Bituminous Coal Combustion Research Articles

Adsorption simulation of gas released during oxidation of bituminous coal

ABSTRACT The adsorption of gases released during coal oxidation have a significant impact on the accuracy of CSC prediction. However, there are few research on the adsorption of C2H4 and C2H6 by coal. Therefore, the adsorption characteristics of N2/CO2/C2H4/C2H6 released during the spontaneous combustion of bituminous coal were investigated by programmed heating experiment and molecular simulation. The results showed that the low-volatile coal exhibited a higher adsorption capacity for CO2, N2, and C2H4 compared to high-volatile coal. The sequence of adsorption capacity for both low-volatile coal and High-volatile coal was CO2 > C2H6. The electrostatic potential of oxygen functional groups was ranked as follows: Ph-OH > Ph-COOH > R-COOH > R-OH. The interaction energy of gases at the -COOH position was greater than that at the -OH position, indicating that -COOH is more likely to provide adsorption sites for gases.

Study on Spontaneous Combustion Characteristics and Microstructure of Bituminous Coal under Water Immersion.

The stagnant water above the coal seam flows into the goaf, causing the goaf coal to be soaked by water for a long time. Compared with dry raw coal, water-soaked coal has a stronger tendency for spontaneous combustion, which poses a serious threat to mining operators. To unravel the impact of water immersion on coal's self-heating properties, an investigation was conducted employing techniques such as simultaneous thermogravimetric analysis/differential scanning calorimetry (TG/DSC), scanning electron microscopy (SEM), low-temperature nitrogen adsorption based on the BET theory, and Fourier transform infrared spectroscopy (FTIR). The variations in the characteristic temperature, microphysical structure, and active functional groups of bituminous coal with water immersion degrees of 10, 30, 50, and 100% were studied, and the experimental results showed that (1) during the initial stage of coal self-ignition oxidation, moisture can cause a delay in the characteristic temperature points of bituminous coal. When the degree of water saturation in bituminous coal reaches 100%, both the critical temperature (T 1) and the cracking temperature (T 2) peak at 48.14 and 205.06 °C, respectively. However, after the water evaporation phase is complete, water soaking promotes the spontaneous combustion of bituminous coal. (2) The number of pores and fractures in bituminous coal is positively correlated with the amount of water soaked, with the average pore diameter increasing from 10.124 nm in raw coal to 15.547 nm in the A4 coal sample. Moreover, when the degree of water immersion reaches 100%, the proportion of mesopores and macropores increases to 38.89 and 19.95%, respectively. (3) Compared to untreated coal, the number of functional groups in water-soaked coal samples increases. With the increase in water immersion, the hydroxyl (-OH) content of raw coal and four kinds of bituminous coal with different degrees of immersion was 40.8, 41.3, 42, 43.9, and 42.9%, respectively, showing a trend of increasing first and then decreasing. When the degree of water immersion of bituminous coal is 50%, the natural tendency is the strongest. These findings contribute to elucidating the underlying mechanism of water immersion's impact on coal self-ignition, thereby holding significant implications for enhancing fire safety measures in mine working areas.

Evaluation of the applicability of carbon-based materials for arsenic removal from flue gases

Arsenic is an highly toxic element which may be released into the atmosphere during the combustion of solid fuels. This paper verifies the possibility of using char from tires CT and lignite dust LD as materials for the adsorption of gaseous forms of As. The source of the gaseous forms of arsenic was coal combustion under laboratory conditions. Adsorption tests included both different sorbent bed temperatures (120–180°C) and various flue gas compositions (resulting from the combustion of bituminous and lignite coals). It was shown that sorption temperature did not affect the arsenic removal efficiency for both analysed sorbents. The average As removal efficiency for tire char and lignite dust was 88 and 92%, respectively. The composition of the burned coal, and thus the composition of the flue gas, significantly influences the efficiency of Asgas adsorption. While for LD the level of As removal was still high (more the 90%), the sorption of Asgas by tire char from the flue gas when lignite was burned was less effective (the efficiency was below 80%). It was additionally indicated via a leachability test that "used" CT could be safely disposed of while LD would require appropriate management. Based on the comparison of the performance of CT and LD with commercial AC activated carbon and the differences in their market price, it can be concluded that the studied alternative sorbents are competitive with AC.

Experimental investigation on the effect of blending bituminous coal with pinus sawdust on combustion performance parameters

Combustion of bituminous coal and pinus sawdust blends was investigated experimentally within a drop tube furnace (DTF) with the aim of determining particle residence times and temperatures during the process. Evaluation of these parameters gives useful information to engineers who want to optimise the co-combustion process of coal and biomass blends. The DTF experimental approach was used to investigate fuel blends with a pinus sawdust mass substitution of 0, 10, 20, and 30% at different furnace temperatures of 1273, 1473 and 1673 K. Results showed that during stage 1 of the experimental setup which mimics devolatilisation, particle residence time at a distance of 520 mm from the injection point decreased from 0.8 to 0.7 s as blending by pinus sawdust increased from 0 to 30 %. During stage 2 of the experimental setup which mimics char combustion, particle residence time at a distance of 1320 mm from the injection point decreased from 3.9 to 2.0 s as blending by pinus sawdust increased from 0 to 30 %. The blending ratios under investigation demonstrated similar profiles of particle temperature at different furnace positions though further analysis showed that the highly blended samples required less time to attain high temperatures. By extension, since fuel blends with higher percentages of pinus sawdust were able to attain higher temperatures at shorter residence time, combustion intensity was deduced to increase with the blending ratio whilst stability decreased. As such, caution should be taken with materials used for furnace and burner design as high-temperature zones move backwards towards the injection point as blending increases.

Thermogravimetric Assessment and Differential Thermal Analysis of Blended Fuels of Coal, Biomass and Oil Sludge

The coupled combustion of biomass and organic solid wastes including oil sludge has attracted much attention. Although the optimal mixing ratio of different coal types and biomass has been extensively studied, little attention has been paid to oil sludge that has undergone co-combustion. In this study, the combustion characteristics of blended fuel for coal, biomass and oil sludge under different mixing ratios are studied via a thermogravimetric test and differential thermal analysis. Kinetic analysis of tri-fuel is performed using the Flynn–Wall–Ozawa (FWO) and Dolye methods. The results show that the bituminous coal combustion process mainly involves the combustion of fixed carbon (236.0–382.0 °C). Wood pellet combustion (383.0–610.0 °C) has two processes involving the combustion of compound carbon and fixed carbon. Blending wood pellets effectively enhances combustion efficiency. Wood pellets from Korla (KOL) have the most obvious effect on reducing the ignition temperature. The blending combustion of bituminous coal (SC), wood pellets from Hutubi (HTB) and oil sludge (OS) have significant synergistic effects. As the OS mixing ratio increases from 10% to 20% with 45% HTB, Ti and Th decrease from 354.9 and 514.3 °C to 269.8 and 452.7 °C, respectively. In addition, f(α) is [−ln(1 − α)]2 for tri-fuel in most mixing ratios when α < 0.5, while f(α) becomes [−ln(1 − α)]3 at α > 0.5. At a high-HTB-level mixing ratio, increasing the OS content causes a decrease in activation energy to 35.87 kJ mol−1. The moderate blending of oil sludge improves the pre-finger factor and the combustion performance.

Comparative Analysis of Real-Emitted Particulate Matter and PM-Bound Chemicals from Residential and Automotive Sources: A Case Study in Poland

The awareness of environmental pollution has been continuously growing in recent decades and is currently reaching its maximum. Europe and most developed countries are determined to ensure safe breathing air for their citizens, and the measures to do so are stricter than ever before. Combustion procedures remain the primary means of producing energy and warmth in Poland. Among the notable constituents of flue gases produced as a result of fuel combustion, solid particles (or particulate matter) hold significant prominence. The paper presents the chemical characterisation of particulate matter emitted from stationary and automotive emission sources. Stationary emission sources included the combustion process of fossil fuels (soft wood, bituminous coal, ecopea coal, culm) in domestic heating units and the process of combustion of bituminous coal in a power plant. Automotive emission sources included light duty and medium duty vehicles fuelled by diesel. Exhaust toxicity tests were carried out maintaining the real conditions of PM emission. In all field measurements particulate matter was gravimetrically measured and collected on quartz or glass fibre filters. Subsequently, the content of carbonaceous fraction, inorganic ions, and metals and metalloids was analyzed using different analytical techniques. The chemical composition of the particulate matter differed depending on the emission source. With respect to stationary combustion sources, the main factors determining solid particle emission are related primarily to the fuel quality. The duty of vehicles was also a factor that influenced the chemical characterisation of the particulate matter emitted from the engines.

Enhancement of hybrid combustion of semi-coke and bituminous coal by rare earth oxides

ABSTRACT The use of semi-coke instead of anthracite coal for blast furnace injection to reduce ironmaking costs is becoming increasingly popular. To optimise the usage of semi-coke, it is essential to investigate the mixed combustion of semi-coke and bituminous coal. Within this study pulverised coal combustion was analysed using a thermogravimetric analyser. The results showed that the proportion of semi-coke in the mixed pulverised coal did not exceed 30%. However, 1 wt-% La2O3 as a catalyst increased the proportion of semi-coke by 15%. In addition, the kinetics of combustion of pulverised coal was investigated using the Flynn Wall Ozawa method and the catalyst reduced the activation energy of the reaction. The average activation energy decreased from 84.24 KJ/mol to 74.59 KJ/mol, especially at a conversion of 0.4, with a maximum reduction of 17.3%. Overall, La2O3 is an effective catalyst to increase the utilisation of semi-coke for practical industrial applications.

The high temperature ashes (HTA) from bituminous coal combustion as a potential resource of rare earth elements

The high temperature ashes (HTA) from bituminous coal combustion as a potential resource of rare earth elements

Ash fouling behavior during the combustion of bituminous coal and high-Ca pyrolytic biochar under air and oxyfuel atmosphere

Co-combustion of coal and pyrolytic biochar under oxy-fuel atmosphere is a promising option for addressing CO2 problems in power plants, where the issue of ash fouling during combustion was considered in this study. A high-Ca pyrolytic biochar from pilot-scale trail and a high-Si Utah bituminous coal were selected for single- and co-combustion on a drop tube furnace (DTF) coupled with fouling sampling system under the atmosphere of air and oxy50 (CO2:O2 = 50:50 vol%) at 1300 ℃. The fouling deposits were collected and characterized by various techniques to investigate the formation mechanism of ash deposits. The results indicated that the combined effects of impaction and capture resulted in the different deposition propensity from coal and biochar combustion under both air and oxy50 conditions. Besides, co-firing can inhibit the formation of ash deposits during coal combustion under air atmosphere when the blended biochar was greater than 50%, while the deposition propensity of the blend with 80% biochar rapidly aggravated under oxy50 atmosphere. The fine particles act as “glue” to fix coarse particles from impaction were the main source of the inside deposits from coal combustion, whereas the inside deposits from biochar combustion were dominated by agglomerated and sintered fine particles. Co-firing can weaken the “glue effect” from coal combustion, and finally presented as mitigated deposition propensity of inside deposits. Switching to oxy50 condition, the enhanced sulfidation of deposits and scavenging of alkali metal suppressed the growth of inside deposits from coal combustion, while that had minor impact on biochar. The inhibitory effect of co-firing on inside deposits diminished with the increased biochar under oxy50, where the deposition propensity of the blend containing 80% biochar was higher than that in air-firing.

Assessment of combustion residual leachate volume, composition, and treatment costs

Combustion residuals and the resulting leachate from storage sites represent a large volume of wastewater in the United States (U.S.) that has not been quantified. This work estimates the constituents present, volume of wastewater, and costs of treatment for both combustion residual landfill leachate and the leachate from surface impoundment closures. Combustion residual landfill leachate produced from contact with bituminous coal combustion byproducts is generally predicted to be higher in lithium and manganese, whereas landfill leachate produced from contact with subbituminous coal combustion byproducts is generally predicted to be higher in mercury and vanadium. The annual volume of a single landfill with combustion residual leachate can reach more than 800,000 cubic meters. This leachate represents an annual volume of 26.8–42.8 million cubic meters nationally. Closing surface impoundments can yield between 830 and 1040 cubic meters of leachate nationally for a three-year closure period. Costs as low as $1.5/m3 or as high as $95/m3 are observed. Treatment trains will need to remove 72% of total suspended solids (TSS), 87% of arsenic, and 64% of mercury from landfill leachate. When applied to impoundments, these treatment trains would need to remove 97% of arsenic.

Gas Particle Partitioning of PAHs Emissions from Typical Solid Fuel Combustions as Well as Their Health Risk Assessment in Rural Guanzhong Plain, China.

Air pollutants from the incomplete combustion of rural solid fuels are seriously harmful to both air quality and human health. To quantify the health effects of different fuel-stove combinations, gas and particle partitioning of twenty-nine species of polycyclic aromatic hydrocarbons (PAHs) emitted from seven fuel-stove combinations were examined in this study, and the benzo (a) pyrene toxicity equivalent (BaPeq) and cancer risks were estimated accordingly. The results showed that the gas phase PAHs (accounting for 68-78% of the total PAHs) had higher emission factors (EFs) than particulate ones. For all combustion combinations, pPAHs accounted for the highest proportion (84.5% to 99.3%) in both the gas and particulate phases, followed by aPAHs (0.63-14.7%), while the proportions of nPAHs and oPAHs were much lower (2-4 orders of magnitude) than pPAHs. For BaPeq, particulate phase PAHs dominated the BaPeq rather than gas ones, which may be due to the greater abundance of 5-ring particle PAHs. Gas and particle pPAHs were both predominant in the BaPeq, with proportions of 95.2-98.6% for all combustion combinations. Cancer risk results showed a descending order of bituminous coal combustion (0.003-0.05), biomass burning (0.002-0.01), and clean briquette coal combustion (10-5-0.001), indicating that local residents caused a severe health threat by solid fuel combustion (the threshold: 10-4). The results also highlighted that clean briquette coal could reduce cancer risks by 1-2 orders of magnitude compared to bulk coal and biomass. For oPAH, BcdPQ (6H-benzo(c,d)pyrene-6-one) had the highest cancer risk, ranging from 4.83 × 10-5 to 2.45 × 10-4, which were even higher than the total of aPAHs and nPAHs. The dramatically high toxicity and cancer risk of PAHs from solid fuel combustion strengthened the necessity and urgency of clean heating innovation in Guanzhong Plain and in similar places.

Thermodynamic Irreversibility Analysis of Thermal Radiation in Coal-Fired Furnace: Effect of Coal Ash Deposits.

In this paper, a three-dimensional (3-D) high-temperature furnace filled with a gas-solid medium was investigated, and the radiative transfer equation and the radiative entropy transfer equation in the chamber were applied in order to analyze the effect of coal deposits on thermal radiation. The heat flux on the walls of the furnace and the entropy generation rate were determined due to the irreversibility of the radiative heat transfer process in the furnace. Furthermore, the effect of ash deposits on the wall surface on the irreversibility of the radiation heat transfer process was investigated. The numerical results show that when burning bituminous and sub-bituminous coal, ash deposits in the furnace led to a 48.2% and 63.2% decrease in wall radiative heat flux and a 9.1% and 12.4% decrease in the radiative entropy rate, respectively. The ash deposits also led to an increase in the entropy generation number and a decrease in the thermodynamic efficiency of the radiative heat transfer process in the furnace.

석탄의 연소과정에서 포집된 입자상 물질의 광학 특성에 관한 연구

In order to improve the reliability of optical-based PM concentration measurements, the optical properties of PM such as the dimensionless light extinction coefficient must be well defined. However, the optical properties of PM produced from burning coal are lacking. Therefore, in this study, the dimensionless light extinction coefficient measurements and optical characterization analysis of PM generated from burning bituminous coal at elevated reaction temperatures were performed. Bituminous coal in the form of powder was burned in a muffle furnace and PM released from flame was then collected on a quartz filter. Morphological investigations through the TEM images and elemental and organic carbon ratio analysis were performed to quantitatively investigate the optical properties of PM. Experimental results clearly indicate that increases in the reaction temperature can increase graphitic nature and morphological dimension (represented by an optical diameter) of PM, eventually enhancing the effects of absorption and scattering of the light and the measured dimensionless light extinction coefficient of PM.

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.

Emission Characterization of Particulate Matters from the Combustion of Pulverized Coals in a Simulated Fluidized Bed Boiler.

Coal-fired power generation is one of the main causes of air pollution, and the fluidized bed technology is currently a commercially used coal-fired technology. Therefore, it is of great significance to investigate the characteristics of particulate matter released from the fluidized bed boiler. In this study, lignite, bituminous coal and anthracite with particle sizes of <75 μm and 180–830 μm were selected and burned completely at 700, 800, and 900 °C for the purpose of simulating the process of pulverized coal combustion in a small sized simulated fluidized bed boiler and exploring the effects of coal rank, particle size, and burning temperature on the characteristics of the released particulate matter. The results show that, under the same mass, bituminous coal combustion releases the most PM1, PM2.5, and PM10, followed by lignite and anthracite. For all combusted coals the released PM1 accounts for half and one-third of the PM2.5 and PM10, respectively, and the released PM2.5 accounts for half of the PM10. A smaller particle size of pulverized coal and a higher burning temperature correspond to the release of more submicron to micron particulate matter. The mass concentration of released particulate matter for lignite and bituminous coal shows a bimodal distribution, with the two peak values in the ranges of 0.1–0.18 and 3.2–10 μm, respectively. As the burning temperature increases and the particle size of pulverized coal decreases, the first peak value falls and the second peak shifts to a small particle size range. This study can serve as reference for diminishing the emission of submicron to micron particulate matter by coal-fired power plants and preventing air pollution.

EP16.03-001 High Frequency of KRAS Mutation, Uncommon EGFR Mutation and TMB-H in Xuanwei Female Patients With Lung Adenocarcinoma

In female patients from Xuanwei county of China, the incidence and mortality of lung adenocarcinoma (LUAC) are extremely high, mainly due to abnormal exposure to carcinogenic polycyclic aromatic hydrocarbons produced during indoor combustion of bituminous coal. Thorough understanding of molecular features of Xuanwei female LUAC patients, when compared to reference Chinese female LUAC patients, could be beneficial to improve the management strategy for precision treatment in this high-risk population.

Effect of central secondary air on flow and combustion characteristics of 600-MWe down-fired boiler: From laboratory to industrial site

The existing central secondary air swirl pulverized coal burner and separated secondary air interval arrangement down-fired boiler combustion technology used for the combustion of blended bituminous coal encounter several problems such as burner nozzle burnout, limited proportion of bituminous coal blending under high load, etc. In this study, the effects of central secondary air on the flow, pulverized coal ignition, burnout, and NOx emissions characteristics of a 600-MWe down-fired boiler with the central secondary air combustion technology were studied by the combination of cold-modeling experiments and industrial-scale experiments. Moreover, the reasons for the burnout of the burner nozzle and limited blending proportion of bituminous coal were analyzed and revealed. Cold-modeling experiments showed that with the increase of the central secondary air ratio, the peak value of the dimensionless vertical velocity increases; however, the flow field asymmetry occurs in the furnace when the air ratio increases to 6%. Considering the symmetry of the flow field and the characteristics of the downdraft, the central secondary air ratio is advised to be less than 3.52%. The industrial-scale experiments of burning bituminous coal under 360-MWe load show that the ignition distance of coal/air flow is about 0.10 m for all the cases at 30, 50, and 75% of the central secondary air damper opening, respectively, which reveal that the serious burner nozzle burnout is caused by the premature ignition of the coal/air flow. Under three types of central secondary air damper openings, the NOx emissions at furnace outlet are 333, 329, and 355 mg m−3 @ 6% O2, respectively. By considering the flow, combustion, and temperature field characteristics in the furnace, reduction in the central secondary air supply air volume can delay the ignition of the coal/air flow, which provides a new idea and method to achieve a high proportion of bituminous coal blending at rated load.

Comparison of oxy-fuel preheated combustion characteristics of high- and low- volatility carbon-based fuels

A comparative evaluation and analysis study of combustion characteristics, main pollutant emission behaviors, and fuel-N conversion paths of high- and low- volatility carbon-based fuels are conducted under O2/CO2 atmospheres in a preheating combustion reactor, i.e., CFB. Compared with conventional air combustion, the oxy combustion with high oxygen concentrations from 21% to 27.3% is studied. The studies show that the net calorific value of the preheated coal gas of semi-coke in O2/CO2 is up to 2 times that in air, and the net calorific value of the preheated coal gas of bituminous coal in O2/CO2 is up to 1.3 times that in air. During the preheating process of semi-coke, CH4 and HCN occupy a discreet proportions of preheating coal gas. Fuel characteristics and preheating atmosphere have no effect on the particle size of preheated coal char. Under an O2/CO2 atmosphere, the highest BET surface area of preheated coal char of bituminous coal is up to 30 times that of raw coal and that of semi-coke is up to 40 times that of raw coal. The carbon structure modification ratio of preheated coal char during the preheating process of bituminous coal is larger than that during the preheating process of semi-coke. With the increase in the concentration of oxygen in the primary stream, the NO emission decreased during the bituminous coal combustion process but increased during the semi-coke combustion process. In addition, the main generation path of NO in the reduction zone in O2/CO2 is NH3-NH2-NH-HNO-NO. In O2/CO2, the total promotion effect of reactions on NO formation in the combustion process of semi-coke preheated fuel is larger than that of bituminous coal.

Assessment of blended coal source fly ashes and blended fly ashes

The availability of traditional siliceous Class F fly ash, produced when burning bituminous coals, is decreasing around the world as many countries begin to switch to renewable energy sources. Existing coal burning power plants are also starting to convert from bituminous to subbituminous coals, which produce calcareous Class C fly ash, or to a blend of the two to reduce emissions and cost. To prolong the availability of siliceous fly ash, suppliers have started distributing blended coal ashes and have also begun to blend siliceous fly ash with other coal combustion products (CCPs), such as calcareous fly ash or bottom ash, or natural pozzolans. A variety of these blended fly ashes were examined in this study and compared to a traditional siliceous fly ash. Although these fly ashes have similar oxide compositions and physical characteristics to a traditional siliceous fly ash, the crystalline and glassy phases present in the fly ash may differ. This can alter cement hydration and result in failure to mitigate expansion due to sulfate attack. In all other performance and durability tests conducted in this study, all fly ashes performed well in cement-based mixtures.

The retention and speciation transformation mechanisms of chromium during bituminous coal combustion: Effects of inorganic minerals and combustion temperature

Coal combustion mainly releases chromium (Cr) as particulates and may oxidize Cr into toxic hexavalent forms. A series of combustion experiments combined with thermodynamic equilibrium calculations were used to study the speciation transformation behavior of Cr during the burning of a typical bituminous coal. Iron-bearing minerals and the combustion temperature were found to be vital for enriching Cr in ash and preventing Cr oxidation at high-temperature combustion process. During coal combustion, an increasing release trend of Cr versus the combustion temperature was observed. However, the degree of Cr oxidation didn't increase with the increased temperature. The fraction of Cr(VI) reached a maximum at 800°C, but gradually decreased as the combustion temperature rose to 1000°C. Further speciation study revealed that Cr was mostly presented in illite and pyrite in coal, which can be transformed into aluminosilicate glass and hematite. The ion-exchangeable, carbonate, and organic-bound Cr were easily released and also partly converted into less soluble residual form. At high combustion temperature (> 800°C), Fe2O3 exhibited a significant effect on Cr transformation and diminished the Cr(VI) ratios in coal ash. This was beneficial to the ash disposal or reutilization since Cr was retained as stable Cr (III) compounds in ash.