Pyrolysis boilers heating: the principle of operation and types of boilers long burning
The years go by, science and technology are moving forward, and solid fuels are still in demand. Burning wood in a traditional stove or in a stove is not very efficient, but pyrolysis boilers have changed the situation.
High efficiency and relatively simple operation are just a few of the benefits of these useful devices.
What is pyrolysis?
Firewood is perhaps the first fuel in human history. Almost everyone knows how quickly they burn in the open air, and that the heat is not so much released. But the situation changes dramatically, if you create other conditions for the combustion process.
The so-called pyrolysis combustion is carried out in closed chambers. Firewood or other solid fuel of this type is loaded there: pellets, sawdust, wood production wastes, etc.The fuel is ignited and then reduces the amount of air entering the chamber.
As is known, oxidation processes occur during combustion, one of the main participants of which is oxygen contained in the air. If there is little oxygen, the reaction slows down and the firewood burns out slowly, in fact in such conditions they simply smolder. In this case, a certain amount of thermal energy, ash and combustible gas is released.
The pyrolysis process does not end there. The gas obtained by burning primary fuel is mixed with air masses and also burns. As a result, thermal energy emits significantly more than with standard heat generators. Therefore, pyrolysis boilers demonstrate a very decent efficiency compared with their purely solid-fuel “brothers”, and often provide an opportunity to significantly save on heating.
The advantage of this type of heating equipment is that the principle of its operation and the device is relatively uncomplicated. The amount of air entering the combustion chambers is regulated by a conventional mechanical damper. A simple design ensures the reliability of the device; breakdowns for pyrolysis boilers are not a frequent occurrence.
Another “plus” of pyrolysis boilers is a long burning period. Full loading of the device with fuel makes it possible not to interfere in the process for several hours, sometimes more than a day, i.e. there is no need to constantly throw firewood into the firebox, as it happens with open burning.
Of course, this does not mean that the pyrolysis boiler can be left unattended. As with other heating technology, there are strict safety guidelines. It is worth remembering that the pyrolysis boiler is not omnivorous - the humidity of the fuel should be low. Otherwise, part of the precious thermal energy will not be spent on heating the coolant, but on drying the fuel.
During the implementation of pyrolysis combustion, the fuel burns almost completely; the device will have to be cleaned much less frequently than during the operation of a traditional solid fuel boiler. Fine ash, obtained after purification, is used as a fertilizer. Combustion of fuel in such boilers is carried out from top to bottom.
Therefore, the possibilities for natural air circulation in the firebox are markedly limited. The use of forced air injection with a fan significantly improves the efficiency of the device, but it also makes the boiler volatile, since the fan requires electricity.
Device and operation of the pyrolysis boiler
The furnace pyrolysis boiler is divided into two sections. In the first, firewood is burned, and in the second, secondary combustion of a mixture of pyrolysis gases and air takes place. It separates the first chamber from the second grate, on which fuel is laid. The air is usually forced by a small fan.Although in small models sometimes to create thrust using the exhauster.
The presence of forced ventilation can be considered the main difference between the pyrolysis boiler and the classical solid-fuel model. The case of the device consists of two parts inserted into each other. The space between the walls is filled with coolant, the role of which is traditionally performed by water.
First, fuel is loaded into the first compartment of the pyrolysis boiler furnace, then a fan is turned on and the fuel is ignited. The resulting combustible gases are transferred to the second compartment, mixed with air and burned. The burning temperature can reach 1200 degrees. The water in the outdoor heat exchanger is heated and circulated through the heating system of the house. The remains of products of combustion are removed through a flue.
In reproach to devices in which work the pyrolysis principle of burning is used, one can put a relatively high price. A conventional solid fuel boiler costs significantly less.But in the long-burning boilers, firewood burns almost completely, which is not the case with the classic boiler.
When choosing a pyrolysis boiler, it should be remembered that low-cost low-power models are usually designed only for firewood. Moreover, loading the fuel into the device will have to the maximum, reducing the load leads to increased formation of ash and soot, and also adversely affects the operation of the unit as a whole.
Boilers top burning
One of the options for the pyrolysis device is the upper combustion boiler. The principle of operation of these two units is very similar. Similarly, a large amount of solid fuel of low humidity is loaded into the furnace, air is forced to force and provide fuel smoldering with a reduced amount of oxygen. The valve that regulates the flow of oxygen is set in the desired position.
But long-burning boilers have neither an ashpit nor a grate. The bottom is a blank metal plate. Such boilers are designed so that the wood burns completely, and the small amount of ash left in the furnace is blown out with air. Such devices are characterized by high efficiency and also operate at temperatures of more than 1000 degrees.
The main feature of such devices - they really provide a long life at full load. The fuel chamber in such devices is usually made in the form of a cylinder. Fuel is loaded into it from above, and the air necessary for burning is injected from above, in the center.
Thus a slow smoldering of the upper layer of fuel is carried out. The fuel gradually burns, its level in the furnace decreases. At the same time, the position of the device for supplying air to the firebox also changes; this element in such models is mobile and it practically lies on the top layer of firewood.
The second stage of combustion is carried out in the upper part of the furnace, which is separated from the lower compartment with a thick metal disc.Hot pyrolysis gases, formed as a result of combustion of fuel below, expand and move upwards. Here they are mixed with air and burned, additionally transferring to the heat exchanger a solid portion of thermal energy.
The beam holding the disk, which divides the combustion chamber into two parts, as well as this disk itself, in the process of operation of the upper combustion boiler is constantly under the influence of high temperature. Over time, these elements are burned, they will have to be replaced periodically.
At the exit from the second part of the fuel chamber, a thrust regulator is usually installed. This is an automatic device that determines the temperature of the coolant and, depending on the data obtained, regulates the intensity of movement of the combustible gas. It protects the device from possible overheating.
It should be noted that the external heat exchanger in such boilers responds to changes in the rate of circulation of the liquid in the heat exchanger, i.e. on temperature fluctuations. A condensate layer is immediately formed on the surface of the device, which causes corrosion, especially when it comes to steel boilers. It is preferable to take a device made of cast iron, which is much better resistant to such effects.
Although the fuel in pyrolysis boilers for long burning should burn without residue, in practice this is not always the case. Occasionally, the ash is sintered, forming particles that are difficult to remove with the help of a stream of air. If a large number of such residues accumulate in the firebox, a noticeable decrease in the thermal efficiency of the unit may be observed. Therefore, the upper combustion boiler should be periodically cleaned nevertheless.
A feature of this type of device is that as it burns, it can be reloaded without waiting for the entire fuel to burn. This is convenient when you need to get rid of household waste. There are also varieties of upper burning boilers, which work not only on wood fuel, but also on coal. Complex automatic control units in pyrolysis boilers of this type are absent, therefore serious breakdowns are observed extremely rarely.
The design of the upper combustion boiler allows loading the furnace only partially, if necessary. However, in this case, igniting the top layer of fuel may not be easy. The fuel itself must be dried, firewood from an open woodpile is not suitable for such a boiler.Fuel of large fractions should also not be used for this type of equipment, i.e. firewood will have to be split into small pieces.
Features of operation of gas-generating boilers
The efficiency of the pyrolysis boiler depends largely on the type and quality of fuel. Technically, it is possible to load not only wood into the furnace, but also coal, and even peat, most modern boiler models are designed to use several types of fuel. Wood burns in about 5-6 hours, depending on the variety. The harder the tree, the longer it burns.
It will take about ten hours to burn black coal, and the same amount of brown coal will fester for eight hours. In practice, the highest heat transfer pyrolysis technology demonstrates when loading dry wood. Firewood is considered to be optimal moisture content of not more than 20%, and a length of about 45-65 cm.
If there is no access to this fuel, you can use coal or other organic fuel: special briquettes and wood pellets, waste obtained from wood processing, peat, materials with cellulose, etc.Before using the boiler, you should carefully study the recommendations of the device manufacturer regarding fuel.
Too wet fuel in such devices is unacceptable. When it is burned, additional water vapors are formed in the furnace, which contribute to the formation of such by-products as tar and soot. The walls of the boiler are polluted, the heat output decreases, over time the boiler may even stop working, die out.
If dry fuel is injected into the furnace and the boiler is set up correctly, the pyrolysis gas obtained as a result of the operation of the device will produce a yellow-white flame. Such burning is accompanied by an insignificant release of combustion by-products.If the color of the flame is colored differently, it makes sense to check the quality of the fuel, as well as the instrument settings.
Unlike conventional solid fuel devices, before loading wood into pyrolysis boilers operating on solid fuel, the firebox should be reheated. To do this, perform the following steps:
- Small fine kindling (paper, chips, etc.) is loaded onto the bottom of the furnace
- Burn it with a torch from similar materials.
- Close the door of the combustion chamber.
- The door of the loading chamber is left slightly ajar.
- Add portions of the kindling as it burns.
- The process is repeated until a layer of glowing coals forms at the bottom.
By this time, the firebox is already warming up to about 500-800 degrees, creating the conditions for loading the main fuel. Do not use gasoline, kerosene or any other similar liquid substances for igniting the fire. Before heating the furnace of a long-burning boiler, make sure that the device is ready for operation.
To do this, check the presence of traction, tightness of the doors, serviceability of locking mechanisms and adjusting equipment, the presence of coolant in the heating system, etc. Then you should turn on the thermostat to make sure that the device is receiving voltage. After that, open the gate straight thrust and ventilate the boiler for 5-10 minutes.
Browse popular models
It should be understood that any pyrolysis boiler is a rather heavy unit that is not intended to be hung on the wall. Such devices can be used for heating a small house, and for spacious cottages. Coppers of long burning differ on power.
This indicator is usually focused buyers. Among the popular models of this technique should be mentioned:
- “Atmos”(Ukraine) - represented by devices that can work on wood and coal, power ranges from 14 to 75 kilowatts.
- “Attack”(Slovakia) - able to cope with heating areas up to 950 square meters. m, some models are able to continue to work even with power outages.
- “Bosch”(Germany) - high-quality products of a famous brand, power varies in the range of 21-38 kilowatts.
- “Buderus”(Germany) is represented by the Elektromet and Logano lines, the first is well known in Europe as a classic version of the pyrolysis boiler, the second is the more modern versions designed for private houses.
- “Gefest”(Ukraine) - high-power devices with efficiency up to 95%.
- KT-2E (Russia) is specially designed for large residential premises, the power of the unit is 95 kilowatts.
- “Opop”(Czech Republic) - relatively inexpensive boilers, reliable and durable, power 25-45 kilowatts.
- “Stropuva”(made in Lithuania or Ukraine) with a power of seven kilowatts is quite suitable for a small house, but more powerful devices are also represented in the model range.
- “Viessmann”(Germany) - an ideal choice for private households, power starts from 12 kilowatts, the use of modern technology saves fuel.
- “Buran”(Ukraine) with a capacity of up to 40 kilowatts is another popular option for owners of large cottages.
- "Logics"(Poland) high-power devices at 20 kilowatts easily heat rooms up to 2 thousand square meters. m, it is rather a boiler for industrial needs: heating shops, offices, greenhouses, etc.
Choosing a pyrolysis boiler for a private house, you should pay attention to the model with two circuits, in order not only to heat the home, but also to provide it with autonomous hot water.
The heat exchanger for hot water is cumulative or flow type. For the latter, models of boilers of increased thermal power are used.
Conclusions and useful video on the topic
This video vividly depicts the principle of operation of the pyrolysis boiler:
A detailed overview of the operation of the upper combustion boiler can be found here:
Pyrolysis boilers are not cheap, but they fully justify the funds invested in their purchase. With proper installation and maintenance, such devices will provide the house with a stable and inexpensive heat.