chimneys for solid fuel boilers are made of stainless and black steel. Black steel structures are unstable to hostile environment, therefore it is undesirable to use them. With the continuous operation of the boiler, such a pipe for a chimney, the price of which is relatively low, will very quickly become unsuitable for use and fire hazardous for your home.
The cost of pipes depends on the grade of steel that is used for their manufacture. So, 1 m of pipes from the most inexpensive corrosion-resistant steel with a diameter of 115 mm has a price of 400 rubles. A similar pipe made of AISI 439 steel with the addition of titanium costs already from 800 rubles / m.
Ceramic chimneys for solid fuel boilers
A great choice for a solid fuel boiler. Ceramic flues have the following properties:
- not afraid of condensate;
- have high refractoriness (the maximum allowable temperature of flue gases is 1200 ° C);
- resistant to mechanical stress;
- resistant to atmospheric effects.
Glass chimneys
Such chimneys are quite rare, they are characterized by low thermal inertness, a rather extravagant appearance and a 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 the material, but also the high cost of installation of this chimney.