• Energy Research

Abstract Compaction of milled walnut shells was carried out at moisture contents of 11.3, 18.3, and 25.3% w.b., material temperatures of 93 °C and 106 °C, agglomerate lengths, la, of 40, 50, 60, 70, and 80 mm and a speed of 100 mm min−1. The phenomenon of friction vibrations occurred at the moisture level of 11.3% w.b. when moving the pellets in die. At a higher temperature of 106 vs. 93 °C the frequencies of the compaction pressure oscillation were lower – 0.16 and 0.21 Hz, respectively, and their vibration amplitudes were also higher – 0.49 and 0.38 MPa, respectively. The relationship between the pellets' compressive strength and the unit pellet density was an inverse for moisture and temperature, and was coherent for the agglomerate length (i.e. die thickness). The good strengths of the pellets with densities higher than 820 kg m−3 were obtained at the moisture level of 18.3% w.b., temperature of 93 °C and an la in the range of 60–70 mm. Using the character correlation method, the set of parameters characterising agglomeration and the pellets were limited from twelve to seven. The novelty of this work lies in the application of spectral analysis and the use of the character correlation method.

Abstract The parameters characterizing biomass flow through the harvester units in laboratory conditions were determined for shoots of big bluestem, giant miscanthus, Spartina pectinata, giant knotweed, Virginia mallow, and Jerusalem artichoke harvested in two growth phases. The input energy for cutting and harvesting of plants was also compared with the outlet energy contained in methane from biomass harvested in the second growth phase. The power needed to cut the biomass was inversely proportional to the power needed to its deformation through the screw scrolls of the harvester and compaction by the feeding rolls. Based on a mathematical model, it was found that biomass with an optimum moisture of 65–70% wet basis (w.b.) required the smallest dry matter (DM) specific work for cutting. The amounts of energy used for cutting and harvesting were 1.22% and 4.87% of the energy contained in the methane produced from the big bluestem, and up to 2.05% and 8.22% for the miscanthus. The input energy values had a greater impact on these indicators than the energy contained in the methane, and this was probably related to the greater reaction of the cutting resistance to moisture.

Abstract An experiment using spent coffee grounds (SCGs) was performed with moisture (6.2, 22.5, 23.2, and 33.4% w.b.) and die height (42, 52, 62, 72, 82, and 92 mm) as influencing parameters at a stable temperature of 93 °C and speed of 100 mm min−1, and the monitoring curves of pressure-displacements were studied. Both pelletization factors were significant parameters for the maximum pressure and corresponding piston displacements, pellet movement, specific work, pellet density, and breaking strength. An interaction was found between these factors, but the moisture had a greater and nonlinear effect on the agglomeration parameters than the die height, which influenced linearly the change of these parameters. The agglomeration parameters values increased with decreasing moisture and increasing the die height. The results suggest that high-strength fuel pellets (>1.0 MPa) could be produced from SCG at a suitable moisture (

Abstract The aim of the study was to explain the effect of pressure and compaction time, number of layers and compaction cycles of biomass from six energy plant species intended for silage on the density of mini silos as well as energy consumption and compaction indicators. A mathematical model was developed to predict the silage density against changed process factors. Chopped biomass was compacted in four layers using three cycles at 17–63 kPa pressure and 6–10 s per cycle. The greatest changes in compacted density were achieved in the first cycle of the first layer. At subsequent stages, the recompression curves were steeper, and more stable and higher densities were obtained. For giant knotweed the required silage dry matter density of 225 kg m−3 was achieved for plants at the physiological maturity stage, with a lower moisture content of 23.6%, than that obtained for plants harvested in June. The silage density was greater for deciduous plants (Virginia mallow and Jerusalem artichoke, but not giant knotweed) than that for grasses (miscanthus, Spartina pectinata, and big bluestem); this result was due to the lower moisture and to differences in the structure of the shoots. Silage density describes the model well in terms of pressure, number of layers, compaction time, particle size and dry matter.

The aim of this study was to investigate the pressure agglomeration process of wheat straw (WS) and the blends of WS with calcium carbonate (CC) or cassava straw (CS) with a ratio of 6% wt./wt. from seven separate fractions with sizes in the range of 0.21–2.81 mm. The agglomeration was performed at a moisture of 30% wb and a material temperature of 78 °C, with a dose of 0.1 g, in a die of diameter 8 mm and height 80 mm. The effects of the process were evaluated based on the compaction parameters and the pellets’ density, tensile strength, and water absorption. The incorporation of additives into the WS improved the pellet process and quality. Refined results were achieved after adding CC, as compared to those achieved after adding CS, and the preferred particle size was in the range of 1.00–1.94 mm. This was because, under the given conditions, the back pressure in the die chamber significantly increased, allowing the achievement of a single pellet density of 800 kg·m−3. The pellets were resistant to compressive loads and cracked only at tensile strength of 6 MPa and a specific compression work of 6.5 mJ·mm−2. The addition of CC to the WS improved the strength of the adhesive and the cohesive bonds between the particles. The water absorption for the uncrushed pellets was considerably less than that for crushed pellets, which results in the safer storage of uncrushed pellets and excellent moisture absorption of crushed pellets. The addition of CC to the WS offers benefits in the form of pellet strength with a high water absorption capability. Notably, a study of crushed pellet litter under broiler rearing conditions and an analysis of the operational costs of using WS additives are required for implementing this study.