• Energy Research

Dry matter losses (DML) and fuel quality changes occurring in storage piles are important parameters for the management of any biomass supply system. This study evaluates the effect of a hot water extraction pretreatment, harvest season, depth in storage pile and initial moisture content on willow biomass fuel quality [moisture, ash, higher (HHV) heating value and lower (LHV) heating value] during storage, and models DML in storage piles based on experimental data. For the summer storage (SS) pile, mesh bags containing freshly harvested chips (FC) were inserted at 0.5–1 m deep in the pile. For the winter storage pile (WS), the mesh bags were filled with FC and hot water extracted chips (HC) with three different initial moisture contents inserted in the shell (<0.45 cm) and the core (1–1.5 m) of the pile. The ash contents through all sampling periods were in the range of 1.1–2.2% for FC and 0.6–2.1% for HC from both the shell and core of the WS pile. Higher ash contents, in the range of 2.1–3.4%, were observed in SS pile. Moisture contents of the storage piles had differing patterns over time. DML was the highest in the SS pile, reaching up to 33.6% after 140 days in storage; in contrast, there was no significant increase in DML over the first winter season. Although DML of FC and HC were in the same range during the initial storage period, DML of HC was 40% lower than FC after 180 days of storage. Higher DML was observed in the core (e.g., 17.3% for FC) compared to the shell (e.g., 12.1% for FC) at the end of the WS trial. There was no particular trend observed between initial moisture and DML. This study suggests that a linear model is sufficient to estimate DML, but a non-linear model may be needed for chips stored in SS piles for 6 months or longer. It also suggests that DML is reduced in storage piles created in winter, and that willow chips kept in SS should be utilized within 2 months for a DML below a 10% threshold.

Dry matter losses (DML) and fuel quality changes occurring in storage piles are important parameters for the management of any biomass supply system. This study evaluates the effect of a hot water extraction pretreatment, harvest season, depth in storage pile and initial moisture content on willow biomass fuel quality [moisture, ash, higher (HHV) heating value and lower (LHV) heating value] during storage, and models DML in storage piles based on experimental data. For the summer storage (SS) pile, mesh bags containing freshly harvested chips (FC) were inserted at 0.5–1 m deep in the pile. For the winter storage pile (WS), the mesh bags were filled with FC and hot water extracted chips (HC) with three different initial moisture contents inserted in the shell (<0.45 cm) and the core (1–1.5 m) of the pile. The ash contents through all sampling periods were in the range of 1.1–2.2% for FC and 0.6–2.1% for HC from both the shell and core of the WS pile. Higher ash contents, in the range of 2.1–3.4%, were observed in SS pile. Moisture contents of the storage piles had differing patterns over time. DML was the highest in the SS pile, reaching up to 33.6% after 140 days in storage; in contrast, there was no significant increase in DML over the first winter season. Although DML of FC and HC were in the same range during the initial storage period, DML of HC was 40% lower than FC after 180 days of storage. Higher DML was observed in the core (e.g., 17.3% for FC) compared to the shell (e.g., 12.1% for FC) at the end of the WS trial. There was no particular trend observed between initial moisture and DML. This study suggests that a linear model is sufficient to estimate DML, but a non-linear model may be needed for chips stored in SS piles for 6 months or longer. It also suggests that DML is reduced in storage piles created in winter, and that willow chips kept in SS should be utilized within 2 months for a DML below a 10% threshold.

Abstract Background The amount of carbon dioxide in the atmosphere has been on the rise for more than a century. Bioenergy crops are seen by the Intergovernmental Panel on Climate Change as an essential part of the solution to addressing climate change. To understand the potential impact of shrub willow (Salix spp.) crop in the northeast United States, effective and transparent life cycle assessment of these systems needs to occur. Results Here we show, ethanol produced from the fermentation of sugars from hot water extract of willow grown on cropland can sequester 0.012 ± 0.003 kg CO2eq MJ−1 for a supply system incorporating summer harvest and storage. Despite decreases in soil organic carbon when willow is instead grown on grassland, the produced fuel still can provide significant climate benefits compared to gasoline. Conclusions Shrub willow converted to ethanol can be a carbon negative source of transportation fuel when the electricity and heat required for the conversion process are generated from renewable biomass. The sequestration of carbon in the belowground portion of the plants is essential for the negative GHG balance for cropland and low GHG emissions in grassland.

Abstract Background The amount of carbon dioxide in the atmosphere has been on the rise for more than a century. Bioenergy crops are seen by the Intergovernmental Panel on Climate Change as an essential part of the solution to addressing climate change. To understand the potential impact of shrub willow (Salix spp.) crop in the northeast United States, effective and transparent life cycle assessment of these systems needs to occur. Results Here we show, ethanol produced from the fermentation of sugars from hot water extract of willow grown on cropland can sequester 0.012 ± 0.003 kg CO2eq MJ−1 for a supply system incorporating summer harvest and storage. Despite decreases in soil organic carbon when willow is instead grown on grassland, the produced fuel still can provide significant climate benefits compared to gasoline. Conclusions Shrub willow converted to ethanol can be a carbon negative source of transportation fuel when the electricity and heat required for the conversion process are generated from renewable biomass. The sequestration of carbon in the belowground portion of the plants is essential for the negative GHG balance for cropland and low GHG emissions in grassland.

Short-rotation coppice (SRC) is an important source of woody biomass for bioenergy. Despite the research carried out on several aspects of SRC production, many uncertainties create barriers to farmers establishing SRC plantations. One of the key economic sources of uncertainty is harvesting methods and costs; more specifically, the performance of contemporary machine methods is reviewed. We collected data from 25 literature references, describing 166 field trials. Three harvesting systems predominate: 127 used single pass cut-and-chip harvesters, 16 used double pass cut-and-store harvesters, 22 used the cut-and-bale harvester, and one study used a cut-and-billet harvester. Mean effective material capacity (EMC) was 30 Mg fresh weight h-1 (cut-and-chip technique), 19 Mg fresh weight h-1 (cut-and-store technique) and 14 Mg fresh weight h-1 (cut-and-bale technique). However, this comparison does not consider engine power, which varies with harvesting technique; cut-and-chip harvesters are by far the most powerful (>200 kW). When limiting harvesters to a maximum engine power of 200 kW, cut-and-chip harvesters achieved the lowest EMC (5 Mg fresh weight h-1), but they also perform a higher degree of material processing (cutting and chipping) than cut-and-store harvesters (only cutting) or than the cut-and-bale harvester (cutting and baling). The trend in commercial machinery is towards increased engine power for cut-and-chip and cut-and-store harvesters. No trends in EMC were documented for the recently developed cut-and-bale harvesting technique, which is presently produced in one version only. Field stocking (5-157 Mg fresh weight ha-1 in the reviewed studies) has a significant effect on harvester EMC. Lower field stocking can constrain the maximum EMC achieved by the machine given that harvesting speed can only be increased to a point. While the reviewed studies did not contain sufficient harvesting cost data for a thorough analysis, harvesting costs ranged between 6 and 99 EUR Mg-1 fresh weight.

Short-rotation coppice (SRC) is an important source of woody biomass for bioenergy. Despite the research carried out on several aspects of SRC production, many uncertainties create barriers to farmers establishing SRC plantations. One of the key economic sources of uncertainty is harvesting methods and costs; more specifically, the performance of contemporary machine methods is reviewed. We collected data from 25 literature references, describing 166 field trials. Three harvesting systems predominate: 127 used single pass cut-and-chip harvesters, 16 used double pass cut-and-store harvesters, 22 used the cut-and-bale harvester, and one study used a cut-and-billet harvester. Mean effective material capacity (EMC) was 30 Mg fresh weight h-1 (cut-and-chip technique), 19 Mg fresh weight h-1 (cut-and-store technique) and 14 Mg fresh weight h-1 (cut-and-bale technique). However, this comparison does not consider engine power, which varies with harvesting technique; cut-and-chip harvesters are by far the most powerful (>200 kW). When limiting harvesters to a maximum engine power of 200 kW, cut-and-chip harvesters achieved the lowest EMC (5 Mg fresh weight h-1), but they also perform a higher degree of material processing (cutting and chipping) than cut-and-store harvesters (only cutting) or than the cut-and-bale harvester (cutting and baling). The trend in commercial machinery is towards increased engine power for cut-and-chip and cut-and-store harvesters. No trends in EMC were documented for the recently developed cut-and-bale harvesting technique, which is presently produced in one version only. Field stocking (5-157 Mg fresh weight ha-1 in the reviewed studies) has a significant effect on harvester EMC. Lower field stocking can constrain the maximum EMC achieved by the machine given that harvesting speed can only be increased to a point. While the reviewed studies did not contain sufficient harvesting cost data for a thorough analysis, harvesting costs ranged between 6 and 99 EUR Mg-1 fresh weight.