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In a large part of Russia, wood is still the most affordable type of fuel, and many are heated by wood-burning boilers. Everything would be fine, but in ordinary solid fuel boilers, the bookmark burns out in 2-3 hours, which is completely inconvenient – you won’t leave the house for a long time. There are long burning boilers. In them, one bookmark of firewood can burn up to 8-10 hours, but they cost a lot of money. However, as usual, there is a way out – to make a pyrolysis boiler with your own hands. Not to say that this is an easy job – welding skills must be at a high level, and the materials cost a lot. However, there are many homemade pyrolyzers.
The principle of operation of the pyrolysis boiler
In relation to heating boilers, pyrolysis is the combustion of fuel with an insufficient amount of oxygen. At the same time, the fuel emits a large amount of gases, almost all of which are combustible. These gases are sent to a special combustion and afterburner chamber, where secondary air is supplied. The gas-air mixture ignites, releasing a large amount of heat. Much more thermal energy is released than can be extracted by conventional combustion of wood or coal. The fact is that many of the volatile substances formed during the combustion of fuel have a very high combustion temperature. As a result, pyrolysis boilers extract more heat from the same amount of fuel.
Due to the peculiarities of the combustion process (the release of a large amount of gases), such installations are also called gas-generating boilers.
A design feature of pyrolysis boilers is a firebox consisting of two chambers. Fuel is placed in one (often this is the upper part of the furnace), gases are released in it, and therefore this part is called the gas generation chamber. Through a narrow neck, gases enter the second chamber – afterburning. Here they mix with secondary air, flare up and burn out almost without residue.
On average, the efficiency of pyrolysis plants is above 85%. There are models that can give out 92% and even a little more. But these indicators are possible only and exclusively when using dry fuel. Its humidity should be 5-8%. At 40% moisture content, combustion can completely die out, and at 20% it will simply be inefficient. And this is one of the main disadvantages of this technology: firewood and coal have to be dried beforehand, for example, by making a platform near the chimney. It’s just that firewood dried in a woodshed will not go, like coal taken from a pile on the street.
The video shows a boiler in which the afterburner is at the top. Although boilers of this type have a simpler structure (the resulting gases themselves rise up), do-it-yourselfers prefer a chamber with a lower location of the afterburner (as in the photo above).
What to pay attention to when making
If you are going to make a pyrolysis boiler with your own hands, you need to clearly understand not only the mechanism and principle of its operation, but also take into account all the unpleasant moments that these units have. First of all, it must be said that almost all pyrolysis gases are poisonous. That is, the unit must be completely sealed, the welds must be of the highest quality.
In addition, to ensure safety, a combustion process control system (temperature, smoke, draft sensors) and automation are needed, which, depending on the readings of the sensors, regulates the combustion processes. If you are going to make a home-made pyrolysis boiler on natural draft, automation can be the simplest – non-volatile. If there is a blower fan to supply air to the current, more serious (and expensive) devices are needed, and they are powered by a 220 V network. The operation of a boiler of this type without automation is dangerous, because an uninterruptible power supply is needed that will ensure the operation of the fan and automation for 10 -12 hours is the burnout time of the bookmark.
Second moment. In some models of pyrolyzers, the temperature in the active phase reaches 1000°C and above. Ordinary structural steel under such conditions will quickly burn out. In order for the boiler to exist for a long time, heat-resistant steel and an internal lining of the most thermally loaded parts are necessary. If the pyrolysis boiler is made by hand, the lining is most often made of fireclay bricks. In the working phase, the fireclay heats up to a crimson glow and becomes very fragile. If, all of a sudden, you have to operate in the furnace at this time, be careful – it is easy to damage the lining at the moment, but it is long and difficult to repair.
How much will materials and parts cost?
How much a do-it-yourself pyrolysis boiler will cost exactly depends on the required power and the chosen design. However, if you buy heat-resistant steel, grate bars, make a lining, install automation (albeit inexpensive), the amount runs up to $ 850-1200. This is the cost of materials and components, but with self-welding. They are voiced by those who have already welded and use pyrolysis. If you have to pay for welding, then the costs should be doubled.
As you can see, in the case of owning welding, there are savings, but far from the biggest. You can find ready-made options for solid fuel pyrolysis boilers for $ 1500. Although, as you know, a cheap product has a low price for a reason. Saved on something. And you can even guess on what: on the lining. It is the secrets of protecting the walls of the furnace from burning out that manufacturers cherish the most, and spend a lot of money on research in this area. This is why high quality equipment costs a lot of money.