• Energy Research

Abstract The innovation of this research was a holistic approach to the problem of linking the biometric characteristics of six energy plants species and the distribution of moisture along the shoot‘ height and determination of linear models of particle sizes in relation to the moisture. The median biometric parameters values for growth phases I and II were as follows: shoot weight: 63 g and 65 g; stalk weight: 45.1 g and 43.8 g; plant length: 1273 mm and 2157 mm; shoot centre of gravity: 698 mm and 968 mm; slenderness ratio 147 and 215, respectively. For big bluestem and Spartina pectinata the largest values were for slenderness ratio and for phase II amounted to 403 and 410, respectively but most other parameters were the smallest values. Regarding the shoots’ growth, the greatest influence was on the stalks by increasing their lengths more than their diameters. The highest difference in the plant length between harvest terms was observed for Spartina pectinata which increased from 793 mm to 2257 mm (by 185%). The lengths of the Jerusalem artichoke, miscanthus and big bluestem plants also significantly increased: from 1345 mm to 2920 mm (117%), 1214 mm to 2065 mm (70%) and 1064 mm to 1779 mm (67%), respectively. Positive correlation coefficient values between parameters (shoot weight, leaf weight, stalk weight and plant length) indicate that to characterize of plant shoots the shoot mass and plant slenderness could be used. The Rosin-Rammler function fit the chopped plan material size distribution data with an R 2 = 0.909–0.991. All the biomass particle sizes belonged to the “very poorly sorted” category (2.00 mm ≤ σ ig ≤ 4.00 mm), and the particle size distributions were “fine skewed” (0.1 ≤ GS is ≤ 0.3) and “mesokurtic” (0.90 ≤ K gs ≤ 1.11). For grasses relation of particle sizes vs. moisture for phase II (August for Spartina and big bluestem or October for miscanthus) was inverted to phase I (June) with slope coefficients −0.11 and 0.09, respectively. For leaf plants direction of the relation was preserved, wherein for phase II (all plants harvested in October) the growth dynamic was lower than for phase I and slope coefficients of the lines were 0.17 and 0.04, respectively. Moisture content of leafy plants was high, and its distribution along the shoots’ heights was different than that for grasses. Varied values of particle size and weight of plant components, together with the change in moisture along the height of the plants, will impact the diversity of the dynamic loads of elements and working units of forage harvesters and can be useful to explain these results.

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.

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.