Wood Chip Piles Research Articles

Assessment of New Techniques for Measuring Volume in Large Wood Chip Piles

Our work aimed to compare the chip pile volumes calculated by laser ground scanning, UAV technology, and laser ground measurement and also to determine the accuracy, speed, and economic efficiency of each method. The large chip pile was measured in seven different ways: band measurement, laser measurement with Vertex, global navigation satellite system, handheld mobile laser scanner, terrestrial laser scanner, drone, and smartphone with a light detection and ranging sensor. All the methods were compared in terms of accuracy, price, user-friendliness, and time required to obtain results. The calculated pile volume, depending on the method, varied from 2588 to 3362 m3. The most accurate results were provided by the terrestrial laser scanning method, which, however, was the most expensive and the most demanding in terms of collecting and evaluating the results. From a time and economic point of view, the most effective methods were UAVs and smartphones with LiDAR.

Evaluation of the Effect of a Spray Coating Applied on Open-Air-Stored Woodchips

The present study aimed at testing the benefits of protecting woodchips with an acrylic crusting product developed for the coal energy industry. In the test carried out, four conical wood chips piles were built, two consisting of fresh biomass, the other two of dry wood chips. A fourth larger pile was built as a reference. One dry and one fresh pile were superficially treated with 25 kg of protective acrylic solution diluted in 250 L of water, providing an average application of coating agent of approximately 85 g m−2, while the other two worked as controls. To monitor the piles’ temperature variation, thermal sensors were placed in the inner part of the five piles during their construction. Moisture content (MC) and dry matter (DM) variations in woodchip piles were recorded. The piles treated with the coating agent did not show any significant differences with the untreated piles: in wet material, the protective film slightly reduced the moisture dispersal from the pile from evaporation rather than limiting water intake from rain; in dry material, this confirms the inability of the coating agent to limit water intake from rainfall.

Spontaneous ignition of rubber woodchip in Thailand

The self-ignition temperature, the safe pile storage dimension and the activation energy of the rubber woodchip pile were determined by Frank-Kamenetskii approach. The woodchip samples with 278 kg/m3 and 458 kg/m3 of the bulk densities and 10.6% w.b. (wet basis) and 46.1% w.b. of the initial moisture contents were used. The samples were put into the cubic baskets with the widths of 8 cm, 10 cm, and 12 cm and placed in the well-ventilated oven. The results showed that the self-ignition temperatures were varied between 182 °C and 199 °C. The increase in the basket sizes decreased the self-ignition temperatures. The initial moisture content did not affect the self-ignition temperature. The dimension and shape of the rubber woodchip piles affect the self-ignition temperature. The size of the safe storage pile could be larger if the moisture content increased. The activation energy of the rubber woodchip ignition increased when the moisture content increased. The activation energies were 97.9 kJ/mol and 104.2 kJ/mol, for the moisture contents of 10.6% w.b. and 46.1% w.b., respectively.

Beef Cattle Preference and Usage of Environmental Enrichments Provided Simultaneously in a Pasture-Based Environment.

Environmental enrichment can improve livestock welfare through increasing environmental complexity to promote a greater range of natural behaviours. However, there is limited understanding of the need for and impacts of enrichments for extensively managed beef cattle that can sometimes be kept in grassed paddocks devoid of additional natural and artificial features, i.e., 'barren pastures'. This trial assessed which enrichments beef cattle preferred and utilised in a barren paddock environment. Eight groups of seven Angus steers housed on pastured paddocks devoid of natural or artificial features were observed during daylight hours for two days a week over a period of three weeks, after being presented with four enrichments simultaneously: a cattle brush, a piece of hanging rope, a tree stump, and a woodchip pile. Although enrichment use generally decreased over time, the brush, stump, and woodchip maintained a higher level of use than the rope, based on the frequency of interactions and number of displacements around the enrichments (both p < 0.001). This suggests that the brush, stump, and woodchip pile were more valuable resources to the cattle, allowing for grooming and lying behaviours, although oral manipulations also occurred on the stump, woodchip, and rope. The inclusion of these enrichments can increase the complexity of barren pasture environments and allow for the increased expression of natural behaviours, potentially contributing to improved welfare.

Microbial community dynamics during the storage of industrial-scale wood chip piles of Picea abies and Populus canadensis and the impact of an alkaline stabilization agent

Storage of woody biomass in large wood chip piles is unavoidable for biotechnological applications, but comes along with considerable biomass-, energy- and thus, economic losses due to exothermic reactions and microbial degradation. The homogeneous amendment of the storage piles with an alkaline stabilization agent, calcium hydroxide (Ca(OH)2), was found to decrease dry matter loss in Picea abies; for Populus canadensis piles the effects cannot clearly be deduced. Here we investigated the bacterial and fungal communities of industrial-scale wood chip piles (250 m3) of these two different tree species and related them to physicochemical conditions and enzymatic activities after 35 and 120 d, representing short- and long-term storage of the wood chips, respectively. Coming from different wood types (hard vs. softwood), we expected the communities to converge over time, due to similar storage conditions. Despite pH posing selective pressure, we expected a minor Ca(OH)2 effect as already known from previous studies.We found that the effectiveness of Ca(OH)2 addition depended on the wood type that determined both the native microbial seeding community and temperature pattern of all piles, thereby exerting selective forces of differing strength. Generally, a thermophilic community consisting of single fungal and variable bacterial taxa were identified. As expected, the microbial communities from P. abies and P. canadensis converged over time. Biomass loss was connected to C-cycle related enzymatic activities and to the abundance and composition of fungal communities. Chaetomium sp. was identified as potential key taxon determining biomass degradation under the given storage conditions.

Forest chip drying in self-heating piles during storage as affected by temperature and relative humidity conditions

Storing is an important part in the value chain of the energy use of forest chips as severe losses of dry mass and energy content and increases in greenhouse gas emissions may occur. During the storage the temperature in the biomass increases affecting the dry mass loss and the material drying. In a field-scale experiment, we monitored temperature inside two uncovered wood chip piles for 175 days and measured the chip gravimetric moisture content at the beginning and end of the experiment. In the laboratory the drying rate of the wood chips under different temperature and relative humidity conditions was determined. We constructed a new two-dimensional simulation model where water vapor diffusion within the pile, and chip moisture change was solved using a finite volume method. The determined chip drying rate was used as a source term in the simulation. The simulation model results were in close agreement with the experimental data in the middle sections of the pile, whereas the model was not able to describe the chip moisture redistribution in the pile tails. Modeling revealed that the pile size and porosity were important factors in determining the chip drying, which indicates that chip drying can be controlled by management, such as planning of pile dimensions and compaction.

Performance of an Innovative Bio-Based Wood Chip Storage Pile Cover—Can It Replace Plastic Tarps?

There is currently great general interest in reducing the use of fossil-based materials. Fossil-based tarps are still widely used as cover for wood chip storage piles, causing additional waste or requiring further waste treatment in the supply chain. This study aimed to investigate the performance of an innovative bio-based wood chip pile cover compared to conventional treatments (plastic-covered and uncovered) in eastern Finnish conditions. The experiment evaluated the drying process during the storage of stemwood chips during 5.9 months of storage. It included the developments of temperature, moisture content, heating value, energy content, basic density, particle size distribution, and the dry matter losses of a total of six piles. As a result, the forest stemwood chips dried by 11%, with dry-matter losses of 4.3%, when covered with the bio-pile cover. Using the plastic covering, the forest stemwood chips dried by 22%, with dry matter losses of 2.9%. At the end of the experiment, the energy content in plastic-covered piles was 6.1% higher than uncovered piles and 3.1% higher than bio-pile-covered piles. While differences in the key drying performance parameters can be observed, the differences between uncovered piles and those covered with plastic tarps, as well as between the bio-based and the uncovered piles, were not statistically significant. We conclude that the bio-based cover, under the studied conditions, do not render better storage conditions than in current practices. However, our study indicates possible fossil-substitutional benefits by using a bio-based cover, which calls for further R&D work in this matter.

SCREENING AND ISOLATION OF THERMOPHILIC FUNGI OBTAINED FROM THREE SELECTED COMPOST WASTES SITES

Thermostable enzymes have found applications in the improvement of products quality in various industries. Despite the discovery of several microorganisms as potential source of thermostable enzymes, more biodiversity explorations are currently been carried out for high activity enzymes producing isolates. The discovery of new isolates having these characters will allow to efficiently carry out reactions in various industrial processes that involve extreme conditions. This study was aimed to screen and isolate thermophilic fungi from three selected compost wastes sites (Palm oil mill, Wood chip piles and Abattoir dump), and identify potential producers of lipases, cellulases and proteases respectively. The thermophilic fungi were obtained from an equal depth of one meter in all the three collection sites with a temperature range of 40 to 45OC and later cultured at 70 OC. Further experimental screening analysis showed the presences of lipase, cellulase and protease producing fungi present in samples collected from palm oil mill, wood chips pills and abattoir dump site respectively. The isolated fungi were used for enzyme production in submerged fermentation for 10 days at 50OC. Culture filtrate obtained from the medium of production were used for the assessment of enzymatic activity. The highest lipase, cellulase and protease activities were obtained from isolates 3 A (56.56 U/mL), 3A (38.35 U/mL) and 2B (3.0 U/mL) respectively. These isolates with high enzymes activities were identified microscopically as Rhizopus sp., Aspergillus flavus and Neurospora sp. accordingly. We believed that these strains could be further exploited for numerous industrial applications that require thermophilic enzymes.

The potential of calcium hydroxide to reduce storage losses: A four months monitoring study of spruce wood chip piles at industrial scale

The objective of this study was to investigate the effect of an alkaline additive on the storage of wood chips from Norway spruce forest residues. Piles of untreated and calcium hydroxide treated wood chips (250 m3) were set up and investigated for four months. It was demonstrated that adding Ca(OH)2 to moist wood chips decreased the dry matter loss by 6%. This was attributed to the increase of the pH to a level of 8, rendering the habitat less suitable for fungal colonisation. The results suggest the set-up storage strategy as a potential alternative method for preserving wood chips when long term storage is required.

Fuel properties, dry matter losses and combustion behavior of wood chips stored at aerobic and anaerobic conditions

Aerobic and anaerobic storage of wood chips from coniferous forest residues, coniferous energy roundwood and short rotation coppice were investigated regarding dry matter losses, energy losses and changes in fuel properties using several approaches, i.e. a field trial with 90 m3 wood chip piles, small-scale storage containers (0.5 m3) incl. greenhouse gas measurements and miniature bunker silos (1.5–2 m3). After storage, selected fuels were combusted in a 30 kW wood chip boiler and emissions (CO, NOX, TPM) were measured.Dry matter losses in fleece-covered piles were 7%–9% after 153 days of storage. Drying compensated for energy losses. Container trials achieved full anaerobic conditions in the lab reducing dry matter losses to 0.4–2% while preserving fuel properties. Methane emissions during anaerobic storage in containers were low. Anaerobic conditions could not be achieved in outdoor bunker silos due to insufficient airtightness. The mass fraction of H2O in fuels increased in bunker silos by 4.2–10.4% due to precipitation and dry matter losses up to 22% were recorded. During combustion, CO and TPM emissions were often increased significantly with materials that were stored in silos or piles compared to technically dried fuels, most likely due to changes in their woody or physical-mechanical structure and their mass fraction of H2O.Anaerobic storage might in theory be an interesting option to reduce dry matter losses but could not sufficiently be realized during this study using miniature bunker silos. For many applications, aerobic storage in fleece-covered piles seems preferable to anaerobic storage.

Managing self-heating & quality changes in forest residue wood waste piles

As renewable energy initiatives intensify, the benefits of optimizing recycled wood waste and forestry residues for bioenergy generation are clear. Self-heating fires and degradation during outdoor pile storage however continue to result in safety risks and economic losses. Furthermore, the storage dynamics of older wood waste material remain understudied. The following presents the longest continuous North American forestry residue storage trial, comparing the storage characteristics of woodchip piles built with fresh and aged material (previously stored for 20 months). Temperature sensors were placed within industrial woodchip piles (consisting primarily of poplar) at Pineland Nurseries (Manitoba, Canada). Monitoring occurred for 459 days (August 2017–November 2018) where samples were periodically characterized for dry-matter loss, pH, bulk density, particle size, moisture, ash and free sugar content. Significantly higher temperatures were sustained in the aged pile throughout the storage trial compared to the fresh pile where temperatures decreased within a month after an initial thermal spike. Decreased particle size and higher moisture content in the aged material appeared to have the most impact on thermal retention. Microorganism reintegration theory supported our findings where initial sugar content did not correlate with higher initial self-heating in the aged pile. This study highlights several critical considerations for forestry residue pile management.

Assessment of Combustion and Gasification Behavior in a Bubbling Fluidized Bed Reactor: A Comparison between Biomass with and without Chemical Additives

During the storage of biogenic materials for energy utilization, destructions by microbial attacks are inevitable. Besides material degradation, self-ignition of wood chip piles also occurs consistently. Treating the feedstock with, for example, mineral additives such as Dolomite can inhibit the microbial destructions, though such treatment may affect the thermochemical conversion of the fuel particles. This study therefore demonstrates the effect of mixing 4 wt % calcium hydroxide with wood chips used as feedstock in a 20 kW (fuel input) bubbling fluidized bed reactor. The reactor consists of a 100 mm (inner diameter) cylindrical column with 1.0 m height, where both gasification and combustion modes can be applied. Six different tests within equivalence ratios of 0.1–1.1 are conducted, and in each run, both fluidization behavior and quality of the product gas at different reaction temperatures (750–900 °C) are analyzed and compared with the results from wood chips of the same particle size but without the additive. The results show that there is no significant difference in the product gas composition, but evidence shows that the chemical additive impacts on the bed pressure drop over the equivalence ratio tested. The gasification window is increased and the energy value of the product gas is higher with a lower hydrogen content. During the combustion, both the exit gas temperature and oxygen concentration are lower, suggesting that additional light molecules such as water vapor are released during the conversion of biomass mixed with additive.

Forecasting leachate generation from pilot woodchip stockpiles using a three-dimensional transient flow model

Leachate generation from open stockpiles of recycled woodchip materials is potentially harmful to aquatic ecosystems. There is growing interest in using numerical models to simulate leachate generation from outdoor piles, but this requires information about the hydraulic properties of the materials. The objectives of this study were to simulate leachate from woodchip piles with the numerical model HYDRUS-3D and to optimize subsets of parameters for single (SPM) and dual (DPM) pore flow models with the Bayesian Markov Chain Monte Carlo algorithm DREAMZS. Three experimental piles, each approximately 30 m3, were setup with mixtures of either once (coarse) or twice (fine) ground woodchips. Leachate continuously collected over a period of six months was similar across piles. As a result, subsets of optimized flow parameters for the coarse and fine woodchips were not different. Leachate predictions by the two pore flow models were similar and agreed reasonably with the field measurements, as indicated by Nash-Sutcliffe efficiency values greater than 0.6. This result suggests the simpler SPM is adequate for field predictions of leachate. However, leachate was consistently under-predicted by both pore models by 13–27% during rainfall events with more than 1 cm in 6 h. The optimized flow models can be used as a tool for studying pile management strategies.

Effect of particle granularity on smoldering fire in wood chips made from wood waste: An experimental study

SummaryFires in wood waste storages cause financial losses, are difficult to extinguish, and emit large amounts of fire effluents. The mechanisms related to fires in wood chip piles are not well elucidated. To find suitable preventive measures for handling such fires in wood waste, a better understanding of the physical properties of wood waste is needed. The present study investigates how granularity affects mechanisms of smoldering fire and transition to flaming in wood chip piles. Eighteen experiments with samples inside a top‐ventilated, vertical cylinder were conducted. Heating from underneath the cylinder induced auto‐ignition and smoldering fire, and temperatures and mass loss of the sample were measured. The results showed that granularity significantly affects the smoldering fire dynamics. Material containing larger wood chips (length 4‐100 mm) demonstrated more irregular temperature development, higher temperatures, faster combustion, and higher mass losses than material of smaller wood chips (length <4 mm). The larger wood chips also underwent transition to flaming fires. Flaming fires were not observed for small wood chips, which instead demonstrated prolonged and steady smoldering propagation. The differences are assumed to be partly due to the different bulk densities of the samples of large and small wood chips affecting the ventilation conditions. Increased knowledge about these combustion processes and transition to flaming is vital to develop risk‐reducing measures when storing wood chips made from wood waste in piles.

Overhead Protection Increases Fuel Quality and Natural Drying of Leaf-On Woody Biomass Storage Piles

Short-rotation woody crops (SRWC) have the potential to make substantial contributions to the supply of biomass feedstock for the production of biofuels and bioproducts. This study evaluated changes in the fuel quality (moisture, ash, and heating value) of stored spring harvested shrub willow (Salix spp.) and hybrid poplar (Populus spp.) chips with respect to pile protection treatments, location within the storage piles, and length of storage. Leaf-on willow and poplar were harvested in the spring, and wood chips and foliage with moisture content in the range of 42.1% to 49.9% (w.b.) were stored in piles for five months, from May to October 2016. Three protection treatments were randomly assigned to the piles. The control treatment had no cover (NC), so piles were exposed to direct solar radiation and rainfall. The second treatment had a canopy (C) installed above the piles to limit direct rainfall. The final treatment had a canopy plus a dome aeration system (CD) installed over the piles. Covering piles reduced and maintained the low moisture content in wood chip piles. Within 30 days of establishment, the moisture content in the core of the C pile decreased to less than 30%, and was maintained between 24%–26% until the end of the storage period. Conversely, the moisture content in the NC piles decreased in the first two months, but then increased to the original moisture content in the core (>45 cm deep) and up to 70% of the original moisture content in the shell (<45 cm deep). For all the treatments in the tested conditions, the core material dried faster than the shell material. The higher heating value (HHV) across all the treatments increased slightly from 18.31 ± 0.06 MJ/kg at harvest to 18.76 ± 0.21 MJ/kg at the end of the storage period. The lower heating value (LHV) increased by about 50% in the C and CD piles by the end of the storage period. However, in the NC piles, the LHV decreased by 3% in the core and 52% in the shell. Leaf-on SRWC biomass stored in piles created in late spring under climatic conditions in central and northern New York showed differing moisture contents when stored for over 60–90 days. Overhead protection could be used to preserve or improve the fuel quality in terms of the moisture content and heating value if more than two months of storage are required. However, the implementation of such management practice will depend on whether the end users are willing to pay a higher price for dryer biomass and biomass with a higher LHV.

Comparative analysis of bark and woodchip biomass piles for enhancing predictability of self-heating

Along with the inherent woody biomass supply needs within the bioenergy industry, self-heating risks associated with stored biomass piles continue to threaten worker safety, have the potential to cause serious damages to plant infrastructure and can result in the complete loss of feedstock stores. Though bark and woodchips can both be utilized as a feedstock, their physical and chemical properties differ significantly. Self-heating risks and dynamic pathways leading up to such events were therefore expected to vary as well. A large-scale industrial storage trial was conducted in Point Tupper, Nova Scotia along with comparative physical tests to determine whether wood self-heating models could be used successfully for piles primarily consisting of softwood bark (from local sawmills). Modeling with established bark variables yielded accurate predictions of pile temperature when compared with actual temperature sensor data (R2 = 0.94). Following the start of the simulation (Day 1 = November 10, 2015), it was found that the average bark pile temperature peaked at 58.4 °C on Day 33 with varying heating rates between the pile layers. The woodchip pile simulation in comparison, was found to peak on Day 23 with an average temperature of 64.9 °C. A sensitivity analysis highlighted significant self-heating variables, revealing those associated with microbial activity as being some of the most influential on temperature profile during initial storage stages. Our overall results indicated that bark piles heat at a slower rate compared to woodchips while retaining more heat over time. Wood parameters are insufficient for modelling bark pile dynamics and the use of specific bark parameters is necessary.

Mapping Three-dimensional Moisture Content of Wood Chip Piles for Energy Production

ABSTRACT The aim of this study was to apply geostatistics to predict the spatial pattern of variations in moisture content of eucalyptus wood chip piles to generate subsidies for adequate sampling and material handling. Wood chip piles were installed in three different storage cycles using newly cut material for 7, 30, and 60 days. Sampling was performed in axial (top, middle, and base) and lateral positions, so that all samples were georeferenced in relation to the distance from the ground and the center of the pile. Moisture values were submitted to geostatistical analysis and kriging. The results confirmed the spatial dependence of moisture content over the piles stored at 7 and 30 days; however, the effect of rainfall was crucial to reduce the spatial dependence of moisture content. The results showed that geostatistics is a useful tool for the creation of reliable sampling protocols.

Influence of the chip format on the development of mass loss, moisture content and chemical composition of poplar chips during storage and drying in open-air piles

In order to use wood chips from short-rotation coppices cost-efficiently, it is necessary to optimise the storage process depending on the planned use of the chips. The goal of all storage is to ensure low dry matter losses. Wood chips intended for energy-related use should have low moisture and ash contents, as well as a low fines fraction. If wood chips are to be put to material use, e.g. as peat substitute, a reduction of the C:N ratio during storage is necessary.The objective of this study was to identify favourable storage conditions to ensure low dry matter losses and high quality of wood chips for energy-related use. Furthermore, the study aimed to examine, whether disintegration processes during storage change the C:N ratio to such an extent that wood chips can be used as raw material for plant substrates.Three wood chip piles with different chip formats (small, medium, large - produced with a forage harvester and a mower chipper) were stored for seven months and compared regarding storage properties and physicochemical parameters.After seven months, medium wood chips displayed with a moisture content of 26w-%, dry matter losses of only 17% and a fines fraction of <5w-% the best results for energy-related use. Small chips with dry matter losses of 19%, moisture contents of 34w-% and a fines fraction of 12.6w-% displayed very unfavourable conditions for energy-related use. However, small chips showed the highest reduction of the C:N ratio (from 145:1 to 57:1) due to the storage process.

Moisture content recognition for wood chips in pile using supervised classification

Wood chips moisture content (MC) is a key parameter for controlling the biofuel product qualities and properties. Since no knowledge-based model is available to recognize MC, machine learning methods are promising techniques to design black-box models for MC prediction or recognition. As wood permittivity strongly changes in the presence of water, an electromagnetic module is used to probe the reflectivity of wood chip piles. In the present paper, the recognition of three wood chip piles of different MC categories is performed using support vector machines (SVMs). SVM-recursive feature elimination is implemented to rank and select reflection coefficients to design optimized linear SVM classifiers that attribute MC class of wood chips in a pile. Experiments show that the proposed approach is effective and requires a limited computational power. The global classification performance exceeds 95%.

Dry matter losses and quality changes during short rotation coppice willow storage in chip or rod form

This study compares dry matter losses and quality changes during the storage of SRC willow as chips and as rods. A wood chip stack consisting of approximately 74 tonnes of fresh biomass, or 31 tonnes dry matter (DM) was built after harvesting in the spring. Three weeks later, four smaller stacks of rods with an average weight of 0.8 tonnes, or 0.4 tonnes DM were built. During the course of the experiment temperature recorders placed in the stacks found that the wood chip pile reached 60 °C within 10 days of construction, but the piles of rods remained mostly at ambient temperatures. Dry matter losses were calculated by using pre-weighed independent samples within the stacks and by weighing the whole stack before and after storage. After 6 months the wood chip stack showed a DM loss of between 19.8 and 22.6%, and mean losses of 23.1% were measured from the 17 independent samples. In comparison, the rod stacks showed an average stack DM loss of between 0 and 9%, and between 1.4% and 10.6% loss from the independent samples. Analysis of the stored material suggests that storing willow in small piles of rods produces a higher quality fuel in terms of lower moisture and ash content; however, it has a higher fine content compared to storage in chip form. Therefore, according to the two storage methods tested here, there may be a compromise between maximising the net dry matter yield from SRC willow and the final fine content of the fuel.