Pelletization raw materials

Before starting your pellet press machines to produce pellets, the foremost consideration is the choice of materials. Typically, several factors related to the raw materials need to be taken into account, including availability, flammability, adhesiveness, and calorific value. Availability determines the capacity and stability of pellet production. Flammability is one of the key factors that affect the feasibility of pellet production. Adhesiveness, which refers to the raw materials’ ability to bond together when compressed by the pellet press machines, is another crucial characteristic. The calorific value of the pellets depends on the selection of raw materials. Nevertheless, nearly any type of vegetation can be condensed into energy-producing pellets, although each type possesses its own unique set of characteristics.

Wood

The primary sources of material for manufacturing wood pellets are typically the by-products from the initial processing of wood at sawmills and plywood facilities, such as bark, sawdust, woodchips, and shavings. These materials are advantageous for the pelletization process because they require fewer preparatory steps before being fed into the pellet mill.

Agricultural waste

In areas without extensive forestry operations, the emphasis has shifted towards converting agricultural waste, particularly straw, into biomass energy. This is attributed to its comparatively high availability and rapid regeneration rate. In Europe alone, approximately 23 million dry tons of straw are produced annually, which exceeds the current demand for pellets by double. Denmark has emerged as a pioneer in converting this agricultural residue into energy.

Reed canary grass

Reed canary grass is harvested annually in the spring, with a dry yield ranging from 5 to 12 tons per hectare and a moisture content of 10 to 15 percent. This plant offers several advantages, including the ability to grow in the same location for several years without rotation, and its low requirement for water and fertilizer. Harvested reed canary grass is typically baled for easier transportation, but it is crucial to store the baled straw in a manner that prevents moisture accumulation.

Miscanthus

Miscanthus can reach heights of over 3.5 meters in a single growing season, making it a viable source of biofuel due to its rapid growth, low mineral content, and high biomass yield. It also demonstrates higher photosynthetic efficiency and reduced water requirements compared to other plants. Additionally, miscanthus has minimal nutritional needs and efficiently processes nitrogen, enabling it to thrive on barren land without extensive fertilization. The plant has the potential to produce 15-25 metric tons of dry biomass per hectare annually, which can be converted into biofuel products like pellets after harvesting.

Switchgrass

Switchgrass, also known as “elephant grass,” is another potential source for pelletization, but with a lower yield of 7-11 metric tons per hectare, it falls behind miscanthus in terms of productivity. This grass thrives in the prairies of North America.

Cardoon

Cardoon, a herbaceous species, has emerged as a viable energy crop in southern European countries. Its dry yield ranges from 3 to 11 metric tons per hectare and thrives in regions with limited rainfall. While cardoon boasts a high calorific value of 15 megajoules per kilogram, its ash content of 13.9 percent is relatively high. Therefore, its greatest potential lies in being used as a supplementary biomass source to create blended biofuel.

Olive and rapeseed

Olive pits, a by-product of olive oil production, can be used as a source of biomass energy, competing with pellets in domestic boilers or through cogeneration in large industrial plants. Unlike pellets, olive pits do not require manufacturing but only conditioning. Olive oil and, consequently, olive pits, are more abundant in southern Europe, while rapeseed is more common in the north. In the north, rape residues are often mixed with wood or other straw materials to produce pellets. Denmark, for instance, has four pellet plants that utilize rape residues as a raw material.

Other agricultural

A wide range of agricultural materials have demonstrated potential for pellet production. Among them, by-products of industrial production, such as coffee and corn waste, have garnered special interest from the biomass community. The availability of these residual materials adds to the attractiveness of niche pellet production, despite the fact that most of them exhibit subpar combustion characteristics.

Mixing raw materials remains uncommon, but it has been proven that blending materials with natural binding qualities into a base feed can enhance pellet durability. Potential additives could include bark mixed with hardwood, brewers’ spent grains, and beech dust. Digestate, a by-product of biogas production, could also be utilized for pellet production.

For those interested in operating a pellet press machine, the agricultural sources available for utilization are virtually endless. However, the quality variations resulting from using different raw materials are also numerous. Significant differences exist between softwoods and hardwoods, different plant species, and even different plant parts. Additionally, climatic and seasonal variations, as well as the duration and method of storage, can also impact the quality of the raw materials.