Devolatilization Rate Research Articles

Study of the high heating rate devolatilization of bituminous and subbituminous coals—Comparison of experimentally monitored devolatilization profiles with predictions issued from single rate, two-competing rate, distributed activation energy and chemical percolation devolatilization models

This paper deals with the measurement and modeling of devolatilization profiles obtained with 7 different coals. To do so, a specifically designed flat flame reactor (FFR) has been used to reproduce industrial heating rates (∼106Ks−1) with peak particle temperatures (PTp) ranging from ∼1000K to ∼1300K. The thermal history of the fuel particles has been characterized by coupling particle image velocimetry (PIV) and pyrometry measurements so as to be integrated in empirical and phenomenological models including single rate, two-competing rate, distributed activation energy (DAE) and chemical percolation devolatilization (CPD) ones. Final yields ranging from ∼70% to ∼89% with respect to the initial fuel volatiles content have been measured for PTp≈1000K. As expected, a decrease of the devolatilized fractions with an increase of the fuel rank has been observed while releases of volatiles exceeding the proximate analysis predictions have been recorded for temperatures higher than ∼1090K. Besides, the experimental conditions investigated in this work and especially the high heating rate delivered by the FFR used allowed testing the ability of devolatilization models from the literature to simulate data obtained in conditions relevant to coal power plant applications which should be of particular interest for future CFD calculations. The main findings highlighted through the comparison work proposed herein can be summed up as follows: 1) The single kinetic rate model integrating the original parameters proposed by Badzioch and Hawksley globally reproduces measured weight losses for bituminous coals while needing adjustments for lower rank fuels; 2) Different kinetic constants tabulated in the literature for two-competing rate models have been tested and turned out to be unsuitable to simulate the devolatilization profiles we monitored. Insights regarding most adapted parameters and optimization procedures that might be operated are, nonetheless, discussed; 3) Adjusting the standard deviation of the activation energy introduced into the DAE model consistently with the thermal gradient experienced by the fuel particles may lead to improved agreements between measured and simulated data; 4) The CPD model slightly overstimates devolatilization rates at low temperatures while showing the best performances to predict the final devolatilization yields for all the studied coals (including the subbituminous one) due to the structural approach integrated in such a modeling tool.

Thermogravimetric and devolatilisation analysis for five plantation species: Effect of extractives, ash compositions, chemical compositions and energy parameters

Woody biomasses from five fast-growth plantations of Costa Rica were evaluated in relation to thermal degradation characteristics and devolatilisation rate (Drate) using thermogravimetric analysis (TGA). The relationship between TGA parameters and Drate with content of cellulose, lignin and extractives were established. The results indicate that during degradation, the five woody biomass types (Cupressus lusitanica, Dipterix panamensis, Gmelina arborea, Tectona grandis and Vochysia ferruginea) show different temperatures and residual mass, as well as different Drate of the polymers conforming them, indicating that each biomass type has unique pyrolysis characteristics. The difference in these parameters is influenced by extractives content, and a little effect is presented due to lignin content, cellulose content and ash composition. A greater amount of extractives decreases the degradation temperatures of the different biomass components, although the residual mass was scarcely affected and if so, a positive correlation was presented. Extractives also affected the Drate more significantly than cellulose, lignin and macro- or micro-nutrients contents. Moreover, the Drate of cellulose was more affected by the extractives content than was Drate of hemicellulose, indicating a higher degree of association of extractives with cellulose than hemicellulose. In this concern, the higher the amount of extractives, the lower the Drate of cellulose.

Combustion Behavior of Relatively Large Pulverized Biomass Particles at Rapid Heating Rates

A pulverized solid fuel particle in a hot gas stream appears to have different characteristic behaviors at several stages, including heat-up, release of volatile matter, gas phase, and solid combustion. The characteristics of these stages may vary distinctly depending on devolatilization rate, the particle temperature history, and its chemical and physical properties. Biomass particles manifest different combustion behavior from that of burning coal particles under the same combustion conditions because they contain more volatiles (less fixed carbon), and they have a relatively lower particle density due to their fibrous structure. This paper presents an experimental study of burning behavior of different types of biomass particles (torrefied wood, coffee waste, and sewage sludge). The main experimental parameters—gas temperatures of 1090 and 1340 K, and O2 concentrations ranging from 10% to 40%—were employed to investigate the burning of biomass through a direct-observation approach using a high-speed ph...

Experimental study on fragmental behavior of coals and biomasses during rapid pyrolysis

In order to study the primary fragmentation behavior of coals and biomasses, experiments of rapid pyrolysis were carried out. This work focused on the devolatilization and fragmentation characteristics including the solid/gas yield, particle density/morphology, particle size and fragmental probability (Sf). The effects of temperature, time and solid property were investigated. The viscous flow model was employed to characterize the pressure difference (ΔP), which was considered as the driving force of diffusion and fragmentation. The Ohm principle was used to establish the linear relation of devolatilization rate and fragmentation rate. The result showed that temperature and time have positive contribution to the fragmentation. The occurrence of fragmentation was observed more apparently with the decreasing of the ash content in the biomass. The pressure difference has a positive correlation with the fragmental rate, which shows the validity of application Ohm principle in the prediction of fragmenting process.

Simulation of large coal particles pyrolysis by circulating ash heat carrier toward the axial dimension of the moving bed

A heat transfer, reaction, pyrolysis mathematical model for the non-isothermal coal particles by using circulating ash as heat carrier toward the moving bed has been established. Combined with the Thermogravimetry-Mass spectrometry technology and Coats–Redfern integral method, the model has the ability to predict the temperature distribution of pyrolysis gas-coal-ash as well as the evolution characteristics of the main volatile products (such as CH4, CO2, H2, CO, C2H4, C2H6, C6H6, C7H8, C8H10, C10H8). The results show that, the maximum temperature difference between the core and surface of coal (10mm) has reached 406K at the bed height of 0.05m. The layer closer to the coal core has a higher but later peak value of the devolatilization rate. The evolution of the main volatile products is concentrated at the bed height of 0.08–0.24m. The velocity of the moving bed, blending ratio of ash to coal, coal particle size, preheating temperature of coal and initial temperature of ash have obvious influence on the devolatilization process. Radiation is the most significant factor affecting the devolatilization behavior. The model can be applied to different coal species. This study can provide a theoretic foundation for the amplification design of the moving-bed reactor in the poly-generation system.

Evaluation of Scenario Uncertainties in Entrained Flow Reactor Tests through CFD Modeling: Devolatilization

A Computational Fluid Dynamic model of oxy-coal devolatilization experiments in a pilot-scale entrained flow reactor is proposed to gain insight into the thermal histories of the cloud of solid fuel particles and to investigate sources of uncertainties that may affect the analysis of devolatilization. Solid fuel particles experience different paths and are characterized by a temperature which is lower than the reactor nominal one at some of the sampling locations used for investigating devolatilization rates. Indeed, neglecting the quick heating up of the particles by assuming their temperature to be equal to the reactor one for calculating kinetics leads to an underestimation of devolatilization rates. A simple hypothesis on a linear dependence of the particle temperature on residence time through an average heating rate, with residence time and heating rate estimated from the numerical model, was found to largely improve the reliability of devolatilization kinetics even with a simple Single First Order ...

Resolved flow simulation of pulverized coal particle devolatilization and ignition in air- and O2/CO2-atmospheres

A resolved laminar flow simulation approach is used to investigate the effect of enhanced oxygen levels on single coal particle ignition, comparing the numerical results against experimental data for well-defined conditions (Molina and Shaddix, 2007). Devolatilization is described by a generic boundary condition at the particle surface that accounts for both convective and diffusive phenomena during pyrolysis. The heating rate history of the particle is obtained by solving for intra-particle heat transfer and heat exchange between the particle and its surroundings. The time evolution of volatile release is captured by using the particle mean temperature to calculate the devolatilization rate from a single kinetic rate law with CPD-fitted parameters. The assumed volatile composition includes both light gases and larger hydrocarbons to represent tars. A skeletal kinetic mechanism for pyrolysis and oxidation of hydrocarbon and oxygenated fuels containing 52 species and 452 reactions is used to accurately describe homogeneous chemistry. Particle heat-up, pyrolysis, ignition and envelope flame stabilization are characterized in four gas atmospheres differing in oxygen content and the use of either N2 or CO2 as balance gas. In agreement with the experimental evidence, enhanced oxygen levels shorten ignition delay time τign and result in a higher intensity of the combustion process according to temperature and radical production peaks for all studied mixtures. For the studied oxy-mixtures the presence of CO2 in substitution of N2 delays ignition. The observed behavior is coherent with the different thermo-physical properties of the gas mixtures. The sensitivity of predicted ignition delay to a set of uncertainties is also discussed. It is found that while the absolute values of predicted ignition delay time are functions of potential particle preheating, particle Reynolds number and the chosen criterion to extract ignition delay, the relative trends among the gas mixtures remain in line with the experimental evidence.

Flamelet LES modeling of coal combustion with detailed devolatilization by directly coupled CPD

A large eddy simulation (LES) with direct CPD devolatilization modeling and gas phase combustion modeling through a new flamelet approach is presented for the CRIEPI flame by Hwang et al., 2005 [1]. The devolatilization rates are directly determined from CPD for each coal particle. The flamelet is generated from non-premixed one-dimensional gaseous flames and is based on mixture fractions for volatiles and methane as well as on enthalpy and scalar dissipation rate. A transport equation for mixture fraction variance is combined with an assumed pdf approach for modeling turbulence-chemistry interaction. Special emphasis is put on the influence of devolatilization, with a comparison of LES with direct CPD coupling to empirical models with fitted and standard rate constants. The results are further analyzed by scatter plots and phase space trajectories of the quantities of interest. The results show that large deviations between CPD and the fitted model exist on the instantaneous particle level. It is shown that the direct use of CPD in the LES is feasible and that the flamelet model is able to perform well. Some weaknesses specific to the CRIEPI flame are also discussed.

Devolatilization Characteristics and Kinetic Analysis of Lump Coal from China COREX3000 Under High Temperature

A devolatilization study of two lump coals used in China COREX3000 was carried out in a self-developed thermo-gravimetry at four temperature conditions [1173 K, 1273 K, 1373 K, and 1473 K (900 °C, 1000 °C, 1100 °C, and 1200 °C)] under N2. This study reveals that the working temperature has a strong impact on the devolatilization rate of the lump coal: the reaction rate increases with the increasing temperature. However, the temperature has little influence on the maximum mass loss. The conversion rate curve shows that the reaction rate of HY lump coal is higher than KG lump coal. The lump coals were analyzed by XRD, FTIR, and optical microscopy to explore the correlation between devolatilization rate and properties of lump coal. The results show that the higher reaction rate of HY lump coal attributes to its more active maceral components, less aromaticity and orientation degree of the crystallite, and more oxygenated functional groups. The random nucleation and nuclei growth model (RNGM), volume model (VM), and unreacted shrinking core model (URCM) were employed to describe the reaction behavior of lump coal. It was concluded from kinetics analysis that RNGM model was the best model for describing the devolatilization of lump coals. The apparent activation energies of isothermal devolatilization of HY lump coal and KG lump coal are 42.35 and 45.83 kJ/mol, respectively. This study has implications for the characteristics and mechanism modeling of devolatilization of lump coal in COREX gasifier.

Multicomponent devolatilization kinetics and thermal conversion of Imperata cylindrica

Imperata cylindrica is a viable bioenergy crop with potential for conversion to clean energy through thermochemical processes such as pyrolysis, gasification and combustion. To facilitate further process development, a mathematical model that represents process kinetics is developed and validated on thermal degradation studies using thermogravimetric analyzer, over a temperature range of 30–1000°C, at four heating rates of 5, 10, 15, and 20°Cmin−1 under Nitrogen atmosphere. Model free and model fitting multicomponent methods are used for determination of pre-exponential factors (ko), activation energies (Ea) and fractional contribution (ξ). In addition, a novel approach is introduced to determine biomass (cellulose, hemicellulose and lignin) compositions by extending model fitting multicomponent method to identify components that correspond to each biomass composition using the pyrolysis temperature range. The model free methods of Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose gave average activation energies of 164.93kJmol−1 and 163.44kJmol−1 and average pre-exponential factor of 1.04×1025min−1 and 4.65×1018min−1 respectively. Using the multicomponent model fitting, the simulation was carried out for 3–14 pseudo components and the best quality of fit (0.75%) was for ten pseudocomponents at a heating rate of 15°Cmin−1 with an activation energy of 101.56kJmol−1, which compares favourably with the model free method. The novel biomass composition algorithm predicted the cellulose, hemicellulose and lignin as 66%, 24% and 10% respectively, varying from experimental composition by ±10%. The results strongly indicate that the pseudocomponent reaction modelling method could be employed to predict the experimental devolatilization rate and biomass composition with a high degree of success.

Pyrolysis of kraft pulp and black liquor precipitates derived from spruce: Thermal and kinetic analysis

The potential of seven kraft cook materials to become functional char materials and fuels is investigated. Thermogravimetric analysis was used to study the thermal properties while a model-free isoconversional method was used to derive kinetic rate expressions. Black liquor precipitates had lower thermal stability (20–60K lower) than pulps and spruce wood and the precipitates decomposed in a wider temperature range, producing chars with similar or higher thermal stability than char from pulps, but lower than those from spruce wood. Samples suitable to produce char were identified based on char yield, devolatilization rate and charring temperature. The highest char yield (46%), achieved from a precipitate, was more than twice as high as that from spruce powder. Under the studied conditions none of the materials had a pyrolysis process that for the whole conversion range could be described with a single set of kinetic parameters. The apparent activation energy varied between 170–260kJ/mol for the pulps and 50–650kJ/mol for the precipitates. The derived kinetic parameters were validated by predicting the conversion at a heating rate outside the range used for its derivation and at quasi-isothermal conditions. Both these tests gave satisfactory results in good agreement with experimental data.

Laminar Burning Velocities of Atmospheric Coal Air Mixtures

The mechanism for laminar dust flame propagation can only be elucidated from a comprehensive mathematical model which incorporates conduction and radiation, as well as the chemical kinetics of particle devolatilization and gas phase and char reaction. The mathematical model for a flat, laminar, premixed coal-air flame is applied to the atmospheric coal-air mixtures studied by Smoot and co-workers, and comparisons are made with their measurements and predictions. Here the principal parameter for comparison is the laminar burning velocity. The studies of Smoot and co-workers are first reviewed and compared with those predicted by the present model. The effects of inlet temperature and devolatilization rate constants on the burning velocities are studied with the present model, and compared with their measurements and predictions. Their measured burning velocities are approximately predicted with the present model at relatively high coal concentrations, with a somewhat increased inlet temperature. From the comparisons, their model might over-estimate particle temperature and rates of devolatilization. This would enable coal-air mixtures to be burned without any form of preheat and would tend to increase their computed values of burning velocity.

Experimental research of particle size and size dispersity on the explosibility characteristics of coal dust

In the present research work, the effects of particle size (D50) and size dispersity (σD) on the explosion severity of coal dust were investigated using a 20L spherical explosion vessel. Coal dust samples with similar median diameter (D50) and different size dispersity (σD) and similar size dispersity (σD) and different size diameter (D50) were specially prepared by mixing original coal samples having a narrow size distribution. The explosion severity of each sample was evaluated by measuring the maximum pressure (Pmax) and the maximum rate of pressure rise ((dP/dt)max). Interestingly, results show that almost all of the selected coal dusts present the same optimum explosion concentration of 250g/m3. The parameters of Pmax and (dP/dt)max show an increasing trend in explosion severity as size dispersity (σD) and particle size (D50) decrease, which indicate a more notable effect due to the contribution of finer coal particles on the dust cloud deflagration dynamics. The higher the volatile matter content, the more severe is the explosion. The presence of the finer particles would greatly increase the total effective specific surface area and speed up the devolatilization rate, which would cause acceleration of the dust explosion process. Furthermore, the effects of dust concentration on the explosion process were analyzed by comparing the defined time span (τ1) from ignition point to reach (dP/dt)max point and time span (τ2) from (dP/dt)max point to reach Pmax point. For the coal dust with lower D50 and lower σD, τ1 and τ2 are always short. Under lower coal dust concentration condition (<250g/m3), τ1 and τ2 present a stronger dependence on σD and dust concentration. However, the effect of σD and dust concentration on τ1 and τ2 becomes weak for the higher coal dust clouds (>250g/m3). Results indicated that the evaluation of coal dust explosion hazard should be considered in terms of not only dust concentration, but also particle size (D50) and size dispersity (σD).

The effect of fuel pyrolysis on the coal particle combustion: An analytical investigation

The aim of this work is to analytically investigate the symmetrical combustion of an isolated coal particle with the fuel pyrolysis effect. The modelling concept of coal particles is similar to that of the liquid droplet combustion but in the case of coal devolatilization, the particles do not shrink like droplet does due to evaporation of liquid fuel. The rate of devolatilization of volatiles can be calculated using the equation that is similar to Arrhenius equation. This model is based on an assumption of combined quasi-steady and transient behaviour of the process and especially focuses on predicting the variations of temperature profile, radius of pyrolysis and transfer number. It is revealed that the entrance of pyrolysis effect into the governing equations leads to the reduction in the film radius and consequently a reduction in the stand-off ratio and transfer number.

Effect of feedstock moisture content on biomass boiler operation

Burning feedstock with high and constantly varying moisture content is a challenge in the operationof the stoker-grate type biomass boilers in pulp and paper mills. A fundamental study was performed, using a thermogravimetric combustor controlled at different temperatures, to systematically investigate the effect of moisture content on the combustion behavior of several woody biomasses. The results show that combustion occurred through three stages: drying, devolatilization, and char burning. Increasing the moisture content of the sample above 30% significantly increased the drying time and the time to ignition of the sample. Moisture content, however, had only a small effect on the devolatilization rate and virtually no effect on the char burning rate. Furnace temperature had a great effect on combustion. Samples containing 40% moisture could still ignite and burn readily at 800°C, but they took a much longer time to ignite at 500°C and did not ignite at 400°C. These results imply that in biomass boiler operation, the high moisture content in feedstock delays combustion and causes the furnace temperature to decrease. The low temperature, in turn, suppresses combustion, further decreasing the furnace temperature and causing more delay in combustion. This downward spiral will eventually lead to a boiler blackout unless the biomass feed rate is significantly reduced or the auxiliary fuel (natural gas and fuel oil) flow rate cofired in the boiler is increased to keep the furnace temperature high.

CO-PYROLYSIS AND CHARACTERISTICS OF MALAYSIAN SUB-BITUMINOUS COAL AND WASTE HDPE BLENDS VIA TGA

Waste polymers co-conversion is an attractive way to dispose of and convert polymer into high value fuel apart from having environmental-friendly advantages. Preliminary studies during pyrolysis and co-pyrolysis of Malaysian sub-bituminous coal, waste High Density Polyethylene (HDPE) and coal/waste HDPE blends have been performed via Thermogravimetry Analysis (TGA apparatus). The tests were carried out in nitrogen atmosphere, under dynamic conditions at a heating rate of 10oC/min. The coal/waste HDPE blends were prepared in the weight ratios of 80:20, 60:40 40:60 and 20:80. The results showed that the thermal decomposition of the materials can be characterized by single reaction stage both for single and blended fuels between a temperature range of 300-530oC. Overlapping DTG curves, the comparison between experimental and theoretical devolatilization rate and deviation in char yield, suggests that the existence of possible synergistic effect for blended fuels are caused by chemical interactions. An increase in reactivity is observed with increasing HDPE blend ratio which is primarily due to the release of high amount of volatiles in the waste polymer. It was suggested that the degradation of polymer waste in the blends form radicals that abstracted hydrogen from coal and resulted in less char being produced.

Simulation Study of Shenmu Coal Pyrolysis by Gas Heat Carrier Based on a Moving Bed

Coats–Redfern integral method combined with thermogravimetry-mass spectrometry technology was applied to study the evolution of the main pyrolysis products for Shenmu bituminous coal. And a heat transfer, reaction, numerical model of coal pyrolysis by gas heat carrier in a moving-bed reactor is developed. The model can predict the internal temperature profile and pyrolysis volatiles evolution of different coal species as well as the temperature distribution of gas heat carrier versus bed height. The results show that when the temperature of the gas heat carrier increases from 700 to 900 °C, the theoretical bed height of pyrolysis drops from 0.26 to 0.14 m, and the maximum of the devolatilization rate increases from 0.954%·s–1 to 1.382%·s–1. The coal species have significant influence on their temperature-rise pyrolysis process in a gas heat carrier moving-bed reactor. Higher initial temperature or velocity of gas heat carrier, smaller particle size, or moving velocity of coal tends to accelerate the devolatilization rate and shorten the pyrolysis time. This work may provide a theoretic foundation for the reactor amplification and different industrial condition prediction of high-volatile coal pyrolysis in a moving-bed reactor.

Pyrolysis Characteristics and Char Reactivity of Oedogonium sp. and Loy Yang Coal

The proposition of combining the application of algae in wastewater treatment, CO2 fixation, and energy production maximizes the opportunity of algal bioremediation. In this paper, the freshwater macroalga Oedogonium, a key target species for the bioremediation of waste waters, was investigated for its utilization in energy production via gasification or co-gasification with coal. The pyrolysis characteristics of Oedogonium and the effects of pyrolysis conditions on char reactivity were investigated in this paper, and an Australian lignite was also studied for comparison purposes. The pyrolysis process of Oedogonium and coal can be divided into three stages: moisture evaporation, volatile release, and decomposition of the remaining carbonaceous compounds. However, the devolatilization of Loy Yang coal was slower and occurred over a wider temperature range compared to Oedogonium. As the heating rate increased, the pyrolysis curves for both Oedogonium and Loy Yang coal shifted to higher temperatures. To investigate the effects of pyrolysis conditions on char reactivity, a tube reactor was employed to generate char samples under a range of pyrolysis conditions. The produced char samples were characterized using a CHN analyzer and scanning electron microscopy technique. It was found that char samples almost maintain their original shape following pyrolysis at a low heating rate. However, evidence of char swelling was observed in the structure of chars prepared at a high heating rate. Pyrolysis conditions also had a significant influence on the reactivity of the derived chars. Char reactivity for both fuels was enhanced at a higher heating rate and lower pyrolysis temperature. Oedogonium char reactivity was around 2–5 times that of Loy Yang char prepared under the same pyrolysis conditions. However, the differences in reactivity became less significant as the pyrolysis temperature increased. Oedogonium has a higher devolatilization rate and higher char reactivity than Loy Yang lignite. It implies that it is easier to be gasified, and the co-gasification with lignite is advantageous.

Influence of inherent moisture on the ignition and combustion of wet Victorian brown coal in air-firing and oxy-fuel modes: Part 1: The volatile ignition and flame propagation

This study for the first time reported the volatile ignition and oxidation for wet Victorian brown coal in both air-firing and oxy-fuel modes. The aim is to quantitatively understand the evaporation of inherent moisture and its overlapping with the subsequent volatile ignition and oxidation steps during pulverised coal combustion. A wet Victorian brown coal sample with the moisture content up to 30wt.% and a size range of 63–104μm has been tested. Its ignition, volatile flame propagation and char oxidation have been diagnosed optically in a laboratory-scale flat-flame burner reactor (FFBR) coupled with a high-speed camera. 1-D modelling was also conducted to predict coal ignition based on the classic coal drying theory and coal devolatilisation rate. As has been confirmed, the release of moisture on the initial drying stage is incomplete prior to the subsequent volatile ignition. The fraction of moisture released upon drying only accounted for 10% of its original amount in wet brown coal prior to ignition. This is due to a firm residence of the moisture within coal capillaries, and a rapid heat feedback from hot gas to the dried particle surface that was ignited instantaneously prior to the release of the remaining moisture. The unevaporated moisture was observed to be released with the volatiles together to form a thick cloud layer in the vicinity of the coal particle, thereby enlarging the sizes of the volatile flame remarkably, which are approximately twice the size of the dried coal flame. However, the intensity of the wet coal flame was much weaker than dried coal, due to the dilution effect of the inherent moisture on the volatile cloud. In the oxy-fuel combustion mode, the inherent moisture interrelated with CO2, a tri-atomic gas with a larger specific heat capacity than N2 to significantly delay the ignition of the wet coal particle and its flame intensity and propagation velocity.

Effects of Particle Shrinkage and Devolatilization Models on High-Temperature Biomass Pyrolysis and Gasification

The effects of two different particle shrinkage and devolatilization models on biomass pyrolysis and gasification behavior in a high-temperature (1400 °C) entrained-flow reactor have been studied employing a three-dimensional Eulerian–Lagrangian computational fluid dynamic model in the framework of open-source codes, OpenFOAM. Both qualitative results (temperature distribution, gas composition, and particle distribution) and quantitative results (pyrolysis time, syngas production, carbon conversion, and particle residence time) are presented and analyzed. Results show that particle shrinkage models significantly affect the simulation results and the constant volume model predicts a faster devolatilization rate, higher H2, CO, and CH4 productions, lower CO2 production, higher carbon conversion, and longer particle residence time than the constant density model. However, the two devolatilization models employed give consistent results on the exit syngas production and carbon conversion, although the constan...