Bituminous Coal Combustion Research Articles

Catalytic Destruction of a Surrogate Organic Hazardous Air Pollutant as a Potential Co-benefit for Coal-Fired Selective Catalytic Reduction Systems

Catalytic destruction of benzene (C6H6), a surrogate for organic hazardous air pollutants (HAPs) produced from coal combustion, was investigated using a commercial selective catalytic reduction (SCR) catalyst for evaluating the potential co-benefit of the SCR technology for reducing organic HAP emissions. Bench-scale experiments were performed using simulated coal combustion flue gases under a broad range of SCR reaction conditions. C6H6 was added at 1 or 17 ppm into the flue gas mixtures with different concentrations of sulfur dioxide (SO2), nitrogen oxide (NO), hydrogen chloride (HCl), and ammonia (NH3) to simulate the combustion of bituminous and sub-bituminous coals. The destruction of the C6H6 across the catalyst was measured by a total hydrocarbon analyzer and a resonance-enhanced multiphoton ionization time-of-flight mass spectrometer (REMPI–TOFMS) for the experiments with high (17 ppm) and low (1 ppm) concentrations of C6H6, respectively. The operating parameters of the SCR process, including the ...

Activity of Fe2O3 with a high index facet for bituminous coal chemical looping combustion: a theoretical and experimental study

Iron-based oxide with high miller index facet Fe2O3(104) effectively promotes oxygen transfer at different oxidation states for oxidizing coal molecules into CO2 and H2O during chemical looping combustion of solid fuel.

Dry sorbent injection of trona to control acid gases from a pilot-scale coal-fired combustion facility

Gaseous and particulate emissions from the combustion of coal have been associated with adverse effects on human and environmental health, and have for that reason been subject to regulation by federal and state governments. Recent regulations by the United States Environmental Protection Agency have further restricted the emissions of acid gases from electricity generating facilities and other industrial facilities, and upcoming deadlines are forcing industry to consider both pre- and post-combustion controls to maintain compliance. As a result of these recent regulations, dry sorbent injection of trona to remove acid gas emissions (e.g. HCl, SO2, and NOx) from coal combustion, specifically 90% removal of HCl, was the focus of the current investigation. Along with the measurement of HCl, SO2, and NOx, measurements of particulate matter (PM), elemental (EC), and organic carbon (OC) were also accomplished on a pilot-scale coal-fired combustion facility. Gaseous and particulate emissions from a coal-fired combustor burning bituminous coal and using dry sorbent injection were the focus of the current study. From this investigation it was shown that high levels of trona were needed to achieve the goal of 90% HCl removal, but with this increased level of trona injection the ESP and BH were still able to achieve greater than 95% fine PM control. In addition to emissions reported, measurement of acid gases by standard EPA methods were compared to those of an infrared multi-component gas analyzer. This comparison revealed good correlation for emissions of HCl and SO2, but poor correlation in the measurement of NOx emissions.

SO3 formation under oxy-CFB combustion conditions

Due to the enrichment of SO2 and H2O, SO3 formation during oxy-fuel circulating fluidized bed (CFB) combustion may significantly increase over the air fired case and this requires special attention in terms of safety consideration. In an attempt to better elucidate the formation mechanism of SO3 under oxy-fuel CFB conditions, homogenous and heterogeneous experiments were performed using a small vertical tube reactor to model the SO3 formation condition in the back pass channels and then the mechanism deduced was further validated by tests and measurements using a pilot-scale 50kWth oxy-fuel CFB combustor with wet flue gas recycle. Results show that replacing N2 by CO2 does not change the SO3 formation levels while the addition of water enhances SO3 formation. The increased O2, SO2, H2O concentrations along with increasing temperature are favorable for enhancing SO3 formation over the range of tested parameters. Fe2O3, CuO and V2O5 are shown to be able to catalyze SO2 conversion to SO3 under oxy-fuel atmosphere; of these V2O5s catalyzing ability is the strongest. Fly ash can either catalyze the SO3 formation or absorb SO3, depending on the temperature and the alkalinity of the ash. The results from the pilot plant burning bituminous coal demonstrate that SO3 concentration in the flue gas is about 4.5 times higher during oxy-fuel combustion than that under air combustion.

Techno-economic analysis of a 15 MW corn-rape oxy-combustion power plant

Oxy-combustion is a promising technology to enable the capture of CO2 from power plants based on diverse raw material. This paper describes and compares the results of technical and economic viability studies of a 15MW power plant based on a corn-rape blend oxy-combustion, a bituminous coal-combustion and a bituminous coal oxy-combustion located in the north of Spain. Technical simulations were implemented in Aspen Plus© software. The economic viability studies were based on the typical economic indicators such as net present value, rate of return, specific total plant investment, cost of electricity, cost of CO2 avoided and energy consumption for CO2 avoided. A sensitivity analysis was carried out in order to identify the most important factors affecting the investment risks. The use of a cryogenic air separation unit was associated with a reduction in oxy-combustion plant viability. While coal-combustion process reported an enough profitability, a supplementary public grant of 63€/MWh and 57€/MWh were required in coal oxy-combustion process and biomass oxy-combustion process respectively to obtain a positive profitability. A stability of raw material and electricity markets was found to be necessary to improve a risk reduction for the potential investment.

An Investigation into the Combustion of Mixed Fuel Consisting of Bituminous Coal and Crude Bio-Oil

The combustion of bituminous coal, bio-oil, and their slurry mixtures were performed under air atmosphere using Thermogravimetric Analyzer (TGA). All samples were run from room temperature to 110°C and held for 10 minutes before the temperature was ramped to 1100°C and held again for 10 minutes at 1100°C at the heating rate of 10°C/min and gas flow rate of 50mL/min. Kinetic evaluation was conducted using a simple Arrhenius-type kinetic model with first-order decomposition reaction. Apparent activation energy, Ea, and pre-exponential factor, A, were calculated from the modelling equation. Results reveal that the reactivity of CBS fuel is higher than a single coal fuel to which the addition of bio-oil helps to increase the combustion performance of the blends. The optimum fuel ratio appears at 50:50 ratio with equal contribution of coal and bio-oil properties that contribute to the increase in volatile matter causing maximum combustion rate achievable at much lower temperature compared to single coal fuel.

Mineralogy and chemical composition of technogenic soils (Technosols) developed from fly ash and bottom ash from selected thermal power stations in Poland

Abstract The aim of the study was to determine the mineral and chemical composition of technogenic soils (Technosols) developed from fly ash and bottom ash from power plants in which bituminous coal and lignite was combusted. The mineral composition of the “fresh” wastes (i.e. fly ash and bottom ash) and soil samples derived from them was examined by X-ray diffraction (XRD) and using a scanning electron microscope (SEM). The chemical composition (content of major elements) was determined using ICP-AES method. Quartz, mullite, and amorphous substances (glass) predominated in the mineral composition of wastes after bituminous coal combustion. Magnetite was also found there. Soils developed from wastes after bituminous coal combustion contained all above mentioned minerals inherited from fly ash and bottom ash. Moreover, small amounts of secondary calcite were identified. In some soil horizons containing large amounts of inherited magnetite, secondary iron oxides and oxyhydroxides (goethite and lepidocrocite) also occurred. Quartz predominated in the mineral composition of the “fresh” wastes after lignite combustion. Relatively small amounts of iron oxides (magnetite and hematite) were also found there. In “fresh” fly ash, apart from minerals mentioned above, anhydrite and calcium oxide (lime) was identified. Soils developed from wastes after lignite combustion contained inherited quartz, magnetite, and hematite. Furthermore, calcite which sometimes was a predominating mineral in certain soil horizons occurred. Moreover, sulphates (gypsum, bassanite, and ettringite), and vaterite (a polymorph of Ca carbonate) were also found in soils. Silicon predominated among major elements in “fresh” ashes after bituminous coal combustion and soil derived from them followed by Al, Fe, K, Ca, Mg, Ti, Na, P, and Mn. On the other hand, the contents of major elements in the samples (ashes and soils) after lignite combustion can be arranged as follows: Si, Ca, Fe, Al, Mg, Ti, K, Mn, Na, and P. However, in some horizons (i.e. in calcareous materials deposited in the topsoil of some profiles) in soil developed on landfills near TPSs combusting lignite, Ca was a predominating element.

Chemical looping combustion of coal in a 5 kWth interconnected fluidized bed reactor using hematite as oxygen carrier

A hematite, which has been operated in CH4-fuelled Chemical Looping Combustion (CLC) for more than 200h, was used as oxygen carriers for in-situ gasification chemical looping combustion (iG-CLC) of Chinese Bituminous coal in this study. The thermal power was varied between 2.0 and 6.0kWth. The total operation time was more than 100h in the hot mode. Hematite displayed high reactivity with this bituminous coal attaining up to 96.33% of combustion efficiency. The carbon capture efficiency ranged from 72.84% to 89.36% as only CO2 was used as coal gasification agent gas in the fuel reactor during the first tests. The CO2 yield in the fuel reactor was up to 92.82% under the operational temperature was 1000°C and the average coal feeding rate corresponding to the 2kWth of thermal power. The effect of operational parameters, such as the fuel reactor temperature, thermal power and the mass flow rates of the fluidization gas agent on three factors – combustion efficiency, carbon capture efficiency and CO2 yield – were investigated. The results illustrated that higher operating temperature and bed inventory per unit of thermal power in the fuel reactor were found to positively affect all the three factors. Upon completion of the experiment, the used samples were collected and analysed using electron microscopy, X-ray diffraction and surface area analysis. The results showed no appreciable sintering and agglomeration in the used sample. It was found that the reactivity of fresh and used samples did not differ significantly.

Co-combustion characteristics of sewage sludge with different rank bituminous coals under the O2/CO2 atmosphere

The effects of sewage sludge (SS) blended ratio, O2/CO2 ratio, and type of bituminous coal on the co-combustion characteristics of SS with bituminous coals were investigated. Thermogravimetric analysis was used to analyze the co-combustion profiles. Results show that TG curve shifts to a lower temperature with increasing SS blended ratio and O2/CO2 ratio. A distinct transition section exists at fixed carbon combustion of the blended fuels stage, and the temperature range of this transition section decreases significantly with increasing O2/CO2 ratio. The combustion property indexes of blended fuel increase with increasing SS blended ratio and O2/CO2 ratio. However, effect of O2/CO2 ratio on increasing the overall co-combustion characteristics becomes smaller when the oxygen concentration exceeds 30 %. Comparing SS blended with Huaibei (HB) bituminous coal, the SS blended with Shenhua (SH) bituminous coal (high-rank bituminous coal) combustion has the good combustion performance.

Soot loading, temperature and size of single coal particle envelope flames in conventional- and oxy-combustion conditions (O2/N2 and O2/CO2)

A fundamental laboratory study on the volatile-phase combustion of pulverized coal was conducted at the particle level. A primary goal has been to simultaneously assess soot volume fraction, fv, and soot temperature, T, in the diffusion flame (soot mantle) forming around a single burning bituminous coal particle, upon ignition of its volatile matter. This assessment was conducted with emission-based pyrometric methods. A secondary goal of this study has been to compare these radiative parameters, fv and T, in conventional air- and in simulated dry oxy-fuel combustion. Both fv, and T measurements were spatially averaged in the flame but temporally resolved throughout the combustion history of single particles. In addition, the size of the volatile envelope flames was assessed both pyrometrically and cinematographically. Combustion of three different bituminous coals took place with various oxygen partial pressures in nitrogen and in carbon dioxide background gases. Single particles, 75–90μm, were injected and burned in a transparent drop-tube furnace (DTF) at laminar-flow atmospheric-pressure and a wall temperature of 1400K. The free-falling bituminous coal particles heated up and devolatilized, their volatile matter ignited and formed bright envelope flames, often with distinctive soot contrails in the wakes of the flames. The radiative parameters fv, T and flame size, of these luminous envelope flames were assessed using different emission-based models for the analysis of the three-color pyrometric intensities. The particle envelope flames of all three coals were found to contain comparable to each other soot volume fractions, in the range of 20–90ppm. At identical furnace gas temperatures and identical O2 mole fractions, when the background N2 gas was replaced with CO2, the particle envelope flames of the bituminous coals were characterized by lower soot volume fractions, lower temperatures and bigger sizes. As the O2 mole fraction increased in either N2 or CO2 background gases, soot volume fractions increased to a maximum and then decreased, temperatures increased monotonically and flame sizes decreased. In CO2-based combustion, an oxygen mole fraction in the neighborhood of 35% was necessary to elevate the measured flame temperature to match that of conventional air-based combustion; however, the soot volume fraction was lower than that in air-based combustion regardless of the oxygen mole fraction.

NO Reduction Scale of Three Typical Chinese Coals during Oxy-Coal Combustion

Oxy-coal combustion has become one of the most promising technologies for its ability to capture carbon dioxide and produce low pollutant emissions. In particular, the NO emission from oxy-coal combustion is found to be much lower than that in air combustion, but the NO reduction degree varies. In order to ascertain a rough NO reduction potential for Chinese coals, three types of coals (lignite, bituminous coal and anthracite) were combusted in a drop-tube furnace (DTF) in air and oxy-coal atmosphere during this study. The results showed that oxy-coal combustion could largely reduce NO emission down to 50% for the three coals. The NO reducing potential of oxy-coal technology for the lignite was higher than that for the bituminous coal and the anthracite. High content of volatiles in the lignite was considered as the major reason. NO removal was suppressed in the bituminous coal combustion due to the impacts of CaO and Fe_2O_3.

발전용 역청탄 및 아역청탄의 파일롯 연소특성 평가

With the depletion of high grade coal, it is indispensable to be used co-combustion of low rank coal with bituminous coal in pulverized coal-fired power plants. This study describes the detailed measurements of combustion characteristics of bituminous and subbituminous coal in a 0.7MWth pilot-scale test facility. This experimental works include the measurement of gas temperature, gas concentrations along with the reactor axial and radial distance at the condition of excess air ratio of 1.2. The solid sampling was carried out and analyzed with the combustion of bituminous coal. The main reaction zone of coal flame in a reactor was formed about 1 m from the swirl burner, and at downstream, the fully developed temperature and species distribution was observed. The sampled particles of bituminous coal in a reactor revealed the complete carbon burn-out was achieved just after an main combustion zone.

Effect of co-precipitation and impregnation on K-decorated Fe2O3/Al2O3 oxygen carrier in Chemical Looping Combustion of bituminous coal

Chemical Looping Combustion (CLC) of coal is an innovative combustion technology for CO2 inherent capture, which uses oxygen carrier (OC) to transfer lattice oxygen to coal. However, coal gasification is the rate-limiting process for CLC of coal. Although carbon conversion and gasification rate are substantially improved with oxygen carriers in the presence of alkali additives, alkali loss in oxygen carrier is still a serious problem in the process of CLC of coal. The present work focuses on the OC–potassium interaction for two preparation methods of K-decorated OC. Different contents of catalyst (K2CO3) were added into the preparation of Fe-based oxygen carrier by both co-precipitation and impregnation. And the effect of K-decorated methods on oxygen carriers was investigated in a fluidized bed reactor. For co-precipitated oxygen carriers, CO2 gas yields (fCO2) were higher and CO gas yields (fCO) were lower than the ones for impregnated oxygen carriers. Total carbon conversions for co-precipitated oxygen carriers were also higher than those for impregnated oxygen carriers, and a shorter time of fast reaction stage always corresponded to co-precipitated oxygen carrier. 9 redox cycles were also conducted to investigate the stability of oxygen carrier reactivity and the potassium loss with cycle number. It was concluded that the reactivity of co-precipitated oxygen carriers was more stable during 9 redox cycles. Especially for K10-cp (oxygen carriers of 10% potassium content by co-precipitation), fCO2 increased slightly and fCO changed very little with cycle number. According to morphological features of oxygen carriers, co-precipitation was superior to impregnation in preventing oxygen carrier particle sintering. On the other hand, although potassium contents of all K-decorated oxygen carriers decreased with cycle number, the potassium loss for co-precipitated oxygen carriers was smaller. K10-cp performed the best characteristic in avoiding potassium loss: the potassium content decreased from 8.47% (fresh oxygen carrier) to 7.79% (after 9 cycles). X-ray diffractometer (XRD) analysis showed that the potassium ferrite, K2Fe22O34, was presented in K-decorated oxygen carriers. Based on the peak intensity ratio of IK2Fe22O34/IFe2O3, the higher the content of K2Fe22O34 in K-decorated Fe2O3/Al2O3 oxygen carrier was, the larger the conversion of CO to CO2 was, and the shorter the time of fast reaction stage was. Therefore, it was inferred that K2Fe22O34 acted as a support with catalytic effect. In addition, the content of K2Fe22O34 was higher in co-precipitated oxygen carriers than that in impregnation oxygen carriers. It can be used to explain that why a better reactivity was always found for co-precipitated oxygen carriers.

Effect of the Devolatilization Process on PM10 Formation during Oxy-fuel Combustion of a Typical Bituminous Coal

The devolatilization process has important influence on the formation of PM10 (particulate matter with an aerodynamic diameter of ≤10.0 μm) in oxy-fuel combustion of pulverized coal but has been explored little. A bituminous coal was devolatilized in either CO2 or N2 at 1573 K on a drop-tube furnace (DTF) to produce CO2-char and N2-char. Coal and its char samples were burned at 1573 K and in 29 vol % O2/71 vol % CO2. PM10 was collected and segregated into 13 size fractions, which were subjected to subsequent analysis. The results show that the particle mass size distributions of PM10 from coal and chars have similar peak and trough sizes, suggesting that the devolatilization process has insignificant influence on the major pathways of PM10 formation. Three particle modes can be identified, i.e., ultrafine mode (<0.5 μm, PM0.5), central mode (0.5–2.5 μm, PM0.5–2.5), and coarse mode (2.5–10 μm, PM2.5–10). Coal combustion produces more PM0.5 and PM0.5–2.5 than char combustion, suggesting that the devolatilization process has important influence on the production of PM0.5 and PM0.5–2.5. In contrast, the PM2.5–10 yield is insignificantly affected by the devolatilization process under the investigated conditions. In addition, the combustion of CO2-char generates more PM0.5 and PM0.5–2.5 than that of N2-char, indicating that the devolatilization in CO2 favors the formation of PM0.5 and PM0.5–2.5.

Chemical and Surface Transformations of Bituminous Coal Fly Ash Used in Israel Following Treatments with Acidic and Neutral Aqueous Solutions

Fly ashes are produced in Israel via the combustion of bituminous coals and are defined as Class F (i.e., very basic because of the high Ca content). Most fly ashes produced in Israel are from South African and Colombian coals and, therefore, were chosen for the present study. It has been shown that fly ash can be used as a scrubber and fixation reagent for acidic wastes (from the phosphate or regeneration of used motor oil industries). Furthermore, the scrubbed product can serve as a partial substitute to sand and cement in concrete, while the produced bricks have proven to be strong enough for concrete standards. To explore the fixation mechanism, the fly ashes have been treated with acidic (0.1 M HCl) and neutral (ultrapure deionized water, denoted as UPDI) aqueous solutions. Chemical compositions and surface analysis before and after treatment were conducted for assessing changes in the coal fly ash particles. The treated fly ash structure has been changed appreciably. For example, dissolution of Ca resulted in exposure of the outer surface. Hence, the treatment may change the modes of interaction of trace elements with the surface of the fly ash particles. Three possible modes of interaction between the fly ash and waste are suggested: cation exchange, chemical bonding, and electrostatic adsorption of very fine precipitate at the fly ash surface. Probably, the silicate and aluminate groups (or aluminosilicates) at the surface of the fly ash particles are involved in these interactions.

NO Formation during Oxy-Fuel Combustion of Coal and Biomass Chars

The yields of NO from combustion of bituminous coal, lignite, and biomass chars were investigated in O2/N2 and O2/CO2 atmospheres. The experiments were performed in a laboratory-scale fixed-bed reactor in the temperature range of 850–1150 °C. To minimize thermal deactivation during char preparation, the chars were generated by in situ pyrolysis at the reaction temperature. The NO yield clearly decreased and the CO yield increased when the atmosphere was altered from O2/N2 to O2/CO2 at 850 °C, but only small differences in NO and CO yields were observed between the two atmospheres at 1050–1150 °C. To examine how CO influences the NO yield, the effect of CO on NO reduction over char as well as NO reduction by CO over ash was investigated in the fixed-bed reactor. Furthermore, the influence of CO on the homogeneous oxidation of HCN, possibly a product of the char-N oxidation, was evaluated using a detailed chemical kinetic model. The results indicate that CO influences the NO yield from char combustion throu...

Numerical simulation of sub-bituminous coal and bituminous coal mixed combustion employing tabulated-devolatilization-process model

To investigate the cause of the increase in the unburned fraction when sub-bituminous coal is mixed with bituminous coal observed in previous experimental research using a 100 kg-coal/h-class coal combustion test furnace, numerical simulations of the mixed combustion of sub-bituminous coal and bituminous coal are performed. To take into account the effect of the particle heating rate on the devolatilization parameters, the tabulated-devolatilization-process model (TDP model) is employed. The results show that the simulation could qualitatively reproduce the experimental results, which are an increase in flame lift-off with increasing sub-bituminous coal mixing ratio and a maximum value of the unburned fraction at a sub-bituminous coal mixing ratio of 25%. Furthermore, it is clarified from the simulation results that the nonlinear increase in the overall unburned fraction in the case of sub-bituminous coal mixing with bituminous coal is caused by the steep increase in the unburned fraction of bituminous coal particles with increasing sub-bituminous coal mixing ratio.

Analysis on the Calculation Methods of Acid Dew Point of Flue Gas

At present, there are lots of calculation methods of acid dew point of flue gas; formula of acid dew point in the thermal calculation from the former U.S.S.R has been widely applied in China. But this formula still has some problems, such as the desulphurization ability of different fuels, classification of sulfur content in fuel and the factors of SO2 transferred into SO3.In order to solve these problems,the formula of the acid dew point in the thermal calculation from the former U.S.S.R is adjusted. It was found that the precision of A.G.O kkes formula is the highest by comparing several formulas. So the last will be the compilation of the new formula and A.G.O kkes formula, the former Soviet union formula and the calculation of burning lean coal,bituminous coal and lignite typical instance of 600 MW,it was found that the precision of new formula calculation has improved.

Comparison of combustion behaviors and pollutant emissions using bituminous coal and corncob in a fluidized bed combustor

ABSTRACTThe combustion behaviors and pollutant emissions of corncob and bituminous coal in a pilot scale vortexing fluidized bed combustor was compared. The flue gas recirculation combustion mode was used in this study. The effects of operating parameters, such as stoichiometric oxygen ratio, and bed temperature on the pollutant emissions were investigated. The results show that the combustion fractions vary with different kinds of fuels, resulting in different CO and NOx emission characteristics. Corncob combusts primarily in the freeboard zone, whereas bituminous coal combusts primarily in the bed zone. Therefore, the CO emission decreases with the increasing bed temperature in bituminous coal combustion, whereas the effect of bed temperature on CO emission is not obvious in corncob combustion. The CO emission of corncob combustion decreases with the stoichiometric oxygen ratio, whereas the CO emission of bituminous coal combustion has the inverse trend. For both fuels, the NOx emissions increase with the bed temperature but decrease with the stoichiometric oxygen ratio. © 2014 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Heterogeneity in coal composition and implications for lung cancer risk in Xuanwei and Fuyuan counties, China

BackgroundXuanwei and Fuyuan counties in Yunnan Province, China have among the highest lung cancer rates in the country. This has been associated with the domestic combustion of bituminous coal (referred to as “smoky” coal). Additionally, significant geographical variation in cancer rates among smoky coal users has been observed, suggesting heterogeneity in fuel source composition and/or combustion characteristics. Research thus far has indicated that smoky coal emits high levels of polycyclic aromatic hydrocarbons (PAHs) and contains high concentrations of fine grained crystalline quartz, however, much of this research is limited in terms of sample size and geographic scope. In order to more fully characterise geochemical and elemental compositions of smoky and smokeless coal use in Xuanwei and Fuyuan, we carried out a large exposure assessment study in households in this region. MethodsFuel samples representing smoky and “smokeless” (anthracite, the major alternative coal type in the region) coals were collected from 137 homes in Xuanwei and Fuyuan. Rock-Eval, Leco-CS, XRF analysis and electron microscopy were used to establish hydrocarbon content (to represent volatile organic compounds), major and trace element composition and mineral composition respectively. Heterogeneity in coal characteristics between and within coal types was assessed by the Kruskal–Wallis test. Results145 coal samples (116 smoky and 29 smokeless coals) were analysed. Statistically significant differences between smoky and smokeless coals with regard to hydrocarbon content, sulfur, trace elements and mineral composition were observed. Of note, smoky coal contained between 5 and 15 times the amount of volatile organic matter and twice the amount of quartz (including respirable quartz) than smokeless coal. Smoky coal generally had lower levels of trace elements (plus aluminium) than smokeless coal. Significant variation was also observed between smoky coal samples from different geographical areas with regard to hydrocarbon content and elemental composition (including aluminium and silicon). DiscussionThis paper has identified compositional differences between and within smoky and smokeless coals sourced from Xuanwei and Fuyuan counties. A decreased ratio of aluminium to silicon in smoky coal suggests elevated free silica, a finding consistent with observed higher levels of quartz. Elevated volatile organic matter content in smoky coal (when compared to smokeless coal) is consistent with the geochemical expectations for smoky and smokeless coals. These findings also reflect previous observations of elevated volatile compound emissions (notably PAHs) from smoky coal in the area. The observed heterogeneity in coal composition between and within coal types may provide leads to the observed heterogeneity in cancer risk observed in this area.