Coal Char Combustion Research Articles

Distribution of polycyclic aromatic hydrocarbons and carcinogenic risk assessment in street-barbecued foods in China

Street-barbecued foods, despite their popularity, produce carcinogenic polycyclic aromatic hydrocarbons (PAHs) such as benzo[a]anthracene (BaA), chrysene (Chr), benzo[b]fluoranthene (BbF), benzo[a]pyrene (BaP) due to incomplete charcoal combustion, direct food-fuel contact, and excessive heating. This study analyzed barbecued foods from high-traffic street vendors using high-performance liquid chromatography. Among five food categories (meat, vegetable, aquatic, starch, and soy products), eight foods exceeded China’s BaP limit (5 µg/kg) and twelve exceeded the EU limit (2 µg/kg). The highest BaP and PAH4 levels were found in barbecued beef and pork belly, respectively. Chr levels were notably high due to open flame exposure. Health risk assessments indicated fourteen foods posed elevated carcinogenic risks. This study highlights the necessity of consumption control to mitigate these risks and provides evidence for improving street food safety and dietary security.

Study on fuel-N conversion mechanism of ammonia-coal co-firing at different combustion stages

The co-combustion of ammonia and pulverized coal can effectively reduce the carbon emission of thermal power generation. However, ammonia, as a carbon-free fuel, is rich in large amounts of nitrogen, which increases the risk of high NOx emissions. Therefore, it is important to clarify the influence mechanism of ammonia on the NO formation of coal volatile-N and coal char-N in the co-combustion, and to reveal the N oxidation pathway in different combustion stages.In this study, simulations were carried out on the CHEMKIN software to investigate the generation characteristics of NO and the transformation mechanism of fuel-N at different combustion stages of ammonia-coal co-firing. The study showed that ammonia-blending combustion promoted the release of coal volatiles and the oxidation to NO. In the total NO generation during the ammonia-coal co-firing, the proportion of NO produced by ammonia-coupled coal char combustion was very low. Compared with ammonia-coupled coal combustion, the amount of NO produced in ammonia-coupled coal volatile combustion was significantly reduced. Sensitivity analysis and rate of production (ROP) analysis indicated that the increase of H, OH, and O free radicals promoted the NO formation, and that NHi free radicals played an important role in the NO reduction. By analyzing the elementary path of NO generated from ammonia-coupled pulverized coal, coal volatiles and coal char combustion at 1400 °C and 10 % ammonia ratio, it can be seen that the main path of NO formation during ammonia-coupled coal volatiles combustion is VOL→HCN→NCO→NO, CHAR→NO, NH2→HNO→NO, compared with ammonia-coupled coal combustion. The proportion of NH2→NH→NO reaction paths decreased, while the proportion of NH2→N2, NCN→NCO→N2, and NH2→NNH→N2 reaction paths increased respectively, indicating that separation combustion promoted the reduction of NO by NHi free radicals while inhibiting the oxidation of N-containing components.

Advanced visualisation of biomass charcoal combustion dynamics using MWIR hyperspectral and LWIR thermal imaging under varied airflow conditions

Biomass charcoal combustion is a complex process, significantly influenced by various operating parameters. Among these parameters, air supply emerges as a critical factor affecting combustion efficiency, gas emissions, and thermal dynamics. In this study, we explored these complex interdependencies using a novel combination of mid-wavelength infrared (MWIR) hyperspectral imaging and long-wavelength infrared (LWIR) thermal imaging, under different airflow rates. Our findings demonstrated that while increased airflow accelerated the overall combustion rate, it simultaneously decreased combustion efficiency. Specifically, the thermal profiles showed an increased surface temperature at a low flowrate (0.5 L/min) while decreasing in temperature with higher flowrates. The decreased system temperature led to a lower combustion efficiency because of the reduced conversion rate from combustible gases (CH4 and CO) into CO2 and H2O. Additionally, the results also demonstrated that cooling effects of the high flowrates primarily impeded the solid-phase combustion stage. This is further corroborated by the temporal and spatial variation in the emissions of key gas species (H2O vapor, CH4, CO, and CO2) observed through hyperspectral imaging. The emission evolution of these gases displayed the different stages of the gas-phase and solid-phase combustion. The spatial distribution of the trace gases showed a decreased distribution radius due to the enhanced diffusion to the fuel surface when the airflow increases, aligning well with the two-film model established in the literature. Furthermore, we utilised spectral radiance ratios (CO/CO2, CH4/CO2, H2O/CO2) to gain additional insights into the combustion dynamics. These ratios evidenced the decrease in combustion efficiency at high airflow rates. Finally, the increased H2O/CO2 ratio further demonstrated the impeded char combustion and a shift towards pyrolysis at higher airflow rates because of the decreased thermal equilibrium of the system. The findings from this study provide critical insights into the dynamics of biomass charcoal combustion and illuminates the path for optimising energy efficiency and assessing the environmental implications from burning biomass fuels.

Catalytic hydrothermal carbonization of corn and rice straws with citric acid: Implications for charcoal production and combustion performance

Hydrothermal carbonization represents a promising environmental approach for converting biomass into high-quality biochar fuel. Despite extensive discourse, limited research has focused on fuel properties and combustion performances of biochar as well as reaction mechanisms under catalysts. This study scrutinized properties of biochar from citric acid-catalyzed carbonization. Straw (corn/rice) was hydrothermally carbonized in 5 % citric acid solution with a solid-liquid ratio of 1:10 g/mL at 190–250 °C for 3 h. Results revealed an increase in C and a decrease in O with elevated temperature and citric acid concentration. The calorific values for corn and rice straw biochar ranged from 23.53 MJ/kg to 29.81 MJ/kg and from 23.14 MJ/kg to 26.98 MJ/kg, respectively. This study highlighted diverse impacts of hydrothermal reaction temperature and citric acid concentration on biochar attributes, calorific value, energy density, mass yield, energy yield, and thermal stability. It elucidated the influence of citric acid concentration on biochar burnout temperature and the role of hydrothermal reaction temperature and heating rate in biochar combustion characteristics. Citric acid effectively reduced biochar activation energy in low-temperature areas and prolonged the biochar combustion reaction time, achieving highly favorable comprehensive combustion characteristics at 47.56×10−7. The findings present the potential for biochar production with enhanced performance for integrating and co-firing with conventional fuels.

Experimental study on the co-firing and NOx emission characteristics of bituminous coal and its medium temperature pyrolysis char

To address the issues of ignition difficulty, incomplete burnout, and high NOx emissions during coal char combustion in industrial applications, a series of co-firing experiments involving bituminous coal and its medium-temperature pyrolysis char were conducted using a micro fluidized bed analysis system. The experiments explored co-firing behaviors and NOx emission characteristics for five different fuel blending ratios in an environment with 21 % oxygen concentration, across temperatures between 923 K and 1223 K. The study delved into the synergistic effects of coal and char co-firing, as well as the influence of combustion temperature and fuel blend ratio on the co-firing efficiency and NOx emissions. The results show a synergistic effect in the co-firing of bituminous coal and char, influenced by reaction temperature and coal-to-char blend ratio, which evolves as combustion progresses. In the 923–1073 K range, initial coal addition to the blend enhances reactivity. However, as the reaction advances or coal content exceeds 75 %, this synergy shifts to an inhibitory effect. At temperatures above 1023 K, increased proportions of coal in the blend are associated with improved burnout rates, especially when the coal content is at or above 50 %. Moreover, at a combustion temperature of 1123K, there is a marked decrease in nitrogen oxide emissions, with coal blend ratio of 25 % and 50 % showing particular efficacy in reducing these emissions. These results provide valuable insights for the efficient and clean utilization of coal char in industrial combustion processes.

Catalytic influence of iron oxide (Fe2O3) on coal pyrolysis and char combustion at various temperatures

The conversion of coal into cleaner energy forms is essential for achieving sustainable development. This study investigates the role of Fe2O3 as a catalyst in enhancing the efficiency of coal pyrolysis and char combustion. A fixed-bed tube furnace (TF) was selected for pyrolysis, and a Thermogravimetric Analyzer coupled with Fourier Transform Infrared Spectroscopy (TG-FTIR) was used for combustion analysis. The produced syngas and tar were characterized using Gas Chromatography (GC) and Gas Chromatography-Mass Spectrometry (GC/MS). Our results show higher volatile release volume (VRV) from coal with catalyst compared with without catalyst and the rise with temperature within the 600–1000 ℃ range. Although hydrogen production decreased with the addition of the catalyst, at 1000 ℃, the catalyst's impact was negligible. The catalyst notably facilitated the breakdown of heavy aromatic rings in tar, eliminating triple-bond aromatic structures. In contrast, tar from raw coal exhibited a 20% yield of such structures. Scanning Electron Microscopy (SEM) revealed a cubic structure of Fe2O3 in char, with an increased surface area compared to raw coal char (338.75 m2/g vs. 313.51 m2/g). TG-FTIR analysis indicated a lower activation energy for catalysts with char combustion. Overall, Fe2O3 improves tar structure, increases char surface area, and lowers activation energy.

Historical trend of polycyclic aromatic hydrocarbons in a sediment core from Osaka Bay during the Meghalayan

Polycyclic aromatic hydrocarbons (PAHs) are produced by incomplete combustion of biomass and fossil fuel, yet PAHs have been rarely analyzed in coastal sediment cores as a tracer for human activities before industrialization. The aim of this study was to assess if the historical trend of PAHs can be related to past human activities. To this end, we have determined the concentrations of PAHs in a 9 m-long sediment core from Osaka Bay, which records history of the last 2400 years. The concentration of PAHs before the beginning of the 17th century CE, the beginning of the peaceful Edo period, was consistently low (<100 ng g−1) and mainly comprised of smoke-derived PAHs reflecting the natural background. A relative higher abundance of 4−6 ring PAHs from the early 17th century CE and a higher PAH concentration from the early 18th century CE until approximately 1800 CE agreed with a population increase, Cu smelting activities and increasing combustion of charcoal. The constant PAH concentration until the late 19th century CE overlapped with a decline in the population in the Osaka area. An increasing PAH concentration from the late 19th century CE marked the beginning of industrialization in the Modern age. The peak in PAH concentration in 1945 CE was likely caused by burning of wooden structures due to air raids on Osaka City. A second peak around 1980 CE indicated the introduction of cleaner energies. We conclude that PAHs in coastal sediment cores can be used to reconstruct past human activities.

An improved semi-global intrinsic kinetics model for high temperature carbon oxidation

Measurements of the oxidation rates of various forms of carbon (soot, graphite, coal char) have often shown an unexplained attenuation with increasing temperatures in the vicinity of 2000 K, even when accounting for diffusional transport limitations and gas-phase chemical effects (e.g. CO2 dissociation). With the development of oxy-fuel combustion approaches for pulverized coal utilization with carbon capture, high particle temperatures are readily achieved in sufficiently oxygen-enriched environments. In this work, a new semi-global intrinsic kinetics model for high temperature carbon oxidation is created by starting with a previously developed 5-step mechanism that was shown to reproduce all major known trends in carbon oxidation, except for its high temperature kinetic falloff, and incorporating a recently discovered surface oxide decomposition step. The predictions of this new model are benchmarked by deploying the kinetic model in a steady-state reacting particle code (SKIPPY) and comparing the simulated results against a carefully measured set of pulverized coal char combustion temperature measurements over a wide range of oxygen concentrations in N2 and CO2 environments. The results show that the inclusion of the spontaneous surface oxide decomposition reaction step significantly improves predictions at high particle temperatures. Furthermore, the simulations reveal that O atoms released from the oxide decomposition step enhance the radical pool in the near-surface region and within the particle interior itself. Incorporation of literature rates for O and OH reactions with the carbon surface results in a reduction in the predicted radical pool concentrations and a very minor enhancement of the overall carbon oxidation rate.

Application of biodrying with hot air aeration system to process solid waste into rdf

Biodrying is a promising method to process municipal solid waste (MSW) while generating refuse-derived fuel (RDF) output. Recent developments in the process of generating refuse-derived fuel (RDF) have led to a renewed interest in minimal pretreatment processes. Although extensive research has been carried out, one of the most significant current discussions about generating refuse-derived fuel (RDF) using biodrying methods is that it has taken a long time to process. The biodrying method using air from the atmosphere takes 21 days to convert solid waste into RDF. As a result of this, Biodrying processes need to be accelerated by flowing hot air into the biodrying reactor. The aim of this study is to analyze the biodrying process temperature profile with a hot air aeration system. The methodological approach taken in this study is to circulate the hot air that comes from the combustion of wood charcoal. Hot air is discharged into solid waste that is inserted into the biodrying reactor. The temperature and concentration of solid wastewater are analyzed every 15 minutes. The results of this study show that the initial MSW temperature of the front reactor was 40o C and that of the rear reactor was 31o C.In the first 15 minutes until 60 minutes, the temperature shows an increase. The MSW temperature of the front reactor was 47o C, and the rear reactor was 35o C.At the 30th minute of the front reactor, it was 63o C, the rear reactor was 61o C; at the 45th minute of the front reactor, it was 81o C, the rear reactor was 73o C; and at the 60th minute of the front reactor, it was 80o C, the rear reactor was 79oC. These findings have significant implications for the understanding of how circulate the hot air aeration system works well.

Influences of ammonia co-firing on the NO generation characteristics of pulverized coal during different combustion stages

As an ideal carbon-free fuel, ammonia is a feasible choice to replace part of coal fuel to reduce carbon emissions from coal-fired power generation. This work used a constant temperature fixed bed experimental platform to study the effects of ammonia mixing on NO formation characteristics of pulverized coal. It was found that the peak time of NO precipitation decreases with the temperature increasing in ammonia-coal coupled combustion, and the increase of ammonia blending ratio promotes the NO formation. In the ammonia-coupled coal char combustion, NO production increases with the increase of ammonia co-firing ratio under different temperature conditions. Compared with coupled combustion, separation combustion can effectively reduced the NO formation, which was not conducive to the conversion of fuel-N to NO, and the ammonia mixing ratio and temperature have a significant impact on the range of NO generation reduction in separation combustion. At the temperature of 1300 °C and 1400 °C, the nitrogen conversion ratio of 0%, 4% and 20% ammonia co-firing ration was reduced by 19.64%, 9.23%, 0.22% and 13.35%, 1.86% and 0.15%, respectively, compared with that of coupled combustion. The results can provide theoretical support for the development of low nitrogen combustion technology of ammonia-coal co-combustion.

Kinetic studies of ignition of coal char particle suspension in hot air

Coal ignition has been a focal point in the pursuit of improved energy efficiency and reduced emissions. This study focuses on investigating the kinetic characteristics of char ignition within a closed reactor. The combustion process is modeled using a one-step global reaction in a quiescent air environment. The results show that particle ignition time increases with equivalence ratio and particle size, while decreases with gas initial pressure and initial temperature. Particle ignition temperature is minimally affected by the particle size, slightly influenced by the gas initial pressure and initial temperature, but substantially influenced by the equivalence ratio. In the fuel-rich condition, the coal char combustion exhibits a thermal runaway stage, primarily driven by the escalating particle temperature, followed by a decaying stage, mainly influenced by the depleting oxygen mass fraction. The dominant kinetic factors affecting the heat release rate (HRR) peak are detailly investigated: the HRR peak shows an initial increase and subsequent decrease with the equivalence ratio, which is mainly controlled by the total particle number and particle temperature; Particle size affects the HRR peak through altering the total particle specific surface area, i.e., the product of the particle number and the particle diameter squared; the gas initial pressure and temperature all affect the HRR peak through directly altering the gas density. Additionally, larger retention coefficient leads to faster particle ignition and higher HRR peak. These findings provide valuable insights into the regulations of coal combustion processes, particularly in scenarios involving elevated pressure and temperature, such as coal/mine explosions.

Mapping forest fire severity using bi-temporal unmixing of Sentinel-2 data - Towards a quantitative understanding of fire impacts

Precise quantification of forest fire impacts is critical for management strategies in support of post-fire mitigation. In this regard, optical remote sensing imagery in combination with spectral unmixing has been widely used to measure fire severity by means of fractional cover of photosynthetic vegetation (PV), non-photosynthetic vegetation (NPV), charcoal (CH) and further ground components such as ash, bare soil and rocks. However, most unmixing analyses have made use of a single post-fire image without accounting for the pre-fire state. We aim to assess fire severity from Sentinel-2 data using a bi-temporal spectral unmixing analysis that provides a quantitative fire impact description and is oriented towards the process of change by including pre-fire and post-fire information. Unmixing was based on Random Forest Regression (RFR) modeling using synthetic training data from a bi-temporal spectral library. We describe fire severity as changes associated with the combustion of photosynthetic vegetation (PV–CH fraction) and dieback of photosynthetic vegetation (PV-NPV fraction). Unburned forest was mapped as stable photosynthetic vegetation (PV-PV fraction). We evaluated our approach on a forest fire that burned in a temperate forest region in eastern Germany in 2018. Independent validation was carried out based on reference fractions obtained from very high-resolution (VHR) imagery such as Plante Scope, SPOT6, orthophotos, aerial photos, and Google Earth. The results underline the effectiveness of our unmixing approach, with Root Mean Squared Errors (RMSE) of 0.072 for PV-CH, 0.09 for PV-NPV, and 0.08 for PV-PV fractions. Most of the errors were caused by spectral similarity between charcoal and shadow effects caused by trees, and the coloring of foliage and NPV in the late phenological season of the post-fire Sentinel-2 image. Based on the two-dimensional feature space of PV-CH and PV-NPV fractions, we calculated two metrics to characterize fire impacts: distance, an indicator of disturbance severity (sum of combustion and dieback), and angle, a measure of disturbance composition (gradient between combustion and dieback). Furthermore, we compared the fraction-based metrics with the difference Normalized Burn Ratio (dNBR). Since the dNBR is most sensitive to combustion and presence of charcoal, it does not fully characterize fire-related vegetation loss associated with dieback. The bi-temporal fraction-based indices provide more ecologically meaningful information on fire severity, particularly for regions that are less prone to severe wildfires such as Central Europe.

Grill workers and air pollution health effects from charcoal combustion in Vientiane capital

Introduction: Grilled street foods are popular in urban communities in Lao People's Democratic Republic (Lao PDR). Charcoal is the main fuel used for, posing a risk of elevated exposure to toxic pollutants. This study explored levels of cooking-related pollutants from grilled food business and workers’ health effects.
 Materials and methods: A quantitative approach using multiple techniques was conducted during March and April 2022 in Vientiane Capital, Lao PDR. Methods included pollutant emission estimation from charcoal-combusting grill shops/street-carts and Particulate Matter (PM2.5) measurement, and examined the exposure and health effects among grill workers. Multiple sampling techniques were applied to identify study samples. Respiratory symptoms were the health effect of interest among grill workers.
 Results: Estimated emission of pollutants was over 75 tons/year from grill shops. Average PM 2.5 level was 84.8 μg/m3 (21.6 - 254.8 μg/m3); which i above standard limits. A very high level of PM2.5 was found in grill markets. Most grill workers were female, worked 6-7 days/week, at least 8 h/day. Factors contributing to the presence of respiratory symptoms among grill workers were female gender, low income, indoor grilling, more years of grill-work, experience of intense smoke-cough, self-reliance on health and cigarette smoking.
 Conclusion: Grilling contributes to ambient air pollution, posing potential adverse environmental and public health impacts. Grill workers are likely to be exposed to high levels of all forms of air pollutants from street food grilling. Effective strategies are required to better protect grill workers from the effect of exposure to these harmful toxins and minimize the negative impacts on their health.

Distribution, composition and risk assessment of PAHs and PCBs in cryospheric watersheds of the eastern Tibetan Plateau

Polycyclic Aromatic Hydrocarbons (PAHs) and Polychlorinated Biphenyls (PCBs) are significant components of persistent organic pollutants (POPs) and pose a threat to both ecosystems and human health. To explore their spatial distribution, origins, and risk assessment, we collected 25 glacial meltwater and downstream river water samples in the eastern Tibetan Plateau (including the Qilian Mountains in the northeast) during the summer of 2022 (June–July). Our results showed that ∑PAHs and ∑PCBs were present in a wide range from ND-1380 ng/L and ND-1421 ng/L, respectively. Compared to other studies worldwide, the ∑PAHs and ∑PCBs in the Hengduan Mountains were at high levels. The PAHs and PCBs mainly consisted of low-molecular-weight homologs, including Ace, Flu, Phe, and PCB52. Phe was the primary component of PAHs. Glacial meltwater samples generally exhibited low concentration of PAHs and PCB52, whereas downstream river water samples typically showed high concentration of PAHs and PCB52. We attributed this characteristic to the influence of pollutants physicochemical properties, altitude effect, long-range transport (LRT), and local environmental conditions. In the eastern Tibetan Plateau glacier basin (especially in the Hailuogou watersheds), the concentration of PAHs and PCB52 in runoff generally increased with decreasing elevation. We believe that the primary factor affecting the concentration of PAHs and PCB52 in the region is the difference in local human activity inputs from various altitudes. The composition characteristics of PAHs and PCBs suggested that incomplete coal combustion and coking discharge mainly caused PAHs, while the combustion of coal and charcoal and the release of capacitors primarily caused PCBs. We assessed the carcinogenic risk of PAHs and PCBs in the glacier basin of the TP and found that the potential threat of PAHs was stronger than that of PCBs. Overall, this study provides new insights into the ecological security of water resources in eastern Tibetan Plateau. It is significant for controlling PAHs and PCBs emissions, assessing the ecological environment of the glacier watershed, and regional human health.

A Turn-On Quinazolinone-Based Fluorescence Probe for Selective Detection of Carbon Monoxide.

Carbon monoxide (CO) is a toxic, hazardous gas that has a colorless and odorless nature. On the other hand, CO possesses some physiological roles as a signaling molecule that regulates neurotransmitters in addition to its hazardous effects. Because of the dual nature of CO, there is a need to develop a sensitive, selective, and rapid method for its detection. Herein, we designed and synthesized a turn-on fluorescence probe, 2-(2'-nitrophenyl)-4(3H)-quinazolinone (NPQ), for the detection of CO. NPQ provided a turn-on fluorescence response to CO and the fluorescence intensity at 500 nm was increased with increasing the concentration of CO. This fluorescence enhancement could be attributed to the conversion of the nitro group of NPQ to an amino group by the reducing ability of CO. The fluorescence assay for CO using NPQ as a reagent was confirmed to have a good linear relationship in the range of 1.0 to 50 µM with an excellent correlation coefficient (r) of 0.997 and good sensitivity down to a limit of detection at 0.73 µM (20 ppb) defined as mean blank+3SD. Finally, we successfully applied NPQ to the preparation of a test paper that can detect CO generated from charcoal combustion.

Experimental study on the contribution of included/excluded minerals to particulate formation during coal char combustion

The contributions of included and excluded minerals to particulate matter formation are quantified in this work. By devolatilization of three typical Chinese coals, three coal chars with low (LA), moderate (MA), and high ash (HA) content (with both included and excluded minerals) were prepared, from which three float coal chars with low (LA−), moderate (MA−), and high ash (HA−) content (without excluded minerals) were separated by density differentiation method. The coal chars before and after separation were burned in a drop-tube furnace at 1600 K, the results of three float coal chars can directly reveal the contribution of included minerals, and the comparison of two kinds of chars with and without excluded minerals would reveal the excluded mineral contribution to ash distribution. The size distributions of the combustion-generated ash particle were obtained from the combination of ELPI+ and laser particle-size analyzer. The fractions of included/excluded minerals were obtained from SEM images. The results from the combustion of the float chars indicate the physical transformation of included minerals, while the results from original coal chars involve the transformation of both included and excluded minerals. Results indicate that the distribution of ash particles from included minerals for HA− char possesses a single peak, while the ash distributions of MA− and LA− char show a bi-modal shape. The excluded minerals in LA and MA chars mainly contribute to the ash emissions with sizes larger than 80 μm. The contribution from excluded minerals reach 86% to the ash particles of 205 μm for HA char, 54% for MA char and 51% for LA char. The number fractions of included minerals continuously decrease with a transformation into excluded minerals during char dynamic combustion.

CFD-DEM simulations of municipal solid waste gasification in a pilot-scale direct-melting furnace

A multiphase CFD-DEM model was built to simulate the waste-to-energy gasifying and direct melting furnace in a pilot demonstration facility. The characterizations of feedstocks, waste pyrolysis kinetics, and charcoal combustion kinetics were first obtained in the laboratory and used as model inputs. The density and heat capacity of waste and charcoal particles were then modelled dynamically under different status, composition, and temperature. A simplified ash melting model was developed to track the final fate of waste particles. The simulation results were in good agreement with the site observations in both temperature and slag/fly-ash generations, verifying the CFD-DEM model settings and gas-particle dynamics. More importantly, the 3-D simulations quantified and visualized the individual functioning zones in the direct-melting gasifier as well as the dynamic changes throughout the whole lifetime of waste particles, which is otherwise technically unachievable for direct plant observations. Hence, the study demonstrates that the established CFD-DEM model together with the developed simulation procedures can be used as a tool for the optimisation of operating conditions and scaled-up design for future prototype waste-to-energy gasifying and direct melting furnace.

A percolation model of fly ash formation during the combustion of non-uniform porous char

An improved percolation model has been introduced to predict the particle size distributions (PSDs) of produced residue during pulverized coal char combustion. A three-dimensional cluster of interconnected sites representing a single char particle is constructed at a given size. These sites are classified into surrounding gas, macropores, carbon, or ash. Non-uniform porous char structures and the melting performances of the ash particle have been considered to approach the most realistic scenario. The char fragmentation and ash coalescence process is simulated by checking the connectivity and proximity of occupied sites. The effects of char particle sizes are addressed by using char PSD data as the input to the model. The numerical results were compared with the measured PSDs of fly ash and show a good agreement. The effects of porous char structure and included minerals on the sizes of produced particles during combustion are further investigated. The simulation results indicate that the mean sizes of produced particles initially decrease (N<0.7) and then increase with char consumption. The char fragmentation behavior dominates in the preliminary and middle stages of char burning, while the ash coalescence is the primary behavior in the char burnout stage. The mean sizes of produced particles increase with the lower char porosity and the higher extent of pore aggregation. The size difference between PM20 and PM20+ increases when the macropores are repositioned to be aggregated. The mean sizes are positively related to the ash content and ash coalescence parameter in the middle and late stages of char burning.

Influence of H2O Thermal Effect on the Formation of Ultrafine PM During Char Combustion

ABSTRACT To clarify the influence of H2O thermal effect on the formation of ultrafine particulate matter (PM), Huangling coal char was burned in a high-temperature drop tube furnace at 1800 K under various O2/N2/H2O and O2/N2/H2O/Ar atmospheres. The introduction of Ar in the simulating atmosphere was designed to counteract the thermal effect of H2O. Results indicated that after eliminating the thermal effect of H2O, the yield of ultrafine PM continuously increased in higher H2O content. Compared with no H2O, the mass and number yield of ultrafine PM in O2/N2/H2O/Ar atmosphere with 30% H2O content increased by 35.5% and 58.9%, respectively. H2O thermal effect, gasification reaction, and char oxidation reaction during coal char combustion played a significant role in the formation of ultrafine PM. Oxidation reaction was the primary factor affecting the formation of ultrafine PM, and its relative contribution was more than 62.9%, whereas the thermal effect of H2O showed an overall negative net effect on the formation of ultrafine PM. With the H2O content varied from 5% to 30%, the contribution of H2O thermal effect to mass yield was in the range of −19.1% to −18.0%, while that to number yield was −33.1% to −30.6%. Once the H2O content reached 10%, the enhancing effect of H2O gasification reaction on the yield of ultrafine PM surpassed the negative contribution of H2O thermal effect. For a given H2O content, elevated O2 concentration weakened the negative contribution of H2O thermal effect.

Iron based oxygen-carrier-aided oxy-fuel combustion of coal char: Reactivity and oxygen transfer mechanism

Adding an active oxygen carrier to the inert bed material may favor the oxygen distribution in fluidized bed (FB) combustors. This so-called method “Oxygen-carrier-aided combustion, OCAC” has been applied recently to air combustion in FB boilers, but could also be potentially interesting in oxy-fuel combustion. Here we analyze OCAC in oxy-fuel combustion by experimental determination of the reactivity of char from three coals (lignite, bituminous and anthracite coal) using three oxygen carriers (OC, analytical reagent Fe2O3, hematite, and steel slag). The tests were conducted in a micro thermo-gravimetric analyzer (micro-TGA) and the combustion kinetics was determined for the nine combinations of char and OC. Additional tests were conducted in a macro-TGA i.e., much sample in a big ceramic crucible, to evaluate the phase composition and crystal quality using X-ray diffraction (XRD) to the combustion residues collected at various degrees of carbon conversion (0.2, 0.5, and 0.8). The results show that the burnout temperature decreases with OCs as the combustion rate increases, while the ignition temperature hardly changes. The enhancement of the rate of char combustion by OCs is in the following order: steel slag < hematite < AR-Fe2O3. The lower the fuel rank, the stronger the effect of the oxygen carrier. The combustion kinetics of chars using OC has a higher activation energy and pre-exponential factor than pure char. The enlarged lattice constant of Fe2O3 measured by XRD during the char combustion indicates that the redox reactions of Fe2O3 accelerate the oxidization of char by enhancing the rate of oxygen transport to the carbon surface.