Producing Wood Chips Research Articles

Wood biomass recovery cost under different harvesting methods and market conditions

ABSTRACT Harvesting woody biomass, often considered a by-product, poses a major challenge in terms of low operational productivity and revenue. However, woody biomass (branches, treetops, and small-diameter trees or SDT) is gaining global attention for its multifaceted uses in soil reclamation, renewable energy production, and carbon offsetting. The operational cost of harvesting woody biomass is a crucial factor influencing the economic feasibility of harvesting and can fluctuate substantially depending on the cost apportioning method used. The objectives of this study were 1) to estimate the cost of producing pulpwood chips from SDT; 2) to examine the factors influencing cost and productivity of whole-tree (WT) and hybrid cut-to-length (Hyb-CTL) treatments; and 3) to compare and estimate the cost of producing sawlog and chips from hardwood pulp with two cost apportioning methods. The total harvesting cost was 53% higher in Hyb-CTL (US$ 17.30 m−3) than that of WT (US$ 11.30 m−3). The cost of producing wood chips from hardwood pulp as a by-product (US$ 3.07 m−3) was half of the cost calculated using the joint-products allocation method (US$ 7.65 m−3). The cost of producing wood chips utilizing exclusive product allocation (US$ 47.53 m−3) was four times the cost of producing sawlogs (US$ 11.23 m−3). This study provides working values that can enable timberland managers and operational foresters to evaluate the cost of harvesting woody biomass under different market conditions (i.e., demand for woody biomass). This study can also aid managerial decisions regarding silvicultural prescriptions and to help efficiently manage stands that have large proportions of SDT.

Stem volume and tree biomass harvested by different thinning intensities from dense and sparse karee stands in Central Bushveld, South Africa

The aim of this study was to determine the aboveground stem volume and tree biomass of the multi-stemmed karee tree (Searsia lancea) for its potential use for producing wood chips and/or pellets. A stratified random sampling was done, by selecting two blocks with both sparse and dense Karee stands. In each block, three sparse and three dense karee stands were identified. Within each block, three thinning treatments of only karee stems (no cutting, 50% cutting and 100% cutting by number of stems) were randomly allocated to the selected stands. The average moisture content of karee wood was 35.43%. A 50% cutting in sparse stands produced a total dry biomass of 8.51 ± 3.63 t ha−1 and stem volume of 11.92 ± 6.28 m3 ha−1, and in dense stands it produced a total dry biomass of 16.05 ± 2.42 t ha−1 and stem volume of 22.97 ± 4.38 m3 ha−1. The 100% cutting (clear-felling) in sparse stands produced a total dry biomass of 10.02 ± 4.48 t ha−1 and stem volume of 14.10 ± 4.01 m3 ha−1, and in dense stands it produced 33.80 ± 2.25 t ha−1 and 60.64 ± 22.97 m3 ha−1. Thus, the clear-felling biomass was significantly higher than that of 50% cutting, which was supported by ANOVA results for tree biomass (p = 0.0078). In contrast, in terms of stem volume, the p-value was 0.08, indicating that 100% cutting was not significantly higher than the 50% cutting treatment. Dense stands were significantly higher than sparse stands in both tree biomass and stem volume comparisons. Generally, this study showed that there is a great potential to utilise stems of karee for biomass.

Roundwood and bioenergy production from forestry: Environmental impact assessment considering different logging systems

The aim of this paper is to analyse the environmental performances of three different extraction systems for forestry considering three different scenarios concerning the valorisation of forest residuals are analysed.The compared tree extraction systems are characterised by felling and processing performed with chainsaw and three different extraction methods: i) by farm tractor equipped with a winch; ii) by skidder and iii) by cable crane. The “Full Tree System” was adopted for all the felling sites; trees were felled and transported to roadside with branches and top intact. For wood chips produced from branches and tops, different scenarios were considered: heat and electricity generation and substitution of wood-chip production.To evaluate the environmental performance the Life Cycle Assessment (LCA) approach was applied. The selected functional unit (FU) is 1 m3 of roundwood; the system boundary involves all the operations carried out in forestry (felling, bunching, extraction, processing, chipping of forest residuals), the transport of the produced wood chips and all the related inputs and emissions. A comparison with previously carried out studies in similar geographic areas were performed.The study's outcomes show how, the environmental results among the different logging systems are not univocal and the best logging system depends on the considered impact category. Though cable yarder is recognised as an extraction method able of reducing the physical impacts on residual stand (wounding) and soil (disturbance and compaction), for 10 of the 12 impact categories evaluated in this study, achieves the worst performances. The logging systems in which the extraction is performed using the tractor and the skidder show the best performance for 6 of the 12 evaluated impact categories. Finally, regarding wood residues utilisation and the impact of particulate matter formation, the energetic valorisation of wood chips does not involve any benefit but involves a worsening of the environmental performances due to wood combustion emissions.

The impact of log surface damage caused by harvester Eucalyptus debarking on pulp value recovery

Mechanised harvesting operations are growing in popularity in South Africa, as motor-manual and manual harvesting operations pose significant health and safety risks to workers. Potential damage inflicted by single-grip harvester feed rollers and delimbing knives on the log surface during debranching and debarking of eucalypts may affect chip size distributions during chip production. Chip size is important as it influences pulp quality and recovery in the kraft pulping process. The study investigated the influence of two mechanised debarking treatments in eucalypts (three feed roller passes and five feed roller passes along the stem surface) with feed-roller-induced log surface damage on pulp value recovery. The two mechanised treatments were compared against chips produced from manually debarked logs with no surface damage. In addition, the effect of two log drying periods (one week and two weeks) and three log classes (base, middle and top logs) on chip quality were also analysed. An economic evaluation was conducted to quantify potential recoverable pulp value losses associated with debarking treatments and log drying periods. Logs subject to manual debarking produced significantly less undesired sized chips than both three-pass and five-pass mechanically debarked logs and therefore had significantly greater pulp value recovery. Mechanically debarked logs had a projected pulp value recovery of R62, R86 and R123 less per bone dry tonne of chips produced from base, middle and top logs, respectively, when compared with manually debarked logs with no log surface damage after a one-week log drying period. Mechanically debarked logs also had a projected pulp value recovery of R77, R40 and R59 less per bone dry tonne of chips produced from base, middle and top logs, respectively, when compared with manually debarked logs with no log surface damage after a two-week log drying period. Logs dried for two weeks also produced significantly less under-sized chips than chips produced from one-week-dried logs and therefore had greater pulp value recovery. However, two-week-dried logs produced wood chips with significantly more over-thick chips than logs dried for one week. The volume of undesirable-sized chips produced during chipping increased with decreasing log size.

Environmental impacts of bioenergy wood production from poplar short‐rotation coppice grown at a marginal agricultural site in Germany

AbstractFor avoiding competition with food production, marginal land is economically and environmentally highly attractive for biomass production with short‐rotation coppices (SRCs) of fast‐growing tree species such as poplars. Herein, we evaluated the environmental impacts of technological, agronomic, and environmental aspects of bioenergy production from hybrid poplar SRC cultivation on marginal land in southern Germany. For this purpose, different management regimes were considered within a 21‐year lifetime (combining measurements and modeling approaches) by means of a holistic Life Cycle Assessment (LCA). We analyzed two coppicing rotation lengths (7 × 3 and 3 × 7 years) and seven nitrogen fertilization rates and included all processes starting from site preparation, planting and coppicing, wood chipping, and heat production up to final stump removal. The 7‐year rotation cycles clearly resulted in higher biomass yields and reduced environmental impacts such as nitrate (NO3) leaching and soil nitrous oxide (N2O) emissions. Fertilization rates were positively related to enhanced biomass accumulation, but these benefits did not counterbalance the negative impacts on the environment due to increased nitrate leaching and N2O emissions. Greenhouse gas (GHG) emissions associated with the heat production from poplar SRC on marginal land ranged between 8 and 46 kg CO2‐eq. GJ−1 (or 11–57 Mg CO2‐eq. ha−1). However, if the produced wood chips substitute oil heating, up to 123 Mg CO2‐eq. ha−1 can be saved, if produced in a 7‐year rotation without fertilization. Dissecting the entire bioenergy production chain, our study shows that environmental impacts occurred mainly during combustion and storage of wood chips, while technological aspects of establishment, harvesting, and transportation played a negligible role.

General productivity model for single grip harvesters in Australian eucalypt plantations

ABSTRACTAustralia’s eucalypt plantation estate (>900 000 ha) has largely been established since 1995. The main species is Eucalyptus globulus producing wood chips for export on a short rotation (~10 years). Two main harvesting methods are used: cut-to-length (CTL) at the stump and infield chipping (IFC). CTL harvesting is typically carried out with single-grip harvesters and forwarders. The study objective was to develop a general productivity model for medium-sized single-grip harvesters performing CTL harvesting at the stump in short-rotation E. globulus plantations under typical Australian operating conditions, as few harvester productivity models have been developed for these plantations. The model was developed from 47 harvester productivity studies carried out in Australian E. globulus plantations. Studies were predominantly short-term counts of the trees cut over at least an hour multiplied by an estimate of mean merchantable tree volume derived from inventory plots measured where the harvester was about to work or an adjacent area. The model developed explained 80% of the variability in harvester productivity (79% was explained by mean tree volume and 1% by harvester engine power). Results from comparable published CTL eucalypt studies generally supported the model. The strength of the relationship suggests the model could be used to estimate harvester productivity for similar site conditions and harvester/harvester head combinations (which represent most Australian E. globulus plantations) where mean merchantable tree volume and harvester engine power were known or estimated.

Controlling moisture content and truck configurations to model and optimise biomass supply chain logistics in Ireland

In the coming years, Ireland will continue to face an increasing demand for wood biomass as a renewable source of energy. This will result in strained supply/demand scenarios, which will call for new planning and logistics systems capable of optimizing the efficient use of the biomass resources. In this study, a linear programming tool was developed which includes moisture content (MC) as a driving factor for the cost optimisation of two supply chains that use short wood and whole trees from thinnings as material feedstock. The tool was designed and implemented to analyse the impact of moisture content and truck configurations (5-axle and 6-axle trucks) on supply chain costs and spatial distribution of the supply materials. The results indicate that the inclusion of wood chips from whole trees reduces the costs of wood energy supply in comparison with only producing wood chips from short wood to satisfy the demand, with 9.8% and 10.2% cost reduction when transported with 5-axle and 6-axle trucks respectively. Constraining the MC of the wood chips delivered to the power plant increases both transport and overall supply chain costs, due, firstly to an increase in the haulage distance and secondly, to the number of counties providing the biomass material. In terms of truck configuration, the use of 6-axle trucks resulted in a 14.8% reduction in the number of truckloads and a 12.3% reduction in haulage costs in comparison to the use of 5-axle trucks across the MC scenarios analysed.

Comparative cost evaluation of heating oil and small-scale wood chips produced from Euro-Mediterranean forests

This work performs a cost evaluation of small-scale produced wood chips from forests in the Euro-Mediterranean region to be used for heating purposes. The study is focused on forests located in the Argençola municipality (Catalonia, northeastern Spain). The use of such easy-to-produce biofuel is appealing since it may be used as a valid substitute of heating oil to produce thermal energy in the same area where it is produced, thus minimizing transportation requirements and reducing dependence on the rising prices of heating oil. Additionally, it allows facing environmental and social concerns related to the current lack of management in the forests under analysis, which has led to an important increase in the biomass stock and wildfires risk. As wildfires in the Euro-Mediterranean region generate important impacts, an average economic cost of wildfires has been evaluated in this paper. The economic assessment of small-scale production and consumption of wood chips as proposed in this study has shown interesting economic benefits when compared with current heating oil prices. Results indicate that it is a realistic option since production costs range from 12.2 €/GJ to 18.5 €/GJ depending on the applied forestry practices, whereas current cost of heating oil is about 23.9 €/GJ. A sensitivity analysis has also been conducted to assess the impact of the data with higher uncertainty on the final results. It has been shown that the key factors that determine the viability of the proposed model are heating oil price, biomass stock growth rate, transportation requirements and applied forest management practices. Results presented prove that wood chips cost is quite independent of fossil fuel prices, thus higher fossil fuel prices greatly favors the use of wood chips when produced and consumed in the same area, thus minimizing transportation requirements. In addition, higher biomass growth rates than those considered in this work may reduce the final cost of small-scale produced wood chips.

Environmental assessment of small-scale production of wood chips as a fuel for residential heating boilers

This work performs a comparative life cycle assessment (LCA) of two fuels for heating boilers, namely wood chips and oil. The LCA methodology allows comparing the environmental impacts of the two analyzed fuels, thus assessing which is environmentally more advantageous. The study is focused on Mediterranean forests located in the Argençola region (Catalonia, northeastern Spain) by applying forest management practices focused to ensure a sustainable exploitation. The direct use of wood chips as a fuel for boilers simplifies notably the number of processes involved in producing such a fuel. The results presented clearly show the environmental benefits of using small-scale produced wood chips instead of fossil oil by analyzing representative impact categories defined by the CML and EDIP methods, even when considering the changes in the carbon stock in the forests under analysis due to the management approach adopted. A sensitivity analysis has also been conducted to assess the impact of the data with higher uncertainty on the final LCA results.

Multi-Objective Buffer Space Allocation with the Cross-Entropy Method

When producing wood chips using a drum chipper, several material, construction, and technological parameters that influence this process need to be observed and controlled. The correct choice of optimal parameters during the production of wood chips is reflected in the amount of used energy deposited within the wood mass. The results of monitoring the thermal characteristics of individually different kinds of wood chips show that biomass using rougher-structured wood fibers is more suitable for larger systems. Dust particles within the wood fractions are undesirable despite however welcome the consistent form and size structures of the wood chips are. Based on the results of computer simulations, real measurements, and testing during the production of wood chips, we found discrepancies between the predicted and actual characteristics of the desired outputted wood fuel. The reasons for the determined discrepancies are stated and commented on. 24 refs. (Received in April 2012, accepted in November 2012. This paper was with the authors 1 month for 2 revisions.)

Comparing hybrid Populus clones for SRF across northern Italy after two biennial rotations: Survival, growth and yield

Short rotation forest (SRF) plantations of hybrid poplars are attractive for Italian farmers due to the availability of public grants and the potential for producing wood chips for energy production. Growth and dendromass yield of new clones for SRF were evaluated after two biennial rotations within a network of experimental fields established in 2003 on three sites of low (Bigarello), medium (Vinovo) and high soil quality (Mira), across northern Italy. Soil preparation, planting density (5900 trees ha −1 ), weed control, tree water status and mechanical harvesting were homogeneous across the sites. Nitrogen fertilization was applied only in Mira (300 kg N ha −1 ). In all sites, survival was high for almost all clones, and stem density increased dramatically, with a decrease of stem dimensions, after the first coppicing. In Bigarello, with limiting soil conditions, there was no significant difference among clone biennial yields, which varied from 10.3 (first rotation) to 14.2 (second rotation) Mg ha −1 in dry matter (dm). In the medium and high quality sites of Vinovo and Mira, there was a significant difference in clone yields, with the new clones performing better than control clones (I-214 and Lux). In Mira, mean biennial yield increased from 30.2 to 40.3 Mg dm ha −1 from the first to second cycle. Preliminary results of new clones on medium and high soil quality need to be further confirmed throughout further coppicing cycles; on a marginal soil, even by using the new clones, poplar SRF is not an advisable option.

Short-Rotation Forest Plantations-Economic Feasibility in Eastern Colorado

ABSTRACT This study examines the economic feasibility of short-rotation intensive culture tree plantations as an alternative crop for farmers and ranchers in eastern Colorado. Numerous wood biomass production scenarios were evaluated using standard economic criteria. All scenarios gave negative economic results even when including a federal subsidy program. The best two scenarios, one irrigated and the other not, applied herbicides and fertilization, and produced wood chips as a product using a 10-year rotation. Compared with other studies land and harvest costs were proportionally less, however unit production costs were higher. The overall economic analysis was most sensitive to changes in yields and market prices. While the economic performance is marginal, rural landowners in eastern Colorado may still wish to consider these plantations given their substantial environmental and sustainability benefits. A reevaluation should be conducted if more comprehensive yield information becomes available or there are changes in technology or market opportunities.

Study of wood chip production from forest residues in Chile

The technical and economic feasibility of producing wood chips from forest residues has been evaluated using a mobile tree chipping machine under different conditions. Some physical and chemical analyses of the chips were carried out and a study made of drying. On the basis of analysis of variables such as price, working hours, transport costs, etc., it was concluded that although the production of wood chips is technically feasible, its economic viability under the conditions investigated depends strongly on the price of alternative fuels and cost of transportation.