How to choose a stove for a long-burning cottage. How to make a long-burning wood-burning stove for your home Homemade long-burning heating stoves

The homemade sawdust stove “Bubafonya” can be equipped with a water circuit. In this case, it is installed in a permanent place. Typically, this stove is used as a mobile stove: it can be placed in a greenhouse during freezing periods, used to heat a workshop or barn in the winter, or used to heat a garage. Subject to fire safety requirements, Bubafonya is safe and effective.

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Stove heating is experiencing a rebirth, and there are good reasons for this. The leitmotif of the stove renaissance is the long-burning stove. Not only and not so much because it can be done with your own hands, having mastered the basic skills of a mechanic and knowing how to somehow weld two pieces of iron to each other. Long-burning stoves have, first of all, important fundamental advantages over others.

Which ones exactly? To understand, you need to measure the total amount of heat released by one completely burned match twice in a physics laboratory, even a school one, using a calorimeter. The first time, holding it with the head down so that it burns better; the second - head up, as long as it somehow burns to the end. In the second case, the match will release significantly more thermal energy.

The point is that directly Pyrolysis of solid fuel occurs near the flame: it decomposes, releasing flammable gases; See below for more details. They are capable of providing a lot more heat, but to burn them out, in addition to oxygen, of course, you also need a fairly high temperature, from 350-400 degrees.

If you hold the match with the head down, the pyrolysis gases slip past the flame and are wasted or, in the oven, fly out into the chimney. And if pyrolysis occurs directly under the flame, pyrogen gases enter it and, with a sufficient air supply, burn, giving more heat. Another good example of the effectiveness of combining pyrolysis with flame combustion is a regular stearin candle. Just try burning a lump of stearin in a bowl! No need, there will be a stink and soot... And in a candle, stearin not only evaporates, but also undergoes pyrolysis. Have you noticed at the very bottom of its flame a narrow zone of blue-violet color? This is where pyrolysis gases are formed and ignite.

In long-burning stoves using solid fuel, it also burns from above, like a match with its head up, and is ignited from above. In “long” liquid fuel stoves, the fuel (most often oil) evaporates, like stearin in a candle, decomposes into easily flammable components by pyrolysis, and they burn. In any case, in addition to additional heat from the same mass of fuel, it becomes possible to regulate the furnace power over a wide range by dosing the air supply, and the flue gases become cleaner.

Why?

A powerful industrial heating boiler has an efficiency of almost 100%. But during the construction of heating plants, up to 30% of heat losses in the main and distribution pipelines are included in the design. New, made according to all the rules and with intact insulation. Autonomous heating of any type does not lose this 30%, and its efficiency is determined only by that of a stove or hot water boiler.

A small, low-power boiler is, in principle, more gluttonous than a large one - the square-cube law applies, and Russia is rich in fuel resources. Therefore, after the revolution in the USSR, a course was set for the development of centralized heating, especially since the environment was not yet pressing.

From memories. The author of this article, having visited Czechoslovakia in the 70s, was surprised: where are the “Aurora” boiler houses? It turned out that there were automatic, autonomous mini-boiler rooms for a house or entrance in an apartment building. Why? They explained diplomatically: “Well, your country is rich, you can afford central heating.”

A lot has changed since then. The bottom of the global fuel tank is already clearly palpable, the ecology is the same for everyone, and science and computer modeling make it possible to obtain an accurate result where in the era of slide rules and Dwight tables one had to only guess.

What does this have to do with homemade stoves? The most direct: a homemade long-burning stove can, although very clumsy in appearance, have an efficiency of more than 90%. And at the same time burn almost any solid fuel, incl. and waste, to carbon dioxide, water and ash. CO2 and H2O, of course, are also greenhouse gases, but with global fuel efficiency at 90% instead of 70%, global warming will have to calm down.

In cyclic furnaces (firing-cooling-firing-cooling-...) the efficiency rarely reaches the fundamentally important 70%. In addition, it gives more than 80%, but is complex, expensive, cumbersome, heavy and poorly adapted to the conditions of modern life. So, improving “long-lasting” stoves is not only a profitable and exciting task, but also important in general for all people.

About pyrolysis and sublimation

How do you get such high efficiency and omnivorousness? Due to the thermochemical decomposition of solid fuel - pyrolysis, firstly. In this case, components that burn easily and completely are formed, and very little flies into the chimney. Therefore, we need to talk about pyrolysis in more detail.

The stages of the pyrolysis process (see next) can be separated in space, then it is said to be a pyrolysis oven. But pyrolysis can occur sequentially over time in the same slowly smoldering fuel layer. In this case, they say that it is a smoldering oven.

Secondly, due to the fact that a lot of heat accumulates in the mass of solid fuel and the release of volatile components occurs through dry sublimation - sublimation. For example, they are also pyrolysis, but the oil must first be evaporated, which requires heat, and it is difficult to obtain an efficiency higher than the same 70%. And the heat reserve in hot vapor is small, therefore, at the slightest deterioration in the quality of the fuel (its water content, for example), either the efficiency drops sharply, or complex injectors with a fuel preparation system are needed.

How does pyrolysis work?

The pyrolysis scheme is shown in the figure. The process consists of 4 stages (stages):

1. Drying – excess moisture is removed from the fuel deposit. Drying can be carried out either separately, during the preparation of fuel, or in the firebox, due to the heat of the kindling.
2. Pyrolysis itself - volatile components are sublimated from the fuel mass, and heavy components - resins and bitumen - decompose to volatiles. Carbonization of the fuel mass begins, i.e. its charring.
3. When the temperature reaches the flash point of pyrolysis gases, combustion begins in the presence of free oxygen. The temperature rises to over 600 degrees and the carbon begins to burn.
4. The volatiles and the bulk of the carbon burned out, and the carbon residues in the hot slag, with a lack of oxygen and a temperature of more than 400 degrees, act as a catalyst for reduction reactions: free hydrogen is released from water vapor, and carbon monoxide and carbon monoxide are released from carbon dioxide; from there and from there - free oxygen.

The last stage is harmful. A lot of energy is spent on the decomposition of water and carbon dioxide, because these reactions are endothermic. At temperatures above 250 degrees, the reduced gases immediately form the original compounds, giving back heat. But, if they cool down quickly, they will not have time to find each other again, and the energy spent on restoration will fly out into the chimney, and carbon monoxide, in addition, is poisonous. Therefore, one of the serious tasks when designing a pyrolysis furnace is to ensure retention of reduced gases in the hot zone, providing access to fresh heated air there. Otherwise, high efficiency cannot be achieved.

Note: Not a fundamental, but significant advantage of long burning is the ease of operation of the stove. Once or twice a day I loaded more fuel, once or twice a week I raked out the ash, and that’s it.

About water burners

Among amateur stove-makers there is a cohort of enthusiasts, usually called water burners. The idea is this: we discharge the cooled flue gases into the catalytic chamber. The catalyst does not have to be amorphous carbon (carbon); There are countless offers of various kinds of cunning membranes and powders. On the catalyst, what is reduced will quickly reconnect back, releasing heat, and - done! Here is a “super-unity” stove with an efficiency of more than 100%!

But the law of conservation of energy is still unshakable, although it often manifests itself in roundabout ways. In this case, it is necessary to heat the incoming reduced ones, otherwise the reaction will not proceed. It is not reasonable to compare it with car burners: the remaining fuel burns out there, still capable of giving a positive heat balance, i.e. the reaction is exothermic.

Where does the heat come from to heat the catalytic chamber? Either from adding fuel, or from an external source, an electric spiral, for example.

If we imagine a catalytic chamber absolutely isolated from the environment, and a heat recovery system that cools the exhaust to absolute zero, then we remain the same: the heat released when combining the recovered components exactly compensates for the cost of heating the components. But, since nothing happens without heat loss (another fundamental principle is at work here - entropy), then the overall heat balance will turn out to be negative. Well, don’t burn the water, it won’t burn...

From theory to practice: firewood and coal

Outside the city, firewood is still one of the most affordable types of fuel. Therefore, a long-burning wood stove is a very relevant and in demand design. It is not difficult to burn wood from a ridge to water vapor, carbon dioxide and ash. But wood is most accessible in waste form, very, very heterogeneous in properties and quality - sawdust, shavings, chips, waste fiberboard and chipboard, small brushwood - khamyr, straw. Therefore systems. We will look at some of the most effective ones, in which you can achieve an efficiency of more than the coveted 70%

Potbelly stove

This stove was not called a potbelly stove because of its bourgeois gluttony. On the contrary, it is very economical, and its taste is not picky. How did this happen?

The potbelly stove appeared in Russia immediately after the revolution, during the times of military communism. It is difficult for a modern person to imagine the deprivations of that time. Mayakovsky, who was by no means a stranger to the Bolsheviks, dedicated one of his poems at that time to how he received “half a log of birch firewood” according to the order. And the “unfinished bourgeoisie”, who did not want or were unable to leave their homeland, did not have to count on any coupons. If you want to live, figure out how.

But among the “formers” there were not only bloodsucking exploiters; Those, back in the prosperous years of 1912-1913, transferred capital abroad, and in 1918, as soon as peace was concluded, they quickly scurried off in all directions. Among those who remained were the best minds in Russia. Although they were the necessary “specialists,” the victorious proletariat did not favor them; probably just for the mind. But they knew how to think.

The potbelly stove is ingeniously simple in design, see fig. Its prototype, undoubtedly, is the Russian stove (which, by the way, the “bourgeois specialists” also repeatedly improved) with its phenomenal efficiency for cyclic stoves. Fuel was thrown into the upper door, and by opening and closing the lower door, the combustion process was regulated by supplying air.

The principle of operation of the potbelly stove is also brilliantly simple, but getting to it was not at all easy.

Task: in at least one room in the harsh winter until the morning, maintain a temperature that does not exclude manifestations of vital activity. It is impossible to heat a brick oven: to warm it up you need 20 pounds of those same “half logs”. But there is a Viennese chair, which, according to physics and chemistry, should be enough if you burn it very slowly and immediately release the heat to the room. Even at the flea market, you can exchange bourgeois belongings for a pound or two of coal, which is approximately the same in terms of calorific value.

But how can a highly active, fast-burning fuel be burned slowly? Stop, there is such a thing - pyrolysis. Until now, in household stoves it was considered only a process accompanying combustion. Pyrolysis is much slower than the combustion chain reaction. Let's stretch the combustion in stages, and we'll get the same total heat slowly, little by little. The stove and chimney will have time to completely give it away, and the room will have time to absorb it.

Yes, the stove should also run on coal, since it can be obtained. In terms of properties, coal is not even quite like wood, but what do they have in common in a stove? Loose, breathable filling. Now, how to organize pyrolysis in it?

It turned out that all you need to do is remove the grate and direct the air flow from the blower directly into the mass of fuel. And also, don’t overcrowd the firebox. The volume of the bookmark is no more than a quarter of the volume of the firebox.

In this case, the oven becomes self-regulating. Let's say we covered the vent. Volatiles in a large free volume burn instantly; there will be no fumes, the burning will simply subside. The temperature in the furnace will drop, the filling will cool, pyrolysis will decrease, i.e. production of volatile and flammable substances. And carbon will not produce waste: all incoming oxygen is immediately intercepted by volatiles. Let's open the vent - vice versa. In terms of reaction time constants, everything agrees well; Pyrolysis and chain, although different processes, are essentially similar.

Experience confirms the calculations: when manipulating the ash door, the hot zone of the chimney moves back and forth along its length, at the same time expanding and contracting, in exact accordance with the calculation. That's it, the potbelly stove is ready!

So what was the result? In a Russian furnace, the afterburning of volatiles and the return of the reduced ones are ensured in the furnace, due to a threshold at its mouth. In a potbelly stove, the afterburning chamber is a long, horizontal or slightly inclined part of the chimney, from the center of the room to the window. When it is made from a metal pipe, almost all the residual heat remains in the room.

The efficiency of the then-bourgeois stoves was repeatedly measured by Grumm-Grzhimailo, Kuznetsov and other authoritative heating engineers. It usually exceeds 80% if the horizontal section of the tin chimney is more than 3 m long. The potbelly stove runs on any solid fuel, except sawdust, etc. It warms up almost instantly; This . It can be made either in a box or round from a barrel. One condition: the chimney diameter is from 85 to 150 mm.

A drawing of a modern-looking potbelly stove is shown in Fig. on right. The main difference is in the design of the blower; Now there is no war communism, and small welding and turning work is quite accessible. In the generatrix of the threaded part of the L-shaped air duct pipe (for the sake of simplicity, it can be made straight) small (6-8 mm) radial holes are drilled. By screwing or unscrewing the blind screw plug, you can precisely and conveniently regulate the combustion. An indicator of proper air supply is heating of the chimney. There should be a hot spot on it, moving closer to the stove as the fuel burns out.

Any potbelly stove becomes red hot when fired, so it is not only a heating stove: its upper surface can be used as a hob. But on the sides you definitely need a screen, spaced from the walls of the furnace body at a certain distance (40-60 mm). It is impossible to weld the radiator fins to improve heat transfer and increase fire safety: a hot interior is an indispensable condition for the effectiveness of a potbelly stove. The screen not only protects the room from overheating by infrared rays. By reflecting back at least half of them, it maintains the furnace temperature at the optimal level for maximum efficiency.

Note: e If the temperature in the chimney somewhere drops below 100 degrees, condensation will form, about which, for more details, see below about sawdust stoves. In this case, a chimney of a special design is required, as discussed there.

Using a potbelly stove, you can easily get a wood-burning hot water boiler. To do this, it is enough to replace the screen with a U-shaped metal water heater; it will reflect back IR just as well. But, again, you cannot move the water heating circuit close to the body of the furnace - it will cool down due to contact (direct) heat transfer, and the efficiency will drop sharply. You need to maintain the same indentation as for the screen.

A potbelly stove of the indicated sizes provides a thermal power of up to 15 kW, depending on the type of fuel, and about a fifth of it will go into the water heater. Therefore, hot water from such a stove can only be obtained for household needs, and the heated area is up to 25 square meters. m. Increasing the size of a potbelly stove for the sake of increasing power is useless - theory prohibits it; due to the same square-cube law, it is not possible to achieve an optimal combustion mode. A potbelly stove was invented to heat one room in a bourgeois apartment. A long-burning furnace must be designed differently and more complex.

More about the potbelly stove

To go further, you will have to return to the potbelly stove and squeeze the very essence out of it. And its essence is in the dimensions of the fuel supply within certain limits and their coordination with the dimensions of the fuel chamber. In this case, the parameters of the stove turn out to be independent of the properties of the fuel - the potbelly stove will squeeze out of it all the heat that it is capable of giving off.

Let's look at the square-cube law in more detail. Oxygen is consumed and heat is generated by the volume of fuel mass, which depends on the linear dimensions of the stack along the cube. And its surface releases heat outward, which depends on them squarely, i.e. with increasing size it increases more slowly.

Hence the first consequence: the optimal temperature for pyrolysis in the fuel mass is ensured only within certain limits of the stack size. If the filling is too small, the excess surface will quickly cool the inside, and the fuel will simply burn as oxygen is supplied.

In a stack that is too large, on the contrary, the inside will overheat due to insufficient surface, everything there will sublimate, and slag and carbon will remain while there is still firewood on the surface. Pyrolysis is again suppressed, and the fuel simply burns layer by layer.

The dimensions of the firebox and the diameter of the chimney must also correspond to the dimensions of the fill. The fact is that the air flow from the ashpit is pressed down and directed into the fuel by the circulation of flue gases, which do not immediately go into the chimney and burn out well. To do this, the convection flow from the surface of the fuel must be somewhat excessive relative to the throughput of the chimney; The potbelly stove works, so to speak, with a virtual high.

In a fuel chamber that is too large and/or with a small filling, the fire simmers and the stove itself is only warm. Convection circulation is sluggish, oxygen from the ash spreads throughout the volume of the firebox, pyrolysis is suppressed, and efficiency is low. When a normal filling burns out, this is no longer scary: the main heat has previously been released and used. But trying to save money by heating one chip at a time is pointless: all the chips will burn one by one, and the room will not warm up - due to the low efficiency, the heat transfer of the stove will be lower than the heat loss of the room.

If the firebox is filled with wood, then there is simply no room left for the convection vortex. Oxygen is instantly consumed by a large mass of fuel, but it does not reach the interior; all of it is spent on surface combustion. The fuel in the mass gradually warms up due to thermal conductivity, but it is low, and pyrolysis is again suppressed: everything that has sublimated immediately burns, only wastingly heating up the inside. The flame does not beat in the stove, but stretches into the chimney. The stove is hot, but not red-hot, and the chimney glows red along almost its entire length.

The second and final consequence: it is impossible to make a potbelly stove of any power and size. Its dimensions are determined by the properties of the pyrolysis gases so that circulation is formed, and the size of the fuel load depends on the size of the furnace. From a potbelly stove with an efficiency of more than 75%, you can get a thermal power of approximately 8 to 20 kW.

From stove to boiler

20 kW is not enough for full heating. And to heat a multi-room home, you need a full-flow water heating circuit built into the stove. That is, it needs a long burning time. Is it possible to obtain it based on the principles inherent in the potbelly stove?

Yes, it is possible, and in two ways. Let's go back a little and squeeze out the quintessence: a potbelly stove is economical thanks to pyrolysis. Pyrolysis fails if the temperature in the fuel mass goes beyond certain limits. And the temperature of the inside of the stowage depends both on the supply of air oxygen and on the nature of convection in the fuel chamber. Let's go from here.

Boiler-1 or method one

• To control the entire process, you need to know only one parameter: the temperature in the combustion chamber. Stays within the optimum range - everything else is OK; the bulk of the heat is released here.
• To optimize heat dissipation for maximum efficiency, you also need to regulate only one value: the boost intensity. The temperature in the combustion chamber is related to the air flow from the boost by a linear relationship, and the automation is extremely simple.
• Since the combustion of pyrolysis gases occurs in a flow, the system is insensitive to the temperature of the walls of the combustion chamber, i.e. The water heater can be built in in any technically convenient way and almost all the generated heat can be transferred into the water.
• When slag with carbon remains in the pyrolysis chamber, reduction is suppressed by increasing the boost, which provides excess oxygen. The natural influx through the ashpit cannot be excessive. Analogue: water, either flowing freely under the influence of gravity, or supplied under pressure.
• It is possible to additionally load a new batch of fuel at any stage of the process and in any acceptable amount - the boost will be increased and purged. A potbelly stove can also be heated, but little by little, so as not to lower the temperature and suppress pyrolysis, otherwise the efficiency will drop sharply and most of the fuel will burn in vain.

Note: the rate of pyrolysis and the composition of pyrolysis gases significantly depend on the type of fuel. These factors can also be taken into account simply by adjusting the back pressure at the outlet by throttling the chimney. In industrial boilers, its regulator is equipped with marks corresponding to the recommended types of fuel.

In once-through boilers with a power of up to 30-40 kW, the temperature in the afterburner can be monitored indirectly, using an important operational parameter - the supply water temperature. At high powers, the thermal inertia of the system can lead to a “boost” of the process - cyclically increasing temperature fluctuations in the combustion chamber, which is already a pre-emergency situation. Therefore, powerful boilers are supplemented with thermocouples in the afterburner and pyrolysis chamber. As long as there is no smell of rocking, the water temperature is maintained. The “burning” thermocouple showed an exorbitant value - we proceed to adjust it, it’s better to let the water cool down a little. It didn’t help - we reduced the pyrolysis temperature using the pyrolysis thermocouple to a minimum. Three-stage adjustment ensures 100% performance, and emergency automation is only triggered by physical influence from the outside. The efficiency of a once-through boiler can exceed 90%

Boiler-2 or method two

A once-through boiler is good for everyone, except for one thing: it needs power. The electricity goes out - the boiler stalls, and then you need to rake out and rip out the sintered mass from the firebox, load a new fill and release your money into the chimney until the process stabilizes.

However, with a power of up to 50 kW, you can make a pyrolysis furnace with a water heater, which does not require automation and electricity (on the right in the figure). The principle of its operation is based on the opposition of two square-cube laws to each other: in the filling of fuel and in the lining of fireclay bricks. This brick oven works according to the following algorithm:

1. At the beginning of pyrolysis, it proceeds most intensely due to the sublimation of the lightest volatiles. This “first heat” passes through the smoke circulation and is absorbed by the lining. In a potbelly stove, the first heat is spent on the formation of a vortex, and in a once-through boiler it is suppressed by reducing the pressure.
2. At the stationary stage of the process, the lining acts as a thermal buffer: when there is an excess of pyrolysis heat, it absorbs it, and releases it when the filling cools.
3. After complete carbonization of the filling, the lining gradually releases heat, preventing the temperature in the furnace from falling below critical, and the reduced ones have time to react before they reach the cold parts of the smoke tract. This is possible because the mass and heat capacity of the lining (proportional to volume) is greater than that of the slag pile. The lining causes it to cool at its own rate, the carbon burns out before the temperature drops, and the reduction catalyst is no longer available below the critical temperature.

A fresh supply of fuel must be loaded gradually into a pyrolysis boiler with a thermal buffer, like into a potbelly stove. A very inertial lining will not be able to fend off sharp temperature fluctuations. And, if the properties of the fuel differ too much from the permissible ones, the furnace with a heat accumulator can either stall (from sluggish fuel), or go into overdrive until it crashes, from fuel that is too flammable. And the efficiency, due to the fact that the first heat is not suppressed, does not exceed 76-78%, which is lower than bourgeois, because the lining eliminates instant heat transfer to the outside.

Incidentally, about fireplaces

Fire is attractive, and its decorative and aesthetic significance is great. There are almost more stoves and fireplaces than heating appliances. And not only oligarchs who can afford any fuel costs want to sit by the fire. Hence the question: is it possible to make a long-burning stove-fireplace? Efficiency and heat transfer are not so important here, as long as the light glows until the end of the evening.

What is there - isn't it possible? There is such a device. This is the good old one, shown in section in the figure.

Note the smoke tooth. It, like a threshold in a Russian stove, forms a circulation of flue gases that does not allow fresh air to escape upward and pushes it into the fuel deposit, as in a potbelly stove. Probably, its unknown authors sat by the fireplace in their “former” bourgeois well-being.

Note: When you light an English fireplace with damp wood, you can see how smoke billows out at the mouth without escaping into the room.

The efficiency of the fireplace due to the large mouth is low even if there are smoke circulations in the chimney; it does not exceed 50%. And smoldering with the release of heat lasts from late evening until morning only when Cornish coal or similar coking coal is added. In the Donbass, anthracite layers of this quality have long been selected, and Karaganda coal burns out in 4-6 hours. They say that in the old days, English lords preferred to heat with the rhizomes of pine trees that grew on coastal cliffs, but now this type of fuel is hardly available to anyone at all.

Along the way. An English lord sits in the evening after a fox hunt by the fireplace, sipping whiskey and smoking a cigar. He lifted his legs up onto the fireplace grate and stared thoughtfully at the fire. The butler approaches: “Sir, I apologize for interrupting your rest, but may I draw your attention to the fact that your socks are starting to smoke” - “Socks? James, do you mean boots?” - “The boots, sir, are already burnt.”

The second option for a “long” fireplace stove is a regular one. Before lighting, you need to close the ashpit, load fuel into a quarter of the firebox by volume, like in a potbelly stove, and keep the firebox door wide open. Most of the heat will fly away into the chimney, but the evening light will last with a rare small flood, and the decorative effect is obvious.

For example

The boilers described above require complex professional work and/or industrial conditions for production. Here, as an example, we provide a drawing of a long-burning stove that can be manufactured by a skilled home-made craftsman at home. Pay attention to the prefabricated unit B, which moves up and down on a telescopic rod. We will soon examine its purpose in detail.

The power of such a furnace is about 35 kW. It runs on coal or fuel pellets. The efficiency is up to 85%; Burning time is about 12 hours. When loaded with firewood, the efficiency decreases to approximately 75%, and the burning duration decreases to 8-10 hours.

Ha ha! Sawdust and dust!

A sawdust stove is a good touchstone for a heating engineer. But not because sawdust and other woodworking waste are lying in heaps everywhere. Saw waste, let the reader know, is a valuable secondary raw material and is disposed of in many ways for a variety of purposes.

But in nature there are huge and almost untapped reserves of mineral fuel, as high in calories as sawdust, and just as poorly burning - oil shale. Until now, the technology for complete and safe combustion of oil shale on an industrial scale does not exist. Underground gasification of shale deposits is environmentally very dangerous, no matter what the authors of the latest developments claim. The United States, which actively offers its shale discoveries to foreign partners, gasifies shale at home sporadically and on a small scale.

But a household sawdust stove is a different matter. Here, enthusiasts have something to apply both their minds and their hands. And there are already examples of successful designs.

Bubafonya

The Baltic states have been actively engaged in shale since the times of the USSR; they have large reserves there; in fact, oil shale is the only type of natural fuel readily available in the Baltics. The STROPUVA oil shale boiler has been mass-produced in Lithuania for a long time. Runet was introduced to it by a user under the pseudonym bubafonja, and now the bubafonja stove is a favorite model for copying by amateur stove makers.

– the stove is not ideal, but its design contains principles that allow the creation of more advanced devices. Therefore, we need to understand the bubafone in more detail. The bubafoni diagram is shown in Fig.

The principle of operation of bubafoni is simple: the fuel filler smolders on top in a thin layer as a solid mass. If you put a solid round wooden block into a bubafonya, it will decay in exactly the same way. All stages of pyrolysis are mixed both in space and time. In the cavity above the filling, minor volatile residues are burned.

Air enters the center of the smoldering zone through a vertical pipe-air duct. And what prevents it from going upward is the pressure with the blades, colloquially called a pancake (part B, remember? Its configuration has been modified for active fuel), welded onto the mouth of the air duct. Contrary to popular belief, the pancake does not press down the bookmark. It needs heaviness in order to fall down under its own weight following the burning fuel without jamming, otherwise the stove will easily stall, and it is very difficult to pick out the unsmoldered sintered filling.

The blades of the pancake are not just partitions that form air channels. They must be curved so that the flue gases escaping from under the pancake swirl clockwise when viewed from above. This is necessary so that the gases, before escaping into the chimney, make several revolutions over the pancake, linger in the firebox and burn out. If the pancake has straight partitions, the efficiency of bubafoni is unlikely to exceed 60%. The incorrect (left) and correct pancakes are shown in Fig.

Note: an unusable sprocket welded in the center of the correct pancake will prevent a column of unburned fuel from forming there (if it is too wet), plugging the air duct. And through the central hole of the sprocket, air will pass into the center of the smoldering zone. A very smart decision.

About the chimney and condensate

For normal operation of the bubafoni, an expanding, smoothly or abruptly, chimney is required, the so-called. a chimney with a draft uneven along its length. A “whistling” chimney of equal cross-sectional length will draw air from under the pancake into itself before it has time to react with the fuel. That is why it is recommended to collect the bubafoni chimney in a countercurrent to the flue gases, i.e. gradually increasing the diameter of its constituent pipes. But this is difficult, but an L-shaped joint of two pipes of different diameters (the far one is larger) will give the same effect due to the formation of a pressure surge at the joint.

For optimal combustion in a bubafone, the size ratios of the gas-air path are also important. The diameter of the air duct should be 1/5-1/7 of the diameter of the fuel chamber. The chimney should be one and a half times wider, and the chimney should be another one and a half times wider. In most cases, this is ensured with a diameter of the air duct of 100 mm, the chimney - 150 mm and the chimney - 250 mm.

Both wood and slate suitable for combustion contain from 8% to 30% moisture. Bubafonya will also digest fuel with 50% humidity. This moisture (by the way, it is this that seduces water burners) in the chimney, where the temperature drops below 100 degrees, forms abundant condensation. It literally pours out of the chimney like a stream. Therefore, it must also have a water collector with a drain ball valve. It is the ball valve - the condensate, to put it mildly, is far from being pure, and the ball valve can be easily cleaned with wire without disassembly.

Bubafonya-cauldron

You can put a water heating circuit on the bubafonya (on the right in the figure above), observing the same condition as for a potbelly stove - a small indentation from the walls. Otherwise, the efficiency will drop sharply, and soot caked into stone will settle on the walls, which will not be removed later. By the way, a screen for a bubafoni is needed in the same way as for a potbelly stove. For normal operation, the bubafonya must also be red-hot. Combustion in the bubafon is regulated by a throttle on the air duct.

A homemade bubafonya from a barrel is shown in Fig. on right. These are its maximum dimensions, and the minimum are:

• The total height, excluding the protruding part of the air duct, is 600 mm.
• The internal diameter of the combustion chamber is 200 mm.
• The diameter of the pancake is 140 mm.
• The diameter of the air duct is 75 mm.
• The diameter of the chimney is 85 mm.
• Chimney diameter – 100 mm.

What's wrong with bubafon?

As already said, bubafonya is not an ideal oven. Firstly, it does not work on highly active fuels - coal, pellets, etc. More precisely, it works for some time after kindling, and then suffocates. When it comes to carbonization, the smoldering layer with the pancake becomes so hot that local microconvection simply does not let air in. When the hot layer cools down, the unnatural, top-down air supply is not enough to flare up again. It is useless to set the boost - a forced impact on the self-regulating system leads to the fact that the air flies over the fuel and flies out into the pipe, taking with it unspent oxygen.

Secondly, the efficiency of the bubafon is, at best, somewhere around 75-78%. Thirdly, the bubafon is not suitable for cooking: the only place where a hob can be installed is occupied by the air duct. And, finally, there is no way to reload fuel until the previous portion has decayed; the loading itself is a bit heavy and inconvenient: you need to lift and somehow fix the heavy air duct with a pancake. So for now, only the Baltic states make bubafoni in series.

Video: example of homemade bubafoni

Slobozhanka

The Slobozhanka stove seems to be a product of folk art in Slobozhanshchina; this is a significant part of the Kharkov, Sumy, Belgorod and Voronezh regions. Although it is similar in principle to bubafonya, it was born independently of it. And, I must say, the result turned out to be much better than the product of former Soviet industrial research institutes, which later became national research centers.

Slobozhanka - . The release of the upper surface under the pans with boiled-off residues is achieved due to the fact that air is supplied to the smoldering layer from the side, describing a U-shaped path: first down the L-shaped air duct, and then through the perforated casing covering it (pos. A in the figure). The solution is, of course, a product of purely Russian ingenuity:

• The air, heating up above the fuel, tends, of course, to go upward, unsupported by anything. But the fuel deposit sags more near the casing, and the flow of oxygen slides over its surface without any pancakes, and the fuel takes as much as it needs.
• The smoldering layer sucks in air as needed, and the excess goes up, ensuring the neutralization of the reduced ones.
• Due to the possibility of air access to all layers of fuel, the hot layer turns out to be thicker than in bubafon, and pyrolysis is more active.

Due to the latter circumstance, the Slobozhanka works perfectly on coal with pellets. Easily combustible pyrolysis gases enter the carbonized layer from below, providing a temperature at which carbon completely burns. Therefore, Slobozhanka is an economical stove. Its efficiency exceeds 80%

The ratio of sizes, the design of the smoke duct and the water heater for Slobozhanka are the same as for bubafoni. A screen is also needed. But with the same dimensions, its power can be increased at the cost of some complication of the design. To do this, the internal perforated casing must be stretched over the entire circumference and connected to the external incomplete partitions. To arrange a blower with a throttle, you will have to make a third, narrow casing that covers the air intakes on the outside (pos. B in the figure; the stove shell is conventionally turned into a plane). In this case, the fuel filling sags from the center to the edges.

Slobozhanka with fungus

The classic, so to speak, Slobozhanka, has two drawbacks. Firstly, it does not tolerate tarry and greasy fuel. Fiberboard, chipboard and household waste produce hard deposits, and most of all exactly where it is most harmful - on the perforated air duct casing or at the edges of the holes in the internal casing.

Secondly, you need to carefully refill the unsmoldered filling. At least a small smoldering area near the perforation of the casing should remain free. This is not always convenient: you only have time to plop everything down at once, and when you leave, the stash will burn out and the stove will cool down, you need to relight it again, enduring the cold and releasing your hard-earned money into the chimney.

Meanwhile, in small remote garrisons of the Soviet Army (individual companies, stationary communications points, etc.) back in the 70s one could find a heating-cooking-incinerator stove produced by some kind of post office, see pos. B in Fig. This is the same Slobozhanka, but with a central conical perforated air duct equipped with a mushroom cap. The cone was inserted freely into the discharge hatch of the firebox and removed for cleaning. The bookmark sagged from the edges to the center.

The role of the fungus was apparently twofold. Firstly, its protruding edges threw the “plumped” fuel to the edges, and under the cap there was always a smoldering ring, sufficient for the stove to “ignite” again. It was possible to add fuel at any time and as much as needed.

Secondly, the brim of the hat directed additional air flow into the smoldering zone. This ensured complete omnivory. What the careless orderlies didn’t throw into the stove - it’s sickening for a decent person to remember...

The efficiency and power of the stove were not measured by the author, but one and a half buckets of coal-seeds were enough for 14 souls of personnel in a single army tent in the frosty winter to sleep well in one cotton and without boots, under army flannel blankets.

Of the shortcomings of the “slobozhanka with fungus”, only one was noticed: when burning with household garbage or damp pine, it was necessary to check the carbon deposits every 2-3 days. If you missed it, the cone stuck tightly in the socket, and it was difficult to swing it and take it out without distorting it.

Video: assembling a homemade Slobozhanka from a barrel

Should I buy it?

Isn’t such a wonderful stove mass-produced? Is it possible to buy it ready-made somewhere? Large manufacturers seem to have focused on those that are in high demand for greenhouses and do not become hot when fired. But small private producers do it and offer it. The sample is shown in Fig.

This Slobozhanka has a small but useful improvement: an external ash pan lying freely under the hearth, second from the left, pos. It can be carefully taken out and emptied without causing ash dust in the living space. But you still have to climb into the oven: the cover of the unloading hatch (it is visible on the bottom in the position on the far right) must be closed when firing.

About fuel

There is no need to look for fuel for a long-burning stove at a household or industrial landfill. Manufacturers are vying with each other to offer excellent smoldering pellets at a price of about 4,000 rubles. per ton. Considering the cost-effectiveness of “long” stoves, this comes out quite inexpensively.

Pellets are made from any burning biomass: the same sawdust, wood chips, straw, onion and garlic peels, sunflower husks, cones, bark, citrus peels, nut shells, etc., etc., see fig. The technology is somewhat reminiscent of MDF production: dry pressing at elevated temperatures.

In terms of thermal properties, fuel pellets are similar to coal. They are produced from “dust” with a diameter of 6 mm to 30-70 mm logs. During the production process, components that can produce harmful volatiles are removed from the mass of raw materials, so the pellets are easily burned to carbon dioxide and water. In general, it is a very good fuel with stable properties.