Biomass Pelletization

Lowering Carbon dioxide emissions and to reduce the dependency on fossil fuels are the main objectives of the EU energy policy. In Denmark the debate concerning environmental friendly and sustainable energy production has reached the highest political level. One way to achieve those ambitious aims are to use renewable biomass as energy resource. Most common sources of biomass are wood and waste products from agriculture, industry and municipality. Biomass as such is a porous and bulky material of low density which makes it difficult and expensive to handle under transportation and storage. One way to upgrade the value of biomass and to use it more effectively is to increase its density by pelletization.

Biomass pellets have several advantages compared to unprocessed biomass. The energy density is significantly higher which saves storage and transportation costs, especially when the biomass has to be transported long distances. Pellets are more homogeneous in shape and composition and standards allow international trading of biomass. Low moisture content and the standardized sizes make them an ideal fuel for small heating systems such as stoves and boilers for domestic use. However the pellets can also be used in full-scale power plants such as Dong Energies Avedøre 2 power plant close to Copenhagen with a total output of 570 MW.

Biomass pellets are produced in a simple mechanical compaction process and the majority of pellets today are produced in pellet mills of the ring matrix type. When the matrix is rotating the adjacent roller forces the raw material into the channels of the matrix as shown in Figure 1.

Figure 1. Schematic drawing of a pellet mill matrix and magnification of a single press channel.

The pelletization of different types of biomass to fuel pellets is frequently met with production-related difficulties that until now have been solved on an ad hoc basis, resulting in no fundamental understanding of the pelletization process. The practical knowledge obtained is usually limited to the biomass in use and cannot necessarily be extended to other kinds of biomass. This hinders the flexible pellet production that is crucial for an effective use of biomass. The aim of the present project is to contribute to the development of such a fundamental understanding in a crucial way. It is the expectation that a significant amount of the biomass utilization for energy purposes in the future will be based on pellets, where a large part of the pellets will be produced in Denmark. In a longer term, it is the aim that the established knowledge should be used to improve and optimize the pellets production, lower energy uptake and broaden the range of biomass that can be pelletized.

Page updated by 09.03.2010