The best replacement for firewood, electricity and gas! Pellet boiler: what is it?
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Pellet heating boiler – a device that heats a liquid heat carrier during the combustion of granulated fuel.
The pellet boiler is a rectangular metal cabinet with a door at the front, pipes for connecting pipes at the back and a funnel-shaped open tank at the side.
Traditional heated objects – cottages, summer houses, utility blocks, shops, rural schools, and other small public buildings.
Content
Construction of a pellet heating boiler
Boiler body, cast iron or steel, forms 4 main zones:
- firebox (combustion chamber);
- ash;
- water (a closed reservoir in which the coolant is heated to the required temperature);
- convective (gas ducts).
Elements of the device
Access to the ash pan and burner is provided through the doors in the front wall of the boiler body. Pellet burner volumetric type increases the efficiency of the pellet boiler to the level of a gas boiler. Flanges, pipes for connection to the chimney and pipeline are located in the rear wall.
Control unit is attached from above, pellet bin, cast iron or made of sheet steel, on the side. It is connected to the burner by a sleeve and an external screw feeder. Internal auger, if the model is equipped with it, moves the pellets directly to the fire. The insulating material covering the boiler body is protected by a steel casing.
Pellet fuel: what is it
Pellets are an element of plant origin in the form of dense small "grains" cylindrical shape. The diameter of the granule does not exceed 1 cm, average length - 4 cm.
Photo 1. Pellets for use in a heating boiler. They are small pressed granules.
Low-quality wood, bark, wood processing waste, as well as straw, sunflower husks, and corn act as energy carriers. Pressing of the raw material is preceded by:
- its coarse grinding, drying;
- fine grinding to a powdery fraction;
- water and steam treatment.
Granulation improves important physical and mechanical properties of the dispersed product, eliminating fluidity, dusting, and sintering during combustion. The result is a bulk material represented by elements of a given shape, size, structure, moisture content, and density.
Operating principle
The energy characteristics of the boiler, the design of the furnace, its operation are determined by the phenomena and processes accompanying the combustion of fuel. Heated wood disintegrates into "volatile" substances and coals. These components, when burned, contribute to the total amount of heat released.
In the boiler firebox and flues, heat is transferred from the fuel to the surfaces convection and radiation. The fan under the burner directs air into the firebox. It passes through the burning solid fuel, mixes with the combustion products and heats the firebox, flues, and tank. The total temperature of the mixture of air and hot gases is 1300—1700 °C.
Reference. The firebox wall is heated by radiant radiation only from those areas of the load that directly “look” at it. Its share is small, but lower part of the combustion chamber, adjacent to the bookmark, is heated mainly by radiation.
The main heating of the firebox and channels is performed by hot gases - combustion products.
Pellets contain a higher proportion of volatile substances than lump wood (not to mention hard and brown coal). Therefore, convective gas ducts pellet boiler developed, multi-pass (after all, that's what happens in them more than 2/3 of heat removal), and the combustion chamber is small.
Wednesday, transmitting generated energy (water, water antifreeze), circulates through a closed pipeline, heating the air in the room by means of heating radiators. In a separate circuit It is possible to supply the building with hot water.
Photo 2. Pellet boiler with a water circuit connected to it, which is used for heating the room.
Pellet boilers are combined with other heating equipment (to supplement their operation in winter, and to save fuel in summer), For example:
- with heat accumulators — heat-insulated tanks in the heating system circuit that accumulate hot water;
- additional heating circuit, for example, a solar system;
- electric boiler.
Important! Not every design of a heating boiler implies possibility of heating antifreeze. Not every model is designed to connect more than one circuit.
Key Features
Reliability pellet boiler, like any equipment, is expressed in the warranty period, inter-repair and inter-service intervals. As a device for producing energy and transferring it to the coolant, The device is characterized by:
- energy efficiency of fuel combustion;
- power;
- battery life on one tab.
Thermal power, what is the smallest
What amount of heat is generated per unit of time as a result of fuel combustion, shows the main characteristic of the heat generator - thermal power.
It is selected based on the purpose of the room, area, ceiling height, and heat loss when passing through enclosing structures.
The power values of the pellet boiler are in the range of 12-500 kW.
Less power makes the device unprofitable, but with more power it loses its advantages over other heat generators:
- operates with efficiency < 0.8 — less efficient than gas, liquid fuel, coal boilers;
- is failing in 3-5 years.
Efficiency
The efficiency of the device shows what share the pellet boiler was able to “take” from the calculated amount of heat that the fuel “gave off” during combustion. Reduces the efficiency insufficient or excessive loading of the firebox, poor quality fuel, improper operation of the equipment.
The higher the heat of combustion, the more efficient the fuel. Fuel oil and diesel fuel are the leaders in efficiency. Heat of combustion of pellets 2.4-4.3 times lower And depends on the type of raw material:
- woody - 17.5-19 (MJ/kg);
- straw - 14.5;
- peat - 10.
In this respect, pellets from wood processing waste are comparable to coal (15-25 MJ/kg) and are superior to the original material - sawdust, chips, shavings (10 MJ/kg).
Fuel consumption and bunker capacity
Average annual consumption of pellets from recycled wood 1/5 less than brown coal (by weight) and several times less than piece wood (it is more moist and less dense).
The exact figure depends on the properties of the boiler and its operating settings, as well as on the volume of the heated room, the material and design of the external walls.
Bunker volume for pellets, it determines how long the heating boiler will not require human intervention and varies from tens of liters to a cubic meter or more.
Reference. Automation of fuel supply is possible if it is initially provided by the boiler design. The fire safety distances in the boiler room also depend on the volume of the bunker.
Additional functions
Automation of the pellet boiler operation is not limited to the mechanized supply of fuel from the operating reserve to the burner. Boiler models with additional functions reduce manual labor for servicing the unit to a minimum:
- optical elements control the flame;
- the electric coil ignites the fuel supply;
- The temperature and pressure of the water is measured by a thermomanometer;
- thermostats turn the burner and pump on and off, and protect the system from overheating;
- the boiler power is adjusted by a potentiometer;
- The fuel burnout sensor reacts to the burner surface temperature.
This is not a complete list of electronic, mechanical, chemical devices., which the manufacturer can equip its products with.
A high degree of automation allows the pellet boiler to operate without human intervention more than 7 days. Connection with a personal computer makes control remote. Manual cleaning or replacement of the ash pan takes no more than half an hour.
Important! The technical parameters of the pellet boiler, declared by the manufacturer, are the result of tests conducted with the prescribed fuel. Instructions for the device contains requirements for the quality of pellets: graininess (mm), calorific value (J/kg), humidity (%), ash content (%).
The properties of the fuel affect the power and efficiency of the heat generator.
Pros of the device
The advantages of pellet boilers are due to the qualities of the energy carrier they process. Solid fuel boilers are cost-effective to operate undemanding to the quality of heated water And cleanliness of the surrounding air.
Solid fuel makes equipment that works with it:
- independent of centralized energy sources (including their availability);
- explosion-proof and flame-retardant;
- does not require costs for connections or a tank for liquid fuel.
Photo 3. Pellet boiler with closed (left) and open firebox (right). The control panel is located at the top of the device.
The woody nature of the fuel gives pellet boilers their positive features:
- environmental safety;
- the possibility of using ash to deoxidize and enrich the soil;
- aesthetic value - the places where firewood and pellets are stored and used remain clean, and are only given away by the smell of wood.
Eco-friendliness
The form of existence of raw materials (dense homogeneous granules), the technology of its production give pellet boilers new qualities, which distinguish them from heat generators on traditional types of fuel. Like lump wood, pellets environmentally friendly and hypoallergenic (no linkers, modifiers).
Coal flue gases contain from 1 to 3% sulfur, smoke from wood pellets - 0.1%There is practically no carbon dioxide in the combustion products of pellets (only the amount that the plant absorbed during growth), which cannot be said about other types of fuel:
- coal - 60 kg/GJ;
- fuel oil - 78;
- gas - 57;
- peat based biofuel - 70.
Efficiency
Calorific value of wood pellets more than one and a half times highert is the same as that of firewood and is comparable to the specific heat of combustion of coal.
The efficiency of a pellet boiler is higher than that of a wood boiler - 8.5-9.5. Temperature of exhaust gases of the first 120—140 °C, the rest of the heat is “absorbed” by the flues.
Convenience
Ash content of wood pellets (0.5-1% by weight) lower than firewood, and in 10-60 times less, than coal. The ash content of straw and peat pellets is slightly higher: 4 and 20% respectively. The boiler ash pan has a capacity of 25 kW cleaned twice a month.
Attention! Ash removal only begins after the burner has cooled down.
Granulated and packaged material convenient to transport, unload, and store. The constancy of the specified physical, mechanical and metric parameters of the fuel elements guarantees long-term combustion with a constant temperature. When burning, the pellets do not "shoot" or spark.
Cons
Heat of combustion of pellets 2.4-4.3 times lower, than fuel oil, diesel, but is comparable with this characteristic of coal. In an hour of combustion of a kilogram of pellets, the stove will transfer to the coolant 150 kcal (or 4.3-4.5 kW) heat.
The burden falls on the consumer's shoulders taking care of purchasing, delivery and storage of fuel.
Despite the fact that the pellet packages are stacked compactly, woodshed for their storage a fairly voluminous and dry one is needed: Granulated wood is sensitive to moisture.
Installation of a pellet boiler accompanied by additional expenses: Air ducts are needed to supply air and chimneys to remove combustion products.
Useful video
Watch the video, which tells about the features of a pellet boiler and explains what it is needed for.
Safe operation
Pellet boiler is required to be installed in a separate, ventilated room outside the residential buildingThe intensity of air exchange in the boiler room depends on the characteristics of the boiler and is indicated in its instructions.
Important! Fuel storage and boiler room are not combined. Even the operational stock of pellets do not leave in the same room with the stove.
The boiler room must be spacious enough so that no objects or walls are adjacent to the boiler body. closer than half a meter. The minimum permissible ceiling height depends on the dimensions of the boiler body together with the bunker and is specified in the instructions.
?
The solid fuel boiler is installed on a durable non-combustible base that is larger in area than the base of the boiler body. not less than 2 cm the base must be visible from each side.
Preparation of the "old" heating system, connection of new equipment, its adjustment, major and scheduled repairs performed by appropriately qualified specialists, with permission for this type of work.
With proper operation, the service life of a pellet boiler reaches two decades.
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