Oxy-coal Combustion Research Articles

Impacts of scattering of non-gray gas particulate mixtures on radiative heat transfer and mid-infrared image temperature in a 2D oxy-coal combustion furnace

Impacts of scattering of non-gray gas particulate mixtures on radiative heat transfer and mid-infrared image temperature in a 2D oxy-coal combustion furnace

ReaxFF simulations on the transformation pathway of nitrogen elements in the heavy tar under oxy-coal combustion

Heavy tar is a crucial intermediate product during coal combustion. To explore the transformation pathway of N atoms in heavy tar under oxy-coal combustion, a comprehensive molecular model of heavy tar with typical N-containing functional groups was constructed. Different temperatures and chemical equivalence ratios were set for the oxy-coal combustion. The ReaxFF was employed to study various products' distribution and molecular numbers. The reaction network among different precursors and NOx was extracted, and the NO to N2 conversion mechanism was summarized. The results indicated that, like char combustion, the proportion of heavy tar gradually declined, the proportion of light tar and organic gas first rose and then gradually declined, and the proportion of inorganic gas continuously rose during heavy tar combustion. As the temperature increased, the proportion of cyanide precursors decreased, while the proportion of amine precursors and NOx increased. The oxidation of N-containing intermediates became more intense as the O2 content rose, but this oxidation effect was inhibited, and the NOx generation was reduced as the O2 content further increased. NO could bond with NHi, HNO, CN, and activate NO, decomposing to produce N2O, and N2O reacted with H radical to produce N2.

Numerical Analysis on the Quantitative Separation of Different NOx Formation and Reduction Routes during MILD Oxy-Coal Combustion with the Improved Nitrogen Chemistry Model

Numerical Analysis on the Quantitative Separation of Different NO_<i>x</i> Formation and Reduction Routes during MILD Oxy-Coal Combustion with the Improved Nitrogen Chemistry Model

Determination of the optimal total oxygen concentration and oxygen partitioning ratio based on the heat transfer characteristics of oxy-coal combustion in a swirl burner

Oxy-coal combustion is an attractive option for CO2 capture from coal-fired power plants due to high carbon capture efficiency and favorable economic performance. It is critical for the operation of the power plants to maintain similar heat transfer characteristics by rationalizing the partitioning strategy of the oxidant streams when retrofitting coal-fired power plants with oxy-fuel combustion technology. In the present work, the oxy-coal combustion characteristics under various total oxygen concentrations XO2,total of 21 %–32 % and oxygen partitioning ratio conditions in a 100 kW vertical swirl burner were numerically investigated by using computational fluid dynamics (CFD) models. And the effects of the XO2,total and oxygen partitioning ratio on the heat transfer characteristics of oxy-coal combustion were numerically simulated to quantitatively obtain the optimal oxygen supply partitioning strategy for the retrofitting of coal-fired power plants. Then the flame structure, heat transfer flux, and char burnout rate at different oxygen partitioning ratios between the primary and secondary streams were systematically analyzed to further determine the optimal oxygen partitioning ratio. The results showed that the maximum flue gas temperature Tmax increased by 220 K and the total heat transfer flux on the furnace wall increased by 42 % when the XO2,total was increased from 21 % to 32 %, respectively. Under oxy-coal combustion conditions, the Tmax at the XO2,total of 32.4 % was consistent with that under air combustion condition, while the total heat transfer flux at the XO2,total of 29.4 % matched with that under air combustion condition. Moreover, the total heat transfer flux and the flame length were increased by 17.3 % and 46.3 %, respectively, as the oxygen concentration of the primary stream XO2,Pri was increased from 6.5 % to 45 % at the XO2,total of 29 %. More importantly, the total heat transfer flux at the XO2,Pri of 31.9 % under oxy-coal combustion condition matched with that under air combustion condition. The optimal total oxygen concentration and oxygen partitioning ratio of oxy-coal combustion based on the heat transfer characteristics were quantitatively determined, which gave an important reference for the oxy-coal combustion retrofitting of traditional coal-fired power plants.

Experimental study of ignition and combustion characteristics assisted by laser-induced plasma during oxy-coal atmosphere by optical emission spectroscopy

This investigation aims to understand the enhancement characteristics of plasma-assisted combustion in oxy-coal combustion. A 1064 nm Nd:YAG laser was added into a laminar flow reactor to produce laser-induced plasmas (LIPs). The high-speed visualization of the coal flame was used to reveal combustion's progress and evolution following laser-induced breakdown. To the best of our knowledge, this is the first time LIP has been applied to the optimization of pulverized coal combustion. The optical emission spectroscopy (OES) demonstrats that LIPs can generate adequate free electrons and ions during combustion. When the laser's pulse interval exceeds 60 ms, the LIP has a beneficial impact on combustion. For the heterogeneous reaction, the thermal effect generated by LIP only improves the intensity of flame radiation by 11–33 %. In contrast, the combination of chemical and thermal effects of plasma can result in significant enhancements of radiation intensity for high-volatile coals, with improvements of 76–203 %. Following laser-induced breakdown, the ignition delay time also decreases from lignite to anthracite, and the flame's peak intensity occurs earlier.

Novel method for temperature prediction in rotary kiln process through machine learning and CFD

Blast furnace high-proportion pellet smelting stands as a pivotal pathway towards achieving low-carbon and environmentally friendly ironmaking. However, challenges in pellet ore production, particularly through the rotary kiln method, have surfaced due to the scarcity of iron ore resources, leading to issues like “ringing” that hamper production efficiency and energy conservation. Effectively predicting and optimally controlling the temperature field within rotary kilns emerges as a crucial strategy to address this pressing challenge. In a pioneering effort, this paper introduces a data-driven machine learning methodology designed to expedite the prediction of temperature field distributions within rotary kilns. Through a detailed analysis of field data from the factory and the insights of experts, the paper has discussed on the key factors influencing the temperature field dynamics in rotary kilns. Leveraging Computational Fluid Dynamics (CFD), a numerical simulation model was established to replicate rotary kiln oxy-coal combustion scenarios. A comprehensive dataset was generated using high-throughput computing technology, encompassing a variety of conditions such as coal injection rates, return air temperature, return airflow volume, fixed carbon content of pulverized coal, and volatile fraction of pulverized coal. This dataset included a total of 625 distinct cases. Subsequently, employing machine learning techniques including random forest (RF) and genetic algorithm-optimized Random forest (GA-RF), predictive models were developed for rotary kiln temperature field dynamics. A rigorous comparative analysis was conducted to explore the impact of different machine learning dataset sizes on the predictive accuracy of the models. The results of this analysis demonstrate that, enhanced by the genetic algorithm of RF, it surpasses the performance of the standard RF approach. This enhancement resulted in a significant improvement in prediction accuracy, as evidenced by the reduction of the Root Mean Square Error (RMSE) from 25.0879 to 17.5330 and the Mean Absolute Error (MAE) from an initial value of 6.5600 to 4.7661. Furthermore, the novel soft-measurement method introduced in this paper significantly reduces simulation time by several orders of magnitude. It has diminished the response time from the traditional industrial methods, which took two to three weeks, to approximately 10 s, as compared to conventional CFD approaches. Remarkably, this approach successfully preserves a high level of accuracy. The implications of these research findings are far-reaching,providing novel insights into the acceleration of CFD simulation calculations and the design of soft measurement sensors customized for black-box reactors in industrial processes.

Effect of water vapor content on the corrosion mechanism of HR3C in simulated oxy-coal combustion environment

The corrosion performance of the HR3C steels covered with salt deposition (Na2SO4:K2SO4 = 1:1) was investigated under various water vapor content at 700 °C. Results show that the HR3C alloy undergoes severe pitting and sulfidation in a dry corrosive atmosphere (0.5SO2-4O2-CO2) and the corrosion products are peculiarly prone to peel off. In comparison, the corrosion behavior is gradually mitigated with increasing water vapor content. In highly humid corrosive gas (0.5SO2-4O2-20H2O-CO2), the corrosion degree is remarkably faint and the dominant corrosion mode is oxidation. The mechanism responsible for the transition of corrosion mode as water vapor content varied is discussed in detail.

Diagnostic investigation of devolatilization, ignition, and flame fluctuation during laminar oxy-coal combustion

The rapid development of measurement technology has created possibilities for the advancement of intelligent combustion diagnostics. The high-speed OH-PLIF was used to investigate homogeneous ignition and combustion characteristics of gas-solid two-phase flame in a laminar flow reactor of oxy-coal combustion. The primary focus is to investigate the physico-chemical processes of gas-solid interaction during the early stages of combustion. The image processing was employed to analyze the flame features and then obtain the ignition mechanism, OH distribution, species radiations, and fluctuation frequency. Results show that the homogeneous reaction dominates the ignition and volatile combustion at the early stages of oxy-coal flame. The ignition delay time and volatile burning time decrease with the increasing gas temperatures and oxygen concentrations. The fluctuation dominant frequency increases from 190.5 Hz to 243.2 Hz at the ambient temperature from 1200 to 1800 K. The dominant frequency stabilizes between 243.2 Hz and 243.5 Hz at the ambient temperature from 1500 to 1800 K. The dominant frequency undergoes a shift to a maximum limit of 243.5 Hz from 1200 to 1800 K. When the oxygen concentration increases from 20 % to 40 %, the dominant frequency continues to rise from 244.8 Hz to 268.7 Hz.

Experimental investigation on the NO formation of pulverized coal combustion under high-temperature and low-oxygen environments simulating MILD oxy-fuel combustion conditions

The NO formation experiments simulating moderate and intense low-oxygen dilution (MILD) oxy-coal combustion conditions were conducted on a laminar diffusion flame burner with the coflow temperatures of 1473–1873 K and the oxygen volume fractions of 5 %–20 % in O2/CO2, O2/Ar and O2/N2 atmospheres. The flame images of pulverized coal combustion were captured to obtain the ignition delay distances, and the axial species concentrations were measured to obtain the variation of NO formation and reduction. The NO yield in O2/Ar atmosphere decreased by nearly 0.2 when the oxygen volume fraction decreased from 20 % to 5 % and by about 0.05 when the coflow temperature decreased from 1873 K to 1473 K. The NO yield in O2/CO2 atmosphere was 0.1–0.15 lower than that in O2/Ar atmosphere. The optimal kinetic parameters of thermal NO and fuel NO formation rate were obtained by a nonlinear fit of nth-order Arrhenius expression. Finally, the relative contribution rates of thermal NO to total NO (Rth) and NO reduction to fuel NO (Rre) were quantitatively separated. Rth decreases with the increase of oxygen volume fraction, below 6 % at 1800 K, 25 % at 2000 K. Rre is almost unaffected by the coflow temperature and affected by the oxygen volume fraction, reaching 30 % at 5 % O2.

Effect of the primary oxidizer stream jet velocities on the ignition and combustion characteristics of pulverized coal under MILD oxy-coal combustion conditions

MILD oxy-coal combustion technology is a prospective technology with the potential for CO2 capture and storage, and it is characterized by the intense flue gas recirculation to preheat the fuel and to dilute the oxidizer due to the oxidizer or fuel jet with high velocity. The effect of the primary oxidizer stream jet velocities ranging from 1.7 m/s to 11.2 m/s on the coal ignition and combustion characteristics were experimentally investigated on a flat flame pulverized coal burner at various oxygen concentrations of 5%-21% and gas temperatures of 1473–1873 K under O2/CO2 and O2/N2 atmospheres. The coal flame images were recorded by the digital camera, and the flame structure evolution and ignition delay times of coal particles were analyzed at different primary oxidizer stream jet velocities and hot coflow conditions. The coal combustion radiation spectrum was monitored by an optical fiber spectrometer and the coal particle temperatures were derived with the two-color pyrometry. The results showed that the bright yellow soot flame gradually disappeared with the decrease of O2 concentration when CO2 replaced N2. The difference of ignition delay times between O2/CO2 atmosphere and O2/N2 atmosphere decreased from 2.8 ms to 0.2 ms when the primary air jet velocity increased from 1.7 m/s to 11.2 m/s at 1473 K and 5% O2. This meant the elevated jet velocity was beneficial to offset the delayed effect of the physicochemical properties of CO2 on coal ignition. The peak coal particle temperature increased by 68 K at 1873 K and 5% O2 under O2/CO2 atmosphere with the highest jet velocity owing to the accelerated diffusion of O2 into coal particle stream. Moreover, a dimensionless coal particle temperature parameter η was proposed to characterize the variation of the peak coal particle temperature caused by the improved heat transfer and mass transport between the coflow and coal particles under high jet velocity. The maximum value of η was 1.053 at 1873 K and 21% O2 under O2/CO2 atmosphere with the jet velocity of 11.2 m/s, indicating the increased jet velocity had the predominant effect on the increase of peak particle temperature at high gas temperature and O2 concentration.

Oxidative combustion law of water-soaked coal under oxygen-lean condition

ABSTRACT Residual coal is easily submerged and damaged by groundwater. In the course of mining underlying coal seam, coal belonging to the overlying gob area tends to spontaneously combust during draining water. To explore the effect of micro-functional group transformation in immersed coal on the coal spontaneous combustion (CSC) traits during the low-temperature oxidation process (LTO), the migrant law of special functional groups under varying oxygen concentration (Co) of immersed coal was discussed by infrared spectroscopy. The endothermal and exothermal properties of the function group inside of coal were studied via thermal analysis. It is shown that the higher Co, the more oxygenic function groups on the soaked, and by contrasted with the Co of 18% the 14% has a small increase and the chain length is shortened. The temperature increment together with the Co content determines the functional group content, the pyrolysis process produces some function group. The lower the Co, endothermic coefficient decreases and endothermic temperature increases, the higher the ignition temperature of coal oxy-combustion, the lower the total heat release. And the speed of the oxygen-absorbing weight gain and the conversion of the functional group would be improved followed by the burnout temperature rising. Below 14% Co, the oxidative combustion process will be greatly inhibited. Those findings complement a theoretical basis for preventing long-term water-soaked coal oxidative spontaneous combusting in shallow buried coal seams.

Design and performance of a laboratory scale pressurized oxy-coal reactor

A pressurized oxy-coal (POC) reactor has been designed, built and tested to investigate key technologies related to oxy-coal combustion including a dry coal feed system, an oxy-coal burner, and a slagging ash management system. The coal feed system utilized a fluidized bed to convey pulverized coal with CO2 from a coal bed into the reactor. The reactor has diagnostic capabilities including optical access, embedded thermocouples, fuel and gas flow rates, exhaust gas analysis (CO2, CO, NO, O2) and heat flux. At 13.6 atm and a firing rate of 89 kWth a mean feed rate of 12.5 kg/h was established with large fluctuations of approximately ±2 kg/h. After polishing the fluid bed walls and removing accumulated large particles on the fluid bed screen, a coal feed rate of 7 kg/h ± 0.5 kg/h was demonstrated. The measured wall temperature profiles, heat flux, and exhaust gas concentrations enabled evaluation of the burner characteristics. The burner produced a long flame as designed but increased mixing is required to improve burnout. Flowing slag was obtained as designed when the reactor remained at the required firing rate and stoichiometric ratio to keep the walls above the slagging temperature.

Effect of demineralization on pyrolysis characteristics of LPS coal based on its chemical structure

The critical issue in developing mature Oxy-Coal Combustion Steam System technology could be the reactivity of demineralized coal which, is closely related to its chemical structure. The chemical structures of Liupanshui raw coal (LPS-R) and Liupanshui demineralized coal (LPS-D) were analyzed by FTIR and solid-state 13C-NMR. The pyrolysis experiments were carried out by TG, and the pyrolysis kinetics was analyzed by three iso-conversional methods. FTIR and 13C-NMR results suggested that the carbon structure of LPS coal was not altered greatly, while demineralization promoted the maturity of coal and the condensation degree of the aromatic ring, making the chemical structure of coal more stable. The oxygen-containing functional groups with low bond energy were reduced, and the ratio of aromatic carbon with high bond energy was increased, decreasing the pyrolysis reactivity. DTG curve-fitting results revealed that the thermal weight loss of LPS coal mainly came from the cleavage of aliphatic covalent bonds. By pyrolysis kinetics analysis of LPS-R and LPS-D, the apparent activation energies were 76 ± 4 to 463 ± 5 kJ/mol and 84 ± 2 to 758 ± 12 kJ/mol, respectively, under different conversion rates. The reactivity of the demineralized coal was inhibited to some extent, as the apparent activation energy of pyrolysis for LPS-D increased by acid treatment.

The ignition modes transformation and critical parameters for single coal particle under O2/CO2 atmospheres

Oxy-coal combustion with the substitution of CO2 for N2 is a state-of-the-art technology for CO2 capture and storage. Pulverized coal particles show various ignition and combustion characteristics under O2/CO2 atmospheres due to various physicochemical properties between CO2 and N2. A modified transient model with an augmented reduced mechanism (ARM) was developed to predict the ignition delays and ignition modes of the coal particle. Ignition modes transformation and critical parameters for single coal particle under O2/CO2 atmospheres were determined by using the modified transient model and the ignition criteria based on different characteristic ignition time scales. The predicted ignition delays were compared with experimental values and the predicted results obtained from the sophisticated model in literature. The ignition processes of the coal particle under O2/CO2 and O2/N2 atmospheres were analyzed in detail. Then, the contributions of the physical properties of CO2 including thermal conductivity and thermal sink, and the chemical properties of CO2 including gas mixture reactivity and char gasification to the variation of homogeneous and heterogeneous ignition delays and the transformation of ignition modes were separated at 1200–1800 K and 5%–60% O2. Finally, the ignition modes map under O2/CO2 atmospheres was firstly depicted and the critical parameters for ignition mode transformation were compared with O2/N2 atmospheres. The results indicated the larger thermal sink of CO2 and the reduced gas mixture reactivity played the dominant roles of the prolonged homogeneous ignition delays under O2/CO2 atmospheres. The critical gas temperature for the appearance of homogeneous ignition increased by 71 K at 27% O2 whereas the critical O2 concentrations for the ignition mode transformation from HI-GI to HI-coal changed insignificantly with the substitution of CO2 for N2.

Effect of Jet Velocity on the Formation of Moderate or Intense Low-Oxygen Dilution Combustion of Pulverized Coal.

Moderate or intense low-oxygen dilution (MILD) combustion of pulverized coal is regarded as a new combustion technology with great potential due to its advantages of reducing NO x emission and improving the uniformity of heat flux in the furnace. Increasing the jet velocity has been proved to be an important technical means to achieve MILD oxy-coal combustion, especially without a high level of preheat, but the transition mechanism of coal combustion modes with the increase of jet velocity is not clear enough. In this work, a high-velocity coal-laden jet combustion system on the basis of a flat-flame burner was designed to study the effect of jet velocity on the formation of MILD combustion of pulverized coal. The combustion mode transition of the pulverized coal jet is revealed by analyzing the flame structure, temperature, radiation, and reaction intensity through a variety of optical measurement methods. Theoretical criteria for combustion mode were applied to predict the formation of MILD combustion and were validated by the experimental data. In the environment with an ambient temperature of 1600 °C, the transition velocity of the coal jet into the MILD combustion regime is about 50 m/s and about 100 m/s at 5 and 15% O2 molar fraction, respectively. The dilution effect, jet entrainment, and turbulent mixing in the high-velocity jet, as the key factors to achieve an MILD combustion regime, were analyzed theoretically and experimentally. The dilution effect inherent in the jet significantly reduces the reactant concentration and ultimately reduces the reaction intensity and flame brightness while the entrainment of the jet promotes the radial dispersion of particles and the flame uniformity, which is dominant at lower jet velocities. Strong turbulent mixing promotes the ignition and volatile combustion, which is dominant at higher jet velocities.

Nitrogen oxide reduction in pressurized oxy-coal combustion

Pressurized oxy-coal combustion is one of the promising technologies for carbon capture in power plant. NOx control is one of the main challenges during solid fuel combustion, which has attracted more interest at higher pressure. Previous results reported that lower NOx emissions were tested during pressurized oxy-coal combustion, however, fundamental studies regarding the NO reduction by coal/char at elevated pressure are scarce. In this paper, NO reduction behaviors during coal combustion in pressurized oxy-environment were systemically studied. Experiments were carried out at pressures from 1 atm to 7 atm, and temperatures of 800 K, 1073 K, and 1273 K, respectively. Equivalence ratios in the range of 0.5 to 1.5 were arranged to evaluate the oxygen effect on the interaction of coal/char with NO. Results show that the high reduction capacity of combusting particles at higher pressure and temperature can significantly reduce the NO concentration in the furnace. A large difference in NO reduction efficiency is also found among coal types at elevated pressure. The influence of equivalence ratio shows marked differences between 1 atm and higher pressure. The reduction tests by char show that the NO reduction activity is notably lower than coal at elevated pressures and varied equivalence ratios, which is due to the much higher reduction efficiency by homogeneous reaction by volatile matter at higher pressure. Compared with the char produced in fixed bed, reduction efficiency of char samples produced in drop tube furnace is much active at 4 atm. ROP analysis shows that the dominant pathway of reducing NO by volatiles is NO+HO2O2+OH among cases, while the main reactions occurred in volatile-NO interaction are not changed, although the global kinetic rate is enhanced obviously at higher pressure.

Dynamic and kinetic studies on the oxy-coal combustion using multi-parameter high-speed diagnostics

Non-intrusive measurement of dynamic and kinetic parameters during oxy-coal combustion has been carried out in an enclosed downward laminar flow reactor. High-speed OH-PLIF, CH* chemiluminescence, and pyrometer were used to determine the luminescence species, particle velocity, and particle temperature. A two-step model was established to predict the release of coal combustible based on the Arrhenius expression. The experimental data from traditional coal char analysis methods verified the optical kinetic model. Experiments showed that homogeneous ignition first occurred and dominated the upstream volatile combustion. The heterogeneous reaction was activated upstream due to volatile oxidization and became dominant downstream. The coal combustion formed an overlapping region between volatile and char oxidations. This region played a critical role in enhancing flame stability. The duration of the overlapping region was smaller in oxy-fuel combustion than in air-alike combustion due to the higher reaction rate and lower heat and mass diffusion. A temperature-dependent kinetic model was found to obey a two-step first-order Arrhenius expression with two pre-exponential factors (103.59±0.22 and 105.81±0.31 s−1) and two activation energies (173.1 and 278.0 kJ/mol) in air-alike combustion, and two pre-exponential factors (105.02±0.47 and 106.37±0.24 s−1) and two activation energies (217.0 and 291.1 kJ/mol) in oxy-fuel combustion. The kinetic predictions agree well with the experimental results of the combustible release in the corresponding tests.

Design and performance analysis of a Swirl Pintle injector for a 1 MWth pressurized oxy-coal combustor

Pressurized Oxy-coal combustion has the potential to achieve high thermal efficiency by recovering the latent heat of steam from flue gases and providing options for up to 95% carbon capture. This study proposes a novel burner technology for pressurized oxy-coal combustion and investigates its operability. Three burner versions are designed and tested; no swirl, swirl numbers 0.9 and 1.2 to identify optimum design parameters and performance. A commercially available Dantec Dynamics software is used to conduct the shadowgraph experiments to observe burner performance. Coal water slurry is used as fuel with three different slurry ratios where the coal percentage by weights were 30, 40 and 50. Droplet size, distribution, spray angle and jet breakup lengths are measured and analyzed to quantify the performance. The study found that increasing the swirl number enhanced atomization. Implementing swirlers allowed the jet to spread through faster primary jet separation, thus improving atomization. In addition, higher slurry ratios improved the generation of smaller particles. However, it was also found that excessive increases in oxidizer momentums negatively impact the atomization process by jet shrinkage. The study concluded that operating a pintle burner at 1.2 swirl conditions with a 40/60 slurry ratio produces optimum performance.

Simultaneous reduction of nitrogen oxides and sulfur dioxide in circulating fluidized bed combustor during oxy-coal combustion

For stable carbon capture utilization and storage, highly-pure CO2 content and low pollutant emissions must be maintained throughout oxy-coal firing operation; however, studies on combining absorbent addition and oxidant staging combustion to eliminate simultaneous nitrogen oxides (NO, N2O) and sulfur dioxide (SO2) have not been reported. Accordingly, the purpose of this study was to investigate the effects of oxidant staging and limestone addition on the reductions of NO, N2O, and SO2 emissions in an oxy-circulating fluidized bed combustor at 25% and 31% input oxygen. The operating parameters considered in this study were: oxidant compositions; corresponding flow rate ratios; primary, secondary, and tertiary oxidants (PO, SO, and TO, respectively); TO supply heights; and limestone addition. The results revealed that compared to the TO supply heights, increasing TO flow rate was more effective at reducing the nitrogen oxide emissions. Under an optimal flow rate ratio (PO:SO:TO = 70:10:20) and TO height (6.4 m), NO, N2O, and SO2 emissions were ≈7.4, 4.2 and 4.1 mg MJ−1, respectively. The increase in SO2 emission caused by the application of oxidant staging could be effectively decreased by 60.6% without impacting combustion performance via limestone injection into the combustor; effectively facilitating the production of >86 vol% CO2. These findings can serve as valuable references for future designs, and the efficient operation of oxy-coal combustion plants constructed at larger scales, thereby ensuring highly-pure CO2 content and low pollutant emissions.

Experimental study and modelling of pressurized oxy-coal combustion: Effect of devolatilization conditions on the physical structure and combustion characteristics of char particles

Pressurized oxy-coal combustion has been regarded as a promising carbon capture and storage (CCS) technology, and the combustion characteristics of char particles under pressurized oxy-fuel combustion conditions have been extensively investigated. However, most previous studies used the char samples prepared under the atmospheric N2 condition rather than under the pressurized CO2 condition, which may lead to the misunderstanding of the combustion characteristics. In this study, the effects of devolatilization atmosphere and pressure on the physical structure of char particles were experimentally investigated. The char particles produced under different devolatilization conditions were then used for the oxy-char combustion experiments conducted in a fluidized bed with the operating pressure between 0.1 and 0.5 MPa. In view of the limitations of the experiment, an experimental verified particle-scale char combustion model was further used for predicting the char particle’s combustion reactivity and temperature, and the influence of physical structure on the combustion characteristics was analyzed. The results obtained from the experiments demonstrated that higher devolatilization pressure led to larger mean pore sizes and specific surface areas of char particles. The char particles obtained with CO2 atmosphere had larger specific surface areas but smaller mean pore sizes than those obtained with N2 atmosphere. Besides, increasing devolatilization pressure resulted in shorter burnout times of char particles. The simulation results showed that using the char samples prepared under the atmospheric N2 condition for the pressurized oxy-fuel combustion experiments led to the underestimations of char combustion reactivity and peak temperature.