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Highlights In a time when global initiatives to lower CO2 emissions are accelerating the shift towards bio‐based products, various efforts are being made to develop wood plastic composites (WPCs) and similar bio‐composites using a variety of raw materials. This paper first showcases benchmark material properties serving as standards and models the composition, for polypropylene‐based WPCs integrating wood flour and maleic anhydride‐modified polypropylene. Subsequently, by applying statistical modeling techniques, we demonstrate an adaptive experimental design that efficiently and rapidly adjusts formulations. Beginning with an empirical dataset (24 samples), we established high‐performing models that articulate the individual contributions of the constituents on ten vital properties of WPCs. Our adaptive experimental design, leveraging nonlinear partial least squares regression and the Bayesian optimization, successfully refined formulations to enhance bending and impact strengths. Notably, we proposed optimal conditions starting from just eight samples with minimal iterations. This study shows that statistical techniques can quickly optimize WPC formulations, making the overall development process faster. By addressing the multiple conflicting properties, these techniques can greatly reduce the time and effort needed for development. Applied several regression methods to analyze ten properties of PP‐based WPCs. Showcased distinct impacts of the formulations of WF and MAPP on WPCs. Implemented the adaptive experimental design for formulation optimization. Enhanced bending and impact strengths in the formulations of WPCs. Advanced sustainable material development with data‐driven approach. [ABSTRACT FROM AUTHOR]

As a renewable fuel, the application of biomass fuel gets more and more attention. Fire and explosion are the main safety problems in the biomass fuel storage process. The characteristic parameters and kinetic analysis of pyrolysis and combustion are significant to guide the safe storage of biomass fuel. In this work, the thermogravimetric analysis (TGA) was used to obtain the pyrolysis and combustion characteristics of corn straw powder, poplar wood chip and rice husk in nitrogen and air, respectively. The Thermogravimetry-Differential Thermogravimetric (TG-DTG) profile shows that the pyrolysis process of these biomass includes three stages of drying, pyrolysis and carbonization, while the combustion process includes three stages of drying, devolatilization and coke combustion. The main reaction stage of biomass pyrolysis and combustion are roughly between 170∼400 °C and 180∼530 °C, respectively. With the increase of the heating rate, TG and DTG profiles shifts to the high temperature side. Furthermore, the kinetic analysis was performed by using Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO), Friedman, and Coats-Redfern (CR) methods, based on the thermogravimetric experimental data. The activation energy of biomass pyrolysis is shown to be between 70∼100 kJ/mol. For the activation energy of biomass combustion, the calculated value from isoconversional methods is between 140∼180 kJ/mol. The calculated value from CR method is between 80∼150 kJ/mol, and the activation energy of the coke combustion stage is greater than that of the devolatilization stage. Finally, the auto-ignition experiment of biomass particles was designed and conducted, indicating that the corn straw powder is more prone to spontaneous combustion, followed by rice husk and poplar wood chip, which corresponds to the results of activation energy. And the fire hazard of the biomass particles was analyzed according to the characteristic parameters. This work provides fundamental data to promote the development of storage techniques and facilitate the safe production of biomass particles. [ABSTRACT FROM AUTHOR]

In some specific situations, solid particles are pneumatically conveyed, requiring a relatively high accuracy for the pipeline pressure drop, the mass flow rate of the solid particles, and the superficial velocity of the carrier gas. At present, sawdust is conveyed in a steel pipeline. To determine the flow characteristics in the pneumatic conveying of sawdust, the influence of the Froude number (Fr) on the solid friction factors (λs, λz), the change in the solid mass (W) over time (T), and the variation tendency of the carrier gas mass flow rate (Q) with the solid mass flow rate (w) are analyzed. For different solid–gas ratios (μ), as Fr increases, λs decreases, and the influence of Fr on λs is greater than that of μ. As Fr increases, μ decreases. The superficial velocity (ua) increases with a more obvious change in the solid mass over time. When the superficial velocity is 5 m/s, the experimental data agree well with the numerical fitting data. While the mass flow rate of the solid is 0.333 kg/s, the required mass flow rate of the carrier gas is minimal, at 0.00269 kg/s, with a minimum pickup velocity of 4.26 m/s. [ABSTRACT FROM AUTHOR]

The influences of several important biomass pyrolysis process parameters such as the biomass feedstock type, flow pressure, biomass feeding rate and biomass particle size play an important role to ensure an efficient pyrolysis process. Unfortunately, the determination of these parameters can be cumbersome and often requires the method of trial and error. As a result, our work discusses the idea of the application of discrete phase modelling (DPM) in the fast pyrolysis process so that the optimum value of these essential parameters can be determined numerically. The numerical test demonstrated in this paper involving the fast pyrolysis of wood indicates that the application of DPM in the simulation is feasible for obtaining the initial prediction of the optimum process parameters. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A new combustion model is developed for thermally thick biomass particles by considering the intraparticle heat conduction, radiation, and reactions as well as the interaction of the internal and external flows of the particle. The particle temperature is solved in a continuous system with a finite element method, while the pyrolysis and char conversion are resolved in a discrete system. Furthermore, the flow fields both inside and outside the particle are modeled by a uniform multiphase CFD algorithm. The integrated model is first validated with the experimental data available in the literature. Numerical simulations not only provide the temperature and mass loss evolutions of the particle, but also reveal the flame structure, porosity evolvement, gas species distribution and streamlines inside and outside the particle which are quite difficult to be obtained in experiment. Moreover, the influences of inflow velocity, oxygen mass fraction, particle size and shape on biomass combustion behavior are also investigated. Results show that, the intraparticle heating and the char oxidation processes have a close relationship with the inflow velocity and particle size. The alteration in the oxygen mass fraction also has an important impact on the particle combustion behavior. In addition, different pyrolysis characteristics and flame structures are observed in the combustion of the square and rectangular particles. Unlabelled Image • A new combustion model is proposed for thermally thick biomass particles. • The intraparticle temperature gradient is resolved. • The flame structure, porosity evolution and streamlines are documented. • Effects of several key operational conditions are also explored. [ABSTRACT FROM AUTHOR]

Abstract A numerical and experimental study on the devolatilization of a large biomass particle is carried out to quantify the effect of homogeneous volatile combustion on the conversion of the particle and on the temperature and species distribution at the particle vicinity. A global chemical kinetic mechanism and a detailed reaction mechanism are considered in a one dimensional numerical model that takes into account preferential diffusivity and a detailed composition of tar species. An adaptive moving mesh is employed to capture the changes in the domain due to particle shrinkage. The effect of gas phase reactions on pyrolysis time, temperature and species distribution close to the particle is studied and compared to experiments. Online in situ measurements of average H 2 O mole fraction and gas temperature above a softwood pellet are conducted in a reactor using tunable diode laser absorption spectroscopy (TDLAS) while recording the particle mass loss. The results show that the volatile combustion plays an important role in the prediction of biomass conversion during the devolatilization stage. It is shown that the global reaction mechanism predicts a thin flame front in the vicinity of the particle deviating from the measured temperature and H 2 O distribution over different heights above the particle. A better agreement between numerical and experimental results is obtained using the detailed reaction mechanism, which predicts a wider reaction zone. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive model for simulating the combustion of large biomass particles. The model implements a set of Eulerian variables that represent the components of solid biomass in a commercial CFD code. The evolution of these variables represents the thermal conversion of biomass and its interaction with the gas flow. The model consists of several reaction submodels of heat transfer and species diffusion. A wood shrinkage submodel was also proposed, and it acts locally in cells according to calculations of the consumption densities and globally in the particle according to mass and energy movements across the mesh. An experimental reactor, in which a biomass particle was irradiated with a xenon lamp, was modelled to simulate the drying and devolatilization stages under controlled conditions. Two documented experiments were simulated, and the predictions were compared with the experimental results. The temperature evolution of the particle at several depths was analysed, and a qualitative comparison of the particle shrinkage was performed. The comparison yielded reasonably good predictions for temperatures inside the particle and similar trends in log shrinkage despite some uncertainties regarding the biomass composition and experimental conditions. [ABSTRACT FROM AUTHOR]

The utilization of biomass for heat and power generation has aroused the interest of most researchers especially those of energy .In converting solid fuel to a usable form of energy, pyrolysis plays an integral role. Understanding this very important phenomenon in the thermochemical conversion processes and representing it with appropriate mathematical models is vital in the design of pyrolysis reactors and biomass gasifiers. Therefore, this study presents analytical solutions to the kinetic and the heat transfer equations that describe the slow pyrolysis of a biomass particle. The effects of Biot number, temperature and residence time on biomass particle decomposition were studied. The results from the proposed analytical models are in good agreement with the reported experimental results. The developed analytical solutions to the heat transfer equations which have been stated to be “analytically involved” showed average percentage error and standard deviations 0.439 and 0.103 from the experimental results respectively as compared with previous model in literature which gives average percentage error and standard deviations 0.75 and 0.106 from the experimental results respectively. This work is of great importance in the design of some pyrolysis reactors/units and in the optimal design of the biomass gasifiers.

A single particle reaction model has been developed to study the char burnout characteristics of co-firing of coal and biomass under air and oxy-fuel combustion conditions. Two types of coal/biomass blend, i.e., Brisbane bituminous coal blended with woodchip, and Loy Yang lignite coal blended with woodchip, have been studied. The model is validated with different sets of experiments and CFD simulation from the literature. The effects of biomass fraction, particle size, oxygen level and gas temperature have been investigated. It is found that increasing biomass blending ratio, oxygen concentration, [ O 2 ] , or the gas temperature, t g , increases char reactivity and conversion rate and reduces char burnout time. The current numerical study demonstrates that comparing to traditional CFD simulation, the proposed single particle reaction model takes much less simulation time and efforts, while able to provide a deep insight into char burnout characteristics in co-combustion process. • A simplified single particle reaction model has been developed to simulate char burnout in coal/biomass co-combustion. • The Effects of biomass fraction, particle size, oxygen concentration and gas temperature, have been investigated in depth. • Biomass blending significantly increases the char conversion rate, and therefore reduces char burnout time. The higher the biomass blending ratio, the shorter the char burnout time. • Char reactivity increases with the increase in biomass blending ratio, with about five times higher for biomass than that of coal. • Char burnout time increases with the increase in fixed carbon content, the increase in d p , the decrease in [ O 2 ], and the decrease in T g. [ABSTRACT FROM AUTHOR]

A numerical and experimental study on the conversion of a biomass particle is carried out to quantify the effect of homogeneous volatile combustion on the biomass pyrolysis. The numerical domain consists of a particle and its surrounding and the model considers detailed chemical kinetic mechanism for reaction of pyrolysis products. A detailed pyrolysis model is employed which provides the composition of pyrolysis products. The effect of gas phase reaction on the conversion time and temperature of the particle is analyzed and it was shown that the gas phase reactions results in shorter pyrolysis time. H 2 O mole fraction and temperature above a biomass pellet from wheat straw (WS) and stem wood (SW) were experimentally measured using tunable diode laser absorption spectroscopy (TDLAS) while recording the particle mass loss. The TDLAS data were used to validate the numerical model developed for biomass conversion. The results showed that by considering the gas phase reactions a good agreement between the measurement and the model prediction for mass loss and temperature can be achieved. For H 2 O mole fraction on top of the particle, on the other hand, some discrepancy between the model prediction and the experimental data was observed. Nevertheless, the difference in H 2 O mole fraction would be much larger by neglecting the gas phase reaction at the particle boundary. [ABSTRACT FROM AUTHOR]

A discrete element method (DEM) was used to numerically investigate the segregation of biomass particles (with multi-sized distribution) in a horizontal stirred bed. An analysis of the following factors was performed: agitator rotational speed, reactor diameter, weir height, particle size distribution on particle segregation, and residence time distribution. The results indicated that particle segregation increased with an increased reactor diameter, decreased weir height, and narrower particle size distribution. The influence of the agitator rotation rate was not as significant as the other three variables. When the ratio of the weir height to the reactor diameter was less than 1/2, then the smaller particles had a higher mean residence time than the larger particles; however, when the ratio was 2/3, the opposite result was obtained. [ABSTRACT FROM AUTHOR]

Char reaction is an important stage of the combustion processes of biomass particles. It dominates the burnout of biomass particles. The instantaneous char reaction processes of biomass particles in a hot gas with temperature fluctuation are studied. Two types of biomass fuels, i.e. pine and thistle, are chosen for the present investigation. The instantaneous mass variations of biomass particles with initial diameters of 100, 200, and 300 μm are calculated under different conditions. The gas temperature fluctuation leads to faster mass loss for both pine and thistle particles. The char reaction of biomass particles is further enhanced by increase in the fluctuation amplitude of gas temperature. [ABSTRACT FROM AUTHOR]

A comprehensive single particle model of biomass drying and pyrolysis is coupled with an ideal reactor model of a bubbling fluidized bed with nitrogen as the fluidizing gas. To predict biomass pyrolysis products yield and composition under steady-state operation, a two-step biomass pyrolysis kinetic mechanism is adopted with primary pyrolysis described by two different reaction kinetic schemes: (a) Three parallel first-order reactions producing primary pyrolysis products (non-condensable gas, tar/bio-oil and char), and (b) a detailed solid state kinetics mechanism based on multiple reactions of lignin, cellulose, and hemicellulose contents of two specific types of biomass (poplar and lodgepole pine). Secondary pyrolysis is modeled by two parallel reactions describing homogeneous thermal cracking of tar to non-condensable gas and char. In addition to the yields of pyrolysis products often modeled as lumped species, this model addresses an existing gap of knowledge in predicting the proportions of major compounds in the pyrolysis gas based on a few simplifying assumptions and CHO elemental balances. This predictive model is a useful tool to relate biomass pyrolysis products yield and composition to process operating parameters such as biomass ultimate analysis, reactor temperature, gas residence time, mean solids residence time inside the reactor, as well as biomass particle size and moisture content. Model predictions for the two kinetic schemes are in good agreement with available experimental data from the literature. [ABSTRACT FROM AUTHOR]

Individual particles of pulverized coals exhibit strikingly different combustion phenomena depending on their rank (anthracite, semi-anthracite, bituminous, sub-bituminous and lignite). Herein a concise review is presented on pertinent findings in the literature to contrast ignition and combustion behavior of such fuels at the particle-level . Emphasis is given to recent investigations performed in the laboratory of the authors, where combustion of a variety of coal particles of the same size-cut took place in the same apparatus under identical operating conditions. Such behaviors were then compared to those reported in the literature to verify their replication under often different, but yet relevant, conditions. The objective has been to relate the effect of coal rank to a number of key qualitative and quantitative parameters, such as modes of ignition and combustion, ignition temperatures, ignition delay times, combustion temperatures and burnout times (both those encountered in the volatile and the char combustion phases), volatile flame sizes as well as extents of particle fragmentation. Besides reviewing combustion behaviors in air, analogous behaviors under simulated dry oxy-combustion conditions were also highlighted. Then the coal rank dependence of the required oxygen mole fraction in dry O 2 /CO 2 blends to match the intensity of air-fired combustion was examined. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the production process of biomass energy with crop straw as the raw material, the indoor dust environment created by smashed plant fiber can affect the health of workers and lead to the risk of fire and explosions. The physical properties of biomass vary with the ambient air conditions, resulting in different deposition processes for airborne biomass particles. In this study, the deposition of biomass particles in different environments in an experimental chamber was examined by independently controlling the internal temperature and relative humidity. The results show that in the ambient temperature range of 20~40 °C and at a relative humidity of 25~65%, the water absorption rates of the biomass particles were 15.4~24.7%. The deposition rates of the airborne biomass particles with different sizes were 0.9~2.9 h -1 , which positively correlated with the particle sizes in the same ambient conditions. The increase in ambient temperature and relative humidity promoted the deposition of biomass particles with diameters over 0.5 μm. For the particles with diameters below 0.5 μm, the deposition rates were nonlinearly related to the ambient temperature and relative humidity and were greater at lower temperatures. The significance levels of the factors influencing the particle deposition were particle size > ambient temperature > ambient relative humidity. For the biomass particles below 0.5 μm, the influence of the relative humidity on the deposition was much weaker than that of the temperature.

Hilbert-Huang transformation was used to investigate the nonlinear characteristics of two-component (biomass particles and quartz sand) mixing flow by analyzing the pressure fluctuation signals in fluidized bed. Based on empirical mode decomposition (EMD), the Hilbert-Huang spectra in bubbling and slugging flow patterns were obtained and analyzed. In bubbling flow pattern, compared with one-component (quartz sand) flow, the energy of two-component mixing flow is lower in 0-5 Hz and higher in 40-50 Hz. In slugging flow pattern, the energy in pressure fluctuation mainly lies in 0-5 Hz. and the effect of biomass particles on the Hilbert-Huang spectrum is not very obvious. Compared with traditional power spectral density (PSD), HHT is much more suitable for investigating pressure fluctuation signals in fluidized beds. [ABSTRACT FROM AUTHOR]

Highlights: [•] The instantaneous devolatilization of pine and almond shell particles are studied. [•] The gas temperature fluctuation leads to faster mass loss of the particles. [•] The effects are enhanced by increasing the fluctuation amplitude of gas temperature. [ABSTRACT FROM AUTHOR]

• Physical and mechanical properties of biomass are quantified by computer vision. • Image measurement methods are proposed and experimental platforms are designed. • Equivalent diameter and density obey the skewed normal distribution in PIMS program. • Elastic modulus and Poisson's ratio are analyzed using the uniaxial tension and DIC. • Tensile strength and failure stress varied with stretching rate and fiber orientation. The combustion and fluidization behavior of biomass depend on the physical properties (size, morphology, and density) and mechanical performances (elastic modulus, Poisson's ratio, tensile strength and failure strain), but their quantitative models have rarely been focused in previous researchers. Hence, a static image measurement for particle physical properties is studied. Combining the uniaxial tension and digital image correlation technology, the dynamic image measurement method for the mechanical properties is proposed. The results indicate that the average roundness, rectangularity, and sphericity of present biomass particles are 0.2, 0.4, and 0.16, respectively. The equivalent diameter and density obey the skewed normal distribution. The tensile strength and failure stress are sensitive to stretching rate, fiber size and orientation. The distribution intervals of elastic modulus and Poisson's ratio are 30–600 MPa and 0.25–0.307, respectively. The stress–strain curves obtained from imaging experiments agree well with the result of finite element method. This study provides the operating parameters for the numerical simulation of particles in the fluidized bed and combustor. Furthermore, the computer vision measurement method can be extended to the investigations of fossil fuels. [ABSTRACT FROM AUTHOR]

The utilization of biomass for heat and power generation has aroused the interest of most researchers especially those of energy. In converting solid fuel to a usable form of energy, pyrolysis plays an integral role. Understanding this very important phenomenon in the thermochemical conversion processes and representing it with appropriate mathematical models is vital in the design of pyrolysis reactors and biomass gasifiers. Therefore, this study presents analytical solutions to the kinetic and the heat transfer equations that describe the slow pyrolysis of a biomass particle. The effects of Biot number, temperature and residence time on biomass particle decomposition were studied. The results from the proposed analytical models are in good agreement with the reported experimental results. The developed analytical solutions to the heat transfer equations which have been stated to be "analytically involved" showed average percentage error and standard deviations 0.439 and 0.103 from the experimental results respectively as compared with previous model in literature which gives average percentage error and standard deviations 0.75 and 0.106 from the experimental results respectively. This work is of great importance in the design of some pyrolysis reactors/units and in the optimal design of the biomass gasifiers. [ABSTRACT FROM AUTHOR]

Abstract: Due to its renewable characteristics, biomass is potentially important to energy conversion processes. Fluidized beds are involved in many processes related to energy conversion of biomass. Hence, detailed insight on the hydrodynamics of biomass fluidized beds is crucial for successful energy conversion as well as to better design and scale-up of fluidized bed reactors. The present work focuses on modeling the mixing and segregation behavior of biomass mixtures in a fluidized bed. Different effects, such as mixture composition, particle size, and superficial gas velocity, on the mixing and segregation are simulated and the results are compared to measurements obtained using X-ray computed tomography. Furthermore, side injection of biomass particles into a fluidized bed is also studied and compared with visual observations. A comparison between the numerical simulations and measurements shows good agreement. [Copyright &y& Elsevier]

Abstract: The aim of this work was to demonstrate a model for a spherical biomass particle combusting at high temperatures with reduced number of variables. The model is based on the observation that combustion of a small particle includes three main phases: heating up, pyrolysis, and char conversion. It is assumed that the pyrolysis begins as soon as the particle surface attains a pyrolysis temperature, yielding a char front, moving towards the center of particle as time passes. The formulation of the heating up and pyrolysis phases is based on an integral method which allows describing the energy conservation with an ordinary differential equation. The char combustion model is according to the shrinking core approximation. Model validation is carried out by comparing the predictions with experiments of sawdust particles taken from the literature, and with computations of partial differential equation-based models. Satisfactory agreement is achieved between the predictions and experimental data. [Copyright &y& Elsevier]

Abstract: Due to the high content of cellulose, hemicellulose and lignin, the anisotropy of biomass particle in spatial structure induces the difference of mechanical properties in different directions. In this paper, based on the finite stochastic breakup model and anisotropy of biomass particles, 2-dimensional finite stochastic breakup model (2D-FSBM) of biomass particle was proposed, and the breakup process of biomass particle was investigated. In this model, the strength difference in different directions and the minimum mass ratio of a sub-particle to the parent particle were both considered. The simulation results agreed well with the experimental results in particle shapes, which indicated that 2D-FSBM could predict the breakup process of biomass particles. [Copyright &y& Elsevier]

Abstract: Combining a volume reaction model and front reaction approximation is proposed to simulate the combustion of a large biomass particle. Two intraparticle processes—drying and char oxidation—are simplified as front reaction because they are transport controlled. The other intraparticle process—pyrolysis—is described as the volume reaction because it is controlled by both heat transfer and kinetics. A new numerical method based on the basic mechanism of the process is applied to mitigate oscillations of the solution of the front reactions. To compare the calculation results with the experimental results presented in the literature, combustion of cubic wood particles between 5 and 25mm is chosen to test the new method. Drying, pyrolysis, char oxidation, vapor condensation, shrinkage of the process, heat transfer via conduction, diffusion, convection, radiation and mass transfer via diffusion, and convection inside particle are taken into account. Finite volumes attached to solid materials are used to discretize the domain and explicit method with variable time step is used to calculate the process. A program was written and the calculation showed that the conversion of a particle is almost independent of computational mesh from 10 cells on. However there is significant instability in the mass loss rate curve when the number of cells is less than 20. Predictions for different particle sizes, furnace temperatures and moisture contents were compared with measurements and they agree reasonably well. The results highlight the significance of pyrolysis kinetics on prediction. Thus, the front reaction model of pyrolysis assuming a constant reaction temperature of 773K is sometimes inadequate. The proposed method also showed that moisture content and pyrolysis reactivity significantly affect the thickness of devolatilizing fuel. [Copyright &y& Elsevier]

Abstract: A detailed one-dimensional model for combustion of a single biomass particle is presented. It accounts for particle heating up, pyrolysis, char gasification and oxidation and gas phase reactions within and in the vicinity of the particle. The biomass pyrolysis is assumed to take place through three competing reactions yielding char, light gas and tar. The model is validated using different sets of experiments reported in the literature. Special emphasis is placed on examination of the effects of pyrolysis kinetic constants and gas phase reactions on the combustion process which have not been thoroughly discussed in previous works. It is shown that depending on the process condition and reactor temperature, correct selection of the pyrolysis kinetic data is a necessary step for simulation of biomass particle conversion. The computer program developed for the purpose of this study enables one to get a deeper insight into the biomass particle combustion process. [Copyright &y& Elsevier]

Abstract: When designing industrial furnaces for combustion of biomass particles, it is of technical importance to know the time of pyrolysis at high heating conditions. We numerically investigated pyrolysis of a single biomass particle using a one-dimensional model which assumes that the conversion process of a pyrolyzing particle takes place through three parallel reactions yielding light gases, tar and char. A novel idea that has been established in this paper is that the heat of pyrolysis in the energy conservation equation is calculated by accounting for the exothermicity of char formation and the endothermicity of volatiles generation in accordance with the correlations proposed in the literature. As the idea is to investigate biomass particle pyrolysis at high heating conditions, three different sets of experimental data conducted at high surrounding temperatures are selected for validation of the improved model. It is found that employing the correlations of Milosavljevic et al. and Mok and Antal to compute the heat of pyrolysis together with kinetic constants of Di Blasi and Branca in the model provides a good prediction of the final char yield and conversion time. In the next stage of the study, the pyrolysis model is utilized to investigate the effects of particle shape, size and initial density on conversion time and final char density of a biomass particle at high heating environments. Typical results are presented which are expected to enable a designer to estimate the pyrolysis time and final char density of a biomass particle undergoing thermochemical conversion at the conditions of industrial combustors. Finally, the homogeneity of the pyrolysis process inside small particles exposed to high reactor temperatures is investigated. It is found that adaption of such an assumption in a particle conversion model may result in undesired reduction of the accuracy of the model predictions. [Copyright &y& Elsevier]

Abstract: An accurate formulation of energy conservation to model pyrolysis of a biomass particle needs to account for variations in the heat of reaction with temperature, usually neglected in most past studies. It is shown that by including this effect in a pyrolysis model with three parallel reactions yielding char, gas and tar, a wide range of experimental data can be accurately predicted. In particular, through comprehensive comparisons of the simulation results with various measurements, a consistent and single value of 25kJ/kg is obtained for enthalpy of pyrolysis, which represents a lumped heat of volatiles and char formation at a reference temperature. It is found that the kinetic parameters of Chan et al. [W.C. Chan, M. Kelbon, B.B. Krieger, Fuel 64 (1985) 1505–1513] and Thurner and Mann [F. Thurner, U. Mann, Ind. Eng. Chem. Process Des. Dev. 20 (1981) 482–488] provide reasonable agreement between the model predictions and experiments compared to other reported kinetic constants. These comparisons also indicate that inclusion of tar cracking reactions to yield additional light gases does not give a better prediction of the process parameters. The presented thermo-kinetic model is capable of successfully predicting various experimental observations such as the internal temperature peak reported in some past studies. It is shown that the sensible heat released due to the conversion of virgin biomass to the reaction products is responsible for this phenomenon. Simulation results reveal that a temperature peak at an internal location of the particle may occur when the corresponding local temperature reaches the particle surface temperature while the local biomass conversion is not finalized yet. [Copyright &y& Elsevier]

Abstract: The mixing and segregation behavior of biomass particle have been investigated experimentally in fluidized bed made up of biomass–sand mixture with different biomass/sand ratios. The biomass is cylindrical-shape cotton stalk, and the sand belongs to the Geldart B category. The initial bed is thoroughly mixed and the gas superficial velocity varies to cover a wide range. The mixing and segregation behavior are analysed in terms of flow patterns, solid concentration profile and mixing index. It is found that as the gas superficial velocity gradually increases, the bed undergoes local segregation, global segregation, local mixing, global mixing and re-segregation. [Copyright &y& Elsevier]

Abstract: The fluid–particle interaction inside a 150g/h fluidised bed reactor is modelled. The biomass particle is injected into the fluidised bed and the momentum transport from the fluidising gas and fluidised sand is modelled. The Eulerian approach is used to model the bubbling behaviour of the sand, which is treated as a continuum. The particle motion inside the reactor is computed using drag laws, dependent on the local volume fraction of each phase, according to the literature. FLUENT 6.2 has been used as the modelling framework of the simulations with a completely revised drag model, in the form of user defined function (UDF), to calculate the forces exerted on the particle as well as its velocity components. 2-D and 3-D simulations are tested and compared. The study is the first part of a complete pyrolysis model in fluidised bed reactors. [Copyright &y& Elsevier]