Particle Heating Rate Research Articles

Pyrolytic Kinetics of Polystyrene Particle in Nitrogen Atmosphere: Particle Size Effects and Application of Distributed Activation Energy Method.

This work was motivated by a study of particle size effects on pyrolysis kinetics and models of polystyrene particle. Micro-size polystyrene particles with four different diameters, 5, 10, 15, and 50 µm, were selected as experimental materials. Activation energies were obtained by isoconversional methods, and pyrolysis model of each particle size and heating rate was examined through different reaction models by the Coats–Redfern method. To identify the controlling model, the Avrami–Eroféev model was identified as the controlling pyrolysis model for polystyrene pyrolysis. Accommodation function effect was employed to modify the Avrami–Eroféev model. The model was then modified to f(α) = nα0.39n − 1.15(1 − α)[−ln(1 − α)]1 − 1/n, by which the polystyrene pyrolysis with different particle sizes can be well explained. It was found that the reaction model cannot be influenced by particle geometric dimension. The reaction rate can be changed because the specific surface area will decrease with particle diameter. To separate each step reaction and identify their distributions to kinetics, distributed activation energy method was introduced to calculate the weight factor and kinetic triplets. Results showed that particle size has big impacts on both first and second step reactions. Smaller size particle can accelerate the process of pyrolysis reaction. Finally, sensitivity analysis was brought to check the sensitivity and weight of each parameter in the model.

Thermal evolution of the oxidation characteristics of pulverized coal with different particle sizes and heating rates

Thermal evolution of the oxidation characteristics of pulverized coal with different particle sizes and heating rates was investigated using a C600 microcalorimeter system. The results show that the evolution of oxidative heat of pulverized coal has obvious stage characteristics. With the increase of temperature, the changes of heat flow and DHF curve increase with the decrease of pulverized coal particle size and the increase of the heating rate. Thermal evolution of the oxidation process of pulverized coal is characterized by heat absorption first and then releasing heat, and the maximum heat release of Stage3 can reach 281.15 J. At the same heating rate, the activation energy of pulverized coal with different particle sizes generally shows E106-180> E75-106> E62-75. The decrease of the particle size and the increase of the heating rate lead to an increase in the spontaneous combustion tendency of coal.

Simulative prediction of ultrafine particulate matter formation by means of different pyrolysis models

In this study, the sensitivity of two different pyrolysis models on the simulative prediction of inorganic ultrafine Particulate Matter (PM) formation is investigated. For consideration of PM formation, the volume-conserved discrete-sectional Population Balance Model (PBM) is used. The volatile release is an input parameter of the PBM and thus influences the calculated PM formation. As a representative of an empirical pyrolysis model, the Fu-Zhang model (FZM) is used. In comparison, the Chemical Percolation Devolatilization model (CPD) is taken as a representative for sophisticated pyrolysis network models. The latter takes influences of fuel composition, heating rate and particle temperature into account. The evaluation of the pyrolysis model impact is determined for a pulverized (dp=65–74μm) Chinese lignite (Zhundong) since this fuel has a relatively high volatile content and thus favors the formation of particulate matter. To investigate the influence of particle heating rate in the models, two different gas temperatures (1200 K and 1500 K, respectively 5.28·104 K s−1 and 7.51 × 104 K s−1 calculated with the energy balance) are considered. Furthermore, these conditions are selected because experimental data of the PM particle size distribution (PSD) from previous studies are available. The modeling of PSD is performed and validated with the existing experimental PSD data. These experimental data were achieved in investigations with a Hencken burner. The results of the two models (FZM and CPD) show recognizable differences in predicting the PSD. This study indicates that the CPD model improves significantly the prediction of ultrafine PM formation.

Sintering and Densification of Fibre Reinforcement in Polymers during Rotational Moulding

In the present work, sintering and densification of fibrous composite structures produced by rotational moulding were investigated. Lack of pressurisation during the process of rotational moulding implies an absence of driving forces to strongly bond two materials together as necessary in composite structures. This means that sintering and densification are the fundamental phases in which two or more materials can create an interface together by which stresses can be transmitted. The sintering study comprised of a novel single-particle interaction test that was developed to study the dynamical interaction between an ideal single polymer particle and a glass fibre bundle. Results showed that, although compatibiliser, as well as particle morphology, have an effect on fibre-particle bonding characteristics at a mesoscale, fibre sizing was shown to be the most significant parameter that affects polymer-fibre compatibility the most. The densification investigation studied the void and bubble formation and disappearance during the rotational moulding cycle as these defects have a detrimental effect on the mechanical performance of rotomoulded composite structures. The results verified previous researchers’ conclusions that particle size, heating rate and peak temperature are the most fundamental parameters to control bubble size and bubble density. Images captured during densification show how formation and evolution of air trapped in bubbles can be controlled by particle size or processing temperature. Finally, work is ongoing to present conclusions as to what resin properties should be more suitable for the rotational moulding of fibrous composite structures.

Characterization of cassava biomass using differential scanning calorimetry and thermogravimetry for energy purposes

Most of the agricultural industries generate daily waste, which due to toxicity or quantity deserve special attention. The cassava starch produces a significant quantity of residues, which must be rationally used for minimizing the environmental impact of the agricultural activities. The present study aims to enhance the use of this solid residue. We analyzed the cassava bagasse by means of the following techniques: thermogravimetric analysis (TG) and differential scanning calorimeters (DSC). It was addressed the effects of operational conditions (final temperature, heating rate, atmosphere, air flow and size of particles). The cassava bagasse samples collected in a cooperative production facility in Paraty-RJ were characterized using TGA/DSC in order to describe the thermal behavior of these residues. The DOE methodology proposed by Taguchi was used to analyze and cover a broader range of operational parameters. The most influential variables were identified for the process of heat production using DOE technique. These variables provide the best combination for heat flux with residence time of 30 min, air flow of 50 mL min−1, particle size sieved to 0.42–0.71 mm and heating rate of 25 °C min−1. The main parameters related with the thermal decomposition, effective activation energy and decomposition mechanism were newly determined using thermal techniques analysis methods (TGA/DSC) for the cassava residue.

Effect of particle size and heating rate on pyrolysis kinetics of Nerium oleander

Nerium oleander is a lignocellulosic biomass which is not consumed by cattle due to its poisonous nature. The effect of two important parameters namely particle size and heating rate on thermal degradation profiles of leaves and stems of N. oleander under pyrolytic conditions were studied using thermogravimetric analysis (TGA). Experiments were conducted using heating rates from 5 to 20 °C min−1 in the pyrolysis temperature range of 0–1200 °C under 100 sccm nitrogen flow. Three different particle sizes 125, 500, and 1000 µ were considered for this study. Three degradation stages (each for hemicellulose, cellulose, and lignin) excluding the moisture loss were found for the chosen biomasses irrespective of particle size and heating rate. The kinetic rate parameters for hemicellulose, cellulose, and lignin were found using mass loss data obtained from TGA assuming first order kinetics using Coats–Redfern model. The assumed first order kinetics was proved correct for all the biomasses chosen based on the R2 value for the experimental data. Lower range of activation energy for hemicellulose and cellulose was observed for all particle sizes at lower heating rate when compared with lignin for both leaves and stems of N. oleander.

Influence of Ultrasonic Transducer Structural Parameters on the Frictional Plasticizing Heat Generation of Polymer Particles

Abstract This paper explores the influence of structural parameters of ultrasonic transducer on the frictional plasticizing heat generation of polymer particles. A three-dimensional model of the interfacial friction plasticizing heating was established, and a transducer with different structural parameters was designed and analyzed. The actual output longitudinal vibration excitation of the transducer obtained by simulation analysis was directly loaded into the heating model, which further investigated the effect of various structural parameters on the frictional plasticizing heating process and temperature distribution of polymer particles. The results demonstrated that the interfacial friction plasticizing heating temperature of polymer particles increases nonlinearly with the longitudinal vibration excitation time, and the heat generation is a transient process. The amplification ratio has the greatest influence on the interfacial friction plasticizing heating rates of polymer particles, followed by both front cover length and piezoelectric ceramic pieces thickness; the effects of length of rear cover, horn and ultrasonic tool head are the smallest. The present work provides an effective basis for further studying the ultrasonic plasticizing of polymer particles in ultrasonic micro-molding.

Biomass pyrolysis kinetics in a fluidized bed reactor: Measurements and plausibility verification for reaction conditions

A small-scale fluidized bed reactor is used to study pyrolysis kinetics of pulverized beech wood particles. The fluidized bed reactor realizes high particle heating rates (104 K/s) and high temperatures (up to 1473 K) to approximate flame-equivalent conditions of pulverized fuel boilers. Mass release rate is calculated based on time-dependent concentration profiles of 22 gas species measured with ex-situ FTIR gas analysis for batch-wise injected fuel samples. To verify if the determination of kinetic data from experiments is taking place in the reaction kinetic controlled regime, the Global Reaction Model (GRM) combined with an Arrhenius approach is used. A comparison with literature data shows that kinetic data can be measured reliable in the temperature range from 523 to 973 K. The obtained data sets are unique regarding their time resolution and number of investigated gas species, which promotes them to be used as validation data for network models in the given temperature range. For higher temperatures, the pyrolysis reaction is distorted by the insufficient gas transport to the ex-situ measurement device.

Characteristics and Kinetics of Huadian Oil Shale Pyrolysis via Non-isothermal Thermogravimetric and Gray Relational Analysis

ABSTRACTThe pyrolysis of Huadian oil shale was carried out in a non-isothermal thermorgravimetric thermal analyzer system. The particle size (0.3–0.45 mm, 0.2–0.3 mm, 0.15–0.2 mm, 0.088–0.15 mm, 0.075–0.088 mm, and <0.075 mm), heating rate (5, 10, 20, and 50℃ min−1), and specimen mass (approximately 5 mg, 10 mg, and 15 mg) were considered to study the effects which caused by mass and heat transfer limitations. The kinetic parameters were determined using Kissinger–Akahira–Sunose (KAS), Friedman, and Coats-Redfern method combining the Avrami-Erofeev AE2 kinetic model. And the gray relational analysis method was employed to investigate the influence of particle size, heating rate, and specimen mass on the pyrolysis behavior as well as kinetic parameter. It is showed that, in the second stage, average activation energy of Huadian oil shale was 225 ± 7 KJ mol−1, 240 ± 6.5 KJ mol−1, and 244 ± 21.5 KJ mol−1, calculated by KAS, Friedman, and Coats-Redfern-Avrami-Erofeev method, respectively, indicating that the second stage can be modeled by Avrami-Erofeev AE2 equation. The order of the gray relational grade showed that the particle size, heating rate, and specimen mass exhibit a noticeable relevance to pyrolysis behavior of Huadian oil shale. The heating rate has a significant effect on both the product release rate and average activation energy. The particle size has the least effect on the product release rate, while specimen mass has the least influence on the average activation energy.

Preparation of ultrafine/nano Mo particles via NaCl-assisted hydrogen reduction of different-sized MoO2 powders

The current study investigated the effects of the amount of NaCl addition, particle size of MoO2, temperature (under isothermal condition) and heating rate (under non-isothermal condition) on the morphology, particle size and dispersivity of prepared Mo by hydrogen reduction of MoO2. The formation of sufficient dispersed Mo nuclei and their controllable growth were crucial for transforming the large MoO2 particles to dispersed ultrafine/nano Mo particles. It was found that in the absence of NaCl, it was hard to control the nucleation and growth of Mo grains, and the morphology and particle size of products still retain those of the raw MoO2 in the temperature range of 840–1000 °C. However, as the amount of NaCl addition was above 0.05%, it was successful to control the nucleation and growth of Mo. Ultrafine/nano Mo powders with the average particle size from 100 nm to 800 nm were successfully prepared via adjusting the particle size of MoO2 and temperature under isothermal condition. The use of MoO2 with small particle sizes can increase the reaction rate and the number of Mo nuclei number, thus improve the particle dispersivity and decrease the particle size. Additionally, after reaction at 900 °C and 1000 °C, the residual Na was reduced to 140 ppm and 33 ppm from the initial value of 380 ppm, respectively. Under non-isothermal condition, the temperatures for the nucleation and growth could be adjusted by changing heating rate and particle size of raw MoO2 particles. Mo nanoparticles with smaller particle size and better dispersivity were successfully prepared, and the average particle size can decrease to about 80 nm.

Non-isothermal thermogravimetric investigation on mutual effect between bituminite and anthracite in blends for blast furnace injection

In order to clarify the mutual effect between bituminite and anthracite in blends during industrial combustion, the influence of particle size and heating rate as well as oxygen concentration in atmosphere was analyzed. The results of non-isothermal thermogravimetric analysis indicated that the combustion behavior of blends was of great difference though blends were prepared with the same volatile content of 20%. The catalysis of bituminite to anthracite changed with the thermal and kinetic condition of combustion reaction, and consequently, blends with different collocations were suitable for various combustion environments. Superior combustion properties of some blends were achieved at high heating rates, while others might react faster under high oxygen-enriched atmosphere. Simultaneously, the volume model and unreacted core model as well as random pore model were introduced to fit the experimental data. The kinetic calculation results showed that the combustion of blends at different heating rates all agreed better with that of random pore model in comparison with the other two models, while the apparent activation energy of samples all decreased with the increase in heating rate. The similarity of functional group structure between bituminite and anthracite is closely related to the accordance in combustion stage of bituminite and anthracite in blends.

Developing a free-fall reactor for rice straw fast pyrolysis to produce bio-products

Recently, the world energy demand is increasing due to the growing world population. Accordingly, many research works are directed toward the new resources of renewable energy in order to compensate the shortage in petroleum based products. The use of biomass as a source for renewable energy is of growing importance. One of the most problematic agriculture wastes in Egypt is rice straw which is generated in huge amounts over a limited harvesting period. In this study the main objective is to develop and design a new rice straw fast pyrolysis reactor that improves some inefficiencies in traditional reactors while maintaining high bio-oil yields. To accomplish this target, a laboratory scale plant with a free-fall reactor was designed to avoid lack of moving parts; Compared it with other plants, the designed under investigation plant has the advantage of simple design. Two basic principles were combined in the design of the free-fall reactor; the first principle dealt with the particle heating rate, while the second considered the particle’s free-fall velocity. Based on this developed and designed free-fall reactor, the fast pyrolysis process of rice straw was carried out at temperatures ranging from 450 °C to 700 °C. The obtained bio-products from this process are liquid bio-oil, bio char and non-condensable gases. The characterization and chemical composition of the bio-oil and non-condensable gases were determined, respectively. It was concluded that the above mentioned free-fall reactor can be used for producing useful bio-products from rice straw and sharing to solve the most problematic agriculture waste.

Prediction of soot formation characteristics in a pulverized-coal combustion field by large eddy simulations with the TDP model

In this study, the soot formation characteristics in a pulverized-coal combustion field formed by a 4 kW Central Research Institute of Electric Power Industry (CRIEPI) jet burner were predicted by large eddy simulation (LES) employing a tabulated-devolatilization-process model (TDP model) [N. Hashimoto et al., Combust. Flame 159 (2012) 353–366]. This model enables to take into account the effect of coal particle heating rate on coal pyrolysis. The coal-derived soot formation model proposed by Brown and Fletcher [A. L. Brown and T. H. Fletcher, Energy Fuels 12 (1998) 745–757] was employed in the LES. A comparison between the data predicted by LES and the soot volume fraction distribution data measured by laser induced incandescence confirmed that the soot formation characteristics in the coal combustion field of the CRIEPI burner can be accurately predicted by LES. A detailed analysis of the data predicted by LES showed that the soot particle distribution in this burner is narrow because the net soot formation rate is negative on both sides of the base of the soot volume fraction. At these positions, soot particles diffused from the peak position of soot volume fraction are oxidized due to a relatively high oxygen concentration. Finally, the effect of soot radiation on the predicted gas temperature distribution was examined by comparing the simulation results obtained with and without soot radiation. This comparison showed that the maximum gas temperature predicted by the simulation performed with soot radiation was over 100 K lower than that predicted by the simulation performed without soot radiation. From result strongly suggests the importance of considering a soot formation model for performing numerical simulations of a pulverized-coal combustion filed.

Internal heat transfer characteristics of large-particle oil shale during pyrolysis

A 2D cylinder transient heat transfer model was developed for single-particle oil shale pyrolysis in the fixed-bed reactor. Variations of physical properties of oil shale were considered in this model. The developed model was solved using ANSYS after determining boundary conditions. And then intraparticle temperature distribution was obtained during oil shale pyrolysis. Moreover, effects of particle size and heating rate on intraparticle temperature distribution were investigated. The radius of 30-mm oil shale and pyrolysis time were divided into ten equal intervals to calculate temperature at any time and any position during the sample pyrolysis. The calculated results reasonably agreed with actually measured temperature.

Assessment of Global and Network Models of Devolatilization for Numerical Analysis of Pulverized Coal Combustion

ABSTRACTMathematical modeling of devolatilization plays a significant role in the prediction of flame development in solid fuel combustion simulations. Commonly implemented devolatilization models available in the literature to simulate pulverized coal combustion are reviewed and evaluated. The effect of the particle heating rate on the onset of devolatilization and on final volatile yield is discussed. Selected devolatilization models are investigated with respect to their implementation in Computational Fluid dynamics (CFD) simulations of methane-assisted pulverized coal jet flame experiments. Differences in volatile release region, particle temperature and species concentration are presented and discussed with comparisons to the experimental data.

Characteristic Study of Shenmu Bituminous Coal Combustion with Online TG-MS-FTIR

The combustion characteristics of Shenmu bituminous pulverized coal (SBC) were comprehensively investigated with a combined TG-MS-FTIR system by considering the effect of particle size, heating rate and total flowrate. The combustion products were accurately quantified by normalization and numerical analysis of MS results. The results indicate that the decrease of the particle size, heating rate and total flowrate result in lower ignition and burnout temperatures. The activation energy tends to be lower with smaller particle size, lower heating rate and total flowrate. The MS and FTIR results demonstrate that lower concentrations of different products, such as NO, NO2, HCN, CH4 and SO2 were produced with smaller particle size, slower heating rate and lower total flowrate. The decrease of particle size would lead to more contact area with oxygen and slower heating rate could provide more sufficient time for the diffusion. High total flowrate would reduce the oxygen adsorbability on the coal particle surface and shorten the residence time of oxygen, which makes the ignition difficult to occur. This work will guide to understand the combustion kinetics of pulverized coals and be beneficial to control the formation of pollutants.

Natural Calcium‐Based Residues for Carbon Dioxide Capture in a Bubbling Fluidized‐Bed Reactor

AbstractUsed clamshells (Paphia undulata), as a precursor of calcium oxide (CaO) sorbents, were employed for carbon dioxide (CO2) adsorption in a bubbling fluidized‐bed reactor. To find the optimal calcination conditions, a 2k experimental design was used to vary the ground clamshell particle size, heating rate, and calcination time at 950 °C under a nitrogen atmosphere. The heating rate was the most significant factor affecting the CO2 adsorption capacity of the obtained CaO sorbent. The maximum CO2 adsorption capacity of the CaO obtained under these study conditions was higher than that of commercial CaO.

A two dimensional Euler-Lagrangian model of wood gasification in a charcoal bed — Particle histories

An Euler-Lagrangian simulation applied to wood gasification in a fluidized bed is used to investigate individual particle histories and to provide a statistical analysis for temperature, apparent density as well as radial and axial positions of charcoal and dry wood particles. The model and several parameter variations have been discussed in detail in previous articles [1–3]. Based on simulation results we find much higher particle heating rates than typically used to measure kinetic data for, e.g., pyrolysis models. Although we presented a rather complex interplay of particle heating rate, biomass decomposition, particle shrinkage and particle fluidization the simulation results emphasize the importance of the usage of realistic particle size distributions for the initial bed as well as the fuel inlet. Furthermore, particle shrinkage data in combination with mass decomposition data appear to be crucial for realistic simulations.

Effects of Particle Size and Heating Rate on Evolution of Products from Pyrolysis of Phenolic Circuit Boards

Abstract Pyrolysis is an attractive means of recovering resources from waste integrated printed circuit boards (PCBs) because organic materials they contain are converted into gas, tar, and char th...

Determination of pyrolysis properties of sirnak (Avgamasya) asphaltite by thermal analysis methods

ABSTRACTIn this study, pyrolysis properties of Sırnak asphaltite have been determined by thermal analysis methods. According to proximate and elemental analysis results, air-dried sample contains 0.56% moisture, 46.51% ash, 34.02% volatile matter, 18.91% fixed carbon, 42.1% C, 3.57% H, 0.50% N, 5.55% S, and 48.28% O by weight. For the determination of pyrolysis properties of the sample, DTA and TGA of thermal analysis methods have been used. DTA and TGA experiments have been carried out by using approximately 10 mg sample, under 50 ml/min nitrogen gas flow rate, from ambient to 900°C temperature range. To investigate the effects of particle size and heating rate on pyrolysis properties, TGA experiments have been carried out by using three different particle sizes and five different heating rates. By examining the TG/DTG thermograms, three different temperature regions have been found that depend on moisture loss, volatile release, and mineral matter decomposition. Also, by using TG/DTG data of the samples, apparent activation energies and Arrhenius constants were calculated by Arrhenius and Coats-Redfern kinetic models, and the results were compared with each other.