Different Types Of Coal Research Articles

Pyrolysis characterization and kinetic analysis of typical coals in western China: effects of coal type, particle size and heating rate

ABSTRACT The three typical coals selected in this study (Shuangyi coal (SY), Hengsheng coal (HS) and Ningxia anthracite (NX)) are widely used in western China, but their pyrolysis characteristics have been less studied. In this study, based on the simultaneous thermal analysis-Fourier transform infrared spectroscopy (STA-FTIR) technique, the effects of different coal types, particle sizes and heating rates on the pyrolysis characteristics of coal powder were investigated. The results showed that the weight loss behaviors of different types of coals with different particle sizes varied, as influenced by the type of coal and heat transfer. When the particle size increased from 170 μm to 380 μm, the weight loss rate decreased by 2.95% and 24.45% for SY and NX coals while increased by 4.81% for HS coals; whereas for the maximum decomposition rate, both SY and HS coals showed an increasing tendency (increased by 2.76% and 9.32%), while NX coals decreased by 21.43%. The R2 of the three coal DTG curves fitted by subcurves was all 0.999, which proved that the nature of coal weight loss was the coupling effect of certain types of chemical reactions or covalent bond breakage. Real-time infrared spectroscopy was combined with covalent bonding to explore the major gas products and their influence by particle size. The activation energies at different temperatures were calculated by the Coats-Redfern method, in which the activation energies of the fast pyrolysis stage of HS coal were 1.68 and 2.75 times higher than those of the other two stages, 1.79 and 3.03 times higher than those of SY coal, and 1.99 and 1.11 times higher than those of NX coal, respectively.

A near-infrared spectroscopy dataset of coal and coal-measure rock under diverse conditions

The identification technology for coal and coal-measure rock is required across multiple stages of coal exploration, mining, separation, and tailings management. However, the construction of identification models necessitates substantial data support. To this end, we have established a near-infrared spectral dataset for coal and coal-measure rock, which includes the reflectance spectra of 24 different types of coal and coal-measure rock. For each type of sample, 11 sub-samples of different granularities were created, and reflectance spectra were collected from sub-samples at five different detection azimuths, 18 different detection zeniths, and under eight different light source zenith conditions. The quality and usability of the dataset were verified using quantitative regression and classification machine learning algorithms. Primarily, this dataset is used to train artificial intelligence-based models for identifying coal and coal-measure rock. Still, it can also be utilized for regression studies using the industrial analysis results contained within the dataset.

Feasibility analysis of the preparation of geopolymers from different types of coal based ash: Reaction, synthesis, and properties

This study compared the feasibility of circulating fluidized bed boiler fly ash (CFBFA), pulverized coal furnace fly ash (PCFA), and coal gasification slag (CGS) for the preparation of geopolymers by investigating the Si and Al dissolution reaction of the raw materials, product structure, and the development of the mechanical properties of the geopolymers. The results indicated that the reaction mechanism for preparing geopolymers were the same for the three kinds of coal based ash, i.e., the depolymerization and repolymerization of Si-O and Al-O bonds in raw materials. The loose and porous microstructure of CFBFA resulted in a high dissolution ratio of amorphous Si and Al, and its self-hardening properties generated ettringite crystals. This resulted in a high initial strength of the CFBFA based geopolymer (CFBFAG). The active Si and Al in PCFA and CGS were released slowly during the curing process, which was conducive to an enhanced compressive strength of the geopolymer in the later stage. The compressive strengths of the CGS based geopolymer (CGSG) after curing for 90 days reached 52.1 MPa, which was 139 % and 11.4 % higher than that of CFBFAG and PCFAG for the same curing time respectively. A microstructure analysis showed that the CGSG had a denser microstructure and more ordered geopolymer gel network than the other geoploymers. Compared with the CFBFA and PCFA, CGS was found to have a greater application potential in the preparation of geopolymers.

Study on precursor features of coal and rock loading failure based on difference network

In order to reveal the spatio-temporal precursor features of coal and rock loading failure, and accurately identify the critical state of coal and rock failure, the development of coal and rock loading failure is regarded as the spatio-temporal evolution dynamical process of the complex network system, the spatio-temporal evolution dynamical characteristics of coal and rock dynamic disasters are analyzed. The precursor features indicators I(t) and Ia(t) of the coal and rock failure based on the difference network are proposed, Brazilian splitting experiments of different types of coal and rock are carried out. Combined with the damage theory, the load model of coal and rock damage characterization based Ia(t) is established. The results show that when the coal-rock system is in the warning critical period, the damage is accelerated, with high potential energy, low rebound and weak robustness, which is reflected in the acoustic emission (AE) and electromagnetic radiation (EMR) data at different spatial monitoring points. When the coal-rock system is in the stable stage, the structure of the correlation network at adjacent moment is similar, and the number of edges in the difference network is small. While when coal or rock is about to fracture, the correlation network at adjacent moment has great structure differences, and there are many edges in the difference network. I(t) and Ia(t) synthesize the signal characteristics of different spatial monitoring points, and reflect the spatio-temporal evolution process and damage state of coal and rock. The damage characterization load based on Ia(t) is in good agreement with the measured load, and the correlation coefficients between the measured load and the calculated load based on Ia(t) of most rock samples are more than 0.80. The research results can be used as the precursor features of coal and rock failure, and have certain significance for the early warning of coal and rock dynamic disasters.

Coal crisis in China: development, mechanism, causes and possible consequences

This article analyzes the dynamics of coal prices and systemic changes in the coal market in the PRC, revealing the internal Chinese mechanism of the coal crisis that broke out in the PRC in 2020. The data studied and the conclusions obtained in the article refute the widely held view in expert circles, according to which the cause of the coal crisis in China was the rejection of Australian coal. The study was carried out by analyzing a data array on the dynamics of changes in the price of coal for different types of coal and for different regions and provinces of China. In particular, the article is based on data on the dynamics of coal prices in Shaanxi and Hubei.
 The results of this research provide useful insight into both the nature of the coal crisis and the patterns of the system of formation of coal prices in the PRC, partially touching on the issue of the integrity of the Chinese coal market. The statistical data referring to the coal prices is viewed through the prism of the concept of a “multi-track” pricing system put forward by M. V. Karpov and, in general, confirms fruitfulness and significance of his theory. Also, the article, based on data from the Hong Kong Stock Exchange, shows the commercial practical significance of the findings and the importance of having up-to-date information data on dynamics of coal prices in China.

Experimental study on the effect of room temperature pre-oxidized time on spontaneous combustion characteristics of coal

The presence of different types of coal at room temperature can lead to self-heating of coal, potentially resulting in spontaneous combustion. To investigate the effect of ambient temperature pre-oxidation (BL) time on the self-combustion characteristics of different coal types, synchronous thermal analysis (STA) and Fourier-transform infrared spectroscopy (FTIR) experiments were conducted. The results of the synchronous thermal analysis experiments indicate that ambient temperature pre-oxidation for 3 months (BL3), BL6, and BL9 coals exhibit faster oxidation reactions compared to the original coal, while BL12 coal shows slower oxidation than the original coal. Among these, BL9 coal demonstrates the most significant changes in oxidation reaction characteristics, with the fastest oxidation reaction time being 35.36 min, which is 1.38 min faster than the original coal. To support this observation, a comparison was made between the relative content of active functional groups in the original coal and BL coal. The study revealed that the BL process affects the relative content of hydroxyl groups, aromatic hydrocarbons, aliphatic hydrocarbons, and oxygen-containing functional groups, thereby influencing the coal-oxygen reaction process. This suggests that pre-oxidized coal, compared to the original coal, has a larger pore structure, which plays a dominant role in promoting coal self-combustion in the first 9 months of the BL process. As BL time continues to increase, the continuous reaction of active functional groups at room temperature leads to excessive consumption, resulting in a more significant role in inhibiting coal self-combustion. The research results provide valuable insights for predicting the spontaneous combustion risk of oxidized coal.

Degradative solvent extraction of low rank coal: Structural evolution of extraction products

The degradative solvent extraction method was proposed to convert low rank coals into carbon-enriched products under mild condition. However, limitations in the understanding of the structure evolution of products and reaction mechanism of the extraction process hinder the targeted regulation of the products. Therefore, in this work the structural evolution of products during the extraction for different types of coals and by different types of solvents were investigated. Synthesized molecular structural models of the products were constructed and the reaction mechanism was then discussed. Results show that the industrial compounding solvent (ICS) is capable of extracting more single-ring aromatic organics from coals and increasing the yields of the main products by approximately 10% compared to 1-methylnaphthalene. During the extraction process, the main reaction of the sub-bituminous coal is the breakage of unstable chemical bonds and functional groups, while the reaction of lignite is the thermal decomposition and deoxygenation of massive small molecules in the coal. Moreover, the ICS promotes aromatization reactions during the extraction, which indicates that the ICS is the appropriate industrial solvent for the degradative solvent extraction. This research proved a theoretical guidance for the industrialization of DSE technology and the targeted regulation of the products.

Environmental performance assessments of different methods of coal preparation for use in small-capacity boilers: experiment and theory

The purpose of this article is to receive environmental assessments of combustion of different types of coal fuel depending on the preparation (unscreened, size-graded, briquetted and heat-treated) in automated boilers and boilers with manual loading. The assessments were made on the basis of data obtained from experimental methods of coal preparation and calculated methods of determining the amount of pollutant and greenhouse gas emissions, as well as the mass of ash and slag waste. The main pollutants from coal combustion are calculated: particulate matter, benz(a)pyrene, nitrogen oxides, sulfur dioxide, carbon monoxide. Of the greenhouse gases carbon dioxide is calculated. As a result of conducted research it is shown that the simplest preliminary preparation (size-graded) of coal significantly improves combustion efficiency and environmental performance: emissions are reduced by 13% for hard coal and up to 20% for brown coal. The introduction of automated boilers with heat-treated coal in small boiler facilities allows to reduce emissions and ash and slag waste by 2–3 times. The best environmental indicators correspond to heat-treated lignite, which is characterized by the absence of sulfur dioxide emissions.

Geologic and Geochemical Features of the Upper Devonian Coals of the North Timan (the Sula River Coal Field)

Abstract —The composition of the oldest coals of the Timan–northern Urals region has been studied comprehensively, and their hydrocarbon and microcomponent characteristics are given. The relationship between different types of coals and Late Devonian plant communities of the North Timan is revealed. It is also determined that some samples contain microspores, megaspores, and plant remains belonging mainly to the lycopod Helenia. The most probable source of jet coals is identified as the wood of the progymnosperm Callixylon. The values of vitrinite reflectance and Tmax and the data on the distribution of polycyclic biomarkers and methylphenanthrenes indicate the low maturation of the coal organic matter. The coal bitumen investigated here is characterized by the dominance of steranes and diaster-13(17)-enes of compositions C28 and C29. The following diterpanes are identified: beyerane, 16α(H)-kaurane, 16β(H)-kaurane, and 16α(H)-atisane. At the same time, phyllocladane is absent.

Estimation of Carbon Content in High-Ash Coal Using Mid-Infrared Fourier-Transform Infrared Spectroscopy

The carbon content of different types of coal determines its utility in industries and thermal power generation. The most popular and widely used is the conventional method (ultimate analysis) to determine coal’s carbon content (C, wt.%), along with H, N, and S. In the present study, the authors attempted to analyze the carbon content (C in %) in coals via data from Fourier-transform infrared (FTIR) spectroscopy, which can be a promising alternative. As a reference, the carbon content in the coal samples, referred to as CCHNS (in wt.%), was determined from the ultimate analysis. The mid-infrared FTIR spectroscopic data were used to investigate the response of functional groups associated with carbon or its compounds, which were used to model and estimate the carbon content in coal samples (referred to as CFTIR, in wt.%). FTIR spectral signatures were utilized in specific zones (between wavenumbers 4000 and 400 cm−1) from a total of 18 coal samples from the Johilla coalfield, Umaria district, Madhya Pradesh, India. These 18 coal samples were used to produce 126 Coal+KBr pellets (at seven known dilution factors for each coal sample), and the spectral response (absorbance) from each pellet was recorded. For model development and validation, the training set and test set were formed using a 17:1 split (K-fold cross validation). The carbon content in the coal samples was modeled using the training set data by applying the piecewise linear regression method employing quasi-Newton (QN) with a breakpoint and least squares loss function. The model was validated using an independent test set. A pairwise comparison of estimates of carbon in the laboratory from the CHNS analyzer (CCHNS) and modeled carbon from FTIR data (CFTIR) exhibited a good correlation, relatively low error, and bias (coefficient of determination (R2) up to 0.93, RMSE of 23.71%, and MBE of −0.52%). Further, the significance tests for the mean and variance using the two-tailed t-test and F-test showed that no significant difference occurred between the pair of observed CCHNS and the model’s estimated CFTIR. For high-ash coals from the Johilla coalfield, the model presented here using mid-infrared FTIR spectroscopy data performs well. Thus, FTIR can potentially serve as an important method for quickly determining the carbon content of high-ash coals from various basins and can potentially be extended to soil and shale samples.

Conceptual design, energy, exergy, economic and water footprint analysis of CO2-ORC integrated dry gasification oxy-combustion power cycle

Among various techniques for CO2 capture and sequestration from coal-fired power plants, Dry Gasification Oxy-Combustion (DGOC) is a promising technology due to its efficiency, in-situ sulphur capture, and low water usage. In this work, a novel DGOC power cycle integrated with CO2-Organic Rankine Cycle (CO2-ORC) has been proposed for power generation and carbon capture. This study presents Energy, Exergy, Economic, and water footprint analysis of DGOC and its integration with CO2-ORC for different operating pressures and with different types of coal using Aspen Plus simulator. Steam cycle and CO2-ORC have been optimized for the process. Integration of CO2-ORC not only reduces the penalty for CO2 capture but also improves the efficiency by providing extra power output. Integration of CO2-ORC shows improvements in energy, exergy, and economics. Energy analysis shows a maximum increase in efficiency of 6.92% points by integrating CO2-ORC with DGOC for Bituminous coal and a maximum increase of about 6.7% points for high ash coal. The highest thermal energy efficiency of about 41.63% was noticed for Bituminous coal DGOC with CO2-ORC. Exergy analysis shows a positive impact of CO2-ORC integration for all operating pressures with a maximum increase of 5.74% points and 5.87% points for bituminous and high ash coals respectively. Economic analysis shows that combining CO2-ORC improves the specific capital cost of the cycle by 13.17% and 13.27% for the Bituminous and high ash coal cases respectively. Levelized cost of electricity (LCOE) analysis shows an improvement of 12.94% for Bituminous coal and 12.69% for high ash coal by the addition of ORC. The water usage for the plant is also reduced significantly with the addition of CO2-ORC.

Assessment of the Costs of Implementing the Best Available Ash Collection Technologies at Coal-fired Thermal Power Plants

According to existing plans, the environmental situation in Russia is going to be improved by modernizing or replacing outdated equipment at industrial enterprises and making a shift to the best available technologies. The thermal power industry is commonly referred to industrial sectors featuring the greatest negative impact on the environment. Emissions of fly ash with flue gases from coal-fired thermal power plants are of much significance from the viewpoint of atmospheric air pollution. Various ash removal technologies are used to reduce them, but a number of them are no longer able to provide the required quality of atmospheric air in areas experiencing a negative impact of thermal power plants. The aim of this work was to assess the possibility of using different types of ash collectors to fulfill the technological indicators of solid fuel ash emissions. For this purpose, the technical and environmental characteristics of various technologies for removing solid fuel ash from the flue gases of thermal power plants were compared, and their main indicators, advantages, and disadvantages were considered. The choice of the most effective ash collection technologies -- electrostatic precipitators and bag filters — to fulfill the technological indicators of ash emissions according to GOST R 50831-95 as the best available technologies is justified. A comparative technical and economic assessment of using electrostatic precipitators (EP) and bag filters (BF) downstream of the boilers of combined heat and power plants (CHPPs) and condensing thermal power plants (CTPPs) combusting the main Russian coals: grade SS Ekibastuz coal, grade SS Kuznetsk coal, grade 2B Irsha-Borodino coal, and Donetsk anthracite culm was carried out. The total capital and operating costs for the implementation, the specific costs for the removal of one ton of ash from different coals in EF and BF for pessimistic and optimistic inflation forecasts are determined. It is shown that an increase in inflation will have a very negative impact on the introduction pace of BATs at Russian thermal power plants and may slow down the introduction of bag filters, which are the most efficient BAT for ash collection. Recommendations on the use of electrostatic precipitators and bag filters at CHPPs and CTPPs for different types of coals have been formed. It is proposed to use bag filters in combusting high-ash coals, the ash of which is characterized by high electrical resistivity. Electrostatic precipitators should be used in combusting low- and medium-ash coals, because the difference in the mass of captured ash in the EF and BF for the same coal is small, whereas the cost of implementing EF is significantly lower. The specific cost of the ash removed differs little for the boilers of CHPPs and CTPPs operating on the same coal; however, it depends strongly on the level of inflation, the growth of which increases significantly the operating costs.

Combustion conditions and feed coals regulating the Fe- and Ti-containing nanoparticles in various coal fly ash.

Quantitative characteristics and sizes of nanoparticles (NPs) in coal fly ash (CFA) produced in coal-fired power plants as a function of coal type and plant design will help reveal the NP emission likelihood and their environmental implications. However, little is known about how combustion conditions and types of coal regulate the NP abundance in CFAs. In this study, based on single particle (SP)-ICP-MS technology, particle number concentrations (PNCs) and sizes of Fe- and Ti-containing NPs in CFAs were determined for samples collected from power plants of different designs and burning different types of coal. The PNCs of Fe- and Ti-containing NPs in all CFAs measured were in the range of 1.3×107 - 3.4×108 and 6.8×106 - 2.2×108 particles/mg, with the average particle sizes of 111nm and 87nm, respectively. The highest Fe-NP PNCs likely relate to the highest contents of Fe and pyrite in the feed coal. In addition, high TOC in CFAs are associated with metal-containing NPs, resulting in elevated abundances of these NPs with relatively large sizes. Moreover, elevated PNCs of NPs were found in CFAs produced by coal-fired power plants burning low-rank coals and with small installed capacity (especially those under 100-MW units). Compared to cyclone filters, ESPs and FFs with higher removal efficiency typically retain more Fe-/Ti- containing NPs with smaller sizes. Based on a structural equation (SE) model, raw coal properties (coal rank and Fe/Ti content), boiler types, and efficiency of particulate emission control devices likely indirectly affect PNCs of Fe- and Ti-containing NPs by influencing TOC contents and their corresponding metal concentrations of CFAs. This study provides the first analytic and comprehensive information concerning the direct and indirect regulating factors on NPs in various CFAs.

Development and investigation of a pollutants emission reduction process from a coal-gasification power plant integrated with fuel cell and solar energy

Abstract Even though coal resources are the most abundant among fossil fuels, coal-fired plants release large amounts of greenhouse gases into the atmosphere. In this regard, reducing environmental challenges and crises caused by coal burning can be a promising option to reduce today's crises in the energy field. The integration of coal-fired plants with renewable-driven energy systems can simultaneously improve thermodynamic performance and reduce pollutants emission rates. This article presents the thermodynamic and pollutant emission investigations of a new coal-fired plant coupled with a linear Fresnel solar collector (LFSC)-driven solar unit, a parabolic trough solar collector (PTSC)-driven solar unit, a high-temperature fuel cell stack (molten carbonate fuel cell stack [MCFCS]) and a heat recovery system (based on the steam turbine and gas turbine-based power cycles). The plant is able to produce electricity and hot water (HW). The main structure of the offered plant is based on coal, whereas, is coupled with renewables-based cycles to mitigate environmental impacts. The plant could generate ~ 207 MW of power and 3728 m3/h of HW. In such conditions, the energy efficiency of 73.1% and exergy efficiency of 44.18% could be achievable. Further, the emitted gas rates of the plant were nearly 403 tons/h. A comprehensive comparison is also presented for the plant's behavior under different types of coal (petcoke and anthracite). In addition, a two-function optimization is developed to determine the maximum value of exergy efficiency and the minimum value of total pollutants emission rate.

Effect of thermal damage on the pore–fracture system during coal spontaneous combustion

Understanding the variation law of pore–fracture system during coal spontaneous combustion (CSC) plays a crucial role in understanding the mechanism of CSC and its prevention as well as control. In this study, three different ranks of coal samples were heat-treated (25–500 °C). Through nuclear magnetic resonance (NMR), scanning electron microscopy (SEM) and uniaxial compression (UC) tests, the changes in the pore-fracture system of different types of coal during CSC were comprehensively summarized. Based on the experimental results, the thermal rupture behavior of coal was simulated using PFC2D software. The results show that During CSC, the pore development of low-rank coal was obvious, the pore development of middle-rank coal was mainly concentrated in the high-temperature stage (T >300 °C), and the pore structure of high-rank coal was more stable. Meanwhile, the heterogeneity of the pore–fracture system of middle- and low-rank coals decreased, and the adsorption and seepage capacities increased. The heterogeneity of the pore–fracture system of high-rank coal was slightly influenced by temperature. The compressive strength of coal decreases with increasing temperature during CSC. The numerical simulation results were similar to the experimental results, i.e., the microcracks in the coal samples increased with temperature during heating; the effect of cracking caused by the high temperature will change the way the sample breaks, and the samples changed from ductile to brittle. The results of this study can serve as a reference for coal-fire control.

The characteristics of methane adsorption capacity and behavior of tectonic coal

The research of methane adsorption on tectonic coal is an important content to gas disaster prevention and coalbed methane (CBM) exploration in outburst coal seams. Many projects of methane adsorption capacity and behavior of tectonic coal, such as adsorption difference between tectonic coal and its untectonic coal, adsorption evaluation of tectonic coal, factors for adsorption capacity of tectonic coal, gas-solid coupling feature in tectonic coal and supercritical adsorption phenomena of tectonic coal, were carried out by scientists. Combined with a long-term study on organic matter structure and methane adsorption of tectonic coal, the author summarized recent-years’ researches on adsorption capacity and behavior of tectonic coal-methane at home and abroad from the dispute of adsorption ability determination, the thermodynamic characterization of methane adsorption capacity, and the methane adsorption behavior of quantum chemical calculation of the adsorption and the gas content calculation based on loss compensation, respectively. It is believed that the coal structure controls the methane adsorption capacity and behavior characteristics of different tectonic coals, and from the perspective of thermodynamics, the adsorption capacity of different types of coals can be better distinguished. In the future, a more scientific and complete quantum chemical calculation of methane adsorption by tectonic coal and a compensation method based on instantaneous emission loss should be established, so as to better reveal the methane adsorption behavior of tectonic coal and the mechanism of coal and gas outburst. The research has a reference to fine research of coal adsorption and CBM exploration practices.

MODELS AND METHODS FOR IMPROVING THE OPERATION OF THE ENERGY FACILITY CONTROL SYSTEM

This article is devoted to improving methods and models for a computer-integrated control system (CICS) that monitors the wear of heat exchange surfaces of pipes in steam boilers at coal-fired thermal power stations (TPP), in particular for coal with unknown abrasive composition. The system uses real-time coal quality data to 1manage the abrasive, optimize coal distribution, and verify coal quality to reduce costs. It is described that the difficulties faced by the global coal industry are related to quality, price and environmental issues, and the transition to sustainable energy is complicated by this diversity. Efficient power generation depends on accurate identification of fuel composition and minimizing damage from abrasive impurities in the fuel of heat exchangers. Despite the existing analytical methods, there is a need for improved diagnostic technology, which involves the integration of automated systems to improve efficiency and sustainability. The paper presents a mathematical model that calculates the effect of different types of coal and impurities on the wear of heat exchange tubes, maximizing service life and minimizing costs. It includes a Cochran sampling rule to improve coal quality control. An automated coal quality management method was also developed to reduce wear from abrasive coal impurities. It includes a stepwise supplier selection and stock utilization method, enhancing wear control using the Cochran stepwise sampling method. In addition, a fuzzy logic-based control device distributes the flow in such a way as to ensure satisfactory coal quality, emphasizing the need for continuous system monitoring. A model-based CICS has been developed that controls coal flow based on real-time impurity identification, resulting in significant cost savings and extended overhaul intervals. Computational experiments confirm that the CICS can more than double the service life of heat exchange tubes by maintaining a satisfactory thickness, thereby postponing repairs and reducing operating costs. Overall, this article presents a comprehensive approach to managing and optimizing heat exchanger tube wear at TPP using modelling, real-time data analysis, and automated control systems to improve efficiency and sustainability.

Effects of Different Coals for Co-Combustion with Palm Oil Waste on Slagging and Fouling Aspects

ABSTRACT Implementing a co-combustion technology in coal-fired plants using biomass waste is a promising option to alleviate environmental pollution, reduce fuel costs, and minimize waste. The considerable potential of palm oil waste is believed to be able to substitute coal as a raw material in a coal-fired power plant. However, since each coal has different compositions and biomass generally has a high alkali content, the propensity of slagging and fouling during co-combustion needs to be clarified. This research evaluates the co-combustion ash characteristics of different types of coal, which is co-combusted with 25% palm oil biomass waste. The combustion test employs a drop tube furnace, where the produced ash composition and its morphology are investigated using scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction. The results show that the ash melting temperature of the three types of coal mixed with biomass is reduced, although insignificant. Bituminous coal has a low potential for slagging and fouling since SiO2 and Al2O3 dominate the coal ash composition. In addition, lignite coal has low SiO2 and Al2O3 contents but high alkali contents (K and Na). As confirmed by SEM-EDS analysis, probe observations also show that lignite coal co-combustion with empty fruit bunch and frond waste has higher slagging and fouling risks.

Characteristics of the particulate matter and its toxic substances from different stationary coal-fired sources

Condensable particulate matter (CPM) and uncaptured fine filterable particulate matter (FPM) from various stationary coal-fired sources cause haze weather to harm human health. In this study, we measured the emissions of FPM, CPM, and polycyclic aromatic hydrocarbons (PAHs) from household stoves, small-capacity boilers, and industrial-scale circulating fluidized bed (CFB) boilers. CFB systems installed with dry and semidry flue gas desulfurization (FGD) systems and ammonia-based NOx control systems (SCR/SNCR) emit lesser filterable PM but substantially higher CPM than household stoves and small-capacity boilers. The results indicate that these air emission control technologies have side effects on promoting the generation and emission of CPM, which is rich in (NH4)2SO4 and NH4HSO4. CFB boilers with wet FGD technology exhibit lower CPM emission, suggesting the positive effects of dissolving and absorbing of gypsum slurry on CPM emission. Various small coal-fired stoves burning different types of coal do not significantly affect CPM but the PAHs emissions. Based on the data of this investigation, we estimated the emission inventory of CPM from various stationary coal-fired sources, aiming to provide valuable insights into setting priorities for improving the atmospheric environment in China.

Evolution behaviors of the nitrogen-containing species and SO2 from coal fast pyrolysis

The nitrogen-containing species and SO2 generated during coal pyrolysis lead to environmental problems. This paper investigated the evolution behaviors of four identified nitrogen-containing species including hydrogen cyanide (HCN), ammonia (NH3), nitric oxide (NO), nitrogen dioxide (NO2), and sulfur dioxide (SO2) from fast pyrolysis of four different types of coal in a fixed bed reactor in the 600–1200 °C temperature range. Results show that HCN yield increases as the temperature increasing while the NH3 maximum yield exists a transition temperature ranging from 800 to 1000 °C that depends on coal category. The impact of pyrolysis temperature on the SO2 yield is not linear. To further quantify the NH3 formation source, a mathematical method was proposed to divide the NH3 evolution profile into gas-gas reaction and gas-solid reaction two categories. The gas-solid reaction predominates the NH3 formation with a ratio up to 75% in 1200 °C high temperature condition. In low temperature condition, which path is predominant depends on the coal category. In addition, the oxynitride including both NO and NO2 were observed in pyrolysis process. Moreover, enhancing temperature can boost NO2 yield and restrain NO yield. The NO and NO2 come from the combination of nitrogen and oxygen functional group which are both directly split off the parent coal. In addition, the elements liberation sequence from fast to slow is carbon > sulfur > nitrogen. To be further, the liberation sequence of pyrolysis species from fast to slow is CO > SO2>NO > NO2>HCN > NH3, which can supply guides to remove pollutants in industry.