Large Wood Particles Research Articles

Development of drum wood-cutting machines construction

Problem. The wood harvested in forests is increasingly being used as an alternative fuel to replace fossil hydrocarbons for heat and electricity generation on an industrial scale and in everyday life as of today. Currently, the need and importance of developing the means of producing wood biomass has been highlighted even by law. Therefore, it is an important and timely task to improve high-performance wood-shredding machines for the technological wood chips production, from which heat can be obtained in various ways. Goal. The purpose is to improve the process of the technological wood chips production on drum cutting machines. Methodology. Solving the tasks involved improving the conditions for cutting wood with a drum knife and additional grinding of too large wood particles with the steps of the calibration stepped sieve in order to obtain technological wood chips of the required size and quality. Results. Technical solutions for improving the process of producing technological wood chips on a drum cutting machine are proposed, which improve the quality of technological wood chips and increase the productivity of obtaining wood particles of the required sizes. Originality/Novelty. Technical solutions were formed on the basis of the improvement of two areas of wood shredding: in the area of interaction of unshredded wood with the drum knife and in the area of interaction of oversized wooden crushed particles with the steps of the stepped sieve (which work as additional cutting blades). Practical value. The application of the proposed technical solutions will make it possible to increase the efficiency of technological wood chips production of the required size and quality on a drum cutting machine.

Fast torrefaction of large biomass particles by superheated steam: Enhanced solid products for multipurpose production

Conventional torrefaction technology upgrade biomass for improved storage or as pretreatment prior to combustion or pyrolysis, and are generally performed on small-scale particles. Superheated steam (SHS) as the carrier gas and sole heat source was proposed to heat biomass rapidly and evenly while generating intensively torrefied biomass. This work revealed the potential of SHS torrefaction to upgrade large wood particles (Φ = 30 mm, H = 60 mm), to improve the feedstock suitability and expand products diversity in torrefaction technology. The effects of SHS torrefaction at different depths in large particles were investigated. A torrefaction time of 30 min was deemed capable of upgrading even the inner sections of large particle to have appropriate fuel properties. The HHV of the torrefied biomass enhanced by 50% reaching 28.76 MJ kg−1. Combustion and pyrolysis behaviour of torrefied biomass demonstrated their properties as benign fuel and pyrolysis feedstock, respectively. Moisture absorption (from 13.52 to 3.42 wt%) and grindability results (386.96–10.52 kWh ton−1) indicated that large particles from SHS torrefaction were easy for handling, transportation, and storage. The investigation of physicochemical properties at different depths of the torrefied biomass helped to understand SHS torrefaction behaviour in large biomass particles, hence, to control the reaction extent in the desired end product.

Fluvial transport of coarse particulate organic matter in a coastal mountain stream of a rainy‐temperate evergreen broadleaf forest in southern Chile

AbstractCoarse particulate organic matter (CPOM, i.e. particles such as leaves, wood fragments, twigs, branches, flowers, seeds and fruits) in aquatic systems influences the flow, provides an important food source, and at the catchment scale, may significantly contribute to total carbon export. CPOM exports have rarely been quantified in subtropical, broadleaf forest streams. We captured CPOM in Bunte traps in the rainfall‐dominated Vuelta de Zorra stream in southern Chile to (a) propose a novel classification to characterize the different CPOM components, (b) analyze the frequency of each matter class (i.e. leaves, wood fragments, and ‘others’) and its seasonal variability, (c) quantify the CPOM transported, (d) derive a model to quantify CPOM transport rates, and (e) compare the transported CPOM data with those from a unique long‐term (> seven years) large wood monitoring dataset. Results showed that leaves were significantly more abundant than other types of CPOM in all seasons. The dry CPOM transport rate ranged over three orders of magnitude, and there was a significant relationship with mean discharge. Mean dry CPOM yield for the study period 2015–2017 was 4.6 kg/ha/yr when normalizing to the total forested catchment area. The 2009–2018 decadal average yield was 6.8 kg/ha/yr when normalizing to the total forested catchment area. These values are similar to measurements from deciduous and coniferous forests in streams in the United States and the Brazilian Mato Grosso and ~1/10 of the yields obtained in a Swiss torrent. Over a three‐year period, the CPOM exports in Vuelta de Zorra ranged between 13 and 36% of the exported large wood (particles with diameters ≥ 100 mm and length ≥ 1 m) exports. Our data collected from an underrepresented area improve the understanding of global carbon budgets and cycling. © 2020 John Wiley & Sons, Ltd.

Ignition of wood and coal particle mixtures in conditions of steam and water boiler furnaces

The results of experimental studies of the ignition processes of a large set of particles (from 100 to 500) of wood-coal composite fuels under conditions of high-temperature radiation-convective heating are presented. The ignition of wood-coal fuel mixture fuel particles was studied under the conditions of their free fall along the quill ceramic cylinder passage in a high-temperature oxidizing medium (air). Such a configuration provides the conditions that most closely match the heating conditions of actual furnaces of heat generating installations.The experiments have been carried out on the mixtures of particles of subbituminous coal (that is quite typical of coal-fired power industry) with the particles of woody biomass of three types: birch, pine and larch, which are widely spread in the territory of many states of the northern part of the Earth hemisphere. The recording of the heating and ignition processes of the fuel mixture particles was carried out with a high-speed Photron FASTCAM CA45 (500 fps) camera. The air temperature in the passage along which the particles moved varied in experiments from 873 K to 1273 K. The purpose of the experiments performed was the ignition delay time (tign). The main variable factors are the ambient temperature and the concentration of woody components. The consistent errors in determining the main characteristics of the process did not exceed 5%, the random ones did not exceed 13%. The size of coal particles in the experiments did not exceed 60 μm, and of the wood - 5 mm.It has been established that in such a fuel system one of the fuel components of the coal particle is “conducting” (or leading), and the second is “conducted” in the reaction of the thermochemical response of the fuel mixture with air oxygen. According to the results of experimental studies, the ignition delay times for the wood-coal particle mixtures have been stated. The increase in the concentration of small-sized coal particles in fuel mixtures from 0% to 100% leads to the decrease in the entire induction period (up to 20%) at the relatively cold temperatures.It was also found that with typical sizes of coal particles up to 60 μm, stable ignition of sufficiently large wood particles (up to 5 mm), present in the mixture, is provided. The conditions and characteristics of ignition of wood-coal mixtures hardly depend on the type of wood, which is the second component of the mixture.According to the results of the research conducted and following the requirements for optimizing the processes of fuel combustion, the use of mixed coal- and wood-based fuels in boilers of large and small power plants is justified.

Properties of flat-pressed wood plastic composites as a function of particle size and mixing ratio

This paper presents the effects of particle size and mixing ratio on the properties including physical, mechanical, and decay resistance of wood plastic composites (WPCs). In addition, it also presents the effects of immersion temperatures on water absorption (WA) and thickness swelling (TS) of the WPCs. WPCs with a thickness of 6 mm were fabricated from Albizia richardiana King & Prain wood particles and recycled polyethylene terephthalate (PET) by the flat-press method. To prepare the WPCs, two different wood particle sizes (0.5–1.0 and 1.01–2.0 mm) were used along with four different mixing ratios (w/w). Subsequently, the physical properties include density, moisture content, WA, and TS, and mechanical properties include modulus of elasticity (MOE) and modulus of rupture (MOR) of the produced WPCs was evaluated. Furthermore, decay resistance was evaluated by the weight loss percentage method. Moreover, the effects of immersion temperatures on WA and TS of WPCs after 24 h of immersion in water at three different temperatures, i.e., 25, 50, and 75 °C were investigated. Results showed that the wood particle size had impact on WPC’s density (only 6% decreased with the increase of particle size); however, the density decreased by 29% when the wood particle content increased from 40 to 70%. The WA and TS gradually increased with the increase of particle content and decrease of particle size. In addition, WA and TS increased proportionately with increasing immersion temperature from 25 to 75 °C. Furthermore, the highest MOE (2570 N/mm2) was found for the WPCs fabricated from large wood particles having the ration of 50:50 (wood particle:PET). For decay resistance, WPCs consisted of larger particles and higher PET content showed greater resistance against decay. Therefore, it is comprehensible that fabrication of the WPCs from 50% large particles and 50% PET is technically feasible and further improvement of WPC performance like enhancement of MOE and reduction of density using coupling agent and agricultural waste fibers, respectively, in the WPC formulation is recommended.

Pyrolysis of large mallee wood particles: Temperature gradients within a pyrolysing particle and effects of moisture content

Temperature profiles inside a large pyrolysing particle were studied and are reported in this paper. Mallee trunks of similar diameter from the same tree were used to prepare cylindrical samples with 40mm length. A fluidised-bed reactor was used to pyrolyse the large particles. The temperature profiles inside the particles were recorded during pyrolysis to allow the calculation of corresponding heating rate profiles inside the particle. The effects of moisture were studied by pyrolysing some particles with 15 to 20% moisture content. The temperature profiles obtained from the pyrolysis of dry and wet samples have been compared to identify the possible effects of moisture on the temperature profiles. A possible change in the thermal conductivity of the wood was identified around 100°C, which caused a peak in the heating rate profile. Some possible exothermic peaks were observed at around 325°C and 425°C. A peak in the heating rate profile at around 200°C in the case of the pyrolysis of wet particles was believed to be related to the changed 3-D macromolecular structure of the biomass in the presence of moisture. Some yields of tar and char along with other analytical results were presented to support our observations on the temperature profiles. Our results indicate that moisture can potentially alter the overall pyrolysis reactions and product distribution, in particular through changes in the 3-D macromolecular structure of biomass.

Experimental study of wood char gasification kinetics in fluidized beds

During gasification two steps take place. The first one is pyrolysis and the second one is gasification of the char that remains back after pyrolysis. The second step is slower than the first one, so this step is the limiting factor in designing fluidized beds. Kinetic data for designing fluidized beds are necessary. The paper describes gravimetric measurements directly applied to fluidized bed with large sample sizes. The samples are char of 6 mm wood pellets and 10–40 mm wood cubes in order to directly measure ”apparent kinetics”. The parameters examined in this paper are particle size, product gases (= hydrogen) in the gasification medium, type of wood and differences in CO2/steam gasification. The results are presented as Arrhenius diagrams and half-value period diagrams. The most important parameters are the temperature and product gases (hydrogen) in the gasification agent. The particle size seems to be less important for large wood particles as the measurements do not show significant differences for gasifying char of wood cubes 10–40 mm. The half-value periods for gasification of char from wood cubes (10 mm - 40 mm) with 100% steam at atmospheric pressure lie between 1000 s at 1023 K and 300 s at 1173 K. For char of 6 mm wood pellets the half-value periods lie between 1900 s at 1023 K and 250 s at 1173 K. The reaction is most likely in pore diffusion regime.

Simplification of devolatilization models for thermally-thick particles: Differences between wood logs and pellets

Many phenomena affects devolatilization of relatively large wood particles, e.g. wood pellets and logs, including mass and heat transfer, chemical reactions and physical transformation such as shrinkage. Many studies investigated the importance of these phenomena through detailed mathematical models at particle scale, but the models need to be simplified at a certain degree to be implemented into large-scale simulation for gasifiers and boilers. This paper first presents how each physical and chemical parameter should be modelled for wood logs (low density and anisotropic) and wood pellets (high density and isotropic) through parametric studies with a detailed particle simulation. They required different sub-models for effective thermal conductivity and heat of reactions due to the difference in isotropy of particles between pellets and logs. Then, we demonstrated that a constitutive equation, i.e. analytical solution of the shrinking core model, is sufficient to express devolatilization rate of thermally-thick particles at the temperature of 1173K with proper sub-models of physical and chemical parameters. The constitutive equation agreed better with experimental data of wood log than wood pellets, mainly because of the error caused during the consideration of the effect of convective cooling of char layer on thermal conductivity. Both detailed and simplified particle models were validated with the experimental data in an isothermal macro thermogravimeter allowing devolatilization of large particles.

An experimental and theoretical investigation on torrefaction of a large wet wood particle

A competitive kinetic scheme representing primary and secondary reactions is proposed for torrefaction of large wet wood particles. Drying and diffusive, convective and radiative mode of heat transfer is considered including particle shrinking during torrefaction. The model prediction compares well with the experimental results of both mass fraction residue and temperature profiles for biomass particles. The effect of temperature, residence time and particle size on torrefaction of cylindrical wood particles is investigated through model simulations. For large biomass particles heat transfer is identified as one of the controlling factor for torrefaction. The optimum torrefaction temperature, residence time and particle size are identified. The model may thus be integrated with CFD analysis to estimate the performance of an existing torrefier for a given feedstock. The performance analysis may also provide useful insight for design and development of an efficient torrefier.

Thermoplastic starch/wood composites: Interfacial interactions and functional properties

Thermoplastic starch (TPS)/wood composites were prepared from starch plasticized with 36wt% glycerol. The components were homogenized by dry-blending, extruded and injection molded to tensile bars. Tensile properties, structure, deformation, water adsorption and shrinkage were determined as a function of wood content, which changed between 0 and 40vol% in 7 steps. The modification of TPS with wood particles improves several properties considerably. Stiffness and strength increases, and the effect is stronger for fibers with larger aspect ratio. Wood fibers reinforce TPS considerably due to poor matrix properties and strong interfacial interactions, the latter resulting in the decreased mobility of starch molecules and in the fracture of large wood particles during deformation. Strong interfacial adhesion leads to smaller water absorption than predicted from additivity, but water uptake remains relatively large even in the presence of wood particles. The shrinkage of injection molded TPS parts is very large, around 10%, and dimensional changes occur on a very long timescale of several hundred hours. Shrinkage decreases to a low level already at 15–20vol% wood content rendering the composites good dimensional stability.

Experimental investigation of intraparticle secondary reactions of tar during wood pyrolysis

This study experimentally investigated intraparticle secondary reactions of tar during the pyrolysis of woody biomass. For this, pyrolysis products (gas, char, and tar) derived from Japanese cypress sawdust (particle size<1mm) and Japanese cypress wood cylinders (8mm in diameter and 9mm long) were compared. The samples were pyrolyzed in a thermobalance under argon atmosphere. The final reactor temperature was 600°C, and the heating rate was 0.5K/s. Under these conditions, the difference between the sawdust and wood cylinder is the intraparticle secondary reactions of tar. The tar yield of the wood cylinder decreases, whereas its total gas and char yields increase when compared with those of the sawdust. These results indicate that intraparticle secondary reactions of tar, which include intraparticle tar decomposition to form gases and polymerization to form char, occur during the pyrolysis of the wood cylinder. It is found that the intraparticle tar decomposition progresses between 400 and 500°C, which is lower than the homogeneous cracking temperature of tar. This observation suggests that the intraparticle tar decomposition can occur heterogeneously on the surface of the microporous char which acts as a catalyst. This study shows that the intraparticle secondary reactions of tar play an important role in the pyrolysis of large wood particles. Moreover, these reactions have the potential to achieve tar reduction in biomass gasification without any additional tar removal process.

Gas transport properties of compost–woodchip and green waste for landfill biocovers and biofilters

Because methane is a potent greenhouse gas emitted from landfills, there is considerable interest in landfill cover materials and biofilters for methane oxidation. Compost and green waste are used as biocovers and biofilters, but the gas transport properties of these materials are not well understood. Large wood particles and high organic matter content are typical for compost and green waste, which will affect air-filled porosity (ɛ), relative gas diffusion coefficient (Dp/D0) and air permeability (ka).Gas transport properties were measured for compost with wood particles >4mm (compost–woodchip) and green waste using repacked samples and intact cores, collected from a landfill biocover and biofilters. The widely used Millington–Quirk model predicted Dp/D0 poorly, particularly for dry conditions (ɛ>0.60). Models that assumed an inactive air-filled pore space through which gases cannot diffuse fitted Dp/D0 data much better: the Troeh model was best with root mean square error three to four times smaller than the Millington–Quirk model. Several models were evaluated for describing ka data, but none were able to match the highly variable data trends well. In some intact cores the relationships between Dp/D0 and ɛ, and ka and ɛ suggested the existence of dual-domain porous media with macropores. By examining gas transport properties of compost samples with and without wood particles, wood particles >4mm were found to increase the total porosity from 0.49 to 0.79 and ka by as much as two orders of magnitude, while Dp/D0 were altered by less than 40%.

Gas products from intra-particle tar decomposition of pyrolysis of large wood particles

Gas products from intra-particle tar decomposition of pyrolysis of large wood particles

Modelling of pyrolysis of large wood particles

A fully transient mathematical model has been developed to describe the pyrolysis of large biomass particles. The kinetic model consists of both primary and secondary reactions. The heat transfer model includes conductive and internal convection within the particle and convective and radiative heat transfer between the external surface and the bulk. An implicit Finite Volume Method (FVM) with Tridiagonal Matrix Algorithm (TDMA) is employed to solve the energy conservation equation. Experimental investigations are carried out for wood fines and large wood cylinder and sphere in an electrically heated furnace under inert atmosphere. The model predictions for temperature and mass loss histories are in excellent agreement with experimental results. The effect of internal convection and particle shrinkage on pyrolysis behaviour is investigated and found to be significant. Finally, simulation studies are carried out to analyze the effect of bulk temperature and particle size on total pyrolysis time and the final yield of char.

Wood flour filled PP composites: adhesion, deformation, failure

AbstractPoly(propylene) (PP) wood composites were prepared in a wide composition range from 0 to 70 wt% wood content. Matrix/wood adhesion was improved by the introduction of two maleinated polypropylenes (MAPPs) with different molecular weights and functionality. MAPP/wood ratio changed from 0 to 0.25 in 0.05 steps. Mechanical properties of the composites were characterized by tensile testing, while their fracture resistance was determined with instrumented impact measurements. Micromechanical deformation processes were followed by acoustic emission and volume strain measurements, which were supported by scanning electron microscopy done on the broken surface of fractured samples. The results show that stiffness increases with wood content and it does not depend very much either on the type or the amount of the functionalized polymer used. However, ultimate tensile properties are strongly influenced by the amount and properties of MAPP; larger molecular weight and smaller functionality are more advantageous both for strength and impact resistance. The optimum MAPP/wood ratio was found to be around 0.05 in accordance with some literature data. Because of their large size, wood particles debond very easily from the matrix leading to volume increase and catastrophic failure at small deformations. When adhesion is improved by the introduction of MAPP, large wood particles fracture thus also contributing to the failure of the composite. At large wood content considerable aggregation of the particles may take place leading to inferior strength. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Effect of fuel properties on biomass combustion: Part I. Experiments—fuel type, equivalence ratio and particle size

Moving bed combustion is commonly used for energy conversion of biomass. Conditions on the moving bed can be conveniently represented by a time dependent fixed bed. The present work experimentally investigates the combustion of four biomass materials having different fuel properties in a fixed bed under fuel-rich conditions. Temperature, gas composition and mass loss curves identified two distinct periods as the combustion progresses in the bed: the ignition propagation and char oxidation. The effects of bulk density, particle size and air flow rate on the combustion characteristics during the two periods are interpreted by using the ignition front speed, burning rate, percentage of mass loss, equivalence ratio and temperature gradient. Different channelling of air was observed for small miscanthus pellets and large wood particles due to the fast propagation of the ignition front around a channel. The elemental ash composition was also analysed, which explained the sintered agglomerates of miscanthus ashes in terms of alkali index.

05/02586 Energy production from biomass pyrolysis: a new coefficient of pyrolytic valorisation

The influence from structural changes, heat transfer properties of dry wood and pyrolysis mechanism on the pyrolysis of large wood particles were studied. Measurements of temperature distribution and mass loss were performed on cylindrical samples of dry birch wood during pyrolysis in an inert atmosphere at 700°C. A model of wood pyrolysis was modified to include structural changes. Comparisons of measurements and model simulations show that the inclusion of a shrinking model reduces the time of pyrolysis substantially. The varying interior heating rate was found to influence the choice of pyrolysis mechanism. Of four pyrolysis mechanisms found in literature, only one was found to be in agreement with the measurements.

04/01482 Pyrolysis of large wood particles: a study of shrinkage importance in simulations: Bellais, M. et al. Fuel, 2003, 82, (12), 1541–1548

04/01482 Pyrolysis of large wood particles: a study of shrinkage importance in simulations: Bellais, M. et al. Fuel, 2003, 82, (12), 1541–1548

Pyrolysis of large wood particles: a study of shrinkage importance in simulations ☆

Shrinkage models have been developed and included in a model for the pyrolysis of large wood particles. Shrinkage is modelled in three different ways: uniform shrinkage, shrinking shell and shrinking cylinders. These models and a reference model without shrinkage are compared with experimental data for mass loss versus time during pyrolysis of birch cylinders at different temperatures. In the experiments a wood particle was introduced into a pyrolysis furnace held at constant temperature. The particle mass and volume were recorded using a balance and a video camera. Uniform shrinkage slows down the pyrolysis whereas shrinking shell and cylinder models enhance the pyrolysis rate. The effect was sufficiently small to be neglected given the uncertainty about some wood physical properties.

Measurements and particle resolved modelling of the thermo- and fluid dynamics of a packed bed

The objective of this study is to investigate experimentally and numerically into heat-up, drying and pyrolysis of a packed bed consisting of large single particles. The novelty of the current approach is that the numerical model contrary to continuum mechanic approaches considers a packed bed as an ensemble of a finite number of particles, which may have different material properties or sizes. The heat-up, drying and pyrolysis process of each particle is described sufficiently accurate by a set of one-dimensional and transient differential conservation equations for mass and energy. Applying this model to all particles, including interactions between them, of a packed bed forms the entire backed bed process as a sum of individual particle processes. The arrangement of particles within a bed defines a void space between the particles. The flow through the void space of a packed bed is modelled as a flow through a porous media taking into account interaction between the solid and the gaseous phase by heat and mass transfer. Experiments for drying and pyrolysis of a packed bed were carried out for validation in a temperature range of T=120–530 °C. The temperatures and the mass loss due to drying and pyrolysis were recorded during the experiments. The measured mass loss of the packed bed due to drying were well predicted by the constant evaporation temperature model of the particles and thus, indicating, that the drying process is transport limited by heat transfer for large wood particles in a temperature range of T=120–530 °C. A comparison between experiments and predictions of pyrolysis yielded reasonable agreement for temperatures above T=300 °C. For temperatures of T≈200 °C the deviations were not acceptable. However, the results show, that a particle resolved approach is well suited to describe packed bed processes.