Compaction of Switchgrass for Value Added Utilization

Abstract

There are increasing concerns about energy prices, availability and utilization in the world. This has led to many governmental and privately sponsored studies and research on the potential of renewable energy from biomass. Switchgrass (Panicum virgatum L.), a potential energy crop, has been evaluated and is being developed as an alternative to fossil fuels. Most lightly dense biomass such as switchgrass are easier to store, transport, and handle after they are densified/pelleted. The optimal pelletization method of switchgrass was obtained by carrying out fundamental studies on the effect of process parameters (moisture content, temperature, and die size) on pelletability, density and specific energy. Pellets were manufactured in a single die apparatus attached to a texture analyzer. Results showed that with a compaction force of 3924 N, the density of the switchgrass pellets increased with decreasing die size (4.8 mm to 7.9 mm). Density also increased with temperature from 60 to 90°C. The density of the compacts was also affected by the moisture content of the feed material. The density varied from 850 kg/m3 to 1250 kg/m3. There was no significant effect of temperature on the specific energy used to make switchgrass pellets. Switchgrass used for investigation of moisture effect on physical properties was pelleted through a 4.8 mm diameter die. It was found that the bulk density, particle density, durability and hardness of the pellets were significantly affected by moisture content. The maximum values of bulk density and particle density were 708 kg/m3 and 1462 kg/m3 respectively. The force required to rupture the pellets varied from 32N at 6.32% to 22N at 17.4% moisture content. Durability of the pellets was also affected by moisture content and was the highest at 8.62% moisture content. The pellets absorbed moisture at rates that were significantly affected by relative humidity of the surrounding air (P<0.05). The equilibrium moisture content and equlibrium relative humidity (EMC-ERH) relationships for the pellets were sigmoidal in shape and were best predicted by the Chung-Pfost equation. Results from compositional analyses showed significant differences between lignin and ash for ground and pelleted switchgrass.