Pellets (granules) – biofuel derived from peat, wood waste and agricultural waste. It is a cylindrical granules of standard size.

Raw materials for production

The raw material for production of pellets can be peat, pulpwood (poor quality) and wood waste: bark, sawdust, wood chips and other forest waste, as well as agricultural waste: waste of corn, straw, cereal production waste, sunflower husks, chicken manure, and other.

Production technology

Pellet-press

Raw materials (sawdust, bark, etc..) are fed to a grinder where pulverized into flour. The resulting mass is supplied to the dryer, then in a pellet press, where the wood flour is compressed into pellets. The high pressure of the press causes the temperature of the wood to increase greatly, and the lignin plasticizes slightly forming a natural “glue” that holds the pellet together as it cools. To product one ton of pellets you need about 2.3 -2.6 cubic meters of wood waste, plus 0.6 cubic meters of sawdust burned per tonne of production.

Ready pellets are cooled, packed in different packaging – from small packages (2-20 kg) up to big bags (large industrial packaging) weighing up to 1 ton – or delivered to the consumer in bulk.

Torrefaction of pellets (carried out in the absence of oxygen)

Here the solid biomass is treated without oxygen at a temperature of 200-330ºC. Torrefied or black pellets have several advantages over conventional ones, otherwise known as white:

• repel moisture, can be stored in the open air, that is, do not require indoor storage;
• do not rot, do not mould, do not swell and do not disintegrate;
• perform better combustion, similar to coal. Hence the name – biochar.

Advantages and disadvantages

Pellets – environmentally friendly fuel with an ash content, usually not more than 3%. In the production of pellets are mainly used sawmill plant and agriculture waste, which was previously mainly taken to the dump, and after a few years began to burn or smolder.

Since granules do not contain dust and spores, they are less susceptible to self-ignition and do not cause allergic reactions in humans.

Granules differ from conventional wood by high dryness (moisture content is only 8-12%, compared to humidity of raw wood – 30-50%) and increased density (about by half). These qualities provide a high calorific value as compared to the firewood or chips – by combustion of 1 ton granules released approximately 3500 kW/h heat, that is bigger by half than of conventional wood.

Low moisture content is not only an advantage of pellets as fuel, but also the complexity of their production. Drying may be one of the main items of expenditure in the waste wood pellets production. Furthermore, depending on the production, the collection process, sorting and cleaning materials may also incur additional costs. The carefully planned drying process will reduce the risks associated with quality of the end product, its cost and fire hazard of production. The best option is production of biofuels from dry chips.

One of the major advantages of pellets considered to be a high and constant bulk density, which makes it relatively easy to transport the bulk product over long distances. Due to correct shape, small size and uniform consistency of the product granules can be poured through special sleeves, that allows you to automate the processes of loading and unloading and also burning this fuel.

Efficient use of fuel pellets requires a special type of furnace – pellet stove.

Quality

The quality and appearance of the granules depend on the manufacturing technology and raw materials. Wood pellets with a high content of bark usually have a dark color, and the pellets from debarked wood – a light one. In the production process – for example, by drying – granules may be slightly “burned” and then become gray from white. Although it does not always affect consumer qualities of granules such as calorific value, ash content, strength and wearability, but can lead to formation of fine dust during transportation due to friction of granules to each other.

Application

Pellets of high quality (white and gray) are used for heating homes by burning in pellet boilers, stoves and fireplaces. They usually are 6-8 mm in diameter and less than 50 mm longwise. The standard package for selling In Europe is 15-20 kg bags.

The demand for wood briquettes and pellets, also combustion and production equipment increases in proportion to the prices of traditional fuels such as oil and gas. In some European countries, where the market of alternative energy sources is most developed, the granules heat up to 2/3 of domestic premises. Such wide spread occurrence is explained also by environmental friendliness of this fuel – at combustion the CO2 emissions are equal to the absorption of this gas during the growth of the tree, and emissions of NO2 and volatile organic components are significantly reduced through use of advanced combustion technologies.

Dark granules with high content of bark are burned in boilers of greater capacity to produce heat and electricity for settlements and industrial enterprises. Dark granules may differ in larger diameter. They are sold in bulk batches from 2 or 3 thousand tons and more.