Roll Press Briquetting of Corn Stover and Switchgrass: A Pilot Scale Continuous Briquetting Study

Experiments on briquetting of corn stover and switchgrass were conducted in a pilot-scale roll press briquetting machine. Briquettes were of almond shape with 28.7 to 31.3-mm in length. The effects of briquetting machine variables such as screw feeder and roll speeds, and biomass variables such as particle size, moisture content, and steam conditioning temperature on the bulk density, durability, and crushing strength of the briquettes were investigated. It was found that no steam conditioning was necessary to produce good quality corn stover briquettes. For switchgrass, a grind temperature of about 75oC obtained by steam conditioning was necessary to produce good quality briquettes. At the optimum roll press briquetting conditions determined, corn stover and switchgrass briquettes with bulk density of 453 and 420 kg m-3, durability of 88 and 70%, and crushing strength of 169 and 171 N, respectively, could be produced. Briquettes produced with the roll press briquetting machine had bulk densities, durabilities, and crushing strengths that were somewhat less than but in a range comparable to the pellets (9.6 to 9.8 mm diameter) produced with a conventional ring-die pelleting machine. Roll press briquetting appears to be a promising low-cost, low-energy, high-capacity approach for commercial production of densified biomass.