The annual increase in the price of basic energy sources, gas and electricity, makes residents look for alternative heating options. Fossil fuels such as coal and peat are familiar to the inhabitants of the hinterland. Do not write off wood fuel. Firewood is still a popular fuel resource for residents of the central and northern regions of our country. The availability, relatively low cost of solid fuel makes it a real competitor to gas and electricity, especially when it comes to individual home heating. Stove heating returns to our lives only in a different, more perfect and modernized form.
For residents of the private sector, owners of country houses, pyrolysis solid fuel boilers are of increased interest. Traditional solid fuel heaters are now giving way to new models with high technological characteristics. The reason for the popularity that pyrolysis boilers enjoy today lies in the high efficiency of units of this type.
What are boilers for heating solid fuel, pyrolysis type, we will understand in more detail.
What is pyrolysis
A solid fuel boiler that runs on coal or wood according to the old, traditional scheme is already a relic of the past. Despite the fact that solid fuels continue to be relatively affordable, many are confused by the low efficiency of heating a dwelling heated by traditional solid fuel boilers. The situation today has changed radically. Pyrolysis boilers, economical, highly efficient and powerful units, have entered the heating equipment market. Huge technological equipment of this kind is due to pyrolysis, an innovative process for burning solid fuels.
Pyrolysis is a process of uniform decomposition of organic compounds under the influence of high temperature. By artificially limiting the access of air, it is possible to turn the usual combustion of fuel into a slowly flowing thermal decomposition of organic compounds. During the smoldering of organic fuel, in addition to thermal energy, a large amount of gaseous combustible substance is released. The process produces wood gas and charcoal. Another name for the final product is coke, an organic substance that is 90% carbon.
The wood gas obtained as a result of pyrolysis is an excellent fuel. Getting into the secondary combustion chamber, saturated with oxygen, during the combustion process, the gaseous substance releases a huge amount of thermal energy.
Important! Contacting with carbon, pyrolysis or wood gas almost completely burns out, leaving behind CO2 and water vapor. The amount of carbon dioxide in this case is three times less than that released during conventional wood combustion. This quality is important for the mass use of solid fuel boilers for residential heating.
The amount of ash left after the combustion of wood gas is insignificant, which greatly facilitates the cleaning of the heating boiler.
Stages of pyrolysis
To understand the principle of operation of a pyrolysis boiler, you need to have an idea of what happens and why at each stage. This type of solid fuel boiler has two combustion chambers. The wood is dried in the first combustion chamber. The boiler temperature at this moment is 450 0C. At this stage, the generation of combustion products into a gaseous substance — wood gas begins. Mixing with the heated, secondary air supplied by the fan, the gaseous substance burns already at a temperature of 560 0FROM.
At this stage, the exothermic reaction is gaining strength, eventually creating a high intensity of combustion. The gas enters the second chamber, where, with the help of the supplied oxygen, it burns much more intensively. The temperature in the second combustion chamber is 1100 0FROM.
At each stage, the maximum possible amount of useful work is squeezed out of the products obtained as a result of combustion, respectively, the efficiency of the boiler increases significantly. To optimize the operation of the heating boiler in operating mode, the design of the pyrolysis boiler has gate valves (gate valves). What is the purpose of these devices?
After switching on, the pyrolysis boiler operates in the normal furnace mode. When the boiler is fully loaded with fuel, using the gate, you can set the most efficient pyrolysis combustion mode. Unlike conventional combustion, the exothermic reaction can be controlled. This feature made it possible to make pyrolysis boilers automated heating devices. Thanks to pyrolysis, it was possible to fully use the fuel potential of wood, bringing the boiler efficiency to high values as a result of combustion. Automation of the entire process minimizes the human factor and reduces fuel consumption.
In terms of fuel choice, pyrolysis boilers are omnivores. For heating a residential building using a pyrolysis-type solid fuel boiler, firewood and sawdust, wood and peat briquettes, and pellets are suitable.
The device and principle of operation of the boiler
It has already been said earlier that boilers of this type have chambers. The furnace is divided into a gasification chamber into which fuel is loaded and directly into a combustion chamber.
The diagram shows the internal structure of a pyrolysis-type solid fuel boiler
Fuel is loaded into the first chamber, where the air flow is limited. The boiler starts up and works normally. With slow combustion, the fuel begins to pyrolyze, wood gas is released, which enters the second part of the furnace, into the combustion chamber. From this moment, the solid fuel boiler goes into operation. Now begins the processes that fundamentally distinguish the pyrolysis type of combustion, solid fuel heating boilers of long burning from the direct combustion process and from traditional boilers.
In the first chamber, heat loss is minimized. Usually, in models of solid fuel boilers for long burning, the space between the first and second chambers is filled with grates, on which fuel is placed.
On a note: already here you can find the first significant difference in the design of pyrolysis boilers from conventional, solid fuel boilers. Primary air enters the chamber from above, so the fuel starts to burn slowly from top to bottom. The so-called principle of the top blast operates. The draft in the first chamber is forced.
The second part of the firebox is the combustion chamber, where combustible wood gas enters. The chamber is filled with secondary, heated air. The principle of double blowing is already in effect here.
After the boiler enters the normal operating mode, air access to the first chamber is significantly limited. The combustion process practically stops, turning into a state of smoldering. Fuel burns out gradually. Each previous layer of fuel in the smoldering process gradually involves the next layer. Slow smoldering is accompanied by a constant release of wood gas. Due to this process, solid fuel pyrolysis boilers are also called long-burning boilers.
For reference: with correct thermal calculations, one load of fuel can last for 12 hours of normal operation of the boiler. In support mode, pyrolysis boilers can operate for a long time without human intervention. In some models, this figure is 24-48 hours.
In the second, main combustion chamber, only wood gas burns, which, when in contact with secondary air (heated up to t 3000 C) gives a huge amount of thermal energy. Only now thermal energy comes into operation, heating the coolant circulating in the heat exchanger. That is, in the design of solid fuel boilers of the pyrolysis type, the heat carrier is heated not due to the direct combustion of solid fuel, but already due to the combustion of the secondary combustion product — pyrolysis gas, a combustible gaseous substance. This is the main difference between this type of boilers and solid fuel boilers of other types.
Advantages of gas generating boilers
Having an idea of how a solid fuel pyrolysis boiler is arranged, what principle of operation underlies this heating device, you can decide for yourself certain conclusions. Is it worth it to install such a unit at home, how much the operation of a long-burning solid fuel boiler will be justified and effective for a home heating system. Here it is important to take into account the advantages that pyrolysis boilers have, namely:
- high efficiency, up to 85%, in comparison with other types of solid fuel heating boilers;
- large loading chamber (the ratio of useful volume to boiler power is the most significant);
- ease and convenience of cleaning the combustion chamber (cleaning is irregular);
- steel heat-resistant heat exchanger;
- environmentally friendly combustion process (no harmful combustion products);
- wide choice of fuel resource;
- economical fuel consumption;
- automation of the process of adjusting the operation of the boiler.
Some points should be considered in more detail.
Ecology is the most important factor to which attention is drawn during the operation of solid fuel boilers. Pyrolysis boilers in this regard are just a gift for the owner of the house. In the process of burning fuel, instead of smoke and burning, carbon dioxide and water vapor are released, odorless and colorless substances. The number of unburned organic fuel particles in this case is minimized. Thanks to pyrolysis, boilers of this type can operate on almost any fossil fuel.
The minimum amount of soot and soot accumulated at the bottom of the combustion chamber is easily removed during boiler cleaning.
On a note: Woodworking and sewing waste can be used as fuel. Here it is appropriate to talk about the use of secondary raw materials as fuel. Simultaneously with heating in pyrolysis-type boilers, waste is disposed of. Such boilers, as a rule, are installed at the enterprises of the woodworking industry, used in the clothing and leather industries.
A large loading chamber allows you to load a significant amount of fuel into the boiler at a time. Among all solid fuel boilers, pyrolysis boilers have the highest ratio of useful volume to boiler power. In other words, the more fuel loaded, the longer the boiler works without your participation. This is the basis for the recipe for the high efficiency of heating devices of this type.
The table shows the technological parameters of pyrolysis solid fuel boilers of various capacities
|L/D logs, no more||cm||38 x 15||40×15||41 x 15||45 x 15||45×15||70 x 15||72×15||90 x 20||90×20||95×25|
|Fuel loading, max||kg||twenty||22||24||thirty||fifty||62||75||170||185||200|
|Working cycle min||hour||8-12|
|Water pressure, max||Bar||1.5|
|Noise level max||dB||eight|
Unlike other models, which are very difficult to adjust due to their inertia, pyrolysis boilers, on the contrary, are perfectly manageable. The presence of automation on new models ensures almost complete autonomy of solid fuel boilers for long burning.
Disadvantages of gas-fired boilers
The principle of operation of solid fuel boilers for long burning is so practical and beneficial that it only takes time to talk about the presence of shortcomings for this heating technique.
The only significant drawback of this technique is the high cost of the equipment. Despite the fact that the boilers are highly profitable and will pay off during operation, you will initially have to invest quite a lot of money.
Another aspect to which attention should be paid is the significant technological limitations on the moisture content of the fuel. Pyrolysis is possible only with dry and prepared fuel.
On a note: if wood or pellets have a moisture content of more than 20%, your gas generator will remain cold. After the supply of primary air, a weak flame will simply go out.
Most of the models of pyrolysis units for industrial use operate on forced draft. Here it is appropriate to talk about the need for a constant power supply of pressure pumps.
Combustion in the first chamber of the pyrolysis-type heating device may disappear due to the low temperature of the coolant circulating through the heating circuit. When heating large rooms, situations often arise when the cooled coolant is returned. To prevent an unscheduled shutdown of the apparatus during connection, an additional circuit with admixture is often used through a three-way valve. You can get by with the installation of a bypass — a bypass pipe.
The use of boilers in everyday life
As a result of acquaintance with pyrolysis-type units, it has already been said about where and how equipment of this type can be used. The ideal place for a solid fuel appliance will be woodworking, furniture and pulp and paper enterprises. In a word, objects where there are constantly, in huge quantities, industrial wood waste.
If you have a desire to equip home autonomous heating based on a pyrolysis boiler, you should think about a wood warehouse. At the same time, all firewood will have to be additionally dried beforehand. A pellet boiler will help solve the problem faster and easier.
Heating equipment of this type is similar in design and construction to long-burning pyrolysis units. The only difference is that combustible granules or pellets, products of the secondary processing of wood and organic production waste, are used as fuel.
Almost all models are equipped with an automated feeding device, which greatly facilitates the process of loading the combustion chamber. The compact dimensions that pellet machines have allow them to be easily installed in private homes.
Proper connection, fuel procurement and compliance with operational requirements make solid fuel gas generators an effective and convenient source of heat.