Figure 3.
Volatile installations
The principle of operation and design of the Wattek PYROTEK pyrolysis boiler.
The unit operates in automatic mode, for which each PYROTEK model has a control panel that allows for modernization by adding other control and control circuits to the circuit. Using the panel, the user can make adjustments to the settings of the central heating and hot water circulation pumps, as well as the exhaust fan based on the data obtained on the temperature of the boiler coolant. The temperature of the water in the system can be controlled using a boiler thermostat. The control panel also has a minimum temperature thermostat, which deactivates the fan if the coolant temperature drops to 50 °C. For convenience, you can also connect a room temperature sensor to the panel, which will affect the functionality of the pyrolysis boiler.
Advantages:
- Various functional modes (summer, DHW priority, with weekly program settings).
- Making sustainable adjustments that are effective over a long period of time (up to 1 week).
- The clear interaction of all functionality with room temperature ensures the specified comfort of the environment.
Flaws:
- relatively high costs for purchasing equipment,
- The dimensions of the working chamber limit the loading volume.
Figure 4.
Non-volatile pyrolysis plants
As an example for consideration, let’s take the pyrolysis non-volatile boiler “Burzhuy-K”.
The coolant is directed to the unit through the return line pipe (8), where, receiving heat energy from the boiler water jacket (12, 13, 14), the supply line pipe (5) is sent to the heating system through the pipe. The fuel should be placed in the combustion chamber (19), into which the combustion procedure is carried out in the absence of oxygen. The volume of air in the chamber is regulated by the primary air supply door (3), the operating mode of which can be found in more detail in the “Firehouse Rules” section. In automated models, its operation is controlled by a temperature control sensor. During the combustion process, pyrolysis gas is produced, which is sent to the exhaust gas afterburning chamber (17), where it is mixed through afterburner injectors with calibrated holes with secondary air, preheated (11). Thus, a thermochemical reaction occurs in which fuel gases burn, releasing thermal energy. Residual carbon monoxide is disposed of through the pipe (6) and the chimney into the atmosphere.
This complexity, which lies in the very design of the boiler and the fuel combustion process, contributes to a significant increase in combustion time per fuel load.
Advantages:
- the consumption of fuel resources is reduced by 4 times; on average, heating 100 m2 will require up to 17 kg of firewood per day;
- time and effort are saved for the user, who only needs to add fuel no more than once every 12 hours for wood and every 15 hours for coal;
- the non-volatility of the boiler eliminates the cost of electricity and protects equipment from power failures;
- The pyrolysis heat generator has relatively small dimensions, which allows it to be installed anywhere;
- The boiler consumes almost all combustible materials as fuel energy resources.
Flaws:
- Inability to make adjustments to the parameters of the set home temperature.
When did solid fuel heating boilers appear? To answer this question, it is necessary to plunge deeply into the history of the development of heating.
After all, man has been using solid fuel virtually since the beginning of his “reasonable” existence. And if earlier a fire, a hearth, and then a stone stove were used for this, requiring constant attention and replenishment of fuel, today their function can be performed by simple or fully automated solid fuel heating boilers.
The principle of their operation is based on obtaining heat from the combustion of solid fuel and transferring it to the coolant (water) circulating in the heating system. Such heating devices are installed where it is not possible to heat with gas or electricity (often for financial reasons).
Often, a combination of different boilers is used in a heating system project for a private home or office premises. For example, the main heating unit runs on gas, and a solid fuel boiler is used as an emergency boiler in case of interruptions in gas supply. Or vice versa - a gas boiler is an alternative option.
In this article we will cover the topic of classifying solid fuel heating boilers, consider their main parameters, additional devices that expand their functionality. In general, we will reveal the basic concepts about this technique so that you can make the right choice if necessary.
Interesting to know!
The authorship of the creation of water heating informally belongs to Martin Trivald from Sweden. While working as a coal mine supervisor, he was the first to use water heating to heat a greenhouse. Only a century later, in 1820, a similar heating method began to be used in private homes in England, and later in other countries.
What is solid fuel?
In modern boilers the following are used as solid fuel:
- firewood;
- wood chips;
- coal;
- brown coal;
- peat briquettes;
- biofuel (pellets).
The use of these substances for heating is economically justified if cheap solid fuel options are available. The most fashionable and convenient solid fuel today is biofuel pellets - these are wood waste pressed into small briquettes.
Let's understand the types of solid fuel heating boilers
Regardless of whether it is a simple boiler or one with a mechanical fuel supply and a self-cleaning system, they still require human attention and participation in the process of their “life activity,” as well as compliance with strict safety rules during their operation.
By type of material, from which they are made, there are two types of boilers:
- steel;
- cast iron.
Each type has its own strengths and weaknesses!
For example, steel boilers are less susceptible to temperature changes, but they are highly susceptible to corrosion. A cast iron boiler is considered “long-lived” compared to a steel one, but it is fragile, afraid of overheating, and warms up slowly.
During operation, it is necessary to monitor the presence of water in the “water” jacket of the boiler. Its absence (which is unlikely, but...) can cause overheating and deformation of the boiler.
According to the combustion mechanism of solid fuel, in particular firewood, boilers can be divided into two groups:
- classical combustion boilers
- long burning boilers
- pyrolysis,
- smoldering.
The first group includes most of the simple cast iron and steel solid fuel boilers, inside which an uncontrolled normal combustion process takes place.
Some kind of “automation” is still present in such boilers. They can have a sensor installed to control the temperature of the water in the boiler, connected mechanically (by a chain) to an air damper, which affects the intensity of the combustion process in the furnace.
When the water temperature exceeds the permissible limit, the damper closes, slowing down the combustion process. A further decrease in water temperature leads to a gradual opening of the damper.
More advanced models have electronic temperature sensors and a controller that analyzes their data and controls the operation of an additional forced-air fan. This brings a significant amount of comfort to working with such solid fuel heating boilers.
Advantages:
- ease of maintenance;
- relatively low cost;
- ability to work autonomously (without electricity);
Flaws:
- the need for fairly frequent fuel replenishment. Frequency: 3-8 hours.
Boilers of this type are often used in a system with a heat storage tank, which allows the water temperature to be maintained for some time after the boiler has died down.
Among the manufacturers of “classical” combustion solid fuel heating boilers, the following have proven themselves well: SAS, Aton, Wichlaczh, Sime, Galmet, Biasi.
Boilers of the second group are called pyrolysis or smoldering.
Pyrolysis boilers use the principle of gasified wood combustion. These are boilers with a long burning time on one “refueling” (about 10-12 hours) and high efficiency (up to 92%), due to the fact that wood gas is first released from the wood under the influence of high temperature, which is then burned in a second firebox.
Such boilers are high-tech devices, “stuffed” with electronics. By the way, their firebox is ceramic, capable of retaining heat for a long time, and is equipped with a fan that regulates the intensity of combustion. It also makes it easier to light the boiler and makes loading a new batch of firewood comfortable, preventing smoke from entering the room.
There are some disadvantages: high cost of boilers, relatively small volume of the working chamber for loading.
The Czech brands Atmos and Verner are recognized as European leaders in the production of pyrolysis boilers. You will be 100% satisfied with their products.
Operating principle of a solid fuel pyrolysis boiler
In their operating principle, “smoldering” type boilers use the phenomenon of smoldering of the upper part of the fuel. This process can “stretch”, in the case of using firewood, up to 30 hours. And the Baltic manufacturer Stropuva has in its arsenal a universal-purpose model with the designation “U”, capable of “holding out” on coal for up to 5 days. In addition, smoldering boilers are relatively inexpensive.
The disadvantages of such boilers include their “demanding” requirements for fuel:
- humidity (wood) up to 15-20%, top quality coal;
- length up to 60 cm;
- power up to 40 kW.
Manufacturers – Baltic countries Stopuva and Candle.
The required power of a solid fuel boiler is approximately calculated based on the proportion: per 10 m2 of insulated room area with ceilings up to 3 m - 1 kW of boiler power. For exact numbers, contact a professional.
Important! Excessive boiler power can only be useful when using low-quality fuel, for example, not enough dry firewood.
Solid fuel boiler STROPUVA - video presentation
Notice! Among the huge range of solid fuel heating boilers, some manufacturers have models that allow the installation of additional gas burners or liquid fuel burners.
Let us separately dwell on another type of heating boilers, which are becoming increasingly popular - pellet boilers.
Pellets- these are cylinders pressed under high pressure from biomass.
Options:
- diameter: from 6 to 1.4 mm;
- length: from 5 to 20 mm;
- density: up to 600kg/m3;
- ash volumetric residue: up to 3%.
The advantages of pellet boilers include, first of all, the possibility of automating their operation, which is not possible either with coal or with wood.
Pellet heating boilers today are one of the safest, environmentally friendly ways to produce heat indoors.
The range of pellet boilers is already huge. What unites them all is a high level of automation of the combustion process and principles of work organization:
- possibility of automatic fuel supply from a bunker or warehouse;
- maintaining a stable temperature;
- centralized control of the entire heating system (circulation pumps, self-cleaning systems, etc.)
Domestic boilers have a power in the range of 10-100 kW, industrial boilers - up to 1500 kW. Efficiency factor - up to 95%!!!
In addition, such boilers do not require constant human presence. The boiler can be equipped with an automatic ash removal system; fuel is supplied not from the bunker, but from the adjacent room - the fuel warehouse, with a volume that allows the boiler to operate for more than a month. Such boilers support remote control via a mobile phone.
To summarize, today there is plenty to choose from in the field of solid fuel heating systems. It all depends on the characteristics of the territory where you live and... on the size of your wallet.
In this article we will introduce the reader to the world of modern solid fuel heating systems. What types of solid fuel water boilers are there?
Is the use of this particular type of fuel economically justified? Does it have any serious flaws? We will try to answer all these questions.
The canonical diagram of the device, including a hob. As we will see later, this is far from the best design.
Boiler classification
It is clear that all solid fuel boilers for water heating are characterized by a number of common features. By definition, they use the heat of combustion of wood (optionally, its processed products), peat or coal. In addition, the coolant temperature at the boiler outlet does not exceed 100 degrees.
How do these devices differ from each other?
Material
We are talking about the material of both the boiler itself and its heat exchanger - the unit through which the coolant comes into contact with the firebox.
There are two main options:
- Steel boilers are on average somewhat cheaper and have much less weight. However, they are also characterized by a shorter service life. Steel is a metal that is afraid of corrosion; flames and very aggressive condensate quickly destroy it.
However: high-quality solid fuel heating boilers made in Russia, like imported ones, are made from heat-resistant grades of corrosion-resistant steel. In addition, the firebox is often additionally protected by a lining of refractory bricks.
- Cast iron is a material that is much less susceptible to corrosion. That is why it is used for the manufacture of grates and doors in furnaces; This is why cast iron boilers are, on average, much more durable than steel ones.
The price of a longer service life is a larger mass of products. As a rule, even boilers of modest (up to 16 kW) thermal power require mandatory installation exclusively on a permanent foundation.
Fuel
The most versatile are solid fuel water boilers that can operate on several types of fuel. Without any adaptation, you can, after cleaning the ash pan, throw coal into the firebox after firewood or peat briquettes after pellets.
However, devices focused on only one type of fuel tend to have higher efficiency. Their design is optimized for combustion with a very specific flame temperature and fuel humidity.
In addition to single-fuel boilers, boilers with two separate fireboxes and two heat exchangers are produced. They allow the combustion of different types of fuel, which require different design of the combustion zone. In fact, a solarium burner will quickly become unusable if it is placed among burning wood.
Efficiency
The efficiency of different types of boilers varies greatly. The factors that determine this parameter are the temperature of the combustion products at the outlet and the amount of solid waste. In both cases, less is more.
The minimum efficiency, often not even reaching 50%, is for the simplest hand-made devices. Yes, a box made of steel sheet with two doors and a coil inside will cost very little; however, to get the amount of heat you need, you will have to burn a LOT of wood.
Factory production of solid fuel boilers relies on accurate calculation of their shape and dimensions of the heat exchanger. Even in younger models, the temperature of combustion products usually does not exceed 120 degrees. In addition to the fact that more heat is transferred to the coolant, this also means greater fire safety.
The so-called pyrolysis, or gas generator boilers, stand apart. How do they work?
- The device contains two fireboxes with heat exchangers in each of them. They communicate with each other and are placed one above the other.
- In the upper firebox, under conditions of lack of oxygen and high temperature, the firewood slowly smolders, gradually disintegrating into ash. There are no large coals left during normal operation of the boiler.
However, due to a lack of oxidizer, the fuel does not burn completely: it releases a large amount of pyrolysis gas, consisting of CO (carbon monoxide) and volatile hydrocarbons.
- This gas is forced into the lower firebox, where it burns completely after oxygen-rich air is mixed with it.
Gas-generating solid fuel water heating boilers have a very high efficiency, reaching 95 percent for the best devices. However, they are 1.5-2 times more expensive than traditional designs and require the use of low-humidity fuel. In addition, younger models ONLY run on wood.
Autonomy
Devices of traditional design require constant human presence - the firebox must be loaded every 2-4 hours. The profession of a fireman was not born out of nowhere. It is this property that is the main disadvantage of solid fuel; This is partly why, if main gas is available, it is rare that a cottage owner will think about firewood or coal.
A pyrolysis boiler, however, due to the principle of its operation, causes the fuel not to burn, but to smolder. On one load the boiler can operate for up to 12 hours.
Relatively recently, the Lithuanian company Stropuva has established in-line production of so-called top-combustion boilers. They provide heating with even greater autonomy: during certification in 2003, the production model, after loading 50 kilograms of fuel, delivered about 6 kW of thermal power for about a day and a half.
How is such a long operating time achieved?
- The volume of the firebox has been increased and can accommodate several tens or even hundreds of kilograms of fuel.
- There is no grate and ash pan.
- Only the top layer of loaded fuel burns. Air to maintain combustion (more precisely, smoldering) is supplied from above through a movable unit, which lowers under its own weight as the wood or coal burns.
- The ashes are carried away with the smoke.
- The fuel smoldering area is separated from the top of the chamber by a massive metal disk (slang name - staskoblin). Above it, air from outside is mixed with the products of incomplete combustion of fuel, and they burn with the release of residual heat.
As we can see, these devices are basically pyrolysis water-heating solid fuel boilers, but with serious design modifications. It is clear that here the price tag will not please the thrifty owner.
Boilers that run on pellets - pressed sawdust granules - stand apart. In them, the problem of autonomy is solved by the controlled supply of granules from the hopper.
The photo shows a boiler with a pellet hopper.
However: in addition to being expensive, these devices have another problem. Pellet production has not been established in our country; Not everywhere you can provide yourself with this type of fuel.
Automation
In classic boilers, all automation is limited to the simplest protection against overheating of the coolant. A mechanical thermostat uses a lever to pull a chain that closes the damper. The air flow rate decreases; the heat output of the boiler decreases.
There are much more possibilities in pyrolysis heaters:
- Mechanically or electrically controlled dampers here also allow you to regulate traction;
- Along with this, in devices with forced draft, their thermal power can be controlled by adjusting the speed of the exhaust fan.
In addition, it is possible to control not the coolant temperature, but the air temperature in the room.
Useful: inexpensive solid fuel heating boilers made in Russia, as a rule, are controlled by a primitive mechanical thermostat or generally only manually. You should not look for devices among the younger models that can independently maintain a comfortable temperature. However, it is precisely due to the simplicity of their design that they are extremely fault-tolerant.
Advantages and disadvantages
Operating costs
At current Russian prices, purchased firewood is the second cheapest after mains gas. The difference between them is small - a few percent. It is clear that we are talking about the cost of generating one kilowatt-hour of thermal energy.
Coal is more expensive, but not much.
Several other factors speak in favor of firewood:
- Mains gas is not available everywhere, and liquefied heating is several times more expensive and is close in cost to electric heating.
- You can prepare firewood yourself, which will reduce costs to zero.
- Solid fuel heating will allow you to profitably dispose of most household waste. The rest will go into compost in a country house and serve to fertilize the soil.
Ease of use
But in this area there are only disadvantages.
- Combustion products must be removed. Moreover, using a coaxial outlet - an air intake, as in gas boilers with a closed burner, it will not be possible to utilize furnace gases. A full chimney is needed.
This decoration on the roof is an invariable attribute of heating with solid fuel.
- Solid fuel boilers are available only in floor-standing versions. They are massive and large in size. In most cases, it is better for them to have a separate room.
- Fuel should be stored close to the boiler, and under a canopy. Compare this requirement with the convenience of connecting to gas or electricity.
- Adding fuel and removing combustion products is often required. Even in long-burning boilers, where there is no ash pan at all, you still have to clean the pan between fuel fills. In addition to being a rather dirty job, this means one more thing: you won’t be able to go away for a few days and leave the house warm.
Installation
All devices of the type we are discussing can be installed independently. No accounting or control of utilities is required.
However, a couple of rules must be followed.
- Massive boilers are mounted, as already mentioned, exclusively on their own foundation. It’s definitely not worth putting 300 - 500 kilograms of cast iron on a wooden floor.
In general, it is better to play it safe with lighter steel ones: for example, Belarusian-made solid fuel boilers KSV 12.5 with a modest power of 12.5 kW weigh 180 kg.
- The second instruction is related to fire safety. The boiler body and chimney become noticeably hot when fuel burns. It is recommended to place the boiler at a distance of at least half a meter from the nearest wall.
If the walls are made of flammable material, they are protected with a brick or a galvanized sheet with an asbestos gasket.
The chimney is separated from combustible ceiling structures or walls by a distance of at least 25 centimeters.
Conclusion
The video at the end of the article will tell you a lot of interesting things about what solid fuel boilers are like - Russian-made and imported from abroad. We hope that you will find answers there to any questions that you might still have.