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Densification of switchgrass into briquettes contributes to efficient handlblg, transportation, storage, and use in bioenergy applications. The effects of fine grinding of switchgrass, adding biomass-based binders (corn stover, corn distillers dried grains with solubles, and starch), and mixing commercial chemical feed binders (lignin-sulfonate, lime, and sodium bentonite) on durability of switchgrass briquettes (about 19.0 mm diameter) were investigated using a uniaxial, piston-cylinder densification apparatus. At a compression pressure of 150 MPa, preheating of switchgrass grind (geometric mean particle diameter of 0.56 mm) to 100 °C without adding any binders improved the briquette durability to 67% compared to the briquette durability of 0% without preheating. In addition to preheating to 100 °C, either mixing of 20% (wt.) of corn stover or 5% (wt.) of lime significantly improved the switchgrass briquette durability to 80%. Mixing of 20% (wt.) corn stover with 80% (wt.) switchgrass appears to be the best strategy to improve switchgrass briquette durability because addition of 20% (wt.) corn stover would involve almost no additional cost for densification compared to the addition of 5% (wt.) of lime. Preheating was essential to fully activate the natural binders in the switchgrass as well as the binding agents added to the switchgrass. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]

Corn stover and switchgrass, potential biomass feedstocks for bioenergy and bioproducts industries, are often harvested during a limited harvest season and stored as bales with bulk densities of about 100 to 200 kg m-3. Because of low bulk density, corn stover and switchgrass are difficult to handle, transport, store, and use in their natural forms. One of the solutions to reduce these problems and the associated costs is to densify these biomass feedstocks into pellets or briquettes. In this study, roll press briquetting characteristics of corn stover and switchgrass were studied using a pilot-scale roll press briquetting machine. Almond-shaped briquettes 28.7 to 31.3 mm in length were made. Results showed that high-durability corn stover and switchgrass briquettes with bulk densities of 480 to 530 kg m-3 could be produced. This corresponds to about a three- to five-fold increase in bulk densities compared to those of bales. Briquettes produced with the roll press briquetting machine had bulk densities (351 to 527 kg m-3), durabilities (39% to 90%), and crushing strengths (28 to 277 N) 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. The bulk density, durability, and hardness of the pellets ranged from 528 to 610 kg m-3, 75% to 95%, and 148 to 224 N, respectively. Micro-structural studies (chemical composition analyses, scanning electron microscopy imaging, and UV auto-fluorescence imaging) on grinds, briquettes, and pellets confirmed that highly dense, strong, and durable briquettes and pellets from corn stover and switchgrass could be produced without adding chemical binders (i.e., additives) by activating (softening) the natural binders such as water-soluble carbohydrates, lignin, protein, starch, and fat in the biomass materials by providing moisture and temperature in the range of glass transition of the biomass materials. No steam conditioning was necessary to produce good-quality corn stover briquettes. For switchgrass, a grind temperature of about 75 °C obtained by steam conditioning was necessary to produce good-quality briquettes. Roll press briquetting appears to be a promising low-cost, low-energy, high-capacity densification approach for commercial production of biomass briquettes. [ABSTRACT FROM AUTHOR]

Corn stover and switchgrass are two important feedstocks considered for producing renewable fuels and energy in the US. Densification of these biomass feedstocks into briquettes/pellets would help reduce the problems and costs of bulk transportation, handling, and storage of biomass feedstocks. In this study, the role of the natural binders in corn stover and switchgrass to make durable particle-particle bonding in briquettes/pellets was investigated by micro-structural analyses. Scanning Electron Microscopy (SEM) images of briquettes made by using a uniaxial piston-cylinder densification apparatus in the laboratory, briquettes made by using a pilot-scale roll-press briquetting machine, and pellets made by using a pilot-scale conventional ring-die pelleting machine were analysed. The SEM images showed that the bonding between particles was created mainly through solid bridges. The solid bridges between particles were made by natural binders in the biomass expressed during the densification process. UV auto-fluorescence images of briquettes and pellets further confirmed that the solid bridges were made mainly by natural binders such as lignin and protein. It was found that activating (softening) the natural binders using moisture and temperature in the range of glass transition is important to make durable particle-particle bonding.

A simple method to obtain predetermined constant cooling rates for insect supercooling point (SCP) determination is described. A transient heat transfer equation was used to design polystyrene cubes of different sizes to yield constant rates of cooling at their centers when held at a constant surrounding temperature. Cubes of 0.29 x 0.29 x 0.29 m and 0.19 x 0.19 x 0.19 m were found to produce cooling rates of about -0.5 and -1 degree C per min, respectively, from 0 to -40 degree C. The observed temperature variations at the geometrical center of the cubes were similar to those predicted by the equation. Temperature plots showed a nearly constant rate of cooling. Supercooling points of Tribolium castaneum (Herbst) at different stages of development were recorded using polystyrene cubes. These SCPs compared favorably with published values. This method of obtaining cooling rates is economical, flexible, and allows for multiple simultaneous SCP measurements.