Pellets. Africa has been created by the World Bioenergy Association (WBA). Africa is the continent with the highest share of bioenergy in its energy balance. Over 50 % of all energy used in Africa is bioenergy. However, the net loss of forest area in Africa has accelerated, according to the most resent FAQ report. In the period between 2010– 2020 the net loss of forest area in Africa has been accelerating and was on average 3,9 Million hectares per year. The need for large amounts of firewood and charcoal is playing an important role in this development which is unsustainable. Using pellets from abundant unused agricultural residues could become a key to protection of forests and sustainable bio energy use that strengthens local economies.
The process of pelletizing biomass overcomes both issues: the pelleting process must include a careful control of the humidity of used biomass. Too humid material needs to be dried before pelletizing as pellets otherwise fall apart. pellets have a very low humidity.
The pelletization process leads to a product, with a high energy density. This means that approximately 5 times more energy can be stored in the same volume compared to untreated biomass. A bag of pellets has approximately the same energy content as a similar sized bag of charcoal but twice the weight.
While charcoal production reduces the energy content of biomass substantially – up to 80 % of the energy content is lost during the transformation of wood to charcoal pelletizing does not reduce the energy content and needs only comparatively small amounts of energy for processing, drying and compressing the biomass.
Due to the small particle size, pellet combustion using the right equipment does not create any smoke. A pellet cookstove can burn almost as clean and stable as an LPG stove but at much lower costs.
You cannot run a car that is designed for gasoline with diesel. If you do so the car will most likely stop working. The same is true for many energy generating devices – if the fuel you feed them does not comply with the design specifications of the device they may stop to work. Of course different appliances can vary in their fuel flexibility – some may accept a wide range of fuel properties, other may need very specific properties.
In terms of size the standard for pellets used in domestic appliances defines that the diameter of pellets should be 6 mm or 8 mm and its length should be anything between 3.50 mm and 40 mm. Humidity should be below 10 % for all quality classes. The ash content is different from quality class to quality class. High quality pellets – the A1 category – must have an ash content below 0.7 %, quality A2 requires an ash content below 1.2 % and quality class B requires an ash content below 2 %.
The ISO-standards also specify the chemical composition of pellets and gives a number of thresholds for certain elements that may not be exceeded. This provision mainly aims at impeding the use of recycled wood that is contaminated with different materials such as paint, glue, etc.
In industries, the procedure of wood pellets production mainly departs in the following steps: wood material crushing, water moisture control, biomass pelletizing, wood pellets cooling, wood pellets weighing and packing. In a wood pellet line, the pelletizing process is the most important. Equaling to the pelletizing part, the die and the roller is the most important part in a pellet machine.