Coal Pyrolysis Reaction Research Articles

Numerical simulation of an externally heated fixed bed reactor for coal pyrolysis based on porous media

A cutting-edge three-dimensional transient model utilizing porous media has been developed to accurately simulate the pyrolysis process of externally heated coal. This innovative model comprehensively considers the evaporation and condensation of water, as well as the release of volatiles. In addition, it meticulously examines the change in coal seam porosity and the interphase heat transfer between pyrolysis gas and solid coal seam. The model's precision has been appropriately confirmed through validation against the central temperature evolution inside the experimental reactor. Notably, this model systematically illustrates various aspects, including the evolution of coal layer temperature, evaporation and moisture density, changes in coal layer density, porosity distribution, volatile release, and interphase heat transfer. The obtained results reveal that the heat absorption by moisture phase change causes the coal seam temperature to relatively stabilize at around the water boiling point for a period, thus delaying the initiation of the coal pyrolysis reaction. The pyrolysis gas released by center coal seam pyrolysis tends to flow radially toward the heating wall before flowing out of the reactor. Additionally, the change in coal seam porosity increases the heat transfer rate by an average of 1.5 °C/min during the rapid heating stage. The analysis also highlights the significant occurrence of interphase heat transfer throughout the pyrolysis process and elucidates its mechanism in various stages. Ultimately, this work offers essential theoretical guidance for the design, optimization, and scaling of subsequent externally heated fixed-bed coal pyrolysis reactors.

Evolution mechanism of organic macromolecular structure during lignite pyrolysis

Understanding the mechanisms governing coal pyrolysis reactions, particularly in relation to the coal macromolecular structure, is crucial for improving energy efficiency and facilitating the transition of coal into a clean energy source. This study employs cutting-edge techniques, such as High-Resolution Transmission Electron Microscopy (HRTEM) and Thermogravimetric Analysis coupled with Fourier Transform Infrared Spectroscopy and Mass Spectrometry (TG–FTIR–MS), to analyze lignite and its residual solid samples subjected to pyrolysis across a range of temperatures from 300 °C to 1100 °C. The variational characteristics of the macromolecular structure during coal pyrolysis are examined. Utilizing molecular dynamics simulations, we analyze the evolution mechanism of the macromolecular carbon structure of organic matter during the coal pyrolysis process. The results show that the pyrolysis can be divided into three distinct phases: activation (30–300 °C), pyrolysis (300–650 °C), and condensation (650–1200 °C). During these phases, the coal structure undergoes complex transformations, including folding, twisting, shedding of small molecular side chains, and breaking of macromolecular side chains, ultimately leading to the directional arrangement of structural fragments. The structural units initially undergo decomposition, followed by growth and alignment in a certain direction. The spatial distribution of aromatic structural units evolves from local ordering to complete disordering, culminating in larger-scale, three-dimensional ordering. The order of bond breaking within the macromolecular structure of lignite pyrolysis is: oxygen-containing functional groups (such as C–O and COOH) > aliphatic structure (N–C and C–C) > aromatic structure (CC). By uncovering the reaction intermediates and pathways involved in lignite pyrolysis, this research provides a comprehensive quantitative description of the coal pyrolysis process. These insights offer invaluable theoretical support for the industrial-scale pyrolysis of coal, paving the way for more efficient and sustainable utilization of this crucial energy resource.

Study on the Influence of Porous Gel on Coal Pyrolysis Performance Based on Experiments and Molecular Simulation

ABSTRACT Studying the kinetics of pyrolysis in pure coals and mixed coals (coals treated with porous gel) holds immense significance in effectively preventing and controlling the spontaneous combustion occurrences in coal. Firstly, porous gel materials were prepared based on physical mixing and chemical crosslinking reaction. Then, based on the thermogravimetric analysis method, the pyrolysis mechanism of porous gel in coal was studied using Flynn-Wall-Ozawa(FWO), Kissinger-Akahira-Sunose(KAS) and Coats Redfern models. Determine the mechanism of coal pyrolysis reaction using the Reaxx FF MD reaction mechanics model. Finally, the inhibition mechanism of porous gel on coal is analyzed through leading temperature rise experiment. The main reaction mechanisms of coal pyrolysis are the diffusion model in the low-conversion-rate range (D4), the R2 and R3 in the high-conversion-rate range, and the Avrami erofeev model (A2, A3). The molecular simulation results indicate that increasing the heating rate can accelerate the rate of coke cracking.

Effects of pressure and heating rate on coal pyrolysis: A study in simulated underground coal gasification

Underground coal gasification (UCG) is a promising technology which in-situ converts coal into fuel gases through controlled chemical reactions. In order to precisely control coal pyrolysis and increase the char yield, it is vital to understand the influences of operating factors such as heating rate and pressure, on coal pyrolysis. In this study, the effects of heating rate and pressure on the char formation of bituminous coal pyrolysis are investigated. The reaction mechanism of coal pyrolysis and the solid-state kinetic model are firstly reviewed. Subsequently, thermal experiments are conducted to study the effects of heating rate and pressure on coal pyrolysis characteristics. Moreover, the connection between the dominant coal pyrolysis reaction type and corresponding solid-state kinetic model is revealed. An empirical model of coal pyrolysis rate, pressure, and heating rate is also developed, which can be used to quantitatively predict pyrolysis rates under varying heating rate and pressure conditions. The results show that the optimal heating rate for char generation is at around 10 °C/min. On the other hand, when the pressure exceeds 2 MPa, it will enhance the char production by obstructing the physical release of volatiles and has insignificant impact on the reaction type. This study contributes to our understanding of the coal pyrolysis mechanism, and the proposed empirical model can provide valuable insights for optimizing operating parameters during UCG process.

Effect of Water Content on Oxidative Combustion and Pyrolysis Characteristics of Gas Coal

ABSTRACT The oxidative combustion and pyrolysis characteristics of gas coal with different water content (2.86%, 9.06%, 15.81%, 22.83%, and 30.12%) were systemically investigated by thermogravimetric – differential scanning calorimetry and low-temperature oxidation experiments. Results show that the mass loss and heat absorption-exothermic pattern are inconsistent in oxidative combustion and pyrolysis processes of gas coal containing water. The behavior of internal water dissipation in gas coal is consistent in oxidative combustion and pyrolysis processes, but the influence on them is significantly different in high-temperature stage (450–600 ℃), the internal water dissipation behavior makes the coal pyrolysis reaction faster and makes the coal oxygen reaction slower.

Effect of red mud-based additives on the formation characteristics of tar and gas produced during coal pyrolysis

Red mud (RM), an industrial solid waste, was introduced into the coal pyrolysis reaction system, and its effect on the formation characteristics of tar and gas products during coal pyrolysis was explored based on the regulation and characterization of RM structure along with a series of fixed-bed pyrolysis experiments. The results show that Fe2O3 in RM could react with reducing agents, e.g., solid carbon, H2 and CO, in coal pyrolysis environment, along with the gradual reduction process of Fe2O3→Fe3O4→FeO→Fe. As a result, coal conversion as well as release of light gas, such as CO and CO2, are both promoted. Influence tendency of RM after acid treatment (ARM) is consistent with that of the initial RM but the magnitude becomes greater. Compared with RM, ARM has a larger specific surface area and more developed mesoporous structure, thus providing a stronger regulation performance on tar composition. In the presence of ARM, contents of phenols, indenes and aliphatics in tar decrease, accompanied by the increase of monocyclic aromatic hydrocarbons, and the content of BTX and its yield increase by 76.25% and 47.90%, respectively. Furthermore, both the light components (boiling point, BP ≤ 360 °C) and light oil (BP ≤ 170 °C) in tar reach higher levels with addition of ARM. Therefore, ARM is an effective multifunctional catalyst for in-situ upgrading of tar during coal pyrolysis process.

Effects of water on pyridine pyrolysis: A reactive force field molecular dynamics study

The emission of nitrogen oxides (NOx) from coal combustion causes serious environmental problems. Fuel splitting and staging is a promising method for NOx control by combustion modification. In this process, nitrogen-containing compounds generated from pyrolysis gas play an important role in regulating NOx generation. Water from coal could potentially change reactions during the coal pyrolysis process. Adjusting the content of water in coal may be an effective way to control coal pyrolysis reactions. This work aims to investigate the effects of water on pyridine (a main nitrogen-containing compound in coal) pyrolysis via reactive force field (ReaxFF) molecular dynamics (MD) simulations. Results indicate that the addition of water during the pyridine pyrolysis process increases the number of OH radicals in the system and accelerates the consumption of pyridine at the initial stage. However, at a later stage, water inhibits the consumption of pyridine as it impedes the condensation reaction of pyridine molecules. Common and unique intermediates are identified and quantified under various water-content conditions. Results suggest that water also reduces the proportion of nitrogen atoms in the polycondensation product. Furthermore, ring opening processes of pyridine molecules are reproduced at the atomic level. The changes in reaction pathways due to the presence of water are also revealed. The new insights into the mechanisms of pyridine pyrolysis under water and water-free conditions provide a possibility to control nitrogen migration during the pyrolysis process, which is of great significance to emission reduction from coal combustion.

Hydrogen production by supercritical water gasification of coal: A reaction kinetic model including nitrogen and sulfur elements

Researches on reaction kinetics and mechanism are crucial to the application of hydrogen production technology by supercritical water gasification of coal from experiment to industrialization. Based on the migration mechanisms of nitrogen and sulfur in the process, this paper developed a general model including nitrogen and sulfur to study the generation path, consumption path and reaction rate of the gasification products. The parameters of the kinetic model were obtained by fitting the experimental data of the gasification products, and the activation energy of each reaction was obtained by the Arrhenius equation. By comparing the reaction rates among the various reactions, the reaction steps for controlling the production or digestion of the product could be obtained. The main source of ammonia production was pyrolysis of coal followed by steam reforming reaction of fixed carbon. The rate of ammonia contribution from ammonia synthesis was extremely low and could be ignored. The consumption path of ammonia was the decomposition reaction of ammonia though its rate was also slow. The pyrolysis reaction of coal was the main source of hydrogen sulfide, followed by the steam reforming reaction of fixed carbon. The difference of the concentration and reactivity between organic sulfur and inorganic sulfur caused the difference in the generation source of hydrogen sulfide in early and late stage of the gasification. The kinetic model can predict not only the production of hydrogen, methane, carbon dioxide, carbon monoxide, ammonia and hydrogen sulfide under different operating conditions, but also the products for different coal types, which may provide a theoretical basis for the targeted regulation of nitrogen and sulfur elements in supercritical water.

Measurement of coal pyrolysis reaction heat by empirical baseline method

ABSTRACT Pyrolysis can be considered as the initial stage or/and paralleling part of coal combustion, gasification, and direct liquefaction, and pyrolysis itself constitutes one of the fundamental technologies in coal conversion. Reaction heat of coal pyrolysis is an important thermodynamic parameter used in reactor design, mechanism study, and energy efficiency assessment. In this study, thermogravimetric & differential scanning calorimetry technique (TG-DSC) was exploited to determine and plot the total heat flux curve along with pyrolysis temperature of Shenmu coal sample, and the varying curves of heat flux baselines in different reaction areas were analyzed and discriminated by empirical method, then the coal pyrolysis reaction heat was figured out. Moreover, the effects of primary test parameters on coal pyrolysis reaction heat were investigated. Results show that during the measurement rational settings including open crucible, ca. 15 mg sample amounts and – 0.074 mm particle size and 80 ml/min carrier gas flows could eliminate both internal and external diffusion effects and help to reduce secondary reactions of coal pyrolysis and heat resistance. When the heating rate increases from 3°C/min to 20°C/min, the total pyrolysis reaction heat of Shenmu coal sample shows an upward trend. Low hysteresis effect of heat transfer and high resolution of heat effect could be observed when the heating rate is 5°C/min, and the reaction heat measured is −12985 J/g, which can objectively express the reaction heat of coal pyrolysis. It could be concluded that coal pyrolysis reaction heat can be conveniently measured by the empirical baseline method with TG-DSC technique.

Experimental investigation of thermal effect in coal pyrolysis process

The thermal effects of five coal types' pyrolysis processes at heating rates of 5, 10, 15, 20, and 30 °C/min in the temperature range of 30–1000 °C were systemically investigated by thermogravimetric - differential scanning calorimetry. The experimental results show that coal pyrolysis process can be roughly divided into four stages, namely the drying and dehydration stage S1, the degassing stage S2, the pyrolysis stage S3, and the polycondensation stage S4. S1, S2, and S3 are endothermic and S4 is exothermic. For a given coal, the temperature at which the process shifts from the endothermic stages (S1 + S2 + S3) to the exothermic stage (S4) increases with increasing heating rate. The heat absorbed in endothermic stages keeps invariable basically, while heat released in exothermic stage decreases with increasing heating rate. The entire pyrolysis process is exothermic when the heating rates are lower than 10 or 15 °C/min, and endothermic at heating rates higher than 15 or 20 °C/min. The temperature corresponding to the peak in the weight loss curve does not correspond to that in the heat flow curve. Therefore, the characterizations of the coal pyrolysis reaction process by weight loss and heat flow are inconsistent with each other.

Characterizations of the coal char using slag as heat carrier in allothermal pyrolysis process

ABSTRACT In this work, the direction of allothermal coal pyrolysis reaction was driven by the waste heat of blast furnace slag. The structure features of the coal char mixed with/without slag was characterized by BET and SEM. The experiments of thermogravimetric analyzer were conducted to obtain the coal pyrolysis characteristics. The kinetic parameters of coal pyrolysis reaction were extracted using the reaction model based on the Arrhenius law and Li Chung-Hsiung method. The BET and SEM results showed that the slag addition could improve the structure features of the coal char effectively. The specific surface area, pore volume & size increased significantly. With the slag addition, characteristic temperatures of pyrolysis reaction did not change obviously. Peak temperature and final temperature increased by approximate 3.38 K and 5.55 K, respectively. However, the maximum weight reduce and pyrolysis characteristic index were enhanced dramatically. A single three-order reaction model was used to deduce the coal pyrolysis reaction successfully. The activation energy of the coal pyrolysis reaction decreased from 116.31 kJ·mol−1 to 90.67 kJ·mol−1, and the pre-exponential factor decreased from 6606.19 min−1 to 2457.91 min−1. Overall, slag provided the heat for the pyrolysis reaction and acted as the catalyst.

Pyrolytic behavior of coal-related model compounds connected with C–C bridged linkages by in-situ pyrolysis vacuum ultraviolet photoionization mass spectrometry

Coal pyrolysis is generally considered to initiate by cleavage of weak covalent bonds bridged between aromatic rings. The C–C covalent bonds are predominant bridged linkages among the framework of coal, which have a critical influence on coal pyrolysis reaction but lack of direct online observation. Five representative coal-related model compounds containing C–C bridged bonds, polypropylene (PP), polyvinylpyrrolidone (PVP), poly-4-vinylpyridine (P4VP), polystyrene (PS) and poly-4-vinylphenol, were selected to pyrolyze in an in-situ pyrolysis vacuum ultraviolet photoionization mass spectrometry (Py-VUV-PIMS). The soft ionized mass spectral detection can provide product distribution and evolved information of original products and intermediates, which are the key evidence to understand the initiation, recombination and reaction routes during pyrolysis process. Online analysis of pyrolysis reaction was found to be priority with cracking of C–C bond in the five polymer samples, and homologous free radicals and original products, which mainly include monomers, dimers and their alkyl and alkenyl radicals, were detected. The results reveal the cleavage temperature of C–C covalent bond is deeply related to its chemical environment, and obvious conjugation effect and steric effect for the bridged linkage were observed. In addition, the effect of hydrogen bond was also observed during the pyrolysis of model compounds containing hydroxyl groups, and intramolecular or intermolecular hydrogen bonding reduced the temperature at which C–C bridged bonds break. The analogous fracture mode and pyrolysis behavior of coal-related model compounds, which are beneficial to understand the reaction route and mechanism of coal pyrolysis, were discussed based on the experimental observations and theoretical calculation.

Pyrolysis of coal by solid heat carrier-experimental study and kinetic modeling

In this paper, the pyrolysis performance and pyrolysis reaction kinetic characteristic of Fuxin coal and Fushun coal using solid blast furnace slag as heat carrier were studied. Parametric studies were conducted to understand the effects of coal type, heating rate and mass ratio of slag to coal on the performance of pyrolysis reaction. The most appropriate mechanism model of coal pyrolysis reaction was selected by methods of Coats-Redfern and Malek. The results showed that the increasing heating rate was beneficial to coal pyrolysis reaction. The characteristic parameters of these two coals increased significantly with the heating rate increasing. The function of slag on coal pyrolysis reaction depended on coal type and slag to coal ratio. Slag improved pyrolysis reaction when the coalification degree was higher and heating rate was lower. Slag had no influence on pyrolysis reaction or even had restraint when the coalification degree and the heating rate showed the opposite trend. Based on the kinetic analysis, the Chemical reaction model (C3 model) was confirmed as the most appropriate mechanism model to describe the pyrolysis of coal using solid slag as heat carrier. The thermal decomposition profiles calculated using the kinetic parameters were in good agreement with the experimental results.

Identification of Primary CO in Coal Seam Based on Oxygen Isotope Method

ABSTRACTAnalysis on the source of CO is very important for prevention of coal spontaneous combustion. In this article, a method of identifying primary CO in coal seams based on an oxygen isotope method is proposed through research. Tests on the oxygen isotopes (δ18O) of CO were generated in coal oxidization reaction and coal pyrolysis reaction. It is found that δ18O of CO will reduce with rising temperature in both reactions, with δ18O of CO being 15–20‰ in air atmosphere and that being 25–28‰ in argon atmosphere in the temperature range of 130–220°C, confirming that the sources of oxygen atoms of CO vary with different atmospheric conditions. Through collecting and testing a number of gas samples from the coal seam and roof in the coal mine, their δ18O of CO is found to be 35.2–37.3‰. The result would improve the prevention of coal spontaneous combustion.

Mathematical modelling of Collie coal pyrolysis considering the effect of steam produced in situ from coal inherent moisture and pyrolytic water

Low-rank coals have high inherent moisture content, and high yield of pyrolytic water formed from the functional groups in the coal during pyrolysis. Steam produced from coal moisture can lead to significant in-situ char gasification during pyrolysis under conditions where there are strong and prolonged interactions between the char and the in-situ steam. This phenomenon can be encountered in many practical processes yet is often overlooked in pyrolysis modelling. Using Collie coal as an example, this study presents a mathematical model on low-rank coal pyrolysis, considering primary and secondary coal pyrolysis reactions, heat transfer, mass transports, as well as char gasification and volatiles cracking/reforming by steam produced in situ during pyrolysis due to both coal inherent moisture and pyrolytic water. Under conditions where there are strong and prolonged interactions between the pyrolysis products (particularly char) and steam produced in situ from the coal inherent moisture and pyrolytic water, lower char yields from both raw and demineralised coal are predicted, in agreement with the experimental data, under the current experimental conditions. This effect increases with increasing coal inherent moisture content, but decreases with increasing particle size due to the slower heating rate incurred during pyrolysis and the pore diffusion effect during char gasification for the large particles. Volatile steam reforming competes with char gasification for available steam, especially at high temperatures and for large particles. Experiments as well as model prediction also clearly demonstrate that char steam gasification reactivity data should be obtained from experiments carried out on the in-situ basis as the in-situ reactivity is significantly higher than that on the ex-situ basis.

00/01122 Analysis of pyrolysis reaction of coal by use of a new distributed activation energy model

00/01122 Analysis of pyrolysis reaction of coal by use of a new distributed activation energy model

00/01121 Analysis of coal pyrolysis reaction using a modified CPD model

00/01121 Analysis of coal pyrolysis reaction using a modified CPD model

99/00715 Simplified method to estimate f(E) in distributed activation energy model for analyzing coal pyrolysis reaction

99/00715 Simplified method to estimate f(E) in distributed activation energy model for analyzing coal pyrolysis reaction

98/02620 An analysis of coal pyrolysis rates using thermogravimetry: Okuo, H. et al. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS '97, Volume 2), 653–656

The modeling of coal pyrolysis reactions has been pursued since the initial studies by Gavalas and Howard. Recently, a large number of models has been reported, such as the FG-VDC, CPD, Flashchain and DEAM models. In these models, the activation energy or their distribution plays an important role. In this study, the weight loss of coals by thermogravimetry (TG) was analyzed to obtain pyrolysis activation energies and fire factors.

Simplified Method to Estimate f(E) in Distributed Activation Energy Model for Analyzing Coal Pyrolysis Reaction.

Recently one of the authors has presented a method (method I) to estimate both the distribution curve of the activation energy, f(E), and the frequency factor, k0, in the so called distributed activation energy model (DAEM) from three sets of experimental data obtained at different heating rates. No a priori assumptions are made for the functional forms of f(E) and k0. The k0 vs. E relationships obtained by this method for pyrolysis of 19 coals are found to be grouped into three groups, depending on coal rank. Utilizing the result, a simple method (method II) for estimating the f(E) curve is presented for analyzing the pyrolysis reaction of coal. The k0 vs. E relationship can be converted to the relationship between E and temperature, T, for a selected constant heating rate, a. Establishing the E vs. T relationship, we can easily estimate the f(E) curve from a single weight loss curve measured at the heating rate of a. The f(E) curve obtained by the simple method is rather close to the f(E) curve estimated by method I. The difference of the peak E values of f(E) curves estimated by both methods is always less then 15 kJ/mol. The f(E) curve estimated by the simple method is utilized well for predicting the weight change under different heating profiles.