The effects of kraft lignin additives on wood fuel pellet quality, energy use and shelf life

In 2011, the total consumption of pellets in Sweden amounted to 1.9 million tons, which represents an energy value of 9 TWh. The pellets are used in large-scale as well as in small-scale applications, and increased demands on pellet quality are likely to force pellet producers to improve on the pellet properties. One way of increasing pellet quality is by using additives. The purpose of this article, therefore, is to examine kraft lignin as an additive. Pellets were produced in a small industrial pellet press located at Karlstad University, Karlstad, Sweden, and 1–4% of kraft lignin was added to the pellets. The results indicate that the addition of an increased amount of kraft lignin to the pellets increases their mechanical durability and their lengths. The results also indicate that dry kraft lignin yields pellets with higher durability as compared to wet kraft lignin. The energy demand was unaffected by the increased use of kraft lignin. The general results presented in this paper are useful for producers of lignin, pellet producers and end-users of pellets, who are interested in developing their products and/or improving the production processes. ► Sawdust pelletized in an industrial scale pellet press with 1–4% of kraft lignin. ► Increased amount of kraft lignin increases their mechanical durability and length. ► Dry kraft lignin yields pellets with higher durability than wet kraft lignin. ► The pellet press energy demand was almost unaffected when kraft lignin were used.