Pyrolysis Of Solid Fuels Research Articles

Experimental and kinetic study on flash pyrolysis of biomass via on-line photoionization mass spectrometry

Experimental and kinetic study on flash pyrolysis of solid fuels is a challenge since its process usually occurs in a very few seconds. To do this successfully, a perfect combination of high heating rates, plug flow reactor, on-line sampling, real-time analysis and fast acquisition (e.g., < 300 ms/spectrum) is indispensable. In this work, a microfluidized-bed reactor (MFBR) was connected to the single photoionization time-of-flight mass spectrometer (SPI-TOFMS) to explore the kinetic process from flash pyrolysis of cellulose. The hydrodynamics of MFBR at different pyrolysis temperatures and with three model compounds were analyzed. The time-evolved profiles of primary tar from flash pyrolysis were recorded by SPI-TOFMS. The effect of experimental conditions (including pyrolysis temperature, transfer-line temperature and the type of carrier gas) on the kinetics of flash pyrolysis was systematically discussed. Besides, experimental measurements were also compared with kinetic modeling results, which shows a much better agreement between them than previous work. The obtained results prove that the MFBR combined with SPI-TOFMS is a potential and reliable method to experimentally study the flash pyrolysis of solid fuels.

The measurement and modeling of partial discharges in solid fossil fuels

The paper is devoted to the study of the characteristics of partial discharges in solid fossil fuels. The appearance of partial discharges in solid fuels occurs at very low voltages, which are not typical for most dielectrics. The activity of partial discharges leads to the onset of rock breakdown. The characteristics of partial discharges in the oil shale of the Huadan deposit (China), presented in the work, indicate the voltage value at which partial discharges arise and breakdown occurs, and also show how these characteristics depend on voltage. We attempted to explain the low value of the voltage of partial discharges in solid fuels, as well as to substantiate the possibility of using partial discharge characteristics to predict the breakdown of the interelectrode space for use in the technology of in-situ heating and the pyrolysis of solid fuels. Keywords: Oil shale, subterranean conversion, field distribution simulation, apparent chage measurement.

Измерение и моделирование частичных разрядов в твердых топливах

The paper is devoted to the study of the characteristics of partial discharges in solid fossil fuels. The appearance of partial discharges in solid fuels occurs at very low voltages, which are not typical for most dielectrics. The activity of partial discharges leads to the onset of rock breakdown. The characteristics of partial discharges in the oil shale of the Huadan deposit (China), presented in the work, indicate the voltage value at which partial discharges arise and breakdown occurs, and also show how these characteristics depend on voltage. We attempted to explain the low value of the voltage of partial discharges in solid fuels, as well as to substantiate the possibility of using partial discharge characteristics to predict the breakdown of the interelectrode space for use in the technology of in-situ heating and the pyrolysis of solid fuels.

A Predictive Physico-chemical Model of Biochar Oxidation

Pyrolysis of solid fuels forms a solid carbon-rich fuel, also called char, whose physico-chemical description is rather complex. Heterogeneous oxidation reactions take place during thermochemical conversion of char. The present work proposes a predictive detailed kinetic model, opening a new path for a deeper understanding of the char conversion process. This model considers porosity, surface area, density of surface sites, and their evolution along the conversion process. The chemical aspects of char oxidation are modeled assuming a carbonaceous bulk structure, surrounded by a variety of surface sites which represent the chemical functionalities typically present in such materials. The heterogeneous chemical reactions and their kinetic parameters are defined based on previous studies in the literature and by analogy to homogeneous gas-phase reactions of aromatic species. A mathematical framework is proposed to couple physical and chemical descriptions of the oxidation process. Although the proposed model benefits from experimental information, it is able to comprehensively describe the conversion rate of a broad range of carbonaceous materials such as carbon nanotubes, graphite, and chars only on the basis of their elemental composition. The proposed model represents a first step in exploring the explicit and coupled treatment given to the physical and chemical evolution of the fuel throughout its conversion, allowing us to consistently describe the particle evolution, opening a path for reliable models to manage the chemistry of char conversion.

A two-dimensional distributed activation energy model for pyrolysis of solid fuels

Pyrolysis kinetic models are pivotal for understanding and optimizing the gasification, distillation, and combustion processes. This paper proposes a novel two-dimensional distributed activation energy model (2D-DAEM), which is achieved via extending the classical DAEM to the 2D plane of activation energy E and pre-exponential factor A. The performance of the proposed model was evaluated based upon comprehensive analyses of complex reactions such as co-pyrolysis. The results show that the 2D-DAEM outperforms the classical DAEM in terms of efficiency and accuracy. Specifically, the co-pyrolysis analysis of pine woodchips (PINE) and polyethylene terephthalate (PET), shows that the classical DAEM tends to underestimate the lnA values (i.e., 43.0 for PINE pyrolysis; 42.0 for PET pyrolysis; but 39.2 for PINE&PET co-pyrolysis), while the lnA value of 2D-DAEM (about 43.0 for all) is more reasonable. Additionally, the 2D-DAEM is employed to study the influence of coal particle size on pyrolysis. It is observed that the 25 μm coal has the highest reaction rate under both 500 K and 1500 K iso-thermal processes. As a more normative, reasonable, and accurate model, the proposed 2D-DAEM is bound to enhance the practice of reaction prediction, material analysis, and process design.

A Review on Detailed Kinetic Modeling and Computational Fluid Dynamics of Thermochemical Processes of Solid Fuels

This review presents the recent advances in computational approaches to understand thermochemical reactions of solid fuels with minimized empirical factors. It includes studies on kinetic modeling of gas-phase reactions of multicomponent molecular mixtures of volatiles derived from primary pyrolysis of solid fuels using a database for elementary reactions. Mechanistic studies to model the devolatilization of biomass and coal upon heating are also mentioned. The efforts to integrate the kinetic model with computational fluid dynamics to understand the flow and heat transfer behavior of industrial reactors for solid fuel conversions, including gasification and combustion, are reviewed. These advances are primarily based on the conventional forward analysis that provides a deeper understanding of chemically reacting flows of fuels undergoing thermochemical reactions. For the further development of the thermochemical conversion technology, it can be expected to develop alternative approaches such as inverse analysis to determine the optimal reactor design and operating conditions.

Unsteady Simulation of Ignition of Turbulent Reactive Swirling Flow of Novel Design of Solid-Fuel Ramjet Motor

This paper presents a numerical investigation of ignition and combustion stabilization of a novel design of a solid-fuel ramjet (SFRJ) motor with and without swirl flow. The proposed design includes two solid fuels, retaining the simple design of the classic SFRJ. Numerical simulations of unsteady, turbulent, reactive, and swirling flow coupled with solid-fuel pyrolysis have been performed using an in-house CFD solver. Experiments on SFRJ were conducted via a connected-pipe test facility to validate the developed code. Furthermore, the code was validated for chemical reactions, heat diffusion, and swirl flow by using benchmark test cases of shock-induced, semi-infinite plate, and dump combustor with swirl flow, respectively. Then, the proposed and classic designs were simulated for the same inflow conditions and configurations, and the results were analyzed and discussed. It is found that the mixing degree, reactant residence time, mass flux, ignition delay time, and regression rate improve when using the proposed design. Moreover, the proposed design reveals interesting observations of a new flame being created and merged with the main flame.

A comparative applicability study of model-fitting and model-free kinetic analysis approaches to non-isothermal pyrolysis of coal and agricultural residues

Comparative applicability of model-fitting and model-free kinetic methods to pyrolysis of two coals and four agricultural residues was analyzed by using two models from each class of methods. The two model-fitting methods were Arrhenius and Coats-Redfern while Friedman and Vyazovkin were selected from the model-free category. According to kinetic analysis by all four models, the fuels could be arranged in following order of activation energy, CC > DC > SD > RH > FS > CH. The two model-fitting methods exhibited different kinetic parameters (E and reaction mechanism). All fuels were found to have a third order reaction mechanism (F3) by using Arrhenius model. In the case of Coats-Redfern model, the CC and RH displayed 3-dimensional diffusion mechanism (D3) whereas CH, SD and FS exhibited third order reaction mechanism (F3). DC was found to decompose according to 2-dimensional diffusion mechanism (D2). The percentage difference between the values of activation energy found from the Arrhenius and Coats-Redfern models was in the range of 6.24–21.64%. The percentage difference between the values of activation energy from two isoconversional models was not more than 3.29% for coals and 4.91% for agricultural residues in the fractional conversion range of 0.1–0.7. Isoconversional models were found to be more reliable and accurate for estimation of non-isothermal kinetics for pyrolysis of solid fuels compared with model-fitting methods.

A New Method for Direct Determination of Char Yield during Solid Fuel Pyrolysis in Drop-Tube Furnace at High Temperature and Its Comparison with Ash Tracer Method

A drop-tube furnace with a novel double-tube configuration was successfully developed to directly determine char yields during the pyrolysis of a wide range of solid fuels (mallee wood; mallee leaf; rice husk; biosolid; and subbituminous, bituminous, and anthracite coal) at a gas temperature of 1573 K. The char yield from pyrolysis of mallee wood and mallee leaf is 85%. This study shows using total ash as ash tracer results in 45–220% overestimation of char yields for biomass fuels and 13–27% for coals due to partial evaporation of ash. Similarly, selecting Na and K results in overestimation of biomass char yields by at least 2.5 times and selecting P leads...

Simulation of fine polydisperse particle condensational growth under an octadecane–nitrogen atmosphere

The evolution of particle size distribution (PSD) of fine polydisperse particles at high number concentrations (>105cm−3) was simulated through a combined model employing direct quadrature method of moments (DQMOM) with heat and mass transfer equations. The PSD was assumed to retain log-normal distribution during the heterogeneous condensation process. The model was first verified by exact solution and experimental data prior to investigating the influence of initial conditions on final PSD under an octadecane–nitrogen atmosphere. Low particle number concentrations and high vapor concentrations were beneficial to shift the PSD to larger particles having a narrower distribution. Additionally, vapor depletion has more influence on the final PSD than the heat release parameter for a number concentration of 106cm−3. This study may assist the design process of a gas–solid separating cyclone, to eliminate dust from high-temperature volatiles by pyrolysis of solid fuels.

Parametric study and performance analysis of hybrid rocket motors with double-tube configuration

The practical implementation of hybrid rocket motors has historically been hampered by the slow regression rate of the solid fuel. In recent years, the research on advanced injector designs has achieved notable results in the enhancement of the regression rate and combustion efficiency of hybrid rockets. Following this path, this work studies a new configuration called double-tube characterized by injecting the gaseous oxidizer through a head end injector and an inner tube with injector holes distributed along the motor longitudinal axis. This design has demonstrated a significant potential for improving the performance of hybrid rockets by means of a better mixing of the species achieved through a customized injection of the oxidizer. Indeed, the CFD analysis of the double-tube configuration has revealed that this design may increase the regression rate over 50% with respect to the same motor with a conventional axial showerhead injector. However, in order to fully exploit the advantages of the double-tube concept, it is necessary to acquire a deeper understanding of the influence of the different design parameters in the overall performance. In this way, a parametric study is carried out taking into account the variation of the oxidizer mass flux rate, the ratio of oxidizer mass flow rate injected through the inner tube to the total oxidizer mass flow rate, and injection angle. The data for the analysis have been gathered from a large series of three-dimensional numerical simulations that considered the changes in the design parameters. The propellant combination adopted consists of gaseous oxygen as oxidizer and high-density polyethylene as solid fuel. Furthermore, the numerical model comprises Navier-Stokes equations, k-ε turbulence model, eddy-dissipation combustion model and solid-fuel pyrolysis, which is computed through user-defined functions. This numerical model was previously validated by analyzing the computational and experimental results obtained for conventional hybrid rocket designs. In addition, a performance analysis is conducted in order to evaluate the influence in the performance provoked by the possible growth of the diameter of the inner fuel grain holes during the motor operation. The latter phenomenon is known as burn through holes. Finally, after a statistical analysis of the data, a regression rate expression as a function of the design parameters is obtained.

Simultaneous investigation into the yields of 22 pyrolysis gases from coal and biomass in a small-scale fluidized bed reactor

Flash pyrolysis gas yields from bituminous coal and torrefied biomass have been investigated in the temperature range between 873 and 1273K for 22 different gas species simultaneously. Recording a larger number of species gives a more detailed insight into pyrolysis of solid fuels than it is provided by other studies in literature, where typically smaller numbers of species are tracked. As processes utilizing biomass are designed for lower process temperatures, literature data for biomass pyrolysis are scarce in the temperature range between 1023 and 1273K. This work, aiming at investigating potential fuels for pulverized solid fuel combustion, approximates pyrolysis conditions in the ignition zone of actual power plant boilers, where possible.Thus, based on results of a literature review, an experiment was designed using a small-scale fluidized bed reactor (FBR) to simultaneously analyze the pyrolysis gas yields for 22 species and to close the temperature gap found for biomass. Small batches of pulverized torrefied biomass from poplar wood and pulverized Colombian bituminous coal (Mina Norte) were rapidly pyrolyzed in the reactor. The two fuels were chosen as exemplary conventional and alternative energy sources for pulverized fuel fired power plants. Experiments have been carried out under atmospheric pressure in pure nitrogen atmosphere.Product gas analysis was carried out by Fourier transform infrared spectroscopy (FTIR) including two different sampling techniques. As a novelty, offline measurements have been used exclusively to improve the gas species selection procedure and reliability of detection. In case of offline measurements, the gas flow to the FTIR gas cell is stopped and the gas is enclosed in the cell allowing longer scan times of the captured gas mixture and thereby enlarging the signal-to-noise ratio (SNR). In succession, regular measurements with continuous flow (online) were performed for the simultaneous quantitative analysis of total pyrolysis yields for 22 selected gas species.Obtained pyrolysis yields show good agreement with available literature data. The larger number of investigated species provides an extended data set also covering minor pyrolysis species, for which quantitative data are scarce. Additionally, trends in the gas yields for biomass agree well with those found by other authors outside the mentioned temperature gap between 1023 and 1273K.

Radiation-induced pyrolysis of solid fuels for ramjet application

A wide variety of hydroxyl-terminated polybutadiene (HTPB) based fuels are experimentally assessed in anaerobic reaction. In this study HTPB pyrolysis is investigated using a CO2 laser as the energy source. The formulation of the solid fuel samples is systematically changed to isolate the effects of carbon black, metal fuel additives, and small amounts of oxidizer. In addition, chemical changes to the fuels including curative type and base polymer are varied. Rates of pyrolysis reaction are reported for a wide range of solid fuels applicable to ramjet application. Processes involving the sintering together of metal particles, accumulation of carbon black, and formation of a melt layer are found to affect the reaction rate. It is determined that the surface composition is the most influential factor influencing the regression rate of HTPB based fuels.

Pyrolysis Study on Solid Fuels: From Conventional Analytical Methods to Synchrotron Vacuum Ultraviolet Photoionization Mass Spectrometry

The demand of modern society for energy keeps increasing as a result of the rapid growth of population and urbanization. Pyrolysis of solid fuels, including biomass, coal, and polymer waste, has recently received special attention because it can provide extra sources of fuels. In the past few years, a variety of analytical techniques have been used to detect the pyrolysis products of solid fuels, such as gas chromatography/mass spectrometry, thermogravimetry, Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy, etc. However, online detection of gas release during the pyrolysis process, which is believed to be closely related to the thermal decomposition mechanisms of solid fuels, is rare. Recently, some progress has been made in real-time diagnostic techniques, the most important one of which is photoionization mass spectrometry (PIMS). This review focuses on recent developments in the pyrolysis study of solid fuels, especially on those performed with synchrot...

Experimental Evaluation of a Chinese Sulfur-Containing Lean Iron Ore as the Oxygen Carrier for Chemical-Looping Combustion

A series of chemical-looping combustion (CLC) tests were conducted in a thermogravimetric analysis (TGA) reactor to investigate the potential of a Chinese sulfur-containing lean iron ore as the oxygen carrier. Two main products of solid-fuel pyrolysis and gasification, namely, CH4 and CO, were selected as the reducing gases. Consecutive reduction–oxidation cycles were first carried out in the TGA reactor to evaluate the cyclic stability and agglomeration tendency of the oxygen carrier. The effects of the temperature, fuel gas concentration, and reaction gas composition on the reduction reaction were further investigated. Increasing the reaction temperature or fuel gas concentration enhanced the reduction rate and reaction degree of the oxygen carrier. Meanwhile, CO showed much higher reduction reactivity than CH4. A comparison of the rate index of the iron ore used with those of high-grade minerals indicated that the iron ore had adequate reactivity for its application in solid-fuel CLC technology. The si...

Pyrolysis of solid fuels: Thermochemical behaviour, kinetics and compensation effect

The paper presents the pyrolysis behaviour of eleven different rank solid fuels, carried out using thermogravimetry (TG). Obtained experimental curves were compared with profiles determined using the Single First Order Reaction (SFOR) model and three different approaches of Distributed Activation Energy Model (DAEM). The aim of this work was to develop different models dedicated to pyrolysis, in particular further investigate the interrelation between the activation energy and the pre-exponential factor, its impact on the results quality and attribution with the fuel properties and pyrolysis mechanism. Obtained results showed that the compensation effect, often noted for SFOR, has also occurred for DAEM. Furthermore, analysis indicated an existence of a relationship between the characteristic temperature Tiso (and ln(kiso)) and fuel properties. Observed interrelation may be attributed to the change in reaction mechanism.

Formation of Anhydro-sugars in the Primary Volatiles and Solid Residues from Cellulose Fast Pyrolysis in a Wire-Mesh Reactor

The unique design of wire-mesh reactors (WMR) enables the collection of primary volatiles with minimized secondary reactions from fast pyrolysis of solid fuels. This paper reports the formation of anhydro-sugars in both primary volatiles and solid residues from the fast pyrolysis of microcrystalline cellulose in a WMR. Under fast pyrolysis, cellulose is rapidly converted into an intermediate phase, and the maximal yield of the water-soluble intermediates achieved in this study is ∼21% on a carbon basis at 450 °C, much higher than those achieved in other pyrolysis reactor systems. The solid residue consists of sugar and anhydro-sugar oligomers with a wide range of degrees of polymerization (DPs). However, only anhydro-sugars with DPs up to 3 can be identified in the primary volatiles, and the presence of these anhydro-sugars is evident even at 300 °C. Because of high boiling points, cellobiosan and cellotriosan are impossible to be released into the vapor phase via evaporation under the conditions. These h...

Isoconversional Kinetic Analysis of Distributed Activation Energy Model Processes for Pyrolysis of Solid Fuels

Seven different distributed activation energy model (DAEM) processes, which were used to describe the pyrolysis kinetics of wood, algae, lignin, corn stalk skin, kerogen, cellulose, and coal, were analyzed by means of the Friedman differential isoconversional method. It has been shown that the activation energies obtained from the Friedman method are independent of the heating rate. For all DAEM processes considered, the effect activation energies evaluated by the Friedman isoconversional method showed significant dependence on the conversion. The kinetic parameters obtained by means of the Friedman isoconversional method were used to reconstruct the conversions and rates data. The agreement between the reconstructed data and the data calculated by the DAEM is excellent at the presimulated and extrapolated conditions for all the DAEM processes. This indicates the DAEM process can be taken as an example to check the accuracy of some integral isoconversional methods in the determination of the activation en...

Improving solid-fuel pyrolysis and gasification for effective cogeneration

The thermal conversion of solid fuel is considered (for the example of biomass), with assessment of the yield of volatiles and coke residue. The optimal temperature range for its pyrolysis (the range corresponding to maximum heat of combustion of the gases per unit mass of the initial product) is identified. The influence of steam and air flow rates on the gasification products is studied. A system for the generation of thermal and electrical energy in the steam-gas cycle is proposed, with a biomass gasification unit. The energy loads of a population center are calculated, with engineering and economic assessment of the steam-gas cycle. Biomass-based cycles are compared, from the perspective of the energy efficiency of a cogeneration system.

Numerical Studies of the Gas-Solid Hydrodynamics at High Temperature in the Riser of a Bench-Scale Circulating Fluidized Bed

The hydrodynamics of circulating fluidized beds (CFBs) is a complex phenomenon that can drastically vary depending on operational setup and geometrical configuration. A research of the literature shows that studies for the prediction of key variables in CFB systems operating at high temperature still need to be implemented aiming at applications in energy conversion, such as combustion, gasification, or fast pyrolysis of solid fuels. In this work the computational fluid dynamics (CFD) technique was used for modeling and simulation of the hydrodynamics of a preheating gas-solid flow in a cylindrical bed section. For the CFD simulations, the two-fluid approach was used to represent the gas-solid flow with the k-epsilon turbulence model being applied for the gas phase and the kinetic theory of granular flow (KTGF) for the properties of the dispersed phase. The information obtained from a semiempirical model was used to implement the initial condition of the simulation. The CFD results were in accordance with experimental data obtained from a bench-scale CFB system and from predictions of the semiempirical model. The initial condition applied in this work was shown to be a viable alternative to a more common constant solid mass flux boundary condition.