Wood pellets — are cylindrical pellets produced from woodworking waste. They are environmentally friendly biofuels and have a number of advantages over conventional firewood and other energy sources.
Pellets contain less moisture than dry wood, have a higher density and take up less space. They are convenient for transportation, unloading, storage, and thanks to their standard dimensions and uniform density, allow the heating process to be fully automated.
When burned, the pellets release more heat than wood and produce significantly less ash. In addition, pellets are made from raw materials that have previously been decayed in forests or burned in landfills. Now it is an economical biofuel that will allow you to heat the premises and receive hot water in a convenient way.
Pellet equipment works great in combination with solar collectors, providing even more savings.
The pellets are used not only for domestic heating but also on an industrial scale for the production of heat and electricity.
The sawdust and sawdust left after the woodworking are saturated and dried in a special chamber, and then pressed into high-pressure pellets. The binder is lignin contained in wood.
The pellets are then cooled, packed in sacks (usually 15 kg), big bags (about 1 tonne) or delivered to the site by special transport.
When burning wood, carbon dioxide (CO2) is released as much as was absorbed by the tree, as it was growing. In addition, if woodworking waste is not burned, it will emit the same amount of CO2 in the decomposition process.
Thus, by burning pellets, we do not bring in additional carbon dioxide into the atmosphere, which occurs when coal, oil or gas is burned, and we do not enhance the greenhouse effect.
Energy stored in pellet pellets, firewood, briquettes and other biofuels also has solar origin, but unlike fossil fuels, is a renewable resource.
Burning heat, also called calorific value or calorific value, is one of the most important consumer parameters. It is measured in megajoules, kilocalories or more commonly known kilowatt-hours. The calorific value of one kilogram of quality pellets is usually from 4.6 to 5.1 kW·h. Just as much heat is released by the complete burning of one kilogram of wood pellets.
Low quality pellets have low combustion heat. So for less money we get less heat. Moreover, such savings inevitably lead to the failure of expensive equipment.
Until 2015, the standard EN 14961-2, was in place in Europe, setting requirements for pellet fuels. It has already been replaced by the more stringent international standard ISO 17225-2. Many Bulgarian pellet manufacturers certify their production to the German standard DIN 51731 or Austrian ÖNORM M 7135.
There is also a voluntary ENplus, certification scheme based on a new international ISO 17225-2 standard, but goes beyond it with more stringent standards and additional requirements for fuel pellets. ENplus implies control over the whole chain (raw material selection, manufacturing process, packaging, delivery and storage), not just the end product. The ENplus scheme was developed by the German Pellet Institute (DEPI) and is being developed by the European Pellet Council (EPC), which is part of the European Biomass Association (AEBIOM).
The ENplus Pellets Class A1 logo with a unique 5-digit ID for a certified manufacturer or trader. The first 2 characters of the ID indicate the country of incorporation, the next 3 characters — company number in the ENplus register for the respective country. All certified companies are published on the international site ENplus
In accordance with ENplus, household pellets are divided into 3 quality classes: A1, A2 and B. The main differences between these classes are the allowable amount of ash formation and its melting temperature. These parameters are important for reliable operation of pellet boilers and stoves, as melting the ash can lead to the accumulation of solid slag and damage to the heating equipment.
NENCOM specialists have already happened to restore the pellet equipment to a faulty condition when using poor quality fuel. It looks like this:
Melted ash has blocked the automatic pellet boiler cleaning system
Also, the ENplus standard limits the chlorine content of pellets, as its high values cause corrosion of the combustion chamber. These are just some of the requirements of this standard:
|Calorific value, kW·h/kg||≥4.6|
|Ash content, mass %||≤0.7||≤1.2||≤2.0|
|t of melting ash, °C||≥1 200||≥1 100||≥1 100|
|Nitrogen, mass %||≤0.3||≤0.5||≤1.0|
|Sulfur, mass %||≤0.04||≤0.05||≤0.05|
|Chlorine, mass %||≤0.02||≤0.02||≤0.03|
|Diameter, mm||6±1 or 8±1|
|Length, mm||3.15 < L ≤ 40|
|Humidity, mass %||≤10|
|Bulk density, kg/m3||600 ≤ BD ≤ 750|
For low-power boilers and fireplaces (up to 50 kW) class A1 pellets are recommended. For medium-sized heating equipment (50 to 100 kW) the use of class A2 pellets is permissible. Class B pellets can only be used in large boilers (from 100 kW) and only when provided for in the instructions of the manufacturer of the heating equipment.
The efficiency of an electric boiler located in a heated room is ~ 100% (if the boundaries of the system are considered part of that room), because in it all the consumed electricity is converted into heat. But if the meter is located away from the heated room, then heating the cable in this section will mean losses. So we take electric heating efficiency for a conditional 99%.
At the same time, the efficiency of modern pellet boilers and stoves is usually 80 to 90%, even in laboratory conditions, since a considerable part of the heat generated by the fuel is lost through the chimney. The actual efficiency will always be lower than the laboratory one because of the not ideal conditions for burning fuel and soot formation on the water jacket.
Without delving into the insignificant details, we can assume that the efficiency of the pellet heater is 78%, and the heat of the pellet granules is 4.8 kW·h/kg. Suppose we need 5 000 kW·h of heat for the season to heat. Let’s calculate how many pellets we will need for this, and compare the cost with electric pellets:
|Required thermal energy, kW·h||5 000||5 000||5 000|
|Boiler efficiency, %||78||99||99|
|Energy consumption, kW·h||6 410||5 050||5 050|
|Calorific value, kW·h/kg||4.8||-||-|
|Mass of the energy carrier, kg||1 335||-||-|
|Price of the energy carrier, BGN/kg||0.50||-||-|
|Price of the energy carrier, BGN/kW·h||0.10||0.12||0.19|
|Heating value, BGN||668||606||960|
The table shows the approximate prices of energy sources in Bulgaria for 2017: pellets — 500 BGN/ton; daily rate electricity — 0.22 BGN/kW·h (16 hours duration); nightly rate electricity — 0.12 BGN/kW·h (8 hours duration)
As the table shows, heating with an electric boiler in a 24-hour mode is 44% more expensive than heating with pellets. By using only the nightly tariff, electricity becomes cheaper by 9%. Price parity is reached with full use of the night tariff (8 hours) and one hour per day tariff:
Of course, for convenience of use, safety and environmental friendliness of the site (without taking into account the production chain) electric heating is out of competition. But if we use electricity for heating, for example, in a coal-fired power plant (efficiency of about 35% and feed losses), we pollute the atmosphere much more than when burning pellets.
In addition, in many cases the installation of an electric boiler with the required power is simply not possible if that power cannot be provided by the grid operator. The risk of losing heat when the power supply is interrupted must also be considered.
Fully reasonable can be a combined heating option: during the day — with a pellet boiler or fireplace, and at night — additional heating or full electric heating.
In this comparison, we do not consider heat pumps, that have a conversion factor (not to be confused with efficiency) of more than one. Such installations, although more expensive than electric boilers, generate more heat than the electricity consumed for that purpose.
Wood heating comes out about 2 times cheaper than pellets when comparing boilers with water circuits:
|Required thermal energy, kW·h||5 000||5 000|
|Boiler efficiency, %||78||63|
|Energy consumption, kW·h||6 410||7 937|
|Calorific value, kW·h/kg||4.8||4.2|
|Weight of the energy carrier, kg||1 335||1 890|
|Volume of the energy carrier, m3||2||4|
|Price of the energy carrier, BGN/kg||0.50||0.17|
|Price of the energy carrier, BGN/kW·h||0.10||0.04|
|Heating value, BGN||668||320|
The table shows the estimated prices of energy sources in Bulgaria for 2017: pellets — 500 BGN/ton; firewoods — 80 BGN/m3 (~470 kg)
But such savings require a lot of time and effort. Woods occupy 2 times more storage space when calculating kW·h useful thermal energy, they are more sensitive to humidity, and ash and smoke are produced when burned. In addition, the processes of fueling and firing are impossible to automate: a wood boiler requires constant attention, even at night.
The modern pellet technology allows to fully automate all the basic stages: ignition, granule feeding into the combustion chamber, maintaining the set temperature, scheduling and even managing via the Internet. Many pellet boiler models also come with automatic cleaning systems:
Installation and start-up of a pellet boiler in a hotel
Pellet feeder and combustion chamber cleaning mechanisms
From a conservation point of view, burning pellets produced from woodworking waste is preferable to burning wood.
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