Using wood waste as fuel for the boiler will help reduce heating costs. But for effective work you need special equipment. A sawdust solid fuel boiler differs from its classic counterparts in design and maintenance.
Principle of operation
The main problem with this type of fuel is its high loading density. This prevents air from entering to support the combustion process. As a result, a boiler using pressed sawdust will not generate the required power, and some of the fuel will remain unburned.
To solve this problem, it is necessary to ensure the flow of air masses into the combustion chamber. This is done using artificially created depressions in the sawdust filling. An alternative is to install air pipes into the combustion zone.
The general principle of operation of heating equipment:
- Fuel loading.
- Ignition at the bottom.
- Providing air supply using an open ash pan door, fan or ducts.
- The gradual combustion of sawdust frees up space for a larger volume of air, circulation improves, and intense heat release occurs.
Sawdust boiler long burning works according to a different scheme. In the large combustion chamber there is no open flame, fuel smoldering. The formed wood gases are sent through the channel to the afterburning chamber, where an air mixture is added to form an intense fire.
Boiler design features
Unlike classic solid fuel equipment, a sawdust boiler has big sizes fuel (loading chamber) and ash pan. This is explained by the requirements for combustion duration - with an increase in the volume of the combustion chamber, the battery life on one tab becomes longer.
You can make a similar boiler on sawdust with your own hands - drawings and general description help determine the best design. The advantage of the models is the ability to develop a unique assembly scheme based on the parameters of a specific heating system.
When manufacturing, you need to take into account the following nuances:
- The combustion chamber. Should occupy up to 2/3 of the volume of the entire boiler. The walls are made of heat-resistant steel with a thickness of at least 2 mm.
- The ash pan is located in the lower part and is separated from the combustion chamber by cast iron grates. The distance between them is minimal - up to 2 cm. There is also a fan or hole for air supply.
- The heat exchanger must be located directly in the fuel combustion zone.
- You can make a classic rectangular design or weld it from pipes.
- Chimney. To ensure traction, the diameter is at least 100 mm, the length is from 4 m and above.
You should think about the boiler maintenance procedure in advance - timely removal of ash, cleaning the walls from burning. Therefore, the loading doors into the fuel chamber are made in the upper part; they are large. Once closed, the seal must be ensured.
Boiler power calculation
One of the problems with homemade heating equipment is determining power. You can do the calculations for a sawdust boiler yourself. To do this, you need to know the basic characteristics of the fuel.
Calculation order.
- Bulk density. On average, this parameter varies from 180 to 230 kg/m?. With a fuel chamber volume of 0.07 m? it will hold about 15 kg of crushed material.
- Calorific value of fuel. The average value for 1 kg of fuel is 2.3 kW.
- Power calculation. The maximum value for this example will be 15 * 2.3 = 34.5 kW.
This simplified method does not take into account fuel moisture and air supply intensity. It is recommended to subtract 10-15% from the obtained value. The actual maximum power will be 29 kW.
Automation method and operating rules
To automatically load sawdust, you can install a screw feed. The shaft is attached to a hole in the combustion chamber, at the bottom. There is a separate storage bin for chopped wood pulp. A temperature sensor is mounted in the automatic sawdust boiler, in the heat exchanger.
It connects to the manager electronic relay. Upon reaching minimum temperature The auger motor turns on and fuel is supplied. Recommended operating time is up to 1 m.
To maintain equipment in working condition, you must follow these rules:
- clean the ash pan from combustion products once a day;
- check traction, remove soot from inner surface pipes;
- To prevent condensation from entering the combustion zone, install a water container at the bottom of the chimney.
The sawdust must be dried before loading. Otherwise, their calorific value will decrease, which will affect heat transfer. To avoid heat loss, it is recommended to insulate the outer walls with basalt wool; the combustion chamber doors must be sealed and double.
Pellet with the ability to work on sawdust
Pellet boiler for a cottage. Works on pellets, sawdust.
Automatic solid fuel boilers using pellets, sawdust, wood chips. Designed for heating cottages, country houses equipped with water heating systems with forced circulation, for heat supply technological processes. Can be used for heating a cottage, country house, cottage, shop, workshop, etc. Feeding of pellets, sawdust, wood chips - automatic from the feeder hopper. Boiler automation provides control of the boiler operation depending on the temperature at the boiler outlet.
The boilers were specially designed to operate on pellets and wood (sawdust, shavings, etc.).
Description of the boiler design
The boiler is steel, fire tube with two gas passages. The boiler body consists of two main parts.
Kolosnikovaya the part is equipped with inclined water-cooled inclined grates, a cavity for collecting ash, a pellet supply retort, a blast air distributor with adjustable dampers for primary and secondary blast. Equipped with doors for cleaning, maintenance and ash removal.
Firebox It is a cylindrical steel water-cooled shell of sufficient volume. The large volume of the firebox ensures maximum combustion of long-flame wood fuel. The walls of the firebox have holes for supplying secondary air for complete combustion of fuel, in particular pellets. The special arrangement of the holes ensures the development of vortex processes in the firebox, facilitating a uniform and rapid supply of air to the burning torch.
Computer modeling of the operation of a boiler using pellets and sawdust allows you to optimize the design and avoid many mistakes
In the combustion area, the firebox is lined with heat-resistant fireclay bricks with operating temperature 1650 °C. The lining allows you to increase the temperature in the combustion zone, which increases the rate of oxidation reactions of fuel components, increases the stability of the boiler at low loads and when using high-moisture firewood and sawdust.
Above the combustion zone is located heat exchange convection unit. Flue gases from the furnace pass through a large diameter heat exchanger pipe to the upper part. Next, the gases unfold in the upper part of the boiler and descend through the pipes of the second pass bundle, where they are collected in the gas receiver and removed into the chimney. This design makes it possible to cool gases to 140-180 °C and achieve an efficiency of 90%. The heat exchange pipes are located vertically and are not clogged with ash deposits. Top cover The heat exchanger allows, if necessary, to easily and quickly clean the heat exchange pipes, so the boiler efficiency does not decrease over time. The boiler body is thermally insulated from the outside and covered with a decorative shell made of sheet metal with durable coating.
This arrangement provides high performance with compact installation dimensions. The design of the firebox allows you to effectively burn wood waste, in no way inferior to “gas generators”.
The pellets are fed into the fuel retort of the grate part using the auger of the fuel supply device, at the command of the automation system. After filling the cavity with pellets, they are poured onto the grate. Primary air is pumped under the grate by a fan; here, mainly charcoal is burned, remaining after the pyrolysis of the pellets and the release of volatiles. Volatile components burn in the flame with an intensive supply of secondary air to the furnace. This achieves very high fuel efficiency. Water-cooled grates prevent an excessive increase in temperature in the combustion zone of the coke residue, thereby preventing the fuel ash from caking. This is especially important when working with low-quality pellets or sawdust with high ash content. The sintering of ash forms a hard crust that interferes with the passage of fuel and air, which can cause the boiler to stop. Thus, the combustion zone is surrounded on all sides by a coolant, and the maximum heat released during the combustion of pellets is transferred to consumers.
Video of an automatic pellet boiler with a power of 30 kW at an exhibition in medium power mode
Boilers for working on sawdust are equipped with a fuel supply device, additionally equipped with a agitator with a separate drive.
The fuel path of all boilers is equipped with multi-stage fire protection.
The boiler delivery set includes:
- - Boiler (grid part, firebox, heat exchanger)
- - Fuel supply device (pellets or sawdust and pellets)
- - Block of control and alarm devices,
- - Blower fan
Parameter nameKW (m) - 0.03KW (m) -0.05
Rated heat output, kW 30 50
Heated area, m2100-400300-800
Heat output adjustment range, % 10-100 5-100
Efficiency of pellets/chips, %90/8690/86
Maximum outlet coolant temperature, °С 95 95
Coolant operating pressure, not more than, MPa 0.3 0.3
Water consumption through the boiler (circulation rate), m3/h 11.75
Flue gas temperature, max °C 180 180
Boiler hydraulic resistance, kPa 35 35
Boiler weight without coolant, kg 450/537 620/707
Installed power, kW0 5/0.320, 5/0.32
Fuel consumption by type, kg/h
Firewood, chopped wood including chips and sawdust.
Humidity 30%, NCV 12.2 MJ/kg 9.8 16.3
Pellets. NTS 17.8 MJ/kg 6.8 11.3
Feeder bin volume, m3 0.8 0.8
Advantages of automation of a solid fuel boiler kW (m)
The boiler automation controls the operation of the boiler based on the outlet water temperature; control occurs by alternating three preset modes in the required sequence.
Modes: maximum power, medium power and "pause" mode.
When the load on the boiler is high, the maximum power mode is activated; as the outlet temperature increases, the boiler switches to the medium power mode. The supply of pellets and air is reduced. Thanks to the presence of the lining, the temperature in the furnace remains sufficient for efficient combustion of fuel. If the heating power in this mode is not enough, it switches to maximum power, but if the temperature rises after switching to medium power, the fan and fuel supply stop, after which the temperature inevitably decreases and the medium power mode starts again.
It turns out that the boiler, in the process of changing the load, switches automatically from one mode to another, depending on the heat removal.
The "pause" mode is the most disadvantageous. On the one hand, there is no fuel supply, which means there are no costs, but a significant amount of cold air passes through the boiler under the influence of pipe draft, taking away heat. Many people are familiar with how quickly a wood-burning stove cools down if the pipe is not laid in time; the same thing happens with the boiler. In addition, in a cooled firebox, effective combustion is not established immediately, but only with heating of the firebox; before this, some of the pellets do not burn completely, increasing the average consumption.
Considering that it is correctly selected in terms of power. The boiler for heating the house works on full power only in the most severe frosts, and the rest of the time at medium power, the effectiveness of three-stage adjustment is obvious.
Most similar boilers have only 2 modes. With average power, typical for most heating season such boilers are in “pause” mode for a significant time, heating the street uselessly.
The idea of using wood waste as fuel is not new. Back in the sixties of the last century, Soviet engineers came up with boilers for heating industrial facilities, in which sawdust was used. But subsequently the idea never spread. At that time, no one wanted to save anything. And especially energy resources, they were too cheap. So, the sawdust boiler remained only on paper.
Principle of operation
On modern Russian market Heating boilers operating on wood waste are represented by foreign devices. Homemade analogues Russian production meet too. Their craftsmen adjusted them to certain operating conditions. So these home-made heating units can work not only on sawdust, but also on wood chips.
The fuel combustion process is carried out according to the so-called controlled combustion. Firstly, it is a three-stage air supply. Secondly, the use of the pyrolysis process, that is, gas generation of exhaust combustion products occurs. In fact, a sawdust boiler is a long-burning unit.
Sawdust supply and combustion diagram
Foreign boilers are heating devices with automatic loading. That is, their design includes a bunker into which a certain amount of fuel is loaded. There are two modifications:
- The hopper is connected to the boiler.
- A bunker is a separate unit that can be located outside the house (boiler room).
So, sawdust is loaded into a hopper, from which it is fed into the combustion chamber using an auger. Here, using the air supply regulator, the degree of combustion is regulated. At the very beginning, when the boiler is heating up, the fuel burns using conventional technology. When temperature regime reaches the required value, the air supply is reduced to a minimum. The process enters the pyrolysis stage.
The carbon monoxide released in this case rises and moves into the second combustion chamber, where it burns when mixed with oxygen. This is where the maximum thermal energy is released.
Heating unit design
The boiler design also includes a heat exchanger for the home heating system. It is located at back wall for two combustion chambers at once. In some models of long-burning boilers, the heat exchanger is a water jacket located over the entire area of two combustion chambers. This boiler works more efficiently.
Screw
Auger for automatic feeding sawdust is important node, ensuring the correct operation of the entire installation. If the loading hopper is located outside the walls of the boiler room, then the supply is carried out in two links: the first - from the hopper to the boiler, the second - from the loading chamber to the firebox.
Fans and automation
Fans provide the necessary supply of fresh air to the two combustion chambers. In this case, two goals are pursued: the first is to create conditions for proper combustion of sawdust, the second is to create a certain swirl of the flame.
The exhaust fan provides draft in the boiler and effective removal of carbon monoxide. The thing is that the process of pyrolysis is a decrease in the temperature of fuel combustion products. This means that, according to the laws of physics, there is a slight upward movement of smoke. To increase the lifting speed, an exhaust fan is installed.
Of course, all modern heating and long-burning boilers are equipped with an automation system that controls all thermal processes inside the installation.
Disadvantages of the unit
What can you say about such boilers? Firstly, these are energy-dependent heating systems. Secondly, they have great overall dimensions. So you will have to organize a boiler room or furnace room for them.
Thirdly, in order to achieve a heat release of 25 kW, 40 kg of sawdust must be loaded into this boiler every hour. That is, you will have to provide the home heating system with an uninterrupted supply of fuel.
Fourthly, these heating devices do not work on wood chips. But this, together with sawdust, is one of the most common types of waste from the woodworking industry.
Homemade boilers
Homemade sawdust boilers are used to heat small country cottages and dachas.
Design
Their design is simple, there is no auger, no hopper. Fuel is loaded directly into the boiler through the top opening lid.
The main installation requirement is complete tightness and minimal air supply to the combustion chamber. Such long-burning boilers, used for heating small spaces, have a two-layer shell. Imagine two pipes inserted into one another. Fuel is placed inside a small-diameter pipe; it smolders here, releasing pyrolysis gas and quite a lot of thermal energy.
The gases move upward, hit the boiler lid, and burn here. Combustion products descend into the gap between the pipes. In the lowest part near the floor on one side there is a chimney opening. Carbon monoxide escapes through it heating installation. Everything happens naturally. Since this sawdust boiler is completely metal, it is the source of heating.
Fuel storage rules
Very important point, which provides effective work boiler of this type is to correctly lay the sawdust with your own hands. The basic models of this type use a press insert.
This will require special device, made of metal or wood in the form of a cone. Its length is half a meter greater than the height of sawdust. Large diameter– 80-100 mm, small – 60-80 mm. The device is installed in the middle of the combustion chamber with a small diameter downwards. After that, sawdust is poured around, which is necessarily pressed. You can compact it with any available materials. What matters here is the quality, not the method. The wedge is then removed.
Ignition
Pay attention to the ignition system. Do not use gasoline or kerosene when spraying sawdust. Spray method only. You need to set it on fire with a torch or a long match.
Common models
There are quite a large number of different models of homemade long-burning boilers that operate on sawdust and wood chips.
For example, the development of Russian Kulibins. This long-burning boiler is called Bubafonya.
Its design differs from others in that it can burn sawdust, wood chips, and firewood. There is no need to tamp the fuel; everything happens under the action of a metal press. The design of this unit contains a gap that provides air supply to the combustion zone of chips or sawdust.
When part of the fuel burns, the press moves lower, preventing the gap from increasing. This is a kind of self-control that ensures the correct course of the pyrolysis process.
Pyrolysis gases pass between the press and the walls of the housing into the second chamber, where they burn. Carbon monoxide throw the unit through the chimney, which is located in the upper side part of the body.
Potbelly stove
Many country developers will be interested in the design of a conventional potbelly stove, which operates on the principle of long-term combustion. To do this, its firebox is divided into two parts by a horizontal partition. In the rear part, a gap is left between the partition and the wall, through which pyrolysis gases will be supplied to the upper firebox.
In the lower combustion chamber, wood chips or firewood are used as fuel. This stove will not work on sawdust. Its horizontal arrangement and side ignition are not suitable for bulk fuel.
It is very important to correctly adjust the air supply to the lower firebox. As mentioned above, the less oxygen, the better for pyrolysis.
Fuel requirements
In order for the operation of the unit to comply with the declared characteristics, and for heating of the premises to be carried out in full without the use of additional heat sources, it is necessary to monitor the quality of the fuel used.
Humidity
Boilers using sawdust and wood chips will operate efficiently only if their humidity does not exceed certain standards - 15-20%. This fully applies to boilers made by yourself.
But there are factory models on the market that can also work on wet sawdust (up to 40%). For this purpose, their design contains a so-called agitator. This is a movable grate that rotates periodically. This is done so that moisture under the influence of heat does not remain inside the material, but comes out of its mass.
Some Russian craftsmen install a fixed grate at a slight angle. And this creates the effect of removing moisture by shedding some of the fuel.
Density
The efficiency of sawdust combustion is affected not only by its moisture content. The dimensions of the material itself, and therefore the density of the fuel, are also of great importance. Here are some examples:
- density is 250 kg/m³, this is sawdust from band sawmill, when half a kilogram is burned per hour, 1 kW of thermal energy is released;
- density 100-150 kg/m³, this is sawdust from milling machine, when burning 0.25 kg per hour, 1 kW of heat is obtained.
That is, the lower the density, the more thermal energy is released during the combustion of sawdust. And accordingly less costs for heating the house. But this is a double-edged sword.
Is it necessary to press sawdust?
This question is posed in terms of convenient use of sawdust. So is it convenient or not? Undoubtedly, this option is convenient. But pressed sawdust generates as much heat as ordinary firewood. And this is with the same volume. Although their cost is several times lower than firewood. By the way, organize pressing with your own hands at your place personal plot not difficult.
Advantages and disadvantages of heating with sawdust
When considering a sawdust boiler, one cannot ignore the pros and cons of its operation. The undeniable advantages include:
- Cheap fuel.
- Output large quantity heat.
- Minimal carbon monoxide emissions.
But when choosing such equipment, you should take into account some of the disadvantages of its use:
- The formation of a large amount of ash and soot, they will have to be disposed of.
- Difficulty storing sawdust and wood chips.
Among household heat generators that use electricity to heat the coolant, the most popular are electrode boilers. Thanks to their many advantages, they have earned many positive reviews from homeowners who are already using the product to heat their own home.
General characteristics of electrode boilers
The principle of heating the coolant between two electrodes due to the movement of charged particles determines the simplest design this type of heaters. Hollow section steel pipe with a metal rod inserted into it - these are all the main elements that make up economical electrode heating boilers. The pipe is hermetically sealed on both sides, and pipes for connecting the heating system pipelines are welded on the sides. A phase is connected to the inner metal rod electrical network, to the device body – zero. Heat generators with a power of over 5 kW are manufactured with three rods for connecting a three-phase network.
Electrode boilers Galan
Passing through electrodes and water alternating current causes the ions of calcium and magnesium salts contained in water to change the direction of their movement 50 times per second, in accordance with the frequency of 50 Hz. Due to this, the electrolysis process becomes incomplete and the substance is not transferred from one electrode to another, as with DC. Based on the above, we can summarize:
- the product has small sizes, it is very convenient during installation;
- the design of the device is very simple and does not require constant maintenance;
- electrode boilers for heating a private house are very efficient in operation (efficiency 97-99%);
- as practice shows, when working with simple tap water cleaning of working surfaces should be done once every 3-4 years;
- the electrical installation is very reliable in operation, since there are simply no parts that can break or deteriorate;
- affordable price for all segments of the population.
Electrode heating systems
When choosing an electric heat source in a private house You can use this advice: if a careful visual inspection shows that the unit is made well, then it will work well and reliably.
Pay attention to the quality of the product as a whole: reliability of fastenings, absence of distortions of the case and contacts, integrity of the paint and varnish coating, quality of welds. As for choosing from the many manufacturers offering you an economical electrode boiler, this is not a very important question, since the principle of operation for all electrode devices is the same and their efficiency is absolutely the same.
Another thing is that before purchasing you will need to select and calculate the electrode boiler according to the required thermal power. In this case, the following statement can be taken as a basis:
The specific amount of heat required to heat 1 m2 of living space up to 3 m high is 100 W, taking into account all reserves and errors.
Knowing the total area of the building based on external measurements, you can easily calculate the required thermal power. According to this, you should select an electric heater from the offered model range, taking the one closest in power, only in a larger direction.
If you plan to expand the heated area in the near future, and then the heating of a private house, then you can purchase an electric boiler with a double reserve; this will not affect the efficiency at all. This fact This is explained by the fact that any electrode heater always operates at full power; the temperature of the coolant or air in the house is regulated by automation, which turns the electrical installation on and off if necessary. More powerful unit It will spend less time heating the coolant and then turn off, that’s the whole difference.
Additional factors
The selection of automation with an actuator must be taken very carefully. The fact is that room regulator temperature or climate control controller cannot directly supply voltage to the electric heater because too much current is flowing in the circuit. For this, intermediary devices are used: relays, starters, and so on. When using electrode boilers for heating in conjunction with electromagnetic starters or contactors, be prepared for loud clicks that can be heard throughout the house when the unit is turned on. To avoid this, it is better to choose a silent control unit based on thyristors.
Many manufacturers, in their technical data sheets or product operating instructions, give recommendations in accordance with which the coolant for electrode boilers should be prepared. This is a very important point; the efficiency of the unit depends on the salt content in the coolant. If their quantity is small, as in distilled water, then the conductivity of the water will be very weak and the electrical resistance will be high. The boiler simply will not function. And vice versa, if the water is “oversalted,” then the process is too rapid and partial transfer of the substance occurs, as in electrolysis. As a result, accelerated wear occurs and a decrease in work surface central electrode. The figure shows an electrode that has worked for 2 years with tap water (right) and salt water from a well (left).
Conclusion
In fact, electrode heat generators are very reliable, and also have a low cost. But it should be taken into account that a large current often occurs in the power circuit of the electric boiler; wires and cables of the appropriate cross-section must be used, this is a matter of your safety. Therefore, it is worth hiring a specialist – an electrician – to install and connect the equipment.
