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Coir is a natural, lignin rich, fiber that can be found between the hard internal shell and the outer coat of a coconut. There are multiple products made from coir fibers but a significant amount of fibers accumulating from coconut processing remains unutilized. Coir fibers obtained from ripe (brown fibers) and unripe (white fibers) have a high lignin content about 41–42 wt%, a low ash content < 15 wt% and a high heating value of about 18.5–19 MJ kg−1. The pelletizing properties were studied in a laboratory scale, single pellet press, and produced pellets were of high mechanical properties. Dynamic mechanical thermal analysis was used to identify the glass transition temperature of coir lignin and indicated that at the applied conditions the softening of coir lignin occurs at about 120–130 °C, which is the usual temperature reached in an industrial scale pellet mill. These properties make coir a suitable raw material for fuel pellet production. Its high availability makes coir fibers a potential replacement for firewood and charcoal in developing countries, and thereby contributes to reduce deforestation. [ABSTRACT FROM AUTHOR]

Combined torrefaction and pelletization is used to increase the fuel value of biomass by increasing its energy density and improving its handling and combustion properties. In the present study, a single-pellet press tool was used to screen for the effects of pellet die temperature, moisture content, additive addition, and the degree of torrefaction on the pelletizing properties and pellet quality, i.e., density, static friction, and pellet strength. Results were compared with pellet production using a bench-scale pelletizer. The results indicate that friction is the key factor when scaling up from single-pellet press to bench-scale pelletizer. Tuning moisture content or increasing the die temperature did not ease the pellet production of torrefied wood chips significantly. The addition of rapeseed oil as a lubricant reduced the static friction by half and stabilized pellet production; however, the pellet quality, strength, and density were negatively affected. The pellets produced from pine wood torrefied at 250 and 280 °C were shorter than pellets produced from untreated wood and their quality did not match conventional wood pellet standards. However, the heating value of the torrefied pellets was higher and the particle size distribution after grinding the pellets was more uniform compared to conventional wood pellets. [ABSTRACT FROM AUTHOR]

The utilization of wheat straw as a renewable energy resource is limited due to its low bulk density. Pelletizing wheat straw into fuel pellets of high density increases its handling properties but is more challenging compared to pelletizing woody biomass. Straw has a lower lignin content and a high concentration of hydrophobic waxes on its outer surface that may limit the pellet strength. The present work studies the impact of the lignin glass transition on the pelletizing properties of wheat straw. Furthermore, the effect of surface waxes on the pelletizing process and pellet strength are investigated by comparing wheat straw before and after organic solvent extraction. The lignin glass transition temperature for wheat straw and extracted wheat straw is determined by dynamic mechanical thermal analysis. At a moisture content of 8%, transitions are identified at 53°C and 63°C, respectively. Pellets are pressed from wheat straw and straw where the waxes have been extracted from. Two pelletizing temperatures were chosen-one below and one above the glass transition temperature of lignin. The pellets compression strength, density, and fracture surface were compared to each other. Pellets pressed at 30°C have a lower density and compression strength and a tendency to expand in length after the pelletizing process compared to pellets pressed at 100°C. At low temperatures, surface extractives have a lubricating effect and reduce the friction in the press channel of a pellet mill while no such effect is observed at elevated temperatures. Fuel pellets made from extracted wheat straw have a slightly higher compression strength which might be explained by a better interparticle adhesion in the absence of hydrophobic surface waxes. [ABSTRACT FROM AUTHOR]