Modern solid fuel boilers. Units with manual loading. What is better to buy, what is more reliable
Quality coal boiler
Need modern man in comfortable warmth indestructible. Therefore, the absence of the usual ways to obtain it - central heating, main gas, sufficient and reliable capacities of electrical energy - served as an impetus for the return to the old-fashioned furnace heating and its improvement. There were smart heads who created modern solid fuel boilers long burning. Consumers of this equipment, as it turned out, had been standing in line for it for a long time, waiting for it to appear.
A little about solid fuel boilers for long burning
When nothing remains for the heating device of a country or private house, except for the purchase and installation of a long-burning solid fuel boiler, it is possible that this will subsequently serve as a reason to rejoice at such a combination of circumstances. Because the use of modern boilers operating on this principle is the most efficient and simple option creating urban comfort, but in a private home.
The reasons for this are that solid fuels (coal, firewood, pellets) are much cheaper liquefied gas, diesel fuel and electricity, and it is much easier to purchase it. Equipped with up-to-date automation for heating system and supplies hot water will provide coziness and comfort in the house at the same level as when using gas units. Therefore, long-burning boilers can be safely called a modern source of heat for private houses.
Types of boilers
Such boilers are divided into several groups. They differ in the type of fuel used (pellets, coal, wood, peat), the way it is fed (automatic loading or manual) and in the design that determines the method and the corresponding burning time.
Manual loading units
They, in turn, are different in the way they burn fuel:
- Boilers of long burning of cyclic type. These units use a patented method top burning fuel. It does not occur as usual from the bottom up, but vice versa - from the top and down. The combustion area moves lower as the fuel burns. An automatic telescopic air supply system delivers it to the combustion zone. The constructive solution of these boilers is quite original, simple and reliable.
Recognized leaders among such units are the Lithuanian Stropuva. it single-circuit boilers, the duration of which from a single fuel filling can reach 70 hours on wood, and 7 days on coal.
- Pyrolysis (gas generating) boilers. The long-term burning mode in these devices is achieved through a special, pyrolysis, method of burning wood gas. Gas is released from firewood under conditions of high temperature and lack of oxygen. This method of combustion avoids the formation of soot, gives a minimum residual amount of ash and ensures almost complete combustion of the fuel. The operating time of such a boiler from a single laying of firewood is 8-10 hours - this is 7 times less than that of the Lithuanian Stropuva. But pyrolysis boilers have a number of advantages. The most popular brand is the Czech DAKON KP PYRO.
Pellet boilers with automatic fuel supply
Types of long-burning boilers
In such units, long-term combustion without human intervention is achieved through the use of pellet - granular fuel. These biogranules fall asleep in the bunker. And their supply to the combustion zone is carried out automatically as necessary, which, in combination with auto-ignition and temperature control, makes it possible to obtain the most automated heating process. As a result, you can not approach the boiler for weeks.
Pellets are made from waste that is finely crushed and pressed. Their sources are shavings, sawdust and the like, nut shells, seed husks, seeds, cake, and so on. If necessary, when pellets are not available, such boilers can be fired with coal and wood. Pellet devices have received a fairly wide application and, as a rule, they are isolated in an independent form.
Reasons for the popularity of solid fuel boilers
Modern Europe pays a lot of attention and means to environmental protection, care for the environment, energy conservation and savings in the production of thermal energy. This is inextricably linked with the ever more frequent recourse to new ways of producing it. And also to those that existed before, having economic benefits and environmental friendliness, despite their lesser popularity.
In this regard, in last years there has been an increase in the use of solid fuel heating systems. In conditions when it is impossible to be heated by main gas, it is precisely such systems that will provide the house with comfort, warmth and coziness. In addition, the cost of such heating is relatively small.
Modern interest in the ancient method of heating with solid fuel is due to the fact that this method has undergone significant technical improvements. Old stoves required constant supervision and regular, every few hours, feeding with wood or coal. They were replaced by new and sometimes extraordinary modern solutions. Even now there is very little natural gas in Europe, and soon the moment will come when it will completely run out - everyone understands this. Supplied from the outside - a very expensive pleasure, and it is not infinite. That is why for European countries the development of solid fuel heating systems for heating low-rise buildings is a promising direction along with renewable energy sources.
For a person of the 21st century, spoiled by the benefits of technological progress and civilization, heating based on the latest generation of solid fuel devices is certainly an acceptable solution. The direction that seemed relatively unpromising recently received a second life thanks to new technologies. Innovative solutions that appeared in recent times undoubtedly deserve interest and promotion.
Advantages of solid fuel units
Coal-wood gasification boilers
- Modern solid fuel boilers are a combination of the best innovative technical solutions.
- Gas is far from being everywhere, and there is no particular hurry to expand the area of its available application. It is much more profitable for a modern business that owns Russian natural resources to sell gas outside our country than to heat their compatriots with it. And solid fuels are available everywhere and are inexpensive.
- It is much cheaper to heat a home with solid fuel than with electricity or diesel.
- Constant control over the combustion regime is not required - there is no need to monitor the temperature, add fuel and regulate the air supply. All modern units are automated to one degree or another. The combustion process without human intervention can last for weeks, which is why such boilers are called long-burning devices.
Energy dependence
Almost all long-burning devices depend on electrical energy. The boilers themselves (most models) do not need power supply, for example, wood-burning Stropuva. But for the optimal operation of the heating system and the boiler, the functioning of the electric circulation pump is necessary.
With gravity (gravitational) heating without forced circulation of the coolant, the system loses its economy and efficiency. In addition, it will become clogged with soot and condensate will flow, which, in the end, will end in premature failure of the boiler. In case of power outages, it is necessary to provide a backup uninterruptible power supply - for example, a battery with a converter.
Ideal working conditions
Binding of the boiler Altep
In order for a solid fuel heating boiler to serve its due date and bring the expected benefits, it is required:
- The presence of a boiler room. This is not a room, but a set of equipment that will ensure optimal operation of the unit in all modes of its operation - during start-up, during heating and at the time of shutdown. Each type of boiler requires its own equipment, but equipment is common circulation pump, expansion tank, comb and mix group.
- Correctly calculated and executed chimney. Excessive or insufficient draft is detrimental to the boiler.
- Properly organized heating system - radiators and pipes.
- It is desirable to have a hot water boiler.
Proper installation of the heating system will ensure its long and trouble-free service.
Russian devices
Russian manufacturers strive to constantly improve their developments, to introduce something new that will be interesting and attract potential consumers. Accordingly, Russian solid fuel boilers are represented by many companies and a wide range of model range.
"Oranges"
The most popular units are manufactured by NCC Biyskenergoproekt. For their bright orange color they are called "oranges". Most models are pellet boilers. Like all pellet units, "Orange" is equipped with electronic control, forced ventilation and automated fuel loading.
With all the technical complexity, the device turned out to be as simple as possible to operate and durable. Fuel quality requirements are minimal and based on the current state of domestic pellet production.
Boiler equipment is represented by a large display showing the state of the boiler and the set work program. By means of built-in electronics, the boiler is set up for long-term operation without human intervention, when the temperature is maintained with a deviation of several degrees.
"Start"
Solid fuel heating boilers"START"
The next are the Start boilers, originally designed for pellet fuel, but also working on sawdust, wood chips and even fine coal. Such versatility appeared after the modernization, which consisted in the introduction of a horizontal fuel supply to the combustion chamber.
"Start" can be easily re-equipped for ordinary firewood - just mount a grate of grate in the firebox. At the same time, the existing elements of the pellet equipment do not need to be dismantled.
"Elephants"
These are powerful boilers with a wide range of models. They are equipped with a horizontal firebox with a fire-tube heat exchanger.
Such units use any solid fuel, and their efficiency reaches 95-97%. The average power of industrial "Elephants" reaches 650-700 kW, and household - from 3 to 120 kW.
Conclusion
You can live outside the city, enjoying all the amenities inherent in urban comfort, even when there is no main gas, and there is only a small amount of allocated power for electrical energy. The main thing is to be able to properly dispose of what you have. This allows you to implement modern, which will provide heat and hot water in almost any place of residence.
The most commonly used gas or electric boilers. However, the main gas is not carried everywhere, and the price of electricity is not small and rises regularly. In addition, in many remote settlements, interruptions in the supply of electricity are not uncommon, which is dangerous when the heating in the house is completely turned off.
It is clear that no one wants to be left without heat in severe frost, so many homeowners prefer proven traditional wood and coal stoves, or their more advanced version - modern solid fuel boilers. Such equipment provides maximum comfort of living in a country house and does not depend on electricity supplies. As fuel in such boilers can be used:
Solid fuel boilers are reliable, but require constant attention: you need to put fuel in them from time to time, as well as clean them from the resulting soot and ash.
Types of solid fuel boilers
A solid fuel heating boiler can be made of steel or cast iron. Depending on this, the equipment will have different characteristics.
Properties | ||
Durability | Cast iron boilers are more durable and have increased heat transfer. However, they also have a drawback - the fragility of the structure, which is especially pronounced when overheated. Therefore, it is so important to monitor the water level in the heating system. | Boilers made of steel are superior in strength to cast iron ones, but they also have a significant drawback - susceptibility to corrosive processes with constant contact with water. |
Design | To cool the cast-iron heating boiler, it is necessary to fill the system with fresh cool water. | The coil is located inside the boiler. If the temperature exceeds the limit value, a special thermostatic tap opens, and cold water fills the container. |
Assembly | Assembly is manual. The various parts of the heat exchanger inside the housing are securely connected with steel studs. | Body welded. If the appliance is heated very strongly, the weld seams may be damaged. |
firebox door | A heat-insulating gasket is installed, which does not allow the door to become very hot. | There is a cooling water element on the furnace door. |
Cleaning | Cleaning of cast iron boilers is carried out manually. | There are special rotary dampers. |
According to the type of space heating, solid fuel boilers are divided into water and air. Water heating devices are more popular, they are joined by a heating pipeline through which water circulates. It is the water in this case that transfers heat to the air of the house. Solid fuel air boilers work like a conventional stove, the surrounding space is heated directly from the device body.
On sale you can find solid fuel boilers with one or two heating circuits. One circuit is used for heating the premises of a private house, the second is designed to prepare hot water for domestic and household needs. At the same time, hot water supply can also be organized using a single-circuit device. To do this, an indirect storage boiler is additionally cut into the heating system, which can be blocked if in hot water not necessary. Such a scheme requires additional costs for the purchase and installation of a storage boiler.
Double-circuit solid fuel boilers are the most convenient and practical heating devices. They allow you to heat the house and organize a hot water system. In summer, when there is no need for heating, it can simply be turned off, and the boiler at minimum power will only work to heat water.
According to the principle of operation, solid fuel boilers are divided into classic and gas-generating. In classical devices, the coolant is heated from the combustion of fuel, and the combustion products are removed using a chimney. Gas-generating (or pyrolysis) boilers for heating the coolant use the energy of combustion not only of fuel, but also of the resulting gas, which significantly increases the efficiency of the unit.
The principle of the device of a solid fuel gas-generating boiler is as follows: there are two chambers in its body, fuel is placed in one of them, during the combustion of which gas is released, which also burns out, but in another chamber. Such boilers have a lot of advantages:
More high efficiency compared to conventional devices. | Additional drying of firewood or compressed fuel. | During operation of the boiler, less soot and soot so that the appliance can be cleaned less frequently. | Selection harmful substances in environment insignificant. | Fan, built into the system, makes it easier to start the boiler and prevents smoke in the boiler room. |
The price of a solid fuel boiler depends on its capacity and manufacturer.
Modern automated solid fuel boilers have a special fuel bunker that allows it to be loaded and used for several days. In this case, fuel is supplied to the furnace in automatic mode. Such a boiler does not require fuel filling every day, which greatly simplifies its operation.
Average service life solid fuel boiler- ten years. However, subject to the rules of operation and timely maintenance, it can function properly for thirty years.
Connection options for solid fuel boilers
There are various ways to use solid fuel boilers. They can serve as the main heating device as well as a backup heat source. Such a unit is easily combined with an electric heating boiler. For example, an electrical appliance can be turned on in spring and autumn, when the temperature outside the window is not very low. A solid-fuel device will be simply irreplaceable in winter, especially in extreme cold, when all its power will be in demand. This will save some money on fuel purchases.
Modern solid fuel boilers
A solid fuel boiler can also serve as a backup source of heat in tandem with the main one, running on liquid fuel or electricity. In the event of an emergency situation, it can be quickly launched.
Rules for installing solid fuel boilers
It is best to entrust the installation of a solid fuel boiler to a specialist. He will not only do everything right, but will also give a guarantee for his work. But you can do it yourself, observing a number of rules:
The distance from the walls of the boiler to the walls and other objects should not be less than twenty centimeters. | |
A non-combustible support must be placed under the base of the boiler. | |
The length of the outlet channel from the boiler to the chimney should not exceed one meter. | |
The heating pipes must be connected to the boiler very securely and carefully, since if the coolant leaks, there is a danger of the boiler breaking. |
The use of solid fuel boilers allows you to create an atmosphere of warmth and comfort in the house, subject to proper operation and timely maintenance.
An interesting fact is that not a single major reputable manufacturer of heating equipment produces so-called long-burning boilers - large barrels in which firewood burns from top to bottom. Such boilers are made only by small firms in the CIS and Baltic countries and are accompanied by aggressive advertising. True, in retail outlets, anything can be called a long-burning boiler, just to sell, ....
Pyrolysis boilers also lost significantly in demand and supply. They have big flaws at their high price - this is not at all what the buyer likes.
Consider why long-burning and pyrolysis boilers cannot be considered as candidates when choosing a boiler for a home. Then we turn our attention to modern models solid fuel boilers that are currently on sale, and which one should be chosen.
Pyrolysis with disadvantages
The sale of pyrolysis boilers is based only on advertising - as if their efficiency is very high (deception), as if there is no ash left (and where does it go? - we will consider further), they can burn for a long time (but is it convenient?) ...- As for the efficiency, everything immediately becomes clear, one has only to look at the temperature of the outgoing gases. It is no less than conventional boilers.
- Ash is a given of any fuel, it cannot disappear by magic, it is blown away by a fan and carried away into the chimney, then settles on top of the house, on a parked car, on the ground ...
- Firewood that emits resin (coniferous, birch) cannot be used - they tar the barrel. And what to heat?
- Can I fire with raw wood? Any boiler can be fired with raw wood. It is possible to heat, only the energy will be 2 times less. Firewood must be purchased only dry or dried before the firebox so that energy is not wasted on creating steam ...
To eliminate the disadvantage, manufacturers directly require the installation of a pyrolysis boiler paired with a buffer tank. But the boiler itself has a fivefold price, the buffer capacity is not very cheap - why such overpayments?
long burning
The situation is even simpler with the so-called long-burning boilers - where the discrepancy between the energy consumption of the house and the energy efficiency of the boiler is very significant. More precisely, the boiler is suitable for heating only in good frosts.They can’t heat a little - which is constantly required in the off-season, only a large load of firewood burns there. And most of the time, they can comfortably drown ... only with a buffer capacity.
What is popular
How is development solid fuel heating in European countries? What is presented at exhibitions of heating equipment by leading manufacturers?Solid fuel cola does not leave the market at all in favor of gas in Europe. They are converted to automated systems.
How can a solid fuel boiler be automated?
Screw loading from the bunker and small-fraction fuel is used. More and more boilers are adapting to wood chips and sawdust, as there is a lot of wood waste that can be burned.
In addition, such fuel is not expensive to prepare from any wood. Pellets and coal of the same fraction are also used (pieces of the same size). The process of combustion and fuel supply is fully controlled by electronics.
True, a ready-made boiler room for a private house based on such a boiler from a leading European manufacturer will cost about $ 25,000. Those. not suitable for wide application.
Before considering what suits us, let's pay attention to the main trend in the development of solid fuel heating.
What parameters should solid fuel heating have?
Now in European countries state standards are being adopted, according to which it is forbidden to use solid fuel boilers (not bunker, not automated) without a buffer heat storage tank. And such a law has already been passed in Germany.Why is it needed?
This rule is introduced so that the solid fuel boiler always works in the optimal mode - with maximum efficiency and produces the least CO (carbon monoxide). This requires an unrestricted supply of air – combustion with an excess of oxygen. Then the boiler works not only with the best efficiency, but also at maximum power, the fuel burns out quickly.
A large amount of energy is released from one firebox, which should be accumulated by a buffer tank and then gradually taken away by the house heating system, which is not at all difficult to organize.
If you do the combustion process with a lack of oxygen (covered damper), stretching the heat transfer over time, then the efficiency of any boiler decreases, and the amount of CO increases.
Thus, the new laws of Europe are aimed at saving fuel, oblige to organize the operation of equipment with maximum efficiency, and also ensure environmental protection.
By the way, other standards for heating equipment are being introduced in developed countries, in particular, the use of condensing equipment becomes mandatory. - read articles about heating.
What is better to buy, what is more reliable
Based on the experience of operating solid fuel boilers, and the development trends of this industry around the world, we can conclude that the heating system in a private house can be based on the following principles.- Maximum oxygen supply is provided, but fuel is supplied in small portions - as much as energy is needed. Then the house can constantly receive energy little by little.
This is possible only with an expensive automated fine fuel boiler with a bunker. In our country, such boilers are also called pellet boilers. But there are modifications on coal and on small wood (shavings). Pleasure is not cheap, but what to do ...
- The furnace is carried out in large portions with daily manual supply of fuel to the boiler. In this case, a conventional modern boiler can be used, but with increased power (2 times the required one).
The system must include a buffer tank - a heat accumulator. This will greatly simplify the process of managing the boiler for use, ensure CO emission standards, increase efficiency and save fuel.
This option is most likely suitable for mass use, due to the fact that unprepared fuel (any large dry firewood and coal) is much cheaper.
Select by manufacturer
The price of a solid simple solid fuel boiler from a well-known European manufacturer is more than 100 thousand rubles, but rather strive for 200 thousand rubles. A boiler of a similar capacity from a good Russian manufacturer will cost 50 - 60 thousand rubles. - 3 times cheaper.Over the past few years, the quality of boilers Russian production improved quite significantly. Solid fuel boilers with long strokes for the movement of gases began to be produced (there are models with vertical and horizontal strokes), and this increases efficiency.
Also, the technology of supplying additional air for afterburning gases, in the presence of CO, has been mastered. Fans are also used to regulate the air supply and electronics control the optimality of the fuel combustion process.
You just need to take a closer look at well-known domestic manufacturers. An ordinary solid fuel boiler paired with a buffer tank will provide the house with heat.
But our manufacturers also produce good pellet boilers. They are best used in large houses - 400 - 800 square meters, then the increased cost of the boiler itself, as well as fuel, does not affect the background of all equipment so much.
Another question that comes up more often than others is
The range of consumption of solid fuel boilers for long burning is quite wide. They are used both in private homes and in large enterprises, schools, hospitals.
It is especially beneficial to use such boilers for enterprises that process wood, since it can also be used as fuel. This helps not only to dispose of industrial waste, but also to save a lot on heating.
Design
Basically, long-burning boilers are not intended for heating water, that is, they are predominantly single-circuit. They are used in systems with forced circulation of water. Even if the water is heated, the temperature of the heated water will not exceed 80 degrees. The equipment is equipped with a control unit, which makes it possible to regulate the performance and intensity of space heating. If an emergency occurs, the device will signal this.
Advantages of solid fuel boilers
Among the main advantages of solid fuel boilers for long burning are the following:
- affordable price for the device and fuel;
- ease of maintenance;
- the possibility of using different types of fuel;
- autonomy;
- high efficiency;
- environmental friendliness;
- safety;
- intuitive control.
Flaws
Heating individual home solid fuel boiler, especially on automation, does not require special time costs for boiler maintenance. It will be sufficient once every few hours (and possibly days) to make a bookmark of fuel.
The disadvantages can, perhaps, include the fact that the entire heating process is a kind of vicious circle: fuel loading, kindling, burning, damping, cleaning. We also note that many models are quite sensitive to fuel quality and practically do not have temperature controllers.
Due to the fact that in recent years solid fuel boilers have gone through many stages of improvement, they have become quite efficient and very economical, which was the reason for the increase in their popularity. There were also automatic solid fuel boilers for a long time burning. Current devices can work with one load from 3-4 hours to a day and a half. The diameter of the firewood used has also changed. Now you can load firewood up to 1 meter in length and up to 20 centimeters in diameter. Such a large size of firewood saves time and financial costs during their preparation.
To better understand what we are dealing with, we present specifications one of the solid fuel boilers - KT-2E (made in Ukraine):
- power - 25 kW;
- heated area - 250 sq.m;
- fuel capacity - 56 kg;
- the volume of the loading chamber - 62 cubic meters;
- firewood length - 46 cm;
- burning time on the 1st tab - in the range of 8-46 hours (depending on the type of fuel);
- Efficiency - 83%;
- water in the boiler - 117 l;
- water pressure - no more than 3 bar;
- chimney diameter - 170x170 mm;
- loading opening parameters - 230x370 mm.
The principle of operation of the long-burning boiler
Solid fuel boilers consist of the following elements:
- fuel bunker;
- heat exchanger;
- smoke exhauster;
- combustion chambers;
- fan.
Based on solid fuel boilers, heating systems are installed in country houses and at cottages
Solid fuel is placed inside the fuel bunker. Let's fire it up. High temperature and limited oxygen cause the release of pyrolysis gas. The resulting gas passes through ceramic nozzles into the combustion chamber of the boiler, while it is combined with secondary air. In the chamber, it burns completely, while releasing CO2. Hot gases leaving the combustion chamber pass into the heat exchanger, and then into the chimney. At the same time, the fan makes an air flow that blows around the heat exchanger. Then the heated air passes into the grids located inside the heat generator or through the ventilation duct system connected to it.
According to this scheme, air heating of the building takes place. With the help of an electronic unit, the air temperature at the exit is regulated within the range of 40-120 degrees. C. On average, a heat generator can work 5-8 hours on one load, but these data can vary significantly, depending on the manufacturer. It must be remembered that in order to preserve the walls of the combustion chamber, it is not recommended to allow the boiler to operate in a critical mode when the temperature exceeds 120 degrees. FROM.
Types of solid fuel boilers (classification)
Solid fuel boilers are capable of using quite a variety of substances as fuel. By type of fuel, they are classified into:
- using coal - coal of any class and fraction is suitable. You need to use coal with a calorie content of up to 7000 kcal per 1 kg. By burning 1 kg of coal with a calorific value of 7000 kcal, the output is 8.14 kW / h, and this figure is close to that of natural gas.
- using firewood - trees of any species are suitable (oak, birch, alder, maple, ash). It is also worth paying attention to the calorie content, because the more it is, the longer the firewood will burn. For combustion, wood with a moisture content of no more than 20% is recommended.
- using pellets - you can burn any pellets (wood, sunflower husk, straw). This is the most profitable fuel option. Pellets are characterized by high calorie content and low ash content. Pellet-powered equipment is one of the most popular nowadays due to its advantages.
- pyrolysis - use wood, molecularly decomposing it during combustion into high temperatures. Wood must be dried in a dry place for at least a year before use.
- universal - work absolutely on all possible types of fuel.
In addition to what fuel they operate on, long-burning boilers can be divided into those with manual loading and automatic feeding using a screw or piston.
Solid fuel boilers, in particular wood-fired boilers, are historically the oldest used in heating systems. First of all, this is due to the availability of wood as a fuel at all times and in many territories. Today, this advantage is reinforced by the independence of solid fuel boilers from the main gas supply, as well as the simplicity of arranging the fuel storage (woodshed, coal bunker, etc.). There are also a number of factors that influence the widespread use of solid fuel boilers as a heat generator, an alternative to gas units.
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AT At the same time, the opinion about solid fuel boilers was fixed as about inefficient heat generators, characterized by low efficiency and, in addition, requiring a lot of attention and trouble during operation - fuel loading, manual ignition, visual monitoring of the combustion process (and sometimes manual control of it), cleaning the ash pan. However modern technologies combustion in boiler furnaces of wood fuel has stepped forward so much that much of the above, and to some extent all of it, can already be classified as vain prejudices.
Advantages and disadvantages of fuel
Wood fuel in the EU belongs to the category of biofuels, which in turn is considered as one of the renewable energy sources. This is already an important advantage that allows you to save natural energy resources.
The cost of wood fuel, taking into account the calorific value, is higher than that of natural gas, but significantly lower than that of diesel fuel (about 1.5 times) and electricity (about 2.5 times for a heating system with an electric boiler and 3.5 times for direct electric heating systems).
It has already been noted above that it is not difficult to equip a storage for coal or wood fuel. Moreover, it does not require approvals from regulatory organizations, which are necessary when constructing a storage facility for diesel fuel, liquefied gas or connecting to the main gas.
Flaws solid fuel are primarily related to the characteristics of its combustion. Let's consider this process on the example of wood as the most common solid fuel in the domestic sphere.
Cellulose is the main substance of which wood is composed, the reaction equation (1) for its complete combustion (oxidation with oxygen) to the formation of end products (carbon dioxide and water vapor) looks like this:
(С6Н10О5)n + 6n О2 -----> 6n CO2 + 5n H2O, (1)
where n is the number of monomers in the cellulose chain involved in the reaction.
To start this reaction, it is necessary to heat the cellulose, and hence the wood fuel placed in the boiler furnace, to a certain temperature. The source of heat can be either an open fire (with manual ignition) - a burning area of a log, wood chips, briquette, or an electric thermoelement. Upon reaching a temperature of about 150 ° C, a gradual charring of the wood occurs with the formation of self-igniting coal. At 300 °C, the process of active thermal decomposition of wood begins, during which white or brown smoke is released from the charred layer. It consists of products of thermal decomposition of wood and steam. The temperature of the heating zone can increase sharply due to the heat from the combustion of pyrolysis gases, the flash point of which lies in the range of 250-300 °C. Ignition of wood occurs at a temperature exceeding 450-470 °C.
Of great importance for the start of combustion are the density of the material and its moisture content. So, porous wood of alder or poplar ignites faster than dense wood - beech or oak. Wet wood is more difficult because additional heat must first be used to evaporate the water. A retarding factor is also the increased thermal conductivity of wet wood; the ignited surface layer of it cools faster.
A necessary condition for any combustion is the access of oxygen to the fuel. In modern gas boilers oxygen and gaseous fuel are easily mixed at the outlet of the nozzles of the burner nozzles, or a mixture of fuel and air is already supplied there - premix burners, which are also used for burning liquid fuels. As the wood fuel burns, it is somewhat more difficult to provide the required amount of oxygen access to the areas of cellulose that have not yet entered into the reaction. Ash is constantly formed from mineral impurities (in firewood from 0.5 to 2%), which, along with water and cellulose, are part of the wood. Ash must be removed from the combustion zone.
An important factor for maintaining the combustion of wood and any fuel in general is the concentration of combustion heat, which is not dissipated, but goes to warm up new adjacent sections of the fuel to the ignition temperature. In the case of solid fuels, this process is also more difficult to control than with gas or liquid ones.
All this greatly complicates the automatic regulation of the wood combustion process, not to mention the fact that firewood can only be loaded manually. However, the improvement of solid fuel furnaces and modern technologies for combustion and pre-treatment of solid fuels make it possible to overcome all these disadvantages, sometimes even turning them into advantages.
Solid fuel traditions
In a traditional solid fuel boiler (Fig. 2), fuel is burned in a firebox on a grate, ash accumulates in an ash pan, flue gases are removed through a flue channel, as a rule, under natural vacuum. The heat obtained in the process of fuel combustion is transferred to the heating system through a heat exchanger. The heat carrier in such a heating system is most often water.
Rice. 2. Traditional solid fuel boiler with top loading (diagram)
A modern solid fuel boiler can operate for several hours on one portion of the loaded fuel. Some models work up to 10 hours. This happens because the boilers use the principle of lower combustion, in which air is supplied both from below and from the sides to the fuel. This increases efficiency and makes the combustion process smoother.
In addition, in modern boilers, the user can independently adjust the power to maintain the required temperature. To do this, turn and set the thermostat head to the required boiler water temperature, while using a steel chain, the damper through which combustion air enters will rise or fall, thereby increasing or decreasing draft and, accordingly, combustion speed and power.
Traditional steel boilers use steel or cast iron heat exchangers. From what material the boiler heat exchanger is made, the features of its design and the possibility of operation depend.
In the furnace of boilers with steel heat exchangers, fuel is usually loaded from above, through a hinged lid. Thanks to this, they are not only more convenient to load, but also clean. These boilers are cheaper than models with a cast-iron heat exchanger, but their service life is somewhat shorter, and they are less resistant to aggressive condensate. To avoid condensation, the temperature in the furnace and exhaust gases must be maintained above the dew point - not lower than 65 °C.
Cast iron is more resistant to condensate, so boilers with a cast-iron heat exchanger can be operated at more low temperatures. Loading in such boilers is frontal.
According to the type of fuel used, traditional solid fuel boilers are divided into "wood" and "universal" or "omnivorous". In the furnaces of wood-burning boilers, only wood fuel is burned, although it can be not only firewood, but also wood waste - chips, sawn timber trimmings, etc. with a moisture content of not more than 30%. Burning coal in them can lead to "burning out" of the steel boiler.
In the furnaces of universal boilers, both coal and wood fuel can be burned, however, they are also conditionally “omnivorous”. The main fuel for such models is still coal, and the use of wood fuel is allowed, but for a short time. This is dictated by the fact that different types of fuel have different combustion temperatures, and the design of the boiler and the materials used in it were initially calculated for certain operating temperature and working mode. First of all, when using a non-primary type of fuel, the performance of the boiler is reduced.
A properly installed chimney made of the appropriate material is another condition for the high-quality functioning of a solid fuel boiler.
It is the traditional models that include those disadvantages that are considered characteristic of solid fuel boilers: low efficiency (70-80%), the impossibility of automating the operation of the boiler, and the complexity of maintenance. Relatively frequent shutdowns of its operation between loads lead to temperature differences in heated rooms by 2-3 °C.
But the operation of traditional solid fuel boilers is completely independent of the power supply, which is important in areas where there are power outages.
Long burning
Relatively short operating time of a solid fuel boiler at one load, and, consequently, most of the troubles of its maintenance are primarily determined by the small volume of loading and the fast burn-out time of the fuel. This drawback is minimized in long-burning solid fuel boilers.
Rice. 3. Solid fuel boiler of long burning with traditional combustion (scheme)
Today, there are several designs of such boilers (Fig. 3, 4), but all of them are characterized by a large volume of the loading chamber, which significantly exceeds the volume of analogues of traditional solid fuel models. This is one of the main factors ensuring long-term operation of the boiler without additional loading.
Rice. 4. Solid fuel boiler of long burning with top combustion of fuel
In most designs of long-burning boilers, the loading chamber also performs the function of a fuel combustion chamber. Obviously, the second important condition for the successful operation of such a boiler is the creation in this chamber of conditions for the slow but complete combustion of a large volume of fuel. They are implemented in several fuel combustion technologies, according to this, long-burning boilers can be classified:
Boilers with traditional bottom-up fuel combustion;
Shaft type with lower combustion;
With pyrolysis (gas generating) combustion of fuel.
The device of a solid fuel boiler for long burning with traditional combustion (bottom-up) is the simplest. Its execution can be cylindrical or rectangular in shape. The design of the boiler is a firebox with a height of 1 m or more, surrounded on the outside by a "water jacket". The walls of the combustion chamber act as a heat exchanger. The loading door is on the top, and the chimney is on the side. Depending on the height and, consequently, the volume of the loading chamber, which is also the fuel combustion chamber, the duration of combustion changes. The location of the loading door allows you to fill the boiler not only with short logs, but also with logs of a rather large length (but not more than the height of the chamber), setting them vertically. Fuel is ignited from below through a special door. After ignition, the speed and, consequently, the duration of burning are regulated by changing the air supply through the blower door. Fuel consumption in such a boiler is somewhat higher than in long-burning boilers of other designs.
In shaft-type boilers, a technology with lower fuel combustion is implemented. The loading chamber is made in the form of a "mine" (hence the name of the type of such heat generators), the height of which is much greater than the cross-sectional dimensions. The fuel is loaded from above, however, the combustion products are removed not like in boilers with traditional combustion - through the loading chamber, but enter the adjacent one, where the heat exchanger is located, and only then enter the chimney. The heat exchanger in such boilers is usually made in the form of a sheet metal rectangle, into which pipes are cut for the passage of fire and hot gases - a fire-tube version. There are also designs with a water-tube heat exchanger, when the coolant circulates through the pipes of the boiler's water circuit located in the combustion chamber. Passing in the heat exchanger thermal energy coolant, flue gases are discharged through the chimney.
In boilers with top-burning fuel (top-down), it is ignited from above and gradually burns to the bottom. This happens with the help of a telescopic pipe for supplying air to the place of combustion, which, as the fuel burns, falls under its own weight. For uniform distribution of air, a nozzle in the form of a distributing disc with blades is provided at the end of the pipe. When loading fuel, the air supply pipe rises. To provide Better conditions combustion of fuel in such a design, the air is preheated in a preheating chamber located at the top of the combustion chamber. The air supply and the combustion rate are controlled by a valve at the inlet to the heating chamber. In the version without a chamber, such a valve is placed directly on the upper end of the pipe. The boiler heat exchanger is usually made in the form of a "water jacket" around the combustion chamber. To increase the efficiency of heat transfer, additional registers from pipes can be installed in the upper part. To load fuel in the upper part of the boiler, a side door is provided, and the removal of ash and fuel residues is carried out through the lower side door. In some models of boilers with top combustion of fuel, the side door is made almost to the entire height of the combustion chamber, which greatly simplifies the process of cleaning the boiler. As a rule, such boilers have a circular cross section.
The pyrolysis or gas generating method of burning solid fuels should be considered in more detail.
Pyrolysis boilers
Pyrolysis is a process of thermochemical destruction of solid fuel with the formation of combustible gaseous products - carbon monoxide (carbon monoxide) and hydrogen. It occurs as a result of heating solid fuel in the absence of oxygen. Heating is provided by the oxidation of part of the gasified fuel (≈ 10-30% depending on the characteristics of solid fuel and gasification equipment) without heat supply from outside. The absence of oxygen in the zones of formation of gas generator gas and pyrolysis (reduction zone and coking zone) is explained by the fact that the gasifying agents supplied to the reactor are balanced in such a way that all the oxygen contained in them is used in the oxidation zone (combustion zone).
In the processes of pyrolysis of solid fuel, usually occurring at a temperature of ≈ 400-900 0С, and the interaction of pyrolysis products with oxygen of gasifying agents at a temperature, as a rule, ≈ 900-1350 0С, heat is released according to exothermic chemical reactions (2), (3):
C + O2 = CO2 + 409 kJ/mol; (2)
2С + О2 = 2СО + 246 kJ/mol. (3)
The heat released as a result of pyrolysis reactions is used in the following processes:
Drying of solid fuel at a temperature of ≈ 150-400 oC;
Interactions of pyrolysis products with carbon dioxide (4) and water vapor (5) at a temperature of ≈ 750-1000 oC according to endothermic chemical reactions:
C + CO2 = 2CO - 162 kJ / mol, (4)
C + H2O \u003d CO + H2 - 137 kJ / mol; (5)
Heating of gasification agents at a temperature of heat carriers (gasification products) ≈ 200-900 °C.
After the above chemical reactions, the formation of carbon monoxide and hydrogen, the main combustible components, occurs. The results of other chemical reactions that take place during the gasification of solid fuel, due to their insignificant effect on the composition and calorific value of the resulting generator gas, can be ignored. The conditions necessary for the occurrence of chemical gasification reactions and their accompanying processes in the corresponding zones of the reactor are provided proper organization heat and mass transfer.
Rice. 5. Burning wood fuel in a pyrolysis boiler (scheme)
In pyrolysis boilers (Figure 5), firewood is loaded into a sealed upper chamber. Small amounts of primary air are supplied to it with the help of a blower fan, and the above-described pyrolysis processes take place in it. The generator gas formed as a result through a nozzle made of refractory material (special concrete or ceramics) enters the lower chamber, where it burns at a temperature of about 1200 °C. For more complete combustion of gas in the nozzle area, secondary air is mixed with it. During the operation of most models of pyrolysis boilers, the flame from the nozzle is directed downwards. The gaseous products of combustion give off heat to the heated water, passing through the fire tubes, and then sent to the chimney.
Loading fuel into such gas-generating boilers and removing ash (once every 3-7 days) is carried out manually. With a normal heating load, wood fuel loaded into the boiler chamber is enough for about 8-12 hours of operation.
Other clear advantages of pyrolysis boilers include complete combustion of fuel and greater control over the operation of the boiler by changing the speed of the blower fan. In automatic mode, this process is controlled by a thermostat or a programmable device.
The efficiency of pyrolysis boilers reaches 85%.
With these advantages, pyrolysis boilers become dependent on the power supply needed to operate the forced air fan and to power the control unit.
The most complete automation of the solid fuel combustion process can be achieved in pellet boilers, where wood fuel is used in a modified form.
Pellet modification
(from the English pellet - granule) are wood pellets (Fig. 6), which are made from small sawdust. This is a standardized product with a low moisture content (less than 10%), characterized by a high calorific value (at least 18 MJ/kg) and low ash content (less than 0.5% for pellets used in domestic boilers).
Rice. 6. Pellets - efficient wood fuel
The properties of high-quality fuel are associated with the technology of their manufacture. Prepared by pressing high pressure made of fine sawdust, essentially wood dust, light pellets contain a significant amount of air, which ensures their rapid and complete combustion in the boiler furnace. Approximately 2 kg of wood pellets in terms of calorific value replace 1 liter of EL fuel oil (according to DIN standard).
Rice. 7. Boiler room based on a pellet boiler with pellet storage (scheme)
Pellets are well stored, do not absorb moisture, and can be automatically transported to the boilers through fuel lines from fuel storage facilities (Fig. 7), which must be arranged in the house where the pellet boiler is installed. Pellet fuel is moved from the storage to the furnace along conveyors with a screw feed mechanism or through plastic pipelines using compressed air.
Pellet combustion is carried out in boiler furnaces (Fig. 8), equipped with burners of various designs: retort, flare, chimney.
Rice. 8. Combustion of fuel in a pellet boiler (scheme)
The designs of pellet boilers were considered in detail in one of the articles of the last issue of the magazine. - Ed.
Flare burners are attachments and can be replaced by gas or liquid fuel burners on some models of boilers.
The automatic supply of pellet fuel to the burner has brought solid fuel boilers to a new level. Loading pellets into the fuel storage is usually required once a year, and the boiler ash pan is cleaned 2-6 times a year, depending on the characteristics of the boiler used, the heat load and the length of the heating season.
Rice. 9. Pellet boiler
Thanks to this, it became possible to equip such boilers with electronic controllers, with the help of which programmable, including weather-dependent, control is carried out.
The efficiency of pellet boilers reaches up to 97%.
There are also multi-fuel (combined) solid fuel boilers on the market today, in the furnace of which not only pellets can be burned, but also other solid fuels - wood chips, wood waste, sunflower husks, as well as mixtures of different kind solid fuels and even coal.
Briquettes, firewood or large fractions of coal in multi-fuel boilers are usually burned in fireboxes with grates, and pellets - in mounted torch burners.
However, full automation of the supply of solid fuel not in the form of pellets cannot be achieved, since there are restrictions on its geometric dimensions, for example, the size of coal lumps.
So, for the Buderus Logano G221 A boilers that appeared on the Russian market in 2014 with automatic fuel supply, operating on coal or pellets, it is allowed to use fine coal or brown coal with a diameter of no more than 10-30 mm. Depending on the type of fuel and mode, this boiler operates on one load from 3 to 7 days.
Article from the Aqua-Therm magazine No. 6 (88) 2015