Pyrolysis Characteristics Of Coal Research Articles

Coal pyrolysis law and mechanism of index gas generation in Linsheng Mine

To provide a theoretical basis for predicting spontaneous combustion in Linsheng coal mine, the pyrolysis characteristics of coal were investigated from both macroscopic laws and microscopic mechanisms. Programmed-temperature gas chromatography was utilised to test the generation and evolution laws of critical indicator gases (CO, C2H4, C2H2). XPS, 13C NMR and FT-IR were employed to elucidate the microscopic compositional and structural changes of coal samples. ReaxFF simulations revealed the product transformations of coal molecules during pyrolysis. The generation mechanisms of indicator gases were examined by FT-IR analysis. The results showed that the detected temperatures for CO, C2H4 and C2H2 generation from coal were approximately 60 °C, 165 °C and 308 °C. Linsheng coal exhibited a low degree of aromatic condensation with the molecular formula of C148H100O11N2S. During pyrolysis, the content of reactive –OH groups in coal increased, while substituted aromatics first increased and then decreased. The carbon content was elevated with a lowered H/C ratio, indicating progressive aromatisation and simplification of the coal structure. Gasification reactions persisted throughout the entire process, leading to continuous cleavage of small molecules to form gases. The formation of indicator gases is closely related to reactive functional groups including ester, ether, alcohol, carbonyl, phenol, alicyclic and substituted aromatics.

Influence of coal structure change caused by different pretreatment methods on Shengli lignite pyrolysis

Coal pyrolysis is one of the methods of clean and efficient utilization of coal. Coal has a complex structure, which has an important influence on its pyrolysis characteristics. In order to further explore the structure–activity relationship between the structure and pyrolysis characteristics of coal, the structure of coal can be artificially changed to investigate the influence of structural changes on its pyrolysis characteristics. In this study, hydrothermal pretreatment (HTP) and solvent swelling pretreatment (SSP) were used to artificially change the structure of Shengli (SL) lignite. The influence of each pretreatment on the physicochemical structure was analysed by Fourier-transform infrared (FT-IR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The evolution of functional groups and the pyrolysis characteristics of the SL/pretreated coal were investigated by using an in-situ FT-IR device and a fluidised bed reactor, respectively. The results showed: HTP could remove some oxygen-containing functional groups and aliphatic side chains, hydrolyze ether bonds and generate phenolic hydroxyl groups, thus destroying the cross-linking structure, promote the release of aromatic CC, the yield of pyrolysis tar increased from 9.4% to 10.6%, and the content of light tar increases from 43.1% to 49.1%. SSP mainly weakening the cross-linking structure by destroying hydrogen bonds and dissolving part of oxygen-containing functional groups, which reduces the pyrolysis activation energy of oxygen-containing functional groups and aliphatic groups, promotes the generation of tar. Accordingly, the yield of tar increases from 9.4% to 11.1%, and the content of light tar increases from 43.1 % to 49.8%. In particular, this research work reveals the structure–activity relationship between the structural changes of coal and the pyrolysis characteristics, which provides a theoretical basis for the directional pyrolysis of lignite.

The effect of hydrothermal pretreatment on the structure and fast pyrolysis behaviors of ShengLi lignite

The structure and composition of coal determine its fast pyrolysis characteristics, and the study of the relationship between them can play an important role in the efficient and clean utilization of coal. So, in this work, hydrothermal pretreatment was used to artificially change the structure and composition of ShengLi (SL) lignite, which was used to investigate the influence of structural changes on pyrolysis. The physicochemical structure and composition of samples were characterized by X-ray diffraction, specific surface area and porosity analyzer, solid-state 13C nuclear magnetic resonance, Fourier transform infrared spectroscopy, and elemental analyzer. Pyrolysis experiments were carried out in a powder-particle fluidized bed reactor, and the distribution and composition of the pyrolysis products were analyzed. The gasification activity of char was investigated by thermogravimetric analysis with a CO2 atmosphere. The results show that hydrothermal pretreatment (HTP) can destroy the cross-linking structure of SL lignite, and affect its aromaticity, pore structure, functional group, and carbon structure to change the distribution and composition of pyrolysis products of SL lignite, especially the composition of tar. Finally, the structure–activity relationship between the structure, composition, and pyrolysis characteristics of coal was comprehensively studied.

Study on Pyrolysis Characteristics of Coal and Combustion Gas Release in Inert Environment

In this study, thermogravimetric analysis (TGA) coupled with Fourier transform infrared (FTIR) spectroscopy was used to heat the coal samples of six different coalification degrees from room temperature to 1000°C at 20°C·min−1 under nitrogen atmosphere. The influence of coal degree and pyrolysis temperature on the content of pyrolysis products of coal was analyzed by the TG/DTG curve. FTIR spectroscopy was used to obtain the IR spectra of generated gases and study their variation at different temperatures in the process of coal heating without oxygen, and the gas release during pyrolysis was discussed. The results showed that the pyrolysis reaction initiated at 400°C and ended at 800°C. The maximum mass loss occurred in the temperature range of 480 to 500°C. The values of maximum and minimum weight loss rates were 32.72 and 18.89%, respectively. The mass loss during the pyrolysis process corresponded well with the volatile matter contained in the sample. Permanent gas analysis and IR spectrum analysis indicated that when the temperature was 600°C, the peak value of methane (CH4) appeared at 3016 wave, indicating the generation of CH4 at this time. When the temperature reached 700°C, the peak area of 2360 wave increased, all coal samples began to release carbon dioxide (CO2), release rate of CH4 gas decreased, and yield of CO2 was maximized. At 800°C, all peaks of 3160 wave disappeared, indicating that there was no unreacted short-chain release at this temperature. At the same time, the pyrolysis reaction tended to remove the excess hydrogen-oxygen conjugates in the carbon structure and release them in the form of water vapor.

Simulation of coal pressurized pyrolysis process in an industrial-scale spout-fluid bed reactor

A three-dimensional Eulerian-Lagrangian model, facilitated with multiphase particle-in-cell (MP-PIC) method, was developed to simulate gas-solid flow and pyrolysis characteristics of coal (with the capacity of 500 thousand tons per year) in an industrial-scale spout-fluid bed reactor (H = 16.6 m and D = 3.1 m), aiming at providing guidance for industrial application of pressurized grade conversion of coal. The performance of the reactor and the effects of operating parameters such as coal feeding rate, semi-coke to coal ratio, and particle sizes were numerically investigated. It was found that the flow pattern in this case is a “jet in the fluidized bed with bubbling”. The raise of pressure has a positive impact on the spouting structure and the flow uniformly. The increase of the semi-coke to coal ratio is beneficial to the coal pyrolysis, but the improvement of the pyrolysis is limited and the number of particles in the reactor will be sharply increased. With the increase of particle sizes, the flow pattern in the pyrolysis reactor tends to be stable while the mixing effectiveness is getting worse. It is suggested that the particle size of the material should range within 0–6 mm.

Simulation of pyrolysis in low rank coal particle by using DAEM kinetics model: Reaction behavior and heat transfer

A comprehensive and systematic study on the fundamental pyrolysis behaviors of a single coal particle was performed in this study. The pyrolysis characteristics of coal was investigated by non-isothermal thermo gravimetric analysis whereas the reaction kinetic parameters were obtained by using the distribute activation energy model (DAEM). As three heating rate profiles were applied (10, 20 and 30°C/min) in TG/DTG experiments with a final pyrolysis temperature of 900°C, the obtained kinetic parameters, i.e., activation energy (E0), pre-exponential factor (k0) and standard deviation (σ) were 186.5kJ/mol, 3.96×1010s−1 and 39.5kJ/mol, respectively. When these calculated kinetic parameters were used to predict devolatilization curves, the simulation results were in well agreement with the experimental data. As such, a one-dimensional, time-dependent particle pyrolysis model was proposed to characterize the detailed chemical and physical phenomena occurred within a pyrolyzing coal particle. It is found that this model successfully predicted the mass fraction residue and temperature profiles inside the coal particle. In addition, the effect of particle size on pyrolysis performance was also investigated through simulation. It is expected that such a model can be integrated with CFD simulation to provide useful insight for the design of a practical coal pyrolysis reactor.

Pyrolysis Characteristics of Coal, Biomass, and Coal–Biomass Blends under High Heating Rate Conditions: Effects of Particle Diameter, Fuel Type, and Mixing Conditions

The pyrolysis characteristics of two Chinese coals, two biomass materials, and their blends were investigated by both experimental and numerical methods. Single particles of the coal and biomass were prepared for the pyrolysis experiment through grinding and pressing, while the blended particles were made by mixing the coal and biomass powder with different ratios before the pressing. Sample particles pyrolyzed in a single-particle reactor system, with the time history of the particle temperature and mass recorded. The analysis of the measured pyrolysis data of the coal, biomass, and coal–biomass blends indicate the absence of a synergistic effect between the coal and biomass pyrolysis. A numerical method coupling the chemical percolation devolatilization (CPD) model with a particle energy equation was employed to analyze the pyrolysis process. The model prediction agreed well with the experimental data for different particle diameters, fuel types, and blend mixing conditions. The fact that the co-pyrolysis of blended coal–biomass particles is well-predicted by the simple addition of the individual pyrolysis characteristics of its components also corroborates the lack of synergistic interactions. These findings will be useful for the co-combustion modeling of coal–biomass blends.

Pyrolysis characteristics of coal and RDF blends in non-isothermal and isothermal conditions

Pyrolysis characteristics of the sub-bituminous coal, Refuse Derived Fuel (RDF) and their blends were determined at non-isothermal (15 °C/min) and isothermal (500–800 °C) conditions in thermo-gravimetric analyzer (TGA) and a thermobalance reactor. The decomposition rates of coal and RDF blends are higher than the calculated values of each fuel at the lower temperature ranges (300–385 °C). In the isothermal condition, activation energies of coal and RDF blends are lower and the pyrolysis reactivity is higher than the calculated values of each fuel. The synergistic effect exhibits remarkably with the RDF blend ratio of 50% at 700 °C. The structural variation and inorganic matters of chars from coal and RDF were determined by using BET, SEM, and XRD techniques. Surface area of the blend char increases and the average pore size decreases with pyrolysis. The addition of RDF into coal produces sulfur fixation of CaS and CaSO 3 based on the XRD data.

各種石炭の熱分解特性に及ぼす燃料比の影響

The present study is concerned with thermal decomposition of ten kinds of coal in different ranks of which fuel ratio ranges relatively widely from 0.9 to 6.6. The pyrolysis characteristics of coal were investigated by TGA (Thermo-gravimetric Analy-sis) in an atmosphere of nitrogen under the following conditions: the coal particle size 37-2000μm, the heating rate 2-200K/min, and such thermal decomposition parameters as the reaction order, the frequency factor and the activation energy were determined. The effects of particle size and also heating rate on the pyrolysis rate were examined. Then, the thermal decomposition parameters thus determined were correlated with the fuel ratio. As a result, it was recognized that the experimental data were well reproduced with respect to TG curves by using these parameters determined in the present study. The validity of the obtained parameters was then demonstrated.