Long-burning solid fuel boilers: top-11 best boilers, types and characteristics

Types of solid fuel boilers for heating a private house

Differences in solid fuel boilers are associated with:

1. Resource delivery technology.
2. The existing combustion system.

Pellet

Automatic loading is done from the hopper. Depending on its volume, one bookmark is enough for a period from a week to a month. Since the solid fuel boiler works independently, it is possible to adjust the heating modes depending on the time of day and day of the week.

Photo 1. Solid fuel pellet boiler. On the right side of the device there is a hopper for loading pellets.

Automatic models of solid fuel boilers only work on pellets. These are wood pellets obtained by pressing sawdust, shavings, bark, husk and other similar wood waste. Pellets do not burn, but smolder for a long time, emitting a significant amount of heat. Therefore, they provide a fairly high efficiency, up to 90-95%.

Important! Automation will require a constant source of electricity. In case of interruptions, it is advisable to purchase a UPS

Manual loading

Other types of solid fuel boilers are loaded only manually. The heat source is:

The service life of one tab depends on the volume of the fuel chamber and the used combustion technologies. For convenience, the boiler door is tilted. This facilitates the loading and further maintenance of the device.

The disadvantage of such models of solid fuel boilers is the impossibility of automatic operation. Periodic human effort is required to maintain the process.

But the dependence on electricity is reduced. In addition, different types of resources are used and it is easier to select the most available in a given area.

Reference. There are models of solid fuel boilers with automatic and mechanical temperature control. In the latter case, a mechanical draft regulator (damper) is used. It does not depend on the availability of electricity.

Solid fuel boilers with manual loading are subdivided into types depending on their design features. There are such technologies:

• classic;
• pyrolysis;
• long burning.

Classic

In such solid fuel boilers, technologies that increase the duration and efficiency of combustion are not used. Therefore, the wood in them burns quickly, in a few hours.

The efficiency of such boilers is low, since a significant part of the heat escapes through the chimney.

The advantages of such models of solid fuel boilers include low cost, due to the fact that the internal structure is simple.

Pyrolysis

As the name suggests, pyrolysis combustion technology is used. During primary combustion with a lack of oxygen, pyrolysis gases are formed, which are also capable of burning, releasing a significant amount of heat.

The design is more complicated in comparison with the classic version of solid fuel boilers. An additional combustion chamber is located above the main combustion chamber, where gases are collected and burned.

Thanks to this, the following increases:

• efficiency (up to 85-95% depending on the type of raw material);
• the duration of one bookmark.

Other advantages of such solid fuel boilers include accurate temperature control and less soot and slag. The disadvantages of boilers are:

1. High price (pays off during operation).
2. The need to use only dry fuel (otherwise the pyrolysis process will not start).

Photo 2. The internal structure of a solid fuel pyrolysis boiler and the principles of its operation at different stages.

Long burning

In solid fuel boilers of this type, a different technology is used. Firewood does not burn from bottom to top, as in the classic version, but from top to bottom. Burning becomes slow and efficient. Therefore, laying firewood in the boiler lasts up to a day or more, and coal - up to a week. Like pyrolysis boilers, these solid fuel boilers work on all types of wood resources.

The main feature of top-fired boilers

Given the difficulties in servicing solid fuel heating devices, manufacturers decided not only to use new technologies in the design of heating equipment, but also to return to traditional technologies. The main task that was solved in the process of modernization of boiler equipment is to increase the duration of fuel combustion for one load. This result was obtained due to the use of the principle of upper combustion in solid fuel boilers.

The technology of the boiler operation due to the upper combustion is not something fundamentally new. The fuel loaded into the furnace burns from top to bottom. Those. on the contrary, not as in traditional boilers. Combustion starts from the uppermost layer, where the required air flow is supplied through a movable distributor. As the fuel mass burns out, the air distributor drops down under its own weight, providing combustion to the next layer. The loaded fuel thus burns evenly layer by layer, releasing a large volume of combustible wood gas.

At this stage, the temperature in the furnace of the unit reaches 450 0 С.

At this stage, the pyrolysis principle comes into play. The smallest combustion products, together with the emitted wood gas, completely burn, releasing a huge amount of thermal energy. As a result of the operation of the unit, practically no fuel residues remain in the combustion chamber.

For reference: Pyrolysis is an exothermic reaction, as a result of which, under the influence of high temperature, the process of decomposition of organic compounds occurs, followed by the release of a combustible gaseous substance. The main heating of a solid fuel boiler in the combustion process is carried out by burning wood gas.

Wood (pyrolysis) gas enters the second chamber through a metal disk, where it ignites due to the forced hot air. The combustion temperature in the second furnace at this moment reaches enormous values, 500-800 0 С. Everything is simple and clear. The main thing is the design of the heating device.

The combustion rate of the fuel depends on the combustion process. In heating equipment of the classic type, firewood is burned quite quickly, giving out the maximum possible heat within a short period of time. In other words, within a short period, the unit reaches its peak of its capacity, after which, without further refueling, the boiler begins to lose load. Constantly loading a new batch of firewood is not always convenient and physically possible. Top-loading solid fuel boilers work in a completely different way. One load with such a device can be enough for 12, 24 and more hours of work. The combustion intensity depends on the load on the heating system.

Everything is simple and straightforward. The main thing is the design of the heating device.

How a homemade long-burning boiler works

Principle of operation

The scheme of operation of such boilers is based on the features of solid fuel to smolder for several hours, while producing a large amount of thermal energy. Typically, the fuel in this case is burned more completely, and the amount of waste, as a result, is significantly reduced.

Boiler drawing

The main element of the boiler is the firebox, where combustion is limited, and the intensity of the air supply is controlled with the help of special devices. The fuel is loaded twice a day in large portions, after which it slowly smolders (the limited amount of oxygen does not allow it to fully burn).

The pipe through which the smoke is removed is passed through heat exchangers and heats the liquid in the heating system. It turns out that it is enough only to load fuel every 12 hours for uninterrupted heating of the house.

Boiler diagram

Main advantages

Long-burning boilers stand out against the background of other types of heating systems. Of course, the main advantage is precisely the duration of the work, but there are other important points:

• low fuel cost;
• autonomy;
• the ability to heat large areas at minimal cost;
• ease of installation and operation;
• security;

• the possibility of making at home.

Device device

For the manufacture of a boiler, it is more convenient to use a metal pipe ø30 cm or more with a wall thickness of at least 5 mm (otherwise the latter will soon burn out due to the high temperature inside the device). The height of the structure can fluctuate between 80 cm and 100 cm, it all depends on the area of ​​the room.

Body pipe

Regardless of the modification, the boiler consists of three main zones:

• loading area;
• zones of smoldering and heat generation;
• final combustion zones where ash is burned and flue gases are evacuated.

This element is made in the form of a metal circle 5-6 mm thick with a hole in the middle through which oxygen is supplied to the furnace using a telescopic pipe. The diameter of the product should be slightly less than the diameter of the body. The height is adjusted by means of a special impeller.

Long burning wood fired boiler

Long burning boiler

Air can be supplied in one of two ways:

• straight out of the atmosphere;
• from a special heating chamber (it is located in the upper part of the structure), which ensures more efficient operation of the boiler.

A special air damper is used for adjustment.

A flue pipe is welded on top. It must run perpendicular to the body for at least 0.5 m, otherwise excessive thrust is generated.

The bottom door is equipped with a door to remove combustion products. Cleaning should be done infrequently, because the fuel will burn more completely.

There are two ways to heat the coolant, each with its own strengths and weaknesses.

Long burning boiler

Method number 1. A coil is connected to the heat exchanger pipe passing through the combustion zone, through which the water in the tank is heated.

Method number 2. A separate metal tank is formed, through which the chimney pipe is passed. The hot smoke heats up the liquid.

The first method is more efficient, but at the same time more difficult to implement. The second one is easier to make, but it is advisable only in small houses.

Advantages of solid fuel boilers for long burning

We will not talk about all the advantages of this type of heating boilers in the article. Let's designate the main ones:

• High heat transfer rates.
• Highest performance with lowest fuel costs.
• Currently, manufacturers offer several models that differ in the number of circuits and the ability to automate the processes of control and regulation of temperature conditions.
• The lowest cost of the fuel used. By the way, it should be noted that boilers of this type work not only on wood or coal. Here you can use sawdust, seed husks, leaves, grass, plant stems and other combustible natural materials. It's just that all this must be brought to a certain density. That is, subject the fuel to the pressing process.
• If we talk about the appearance of the boilers, then the manufacturers made sure that their design meets all the standards and requirements of our time.

Full compliance with installation requirements

How to choose the right boiler connection diagram

In order for the house to be warm, it is not enough to know about what heating schemes are with a solid fuel boiler. Masters who have been creating heating systems for more than one year give the following recommendations:

1. When creating a drawing of a heating scheme for a solid fuel boiler, you should first familiarize yourself with the types and principles of operation of such heat generators.It can be a heater for continuous or long burning, a pyrolysis or pellet unit, a buffer. Each of these devices has its own criteria for work, which for some may become minuses, and for others pluses.

1. To get an ideal heat supply scheme, you need to be able to combine the functioning of the boiler with the tank, since this element accumulates thermal energy. This is due to the fact that the water heating element can change its temperature in the range from 60 to 90 degrees. There is no constant indicator. Since solid fuel boilers are inert devices, this distinguishes them favorably from gas, diesel and electric counterparts.
2. When choosing a heating scheme, you need to objectively assess the risk of a power outage. If there is often a blackout in the area, then the system with a water pump will not only not pay for itself, but can also quickly fail. Therefore, it is better to choose the type of heating with natural circulation.
3. When choosing a piping, it is worth considering in advance the safety lines between the boiler and the tank. They are located at the points of the inlet and outlet pipes so that they are as close to the water heater as possible. Also, to achieve the maximum effect, you need to try to keep the distance between the boiler and the expansion tank as small as possible. But here it is no longer possible to install safety valves or taps.
4. If a scheme with a pump was chosen, then it is installed on the return pipe, as close as possible to the heat generator. Thus, even if the light is turned off and the pump stops working, the water will continue to move along the circuit, that is, the minimum heat will be retained. The device must be mounted along the bypass path. Only then will it be possible to disconnect it from the network (if necessary), and close the bypass itself by means of taps.

1. There is such a thing as bypass. These are jumpers with taps, which are placed between the supply line and the return pipe. This arrangement facilitates the return of "excess" hot water when the volume is changed by means of a thermostat.
2. A stainless steel valve must be installed in the chimney. Since there is moisture in the smoke, albeit in small quantities, but it is this moisture that can provoke the destruction of the inside.

Strapping is a process that should be given special attention. Therefore, they design and install it only if there is complete confidence in their abilities. Nikolay Avramenko, 51 years old,

Energodar

Nikolay Avramenko, 51 years old, Energodar

After reading the article, I would like to add my own note. The topic of the operational characteristics of solid fuel boilers was touched upon here. It was indicated that they have such a feature as high inertia. I would like to say that this phenomenon is not characteristic of pellet boilers. This is due to the fact that such devices have a burner that receives wood pellets in batches. Therefore, when the supply of raw materials stops, then the flame immediately extinguishes. Although such boilers are not so cheap.

Anton Abramov, 29 years old, Omsk

At one time, I was interested in the work of solid fuel boilers, as I was offered a position related to this area. I would like to leave a few words about the thermostat and its regulating features. You need to understand when a certain temperature is set, for example, at 85 degrees, although the damper is closed, but burning and smoldering continues. Because of this, the water is still heated by a couple of degrees, and only then it will be set exactly. Therefore, do not turn the thermostat back and forth, otherwise, it can lead to breakdown of the entire system.

Nikita Karpenko, 37 years old, Arkhangelsk

When we built the house outside the city, we planned to live there all year round.The time came when it came to heating, and I settled on a closed type system with natural circulation. Firstly, it was easy enough for me to create it with my own hands, and secondly, we were already a little limited in money. I didn't have any particular problems in installation, but when the first cold weather came, I realized that there was clearly not enough heat for the house. So at school I was good friends with physics, then I realized that the heat is "lost" in the areas where the pipes remained open. Taking a roll of rock wool, I wrapped all the pipes that pass in open areas. By the end of the first day, our family felt a significant warming in the rooms. Therefore, such moments must be remembered.

Types of heating boilers

The type of boilers we are interested in is produced only in floor-standing design - its weight is too large. And if you do not take into account the positions already described, then these are ordinary solid fuel boilers. Logic suggests that the power of such models depends on the direct purpose of the fuel unit. There are devices with minimum parameters - 7 kilowatts, and there are also devices with maximum parameters - up to 95 kilowatts. These colas are mainly used for heating small houses. But there are also more powerful installations, for example, with a 200-kilowatt power. They are used to heat homes over 2,000 square meters.

In the production of boilers, steel or cast iron is used, but even steel differs from different manufacturers, which will affect the cost of the device. For example, heat-resistant metal is several times more expensive than low-grade, and, accordingly, such a boiler will cost more. In some models, fireclay bricks are used, with which the firebox is lined. This increases not only the cost of the unit, but also its strength and durability. By the way, such models can be single-circuit and double-circuit.

Heating boilers installation

This is not a gas equipment, so you can install it yourself. True, there are several important warnings from experts:

1. The boiler must be installed at a distance of at least half a meter from the nearest walls. The fact is that this heating device, even if there is a water jacket in its design, heats up very much. And if the walls of the house are built of combustible materials, they must be additionally sheathed with protection. For example, asbestos sheet, brick or galvanized steel sheet, under which you still have to lay asbestos.
2. Any, even the smallest boiler from this category, has a significant mass. Therefore, you need to take care of the skeleton on which it will be placed. The frame must be strong, non-combustible and reliable. Keep in mind that the weight of the boiler will increase due to the weight of the tab. Therefore, the best option is a free-standing foundation, built according to all building canons with the laying of a crushed stone pillow and a reinforcing frame made of metal reinforcement. By the way, experts advise to fill the foundation with a height of at least half a meter.

Pyrolysis boilers

The principle of operation of these heat generators is based on separate combustion in two chambers communicating with each other through a refractory brick nozzle. In the primary chamber located on top, firewood is smoldering with a limited air supply by a fan. As a result, the process of pyrolysis occurs, otherwise - gasification, in which a mixture of combustible gases is released. It moves to the second chamber, where it is burned out when secondary air enters. The working diagram of a solid fuel pyrolysis boiler is as follows:

Flue gases from the secondary furnace enter the fire-tube heat exchanger in the form of vertical gas ducts surrounded by a water jacket. There they cool down, transferring heat to the water, and leave the boiler through the chimney. The fan performance is controlled by an electronic unit - controller, being guided by the readings of pressure and temperature sensors.

In general, the heat generator has good efficiency indicators - about 80%, but at the same time the unit is much more expensive than the classic one.In addition, the boiler shows high efficiency only when working on dry wood, although this statement is also true for other solid fuel units.

Recommendations for use

When installing the boiler, first of all, attention should be paid to the quality of the chimney. It is best suited for stainless steel pipes with a diameter of 120 to 200 mm (depending on the model)

The ideal option would be a finished pipe with thermal insulation - a sandwich. Thick-walled pipes are not recommended. They take longer to warm up, and soot remains on the walls. It is necessary to clean the chimney once every 2 months.

An unpleasant odor may appear when the boiler is switched on for the first time. Do not worry - this is normal, since a special oil is applied to the metal during production. The first heating must be started in a ventilated room, and the boiler is turned on at maximum power. The duration of its work in this mode is 1 hour.

The fuel is placed in the chamber in a loose layer so that an air gap remains between the woods. This will allow them to fire up better. To control the combustion process in the ash chamber, a damper is opened and closed.

The boiler may only be cleaned after it has cooled down completely. During cleaning, it is recommended to leave part of the ash on the grate, which will serve as natural thermal insulation. This will extend the life of the element. A wire brush or scraper is used to clean the boiler itself. The smoke damper must be open at this time.

Depending on the type of fuel used, a certain amount of soot is formed during the operation of the boiler. Conifers give more waste. Sometimes condensation can form in the chimney: this depends on the level of thermal insulation and the moisture content of the fuel. It is recommended to use aspen wood to reduce the soot layer.

How does a pyrolysis boiler work. The device and principle of operation of the pyrolysis boiler.

The principle of operation of a pyrolysis solid fuel boiler is based on the process of decomposition of solid fuel into pyrolysis gas and coke. This is achieved by insufficient air supply. Due to the weak air supply, the fuel slowly smolders, but does not burn, as a result, pyrolysis gas is formed. As a result, the gas combines with air. combustion occurs and heat is released, which heats the coolant. Thanks to this process, there are very few harmful substances in the smoke, and soot and ash are negligible. So in the case of pyrolysis boilers, you can also talk about environmental friendliness.

So, let's take a closer look at the principle of operation of a pyrolysis boiler.

• What is pyrolysis? Pyrolysis is a combustion process under conditions of insufficient oxygen. The result of such combustion is solid combustion products and gas: solid waste is ash and a mixture of volatile hydrocarbons plus carbon dioxide.
• The principle of operation of a gas generator (or pyrolysis boiler) is that such a solid fuel boiler divides the heating process into two processes. First, this is the usual process of burning solid fuel, while limiting the supply of oxygen. When there is a shortage of air, solid fuel smolders very slowly, releasing gas. It limits the oxygen supply, the boiler is very simple, with a mechanical damper, which, depending on the amount of air in the furnace, either opens or closes. In this case, you can manually "turn on the heat" by slightly opening the damper.
• The second part of the fuel combustion process consists in burning out the volatile waste of the combustion process in the first furnace. In the second furnace, the so-called pyrolysis gas burns out - the result of burning solid fuel in the first furnace.
• In this case, the adjustment, as well as in the case of supplying air to the first furnace, is very simple. The thermostat controls the combustion process and changes the operation of the boiler just as much as necessary to generate the required amount of heat. In principle, it does not differ much from a thermostat for a water heater.
• The efficiency of pyrolysis boilers. By far the most efficient boilers are those in which combustion occurs from top to bottom. Of course, this imposes certain difficulties, for example, in such boilers, forced draft has to be done, because the second afterburner of pyrolysis gas is located under the grate. To put it simply: the fuel is scattered into the waste product of the combustion process - into ash. In this case, gas is formed, which is also afterburned. The result: maximum heat release, with virtually waste-free combustion. Plus, the ash can be used as fertilizer.

The principle of operation of a pyrolysis boiler is designed in such a way that, in addition to the most efficient combustion of fuel, we also have minimal waste from the combustion process. The main disadvantage is the price of pyrolysis boilers, but there are actually a lot of positive aspects:

• Minimum waste and minimum cleaning of the furnace, in comparison with other solid fuel boilers.
• Long battery life without additional loads due to economical air supply.
• Combustion process automation. The boiler itself regulates when to increase combustion and when to decrease.
• Large solid fuels are suitable for such boilers, since in any case the afterburning of the fuel takes place almost completely.

DIY long-burning boiler making video

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Protection of a solid fuel boiler from overheating

In a solid fuel boiler, burning fuel, and the boiler itself, has a rather large mass. Therefore, the heat release process in the boiler has a large inertia. The combustion of fuel and the heating of water in a solid fuel boiler cannot be instantly stopped by stopping the fuel supply, as is done in a gas boiler.

Solid fuel boilers, more than others, are prone to overheating of the coolant - water boiling if heat extraction is lost, for example, when the circulation of water in the heating system suddenly stops, or more heat is released in the boiler than is consumed.

Boiling water in the boiler leads to an increase in temperature and pressure in the heating system with all serious consequences - destruction of the heating system equipment, injury to people, damage to property.

Modern closed heating systems with a solid fuel boiler are especially prone to overheating, since they contain a relatively small volume of coolant.

In heating systems, polymer pipes, manifold control and distribution units, various taps, valves and other fittings are usually used. Most elements of the heating system are very sensitive to overheating of the coolant and pressure surges caused by the boiling of water in the system.

A solid fuel boiler in the heating system must be protected against overheating of the coolant.

To protect the solid fuel boiler from overheating in a closed heating system that has no connection to the atmosphere, two steps must be taken:

1. Shut off the combustion air supply to the boiler furnace in order to reduce the intensity of fuel combustion as soon as possible.
2. Ensure cooling of the heat carrier at the outlet of the boiler and prevent the water temperature from rising to boiling. Cooling should take place until the heat release is reduced to a level at which the boiling of water becomes impossible.

Let's consider how to protect the boiler from overheating, using the example of the heating circuit, which is shown below.

Diagram of connecting a solid fuel boiler to a closed heating system

Diagram of a closed heating system with a solid fuel boiler.

1 - boiler safety group (safety valve, automatic air vent, pressure gauge); 2 - a tank with a water supply for cooling the coolant when the boiler overheats; 3 - float shut-off valve; 4 - thermal valve; 5 - connection group of the expansion membrane tank; 6 - unit for coolant circulation and boiler protection against low-temperature corrosion (with a pump and a three-way valve); 7 - heat exchanger for overheating protection.

Boiler overheating protection works as follows. When the temperature of the coolant rises above 95 degrees, the thermostat on the boiler closes the air supply damper to the boiler combustion chamber.

The thermal valve, pos. 4, opens the supply of cold water from the tank, pos. 2, to the heat exchanger, pos. 7. Cold water flowing through the heat exchanger cools the heating medium leaving the boiler, preventing boiling.

The supply of water in the tank (pos. 2) is necessary in the event of a lack of water in the water supply system, for example, during a power outage. Often, a common storage tank is installed in the water supply system at home. Then the water for cooling the boiler is taken from this tank.

A heat exchanger to protect the boiler from overheating and cool the coolant, pos. 7 and a thermal valve, pos. 4, are usually built into the boiler drum by boiler manufacturers. This has become the standard equipment for boilers designed for closed heating systems.

In heating systems with a solid fuel boiler (with the exception of systems with a buffer tank), thermostatic valves and other automatic devices that reduce heat extraction must not be installed on heating devices (radiators). Automation can reduce heat consumption during the period of intensive fuel burning in the boiler, and this can trigger the overheating protection.

Another way to protect a solid fuel boiler from overheating is described in the article:

Read: Buffer tank - protection of a solid fuel boiler from overheating.

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