Temperature control in energy grass pellet production – Effects on process stability and pellet quality

► A pilot scale pelletizer with die temperature control was custom made for the study. ► Moisture content, steam addition, and die temperature was varied independently. ► Continuous production conditions were obtained at low die temperatures. ► High bulk density and high pellet durability was obtained at low die temperatures. Pilot scale ring and die pelletizing of reed canary grass (Phalaris arundinacea L.) was performed in experimental designs for screening and optimization of pellet quality parameters bulk density and durability and for determination of specific energy consumption under different settings. Control variables included die temperature, raw material moisture content, and steam conditioning. By using a unique experimental setup, where die temperature could be controlled, all factors could be varied independently. Results from the screening design, showed that a low die temperature was necessary to avoid discontinuous production conditions and guided the choice of settings in the optimization design for obtaining high pellet quality. Settings for reaching the suggested quality criteria of pellets for non-industrial use with a durability ⩾97.5% and a bulk density of ⩾600kg/m3 were easiest to meet at die temperatures around 30°C and a material temperature of approximately 30–40°C (equal to 2–4kg steam/h) for the full range of raw material moisture content (12–16%).