Coal Devolatilization Research Articles

Insight into Ca-based compounds on different coal devolatilization behavior by TG-MS

Catalytic pyrolysis, as an indispensable technology, can efficiently achieve clean coal conversion. In this work, the effect of calcium-based compounds (CaO and CaCl2) on devolatilization characteristics and gas evolution behavior of three coals were investigated by thermogravimetry-mass spectrometry (TG-MS). The catalytic mechanism was further explored in combination with the bond cleavage and gas kinetics. The results showed that both catalysts increased the weight loss rate and pyrolysis characteristic index, which also promoted the early release of CH4, H2, CO2 and C6H6, leading to an increase on the amount of CH4 and H2 production. CaO had a better catalytic effect than that of CaCl2. In addition, the kinetic results indicated that both compounds significantly reduced the activation energy of the methane I and IV stages, by 21.33%–34.66 % and 0.8%–18.60 %, respectively. And the activation energy of hydrogen III stage evolution was also reduced by 2%–18.98 % with catalysts. The calcium-based compounds tended to act on the Cal-O, Cal-Car and Car-H structures, improved the coal devolatilization behavior. The results aim to provide theoretical understanding for the practical application of catalytic pyrolysis technology.

Numerical investigation on pyrolysis and ignition of ammonia/coal blends during co-firing

Co-firing ammonia with coal is a promising and feasible technology for reducing coal-related carbon emissions. Pyrolysis and ignition of ammonia-coal blended fuels are the key steps for flame stability and boiler operation safety throughout the conversion process but remain unclear. In this work, an extended Euler–Lagrange framework coupled to detailed solid-phase pyrolysis kinetics and gas-phase reactions mechanism is introduced and validated against experimental results for ammonia-coal co-firing in a two-stage flat flame burner. First, the CRECK-S coal pyrolysis model was validated with TGA experiments and the CPD model at different heating rates to determine parameters for a competing two-step model for CFD simulations. Second, a detailed gas-phase mechanism with 116 species and 1513 elementary reactions was derived from the volatile and ammonia reaction mechanisms. Thirdly, the co-firing simulations were validated for the ignition delay time for various ammonia co-firing ratios. The results show that increasing the co-firing ratios from 0.0 to 1.0 results in gradually increasing ignition delay times in a low-oxygen atmosphere. Further analysis demonstrates that adding ammonia accelerates the coal particle heating rate due to the reduced coal particle number density and ammonia reaction induced gas-phase temperature increase, and thus the coal devolatilization rate is increased. The latter plays a dominant role. Hydrogen produced from ammonia pyrolysis is negligible, so ammonia predominantly participates in the ignition. Time scale analysis shows that homogeneous ignition is dominant during the ignition process. The presence of ammonia inhibits the inward oxygen diffusion and causes the reaction zone to move away from the pulverized coal particle flow. The oxygen diffusion inhibition and low reactivity of ammonia compared to volatiles lead to an increase in ignition delay time for ammonia co-firing, even though pulverized coal devolatilization is accelerated.

Thermodynamic and kinetic modeling and experiment on plasma ignition of pulverized high-ash coal

Solid fuels are relatively inexpensive and widely available, making them an attractive option for energy producers. However, they are currently inefficient in converting heat energy into electricity, and new technological advances are needed to make them more efficient. Plasma ignition and stabilization of pulverized coal flame provides a cost-effective and sustainable approach to boiler start-up and combustion stabilization, avoiding the traditionally used fuel oil or gas. This technology consists of heating the air-coal mixture with electric arc plasma to the temperature of coal devolatilization and partial gasification of the coke residue. Thus, a highly reactive two-component fuel, consisting of combustible gas and coke residue, is obtained from the original coal. In this paper, a comprehensive thermodynamic and kinetic analysis was carried out. A thermodynamic analysis was carried out to study the optimal parameters of plasma ignition and stabilization of combustion of a pulverized fuel flame. Kinetic modeling of the process of plasma ignition and stabilization of combustion of pulverized fuel made it possible to obtain changes in temperatures, velocities and concentrations of high-temperature two-component fuel components along the length of the plasma-fuel system. In experiments on plasma ignition of thermal coal, a stable coal-dust flame was obtained, and its temperature, composition and degree of carbon gasification were determined. Comparison of experimental and calculated data showed satisfactory agreement.

Enhancing Graphitic Carbon Precursors from Coal Pyrolysis: A Comparative Analysis of Microwave Plasma and Conventional Thermal Upgradation Methods.

This study investigates and compares the efficacy of conventional thermal pyrolysis and microwave (MW) plasma pyrolysis in upgrading coal-derived precursors. Coal samples presenting a range of ranks were pyrolyzed under various reactive and nonreactive atmospheres using a pyroprobe, with the pyrolyzates analyzed by gas chromatography-mass spectrometry (GC-MS). Comparative MW plasma tests were conducted using a modified countertop MW unit, with condensed products similarly analyzed by GC-MS. A predominant coal devolatilization product-benzene was selected for analyzing the reactive MW plasma upgradation. Results demonstrate that conventional thermal pyrolysis lacks effectiveness in upgrading the precursors. To gain insight into the underlying reasons, chemical kinetic simulations were conducted. Oppositely, reactive MW plasma pyrolysis demonstrated remarkable precursor upgradation. These condensed MW plasma pyrolysis products were then subjected to a carbonization and graphitization heat-treatment with a comprehensive graphitic quality assessment conducted using X-ray diffraction and transmission electron microscopy. After graphitization, the MW plasma-upgraded precursor produced a carbon with a crystallite size several times greater than that of the initial benzene. By MW plasma processing, the poorly graphitizable benzene precursor was transformed into a highly graphitizable precursor comparable to coal tar pitch. The underlying reasons for this significant improvement were investigated by analyzing the compositional changes in the precursor under various reactive environments.

A DNS study of pulverized coal combustion in a hot turbulent environment: Effects of particle size, mass loading and preferential concentration

In the present study, pulverized coal combustion in a hot turbulent environment is investigated using direct numerical simulation (DNS). The coal particles are tracked in the Lagrangian framework while the flow is solved in an Eulerian way. A model involving two competing reactions is used for describing the process of coal devolatilization. The volatile matter is treated as a postulated substance (CaHbOc) and a two-step global reaction mechanism for volatile combustion is adopted. The char combustion is modeled using a one-step global reaction model. The effects of various factors, such as particle size, mass loading and preferential concentration, on the combustion process of coal particles were explored. It was found that, the location of reaction zones appears more upstream and the volatile matter concentration is higher for the cases with smaller particles. The combustion modes were examined. It was shown that the contribution of premixed combustion decreases with increasing particle size while non-premixed combustion prevails in all cases. The increase of particle mass loading results in an increase of volatile matter mass fraction, which leads to higher heat release rate and combustion temperature. Through Voronoï analysis, the preferential concentration of particles was examined. It was found that the preferential concentration behavior of particles is more prominent when the particle Stokes number (St) is close to unity. The volatile matter concentration is higher when particles are preferentially concentrated, facilitating coal particles to ignite.

Exploring pyrolysis characteristics of bituminous coal: a combined modelling and experimental investigation with TG-IR

This research investigates the pyrolysis characteristics of Barapukurian bituminous coal from Bangladesh. The aim is to address the escalating energy demand and mitigate reliance on rapidly depleting natural gas reserves. A thermogravimetry analyser (TGA) combined with infrared spectroscopy (IR) was employed to carry out the study. Kinetic parameters are derived from a two-stage kinetic model, followed by the validation against experimental data. The release of functional groups and the evolution of gas species were identified from IR. Results demonstrate the sensitivity of coal devolatilisation to operating conditions such as sample mass, particle size, and heating rate. The weight loss profile and its first-order derivatives reveal the multi-stage nature of the pyrolysis process, with most of the mass loss occurring during the rapid pyrolysis stage. The average activation energy determined from the kinetic model is 145.7 kJ/mol. The IR spectrum obtained from the study can be categorised into five main groups: OH, group stretching, CH group stretching, oxygen-containing stretching, C=C stretching, and absorption of inorganic metals.

Process analysis of Pb transformation in the coal devolatilization stage

The transformation of Pb during coal devolatilization affects its emission characteristics. Herein, devolatilization experiments were conducted at 1100–1300 °C in a fixed-bed experimental system using four types of coal samples. The occurrences of Pb in coal and devolatilization products were characterized. The release ratio of Pb first increased and then stabilized with time. The Pb release ratio and rate were higher at higher temperatures. Pb in some coal samples was completely released at 1100 °C. Pb in coal was mainly in carbonate- and oxide-bound, sulfide-bound, and residual forms. During devolatilization, carbonate-, oxide-, and sulfide-bound Pb gradually disappeared. Organic-bound and residual Pb first increased and then decreased owing to the conversion of gaseous Pb into Char-Pb by char, according to further form analysis of residual Pb and the experiments of char retaining PbCl2 and PbO. The effects of different volatile components on residual Pb were compared, and H2S was found to significantly promote the release of residual Pb in coal. The transformation paths of Pb during coal devolatilization were proposed, including the release of original Pb in coal and the reversible conversion between gaseous Pb and Char-Pb. The results help understanding Pb emission and developing control techniques for coal-fired plants.

Effects of oxygen concentration on devolatilization and combustion behavior of coal particles: A multi-parameter study

The devolatilization and volatile combustion of lignite coal (LC), sub-bituminous coal (SBC) and bituminous coal (BC) with different O2 concentrations (21%-50%) were investigated on a concentrating photothermal experiment platform. The characteristics and mechanism of different coal particle combustion were analyzed by using multiple diagnostics, including Planar Laser Induced Fluorescence (PLIF) of OH radicals and polycyclic aromatic hydrocarbons (PAHs), high-speed cinematography and FT-IR. The results showed that, with increasing O2 concentration, the ignition delay time (tign) of different ranks of coal decreased, which was associated with the increase of OH concentrations during the ignition stage. The good correlation between tign and OH concentration was observed. For the volatile combustion, the OH concentration, volatile release amount and volatile flame duration time (tvol) significantly increased with the increasing of O2 concentration at low O2 concentrations. In the higher O2 concentrations, coals with different PAHs generation amount responded differently on the increasing of O2 concentration. On one hand, for the coals with lower PAHs generation amount, the OH concentration increased with the increasing of O2 concentration, while the tvol was not sensitive to changes of the O2 concentration. On the other hand, for the coals with higher PAHs generation amount, the OH concentration decreased with the increasing of O2 concentration while the tvol increased with the increasing of O2 concentration. It can be concluded that PAHs inhibited the OH generation, and the generation characteristics of OH and PAHs affected the sustained state of volatile combustion. The higher PAHs concentration consumed higher amount of OH during the volatile combustion. Meanwhile, with the increasing of PAHs concentration, the reaction rate of H + O2+M→HO2+M in which PAHs participate was increased, inhibiting the reaction H + O2→OH+O, and the increasing of polymer soot of PAHs will reduce the flame temperature through thermal radiation, which further inhibited the OH formation.

New insights into the oxidation chemistry of pyrrole, an N-containing biomass tar component

Pyrrole, the smallest molecule with a nitrogen atom in the heterocycle ring, is an important tar component from coal and nitrogen-rich biomass devolatilization. Understanding the combustion chemistry of pyrrole can help to elucidate the pollutant formation chemistry from fuel nitrogen, thus enabling cleaner biomass energy utilization technologies. Experimental measurements were performed in a jet stirred reactor coupled with time of flight molecular beam mass spectrometry using synchrotron vacuum ultraviolet beam as photon ionization source, and gas chromatography-mass spectrometry to provide comprehensive measurements of 31 species including nine C4 and C5 N-containing compounds. Based on the evidence from the experiments and aiming to improve the kinetic model performance, possible formation routes are proposed with OH addition as the entrance reaction. Reaction rate coefficients for the OH addition channel as well as those for key H-atom abstraction reactions (H, OH, CH3, and HO2) were calculated by quantum chemical methods and updated in the model. The updated model can qualitatively predict the identified C4 N-containing species and perform reasonably well for a large set of experimental data considered for validation, overall improving the performance of the previous model. The influence of the investigated reactions on the predictions of fuel reactivity and pollutant formation motivates further investigations of N-containing fuel chemistry.

Volatilization characteristics and relationship of arsenic and sulfur during coal pyrolysis

Similarities concerning the occurrence of arsenic and sulfur in coal are the reasons for studying the relationship between the volatilization of arsenic and sulfur during the pyrolysis process. For this purpose, three coals with different arsenic and sulfur contents were selected. Combined application of electron probe microanalysis (EPMA) and sequential chemical extraction determined the relationship between the speciation of arsenic and sulfur (especially pyrite) in coal. Effects of temperature and speciation on the volatilization of arsenic and sulfur were discussed. Results show that arsenic in all coals is significantly enriched in the distribution area of pyrite. The volatilization ratio of sulfur and arsenic increases with temperature, and their volatilization mainly occurs at 300–600 °C. Before 500 °C, aliphatic sulfur and organic arsenous are the main contributors to the volatilization of sulfur and arsenic, respectively. At 500–600 °C, the volatile sulfur and arsenic mainly come from the decomposition of pyrite. A characteristic peak is observed for the volatilization rate of arsenic and sulfur, and it almost coincided with the weight loss peak of coal. Moreover, the simultaneous volatilization behavior of arsenic and sulfur is observed in Gansu (GS) coal at 400 °C due to the devolatilization of coal and in Chongqing (CQ) coal at 550 °C due to the decomposition of pyrite. Sulfate in coal has a negative effect on the volatilization of arsenic. The possible reaction paths were predicted by the thermodynamic analysis of FactSage 7.3 software. Fe2O3 and CaS could adsorb arsenic to form stable arsenate (FeAsO4 and Ca3(AsO4)2) during the pyrolysis process.

The role of H2O in structural nitrogen migration during coal devolatilization under oxy-steam combustion conditions

Oxy-steam combustion is a promising technology for reducing CO2 emissions. During coal devolatilization under oxy-steam condition, the high steam concentration has a considerable influence on the migration of structural nitrogen. In this paper, the transformation of nitrogenous functionalities and the release of nitrogen-containing precursors in N2 and N2/H2O atmospheres at 1173–1373 K were measured experimentally. Using density functional theory calculation, the reaction networks of nitrogen migration under N2 and N2/H2O conditions were established, with the corresponding thermodynamics data. On this basis, a detailed kinetics analysis was conducted. Results showed that compared to a N2 atmosphere, the char prepared in a N2/H2O atmosphere exhibits a lower content of pyridinic N and higher contents of quaternary and pyrrolic N. This is because high OH radical concentrations inhibit the transformation of N-Q to N-6. Moreover, the adsorption of OH on pyridinic N leads to the formation of 2-pyridone, thereby making the conversion of N-6 to N-5 feasible. Furthermore, the decomposition of both N-6 and N-5 leads to the formation of HCN, while N-5 is the major source of NH3. In this process, the presence of hydroxyl groups inhibit the release of HCN and NH3, leading to lower emissions under N2/H2O than N2 conditions.

Large‐eddy simulation of coal combustion in 15 MW pilot‐scale boiler‐simulation facility

AbstractHigh‐fidelity modeling provides a useful approach to investigate the multiscale multiphysics mechanism in the pulverized coal combustion. This research focuses on understanding the pulverized coal combustion in a pilot‐up facility: General electric (GE) 15 MW pilot‐scale boiler simulation facility (BSF). The heat flux to the boiler water wall, O2 concentration, and gas temperature are the quality of interest (QoI's) for this research, as they are the most important parameters for designing a full‐scale pulverized coal boiler. Even the heat flux in boiler is largely determined by the heat transfer mechanism, and other detailed multiphysics mechanisms, including multiphase turbulent flow, radiation heat transfer, ash deposition, coal devolatilization, and oxidation, also need to be accounted. This work applies large‐eddy simulation (LES) code on high‐performance computing facility to simulate pulverized coal combustion in BSF. The physics‐based submodel that contains the significant sensitivity for QoI's has been identified using the detailed impact factor analysis on this high‐fidelity modeling. Results indicate that the most sensitive submodel on QoI's is the wall‐heat‐transfer coupling with the ash‐deposition model, which allows us to prioritize to improve this submodel in the LES simulation. Thus, ash deposition and wall‐heat‐transfer processes have been modeled and integrated into coal combustion numerical simulation. The simulation results show quantitative agreement between the simulation with experimental data regarding gas temperature, O2 concentration, and heat‐flux profile across the exposed boiler walls. Another implication of this research is to demonstrate a positive societal impact of extreme computing and accelerate the development of new combustion technology using a capable exascale computing technique.

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.

Study of pyrite transformation during coal samples heated in CO2 atmosphere

Pyrite transformation in two coals heated in CO2 was investigated. It was found that the pyrite experienced two visibility DTG peaks at temperature above 840 °C in CO2. It may be due to the pyrite decomposed products further reacting with CO2 to form iron oxides, sulfur oxide and CO as temperature increased. There are two main parts during the coal-pyrite blends heated to 1300 °C in CO2, which are the main pyrolysis part and the main gasification part, respectively. It shown that the coal decomposition processes did influence the pyrite transformation behaviors. During the main pyrolysis part, two DTG peaks were significantly observed related to the devolatilization of acid-washed coal and the pyrite pyrolysis desulfurization, respectively. The pyrite in coal-pyrite blends decomposed at lower temperature than the pure pyrite. The decomposition temperature of pyrite in coal-pyrite blends are decreased as the pyrite content in blends decreased in the main pyrolysis part. The flue gas analysis shows that, H2S is the main sulfur-containing gaseous product in the main pyrolysis part, SO2 and CO are the major gas products in the main gasification part of the coal-pyrite blends. During the main gasification process, the SO2 and CO release peaks move to high temperature zone as the pyrite content decreased. The ashes from the fix-bed reactor were also analyzed. It was shown that the iron oxide (magnetite) may be formed at temperature as low as 600 °C in the coal-pyrite blends. At higher temperature (main gasification part), it suggested the pyrite in coal-pyrite blends may be transformed together with char gasification and the co-transformation temperature is different with the coal type.

Coal Particle Devolatilization and Soot Formation in Pulverized Coal Combustion Fields

In this paper, recent developments of the devolatilization model and soot-formation model for the numerical simulations of pulverized-coal combustion fields, and the technology used to measure soot particles in pulverized-coal combustion fields are reviewed. For the development of new models, the validation of the developed models using measurement is necessary to check the accuracy of the models because new models without validation have a possibility to make large errors in simulations. We have developed the tabulated devolatilization process model (TDP model) that can take into account the effect of particle heating rate on the volatile matter amount and the devolatilization-rate parameters. The accuracy of the developed TDP model was validated by using the laser Doppler velocimetry data for the bench-scale coal combustion test furnace. The soot-formation model combined with TDP model for the large eddy simulation (LES) has been also developed. The spatial distributions of both the soot-volume fraction and the polycyclic aromatic hydrocarbons were measured by virtue of laser-induced incandescence (LII) and laser-induced chemiluminescence (PAHs-LIF). The accuracy of the developed soot-formation model was validated by using the measured data.

Coal/biomass co-combustion investigation by thermogravimetric analysis

In this study, the thermal characteristics and kinetic parameters of coal/biomass blended fuels (75:25, 50:50 and 25:75 wt.%/wt.%) were investigated by using the thermogravimetric technique under atmospheric air. Three types of agricultural waste biomass including cassava root, palm kernel shell and rice husk were used as raw materials. The experiments were performed under different temperatures, ranging from 313-973 K with the heating rate of 5, 10, 20 and 40 K/min. The results show that the thermal decomposition of biomass exhibit three-four stages including moisture and some light volatile removal stage (up to 463 K), volatile oxidation stage (423-663 K), char combustion stage (663-823 K) and inorganic oxidation stage (803-953 K). Lignite on the other hand exhibits only two main peaks during the entire combustion process, corresponding to the moisture removal (up to 433 K) and the decomposition/oxidation (433-833 K), respectively. In addition, it was also found that the blending of biomass residues improved the ignition temperature of the blended fuels, indicating an improvement of devolatilization of coal. Kinetic studies show that the average apparent activation energies of the co-combustion of coal/cassava root, coal/palm kernel shell and coal/rice husk calculated from the Kissinger-Akahira-Sunose method are reported at ca. 105.25, 179.66 and 121.84 kJ/mol, respectively.

Study on combustion performance of hydrothermally dewatered lignite by thermal analysis technique

The high water content of lignite has raised serious environmental and efficient issues, which are obstacles to its large scale utilization. In this study, hydrothermal dewatering (HTD) method was used to upgrade a lignite from Inner Mongolia in China at 230–330 °C. The combustion behaviors of raw lignite and HTD samples were investigated by thermogravimetry with differential scanning calorimetry (TG-DSC). By changes of mass and heat flow, the lignite combustion process was described from three stages: water evaporation, coal devolatilization and char combustion. Compared with raw lignite, the combustion reactivity of HTD samples upgraded at 230–300 °C was improved, while that of sample upgraded at 330 °C decreased. The temperatures at maximum combustion rate of 230–300 °C samples (below 397.6 °C) were lower and that of 330 °C samples (448.9 °C) was higher than that of raw lignite (399.8 °C). The released heat at char combustion stage increased for HTD samples. Then the physico-chemical structures of lignite before and after HTD process were analyzed to investigate the effect of HTD on coal combustion characteristics. Results showed that HTD process could affect the heat at water evaporation and initial devolatilization stages during coal combustion through removing oxygen functional groups in lignite. The enhancement in aromaticity of lignite after HTD increased activation energy of intrinsic reaction, whereas the large pore volume and high surface area of 230–300 °C samples decreased diffusion activation energy at char combustion stage. The effect of pore structure predominated on combustion reactivity compared with aromaticity for HTD samples.

Comprehensive study on co-combustion behavior of pelletized coal-biomass mixtures in a concentrating photothermal reactor

Co-combustion of biomass offers a great potential to reduce CO2 emissions but rarely mentioned co-combustion behavior of pelletized coal-biomass mixtures and inconclusive results based on single determinants formed obstacle for industrial application. In this study, ignition and flame characteristics, reaction and kinetic parameters and pollutant generation path were comprehensively investigated. Intrinsic combustion experiments were carried with the gas phase maintaining at room temperature in a concentrating photothermal reactor at heating rate over 200 °C/s. Same “homogeneous” ignition was evidenced while advanced devolatilization but more intense slagging behaviors were identified with the increase of biomass proportion. With the biomass proportion increased from 0% to 40%, the activation energies during devolatilization to ignition decreased non-linearly from 47.44 kJ/mol to 8.03 kJ/mol, indicating the existence of synergistic effect. CO exhibited relative high generation rates and the generation rate increased with the biomass content. Three fitted CO peaks were identified during co-combustion, which were contributed by devolatilization of coal and biomass, and combustion of char, respectively. First increased and then decreased NO emission with the increase of biomass proportion was evidenced for the higher N content in biomass but enhanced reduction by char and NH radicals with higher biomass proportion.

Simulation Study of the Formation of Corrosive Gases in Coal Combustion in an Entrained Flow Reactor

Gaseous sulfur species play a major role in high temperature corrosion of pulverized coal fired furnaces. The prediction of sulfur species concentrations by 3D-Computational Fluid Dynamics (CFD) simulation allows the identification of furnace wall regions that are exposed to corrosive gases, so that countermeasures against corrosion can be applied. In the present work, a model for the release of sulfur and chlorine species during coal combustion is presented. The model is based on the mineral matter transformation of sulfur and chlorine bearing minerals under coal combustion conditions. The model is appended to a detailed reaction mechanism for gaseous sulfur and chlorine species and hydrocarbon related reactions, as well as a global three-step mechanism for coal devolatilization, char combustion, and char gasification. Experiments in an entrained flow were carried out to validate the developed model. Three-dimensional numerical simulations of an entrained flow reactor were performed by CFD using the developed model. Calculated concentrations of SO2, H2S, COS, and HCl showed good agreement with the measurements. Hence, the developed model can be regarded as a reliable method for the prediction of corrosive sulfur and chlorine species in coal fired furnaces. Further improvement is needed in the prediction of some minor trace species.

Recent advances in high-fidelity simulations of pulverized coal combustion

Although renewable energy has recently attracted a lot of attention, coal-fired power plants will still play an important role in electricity production in the future due to coal’s abundance in the world. However, combustion of pulverized coal is extremely complex which makes experimental measurements very challenging even impossible. As an alternative, computational fluid dynamics (CFD) is a powerful tool to investigate pulverized coal combustion (PCC), and can help to design and develop advanced coal-fired facilities. With the development of computational capacity, high-fidelity simulations of PCC have been developed and significant achievements have been obtained in the recent years. In this review, the recent advances in CFD of PCC, especially in fully-resolved direct numerical simulation (DNS), point-particle DNS and large eddy simulation (LES) of PCC are summarized. The progresses on both numerical methods and coal combustion models are highlighted. The state-of-the-art applications of these high-fidelity simulations are also reviewed, including the investigation of combustion characteristics of pulverized coals, the development of advanced coal combustion models, and the development of clean coal technologies. It is concluded that fully-resolved DNS, point-particle DNS, and LES have their merits and demerits, so the optimal use of each approach depends on specific research purpose. For coal devolatilization and char-oxidation models, the combined models in which advanced models are used to calibrate the kinetic parameters of simple models are quite attractive in terms of computational accuracy and computational burden. For chemical reactions, the flamelet model is popular, but the predictive capability and robustness need to be further improved. Besides, LES is rapidly approaching to simulate industrial PCC. However, the computational cost is still quite expensive, and more efficient algorithms and sub-grid models are required. To this end, DNS database, benchmark measurements, and international collaborations are important. Machine learning may also play an important role in promoting the development of high-fidelity simulations of PCC in the future.