Corn stover and switchgrass are two important biomass feedstocks being considered for commercial production of renewable fuels (ethanol), combined heat and power, chemicals, and bio-products in the U.S. These biomass feedstocks currently are collected as low-density bales involving high cost and energy for handling, transportation, storage, and use. Densification of biomass feedstocks into pellets/briquettes is a cost- and energy-effective strategy for a consistent, year-round supply of these biomass feedstocks for biobased and bioenergy industries. In this research, densification characteristics of corn stover and switchgrass were studied using a piston-cylinder densification apparatus to understand the densification and binding mechanisms, and to determine the optimum densification conditions for commercial production of pellets/briquettes from these biomass materials. The effects of densification process variables such as pressure (100 to 150 MPa), moisture content (8% to 20% wet basis), particle size (0.34 to 0.80 mm), and preheating temperature (75°C to 200°C) on the densification characteristics of corn stover and switchgrass were studied. At room temperature (about 25°C), corn stover briquettes (about 19.2 mm diameter) with relaxed densities (i.e., individual briquette densities measured one week after forming) of 745 to 1013 kg m-3 and switchgrass briquettes (about 19.4 mm diameter) with relaxed densities of 417 to 825 kg m-3 were produced. Densification at 25°C resulted in briquette durability of 50% to 96% for corn stover and 0% for switchgrass. Preheating corn stover and switchgrass to 75 C to 100 C increased the density further and resulted in briquettes with maximum durability of 97% for corn stover, and 67% for switchgrass. The measured glass transition (i.e., softening) temperature of both corn stover and switchgrass averaged 75°C. Densification conditions causing glass transition in the biomass was essential to fully activate the natural binding components such as lignin, protein, starch, and water-soluble carbohydrates in the biomass to help effective particle binding. The optimum densification condition to produce highly durable corn stover pellets/briquettes in commercial-scale systems is either conditioning the grind to a moisture content of 15% to 20% (wet basis) at room temperature (25°C) or preheating the grind to 75°C at a moisture content of 10% to 15% (wet basis). The optimum densification condition for switchgrass is preheating the grind to >75°C at a moisture content of 8% to 15% (wet basis).
|Original language||English (US)|
|Number of pages||14|
|Journal||Transactions of the ASABE|
|State||Published - May 1 2009|
- Corn stover
- Glass transition temperature
- Natural binders