Char Combustion Processes Research Articles

Experimental study on char nitrogen conversion characteristics during char combustion process in pressurized O2/CO2/H2O atmosphere

Pressurized oxy-fuel combustion is an advanced CO₂ capture technology with potential applications in coal-fired power generation. In this study, the conversion behavior of char-nitrogen under pressurized oxy-fuel combustion conditions was investigated using a horizontal furnace across a pressure range of 0.1–1.3 MPa in an O₂/CO₂/H₂O atmosphere. The influences of pressure, gas composition, and residence time on nitrogen conversion were examined, and key factors affecting nitrogen transformation pathways were identified. Results indicated that elevated pressures favored NH₃ formation while inhibiting the formation of NO and NO₂, particularly at pressures above 0.7 MPa. Under pressurized conditions (0.7/1.3 MPa), increasing the O₂/CO₂ ratio further suppressed the conversion of char-N to NO, a contrast to behavior observed at atmospheric pressure. X-ray photoelectron spectroscopy analysis revealed a preferential consumption of nitrogen species, such as pyridinic and pyrrolic nitrogen, with pressurization enhancing the depletion of protonated nitrogen. Furthermore, an increased O₂/CO₂ ratio promoted the conversion of nitrogen oxides and other nitrogenous forms.

Structure characteristics and combustion kinetics of the co-pyrolytic char of rice straw and coal gangue

Co-combustion is a technology that enables the simultaneous and efficient utilization of biomass and coal gangue (CG). Nevertheless, the factors that affect the combustibility of co-pyrolytic char, which represents the rate-determining step of the entire co-combustion process, remain unclear. This study investigates the impact of the physicochemical properties of co-pyrolytic char, including pore structure, carbon structure, and alkali metals, on the combustion characteristics. The TGA analysis indicates that the ignition and burnout temperatures of the co-pyrolytic char increase as the CG mixing ratio increases, resulting in a prolonged combustion. This is due to the fact that the carbon structure of the co-pyrolytic char becomes increasingly aromatic, accompanied by a reduction in aliphatic hydrocarbons and oxygen-containing groups as the CG mixing ratio increases. Furthermore, the high ash content of the CG is another significant factor contributing to the observed reduction in combustibility. The reaction between mullite, quartz in CG, and alkali metals in biomass results in the formation of aluminosilicate, which reduces the catalytic ability of alkali metals. Furthermore, the char combustion kinetics are analyzed by the KAS method, and the results indicate that the introduction of CG increases the activation energy of the entire char combustion process. The activation energy of the 80RS20CG is within the range of 102.22–164.99 kJ/mol, while the RS char is within the range of 89.87–144.67 kJ/mol.

Modeling the co-combustion of bi-fuel blends in a drop tube furnace: A numerical approach

The present study focuses on the numerical modeling of the co-combustion of reject coal (RC) and sal leaves (SL) in a drop tube furnace (DTF) under different conditions, including air-fuel and oxy-fuel environments. The numerical results highlight the significant influence of replacing the N2 atmosphere with CO2 on the temperature profiles of individual fuels and their blends. For instance, when exposed to a 21%O2/79%CO2 atmosphere, Blend SL3 and Blend SL5 experience a decrease in temperature from 1372 K to 1559 K to 1327 K and 1395 K, respectively. Conversely, increasing the O2 concentration to 35% leads to a temperature rise. Furthermore, the combustion analysis reveals that the addition of 10% SL to RC in a 21%O2/79%N2 environment enhances the devolatilization rate from 1.41 × 10−12 kg/s to 1.77 × 10−12 kg/s. Additionally, the char combustion process for all blends is completed closer to the DTF inlet at 0.28 m, compared to 0.32 m for RC alone. These findings indicate that blending SL with RC promotes a favorable combustion process. Moreover, increasing the O2 concentration to 35% in oxy-fuel conditions enhances the temperature profiles. The numerical analysis demonstrates good agreement with experimental data within a range of ±5%–11%. This suggests that the developed model can be effectively utilized for optimizing and designing biomass co-firing systems in industrial applications, considering both air-fuel and oxy-fuel conditions.

Transformation mechanism of C and N during rapid devolatilization of pulverized coal particles under the pressurized atmospheres

Pressurized O2/CO2 combustion technology is a new power generation technology that can achieve CO2 capture efficiently. In this study, we investigated the pressurized devolatilization of Shenhua bituminous coal in a pressurized drop tube furnace experimental system at 1273 K. The evolution mechanism of carbon/nitrogen gas–solid products during the pressurized devolatilization process was analyzed using online measurements and offline analysis. We found that increasing the pressure from 0.3 to 1.2 MPa promoted the emission of CO and inhibited emission of NO. N2O emissions were insensitive to the change of pressure, and NO2 emissions were almost zero under the experimental conditions. The introduction of CO2 decreased the production of NOx and primary sources of nitrogen-containing gas-phase products were N-5 and N-6 active groups. Therefore, pressurized O2/CO2 combustion technology can effectively reduce NOx emissions in the devolatilization of pulverized coal and impact the subsequent char-combustion process.

Eulerian based population balance modeling of agglomeration in a bubbling fluidized bed combustor

Renewable energy sources are contributing to the displacement of fossil fuel use for power generation and biomass combustion is a viable alternative for baseload power. Fluidized bed combustion (FBC) technology has become a favorable option for biomass (including industrial wastes) fired boilers for its benefits including fuel flexibility, high combustion efficiency, lower emissions (NO x , SO x ) in comparison to other solid fuel fired boilers. However, the variation of inorganic species and corrosive deposits lead to bed agglomeration resulting in unscheduled outages. In the present work, biomass combustion and bed agglomeration in a pilot scale atmospheric-fluidized bed combustor is simulated and analyzed. The Eulerian–Eulerian simulation is validated with the experimental data available in literature using a two-dimensional simplified geometry of a pilot scale fluidized bed combustor. Two each homogeneous and heterogeneous reactions are considered for devolatilization and char combustion processes during combustion with the species transport model. Population Balance Model (PBM) is implemented to calculate agglomerate hydrodynamics with air fed as fluidizing medium from the bottom of the combustor. The model results compared well and found consistent with available experimental data. Prediction of defluidization time of the bed showed a good agreement with the results of experiments.

Preheating pyrolysis-char combustion characteristics and kinetic analysis of ultra-low calorific value coal gangue: Thermogravimetric study

A massive amount of coal gangue is produced during the mining and washing processes of coal, and it has become China's largest solid waste. Therefore, the disposal of coal gangue is extremely urgent. In this paper, a norvel coal gangue disposal technology is proposed, which is mainly divided into two stages: high temperature preheating pyrolysis and char combustion. A 300,000 tons/year demostration project of self-sustainable direct combustion decarbonization without auxiliary fuel is eatablished. The weight loss characteristics and kinetic analysis of ultra-low calorific value coal gangue in this process were studied by thermogravimetric analysis, compared with the normal calorific value coal gangue. The results show that the equipment has advantages and stability for the disposal of ultra-low calorific value coal gangue, and the removal rate of combustible components can reach 88.47 % on average. Based on analysis of TG data, it is determined that the best model describing stage 1, stage 2 and stage 3 of coal gangue pyrolysis process is D3, F2 and F2 model respectively, and the best model describing char combustion process is D2 model. Comparison experiments were carried out for ultra-low caloric value coal gangue under different heating rates and combustion temperatures. It is concluded that the residence time and combustion temperature in actual engineering have influence on the process, and it is suggested that the combustion temperature of char should be 800 ∼ 900 ℃. The research presented in this paper can provide innovative solutions for the disposal of coal gangue, and provide corresponding theoretical guidance.

Dynamic investigation on potassium migration and transformation during biochar combustion and its correlation with combustion reactivity

For agricultural biomass combustion, K migration and transformation is a key factor affecting boiler operation and reaction characteristics. In this study, dynamic K migration and transformation characteristics during rice straw char combustion process under different O2 concentrations were studied using chemical fractionation analysis (CFA), X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX). Furthermore, the correlation between K migration/transformation and char combustion reactivity was discussed. The results showed that most of K in rice straw char was H2O-soluble K. And the main forms of H2O-soluble K and insoluble K are KCl and KAlSi3O8, respectively. As reaction proceeded, the contents of H2O-soluble K and insoluble K decreased but those of NH4Ac-soluble K and HCl-soluble K increased. Most of the released K is H2O-soluble K. H2O-soluble K would be transformed into NH4Ac-soluble K and HCl-soluble K, and some insoluble K would be transformed into H2O-soluble K. The increase of O2 concentration would stimulate the transformation of H2O-soluble K into NH4Ac-soluble K, HCl-soluble K and released K. However, the reaction to form K-aluminosilicate was hardly found during the combustion process at 400 ℃. Ultimately, it is found that H2O-soluble K is the key occurrence form K affecting the combustion characteristics of rice straw char.

Experimental and modeling study on centimeter pine char combustion in fast-heating Macro TGA

Biomass energy is an important renewable resource, and thermochemical conversion, including pyrolysis and combustion, is one of the main methods of biomass energy utilization. In industrial reactors, the biomass particles will experience a fast heating (∼1000 °C/min) process during pyrolysis. The particle size of biomass applied in industry has a wide range (from millimeter to centimeter scale). The study of the reaction characteristics of biomass pyrolysis and combustion is helpful for optimizing furnace design and working condition selection. In this research, the combustion of centimeter-scale pine char was studied with a newly built fast-heating Macro Thermal Gravimetric Analyzer (Macro TGA). This Macro TGA is able to conduct the pyrolysis and combustion of large biomass samples (up to 40 mm) with a fast heating rate (∼1000 °C/min), which is able to reflect the working conditions in industrial-scale reactors such as grate furnaces and dual fluidized beds. This Macro TGA can measure the online sample weight, temperature and sample size simultaneously during pyrolysis and combustion experiments. The combustion characteristics of different sizes of pine chars were investigated at various temperatures and oxygen concentrations. A zero-dimensional model was established to predict the sample weight loss, temperature change and sample shrinkage during the pine char combustion process. Three kinetic parameters α, A and E were applied in the model, and the values of the kinetic parameters were optimized by a genetic algorithm. The model prediction and experimental results are consistent with each other. Compared with previous studies, this study developed a new experimental method to measure the reaction characteristics (including sample weight, temperature and size) of centimeter-scale biomass under similar pyrolysis and combustion reaction conditions compared to industrial reactors, and a zero-dimensional model was established to describe the pine char combustion process.

Quantifying the effect of CO2 gasification on pulverized coal char oxy-fuel combustion

Previous research has provided strong evidence that CO2 and H2O gasification reactions can provide non-negligible contributions to the consumption rates of pulverized coal (pc) char during combustion, particularly in oxy-fuel environments. Fully quantifying the contribution of these gasification reactions has proven to be difficult, due to the dearth of knowledge of gasification rates at the elevated particle temperatures associated with typical pc char combustion processes, as well as the complex interaction of oxidation and gasification reactions. Gasification reactions tend to become more important at higher char particle temperatures (because of their high activation energy) and they tend to reduce pc oxidation due to their endothermicity (i.e. cooling effect). The work reported here attempts to quantify the influence of the gasification reaction of CO2 in a rigorous manner by combining experimental measurements of the particle temperatures and consumption rates of size-classified pc char particles in tailored oxy-fuel environments with simulations from a detailed reacting porous particle model. The results demonstrate that a specific gasification reaction rate relative to the oxidation rate (within an accuracy of approximately +/- 20% of the pre-exponential value), is consistent with the experimentally measured char particle temperatures and burnout rates in oxy-fuel combustion environments. Conversely, the results also show, in agreement with past calculations, that it is extremely difficult to construct a set of kinetics that does not substantially overpredict particle temperature increase in strongly oxygen-enriched N2 environments. This latter result is believed to result from deficiencies in standard oxidation mechanisms that fail to account for falloff in char oxidation rates at high temperatures.

Study on the Effect of Pyrolysis Conditions on the Combustion Behavior and Char Structure Evolution.

Pyrolysis polygeneration technology has been widely applied due to its wide adaptability to coal types and mild reaction conditions. In this paper, the in situ process test combining pyrolysis and combustion of Pingshuo coal was carried out using a thermogravimetric analyzer and a fluidized-bed reactor. The influence of pyrolysis conditions on the combustion behavior and char structure was studied. The reduction of the pyrolysis temperature and the increase in pyrolysis residence time resulted in a lower burnout temperature of char, thereby improving the combustion characteristics of char. Furthermore, the maximum CO2 release rate reached 2.8 mg/(g·s) during the combustion process. The decrease in the pyrolysis temperature was conducive to the increase of CO2 release mass, suggesting a more complete burning of char. The char combustion process was mainly controlled by the chemical reaction according to the reaction kinetics study. The apparent rate constant of the combustion process increased gradually with the decrease in the pyrolysis temperature of char, and the rate of the combustion reaction increased, which contributed to the enhancement of the combustion performance of the char within the range of 850–950 °C. Meanwhile, the crystal structure inside the char changed significantly after different pyrolysis conditions. However, it had little influence on the molar content of carbon structure, which suggested that the amount of CO2 released was mainly caused by the different resistances of oxygen diffusion to the reaction interface.

Dynamic behaviors of the sodium, calcium and iron release during coal combustion using multi-point LIBS

A novel application of multi-point LIBS was used to investigate the mineral release for dispersed-particle streams during coal combustion in an enclosed laminar flow reactor. A 1064 nm Nd: YAG laser was used to ablate the pulverized coal in air-like combustion environments at atmospheric pressure. The electron temperature (Te) and electron density (Ne) were calculated to evaluate the characteristics of the laser-induced plasma along the height from the burner surface, and LS-coupling method was further used to distinguish whether self-absorption occurred. The particle temperature was measured by a two-color pyrometer, and the time-resolved behaviors of Na, Ca and Fe along with the combustion process were measured by LIBS. Results show that the Te and Ne of laser-induced plasmas decreased with the flow of coal flame upon devolatilization, and became relatively stable during char combustion. There was little atomic self-absorption during char-combustion process, which provided theoretical support for quantitative combustion analysis. The Na release, mainly atomic forms, decreased with the particle flow upon devolatilization and showed a trend from rise to decline following devolatilization. The Fe and Ca was rarely released upon devolatilization. During char combustion, the Ca have a similar behavior to Na release, while the Fe increased and then remained constant. The temperature dependent kinetics of the Na and Ca release rate was found to obey an Arrhenius expression. The kinetics of Na and Ca atomic release determined by a first-order model had the pre-exponential factor of 101.16 and 102.67s−1 and the activation energy of 87.2 and 150.8 kJ/mol, respectively.

Numerical analysis of kinetics of char combustion process and selection of mechanism functions

Low and medium temperature pyrolysis technology is an important way of clean and utilization of low metamorphic coal. In this paper, three kinds of char samples were prepared in tube furnace according to different pyrolysis temperatures, and their combustion characteristics were compared by means of thermal analysis. Three modeless kinetic methods, KAS, FWO and Fredman, were used to study the combustion reaction activity under nonisothermal conditions from TG curve and DSC curve. In the end, Malek method is used to explore the mechanism function of the reaction process, and the results are analyzed numerically. The objective programming model and MATLAB are used to calculate the combined mechanism function of the reaction process. The results show that with the increase in the pyrolysis temperature, the combustion of char gradually shifts to the high temperature zone and shows a secondary effect between the volatile matter and the combustion characteristic temperature. The results show that the flammability index and burnout index increase first and then decrease, and the char prepared at 550 °C has the most developed pores and the best combustion performance with the increase in pyrolysis temperature, the average reaction activation energy decreases first and then increases, and the char prepared at 550 °C has the lowest activation energy. When the combustion heating rate is 5 °C min−1, the experimental curve and theoretical curve have a higher coincidence, and the combined mechanism function is adopted. The number is more suitable than the single most probable mechanism function to describe the combustion process of char. At this heating rate, the fuel reaction conforms to Z–L–T equation and reaction order model, which is limited by three-dimensional diffusion and chemical reaction. The distribution coefficients of the combined mechanism function are 0.4207 and 0.5886.

Movement and combustion characteristics of densified rice hull pellets in a fluidized bed combustor at elevated pressures

Pressurized oxy-fuel fluidized bed combustion is regarded as a promising carbon capture technology, which can realize negative CO2 emission through burning biomass. However, given its high volatile content and low density, biomass has been frequently reported to demonstrate poor mixing in industrial FB combustors. Especially in the case of pressurized oxy-fuel combustion, the gas-solid flow in the reactor, fuel particle motion and combustion process will all change and influence each other, which is very important for the particle conversion process and the safety of boiler operation. To correlate the location information with the combustion process in pressurized oxy-fuel combustion, densified rice hull pellets, serving as a typical biomass, were selected as the fuel, and entire whole combustion process was recorded by a color video camera to facilitate the temperature measurement of the volatile flame and char particle by two-color pyrometry. The distribution of a densified rice hull pellet at any given location was obtained from statistics derived from the images. Results showed that the pressure and atmosphere change does not strongly affect the probability of densified rice hull pellets appearing at a given location during the devolatilization process itself. However, during the char combustion process, the probability of finding a particle at the bed surface increased with pressure whereas particle concentrations in the splash zone showed little change, despite the enhanced bubble collapse at elevated pressures. However, the temperature of the volatile flame and char particles increases with the pressure whereas the burnout time of biomass particle decreases due to better oxygen transport.

Numerical investigation on the effect of electron injected air for thermal decomposition of solid waste

Many organizations in the world are interested in waste management problems and their potential solutions. In order to solve these problems, a Japanese venture company has developed an innovative thermal decomposer for organic wastes called ERCM (Earth-Resource-Ceramic-Machine). The ERCM reactor employs electron injected air to promote the thermal decomposition reaction, while the effect of electron injection into air has not yet been clarified. An experimental work was performed using a fixed bed reactor to explore the effects of different parameters of electron injection into air, the reaction temperature and different feedstock on the syngas generation. The main purpose of this study is to clarify the phenomena occurring in the ERCM reactor where a direct current electric field is produced in the flame reaction zone to enhance the thermal decomposition of wastes. In this regard, a mathematical model for simulating the thermal decomposition of solid waste in the presence of an electric field have been developed. The equations of aero-thermochemistry are coupled to the balance equations for densities of charged species, and the Poisson equation for the electrical potential is solved. The model was validated by the experimental data and showed a good agreement. The results showed that the electric field significantly improves the stabilization of the flame. From the release behavior of CO and CO2, it is noted that the electron injection would affect the char combustion process significantly. Finally the effect of the flame reaction zone generated by the field induced ion wind on the thermal decomposition was investigated.

Synergistic effect of hydrothermal co-carbonization of sewage sludge with fruit and agricultural wastes on hydrochar fuel quality and combustion behavior

In order to improve fuel quality of sewage sludge, fruit and agricultural wastes have been selected for hydrothermal co-carbonization. After hydrothermal co-carbonization, organics retention was facilitated, while O/C and H/C atomic ratios of hydrochars were substantially upgraded. Particularly, hydrochar from hydrothermal co-carbonization of sewage sludge with peanut shells at mass ratio of 1:3 (denoted as “SS:PS = 1:3”) showed the highest fuel ratio of 0.79 and its carbon content was increased to 50.0% with significantly decreased O/C and H/C atomic ratios. Furthermore, higher heating value of hydrochars from hydrothermal co-carbonization was increased by nearly 2.65-fold and reached 21.72 MJ/kg. Moreover, the most favorable aromatization occurred when sewage sludge and peanut shells blending ratio was 3:1 or 1:1, whereas hydrothermal co-carbonization induced more CO and OH than COOH in hydrochars due to synergistic decarboxylation. A relatively higher value of point of zero charge for hydrochars from hydrothermal co-carbonization implied improved hydrophobicity. Combustion kinetics results indicated that hydrothermal co-carbonization balanced activation energies of hydrochars in devolatilization/combustion stage and char combustion process, rendering a more stable and lasting combustion profile. Hydrochars “SS:PS = 1:3” demonstrated desirable combustion performance. Therefore, hydrothermal co-carbonization can realize sustainable utilization of organic solid wastes towards superior hydrochar solid biofuels.

Characterizing flame stability and radiative heat transfer in non-swirling oxy-coal flames using different multiphase modeling frameworks

The ability of two multiphase modeling frameworks (Euler-Lagrangian and Euler-Euler) to capture the experimentally observed flame ignition characteristics in non-swirling oxy-coal flames were investigated. The interphase interaction terms were modeled employing identical phenomenological laws. Simulations of inert particles were carried out first and were found to yield identical predictions across both frameworks. Next, user-defined functions were utilized to: model the diffusional and kinetic resistances associated with the heterogeneous char oxidation (in the Euler-Euler framework), the non-gray effects of gas radiation, and the variations in the radiative properties of the solid phase (in the Euler-Lagrangian framework). Only the Euler-Euler framework was able to capture the experimental observed trends in flame stand-off as a function of oxygen concentration in the primary burner. The interval between the devolatilization and char combustion processes varied between the two frameworks and were a contributing factor to the prediction differences. Representing the coal PSD by a single granular phase in the Eulerian framework was deemed adequate for capturing flame stand-off since solving additional phase equations did not significantly impact the flame stand-off predictions. Further, the experimentally observed effects of: primary oxidizer composition variations, secondary oxidizer temperature and wall temperature on flame stand-off were also adequately predicted reasonably well by the Euler-Euler framework. Radiation was the dominant mode of heat transfer in these flames with the radiant heat loss fraction (Radiative heat loss/Total chemical heat release) determined to be 0.6 for both flames. Radiation from the participating gases accounted for 75% of the total radiative heat transfer.

Study on the Influence of the Activation Energy on the Simulation of Char Combustion

The numerical simulation of coal char combustion process can quickly obtain the combustion characteristics of char. It has guiding significance for the design and operation industrial boilers. But during the numerical simulation, how to choose the appropriate kinetic parameters is a difficult problem. The values of combustion activation energy in previous literatures were different. This paper focused on the influence of activation energy on the simulation results of char combustion. The activation energies of 20 Chinese typical coals were measured by a two-step in-situ reaction analyzer. CBK (Carbon burnout kinetics) model was used to simulate char combustion process. Results showed that when activation energy varied greatly, the the predicted combustion rate and particle temperature were very different, especially in the later stage of char combustion.

Investigation of demineralized coal char surface behaviour and reducing characteristics after partial oxidative treatment under an O2 atmosphere

Shenhua (SH) demineralized char was employed to determine the relationship between the char conversion ratio and the surface behavior of particles. The amount, distribution and thermal stability of C(O) generated during the combustion process were clarified by temperature-programmed desorption (TPD) and Fourier transform infrared spectroscopy (FTIR). CO2 was the primary gaseous product released during the TPD process of each partially oxidized sample. Based on the TPD and FTIR deconvolution results, the decomposition temperature of each functional group could be determined as follows: phenol (1000 K) < carboxyl (1150 K) < ether/anhydride (1400 K) < quinone (1600 K) < lactone (1650 K). Partial oxidative treatment promoted the generation of C(O) on the particle surface, with the maximum amount of C(O) existing on the surface of samples with an intermediate conversion ratio (0.33–0.47). Due to the increase in C(O), the reducibility of the partially oxidized sample was also enhanced. The demineralized chars collected in the intermediate stage (0.33–0.47) expressed the strongest reducibility, and the maximum NO was consumed by per unit mass of these samples. Phenol, carboxyl, anhydride and ether were the main forms of C(O) and were involved in the rapid and successive consumption of NO as major reactants, leading to an apparent reduction of the NO released during the char combustion process.

Effect of microwave pretreatment on the combustion behavior of lignite/solid waste briquettes

Lignite is one of common applied fossil fuels worldwide, and solid wastes like biomass as well as sewage sludge are promising alternatives of fossil fuels. The isothermal combustion performances of lignite/solid wastes (eucalyptus bark and sewage sludge) briquettes between 500 °C and 800 °C in a bench-scale fixed bed furnace were examined based on a macro-thermogravimetric analysis approach. Compared with untreated samples, the average combustion rates of lignite and sewage sludge with the microwave treatment decreased, while those for treated eucalyptus bark increased. The drying, devolatilization and char combustion processes overlapped in the isothermal combustion for all samples. The treated lignite had a high aromatic hydrocarbon, while both the treated sewage sludge and eucalyptus bark had high hydroxyl and methyl group (CH3). After the microwave pretreatment, the fuel rank of lignite was prompted, while that for eucalyptus bark and sewage sludge degraded. Through the microwave pretreatment, the activation energies of lignite, sewage sludge, and eucalyptus bark grew from 15.45 to 21.20 kJ mol−1, 18.23–20.77 kJ mol−1, and 13.27–14.22 kJ mol−1. The study can provide some basic data for the energy utilization of lignite and solid wastes.

Preliminary Research on the Effects of Coal Devolatilization and Char Combustion Processes on the Emission of Particulate Matter during Lignite Combustion under Air and Oxy-fuel Conditions

The pulverized coal combustion in both air and oxy-fuel conditions generally experiences successive coal devolatilization and char combustion processes. The effects of these two processes have important influence on the emission characteristics of particulate matter. With some different characteristics of lignite from the higher rank coal, including the high contents of organically bound cations and the apparent char–CO2 gasification reaction upon oxy-fuel combustion, the effects of both coal devolatilization and char combustion processes on the emission characteristics of particulate matter during oxy-fuel combustion of lignite would accordingly be distinctive. A typical Chinese lignite was devolatilized in a N2 or CO2 atmosphere to generate N2–char and CO2–char, respectively. Raw coal and the two chars were burned in a drop-tube furnace under both air and oxy-fuel conditions. Afterward, the yields and inorganic compositions of segregated PM10 were carefully analyzed. The results have shown that the devo...